Thermal expansion characteristics of quartzite particles up to 1600 °C

Using a LEITZ-II thermal microscope, thermal expansion characteristics of quartzite particles with different proportions of silicon dioxide (SiO2) were investigated at temperatures ranging from room temperature to 1600 °C. The experimental results showed that the thermal expansion of the quartzite particles with the temperature can be divided into three temperature regions, namely: the slow-expansion region, the temperature-independent region where the linear expansion coefficient tends to be zero and the fast-expansion region with a sharp wave crest. A particle with high proportion of SiO2 (high purity particle) has higher melting characteristic temperatures and higher starting temperature of the fast-expansion region. In addition, the microstructure of high purity quartzite particles heated to different terminal temperatures were also observed through a HITACHI scanning electron microscope (SEM). Lots of micro-cracks (∼10 μm wide on the sample surface and ∼1 μm wide inside the sample) can be formed at temperatures exceeding the starting temperature of the fast-expansion region. Calculating the residual deformations of the cooled particles which had been heated up to the different terminal temperatures indicated that these micro-cracks can greatly weaken the elasticity of the quartzite particles.