Abstract: In the process according to the invention, a gel is prepared by hydrolysis and polycondensation of precursor compounds which comprise at least silicon alcoholate and aluminum alcoholate and inorganic compounds of lithium and/or magnesium, the solvent is removed, and the gel obtained is subjected to a heat treatment resulting in dehydration and oxidation, then to compacting and ceramisization.The composition obtained is substantially in the form of solid ceramic solutions, such as .beta.-spodumene, cordierite and mullite.

Abstract: The matrix is formed by particles of ceramic material which are introduced into the empty spaces of a fibrous structure and are bonded to one another by bridges of ceramic material obtained by in situ pyrolysis of a liquid polymer.By means of this process, a composite material of low porosity, despite a high reduction in volume during pyrolysis, is obtained relatively rapidly.

Abstract: Low viscosity, crosslinkable polysilanes that are liquid at ambient temperatures and essentially free of volatiles, well adapted for conversion into silicon carbide ceramics at elevated temperatures, are prepared by (a) reacting at least one silane monomer of the formula (1):R.sup.1 R.sup.2 SiCl.sub.2 (1)in which R.sup.1 is a hydrogen atom or a hydrocarbon radical and R.sup.2 is a vinyl radical, with at least one organic or organosilicon monochlorinated comonomer, in the presence of molten sodium in an organic solvent and wherein the ratio r.sub.1 of the number of moles of the silane monomer of formula (1) to the number of moles of the monochlorinated comonomer ranges from 0.

Abstract: A method for the high temperature, high pressure impregnation of thick woven carbon substrates with pitches to form carbon impregnated carbon bodies. The use of pitch with high (about 30%) levels of free carbon as the impregnating pitch reduces the number of cycles to obtain a product of given density as compared to carbon free pitch. The impregnation is conducted in hydrogen permeable aneroid vessels.

Abstract: The present invention relates to a process and device for the accelerated densification of a porous carbonaceous substrate, of the type consisting in decomposing a hydrocarbon substance in the presence of said substrate under high pressure and at high temperature, decomposition being effected inside a closed reactor allowing the elimination of the hydrogen emitted during the reaction as it is produced, the walls of said reactor having the necessary suppleness for the inner volume thereof to be adapted at any instant, under the effect of the pressure applied, to the volume of the liquid phase which it contains, wherein the hydrocarbon substance to be decomposed is chosen from the group comprising pitches, acenaphthylene, phenanthrene or mixtures of these products. The invention also relates to a process for preparing said substance.

Abstract: The invention relates to ceramized composite materials comprising a substrate formed of weavable ceramic fibres with high thermomechanical properties and a matrix formed from a ceramic oxide selected from the group comprising silica, chromic oxide and magnesium oxide, the cohesion of the oxide particles being such that it permits, under stress, microfissurization which progresses to the level of the fibres.