Showing papers on "Diamond published in 1972"

Elastic Moduli of Diamond as a Function of Pressure and Temperature

Abstract: Values of wave velocities and elastic moduli at 25°C were measured for hydrostatic pressures to 20 000 psi (excess over 1 atm). Variations of velocities and moduli at 1 atm were obtained over a temperature range of +50°C to −195.8°C. Adiabatic stiffness moduli (units of 1012 dyn/cm2), their pressure derivatives, and their temperature coefficients (units of 10−5/C), are shown below for 1 atm and 25°C. ModulusValuePressure derivativesTemperature coefficientc1110.79±0.055.98±0.7−1.37±0.2c12 1.24±0.053.06±0.7−5.70±1.5c44 5.78±0.022.98±0.3−1.25±0.1

The Elastic Stiffness Moduli of Diamond

Abstract: The elastic stiffness moduli of a 22‐carat Type II diamond have been measured at 25.0°C by the ultrasonic technique described by H. J. McSkimin. Basic wave velocities were obtained over a frequency range of 20–500 MHz in order to minimize errors due to diffraction and coupling effects. Moduli (in units of 1012 dyn/cm2) are as follows: c11=10.79±0.05, c12=1.24±0.05, c44=5.78±0.02. Comparison with literature values is made.

Gamma-ray compton profiles of diamond, silicon, and germanium.

Abstract: 160-keV $\ensuremath{\gamma}$ rays were used to measure the Compton profiles of diamond, silicon, and germanium single crystals in five crystallographic directions ($〈100〉$, $〈110〉$, $〈111〉$, $〈112〉$, and $〈221〉$). The data are analyzed so as to obtain the differences in the profiles in the various directions for each material. A direct comparison of the data is made with band calculations for Si which suggests that the differences in the profiles can provide a sensitive test of band calculations. Interesting comparisons between the three materials are made by normalizing the data to equal electron density for the outer valence electrons. In addition to providing information on the three materials studied, this work demonstrates that systematic studies of families of solid-state systems by Compton scattering can be a very powerful experimental technique.

Graphitization of Diamond at Zero Pressure and at a High Pressure

Abstract: Natural diamonds have been heated in the temperature range of 1850 to 2000 degrees C at zero pressure and the rates at which diamond transforms to graphite measured. For {111} and {110} surfaces activation energies of 253 $\pm $ 18 and 174 $\pm $ 12 kcal mol$^{-1}$ (1159 $\pm $ 75 and 728 $\pm $ 50 kJ/mol) respectively have been obtained. Diamonds have also been heated in the temperature range of 1950 to 2200 degrees C under a pressure of 48 $\pm $ 3 kbar (4.8 $\pm $ 0.3 GPa) and an activation volume of about 10 cm$^{3}$ mol$^{-1}$ obtained for both {111} and {110} surfaces. It is proposed that the rate controlling process in the graphitization of diamond is the detachment of a single atom from the diamond surface. This is contrary to previous proposals in which the detachment of groups of atoms have been considered to be the rate-controlling process. In the present work, it is suggested that the rate-controlling step for graphitization is the detachment of a triply bonded atom from a {111} surface and of a doubly bonded atom from a {110} surface.

The resistance of diamond to abrasion

Abstract: These experiments are a continuation of earlier work on the resistance of diamond to abrasion whilst being polished and ground. The most striking feature of the results is the very great difference in the resistance, or abrasion hardness, observed on the various faces for different directions of abrasion. A discussion of the variations shows that grinding and polishing generally proceed by a process of cleavage, on a microscopic scale.

Physical properties and finished surface texture of composite restorative resins.

Abstract: Four composite resins were used in various aspects of this study in which their physical and mechanical properties were determined Polymerization contraction, thermal dimensional change, indentation resistance and recovery, compressive properties, and tensile strength were among the properties evaluated Water sorption and solubility were tested also In a test for surface roughness, the effects of 15 finishing procedures on one composite resin were evaluated Smoother finishes were obtained with use of white Arkansas stones and silicon carbide disks; use of green or diamond stones is recommended for removal of gross excesses which are away from the enamel margin

The growth of large diamond crystals

Abstract: Large diamond crystals up to 6 mm in average diameter may be grown at high pressures (55–60 kbar) and temperatures (1400–1500 °C) by causing diamond to dissolve in a molten catalyst metal (Fe, Ni, Co, etc.) in a hot region and deposit upon a seed crystal in a slightly cooler region. Several days are required to produce a high quality single crystal. The process can be controlled to produce different kinds of diamonds whose properties have been studied.

Calculation of Local Effective Fields: Optical Spectrum of Diamond

Abstract: The random-phase-approximation formalism describing local fields developed by Adler and by Wiser is evaluated for an insulator for the first time. It is shown that umklapp effects decrease the low-frequency electronic dielectric constant, contrary to what is required to reconcile theory with experiment for most semiconductors. A simple prescription for effects of dynamical correlation is shown to improve agreement with experiment for diamond.

