Gauze manufacture

Among the first dermal dosimeters used in exposure research were 4 x 4-in cellulose or gauze patches which were pinned to the outer and inner surfaces of clothing or vests which farm workers would wear during the application or re-entry phase of the smdy. These patches were easy to manufacture and when pinned to the shirt or pants of the worker made for an easily used dosimeter pad. The major advantage to the use of the patch to estimate worker exposure was this method s ability to differentiate the relative contributions of pesticide residues to different parts of the worker s body. This sampling technique in turn could lead to recommendations (i.e., the use of... 

In the past, 4 x 4 in cotton patches (gauze or cellulose) have been used to estimate face and neck exposure. The patches are designed and manufactured as described above and are pinned or attached with Velcro to the back and front of a hat or protective headgear of the worker. When the exposure period is complete, the patches are removed, and... 

These catalysts are manufactured as smooth wires with no internal pores and then woven into gauze pads. Mechanical rigidity is important since the reactors are usually large in diameter (i.e., 4-12 ft) and are used in the reactor with minimum physical support. Furthermore, the conditions of operation are quite severe with respect to temperature and corrosion, and thus metallurgical integrity must be maximized. The most important properties are the purity of composition, wire diameter, and mesh size as well as mechanical strength. 

The manufacture of nitric acid by the oxidation of ammonia on platinum-type metal gauzes uses a technology which has change little since its first introduction in 1902. Although the conversion proceeds with an efficiency in excess of 90%, the loss of... 

Not all catalysts need the extended smface provided by a porous structure, however. Some are sufficiently active so that the effort required to create a porous catalyst would be wasted. For such situations one type of catalyst is the monolithic catalyst. Monolithic catalysts are normally encountered in processes where pressure drop and heat removal are major considerations. Typical examples include the platinum gauze reactor used in the ammonia oxidation portion of nitric acid manufacture and catalytic converters used to oxidize pollutants in automobile exhaust. They can be porous (honeycomb) or non-porous (wire gauze). A photograph of a automotive catalytic converter is shown in Figure CD 11-2. Platinum is a primary catalytic material in the monolith. 

In some cases a catalyst consists of minute particles of an active material dispersed over a less active substance called a support. The active material is frequently a pure metal or metal alloy. Such catalysts are called supported catalysts, as distinguished from unsupported catalysts, whose active ingredients are major amounts of other substances called promoters, which increase the activity. Examples of supported catalysts are the automobile-muffler catalysts mentioned above, the platinum-on-alumina catalyst used in petroleum reforming, and the vanadium pentoxide on silica used to oxidize sulfur dioxide in manufacturing sulfuric acid. On the other hand, the platinum gauze for ammonia oxidation, the promoted iron for ammonia synthesis, and the silica-alumina dehydrogenation catalyst used in butadiene manufacture typify unsupported catalysts. 

Topical Not for ophthalmic use for skin disorders apply directly to affected area or put on gauze or bandage, which is then applied to the skin for mucous membrane use apply to desired area using manufacturer s insert administer the lowest dose possible that still provides anesthesia. 

Metal films and powders are scarcely applied in practical catalysis, but gauzes are used, for example, in the oxidation of NO for the manufacture of nitric acid. The Pt catalyst is so active that the rate of reaction is largely determined by how fast the reactants are transported through the gas phase to the gauze surface therefore, there is little practical incentive to increase the surface area of the metal by dispersing it on a support. Occasionally, metals are used as porous solids with internal surface areas of 10 mVkg or more. Porous Raney nickel particles are used for hydrogenation of fats. The pore structure in the nickel is formed by extraction of A1 from a Ni— A1 alloy with NaOH. 

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