摘要
Willemite Zn_(2)SiO_(4)crystallizes in such a way that Zn and Si are tetrahedrally coordinated with O in an ionic–covalent manner to form ZnO_(4)and SiO_(4)tetrahedra as the building units.The tetrahedra are corner-sharing,of which one SiO_(4)tetrahedron connects eight ZnO_(4)tetrahedra,and one ZnO_(4)tetrahedron links four ZnO_(4)tetrahedra and four SiO_(4)tetrahedra.The unique crystallographic configuration gives rise to parallel tunnels with a diameter of 5.7Åalong the c-axis direction.The tunnel structure of Zn_(2)SiO_(4)definitely correlates with its interesting elastic and thermal properties.On the one hand,the elastic modulus,coefficient of thermal expansion(CTE),and thermal conductivity are low.Zn_(2)SiO_(4)has low Vickers hardness of 6.6 GPa at 10 N and low thermal conductivity of 2.34 W/(m·K)at 1073 K.On the other hand,the elastic modulus and CTE along the c-axis are significantly larger than those along the a-and b-axes,showing obvious elastic and thermal expansion anisotropy.Specifically,the Young’s modulus along the z direction(Ez=179 GPa)is almost twice those in the x and y directions(Ex=Ey=93 GPa).The high thermal expansion anisotropy is ascribed to the empty tunnels along the c-axis,which are capable of more accommodating the thermal expansion along the a-and b-axes.The striking properties of Zn_(2)SiO_(4)in elastic modulus,hardness,CTE,and thermal conductivity make it much useful in various fields of ceramics,such as low thermal expansion,thermal insulation,and machining tools.
基金
This work was supported by Shenyang National Laboratory for Materials Science,Institute of Metal Research,Chinese Academy of Sciences.
