Chemistry of inorganic compounds – Nitrogen or compound thereof – Binary compound
Patent
1991-10-17
1992-12-01
Bell, Mark L.
Chemistry of inorganic compounds
Nitrogen or compound thereof
Binary compound
423344, 501 96, C01B 21072
Patent
active
051679442
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for the production of an aluminum nitride based sintered product, in which the reaction heat of ultrafine aluminum powder with nitrogen gas is utilized, and thus the aluminum nitride-based sintered product can be produced at a relatively low heating temperature.
BACKGROUND OF THE INVENTION
An aluminum nitride sintered product has been conventionally produced by such a method wherein a mixture of aluminum nitride powder (having a size of 1 .mu.m or more) with a sintering auxiliary is molded to a desired shape, and the molded article is heated in a non-oxidizing gas, such as nitrogen or argon, of an atmospheric pressure to a high temperature of the order of 1600.degree. to 1850.degree. C. to effect sintering.
As a special method, in J. Ceram. Assoc. Japan, 73 (2) 1965, pages 34-38, Shigetomo MATSUO et al. disclose production of an AlN sintered article by heating a molded mixed powder of AlN and Al in an nitrogen atmosphere. According to MATSUO et al., AlN powder of an average size of 5.67 .mu.m is mixed with Al powder of an average size of 3.27 .mu.m, the proportion of the Al powder being 20% by weight or less; and the mixed powder is molded under pressure and placed in a heating furnace, where nitrogen gas is caused to flow at a flow rate of 0.5 liter/minute to maintain a pressure of one atmosphere and the furnace temperature is raised at a heating rate of 300.degree. C./hour to 1400.degree. C. to produce an AlN sintered article. The Al powder reacts with the nitrogen gas to form AlN, and eventually a uniform AlN sintered article is produced. It is said that in an example wherein the mixed powder contained 20% by weight of Al powder, a heating temperature of at least 700.degree. C. was necessary for all of the Al powder to react with the nitrogen gas. Examples wherein the mixed powder contained 15, 10, 5 and 0% by weight of Al powder, respectively, are also shown. Furthermore, effects of the sintering temperature (furnace temperature) on the density and flexual strength of the sintered product are graphically shown (FIGS. 1 and 2). It is said that the nitridation of Al powder slowly proceeds, irrespective of the tested mixing ratio of Al powder, when the sintering temperature is raised from about 500.degree. C. to about 700.degree. C., and this is substantiated by the results shown in FIGS. 1 and 2. In other words, it is not shown that the density or flexual strength of the sintered product shows any peak value at a certain sintering temperature.
PROBLEMS IN THE ART THE INVENTION AIMS TO SOLVE
When aluminum nitride powder is used as a raw material to be sintered, a molded powder of aluminum nitride should be externally heated to a temperature of about 1800.degree. C., or otherwise the molded powder is not sintered. This is because aluminum nitride, when heated, is sublimated and decomposed at a temperature of 2450.degree. C. without taking a liquid phase. Thus, the sintering force of aluminum nitride under atmospheric pressure is solely based on solid diffusion between particles, which requires an extremely prolonged period time or a very high temperature. On that account, the conventional method for producing aluminum nitride sinter requires a high temperature furnace and the method steps in themselves are complicated.
In a case wherein a mixed powder of Al powder and AlN powder is used as a raw material to be sintered, as proposed by MATSUO et al., the Al powder existing in clearances between particles of the AlN powder is transformed to AlN, and eventually AlN is sintered, and therefore, in order to effect satisfactory sintering, external heating to a high temperature is necessary even after the completion of the nitridation of the Al powder. While the high temperature needed in this case may be somewhat lower than that used in the above-mentioned conventional method, a high temperature furnace capable of heating to a temperature of at least 1000.degree. C. is required again.
An object of the invention is to provide an improved metho
REFERENCES:
patent: 4243621 (1981-01-01), Mori et al.
patent: 4627815 (1986-12-01), Aldinger et al.
Morita Yoshikazu
Ohsaki Katsuhisa
Uda Masahiro
Bell Mark L.
Gallo Chris
Nisshin Steel Co. Ltd.
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