Effect Of Heat Treatment Process On Crystallization And Property Of Augite-based Glass Ceramics

Using Baiyun Obo tailings as the main raw material,the augite phase glass ceramicswere prepared by melting method according to the glass phase diagram design of CaO-MgO-Al₂O₃-SiO₂?CMAS?system.XRD,SEM,DSC and physical and chemical properties were used in the experiment to analyze the phase structure and physical and chemicalproperties of glass ceramics.Firstly,the variation of the crystallization curve of augite phase glass ceramics prepared by glass water quenching of Baiyun Obo tailings was measured by differential thermal analysis.The crystallization activation energy of the glass ceramics was calculated to be 221.080 KJ/mol.Secondly,according to the thermodynamic characteristics of glass ceramics,the heat treatment process parameters were designed by using different crystallization heating rates and nucleating crystallization holding time to change the free energy of glass crystallization.The effects of heat treatment process parameters and magnetic field assisted heating on the crystallization behavior of augite phase glass ceramics were investigated by adjusting the regulation of glass crystallization temperature,crystallization holding time and magnetic field assisting effect.The relationship between the change of crystallization energy and the crystallization behavior of glass was analyzed,and the influence of heat treatment process parameters on the crystallization behavior of augite glass ceramics was revealed.The results show that the one-step heat treatment sample,i.e.,the 720°C crystallized sample is spherical shape.There is no obvious coarsening phenomenon in the grain size of the augite phase,but agglomeration occurs in the crystal.The crystal morphology of the augite phase in the sample crystallized at 820°C changes from the island-like structure to the irregular spindle shape with the decrease of crystallization heating rate,and the grain size of the crystallization sample increases gradually with the increase of holding time at the same crystallization temperature.The two-step heat treatment sample was used to nucleate the 820°C-crystallized sample at 720°C.With the heating rate and holding time of the crystallization heat treatment,the evolution law of theaugite phase was as follows:island—connected island—spindle-granular—wide Shape—fine grain.The physical and chemical properties of glass ceramics are affected by different crystal morphologies.The overall physical and chemical properties of glass ceramics are enhanced with the increase of heat treatment crystallization heat preservation.The sample was heat-treated at different crystallization temperatures by a two-step method.The crystal morphology of the augite phase was granular,and the crystal growth was promoted with the increase of the crystallization temperature,and the grain size was coarsened.The magnetic field-assisted heat treatment of the samples has no significant effect on the crystal morphology of the augite phase.The crystal is mainly granular,but it promotes the growth of the second phase magneto-iron crystal along the{111}crystal plane,which regulates the crystallization orientation of magnetite.It is proved by the research that the crystal morphology of the augite phase can be changed by the change of different heat treatment systems and the effect of magnetic field assisted heat treatment.The prolongation of crystallization holding time can promote the crystal development and improve the crystallization degree of the main crystal phase,so that the flexural strength and fracture toughness of glass ceramics can be gradually enhanced.As a result,the flexural strength is up to 240 N/mm²,and the fracture toughness is up to 9.6 MPa.m^1/2.