Processamento e caracterização de filtros cerâmicos fibrosos

Abstract

ResumoNeste trabalho, filtros com estrutura fibrosa foram produzidos utilizando-se matéria-prima de baixo custo, disponível comercialmente e caracterizados para aplicações em filtração de aerossóis. Mantas refratárias sílico-aluminosas comerciais foram prensadas uniaxialmente, utilizando-se 10% em massa de acetato de polivinila como ligante. Nesta etapa, as amostras foram submetidas à compactação com diferentes pressões para obtenção de diferentes porosidades. Após a prensagem, as amostras foram submetidas a um tratamento térmico a 500 °C durante 1 h para a degradação do polímero. Subseqüentemente, as amostras foram sinterizadas a 1200 °C durante 1 h, resultando em uma estrutura fibrilar porosa, composta por mulita (3SiO 2 .2Al 2 O 3 ), com porosidade na faixa de 50 a 75%. A morfologia dos filtros fibrosos foi caracterizada através de microscopia eletrônica de varredura, que revelou uma estrutura tridimensional porosa de fibras interconectadas. A resistência mecânica foi avaliada através de ensaios de compressão e de flexão em quatro pontos. Ensaios de permeabilidade e eficiência de coleta de partículas com diferentes diâmetros foram efetuados e os resultados comparados a filtros comerciais. Os valores obtidos para a permeabilidade e eficiência de coleta estão na ordem de grandeza esperada para filtros de gases, apresentando assim grande potencial para aplicações industriais. Palavras-chave: filtros cerâmicos fibrosos, propriedades mecânicas, permeabilidade, filtração de aerossóis. AbstractFilters with fibrous structure were produced from low cost, commercially available raw materials and characterized for aerosol filtration. Refractory aluminosilicate fibers were uniaxially pressed with polyvinyl acetate as binder. Different pressures were applied, which yielded samples with different porosities. After pressing, the samples were heat treated at 500 °C during 1 h in air for debinding with subsequent sintering at 1200 °C for 1 h, which resulted in porous fibrous structures composed mainly by mullite (3SiO 2 .2Al 2 O 3 ) with porosity in the range of 50%-75%. The microstructure of the fibrous filters was evaluated by scanning electron microscopy, which revealed a porous morphology comprised by three-dimensional interconnected fibers. Mechanical strength was measured by compressive and 4-point bending tests. Permeability and particle collection efficiency were evaluated and compared with commercially available filters. The permeability and collection efficiency values are in the order of magnitude of cellular supports for aerosol filters and, therefore, suitable for several technological applications.

Evaluation of resistances to fluid flow in fibrous ceramic medium

“…Fig. 3 clearly shows that the porosity of the material and the temperature of the fluid have a strong influence on the behavior of the pressure drop, as previously observed by Muller et al [3]. As the porosity decreased, the nonlinearity of the profile of Dp increased.…”

“…Ceramic filters with fibrous structure were obtained from commercially available refractory blankets, containing 50% SiO 2 , 49% Al 2 O 3 and traces of inorganic compounds, according to a previously reported methodology [3]. A binder agent based on polyvinyl acetate (PVA) was added to the fibers and the material was submitted to uniaxial pressures in the range of 17 to 41 MPa, yielding blocks with cylindrical shape (50 mm in diameter and 10 mm in height) and different porosities.…”

“…Results and discussion Fig. 3 presents the results for the pressure drop obtained experimentally [3] in the wind tunnel and the predicted curves obtained from the simulations carried out with the commercial code ANSYS Ò CFD (FLUENT Ò ), for the two temperatures evaluated (300 and 973 K), as a function of the material porosity (0.50, 0.65 and 0.73). Good agreement between the experimental and the numerically predicted profiles can be observed and it can be noted that lower deviations were obtained as the material porosity increased.…”

“…Moreover, these devices may be successfully applied even at high temperatures, which allows their use in the control of particulates generated in processes such as residue burning, metal refinement, diesel combustion and hot gas filtration [1][2][3].…”

Mechanical Characterization of Fiber Ceramics: Effect of Temperature**

“…[4][5][6] However, due to the discontinuous and heterogeneous structure, it is unclear if conventional models, such as Weibull theory, are suitable to describe mechanical properties of these fibrous structures. Several studies have investigated that with conventional methods, such as mechanical testing by compressive and four-point bending tests.…”