The melting characteristics and thermal expanson behavior of quartzite particles during heated-up were studied by using a thermal microscope (LEIAZ-Ⅱ)made in Germany.The results showed that the linear expansion rate of high purity quartzite had three different regions at different temperatures

namely

slow-expansion region(room temperature—870℃)

halted expansion region (1000—1350℃)in which the linear expansion rate tended to be zero

and fast-expansion region (1400—1550℃) with a sharp wave crest

respectively.These regions were corresponding to the isomer conversion of SiO2.The comparison between two samples with different purities showed that the purity of quartzite particle had a remarkably influence on its melting characteristics.A particle with higher purity tended to have a higher characteristic temperature of melting characteristics.Furthermore

the surface microstructure of the high purity quartzite particles heated at different terminal temperatures was also observed by using a scanning electron microscope (HITACHI) S2150.Numerous micro-cracks (about ten microns) would be formed on the surface of the sample when the terminal temperature reached the fast expansion region

and the structure inner the sample was very loosen with numerous of minor-cracks(about one micron in width).These minor-cracks lead to the lose of elasticity and worsened mechanical properties of samples.