Showing papers on "Diamond published in 1975"

Thermal expansion of some diamondlike crystals

Abstract: The thermal expansion of AlN, cubic BN, and BP has been measured from 77 to 1300 K by x−ray techniques The derived thermal expansion coefficients are compared with those of diamond, Si, Ge, SiC, GaP, and BeO using the Debye temperature as a scaling parameter It is apparent that the thermal expansion of Si is the smallest, SiC is intermediate, and all of the others are larger The thermal expansion of Mo and W is also reviewed in order to determine how well these metals match the thermal expansion of the adamantine or diamondlike crystals

Preparation and Characteristics of Natural Diamond Nuclear Radiation Detectors

Abstract: It is shown that natural diamond can be used as a homogeneous conduction counter with near complete charge collection, even over a long period of time. Indeed, polarization effects have been suppressed by making the back contact of the detector injecting under the influence of the applied field in order to compensate for trapped charge carriers. The electric and detection characteristics of these counters have been investigated. Possible application fields are briefly discussed.

Accurate lattice constants from multiple reflection measurements. II. Lattice constants of germanium silicon, and diamond

Abstract: The lattice constants of a diamond platelet and of large single, undoped, crystals of silicon and germanium have been determined from measurements of multiple diffraction patterns by the method described in Part I [Post (1975). J. Appl. Cryst. 8, 452–456]. The mean values, based on measurements of eight to twelve reflections, and their standard deviations are: diamond a = 3.566986 A, Aa/a = 2.6 × 10−6; silicon a = 5.430941 A, Aa/a = 2 × 10−6; germanium a = 5.657820 A, Δa/a = 1.6 × 10−6.

Diamond abrasive tool

Abstract: An improved diamond abrasive tool and method of manufacture characterized by a direct brazing technique of diamond crystals to a substrate surface which requires no pre-conditioning of the surface of the diamond in order to obtain the necessary wetting thereof. The method employed utilizes readily available, very hard and durable brazing alloys which have been discovered to readily wet the diamond surface to obtain a final product wherein the minimum depth of the alloy bond tends to occur intermediate adjacent diamond crystals with outstanding retention of the crystals and greatly extended tool life.

The wetting and bonding of diamonds by copper-base binary alloys

Abstract: The wetting and bonding behaviour between diamond plaques and copper alloyed with chromium, titanium or vanadium has been studied using the sessile drop technique. Wetting was induced at 1150° C by additions of more than 0.1 at. % of titanium, but additions of vanadium up to and beyond the solubility limit did not cause wetting to occur. The room temperature strengths of the interfaces between the diamond plaques and the solidified sessile drops increased with increasing alloying element concentration, reached a maximum value at a concentration less than that needed to induce wetting, and thereafter decreased. The maximum strengths achieved by alloying with chromium, titanium or vanadium were 35.5, 42.0 and 69.8 kg mm−2 respectively. The reactivity of the alloyed sessile drops was assessed using metallography, EPMA and a surface contour device. A tentative picture of the effects of diamond-metal interactions on wetting and bonding behaviour was developed.

High thermal conductivity substrate

Abstract: A high thermal conductivity substrate is formed by making a sintered diamond composite and thereafter modifying the electrical properties of the composite by leaching graphite and other non-diamond materials from the composite and subsequently infusing the leached composite with material having known electrical properties. Alternatively, a diamond composite having high thermal conductivity known electrical properties if prepared and subsequently leached to remove graphite and other materials which interfere with the known electrical properties of the composite material.

Nitrogen in diamond: evidence from thermal conductivity

Abstract: Measurements of the thermal conductivity of type I diamonds have been analysed in terms of various phonon-scattering processes. From the relations between the point-defect scattering rates and the total nitrogen contents, it appears that the nitrogen occurs in groups of approximately 10 atoms. The relation between nitrogen content and point-defect scattering was the same in a specimen which had a very high concentration of 'platelet' imperfections, suggesting that there is little, if any, nitrogen in the platelets. Moreover, the scattering by the platelet is approximately 50 times smaller than has been calculated on a specific model of platelets made of nitrogen.

