Pore Size Of Channels Research Articles

Synthesis and characterization of a mesoporous silica (MCM-48) membrane on a large-pore α-Al2O3 ceramic tube

Abstract A mesoporous silica MCM-48 membrane was synthesized on a large-pore α-Al 2 O 3 tubular support with an average pore size of 3–5 μm by adopting the pore-prefilling method. The membranes and powders were characterized by small-angle X-ray diffraction, SEM measurement, N 2 adsorption, and thermogravimetric analysis. X-ray diffraction (XRD) results showed the membrane possessed a periodic mesostructure. The N 2 adsorption and desorption isotherms also showed that the membrane was a typical mesoporous material with pore channel size of about 2.7 nm. The TGA experiment proved that the removal of the surfactant is a stepwise mechanism. The permeability of the calcined mesoporous MCM-48 membrane was evaluated by the permeation of single gases (H 2 and N 2 ) with pressure drops across the membrane of 40–240 kPa. The permeation of these gases through the calcined MCM-48 membrane was strongly governed by Knudsen diffusion. The permeance of the single gas was independent of the pressure drop, indicating that there was no contribution of viscous flow to the total permeation. This result supports that there exist no large pinhole and crack in the mesoporous MCM-48 membrane, in agreement with SEM observation.

Microstructure changes in fired ceramics quantified by magnetic resonance relaxation and imaging

Nuclear magnetic resonance (NMR) relaxation and imaging are shown to give information on the changes of the pore space structure in ceramics during the sintering process. On a set of ceramic samples held at fixed maximum firing temperature of 1280 °C for different lengths of time, called “soaking times” in the ceramics industry, NMR methods were applied to quantify pore space properties such as connected porosity and pore size distributions. The longer the soaking time the lower the connected porosity, but no corresponding general statement can be made with regard to the pore size distribution. The homogeneous distribution of pores where the porosity is 17% for minimal soaking times becomes heterogeneous and with bigger pores but with porosity only about 5% after 10 min of soaking time. The results obtained are combined with those from traditional techniques such as scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The measured connected porosities and SEM analysis are in agreement with the NMR results. The “pore size” distributions obtained by magnetic resonance relaxation and MIP differ substantially and give complementary information, because in relaxation measurements “size” tends to correspond to pore dimensions, while in MIP “size” corresponds to the dimensions of the pore “throats,” the channels connecting the pores. The discrepancy between pore and pore-channel size increases with the soaking time and makes it clear that a higher level of sintering allows the formation of larger pores connected by smaller channels. For the longest soaking time sample, the SEM photos and the lack of a NMR signal make it clear that there is substantial isolated porosity and essentially no connected porosity.

Previsão da permeabilidade a partir de propriedades físicas de concretos refratários

A caracterização física de um material cerâmico auxilia na avaliação do seu processamento e desempenho em altas temperaturas. Dentre as técnicas de avaliação microestrutural, três delas foram estudadas neste trabalho: método de imersão (Arquimedes), de expulsão de água e de intrusão de mercúrio. O objetivo do estudo foi o de avaliar quais delas fornecem parâmetros mais representativos para estimar as constantes de permeabilidade de concretos refratários auto-escoantes de alta alumina. Os valores de permeabilidade foram calculados pela equação de Ergun e comparados com resultados de permeabilidade obtidos experimentalmente. A estimativa da permeabilidade a partir da utilização conjunta de parâmetros obtidos pelos métodos de imersão (porosidade aparente) e de expulsão de água (diâmetro máximo de poro) se mostrou mais adequada que a obtida a partir de resultados fornecidos pela técnica de porosimetria de mercúrio.

Preparation of mesoporous silica films on a glass slide: surfactant template removal by solvent extraction

Mesoporous silica films have been deposited on glass slides by the dip-coating method. Solvent extraction was used to completely remove the structure-directing surfactant with a carefully selected dilute HCl/EtOH solution, which was confirmed by Fourier-Transform infrared spectroscopy (FT-IR), and the films' ordered mesostructure was maintained. The weak bonding between template ions and inorganic species of thin film materials also resulted in the complete extraction of surfactant template with the ethanol solution. Small-angle X-ray diffraction (SAXRD) patterns and transmission electron microscope (TEM) images indicated that as-deposited and extracted films had a periodic hexagonal structure with the channels parallel to the substrate surface. The N 2 adsorption and desorption isotherms also showed that the film was a typical mesoporous material with pore channel size of about 2.4 nm.

Formation of a thick-diffusion-zone wear-resistant coating by deposition from a gaseous phase

An investigation into deposition by various methods and under various conditions has shown that a wear-resistant diffusion zone of considerable thickness (up to 1200 μm) can be obtained by deposition from a gaseous phase in a closed space at a low pressure. As a result of this investigation it has been established that the depth of such a diffusion zone grows with increasing duration of treatment and pore channel size and with rising process temperature.

Diffusion chromizing of sintered porous permeable materials from iron powder

1. In the diffusion chromizing of a sintered porous permeable material from iron powder a transition from volume to surface chromizing is observed at a pore channel size of ∼2.5μm. 2. The chromium weight gain of a porous material is determined chiefly by its pore channel size and is only little affected by its porosity.