Showing papers on "Diamond published in 1968"

Growth of Diamond Seed Crystals by Vapor Deposition

Abstract: Carbon was deposited on virgin, natural diamond powder from methane gas at 1050°C and 0.3 Torr. The deposits were identified as new diamond by chemical analysis, chemical etching, density measurements, x‐ray and electron diffraction, microwave absorption, electron spin resonance, and visual observations. The crystalline quality of the new diamond layers has not been established; it cound range from polycrystalline material with a large number of defects to true epitaxial layers.

Hardness and low-temperature deformation of silica glass.

Abstract: Vickers diamond pyramid hardness measurements have been made on silica glass with varying thermal history using loads up to 1000 g. Hardness was independent of load and source. From interference photographs and subsequent anneal of the indentations at temperatures belowT g, it was concluded that indentation leads primarily to densification of a volume of glass in the vicinity of the indenter. A portion of the densification which is recoverable at relatively low temperatures is attributed to molecular entanglement of the glassy network due to high pressure and shear. The other portion which is not recoverable belowT g represents an approach to the final equilibrium density of the glass. Hardness of silica glass as determined by this method is thus defined as a resistance of the material to densification.

Process for producing sintered diamond compact and products

Abstract: PROCESS INCLUDING PRELIMINARY CLEANSING AND ESSENTIAL PRECONDITIONING TREATMENT OF FINELY DIVIDED DIAMOND PARTICLES FOLLOWED BY COMPACTION OF THE PRECONDITIONED PARTICLES AT HIGH TEMPERATURES AND PRESSURES IN THE DIAMOND STABLE REGION TO PRODUCE DENSE SELF-BONDED SINTERED DIAMOND COMPACT. INCORPORATION OF FORON, SILICON OR BERYLLIUM AS SINTERING AID AGENTS WITH THE PRECONDITIONED PARTICLES STILL FURTHER PROMOTES SINTERING AND BONDING OF THE COMPACT.

The genesis of diamond deposits

Abstract: It is suggested that these mineral deposits were emplaced by an explosive CO 2 gas drive and that the diamond-bearing rocks have come up from a depth of not less than 200 km. CO 2 vacuoles in minerals associated with the diamonds (Roedder) suggest partial pressure of CO 2 equal to confining pressure at time of diamond formation. Thermodynamic calculations show that this condition is required in order to have diamond crystals stable in an environment that contains substantial ferrous and some ferric iron. Thus a vital role is attributed to CO 2 in both the genesis and emplacement of diamond deposits.

An Electron‐Microscope Study of Shock‐Synthesized Diamond

Abstract: The microstructure of diamonds formed from the graphite in cast iron by an explosive shock process was investigated by means of transmission electron microscopy electron, diffraction, and selected beam microscopy. Morphologically, the material consists of a mixture of two different forms: compact aggregates of of usually acicular crystallites with a strong preferred orientation, and single crystals. The latter partly consist of hexagonal diamond, the recently discovered modification of carbon, and contain many stacking faults. Hexagonal diamond is also randomly distributed in the polycrystalline fraction.

Chrome Pyrope: An Inclusion in Natural Diamond

Abstract: Electron probe analyses of garnets that are rich in magnesium and that occur as inclusions in natural diamonds show that the chrome-garnet end member, Mg3Cr2Si3O12, is a major constituent (30 percent).

Exciton Interpretation of the Vacuum‐Ultraviolet Absorption Spectra of Saturated Organic Polymers

Abstract: A recent application of the molecular exciton theory to the σ bond absorptions of simple gaseous alkanes has prompted the extension of the theory here to saturated organic polymers in the solid phase. The theory explains the experimentally observed insensitivity of the absorption spectra to changes in polymer chain conformation and, in the case of simple alkanes, to changes from gas to solid phase. It also explains the observed similarity between the low‐energy portions of the absorption spectra of such diverse materials as diamond and gaseous alkanes. The exciton energy levels of polyethylene, polypropylene, and diamond are calculated and are found to give very reasonable agreement with the previous experimental data on polyethylene and diamond, and with the absorption spectrum of polypropylene which is presented here between 2500 and 584 A. The polarizations of the optically allowed transitions are also obtained but no experimental data is yet available on these. The possible implications of this excito...

