Research On ZnZr₄(PO₄)₆ Powder And The Low Thermal Expansion Materials

Low thermal expansion character is a kind of important performances for ceramics. ZnZr4(PO4)6 low expansion ceramics with NZP structure were mainly studied in this subject matter. As a new kind of low expansion materials, the thermal expansion coefficient of ZnZr4(PO4)6 could been continuously setted by designning the constitution, so had a good using foreground.ZnZr4(PO4)6 powders were synthesized by coprecipitate method in this study, and the low expansion ceramic had been prepared by using ZnZr4(PO4)6 powder maden at the earlier stage as raw materials. ZnZr4(PO4)6 powder had been synthesized by using ZrOCl2·8H2O, (NH4)H2PO4, NH3·H2O and ZnS as raw materials. The low expansion ceramic was prepared by dry pressing confectioning and room temperature calcination in later. Some mesuring and testing techniques such as XRD, TG-DTA, SEM, IR, TEM had been used to analyze and characterize the composition and microstructure of the slurry and ZnZr4(PO4)6 powder. The relationship among the technological parameters and the quality of powder had been discussed. The SEM, thermal expansion and resist compression strength measurements had been used to analyze and characterize the influence of sintering schedule and powder technological conditions on mechanical and thermal performance of ZnZr4(PO4)6 ceramic.The affection on grain structure and pattern of ZnZr4(PO4)6 powder by charging sequence, pH values, solution concentration, dispersant agent, washing of precipitate and calcination temperatures had been studied. And the affection on the performance of ZnZr4(PO4)6 ceramic by factors such as sintering schedule, types of additives, addition of additives, addition methods and experiment conditions had been discussed. The relationship between the pH values, Zeta potential of slurry and average particle size had been emphasisly discussed. And the pyknosis mechanics of MgO, ZnO and SiO2 for the ceramics had been studied. The weak point that low mechanical strength of ZnZr4(PO4)6 ceramics had been overcome by compound additiving MgO and SiO2 during the sintering process.After analytical studying, the single-phase ZnZr4(PO4)6 powders with a narrow size distribution and high rate of purity and good crystallization fabric could be obtained by charging plus sequence, controlling the pH value at 9, dispersing with alcohol during synthesis and sintering the sediment at 900~950℃for 2 hours. The average particle size was about 2μm. The best performance of high mechanical strength and low thermal expansion character for ZnZr4(PO4)6 ceramic can be obtained by calcinate the coprecipitation at 1200℃for 2 hours. The resist compression strength was 165.4MPa, and the thermal expansion coefficient was 1.1×10-6/℃. And a high mechanical property and low thermal expansion character of ZnZr4(PO4)6 ceramic was obtained by compound additiving MgO(4wt%) and SiO2(2wt%) during the sintering process. The best synthesis performance: The resist compression strength was 180.1MPa, and the thermal expansion coefficient was 1.2×10-6/℃.