Preparation of Cordierite Glass-ceramics from Fly Ash

Cordierite is a silicate mineral with the advantages of low density, low thermal expansion coefficient, good thermal shock resistance, excellent chemical thermal stability, and high infrared radiation rate. Widely used in refractory materials, catalyst carrier materials and infrared radiation materials. People use kaolinite, talc and other mineral raw materials and industrial alumina to synthesize cordierite ceramics. It has been reported abroad that the use of fly ash to synthesize cordierite has not yet been reported in China. Fly ash is solid waste discharged from thermal power plants. It occupies farmland and pollutes air. It is an environmental issue that needs to be solved in all countries of the world. According to statistics, in 2000, China's fly ash emissions have reached 160 million tons. How to properly develop and utilize fly ash resources and turn waste into treasure is an important issue that needs to be studied in depth.
It is reported that the research group of the School of Materials Science and Chemical Engineering of China University of Geosciences has successfully used fly ash as the main raw material to prepare cordierite glass-ceramics with excellent thermal shock resistance. For the ceramic industry to rationally use fly ash, ease environmental pollution, reduce the cost of ceramic production, opened up new ways, has a good promotion and application value, and now its specific practices are described as follows:
First, raw materials The raw materials used are: fly ash, industrial alumina, basic magnesium carbonate and so on. Among them, the particle size of fly ash is 325 mesh and that of industrial alumina is 180 mesh. Fly ash is heat treated at 900°C for 2h to burn out the free carbon particles.
Chemical composition of fly ash (%): SiO2 53.87, TiO2 1.32, Al2O3 26.92, Fe2O3 4.02, CaO 2.49, Na2O 0.25 K2O 1.22 IL 7.1
Second, the preparation of cordierite glass-ceramics The basic formula of glass-ceramics: fly ash: 68%, industrial alumina: 10%, basic magnesium carbonate: 22%, methyl cellulose: 5%, stearic acid :1%. After accurately weighed according to the basic formula, the mixture of fly ash, industrial alumina and basic magnesium carbonate was mixed in a ball mill, then methylcellulose and stearic acid were added, and the mixture was mixed again. After taking the mixture and adding water, the clay was pressed to form a sample with a pressure of 15 MP. After the samples were dried, they were sintered in a high-temperature electric furnace using the temperatures of 1000° C., 1100° C., 1150° C., 1200° C., 1250° C., and 1300° C. respectively, and the holding time was 4 hours.
Third, test and analysis The performance test of the fired sample is mainly the thermal shock resistance test, which is characterized by the number of times that the high temperature water cooling cycle does not break. The test procedure is: Put the sample into a high temperature furnace, hold it at 1200°C for 15 minutes, take it out and put it into water at 28°C to quench it. After drying, re-insert the sample in a high-temperature furnace at 1200°C for 15 minutes, then take it out and put it in at 28°C. Cold water, so repeated until the sample ruptured. The prepared sample was subjected to 37 thermal shocks of 1200°C to 28°C and ruptured 38 times.
The phase analysis of six fired samples using the Rigaku Powder Diffractometer showed that the samples fired at 1000°C/4h contained a large amount of glassy phase and quartz, mullite, periclase, enstatite, and other crystal phases. Samples fired at 1100[deg.] C./4 h, mullite, quartz, periclase, and enstatite significantly reduced, while cordierite and spinel were formed. At 1150°C/4h, a large amount of cordierite was formed. There was still a small amount of enstatite, spinel and a certain amount of glass phase. With the gradual increase of temperature, the glass phase decreases, the cordierite phase gradually increases, and the degree of crystallization increases. In the samples fired at 1250°C/4h and 1300°C/4h, the cordierite crystallinity is high, and the impurity phase and the glassy phase are few. The analysis of the 1300°C/4h fired sample by the electron probe also showed the same result.
Samples sintered at 1300°C/4h contained more pores, the apparent porosity of the material reached 40%, and the pore size was large. Many of them reached 50 μm. However, larger pores do not reduce the thermal shock resistance of the sample, which may also be uniform distribution of large pores to disperse the thermal stress of the material and reduce the thickness of the sample, making it more conducive to exerting the material's heat resistance Seismic performance. This is in agreement with the results of the performance test of the sample that the water quenching cycle of 1200° C. to 28° C. does not break for 37 times.
IV. Conclusions The glass-ceramic material sintered at 1300°C/4h using the main raw material of fly ash has a fine grain of cordierite with a content of 80%. It is interlaced with the glass and spreads evenly. The glass-ceramics have a uniform distribution. Many pores, but with even distribution and large pore size, have good thermal shock resistance.