Porous Structures with Graded Pore Size

Porous Structures with Graded Pore Size 

It is readily predicted by Eq. (1) that the transport of ionic species can be much improved when the stmcture has graded pores. Schematically shown in Fig. 1(c) is a simplified stmcture with a graded pore size. The graded porous stmcture with large pores around the orifice makes the reactants in the bulk electrolyte quite accessible to the porous stmcture and at the same time allows the products to move out of it. 

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Porous Structures with Graded Pore Size... 

Figure 1. (a) Simplified porous structure comprising of nano-particles, (b) 1-D channeled porous slructme. (c) Porous siructme with a graded pore size. 

Experiments were started with the metal powder in order to reveal principal possibilities of laser sintering of powder layers deposited onto a substrate [2], In these experiments, the layer of Ni powder (with particle size about 0.5 pm) was deposited onto the surface of Ni substrate manufactured by traditional powder metallurgy (with particle size about 5 pm) and subjected to sintering by CW-Nd YAG laser (X = 1.06 pm). Layer thickness was about 2 pm. The joining of powder layer with the substrate was provided during sintering. The graded porous structure was formed on the surface as it is shown in Fig. 1 (the size of pores is about 2 pm for the sintered layer and 6 pm for the substrate). 

Four main types of porous silica adsorbents have been identified compacts of pyrogenic powders, precipitated silicas, silica gels, and zeolitic silicas. The importance of porosity relative to the adsorptive properties of each group is reviewed, with particular reference to the adsorption of nitrogen, argon, and water vapor. The differences in size and specificity of these adsorptive molecules may be exploited to explore the surface properties of each grade of silica. A notable feature cf Silicalite I, which is the best known of the zeolitic silicas, is its remarkable hydrophobic character. Furthermore, the uniform tubular pore structure of this microporous silica is responsible for other highly distinctive properties. 

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