The best frictional coefficient of single material [53, 54].
\r\n\t
\r\n\tThe aims of this book are to present the updates and advances in the field of resuscitation including AHA guidelines, latest evidence for the airway protection equipment, the role of AED in cardiac arrest, latest advances and the evidence including ongoing updated research including return of spontaneous circulation and post resuscitation care and support including neurological and hemodynamic stability.
\r\n\t
\r\n\tThe content of this book will be focused on latest research in the field which will create a concise updated information for medical, nursing and paramedical personnel. Furthermore, the book will also touch upon controversial topics in resuscitation and will try to bring out latest evidence intending to solve the controversies in the field of resuscitation. This book will be an excellent extract of all available updates and ongoing research for a complete knowledge of resuscitation.
The last twelve years have seen enormous growth in many aspects of doped carbon nanotubes. The idea of doping carbon nanotubes has come from microelectronics and now develops both in a traditional donor-acceptor direction (Miyamoto et al., 1995; Lee et al., 1997; Rao et al., 1997; Grigorian et al., 1998; Esfarjani et al., 1999) and in a number of new aspects of application. Among recent trends of application of a doping of nanotubes it is necessary to term such as forming for them magnetic properties (Esfarjani et al., 2003; Farajian et al., 2002), change of their optical performances (Bondarev, 2007), embodying of hydrogen storages (Zidan et al., 2003), amplification of catalytic properties (Gong et al., 2009) and improving of emission characteristics (Yao et al., 2002).
\n\t\t\tIn the present chapter we discuss influence of impurities on properties of semiconductor carbon nanotubes with chiral vectors (10,0) and (6,5) which are representative of groups of nanotubes of type "zigzag" and the twirled chirality, accordingly.
\n\t\t\tAt doping nanotubes usually view an intercalation of impurity inside of a nanotube or in space between separate nanotubes. We view doping nanotubes in traditional sense when impurity ranks one of atoms of a nanotube. It allows to hope, that impurity after such localization will not be lightly to migrate in a nanotube or between separate nanotubes. At such approach to a problem of doping of a periodic nanostructure presence in it of vacancies is supposed. Energy of forming of vacancy in a nanotube makes 5...7 eV (Griadun, 2006). It is a little bit more in comparison with energy of forming of vacancy in silicon, but nevertheless leaves probability of substantial existence of vacancies in nanotubes.
\n\t\t\tProfound knowledges are necessary for an effective utilization carbon nanotubes in nanoelectronic about their local electro-physical performances. In particular extensive data on concentration and parameters of the impurity centers by means of which it is possible to shape fields with the given type and the quantity of an electrical conductivity reproduced by quantities of a lifetime and a diffusion length of non-equilibrium charge carriers are necessary.
\n\t\t\tInterest to these examinations is called by necessity of development of designs of integrated transistors and logical units for build-up of complete sets of integrated circuits with use semiconductor carbon nanotubes (Martel et al., 1998; Derycke et al., XXXX).
\n\t\t\tThe solution of a problem guesses an opportunity to drive equilibrium concentrations of electrons and holes in semiconductor carbon nanotubes by their doping.
\n\t\tModels developed within the limits of a method of molecular mechanics model operation MM + (Berkert & Allinger, 1982) with next parameters:
\n\t\t\t\ta quadratic and a cubic stretch term in the potential;
atom types;
nonbonded electrostatic interactions are calculated using bond dipole, which values come from the MM+ stretch parameters;
the electrostatic contribution comes from defining a set of bond dipole moments associated with polar bonds;
cutoffs determine the distance limits for calculating nonbonded interactions of the periodic nanostructure;
inner cutoff radius is the maximum interatomic distance for full nonbonded interactions - 10 Å;
outer radius is the minimum distance at which nonbonded interactions are set to zero - 14 Å.
The base model of the nanotube consisting from two hundred of atoms of carbon, is presented on Figure 1. In models aromatic bonds, providing interacting of valence electrons of carbon atoms are used.
\n\t\t\t\tBasic model of the carbon nanotube with indices (10,0).
The energy-band structure of a nanotube was calculated by the Extended Hückel method (Hoffmann, 1963). The total energy of 200-atomic model of a nanotube has made quantity -323079.99 kcal/mol. On the diagram of its energy structure of a forbidden gap (Figure 2) is observed a series of levels with energies: -10.60226; -10.37579; -10.37578; -10.36441; -10.36440; -10.30684; -10.27539; -10.26634; -10.26634; -10.24621; -10.24621; -10.19875; -10.19875; -9.6362; -9.6362 eV - matching orbitals with numbers 401 - 415, accordingly.
\n\t\t\t\tAll from the termed orbitals to a greater or lesser extent match to edges of a nanotube, for example orbital 413 (Figure 3), and higher orbitals match to a volume part of a nanotube.
\n\t\t\t\tStructure of a forbidden gap of the nanotube with indices (10,0).
Thus, in a forbidden gap of a nanotube is 30 electronic states matching 15 orbitals. A part from viewed states match to the dangling bonds on edges of a nanotube. For acknowledging this we shall simulate passivation of dangling bonds by atoms of hydrogen.
\n\t\t\t\tOrbital 413 of the carbon nanotube with indices (10,0).
On Figure 4 the model of a 200-atomic nanotube after hydrogen endings and geometrical optimization of nanostructure within the limits of a method of molecular mechanic modeling MM + is figured. Apparently on the model, atoms of hydrogen have filled 20 dangling carbon bonds - on 10 on each edges of a nanotube. Thus, the remained three orbitals feature six states which parent of origination is unknown.
\n\t\t\t\tThe band of energy diagram in the field of a forbidden gap (Figure 5) after passivation by hydrogen of the broken off bonds of a nanotube on its edges essentially differs from the diagram of the starting model figured on Figure 2:
\n\t\t\t\t1) The forbidden gap has essentially cleared from energy levels - from 15 remains only 5, that is 10 orbitals that matches to 20 electronic states, were moved in a valence band;
\n\t\t\t\t2) Three from five remained energy levels in a forbidden gap should be the acceptor as they are close to a valence band with energies -10.44002 eV (an orbital 411), -10.41608 eV (an orbital 412), and -10.41608 eV (an orbital 413);
\n\t\t\t\t3) Passivation by atoms of hydrogen has affected quantity of energy of a ceiling of a valence band (an orbital 410) which has made -10.44002 eV (before passivation was -10.60226 eV);
\n\t\t\t\t4) The magnification of energy in item 3 is caused by electronic states of atoms of hydrogen;
\n\t\t\t\t5) Passivation by atoms of hydrogen has affected quantity of energy of a bottom of conduction band (an orbital 416) which has made -9.156353 eV (before passivation was -9.147926 eV);
\n\t\t\t\t6) The breadth of a forbidden gap of viewed model has made quantity 1.2837 eV (before passivation was 1.4543 eV);
\n\t\t\t\t7) The overestimated value of an energy gap in this case is caused by a trace amount of atoms and, accordingly, small length of a nanotube 19.6 Å.
\n\t\t\t\tHydrogen endings of the carbon nanotube with indices (10,0).
Structure of a forbidden gap of the (10,0) nanotube after hydrogen endings.
Analogous calculations are lead also for the nanotubes consisting from three hundred and four hundred of atoms of carbon in length ~ 30.15 and 40.63 Å, accordingly. Hydrogen endings of this models also well refines forbidden regions of the energy levels matching broken off bonds. The breadth of a forbidden gap has naturally decreased up to values 1.06 and 0.90 eV, accordingly for 300-atomic and 400-atomic models of nanotubes.
\n\t\t\tSimulation of doping of the nanotube by atom of boron we shall carry out within the limits of a method of MM +, exchanging in the program of basic model the chosen atom of carbon on atom of boron (Griadun, 2007). Thus we can use aromatic bonds of atom of boron with atoms of carbon or exchange them on single bonds, as boron trivalent. We shall consider also at model operation spin multiplicity of a nanostructure.
\n\t\t\t\tThe geometry of a 200-atomic nanotube doped by atom of boron, is presented on Figure 6. We see, that at modeling of impurity of boron by aromatic bonds with atoms of carbon the nanostructure distorts feebly. In case of single bonds B-C the nanostructure noticeably distorts in the field of localization of atom of boron. It is related by that single bonds B-C are longer than aromatic on 0.08 Å.
\n\t\t\t\tExtended-Hückel energy of the nanostructure with aromatic bonds of atom of boron is less than energy of the nanostructure with single bonds on 2.22 kcal/mol, therefore it is necessary to expect, that in real experiment embodying of the nanostructure with aromatic bonds of atom of boron is more probable.
\n\t\t\t\tThe energy band diagram of the viewed nanotube doped by atom of boron (Fig. 7a), differs from an energy-band structure of basic model (Figure 2), however, only quantities of values of energy levels. The expected new acceptor level localized on atom of boron, we do not observe. As well as in basic model three acceptor energy levels, but with other values of energy are observed: -10.60; -10.38 and -10.37 eV. It, visible, is related by that bonds B-C the 1S-electron of atom of boron shares. Except for that removal of degeneration of some orbitals is observed, for example orbitals 414 and 415 with energy -9.636 eV borrow levels with energies -9.641 and -9.611 eV.
\n\t\t\t\tGeometry optimised model of the carbon B-doped (10,0) nanotube with aromatic bonds B-C.
Hydrogen endings of a nanotube doped by atom of boron practically does not influence geometry of a nanostructure near to atom of boron, however noticeably influences its energy distribution (Fig. 7b). Really, upper occupied level HOMO-0, featured 410-th orbital, has energy -10,46021 eV. Following three orbitals with numbers 411 - 413 are at levels -10.45723, -10.43564, and -10.42292 eV, accordingly. As a whole, such effect is normal as levels of energy of electrons of hydrogen atoms have placed in a valence band and biased its ceiling on 0.15 eV upwards.
\n\t\t\t\tEnergy band structure of the B-doped (10,0) carbon nanotube before (a) and after (b) hydrogen endings.
