Pellet microstructuring

It should be noted that similar results could be achieved by reducing the size of distinct catalyst and adsorbent particles in a conventional mixed fixed bed, insofar as pressure drop considerations do not militate against such an approach. The precise structuring of the catalytic activity and adsorptive capacity within the pellet can also be shown to be much less important than their integration, the reason being that a hybrid pellet at any given location in the fixed bed is exposed to a range of concentration conditions over the course of the cycle. Thus, it is next to impossible to 

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Figure 4. Effect of NaF addition on the metallization rate of pellets Microstructures of Reduction Pellets...

For the chemical reactor, the researchers used a nanoparticle catalyst deposited on metallic micro-structured foils. They tested Cu/ZnO and Pd/ZnO catalysts deposited on the microstructured foils. The Cu/ZnO catalyst was more active than the Pd/ZnO catalyst and had a lower selectivity to undesired carbon monoxide. However, because the Pd/ZnO catalyst was more stable, it was selected for use in their fuel processor. The Pd/ZnO carbon monoxide selectivity of the powder catalyst pressed into a pellet was lower than that of the nanoparticle catalyst deposited on the microstructured foils. This effect was attributed to contact phases between the catalyst and the metal foils. ... 

Figure 9-8 Microstructures of solid films and pellets. Variations can occur across a film or sphere as well as within individual particles in flie film or sphere.

Walker, C. T., Kameyama, T., Kitajima, S. Kinoshita, M. 1992. Concerning the microstructure changes that occur at the surface of U02 pellets on irradiation to high bumup. Journal of Nuclear Materials, 188, 73-79. 

One step closer to up-scaling to industrial environments is the multiple-bead reactor shown in Fig. 4.9. Here pellet-type catalyst carriers, so-called beads, are positioned in square containers. The beads are made of alumina and are 1 mm in diameter. Gases are passed over these beads through microstructured pore membranes in the cover and the base plate of the containers. 

If the compatibilizer is reactive, the rapid and effective melting and mixing will establish the proper conditions for a uniform molten-phase reaction to take place. Thus, by employing TSEs, polymer processors (compounders or product fabricators) can create customized, microstructured polymer systems, which we have coined as designer pellets (22), to best serve the special product property needs of their customers they are no longer solely dependent on polymer resin manufacturers. 

The conceptual breakdown in Fig. 1.9 (27) simply indicates the fact that in compounding, blending, and reactive processing, the base polymer(s) undergo two thermomechanical elementary-step experiences, and that the product of the first are value-added and microstructured pellets, while the second is used primarily for fabricating finished products. The important elementary steps for each experience, and the physical mechanisms that affect them, are different, because of the different objectives in each. 

Fig. 7.17. Extension of cycle times [t) due to microstructuring of hybrid catalyst-adsorbent pellets for the Claus and water-gas shift reactions compared to the use of comparable distinct catalyst and adsorbent pellets as a function of the Thiele modulus (< )) and Stanton number (St) [52]. In the water-gas shift reaction preloaded adsorbent is used to enhance the level of excess steam both with and without an additional steam supply in the reactor inlet.

The morphology or microstructure of powders and well-polished pellets was observed with TEM (H-800) and SEM (Hitachi X-650). Au coating was applied on the surfaces or fracture surfaces to prevent charging before observation and photo-taken. 

The sintered pellets were exposed to H2 at 750°C for 5 h, followed by XRD measurement and SEM observation to examine whether there is any change on both phase structure and microstructure after heat treatment in a strong reducing atmosphere. 

SEM photographs of the surfaces of the sintered samples are shown in Fig. 4 (A). The surface microstructure reveals uniform and fine grain growth about 2-3 pm. No pores were observed on the surface of the sample, but there were some pores from the fracture surface of the sample, as shown in Fig. 4 (C). The sintered density is 6.6 g/cm, which is over 95% of the theoretical value. The residual pores may be partly attributed to the agglomerates in the source powders that lowered the sinterability of the green bodies. It can also be seen that there are no great changes between the pellets sintered in air before and after heat treatment at 750°C for 5h in H2. This result is in aecordance with that of XRD. It confirms that the samples are chemically stable in H2 atmosphere at least below 750°C. 

Figure 4. Microstructure of the surfaces and fracture of LSGMn pellets. (A) LSGMn-1043 after sintering at I500°C in air without treatment in H2 at 750°C (B) with treatment in H2 at 750°C and (C) fracture in air.

Suction controlled oedometer tests were performed to gain insight into the characterization of the material, which exhibits a marked double structure a microstructure, which describes the dense aggregates of clay platelets and a macrostructure which includes the inter-aggregate and inter-pellet voids. An important feature of this material is the evolution of the microstructure as the mixture hydrates. 

The microstructure observation of the sintered ceramics surface was performed by means of scanning electron microscopy (SEM, JEOL JSM 6400, Japan). The crystalline phase of sintered ceramics was identified by X-ray diflfaction (XRD, RIGAKU D/max 2.B) with CuKa radiation (X=l. 541SA at 40 kV and 30 mA) and scanned from 20° to 70° with scanning speed of 4°/min. The bulk densities of the sintered pellets were measured by the Archimedes method. The dielectric constant ( ,) and the quality factor values (Qxf) at microwave frequencies were measured using the Hakki-Coleman dielectric resonator method which had been modified and improved by Courtney The dielectric resonator was positioned between two brass plates. Microwave... 

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