Abrasive scratches

The uses of CVD silicon dioxide films are numerous and include insulation between conductive layers, diffusion masks, and ion-implantation masks for the diffusion of doped oxides, passivation against abrasion, scratches, and the penetration of impurities and moisture. Indeed, Si02 has been called the pivotal material of IC s.1 1 Several CVD reactions are presently used in the production of Si02 films, each having somewhat different characteristics. These reactions are described in Ch. 11. 

Coupling agent Abrasion scratch" Microwave bacon (cycles) Boil-and-soak time (h)r... 

As with most photochromic lenses, the performance of plastic photochromic lenses is temperature-dependent. In addition to variable light attenuation, photochromic lenses offer protection against UV light. Photochromic plastics coated onto classical glass lenses provide abrasion/scratch resistance and highly functional antireflectivity. For further details, the reader is referred to a review article [61]. 

Chem. Descrip. Micronized modified polyethylene and PTFE Uses Lubricant, abrasion/scratch resist, aid for inks, paints/coatings incl. solvent- and water-based printing inks, lacquers and coatings applied on nonporous substrates, wood and leather finishes, coil and can coatings, industrial finishes, and low energy heat-set cover inks Features Provides abrasion, scratch and heat resist., smooth, silky feel, and surf, lubricity... 

Co-Cr-Mo + Co-Cr-Mo (McKee-Farrar) 0.013 mm/ 1.8x10 cycles NA Hip joint simulator 2.5 kN static load Lub bovine serum Duration 1.8x10 cycles Velocity = 30 cycles/min Abrasion, scratching. Max cup wear depth. Weightman et al (1972)... 

Surfaces with similar material composition or high compound tendency are particularly endangered. The consequences are cold welding, abrasion, scratches, holes, fretting, built-up edges, and even mold breakage (Table 5.5). 

OUTSTANDING PROPERTIES improves abrasion, scratch, scuff resistance increases slip, surface smoothness gloss, improves wear resistance, nonstick properties, lubricity frictional characteristics minimizes surface blemishes, improves chemical stain resistance ... 

Low-stress abrasion (scratching) is defined as wear that occurs clue to relatively light rubbing contact of abrasive particles with the metal. The criteria established for low-stress abrasion is that the forces must be low enough to prevent crushing of the abradant. Wear scars usually show scratches, and the amount of subsurface deformation is minimal. Consequently, the surface does not work harden appreciably. Parts such as screens, chute liners, blades, and belts that are exposed to sand slurries or abrasive atmospheres could experience low-stress abrasion. Many machine components such as bushings, seals, and chains that operate in dust will wear by low-stress abrasion. Figure 6(a) shows a siuface that was subjected to low-stress abrasion. 

Hardness. Glass hardness tests usually measure the resistance to abrasion by grinding or grit-blasting, resistance to scratching, or penetration by an indenter. The method to be used depends on expected service conditions. Knoop hardness (Table 4) is commonly used, because other methods usually fracture the glass. 

Abrasion Resistance. Porcelain enamel is the most scratch resistant and hardest of commercial coatings (see Hardness). This property is used to distinguish between porcelain enamel and organic enamel or painted coatings. The rate of abrasive wear in surface abrasion increases with time, and the subsurface abrasion which follows exhibits a higher, but constant rate of wear. Abrasion resistance can be evaluated by loss of gloss or weight (35). 

Each mechanism of breakage implies a different functional dependence of breakage rate on material properties. For the case of abrasive wear of ceramics due to surface scratching by loaded indentors, Evans Wilshaw [Acta Metallurgica, 24, 939 (1976)] determined a volumetric wear rate V of... 

Abrasive wear can be classified into three types. Gouging abrasion is a high stress phenomenon that is likely to be accomplished by high comprehensive stress and impact. Grinding abrasion is a high stress abrasion that pulverizes fragments of the abrasive that become sandwiched between metal faces. And erosion is a low-stress scratching abrasion. 

