Sheet forming device, commercial

In paper chromatography we use filter paper, marketed for this purpose. It comes usually in the form of a 2-5 cm-wide tape, from which a strip of the necessary length can easily be cut. The more modern technique of thin layer chromatography (TLC), makes use of thin sheets of aluminium oxide, silica-gel, cellulose or some other material, supported by a metal sheet or a polymer. Chromatographic thin layers can be prepared in the laboratory from commercially available adsorbents. A thick suspension of these is made with water (usually a 2 1 w/w mixture of water adsorbent is made up) and this is then spread on a metal plate with a suitable spreader device. Techniques vary from device to device, and the instructions of the manufacturer should be followed whenever thin layer plates are to be prepared. Ready-made thin layer sheets are also available commercially. These contain the active material spread on a plastic support. Thin-layer chromatographic materials, especially ready-made plates, are much more expensive than chromatographic paper, but normally offer faster and sharper separations than the paper. The procedures described in Section VI.20 can be carried out both on a slow chromatographic paper (e.g. Whatman No. 1) or on a cellulose thin layer (e.g. Whatman cellulose). 

Membranes are available in sheet, roll, disk, capsule, cartridge, and hollow-fiber formats. For sample filtration, disk-format membranes are the most popular devices. Disks are sold in loose form or packed in disposable syringe filters or cartridges common diameters commercially available are 3, 7, 13, 25, 47, and 96 mm, or even larger. Samples are filtered by manually applying a positive pressure or in a vacuum manifold. 

UF membranes are mnde commercially in sheet, capillary, and tubular forms, Sheet membrane is used in plate-and-fiame devices, slack devices, and spiral elements. Capillary membranes are generally 0.4-1 mm diameter, are self-supporting, and are pressurized from inside. Usually, they are mnde with a skin on both inside and outside surfaces so that they can be pressure reversed for cleaning. Tubular devices are cast on supports and are generally in the 10-25 mm diameter moge. 

A dot-matrix printer is the first widely commercialized product using ceramic actuators. Each character formed by such a printer is composed of a 24 x 24 dot matrix. A printing ribbon is subsequently impacted by a multiwire array. A sketch of the printer head appears in Figure 4.1.28a [51]. The printing element is composed of a multilayer piezoelectric device, in which 100 thin ceramic sheets 100 xm in thickness are stacked, together with a sophisticated magnihca-tion mechanism (Fig. 4.1.28b). The magnihcation unit is based on a monolithic... 

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