Abstract: This ceramic composition is produced from a mixture of yttrium oxide and heavy rare earth oxides having an atomic number of from 64-71 in selected proportions for the construction of crucibles and the lining of molds employed in making castings of reactive metals, such as titanium and alloys thereof. The elements utilized in the composition impart a minimum of contamination to the molten metal during the melting and casting phases and are produced from an ore with only the refinement steps necessary so as to secure maximum economy and yet insure the production of castings of the highest quality.

Abstract: A ceramic resistance gas igniter comprised of 10 to 60% by weight of silicon carbide and 40 to 90% by weight of silicon nitride, slicon oxynitride, or silicon aluminum oxynitride, and having a density preferably greater than 95% of the theoretical density of the composite. As a result of the combination of high density and composition, the igniters have moduli of rupture in excess of 80,000 p.s.i., a resistivity range of from 0.1 to 10.sup.4 ohm centimeters, and superior resistance to corrosive gases.