Precipitation of calcium carbonate particles by gas–liquid reaction: Morphology and size distribution of particles in Couette-Taylor and stirred tank reactors

The morphology and size of CaCO₃ precipitated by CO₂–Ca(OH)₂ reaction in stirred tank and Couette-Taylor reactors were experimentally investigated. The Taylor vortex in CT reactor encouraged more homogeneous mixing conditions, resulting in the production of smaller particles with a uniform shape throughout the reactor. However, in the stirred tank reactor, the local non-homogeneity of the mixing intensity led to the simultaneous production of cube-like and spindle-like particles at a high reactant concentration. The agglomeration of CaCO₃ resulted in a bimodal size distribution. However, the morphology and size of a single particle were predominantly changed by the excess species in the solution. The largest mean size and cube-like particles were observed under stoichiometric reaction conditions. As the excess species concentration increased, the morphology was transformed to a spindle-like shape and the mean size decreased due to selective adsorption of the excess species on the crystal faces.     

Effect of pulverization and dehydration on the pharmaceutical properties of calcium lactate pentahydrate tablets

The effects of heat conduction and pulverization on dehydration kinetics and tablet hardness were studied by a variety of kinetic equations and physical models. The dehydration behavior of unpulverized calcium lactate pentahydrate (UCLP) and pulverized calcium lactate pentahydrate (PCLP) tablets was investigated by using differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). The hardness of both UCLP and PCLP tablets was significantly decreased after dehydration. The relationship between the extent of dehydration and the tablet hardness of both UCLP and PCLP tablets was linear. The results suggest that the reduction in tablet hardness is dependent on the dehydration of crystal water, and the values of the slopes indicate that the bonding energy of the UCLP was stronger than that of the PCLP. The dehydration of both UCLP and PCLP tablets at 55 °C followed a one-dimensional diffusion mechanism, whereas dehydration at storage temperatures of 60–80 °C followed a three-dimensional diffusion mechanism. UCLP and PCLP tablets contracted in thickness and diameter during dehydration, but final contraction ratios showed that PCLP tablets were more affected than UCLP tablets. In contrast, the micropore radius of both UCLP and PCLP tablets increased after dehydration. Thus, the pharmaceutical properties of calcium lactate pentahydrate (CLP) tablets are affected both by pulverization and by the extent of dehydration of the bulk powder in the tablet formulation.     

Syntheses, Structure Characterizations and Fluorescent Properties of Two Reduced Molybdenum (V) Phosphates Functionalized by Zinc Coordination Complexes

Two new materials built from reduced molybdenum (V) phosphates as building blocks and zinc coordination complexes as linkers, (H₃O)₂[Zn(2,2′-bpy)]₄[Zn(H₂O)]₂[Zn(HPO₄)₂ (PO₄)₆(MoO₂)₁₂(OH)₆] · 6H₂O (2,2′-bpy=2,2′-bpyridine) 1 and [Zn(phen)(H₂O)₂]₂[Zn(phen) (H₂O)]₂[Zn(H₂O)]₂[Zn(HPO₄)₄ (PO₄)₄(MoO₂)₁₂ (OH)₆] · 7H₂O (phen=1,10-phenanthroline) 2, have been synthesized and characterized by elemental analyses, IR, TG, and single crystal X-ray diffraction. Compound 1 is a new 3-D structure which constructed from Zn[P₄Mo₆]₂ dimers bonded together with [Zn(2,2′-bpy)] coordination complexes and [Zn(H₂O)] fragments. In compound 2, the Zn[P₄Mo₆]₂ dimeric units are linked by [Zn(phen)(H₂O)] coordination complexes and [Zn(H₂O)] fragments to form a new 2-D framework. The fluorescent activities of compounds 1 and 2 were reported. The crystal data for the two compounds are the following: 1, triclinic, P−1, a=13.036(3) ?, b=13.765(3) ?, c=14.459(3) ?, , Z=1; 2, triclinic, P−1, a=12.708(3) ?, b=14.016(3) ?, c=14.646(3) ?, , Z=1.Dedicated to Professor Michael T. Pope on the occasion of his retirement.     

