Calcium Citrate Tetrahydrate Research Articles

Solid state formation of calcium ferrites from thermal decomposition of mixtures Ca 3(C 6H 5O 7) 2·4H 2O–Fe 2(C 2O 4) 3·6H 2O : The role of mechanical activation on the mechanism of the thermal decomposition and the temperature of the ferrites formation

The present paper reports a novel synthetic procedure of both calcium ferrites (CaFe 2O 4 and Ca 2Fe 2O 5) starting from mechanically activated mixtures of organic precursors (calcium citrate tetrahydrate and iron(III) oxalate hexahydrate). With the help of TG analysis the different stages of the mass loss process taking place could be individuated and their chemical nature assessed. The DSC signal, recorded on the same sample, revealed that much higher enthalpies are released from the milled mixtures than those expected on the basis of the reactions taking place. From such enthalpic excess the enthalpies of formation of Ca 2Fe 2O 5 and CaFe 2O 4 have been obtained. X-ray powder diffraction (XRPD) indicated that the mechanically activated mixtures yield, after an 18 h-annealing at 800 °C (or 750 °C), Ca 2Fe 2O 5 (or CaFe 2O 4). On the contrary, the same compounds could be obtained, when starting from physical mixtures, only by performing thermal treatments (for t > 18 h) at 1180 °C (Ca 2Fe 2O 5) or 1100 °C (CaFe 2O 4).

Determination of calcium salt solubility with changes in pH and PCO2, simulating varying gastrointestinal environments

The amount of calcium available for absorption is dependent, in part, on its sustained solubility in the gastrointestinal (GI) tract. Many calcium salts, which are the calcium sources in supplements and food, have pH-dependent solubility and may have limited availability in the small intestine, the major site of absorption. The equilibrium solubility of four calcium salts (calcium oxalate hydrate, calcium citrate tetrahydrate, calcium phosphate, calcium glycerophosphate) were determined at controlled pH values (7.5, 6.0, 4.5 and < or = 3.0) and in distilled water. The solubility of calcium carbonate was also measured at pH 7.5, 6.0 and 4.5 with two CO(2) environments (0.3 and 152 mmHg) above the solution. The precipitation profile of CaCO(3) was calculated using in-vivo data for bicarbonate and pH from literature and equilibrium calculations. As pH increased, the solubility of each calcium salt increased. However, in distilled water each salt produced a different pH, affecting its solubility value. Although calcium citrate does have a higher solubility than CaCO(3) in water, there is little difference when the pH is controlled at pH 7.5. The partial pressure of CO(2) also played a role in calcium carbonate solubility, depressing the solubility at pH 7.5. The calculations of soluble calcium resulted in profiles of available calcium, which agreed with previously published in-vivo data on absorbed calcium. The experimental data illustrate the impact of pH and CO(2) on the solubility of many calcium salts in the presence of bicarbonate secretions in the intestine. Calculated profiles using in-vivo calcium and bicarbonate concentrations demonstrate that large calcium doses may not further increase intestinal calcium absorption once the calcium carbonate solubility product has been reached.

Thermal decomposition of calcium citrate tetrahydrate

The thermal decomposition of calcium citrate tetrahydrate in dynamic air or dry nitrogen has been studied thoroughly. Thermal events encountered throughout the decomposition range (room temperature to 1000°C) have been monitored by TG, DTA and DSC. The encountered events have been characterized by analysing the decomposition solid products using X-ray diffractometry, IR spectroscopy and scanning electron microscopy (SEM). Non-isothermal kinetic and thermodynamic parameters ( A, k, Δ E, Δ H, C p and Δ S) have been determined. The results show that Ca 3(C 6H 5O 7) 2·4H 2O dehydrates in two successive steps at 60–140°C and 140–190°C each involving release of two moles of water. The ultimate decomposition product has been found to be CaO which formed above 640°C in air or dry nitrogen flow. SEM examinations indicate the formation of fusion nuclei accompanying the second dehydration step. Decomposition pathways in air and nitrogen are proposed.

Gypsum crystals formed on decomposing calcium citrate

Abstract Particle size and the specific surface area of gypsum crystals formed on decomposing an aqueous suspension of solid calcium citrate tetrahydrate by diluted 50% sulphuric acid at 25, 40, 60, 80 and 100°C was studied. The size of the gypsum crystals increases with increasing temperature of decomposition. At a constant temperature within the range of 25 to 100°C the median of gypsum crystal size distribution (PSD) increases for approximately 4 h after commencing decomposition and then reaches a virtually constant value. The specific surface area of gypsum crystals decreases after commencement of the reaction for approximately 6 h before reaching a constant value. Gypsum crystal growth by solute deposition from the liquid is responsible for PSD changes for approximately one hour at the commencement of reaction. Then the growth of larger crystals at the expense of smaller crystals, i.e. ripening, is apparently responsible for further changes in the PSD.