X-ray determination of the electron momentum density in diamond, graphite, and carbon black.

Abstract: Electron momentum density in diamond, graphite and carbon black from Compton profile measurement by X ray scattering vector

One-phonon band-mode absorption by impurity resonances in diamond and silicon

Abstract: The one-phonon, band-mode, infrared absorption spectra activated by antimony, arsenic, boron, oxygen and phosphorus in silicon, and by isolated nitrogen atoms and radiation damage centres in diamond have been investigated. Absorption features attributed to in-band resonances are observed in most cases. Neither the shape nor the strength of the absorption spectra can be accounted for adequately in terms of the isotopic-defect theory of Dawber & Elliott. In the case of silicon, the absorption strengths suggest that the effective charge is not confined exclusively to the impurity atoms.

Diamond growth process

Abstract: There is provided an improved process for the growth of diamonds from seed crystal with a gaseous monocarbon atom compound which is characterized by extremely low pressures not in excess of 1 X 10 2 (Torr) and at temperatures in the range of 800* to 1,450* C Interesting products including semiconductors and colored diamond crystals may be prepared by ''''doping'''' the gas with certain materials

Manufacture of synthetic diamonds

Abstract: There is provided an improvement on a low-pressure process for the growth of synthetic diamonds from diamond seed crystals by contacting them with a monocarbon atom gas which also contains a ''''doping agent'''' such as a compound of boron or aluminum or lithium vapor in the gas phase at a pressure of from 760 (Torr.) to 1 X 10 1 (Torr.) and at a temperature in the range of from 900* C. to 1450* C. and for deposition-cleaning cycle periods in the range of from 4 to 28 hours.

Recent researches on kimberlite and diamond geology

Abstract: New developments since Wyllie9s (1967) book include new discoveries (India, USSR); observations on zoning of xenoliths in pipes; a newmineral (amakinite) and several minerals reported from kimberlite for the first time; new data on composition and geochemistry of kimberlite; observations on maximum size, abundance, and banding of xenoliths. New isotopic ages (South Africa, U.S.A.) indicate that although xenoliths may give Precambrian dates, kimberlite minerals crystallized at times that fit field relations. Researches on diamond give data on included material (nitrogen, pyrrhotite, rutile) and new syntheses (one in the graphite stability field). A scheme for appraising diamond deposits is based on kimberlite composition and diamond morphology.

Diamond growth process

Abstract: There is provided an improved process for the growth of diamonds on seed crystals with a gaseous polycarbon atom compound which is characterized by extremely low pressures not in excess of 1 X 10 2 (torr) and at temperatures in the range of 800* C. to 1,450* C. Interesting products including semiconductors and colored diamond crystals may be prepared by ''''doping'''' the gas with certain materials.

Diamond as an insulating heat sink for a series combination of IMPATT diodes

Abstract: Series connections of IMPATT diodes are capable of giving high microwave power output at a reasonably high impedance level. The series combination avoids many of the stability problems associated with parallel combinations. A series combination of three diodes mounted on a diamond heat sink produced a C3V 13-GHz output of 4.5 watts with an efficiency of 6.4 percent.

Band Structure and Interband Optical Absorption in Diamond

Abstract: In the present paper we compute the interband contribution to the imaginary part ${\ensuremath{\epsilon}}_{2}(\ensuremath{\omega})$ of the dielectric constant in diamond. This is done for several model band structures. In particular, we conclude that either the present first-principles calculations have to be modified or there are extremely large many-particle corrections to the interband current near the fundamental ultraviolet absorption edge.

A study of wetting of diamond and graphite by fused metals and alloys VII. The effect of vanadium, niobium, manganese, molybdenum, and tungsten on wetting of graphite by copper-based alloys

Abstract: 1. The interaction between a graphite or diamond surface and the investigated transition metals is due to formation of strong chemical bonds at the interface. Spreading of these metals or alloys containing them on the graphite or diamond surface is due to a chemical reaction at the solid-liquid boundary (formation of carbides or solution). 2. For the investigated transition metals, the authors established that the interphase activities at the boundary with graphite decrease with decreasing defect in their d-electron zones as we go along the periods of the periodic table.

