| Foam ceramics, with particular structure of 3D open porosity and excellent texture properties, have showed great superiority in the field of molten metal filtration. Organic sponge impregnation technology, due to its simple process and low cost, is an economical and practical method for aluminum ceramic foam filters(CFF). Presently, the main technical problems for aluminum CFF lie in its low thermal strength, poor thermal shock resistance and long-term stability. All these restrain the elevation for the aluminium alloy properties, and therefore having become the hotspots of CFF research.Laboratory studies of this paper started from the porcelain-forming mechanism investigation for the dry-pressed concrete ceramic. By means of binder ratio optimizing, sintering enhancement, and the addition of mixed rare earth, talc, kyanite, industrial alumina and TiO2, ceramic matrixs with high-strength have been obtained. Based on slurry coating optimization, foam ceramics were prepared in lab using organic foam impregnation technique, which is followed by characterization of mechanical properties, thermal shock stabilities, pore size distributions, specific surface areas, etc. Then, according to the optimized formulas and slurry coating techniques, pilot studies were carried out firstly to prepare new types of aluminium-used CFF, then the new filters were applied to on-site A356 aluminum alloy filtration tests, and comprehensive comparison and evaluation were done on the aspects of specimen mechanical properties, alloy composition, etc.Form the mechanical property and porcelain-forming mechanism studies of the original formula dry-pressed concrete ceramics, which induded coruadum, silica, K-feldspar and kaolinite, as raw materials, it showed that:low sintering density and matrix intensity can be mainly attributed to the lack of active Al2O3, the excessiveα-cristobalite and low secondary acerate mullite generated in the ceramics.By studing the effect of the additive concentration, on the mechanical preoperties of the matrix, it is found that the optimal phosphoric acid addition amount was 85% phosphoric acid and deionized with the ratio of 20/65 in matrix. In this case, the compressive and flexural strength at room temperature of the dry-pressed ceramics were 50.5% and 55.4% respectively, which was more than the original formula. This is mainly due to the low stoichiometric phosphoric acid which supplies more activiteγ-Al2O3. And the activeγ-Al2O3 is much propitious to the formation of secondary mullite and firm aluminum phosphate ceramic net.Sintering system has great impact on the mechanical properties of the sintered body. Two optimized sintering curves with their highest temperatures being 1350℃and 1400℃were determined. The compressive and flexural strength of ceramic matrix were increased by 6.8% and 13.1% respectively for 1350℃sinters, and 44.3% and 52.8% respectively for 1400℃sinters.Effects of multiform additives on the mechanical properties of the dry-pressed ceramics entities were systematically studied. Three kinds of optimized formulas were determined based on the phosphoric acid strengthended formula(A), which were the 6% talc+4% kyanite modified formula(B); the 3% mixed rare earth modified formula(C); and the TiO2+industrial Al2O3 co-milled formula(D). The main results and achievementsa are as following:·Adding 6wt% raw talc, the compressive and flexural strength of the dry-pressed sintered bodies can be increased by 108.9% and 33% respectively compared to that of A. Then further adding 4% ball milled kyanite on this basis, the elevation of the compressive and flexural strength further reached 20.1% and 29.1% respectively. The strengthening mechanism of talc addition mainly lies in the mullitization promoting effect by the generation of large number of glass phase, as well as the fine-grain strengthening effect of the generated aluminum-magnesium spinel solid solution. The role of kyanite in strengthening is mainly due to its high temperature inreversible mullitization, and its volume expansion effects fetching up the matrix shrinkage.·Adding 3% CeO2-riched mixed rare earth(formula C), the compressive and flexural strength of the dry-pressed ceramics entities can be improved by 25.4% and 23.3% respectively compared to that of formula A. The strengthening effects mainly lie in the CeO2 lattice defects generated at high-temperature which acts as activation centers for mullite crystallization, and promotes liquid-phase formation and aggregation, and the fine-grain strengthening function.