Preparation And Properties Of MgO-Al₂O₃-SiO₂-ZnO Glass-ceranic

The glass-ceramics containing spinel-type nanocrystal.,possess excellent mechanical properties,optic properties and chemical stability,are part of the magnesium-aluminium-silicon system.The spinel glass-ceramics are mainly used in safety protection,which have potential application in broadband optical amplifiers,tunable lasers and the protective glass of fingerprint identification sensors and camera chip or lenses.So little research on mechanics,physics and chemical property was reported that it is meaningful to improve the properties of glass-ceramics.In this paper,the relationship among glass composition,crystalline phase,microstructure and Vickers Hardness of MgO-Al₂O₃-SiO₂-ZnO（MASZ）system glass-ceramics were investigated by differential scanning calorimetry（DSC）,X-ray diffraction（XRD）,Scanning Electron Microscope（SEM）,Vickers hardness tester and chemical stability etc.Then,the grain sizes of glass-ceramics were changed by heat treatment.Further research was conducted to determine the relationship between the Vickers hardness and different grain sizes.The results show as follows,TiO₂+ZrO₂ was used as the complex nucleating agent.With the mass ratios of ZnO/MgO increased,the crystal phase was changed from quartz phase and spinel phase to single spinel phase.The grain size was reduced form 10～360nm to 10-30nm and the distribution of crystal phase trends to be homogeneous.The density increased from 2.76 g/cm³ to 3.33 g/cm³,the acid resistance increased from 95.82%to 98.12%,the water absorption decreased from 0.25%to 0.11%,and the Vickers hardness increased form 886HV to 1135HV.With the TiO₂ as nucleating agent,the △T of the glass-ceramics decreased which suggested the thermal stability decreases.With the increasing of the mole percentage of TiO₂ from 1.9%to 9.5%,the glass transition temperature and the crystallization temperature decreased from 780℃ and 894 ℃ to 743 ℃ and 821 ℃.The main crystal phase was changed from spinel phase and mullite phase to single spinel phase.When the mole percentage of TiO₂ was less than 5.7%,the grain size tended to be uniform and the grain size decreased.The density increased from 2.78 g/m³ to 3.12 g/cm³,the water absorption decreased from 0.18%to 0.11%,the acid resistance increased from 95.38%to 97.62%,and the Vickers Hardness increased from 812HV to 938HV.When the mole percentage of TiO₂ was more than 5.7%,the aggregation of crystal was enhanced and the connected structure was destroyed and agglomerated.The density decreased from 3.12 g/cm³ to 2.96 g/cm³,the water absorption increased from 0.11%to 0.15%.The acid resistance decreased from 97.62%to 96.03%and the Vickers hardness decreased from 938HV to 852HV,Therefore,the glass-ceramics has the best performance when the mole percentage of TiO₂ is 5.7%and the mass ratio of ZnO/MgO is 7:1.On that basis,the grain sizes of glass-ceramics were changed by heat treatment.The research on the relationship between grain size and Vickers Hardness show as follows:With the decreasing of the grain size,the Vickers Hardness of the glass gradually increases.When the grain size decreases to about 22nm,the hardness starts to increase sharply,and existed a variation,when the grain size is between 12 and 20nm.The grain size continued declining,the Vickers Hardness started to decrease rapidly.When the grain reached the threshold,the Vickers Hardness has been reduced to 916HV.The theoretical value of the critical size is 12.5 nm,which was calculated by the data of Impulse Excitation Technique.The calculation is in good agreement with the measured results.