The atom of nitrogen also is well inscribed in geometry of a nanotube, not calling essential strain of its nanostructure (Figure 8). It is caused by that lengths of bonds N-C and C-C differ a little - 1.28 Å and 1.40 Å, accordingly.
\n\t\t\t\tModel of the nanotube with indices (10,0) doped by atom of nitrogen.
The energy band distribution of a nanotube without hydrogen endings, doped by atom of nitrogen, is presented on Fig. 9a. Under effect of impurity atom in a spectrum of energy levels of a nanostructure there was an orbital filled by an electron the number 401. This orbital matches to the fifth valence electron of atom of nitrogen and is presented by an energy level equal to quantity -10.6018 eV. The ceiling of a valence band of a model nanostructure is featured by an orbital the number 400 with energy -10.6023 eV. Thus, the extrinsic energy level of atom of nitrogen will not display the donor properties as is near to a valence band, it only will neutralize the inferior acceptor level of a basic nanotube.
\n\t\t\t\tIn case of nitrogen doping a carbon nanotube with hydrogen endings, the fifth valence electron of atom of nitrogen also occupies the inferior acceptor level near to a valence band (Fig. 9b). Quantity of energy of a level which value makes in this case -10.4579 eV varies only.
\n\t\t\t\tEffect of impurity atom of nitrogen on energy spectrum of the carbon (10,0) nanotube before (a) and after (b) hydrogen ending.
Thus, doping by atom of nitrogen of a carbon nanotube with indices (10,0) does not result in to formation of a donor centre, and only results in to blocking of one of acceptor levels of a nanostructure.
\n\t\t\tAtom of aluminium as the device of the third group, well approaches for doping carbon nanotubes. As if to its influence on geometrical and other properties of a carbon nanotube with coefficients (10,0) we shall view on model of a nanostructure in which atom №133 of the basic model of nanotube we shall replace with atom of aluminium. After geometrical optimization of a nanostructure in which aromatic bonds Al-C use, the model gets a view figured on Figure 10.
\n\t\t\t\tWe see, that the atom of aluminium is not inscribed in wall of a nanotube, but located in immediate proximity from it apart 1 Å. Besides atoms of carbon with which bound atom of aluminium, are noticeably drifted for limits of a nanotube. In case of use in model of a nanostructure of single bonds Al-C results in to even greater infringements of geometry of a nanotube. The atom of aluminium settles down thus apart 1.2 Å from geometrical wall of a nanotube. The Extended Hückel calculation of energy distribution in area of a forbidden gap of the Al-doped nanotube is presented on Figure 11.
\n\t\t\t\tOptimised geometry of the Al-doped carbon (10,0) nanotube.
It is visible, that the type of bonds of atom of aluminium with atoms of carbon very feebly influences quantity of energy levels. In comparison with a spectrum of basic model of the carbon (10,0) nanotube (Figure 2) has occurred an acceptor level with energy -10.532 eV. Also there were splits of levels -9.636 and -9.148 eV. The parent of this split is spin multiplicity of the nanostructure doped by aluminium which quantity is equal to two.
\n\t\t\t\tIt is necessary to note, that the nanostructure with aromatic bonds Al-C should be realized with greater probability as the nanostructure with single bonds Al-C is more on 10 kcal/mol.
\n\t\t\t\tEnergy band structure of a forbidden gap region of the Al-doped carbon (10,0) nanotube: (a) - aromatic bond Al-C; (b) - unary bonds Al-C.
Passivation of the Al-doped carbon (10,0) nanotube by hydrogen endings (Fig. 12a) renders appreciable influence on its energy distribution in the field of a forbidden gap (Fig. 12b). We see, that after passivation of edges of a nanotube by hydrogen in a forbidden region of a nanostructure some level by quantity -10.289 eV which visible is related to the defect created by impurity atom of aluminium was displayed.
\n\t\t\t\tAl-doped carbon (10,0) nanotube with hydrogen endings: (a) - geometry of nanostructure; (b) - energy band structure of a forbidden gap.
Doping of the carbon (10,0) nanotube by atom of phosphorus results in appreciable strain of geometry of a nanostructure (Figure 13). It is related by that bonds C-P, having quantities 1.80, 1.80 and 1.79 Å, longer in comparison to typical length of bonds C-C, Equation 1.41 Å. Besides the atom of phosphorus has on 0.3 Е greater atomic radius than at atom of carbon that results in to its replacement for limits of a nanotube.
\n\t\t\t\tMolecular mechanics model of the 200-atomic carbon (10.0) nanotube doped by atom of phosphorus.
It is necessary to note, that the atom of phosphorus shapes in a viewed nanostructure an essential lapse rate of mechanical stresses which value Equation 0.05 kcal/(Å mol). In a basic nanotube geometrical optimization is attained at a root-mean-square lapse rate Equation 0.000001 kcal/(Å mol).
\n\t\t\t\tThe energy diagram of a viewed nanostructure is presented on Figure 14. We see, that in a forbidden gap of the doped nanotube there was a level (-10.082 eV), which probably matches to the flaw created by atom of phosphorus.
\n\t\t\t\tEnergy levels in a forbidden gap of the carbon(10,0) nanotube doped by atom of phosphorus.
The model of a phosphorus-doped (10,0) nanotube with hydrogen passivation of dangling bonds and its energy band structure are presented on Figure 15. We see, that the geometry of a viewed nanostructure in the field of localization of atom of phosphorus after hydrogen passivation of dangling bonds on its edges has not changed.
\n\t\t\t\tP-doped carbon (10,0) nanotube with hydrogen endings: (a) - geometry of the molecular mechanics model; (b) - Extended Hückel calculation of energies of orbitals.
In an energy distribution of a forbidden gap there were changes (Fig. 15b):
\n\t\t\t\tthe upper filled level has risen up to quantity -10.46 эВ;
\n\t\t\t\tdegeneration of some energy levels is removed;
\n\t\t\t\tquantities of energy levels have changed.
\n\t\t\t\tIt is necessary to note, that the new level with energy -10.098 eV under effect of hydrogen endings has not changed the quantity.
\n\t\t\t\tThe magnification of number of atoms of carbon in model of a phosphorus-doped nanotube up to 300 pieces results in to diminution of breadth of a forbidden gap and small bias of a new level up to quantity -10.11 eV.
\n\t\t\tThere are many methods of model operation of those or other processes and structures. For nanotechnologies the method of the molecular mechanic model operation which basic element is the molecule well approaches. The separate atom too is considered as a molecule. In case of a nanotube the molecule is the nanotube. Atoms of a nanotube are foliated, featured by coordinates and type and also quantity of bonds.
\n\t\t\t\tOur model of nanotube consists from two hundred atoms of carbon, which geometrical optimization was led by method MM + with application the block-diagonal of the Newton-Raphson algorithm (Figure 16). The length of a nanotube is Equation 22 Å, diameter - 7.3 Å. The distance between atoms is Equation 1.41 Å. Chirality of the nanotube which it is well visible on figure, defined by its indices (6,5).
\n\t\t\t\tAt model operation the applied aromatic bonds which well justify itself when atoms of carbon create rings as in this case. There is one more expedient of the plotting of bonds which total for atom of carbon should equate to four.
\n\t\t\t\tTo calculation of energy properties of a nanotube we applied Extented Hückel Method (Hoffmann, 1963) without taking into account d-orbitals, with unit spin multiplisity and unweighted Hückel constant Equation 1.75. Energy has made quantity equal -323263.1900 kcal/mol.
\n\t\t\t\tatoms basic model (a) and energy-band structure (b) of a carbon nanotube with indices (6,5).
The energy-band structure of a basic nanotube (6,5) is presented on Fig. 16b. The upper filled level (HOMO 0), which is featured by orbital number 400, makes quantity -10.788 eV. Energy of bottom of a conduction band is equated -9.91 eV. In fact the forbidden region has breadth Equation 0.88 eV.
\n\t\t\t\tIn a forbidden gap there is a series of levels which are caused by dangling bonds on edges of the nanotube. So, it is possible to apply atoms of hydrogen or nitrogen to passivation of the broken off bonds. On Figure 17 passivation by atoms of hydrogen which are optimum in such cases is shown.
\n\t\t\t\tAtoms of hydrogen fill dangling bonds on edges of the carbon (6,5) nanotube.
The energy of the nanotube with passivated ends has decreased to value -332889.25 kcal/mol that is caused by both H-atoms and a relaxation of a nanotube on edges where bonds have been broken off. The energy-band structure presented on Fig. 18a, considerably has changed in this case. The forbidden gap became clear from energy levels of the dangling bonds. Apparently from this figure, that the forbidden gap quantity is defined by a difference
\n\t\t\t\tThe greater width of the gap is caused by a trace amount of carbon atoms.
\n\t\t\t\tThe energy-band structure of the base nanotube with indices (6,5) after passivation the dangling bonds by atoms of hydrogen: (a) - 200-atomic model; (b) - 400-atomic model.
The magnification of length of a nanotube twice results in to a raising of a ceiling of valence band on 0.1 eV, and the breadth of a forbidden region thus accordingly on as much decreases (Fig. 18b).
\n\t\t\tDoping of a carbon nanotube with indices (6,5) we shall carry out by replacement in the program of model operation of a nanostructure of the arbitrary atom of carbon by atom of boron. We exchange also aromatic bonds on single bonds, as boron trivalent. The nanotube (Fig. 19a) distorts in the field of localization of the alloyed atom of boron due to longer B-C bonds, Equation 1.65 Å, that on 0.24 Å it is more than for C-C bonds. Though the nuclear sizes of boron (1.17 Å) and carbon (0.91 Å) different enough, but covalent radiuses at them close enough, 0.82 and 0.79 Å, therefore the geometry of a tube is broken poorly. The energy-band structure of the B-doped nanotube (Fig. 19b) has a little changed in comparison with a spectrum of basic model (Fig. 16b):
\n\t\t\t\tdegeneration of levels -10.240 and -10.379 eV is removed;
\n\t\t\t\tnumerical values of other energy levels have a little changed.
