Kinetics of the Thermal Decomposition of Wangjiatan Siderite

The thermal decomposition processes of Wangjiatan siderite samples were studied in nitrogen by thermogravimetric（TG）analysis.The mechanism of thermal decomposition of the siderite obeyed an F n kinetic law and the n-order was between 1.16 and 1.29.The results from non-isothermal experiments show that the size of particles has an obvious effect on the logarithm of pre-exponential factor in kinetics parameter of the thermal decomposition of Wangjiatan siderite.A linear relationship is shown between the size of particles and the logarithm of pre-exponential factor.An F 1 kinetic model containing size factor describes the thermal decomposition of Wangjiatan siderite well.

Influences of Heat Treatments on Crystallization in SiO_2-Al_2O_3-MgO-K_2O-F Glass-ceramics

Five kinds of heating treatment processing were chosen according to the experiment result of differential scanning calorimeter to prepare SiO2-Al2O3-MgO-K2O-F glass ceramics samples.The effects of heat treatment processing on the crystallization of these samples were explored by X-ray diffraction and scanning electron microscopy techniques.The results indicate that phase separations can occur in the bulk regions of the glass sample when holding at 670 ℃ for 3 h.The phase separation can accelerate the precipitation of the crystallization phase： when the temperature directly rises to 950 ℃ after the phase separation,there are mainly interlocked plate-shapes mica phases;If holding at 860 ℃ for 3 h first after the phase separation,the star-shape cordierite phases form;Thereby,elevating temperature to 950 ℃ and holding for 1 h will bring plate-shapes mica phases growing at inter-phases of the star-shape cordierite and finally the homogeneously distributed mica- cordierite composites form.However,if heating at 950 ℃ directly without holding at 670 ℃,there is a small quantity of phase separation appearing at 670 ℃ and a little crystallization phases precipitating at last.