Preparation And Properties Of Ca_1-xSr_xZr₄?PO₄?₆-based Low Thermal Expansion Ceramics

Materials have the property of 'hot expand and cold shrink'.When the device is faced with a large temperature change,the thermal expansion imbalance caused by thermal expansion and contraction will lead to thermal stress,causing performance degradation,failure and shedding.Therefore,to improve the application of aerospace devices has become a hot research topic.NZP materials have become one of the hot spots of aerospace materials due to their low thermal expansion and excellent impact resistance.Low expansion ceramics refer to materials with thermal expansion coefficient less than 2×10^-6/?,including NZP ceramics,cordierite ceramics,aluminum titanate ceramics,etc.Ca_0.5Sr_0.5Zr₄?PO₄?₆ ceramics in NZP system have low thermal expansion coefficient,low anisotropy of thermal expansion and good thermal shock resistance,and it is expected to be used in aerospace,but have poor mechanical properties.Therefore,it is of great importance to research the Ca_0.5Sr_0.5Zr₄?PO₄?₆-based ceramics with both good mechanical properties and low thermal expansion properties.In this paper,the Ca_0.5Sr_0.5Zr₄?PO₄?₆-based powders were prepared by co-precipitation method,and then the Ca_0.5Sr_0.5Zr₄?PO₄?₆-based low expansion ceramics were prepared high temperature sintering.The comprehensive properties were optimized by different ion substitution and compound composition.The crystal structure,sintering property,mechanical property and thermal expansion property of the samples were analyzed,the relationship between thermal expansion and structure was discussed,and the effects of sintering temperature and different components on the structure and properties were studied.?1?The effects of Ti⁴⁺content on the crystal structure,mechanical and thermal expansion properties of Ca_0.5Sr_0.5Zr₄?PO₄?₆ ceramics were investigated.All samples exhibited the typical NZP structure.The Ti⁴⁺-substitution could significantly improve the mechanical property,and the flexural strength increased to 66.5MPa.With the increase of Ti⁴⁺content,the thermal expansion coefficient varied from 1.8 to 3.4×10^-6/?.It can be seen that the substitution of Ti⁴⁺for Zr⁴⁺has a significant effect on the sintering characteristics,mechanical and thermal expansion properties of Ca_0.5Sr_0.5Zr₄?PO₄?₆ ceramics.The effects of Sn⁴⁺content on the crystal structure,mechanical and thermal expansion properties of Ca_0.5Sr_0.5Zr₄?PO₄?₆ ceramics were discussed.XRD showed that all the components formed a single phase.Rietveld refinement was used to analyze the crystal structure,and the lattice parameters exhibited a satisfactory structural convergence of R-factors.Sn⁴⁺ content could effectively improve the sintering performance.The flexural strength and Vickers hardness can reach 60.2MPa and 3.05GPa,respectively.With the increase of Sn⁴⁺content,the thermal expansion varied from 1.72 to 2.78×10^-6/?.?2?The effects of Si⁴⁺content on the crystal structure,mechanical and thermal expansion properties of Ca_0.5Sr_0.5Zr₄?PO₄?₆ ceramics were discussed.The single-phase ceramics with typical NZP structure were obtained by controlling the appropriate composition and sintering temperature.The Si⁴⁺-substitution could reduce the mechanical property.However,the thermal expansion coefficient decreased from 1.8 to 0.8×10^-6/?.?3?Ca_0.5Sr_0.5Zr₄P₆O₂₄ ceramics added with different amount of ZrP₂O₇ addition were prepared and characterized,and the effects of ZrP₂O₇ on the crystal structure,sintering characteristics,mechanical and thermal expansion properties of Ca_0.5Sr_0.5Zr₄P₆O₂₄ ceramics were discussed.The ZrP₂O₇ addition could effectively improve the flexural strength and Vickers hardness.In addition,the thermal expansion coefficient was reduced to 1.3×10^-6/?.Considering the low thermal expansion and excellent mechanical property,Ca_0.5Sr_0.5Zr₄P₆O₂₄ ceramics added with ZrP₂O₇ can be a promising low thermal expansion material.