\n\t\t\t\tGeometry of the boron-doped carbon (6.5) nanotube (a) and its energy-band structure (b).
To passivation of dangling bonds on edges of a nanotube we shall apply hydrogen endings (Fig. 20a).
\n\t\t\t\tApparently from Extended-Hückel calculations of the energy band structure diagram (Fig. 20b), that under effect of atom of boron and hydrogen passivation of dangling bonds the structure of the forbidden gap and its width which has become Equation 0.898 eV (it was Equation 1.03 eV) has changed. The local orbital the number 411 is filled only by one electron, as amount of valence electrons equally to eight hundred twenty one. It is acceptor with energy -10.71 eV (0,08 eV above valence band).
\n\t\t\t\tThus atoms of carbon with numbers 157, 158 charged by the negative low fidelity equal charges on quantity 0.41е (е - electron charge), and the atom of carbon number 161 has negative charge 0.37е. The atom of boron has positive charge equal -0.66е.
\n\t\t\t\tThe B-doped carbon (6,5) nanotube with hydrogen endings: (a) - geometry of the nanostructure; (b) - energy band structure.
Thus around of atom of boron in a carbon nanotube complicated enough electronic pattern which corresponds to an orbital 411 and as which it is possible to term as acceptor local centre is created. It is necessary to note, that acceptor properties of this orbital can be realized at a heat (more than 900 K), as an energy level deep enough.
\n\t\t\tFor forming model of the N-doped carbon nanotube, we shall replace 163-rd atom of carbon with atom of nitrogen. The nanostructure does not distort almost under influence of the alloyed atom of nitrogen (Figure 21) as lengths of bonds C-C and N-C differ feebly - 1.40 Å and 1.28 Å, accordingly.
\n\t\t\t\tCovalent and nuclear radiuses of atom of nitrogen are Equation 0.75 Å, i.e. smaller radiuse of atom of carbon which Equation 0.77 Å and 0.91 Å, accordingly. In this connection, intensity around of atom of nitrogen is not minimal - the RMS gradient of mechanical stress is Equation 0.0045 kcal/(Å mol).
\n\t\t\t\tTotal energy of the nanotube doped by nitrogen is calculated by Extended Hückel method and has made quantity -323849.25 kcal/mol. It is less than for the base nanotube which energy is equaled -323263.19 kcal/mol that speaks in the smaller sizes of radiuses and bonds of atom of nitrogen.
\n\t\t\t\tCross view of the nanotube with indices (6,5) doped by atom of nitrogen.
As we see on the diagram of energy spectrum of the nanostructure (Figure 22), the fifth electron of atom of nitrogen has formed and has filled a level with energy -10.75 eV. On the one hand this level donor as it is filled by an electron and is level HOMO 0 (the highest among the levels filled by electrons), and from the second side - it is near to valence band and should be the acceptor. So it is necessary to consider this level as very deep donor level.The forbidden gap in case of presence of impurity of atom of nitrogen is defined by a difference ΔЕ =-9.92+10.79 =0.87 eV.
\n\t\t\t\tEnergy-band structure of a N-doped carbon nanotube with indices (6,5).
Also we see on Figure 22 in a forbidden region there are some levels which are caused by the broken off bonds on edges of a nanotube. To neutralization of these levels we shall apply atoms of hydrogen (Figure 23). Energy band diagram of the nanostructure in this case is shown on Figure 24.
\n\t\t\t\tPassivation of the torn off bonds on edges of the N-doped carbon (6,5) nanotube.
As we see on Figure 24, the atom of nitrogen has formed occupied level with energy -9,829 eV, which is level HOMO 0 in this case.
\n\t\t\t\tEnergy band diagram of the N-doped carbon (6,5) nanotube with hydrogen endings.
To term its donor it is impossible, as it deep enough (0.071 eV from level LUMO 0 with energy -9.758 eV). Presence of such energy level filled by an electron highly above valence band in the tubes alloyed by nitrogen should result in to improvement of their properties of electron emission.
\n\t\t\tFor construction of model of the doped nanotube the 116-th atom of carbon on the atom of aluminium is replaceable in the program of its basic model. We shall replace also aromatic bonds of atom with atoms of carbon on unary. After embodying the given changes in the program and carryings out of geometrical optimization of a nanostructure, we shall receive model of the aluminium-doped carbon (6,5) nanotube (Fig. 25a). We see, that the nanotube essentially distorted under influence of the doped atom. It speaks the following parents:
\n\t\t\t\ta) Atom of aluminium has twice greater radius (1.92 Å) than radius of atom of carbon (0.91 Å);
b) Covalent radius of atom of aluminium also greater than at atom of carbon, 1.18 Å against 0.77 Å;
c) Length of bonds C-Al which is Equation 1.94 Å, is more than length of bonds C-C Equation 1.41 Å.
It results in to that the atom of aluminium is pushed out of limits of the nanotube and its effective diameter increases up to quantity Equation 8.51 Å.
\n\t\t\t\tBesides under influence of elastic forces of strain, atoms of carbon which are bound to atom of aluminium also are superseded from the optimum places and take new geometrical positions which are normal for the doped nanotube.
\n\t\t\t\tExtended Hückel calculation of energy of the aluminium-doped nanostructure yields value -322454.33 kcal/mol. It on 808 kcal/mol is more than for a basic (6,5) nanotube. Thus for doping a nanotube (6,5) by aluminium the significant energy is required.
\n\t\t\t\tThe zone diagram of the Al-doped nanostructure in this case is shown on Fig. 25b. We see, that the orbital number 400 (HOMO 0) is filled half, hence, there was a vacant level with energy -10.41 eV. Thus, the atom of aluminium shapes an acceptor level near to valence band.
\n\t\t\t\tAl-doped carbon (6,5) nanotube: (a) - a dilatational view; (b) - an energy-band structure.
The nanostructure with hydrogen endings is shown on Figure 26. Its Extended-Hückel energy is equaled -332121.573 kcal/mol. Electrical dipole moment of a nanotube, is Equation 297.4 D - greater enough in comparison with a boron-doped nanotube (6,5).
\n\t\t\t\tDoped by atom of aluminium the carbon (6,5) nanotube with hydrogen endings.
Doping by atom of aluminium very strongly influences an energy band spectrum (Figure 27) nanotubes that is related to its significant strain after doping, and also spin density of a nanostructure. In this case the impurity atom of aluminium creates an acceptor level (-10.373 eV) with an ionization energy Equation 0.015 eV.
\n\t\t\t\tEnergy-band structure of the Al-doped (6,5) nanotube with hydrogen endings.
The atom of phosphorus has five valence electrons, therefore it is necessary to expect occurrence in a nanotube of a donor centre near to it, as for aromatic bonds with atoms of carbon enough four electrons. We shall exchange in basic model of a 200-atomic nanotube the any atom of carbon with atom of phosphorus, having applied aromatic bonds C-P. For carrying out of geometrical optimization of the constructed P-doped nanostructure we shall use the molecular mechanic method MM + with application of the block-diagonal algorithm of Newton-Raphson. We shall gain model of the P-doped carbon (6,5) nanotube presented on Figure 28. Apparently on pattern, that the atom of phosphorus has taken a place in exterior area near to a nanotube. It is caused by that bond C-P and atomic radius of phosphorus is more than bonds C-C and atomic radius of carbon on 0.4 and 0.3 Å, accordingly.
\n\t\t\t\tThe molecular mechanics model 200-atomic carbon (6.5) nanotube doped by atom of phosphorus.
In connection with mechanical stresses near to the impurity atom it is necessary to note, that the considered nanostructure is optimized only at RMS gradients of greater 0.015 kcal/(Å mol), and for a basic nanotube analogous magnitude makes 0.000001 kcal/(Å mol).
\n\t\t\t\tThe band diagram of a viewed nanostructure is presented on Figure 29. Comparing the gained diagram with the diagram of a basic nanotube (Fig. 16b), we see, that the fifth electron of atom of phosphorus has occupied the free orbital 401 with an energy -10.758 eV and that in a forbidden region the level with an energy -10.082 eV was generated.
\n\t\t\t\tEnergy band structure of the 200-atomic carbon (6.5) nanotube doped by atom of phosphorus.
The models of a phosphorus-doped (6,5) nanotube with hydrogen passivation of dangling bonds is presented on Figure 30.
\n\t\t\t\tMolecular mechanics models of the P-doped carbon (6,5) nanotube : (a) - hydrogen endings on edges of a nanostructure; (b) - the complete hydrogen endings.
We see, that the doped nanotube has one broken off bond on atom of phosphorus. If such bond to leave without hydrogen passivation to it any other radical including the same nanotube can be affiliated.
\n\t\t\t\tApparently on Figure 31, passivation of the dangling bonds has essentially changed an energy distributions of a viewed nanostructure:
\n\t\t\t\tthe upper filled levels have risen up to magnitudes -10.077 eV (a) and -10.487 eV (b);
\n\t\t\t\tdegeneration of some energy levels is taken off;
\n\t\t\t\tquantities of energy levels have changed.
\n\t\t\t\tThe phosphorus-doped 200-atomic carbon (6,5) nanotube: (a) - hydrogen endings on edges of a nanostructure; (b) - complete hydrogen endings.
The magnification of number of atoms of carbon in model of a phosphorus-doped nanotube up to 410 pieces results in to diminution of breadth of a forbidden gap and bias of a HOMO 0 levels up to quantities -10.466 eV (Fig. 32a) and -9.852 eV (Fig. 32b).
\n\t\t\t\tThe phosphorus-doped 410-atomic carbon (6,5) nanotube: (a) - hydrogen endings on edges of a nanostructure; (b) - the complete hydrogen endings.
Thus, the impurity atom of phosphorus without hydrogen ending of its dangling bond can create in a nanotube a deep donor level with an ionization energy Equation 0.28 eV. In case of when the free bond of atom of phosphorus is neutralized by atom of hydrogen the recombination centre is formed. Besides in any case, the impurity atom of phosphorus will reinforce emissivity of a nanotube as its valence electron occupies higher energy levels.