The effect of nitrogen impurity on the annealing of radiation damage in diamond

Abstract: Impurity nitrogen in type Ia diamond is known to trap radiation damage centres during annealing. Most of the nitrogen is also known to be present in two forms, labelled A and B from the absorption peaks produced by them in the range 1000-1332 cm-1. In this paper, the effect of these different forms of nitrogen on the annealing of radiation damage is considered. The visible absorption spectra of 41 annealed diamonds have been compared with their infrared spectra. The results suggest that the A form of nitrogen produces the 2.463 eV centre, while the B form gives the 2.499 eV centre, by trapping a radiation damage centre during annealing. The trapping centres compete with each other for the damage centres. In natural type Ib diamond (containing paramagnetic nitrogen), the 640nm (1.945 eV) centre is produced by the annealing, in agreement with du Preez (1965).

Sliding friction under a negative load

Abstract: Microfriction experiments in a scanning electron microscope have shown that continuous sliding under a tensile force (negative load) is possible between a soft metal stylus and a hard smooth surface of graphite or diamond. The stylus was first deformed plastically with a positive load to produce a relatively large apparent contact area; the load could then be reduced and made negative under either static or sliding conditions and the static adhesion or negative friction measured. The friction force was found to decrease with increasing negative load, and the interpolated load for zero friction was found to correspond closely to the pull-off load for the static adhesion experiments. The apparent contact area was typically 5 μm2 and the maximum adhesive stresses were about 5 × 107 N m−2 (5 kg mm−2) on diamond and 3 × 106 N m−2 on the cleaved basal plane of a graphite single crystal. Possible mechanisms of attraction are considered in relation to the magnitude of the attractive stres. It is concluded that van der Waals forces are sufficient to explain the observed adhesion, but stronger short-range forces may also be playing a significant role in the case of diamond. The effect of interfacial geometry is discussed and possible reasons are considered for the absence of previous observations of attractive stresses of this magnitude in larger-scale experiments.

Plural molded diamond articles and their manufacture from diamond powders under high temperature and pressure

Abstract: A SINTERED DIAMOND ARTICLE AND PROCESS FOR PRODUCING SAME, THE PROCESS INCLUDING PROVIDING A PLURAL CAVITY MOLD, PACKING THE MOLD CAVITY WITH PARTICULATE DIAMOND WITH OR WITHOUT ADDITIVES AND THEREAFTER SINTERING THE PARTICULATE DIAMOND UNDER HIGH TEMPERATURE AND HIGH PRESSURE TO FORM A SOLID, NON-POROUS DIAMOND MASS IN THE CONFIGURATION OF THE MOLD CAVITY.

Method of producing an artificial diamond film

Abstract: 1. A METHOD OF PRODUCING ARTIFICIAL DIAMOND FILMS WHICH COMPRISES SPUTTERING AT LEAST TWO GRAPHITE CATHODES SIMULTANEOUSLY BY IONS OF AN ELECTRIC DISCHARGE IN AN INERT GAS AT A PRESSURE OF ABOUT 10-7 TO 10-4 TORR, TO THEREBY FORM AT LEAST TWO ATOMIC BEAMS OF CARBON, THE INERT GAS PRESSURE BEING MAINTAINED SUCH THAT NEUTRAL CARBON ATOMS EMITTED FROM THE CATHODES REACH THE SUBSTRATE SURFACE WITHOUT COLLIDING WITH THE INERT GAS PARTICLES, SAID ATOMIC BEAMS OF CARBON BEING DEPOSITED ON SAID COMMON SOLID SUBSTRATE WITH OVERLAPPING ON THE SURFACE THEREOF TO THEREBY FORM SAID DIAMOND FILM.

Induced graphitisation around crystalline inclusions in diamond

Abstract: In an external vacuum and at temperatures between 900° C and 1650° C internal graphitisation takes place on or around mineral inclusions in diamond, and appears to be responsible for similar features previously reported in diamond from several localities. Several mechanisms are proposed and discussed for internal graphitisation at temperatures as low as 900° C: it is proposed that at low external pressures CO2 exsolves from inclusions and causes internal graphitisation. The results also indicate that immediately after pressure release arising from volcanic breakthrough of kimberlites of different geological ages at several localities in West and South Africa, the temperature was not in excess of 800° C to 900° C in certain regions of the diatremes.

