The Technology And Characteristic Of Negative Thermal Expansion Material ZrW₂O₈,ZrV₂O₇ With Metal Cu,Al

ZrW₂O₈ and ZrV₂O₇ demonstrated the isotropic and a large negative thermal expansion coefficient over a wide range of temperatures, but they both existed certainly defects. The purpose of this research aimed to overcome the inadequacies of the two compounds, and displayed their respective advantages. In order to facilitate the application of the thermal expansion materials and expand its application areas, compound technology and thermal expansion characteristics of ZrW₂O₈/Cu,ZrV₂O₇/Al were further studied.ZrV₂O₇ and ZrW₂O₈ were compounded by two different methods: directly-calcined synthesis from oxides and calcined synthesis with the precursor. The results by XRD,SEM,EPS and thermal-expansion test indicated that the composite can be achieved by both methods. The ceramics of Zr(V,W)xOy was obtained from 650℃～700℃by calcined, and its structure kept the identical lattice structure with ZrV₂O₇. The ceramics kept NTE and belonged to one kind of doping W6+ in ZrV₂O₇. But the thermal expansion coefficient was remarkably dropped to -2.9×10-6/℃from 20℃to 120℃, and the thermal expansion coefficient already closed to the request of the ideal electronic packing materials. Moreover, the method of calcined synthesis with the precursor is advantageous, and more useful for engineering applications.ZrW₂O₈/Cu composites was obtained by exothermic reaction of Al,CuO and ZrW₂O₈. The results by XRD,SEM,EPS and thermal-expansion test indicated that the microstructure by this method was compacted and formed spatial grid structure of Cu. The thermal expansion of this material was performance zero inflation from 30℃to 60℃, and the coefficient was 4.2×10-6/℃from 60℃to 300℃. This material shows very excellent thermal expansion characteristics.ZrV₂O₇/Al was compounded by two different methods: one was pressureless sintering by the powder of ZrV₂O₇ and Al, and another was the precursor of ZrV₂O₇ coated Al powder. The result by XRD,SEM,EPS and thermal-expansion test indicated that the ZrV₂O₇/Al compositeby the precursor coated Al had the good contact surface between Al and ZrV2O7, and the purity of ZrV2O7 was high. The thermal expansion coefficient is 18.5×10-6/℃from 10℃to 120℃. And the thermal expansion coefficient is 4.04×10-6/℃from 120℃to 400℃. From 400℃to 500℃the thermal expansion coefficient is 7.3×10-6/℃. This material displayed normal thermal expansion, but compared Al remarkably dropped. Based the foundation, the gradient material of ZrV2O7/Al was achieved by the method of powder metallurgy. This material had the good microstructure and fine heat-resistant performance.