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Preparation Of Porous Materials From Fly Ash By Sintering At Low Temperatures And The Modulation Mechanism Of Pore Structure

Posted on:2015-03-02Degree:MasterType:Thesis
Country:ChinaCandidate:J L DuFull Text:PDF
GTID:2191330479484085Subject:Materials engineering
Abstract/Summary:PDF Full Text Request
The morphology of the pores and the pores size distribution have a great influence on the mechanical property, the heat-insulating property and the sound absorption performance of the porous materials. In this thesis fly ash was used as the main materials and the foaming gas was from the reaction of Na2CO3 and SiO2, the Na2O-CaO-SiO2-B2O3-F(NCSBF) porous materials were prepared by a low temperature melt foaming process, we have studied how to control the amount of the gas in the porous materials from the gas generation process and the gas dissipation process; we put forward the thoughts that solving the problem by controling the foaming process and study the mechanism of the action of SiC and Si on the pore structure respectively.Research on the amount of gas inside the porous materials has showed that: the apparent activation energy of the reaction of Na2CO3 and SiO2 is 207KJ/mol and the apparent activation factor is 1.96×108min-1, However, When this reaction in the mixtures the apparent activation energy is 86kJ/mol and the apparent activation factor is 6.47×103min-1, it must be the other ingredients which help to reduce the apparent activation energy and the apparent activation factor; Due to the weak process of the gas escaping under 850℃ in the porous materials, we just need to control the generation process of the gas inside the porous materials, when we improved the heating-rate there will be less gas loss in the molt. When increase the heating-rate from 5℃/min to 20℃/min, the volume density of the porous materials will be reduced from 0.72g/cm3 to 0.66g/cm3Research on the effects of the SiC particles addition on the porous materials has showed that: the particle size of the SiC in the molt of the Na2O-CaO-SiO2-B2O3-F porous materials decreased with oxidation time, when the addition of the SiC is 3%. The oxidation time is 4h, the particle size of the SiC will be ruduced from 196 um to 150.7μm, then the particle size will remain unchanged;When the particle size of the SiC is 198μm, the pores mainly distributed in the edge of the SiC particle, this phenomenon indirectly proves that the SiC particles can promote the effect of bubble nucleation, and the nucleation effect weakened gradually with the decrease of the particle size, when the particle size of the SiC is 10μm, the SiC has lose the effect of promoting nucleation; the degree of the bubble coalescence in the porous materials is intimately associated with the content of SiC, the pore wall will be damaged with the addition of SiC and so the pores will be connected to each other in the porous materials, when the content of the SiC is 5%, the degree of the bubble coalescence is most serious, the connected area accounts for 19.88% of the area of the plane which is randomly selected.Research on the effects of the Si particles addition on the porous materials has showed that:he particle size of the SiC in the molt of the Na2O-CaO-SiO2-B2O3-F porous materials remain unchanged with oxidation time; When the particle size of the Si is 100μm, the pores mainly distributed in the edge of the Si particle, this phenomenon indirectly proves that the Si particles can promote the effect of bubble nucleation, and the nucleation effect weakened gradually with the decrease of the particle size, when the particle size of the Si is 1200 mesh, the Si has lose the effect of promoting nucleation; when the particle size of the Si less than 25μm, the volume density of the porous materials reduced with the decreased of the Si particle size, this may be caused by the generating of SiO with the Si particle size smaller; when the content of the Si is 9%, there will be many cracks inside the porous materials and when the content is less than 9%, with the content of the Si increased, the volume density of the porous materials increased, the mean pores size decreased and the pore size distribution become more uniform.
Keywords/Search Tags:Fly ash, Low temperature sintering, Porous materials, Heterogeneous nucleation, Pore structure
PDF Full Text Request
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