Refractory composite materials protected against oxidising at high temperature, precursors of the said materials, their preparation

A method of preparing composite materials comprising a highly refractory ceramic matrix reinforced by fibers that are sensitive to oxygen, said method comprising making said materials by a solid process from said fibers and a slip containing ceramic powder and at least one densification additive, and also comprising,

• depositing over the entire outside surface of said composite materials obtained by a solid process, at least one layer of a precursor of a borosilicate glass;
• optionally performing heat treatment in an inert atmosphere on said coated materials in order to convert said glass precursor into a borosilicate glass to obtain said materials coated with a layer of borosilicate glass;
• optionally applying heat treatment in an oxidizing atmosphere to said materials coated with the layer of borosilicate glass to obtain said materials coated with a complex layer containing at least one silicate corresponding to said densification additive, silica, and a vitreous boron-containing silicate phase;
• said layer protecting said materials from being oxidized, even at high temperature.