Reaction of boron carbide powders with biochemical media

The EPR signals have been detected in boron nitride powders (BN_g and hexanite-A) from: carbon atoms substituting for nitrogen atoms in the BN_g lattice; iron-containing formations; various carbon-containing inclusions. Treatment of these powders in different biochemical and control inorganic media was generally accompanied by changes in the intensity of some signals (in the BN_g specimens) which reflect reactions with the media of real inclusions present in the commercial powders. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 82–88, January–February, 2000.     

Reaction of boron carbide with titanium under ordinary and plasma heating conditions

Conclusions As a result of an investigation, into the high-temperature solid-phase reaction of boron carbide with titanium under ordinary and plasma heating conditions, it has been established that the reaction, which begins at 1300°C, is slow in its final stage, which is due to the appearance of a zone of porosity and to disturbed contact between the reactants. Because of this, in spite of its being accompanied by an appreciable thermal effect, the reaction fails to proceed to completion under conditions of both continual ordinary heating (to 1600°C) and plasma heating. It is possible to obtain spray-deposited coatings of the required composition (TiC+TiB₂) by employing preconglomerated or clad Ti -B₄C powders and preheated basis plates.Translated from Poroshkovaya Metallurgiya, No. 9(213), pp. 47—53, September, 1980.     

助烧体系对注射成形碳化硼陶瓷烧结性能的影响

采用粉末注射成形技术制备碳化硼陶瓷微结构零件,用SiC-Al2O3-Y2O3和SiC-ZrO2两种助烧体系进行烧结。分析助烧体系(SiC-Al2O3-Y2O3和SiC-ZrO2)对零件的致密度、相组成、微观组织和断裂机制的影响。结果表明:添加助烧剂可有效提高碳化硼制品的烧结性能。采用SiC-Al2O3-Y2O3助烧体系烧结的零件由B4C、SiC、B2YC2和YAG等4种相组成,随烧结温度升高,其致密度先增加后减小,在1 950℃烧结时达到最大值,为97.1%。而采用SiC-ZrO2助烧体系时致密度随烧结温度升高而增加,在2 240℃达到最大值,为95.1%,相组成为B4C、SiC和ZrB2相。零件的断裂形式都以穿晶断裂为主,含有一定的沿晶断裂。     

添加氧化铝烧结助剂的碳化硼陶瓷无压烧结工艺研究

采用无压烧结工艺,通过添加质量分数为5%的氧化铝烧结助剂,制备得到了碳化硼陶瓷,其中烧结温度从2000℃到2250℃,保温时间为1、2和3 h。对烧结试样进行了体积密度、显气孔率、维氏硬度、显微形貌和晶体结构测试,并与2250℃下烧结得到的不添加烧结助剂碳化硼试样进行了比较。实验结果表明:由于烧结助剂与碳化硼在扩散运动中的相互作用,导致添加氧化铝助剂无压烧结碳化硼晶粒的形态变化具有温度选择性;氧化铝助剂所体现的液相扩散作用和钉扎作用,既可阻碍碳化硼晶粒长大,又可大幅度降低碳化硼的气孔率;通过烧结工艺控制氧化铝助剂成分在晶粒烧结体中的比例,可以将氧化铝成分完全包裹在碳化硼晶粒内部,有利于碳化硼烧结中的晶粒控制和空隙调整,从而避免助剂成分对烧结碳化硼可能造成的不利影响。     

Reaction of aqueous titanium carbide suspensions with an acid and an alkali

Conclusions Using the techniques of conductometrie and potentiometric titrations of suspensions and aqueous and salt extracts, a study was made of the reaction of titanium carbide with hydrochloric acid and caustic soda. The absorption of the acid and the alkali by commercial titanium carbide is mainly due to the impurities present in it. Titanium carbide freed from impurities picks up hydrogen and hydroxyl ions by an adsorption mechanism, the adsorption taking place in the inner lining of the double electric layer of the solid phase in suspension.Translated from Poroshkovaya Metallurgiya, No. 7 (91), pp. 72–78, July, 1970.     

Reaction of titanium carbide with water

Summary Contrary to the generally held view that carbides of the transition metals of groups IV and V are inert with respect to water, the authors show on the example of titanium carbide that the carbides are decomposed by water, although the extent of attack is not more than 5–30 atomic layers, i. e., not more than 100–150 A.The hydrolysis of TiC proceeds according to the reaction: TiC+xH₂O CH₄ + TiO₂ · xH₂O.Methane is the principal constituent of the gaseous hydrolysis products, and consequently it is possible to regard carbides of the transition metals of groups IV and V as methane derivatives. Hydrogen evolution in both carbides of group V and nonstoichiometric carbides of group IV is believed to take place as a result of the presence of free electrons in the carbides. The complex polymer acid TiO₂ · xH₂O undergoes dissociation, which becomes intensified in the course of time and results in a rise of hydrogen ion concentration. TiC powder particles are negatively charged. With the results obtained it is possible to choose suitable dispersion media for such powder metallurgical operations as fine milling, slip casting, and others.Translated from Poroshkovaya Metallurgiya, No. 6(54), pp. 53–57, June, 1967.