\n\t\t\tOn models of semiconductor carbon nanotubes with chiral vectors (10,0) and (6,5), consisting of 200 atoms, effect of impurities of atoms Al, B, N and P on performances of their energy-band structure is viewed. The magnification of number of atoms of carbon of the doped nanostructure twice feebly influences its energy distribution, but results in to diminution of a forbidden gap of a nanotube approximately on 0.1 eV.
\n\t\t\tProcess of doping of a carbon nanotube was simulated by replacement of one of its atoms of carbon on an impurity atom. Such doping of a nanotube in experiment can be implemented at existence of vacancies in it. Theories about equilibrium concentration of vacancies in nanotubes are not present, therefore it can become the purpose of the further developments.
\n\t\t\tIt is necessary to note, that intercalation atoms in nanotubes can be viewed as interstitial atoms in crystals. Then their presence at a nanotube can determine process of doping also.
\n\t\t\tIt is shown, that the energy distribution of levels in the field of a forbidden gap of the doped nanostructure strongly depends on passivation of its torn off bonds. In the present investigation modeling of process of such passivation was carried out by hydrogen endings. Also it is shown, that doping of a carbon nanotube by atom of phosphorus results in to occurrence of dangling bond on its fifth valence electron, as for support of aromatic bonds with atoms of carbon enough four electrons. Passivation of this bond by atom of hydrogen results in to changes in an energy band structure of the doped nanotube.
\n\t\t\tImpurity atoms of boron and aluminium are representatives of the third group of a periodic system of elements, therefore they create similar acceptor levels in carbon nanotubes with chiral vectors (10,0) and (6,5):
\n\t\t\ta) atom of boron creates levels with activation energies 0.17 and 0.08 eV, accordingly;
b) atom of aluminium creates levels with identical activation energies 0.08 eV.
Atoms of nitrogen and phosphorus are representatives of the fifth group of a periodic system of elements, therefore it was expected, that they will create similar donor levels, but it has not proved to be true. The impurity atom of nitrogen creates in a carbon nanotube with a chiral vector (6,5) donor level with an ionization energy 0.07 eV, and in a nanotube (10,0) - very deep donor level near to valence band. The impurity atom of phosphorus creates in a carbon nanotube with a chiral vector (6,5) donor level with an ionization energy 0.28 eV, and in a nanotube (10,0) - very deep donor level near to valence band and a level with energy 10.1 eV.
\n\t\tSliding bearings are widely used as the basic components in marine power, aerospace, water conservancy and hydropower industries. As shown in Figure 1, the sliding bearings are divided into integral sliding bearings and split sliding bearings according to their structures. They have some features, such as low noise, stable work operation, compact structure and heavy load bearing capacity [1]. With the advancement of science and technology, the automotive, marine, electric power transportation and some other industries are developing into ‘serious conditions’ such as high speed and high load, making the sliding bearing under a wide temperature environment. For example, the work temperature of engine rises from room temperature to about 140°C during different operating conditions, such as starting, accelerating, constant speed, deceleration and shutdown. From the research data, the temperature even rises up to 200°C at the time of bearing broken [2]. The work temperature of some bearings is high, for example, the working temperature of the socket bearing of missile launching mechanism exceeds 800°C. Under high temperature conditions, grease and lubricating oil fail, and unlubricated bearings will quickly be broken under the action of high friction coefficient and wear. Ordinary sliding bearings are normally lubricated due to lubricating oil with the hydrodynamic lubricating oil film. Under normal conditions, sliding bearings can generally satisfy the requirements of long-term service. However, the reasons of ablation and friction damage of the bearings 12.5% are due to poor lubrication the investigation.
The applications of plain bearings and their structures.
As shown in Figure 2, the sliding bearing damage quickly due to the lacking of self-lubricating properties of bearing, and the mixed lubrication and even dry contact friction at the start-stop stage of engine [3]. Therefore, researching and improving the friction mechanical properties of the bearing under dry friction conditions is one of the key technologies for improving the bearing life of at start-stop stage. In the case of large dust, high temperature and no lubricating oil or grease, the life of the sliding bearing will be drastically reduced. For example, the working environment temperature of rolling steel rolling mill is about 200°C, and the maximum service life of the bearing is no longer than 3 months. In order to avoid the bearing damage and improve the service life of the sliding bearing at the dry friction stage, it requires the sliding bearing should have self-lubricating property to reduce the high torque requirement and tribology at the stages of start-stop under different temperature conditions [4].
Friction damage of sliding bearings.
The self-lubricating treatment technology of sliding bearings in China is still backward. Bearings with self-lubricating properties at different temperature conditions are still very rare. Compared with the advanced bearings of European and North American, the sliding bearings of China have short life, low carrying capacity, poor self-lubricating performance and overcapacity. High-performance sliding bearings such as, self-lubricating, high-load, and long-life are relied on import. The lack of high-performance sliding bearings restricts the development of China’s basic manufacturing industry, especially the military industry. Therefore, the self-lubricating performance of the sliding bearing during in wide temperature range should be improved, and the different lubricating methods for different bearings at different temperature should be selected.
The development, manufacturing and processing capabilities of sliding bearing materials of China should be improved. At present, the main production technologies sliding bearings are centrifugal casting and alloy powders metallurgical. However, most bearings have no surface lubrication and will be quick broken. For example, more than 90% of the bearing bushes prepared by powder metallurgy in the automotive industry are not subjected to surface self-lubricating treatment such as electroplating and magnetron sputtering. Powder metallurgy technology of sliding bearing preparation has high production efficiency and low cost. The sliding bearing prepared by metallurgical process has high porosity without centrifugal force. In addition, the bearing alloys such as copper, aluminum and tin are easily oxidized at high temperature during the metallurgy preparation of sliding bearing, and metallographic organization is not uniform [5]. Centrifugal casting is another common production process for sliding bearings. The integral and thick-walled plain bearings are usually produced by centrifugal casting. However, most of the sliding bearings produced by centrifugal casting process are not subjected to inert gas protection or vacuum environmental protection, therefore, the bearing alloys are oxidized and the alloy grains size are not uniform [6].
With high dry friction coefficient and low load bearing capacity of bearings, the common methods are the surface treatments which improve the bearing life effectively. The electroplating, magnetron sputtering, self-lubricating liner antifriction, and inlaying self-lubricating materials are the main surface treatments for bearings. The lubrication and mechanical properties of the sliding bearing surface are changed by one or several electro-plating alloy layers. However, the plating solution is highly polluted, and electroplating technology of sliding bearings is seeking alternative process technology [7].
The magnetron sputtering is one of the most advanced technologies for the preparation of sliding bearings. Compared with electroplated bearings, magnetron sputtering bearings have better bonding strength and surface lubricity. However, magnetron sputtering requires a process such as pumping, vacuuming, and sputtering to form a uniform film. The magnetron process needs long production time and high production cost, and its target materials utilization rate are lower than 40%, which cannot satisfy the requirements of large-scale production. What is more, due to the constraints such as size and structure, just small bearings are able to be prepared by magnetron sputtering [8]. At present, it is an urgent problem to find a mass production of sliding bearing to satisfy the requirements of self-lubrication at wide temperature range, and having good lubricity under special working conditions such as start-stop, lean lubrication or even dry friction. The materials of electroplated plain bearing are mainly babbitt alloy, ternary and quaternary indium alloys which friction coefficient is large under dry friction conditions, and it does not have wide temperature range self-lubricating performance. The Kevlar aramid fiber modified with nano-solid lubricants, and pasted on the surface of the sliding bearing that is the liner anti-friction technology. The liner and pasted glue cannot be used at high temperature conditions, and it does not have self-lubricating properties at wide temperature. The sliding bearing inlaid solid self-lubricating materials such as graphite, MoS2, WS2 and so on, and they are punched on the working surface of the sliding bearing. With self-lubricating materials, the self-lubricating materials are crushed to form a self-lubricating film to reduce the friction coefficient of the bearing. However, single-phase self-lubricating material such as graphite and MoS2 cannot satisfy the requirements of wide temperature range self-lubrication, and the inlaid holes will reduce the mechanical strength and load capacity of the bearing. The temperature environment of the joint bearing, machine tool and electric equipment sliding bearings is room temperature environment; the working temperature of the sliding bearing for hot-burning furnace, gas pump and rolling steel rolling roller is about 200°C; the working temperature of the bearing socket for aviation is above 800°C, and they require self-lubricating materials at different temperature environments. Studies have shown that the use of coating lubrication technology improves the friction and wear, impact resistance, high temperature and longevity of the sliding shaft without changing the bearing matrix structure and composition [9]. Therefore, bearing surface coating technologies are one of the most critical and feasible methods to improve the overall technology of the domestic sliding bearing industry.
Due to the higher requirements of high-speed, high-load and high-temperature, the lubrication of sliding bearings under different temperature conditions and different load conditions will directly determine the working state and service life of the bearings and the whole machine. Many scholars have studied the self-lubricating methods of sliding bearings such as electroplating, magnetron sputtering, inlaying solid lubricants, and adhesive self-lubricating liner. However, these traditional sliding bearing self-lubricating methods have some defects. With the improvement of environmental protection requirements, the sliding bearings prepared under large-scale and high-volume production conditions have excellent self-lubricating properties under different temperature conditions, which are the keys of the current research. One of the current advanced treatment technologies for self-lubricating sliding bearings is liquid coating technology, but the theoretical calculation of bearing spraying is litter. The phenomenon of bearing sag and leveling has not been studied deeply. The optimum thickness of coating, the best surface roughness of the substrate, and coating the optimum curing temperature and optimum cooling temperature of the layer also lack of relevant details and theoretical analysis. The studies of sliding bearings with wide temperature range self-lubricating coating materials under different temperature conditions are lacking.
The traditional self-lubricating sliding bearing production and preparation processes are mainly electroplating, magnetron sputtering, inlaying solid lubricants, and adhesive self-lubricating liner and so on. The self-lubricating bearing processes and their performances are summarized as follows.
