Study On Crystallization And Properties Of Glass-ceramics Binder At Low Temperature

In the development of binder for superhard abrasives,glass-ceramics with low sintering temperature is often used as a binder for superhard abrasives.It is studied and put into production widely due to its advantages of large number of crystals,small size,low temperature sintering,good mechanical properties,adjustable thermal expansion coefficient.The principle of phase separation and crystallization is usually involved in the preparation of glass-ceramics.Phase separation causes the original network of glass to break down into independent phases,nucleation always takes place preferentially at the phase interface and provides conditions for the formation of crystalline phase.In the research on the preparation of glass-ceramics by using the principle of phase separation and crystallization,the phase separation of a single glass system is usually carried out at higher heat treatment temperatures;Due to the sintering temperature of ceramic and glass is different,when the glass phase is mixed with the ceramic phase,the optimal sintering temperature of both can not be reached at the same time during sintering,so it is impossible to guarantee the high density and strength of sintered samples.In this paper,two kinds of glass materials with similar refractoriness were mixed for sintering to make low-temperature sintered glass-ceramics.The glass-ceramics were prepared by crystals formed at the phase interface in a mixed glass system of phase separation environment.The strength of the base glass was enhanced;The sintering temperature of the base glass was below 800℃,which ensured the mixing system has a lower sintering temperature.In this experiment,Al₂O₃-B₂O₃-Si O₂（A-B-S）and Li₂O-Al₂O₃-B₂O₃-Si O₂（L-A-B-S）series of A1,A2,A3 basic glass materials were prepared.The refractoriness of the three is kept below 800℃,and the base glass were not crystallized.The influence of the crystallinity of the base glass on the experiment need not be considered in the later analysis.Firstly,the crystallization properties of pure mixed glass system were studied.For A1&A2 systems（A1and A2 mixed systems）,the bending strength of the system reaches the maximum value of52.46MPa when the sintering temperature was 620℃,the holding time was 2h,and the mass ratio of A1 to A2 was 1:1.Compared with A1&A2,the A1+A3 system was heat treated at the sintering temperature of 650℃,its maximum flexural strength is 53MPa.There is a small difference in refractability（30℃）between A1 and A3.No crystal was detected in the sintered samples of A1&A2 and A1&A3 systems at corresponding sintering temperatures.In order to crystallize in mixed glass system,A1+A3 glass system was taken as the research object.ZrO₂ and P₂O₅,as crystal nucleating agents,were introduced into A1+A3glass system.The effect on crystallization properties of mixed glass systems was explored by adding different nucleating agent,different addition amount,compound addition amount and their proportion.In the A1+A3 mixed glass system with 2.5wt%ZrO₂,3wt%ZrO₂ and2wt%P₂O₅,few weak diffraction peaks was discovered in the XRD pattern,and the maximum bending strength is 58.71MPa and 56.22MPa,respectively.In the A1+A3 glass system with 4.5wt%ZrO₂+P₂O₅,and when the mass ratio of ZrO₂ to P₂O₅ was 2:1,the maximum flexural strength of the sample is 74.95 MPa;The number of crystals precipitated out of the sintered sample increased,and the microcrystal size increased from 50nm to80-100nm.However,the thermal expansion coefficient of the system were not significantly reduced with precipitation of a few microcrystals.The sintering samples were prepared by different molding methods and their strength was compared.