Preparation And Mechanical Properties Of High Strength And Toughness Glass-ceramics Sintered From Granite Waste

Glass-ceramics exhibit the characteristics of high strength,low water absorption and excellent decorative appearance.They could be used as high-grade construction materials to replace such decorative stones as granite and marble.In this thesis,the decorative glass-ceramics with high strength and toughness have been prepared from granite waste by the rapid powder sintering.The preparation of glass-ceramics from granite waste not only significantly reduces the cost of raw materials,but also eliminates environmental impact,presenting significant economic and social benefits.High strength and toughness glass-ceramics have been prepared by using the granite powder as the main feedstock,silane coupling agent as the powder modifier and small quantity of sintering additives.The sintering behavior and microstructure of glass-ceramics were studied with respect to their relationship with the mechanical properties.Among the sintering aids,the boehmite was superior to the silica sol and waste glass powder in the densification and strengthening of glass-ceramics.With the increase of sintering temperature,the bulk density and flexural strength of glass-ceramics firstly increased and then decreased,while the degree of crystallization decreased successively.The optimum sintering temperature was 1075°C,leading to the maximum bulk density of 2.49 g/cm³ and flexural strength of 125 MPa.The flexural strength firstly increased and then decreased with increasing the boehmite content,and the degree of crystallization increased gradually.The optimum boehmite addition was3%,resulting in the maximum crystallinity of 63%.The sintering experiments of modified granite powder showed that the increase of heating rate was beneficial to improve the densification,crystallization and mechanical properties of the glass-ceramics.When the heating rate was 50°C/min,the maximum bending strength of 143 MPa and fracture toughness of 2.1 MPa·m¹/2/2 were achieved.When the heating rate was increased from 5°C/min to 50°C/min,the Vickers hardness increased from 5.6 GPa to 6.5 GPa.In addition,the strengthening and toughening of glass-ceramics were closely related to the improved densification and crystallization.Results of fiber toughening indicated that the addition of pickling asbestos resulted in the maximum bending strength of 144 MPa and fracture toughness of 3.0 MPa·m^1/2.The mechanical properties of glass-ceramics with pickling asbestos were highly superior to that with the other toughening fibers.The enhanced toughening was related to the small size effect of asbestos fibers.Smaller-sized fibers promoted the uniform distribution of fibers in the matrix.As a result,the matrix toughening could be achieved with lower fiber contents.The toughening mechanism of glass-ceramics involves the crack deflection and bridging,while the strengthening mechanism refers to the matrix strengthening by the inorganic fibers and the transgranular fracture of glass-ceramics.The decorative glass-ceramics have been prepared from granite powder by the rapid sintering.The optimum sintering process was conducted at 1115°C for 120 min with a heating rate of 30°C/min.As the composite nucleating agent was 4%,the decorative glass-ceramic with a glossiness of 66% was achieved.