Metal oxides plus acid

Ethjl Silicate-Bonded Investments. These investments are mixtures of powder and Uquid. The powder consists of refractory particles of sUica glass, crystobahte, and other metal oxides plus magnesium oxide. The Uquid is a hydrated sUica, tetrasUicic acid [10193-36-9] Si [OH], that is suppUed in a stabUized form it can be developed by mixing ethyl sUicate [78-10 ] denatured ethyl alcohol [64-17-5] and hydrochloric acid [7647-01 -OJ. The binding of the powder is accompUshed by the formation of a sUica gel according to the reaction ... 

The rate at which sulfur will react with the unsaturated polymer chains can be increased by the addition of activators a metal oxide plus fatty acid. The most common combination is zinc oxide and stearic acid, with the primary fimction of the fatty acid being to solubilize the zinc in the elastomer. In the presence of the metal, it is believed that the sulfur reacts as a cation at the double bond which results in charged and uncharged polysulfides, the latter of which could in turn form free radicals. Metal activated sulfur vulcanization will proceed more rapidly than crosslinking by sulfur alone, but still too slow for most production purposes. The metal oxide/fatty acid is, in practice, used not to activate the sulfur itself, but to activate the organic compounds used as vulcanization accelerators. 

Vanadium dioxide, VO2 is dark blue (V2O5 plus SO2) but is readily reduced further to Vo.i86-V,.6a. VO2 gives the (VO) ion with acids and vanadates(IV) with alkalis and as mixed metal oxides. 

Luo et al. [43] proposed the dispersion of CNTs in 4.0 M HCl for 4 hours imder ultrasonie agitation to eliminate metal oxide catalysts. After rinsing earefully with water until neutral pH and drying, the CNTs were dispersed in 60 mL mixture of eoneentrated nitric acid plus sulfuric acid (1 3) with ultrasonic agitation for 4 hours in a water bath followed by washing until neutral pH and finally drying. 

Even metal oxides that are insoluble in water demonstrate their basicity by reacting with acids to form a salt plus water, as illustrated in FIGURE 7.15 ... 

Concerning the nature of the acid sites involved, it is a general consensus that properly activated sulfated metal oxides contain both Bronsted and Lewis acid sites. Discrepancies can be found on the predominant role played by a particular site or even by the coupled Bronsted plus Lewis sites with respect to the final activity showed by these materials [40-46], As an example, for models showing the possibilities of sulfated itconia acting as a Bronsted acid (Kustov et ai. [46]), Lewis acid (Pinna et al. [43]), and Bronsted plus Lewis acid (Adeeva et al. [47 ]), sec Figure 9. 

The general applicability of these ideas was perhaps first pointed out in the classic articles of Flood and Forland (1947) where the stability properties of a wide variety of oxyanions were correlated with the nature of the cation. Since the decomposition reaction in such cases can be viewed as the production of a smaller or more basic fragment ion plus a more molecular species, the reaction obviously will be enhanced by a more acidic or polarizing cation. For example, the stability of the COs " ion with respect to decomposition to oxide and CO2 decreases with a decrease in atomic number and hence size in either the alkali metal or the alkaline earth metal series, whereas the stability progressively decreases even more with the smaller ions Mg +, Mn +, Cd +, Pb +, Ag+, Zn +, and Fe +. Of course, the relative stabilities of the product oxides must also be considered in a quantitative comparison. Electrostatically the process can be viewed as a competition between the formation of the more stable oxide lattice (plus CO2) and the lower lattice energy of the carbonate plus the bond energy associated with CO2 + CO,3. The elimination of oxide plus SO3... 

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