★★金刚石特性.doc

In terms of the ultimate, diamond is the hardest material known. It has the highest thermal conductivity at room temperature and several of its mechanical properties, such as bulk modulus and critical tensile stress for cleavage, are also the highest known. It has an extremely low coefficient of friction, is an excellent electrical insulator (except for semiconducting Type IIb) and will not corrode. Despite its many unique properties, however, diamond is not completely indestructible. It can be split or cleaved quite easily in certain directions, and will not corrode. Despite its many unique properties, however, diamond is not completely indestructible. It can be split or cleaved quite easily in certain directions, and will start to graphitize at temperatures in the region of 873 K in air. Much has been written about the properties of diamond, and a list of titles is appended at the conclusion of this booklet as a handy and compact reference quide.GENERAL PROPERTIESI Chemical compositionDiamond is composed of the element carbon. Only nitrogen and boron are known with certainty to be incorporated in the diamond lattice.Major impurities:Nitrogen, up to 0.2% in natural Type Ia diamond (see Section II below).Nickel, iron, etc, up to 10% as inclusions in synthetic diamond (p.p.m. or less in natural diamond).Aluminium, up to 10 p.p.m in natural diamond. Boron, up to 0.25p.p.m. in natural Type IIb and 270p.p.m. in specifically doped Type IIb synthetic diamondnow thought to be responsible for semiconducting properties of Type IIb diamond. Many other impurities are also believed to be present in the form of inclusions.Inclusions:Twenty-five mineral species have been positively identifiedsee third reference below (HARRIS, J. W.).References: LIGHTOWLERS, E. C., Science and Technology of Industrial Diamonds, Vol 1, p 27, Ed. J. Burls, Industrial Diamond Information Bureau (1967); COLLINS, A.T. and WILLIAMS, A. W. S., Diamond Research 1971, p 23; HARRIS, J. W., Industrial Diamond Review, 28, p 458 (1968); CHRENKO, R. M., NaturePhys Science, 229, p 165 (1971); SELLSCHOP, J. P. F., Diamond Research 1975, p 35.II ClassificationType Ia diamond:Contains nitrogen as an impurity in fairly substantial amounts (of the order of 0.1%), and which appears to have segregated into small aggregates. Also contains platelets, associated with the nitrogen impurity, the exact structure of which is not known. Most natural diamonds are of this type.Type Ib diamond:Also contains nitrogen as an impurity but in dispersed substitutional form. Almost all synthetic diamonds are of this type.Type IIa diamond:Effectively free of nitrogen impurity. Very rare in nature, these diamonds have enhanced optical and thermal properties.Type IIb diamond:A very pure type of diamond which has semiconducting properties: generally blue in colour. Extremely rare in nature. Semiconducting properties can be imparted to synthetic crystals by the incorporation of boron.References: ROBERTSON, R., FOX, J. J. and MARTIN, A. E., Phil Trans Roy Soc, A232, p 463 (1934); CUSTERS, J. F. H., Physica, 18, p 489 (1952); KAISER, W. and BOND, W. L., Phys Rev 115, p 857 (1959); DYER, H. B. et al. Phil Mag 11, p 763 (1965); EVANS, T. and DAVIES, G., Diamond Research 1973, p 2.Note:Classification is based principally on optical properties. Further subdivisions can be made almost ad infinitum (indeed, almost every diamond is different in some way) but the above classification is universally accepted. Some diamonds have been shown to consist of more than one type, eg a complex interweaving of Type I and Type II material.III Crystal structureSpace Group: Cubic Fd3m-O.Unit cell: Lattice constant between 0.356683 0.000001 and 0.356725 0.000003 nm at 298 K.Atoms located at: (000), 0, 0, 0, , , , .Nearest neighbour distance: 0.154450 0.000005 nm at 298K.Atomic weight: 12.01Atomic radius: 0.077 nmNumber of atoms in a unit cell: 8Number of atoms m3: 1.77 x 1029References: KAISER, W. and BOND, W. L., Phys Rev 115, 4, p 857 (1959); LONSDALE, K., Phil Trans Roy Soc, A240, p 219 (1947); SKINNER, B. J., Amer Min 42, p 39 (1957).IV DensityAverage of 35 diamonds (3.51524 0.00005) x 103 kgm3 