Study On The Atmosphere Effect And Control Of Foaming Of Porcelain Polished Tiles Waste During Firing

In recent years,with the improvement of the national economy,people have higher requirements for their living conditions,and the porcelain polished tiles are more and more widely used in various architectural areas.With the porcelain polished tiles enrich people's living conditions with their excellent physical and chemical properties.At the same time,a series of resource and environmental problems,such as resource waste,environmental pollution,land occupation,caused by the large-scale production and recycling difficult of porcelain tiles polishing waste?PTPW?seriously restrict the sustainable development of the ceramic industry.The preliminary research results show that the PTPW contains a small amount of SiC,and the main reason for the difficulty in resource utilization of PTPW was the foaming and deformation of ceramics caused by the oxidation of SiC.If the SiC foaming can be controlled,the PTPW can be directly applied into the production of porcelain tiles,it will greatly alleviate the resource and environmental problems caused by the PTPW.The literature indicated that the oxidation mechanism of SiC was closely related to the atmosphere and temperature conditions.Therefore,this thesis studied the effects of atmosphere on SiC foaming in ceramics by controlling the atmosphere conditions and temperature conditions,and discusses the related mechanisms;at the same time,a kind of dense porcelain polishing tiles which can be fired at low temperature was developed by using PTPW,and its properties were studied.Firstly,in this thesis,the effect of SiC content on the sinter behavior of ceramics in different atmospheres was studied.By analyzing the bulk density,water absorption and fracture surface morphology of the samples,it was found that the oxidation of SiC in air atmosphere caused serious foaming of ceramics,while the oxidation of SiC in N₂ and Ar atmosphere without foaming.Then,the isothermal oxidation experiment was carried out.And the oxidation mechanism of SiC in different atmospheric conditions was studied by EDS analysis,weight loss analysis and phase content analysis.The results show that passive oxidation and active oxidation of SiC occurred in air atmosphere and N₂ atmosphere respectively.Compared with N₂ atmosphere,the samples fired in air atmosphere produced more liquid phase.At 1170oC,about 0.51 wt%SiC was oxidized during 180 minutes isothermal oxidation in air atmosphere,while less than 0.1 wt%of SiC was oxidized in N₂ atmosphere.In the densification process of ceramic,the SiO₂ protective scale formed on the surface of SiC cannot effectively prevent the oxidation of SiC,but prolonged the oxidation time.Therefore,the total amount of passive oxidation of SiC is larger,which causing foaming of ceramics.However,the active oxidation of SiC was inhibited in this process,and the total amount of reaction was small,which had less effect on the densification process of ceramics.At same time,in this thesis,the effects of four basic oxides,Na₂O,K₂O,MgO and CaO,on the foaming of SiC in ceramics were studied by quantitative analysis and orthogonal test.The results show that Na₂O can react with the SiO₂ scale of SiC to form Na₂SiO₃ liquid phase,which would result in the continuous oxidation of SiC.While K₂O,MgO,and CaO affect the oxidation of SiC through affecting reaction environment that affects this corrosion reaction.The results of orthogonal analysis show that the order of influence of four basic oxides on SiC firing foaming was:Na₂O>K₂O>MgO>CaO.On this basis,by adjusting the content of porcelain polished tiles waste,black mud,potassium feldspar and talc in the formula,the alkaline oxide content in the formula can be controlled.A dense porcelain polished tile was prepared by using30 wt%PTPW,46.3 wt%black mud,21.0 wt%potassium feldspar,and 2.7 wt%talc fired at1100°C for 30 minutes.The bulk density was 2.41 g/cm³,the water absorption rate was 0.04%,the flexural strength was 51.60 MPa,and the crystal phase composition was consistent with the polished tiles.All parameters can meet the requirements of polished tiles(?bulk density was2.37 g/cm³,water absorption<0.05%,flexural strength was 44-46 MPa?.The sintering temperature was 70oC lower than that of traditional ceramics.There were three innovations in this thesis:1.Quantitative study of the phase composition in the green body,systematically studied the foaming mechanism of SiC in ceramics in different atmospheres;2.The effects of Na₂O,K₂O,MgO and CaO on the foaming of SiC in ceramics were quantitatively analyzed.3.A low-temperature firing technique of porcelain polished tiles using 30wt%porcelain polished tiles waste as raw material was developed.