Heat Capacity and Quasi‐Chain Dynamics of Diamond‐Like Structures

Abstract: The heat capacities of a number of semiconducting substances (Si, GaAs, GaP, etc.) have been calculated on the basis of the quasi-chain dynamics of covalent crystals [9]. It is shown that the characteristic frequencies v3 and v1 correspond to the respective dispersion frequencies at the points Γ(0, 0, 0), X(1, 0, 0), and L(0.5, 0.5, 0.5) of the Brillouin zone determined from the inelastic scattering of slow neutrons, and that it is possible to calculate the parameters ϑ1 and ϑ3 from the data of multi-phonon absorption. The heat capacities of GaP, measured in the range 55 to 300°K, are given. [Russian Text Ignored].

Lattice strain in tungsten carbide

Abstract: X-ray-diffraction measurements have shown that ball-milling of tungsten carbide powder gives rise to considerable line broadening. Analysis of this broadening by integral-breadth and Fourier methods indicates that the main cause of the broadening is lattice microstrains. X-ray studies have been made on tungsten carbide powders, sintered blocks, and tool tips with cobalt binding, to determine how this strain varies at different stages of treatment of the material. It was found that, after sintering, the tungsten carbide was strain-free, but diamond polishing and mechanical work induced strain in the surface layers.

Total single-particle energy of isotropic semiconductors.

Abstract: Total single particle energy of isotropic semiconductors, discussing energy spectra of bonded crystals for diamond and silicon

Growth History of Crystals in Nature

Abstract: Nakaya wrote a poem in which he says “Snowflake is a letter to us from the sky”. If expressed similarly, mineral crystals in nature are the letters to us from the depth of the earth. They convey the message telling us what has happened under the earth, what was the conditions when they were grown, and what they have experienced since they born. It is clearly worth doing our best to read these letters. As Nakaya tried to read the message that snowflakes convey by studying their crystal morphology, we can obtain much information through detailed studies of the nature of crystals. Surface microstructure of crystal faces, zonal structures inside a crystal, distribution of foreign crystals and lattice defects, as well as impurity atoms, in addition to crystal morphology, will serve as useful key codes to decode the letters.In this paper, diamond crystals are used as an example how to decode the letter from deep under the earth. Analysis of crystal morphology of diamond suggest that natural diamonds were grown under near-equilibrium conditions, whereas synthetic crystals under the conditions apart from the equilibrium. Universal occurrence of rounded crystals in natural diamonds suggests that they have experienced dissolution process while they were transported to the earth's surface from the depth, and that the speed of transportation was much higher than our general conjecture. It is also conjectured that diamond will occur only in continental shield and not in the orogenic zones. Observations on the surface microstructures of diamond crystals shows that diamonds were grown from solution phase by condensation and neither from melt phase nor by solid state recrystallization. Zonal structures revealed by chemical etching show that the growth of diamonds was carried out by layer spreading mainly on {111} and that the growth history of individual crystals was very complicated. During the whole history of growth, crystals have experienced partial dissolution, changes in growth speed as well as the rate of impurity adsorption. Recent observations on the nitrogen platelets in natural diamond crystals give an idea that diamond crystals have experienced annealing stage after they were formed, and that the possible origin of carbon of diamond would be carbonaceous material deposited on the ocean bed, which was then transported by an active thrust or heat flow to the depth of 5 to 7 hundreds km, where it was crystallized as diamond. These considerations are mainly based on the hypothesis on the origin of diamond which has recently been proposed by F. C. Frank.

Investigation of the wetting of diamond and graphite by molten metals and alloys V. Carbide-formation kinetics at the graphite/metallic melt interface

Abstract: An investigation was conducted of the properties of the intermediate layer on the graphite/liquid copper-chromium alloy interface. It has been established that this layer consists of carbides. The kinetics of growth of the carbide layer was studied. It has been found that the rate of increase of the layer thickness as a function of time over the temperature range 1150–1250°C obeys the law h1.5 = S · t.