Study On The Synthesis Of Porous Mullite Ceramics Using Electroceramics Waste As Raw Material

Our country is a ceramic power, a large number of ceramic waste has been produced due to the continuous development of the ceramic industry. How to convert the waste into a useful material has become an urgent matter for the sustainable development of the whole industry. Many researches on the utilization of inorganic solid waste have focused on the fly ash and coal gangue. But the electroceramics waste are increasing everyday, so the synthesis of porous mullite ceramics by electroceramics waste is very important for the call of energy-saving and sustainable development, the realization of electroceramics waste value and the reduction of synthesis cost.The porous mullite ceramics were fabricated using electroceramics waste as raw material, adding CMCC and graphite as pore-forming agents by different forming techniques; the effects of pore-forming agents and its additive amount, sintering temperature, holding time and alumina-silica ratio on the structure and properties of porous mullite ceramics were studied; the effects of solid content and p H value were studied in the gel-casting technique; the gelatinization mechanism was analyzed, the dosage of initiator and catalyst were determined; the advantages and disadvantages of porous mullite ceramics fabricated by dry pressing and gel-casting respectively were compared. The conclusions were as follows:(1)The structure and properties of porous mullite ceramics fabricated using graphite as pore-forming agent were better than CMCC. The comprehensive properties were the best when pore-forming agent content was 20wt%. The porosity was 45.18%, bulk density was 1.89g/cm3, compressive strength was 11.25 MPa when the sintering temperature was 1400℃, the comprehensive properties were the best and the phase content of mullite was the maximum. In order to guarantee the comprehensive properties and consider the energy-saving, 4h was the optimum holding time. With the SiO2 being added, the phase content of mullite reached the maximum and the comprehensive properties were the best when the alumina-silica ratio was 3:2.(2)In the gel-casting technique, the solid content and pH value would affect the viscosity. The viscosity would increase from 150mPa·s to 340mPa·s when the solid content increased from 50wt% to 60wt%. And when the solid content exceeded 60wt%, the viscosity increased quickly. So in order to meet the viscosity and high solid content, 60wt% was the optimum solid content. With the rise of pH value, the viscosity would decrease. When the pH value reached 9, the electrostatic interaction between particles was strongest and the particles were uniformly dispersed; moreover, the viscosity was lower and the slurry was relatively stable.(3)The gelation time of slurry was getting shorter and shorter with the increased dosage of the initiator. The gelation time had a small changing scale decreased from 25 min to 20 min when the dosage of initiator increased from 0.6wt% to 0.7wt%. Through overall consideration, 25 min was the optimum gelation time and the optimum dosage of initiator was 0.6wt%. The gelation time of slurry was getting shorter and shorter with the increased dosage of catalyst. The gelation time had a small changing scale when the dosage of initiator ranged from 0.3wt% to 0.5wt%. So through overall consideration, the optimum dosage of catalyst was 0.4wt% when the gelation time was 25 min.(4)Under the optimum parameters, the porosity of sample fabricated by gel-casting technique was 51.40% which increased 10% in comparison to the sample fabricated by dry pressing technique; the bulk density of sample fabricated by gel-casting technique was 1.54g/cm3, and that the bulk density of sample fabricated by dry pressing technique was 2.01g/cm3; the compressive strength of sample fabricated by gel-casting technique was 17.99 MPa, both strength didn’t appear to be much different. The gel-casting technique was an ideal forming method in comparison to the dry pressing technique because of the properties of sample fabricated by the former were advantageous than the latter, having higher strength as well as holding high porosity and low bulk density.