In the severe conditions such as large dust, high pollution, high load bearing, lacking of lubricating oil and grease, sliding bearings only rely on their own lubrication to improve work performance. For example, in the automobile manufacturing, cement production and coal mining industries, the inlaying solid lubricants and adhesive self-lubricating liner are the common methods of the joint bearings and bushing sleeves.
The friction coefficient of the bearing is reduced, the wear resistance is improved and the working life is prolonged through the modified liners for sliding bearings. Braided liners are generally composed of Kevlar aramid fiber materials (KEVLAR), polytetrafluoroethylene (PTFE), modified carbon fiber materials, and nano-additives [10]. The structure of sliding bearing with liner is shown in Figure 3. In order to obtain a small shear force and a large bonding strength, the fabric liner is bonded on the bearing surface through the adhesive glue. The frictional coefficient is decreased by changing the metal to metal contact to metal to liner contact. Aderikha studied the friction and wear properties of the liner based on PTFE and plasma treated polymer fibers. The results showed that the friction coefficient was 0.15–0.2 under different loads [11]. Li studied the friction and wear properties of nano-materials SiC and WS2, and the friction coefficient of surface liner under dry friction was about 0.05–0.06 [12]. Fabrics were treated with rare earths CeO2, LaCl3, La2O3 and CeF3 by Shen, Zhan and some scholars, and their friction, wear properties and bonding properties of the joint bearings with the modified rare earths were studied. The results shown that the bonding strength was higher under the action of rare earths, the film formation is faster, and the coefficient of friction is generally less than 0.1 [13, 14, 15, 16]. Liners and adhesive glue as the main component cannot be used at medium and high temperatures, and the bonding liner method is generally applicable to small thick-walled sliding bearings, which has certain limitations for medium and large sliding bearings.
Join bearing with self-lubricating liner.
The self-lubricating materials are inlayed on the surface of bearing. As shown in Figure 4, the solid lubrications will be expanded when sliding bearing subjected to load, and the bulged out lubrications are ground to tiny wear debris. With the sliding movement of bearing, the frictional coefficient is decreased with the formation of lubricating film from the debris. The inlaid materials are generally the solid lubricant materials such as graphite, molybdenum disulfide and PTFE. Wei prepared a new self-lubricating material consisted of PTFE, graphite and glass fiber. The results showed that the friction and wear properties of self-lubricating materials prepared by 40% PTFE + 20% graphite + 20% lead powder + 20% glass fiber were the best [17]. MoS2/Sb2O3 mixed powders were produced to form solid lubricant by Zabinski with thermosetting bonding method. The results pointed out that MoS2 and Sb2O3 have synergistic antifriction effect on friction work, and Sb2O3 can prevent MoS2 from oxidizing [18]. Li prepared FeS/copper-tin alloys as the inlaying materials by powder metallurgy. The research showed that the increase of FeS content reduce the friction coefficient. When the FeS content is 10%, the friction coefficient is 0.15 [19]. The research studies of inlaid solid self-lubricating materials showed that the working conditions of the prepared materials were mostly room temperature environment, and the studies of medium and high temperature self-lubricating materials were few. Therefore, the working conditions of sliding bearings embedded with solid self-lubricating materials on the market are mostly room temperature environments. In addition, the inlaid structure will reduce the strength of the bearing, resulting in low bearing capacity.
Plain bearing inlaying with solid lubrications.
Sliding bearings prepared by modified liner technology and inlaid solid self-lubricating technology satisfy the self-lubricating requirements of room temperature conditions, but the fiber fabric materials cannot be used at high temperature. However, there are few studies of solid self-lubricating materials that satisfy the self-lubricating under the wide temperature range. Generally, bearings with inlaying solid materials are used at room temperature environment, and the structural strength of the bearing will be reduced by this technology.
The working temperature of bearing bush, plain bearing of rolling mills near to furnace and sleeves is from 100 to 200°C. At the start and stop stages, the automobile bearing bush is under a boundary lubrication or even a dry friction state because the lubricating oil film is not formed at start stage or broken at stop stage. However, the sliding bearings of rolling steel and the bearings in the heating furnace may cause the lubricating oil and grease to fail due to the high working environment temperature. In order to improve the performance of the bearing and prolong its service life, bearings need to be self-lubricated. The most common self-lubricating treatment methods for plain bearings represented by bearing bushes are electroplating and magnetron sputtering. As shown in Figure 5, one or more layers can be prepared on the surface of the bearing to improve bearing lubrication and improve bearing fatigue strength and service life. Wang studied Ni/SiC and Ni/Al2O3 electroplating techniques, and ceramics such as SiC and Al2O3 were added to the coating material, which improve the wear resistance of the bearing [20]. Li studied the friction and wear behavior of nano-Ni-PTFE composite coating on steel substrate. The results showed that the coating friction coefficient range was 0.05–0.15 under different loads [21]. Zhang prepared a MoS2 coating containing nano-graphite particles by electroplating brush, and tested the friction coefficient was from 0.05 to 0.15 [22]. However, the plating prepared by the electroplating brush is not uniform, and the bonding strength is not as good as that of chemical electrophoresis. Studies had shown that metals such as In, Ni, and W improve the wear resistance of sliding bearing coatings [23, 24]. The addition of rare earth metals such as La, Ta, Nb significantly improved the frictional mechanical properties of the sliding bearing coating [25, 26, 27]. The friction coefficient of electroplated copper-tin alloy, aluminum-tin alloy and babbitt alloys under dry friction conditions is generally 0.3–0.6, which needs to be combined with lubricating oil and grease to satisfy the lubrication requirements [28]. Electroplated plain bearings are currently the most widely used preparation methods, but the plating solution is highly polluting and does not satisfy environmental production requirements.
Technology of electroplating of bearings.
Unlike electroplating, magnetron sputtering does not cause environmental pollution. The magnetron sputtering process shown in Figure 6 has a dense film, and the thin metallographic structure in a vacuum environment makes the performance of the sliding bearing superior to that of the electroplated production. Li prepared a Babbitt Cu-Sn-Sb film on a steel substrate by magnetron sputtering. The friction coefficient was from 0.1 to 0.25 after dry friction experiment of 4000 rpm [29]. The Max- phase Ti3SiC2 material was sputtered during magnetron sputtering of Cu film. It studied by Li, and results showed that the physical and mechanical properties of Cu film were significantly improved after adding new materials [30]. Guo studied the metallographic properties and hardness of the magnetron sputtering bearing of AlSn20 material, and the experimental results reached the international advanced level like Miba bearings [31]. Song prepared AlSn20Cu thin films by magnetron sputtering. The hardness of the tested films was 120 HV, and the friction coefficient was less than 0.1 under oil lubrication [32]. Although the high hardness film improves the bearing capacity of the bearing, it also reduces the adhesion of the bearing. However, if the surface hardness of bearing is less than 50 HV will have better embedding performance [33].
Technology of magnetron sputtering.
The different compound films can be synthesized and synthesized because maximum as eight targets can be sputtered simultaneously from magnetron sputtering. In the existing research, bearing alloy composite films such as Ti/Cu/N CuxSny, TiN/Cu had been prepared, and adhesin strength of these films is excellent [34, 35]. However, the tribological properties of above materials are the same as the bearing materials such as AlSn20 and AlSn20Cu. The friction coefficient is higher under dry friction conditions and mixed lubrication conditions, which cannot satisfy the self-lubricating performance requirements at wide temperature.
To improve the tribological and mechanical properties, the noble metal materials such as indium or rare earth materials are used during the electroplating plating process. However, the plating solution is a strong acid or a strong alkali substance, which is likely to cause serious environmental pollution. Magnetron sputtering equipment is expensive to manufacture. Many magnetron sputtering equipment only produce small test specimens in a laboratory environment, and cannot be mass-produced or mass-produced for large-sized sliding bearings. The utilization rate of magnetron sputtering target is generally less than 40%, and the working time is long and the production efficiency is not high when vacuuming, injection and depositing materials [36]. Therefore, it is necessary to find a new technology to prepare a self-lubricating sliding bearing.
The most advanced surface treatment method available today is the surface spraying coating method. Compared with traditional surface treatment processes such as electroplating and magnetron sputtering, it has the advantages of environmental friendliness, high production efficiency, coating processing, and good coating lubrication performance. Spraying sliding bearings are characterized by high speed and high efficiency. It takes only several seconds to spray lubricating liquids, and large-scale and large-scale production will be realized if solidification furnaces and cooling furnaces are enough. For example, an automatic spraying production line of Shanghai Federal-Mogul company produces more than 12 million bushings with spraying coating (Figure 7 and Figure 9).
Plain bearings with dope coating of overseas.
The north Americans first began to study the coating technology of sliding bearing coatings and applied for related technology patents. For example, in the 1970s, Campbell used MoS2 and Sb2O3 as solid fillers and epoxy resin as a binder to prepare self-lubricating coating, which was applied to sliding bearings [37]. The bearing coating prepared from materials such as MoS2, Sb2O3 and epoxy resin has the advantage of low friction coefficient, but the ordinary epoxy resin working temperature generally does not exceed 140°C, which does not satisfy the long-term use requirements of temperature conditions above 200°C.
After several decades of development, the of plain bearings with self-lubricating coating made from liquid spraying have been large scale produced by developed companies such as Federal-Mogul Co., Austrian Miba Co., Japan TAIHO KOGYO Co. However, there are few research materials on self-lubricating coatings in China. In the year of 1983, the first MoS2 self-lubricating coatings prepared by liquid dope was studied by Liu of the Institute of Coatings, however, the coatings were not applied to sliding bearings [38]. The sliding bearing surface coating technology of China started late, and it is still a new technology. In recent years, many bearing research institutes and manufacturers in China have begun to study the coating technology of sliding bearing made by liquid spraying. As shown in Figure 8, bearings with MoS2 lubricating coating made by liquid spraying, and prepared with Zhejiang CSB Co. and the ZYNP Co.
Plain bearings with dope coating of China.
