M. D. M. Innocentini

Prediction of Ceramic Foams Permeability Using Ergun's Equation

SiC-Al2O3 ceramic foams with 30 to 75 pores per linear inch (ppi) were used to access the application of pore size obtained by image analysis to estimate the cellular materials permeability through Erguns equation. Samples were sliced and the pore size distribution, cross-sectional porosity and pore density were evaluated as a function of the slice thickness based on optical and X-ray computerized tomography acquired images. The average pore sizes were used to calculate permeability constants (k1 and k2) of Erguns equation, which were compared to those experimentally obtained under water flow. Results indicated that the optical diameter distribution was very sensitive to the number of pore layers. Deviation between experimental and calculated values depended on the slice thickness. Nevertheless, the introduction of pore size obtained by image analysis into Erguns equations seems to give fair results to assess the permeability of ceramic foams.

Drying behavior of hydratable alumina-bonded refractory castables

Abstract The drying behavior of a hydratable alumina-bonded (HAB) refractory castable was evaluated by thermogravimetric tests and compared with an ultra-low cement composition (CAC). The key properties of monolithic refractory dry-out performance, such as fluid permeability and mechanical strength, were also determined. The results showed significant differences among the drying profiles ascribed to the distinct hydrated binding phases, which affect the castables’ physical properties to a differing extent. The consequences of these features on the explosive spalling tendencies of the compositions are discussed.

Permeability optimization and performance evaluation of hot aerosol filters made using foam incorporated alumina suspension

Porous ceramic samples were prepared from aqueous foam incorporated alumina suspension for application as hot aerosol filtering membrane. The procedure for establishment of membrane features required to maintain a desired flow condition was theoretically described and experimental work was designed to prepare ceramic membranes to meet the predicted criteria. Two best membranes, thus prepared, were selected for permeability tests up to 700 degrees C and their total and fractional collection efficiencies were experimentally evaluated. Reasonably good performance was achieved at room temperature, while at 700 degrees C, increased permeability was obtained with significant reduction in collection efficiency, which was explained by a combination of thermal expansion of the structure and changes in the gas properties.

Ceramic foams porous microstructure characterization by X-ray microtomography

Knowledge of the porous structure of amorphous materials is of fundamental importance in calculating geometrical parameters such as total porosity, pore size distribution and physical parameters relating to fluid flow inside void space. The present work deals with the measurement of the microstructural parameters of porous ceramic filters. Microtomographic measurements of samples were taken using an X-ray tube. Bremsstrahlung radiation was filtered in transmission mode with a Sn filter at 58.5 and 28.3 keV and the images analyzed in two ways. The first method consisted in analyzing transepts of the images in order to calculate total porosity based on the average particle size and media linear attenuation coefficients. The second method involved a study of the images using an image analysis software, called Imago, which allows one to calculate total porosity and pore size distribution. The total measured porosity of the filter C90 was 73.8%, 71.1%, 74.4% and 71.5% by, respectively, the Arquimedes method, simple gamma ray transmission, transept analysis and analysis of the microtomographic images at 28.3 keV.

Efeito da técnica de aeração sobre a macroestrutura e a permeabilidade de espumas cerâmicas produzidas via "gelcasting"

The production of porous ceramics through the aeration of suspensions associated with the gelcasting process provides cellular porous ceramics with excellent properties and a wide range of densities. Nonetheless, the use of this material in applications such as filtering, thermal insulation, or catalyst supports requires a macrostructural tailoring in order to favor specific properties, such as permeability, thermal conductivity or specific surface area. These properties are determined by characteristics such as density, pore size distribution and connectivity between neighboring cells, which are defined during foam formation. The aim of this work was to assess the influence of the aeration process on the macrostructure of ceramic foams. A planetary mixer and a stirring vessel with a bubbling ring at the bottom surface were studied in this work. Alumina suspensions containing different foaming agent concentrations were submitted to mixing cycles in both foam generators. After gelling, samples were sintered and had their pore size distribution evaluated using image analysis and mercury porosimetry. The air permeability was also evaluated. The results showed that the aeration process may strongly influence the density and the mode pore size, having a significant effect on the materials permeability. It was observed that mercury porosimetry and image analysis lead to different pore size distributions. However, both results are useful, depending on the aim of the analysis.

