Abrading

The immobility of the surface atoms of a refractory solid has the consequence that the surface energy and other physical properties depend greatly on the immediate history of the material. A clean cleavage surface of a crystal will have a different (and probably lower) surface energy than a ground, abraded, heat-treated or polished surface of the same material. 

The existence of anode and cathode areas can be seen by the following experiment. A few drops of phenolphthalein are added to a solution of potassium hexacyanoferrate(III) and hydrochloric acid added, drop by drop, until the solution is colourless. (The phenolphthalein turns pink due to hydrolysis of the potassium hexacyano-ferrate(III).) Drops of this solution, about 1 cm in diameter, are now placed on a sheet of freshly abraded steel when pink cathode areas and blue anode areas appear. 

An abrasive is a substance used to abrade, smooth, or polish an object. If the object is soft, such as wood, then relatively soft abrasive materials may be used. Usually, however, abrasive coimotes very hard substances ranging from naturally occuring sands to the hardest material known, diamond. 

The abihty of organically modified ceramics based on alumina, zkconia, titania, or siUca (and mixtures of each) to function as abrasion-resistant coatings has also been studied (62). Eor example, polycarbonate, when coated with an epoxy—aluminosihcate system, experiences a significant reduction in the degree of hazing induced by an abrader, as compared to uncoated polycarbonate. 

Henna can be used only to color hair with the exception of eyelashes, eyebrows, or generally ia the area of the eye. The label for products containing henna must caution the consumer not to use ia the area of the eye or on cut or abraded scalp. 

Health and Safety. The dermal toxicology of alkaline solutions of thioglycolic acid has been reviewed extensively (63—65). The reagent has been found harmless to normal skin when used under conditions adopted for cold waving. Some irritation is observed on abraded skin but this appears to be associated with the alkaline component of the waving solution (65). Hand protection is recommended for the professional hairdressers who routinely handle these products. 

In industiial metal finishing, pohshing is an abrading operation involving the use of coarse abrasives, which remove significant amounts of metal from a... 

Hoses must be made for anhydrous ammonia service 2500 kPa (348 psig) working pressure and stamped for this service. In locations where hoses may be abraded, wke braid armored or reinforced hose types should be used. Hose ends should have boss or other acceptable ak kon ferruled couplings. 

For dry traction more contact is desired and the stopping distance is directiy related, ie, the more contact area the shorter the stopping distance. A softer, more pHable compound conforms to the road surface topography. Too soft a compound (low mechanical strength) abrades more easily and can therefore acts as a roUer and not allow sufficient contact area to be maintained. This is not readily encountered in nominal tires and conditions but has been encountered in cases of extremely high torque conditions for very fast acceleration and sudden stops. 

Inflated Diaphragm Method (ASTM D3886). This method is appHcable both to woven and knitted fabrics. The specimen is abraded by mbbing either unidirectionally or multidirectionally against an abradant having specified surface characteristics. The specimen is supported by an inflated mbber diaphragm under a constant pressure. Evaluation of abrasion resistance can be either by determination of the number of cycles required to wear through the center of the fabric completely or by visual examination of the specimens after a specified number of cycles. 

The 3M Abrasion Test (51) is used to assess the durabUity of a protective fluorochemical finish by evaluating its resistance to abrasion and wear. The surface is abraded with an AATCC crockmeter fitted with sandpaper. 

Chelated complexes such as sodium zirconium lactate [15529-67-6] or ammonium zirconium carbonate [22829-17-0] and acidic forms such as zirconium hydroxy oxide chloride [18428-88-1] have been used in preparations in deodorants or for treatment for poison oak and poison ivy dermatitis. In such occasions, when the skin had been cut or abraded, a few users developed granulomas which have been identified as a delayed hypersensitivity to zirconium (99). These may take several weeks to develop, and commonly persist for 6 months to over a year. 

Attrition Loss. The tendency of a support body to be reduced to powder is termed susceptibiHty to attrition, and the measurement of such susceptibiHty is termed attrition loss. Attrition can occur when support bodies mb against one another and abrade the surface, such as during calcination in a rotary kiln or sizing on moving screens. 

Methylene chloride, appHed to both intact and abraded skin of rabbits in doses as large as 0.5 g/kg body weight per day, five times per week, for a period of 90 days, caused no apparent adverse effects. Absorption through the skin is not usually a ha2ard when good working practices are followed. 

Abrasive wear is encountered when hard particles, or hard projections on a counter-face, are forced against and moved relative to a surface. In aUoys such as the cobalt-base wear aUoys which contain a hard phase, the abrasion resistance generaUy increases as the volume fraction of the hard phase increases. Abrasion resistance is, however, strongly influenced by the size and shape of the hard-phase precipitates within the microstmcture, and the size and shape of the abrading species (see Abrasives). 

Because the melting temperature range of Ni—Cr alloy is 1220—1345°C, it is necessary to heat the investment molds to 800—935°C. The castings should not be pickled in acid because of their high nickel content and should be cleaned by sandblasting. The alloys are generally hard and are difficult to finish and to abrade for clinical adjustment in the mouth. 

Dental abrasives range in fineness from those that do not damage tooth stmcture to those that cut tooth enamel. Abrasive particles should be irregular and jagged so that they always present a sharp edge, and should be harder than the material abraded. Another property of an abrasive is its impact strength, ie, if the particle shatters on impact it is ineffective if it never fractures, the edge becomes dull. Other desirable characteristics include the abiUty to resist wear and solvation. 

Dental abrasives can be classified either according to their use or according to the degree of their abiUty to abrade (see Dentifrices). The use classification, adopted for the ADA specification no. 37 for powdered dental abrasive materials, is based on removal of stain from natural teeth or on restorations of all types. Several abrasives are used in dentistry in a variety of grit sizes and shapes. 

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