Abrasive Procedures

The electrochemical detector in the form described above is extremely sensitive but suffers from a number of drawbacks. Firstly, the mobile phase must be extremely pure and in particular free of oxygen and metal ions. A more serious problem arises, however, from the adsorption of the oxidation or reduction products on the surface of the working electrode. The consequent electrode contamination requires that the electrode system must be frequently calibrated to ensure accurate quantitative analysis. Ultimately, the detector must be dissembled and cleaned, usually by a mechanical abrasion procedure. Much effort has been put into reducing this contamination problem but, although diminished, the problem has not been completely eliminated particularly in the amperometric form of operation. Due to potentially low sensing volume the detector is very suitable for use with small bore columns. 

Technical error during the treatment of stretch marks using an abrasive procedure (see Chapter 21). Typically, a halo of hyperpigmentation surrounds the depigmented area, which in turn surround a scar response. Hyperpigmentation develops where the peel solution goes slightly deeper than it should, and scars form where the peel is much too deep. 

Pigmented coatings that had been exposed In Florida for 2 years were depth profiled, via the abrasion procedure described In the Experimental Section. One part of the coating was exposed to sunlight and the second part was protected from sunlight but exposed to all other elements. Seventeen and twelve samples were collected for the exposed and covered portions of the coating respectively and analyzed by diffuse reflectance Infrared... 

Carbon fiber-epoxy composites (A) Solvent wipe (MEK, toluene, trichloroethylene, etc.) (B) Use peel ply during initial curing. (C) See Ref. 15 for the effect of abrasion procedures. See also Refs. 16 and 17. (A) Lightly abrade with medium-grit emeiy paper. Avoid exposing the reinforcing fibers. (A) Wipe with solvent. Check surface by water break test. Retreat, if necessaiy. 

Knoop developed an accepted method of measuring abrasive hardness using a diamond indenter of pyramidal shape and forcing it into the material to be evaluated with a fixed, often 100-g, load. The depth of penetration is then determined from the length and width of the indentation produced. Unlike WoodeU s method, Knoop values are static and primarily measure resistance to plastic flow and surface deformation. Variables such as load, temperature, and environment, which affect determination of hardness by the Knoop procedure, have been examined in detail (9). 

Procedure for Fdabihty of Abrasive Grain," ANSI StandardB74.8-1987, American National Standards Institute, New York, 1987. 

To remain safe and efficacious on the eye, contact lenses must maintain clear and wetted surfaces, provide an adequate supply of atmospheric oxygen to and adequate expulsion of carbon dioxide from the cornea, allow adequate flow of the eye s tear fluid, and avoid excessive abrasion of the ocular surface or eyeflds, all under a variety of environmental conditions. The clinical performance of a contact lens is controlled by the nature of the lens material the lens design the method and quaUty of manufacture the lens parameters or specifications prescribed by the practitioner and the cleaning, disinfection, and wearing procedures used by the patient. 

Mechanical cleaning includes scrubbing, scraping, brushing, mechanical shocking, and ultrasonic procedures. Scrubbing with a bristle brush and a mild abrasive is the most widely used of these methods the others are used principally as supplements to remove heavily encrusted corrosion products before scrubbing. Care should be used to avoid the removal of sound metal. 

This review concerns the long-term behavior of plastics when exposed to conditions that include continuous stresses, environment, excessive heat, abrasion, and continuous contact with liquids. This subject has been reviewed in Chapter 2 (LONG-TERM LOAD BEHAVIOR) but since it is a very important subject the review is continuing. Tests such as those outlined by ASTM D 2990 that describe in detail the specimen preparations and testing procedure are intended to produce consistency in observations and records by various manufacturers, so that they can be correlated to provide meaningful information to product designers. 

In friability tests the material s susceptibility to attrition is evaluated. But it is not as simple as it may seem at first to select the suitable test procedure. In this context Pell (1990) gave a simple thought experiment to illustrate the difficulties If we took a batch of rubber stoppers and a batch of diamonds, and rubbed them on abrasive paper, we would conclude that the diamonds were more attrition resistant. If we instead struck the particles with a hammer we would conclude that the rubber were more attrition resistant. So, different test methods can rank materials differently with respect to their attritability. This effect was for example observed by Knight and Bridgwater (1985). They subjected spray-dried powders to a compression test, a shear test and a test in a spiral classifier. They found that each test gave a different ranking of the materials. Obviously, there is no... 

Some workers repeat this procedure with a range of abrasives of different particle sizes, starting with the coarsest and finishing with the smallest. 

The most convenient method is ultrasonic treatment with a subsequent solvent rinse of the surface. Other intermediate procedures are abrasive scrubbing, filing, or detergent cleaning. 

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