Thermal mismatch between different components of a system could cause of problems like residual stress induced cracking, thermal fatigue or even optical misalignment in certain high technology applications. Use of materials with customized thermal expansion coefficient is a counter-measure to resolve such problems. Zirconium tungstate (ZrW2O8) with negative thermal expansion coefficient is capable of being used in synthesis of composites with tailored coefficient of thermal expansion (CTE). In this work, the sol-gel method which had been already set up in our group was characterized and the sources of the factors imposing impurities in the product were distinguished in all the steps of precursor preparation and heat treatment. In the second part of study, zirconium tungstate particles synthesized by the sol-gel method were utilized as core in synthesis of ZrW2O8&ndash / ZrO2 core&ndash / shell composite particles. Shell layer was composed of ZrO2 nanocrystallites and precipitated from an aqueous solution by urea hydrolysis. Volume of the shell was effectively controlled by concentration of the initial zirconium ion in the solutions. The rate of precipitation was a function of the ratio of initial urea concentration to zirconium ion. It is hypothesized that isolation of the ZrW2O8 within a layer of ZrO2, will be a key element in solving problems associated with reactivity of ZrW2O8 towards other components in sintering of ceramic&ndash / ceramic composites with tuned or zero thermal expansion coefficient.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12615316/index.pdf |
| Date | 01 January 2013 |
| Creators | Khazeni, Nasser |
| Contributors | Gunduz, Gungor |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for METU campus |
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