Alkaline earth carbonates

Heterogeneous Catalytic Polymerization. The preparation of polymers of ethylene oxide with molecular weights greater than 100,000 was first reported in 1933. The polymer was produced by placing ethylene oxide in contact with an alkaline-earth oxide for extended periods (61). In the 1950s, the low yield and low polymerization rates of the eady work were improved upon by the use of alkaline-earth carbonates as the catalysts (62). 

The acidic character of siUca is shown by its reaction with a large number of basic oxides to form siUcates. The phase relations of numerous oxide systems involving siUca have been summarized (23). Reactions of siUca at elevated temperatures with alkaU and alkaline-earth carbonates result in the displacement of the more volatile acid, CO2, and the formation of the corresponding siUcates. Similar reactions occur with a number of nitrates and sulfates. Sihca at high temperature in the presence of sulfides gives thiosiUcates or siUcon disulfide, SiS2. 

Oxygen evolved from the anodes as well as some hydrogen from the cathodes produces a mist which is trapped by a froth maintained by adding cresyhc acid, sodium siUcate, and gum arabic, or glue plus cresol. Alkaline-earth carbonates prevent lead contamination of the cathode ziac. Most of the lead is deposited ia the cell sludge as iasoluble carbonate—sulfate. 

Of the alkaline-earth carbonates, BaCO requires the greatest amount of heat to undergo decomposition to the oxide. Thus carbon in the form of coke, tar, or carbon black, is added to the carbonate to lower reaction temperature from about 1300°C in the absence of carbon to about 1050°C. The potential for the reverse reaction is decreased by removing the CO2 as shown in equation lb. 

Sohnel, O. and Matejckova, E., 1981. Batch precipitation of alkaline earth carbonates. Effect of reaction conditions on filterability of resulting suspensions. Industrial and Engineering Chemistry Process Design and Development, 20, 525-528. 

The host lattices are frequently prepared from ZnS, Zn xCdxS2, alkaline earth carbonates, MHP04 (M = Ca, Sr, or Ba), and MNH4P04 H20 (M = Cd or Mn).8 The general (industrial method) of preparation involves precipitation of the phosphor itself, or an intermediate, from solutions of pure cationic and anionic precursors. The purity of all materials used is vital, and impurities must not be present at levels great than 1.0 ppm. Impurities, which are detrimental to phosphor quality and are usually referred to as killers , 4 may include M2+ (M = Fe, Co, Ni, Cu, Pd, and Pt), M3+ (M = Ti, V, Cr, Fe, Ru, Zr, Nb, Mo, Rh, Hf, Ta, and W), and M4+ (M = Os, Ir, and Re). Such cations are usually removed by precipitation or sequestration by selective chelation on solutions before processing.8... 

Alkaline coupling, 9 358 Alkaline deoxidizers, 16 223 Alkaline derusting, 9 785 Alkaline-earth carbonate catalysts,... 

T. Kodama, Government Industrial Research Institute, Osaka, "Cell Performance of Molten Carbonate Fuel Cell with Alkali and Alkaline Earth Carbonate Mixtures," in The International... 

Apatites are complexes of cationic Ca " matched by HP04, COa ", OH , or F as anions. Depending on the counter-ion, apatite can occur in the forms carbonate apatite Caio(P04)6C03, as hydroxyapatite Caio(P04)e (0H)2, or fluoroapatite Caio(P04)6F2. In addition, alkaline earth carbonates also occur in bone. In adults, more than 1 kg calcium is stored in bone. 

The colloidal particles are often deposited on metallic electrodes in the form of adsorbed coatings. Rubber and graphite coatings can be formed in this way, using solvent mixtures (water-acetone) as the dispersion media. The advantage of this method is that additives can firmly be codeposited with, for example, rubber latex. Thermionic emitters for radio valves are produced in a similar manner. The colloidal suspensions of alkaline earth carbonates are deposited electrophoretically on the electrode and are later converted to oxides by using an ignition process. 

