| abstract |
The invention relates to a process for the manufacture of substantially pore-free shaped articles of polycrystalline material such as aluminium oxide, titanium boride, silicon nitride or silicon carbide, in which pulverulent materials or preformed articles having pores open towards the surface, in a vacuum-tight sealed glass casing that has a viscosity of less than 10 6 Pas at the pressing temperature employed, are isostatically hot-pressed in a high-pressure autoclave using an inert gas as pressure-transfer medium. By being embedded in a flowable pile or by having a layer applied to them in the form of a suspension, the glass-encased powders or articles are brought into contact with a heat-resistant pulverulent material that, upon softening of the glass casing, penetrates into the surface of the glass of reacts with it, with the result that the glass casing is reinforced from the outside at the pressing temperature. As pulverulent materials, there may be used titanium boride, graphite, SiC or boron nitride, which do not react with the glass casing, or glass powder or silica, which react with the glass casing to form a glass melt of at least the same viscosity as, or of a higher viscosity than, the glass casing. |