Otimização do processamento para a fabricação de filtros no sistema Al2O3-SiC

The objective of this work was to evaluate the effect of processing parameters on the permeability and mechanical resistance of cellular ceramic filters. Analyses included processing and characterization of 8 ppi Al2O3-SiC filters produced from ceramic suspensions with different particle size distributions. The purpose was to optimize the particle packing in the solid struts and thus improve the mechanical properties of the filter without reducing its permeability. Characterization included evaluation of rheological properties of suspensions as well as measurements of porosity, permeability and mechanical resistance of the produced filters.

Correlação entre permeabilidade e resistência mecânica de filtros cerâmicos no sistema Al2O3-SiC

Reticulate ceramics have been increasingly employed in purification of gases, liquid metals and in catalytic processes. The application area usually depends on the chemical composition and the physical properties (porosity, pore size and pore counting (ppi)). In most cases, reticulate ceramics are submitted to compression loads at high temperatures, which makes the durability of these cellular materials be ultimately related to the mechanical quality of the struts. In filtration applications, it is also important the evaluation of fluid dynamic properties of the ceramic, specifically its permeability to fluid flow. In this work, a relationship between mechanical properties and permeability constants of Al2O3-SiC ceramic foam filters with 8 to 90 ppi is presented. Results were associated with the processing technique and with the mechanical modeling presented in the literature.

Influência de aditivos dispersantes nas propriedades de concretos refratários de Al2O3 e Al2O3-MgO

The state of dispersion of the castables matrix particles presents a direct influence in their rheological behavior, determining the techniques that can be used for their installation. Different additives have been used aiming an efficient dispersion, which constitutes an important requirement in the optimization of the particles packing and mechanical resistance of castables. However, the influence of those additives in the castables properties has not been extensively studied. In this work, the effect of 3 dispersants was investigated in the properties and drying behavior of different refractory compositions. The presence of sodium polyacrylate resulted in castables with higher permeability and larger porosity. On the other hand, in Al2O3-MgO compositions the presence of sodium hexametaphosphate provided extremely low permeability castables resulting in a slower drying, whereas the citric acid presented an intermediate behavior. Such effects in the castables properties were correlated to intrinsic characteristics of the additives.

Avaliação in-situ do módulo de cisalhamento como ferramenta para a determinação da cinética de cura de concretos refratários

This work attempts to evaluate the setting kinetics of a high-alumina refractory castable with ultra-low cement content (2 wt-%) via in-situ measurements of the shear modulus, G, applying a bar resonance method. The main advantages of the present study are the use of a non-destructive technique, which allows great reduction in the required number of samples and a better reliability in the results due to the higher sensitivity of the equipment. Moreover, the stiffness is suggested to be a more adequate parameter for castable demoulding. Results showed that temperature peaks are generated with the shear modulus changes along the setting time and that they were related to specific processes during castables setting, with or without aluminum powder added as drying agent.

Influência das condições de processamento cerâmico na resistência mecânica e na permeabilidade dos filtros de Al2O3-SiC

Ceramic filters must present not only high permeability and particle trapping efficiency, but also suitable mechanical strength. However, these parameters are influenced in different ways by the cellular structure. Large pores favor permeability, but lower removal efficiency of small particles. Small pores, on the other hand, enhance particle collection, although the filter pressure drop increases. The porosity is also essential for determining ceramic foam performance. Mechanical strength generally decreases with increasing porosity, even though permeability is improved. In this work, the relationship between mechanical strength and permeability has been investigated for 10 ppi (pores per linear inch) Al2O3-SiC filters. The amount of slurry impregnated on the organic struts walls during processing has been chosen as the control variable. The results have been compared with those obtained from cellular structures where the pore count variation ranged from 10 to 90 ppi.