Ceramic materials with low thermal conductivity and low coeffici

Details Ceramic materials with low thermal conductivity and low coeffici Ceramic materials with low thermal conductivity and low coeffici

1990-06-06

1992-04-07

Dixon, Jr., William R.

Compositions: ceramic

Ceramic compositions

Refractory

501102, 501111, 264 66, C04B 3548

Patent

active

051028360

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 present invention are also formed by combination with a polymeric powder and a binding agent, and sintering at high temperatures. The porosity of the resulting macrostructures can be adjusted by varying the particle size of the polymeric powder used.

REFERENCES:
patent: 4247249 (1981-01-01), Siemers
patent: 4751206 (1988-06-01), Yamai et al.
patent: 4801566 (1989-01-01), Limaye et al.
patent: 4883781 (1989-11-01), Watanabe et al.
patent: 4888312 (1989-12-01), Watanabe et al.
patent: 4925816 (1990-05-01), Watanabe et al.
Limaye, S. Y., et al., "Synthesis and Thermal Expansion of MZr.sub.4 P.sub.6 O.sub.24 (M=Mg, Ca, Sr, Ba)", J. A. Ceram. Soc., 70 [10] C-232-C-236, (1987).
Kazokos-Kijowski et al., "Synthesis, Crystal Data and Thermal Stability of Magnesium Zirconium Phosphate [MgZr.sub.4 P.sub.6 O.sub.24 ]", Mat. Res. Bull., vol. 23, pp. 1177-1184, (1988).
Komarneni et al., "Hydrothermal Preparation of the Low-Expansion NZP Family of Materials", Int. J. High Technology Ceramics, 4, pp. 31-39, (1988).
Agrawal et al., "Synthesis and Sinterning of Ca.sub.0.5 Zr.sub.2 P.sub.3 O.sub.12 A Low Thermal Expansion Material", Mat. Res. Bull., vol. 20, No. 2, pp. 99-106, (1985).
Lange et al., "Open-Cell, Low-Density Ceramics Fabricated from Reticulated Polymer Substrates", Advanced Ceramic Materials, vol. 2, No. 4, pp. 827-831, (1987).

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