Diamond cutter rock bit with penetration limiting

Abstract: A rock bit for recovering core samples is described, along with variations for drilling oil wells or the like. In each of these embodiments a plurality of diamond cutters are mounted on the bit body for cutting rock by a shearing action. Each diamond cutter is in the form of a thin diamond plate bonded to a carbide slug that is inserted into the bit body. Means are also provided for limiting the depth of penetration of the diamond cutters into the rock formation being drilled preferably in the form of rolling cone cutters having a plurality of carbide insects protruding from their surfaces. The protrusion of the carbide inserts from the surface of the cutter cones is less than the length of the diamond plate. This limits the depth that the diamond can penetrate in the rock and inhibits damage. Typically the diamond cutters are mounted for cutting one portion of the hole area by shearing action and the rolling cone cutters are mounted for cutting another portion of its area by chipping-crushing action.

Ultrahigh pressure apparatus using cemented tungsten carbide pistons with sintered diamond tips

Abstract: A Drickamer‐type apparatus has been made in which the highly‐stressed tip regions of the Carboloy pistons are of dense sintered diamond. Experiments indicate that this apparatus is capable of attaining static pressures of over 400 kilobar on a newly revised scale. The results show that the 1970 revised pressure scale of Drickamer needs further revision downwards for the range above about 150 kilobar. A pressure scale based on electric resistance transitions up to 400 kilobar is proposed. Resistance vs press force curves are shown for Bi, Fe20Co, Fe40Co, CdS, GaP, BP, NaCl, and graphite.

Ultrasharp diamond edges and points and method of making

Abstract: Ultrasharp diamond edges and points which are usable as cutting instruments and as high intensity point sources for the emission of electrons, ions, x-rays, coherent and incoherent light and high frequency electromagnetic radiation are produced by preparing and classifying ultrafine diamond powder having a particle size of 10 to 100 angstroms placing the powder in a diamond mold defining the ultrasharp edge or point to be produced and applying a pressure of the order of 80 to 90 kb while heating the powder to a temperature of the order of 2440° to 2500° K in an ultrahigh vacuum or inert atmosphere after degasing to avoid oxidation of the diamond powder.

Wear of synthetic diamond when grinding ferrous metals

Abstract: IT is well established that diamond is an inefficient abrasive for grinding ferrous materials especially the low carbon variety The widely held view is that as ordinary carbon has a strong affinity for iron forming iron carbide (Fe3C) this should also be the case with diamond (cubic carbon) when grinding steel The high rate at which diamond grinding wheels wear down when grinding low carbon steel is said to be a consequence of this action We suggest here another mechanism evidence of which is provided by scanning electron micrographic (SEM) data

Artificial intraocular lens

Abstract: A chemically durable, biologically inert optical implant lens formed of a low density natural or synthetic crystal, such as Corundum, Sapphrie, Ruby, Sircon, Strontium Titanate, Diamond, Anatase or Ruby.

A classification scheme for diamond and a comparative study of South African diamond characteristics

Abstract: A diamond classification system based on the physical features of diamond as a function of size is described. Crystal form, crystal angularity, crystal regularity determine the major morphological divisions of the classification, but transparency or opacity, colour, the number of inclusions and surface features allow further subdivision. The system has been used to define uniquely samples of diamonds from three kimberlite diatremes, Premier, Finsch, and Koffyfontein, and an alluvial source, Dreyers Pan. In the cases of the diatreme occurrences variations in diamond crystal shape versus size are explained in terms of a primary crystal population of octahedra and twinned crystals (macles) subsequently altered by secondary processes in the kimberlite magma. Variations in colour are discussed in terms of aggregation of nitrogen into platelets in the diamond crystal lattice as the diamond grew. Characteristic features of alluvial diamonds from Dreyers Pan allow some conclusions to be drawn relating to the nature of the original kimberlite(s) from which the diamonds are derived. The usefulness of the classification scheme as a framework into which other quantitative diamond studies can be fitted, is outlined.

Modifying the surface of diamond particles

Abstract: Abrasive particles are prepared by milling diamond particles, metal compound and milling balls to smear a coating of the compound on the diamond particles and firing the compound-coated diamond particles producing a rough granular adherent covering of metal and/or metal carbide surface coating chemically bonded to the diamond surface by metal carbide.

