Calcium carbonate thermal stability

Group II hydrogencarbonates have insufficient thermal stability for them to be isolated as solids. However, in areas where natural deposits of calcium and magnesium carbonates are found a reaction between the carbonate, water and carbon dioxide occurs ... 

Alkaline earth metal alkoxides decompose to carbonates, olefins, hydrogen, and methane calcium alkoxides give ketones (65). For aluminum alkoxides, thermal stability decreases as follows primary > secondary > tertiary the respective decomposition temperatures are ca 320°C, 250°C, and 140°C. Decomposition products are ethers, alcohols, and olefins. 

See how the carbonates of various metals change when heated. For this purpose, roast the following salts in test tubes basic copper carbonate, magnesium, calcium, and sodium carbonates, and sodium bicarbonate. Pass the evolving gas into lime water. Write the equations of the reactions. Explain why the thermal stability of the studied carbonates differs. 

The methods of synthesis of fluorapatite have been widely dis cussed (J ). It is for example possible to obtain fluorapatite by substituting the hydroxyl ion for the fluoride ion, either in a-queous solution at room temperature, or through a solid state reaction at 800°C. It can also be prepared by the action of 6-tricalcium phosphate on calcium fluoride at about 800°C. Its solubility and thermal stability have already been established. While much is known about fluorapatite, many questions still exist concerning the mechanism of their formation, their composition and the structure of some of them. Two of these problems are dealt with here. First, we discuss the formation mechanism of fluorapatite by a solid state reaction between calcium fluoride and apa-titic tricalcium phosphate. Then we present the preparation and the structure of a carbonated apatite rich in fluoride ions. 

Calcium borate-detergent and calcium carbonate-detergent hard-core RMs Calcium borate is stabilized in hard-core RMs with detergents such as sulfonate, salicylate and phenate and evaluated in comparison with calcium carbonate-detergent RMs. The hydrolytic stability, oxidation stability, thermal stability, friction and wear characteristics of both systems are shown in Table 3.7. Why have borate-detergent RMs been recently recognized as an efficient multifunctional class of anticorrosive-antiwear additive ... 

Thermal stability. The degree to which a compound resists dissociation or other chemical alteration at elevated temperatures. Magnesium oxide is stable up to its melting point (2800° C.) and beyond, and hence is considered to have high thermal stability calcium bicarbonate decomposes at 100° to carbon dioxide, water, and calcium carbonate, and hence is thermally unstable. As used in the text, the term indicates chemical integrity up to a designated temperature. 

Very little information is available concerning the thermal stability of the metallic salts of the acid carbonates and thiocarbonates. Calcium glyc-eritol dicarbonate [C3H60H(C0s )2Ca ], although very unstable in solution, could be stored at room temperature in an anhydrous state for a short period of time. On being strongly heated it charred, with the evolution of acrolein. A hydrated 0-(sodium thiocarbonyl) derivative of cellulose became insoluble in alkali within 24 hours at room temperature, due to decomposition. On the other hand, many metal xanthates, particularly the insoluble copper salts, which are readily obtained in a pure, anhydrous state, appear to be reasonably stable at about 20°. This very limited evi-... 

Figure 12.14 shows the effect of calcium carbonate on PVC reprocessing. An addition of 10% chalk improves the thermal stability of the material to the extent that it performs better than the material before reprocessing. 

Special considerations carbon black is the best UV stabilizer printability of POM is obtained by addition of talc or calcium carbonate 0.2-0.3% moisture may reduce thermal stability by 20-30°C (y-sterilization degrades POM rapidly)... 

Special considerations chemical composition of filler surface affects nucleation of filler traces of heavy metals decrease thermal stability and cause discoloration siuface free energy of fillers determines interaction large difference in thermal properties of fillers and polymer may cause stress hydrotalcite is used as acid neutralizer with stabilizing packages anatase titanium dioxide decreases UV stability presence of transition metals (Ni, Zn, Fe, Co) affects thermal and UV stability calcium carbonate and talc were found to immobilize HALS stabilizers in PP with organic masterbatches such as ethylene diamine phosphate V-0 classification can be obtained with 20-25 wt%, at the same time tensile strength and impact strength are substantially reduced... 

Special considerations zinc oxide decreases thermal stability combination of zinc oxide with carbon black reduces UV stability high concentrations of TiO2 or carbon black are needed to improve UV stability, at lower concentrations these fillers will reduce UV stability copper-containing compounds, iron salts, cadmium, cobalt, manganese, lead salts reduce thermal stabihty of PVC (also fillers containing these metals) sand was found to protect PVC from UV degradation calcium carbonate interferes with radiation crosslinking of... 

