Magnesium accelerated tests

In considering the corrosion of magnesium and its alloys it is important to examine the methods available for assessing corrosion tendencies and particularly those known as accelerated tests. Tests carried out by immersion in salt water or by spraying specimens regularly with sea-water are worthless as a means of determining the resistance of magnesium alloys under any other than the particular test conditions. Extrapolation to less corrosive conditions is not valid and even the assessment of the value of protective measures by such means is hardly possible. The reason is to be found in the fact that corrosion behaviour is directly related to the formation of insoluble... 

Differences between field-exposed magnesium (Mg) and accelerated tests... 

The same undesired effect—oxidative degradation catalyzed by impurities— was noticed when talc (hydrated magnesium silicate) was employed in such PP formulations up to 15 wt% [84]. The study concluded that the outdoor conditions concurred to the overall degradation, despite the low energy of the UV radiation as compared with the accelerated test. It was demonstrated that the presence of talc did not inhibit the degradation rate and the photochemical behavior was severely affected by the presence of the acidic rain. 

The properties of 1,1-dichloroethane are Hsted ia Table 1. 1,1-Dichloroethane decomposes at 356—453°C by a homogeneous first-order dehydrochlofination, giving vinyl chloride and hydrogen chloride (1,2). Dehydrochlofination can also occur on activated alumina (3,4), magnesium sulfate, or potassium carbonate (5). Dehydrochlofination ia the presence of anhydrous aluminum chloride (6) proceeds readily. The 48-h accelerated oxidation test with 1,1-dichloroethane at reflux temperatures gives a 0.025% yield of hydrogen chloride as compared to 0.4% HCl for trichloroethylene and 0.6% HCl for tetrachloroethylene. Reaction with an amine gives low yields of chloride ion and the dimer 2,3-dichlorobutane, CH CHCICHCICH. 2-Methyl-l,3-dioxaindan [14046-39-0] can be prepared by a reaction of catechol [120-80-9] with 1,1-dichloroethane (7). 

Accelerated shelf life tests take at least 48 hr or one week to provide results. More rapid predictions of beer stability are sometimes obtained using chemical precipitants such as ethanol [185] or formaldehyde [186]. Proteins can be precipitated with ammonium sulphate [187], magnesium sulphate, or gallic tannic acid [188]. 

To evaluate magnesium alloys both immersion and salt spray tests are often used. Table 7.6 shows corrosion rates obtained after different types of accelerated corrosion tests taken from the literature (52, 62, 63). The corrosion rates show a wide scatter. For some of the accelerated corrosion tests such as the immersion in NaCl solution the corrosion rates are extremely high. 

M. Jonsson and D. Persson, Accelerated corrosion tests for magnesium alloys Do they really simulate field conditions The Annual World Magnesium Conference, Warsaw, Poland (2008). 

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