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Slurry-pressing consolidation of silicon nitride

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A baseline slurry-pressing method for a silicon nitride material is developed. The Si3N4 composition contained 5.8 wt percent SiO2 and 6.4 wt percent Y2O3. Slurry-pressing variables included volume percent solids, application of ultrasonic energy, and pH. Twenty vol percent slurry-pressed material was approximately 11 percent stronger than both 30 vol percent slurry-pressed and dry-pressed materials. The Student's t-test showed the difference to be significant at the 99 percent confidence level. Twenty volume percent (300 h) slurry-pressed test bars exhibited strengths as high as 980 MPa. Large, columnar beta-Si3N4 grains caused failure in the highest strength specimens. The improved strength correlated with better structural uniformity as determined by radiography, optical microscopy, and image analysis.

CERAMICSCONSOLIDATIONPRESSINGSILICON NITRIDESSLURRIESPH FACTORSILICON OXIDESULTRASONIC RADIATIONYTTRIUM

Sanders, William A.、Kiser, James D.、Freedman, Marc R.

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Glenn Research Center

NASATM101365

19

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