Mg Metal and its Alloys

Toxicity data on niobium and its compounds are sparse. The most common materials, e.g., niobium concentrates, ferroniobium, niobium metal and niobium alloys, appear to be relatively inert biologically. Limited animal experiments show high toxicity for some salts, which arc related to disturbance of enzyme action, Niobium hydride lias moderate fibiogenic and general toxic action. Recommended maximum allowable concentrations arc 6 mg/m3. Recommended maximum permissible concentration of Nb ill reservoir water is 0.01 mg/L. The threshold for affecting clarity and biological oxygen demand (BOD) is 0.1 mg/L. 

Magnesium is thermodynamically one of the less noble metals, and it can protect most other metals when used as sacrificial anodes (see Section 10.4). In the atmosphere the metal is covered by an oxide film. Therefore it resists rural atmospheres but is subject to pitting in marine atmospheres. Magnesium alloys are also liable to SCC and erosion corrosion, and are attacked by most acids. Mg alloys are used in automobile engines, aircraft, missiles and various movable and portable equipment, in all cases primarily because of their low density (1.76 g/cm ). 

The H2 oxidation reaction (HOR) and the O2 reduction reaction (ORR) require catalysts to achieve useful reaction rates. The best catalysts are platinum (Pt) and its alloys with certain transition metals. The catalysts are normally made into nanoparticles with diameters between 1.5 and 5 nm. H2 oxidation proceeds faster than O2 reduction, and thus it requires less of a catalyst. With pure H2 as the reactant, a Pt loading of 0.05 mg cm" is enough, while the catalyst loading for O2 reduction is typically several times higher. 

In general only poor corrosion behavior is attributed to Mg and its alloys. This is mainly true when Mg is in contact with other metals and alloys in accordance with the electrochemical potential series of metals. Therefore, special care has to be taken to avoid conductive contact between Mg alloys and other metals with different electrochemical potentials. When joining Mg parts with other materials, insulating washers, surface-coated screws or nonconducting films and surface coatings can be applied. When investigating a Mg... 

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