Role of structural ordering of the original components in formation of boron nitride

Conclusions The process of formation of boron nitride from homogeneous highly dispersed charges prepared from a solution of boric acid and sucrose is retarded by the carbide formation reaction. The addition in the stage of preparation of the solutions of additions which in subsequent heat treatment hinder appearance of highly defective forms of B₂O₃ and carbon promotes an increase in yield of nitride.Translated from Poroshkovaya Metallurgiya, No. 6(342), pp. 54–61, June, 1991.     

Effect of lithium on structure formation of graphite-like boron nitride with carbothermal synthesis

Formation of a graphite-like boron nitride structure during carbothermal analysis in the presence of lithium compounds in a stream of nitrogen or ammonia is studied by electron microscopy, x-ray, and chemical methods. A marked reduction in the formation temperature for graphite-like boron nitride with a highly ordered structure is observed and chemical aspects of the process are discussed.Institute of Problems of Materials Science, National Academy of Sciencesof the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 1–8, July–August, 1994.     

Effect of the different crystal structures of boron nitride on its high-temperature stability in oxygen

Conclusions The crystal structure of boron nitride has a pronounced effect on its high-temperature stability in oxygen. The least oxidation resistance is exhibited by wurtzite-type boron nitride, which is due to its extremely defective structure, and the highest oxidation resistance by cubic boron nitride, which has a perfect crystal structure. The oxidation of all three modifications of boron nitride is accompanied by the formation of boric anhydride, elemental nitrogen, and nitrogen dioxide. The observed intense evolution of nitrogen dioxide from BN_g is apparently linked with differences in electronic structure between this boron nitride form and the diamondlike modifications (BN_s and BN_w). The amount of nitrogen dioxide liberated from each modification is a maximum at a temperature of 1100°C.Translated from Poroshkovaya Metallurgiya, No. 7(223), pp. 83–86, July, 1981.     

含硼矿中硼的提取工艺技术现状及趋势

硼化合物是重要的工业原料,从矿石中提取出的硼主要以硼酸和硼砂的形式存在.我国从 20 世纪 60 年代开始建立硼工业以来,先后采用以硫酸法为主生产硼酸、碳碱法为主生产硼砂的工艺技术.由于近年来硼资源品位的下降、环境问题的涌现以及产品纯度要求的提高,催生了不同提硼新方法的研究,希望能从改善硼矿中硼的浸出率、减少环境污染及提高产品纯度等方面着手逐步取代传统的提取工艺.论文首先介绍了硼酸和硼砂的应用,然后重点介绍了我国现有的提硼工艺技术.最后,介绍了提取硼的非传统工艺并分析了其发展前景.      

Structural changes occurring in boron nitride during shock compression in the presence of water

Conclusions The presence of a small amount of water in the process of shock compression of graphite-like boron nitride hinders the formation of crystal structure defects in BNg and suppresses the reverse transformation of the wurtzite phase. As a result, the amount of the wurtzite phase grows compared with that of the graphitelike phase. However, the extent of this phenomenon is decreased by partial hydrolysis of boron nitride, leading to the formation of boric anhydride. The monocrystalline particles of the wurtzite phase forming during shock compression with water are much larger than the particles produced in the absence of additions. The level of internal defectiveness in BN_w particles, which determines the widths of lines in x-ray diffraction photographs, is virtually independent of compression conditions.Translated from Poroshkovaya Metallurgiya, No. 9(189), pp. 76–80, September, 1978.     

Sintered nickel-boron nitride materials

Summary As a result of tests made on sintered nickel-boron nitride materials, it was ascertained that during compaction boron nitride helps to increase the density of compacts and during sintering is responsible for their volume growth. Shrinkage of these materials is only observed at boron nitride contest below 4% and at sintering temperatures above 1150° C. The materials investigated have satisfactory oxidation resistance at temperatures up to 700–800° C, the degree of oxidation increasing with increasing boron nitride content. They are also adequately corrosion resistant in sulfuric and hydrofluoric acids.When their boron nitride content is raised, particularly above 8%, their coefficient of friction and specific wear rise substantially, but nevertheless the naterials investigated are easily run-in by labyrinth projections.Sintered nickel-boron materials with low boron nitride contents (up to 8% may be recommended, after further tests, for application in gas seals of transport gas turbines operating at medium temperatures.Translated from Poroshkovaya Metallurgiya, No. 11(47), pp. 29–34, November, 1966.     

