Mixture Of Oxalate Research Articles

Caracterização de cálculos renais por análise térmica

Dez amostras de cálculos renais foram estudadas por Análise Elementar de CHN (EA), Espectroscopia de Absorção no Infravermelho (IV) e Difração de raios X pelo método de Pó (XRD). O comportamento térmico das amostras foi estudado por Termogravimetria/Termogravimetria Derivada (TG/DTG) e por Calorimetria Exploratória Diferencial (DSC). Os resultados de EA, Espectroscopia de Absorção IV e XRD mostraram a presença de estruvita [NH4Mg(PO4).6H2O], apatita, oxalato de cálcio monohidratado e oxalato de cálcio dihidratado. As curvas TG e DSC permitiram classificar as amostras em dois grupos diferentes: Grupo I mostrando comportamento térmico típico de estruvita e Grupo II apresentando um perfil termoanalítico característico de mistura de oxalatos.

Direct carbothermic reduction of actinide oxalates: Example of Nd(III) oxalate–carbon mixtures conversion

Mixed uranium–plutonium monocarbide was obtained by carbothermic reduction of mixture of UO 2, PuO 2 and C at around 1500 °C under vacuum or argon for 4 h followed by sintering at around 1650 °C under mixture of Ar + 8%H 2 for 10 h. Moreover, PuO 2 was synthesized by oxalic precipitation followed by calcination at around 700 °C (PUREX process). This work deals with a process simplification, i.e. fabrication of carbide by calcination of actinide oxalate, precipitated in presence of carbon, at 1600 °C for 13 h under argon. In this preliminary study, neodymium was used as a surrogate of actinides. No carbon influence was noticed during calcination of neodymium oxalate into oxide. Carbon content was the same before and after calcination making possible conversion to carbide directly from mixture of neodymium oxalate and C.

Mixed Urolith (Struvite and Calcium Oxalate) in a Ferret (Mustela Putorius Furo)

Urolithiasis has been reported in veterinary literature in some species of the Mustelidae family, including ferrets. In this species, the most common form of urolithiasis is that caused by struvite. The current study examined the case of mixed urolith in an 8-month-old female ferret (Mustela putorius furo) with antecedents of strangury and hematuria. A cystotomy was carried out to remove the urolith, which had a rough surface and a homogeneously porous interior and was formed by a mixture of struvite (60%) and calcium oxalate dehydrated (40%).

Use of oxalate sacrificial compounds to improve the photocatalytic performance of titanium dioxide

Our study demonstrated that the performance of TiO2 photocatalysts in eliminating organic compounds in water can be improved by combining them with calcium oxalate. The adsorption maximum capacity of Orange II on various pure photocatalysts is dependent on the specific area. Concerning the mixed TiO2/calcium oxalate catalysts, we observed that adsorption is still higher than that of pure correspondent photocatalysts. The influence of the sacrificial agent differs according to the photocatalyst used. Thus performance of the P25-TiO2 photocatalyst is positively slightly affected by the presence of calcium oxalate, whereas with TiO2-PC500 a decline in photocatalytic activity can be noted. The use of calcium oxalate significantly improves the performance of titanium dioxide prepared by sol–gel. We observed similar results with the kinetics of mineralization. It seems that the effect of oxygen is the same whether pure TiO2 samples or 70%TiO2/30%calcium oxalate mixtures are used, regarding the rate of conversion of Orange II after 30min of irradiation.

