Microstructure and mechanical characteristics of nanodiamond-SiC compacts

Superhard nanodiamond-SiC ceramics are prepared by infiltrating liquid Si into porous nanodiamond compacts under pressure. Synthesized samples are 2.2 mm thick and 3–4 mm in diameter. The effect of particle size of dynamically synthesized nanodiamond powders on silicon infiltration and SiC phase formation is studied. It is established that silicon does not penetrate into the pores of nanodiamond powders if the original particle size is smaller than 0.5–1.0 μm. The critical pore size for infiltration is 100–200 nm. A study of the microstructure of the samples showed the presence of the nanometer-and submicron-scale SiC phase. The ultrasound velocities are measured in the prepared compacts, and the elastic moduli are calculated. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 4, 2004, pp. 734–736. Original Russian Text Copyright ? 2004 by Ekimov, Gromnitskaya, Mazalov, Pal’, Pichugin, Gierlotka, Palosz, Kozubowski.     

Transformations ofmyo-inositol hexa-O-nitrate under the action of amines

Reactions ofmyo-inositiol hexa-O-nitrate with ammonia and primary amines yield tetrahydroxy-1,4-benzoquinone derivatives,viz., its tetraammonium salt and its diimines, respectively. Reactions with secondary and tertiary amines give salts of rhodizonic acid, which are converted into salts of croconic acid under certain conditions. The reactions with secondary amines involve intermediate formation of radical species, which were dectected by ESR spectroscopy. A scheme for the chemical transformations ofmyo-inositol hexa-O-nitrate under the action of amines was proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2962–2967, December, 1996.     

Adhesion properties of a silicon-containing calcium phosphate coating deposited by RF magnetron sputtering on a heated substrate

Silicon-containing hydroxyapatite coatings 400–700 nm in thickness are prepared by means of radio-frequency (RF) magnetron sputtering on a heated (to 200°C) titanium substrate chemically etched and treated with a pulsed electron beam. The morphology and phase composition of the coating are studied. The morphology and roughness of the composite “calcium-phosphate coating-titanium substrate” differ depending on the treatment procedure of the substrate before deposition. The scratch test method is used to assess the adhesion strength of the coatings formed at different values of bias potential applied to the substrate. It is observed that the adhesion strength of the coating changes with decreasing crystallite size.     

Synthesis and evaluation of properties of the optically transparent (co)polyimides based on cyclic and alicyclic diamines and dianhydrides of aromatic tetracarboxylic acids

Russian Chemical Bulletin - Optically transparent polyimides (PIs) containing adamantane moieties in the structure of diamine unit were synthesized, and their properties were evaluated. The...     

Anisotropy of Isobaric Instability in a Partially Ionized Plasma in a Magnetic Field

Bulletin of the Lebedev Physics Institute - Linear equations describing the dynamics of small perturbations in partially ionized heat-releasing plasma in an external magnetic field with an...     

Chemical etching of sapphire

The results on etching of sapphire substrates with different orientation are discussed. High temperature etching in hydrogen stream and etching in the mixture of H₃PO₄ and H₂SO₄ were used in experiments. The relation of etching rates for different sapphire orientations were established in both cases. The conditions of nonselective etching were determined.     

The Growth Kinetics and Surface Morphology of GaN Epitaxial Layers on Sapphire

The growth kinetics of GaN on Sapphire was analyed on the base of some experimental data such as: the growth rate temperature depandence, on the base of some experimental data such as: the growth rate temperature dependence, the grwoth rate dependence on the gas flow velocity, the growth rate depandence on the crystallographic and spatial orientation of the substrate. The limiting stage of the epitaxy process was established at different growth conditions. The morphology of GaN epitaxial layers obtained at these conditions is described.     

Growth kinetics,structure and surface morphology of AlN/α-Al2O3 epitaxial layers

The gas-phase epitaxy of AlN on saphire substrates in the system Al HCl NH₃–Ar was investigated. The uniformity and structural perfection of the layers were shown to be determined by gas dynamics in the growth zone. The growth rate of AlN-layer is proportional to AlCl concentration in the growth zone and does not depend on NH₃ partial pressure. This is in accordance with the law of diffusional stoichiometry. The morphology of AlN-layers was shown to be dependent on the growth rate and the substrate orientation. Smooth mirror-like layers were prepared on the sapphire planes (0001) and (1120) at low growth rates. X-ray microanalysis showed the oxygen impurity content at the level 1 — 5 · 10²¹ cm⁻³. Other impurities were not available.     

Magnetic,resonant, and thermal properties of Fe<Subscript>0.27</Subscript>Mn<Subscript>0.73</Subscript>S crystals

Fe_0.27Mn_0.73S single crystals were studied. A magnetic transition is detected near 197 K, which is accompanied by anomalies of the thermal, electrical, and resonant properties.