at 298 K. Spread 0.77 kg m3.Average of 19 Type I (3.51537 0.00005) 103 kgm3.Average of 14 Type II (3.51506 0.00005) 103 kgm3.Note:Calculations from the lattice constant gives 3.51525 x 103 kgm3; the spread is due to lattice faults and impurities and not to experimental error.Reference: MYKOLAJEWYCZ, R., KALNAJS, J., and SMAKULA, A., JAppl Phys 35, p 1773 (1964).Note:Additional values (including diamond coat and polycrystalline diamond) are given by BOCHKO, V. A. and ORLOV, Y. L. in Doklady Akad Nauk SSSR, 191, p 341 (1970) and by DERYAGIN, B. V. et al. in Doklady Akad Nauk SSSR, 196, p 1320 (1971).V GraphitizationWhen diamonds are heated to a high temperature, the changes that take place depend markedly on the environment around the diamond. If oxygen (or other active agent) is present, a black coating can form on the surface of diamond above about 900 K. This is not true graphitization (which involves the transition of diamond to graphite without the aid of external agents). If diamonds are heated in an inert atmosphere, the onset of graphitization can just be detected at 1800 K and the rate of graphitization increases rapidly until at 2400 K a 0.1 carat octahedron is converted totally into graphite in less than 3 minutes. The octahedral diamond surface graphitizes with an activation energy of 1060 80 kJmol1 and the dodecahedral surface graphitizes more rapidly with an activation energy of 730 50 kJ kJmol1. The activation volume for the graphitization process is about 10 cm3mol1. It appears that the graphitization process involves the removal of one atom at a time from the diamond surface. For an octahedral surface, three carbon-carbon bonds are broken when the atom is detached and for the dodecahedral face, two carbon-carbon bonds are broken.References: EVANS, T. and JAMES, P. F., Proc Roy Soc, A271, p 260 (1964), SEAL, M., Physica Status Solidi, 3, p 658 (1963); DAVIES G. and EVANS, T., Proc Roy Soc, A328, pp 413-427 (1972).VI Resistance to chemical attackDiamond is extremely inert chemically and is not affected at all by any acids or any other chemicals, except those which at high temperatures act as oxidising agentsthese provide the only effective way to attack diamond at temperatures below 1300 K and at normal pressures. Substances such as sodium nitrate are known to attack diamond in the molten state at temperatures as low as 700 K. In oxygen itself, diamond starts to be oxidised at perhaps 900 K.The only other possible form of chemical attack is by two groups of metals. The members of the first group are avid carbide formers, and include tungsten, tantalum, titanium and zirconium. At high temperatures these will react chemically with diamond to form their respective carbides. The second group includes iron, cobalt, manganese, nickel and chromium, and also the platinum group of metals. In the molten state these metals are true solvents for carbon.MECHANICAL PROPERTIESI Hardness(a) Scratch hardness (Mohs Scale)The Mohs hardness is a scratch hardness test and is related to the indentation hardness of the solid (see below). If the Mohs number is M and the indentation hardness in kg/mm2 is H, the relation between these quantities is approximatelylog H = 0.2 M + 1.5There is reasonable equality of intervals between the first 9 integers on the Mohs scale, but the interval between 9 (corundum) and 10 (diamond) represents a much larger difference in indentation hardness than a single unit on the Mohs scale would suggest.Typical values of very hard materials are:SiC (carborundum), Al2O39WC, W2C, VC99.5Diamond10Reference: TABOR, D. Proc Phys Soc, B67, p 249 (1954).