Changes in the Defect Structure of Diamond Due to High Temperature+High Pressure Treatment

Abstract: Type Ia and type IIa diamonds have been heated to temperatures in the range 2000-2300 degrees C under a pressure of about 4.8 GPa. The changes in the defect structure of these diamonds as a result of the heat treatment have been examined by optical absorption measurements, integrated X-ray spike measurements and by electron microscopy. Type Ia diamonds changed colour from colourless to yellow after being heated for 1 min in the temperature range 2250-2300 degrees C and it has been shown that the yellowing was due to scattering. The scattering centres responsible were elliptically shaped cracks in the cube planes with their longest dimension in a $\langle $100 $\rangle $ direction. It is proposed that these cracks emanated from the platelets which are present in this type of diamond, owing to the breaking of carbon-carbon bonds at the periphery of the platelets where there is a tensile strain present. It is very probable that the cracks contained amorphous or partially crystallized carbon. Evidence is also presented for bond breaking and crack formation at edge dislocations in type IIa diamonds as a result of the treatment with the crack again filled with amorphous or partially crystallized carbon. Type IIa diamonds did not turn yellow as a result of the treatment. Prolonged heating of both types of diamond resulted in a catastrophic reduction in strength due to the growth of the cracks. Integrated X-ray spike intensity measurements and electron microscopy observations showed no apparent change in the structure of the platelets as a result of heating type Ia diamonds in the temperature range 2200-2250 degrees C. However, the optical absorption measurements indicated that changes were taking place at the platelets. It is proposed that nitrogen atoms diffused away from the platelets and combined with other point defects to produce colour centres. It is also proposed that the apparently unchanged structure of the platelets was because the nitrogen is present in platelets as a minority species and the platelets consist mostly of segregated interstitial carbon atoms with the nitrogen atoms dispersed, probably at random, in the platelets. Localized bond breaking also probably occurred at the periphery of the platelets as a result of heating in this temperature range.

Transitions between high-spin nuclear states

Abstract: Author(s): Banaschik, M.V.; Simon, R.S.; Colombani, P.; Soroka, D.P.; Stephens, F.S.; Diamond, R.M.

Anharmonic decay of optical phonon in diamond

Abstract: The width of the 1332-${\mathrm{cm}}^{\ensuremath{-}1}$ first-order Raman line in diamond, measured by Krishnan and by Solin and Ramdas from 15 to 970 K, varies with temperature as expected from the anharmonic interaction of the optical phonon with two phonons of half the frequency. The magnitude of the width agrees with a theoretical estimate by Klemens.

Metal-coated diamond abrasive article containing metal fillers

Abstract: A diamond abrasive article preferably in the form of a grinding wheel, the work-contacting portion of which has a resinoid body containing metal coated diamond particles and also containing powdered metal of two kinds, one of the powdered metals having a relatively low melting point and the other having a substantially higher melting point, such as tin and copper, respectively.

Study of Defects Introduced by Ion Implantation in Diamond

Abstract: Natural type IIa diamonds have been implanted with 70 keV carbon, nitrogen and boron ions. The behaviour of the defects introduced is monitored using electron paramagnetic resonance, absorption, luminescence and Raman scattering measurements. We first describe and discuss the applicability of these techniques. We then present results concerning the introduction rate of the defects and their annealing; these results are briefly discussed.

Wire cutting machine

Abstract: A machine for cutting a preselected shape in a work piece along X and Y axes, the machine utilizing a diamond wire cutting means traveling along a Z axis. A diamond wire cutting machine adapted for use with a milling machine. The cutting machine includes servo-driven caster-type pulleys movable about the Z axis and closely positioned above and below the work. Positioning of the rotatable pulleys is in accordance with the changes in configuration of the work being cut so that the diamond wire is directly supported against the pressure of the work as the work is turned in accordance with the pattern or shape to be cut.

Theoretical models for the GRI doublet in diamond

Abstract: The defect molecular model for the vacancy in diamond originally proposed by Coulson and Kersley requires some extension before it accounts for the observed symmetry of the states involved in the GR1 doublet. Models involving spin-orbit interaction and also Jahn-Teller effects are examined in the light of recent stress results. It is suggested that the GR1 transitions are between vibronic states in a ground electronic E state and an electronic T states; the latter being weakly coupled to the e modes.