Study On The Preparation Of NZP Family Phosphate Ceramics By Solid-phase Method And Their Thermal Expansion Properties

Phosphate ceramic with low thermal expansion performance belonging to NZP family shows important application value as thermal-shock resistance structural ceramic.In this paper,KZr₂?PO₄?₃?KZP,alkali metal series?and CaZr₄?PO₄?₆ and SrZr₄?PO₄?₆?CZP and SZP,alkali earth metal series?prepared by solid-state method were taken as examples,the suitable conditions for preparing NZP family ceramic powders by solid phase method were studied emphatically.The effects of source of reactants,ball milling time,hydrothermal crystallization conditions and calcined-sintered crystallization conditions on the crystalline state of the powders were studied,and the suitable conditions for solid state preparation of NZP ceramic powders were obtained.KZP and CZP and SZP powders were formed by dry pressing and sintered into ceramics at high temperature.The effects of the amount of sintering aids,sintering temperature and sintering time on the densification process were studied,and the sintering conditions of NZP ceramics were optimized.Based on the optimized solid-phase preparation conditions,NZP bin ary solid solution ceramic materials K_2?1-x?Sr_x Zr₄?PO₄?₆?KSZP,0?x?1?and Ca_1-xSr_x Zr₄?PO₄?₆?CSZP,0?x?1?were prepared by solid-phase method.The average thermal expansion coefficients of ceramics with different x values were measured at room temperature to 1000?.The relationship between the chemical composition of ceramics and thermal expansion coefficients was discussed.Zero expansion binary solid solution ceramics with good thermal shock resistance were obtained:?1?Using KH₂PO₄ and ZrOCl₂·8H₂O as reactant sources,the well-crystallized KZr₂?PO₄?₃ can been synthesized by mechanochemical activation for 10h conbined with hydrothermal crystallization method.The hydrothermal system is acidic,and to maintain the addition quantity of mineralizer F^-is n?F^-?/n(Zr⁴⁺)=1,the single-phase KZr₂?PO₄?₃ crystals can be obtained when hydrothermally crystallized at 140?for48h.CZP powder could not be prepared under the same conditions,it is difficult to convert the amorphous precursor obtained by mechanochemical activation conbined with calcination crystallization method into the crystalline CZP.?2?Using ZrO₂,?NH₄?H₂?PO₄?₃ and metal carbonate as reactant sources,then mill these reactants for 10 hours getting precursor,calcining the precursor at 900?can get ceramic powder.The crystalline KZP,CZP and SZP ceramics can be prepared by sintering the powders at 1300?for 2 hours.?3?The suitable sintering conditions for NZP ceramics a re adding 3wt%MgO or ZnO and sintering for 2h at 1300 C.When MgO is used as sintering aids,the densities of KZP,CZP and SZP ceramics are 2.44g/cm³,2.38g/cm³ and 2.78g/cm³,respectively.When ZnO is used as sintering aids,the densities of KZP,CZP and SZP ceramics are2.39g/cm³,2.35g/cm³ and 2.50g/cm³,respectively.?4?The thermal expansion coefficients of NZP family single-phase ceramics KZP and CZP prepared by solid-state method are negative at 25?¹000?,while SZP ceramics are positive at the same temperature range?5?The binary solid solution ceramics K_2?1-x?Sr_x Zr₄?PO₄?₆?KSZP,0?x?1?and Ca_1-x-x Sr_x Zr₄?PO₄?₆?CSZP,0?x?1?were prepared by using two single-phase NZP compounds KZP and SZP and CZP and SZP with opposite thermal expansion anisotropy.With the change of x value from 0 to 1,the thermal expansion coefficient of the binary solid solution ceramics KSZP and CSZP can be changed from negative to positive.For KSZP series,when x=0.25,it is composed of zero expansion,and the average thermal expansion coefficient is-0.41×10^-6/K at 25?¹000?.For CSZP series ceramics,when x=0.5,it is composed of zero expansion,and the average thermal expansion coefficient is 0.91×10^-6/K at 25?⁷00?.