Dissolved magnesium alloys

Very small quantities of bismuthine are obtained when a bismuth-magnesium alloy, BijMgj, is dissolved in hydrochloric acid. As would be expected, it is extremely unstable, decomposing at room temperature to bismuth and hydrogen. Alkyl and aryl derivatives, for example trimethylbismuthine, Bi(CHj)3, are more stable. 

Pattison and Degering (16) have prepared a catalyst of the Raney type from a nickel-magnesium alloy. These authors used acetic acid to dissolve the inactive portion of the alloy. The catalyst was found to be as active as the W-4 Raney nickel of Pavlic and Adkins (10) and twice as active as the W-2 catalyst of Mozingo (9). 

Filiform corrosion of AZ 91 magnesium alloy has been studied in detail and the mechanism different from the conventional mechanism has been postulated. In this case dissolved oxygen is not necessary and the filiform propagation is fueled by hydrogen evolution at the filament head and is controlled by mass transfer due to the salt film on the tip of the filament.32,33... 

Uranium carbide is formed directly from the elements in an arc furnace by means of melting uranium with graphite. The uniformity of the product may be improved by remelting. The monocarbide also results from heating an intimate mixture of uranium and carbon particles above 1100°C. Uranium dissolved in a molten zinc magesium alloy can be heated with graphite powder. The residual zinc-magnesium alloy is removed by vacuum distillation. 

It may be added that the pyrotechnic manufacturer should not rely on vague notions of corrosion resistance when faced with problems such as attack by sea water, burial in the ground, etc. of completed items. Sea water is particularly detrimental even to stainless steels because of the combined optimal effect of 3-4% sodium chloride and of dissolved oxygen. Even bacteria, acting as depolarizers and activators,contribute to corrosion of steels. On the other hand, certain aluminum and magnesium alloys are resistant in varying degrees to sea water. ... 

An electrochemical cell is formed and the anodic metal dissolves. This can be corrected by applying a counter current or voltage or by introducing a more reactive, sacrificial anode, for example, adding magnesium alloy to the above Zn-Fe-Cu system, a procedure commonly used for hot-water pipes in renovated buildings. 

Zinc, aluminum, or magnesium alloys are being used in reserve batteries using air as the cathode. With aluminum or magnesium, these batteries may be activated with saline electrolytes, and in some underwater application they may use oxygen dissolved in the seawater. Reserve or mechanically rechargeable air batteries, for higher-power applications such as for standby power or electric-vehicle propulsion, use zinc or aluminum alloys with alkaline electrolytes (also see Chapter 38). 

This reaction stops in alkaline electrolytes because of the formation of an insoluble film of magnesium hydroxide on the electrode surface which prevents further reaction. Acid tends to dissolve the film. An important consequence of the film on magnesium elecfrodes (see also Chap. 9) is that there is a delayed response to an increase in the load because of the need to disrupt the film to create new bare surfaces for reaction. Pure magnesium anodes usually do not give good cell performance, and several magnesium alloys have been developed for use as anodes tailored to provide the desired characteristics. 

Magnesium/air batteries have not been sueeessfully commercialized and an effort has been directed to undersea applications using the dissolved oxygen in seawater as the reactant. The battery uses a magnesium alloy anode and a catalytic membrane cathode, and is activated by the seawater. The main advantage of this system is that, with the exception of the magnesium, all of the reactants are supplied by the seawater. The battery can have a specific energy of about 700 Wh/kg. 

The procedure of Mortier et al. (32) for the determination of boron in aluminium and aluminium-magnesium alloy is as follows The sample is irradiated for 20 min with a 2 uA beam of 7 MeV deuterons, which are degraded to 5.3-5.7 MeV, and a surface layer is removed by chemical etching (2.3.1). To separate the sample is dissolved in an oxidizing mixture of phosphoric acid, sulphuric acid and potassium dichromate. The C02 released is absorbed in 0.5 M sodium hydroxide and the activity measured with a t-t coincidence set-up. A pure decay is obtained. The chemical yield was checked by comparing, in a separate experiment, the activity of an aluminium sample, doped with 5000 tig/g of boron, measured instrumentally and after chemical separation. The yield was 100 %. 

In commercial alloys, 2inc is usually dissolved in the magnesium matrix and in the hard magnesium—aluminum phase when aluminum is present. Zinc additions to magnesium—aluminum alloys change the eutectic stmcture to a so-called divorced eutectic, characteri2ed by the presence of massive compound particles surrounded by a magnesium-rich sohd solution. 

Magnesium ferrosihcon alloys react vigorously when added to molten iron. As the magnesium vaporizes and cools, it reacts with residual surface tension modifiers such as sulfur and oxygen and greatly increases the surface tension of the molten iron. The dissolved graphite in the molten iron nucleates and grows into a spheroidal shape because of the increased surface tension of the molten iron. 

Of the generic aluminium alloys (see Chapter 1, Table 1.4), the 5000 series derives most of its strength from solution hardening. The Al-Mg phase diagram (Fig. 10.1) shows why at room temperature aluminium can dissolve up to 1.8 wt% magnesium at equilibrium. In practice, Al-Mg alloys can contain as much as 5.5 wt% Mg in solid solution at room temperature - a supersaturation of 5.5 - 1.8 = 3.7 wt%. In order to get this supersaturation the alloy is given the following schedule of heat treatments. 

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