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Silicon nitride-cordierite ceramic article, and process of manufacture thereof
| Details |
Inventors: Pasto, Arvid E.;
Assignee: GTE Laboratories Incorporated (Waltham, MA)
Primary Examiner:
Assistant Examiner:
Attorney, Agent or Firm:
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. |
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DETAILED DESCRIPTION OF THE INVENTION The new and improved ceramic compositions of the present invention comprise silicon nitride and cordierite.
Cordierite is represented by the formula 2MgO.
2Al.
sub.
2 O.
sub.
3.
5SiO.
sub.
2 and silicon nitride by Si.
sub.
3 N.
sub.
4.
The silicon nitride imparts a high mechanical strength and the cordierite lowers the thermal conductivity making the composition especially useful for internal parts of an adiabatic diesel engine.
The new compositions lend themselves to consolidation by hot-pressing, cold pressing, or other cold forming processes such as injection molding or slip casting, and sintering to form a densified ceramic article having a density greater than 95% of theoretical.
The densified ceramic article can have a modulus of rupture greater than 110 KSI (kilopound per square inch) at temperatures about 900.
degree.
C.
and greater than 35 KSI at temperatures greater than 1000.
degree.
C.
depending on its composition (see Table VI).
Some of the compositions contain sufficient levels of a continuous glassy or amorphous cordierite phase so that an article can be formed by other techniques, e.
g.
glass-forming methods.
The continuous glassy cordierite phase may be crystallized by the addition of a nucleating agent such as ZrO.
sub.
2 and a subsequent reheating step in the processing steps.
Crystallizing the continuous cordierite phase will increase the mechanical strength of the resulting densified ceramic article.
The first phase of silicon nitride is a dispersed phase within the continuous cordierite phase.
EXAMPLES Articles having various compositions, indicated by Mix #1 through 5 in Table I, were prepared by blending together the powders of the various components, such as silicon nitride, aluminum sequioxide, silicon dioxide, magnesium oxide and with or without a nucleating agent such as zirconium dioxide, titanium dioxide, in a plastic ball mill using milling media such as silicon nitride, cordierite, or zirconium dioxide to avoid contamination.
The powders were pressed at pressures of about 5,000 psig (pounds per square inch gauge) to about 20,000 psig, preferably from about 10,000 psig to about 20,000 psig in a steel die into pellets and sintered in a flowing inert atmosphere such as N
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Manufacturing Materials 
