Thermal decomposition features of calcium and rare-earth oxalates

Thermal decomposition of Ln₂(C₂O₄)₃ · 9H₂O concentrate (Ln = La, Ce, Pr, Nd) in the presence of CaC₂O₄ · H₂O was studied by X-ray diffraction, thermogravimetry, and chemical analysis. Annealing at temperatures above 374°C in the absence of calcium oxalate gives rise to the solid solution of CeO₂-based rare-earth oxides. Calcite CaCO₃ is formed in the presence of calcium oxalate at annealing temperatures above 442°C, which impedes the formation of lanthanide oxide solid solution and favors crystallization of oxides as individual La₂O₃, CeO₂, Pr₆O₁₁, and Nd₂O₃ phases. An increase in temperature above 736°C is accompanied by decomposition of calcium carbonate to give rise to an individual CaO phase and an individual phase of CeO₂-based lanthanide oxide solid solution.     

Inhibition of the crystal growth and aggregation of calcium oxalate by elemental selenium nanoparticles

Chemical modulation of calcium oxalate (CaC₂O₄) crystals morphologies by elemental selenium nanoparticles (nanoSe⁰) was investigated with scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), Fourier transform infrared spectrometry (FTIR), and X-ray diffraction (XRD) analysis. The coordination between nanoSe⁰ and C₂O₄²⁻ had great effect on the formation of CaC₂O₄ crystals. NanoSe⁰ inhibited the growth of calcium oxalate monohydrate (COM) crystals, prevented the aggregation of COM crystals and induced the formation of the spherical calcium oxalate dihydrate (COD) crystals containing selenium, which are the thermodynamically less stable phase and has a weaker affinity to the cell membranes than COM crystals. The inhibition of the crystal growth and aggregation of CaC₂O₄ crystals by nanoSe⁰ displayed concentration effects.     

Synthesis of different polymorphic modifications of calcium oxalate by electrodeposition

Different hydrates of calcium oxalate have been electrodeposited by electrogeneration of acid at the anode from an EDTA-stabilized calcium nitrate bath containing dissolved oxalate ions. The deposition is controlled by varying the bath pH, temperature, and current density. Formation of metastable CaC₂O₄·2H₂O is favored at high current densities at ambient temperature, whereas the thermodynamically stable CaC₂O₄·H₂O is formed at elevated bath temperatures. Both the polymorphs show oriented growth with respect to the substrate normal under different deposition conditions.     

Soft template inducing synthesis of CaC2O4 nanotubes

CaC₂O₄ nanotubes were controllably synthesized via the tiny water channels in the bicontinuous microemulsion at room temperature. The products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FT-IR). The results indicate that as-obtained products are calcium oxalate monohydrate (COM) crystal. These nanotubes have diameters of about 100 nm and lengths of about 700 nm. The key controlling parameters such as the reactant concentration (ratio) and the aging time have been investigated. The possible formation mechanism of the CaC₂O₄ nanotubes was also discussed.     

INDUCTION OF CRYSTALLIZATION OF SPECIFIC CALCIUM OXALATE HYDRATES IN MICELLAR SOLUTIONS OF SURFACTANTS

ABSTRACT

The influence of octaethylene glycol mono-n-hexadecyl ether (C₁₆EO₈) and sodium dodecyl sulphate (SDS) on the crystallization of calcium oxalate from 0.3 mol dm^?3 sodium chloride solutions has been investigated. The critical micellar concentration (CMC) of C₁₆EO₈ in water and 0.3 mol dm^?3 NaCl was determined by surface tension measurements (CMC_H2O=CMC_NaCl = 7.2.10^?6 mol dm^?3). The kinetics of precipitation of calcium oxalate was followed by Coulter counter, and solid phases were characterized by polarized microscopy, thermal analysis and X-ray powder diffraction patterns. Under the precipitation conditions employed, the thermodynamically stable monohydrate, CaC₂O₄?H₂O (COM) was the predominant crystalline form. In the presence of micellar solutions of C₁₆EO₈ precipitation of this phase was facilitated as evidenced by higher initial precipitation rates and higher precipitate volume and number of particles, as compared to the controls. Micellar solutions of 50S retarded precipitation but induced crystallization of calcium oxalate dihydrate, CaC₂O₄?(2+×)H₂O (COD, x≤0.5). Thus at c(SDS>CMC the precipitates contained ≥85 mass % COD. The results are discussed in relation to previously reported data on the precipitation of calcium oxalate in the presence of dodecyl ammonium chloride     

