Magnesium aqueous system

Examples of the sacrificial-anode method include the use of zinc, magnesium, or aluminum as anodes in electrical contact with the metal to be protected. These may be anodes buried in the ground for protection of underground pipe lines or attachments to the surfaces of equipment such as condenser water boxes or on ship hulls. The current required is generated in this method by corrosion of the sacrificial-anode material. In the case of the impressed emf, the direct current is provided by external sources and is passed through the system by use of essentially nonsacrificial anodes such as carbon, noncor-rodible alloys, or platinum buried in the ground or suspended in the electrolyte in the case of aqueous systems. 

A study was made of the comparative stabilities at various exposures of an upset stomach remedy suspension. This product consisted of a dispersion of bismuth subsalicylate and phenylsalicylate in an aqueous system. Methyl-cellulose and magnesium aluminum silicate were selected as the suspending agents, because the presence of polyvalent metallic ions precluded the use of hydrocolloids affected by these ions. In addition, it was found that methyl-cellulose contributed a demulcent effect. The viscosity, as well as the suspension characteristics of the combination of protective colloids used, was of a synergistic nature. These colloids formed a thixotropic system. The thixotropy undoubtedly aids in stabilizing this system. In order to make this product palatable and impart elegance, color and flavor were added. Sample 1 (with protective colloids) showed no separation, while sample 2 (without... 

The stability characteristics of two different antiperspirant lotion systems were compared. Sample 1 represented an aqueous emulsion containing an aluminum salt. The internal phase consisted of stearyl alcohol and ethylene oxide reaction products, polyoxyethylene sorbitan monostearate and polyoxyethylene sorbitan tristearate. Methylcellulose was used as a stabilizer and bodying agent. Sample 2 represented a dispersion of magnesium aluminum silicate in an aqueous system containing aluminum ions. Because of its com-... 

Under ordinary conditions, anhydrous magnesium carbonate cannot be prepared in aqueous systems. The anhydrous salt, however, can be made under very high partial pressures of carbon dioxide. 

The reaction of lithium with the electrolyte to form a surface film significantly modifies its behaviour. On the one hand, the film confers chemical stability and useful shelf life on the system. On the other, it is responsible for greatly depressed exchange currents and the consequent phenomenon of voltage delay, as discussed in Chapter 3 in connection with magnesium aqueous batteries. It is convenient to discuss separately film formation with insoluble and with liquid and soluble cathode systems. 

X-Ray diffraction studies of aqueous CdS04 solutions have clearly demonstrated the formation of O-sulfato complexes.668-670 These are of the general form [Cd(H20)6- (0S03) ](2-2")+, and appear to be the major species present in concentrated solutions. These results are fully in accord with tensimetric studies of the cadmium and magnesium sulfate aqueous systems, which indicate an increased interionic attraction at elevated temperatures.671 In contrast, X-ray diffraction studies on cadmium perchlorate solutions show no evidence for the coordination of the perchlorate ion to the metal, the only cationic species present being [Cd(H20)6]2+(Cd—O, 2.292 A, cf. Cd—O, 2.292 A in solid [Cd(H20)6][C104]2),670... 

At present, many studies are ongoing to identify a means of enhancing the carbonation chemistry of magnesium silicates in aqueous systems, using weak acids and additives that will improve silica dissolution, such as citrates, oxalates, and EDTA [105, 111]. In this case, a near-complete recovery and reuse, thereby minimizing the losses of such chemicals, will be essential for viable process economics. Likewise, there is much to improve with regards to the reaction rates and/ or times. 

Many magnesium borate systems have been investigated a few of the major studies are listed in Table VII. The main magnesium borates stable in contact with aqueous solutions are the 1 1 3 (pinnoite), 1 3 x, 2 1 1, and 2 3 15 (inderite) compounds. 

Although com can be adequately steeped in sterile, aqueous solutions of sulfur dioxide or sodium, magnesium or potassium bisulfite (hydrogen sulfite) in the laboratory,164-166 commercial steeping involves microorganisms. Raw com carries natural populations of bacteria, yeasts and molds which are capable of rapid multiplication in aqueous systems. Wet-millers learned early that com steeped at temperatures of 45-55°C was sweet, but that putrefaction and butyric acid or alcohol production... 

The behavior of zeolites in biological systems is a bit mysterious. For example, treatment of yeast mitochondria with zeolite A or X in the sodium or potassium cation forms disaggregates the mitochondria and solubilizes cytochrome oxidase in an aqueous system. However, the same zeolites in calcium or magnesium form showed little activity of this type (67). Similarly, zeolite A can disrupt bacterial cells (83). 

Finally, we stress that the free volume approach is only applicable to nonpolar systems. Aqueous dispersions fall outside its scope. This is vividly illustrated by the data of Evans et al. (1975), who determined experimentally that d(UCFT)/d7 = — 1 x 10 KPa for latex particles sterically stabilized by poly(oxyethylene) in aqueous 0-43 molal magnesium sulphate solutions. Both the sign and magnitude of this quantity is different from that predicted by free volume theory for the UCFT of non aqueous dispersions. Paradoxically, it falls in line with the predictions, both in sign and magnitude, published by Croucher and Hair (1979) for the pressure dependence of the LCFT of poly(a-methylstyrene) in -butyl chloride. This may be merely coincidental, but the very small pressure dependence exhibited by the UCFT of aqueous sterically stabilized dispersions emphasizes the major differences between the origins of flocculation at the UCI T for aqueous and nonaqueous dispersions. The small pressure dependence observed for aqueous systems is scarcely surprising since the UCFT of an aqueous dispersion occurs far from the critical point of water whereas that for nonaqueous dispersions is quite close to the critical point of the dispersion medium. 

Separate n.m.r. signals could be obtained from the hydroxy-groups of free and bound ethanol in low-temperature studies on solutions of magnesium perchlorate. From relative intensity measurements below — 60 °C, the solvation number of Mg + was shown to be six. The rate parameters for the exchange process provide an interesting comparison with those for the aqueous system A = 2-8 x 10 s (5-3 x 10 s at 25 °C for HaO), Am = 17-7 kcalmol- (10-2 kcalmol i), ASi = 30 e.u. (2 e.u.). 

Figure 4.4. Pourbalx diagram for the magnesium-water system at 25°C [3]. (M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions, 2nd English edition, p. 141, copyright NACE International 1974 and CEBELCOR.)...

Fig. 13 Log/o2-pFl diagram showing distribution of uranyl com-ple.xes, solubility of uranium oxides, distribution of iron phases, relative stability of chalcopyrite and bornite and relative stability of potassium and magnesium silicates at 200 C in aqueous system containing lOppm Fe, lOOppm F, lOOOppm S, lOOOppm K, lOOppm Mg and 1 in NaCl at Pco. of lOatm (see text for explanation)...

The other major source - dissolved solids - is common to practically all aqueous systems and will result in the formation of calcium, magnesium, or iron scales. Tightly adherent calcium carbonate or phosphate, magnesium hydroxide or silicate, or deposits of iron compounds are laid down on the... 

Sa.lts Salting out metal chlorides from aqueous solutions by the common ion effect upon addition of HCl is utilized in many practical apphcations. Typical data for ferrous chloride [13478-10-9] FeCl2, potassium chloride [7447-40-7] KCl, and NaCl are shown in Table 9. The properties of the FeCl2-HCL-H2 0 system are important to the steel-pickling industry (see Metal SURFACE TREATMENTS Steel). Other metal chlorides that are salted out by the addition of hydrogen chloride to aqueous solutions include those of magnesium, strontium, and barium. 

---