Solid-state reaction and sol-gel, processing techniques were used extensively to form chemically-modified mullite solid solutions in an effort to lower their thermal expansion coefficients. TiO₂, B₂O₃, CrPO₄, P2O₅, Ga₂O₃, Cr2O₃, and WO₃ and the half-breed SiO₂ compounds AlPas, BPO₄, GaPO₄, BAsO₄, AIAsO₄, GaAsO₄, and GeO₂ were chosen as the modifiers. The results indicate that, apart from TiO₂, none of the substitutions made in mullite significantly change the thermal expansion properties. The solubility of 3 wt% TiO₂ in mullite reduces the coefficient of thermal expansion by about 10%; That corresponds to a reduction in AAl₂O₃/SiO₂ molar ratio ( < 1.5) compared to stoichiometric mullite (3Al₂O₃·2SiO₂). The formation of TiO₂-modified mullite depends on processing condition and heat treatment. The possible mechanism of lowering the CTE of mullite by the addition of TiO₂ is discussed in terms of the bond strength. The axial expansion of a Ga2O₃-modified mullite was measured' up to 1200°C to show that the expansion is increased along the c-axis compared with that of the stoichiometric mullite. / Master of Science
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/43063 |
| Date | 10 June 2012 |
| Creators | Tu, Jie |
| Contributors | Materials Engineering, Brown, Jesse J. Jr., Swanson, Robert E., Ribbe, Paul H. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | vii, 53 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 18562781, LD5655.V855_1988.T84.pdf |
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