The widely used coating dopes in China are MoS2 and PTFE dopes, which wear resistance and temperature resistance are poor, and the tribological properties of composition elements such as resin and auxiliary are lower than that of Dow Corning D7409 and Kawanori of Japan. However, self-lubricating coatings for bearings under the medium (200°C) and high temperature (800°C) dopes are lacking of. The special lubricating materials of coating dopes of American D7409 and Kawanori of Japan did not particularly be selected according to the special alloys of bearing likewise the different aluminum alloys, copper alloys, and babbitt alloys, and these coatings drop easily if the temperature varies with time. Therefore, it is important to develop new coating dope for special alloys at different temperature.
The coating spraying technology includes coating dope preparation, liquid dope spraying through spraying gun and solid coating formation. The coating dope consists of self-lubricating materials, anti-wear materials, resins, auxiliaries and solvents. The different lubrications and anti-wear materials easily mixed together due to the liquid solution, and the coating made from dope will have the excellent tribological properties. The principle of paint spraying is shown in Figure 9. There are two ports on the spray gun connected to the spraying gas and dope respectively. The paint dope is in a pressure tank with automatic stirring. It is driven into the spraying gun by the action of the pump to adjust the size of the gas source, liquid flow rate and spraying distance to control the amount of spraying dope.
Work principle of coating dope spraying
Guo used epoxy resin as the binder, and MoS2 and PTFE were used as the main lubricating materials to prepare the antifriction coating. The friction mechanical properties of the coating were studied at different curing temperatures. The results showed that the coating performance was the best when the coating formation temperature was 120°C. The coefficient of friction is 0.125, and the adhesion is 16.73 N [39]. However, ordinary epoxy resins have poor temperature resistance, and the coating thus prepared cannot be operated for a long period of time at 200° C. Cao studied the spraying distance effects on coating spraying efficiency and coating thickness uniformity. He pointed out that reducing the spraying distance improves the adhesion between the coating and the substrate. However, the shorter the distance was, the worse the coating thickness uniformity could be [40]. Yang used sagging as the object of assessment, and studied the spraying distance and spraying temperature during the PTFE coating preparation, but the principle and theory of sag phenomenon had not studied [41].
The heating temperature of the coating to form a coating is generally from 120 to 220°C. Under the action of materials such as resin and polyimide, the liquid coating has a sealing effect on the solid coating process which leads to low coating porosity. Li uses rare earth materials and a rapid thermosetting method to prepare a coating, and the porosity of coating is just only 0.35% [42]. The porosity of sliding bearing produced by the powder metallurgy and electro-plating is high. Lins et al. studied the effect of current density on the porosity of nickel deposited with copper substrates. The porosity of nickel coatings was 6.22% according to different current magnitude tests [43]. The films prepared by magnetron sputtering are relatively dense, and the porosity is generally from 0.5 to 5% [44, 45]. If 1–2% reduction in porosity, the fatigue strength of the workpiece will increase from 10 to 30%, so low porosity is one of the necessary conditions for sliding bearings [46].
The initial state of the coating prepared on the surface of the bearing is liquid. In order to avoid sagging of the coating, the coating thickness should not be too thick. The optimum coating thickness of the coating method is less than 20 μm, and the infiltration method and the brushing method are prepared. The thickness of the coating should not exceed 120 μm. The bonding strength of the coating to the substrate is influenced by surface roughness of the substrate, the type of coating adhesive, the preheating and the curing temperature. Therefore, it is particularly important to study the coating forming process to improve the bonding strength of the coating. An used epoxy resin and polyvinyl butyral as binder to prepare coating with TiO2 as filler. The bond strength of the steel matrix is from 9 to 12 MPa [47]. Mao prepared a coating of made by graphite, MoS2, PPS (polyphenylene sulfide) and PES (polyethersulfone resin) by regression test. The optimum bonding strength of the tested coating was 42 MPa [48]. The self-lubricating coatings with polyamide-imide used as the binder, and the main lubricants were MoS2 and PTFE. The adhesive strength studied by Song according to the GB9286-88 paint film rating test of China is poor as level 1, which does not reach the optimal bonding strength [49].
Self-lubricating coatings are mainly composed of solid lubricating fillers such as MoS2, PTFE, WS2, graphite, and some additives such as polyimide, epoxy resin, phenolic resin, leveling agent, dispersing agent, defoaming agent, etc. Gao used PAI (polyamide-imide polyamide-imide) as a binder, and the coating prepared by mixing 8% MoS2, 5.4% PTFE and 1.5% graphite had the best performance. The coating had not changed which was tested at 80°C and −40°C, and it was not changed for socking in 10% HCl over 3 months [50]. Li made PTFE coating which added MoS2 and graphite as the solid lubricants. The PTFE used as the main component, and PEEK (polyether ether ketone), PI (polyamide) and PPS as binders. The coefficient of friction of the PTFE coating was 0.12 [51]. The studies of self-lubricating sliding bearing coatings are mainly concentrated in recent years, so there are few researches of self-lubricating coatings which used at wide-temperature. Ordinary epoxy resins and polyimide materials are generally used in coatings, however, they cannot work for long under condition of 200°C. In addition, the sagging and leveling phenomenon of the sprayed sliding bearing have not been studied in detail. The theory of optimal thickness of coating, optimum roughness of the substrate, optimum curing temperature of the coating and cooling temperature of the coating are also very few.
Compared with the self-lubricating sliding bearings prepared by electroplating and magnetron sputtering, the paint-coated bearings have the advantages of environmental protection and high production efficiency. The review of coating research shows that the development of self-lubricating coatings under different temperature is one of the best technologies for preparing sliding bearings due to the excellent wear resistance and low friction performance.
The work temperature of socket bearings in the missile launcher mechanism is higher than 800°C. Materials such as resins used as components in dope coating cannot be operated under ultra-high temperature conditions. At present, the maximum working temperature of grease-based lubricating materials generally do not exceed 200°C, and the maximum using temperature of polymer-based self-lubricating materials (single-phase) generally does not exceed 400°C [52]. The ranges of optimum lubrication for single-phase materials are shown in Table 1.
Graphite | MoS2 | WS2 | WSe2 | |
---|---|---|---|---|
Frictional coefficient | 0.05–0.15 | 0.05–0.20 | 0.08–0.20 | 0.09–0.20 |
Max using temperature | 300°C | 340°C | 450°C | 450°C |
TaS2 | PbO | BN | BC4 | |
Frictional coefficient | 0.05–0.20 | 0.07–0.20 | 0.06–0.20 | 0.10–0.30 |
Max using temperature | 550°C | 700°C | 900°C | 1200°C |
The frictional coefficient of MoS2 is generally lower than 0.1 under room temperature. The oxidations of Mo element will be generated if MoS2 working temperature exceeds 200°C, that the self-lubricity of MoS2 is reduced. The MoS2 lubrication performance will be further reduced and the self-lubricating effect will be lost if the temperature exceeds 350°C. In Table 1, B2O3 produced by BC4 under high temperature has self-lubricity, and its friction coefficient is from 0.10 to 0.30, while the BC4 friction coefficient is from 0.35 to 0.40 at room temperature [55]. Single coatings are difficult to maintain self-lubricating performance over a wide temperature range. Ouyang used BaSO4, BaCrO4, Ag as the main materials to prepare self-lubricating materials. The results of friction and wear tests showed that the friction coefficient was from 0.38 to 0.55 when the temperature was from room temperature to 800°C [56]. Zhen studied a self-lubricating material mainly consisted of CaF2, BaF2 fluoride and noble metal Ag, and the frictional coefficient of the composite material is from 0.24 to 0.3 at the temperature from room temperature to 800°C [57]. The physical and phase change will vary with temperature, for example, the structure and tribological properties of Ti2AlC coating made by thermal spraying are different at room temperature and 800°C [58]. The coating shown in Figure 10a is spongy and many pores, however, the coating was oxidized and became dense at 800°C.
Structure and abrasion marks of Ti2AlC coating at different temperature: (a) room temperature; (b) 800°C.
In order to make the bearings have self-lubricating performance under ultra-high temperature conditions, the common method is to prepare self-lubricating coating by powder metallurgy method. In the powder sintering method, the self-lubricating powders often mixed with some functional powders, and placed together in a high-temperature furnace to prepare a self-lubricating composite material. In the preparation of self-lubricating composites by powder metallurgy, local unevenness will be generated due to uneven powder mixing, uneven laying, uneven powder size or incomplete sintering of the powder during sintering [59].
Chen studied the uneven microstructure of AlSi alloy powder. The study showed that when the mass fraction of AlSi alloy powder is 50%, it can effectively reduce the unevenness of the product and improve the stability of the alloy [60]. Ding studied the powder metallurgy oxidation behavior at different temperatures, different processes and different atmospheres, and results pointed out that the amino atmosphere was more protective than nitrogen [61]. Cao prepared Ti6Al4V coating by sintering 23 μm Ti particles and 40 μm Al-V powder. The powder was cold pressed to 180 MPa before sintering, and then sintered at 1250°C in vacuum to prepare Ti6Al4V coating. The layer porosity was only 3.5% [62]. Studies had shown that increasing pressure during powder metallurgy preparation of products, and using an atmosphere to protect the environment or vacuum environment is conducive to the reduction of porosity.
As shown in Table 2, the frictional coefficient of self-lubricating materials prepared by the powder sintering method is from 0.26 to 0.8 under different temperature conditions. Although self-lubricating materials at wide temperature domain had achieved some success, they had not been applied to sliding bearings. Most of the results were in the laboratory stage, and the self-lubricating composite materials prepared by powder sintering had defects such as high oxidation and high porosity. In Table 2, in order to reduce the high temperature frictional coefficient, a highly toxic fluoride material under high temperature conditions was used, which was not conducive to safe production.