Because distribution coefficients are often dependent on pH, buffers were used. The pH of 5 was selected.for most of the experiments because montmorillonite is stable at this acidity, interference of observations from hydrolysis and from precipitation of alkaline earth carbonates is precluded, and adsorption on possible hydrous oxide impurities is minimized. An acetate buffer was usually used to maintain pH because acetate does not have a strong tendency to complex many ions. 

Purification of the clay did not seem to have a marked effect on adsorptive properties. In this connection, it should be mentioned that in bringing the sample to a controlled ionic form before measurement, alkaline earth carbonates, if present, were probably removed, because the operation usually involved equilibration at pH 5. However, oxidation to remove organic matter and treatment with complexing agents to remove iron oxides apparently had little effect. 

Molybdenum-based anticorrosive pigments offer a nontoxic alternative to the zinc chromate pigments [5.120], They all have a neutral color (white) but the pure compounds are very expensive. To produce economically competitive pigments molybdate and phosphate pigments are combined, or molybdate compounds are applied to inorganic fillers (e.g., zinc oxide, alkaline-earth carbonates, or talc) [5.75], [5.121]—[5.123]. 

The basis for other correlations between size, charge, and chemical properties is not so clearcut. Chemical reactions can often be rationalized in terms of the polarizing power of a particular cation. In the alkaline earth carbonates, for example, there is a tendency toward decomposition with the evolution of carbon dioxide ... 

ELECTRODEPOSITION. The precipitation of a material at an electrode as the result of the passage of an electric current through a solution or suspension of the material, for example, alkaline-earth carbonates, rubber from latex, paint films on metal. A technique for electrodepositing refractory carbide coatings on metal has been reported. The electrode is in ihe shape of the desired article. An important advantage or electrodeposition is its ability lo coat complex shapes having small and irregular cavities with exact thickness control. 

Accumulation of alkaline-earth carbonate (e.g., calcium) Accumulation of calcium sulfate... 

This prediction is indeed correct. Consider, e.g., the alkaline earth carbonates, where a regular increase in thermal stability is observed going down the alkaline earth family (increasing size of the cation) and progressively higher decomposition temperatures are required for this series of compounds (Table 3.8). 

This is achieved in the electrochemical C02 sensor to be described now. The gas sensitive electrode in the emf sensors for C02 detection is based on an alkaline or alkaline earth carbonate.41"43 If Na2C03 is to be used, Na- (5" -alumina or Nasicon (Part I2) are suitable electrolytes. A thermodynamically well-defined sensor is obtained by using a mixture of a binary and a ternary oxide such as42 Na2C03, C02 Na+ -conductorj Na2M03, M02... 

Figure 12.18. Influence on salt production by liming with various alkaline earth carbonates at half the needed quantity and all the needed quantity (from Evangelou, 1997, unpublished data, with permission).

After the invention of the Hollander beater in the late 1600s, metallic impurities (copper and iron) got into the paper pulp by contact with the metal rotary grinders. This type of beater is blamed also for the accelerated decline of quality in papers because its particular beating action shortened the fibers. Another production change reduced the amounts of alkaline earth carbonates present new forms of gelatin, made from sinew and muscle, did not possess the natural alkalinity of the byproduct of the parchment maker. 

The fusion of uranium oxides with alkali or alkaline earth carbonates, or thermal decomposition of salts of the uranyl acetate anion, gives orange or yellow materials generally referred to as uranates, for example,... 

As is to be expected from relative solubility, the first minerals to form from concentrating waters are the alkaline-earth carbonates. The equilibrium precipitation of calcite also illustrates... 

Primary minerals formed in the ore deposit prior to weathering and erosion, including a wide variety of metal sulfides and sulfosalts, metal oxides, metal- and alkaline-earth carbonates, sulfates, crystalline silica, clays, and other silicates. Many metal sulfides (especially iron sulfides such as pyrite), when exposed by erosion or mining to atmospheric oxygen and water, can form acid-rock drainage (ARD). 

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