(b) Indentation hardness (Knoop Scale)Value (001) diamond surface): 5,70010,400 kg/mm2, depending on crystallographic direction and with normal loads of 500 g, 1 kg and 2 kg.Comment:There are many other scales, some appropriate to all materials, some only to metals. A Knoop indenter produces a wedge-shaped indentation in the form of a parallelogram with one diagonal at least seven times longer than the other diagonal, and this method is generally considered to be the most accurate for crystalline solids. On any scale diamond is the hardest known material.It has been shown that the measured hardness value is significantly influenced by the normal load, the indenter shape and its crystallographic relationship with that of the intended surface. It has also been shown that the indentation hardness of diamond decreases with increasing temperature.cf.Diamond (111) surface, direction, 500 g load): 9,000 kg/mm2Cubic boron nitride (111) surface, direction, 500 g load): 4,500 kg/mm2Boron carbide (surface, direction and load not known): 2,250 kg/mm2Silicon carbide (surface, direction and load not known): 1,8753,980 kg/mm2Tungsten carbide (surface, direction and load not known): 2,190 kg/mm2Titanium carbide (surface, direction and load not known): 2,190 kg/mm2Aluminium oxide (surface, direction and load not known): 2,000 kg/mm2Note: All above measurements at 298 K.References: KNOOP, F., PETERS, C. G., and EMERSON, W. B., J Res Nat Bur Standards, 23, (1939); BROOKES, C. A., Nature, 228, p 660 (1970); BROOKES, C. A., Diamond Research 1971, p 12 (1971); LOLADZE, T. N., BOKUCHAVA, G. V. and DADYDOVA, G. E., Industrial Laboratory, 33, p 1187 (1967); BROOKES, C. A., GREEN, P. and HARRISON, P. H., Diamond Research 1974, p 11.(c) Abrasion resistanceThe resistance of diamond to abrasion depends greatly on the method of abrasion. For a description of the very great dependence of the rates of polishing diamond by the normal polishing methods see Wilks and Wilks (1972). For a comparison of the abrasion resistance of diamond with other gemstones see Wilks (1973). For the wear of diamond when rubbing at low speeds, under loads, on a range of metals, see Crompton et al. (1973).References: CROMPTON, D., HIRST, W. and HOWSE, M. G. W., (1972), Proc Roy Soc A333, p 435; WILKS, E. M. and WILKS, J. (1972), J Appl Phys 5, pp 1902-1919; WILKS, E. M. (1973), Industrial Diamond Review, pp 186-189.(d) FrictionThe coefficient of friction in air, , is about 0.1, but the value depends on load, geometry, polishing direction and especially orientation. On the (111) plane 0.05 and is approximately constant in all directions. On the (100) cube plane values vary between 0.05 along to 0.10.15 along for polishing along . After polishing in other directions the fourfold symmetry can change to twofold. in air is little affected by lubricants or sliding speed in the range a few microns per second up to a few millimetres per second. in vacuum approaches 1 (Bowden and Hanwell, 1966).References: BOWDEN, F. P. and HANWELL, A. E. (1966), Proc R Soc Lond, A295, pp 233-243; CASEY, M. and WILKS, J. (1972), J Phys D Appl Phys 6, pp 1772-1781; SEAL, M. (1958), Proc R Soc Lond, A248, pp 379-393; The Properties of Diamond, FIELD, J. E. (1979), pp 326-350, Academic Press, London; WILKS, E. M. and WILKS, J. (1972), J Phys D Appl Phys, 5, pp 1902-1919.II Elastic properties(a) Elastic moduliBhagavantam and Bhimasenachar (1946)C11 = 9.5C12 = 3.9C44 = 4.3Prince and Wooster (1953)C11 = 11.0C12 = 3.3C44 = 4.4McSkimin and Bond (1957)C11 = 10.76C12 = 1.25C44 = 5.76Markham (1965)C11 = 10.76C12 = 2.75C44 = 5.19McSkimin and Andreatch (1972)C11 = 10.79C12 = 1.24C44 =5.78Grimsditch and Ramdas (1975)C11 = 10.764C12 = 1.252C44 = 5.774(all x 1011 Nm2)Pressure and Temperature Coefficients (McSkimin and Andreatch)dc / dP K1C116.0 + 0.7 (1.4 0.2) x 105C123.1 + 0.7 (5.7 1.5) x 105C443.0 + 0.3 (1.25 0.1) x 105(b) Bulk modulusK = (C11 + 2C12)Bhagavantam and Bhimasenachar (1946)K = 5.8 x 1011 Nm2Prince and Wooster (1953)K = 5.9 x 1011 Nm2McSkimin and Bond (1957)K = 4.42 x 1011 Nm2Markham (1965)K = 5.42 x 1011 Nm2Drickhamer et al. (1966)K = 5.6 x 1011 Nm2McSkimin and Andreatch (1972)K = 4.42 x 1011 Nm2Grimsditch and Ramdas (1975)K = 4.42 x 1011 Nm2References: BHAGAVANTAM, S. and BHIMASENACHAR, J. (1946), Proc R Soc Lond, A187, pp 381-384; DRICKAMER, H. G., LYNCH, R. W., CLENENDEN, R. L. and PEREZ-ALBUERNE, E. A. (1966), In Solid State Physics, (F. SEITZ and D. TURNBULL eds) Vol 19, pp 135-228; GRIMSDITCH, M. H. and RAMDAS, A. K. (1975), Phys Rev, B11, pp 3139-3148; MARKHAM, H. F. (1965), National Physical Laboratory (UK), presented MUSGRAVE, M. J. P., Diamond Conference, Reading (unpublished); McSKIMIN, H. J. and BOND, W. L. (1957), Phys Rev, 105, pp 116-987; McSKIMIN, H. J. and ANDREATCH, P. (1972), J Appl Phys, 43, pp985, 2944-2948; PRINCE, E. and WOOSTER, W. A. (1953)., Acta Cryst, 6, p 43.Comment:Highest values of elastic moduli of any material cf. tungsten: K = 2.99 x 1011 Nm2 calculated from C11 = 5.01, C12 = 1.98, C44 = 1.514Note: Compressibility is the reciprocal of the Bulk Modulus.