Materials | Lubrications | CoF at room temperature | CoF at 600°C | CoF at 800°C |
---|---|---|---|---|
Ag-Pb-Cu-Sn [63] | Ag-Pb | 0.35 | 0.3 | — |
ZrO2-MoS2-CaF2 [64] | MoS2-CaF2 | 0.3 | 0.8 | 0.27 |
Ni3Al-Ag-Mo-BaF2/CaF2 [65] | Ag, BaF2/CaF2 | 0.35 | 0.38 | 0.32 |
Ni-Ag-BaF2/CaF2 [66] | Ag, BaF2/CaF2 | 0.3 | 0.32 | 0.26 |
NiCr/Cr3C2-WS2 [67] | WS2 | 0.42 | 0.28 | — |
CoFs of self-lubricating composite materials at high temperature.
The CoFs (coefficients of friction) of self-lubricating materials studied in Table 2 is high and at 800°C. In order to satisfy the requirements of self-lubrication of sliding bearings used at wide temperature range, the new process and method should be used.
The solid self-lubricating powder particles are heated and molten by thermal spraying, and then directly sprayed onto the surface of the sliding bearing to form a coating. Since there is no resin, the prepared coating can be applied to a super-high temperature working condition. The kerosene, propane, or hydrogen used as burn gas during the supersonic flame spraying, and the molten or semi-molten alloy powders are sprayed with high speed on the surface of substrate by flame spraying. The time of alloys contact with oxygen in the air is very short due to the high spraying speed of 500 m/s. Supersonic flame spraying technology widely used as surface additive processing technology, and have high production efficiency and good coating bonding strength. A variety of coatings had been successfully prepared by thermal spraying technology, and which also can be used as sliding bearing materials. Thus, the preparation of sliding bearing coatings in combination with thermal spraying technology is reliable. Supersonic flame spraying is shown in Figure 11. The self-lubricating powders enter the spraying gun firstly, then, with the action of prismatic shock wave, the molten powders are sprayed on the surface of substrate to form a coating.
Principle of supersonic flame spraying.
High bonding strength is one of the advantages of supersonic flame spraying. The bonding strength of WC-10Co-4Cr coating made by supersonic flame sprayed and prepared by Zhu was 72.63 MPa, and the porosity was 1.5% [68]. WC–Co coating studied by Tang, and prepared on the surface of the screw material substrate had a bonding strength of 65 MPa [69]. The bonding strength of MoSi2 coating prepared by Wu was only 14.5 MPa, indicating that the material and spraying parameters were important factors for the bonding strength of the coating. If bonding strength is low, the bonding strength can be improved by optimizing the spraying parameters [70].
The 54% Cr3C2 added with 34% NiCr and 12% CaF2/BaF2 mixed powders, and sprayed as coating was studied by Xue. The frictional coefficient of coating was 0.75 and 0.37 at room temperature and 500°C respectively [71]. Hou used supersonic flame spraying process to prepare aluminum bronze alloy coating on steel substrate, and the frictional coefficient of coating was from 0.08 to 0.12 under different oil lubrication conditions [72]. Copper alloy and aluminum alloy materials are also suitable for supersonic spraying to prepare coatings. The studies like AgSnO2/Cu coating prepared by Chong, Al-Si coating prepared by Wu, and Cu(ln, Ga)(S, Se)2 coating prepared by Park [73, 74].
Cold spray technology is a new spray technology developed from thermal spray technology in recent decades. The obvious spraying characteristics are low temperature and high speed. As shown in Figure 12, under the action of high pressure gas, the powder particles are supersonic flying through the Lava tube and deposited directly on the surface of the plain bearing to form a coating by the pure plastic deformation.
Principle of supersonic cold spraying.
The sliding bearing materials are generally copper alloys, aluminum alloys and tin alloys. These metal materials have an ability of excellent plastic deformation during the formation of coating by cold spraying. Guo, Li and some scholars studied the coating properties of bearing alloy materials such as CuSn6, CuSn8, Cu5Sn95, AlSn5, AlSn10 and AlSn20 made by cold spraying, and the frictional coefficient of bearing alloy materials under dry friction conditions were generally higher than 0.5 [75, 76, 77, 78, 79]. The preparation of supersonic cold spray coating is mainly based on the plastic deformation ability of powder particles, so the material should have excellent elastoplasticity [80]. The self-lubricating powder materials such as MoS2, graphite and h-BN have poor elastoplastic deformation ability, and they are difficult to deposit on the bearing to form a coating.
The material frictional tests of coatings made by powder sintering, supersonic thermal spraying and supersonic cold spraying showed that the supersonic flame spraying and cold spraying are the desired methods to prepare coating used at high temperature. However, many materials lack of plastic deformation ability that the liquid dope spraying is the best method to deposit coating used at temperature lower than 200°C.
According to the studies of self-lubricating sliding bearing and self-lubricating composite materials at room temperature, medium temperature and high temperature, bearings with self-lubricating liners and bearings inlaying with solid lubricating materials are used at room temperature commonly. Bearings treated by electroplating, magnetron sputtering and liquid spraying are used at the temperature lower than 200°C. However, there are no bearings that have the continue self-lubricating performance from room temperature to 800°C, though the coating made by powder sintering, supersonic thermal spraying and cold spraying.
The production efficiency, oxidation rate, coating thickness, porosity and bonding strength compared and shown in Table 3 according to the different surface treatments and bearing using temperature. As shown in Table 3, the coating thicknesses prepared by electroplating, magnetron sputtering and liquid dope spraying is thin. The electroplating is environment polluting.
Technologies | Production efficiency | Oxidation | Coating thickness | Porosity | Adhesive strength | Shortages |
---|---|---|---|---|---|---|
Electro-plating | Middle | Low | <15 μm | Middle | Low | Pollution |
Magnetron sputtering | Low | Low | <15 μm | Low | High | Less utilization of target |
Fabric liner | Low | — | — | — | High | Woven fabric invalid at high temperature |
Supersonic flame spraying | High | Middle | <1 mm | Low | High | Spherical powders |
Cold spraying | High | Low | >1 mm | Low | High | Powders need plastic deformation ability |
Powders sintering | High | High | >1 mm | High | High | High oxidation |
Inlaying lubrications | Low | Low | — | — | — | Structure strength is decreased |
Liquid dope spraying | High | Low | <20 μm | Low | Middle | — |
Comparisons of different self-lubricating methods.
The production efficiency of film produced by magnetron sputtering is low. It takes more than 20 h to prepare a film which thickness is 10 μm. The film of large sliding bearing cannot be prepared due to the structure limit. The self-lubricating liner that added on the surface of bearing has low temperature resistance due to the fail of adhesive glue and fiber braid. The structure strength is decreased as the structure of bearing changing with inlaying solid materials. The oxidation and high porosity of bearing will be generated by the method of powder sintering. The structure of materials used for thermal and cold spraying should be spherical, and the materials used for cold spraying should have plastic deformation performance. The ceramic materials such as WC, SiC, h-BN are limit to use by the thermal spraying and cold spraying. The coating made by liquid dope spraying has the advantages of high production efficiency, green materials and good lubricity. The thickness more than 1 mm of coating on bearing prepared by supersonic flame spraying can be obtained, and it has the advantages of low porosity, good bonding strength and high production efficiency. Therefore, low- temperature and medium-temperature self-lubricating coatings should be prepared by liquid dope spray method, and ultra-high temperature wear-resistant anti-friction coatings should be prepared by thermal spraying.
The micro structure of tin and cooper coating made by different manufacturing technologies are shown in Figure 13 [81, 82, 83, 84, 85]. The obvious cracks can be found in Figure 13a,b which manufactured by centrifugal casting and powder metallurgy sintering respectively. The coating made by magnetron sputtering is more smooth than that of electroplating, and the porosity of coating made by magnetron sputtering is little than that of electroplating. The tribological and mechanical properties of alloy coating made by centrifugal casting and powder metallurgy sintering are poor from the results shown in Figure 13. However, the shortages of electroplating and magnetron sputtering are the pollutions and low efficiency respectively. The new coating formation technologies such as liquid dope spraying and supersonic flame spraying should be applied for sliding bearings.
Microstructure of Cu-Sn alloy of different manufacturing technologies: (a) centrifugal casting; (b) sintering; (c) electroplating; (d) magnetron sputtering.
The traditional self-lubricating treatments of sliding bearings are mainly electroplating, magnetron sputtering, bonding self-lubricating liners and inlaying solid self-lubricating materials. The new self-lubricating preparation technologies of sliding bearings are mainly the liquid dope spraying and supersonic flame spraying. The problems of sliding bearings are listed as follows through above investigations and discussions.
High friction coefficient and low fatigue life
Most of the sliding bearings have not been surface treated, and these bearings have high dry frictional coefficients, low fatigue strength, low life and low bearing capacity. The frictional coefficient of copper alloy, aluminum alloy and tin alloy of sliding bearings is generally higher than 0.5 under dry friction condition, and it does not have self-lubricity under a wide temperature range. The traditional copper alloys of sliding bearings contain Pb metal, which is polluting and harmful to human. The self-lubricating materials at ultra-high temperature are still in the laboratory research stage, and the sliding bearing with self-lubricating cannot be produced on a large scale.
Environmental pollution and low production efficiency
The usage of acid, alkali and heavy metal solutions during the production of self-lubricating sliding bearings will cause serious environmental pollution. Magnetron sputtering takes long time during vacuuming and injection processes, and the efficiency of depositing thin films is lower than other processes. The utilization efficiency of target materials of magnetron sputtering is generally less than 40%. The multiple modification treatment processes and bonding processes are required for preparing self-lubricating bearings using of bonding self-lubricating fabric liners and bearings with inlaid solid self-lubricating materials. The punching holes and inlaying solid lubricating materials are required during the production. The production efficiency of inlaying solid lubrications is low, which cannot satisfy the requirements of large-scale mass production.
The theory of spraying process for sliding bearing is not deep enough
The liquid dope spraying method is one of the best methods for preparing self-lubricating sliding bearings which used at room temperature and medium temperature. However, the spraying mechanisms such as leveling and sagging coating on bearing surface have not been studied. The optimum thickness of the coating, the optimum surface roughness of the substrate, the optimum curing temperature of the coating, and the optimum cooling temperature of the coating were not studied in details.
