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The Process And Mechanism Of Preparing Tobermorite Whiskers With Fly ASH

Posted on:2016-02-01Degree:MasterType:Thesis
Country:ChinaCandidate:S Q LvFull Text:PDF
GTID:2271330473462767Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
Tobermorite materials has many outstanding advantages. For example, high capacity in market, high strength, low thermal conductivity and low specific gravity. Application prospect of tobermorite materials is very broad in important energy saving fields, such as the fields of building external wall and industry furnaces kilns. Fly ash is the largest single solid industrial wastes in China. Vast accumulation of fly ash causes serious environmental and social problems to our country. Starting point of the study is developing the approach of fly ash comprehensive utilization which can expend a large amount of fly ash and the preparing product have wider application. And in view of the great demand of energy conservation and emission reduction in our country, the paper comes up with a new method of compounding tobermorite crystal using fly ash as silica raw material through dynamic hydrothermal synthesis method. This paper focuses on the new technology and reaction mechanism of compounding tobermorite whiskers using fly ash.Innovative achievements in this paper including:(1) New process for preparation of tobermorite whiskers using fly ash as silica raw material is explore and optimize. Geting the best process conditions: molar ratios of Ca/(A1+Si) is 1, reaction time is 5h, reaction temperature is 220℃, ratio of liquid to solid is 30mL/g, and stirring intensity is 200-400rpm. Synthesis nanocomposite tobermorite whiskers are intertwined into hollow spherical particles under the best conditions.(2) The paper thorough studies on the influence of mechanical activation on enhancing reactivity of fly ash. The results showed that mechanical activation can increase significantly the specific surface area and reactivity point of fly ash. Therefore, the activity of fly ash is improved sharply, so that crystal form of synthesis tobermorite becomes more complete, the ratio of length to diameter of formative tobermorite whiskers gets bigger, the surface of spherical secondary particles which whiskers is intertwined into becomes more smooth, the cumulative pore volume of spherical secondary particles increased markedly. These changes would be very conducive to improve heat insulation performance and strength of tobermorite product.(3) Understanding reaction mechanism of compounding tobermorite with fly ash. In the process of reaction, Ca(OH)2 reacts with active SiO2 on the surface of fly ash preferentially, generating C-S-H gel. Meanwhile, under the action of OH" in the solution, inactive SiO2 is activated continually on the surface of fly ash, and react with Ca(OH)2. Under the specific reaction system, C-S-H gel growing on the surface of fly ash is crystallize constantly and become fiber. And then these fiber is intertwined reciprocally into the spherical secondary particles. Al can replace Si of [SiO4]4- partly because Al and Si own similar properties in fly ash. Substitution position gives priority to Q2 and Q3 position, and instead proportion is up to 16%. Due to the substitution of aluminium, heat-resistance temperature of the Al tobermorite is 90℃ higher than the pure tobermorite.
Keywords/Search Tags:fly ash, dynamic hydrothermal method, tobermorite, whiskers
PDF Full Text Request
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