High temperature alkali corrosion of ceramics in coal gas. Eighth quarterly progress report, June 1, 1993--September 1, 1993
Gaseous alkali corrosion kinetics of Si{sub 3}N{sub 4} were investigated from 950 to 1100{degrees}C in an atmosphere containing 0.98 vol % sodium nitrate vapors. Linear reaction rates from 950 to 1100{degrees}C indicate that the alkali reaction Of Si{sub 3}N{sub 4} is interface-controlled with an activation energy of 199 kJ/mol. Rate controlling step of overall reaction appears to be the oxidation of Si{sub 3}N{sub 4} to SiO{sub 2}.An alkali reaction mechanism, involving a complex dissolution-oxidation process, was proposed. The difference between oxidation of Si{sub 3}N{sub 4} in air and reaction of Si{sub 3}N{sub 4} in presence of alkali is dissolution process of SiO{sub 2} in sodium silicate liquid. Gaseous alkali corrosion kinetics of alumina were also investigated at 1100 and 1150{degrees}C. The reaction thickness is linearly related to the reaction time, suggesting an interface-controlled reaction mechanism. The reaction rate constants are 0.24 {mu}m/h and 0.45 {mu}m/h at 1100 and 1150{degrees}C. The alumina grains seemed to be preferentially attacked along certain crystallographic directions. Subsolidus phase relations in the Na{sub 2}O-Al{sub 2}O{sub 3}-TiO{sub 2} system were also studied. Phase analysis indicates that the Na{sub 2}O-Al{sub 2}TiO{sub 5} section is not a true binary system. A revised phase diagram was constructed.
- Research Organization:
- Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Center for Advanced Ceramic Materials
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG22-91PC91309
- OSTI ID:
- 10191749
- Report Number(s):
- DOE/PC/91309-T9; ON: DE94001966; BR: AA1525050
- Resource Relation:
- Other Information: PBD: 24 Aug 1993
- Country of Publication:
- United States
- Language:
- English
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