(c) Poissons ration21 = = 0.104 varies between 0.1 and 0.29 0.2(d) Youngs modulusE11 = = McSkimin and Andreatch (1972)E = 10.54 x 1011 Nm2Grimsditch and Ramdas (1975)E = 10.50 x 1011 Nm2(e) AnistropyThe condition for isotropy is = 1For diamond this ration is close to unity (1.21), so that Youngs Modulus does not vary greatly with orientation.III Strength(a) Cleavage planeDiamond normally cleaves on the (111) plane, but cleavage has been observed on the (110) plane, and, to a lesser extent, some other planes (J. R. Sutton, Diamond, Murby & Co, London, 1928). Curved cracks can be produced by gradual loading with a spherical indenter (Levitt and Nabarro, Proc Roy Soc, A293, 1966, Plate 6). Ring cracks are found frequently on diamond surfaces and can be made by both slow and impact loading with indenters, not necessarily diamond.(b) Cleavage energyTheoretical cleavage energies for diamondPlaneAngle between planeCleavage energyand (111) plane(Jm2)1110 and 70 3210.633210 011.722115 4812.233122 012.611035 16 and 9013.032211 2413.432122 1214.321119 2815.032036 4815.321039 1416.431129 3016.610054 4418.4Note: to obtain a fracture surface energy, , divide by 2.Cleavage energy can be computed by calculating the number of bonds which cross the unit area of a chosen plane and multiplying this by the CC bond strength. The values are obtained by using a value of 93 kcalmol1 or 5.8 x 1019 J for the CC bond (Pauling, The Nature of the Chemical Bond, Cornell Universal Press, 1960, p 85).A value of 5.3 Jm2 is predicted for the fracture surface energy of the (111) plane. An experimental measurement (Field, 1979) giving 6J m2 suggests that there is a negligible contribution from plastic deformation fracture at room temperature.(c) Velocity of cleavageCleavage velocities of a few thousand metres per second are common. Velocities up to 7,200 ms1 have been recorded (Field, Physical Properties of Diamond, Academic Press, 1979, Chapter 9).(d) Theoretical strengthTheoretical strengths of ideal solids (Field, 1979)MaterialStrength in tensionStrength in shear Direction th(1010 Nm2) th/E System th(1010 Nm2) th/C (diamond)19.00.1711112.10.24Si3.20.171111.370.24MgO3.70.151101.60.12NaCl0.430.101100.280.12Cu3.90.201110.120.039Ag2.40.201110.0770.039The ratio of tensile to shear strengths is predicted to close to unity, but as the table is descended the ratio becomes large, i.e. the materials in the table range from highly brittle (top) to highly ductile (bottom).Note: Accurate calculations on diamond are difficult.(e) Tensile strengthExperimental values for strength show wide variations. This is partly a reflection of the difficulty encountered in making tests with diamonds, but also indicates that the strength of individual diamonds is significantly affected by the defects, inclusions and impurities which they contain. Values quoted in the literature are also dependent on the values chosen by the authors for the elastic moduli and Poisson ratio.pc an pc are the average stresses obtained by dividing the load by the crack area and the observed, or calculated, area respectively, when determining tensile strength using the ring crack indentation method.Strength data for diamond. Data recalculated with E = 10.5 x 1011 Nm2 and = 0.2 (Field, 1979).Strength data for diamond. Data recalculatedwith E = 10.5 x 1011 Nm2 and = 0.2 (Field, 1979)AuthorFaceIndenter radius/mmPc(109Nm2)Pc(109Nm2)aOctahedralCubeDodecahedral00.5tungstencarbide10.313.211.8aOctahedralCubeDodecahedral00.39diamond10.810.817.613.832.4bCube0.28diamond13.732.4cCube0.245diamond29.9dCube0.25diamond16.432.4dSynthetic octahedral and cube0.25diamond21.632.4a Howes (1965); b Bowden & Tabor (1965); c Bell et al.(1977); d Chrenko & Strong (1975)References: HOWES, V. R., Physical Properties of Diamond, pp 174-183, Ed. R. Berman, Clarendon Press (1965); BOWDEN, F.