Ceramic materials with low thermal conductivity and low coefficients of thermal expansion
US5102836A · kind A · utility
Assignees
Inventors
Key dates
| Filing date | Jun 6, 1990 |
| Grant date | Apr 7, 1992 |
| Priority date | — |
| Expiry date | Jun 6, 2010 |
Classification
- Technology area (CPC C)Chemistry; Metallurgy
- CPC primaryC04B35/447
- WIPO fieldMaterials, metallurgy
- WIPO sectorChemistry
Abstract
Compositions having the general formula (Ca.sub.x Mg.sub.1-x)Zr.sub.4 (PO.sub.4).sub.6 where x is between 0.5 and 0.99 are produced by solid state and sol-gel processes. In a preferred embodiment, when x is between 0.5 and 0.8, the MgCZP materials have near-zero coefficients of thermal expansion. The MgCZPs of the present invention also show unusually low thermal conductivities, and are stable at high temperatures. Macrostructures formed from MgCZP are useful in a wide variety of high-temperature applications. In a preferred process, calcium, magnesium, and zirconium nitrate solutions have their pH adjusted to between 7 and 9 either before or after the addition of ammonium dihydrogen phosphate. After dehydration to a gel, and calcination at temperatures in excess of 850.degree. C. for approximately 16 hours, single phase crystalline MgCZP powders with particle sizes ranging from approximately 20 nm to 50 nm result. The MgCZP powders are then sintered at temperatures ranging from 1200.degree. C. to 1350.degree. C. to form solid macrostructures with near-zero bulk coefficients of thermal expansion and low thermal conductivities. Porous macrostructures of the MgCZP powders of the pres…
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