Porous plastic tubes

One example of a liquid-based ion-selective electrode is that for Ca +, which uses a porous plastic membrane saturated with di-(n-decyl) phosphate (Figure 11.13). As shown in Figure 11.14, the membrane is placed at the end of a nonconducting cylindrical tube and is in contact with two reservoirs. The outer reservoir contains di-(n-decyl) phosphate in di- -octylphenylphosphonate, which soaks into the porous membrane. The inner reservoir contains a standard aqueous solution of Ca + and a Ag/AgCl reference electrode. Calcium ion-selective electrodes are also available in which the di-(n-decyl) phosphate is immobilized in a polyvinyl chloride... 

The principle reference electrodes used in the onshore and offshore industries have remained unchanged. The CU/CUSO4 cell is used almost exclusively onshore in the form based on the plastic tube and porous wooden plug illustrated in Fig. 10.40, although certain potential survey instruments have... 

Tensiometer Measures the matric potential of a given soil, which is converted to soil moisture content Commonly consists of a porous ceramic cup connected to a pressure-measuring device through a rigid plastic tube... 

Tubular - Manufactured from ceramic, carbon, or any number of porous plastics, these tubes have inside diameters ranging from 1/8 inch up to approximately 1 inch. The membrane is typically coated on the inside of the tube, and the feed solution flows through the interior from one end to the other, with the "permeate" or "filtrate" passing through the wall to be collected on the outside of the tube. 

Nicotine is contained in an impregnated porous polyethylene plug inside a plastic tube, and is used in the same way as a cigarette, with puffs taken as desired. 

The tubular reverse osmosis device is shown in Figure 4.10. The tube serves as the pressure vessel and the membrane is installed inside the tube. Tubes with inside diameters of % and 1 inch have been used. Uniformly porous fiberglass reinforced plastic tubes have been used and nonporous but perforated copper, stainless steel and fiberglass tubes have also been successfully used. The membrane can be bonded to the tube in which case it is cast in situ or the membrane can be loose. The loose membrane is cast in sheet form and a cylindrical section is formed and placed in the tube. Packing densities for the Vi-inch diameter tube are about 100 square feet per cubic foot and about 50 square feet per cubic foot for the 1-inch diameter tube. 

As an alternative to the use of a porous disk as a rigid supporting medium, it is possible to immobilize liquid exchangers in tough I VC membranes. In this type of electrode, the liquid ion exchanger and PVC are dissolved in a solvent such as tetrahydrofuran. The soivcnl is evaporated to leave behind a flexible membrane lhal can be cut. shaped, and bonded to the end of a glass or plastic tube. Membranes formed in this way behave in much the same way is those in which the ion exchanger is encased as a ljt uid in the pores of a disk. Most liquid-membrane electrodes arc of this newer type. 

F, porous plastic filters E. PTFE tubings with flanged ends and R. sorbent packing... 

In contrast to capillaries and hollow fibers, tubular membranes are not self-supporting. Such membranes are placed inside a porous stainless steel, ceramic or plastic tube with the diameter of the tube being, in general, more than 10 mm. The number of tubes put together in the module may vary... 

In such cases, the reference electrode can be extended by a long salt bridge which consists of a flexible plastic tube with a porous plug at its end and filled with a high conductivity solution compatible with the reference electrode. The size of the plug will be decided by two considerations, the resistance of the plug through the electrolyte and the uniqueness of the potential that the cell measures. 

The tubular positive plate uses rigid, porous fiber glass tubes covered with a perforated plastic foil as the active material retainer (Fig. 2). Dry lead oxide, PbO, and red lead, Pb O, are typically shaken into the tubes which are threaded over the grid spines. The open end is then sealed by a polyethylene bar. Patents describe a procedure for making a type of tube for the tubular positive plate (90) and a method for filling tubular plates of lead—acid batteries (91). Tubular positive plates are pickled by soaking in a sulfate solution and are then cured. Some proceed directiy to formation and do not requite the curing procedure. 

Rigid Porous Media These are available in sheets or plates and tubes. Materials used include sintered stainless steel and other metals, graphite, aluminum oxide, silica, porcelain, and some plastics—a gamut that allows a wide range of chemical and temperature resistance. Most applications are for clarification. 

External-Cake Tubular Filters Several filter designs are available with vertical tubes supported by a filtrate-chamber tube sheet in a vertical cylindrical vessel (Fig. 18-115). The tubes may be made of wire cloth porous ceramic, carbon, plastic, or metal or closely wound wire. The tubes may have a filter cloth on the outside. Frequently a filter-aid precoat will be applied to the tubes. The prefilt slurry is fed near the bottom of the vertical vessel. The filtrate passes from the outside to the inside of the tubes and into a filtrate chamber at the top or the bottom of the vessel. The sohds form a cake on the outside ofthe tubes with the filter area actually increasing as the cake builds up, partially compensating for the increased flow resistance of the thicker cake. The filtration cycle continues until the differential pressure reaches a specified level, or until about 25 mm (1 in) of cake thickness is obtainea... 

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