Crystal growth and magnetic properties of the copper coordination polymer [Cu(µ ‐C2O4)(4‐aminopyridine)2(H2O)]n

AbstractIn this paper, we consider various ways of crystal growth of the polymer [Cu(µ ‐C2O4)(4‐aminopyridine)2(H2O)]n. Single crystals of the size of 1.5×1.5×0.2 mm3 have been grown by a slow diffusion technique from solutions of the monoammine copper complex and of the mixture of potassium oxalate and aminopyridine with the stoichiometric ratio. Magnetic susceptibility and ESR measurements have been performed on single crystals large enough for investigating anisotropic properties. The susceptibility can be well described within the model of a Heisenberg antiferromagnetic spin chain. The magnetic measurements reveal a small concentration of paramagnetic moments reflecting the high quality of the single crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanocrystalline Fe–Ni and Fe–Co samples prepared by powder processing

Preparation and properties of nanocrystalline samples of Ni 3 Fe and FeCo alloys by calcination of mixtures of Fe, Co, and Ni oxalates are described. The samples contain according to XRD single Ni 3 Fe and FeCo phases with grain size about 40 and 45 nm, respectively. The parameters derived from the Mössbauer spectra confirm the single phase samples. The saturation induction values are close to the coarse polycrystals but coercive force is importantly higher and permeability lower. The magnetic behaviour is explained by the role of interfacial regions in the samples.

In-Situ Infrared Study of the Adsorption and Oxidation of Oxalic Acid at Single-Crystal and Thin-Film Gold Electrodes: A Combined External Reflection Infrared and ATR−SEIRAS Approach

The adsorption and oxidation of oxalic acid at gold electrodes were studied by in-situ infrared spectroscopy. External reflection experiments carried out with gold single-crystal electrodes were combined with internal reflection (ATR-SEIRAS) experiments with gold thin-film electrodes. These gold thin films, with a typical thickness of ca. 35 nm, were deposited on silicon substrates by argon sputtering. As previously reported for evaporated gold films, the voltammetric curves obtained in sulfuric acid solutions after electrochemical annealing show typical features related to the presence of wide bidimensional (111) domains with long-range order. The in-situ infrared data collected for solutions of pH 1 confirmed the potential-dependent adsorption of either oxalate (Au(100)) or a mixture of bioxalate and oxalate (Au(111), Au(110), and gold thin films) anions in a bidentate configuration. The better signal-to-noise ratio associated with the SEIRA effect in the case of the gold thin-film electrodes allows the observation of the carbonyl band for adsorbed bioxalate that was not detected in the external reflection experiments. Besides, additional bands are observed between 2000 and 3000 cm(-)(1) that can be tentatively related to the formation of hydrogen bonds between neighboring bioxalate anions. The intensities of these bands decrease with increasing solution pH values, disappearing for pH 3 solutions in which adsorbed oxalate anions are the predominant species. The analysis of the intensities of the nu(s)(O-C-O) and nu(C-OH) + delta(C-O-H) bands for adsorbed oxalate and bioxalate, respectively, suggests that the pK(a) for the surface equilibrium between these species is significantly lower than that for the solution equilibrium.

Synthesis and magnetic properties of ZnFe 2O 4 obtained by mechanochemically assisted low-temperature annealing of mixtures of Zn and Fe oxalates

The mechanism of formation of zinc ferrite (ZnFe 2O 4) from ZnC 2O 4·1.8H 2O–2Fe IIC 2O 4·2H 2O and ZnC 2O 4·1.8H 2O–Fe 2 III(C 2O 4) 3·6H 2O mixtures is investigated. By combination of TG and XRPD measurements it has been shown that microcrystalline ZnFe 2O 4 forms from physical mixtures after prolonged annealing at 1000 °C while nanocrystalline ZnFe 2O 4 powders are produced by mild annealing (1 h at 500 °C in air) of mechanically activated mixtures. The magnetic properties of ZnFe 2O 4 powders obtained from physical and from milled mixtures are compared.

A coprecipitation technique to prepare Sro.5Bao.5Nb206

An aqueous mixture of ammonium oxalate and ammonium hydroxide was used to coprecipitate barium and strontium ions as oxalates and niobium ions as hydroxide under basic conditions. This precursor on calcining at 750°C yielded Sr0.5Ba0.5Nb2O6 phase. This is a much lower temperature than that prepared by traditional solid state method (1000°C) as reported for the formation of Sr0.5Ba0.5Nb206 (SBN). Transmission electron microscopic (TEM) investigations revealed that the average particle size was 80 nm for the calcined powders. The room temperature dielectric constant at 1 kHz was found to be 1100. The ferroelectric hysteresis loop parameters of these samples were also studied.