乌梅提取液对草酸钙晶体生长的抑制作用研究

本文研究了水体系中加入乌梅提取液对草酸钙晶体生长的抑制作用,通过FTIR、SEM及XRD等测试方法对所得晶体进行表征。结果表明,不加乌梅提取液的体系中形成的晶体为一水合草酸钙(COM)晶体,加入乌梅提取液后,形成的是二水合草酸钙(COD)晶体,而且COD晶体的尺寸随着乌梅提取液浓度的增大而减小,直至消失,这说明乌梅提取液具有抑制草酸钙晶体生长的作用,且这种抑制作用随乌梅浓度的增大而增大。本文还通过电导率法研究了草酸钙晶体生长的动力学过程,发现乌梅提取液主要能抑制草酸钙晶体的成核过程。     

Synthesis of nanoparticles of the giant dielectric material,CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> from a precursor route

A complex oxalate precursor, CaCu₃(TiO)₄(C₂O₄)₈·9H₂O, (CCT-OX), was synthesized and the precipitate that obtained was confirmed to be monophasic by the wet chemical analyses, X-ray diffraction, FTIR absorption and TG/DTA analyses. The thermal decomposition of this oxalate precursor led to the formation of phase-pure calcium copper titanate, CaCu₃Ti₄O₁₂, (CCTO) at ≥680°C. The bright-field TEM micrographs revealed that the size of the as synthesized crystallites to be in the 30–80 nm range. The powders so obtained had excellent sinterability resulting in high density ceramics which exhibited giant dielectric constants upto 40000 (1 kHz) at 25°C, accompanied by low dielectric losses, <0.07.     

卵磷脂-水体系中草酸钙模拟生物矿化的研究

草酸钙通常以三种水化物的形式存在：热力学稳定的一水草酸钙（以下简称COM），亚稳态的二水草酸钙（以下简称COD）和三水草酸钙（以下简称COT）。前人研究已经表明引起草酸钙不同水化物成核、生长以及聚集的因素，不仅仅在于钙离子和草酸根离子浓度的过量，而且与晶体成长所处环境包括离子种类、浓度、环境等有关。有关表面活性剂对草酸钙结晶过程的影响，例如SkriticD．小组做了大量的研究工作犤１～３犦。他们指出草酸钙晶体的成核、生长、组成以及晶体结构同表面活性剂水溶液的状态间存在着复杂的相关性犤１犦。本文选用卵磷脂（P…     

Computational prediction of the pattern of thermal gravimetry data for the thermal decomposition of calcium oxalate monohydrate

The multistep decomposition of CaC₂O₄·H₂O in the gaseous phase was explored at the MP2/cc-pVDZ level of theory. As a result, the structure and energy of the entities occurring at stationary points along the reaction pathway were determined. Statistical thermodynamics routines were used to obtain thermal energies/enthalpies and entropies. The results demonstrated the consecutive release of H₂O, CO and CO₂ from the substrate with increasing temperature. Moreover, the application of thermodynamic and kinetic characteristics to relevant phenomenological relationships enabled the decomposition pattern in equilibrium and non-equilibrium conditions to be predicted. The forecast patterns qualitatively match the experimental thermal gravimetry data. This study supplies much important information on the molecular changes taking place in a stoichiometric unit of calcium oxalate monohydrate during continuous heating     

沙苑子提取液对不同体系中草酸钙晶体生长影响的研究

通过与水、氯化钠、正常人尿液体系的比较,重点研究了结石患者尿液体系中加入中药沙苑子提取液对草酸钙晶体生长的的影响,利用SEM,FTIR和XRD等测试手段对所得晶体进行表征。结果发现:在结石患者尿液体系中形成的草酸钙晶体为一水草酸钙(COM)晶体,而在这4种体系中加入沙苑子提取液后,只形成二水草酸钙(COD)晶体,表明沙苑子提取液能抑制COM晶体生长,并且随着沙苑子提取液浓度增大,抑制作用增强。沙苑子抑制草酸钙晶体生长的可能机理进行了探讨。     

NOx and N2O precursors from co-pyrolysis of biomass and sludge

Heterobimetallic oxalate complex precursor, Ca₃[La(C₂O₄)₃(H₂O)₄]₂·5H₂O (CaOLa) was synthesized in aqueous medium and characterized by elemental analysis, IR, electronic spectral, and powder X-ray diffraction studies. It is found to be fined crystalline in nature with triclinic symmetry. Thermal studies (TG, DTG, and DTA) in air showed that the departure of aqua ligands completed at ca. 240 °C. A mixture of mainly CaO, La₂O₃, and La₂CaO _x along with a trace of carbides of calcium and lanthanum were identified in the end products at 1,000 °C. The nature of decomposition in nitrogen was explored from DSC study and discussed the evaluated kinetic parameters.     

