Degradation surfaces

The most common form of corrosion is uniform corrosion, in which the entire metal surface degrades at a near uniform rate (1 3). Often the surface is covered by the corrosion products. The msting of iron (qv) in a humid atmosphere or the tarnishing of copper (qv) or silver alloys in sulfur-containing environments are examples (see also SiLVERAND SILVER ALLOYS). High temperature, or dry, oxidation, is also usually uniform in character. Uniform corrosion, the most visible form of corrosion, is the least insidious because the weight lost by metal dissolution can be monitored and predicted. 

Homma, H., Kuroyagi, T., Izumi, K., Mirley, C.L., Ronzello, J. and Boggs, S.A., Evaluation of surface degradation of silicone rubber using thermogravimetric analysis, Proc. Int. Symp. Electr. Insul. Mater., 2nd. 1998, 1, pp. 631-634. 

Restall, J. E., Surface Degradation and Protective Treatments. In Developments in Gas Turbine Materials - /, Meetham, G. W. (ed). Applied Science Publishers, London, ch. 10 (1981)... 

Upadhyay et al. [98] used primarily correlated XPS and water contact angle measurements to study the surface degradation and recovery of amorphous films of a PMMA and a poly (aryl ether ether ketone) (PEEK). Surface modification of the films was carried out in a dielectric barrier discharge (DBD) unit, samples being treated with different dose levels of dielectric discharge. The modified (treated) samples were then stored for one month and re-examined. Figure 35 shows C(ls) and 0(1 s) XPS envelopes and their curve-fitting deconvolutions,... 

The economical use of material, the almost non-destructive nature, cheapness and simplicity make hardness measurements very attractive for monitoring surface degradation. A single test piece can be used for successive ageing periods, improving reproducibility and reducing the space required for exposure. 

We also note two reports on the degradation of stacked films of oriented PET. In the first [36], photodegradation is said to be two-step in nature with weak links cleaving first followed by a much slower cleaving of the strong links . The chain scission process was tracked versus exposure time by measurement of solution viscosity [37], In the second paper [38], the surface nature of the degradation was reported and the rationale elucidated for why surface degradation causes overall mechanical failure limited by that layer, much as we have discussed in the impact properties of the PECT (see above). 

A recent study, however, has shown that aminopeptidase activity is present on the surface of porcine buccal mucosa, and that various aminopeptidase inhibitors, including amastatin and sodium deoxycholate, reduce the mucosal surface degradation of the aminopeptidase substrate, leucine-enkephalin [149], Since the peptidases are present on the surface of the buccal mucosa, they may act as a significant barrier to the permeability of compounds which are substrates for the enzyme. In addition to proteolytic enzymes, there exist some esterases, oxidases, and reductases originating from buccal epithelial cells, as well as phosphatases and carbohydrases present in saliva [154], all of which may potentially be involved in the metabolism of topically applied compounds. 

The technical consequences of weathering are similar to heat ageing with more pronounced surface degradation and notably ... 

The conversion of parathion is affected by soil constituents in the order kaolinite > smectite > organic matter and is related inversely to the adsorption affinity of these materials for this contaminant (Mingelgrin and Saltzman 1977). Although the extent of hydrolysis differs among soils, it is apparent that soil-surface degradation of parathion is caused by hydrolysis of the phosphate ester bond. The presence of water in the soil-parathion system led to a decrease in the surface-induced degradation of the organic molecule and diminished the effect of natural soil properties on its persistence. 

Figure 6.11. ARUPS spectra taken at kp showing the etfect of photon-induced surface degradation hco 25 eV, r 61 K). Reprinted with permission from M. Sing, U. Schwingenschlolgl, R. Claessen, P. Blaha, J. M. P. Carmelo, L. M. Martelo, P. D. Sacramento, M. Dressel and C. S. Jacobsen, Physical Review B, 68, 125111 (2003). Copyright (2003) by the American Physical Society.

Varshney et al. (3) prepared biocompatible and bioerodable poly(lactide-co-succinic anhydride) derivatives having a Young s modulus between about 1.5 and 3, which had enhanced surface degradation rates. 

It has been proposed that surface degradation after UV exposure promotes brittleness and may therefore influence the failure mechanism. This is of particular importance for ABS pressure pipes that are continuously under static loading. A methodology for estimating the lifetime of UV exposed ABS pipes has been proposed (62). 

Less is known about the combustion pathway. Using IR spectroscopy, formate, carboxylate, bidentate carbonate, monodentate carbonate, and acetate bands have been observed when butene is adsorbed on [Pg.180]

Brittle Surface Degradation and Mechanism of Crack Nucleation under Indentation... 

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