Properties and structure of periclase — Yttrium materials

Conclusions An analysis was carried out of the properties of a ceramic material in the system MgO-Y₂O₃ containing 5–64.8% yttrium oxide.The vaporization of a periclase-yttrium ceramic is attributable to its large surface area and to the state of the material (monocrystalline grains and a fine-ground component). The addition of yttrium oxide to the periclase material results in a lower weight loss in a vacuum of 1.5·10^–5 mm Hg at 1700°C, more especially in the case of a mix produced from chemically pure materials. The weight loss was lowest for a composition designed as a chemical compound, viz., 1.1% after holding for 20 h.Granular mixes (2-0, 1-0 mm) are more stable to vacuum than a fine-grain material. An analysis of the structure of the cylindrical surface of the specimens showed that the vaporization rate is greater for the fine-ground component.Translated from Ogneupory, No. 1, pp. 50–54, January, 1976.     

Role of bulk and mass effects of reactions in reaction sintering processes

Peculiarities of the fabrication of ceramic porous and dense composite materials based on compounds of the Si–C–O–N system with the participation of chemical reactions and the formation of new phases are discussed. An analysis of comparatively new technologies is attempted in terms developed in earlier studies on the reaction sintering of silicon nitride, carbide, and oxynitride. It is shown that the approach to reaction sintering that includes the selection of promising reaction systems allowing for the bulk effect of reactions accompanying material formation can be extended to the fabrication of porous and highly porous materials. In contrast to the fabrication of dense materials, when reaction systems with positive bulk effects are used, the reaction systems with negative bulk effects can be used in the fabrication of highly porous materials.     

Interaction of Aluminum with Detonation Products

A method of electrical conductivity and an analysis of recovered explosion products are used to study interaction of aluminum with detonation products of condensed high explosives. The electrical conductivity of HMX/Al and RDX/Al mixtures is inhomogeneous; a region with the maximum electrical conductivity is adjacent to the detonation front, whereas the electrical conductivity decreases with distance from the front. If the wave is incident onto a wall, the electrical resistance of the composite high explosive increases, which indicates that the high-conducting zone disappears. The electrical conductivity, resistance of the conducting zone, and the time of resistance growth are found as functions of the particle size of the additive. The results obtained confirm the reaction of the metal additive with detonation products in a microsecond range of time. An analysis of condensed explosion products shows that the reaction of aluminum with detonation products proceeds on the particle surface. The amount of reacted aluminum and the oxide-layer thickness are estimated. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 120–129, Jnuary–February, 2006.     

Special features of manufacturing highly porous materials from silicon nitride,silicon oxynitride,and sialons

Results obtained in a study of factors that affect shaping and sintering of highly porous materials are presented. A technology providing highly porous silicon nitride materials that is based on shaping preliminarily fabricated pieces of thermoplastic slip makes it possible to use initial silicon powders of different dispersities. Highly porous materials can also be produced on the basis of sialons and exhibit a diminished thermal conductivity and a heat resistance at the level of similar silicon nitride materials.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 8 – 13, November, 1996.     

Rapid Fracture of Layered Shields Based on Al – Si3N4 Composite Material

Structures of anti-bullet shields with an armor layer of an Al – Si₃N₄ composite material based on aluminum alloys AK5M2 and AL-23-1 reinforced by a porous Si₃N₄ ceramic formed from the components are considered. The effects of the amount of Si₃N₄ in the composite material, the thickness of the components in the ceramics, and the size proportions in the structure are studied. Shields of layered and layered-lattice types are shown to have high bullet resistance.     

Reaction Sintering with Negative Volume Changes

The preparation of high-porosity sialon and SiC materials by reaction sintering accompanied by weight loss and shrinkage is considered. -Sialon ceramics with a 60% porosity, pore size of 0.7 m, and gas permeability K = 0.04 m² are obtained via carbothermal reduction and simultaneous nitriding of kaolin in kaolin + graphite green compacts. The SiC materials prepared from mixtures of SiO₂ and graphite have a porosity of 83% and a pore size of 1 m. The most promising technique is elemental synthesis. In the SiC materials prepared by milling silicon + graphite mixtures to a specific surface area of 80 m²/g, pressing at 100–200 MPa, and sintering in argon at 1600°C for 15 min, the pore size is as small as 0.2–0.3 m.     

Infrared Spectra and Structure of Si3N4, Si2ON2, and Sialons

Sialon powders are prepared from Kyshtymskoe kaolin with 12 – 28 wt.% carbon mixtures by the carbothermal reduction-nitridation method. The infrared spectra of -, O-, C- and 15R-phases in the Si – Al – O – N system are recorded and compared with the IR spectra of Si₃N₄, Si₂ON₂, and kaolin. The IR data are shown to correlate with the chemical composition of sialons and provide information supplementary to x-ray phase analysis data. The spectra of sialon powders differ from each other and from the spectrum of silicon nitride.     

Wear resistance of composite materials based on silicon nitride and carbide with ceramic melt infiltrations

Fabrication of composite materials is considered. Porous preforms from reaction-sintered silicon nitride (RSSN) and RSSN with SiC particles have been infiltrated with CaF₂ and CaSiO₃ melts at a temperature of 1450 and 1600‡C, respectively. The wear resistance of the composite (with infiltrations) materials turned out to be much higher than that of original (without infiltrations) materials of the RSSN and RSSN — 50% SiC type. A composite material with the composition RSSN — 50% SiC — CaSiO₃ is shown to possess the highest hardness and abrasive resistance. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 7–10, March, 2000.     

A method of reducing the number of members of the committee systems of linear inequalities

The problem of discriminant analysis under mild conditions is reduced to a system of linear inequalities. However, this system can turn out to be inconsistent, which happens rather frequently. This is when the method of committees is used. The quality of a committee is improved as the number of its members drops. A method of reducing the number of members of committees, if this is fundamentally possible, is considered.