Desenvolvimento de compósito cerâmico com diatomita, alfa-Al2O3 e ZrO2 parcialmente estabilizada
In Brazil, the largest producers of diatomite are Bahia and Rio Grande do Norte, corresponding respectively to 45% and 35%, and is mainly composed of hydrated silica. This research assessed the scientific and technical feasibility of using comminuted diatomite in a ceramic composite. Diatomite, afte...
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| Formato: | doctoralThesis |
| Idioma: | por |
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Brasil
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/25221 |
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| Resumo: | In Brazil, the largest producers of diatomite are Bahia and Rio Grande do Norte, corresponding respectively to 45% and 35%, and is mainly composed of hydrated silica. This research assessed the scientific and technical feasibility of using comminuted diatomite in a ceramic composite. Diatomite, after comminution for 20 hours in a ball milling, reached D90 equal to 11.40 μm and was aggregated to the ceramic composite with a matrix containing α-Al2O3 and ZrO2 partially stabilized with 3% Y2O3, purchased commercially and with granulometry D90 2.86 μm and 7.68 μm respectively. The testing materials were shaped in a uniaxial press with the application of 270 MPa compactness pressure. Two experimental series were developed: D1A and D2A, with respectively 10% and 25% of diatomite and 5% and 10% of ZrO2 in their formulations and sintered in a conventional manner, with levels ranging from 1350 °C to 1600 °C and most of them with a permanence time of 120 min. Technological tests were performed to characterize the raw materials and those sintered by: granulometry, XRF, XRD, SEM, dilatometry, TG, DSC, μv, Rlq, μapa, μreal, PA, AA,Vickers microhardness, σmx and toughness to KIC fracture. In several formulations, one found mainly the formation of the following phases: mullite, corundum, sillimanite, tetragonal and monoclinic zirconia. The testing materials of the formulation R6 D1A, thermal cycle with a level of 1600 °C, heating rate of 5 °C/min, permanence time of 120 min, achieved the best overall result of microhardness 1662 HV, with microstructure of oval pores, greater frequency of diameters smaller than 1 μm, porosity density of 0.08 p/μm2, sintering coinciding with greatest point of densification and higher incidence of corundum, mullite and silimanite phases, this factors may have contributed to the result achieved. The best result for the σmx was in the sample of the formulation R6 D1AZ10, with a value of 115 MPa. The sample R1 D2A achieved the best result of KIC with 7.0 MPa.m1/2. From the sintering process used in this research, from the technical and scientific point of view, it is feasible to use particulate diatomite in composites with α-Al2O3 and ZrO2 partially stabilized with 3% Y2O3, for applications with requirements for mechanical properties of microhardness up to 1662 HV, σmx with values up to 115 MPa and KIC up to 7.0 MPa.m1/2. |
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