Chemistry of inorganic compounds – Boron or compound thereof – Binary compound
Patent
1986-07-16
1988-06-21
Straub, Gary P.
Chemistry of inorganic compounds
Boron or compound thereof
Binary compound
25218314, 423345, 423346, 423439, 423440, 423442, 501 87, 502177, 502182, C01B 3130, C01B 3134, C01B 3136, C04B 3552
Patent
active
047524561
DESCRIPTION:
BRIEF SUMMARY
FIELD OF ART
The present invention relates to a process for preparing metal carbides and precursors thereof. More particularly, it is concerned with a process for preparing novel carbon-containing mixtures and metal carbides obtained therethrough.
BACKGROUND ART
Sintered metal carbides such as sintered silicon carbide are known to have superior characteristics as ceramic materials, etc.
Heretofore, metal carbides have been produced mainly by reacting metal elements or metal oxides and carbon under a strong heat. For example, a method in which one or more of, for example, such metal elements as silicon, titanium, tungsten, boron, aluminum, zirconium, hafnium, niobium, cobalt, molybdenum, tantalum, chromium and vanadium, or of oxides of these metals, and carbon are mixed and reacted under a strong heat, has already been practiced on an industrial scale. In this industrial method, the said mixture as it is, or together with an inert gas, e.g. argon or helium, is heated by using a high-frequency heating furnace, an Acheson type direct electric resistance furnace, or the like, to allow a reducing reaction and a carburizing reaction to take place, whereby there are obtained powdered metal carbides according to the starting materials used, e.g. SiC, TiC, WC, B.sub.4 C, ZrC, HfC, NbC, Mo.sub.2 C, TaC, Cr.sub.3 C.sub.2, VC, (SiTi)C, (WTi)C, (MoW)C, (WTiTaNb)C.
The thus obtained powders of metal carbides have a characteristic such that the finer the powders, the higher the strength of moldings obtained by subsequent sintering and the higher the sintering rate. This inevitably requires that the mixture of metal element or metal oxide and carbon, as an intermediate material, be of uniform and fine particles. In this connection, according to the prior art, the mixture in question is produced usually by pulverizing and mixing a coarse-grained or agglomerated metal element or metal oxide and carbon mechanically simultaneously and batchwise by means of a ball mill, a hammer mill, or the like. In this method, however, not only the material charging and product carrying out operations are troublesome because of the batch process, but also problems associated with working environment such as the formation of dust and the generation of noise during the pulverizing and mixing operation are unavoidable. Moreover, the mechanical pulverization requires a long time for obtaining a finely divided powder, and this long-time pulverization inevitably results in an increased amount of impurities incorporated which is ascribable to wear of the pulverizing machine itself, which in turn requires an impurity removing step as an after step such as chemical washing or adsorption. Because of these problems, it is next to impossible for the mechanical method to afford a finely divided mixture of below one micron.
There has also been known a method in which fine powders which have separately been obtained in advance by some suitable means are mixed together by using a mixer, a kneader, or the like. Even according to this method, however, biasing in the contents of the resultant mixture is unavoidable due to the difference in particle size, orientating property and specific gravity peculiar to each powder. In an effort to remedy this drawback, there has further been proposed a method in which a fine powder is dispersed in water in the form of colloid by means of a wet vibration mill or the like and then spray-dried by using a spray drier or the like. However, even according to this method, biasing in the mixed contents is apt to occur, and there is a fundamental problem such that because silicon oxide powder, titanium oxide powder and carbon powder which are aggregates with each individual particle being incapable of separating easily remain as aggregates as they are, it is difficult for them to constitute a mixture consisting of individual particles. Further, also from economic aspects such as equipment and energy costs, such conventional method is not desirable because it goes through fine powder manufacturing, wet mixing and spray drying
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Horita Makoto
Isogaya Kazuyoshi
Kawamura Norimasa
Kuramitsu Noriaki
Maruyama Kensaku
Mitsui Toatsu Chemicals Inc.
Straub Gary P.
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