Study On The Preparation Of Ceramics From Fly Ash

Fly ash (FA) is an industrial by-product generated from coal-fired thermal powerstations, and also is the main cause ofparticle pollutant pm2.5, which become a greatthreat to our existence. On the other hand, FA could be reused due to its chemicalcomposition, and bring significant social and economic benefits.In the present thesis, we have investigated theprocessing and manufacture ofceramics developed from fly ash through various sintering methods, on the basis ofoptimization of components design and pretreatment of raw materials. The rawmaterials were mixed by milling. The obtained composite powders were preheated,milled, compacted and sintered to form fly ash ceramics. The sintering was conductedat the temperature range850oC~950oC, viaconventional sintering and vacuumsintering respectively. Water absorption, bulk density and vickers hardness weremeasured. The crystal structureand microstructure of materials were analyzed with X-ray diffraction (XRD) and scan electron microscopy (SEM). The mainly results wereshown as follows:(1) Fly ash ceramics were successfully fabricated by one-step sintering with theaddition of K2CO3. XRD result shows principle components silica and aluminamainly exist in amorphous phase and crystal phases of fly ash. The addition of K2CO3made the polymeric phase transformed significantly, and got leucite and potassuimaluminum silicate equiaxial crystal phases. The optimum proportion of fly ash toK2CO3is3:2(by mass ratio). Water absorption value is4.3%. During sintering, thereaction process produces gas, liquid phase, which negatively affects thedensification.(2) Two-step conventional sintering method was applied to form fly ash ceramicswith the optimum proportion of fly ash to K2CO3. According to the analysis of XRDand SEM, one phase, potassium aluminun sillicate (KAlSiO4) can be identified in thesamples sintered at the temperature range of850oC~950oC,after the raw materialsprocessing at the optimal preheating temperature730oC. With the increase oftemperature, the obtained crystals grewbetter and the amount of eutectic liquid phase increased, leading to a density increase of the obtained ceramics. The properties ofthe obtained ceramics achieved the maximum value at925oC. Preheating method isconducive to densification of material by removing water content and reactant gasand completing phase transformation.(3)Powders preheated at730oC were then sintered by vacuum sintering toprepare fly ash ceramics. According to the analysis of XRD and SEM, Theperformance is improved compared with that of conventional sintering. Eutecticliquid phase increased considerably as the sintering temperature rising, and theproducts appeared to have a viterous texture. Observation of the corrosive surface ofthe products showed the obtained grains present tiny forms and distribution evenlywith the size of0.4~0.5μm. Vacuum stops the oxidation reaction of sintering process.It results in the improvement of compactness and optimizationof performance.