Reaction of cubic boron nitride with titanium iodides

Conclusions The reaction of cubic boron nitride with the gaseous phase of titanium iodides (process duration 0.25–2.0 h, total pressure of titanium iodides 100 Pa) results in the preferential formation of TIN in the temperature range 900–1200°K and of titanium nitride and titanium diboride at 1200–1300°K.Translated from Poroshkovaya Metallurgiya, No. 10(262), pp. 57–59, October, 1984.     

Preparation of Boron Nitride Fibers Using Hydrated Cellulose. Part 3. Nitriding Hydrated Cellulose Fibers Impregnated with Boric Acid

The effect of preliminary heat treatment (PHT) for hydrated cellulose fibers impregnated with boric acid on the composition and structure of nitrided products is studied. Subsequent nitriding after PHT in helium leads to formation of carbon fibers coated with boron nitride, but after PHT in air there is formation of hexagonal and rhombohedral boron nitride powder. Data obtained are compared with results reported previously.

     

Preparation of Boron Nitride Fibers Using Hydrated Cellulose. Part 3. Nitriding Hydrated Cellulose Fibers Impregnated with Boric Acid

The effect of preliminary heat treatment (PHT) for hydrated cellulose fibers impregnated with boric acid on the composition and structure of nitrided products is studied. Subsequent nitriding after PHT in helium leads to formation of carbon fibers coated with boron nitride, but after PHT in air there is formation of hexagonal and rhombohedral boron nitride powder. Data obtained are compared with results reported previously.     

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.     

Microstructure formation in wurtzite BN (Geksanit-R) sinterings

Conclusions The loading of wurtzite boron nitride to high static pressures (55–100 kbar) under room-temperature conditions is accompanied by the processes of comminution of polycrystalline powder particles and their monocrystalline grains. Comminution of wurtzite boron nitride particles and grains has been found to take place also during sintering at high pressures and temperatures. The intensity of particle and grain comminution during loading and compression grows with increasing size of the particles in the starting condition. The comminution of particles and grains has a marked effect on structure formation in polycrystalline Geksanit-R alloy sintering.Translated from Poroshkovaya Metallurgiya, No. 8(236), pp. 32–37, August, 1982.     

Preparation of powders of titanium boronitrides in superhigh-frequency discharge plasma

Conclusions It is shown that alloys of the system titanium-boron-nitrogen can be prepared by the simultaneous reduction and nitriding of titanium and boron chlorides during their very brief residence time in a plasma type chemical reactor. The dissolution of about 6 wt.%of boron in titanium nitride lowers the temperature coefficient of electrical resistivity of titanium boronitrides by a factor of 2.5 compared with pure titanium nitride.Translated from Poroshkovaya Metallurgiya, No. 11 (131), pp. 6–9, November, 1973.     

Antifriction properties of boron nitride during dry friction in gaseous media and at low temperatures

Summary The article presents the results of an experimental study of the dry friction of boron nitride in gaseous environments and at low temperatures. It is shown that the environment exerts a substantial influence on the wear of boron nitride. Experimental data are given on the wear of boron nitride rubbing against hard nitrided 1Kh18N9T steel in gaseous enviroments (air, argon, nitrogen, and helium) and at liquid nitrogen temperature.Translated from Poroshkovaya Metallurgiya, No. 7 (43), pp. 49–52, July, 1966.     

Electrochemical behavior of transition metals and refractory compounds of titanium in synthetic sea water

Conclusions Investigations were conducted into the corrosion-electrochemical behavior of the compounds of titanium with boron, carbon, and nitrogen produced by powder metallurgy and also of the transition metals in synthetic sea water. The results show that the start of pitting coincides with the process of intensive oxidation on the surface of the refractory compound. On the basis of the increasing corrosion resistance the examined compounds can be arranged in the following sequence: TiB₂-TiC-TiN. The highest corrosion resistance of the titanium nitride is explained by the special features of the effect of the titanium oxynitride, formed in the corrosion process, on the protective coating. In contrast to the acid media, the corrosion resistance of titanium nitride is not higher than that of titanium.Translated from Poroshkovaya Metallurgiya, No. 2(302), pp. 81–87, February, 1988.The authors are grateful to L. N. Kurilenko for carrying out atomic absorption analysis.     

