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Fly Ash study of low temperature ceramic foam

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Tutor: ZhangZhaoShu
School: Kunming University of Science and Technology
Course: Chemical processes
Keywords: Fly Ash,Activation,Low-temperature Ceramic,Foam Material
Type: Master's thesis
Year:  2011
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Fly ash is the solid waste combustion product of coal-fired power plants. Its main components are SiO2 and Al2O3. In 2003, the annual emission of fly ash in our country is about 200 million tons. Large accumulation of fly ash is not only taking up land, polluting environment, but also causing wastage of available resources. So the comprehensive utilization of fly ash is a major problem of resource and environment in the process of sustainable development of our country.After years of development, in 2009, the utilization rate of fly ash is up to 65% in my country. But the utilization is mainly in concrete admixture, wall materials and it is on a low technological level. So the development of new technologies with high added value and waste utilization is always the research focus in the field of fly ash utilization.This paper mainly takes fly ash as the research object. The physical and chemical activation methods were adopted to stimulate the potential activity of fly ash and then the cementitious material with hydration activity was prepared. Quartz sand, mountain sand, slag and other aggregates were used to enhance the performance of cementitious materials. Then, the composite material with better performance was prepared. The chemical methods were used to make composite material foam. Thus, the low-temperature ceramic foam material was obtained. The research indicates that:(1) Mechanical grinding increased the specific surface area of the fly ash particles, scattered the adhesive particles, improved their fineness, damaged the long-range orderly structure of fly ash vitreous, and increased the new surface. So it was benefit for external ions to damage Si-Al structure of fly ash and fasten the dissolution of active SiO2 and Al2O3. And it also created conditions to stimulate the activity of fly ash deeply.(2) Chemical activation includes alkaline and salt stimulation. By adding several kinds of stimulated material, I found that the metasilicate and natrimaluminate network structure with high polymerization degree were disintegrated into single SiO2 and Al2O3, then generated hydration aluminum silicate, CAH, CSH, AFm, AFm, and other activator substances. As a result, it could make fly ash reflect curing cementation performance. (3) Some activators, such as lime, gypsum, sodium hydroxide, red mud and minerals activator all had shown inspired effect in some way. If two or more materials were mixed together, it would have better effects. Then CaO-CaSO4-mineral activator composite material stimulating system was filtrated. On the basis, Si-Al minerals with high activity and water reducer could further improve the performance of cementitious material.(4) The effect on the composite material of the aggregate types, cement- aggregate ratio, water-cement ratio as well as curing condition was examined. Under laboratory conditions, if steam curing was used and pieces of stones were taken as reinforcement, the material’s compressive strength can be up to 90MPa. If the aggregate was slag, the material’s compressive strength can be up to 65 MPa. They both had the basic conditions for bubble.(5) The amount of aluminum powder, surfactant and NaOH had significant effect on the bubble process of the material. They have great effect on gas-foaming process by influencing the fluidity and the rate of slurry thickening. If the fluidity was too big, the aggregates were prone to uneven settlement. During the process, it damaged stomata formation. If the fluidity was too small, it was difficult for gas core to grow up smoothly in the slurry. So it got low foam formation rate. Therefore, coordination of the fluidity, gas formation speed and slurry thickening speed is very important.(6) XRD revealed that:The main crystalline hydration products of the low-temperature ceramic foam material were CaH4Si2O7、Ca6Al2O6(OH)6-32H2O、Ca4Al2(SO4) (OH)12-6H2O and CaeAl2(SO4)3 (OH)12·26H2O. The Amorphous phase with the zeolite amorphous characteristics was the dominant mineral of the material. The connection between materials was the Al-Si long chain mainly. So it is a kind of chemically bonding ceramics. SEM showed that the integrations between matrix phase and enhanced phase composites were tight and there was no obvious interface. Its mineral structure is more compact than that of spelled stack wool shape of Portland cement hydration products. That is why its overall performance is much better than that of cement-based materials.(7) Comparing to traditional materials, take aerated concrete as an example, low-temperature ceramic foam material made from fly ash has good mechanical, corrosion resistance, heat resistance and anti-freeze properties. The manufacture process is simple. Solid waste utilization rate is high. The emission rate of pollution is less. So it is in line with the national industrial policies. The expected economic, social and environmental benefits will be significant. So it will provide a new technical solution for the resource utilization of fly ash and other industrial solid wastes.
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