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AssigneeBritish Technology Group Limited
InventorsLydia Nikolaevna Rusanova, Alexander Gavrilovia Romashin, Lydia Ivanovna Gorchakova, Galina Ivanovna Kulikova, Michael Kirillovia Alexeev
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Boron nitride articles are made by heat treating turbostratic BN powder to reduce its oxygen content to 5-8% (mesographitic BN), washing this heat-treated powder, mixing it with 5-8% amorphous boron, shaping the mixture, explosively compacting the shape by a hydrodynamic method and reaction sintering the compacted shape, to form the article. The article is then buried in a powder mixture of BN and SiC and heat treated, to getter residual B.sub.2 O.sub.3. After this, the article is impregnated with low-viscosity oligomers (MW<1000) of methylsilanes selected to yield a high proportion of SiC on pyrolysis, and the article is heat-treated to fill the pores evenly throughout its thickness with SiC.
A method of making a boron nitride ceramic article from a mixture of mesographitic boron nitride powder and a reaction sintering agent other than elemental boron powder, comprising shaping the mixture into the form of the article, compacting the shaped mixture under pressure and reaction sintering the compacted mixture in a vacuum or inert or nitrogen atmosphere, wherein the mesographitic boron nitride contains from 5 to 10% by mass chemically bound oxygen, and the reaction sintering agent is at least stoichiometrically equivalent to the chemically bound oxygen and can react chemically with the available B, N and/or O under the sintering conditions to form only refractory compounds including a minor proportion of volatile products.
A method of making a boron nitride ceramic article from a mixture of mesographitic boron nitride powder and elemental boron powder, comprising shaping the mixture into the form of the article, compacting the shaped mixture under pressure and reaction sintering the compacted mixture in a vacuum or nitrogen atmosphere, wherein the mesographitic boron nitride contains from 5 to 10% by mass chemically bound oxygen, and the elemental boron is at least stoichiometrically equivalent to the chemically bound oxygen, further comprising the step of impregnating the resulting article with an organosilicon compound, which is itself liquid or which is in the form of a solution, the organosilicon compound having a molecular weight not exceeding 1000, and heat-treating the impregnated article at 600.degree.-1700.degree. C. in a vacuum or inert atmosphere.
A method of making a boron nitride ceramic article from a mixture of mesographitic boron nitride powder and elemental boron powder, comprising shaping the mixture into the form of the article, hydrodynamically compacting the shaped mixture by an explosive shock wave in a hydraulic fluid surrounding the shaped mixture, and reaction sintering the compacted mixture in a vacuum or nitrogen atmosphere, wherein the mesographitic boron nitride contains from 5 to 10% by mass chemically bound oxygen, and the elemental boron is at least stoichiometrically equivalent to the chemically bound oxygen.
Dependencies are inferred from the claim text.