Patent ID: 7118802

Claim:
A multi-layer ceramic composite material having a thermal protective effect, comprising: an oxidic carbon-free fiber-reinforced ceramic layer, comprising at least 30% by volume of high-strength oxide-ceramic full fibers, and an oxidic carbon-free matrix having characteristics at room temperature of a tensile strength >140 MPa, a heat conductivity <2 W/mK, a real part of a dielectric constant ε′<6, and a loss factor tan δ<0.002; and a thermal insulation layer comprising an oxidic foam having a density between about 0.2 and about 1.4 g/cm 3 , a heat conductivity <0.25 W/mK, a real part of a dielectric constant ε′ between 1.5 and 2.5, and a loss factor tan δ<0.01, wherein a process for forming said oxidic carbon-free matrix comprises: consolidating an aqueous colloidal suspension having a solids fraction from 40% by volume to 50% by volume, wherein said consolidation of the fibers and matrix takes place in a closed, non-porous mold at room temperature at a pressure from about 0.1 bar to about 1 bar, and wherein the zeta potential of solids in the suspension is reduced to a value of between +5 mV and −5 mV; drying the composite of the matrix and the fibers in a free-standing manner at a temperature between about 20 C and 95 C after removing said composite from the mold; and sintering the composite of the matrix and the fibers to a desired density in a free-standing manner in air.