Surface deterioration

Gear tooth surface deterioration Low oil viscosity and/or excessive... 

Gear tooth surface deterioration Misalignment, high sliding velocity... 

Transparent guards for foodstuffs, machines and even baby incubators may be fabricated simply from acrylic sheet. It should, however, be pointed out that due to rather rapid surface deterioration and the lack of sparkle the material is not ideally suited as a cover for displayed goods. 

Common packaging materials are a potential source of aggressive substance s, and careful selection is recommended to avoid surface deterioration. Where paper is in contact with aluminium, the chloride content should be below 0-05 7o, sulphate content below 0-25 7o, copper content below 0-01% and the pH of aqueous extracts in the range pH 5-5-7-5, in order to avoid corrosion in damp conditions. Papers and felts used in building applications should also conform to this specification as a minimum requirement and be of the highest quality, since metallic copper found in materials of inferior origin can result in severe local galvanic attack of aluminium. 

In the pyrot area, paraffin is widely used in the manuf of book and wooden matches, as a protective coating to counteract possible surface deterioration of metal powders, as a lubricant and waterproofing agent for the interior surfaces of kraft paper flare and signal cases, and as a binder which tends to fill interstices between particles on press loading (Ref 7, pp 69, 71, 302 316)... 

Physical deterioration includes compaction by creeping and surface deteriorations by scratching and vibration. Creeping is accelerated at higher temperatures and pressures, resulting in the membrane compaction. This phenomenon is well analyzed and the membrane characteristics of compaction can be estimated in terms of m-value. Scratching and vibration can develop the microscopic defects in the surface structure of membranes, and give poor performances. We discussed this type of deterioration in Mexico in 1976 ( ). 

Sun checking - Surface deterioration in the form of cracks, checks or crazing caused by exposure to direct or indirect sunlight. 

Weathering - A surface deterioration of a rubber article during outdoor... 

Failure may be mechanical, due to wear, abrasion and erosion, britle fracture, surface deterioration, cyclic loading, embrittlement, thermal or pressure shock, or fatigue. Failure may also be chemical, in essence due to corrosion. 

Graham, D.E., Phillips, M.C. 1979. Proteins at liquid interfaces. I. Kinetics of adsorption and surface deterioration. J. Coll. Interface Sci. 70, 403-414. 

A detailed long-term study of the photochemical behaviour of 95 (R = H) revealed that after several thousands of hours of accelerated ageing, surface deterioration becomes noticeable [342]. This deterioration was due to some photochemical oxidation of the methyl methacrylate units. The benzotriazole chromophore moiety remained unchanged. 

Keep hoses from kinking or being rubbed. Rinse them often, inside and outside, to prolong hfe. During the off season, store the unit out of the sun. Replace hoses at the first sign of surface deterioration (cracking or checking). 

Figure 1.33 Detail of old pressed amber beads, showing surface deterioration.

Surface deterioration displaying crazing may indicate very old, oxidised amber. The presence of white powder with the crazing indicates copal (Fig. 1.35). 

Copal is generally paler than amber, and is often the pale yellow colour of dry sherry (Fig. 1.34). Having been produced in the same way as amber it, too, can contain lots of flora and fauna inclusions. Copal is less stable than amber and the surface deteriorates relatively quickly, displaying the typical crazing which produces a whitish powder, sometimes referred to as dandruff (Fig. 1.35). The surface of amber can also craze with time, but the pattern is darker and does not produce white powder. 

A microtomed transverse wood face was exposed to UV light for 500 h. Surface deterioration of the exposed wood surface was observed readily from the SEM micrograph (Figure 10). The cell walls were separated at the middle lamella zone. In the extreme case, the secondary wall almost collapsed. Roughening of the surfaces could... 

Also has greater resistance to chemical attack and is less liable to surface deterioration with age. 

Inour T, Ishiwata H, Yoshirhira K. 1987. Chemical, physical and microbiological indexes to the surface deterioration of melamine resin. J Food Hyg Soc Jpn 28 348-353. 

Photo 2c is a photomicrograph of IPS that contained the combination of light stabilizers (LS I and LS II) which was exposed outdoors in Florida for six months. Note the minimal amount of surface deterioration. Some surface dirt is present in the photo. 

After 9 months of outdoor exposure in Florida (Figure 5), and even after 12 months (Figure 6), the SEM photomicrographs of the IPS (impact polystyrene) show minimal surface deterioration for the samples that contain 0.5% LS I and 0.5% LS II, while the samples that contain no light stabilizers show extreme surface erosion and the presence of mildew. 

This erosion or weathering is not to be confused with decay. Decay is caused by fungi and can lead to rapid deterioration throughout the volume of the wood. Weathering, on the other hand, is a surface deterioration and, although the initial color changes can be seen within days or even hours, the surface erosion proceeds very slowly. The erosion rate for solid wood in temperate zones is in the order of 1/8 to 1/2 inch per century and depends mainly on amount of UV exposure and the wood species (1, 2). Other degrading factors include moisture, mechanical abrasion, temperature, and pollution (3). 

Not all v/oods i< y show a predisposition to invasion by disease pathogens and insects. As Scheffer and Cowling (51.) pointed out, woods do vary in the extent to which they will inherently resist heartwood decay. Certain types of oak and redwood are resistant to decay while some pines, birches and hickories are slightly or not resistant to heartwood decay. Two of the members of this slightly or not resistant decay category did show surface deterioration in work done by Banks et al. (49). It seems feasible that wood from these trees could be affected by acid rain and possibly other pollutants in combination with light and water. The result of this multiple factor interaction may then be impacted by insects or diseases. 

Fretting corrosion occurs where there is friction, generally caused by vibrations, between two metal surfaces. The debris formed by fretting corrosion accelerates the initial damage done by contact welding. Vibrations cause contact welds to break with subsequent surface deterioration. Debris formed acts to accelerate this form of corrosion by serving as an abrasive. Fretting corrosion is especially prevalent in areas where motion between surfaces is not foreseen. 

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