Robert Charles Devries

Crystallization of diamond from the gas phase; Part 1

Abstract The paper discusses growth mechanisms of diamond from the gas phase taking into account previously presented theory and experimental data. A chemical kinetics model for the deposition of diamond and graphite from hydrocarbon gases is presented, based on the work of Derjaguin, Fedoseev and coworkers. The mechanism proposed by Derjaguin et al. is expanded to consider the relationship between temperature dependence of the growth rate and the atomic reconstruction of the diamond surface. A diamond growth process is proposed which integrates chemical factors (thermodynamics, kinetics, chemisorption) and physical factors (thermal vibrations, surface transformation surface diffusion).

Plastic deformation and “work-hardening” of diamond

Abstract Extensive plastic deformation of diamond crystals can be accomplished by squeezing diamond embedded in diamond powder at high pressures and temperatures. By inhibiting brittle fracture, deformation takes place at temperatures as low as 900°C at 60kb. The {111} deformation lamellae have a higher abrasion resistance than even the {111} plane of diamond.

The system Li3BN2 at high pressures and temperatures

Abstract The system Li3BN2 was studied over the pressure and temperature range from 10 to 65 kb and 300–1900°C, respectively. The stability region of a quenchable high pressure modification, Li3BN2(W), was defined, and the data also suggest the possibility of another nonquenchable high pressure modification. Li3BN2(W) is the phase which appears to be in equilibrium with borazon (cubic BN) during growth of this phase from the system Li3N-BN, and the P-T data obtained on the melting of Li3BN2(W) are useful for defining the growth conditions for borazon.

Epitaxial growth of CrO2

Abstract Oriented layers of CrO2 have been grown epitaxially on {100}, {110}, {210} and {001} surfaces of single crystal TiO2 (rutile) and on the {0001} planes of single crystal Al2O3 and Fe2O3 by the decomposition of CrO3 on the substrate contained in a pressure vessel. The area of these layers is limited primarily by the size of the single crystal substrates. Beside meeting structural requirements the substrate must not form stable compounds with molten CrO3 or the other chromium oxides resulting from CrO3 decomposition. The CrO2 layer begins to form during the decomposition of Cr2O5 by nucleation of oriented CrO2 at many sites on the substrate surface. Defects on the surface of the substrates limit the perfection of the oriented layer. Characterization of the films by both chemical analysis and x-ray techniques indicate that the epitaxial CrO2 is identical in all respects to the bulk material. The oriented layers have been used for magnetic measurements.

Stability of CrO2 at high pressures and temperatures in the “belt” apparatus

Abstract An investigation of the decomposition of CrO 2 to Cr 2 O 3 from 800° to 1580°C and 15 to 65 kb was made in the “belt” apparatus. CrO 2 can be held for at least 10 minutes without decomposition at temperatures to above 1500°C at pressures of 60 to 65 kb. These results indicate the feasibility of reacting other oxides with CrO 2 for the formation of new compounds.

Evidence for plastic deformation in the natural polycrystalline diamond, framesite☆

Abstract Relief-polished striations have been found within grains in polished sections of framesite, a naturally occurring polycrystalline diamond. Because the narrow zones represented by these surface striations are harder than any orientation of the matrix (as revealed by abrasion resistance) and because they etch preferentially, they have been interpreted as representing oriented deformation bands within the grains. It is concluded that the microstructure of framesite is the result of plastic deformation of diamond grains probably under conditions such that brittle fracture was inhibited.

On the decomposition of CrO2 in air

Abstract Literature values for the decomposition temperature of CrO 2 (metastable at 1 atm) to Cr 2 O 3 in air range from 250° to 500°C. Experiments on both single crystals and powders made from the decomposition of CrO 3 show that no measurable decomposition of CrO 2 occurred at temperatures up to 400°C for at least 48 hours unless the Cr 2 O 3 phase is first nucleated by a rapid heating to about 475°C. Once nucleated, Cr 2 O 3 will grow at observable rates at 400°C as seen on single-crystal films. It is concluded that property measurements on CrO 2 can be made safely to 400°C for a few hours, provided nucleation of Cr 2 O 3 is avoided.

Phase equilibria and crystal growth in the systems PbO·PbCrO4PbO·PbMoO4, PbO·PbCrO4PbO·PbWO4 and PbO·PbCrO4PbO·PbSO4

Abstract PbO·PbCrO4 is a paint pigment with interesting semiconductor and thermochromic properties. Preparatory to crystal growth and property measurements of this material, phase equilibria studies were made in the systems PbO·PbCrO4-PbO·PbMoO4, PbO·PbCrO4-PbO·PbWO4 and PbO·PbCrO4-PbO·PbSO4. In each case complete miscibility in the solid and liquid states was found. The small separation between solidus and liquidus in each system and rapid attainment of equilibrium permits the growth of large homogeneous crystals by pulling from the melt.

Thermal stability of hydronium and ammonium beta alumina at high pressure

Abstract The high pressure thermal stability of hydronium beta alumina and ammonium beta alumina have been investigated from 5 to 50 Kb pressure and from room temperature to 550°C. Both phases are stable at 400°C to 50 Kb pressure. At 50 Kb and 450°C, ammonium beta alumina decomposes into α-Al 2 O 3 and hydronium beta alumina decomposes into H 2 O.5Al 2 O 3 (Tohdite) and α-Al 2 O 3 . A tentative phase diagram is suggested for the stability range of hydronium beta alumina in the Al 2 O 3 -H 2 O system.

Pressure-temperature diagram for the system SrSiO3

Abstract The P-T diagram from the system SrSiO 3 was determined by equilibration and quenching of SrSiO 3 in a “belt”-type high-pressure apparatus up to nearly 70 kb and 1600°C. In agreement with others, three crystalline phases were found to be quenchable and are in equilibrium at about 47 kb and 750°C. The low-temperature form has a melting curve with a negative slope as predicted by Buckner and Roy (1).