Abstract
The properties, applications and methods for producing titanium and vanadium diborides are considered. These diborides are oxygen-free refractory metal-like compounds. As a result, they are characterized by high values of thermal and electrical conductivity. Their hardness is relatively high. Titanium and vanadium diborides exhibit significant chemical resistance in aggressive environments. For these reasons, they have found application in modern technics. So, they are used as surfacing materials when applying wear-resistant coatings on steel products. It is also possible to use vanadium diboride as a catalyst in organic synthesis and the anode in renewable electrochemical current sources. Perspective are ceramics B4C – TiB2and B4C – VB2, which make it possible to obtain products based on boron carbide with high-quality performance characteristics, in particular, with increased crack resistance. Such composite ceramics are obtained by means of hot pressing, spark plasma sintering and pressureless sintering. The properties of refractory compounds depend on the content of impurities and dispersion. Therefore, to solve a specific problem associated with the use of refractory compounds, it is important to choose the method of their preparation correctly, to determine the admissible content of impurities in the starting components. This leads to the presence of different methods for the synthesis of borides. The main methods for their preparation are: synthesis from simple substances (metals and boron); borothermal reduction of oxides; carbothermal reduction (reduction of mixtures of metal oxides and boron with carbon; metallothermal reduction of mixtures of metal oxides and boron; carbide-boron reduction. Plasma-chemical synthesis (deposition from the vapor-gas phase) is also used to obtain diboride nanopowders. Each of these methods is characterized in the article.
Highlights
they are characterized by high values
с использованием высокодисперсного карбида бора с содержанием примесей примерно 1 %
Yeh C.L., Wang H.J. Combustion synthesis of vanadium borides // Journal of Alloys and Compounds
Summary
Диаграммы состояния систем Ti – B и V – B [1, 2] приведены на рисунке. В системе Ti – B установлено наличие следующих боридов: TiB, Ti3B4 и TiB2. Диборид титана имеет узкую область гомогенности (65,6 – 67,9 % В (ат.) при 1730 °С). При избытке бора образуется смесь фаз (TiB2 + B) с эвтектической температурой плавления приблизительно 2080 °С, а при избытке титана – две боридные фазы (Ti3B4 + TiB2) с перитектической температурой плавления приблизительно 2200 °С. Диборид ванадия имеет узкую область гомогенности (ориентировочно 66 – 68 % В (ат.)). При избытке бора образуется смесь фаз (VB2 + B) с эвтектической температурой плавления приблизительно 2000 °С, а при избытке ванадия – две боридные фазы (V3B4 + VB2 ) с температурой плавления приблизительно 2300 °С. Дибориды титана и ванадия характеризуются высо кими температурами плавления и узкими областями гомогенности. Такие значения этих параметров объясняются тем, что дибориды титана и ванадия относятся к металлоподобным тугоплавким соединениям [2]. Стойкость этих соединений к высокотемпературному окислению сравнительно велика, что связано с защитным действием образующейся на поверхности их частиц жидкой пленки из оксида В2О3 (температура плавления приблизительно 450 °С [4])
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