Crystal structure and phase transformations of calcium yttrium orthophosphate, Ca3Y(PO4)3

Crystal structure and phase transformations of calcium yttrium orthophosphate Ca₃Y(PO₄)₃ were investigated by X-ray powder diffraction, selected-area electron diffraction, transmission electron microscopy and optical microscopy. The high-temperature phase is isostructural with eulytite, cubic (space group ) with a=0.983320(5) nm, V=0.950790(8) nm³, Z=4 and D_x=3.45 Mg m⁻³. The crystal structure was refined with a split-atom model, in which the oxygen atoms are distributed over two partially occupied sites. Below the stable temperature range of eulytite, the crystal underwent a martensitic transformation, which is accompanied by the formation of platelike surface reliefs. The inverted crystal is triclinic (space group P1) with a=1.5726(1) nm, b=0.84267(9) nm, c=0.81244(8) nm, α=109.739(4)°, β=90.119(5)°, γ=89.908(7)°, V=1.0134(1) nm³, Z=4 and D_x=3.24 Mg m⁻³. The crystal grains were composed of pseudo-merohedral twins. The adjacent twin domains were related by the pseudo-symmetry mirror planes parallel to with the composition surface . When the eulytite was cooled relatively slowly from the stable temperature range, the decomposition reaction of Ca₃Y(PO₄)₃→β-Ca₃(PO₄)₂+YPO₄ occurred.     

Nucleation and growth of calcium-phosphate on Ca-implanted titanium surface

Calcium phosphate formation on Ca-implanted titanium surfaces is studied. Experimental results show that octacalcium phosphate (OCP) is the more energetically favorable phase to precipitate on the positively charged Ca-implanted titanium surfaces compared to hydroxylapatite (HA), especially with the existence of a large amount of ions. A solution-based cluster theory is employed to explain the process of the formation of calcium phosphate on the Ca-implanted titanium surfaces. Thermodynamic and kinetic calculations show that OCP is the kinetically favored phase to precipitate in the SBF solution than HA. The nucleation rate is much higher than that of HA, but HA is more stable thermodynamically.     

A microchip sensor for calcium determination

A newly designed glass-PDMS microchip-based sensor for use in the determination of Ca²⁺ ions has been developed, utilizing reflectance measurements from arsenazo III (1,8-dihydroxynaphthalene-3,6-disulfonic acid-2,7-bis[(azo-2)-phenyl arsenic acid]) immobilized on the surface of polymer beads. The beads, produced from cross-linked poly(p-chloromethylstyrene) (PCMS), were covalently modified with polyethylenimine (PEI) to which the Arsenazo III could be adsorbed. The maximum amount of Arsenazo III which could be immobilized onto the PEI-attached PCMS beads was found to be 373.71 mg g⁻¹ polymer at pH 1. Once fabricated, the beads were utilized at the detection point of the microfluidic sensor device with a fiber optic assembly for reflectance measurements. Samples were mobilized past the detection point in the sensor where they interact with the immobilized dye. The sensor could be regenerated and re-used by rinsing with HCl solution. The pH, voltage, linear range, and the effect of interfering ions were evaluated for Ca²⁺ determination using this microchip sensor. At the optimum potential, 0.8 kV, and pH 9.0, the linear range of the microchip sensor was 3.57 × 10⁻⁵ – 5.71 × 10⁻⁴ M Ca²⁺, with a limit of detection (LOD) of 2.68 × 10⁻⁵ M. The microchip biosensor was then applied for clinical analysis of calcium ions in serum with good results. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

