Stability of calcium carbonate

Fig. 6.2 Thermodynamic stability of calcium carbonates. Change in enthalpy is shown with polymorph.

Winland H.D. (1969) Stability of calcium carbonate polymorphs in warm, shallow seawater. J. Sediment. Petrol. 39, 1579-1587. 

Cui Yanzhen. Study on Formability and Foam Stability of Calcium Carbonate Nanoparticles-surfactant Mixtures[D]. Wuxi City University of the South, 2009 17-25. 

The thermal stability of calcium carbonate (CaC03) nanoparticles on polybutadiene rubber (PBR) were studied by Shimpi and Mishra [105]. They observed that the incorporation of nano CaCOs in PBR shows better thermal stability. At 12 wt% of nano CaCOs (21, 15, and 9 nm) filled in PBR shows decomposition temperature at 491, 483, and 472 °C, respectively. At 4 wt% loading of filler, decomposition temperature is observed to be 488,480,450 °C for nano CaCOs (21, 15, and 9 nm), respectively. This enhancement in thermal stability is due to uniform dispersion of nano CaCOs throughout the matrix that keeps the rubber chains intact on cross-linking, which prevent out diffusion of the volatile decomposition product [106]. The presence of nanoinorganic particles in between the mbber chains is responsible for preventing the diffusion of the volatile decomposition products firom the mbber nanocomposites at same time. It is clear that nanoinorganic filler provides better thermal stability as compared with commercial micron size filler. 

A commercial grade of ethyl chlorocarbonate, stabilized with calcium carbonate, was employed without purification. 

Calcium carbonate is one of the most common filler/extenders used in the paint and coatings industry. Consumer and contractor paint formulas can include products from submicrometer size to coarse mesh sizes. The main function of calcium carbonate in paint is as a low cost extender. It is also used to improve brightness, application properties, stability, and exposure resistance. Coarse products help to lower gloss and sheen or even provide textured finishes. The selection of product type and particle size is determined by the desired performance and cost of the coating. 

In France it is customary to add 1-2% of calcium carbonate to the water in which the pulped nitrocellulose is poached for at least 4 hr. The stability of the resulting nitrocellulose is examined by means of the heat test, and if necessary poaching is repeated. This is carried out by allowing the contents of the boiler to settle for several hours, so that the nitrocellulose sinks to the bottom. The water is then decanted from above the nitrocellulose layer, fresh water and calcium carbonate are added, and the poaching is started again, and continued for 2-4 hr. 

With high nitrated guncotton (CP,) the stabilizing process usually consists of two 4-hr poachings, each boil being followed by decantation, for which an outlet tube ending with a funnel is usually used. The stability of the nitrocellulose is then tested, and one or more further poachings in the presence of calcium carbonate,... 

Another major manufacturer was the Eastern Dynamite Corporation, at Wilmington, Delaware, which developed the patents of Holmes [26]. The starch was nitrated by means of mixed nitric-sulphuric acid and then stabilized by prolonged boiling with water in the presence of calcium carbonate, for 75-100 hr. In later patents the addition of ammonium salts to the water was recommended. 

Rachakomkij, 2007, 602-603). The released As(V) then reacted with calcium to form calcium arsenates. As previously mentioned, the long-term stability of calcium arsenates depends on ambient conditions. In the presence of carbon dioxide from air or carbonate in water, calcium arsenates may decompose over time and release arsenic (Robins and Tozawa, 1982 Ghimire el al., 2003, 4946 Jing, Korfiatis and Meng, 2003, 5055-5056). 

As mentioned earlier, pH changes occur from pollution stresses such as acid rain or mine runoff of from geochemical reactions such as dissolution of calcium carbonate. In acidified regions, species diversity and population density drop dramatically with some lakes and streams becoming devoid of life. Changes in metal complexes occur both naturally and biologically, with direct and indirect effects on ligand concentration and complex stability. 

Polyvinyl acetate emulsions for manual application in the production of adhesive bound books were examined for stability. It was found, among other things, that plasticized homopolymers had poor or moderate stability, while copolymer types showed very high stability. The addition of calcium carbonate and calcium acetate could improve the lasting qualities of unstable materials but had little effect on the very stable ones. The addition of these buffering agents made the adhesive less acid and less damaging to papers (6). 

Other Plastics Uses. The plasticizer range alcohols have a number of other uses in plastics liexanol and 2-ethylliexanol are used as part of the catalyst system in the polymerization of acrylates, ethylene, and propylene (55) the peroxydicarbonate of 2-ethylliexanol is utilized as a polymerization initiator for vinyl chloride various trialkyl phosphites find usage as heat and light stabilizers for plastics organotin derivatives are used as heat stabilizers for PVC octanol improves the compatibility of calcium carbonate filler in various plastics 2-ethylliexanol is used to make expanded polystyrene beads (56) and acrylate esters serve as pressure sensitive adhesives. 

The variety of substances used as additives in polymers is considerable. For example, the fillers may include china clay, various forms of calcium carbonate, talc, silicas (diatomaceous silica), silicates, carbon black, etc. The impact modifiers typically include other polymers. Plasticizers include certain polymers with low (oligomers), dialkyl phthalates, dialkyl sebacates, chlorinated paraffin waxes, liquid paraffinic fractions, oil extracts, etc. Heat stabilizers include heavy metals salts such as basic lead carbonate, basic lead sulfate, dibasic lead phosphite (also acting as a light stabilizer), dibasic lead phthalate, stearates, ricinoleates, palmitates and octanoates of cadmium and barium, epoxide resins and oils, amines, diphenylurea, 2-phenylindole, aminocrotonates. The antioxidants include tris-nonyl phenyl phosphite, 2,6-di-ferf-butyl-p-cresol (BHT), octadecyl-3,5-di-terf-butyl-4-hydroxyhydrocinnamate, etc. The UV stabilizers include modified benzophenones and benzotriazoles. Processing lubricants include calcium stearate, stearic acid, lead stearate, various wax derivatives, glyceryl esters and long-chain acids. Fire retardants include antimony oxide, some pyrophosphates, etc. 

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