750-mm Ruling Engine Producing Large Gratings and Echelles*

Abstract: A ruling engine that has produced gratings of larger size and greater power than hitherto available is described, as are the characteristics of gratings and echelles ruled by it. This MIT C engine, now fitted to rule blanks of sizes up to 450 × 650 × 125 mm weighing up to several hundred kg, was constructed by applying interferometric translation and mirror-parallelism control to a modified Moore No. 4 Universal Measuring Machine without Y or Z motion. To the base of this were added monorail diamond ways, two diamond carriages and lifters, special end-thrust bearings, mountings for lasers, and a diamond drive with heavy flywheels. Developed by use of the results of experience with our B and A engines, the new machine shows greater mechanical and thermal stability than either, and has produced well-blazed echelles and gratings of superior quality up to the 580-mm (23 in.) diagonal size, at spacings between 632 and 31.6 grooves/mm. The total length of groove per grating is limited at present to about 80 km by diamond wear, and the speed of ruling by internal vibrations and electronic noise. Ghost, satellite, and scatter intensities are at the low levels characteristic of B-engine gratings.

Black material on mineral inclusions and in internal fracture planes in diamond

Abstract: The black material observed on the surface of crystalline inclusions in diamond and also in adjacent internal fracture planes has been classified as a result of a preliminary examination of several hundred diamonds from Sierra Leone, Ghana, and South Africa (particularly the Premier Mine), as well as diamond slices of unknown origin, followed by a detailed examination of some 100 diamonds. X-ray, electron diffraction, and qualitative electron microprobe techniques were used in identifying this material as graphite, pyrrhotite and pentlandite. The possible origins of these minerals are discussed.

Properties of amorphous carbon films

Abstract: The temperature dependence of the electrical conductivity, piezoresistance and thermopower as well as optical absorption have been measured on amorphous carbon films deposited by electron beam evaporation on silica substrates In as-deposited films transport properties and optical absorption imply the existence of an energy pseudo-gap of ⪆ 065 eV All the results lead to a structural model in which the carbon atoms are bound together by intimately intermixed trigonal and tetrahedral links Annealing above 750°K gives the films transport and optical properties quite similar to those of polycrystalline graphite and also induces optical absorption peaks situated at 7–8 eV characteristic for diamond only It is therefore concluded that annealed films consist of tiny islands with alternatively graphite and diamond structure

Natural and Laboratory α-Particle Irradiation of Diamond

Abstract: To produce a lattice expansion readily detectable by conventional X-ray photographic means in α-irradiated diamond, a dose of order 1018 α.cm−2 is required. Such a dose could be produced by pitchblende in ∼2 × 108 yr. and a previously reported lattice expansion in a natural diamond could therefore have occurred by long-term contact with a radioactive material. α-particle doses greater than ∼1014 cm−2 produce observable green colouration on the surface of an initially colourless diamond.

Dechanneling of heavy charged particles in diamond lattices

Abstract: Dechanneling rates of 1.5 MeV protons, deuterons and helium ions in the 〈100〉 axial and {110} planar channels are obtained by analysing their back-scattering energy spectra for the aligned and random directions. The experimental dechanneling rates in the axial channels, inclusive of those in Si, Gap, NaCl, KCl, and KBr single crystals, follow a universal expression for the dechanneling which is derived using the diffusion model according to the Lindhard's theory. Comparing with the theory, the contribution of the electronic collisions to the dechanneling is separated from the contribution of the nuclear collisions. The experimental value of the electronic contribution agrees well with the theoretical value. The experimental value of the nuclear contribution is smaller than the theoretical value by a factor of about 3. The discrepancy between the experimental and the theoretical value of the nuclear contribution is discussed.

Cutting tool and method of making same

Abstract: A cutting tool of the type used in machining operations has a supporting substrate of metal-cemented carbide which was formed prior to being placed in a pressure chamber. The cutting edge of the tool is composed of diamond integral with the substrate which was grown on the substrate from nondiamond carbon by subjecting the preformed substrate with the carbon in contact therewith to pressures of about 45 kilobars in the pressure chamber at temperatures of 1,400*-1,600*C. The carbide-cementing metal is chosen from among cobalt, nickel and iron - all of which are catalyst metals for the formation of diamond. Under diamondstable thermodynamic pressure and temperature conditions, the nondiamond carbon is catalyzed by the cementing material to form diamond in predominantly a (111) crystallographic orientation plane to produce columnar grains perpendicular to the diamondcarbide interface.

Novel diamond particle particularly for use in heat sinks

Abstract: The invention provides a rounded diamond particle, which is preferably of the Type IIa, truncated by a single planar surface or by a planar surface at each of opposed poles. These particles find particular use in heat sinks for electronic devices, the heat sink consisting of a body of a metal of good heat conductivity such as copper and a truncated diamond particle in thermal contact with the body such that a planar surface is presented away from the body and thus able to make thermal contact with an electronic device.

Diamond scanning element

Abstract: In a signal scanner for the scanning of signals stored on an information carrier which is moving with a velocity relative to the signal scanner, an element including a diamond adapted at least for guiding the signal scanner by following a groove, which diamond has at least one part of its bounding surfaces selected from the natural crystal surfaces of diamond, on which part the crystallographic orientation of the diamond is recognizable.