Accelerating factor

Oxygen corrosion involves many accelerating factors such as the concentration of aggressive anions beneath deposits, intermittent operation, and variable water chemistry. How each factor contributes to attack is often difficult to assess by visual inspection alone. Chemical analysis of corrosion products and deposits is often beneficial, as is more detailed microscopic examination of corrosion products and wasted regions. 

If the cavitation intensity is low and corrosion is a significant accelerating factor, appropriate inhibitors can be useful. Notable successes have been achieved with diesel engine cylinder liners. 

Dealloying is influenced by many factors. In general, any process that increases general corrosion will promote dealloying. However, specific acceleration factors may be further classified into one of three categories metallurgy, environment, and water chemistry. 

Coupled metal (wrought form) Uncoupled corrosion rale (mm/y) Acceleration factor- due to dissimilar metal coupling with Titanium Mild steel ... 

Corrosion rates relate to general corro.sion only and are average rates obtained over about one year s exposure, t Acceleration factors quoted for coupled metal corroding unless indicated by suffix (MS) for mild steel corroding. 

Organic acids Dilute solutions of organic acids, especially if well aerated, attack cast iron at uneconomical rates. Temperature and velocity are also accelerating factors. 

Kern et al83, 84 carried out hydrolyses of peptides, such as glycylvarylalanine, glycyltryptophan and bovine serum albumin, in the presence of polyethylenesulfonic acid 38 (HPES) and 37 (HPSt) in the aqueous homogeneous systems. The observed acceleration factors ranged between 3 to 50. 

Yoshikawa and Kim85, 86 hydrolyzed aminoacid esters ((3-alaninemethylester, etc.) with 37 (HPSt) and 38 (HPES). They found an accelerating factor of ca. 10. 

Sakurada et al.88, 145, 146 hydrolyzed aliphatic esters having various hydrophobicities with cation-exchange resins, Dowex 50 w, and found a close correlation between the accelerating factor and the degree of ester adsorption toward the resins. 

Anchimeric assistance in the solvolysis of /3-arylthiovinyl sulfonates was demonstrated by means of kinetic studies on model compounds (182). In a variety of solvents ranging from nitromethane and methanol to acetic acid, the /3-arylthiovinyl sulfonate 216 was shown to react 20 to 33 times faster than the triphenylvinyl sulfonate 217. Different accelerating factors were... 

FIGURE 34.23 Acceleration factor versus temperature. Phoenix field data point is shifted 5°K based on work published by Ahagon. (From Kaidou, H. and Ahagon, A., Rubber Chem. Technol., 63, 698, 1990.)... 

An acceleration factor of 31 means that reproducing the age of an average six-year-old tire in Phoenix would require -10 weeks in the oven at 70°C using air as the inflation media. The time can be shortened to about 8.5 weeks using 65°C and 50/50 N2/O2 inflation or seven weeks using 70°C and 50/50 N2/O2. Other conditions can be estimated from the different shift factors. 

Paroxysmal nocturnal hemoglobinuria (MIM 311770) Acquired defect in biosynthesis of the GPf structures of decay accelerating factor (DAF) and CD59. 

Sharma et al. [153] have devised a gentle accelerated corrosion test using a kinetic rate equation to establish appropriate acceleration factors due to relative humidity and thermal effects. Using an estimate for the thermal activation energy of 0.6 eV and determining the amount of adsorbed water by a BET analysis on Au, Cu and Ni, they obtain an acceleration factor of 154 at 65°C/80% RH with respect to 25 °C/35-40% RH. 

Although such acceleration factors were applied by Fisher et al. [129] in their discussion of the corrosion of Co alloys, there are only a few papers trying to establish the experimental acceleration factors for disk materials. One of these is the work of Novotny et al. [154], These authors observed that carbon-coated CoCr, CoPt, or CoP disks, when exposed to elevated humidity and temperature, show an accumulation of a corrosion product, similar to those seen on uncoated alloys, on the top surface of the carbon. For both overcoated and uncoated disks, oxides and hydroxides of cobalt were detected on the surface, but there was no detectable Cr, Pt, or P. The amount of Co was on the average less on the C-covered disks. The surface Co resulted... 

Examples of their results [154] are shown in the set of curves in Fig. 13. At a given humidity, the Co concentration increases with T the thermal activation energy is about 0.4 eV. At a given temperature, the corrosion increases with an increase in humidity. As the humidity changes from 30 to 90%, the corrosion rate increases about an order of magnitude. The data allow a calculation of the acceleration factors for a variety of conditions. For example, the acceleration factor for 90°C/90% RH with respect to 30°C/40% RH is calculated to be 150. If the product passes a 2-week exposure to 90 °C/90% RH, the test indicates that it will survive in excess of 6 years at 30 °C/40% RH. The values of the acceleration factors, however, may vary from film to film. 

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