研究目的
To measure elastic moduli and hardness of polycrystalline SiO2 coesite and compare its mechanical properties with other silica materials.
研究成果
Coesite is as hard as other four-fold coordinated silica materials such as quartz and densified silica glasses. The hardness values of the four-fold coordinated silica materials are about one-third of those of six-fold coordinated silica materials, which are the hardest known oxides.
研究不足
The study does not explore the crystallographic orientation dependence of hardness in coesite, and the effect of microstructure (e.g., grain size) on hardness is not fully investigated.
1：Experimental Design and Method Selection:
Fabrication of translucent polycrystalline bulk coesite at 8 GPa and 1600°C using a Kawai-type multi-anvil apparatus. Measurement of elastic moduli and hardness.
2：Sample Selection and Data Sources:
High-purity synthetic fused silica with OH content less than 1 ppm was used as the starting material.
3：List of Experimental Equipment and Materials:
Kawai-type multi-anvil apparatus, tungsten carbide cubes, Cr-doped MgO octahedron, benchtop diffractometer with Cu-Kα radiation, ultrasonic pulse-echo method setup, microhardness indenter.
4：Experimental Procedures and Operational Workflow:
High-pressure and -temperature treatment, XRD measurements, ultrasonic wave velocities measurement, Vickers and Knoop hardness measurements.
5：Data Analysis Methods:
Calculation of bulk and shear moduli from sound velocity measurements, calculation of Vickers and Knoop hardness values.
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