电感耦合等离子体原子发射光谱法测定轻质隔墙板中镁钙铝铁锰氯

10 g轻质隔墙板试样溶于8 mol.L-1硝酸溶液100 mL中,于此溶液中定量加入相当于氯离子估计量(物质的量)1.2倍的硝酸银溶液使其中氯离子定量生成AgCl沉淀。经陈化后,将混合物滤入于200 mL容量瓶中,加水定容。分取此溶液一份,用水稀释200倍后,用电感耦合等离子体原子发射光谱法(ICP-AES)测定其中镁、钙及银的含量。所得银的量为定量生成AgCl沉淀后留存的过量硝酸银溶液。按此银的测定值间接换算成试样中氯的含量。从上述定容为200 mL溶液中,另分取一份溶液加水稀释5倍后,按ICP-AES法测定其中痕量铝、铁及锰的含量。按所提出的方法测定了实样中镁、钙、氯及铝、铁、锰的含量,测定值的相对标准偏差(n=6)均小于2%。     

Structural study of polymorphism and thermal behavior of CaZr(PO4)2

The crystal structure of CaZr(PO₄)₂ has been revised by ab initio Rietveld analysis of X-ray powder diffraction data. At room temperature, CaZr(PO₄)₂ crystallizes in the orthorhombic space group Pna2₁ (Z = 4). Differential thermal analysis suggests a reversible second order transition at 1000 °C confirmed by high temperature XRD analysis that brings out the existence of a high temperature form, very similar to the room temperature one, but more symmetrical (Pnma, Z = 4). Analysis of the crystal parameters evolution during heating reveals that CaZr(PO₄)₂ exhibits a quite low thermal expansion coefficient of 6.11·10⁻⁶ K⁻¹. This value stems from a combination of several mechanisms, including Coulombic repulsion and bridging oxygen rocking motion.     

Isopiestic measurement and solubility evaluation of the ternary system (CaCl2 + SrCl2 + H2O) at T = 298.15 K

Water activities in the ternary system (CaCl₂ + SrCl₂ + H₂O) and its sub-binary system (CaCl₂ + H₂O) at T = 298.15 K have been elaborately measured by an isopiestic method. The data of the measured water activity were used to justify the reliability of solubility isotherms reported in the literature by correlating them with a thermodynamic Pitzer–Simonson–Clegg (PSC) model. The model parameters for representing the thermodynamic properties of the (CaCl₂ + H₂O) system from (0 to 11) mol ⋅ kg⁻¹ at T = 298.15 K were determined, and the experimental water activity data in the ternary system were compared with those predicted by the parameters determined in the binary systems. Their agreement indicates that the PSC model parameters can reliably represent the properties of the ternary system. Under the assumption that the equilibrium solid phases are the pure solid phases (SrCl₂ ⋅ 6H₂O and CaCl₂ ⋅ 6H₂O)_(s) or the ideal solid solution consisting of CaCl₂ ⋅ 6H₂O_(s) and SrCl₂ ⋅ 6H₂O_(s), the solubility isotherms were predicted and compared with experimental data from the literature. It was found that the predicted solubility isotherm agrees with experimental data over the entire concentration range at T = 298.15 K under the second assumption described above; however, it does not under the first assumption. The modeling results reveal that the solid phase in equilibrium with the aqueous solution in the ternary system is an ideal solid solution consisting of SrCl₂ ⋅ 6H₂O_(s) and CaCl₂ ⋅ 6H₂O_(s). Based on the theoretical calculation, the possibility of the co-saturated points between SrCl₂ ⋅ 6H₂O_(s) and the solid solution (CaCl₂ ⋅ 6H₂O + SrCl₂ ⋅ 6H₂O)_(s) and between CaCl₂ ⋅ 6H₂O_(s) and the solid solution (CaCl₂ ⋅ 6H₂O + SrCl₂ ⋅ 6H₂O)_(s), which were reported by experimental researchers, has been discussed, and the Lippann diagram of this system has been presented.