Poor tribological properties
The wear-resisting and self-lubricating performances of coatings are poor, and their service life under the medium temperature (200°C) is short. There are no special materials which have low difference of thermal expansion and similar physical properties with the given materials of bearings. The self-lubricating materials used at high temperature are currently in the state of laboratory research stage, and have not been prepared for bearings at large production scale.
The processing technologies and material properties of self-lubricating sliding bearings made by electroplating, magnetron sputtering, bonded self-lubricating liners, and embedded solid self-lubricating materials are studied and summarized in this paper. The advantages and disadvantages of self-lubricating bearings made by different technologies are shown. The widely surface treatment of sliding bearing is electro-plating, however, the bond strength is lower than magnetron sputtering, supersonic flame spraying, cold spraying and powder sintering technologies, and the solutions of electro-plating is pollution and harmful to human. The properties of thin film made by magnetron sputtering is excellent, however, the production efficiency is too low due to the vacuum and deposition process. The large-scale size of bearings such as bearings used in ship diesel engine cannot be deposited due to the structure limit of magnetron sputtering machine. The porosity of bearing made by powder sintering is high, and the alloys are oxidized at the high sintering temperature. The mechanical properties of cold spraying are better than thermal spraying, however, the materials of cold spraying should have excellent plastic deformation ability, that the materials such as MoS2, C, h-BN and many ceramics materials are not able to be deposit on the surface of bearing.
Through comparative analysis, liquid dope spraying method is suggested to be adopted as the surface treatment process for bearing using at room temperature and medium temperature. The solid powder thermal spraying is suggested to be used for preparation of bearings working at high temperature. The liquid dope spraying is used in the advanced sliding bearing manufacturing companies, and the materials of liquid dope should be improved due to the wide range temperature variation at start and stop stage. The self-lubricating coating at high temperature is lacking, and the tribological properties of bearings at high temperature are poor. There were few materials that had continuous self-lubricating properties at the wide range temperature. According to the review, the lubrication materials used at high temperature mostly were the fluorides which were poisonous at high temperature. According to the summaries of self-lubricating treatments, the green materials, coating formation mechanisms, technology processes and tribological properties of liquid dope spraying and supersonic flame spraying for sliding bearings should be studied further.
This research was supported by Shanghai Xiangsheng beco engine bearing Co, Ltd. and its chairman of Shengxiang Zhu.
IntechOpen implements a robust policy to minimize and deal with instances of fraud or misconduct. As part of our general commitment to transparency and openness, and in order to maintain high scientific standards, we have a well-defined editorial policy regarding Retractions and Corrections.
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\\n\\nA published Erratum will adhere to the Retraction Notice publishing guidelines outlined above.
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\\n"}]'},components:[{type:"htmlEditorComponent",content:'IntechOpen’s Retraction and Correction Policy has been developed in accordance with the Committee on Publication Ethics (COPE) publication guidelines relating to scientific misconduct and research ethics:
\n\n1. RETRACTIONS
\n\nA Retraction of a Chapter will be issued by the Academic Editor, either following an Author’s request to do so or when there is a 3rd party report of scientific misconduct. Upon receipt of a report by a 3rd party, the Academic Editor will investigate any allegations of scientific misconduct, working in cooperation with the Author(s) and their institution(s).
\n\nA formal Retraction will be issued when there is clear and conclusive evidence of any of the following:
\n\nPublishing of a Retraction Notice will adhere to the following guidelines:
\n\n1.2. REMOVALS AND CANCELLATIONS
\n\n2. STATEMENTS OF CONCERN
\n\nA Statement of Concern detailing alleged misconduct will be issued by the Academic Editor or publisher following a 3rd party report of scientific misconduct when:
\n\nIntechOpen believes that the number of occasions on which a Statement of Concern is issued will be very few in number. In all cases when such a decision has been taken by the Academic Editor the decision will be reviewed by another editor to whom the author can make representations.
\n\n3. CORRECTIONS
\n\nA Correction will be issued by the Academic Editor when:
\n\n3.1. ERRATUM
\n\nAn Erratum will be issued by the Academic Editor when it is determined that a mistake in a Chapter originates from the production process handled by the publisher.
\n\nA published Erratum will adhere to the Retraction Notice publishing guidelines outlined above.
\n\n3.2. CORRIGENDUM
\n\nA Corrigendum will be issued by the Academic Editor when it is determined that a mistake in a Chapter is a result of an Author’s miscalculation or oversight. A published Corrigendum will adhere to the Retraction Notice publishing guidelines outlined above.
\n\n4. FINAL REMARKS
\n\nIntechOpen wishes to emphasize that the final decision on whether a Retraction, Statement of Concern, or a Correction will be issued rests with the Academic Editor. The publisher is obliged to act upon any reports of scientific misconduct in its publications and to make a reasonable effort to facilitate any subsequent investigation of such claims.
\n\nIn the case of Retraction or removal of the Work, the publisher will be under no obligation to refund the APC.
\n\nThe general principles set out above apply to Retractions and Corrections issued in all IntechOpen publications.
\n\nAny suggestions or comments on this Policy are welcome and may be sent to permissions@intechopen.com.
\n\nPolicy last updated: 2017-09-11
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I am also a member of the team in charge for the supervision of Ph.D. students in the fields of development of silicon based planar waveguide sensor devices, study of inelastic electron tunnelling in planar tunnelling nanostructures for sensing applications and development of organotellurium(IV) compounds for semiconductor applications. I am a specialist in data analysis techniques and nanosurface structure. 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After obtaining a Master's degree in Mechanical Engineering, he continued his PhD studies in Robotics at the Vienna University of Technology. Here he worked as a robotic researcher with the university's Intelligent Manufacturing Systems Group as well as a guest researcher at various European universities, including the Swiss Federal Institute of Technology Lausanne (EPFL). During this time he published more than 20 scientific papers, gave presentations, served as a reviewer for major robotic journals and conferences and most importantly he co-founded and built the International Journal of Advanced Robotic Systems- world's first Open Access journal in the field of robotics. Starting this journal was a pivotal point in his career, since it was a pathway to founding IntechOpen - Open Access publisher focused on addressing academic researchers needs. Alex is a personification of IntechOpen key values being trusted, open and entrepreneurial. Today his focus is on defining the growth and development strategy for the company.",institutionString:null,institution:{name:"TU Wien",country:{name:"Austria"}}},{id:"19816",title:"Prof.",name:"Alexander",middleName:null,surname:"Kokorin",slug:"alexander-kokorin",fullName:"Alexander Kokorin",position:null,profilePictureURL:"https://mts.intechopen.com/storage/users/19816/images/1607_n.jpg",biography:"Alexander I. Kokorin: born: 1947, Moscow; DSc., PhD; Principal Research Fellow (Research Professor) of Department of Kinetics and Catalysis, N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow.\r\nArea of research interests: physical chemistry of complex-organized molecular and nanosized systems, including polymer-metal complexes; the surface of doped oxide semiconductors. He is an expert in structural, absorptive, catalytic and photocatalytic properties, in structural organization and dynamic features of ionic liquids, in magnetic interactions between paramagnetic centers. The author or co-author of 3 books, over 200 articles and reviews in scientific journals and books. He is an actual member of the International EPR/ESR Society, European Society on Quantum Solar Energy Conversion, Moscow House of Scientists, of the Board of Moscow Physical Society.",institutionString:null,institution:{name:"Semenov Institute of Chemical Physics",country:{name:"Russia"}}},{id:"62389",title:"PhD.",name:"Ali Demir",middleName:null,surname:"Sezer",slug:"ali-demir-sezer",fullName:"Ali Demir Sezer",position:null,profilePictureURL:"https://mts.intechopen.com/storage/users/62389/images/3413_n.jpg",biography:"Dr. Ali Demir Sezer has a Ph.D. from Pharmaceutical Biotechnology at the Faculty of Pharmacy, University of Marmara (Turkey). 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Focus of his research activity is drug delivery, physico-chemical characterization and biological evaluation of biopolymers micro and nanoparticles as modified drug delivery system, and colloidal drug carriers (liposomes, nanoparticles etc.).",institutionString:null,institution:{name:"Marmara University",country:{name:"Turkey"}}},{id:"61051",title:"Prof.",name:"Andrea",middleName:null,surname:"Natale",slug:"andrea-natale",fullName:"Andrea Natale",position:null,profilePictureURL:"//cdnintech.com/web/frontend/www/assets/author.svg",biography:null,institutionString:null,institution:null},{id:"100762",title:"Prof.",name:"Andrea",middleName:null,surname:"Natale",slug:"andrea-natale",fullName:"Andrea Natale",position:null,profilePictureURL:"//cdnintech.com/web/frontend/www/assets/author.svg",biography:null,institutionString:null,institution:{name:"St David's Medical Center",country:{name:"United States of America"}}},{id:"107416",title:"Dr.",name:"Andrea",middleName:null,surname:"Natale",slug:"andrea-natale",fullName:"Andrea Natale",position:null,profilePictureURL:"//cdnintech.com/web/frontend/www/assets/author.svg",biography:null,institutionString:null,institution:{name:"Texas Cardiac Arrhythmia",country:{name:"United States of America"}}},{id:"64434",title:"Dr.",name:"Angkoon",middleName:null,surname:"Phinyomark",slug:"angkoon-phinyomark",fullName:"Angkoon Phinyomark",position:null,profilePictureURL:"https://mts.intechopen.com/storage/users/64434/images/2619_n.jpg",biography:"My name is Angkoon Phinyomark. I received a B.Eng. degree in Computer Engineering with First Class Honors in 2008 from Prince of Songkla University, Songkhla, Thailand, where I received a Ph.D. degree in Electrical Engineering. My research interests are primarily in the area of biomedical signal processing and classification notably EMG (electromyography signal), EOG (electrooculography signal), and EEG (electroencephalography signal), image analysis notably breast cancer analysis and optical coherence tomography, and rehabilitation engineering. I became a student member of IEEE in 2008. During October 2011-March 2012, I had worked at School of Computer Science and Electronic Engineering, University of Essex, Colchester, Essex, United Kingdom. In addition, during a B.Eng. 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