Stabilization. For example, calcium stearate may play the role of an associate thermal stabilizer when used in a system with calcium salts of fatty acids. These stabilizers use combinations of two or more metals - one of which (e.g. zinc) produces metal chlorides which accelerate PVC degradation. The presence of large amount of calcium salts helps to convert this chloride to calcium chloride which does not increase the degradation rate of PVC. Also, calcium carbonate can react with hydrogen chloride which is produced as PVC degrades. On the other hand, inclusion of fillers which contain admixtures of metals such as iron, nickel, copper, etc. reduces PVC thermal stability. Fillers also affect UV stabilization by adsorption of HALS stabilizers which immobilizes them and prevents them from performing as radical scavengers. 

The elements form an enormous range of compounds with oxoanions, many of those with calcium (carbonate, silicate, phosphate, sulfate) being common minerals in the Earth s crust. Hydrated forms are common. Their thermal stability towards decomposition to the oxide is less than that for the alkali metals, and increases with cation size. Thus Be (like Al) does not form a stable carbonate the decomposition temperatures for the others range from 400°C for MgC03 to 1400°C for BaC03. 

Barium is a member of the alkaline-earth group of elements in Group 2 (IIA) of the period table. Calcium [7440-70-2], Ca, strontium [7440-24-6], Sr, and barium form a closely allied series in which the chemical and physical properties of the elements and their compounds vary systematically with increasing size, the ionic and electropositive nature being greatest for barium (see Calcium and calcium alloys Calcium compounds Strontium and STRONTIUM COMPOUNDS). As size increases, hydration tendencies of the crystalline salts increase solubilities of sulfates, nitrates, chlorides, etc, decrease (except fluorides) solubilities of halides in ethanol decrease thermal stabilities of carbonates, nitrates, and peroxides increase and the rates of reaction of the metals with hydrogen increase. 

Reasons for use abrasion resistance, cost reduction, electric conductivity (metal fibers, carbon fibers, carbon black), EMI shielding (metal and carbon fibers), electric resistivity (mica), flame retarding properties (aluminum hydroxide, antimony trioxide, magnesium hydroxide), impact resistance improvement (small particle size calcium carbonate), improvement of radiation stability (zeolite), increase of density, increase of flexural modulus, impact strength, and stiffness (talc), nucleating agent for bubble formation, permeability (mica), smoke suppression (magnesium hydroxide), thermal stabilization (calcium carbonate), wear resistance (aluminum oxide, silica carbide, wollastonite)... 

Potential adverse effeets calcium carbonate interferes with radiation curing, calcium caibonate may react with pollutant (SO2) to form sulfate, fillers eontaining cadmium, cobalt, copper, iron, lead, or nickel reduce thermal stabihty, low concentration of carbon black and titanium dioxide reduces UV stability, zinc oxide decreases thermal stability, zinc oxide in combination with carbon black reduces UV stability... 

Kim, H.S., Park, B.H., Choi, J.H., Yoon, J.S. Mechanical properties and thermal stability of poly(L-lactide)/calcium carbonate composites. J. Appl. Polym. Sci. 109, 3087-3092 (2008)... 

Secondary stabilizers ate often found in PVC formulations, and are materials such as epoxidized soybean oil, also a plasticizer, and fillers like calcium carbonate, which can react with HCl. They ate often in a formulation for another reason and the additional thermal stability produced is a bonus. These materials usually provide insufficient protection to be used in the absence of true thermal stabilizers. 

More recently nanoscale fillers such as clay platelets, silica, nano-calcium carbonate, titanium dioxide, and carbon nanotube nanoparticles have been used extensively to achieve reinforcement, improve barrier properties, flame retardancy and thermal stability, as well as synthesize electrically conductive composites. In contrast to micron-size fillers, the desired effects can be usually achieved through addihon of very small amounts (a few weight percent) of nanofillers [4]. For example, it has been reported that the addition of 5 wt% of nanoclays to a thermoplastic matrix provides the same degree of reinforcement as 20 wt% of talc [5]. The dispersion and/or exfoliahon of nanofillers have been identified as a critical factor in order to reach optimum performance. Techniques such as filler modification and matrix functionalization have been employed to facilitate the breakup of filler agglomerates and to improve their interactions with the polymeric matrix. 

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