Synthesis, sintering and thermal expansion of porous low expansion ceramics

In this paper we report on the preparation and characterization of porous ceramic substrates in the group of NaZr2(PO4)3, CaZr4(PO4)6, SrZr4(PO4)6 and BaZr4(PO4)6 with low thermal expansion coefficients. The starting powders were obtained by a sol–gel process and attrition milling both before and after calcination. The resulting sintered bodies exhibited high porosity also after further thermal treatments at high temperature. On the other hand their thermal expansion coefficient (CTE) is low over the range 25–1000 °C. In particular the blend between NaZr2(PO4)3 and SrZr4(PO4)6 has a CTE close to zero in the whole temperature range. According to these properties the above mentioned materials seem to be potential candidates as ceramic substrates for catalytic applications in combustion reactions since they maintain a high level of micrometric porosity when operating at temperatures exceeding 1000 °C.