Oxides of calcium

Limestone and marble have been mined as building materials and the oxide of calcium, lime [1305-78-8], has been used ia the manufacture of mortar for centuries (see Building materials, survey Lime and limestone). Lime-burning was one of the first iadustries ia the American colonies, where calcining of limestone was accompHshed ia kilns dug out of the sides of hills. 

The ash content of furnace blacks is normally a few tenths of a percent but in some products may be as high as one percent. The chief sources of ash are the water used to quench the hot black from the reactors during manufacture and for wet pelletizing the black. The hardness of the water, and the amount used determines the ash content of the products. The ash consists principally of the salts and oxides of calcium, magnesium, and sodium and accounts for the basic pH (8—10) commonly found in furnace blacks. In some products potassium, in small amounts, is present in the ash content. Potassium salts are used in most carbon black manufacture to control stmcture and mbber vulcanizate modulus (22). The basic mineral salts and oxides have a slight accelerating effect on the vulcanization reaction in mbber. 

Reactant for /-butyl phenolic resins. Magnesium oxide reacts in solution with /-butyl phenolic resin to produce an infusible resinate (Fig. 36) which provides improved heat resistance. The resinate has no melting point and decomposes above 200°C. Although oxides of calcium, lead and lithium can also be used, they are not as efficient as magnesium oxide and also tend to separate from solution. Where clear adhesive solutions are required epoxide resins, zinc-calcium resinates or zinc carbonate can be used. 

In 1817 Dobereiner found that if certain elements were combined with oxygen in binary compounds, a numerical relationship could be discerned among the equivalent weights of these compounds. Thus when oxides of calcium, strontium, and barium were considered, the equivalent weight of strontium oxide was approximately the mean of those of calcium oxide and barium oxide. The three elements in question, strontium, calcium, and barium were said to form a triad. 

If the free energy changes for the reduction of the sulfate to make H2S rather than SO2 had been considered in this analysis, the oxides of several more elements would have been included in the boxed-off area of appropriate materials. From past practice, however, it is known that oxides of calcium, strontium and lithium, for instance, are not as effective. An appropriate future area of research would be to investigate those materials more thoroughly. 

Determine the empirical formula of an oxide of calcium formed when 0.4g of calcium reacts with 0.16g of oxygen. 

Carbon dioxide reacts with oxides of calcium and magnesium to form their carbonates. 

Waste materials such as calcium sulfite are difficult to dewater and cannot support a load. It is often desirable to stabilize such wastes before disposal. Methods for the stabilization of these materials, such as oxidation of calcium sulfite to gypsum, have been developed. In certain countries (such as W. Germany and Japan), waste materials like gypsum can be sold however, this is not generally true in the United States. 

The choice of the chlorination technique and equipment for the process greatly depends on the compositon of raw stock for chlorination. For shaft furnaces and fluidised layer apparatuses, it is advisable to chlorinate titanium raw stock with relatively small amounts of oxides of calcium, magnesium, manganese and other metals which form low-melting chlorides in chlorination. On the other hand, in chlorination in salt melt these oxides do not have any significant effect on the process. 

The literature review in Chapter 2 reveals that divalent metal oxides such as oxides of calcium, magnesium, and zinc (CaO, MgO, and ZnO) are the major candidates for forming phosphate ceramics. These oxides are sparsely soluble in acidic solution, and as we shall see in Chapter 4, they are the most suitable ones to form ceramics. In addition, following the methods discussed in subsequent chapters in this book, aluminum oxide (alumina, AI2O3) and iron oxide (Fe203), which are abundant in earth s crust have excellent potential to form low cost CBPCs. For this reason, we have provided relevant information on these oxides. Table 3.2 gives some details. 

Since calcium oxide is more than sparsely soluble and its reaction with phosphoric acid or a soluble phosphate is highly exothermic, researchers have used less soluble salts of calcium to react with the phosphates and form a phosphate ceramic [4-12]. In the acidic medium of the phosphate solutions, the salts of calcium dissolve slowly and release Ca (aq) into the solution, which subsequently reacts with phosphate anions and forms calcium phosphates. The best calcium minerals for forming CBPCs are combination of oxides of calcium and insoluble oxides such as silica or alumina, e.g., calcium silicate (CaSi03) and calcium aluminate (CaAl204), or even a phosphate of calcium such as tetracalcium phosphate (Ca4(P04)2 0). These minerals are reacted with acid phosphate salts to form phosphate cements. 

Calcium ferricyanide, Ca3 [Fe(CN) 6] 2( )12H20, may be obtained 9 by oxidising aqueous calcium ferrocyanide with calcium plumbate and carbon dioxide under pressure, at the ordinary temperature. The solid salt is separated by evaporation under reduced pressure. The salt may also be obtained by oxidation of calcium ferrocyanide with chlorine 10 and by neutralising ferricyanic acid with calcium carbonate. It yields needle-shaped crystals, which are stable in dry air. 

