Special features of the electron structure of ultradisperse powders of cubic boron nitride

Translated from Poroshkovaya Metallurgiya, No. 1(337), pp. 72–76, January, 1991.     

Influence of arsenic on the crystallization processes of sphaleritic boron nitride

Translated from Poroshkovaya Metallurgiya, No. 2(314), pp. 43–47, February, 1989.     

Sintering of turbostratic-structure boron nitride powders

Translated from Poroshkovaya Metallurgiya, No. 2(314), pp. 38–42 February, 1989.     

Structural changes accompanying the sintering of ultrafine aluminum nitride powders

Conclusions An electron-microscopical investigation has established that the sintering of compacts from an ultrafine plasma-chemical AlN powder is determined by the following processes: coagulation, with the formation of strong polycrystalline aggregates (1000–1400°C); coalescence, made possible by a geometric grain boundary match inside the aggregates, and formation of high-angle boundaries between aggregates (1200–1600°C); and collective recrystallization (above 1600°C). In an x-ray diffraction study annealing at temperatures above 1700°C was found to decrease the parameter c of AlN by 0.002 Å as a result of dissolution of oxygen in the lattice without affecting its parametera. The results of both electron-microscopical and x-ray diffraction studies show that annealing at temperatures above 1600°C increases the defectiveness of the wurtzite structure of AlN, brings about twinning and the formation of polytypal interlayers in recrystallized grains, and raises the concentration of other defects causing a broadening of lines in x-ray diffraction photographs. As a result of these phenomena the material experiences a strengthening at sintering temperatures of 1700–1800°C.Translated from Poroshkovaya Metallurgiya, No. 10(226), pp. 35–40, October, 1981.The authors wish to thank A. N. Pilyankevich for helpful discussion.     

Special features of compacting aluminum powders in cold pressing

Translated from Poroshkovaya Metallurgiya, No. 3(303), pp. 33–38, March, 1988.     

Effect of weak shock waves on diamond powders and compacted modifications of boron nitride

Conclusions The effect of weak shockwaves causes extensive compacting of the C_diam, BN_sp, and BN_sp-BN_w powders.In contrast to the static pressures, compacting with the shockwave is accompanied not only by failure but also plastic deformation of the particles.In compacting, agglomerates of particles, subjected to maximum deformation under the given shockwave parameters, form in the volume. The bonding strength between the particles in the aggregates is determined by the degree of their plastic deformation, the density and type of resultant defects, and restoration of the ruptured interatomic bonds on the physical contact areas.In passage of a weak shockwave a substructure forms in the grains and has a beneficial effect on their properties.Deceased.Translated from Poroshkovaya Metallurgiya, No. 7(343), pp. 79–84, July, 1991.     

Structure and properties of powders of some composite materials based on wurtzite boron nitride

Conclusions Addition of titanium carbide and zinc or aluminum oxide to a granulating blend of wurtzite boron nitride produces a low-strength sintered mass which disintegrates easily along the BN granule boundaries under mechanical action, ensuring the production of granules of a given grain size.Individual particles of composite material based on wurtzite boron nitride obtained with admixtures of zinc oxide are characterized by good compressive strength.Translated from Poroshkovaya Metallurgiya, No. 6(270), pp. 81–85, June, 1985.     

Structural special features and infrared spectra of absorption of ultradisperse boron nitride

Conclusions The ultradisperse powders of boron nitride with the mean particle size of 5.3–66 nm showed marked anisotropic deformation of the crystal lattice as a result of the structural stresses which are caused by the dimensional factor and are distributed nonuniformly through the volume of the particle.The turbostratic strain leads mainly to weakening of the interlayer bonds and shifts the maximum of the band of the interplanar oscillations to lower frequency by 17 cm^–1 for the specimen with a dispersion of 5.3 nm. In addition to this, the turbostratic strain causes asymmetric widening of the band of the intraplanar oscillations in the short-wave wing of the curve and displaces the maximum of this band by 20 cm^–1 to the short-wave range (for the specimen with a dispersion of 5.3 nm).Examination by the IR spectral method showed that the interatomic bonds shorten on the average by 10^–4 nm within the limits of the flat lattices. The investigations revealed the regular nature of the removal of the strain of the crystal lattice from the ultradisperse boron nitride during vacuum heat treatment accompanied by sintering of the powder.Translated from Poroshkovaya Metallurgiya, No. 1(301), pp. 85–91, January, 1988.