Mineral and microelement compositions of urinary stones

The mineral and microelement compositions of urinary stones from patients in various districts of the Novosibirsk region are analyzed. The mineral composition is determined using X-ray powder diffraction and vibrational spectroscopy. The microelement composition is identified using synchrotron radiation X-ray fluorescence analysis. Calcium oxalates (whewellite CaC₂O₄ · H₂O and weddellite CaC₂O₄ · 2H₂O) are the most frequent components of the urinary stones. Oxalate uroliths contain a variety of microelements in significant amounts. Phosphate uroliths, represented by hydroxylapatite Ca₅(PO₄)₃(OH) and struvite MgNH₄PO₄ · 6H₂O, account for about one-fifth of the collection. Apatite urinary stones contain maximal strontium amounts. The struvite uroliths have higher rubidium levels. Uric acid uroliths (C₅H₄N₄O₃) account for about 11% of the collection. Their strontium concentrations are minimal. The element composition of the urinary stones is a function of their mineral constituents, the environmental surroundings, and the metabolism specifics of the patient.     

Oxalate-2-ethanolamine complexes of some bivalent cations (Mn,Co, Ni,Cu, Zn and Cd)

On the refluxing ofM(II) oxalate (M=Mn, Co, Ni, Cu, Zn or Cd) and 2-ethanolamine in chloroform, the following complexes were obtained: MnC₂O₄·HOCH₂CH₂NH₂·H₂O, CoC₂O₄·2HOCH₂CH₂NH₂, Ni₂(C₂O₄)₂·5HOCH₂CH₂NH₂·3H₂O, Cu₂(C₂O₄)₂·5HOCH₂CH₂NH₂, Zn₂(C₂O₄)₂·5HOCH₂CH₂NH₂·2H₂O and Cd₂(C₂O₄)₂·HOCH₂CH₂NH₂·2H₂O. Following the reaction ofM(II) oxalate with 2-ethanolamine in the presence of ethanolammonium oxalate, a compound with the empirical formula ZnC₂O₄·HOCH₂CH₂NH₂·2H₂O¹ was isolated. The complexes were identified by using elemental analysis, X-ray powder diffraction patterns, IR spectra, and thermogravimetric and differential thermal analysis. The IR spectra and X-ray powder diffraction patterns showed that the complexes obtained were not isostructural. Their thermal decompositions, in the temperature interval between 20 and about 900°C, also take place in different ways, mainly through the formation of different amine complexes. The DTA curves exhibit a number of thermal effects.     

The enthalpies of interactions of Ca2+(aq) and C2O 4 2− (aq) ions in complexon solutions: Competition between complexation and precipitation

The thermal effects of mixing of aqueous calcium chloride with sodium citrate and ethylenedi-aminetetraacetate in the absence and presence of sodium oxalate have been measured at 25°C. The thermal effects of dilution of aqueous calcium chloride solutions were determined. The thermal effects of calcium oxalate precipitation and formation of calcium complexes with citrate and ethylenediaminetetraacetate ions were calculated. The 1% solution of sodium citrate inhibited the formation of CaC₂O₄ (s); in a 1% solution of sodium ethylenediaminetetraacetate with [Ca²⁺][C₂O ₄ ^2? ] > 10^?5, the endothermal formation of the [CaEdta]^2? complex quickly changed to exothermal precipitation. The 3 and 5% solutions of complexons showed a pronounced inhibiting effect on the formation of urinary stones even when the concentration of calcium and oxalate ions in solution exceeded the product of solubility of CaC₂O₄ by four and more orders of magnitude.     

Some studies on thallium oxalates. VI

The effect of the thallium(I) concentration on the potentiometric titration of thallium(III) with oxalic acid in 0.1M HNO₃ or 0.05M H₂SO₄ is studied, and conditions are established for the preparation of the thallium(I) bis-oxalato diaquo thallate(III) complex. Chemical analysis of the salt corresponds to the formula T1^I(T1^III(C₂O₄)₂) · 5 H₂O. Thermal decomposition studies on the complex using TG, DTG and DTA techniques indicate the formation of thallium(I) oxalate (stable from 130° to 320°) as the intermediate, the final product being a mixture of thallium(I) oxide and thallium(III) oxide (stable from 520° to 600°). Infrared absorption spectra, X-ray diffraction patterns and microscopic observations are used to characterise the complex and the intermediate.     

