| After long-term coal mining,coal gangue has become a large reserve of industrial solid waste,which not only occupies land,but also causes serious environmental pollution.However,coal gangue is currently used as raw materials for roadbeds,bricks,etc.,and its utilization value is low.Many scholars have devoted to the study of coal gangue in ceramic preparation,but the performance of the samples is poor due to the influence of impurities in coal gangue.In this paper,firstly,porous ceramics were prepared with solid waste such as coal gangue and coal slime as raw materials.As an additive,the effect of glass powder and its content on the mechanical properties and pore structure of the sample is studied.Secondly,the high-purity nano-needle mullite prepared by molten salt method is used as a reinforcing material/matrix material to prepare mullite/alumina composite ceramics and zirconia/mullite composite ceramics.Mullite/alumina composite ceramics have been studied on the effects of mullite addition and sintering temperature on the density,microscopic morphology,and mechanical properties of the sample.Zirconia/mullite composite ceramics studied the effects of different zirconium sources,zirconia addition amount and sintering temperature on the phase content,microscopic morphology,and mechanical properties of the samples.And the enhancement mechanism of mechanical properties is studied.The following conclusions are obtained through the above research:(1)Orthogonal experiment was used to study the influence of three factors,namely the ratio of coal gangue to coal slime,sintering temperature,and the ratio of different coal gangue particle sizes on the apparent porosity and linear shrinkage of the sample.125 μm coal gangue and 74 μm coal slime were used as the main raw materials for subsequent experiments,and their mass ratio was controlled to 7:3,and the sintering temperature was set at～1150℃.Due to the poor hardness of the sample,glass powder is used as an additive to promote the reaction between the raw materials by forming a certain amount of liquid phase at high temperature and improve the mechanical properties of the sample.The results show that glass powder can promote the reaction of the sample and reduce the sintering temperature.In addition,the pore structure built by coal slime and wood chips will be improved by temperature and glass powder.The sample with 6%glass powder,after sintering at 1180℃ for 3 h,the apparent porosity decreased from 40.92%(without glass powder)to 31.22%,and the pore structure(the number ratio of<8 μm pores to 8-20 μm pores)was adjusted from 7:2 to 2:7.The flexural strength is increased from 7.70 MPa to 28.36 MPa.(2)Coal gangue and alum are used as raw materials to synthesize high-purity nano-acicular mullite powder with molten salt method at 850℃.The mullite and alumina are used to prepare mullite-alumina composite ceramics,and the nano-needle morphology of mullite has the effect of enhancing the mechanical properties of the alumina ceramics.The test results show that the composite ceramic with 25%mullite(MTA25)sintered at 1550℃ has the highest relative density of 96.43%and the lowest apparent porosity of 0.98%.The flexural strength and fracture toughness of the sample are 263.73 MPa and 5.01 MPa·m1/2,respectively,which are higher than the reported data.Transgranular fracture consumes a lot of energy so that the mechanical properties are improved.Griffith fracture theory further confirms that the sample has the largest critical crack size and the highest fracture work,which are 173.86 μm and 127.55 J/m2,respectively.(3)The phase,microscopic morphology and mechanical properties of zirconia mullite ceramics were studied by controlling the two zirconium sources of zirconia and zirconium oxychloride,their content,and sintering temperature.The results show that the sample with 12%zirconia has the best density,and the density increases from 2.50 g/cm3 to 2.83 g/cm3.In addition,the addition of zirconium oxychloride will cause the presence of quantitative t-ZrO2 in the ceramic matrix,which further improves the mechanical properties of the sample.The flexural strength increases from 162.40 MPa to 285.04 MPa,and the fracture toughness increases from 2.38 MPa·m1/2 To 3.55 MPa·m1/2.Figure[42]Table[16]References[146]... |
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