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.     

Preparation of technical zirconium diboride by the carbothermic reduction of mixtures of zirconium and boron oxides

Conclusions A study was made of the preparation of technical zirconium diboride by the reduction of mixtures of zirconium and boron oxides with carbon under industrial conditions. It is shown that the optimum conditions for the preparation of zirconium diboride by the carbothermic method are established when a charge having the composition ZrO₂+1.2 B₂O₃+5 C (i.e., with a 20% excess of boric anhydride over the stoichiometric composition) is reduced at 2000°C in a hydrogen or converted gas atmosphere. The resultant ZrB₂ contains 18–19% B (compared with the theoretical boron content of 19.25%) and not more than 0.8% C.Translated from Poroshkovaya Metallurgiya, No. 11 (131), pp. 80–84, November, 1973.     

The structural aspect of high-pressure superhard phase synthesis

Structural aspects are considered for the direct phase transitions in carbon and boron nitride at high pressures from the viewpoint of martensite and diffusion transitions. The mechanism for the transitions of graphite and graphite-type BN into superhardphases is controlled primarily by the crystalline perfection of the initial structures that show martensite transformations to metastable phases (lonsdaleite and BN wurtzite allotrope), while highly defective ones show diffusion transformation to high-pressure stable phases (diamond and cubic boron nitride). The perfection in the initial structure has a very marked effect on the transformation mechanism during shock compression, which is the main technique in the commercial production of superhard phases.Institute of Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7/8(380), pp. 83–92, July–August, 1995.     

Contact reaction of Kh20N80 alloy with boron nitride

Conclusions A study was made of the causes of the contact reaction between Kh20N80 alloy and boron nitride during the sintering of composite compacts in various environments at temperatures of 1170–1330°C. It was established that the contact reaction between Kh20N80 alloy and boron nitride occurs in the following stages:partial dissociation of the boron nitride, with the evolution of free nitrogen, which then reacts with the chromium;reaction of boron with the nickel and chromium, with the formation of boride phases;enrichment of the nickel-base solid solution in chromium and the appearance of a chromium-base solid solution.In sintering in various gaseous environments the temperature at which partial melting begins during the contact reaction falls in the order argon (1330°C) > hydrogen and cracked ammonia (1250°C) > vacuum (1170°C).A 20% Cr-80% Ni alloy - Translator.Translated from Poroshkovaya Metallurgiya, No. 5(161), pp. 31–39, May, 1976.     

Interaction in the system Li-B and some properties of lithium boride phases

Theoretical prerequisites are given for the formation of boride phases in castings. Lithium borides LiB₂ and LiB₁₀ are synthesized and identified by x-ray photoelectron spectroscopy and x-ray phase and chemical analyses. Lithium diboride is a rather unstable compound which easily decomposes in weak mineral acid solutions. In contrast the decaboride is highly resistant to corrosive media. It decomposes completely in HNO₃-H₂O₂ and H₂SO₄-HNO₃ mixtures. A small amount of boron hydride is released as a result of lithium decaboride reaction with acids. Some physical properties (magnetic susceptibility, resistivity) are studied. The physicochemical properties of the Li-B system resemble those of the Be-B system. The highest lithium boride LiB₁₀ pertains to covalent crystals and like boron it possesses semiconducting properties.Institute of Problems in Materials Science, Academy of Science of the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 54–58, January–February, 1994.     

Elastic constants and elasticity moduli of cubic and wurtzitic boron nitride

Elasticity moduli and elastic constants for sphaleritic and wurtzitic boron nitride are calculated and determined by experiment. Numerical values are given for single crystals of these materials and polycrystals of hexanite-R, elbor-R, belbor, kiborite, and other superhard materials. An approach is suggested for combining hot pressing at ultrahigh pressures and a pulsed ultrasonic technique which may be used to determine the elasticity modulus and elastic constants of the majority of refractory compounds which are difficult to determine by other techniques.Institute of Materials Science, Ukrainian Academy of Sciences, Kiev. Institute of Metal Physics, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7/8(380), pp. 92–99, July–August, 1995.