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  • 1
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    Improved consolidation of silicon carbide (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Alpha silicon carbide powder was consolidated by both dry and wet methods. Dry pressing in a double acting steel die yielded sintered test bars with an average flexural strength of 235.6 MPa with a critical flaw size of approximately 100 micro m. An aqueous slurry pressing technique produced sintered test bars with an average flexural strength of 440.8 MPa with a critical flaw size of approximately 25 micro m. Image analysis revealed a reduction in both pore area and pore size distribution in the slurry pressed sintered test bars. The improvements in the slurry pressed material properties are discussed in terms of reduced agglomeration and improved particle packing during consolidation.
    Keywords: NONMETALLIC MATERIALS
    Type: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 7; 884-892
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Particle-size reduction of Si3N4 powder with Si3N4 milling hardware (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The grinding of Si3N4 powder using reaction bonded Si3N4 attrition, vibratory, and ball mills with Si3N4 media was examined. The rate of particle size reduction and the change in the chemical composition of the powder were determined in order to compare the grinding efficiency and the increase in impurity content resulting from mill and media wear for each technique. Attrition and vibratory milling exhibited rates of specific surface area increase that were approximately eight times that observed in ball milling. Vibratory milling introduced the greatest impurity pickup.
    Keywords: NONMETALLIC MATERIALS
    Type: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 7; 817-827
    Format: text
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  • 3
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    Slurry-pressing consolidation of silicon nitride (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: 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.
    Keywords: NONMETALLIC MATERIALS
    Type: American Ceramic Society Bulletin (ISSN 0002-7812); 68; 1836-184
    Format: text
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  • 4
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    Parametric evaluation of ball milling of SiC in water (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A statistically designed experiment was conducted to determine optimum conditions for ball milling alpha-SiC in water. The influence of pH adjustment, volume percent solids loading, and mill rotational speed on grinding effectiveness was examined. An equation defining the effect of those milling variables on specific surface area was obtained. The volume percent solids loading of the slurry had the greatest influence on the grinding effectiveness in terms of increase in specific surface area. As grinding effectiveness improved, mill and media wear also increased. Contamination was minimized by use of sintered alpha-SiC milling hardware.
    Keywords: NONMETALLIC MATERIALS
    Type: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 6; 1135-114
    Format: text
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  • 5
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    Factors influencing the ball milling of Si3N4 in water (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A statistical study of the ball milling of Si3N4 powder in Si3N4 hardware was undertaken to understand how the resulting increase in specific surface area is related to solids loading and mill speed. An attempt was made to optimize milling conditions. The degree of communication was more dependent upon solids loading than mill speed. A practical grinding limit between 0.5 and 0.75 microns was achieved in 144 hr independent of solids loading. Ball mill wear and media wear were independent of both solids loading and mill speed.
    Keywords: NONMETALLIC MATERIALS
    Type: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 6; 1124-113
    Format: text
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  • 6
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    Slurry-pressing consolidation of silicon nitride (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: 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.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-TM-101365 , E-4352 , NAS 1.15:101365
    Format: application/pdf
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  • 7
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    Mechanical behaviour and failure phenomenon of an in situ toughened silicon nitride (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The Weibull modulus, fracture toughness and crack growth resistance of an in-situ toughened, silicon nitride material used to manufacture a turbine combustor were determined from room temperature to 1371 C. The material exhibited an elongated grain structure that resulted in improved fracture toughness, nonlinear crack growth resistance, and good elevated temperature strength. However, low temperature strength was limited by grains of excessive length (30 to 100 microns). These excessively long grains were surrounded by regions rich in sintering additives.
    Keywords: NONMETALLIC MATERIALS
    Type: Journal of Materials Science (ISSN 0022-2461); 27; 16 A; 4421-442
    Format: text
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  • 8
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    A sintering model for SiC(sub)w/Si3N4 composites (1988)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Presented is a model which suggests that it should be possible to pressureless sinter a SiC(sub w)/ Si3N4 composite to theoretical density. Prior failure to achieve complete densification by sintering is attributed to the use of compositions which result in a glass deficit. There is one basic premise for this model. The ratio of glass amount to surface area of nonglass constituents must be the same for both composite and sinterable monolithic Si3N4. This model suggests that whisker and grain sizes and whisker loading influence the glass amount necessary for successful sintering of composites. According to the model, a large glass amount will be necessary for successful sintering of these composites. However, grain boundary thicknesses in the composite will be less than those in the analogous monolithic materials. This suggests that good high temperature strength may still be attained. A recent report supports the predictions of the model.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-TM-101336 , E-4354 , NAS 1.15:101336 , Annual Meeting of the American Ceramic Society; May 01, 1988 - May 05, 1988; Cincinnati, OH; United States
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  • 9
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    Parametric evaluation of ball milling of SiC in water (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A statistically designed experiment was conducted to determine optimum conditions for ball milling alpha-SiC in water. The influence of pH adjustment, volume percent solids loading, and mill rotational speed on grinding effectiveness was examined. An equation defining the effect of those milling variables on specific surface area was obtained. The volume percent solids loading of the slurry had the greatest influence on the grinding effectiveness in terms of increase in specific surface area. As grinding effectiveness improved, mill and media wear also increased. Contamination was minimized by use of sintered alpha-SiC milling hardware.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-TM-86974 , E-2399 , NAS 1.15:86974 , Ann. Conf. on Composites and Advanced Ceramic Mater.; Jan 20, 1985 - Jan 23, 1985; Cocoa Beach, FL; United States
    Format: application/pdf
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  • 10
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    Particle size reduction of Si3N4 with Si3N4 milling hardware (1986)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The grinding of Si3N4 powder using reaction bonded Si3N4 attrition, vibratory, and ball mills with Si3N4 media was examined. The rate of particle size reduction and the change in the chemical composition of the powder were determined in order to compare the grinding efficiency and the increase in impurity content resulting from mill and media wear for each technique. Attrition and vibratory milling exhibited rates of specific surface area increase that were approximately eight times that observed in ball milling. Vibratory milling introduced the greatest impurity pickup.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-TM-86864-REV , E-2328-1 , NAS 1.15:86864-REV , Annual Conference on Composites and Advanced Ceramic Materials; Jan 19, 1986 - Jan 24, 1986; Cocoa Beach, FL; United States
    Format: application/pdf
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