Electrical conductivity of polycrystalline sphalerite boron nitride BNsp obtained by direct phase transformation from pyrolytic boron nitride

Translated from Poroshkovaya Metallurgiya, No. 8(356), pp. 14–18, August, 1992.     

NaCl-CaCl2-CaWO4熔盐体系电导率的研究

电导率作为一个重要的物理化学参数,对熔盐电解选择最佳电解质及电解温度等具有重要指导意义,通过对熔盐电导率的研究,可以间接地了解熔盐体系的离子结构。因此,关于NaCl-CaCl2-CaWO4熔盐体系导电性质的研究,对深入研究其电解机理则凸显重要,实验采用CVCC法测定NaCl-CaCl2-CaWO4熔盐体系的电导率,并通过正交试验分析,研究该体系电导率与温度和熔盐组成摩尔比的关系。结果表明：升高温度或是增大NaCl对CaCl2的摩尔比,均能提高体系电导率,而组分摩尔比是影响体系电导率的主要因素,当n（NaCl）∶n（CaCl2）为1∶1时,即体系最低共熔点附近出现了电导率的最低值,并随着NaCl或CaCl2的增加,电导率也增加。     

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.     

NaCl-CaCl2-CaWO4熔盐体系电导率的研究

电导率作为一个重要的物理化学参数,对熔盐电解选择最佳电解质及电解温度等具有重要指导意义,通过对熔盐电导率的研究,可以间接地了解熔盐体系的离子结构.因此,关于NaCl-CaCl₂-CaWO₄ 熔盐体系导电性质的研究,对深入研究其电解机理则凸显重要,实验采用 CVCC 法测定 NaCl-CaCl₂- CaWO₄ 熔盐体系的电导率,并通过正交试验分析,研究该体系电导率与温度和熔盐组成摩尔比的关系.结果表明:升高温度或是增大 NaCl 对 CaCl₂ 的摩尔比,均能提高体系电导率,而组分摩尔比是影响体系电导率的主要因素,当 n（NaCl）∶n（CaCl₂）为 1∶1 时,即体系最低共熔点附近出现了电导率的最低值,并随着 NaCl 或 CaCl₂ 的增加,电导率也增加.      

Electrical conductivity of REF_3-LiF(RE=La and Nd) molten salts

The electrical conductivity of REF3-LiF(RE=La and Nd) molten salts(xREF_3=5 mol%-40 mol%) was systematically measured over the temperature range from 1223 to 1423 K by using continuously varying cell constant(CVCC) method.Electrical conductivity values of LaF3-LiF and NdF_3-LiF molten salts within the studied ranges are 4.11-9.39 and 3.62-9.51 S/cm,respectively.The composition and temperature dependences of electrical conductivity and the factor of RE_2 O_3 on electrical conductivity were investigated.The electrical conductivity nonlinearly decreases with the increasing mole percent of REF_3 for the changing of structural ion in molten salts.A good linear relationship between the natural logarithm of electrical conductivity(lnκ) and the reciprocal of the absolute temperature(T~(-1)) can be interpreted by the trend that electrical conductivity linearly increases with increasing temperature.Although it is an important factor of RE_2 O_3 on electrical conductivity,the influence of RE_2 O_3 on conductivity is small for the very limited solubility of RE_2 O_3 in REF_3-LiF molten salts.The results of this work supplement the present electrical conductivity data of rare earth fluoride electrolyte.     

Oxidation of a composite material based on cubic boron nitride

Powder Metallurgy and Metal Ceramics -     

Crystallization of boron nitride from solution in a lithium borate melt

We have investigated the reaction between disordered (turbostratic) boron nitride and lithium carbonate under a nitrogen atmosphere using x rays and electron microscopy. Lithium borate and cyanamide were found to be the reaction products at a temperature of 650°C. Spontaneous crystallization of highly, ordered graphitic boron nitride occurs from solution in a melt of lithium borates at 1000°C. Three-dimensional ordering and crystal size increase with elevation of the temperature to 1450°C.     

Chemical compatibility of a TiAl-Nb melt with oxygen-free crucible ceramics made of aluminum nitride

The problem of uncontrolled oxygen contamination of intermetallic TiAl ingots is considered for the application of crucibles and molds based on traditional oxide ceramics. A synthesized Ti-45.9Al-8Nb (at %) alloy is solidified in alternative oxygen-free crucibles made of high-purity aluminum nitride (99.99% AlN) upon holding at 1670°C for 5, 12, and 25 min and subsequent quenching in a high-purity argon atmosphere. The initial material and the solidified ingots are studied by scanning electron microscopy, optical microscopy, X-ray diffraction, electron-probe microanalysis, and gas-content chemical analysis. The key features of the interaction of the TiAl-Nb melt with AlN ceramics are revealed. Partial thermal dissociation of the crucible material according to the reaction AlN → Al + N and the reaction of atomic nitrogen with the melt lead to the formation of a solid 6.4-μm-thick TiN coating on the ingot surface and provide perfect wettability of the crucible by the melt and easy removal of solidified casting items from the mold. The TiN coating serves as a diffusion barrier that hinders the diffusion of nitrogen and residual oxygen from the pores in the crucible toward the melt. As a result, no oxide particles are detected in the ingots. However, few single microprecipitates of two nitride phases ((Ti,Al) _x N _y , NbN) are detected in the near-bottom region, 300 μm thick, in the alloy after holding at 1670°C for 25 min. The total oxygen contamination in a two-phase α₂ + γ ingot does not exceed 1100 wt ppm, which is 1.5–2 times lower than that obtained in the experiments performed with modern advanced oxide crucibles made of yttrium ceramics Y₂O₃. AlN is shown to be a promising crucible material that can be considered as an alternative to oxide ceramics in the metallurgy of TiAl intermetallics.     

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.     

Phase transformations of the rhombohedral modification of boron nitride with shock compression

Features of crystal-orientated transformations of the rhombohedral modification of boron nitride (rBN) into dense modifications of the wurtzite (wBN) and sphalerite (spBN) types with shock compression in the range from 15 to 50 GPa are studied. Three compression schemes are used: in annular ampules (～15 GPa); in the ampules of K. M. Rabinin (25–35 GPa); in a plane shock wave (～50 GPa). With an increase in pressure from 15 to 50 GPa and a corresponding change in the loading scheme the degree of rBN transformation into dense modifications increases from 0 to 40%. There is a change in the rBN transformation mechanism: from longitudinal bending of layers (as a result of which wBN forms, and spBN is formed from it) to corrugation leading to spBN formation directly from rBN.     

六方氮化硼填充导热树脂复合材料的研究进展

总结了电气电子领域使用的六方氮化硼(hexagonal boron nitride,h BN)导热填料制备方法,介绍了近几年h BN填充树脂基复合材料的研究进展,研究了导热树脂复合材料的导热机理和导热模型,讨论了h BN填料的形貌、粒度、颗粒复配及表面改性方法等因素对材料导热性能的影响,并对h BN填充高导热树脂复合材料的发展方向进行了展望。