Flat supports

Photo/Thermal Reactions. The fifth basic class of photopolymer chemistry that can be used in commercial applications is based more on physical changes in a polymer-based matrix than on chemical reactions. A recent application of this technology is the laser ablation (77) of an organic coating on a flat support to directly produce a printing plate. The availability of newer high energy lasers will allow more applications to be based on the photo/thermal mechanism. 

Other successful applications of RBS on flat supported model catalysts include such systems as Rh/ATCF/Al [38,39] and ZrCF/SiCVSi [40]. The reason that RBS... 

AFM in principle gives images of all surfaces, including those of a supported catalyst, provided the powder particles can be immobilized, for example in glue. It remains difficult, however, to tell the difference between a catalyst particle and features of the support. Model systems of particles on a flat support offer better opportunities, as Fig. 7.15 and the following example shows. 

Membrane extraction offers attractive alternatives to conventional solvent extraction through the use of dialysis or ultrafiltration procedures (41). The choice of the right membrane depends on a number of parameters such as tlie degree of retention of the analyte, flow rate, some environmental characteristics, and tlie analyte recovery. Many early methods used flat, supported membranes, but recent membrane technology has focused on the use of hollow fibers (42-45). Although most membranes are made of inert polymers, undesired adsorption of analytes onto the membrane surface may be observed, especially in dilute solutions and when certain buffer systems are applied. 

Tallmadge, J. A. A Theory of Entrainment for Angular Withdrawal of Flat Supports. AIChE J. 1971c, 17, 243-245. 

Other successful applications of RBS on flat supported model catalysts include systems such as RI1/AI2O3/AI [47, 48] and Zr02 [49], PtCo [50] and Cr on Si02/ Si(100) [51]. The reason why RBS is so effective with these systems is that they consist of heavy elements on top of a lighter support, with the fortunate consequence that peaks due to the elements of interest appear on a background of almost zero. 

Fig. 10.11. Steps for micro-contact printing. The stamp is first inked with a solution of a material that is capable of forming a self assembled monolayer (SAM) on the substrate that will be printed. In the case illustrated here, the ink is a millimolar concentration of hexadecanethiol (HDT) in ethanol. The substrate consists of a thin layer of Au on a flat support. Removing the stamp after a few...

A specimen, located at the sample plane, is supported on a flat support bench that is free to rotate about its perpendicular axis, which is located at the origin (see Figures 1.24 and 1.25). The rotation is such that the angle of the incident x-ray beam with respect to the sample plane is 0, and the angle between the diffracted beam and the incident beam is 20. 

For the preparation of high-quality membranes, also high quality supports are needed. It was decided that the project would start with the development of colloidal filtrated flat supports and centrifugal cast tubular supports, which have a higher degree of homogeneity than conventional die-pressed, tape-cast and extruded supports. The development of these new supports is described in chapter 4 of this thesis. 

In this work, two support shapes are of particular interest tubular and flat supports, which are currently the most used supports in membrane research. Apart from these shapes also ceramic multi-bore tubes and honeycomb structures are produced for membrane applications and recently a-alumina hollow fibre supports were developed as well [1],... 

Though the majority of this chapter is related to the production of tubular supports, a few comments on the preparation of flat supports will be made. Emphasis is put on the stabilisation of the suspensions used in the preparation of the supports. Experimental procedures are provided in more detail in chapter 4 of this thesis the present chapter mainly provides the basic knowledge for suspension preparation and shaping techniques. 

The porosity of the resulting flat supports was measured after firing of AKP-30 and AKP-15 at respectively 1100°C and 1150°C with the Archimedes method by immersion in mercury. 

Next to the experiments with modified silica on flat supports, also coating experiments of commercially available tubular a-alumina supports with state-of-the-art silica are described. 

To realise this, first very homogeneous OC-AI2O3 supports were prepared by using colloidal techniques. Colloidal filtration was used for the preparation of flat supports, while a centrifugal casting technique was developed to prepare highly smooth and round tubular supports. 

If a solid body is compressed by a normal force against a flat support and subjected to a tangential force it will start to move if... 

Sample The dosage and spreading of an emulsion on a flat support is difficult and requires special attention. A roughened support surface is recommended. 

Here, we also mention a composite system developed by Van der Puil et al. [90] in which an MFI (Silicalite-1) layer is completely covering a platinum-on-flat support catalyst. The zeolite layer is governing the acces to the platinum and this leads in the competitive hydrogenation of 1-heptene and 3,3-dimethyl-l-butene seeFigure 31 + 32) to highly selective conversion of 1-... 

Different supports are used, (see Section 10.6.4) with different geometry (discs or tubes), thickness, porosity, tortuosity, composition (alumina, stainless steel, silicon carbide, mullite, zirconia, titania, etc.), and symmetry or asymmetry in its stmcture. Tubular supports are preferable compared to flat supports because they are easier to scale-up (implemented as multichannel modules). However, in laboratory-scale synthesis, it is usually found that making good quality zeolite membranes on a tubular support is more difficult than on a porous plate. One obvious reason is the fact that the area is usually smaller in flat supports, which decreases the likelihood of defects. In Figure 10.1, two commercial tubular supports, one made of a-alumina (left side) and the other of stainless steel (right side) used in zeolite membrane synthesis, are shown. Both ends of the a-alumina support are glazed and both ends of the stainless steel support are welded with nonporous stainless steel to assure a correct sealing in the membrane module and prevent gas bypass. 

Firstly, the geometry of the support must be considered. The radial flow through a cylindrical support is quite different from the unidirectional flow encountered in flat supports. Fortunately, in most cases the compact layer thickness is small compared to the curvature radius of the support surface. The filtration process can then approximately be described as one-dimensional filtration [54]. 

This idea has been realized in the excellent study [39]. The quasi- crystalline monolayer of the protein from the thermophilic bacterium Sulfolobus acidocaldarius was prepared on the flat support. Then the deposition of metal (Ta/W) on the obtained layer of adsorbed protein was followed by the removal of both the protein and the metal deposited on the protein using the ion bombardment. As a result the regular network of metal islands with the lattice parameter 22 nm equal to the distance between the centres of the adsorbed proteins was obtained. The islands of metal have a diameter of 15 nm and a thickness of Inm. 

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