Powders for advanced structural ceramics

Si{sub 3}N{sub 4}, SiC, ZrO{sub 2}, and Al{sub 2}O{sub 3} compounds are useful in many advanced structural ceramics applications. Si{sub 3}N{sub 4} and SiC are the major materials of interest for high-temperature heat engine applications because of their excellent thermal shock resistance, high-temperature strength, and oxidation resistance. ZrO{sub 2} is employed for structural applications in the partially stabilized form (containing stabilizers such as Y{sub 2}O{sub 3}, CaO, or MgO) which makes use of a controlled martensitic phase transformation that results in high strength and toughness. Structural applications are usually limited to less than 800 {degrees}C, below the temperature region of the phase transformation. ZrO{sub 2}, because of its low thermal conductivity and reasonable match in thermal expansion coefficient to that of metals, is being considered as a thermal barrier coating in heat engines.