Colouring is not usually restricted to the surface but is throughout the mass so that damage due to scratching and abrasion is less obvious than with coated metals. 

Ritzel, n. (Mach.) pinion, ritzen, v.t. crack slit scratch etch cut. RitzhlLrte, /. hardness to scratching, -probe, /. abrasive hardness test, scratch test, -priifer, m. abrasive hardness tester, aclerometer. -verfahren, n. = Ritzharteprobe. -zahl, /. (scratch) hardness number. 

Schurf, n. scratch, abrasion hole, pit pros pecting. 

Figure 53.3 illustrates a pit in a stainless steel such as type 534 or 316 austenitic alloy. Pitting starts at heterogeneity in the steel surface, such as an outcropping sulfide inclusion, the shielded region beneath a deposit or even a discontinuity in the naturally present oxide film caused by a scratch or embedded particle of abrasive grit. This initiation phase of pitting corrosion may take seconds... 

Salt solutions When a zinc sheet is immersed in a solution of a salt, such as potassium chloride or potassium sulphate, corrosion usually starts at a number of points on the surface of the metal, probably where there are defects or impurities present. From these it spreads downwards in streams, if the plate is vertical. Corrosion will start at a scratch or abrasion made on the surface but it is observed that it does not necessarily occur at all such places. In the case of potassium chloride (or sodium chloride) the corrosion spreads downwards and outwards to cover a parabolic area. Evans explains this in terms of the dissolution of the protective layer of zinc oxide by zinc chloride to form a basic zinc chloride which remains in solution. 

Pseudomorphism has less desirable consequences, and usually means are sought to suppress it. If the substrate has been scratched, ground or abrasively polished, or if it has been cold rolled or cold formed, the surface is left in a peculiar state. Cold working reduces the surface grain size, and produces deformed, shattered and partly reoriented metal. It may produce microcrevices between the deformed grains, and, with some processes, non-metallic impurities and oxides are embedded in the surface. The disturbed state of the substrate is copied by a pseudomorphic electrodeposit with several consequences (Fig. 12.7). One is aesthetic it has often been noted that almost invisible abrasion of the substrate develops as more prominent... 

This group includes such items as surface hardness, i.e. scratch and abrasion resistance, adhesion and resistance to chipping, crazing and impact. All of... 

The hardness of an enamel surface is an important property for such items as enamelled sink units, domestic appliances, washing machine tubs which have to withstand the abrasive action of buttons, etc. On Moh s scale most enamels have a hardness of up to 6 (orthoclase). There are two types of hardness of importance to users of enamel, viz. surface and subsurface. The former is more important for domestic uses when one considers the scratching action of cutlery, pans, etc. whereas subsurface hardness is the prime factor in prolonging the life of enamelled scoops, buckets, etc. in such applications as elevators or conveyors of coal and other minerals. 

Currently, these tests are of no practical value to the designer and the only approach to the problem of scratch, mar, and abrasion resistance is to simulate actual performance needs. For optical purposes, a cast sheet in the allyl family of plastics known as CR39 has been used as a standard of comparison in evaluating scratch and mar resistance of a material. The CR39 is used for eye lenses and other optical products where the advantages of plastics are a consideration. Coatings have been developed for polycarbonate, acrylics, and other plastics that dramatically improve the scratch and mar resistance of these materials. 

Although hardness is a somewhat nebulous term, it can be defined in terms of the tensile modulus of elasticity. From a more practical side, it is usually characterized by a combination of three measurable parameters (1) scratch resistance (2) abrasion or mar resistance and (3) indentation under load. To measure scratch resistance or hardness, an approach is where a specimen is moved laterally under a loaded diamond point. The hardness value is expressed as the load divided by the width of the scratch. In other tests, especially in the paint industry, the surface is scratched with lead pencils of different hardnesses. The hardness of the surface is defined by the pencil hardness that first causes a visible scratch. Other tests include a sand-blast spray evaluation. 

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