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Vaporization Thermodynamics of the Aluminum-Silicon Carbides Al4SiC4 and Al8SiC7.


PB89118079

Publication Date 1988
Personal Author Johnson, E. A.; Oden, L. L.; Adams, A.
Page Count 18
Abstract The vaporization thermodynamics of the aluminum-silicon carbides Al4SiC4 and Al8SiC7 were studied by the Bureau of Mines over the temperature range of approximately 1,500 to 1,700 K. Vapor pressures were measured by a Knudsen effusion-mass spectrometry technique in which powdered samples were effused from graphite crucibles through small orifices. For each compound, a total of six orifice diameters was tested to verify equilibrium within the cell. Aluminum, mass number 27, was the only vapor species detected over the range 4 to 200 amu. Experimental results are based on the following equations for incongruent decomposition: Al4SiC4(cr)=4Al(g) + SiC(alpha,hex) + 3C(gr); Al8Sic7(cr) = 8Al(g) + SiC(alpha,hex) + 6C(gr). The observed vapor pressure-temperature relationships determined with a cell orifice area of 2.0 X 10(-3) cm(2) for Al4SiC4 and 1.81 X 10(-3) cm(2) for Al8SiC7 are the following: Log P = (-18,682/T) + 12.476, for Al4SiC4 (1,550 to 1,643 K) and Log P = (-19,308/T) + 12.421, for Al8SiC7 (1,526 to 1,784 K), with P in pascals and T in kelvins. Third law analysis of the data provided the following heats of formation at 298.15K: Al4SiC4 -50.0 kcal/mol and Al8SiC7 -92.1 kcal/mol.
Keywords
  • Vaporizing
  • Aluminum silicon alloys
  • Silicon carbides
  • Thermodynamics
  • Enthalpy
  • High temperature tests
  • Mass spectrometry
  • Knudsen flow
  • Vapor pressure
  • Graphs(Charts)
Source Agency
  • Bureau of Mines
NTIS Subject Category
  • 99F - Physical & Theoretical Chemistry
  • 71N - Nonferrous Metals & Alloys
  • 97 - Energy
Corporate Authors Bureau of Mines, Albany, OR. Albany Research Center.
Document Type Technical Report
Title Note Open file rept.,
NTIS Issue Number 198903
Vaporization Thermodynamics of the Aluminum-Silicon Carbides Al4SiC4 and Al8SiC7.
Vaporization Thermodynamics of the Aluminum-Silicon Carbides Al4SiC4 and Al8SiC7.
PB89118079

  • Vaporizing
  • Aluminum silicon alloys
  • Silicon carbides
  • Thermodynamics
  • Enthalpy
  • High temperature tests
  • Mass spectrometry
  • Knudsen flow
  • Vapor pressure
  • Graphs(Charts)
  • Bureau of Mines
  • 99F - Physical & Theoretical Chemistry
  • 71N - Nonferrous Metals & Alloys
  • 97 - Energy
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