Negative Thermal Expansion Properties Of Cu₂V₂O₇ And Research Of Al/Cu₂V₂O₇ Composite Material

Due to the nature of thermal expansion and contraction for most materials, As temperature increases, instruments and equipment may occur some deformations, reducing the sensitivity and affecting the reliability. The research of negative thermal expansion (NTE) materials and metal composite materials can not only maintain the high heat conductivity and high elastic modulus of metal, but also take advantage of the negative thermal properties and low density of the negative thermal expansion materials. In recent years, NTE materials researches have received widespread attention. Different kinds of negative thermal expansion materials have been found, but rarely have been practically applied. Our research consists of two sections, the first part is preparation and negative thermal expansion mechanism of Cu2V2O7 material while the second is the preparation and physical properties of Cu2V2O7 and Al composite materials. The detailed contents are presented as follows:In the first part, we introduce the definition of negative thermal expansion effect and further introduce the classification and advantages and disadvantages of different kinds of NTE materials. We review the NTE materials research status from home and abroad. And then, we give a overview of the current research status of metal matrix composites.In the second part, we present a general introduction of the experimental instruments and performance characterization methods, which are the basis for the research of NTE materials.In the third part, we prepare Cu2V2O7 sample using conventional solid-state reaction method. For the first time, we find the negative thermal expansion property of Cu2V2O7 sample. A lot of testing have been conducted to study its negative thermal expansion mechanism. It is found that the sample is relatively dense with homogenous particles of 4um grain size. Cu2V2O7 exhibits a obvious NTE property from room temperature (RT) to 600℃. Especially from RT to 330℃, the average linear NTE coefficient is calculated to be -7.86×10-6 ℃-1. We propose that the thermal property of Cu2V2O7 is related to its structure. For Cu2V2O7, he atomic arrangement contains two symmetrically independent Cu2+cations. The Cu(1) site is coordinated by six O atoms to form a distorted Cu(i)06 octahedron, whereas the Cu(2) site is coordinated by five O atoms arranged at the vertices of an elongate Cu(2)O5 square pyramid. Two symmetrically independent V5+ cations are tetrahedrally coordinated by four O atoms each. The O(5) atom bridges the V(1)O4 and V(2)O4 tetrahedra. The CuO6 octahedra and CuO5 square pyramids form two types of chains running parallel to the a axis. The chains are linked by V2O7 groups into a complex heteropolyhedral framework. The low-energy transverse vibration of the bridging oxygen of the Cu-V-0 bond and the coupling rotation between corner-shared CuO5 and VO4 are likely attributed to causing the NTE of Cu2V2O7. Furthermore, as temperature rising, some β-CU2V2O7 with positive thermal expansion appear in the sample as can be seen from the high temperature XRD pattern. It results in the break point of the thermal expansion curve while it does not change the negative thermal property for Cu2V2O7.In the last part, we conduct the research on Al and Cu2V2O7 composite material. We prepare the composite material using powder metallurgy method and started a systematic study on the synthesis method, phase and electrochemical performance of Cu2V2O7. It is found that there are only Al and Cu2V2O7 diffraction peaks without other impurity peaks. In other words, there is no chemical reaction between Al and Cu2V2O7. From the SEM images, we can see the microstructure of the composite materials. During the cooling stage, the molten Al integrates with particles thus forming Al-Cu2V2O7 condensed blocks. Because of its NTE characteristics, Cu2V2O7 can closely interact with Al when they condense together. The thermal expansion test reveals that the coefficient of thermal expansion (CTE) of the composite (11.9×10-6 ℃-1) is only half of Al (23.79×10-6℃-1) when the mass ratio of Al and Cu2V2O7 is 6:4. Besides, with the mass ratio change of Al and Cu2V2O7, the CTE of the composite material may increase from negative to positive.