Silicon nitride-cordierite ceramic article, and process of manufacture thereof
AssigneeGTE Laboratories Incorporated
InventorArvid E. Pasto
Life of this patent
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Abstract
A silicon nitride-cordierite article, and process for fabricating is described. The silicon nitride imparts a high mechanical strength, and the cordierite contributes to a lower thermal conductivity making the composition especially useful for internal parts of a diesel engine. The mechanical strength can be increased by crystallizing the continuous cordierite glassy phase of the article. Crystallization of the continuous cordierite glassy phase is accomplished by the addition of a nucleating agent such as zirconium dioxide in the formulation and a subsequent reheating step after densification.
Claims19
A ceramic article consisting essentially of a first phase of silicon nitride, a second continuous phase of cordierite, and a nucleating agent, said ceramic article having a density greater than 95 percent of theoretical density, said second continuous phase of cordierite being essentially crystalline.
A ceramic article having a composition comprising of silicon nitride, and cordierite, said composition having an approximate formula (Si.sub.3 N.sub.4).sub.(1-x) (2MgO.2Al.sub.2 O.sub.3.5SiO.sub.2).sub.x wherein x is from about 0.05 to about 0.75, said ceramic article having a density greater than 95 percent of theoretical density.
A process for fabricating a densified ceramic article comprising
- blending silicon nitride, magnesium oxide, silicon dioxide, aluminum sesquioxide, and a nucleating agent to form a powder mixture;
- pressing said powder mixture to form a ceramic article;
- sintering said ceramic article at an effective temperature in an inert atmosphere to form a densified ceramic article consisting essentially of a first phase of silicon nitride and a second continuous phase of cordierite and a nucleating agent;
- and
- reheating said densified ceramic article at an effective temperature for an effective time to crystallize said second continuous phase of cordierite.
A process for fabricating a molded densified ceramic article comprising
- blending silicon nitride, magnesium oxide, silicon dioxide, aluminum sesquioxide and a nucleating agent to form a powder mixture;
- densifying said powder mixture to form a densified ceramic article having a crystalline silicon nitride first phase, a continuous glassy cordierite second phase and a nucleating agent;
- heating said densified ceramic article at a temperature sufficient to form a plastic densified ceramic article;
- molding said plastic densified ceramic article to form a molded densified ceramic article;
- crystallizing said continuous glassy cordierite second phase of said molded densified ceramic article to form a rigid, molded densified ceramic article.
Dependencies are inferred from the claim text.