Thermal decomposition of barium oxomolybdenum(VI) oxalate

A new molybdenum(VI) oxalato complex, Ba[MoO₃(C₂O₄)]·3H₂O (BMO), was prepared and characterized by chemical analysis and infrared spectral studies. Thermal decomposition studies were made using thermogravimetry and differential thermal analysis. Dehydration reactions take place up to 280°C in three stages with loss of one half, one and a half and one mole of water per mole of BMO, respectively. Decomposition of oxalate takes place between 280 and 435°C in a single step to give BaMoO₄ as the end product, which was characterized by chemical analysis, infrared and X-ray studies. The X-ray diffraction pattern of BMO shows that it is an amorphous compound. A chain structure containing MoO₆ octahedra linked through oxygen is proposed on the basis of the infrared absorption spectrum.     

Partial thermal reduction of ammonium paratungstate tetrahydrate

Thermal decomposition of ammonium paratungstate tetrahydrate, (NH₄)₁₀[H₂W₁₂O₄₂]·4H₂O has been followed by simultaneous TG/DTA and online evolved gas analysis (TG/DTA-MS) in flowing 10% H₂/Ar directly up to 900°C. Solid intermediate products have been structurally evaluated by FTIR spectroscopy and powder X-ray diffraction (XRD). A previously unexplained exothermic heat effect has been detected at 700–750°C. On the basis of TG/DTA as well as H₂O and NH₃ evolution curves and XRD patterns, it has been assigned to the formation and crystallization heat of γ-tungsten-oxide (WO_2.72/W₁₈O₄₉) from β-tungsten-oxide (WO_2.9/W₂₀O₅₈) and residual ammonium tungsten bronze.     

Thermal decomposition of cadmium succinate dihydrate

Thermal decomposition of cadmium succinate dihydrate, CdC₄H₄O₄·2H₂O, was studied in dynamic helium and air atmospheres by means of simultaneous TG, DTA and MS analysis. It was found that dehydration of CdC₄H₄O₄·2H₂O takes place in the temperature range 80–165°C and at low heating rates formation of monohydrate was stated. The anhydrous cadmium succinate decomposes at about 350°C to metallic cadmium. The gaseous products of cadmium succinate decomposition are CO₂ and H₂O. Formation of small amounts of 3-phenylpropanal and 1,7-octadiene during decomposition in helium was revealed. In helium cadmium evaporates at the temperature of decomposition and the residue consists of small amount of elementary carbon formed in result of pyrolysis of succinate groups. In air cadmium oxidizes and the final solid product of decomposition is CdO.     

Synthesis, TG, DSC and infrared spectral study of NiMn2(C4H4O4)3·6N2H4

Nickel manganese succinato-hydrazinate (NiMn₂(C₄H₄O₄)₃·6N₂H₄), has been synthesized for the first time by a novel precursor technique and characterized by IR, AAS and XRD. Thermal decomposition of the compound was studied from room temperature (rT) to 800°C by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis besides isothermal mass loss studies. The compound was found to decompose autocatalytically, once ignited. TG-DSC shows two steps decomposition i.e. dehydrazination followed by decarboxylation. The infrared spectral studies show the N–N stretching frequency at 972 cm^–1 suggesting a bidentate bridging structure of hydrazine molecule in (NiMn₂(C₄H₄O₄)₃·6N₂H₄).     

Separate Crystallization of Lanthanide Oxalates and Calcium Oxalates from Nitric Acid Solutions

The separation of lanthanides from calcium compounds in the form of oxalates from hot nitric acid solutions of Ln(NO₃)₃ and Ca(NO₃)₂ with the insertion of oxalic acid and a Ln₂(C₂O₄)₃ · nH₂O crystal seed was studied by mass-spectrometric, atomic emission, microscopic, X-ray diffraction, and fluorescence analyses. The produced single-phase precipitate was found to contain an isomorphic impurity of La–Sm oxalates, while calcium oxalate remained in the hot nitric acid solution (95°С) saturated with oxalic acid. This facile and efficient method provides Ln₂(C₂O₄)₃ · nH₂O (n = 9.5 mol) in one step in a 80.1 rel. % yield, with the major phase being at least 99.4 wt %. The unit cell parameters were determined for the crystals of the isomorphic lanthanide oxalate mixture: a = 11.243(2) Å, b = 9.591(2) Å, c = 10.306(2) Å; α = γ = 90°, β = 114.12(1)°; Z = 2; V = 1013.7(5) ų.