Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Patent
1994-12-08
1996-04-16
Beck, Shrive
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
428403, 428405, 427212, 427215, 4273977, B32B 516, B05D 700
Patent
active
055081100
DESCRIPTION:
BRIEF SUMMARY
RELATED APPLICATIONS
This application is a 371 of PCT/US93/00978.
TECHNICAL FIELD
This invention relates to a method for treating aluminum nitride-containing powder to form a protective layer on its surface and the treated powder produced thereby.
BACKGROUND OF THE INVENTION
Aluminum nitride (AlN) powder is an excellent filler material for thermally-conductive polymer composites used as heat sink materials in the electronics industry. However, using virgin aluminum nitride powder in polymer composites is not without its problems. Polymer composites exhibit some water permeability, and, because aluminum nitride is sensitive to hydrolysis, some protection of the aluminum nitride powder from hydrolysis is desired. Additionally, when virgin aluminum nitride powder is stored, air-borne moisture attacks the aluminum nitride powder causing the powder to experience an increase in oxygen content and a concomitant weight gain.
It is, therefore, desirable to provide a moisture-resistant aluminum nitride-containing powder and an easy method for its manufacture.
SUMMARY OF THE INVENTION
A method for making a moisture-resistant aluminum nitride-containing powder is disclosed which comprises powder having aluminum nitride on at least a portion of its surface, the silicate having substituents thereon selected from the group consisting of alkyl and alkoxyalkyl radicals, and temperature of from about 350.degree. to about 1000.degree. C. for a period of time sufficient to cause the silicate to react with the surface aluminum nitride thereby forming treated aluminum nitride-containing powder having a layer of Si--Al--O--N bonded to the surface aluminum nitride.
In another embodiment of the invention, a method for making a moisture-resistant aluminum nitride powder is disclosed which comprises: from 1 to 4 carbon atoms, inclusive, to form a dispersion, and 4 carbon atoms, inclusive, the silicate having substituents thereon selected from the group consisting of alkyl and alkoxyalkyl radicals, the silicate being employed in an amount of from 1 to 150 weight percent based on the weight of the aluminum nitride powder, the first and second alkyl alcohols being employed in an amount of from 50 to 300 volume percent based on the volume of the aluminum nitride powder, based on the weight of the silicate, and acid, formic acid, and propionic acid or an inorganic acid selected from hydrochloric acid and sulfuric acid or a base selected fro sodium hydroxide, potassium hydroxide and ammonium hydroxide, the hydrolysis catalyst being employed in an amount of from 10 to 75 weight percent based on the weight of the water, and the hydrolysis catalyst forming a dispersion-solution, components in the dispersion-solution for at least 5 minutes, form coated aluminum nitride powder, and from 350.degree. to 1000.degree. C. for a period of time sufficient to cause the silicate to react with the aluminum nitride powder thereby forming a layer of Si--Al--O--N bonded to the aluminum nitride powder.
The aluminum nitride-containing powder produced has a layer of Si--Al--O--N reaction-bonded to at least a portion of its surface.
DETAILED DESCRIPTION OF THE INVENTION
The aluminum nitride-containing powder treated in this invention may be (a) a composite powder containing aluminum nitride, at least some of which is at the surface of the powder, or (b) a powder formed substantially of aluminum nitride. With either type of powder, the surface aluminum nitride may or may not have a "skin" of Al--O--N thereon. Although there is no minimum level of surface aluminum nitride for the aluminum nitride-containing powder used in this invention, the level of aluminum nitride in the composite powder is typically at least about 10 weight percent of the composite powder. Examples of other materials which could be combined with aluminum nitride to form composite powders include ceramics, such as silicon carbide, boron nitride, and silicon nitride, or metals, such as titanium, aluminum, and silicon. The aluminum nitride-containing powder which may be used in thi
REFERENCES:
patent: 4572844 (1986-02-01), Inoue et al.
patent: 5234712 (1993-08-01), Howard
Beck Shrive
Maiorana David M.
The Dow Chemical Company
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