·Adding TiO2+industrial Al2O3 co-milled powder(formula D), the compressive and flexural strength of the dry-pressed ceramic sintered body can be increased by 80.2% and 85.3% respectively compared to that of formula A. The strengthening mechanism of mainly lies in the promoting effect of the highly activated Al2O3 and TiO2, together with the metastabilized phase generated during the ball-milling process, and the stabilizing effect of mullite, silica and Fe2O3 on the aluminium titanate crystal.Dispersity and thixotropy of the above mentioned four optimized formula slurries were studied. formula D showed best dispersity followed by formula A,C,and B. The bad dispersity for formula B is due to the inherent hydrophobic interaction and surface air film on the talc particles; and for formula C, weaker surface ionic polarization for CeO2 particles resulted in compressure to the Al2O3 electric double layer. Well for formula D, high energetic ball milling improved the solid-liquid interface compatibility, and thus improving the slurry dispersity. Thixotropy studies showed that:when the solid-liquid ratio exceeded 1:4, the four kinds of slurries all put up the feature of pseudo-plastic fluid to some extent with shear thinning behavior and different stress overshoots. Formula B showed best thixotropy properties followed by formulaC,A and D. These are mainly associated with the different effects of the additives on the kaolinite "card structure" in the slurries.The polyurethane foam interosseous membrane can be removed effectively when hydrolyzed in 15% NaOH solution at 60℃for 40min, with its surface roughness increasing and no significant decline in elasticity. Idea slurry coating was derived when adjusting the compression ratio to 5:1. Soaked in certain solutions containing sodium carboxymethyl cellulose (CMC), sodium dodecyl sulfate (SDS), silica sol, and a home-made aluminum sol respectively, the slurry coating performances for the polyurethane foam were improved to different degrees, among which the home-made aluminum sol showed best coating effect. Laboratory preparation and property characterizations of foam ceramics based on above studies have been carried out with formula A as comparison. Mechanical properties studies showed that:the compressive strength for formula B,C and D were increased by 64.4%,28.8% and 48.1% respectively compared to that of formula A; as for the bending strength, the elevations were 24.9%,15%,72.6% respectively. Formula D showed highest number of thermal shock cycles, followed by formula C,B and A, this showed the effects of aluminum titanate stability on the improvement of matrix thermal shock resistance. As the bending strength variation after one thermal shock cycle, formula B showed smallest decline, followed by formula C,D and A.Mercury injection method was used to test the surface pore size distribution and the specific surface area of the sinters. At low-pressure, pore size distribution curve for formula A showed highest functional peak and widest pore size distribution, followed by formula C,B and D. This may be attributed to liquid aggregation and particle rearrangement in the matrix. While the presence of nano-sized pores in the matrix may be associated with gas emission, phase change shrinkage, micro-cracks and the mullitation in the sintering bodies. It was ulteriorly found that: inflicting the adobe of formula with vacuum freeze drying, the pore size distribution of the sinter was much wider than the unfrozen sinter. This is due to the formation of amouts of large pores with 10:1 aspect ratio on the cross-bars between the struts during freeze-drying process.Formula A,B and C were adopted in the pilot tests to prepare new types of aluminum CFF. The new products showed the advantages of high porosity, clean appearance, with no dregs, cracks and other defects. The compressive strength for the specimen of formula A,B and C were increased by 17.6%,104%,64.9% respectively, while the flexural strength,20.8%,163.6%,74% respectively, both of which are more than that of original formula.The on-site A356 aluminum alloy filtration tests showed that:the new filters met the actual production needs completely with high temperature stability, and good removing effects on fine inclusions. Hydrogen content testing to the various casting stages indicated that: filtration processes had certain removing effects on the hydrogen. Tensile strength and elongation tests for the alloy samples before and after filtration showed that:the tensile strength elevation rates for filters of the fomula A,B,C were 18.9%,13.1%,12.9%,respectively; while for the elongation, elevation rate for fomula A,B,C were 4%,11.4% and 8.3% respectively.
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