Magnesium corrosion characteristics

Properties. Uranium metal is a dense, bright silvery, ductile, and malleable metal. Uranium is highly electropositive, resembling magnesium, and tarnishes rapidly on exposure to air. Even a poHshed surface becomes coated with a dark-colored oxide layer in a short time upon exposure to air. At elevated temperatures, uranium metal reacts with most common metals and refractories. Finely divided uranium reacts, even at room temperature, with all components of the atmosphere except the noble gases. The silvery luster of freshly cleaned uranium metal is rapidly converted first to a golden yellow, and then to a black oxide—nitride film within three to four days. Powdered uranium is usually pyrophoric, an important safety consideration in the machining of uranium parts. The corrosion characteristics of uranium have been discussed in detail (28). 

Olsen, A. L. (1991), Corrosion characteristics of new magnesium alloys. Translation of paper presented at the Deutscher Verband Fur Materialfor-schung u. Priifung e. v. Bauteil 91, Berlin, 1991,... 

This chapter presents electrochemical reactions and corrosion processes of Mg and its alloys. First, an analysis of the thermodynamics of magnesium and possible electrochemical reactions associated with Mg are presented. After that an illustration of the nature of surface films formed on Mg and its alloys follows. To comprehensively understand the corrosion of Mg and its alloys, the anodic and cathodic processes are analyzed separately. Having understood the electrochemistry of Mg and its alloys, the corrosion characteristics and behavior of Mg and its alloys are discussed, including self-corrosion reaction, hydrogen evolution, the alkalization effect, corrosion potential, macro-galvanic corrosion, the micro-galvanic effect, impurity tolerance, influence of the chemical composition of the matrix phase, role of the secondary and other phases, localized corrosion and overall corrosivity of alloys. 

Song G.-L, Song S. (2006b), Corrosion characteristics and Bio-compatibility of magnesium , 2006 Beijing International Materials Week (2006BIMW), C-MIRS, June, Beijing 2006, A-56. 

LSI Langelier Saturation Index indicates the corrosive (negative) or scale-forming (positive) characteristics. Hardness Expressed as CaC03, this is the total calcium and magnesium salts in the water. Hardness figures given as ppm or mg/1 are important, as the compounds of these two elements are responsible for most scale deposition. 

The concentrations of specific elements can be useful indicators of some coal quality characteristics. Huggins et al. (5) and Reid (6) demonstrated that the aluminum, silicon, potassium, calcium, magnesium, and sodium values of a coal ash can be used to estimate ash fusion temperature. The Si/Al ratio of coal ash has been used as an indicator of the abrasiveness of a coal. Sodium is a major contributor to boiler fouling and metal corrosion and contributes to agglomeration in fluidized-bed reactors. Trace elements are generally defined as those elements with concentrations below 0.1 wt. % (1000 ppm). Despite concentrations in the parts-per-million range, certain trace elements can have a significant impact on coal... 

Pure magnesium substrates were chemically pretreated at 70 °C with a Ca/Na phosphate solution to obtain a porous brushite layer and subsequently PEO at a voltage of 450 V, a frequency of 1000 Hz and a duty cycle of 40% to deposit strontium-containing hydroxyapatite (Lu et al., 2014). Figure 7.59 shows that the Sr-hydroxyapatite coating provided improved corrosion resistance in HBSS to the pure Mg substrate. The characteristic corrosion parameters are presented in Table 7.6. 

The lower limits of relative humidity near which the corrosion rate becomes negligible depend on the characteristics of the concrete, on the amount of chlorides in the concrete and the type of salt they originate from. In any case, this limit is at much lower relative humidity than that which makes carbonation-induced corrosion negligible. In the presence of high chloride contents, above all with hygroscopic salts admixed like calcium or magnesium chloride, even for relative humidities of 40-50%, the corrosion rate can be up to 2 pm/y. 

Aluminum and aluminum-zinc alloy anodes have become the preferred sacrificial anodes for the cathodic protection of offshore platforms. This preference is because aluminum anodes demonstrate reliable long-term performance when compared with magnesium, which might be consumed before the platform has served its useful hfe. Aluminum also has better current/weight characteristics than zinc. Weight can be a major consideration for large offshore platforms. The major disadvantage of aluminum for some applications, for example, the protection of painted ship hulls, is that aluminum is too corrosion resistant in many environments. Aluminum alloys will not corrode reliably onshore or in freshwater [37]. In marine... 

A hydroxide or carbonate of an alkali metal (e.g., lithium, sodium, potassium, etc), the aqueous solution of which is characteristically basic in chemical reactions. The term may be extended to apply to hydroxides and carbonates of barium, calcium, magnesium, and the ammonium ion. The term alkali should be viewed in relation to the terms corrosive, bases and acids. The EPA defines corrosivity in terms of pH (i.e., wastes with pH <2 or 2.5) or in terms of ability to corrode steel (SAE 20) at a rate of > 6.35 mm (0.250 in.) per year at a temperature of 55° C (13° F). This discussion will address corrosivity as it applies to acids and caustics (i.e., alkali materials). Acids are compounds that yield H ions (actually HjO " ions) when dissolved in water. Common industrial acids include acetic, nitric, hydrochloric, and sulfuric acids. The terms concentrated and dilute refer to the concentrations in solution. Mixing a concentrated acid with enough water will produce a dilute acid. For example, a bottle of concentrated HCl direct from the manufacturer is approximately 12N in HCl, while a solution of HCl used in a titration may be only 0.5N. The latter is a dilute acid solution. 

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