Cordierite synthesis method based on mechanical activation of mixtures of hydrated oxides of calcium, aluminium and silicon, as well as natural hydrated compounds (talc, kaolinite and gibbsite), has been developed in [2, 3]. Mechanical activation of these mixtures does not lead to the formation of new phases but provides good mixing at the cluster level giving aggregates that form cordierite during the subsequent thermal treatment. 

Bismuth oxide forms a number of complex mixed-metal phases with the divalent metal oxides of calcium, strontium, barium, lead, and cadmium, and these show a wide variety in composition. With transition metal oxides, mixed-metal oxide phases have been observed which are based upon a Perovskite-type lattice (10) containing layers of Bi202. It is notable that the high Tc superconducting materials which include bismuth also have this Perovskite-type of lattice with layers of copper oxide interleaved with bismuth oxide layers. 

The simplest models for the composition of the planets presume that the differences between them can be explained in terms of an equilibrium condensation. At the highest temperatures a sequence of mixed oxides of calcium, titanium, and aluminum would be found (>1,400 K). This would be followed, at lower temperatures, by metal and silicate fractions. At temperatures somewhat greater than 600 K alkali metals enter the silicate phase along with sulfur, which combines with iron at 650 K to form triolite... 

Insoluble solids, regardless of particle size, that have a relatively low interfacial tension and are readily wetted by water are called hydrophilic solids. These solids include clays (bentonite, kaolin, talc, magnesium aluminum silicate) bismuth salts, barium sulfate, carbonates, hydroxides, or oxides of calcium, magnesium, zinc, and aluminum and titanium dioxide. The hydro-philicity of a powder surface can be investigated with the help of moisture absorption studies in which the solid particles are exposed to varying relative humidities. Insoluble powders that absorb moisture below relative humidities of 70-80% at room temperature are said to be hydrophilic solids. 

D-Galactopyranosyl-D-arabinose was prepared from lactose oxime by dehydration with acetic anhydride and degradation of the resultant nitrile with sodium methoxide in chloroform. This galactosylarabinose has also been prepared by the oxidation of calcium lactobionate with hydrogen peroxide and a ferric salt (the Ruff degradation ). Under... 

The successful degradation of o[ -D-glucosaccharinic acid to a 1-deoxy-pentulose has apparently not been recorded. Experiments in the author s laboratory have indicated that the oxidation of calcium a -D-glucosac-charinate with hydrogen peroxide and ferric acetate (the Ruff degradation) proceeds normally to yield a reducing product. However, no crystalline derivative of the expected deoxypentulose has been obtained as yet. 

Calcium carbonate as limestone was used to build the Roman aqueduct in Figure 7-6. When calcium carbonate decomposes, it forms an oxide of calcium called lime. Lime is one of the most important industrial compounds. For example, lime plays a role in the manufacture of steel, paper, and glass. Gardeners use lime to make soil less acidic. Wastewater treatment plants use lime, as do devices that remove pollutants from smokestacks. Lime is mixed with sand and water to form a paste called mortar. 

There is a positive effect of the SCR unit on downstream equipment such as flue gas desulfurization, which produces gypsum. In the absence of a SCR unit, water from a FGD unit contains hydroxyl amine disulfonic acid which has been formed from NO2, water, and SO2. This compound acts probably as an inhibitor for the oxidation of calcium sulfite into calcium sulfate [129]. 

Even artificial stone illustrates the central role of oxygen Portland cement is made of the oxides of calcium, silicon, aluminum, iron, magnesium, and sulfur. 

A model has been developed for oxidation of calcium sulfite in a three-phase, semibatch reactor, The overall rate of conversion to sulfate depends on the rates of solid dissolution and liquid phase chemical reaction. In this first treatment of the problem, gas-liquid mass transfer resistance did not affect the overall rate of oxidation. 

A considerable amount of work has been done on the oxidation of sulfite and bisulfite anions in aqueous solutions (25). In this paper the discussion is limited to oxidation of calcium sulfite (9), which has received much less attention than oxidation of sodium salts. The attention here is on the oxidation of calcium sulfite, catalyzed by metal ions in the presence of organic acid buffers, occuring in solid-liquid-gas slurry reactors. The organic acid buffers not only moderate pH changes during the reaction, but also inhibit the rate of chemical reaction (10). 

At the Shawnee Test Facility, major emphasis has been placed on the use of adipic acid in conjunction with forced oxidation of calcium sulfite to calcium sulfate, since this system results in better sludge dewatering properties and reduced waste solids disposal costs. Furthermore, the more tightly closed liquor loop,... 

The observed catalytic effect of the alkali metal carbonates and oxides and the alkaline earth oxides upon the gasification of the ESC deposit in water vapour again most probably derived from successive oxidation and reduction processes. A possible cycle carbonate-metal-hydroxide could be feasible at this temperature, at least for sodium, potassium and lithium (3) and conceivably also for cesium and rubidium. For barium and strontium the cycle could be between a higher and a lower oxide. Calcium, in contrast to barium and strontium, does not form a peroxide by oxidation of calcium oxide and in any case this would not be stable above 200°C, which could explain why calcium oxide was not an active catalyst. 

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