Effect of ammonium oxalate/strontium carbonate on the burning rate characteristics of composite propellants

AP/HTPB based composite propellants with additives such as ammonium oxalate (AO), mixture of ammonium oxalate and strontium carbonate (SC) was investigated by burning rate, TG-DTG and FTIR experiments. The results show that the burning rates of these propellants are decreased significantly. TG-DTG experiments indicate that decomposition temperatures of AP with these additives are increased. Furthermore, the activation energy of the decomposition reaction of AP is also increased in the presence of AO or AO/SC. These results show that AO or AO/SC restrains the decomposition of AP. The burning rates of these propellants are decreased. The burning rate temperature sensitivity of AP/HTPB based propellants is reduced significantly by the addition of AO or AO/SC. But the effect of AO is less than that of AO/SC. AO/SC is better effect to reduce temperature sensitivity and at the same time, to reduce pressure exponent. The reduced heat release at the burning surface of AP/HTPB/AO is responsible for the reduced temperature sensitivity. Synergetic action is probably produced between AO and SC within AP/HTPB based propellants in the pressure range tested. This synergetic effect causes the heat release to reduce and the burning surface temperature to increase. Moreover, it makes the net exothermal reaction of condensed phase become little dependent on T0. Thus, the burning rate temperature sensitivity is reduced.

Inorganic–organic hybrid structures: Synthesis, structure and magnetic properties of a new iron oxalatoarsenate, [NH 3(CH 2)CH(NH 3)CH 3] 3[Fe 6(AsO 4) 2(HAsO 4) 6(C 2O 4) 3

A hydrothermal reaction of a mixture of iron oxalate, arsenic acid, 1,2-diaminopropane and water at 150 °C gave rise to a new three-dimensional iron oxalatoarsenate, [NH 3(CH 2)CH(NH 3)CH 3] 3[Fe 6(AsO 4) 2(HAsO 4) 6(C 2O 4) 3], I. Crystal data: hexagonal, space group = P-3c1, a = 13.9899 ( 12 ) , c = 14.936 ( 3 ) Å , V = 2531.6 ( 5 ) Å 3 . The structure consists of layers of vertex-sharing FeO 6 octahedral and AsO 4 tetrahedral units that form 12-membered apertures. The layers are connected together by the oxalate units, forming a uniform one-dimensional channel that is occupied by protonated amine molecules. Variable temperature powder XRD studies indicates that I loses crystallinity at ∼300 °C forming an amorphous phase that gives way to crystalline FeAsO 4 at ∼650 °C. Magnetic studies reveal that I is antiferromagnetic with T N = 31 K .

Hydrothermal synthesis, structure and magnetic properties of a new three-dimensional iron arsenate [C 6N 4H 21][Fe III3(HAsO 4) 6

A hydrothermal reaction of a mixture of iron oxalate, arsenic pentoxide, hydrofluoric acid and triethylenetetramine (TETA) at 150 °C for 48 h gives rise to a new iron arsenate [C 6N 4H 21][Fe 3(HAsO 4) 6], I. The structure consists of a network of FeO 6 and AsO 4 building units connected through their vertices giving rise to a new secondary building unit, SBU-5. The SBU-5 units are through their corners forming a three-dimensional structure possessing one-dimensional channels bound by 8-T atoms (T = Fe, As). The formation of SBU-5 units is noteworthy. Variable temperature magnetic studies indicate antiferromagnetic interactions between the Fe centers with T N of 21.9 K. Crystal data: M = 1156.36, monoclinic, space group = C2/ c (no. 15), a = 18.422(3) Å, b = 8.8527(13) Å, c = 16.169(2) Å, β = 111.592(2)°, V = 2451.9(6) Å 3, Z = 8, ρ calc = 3.037 g cm −3, μ(Mo Kα) = 9.903 mm −1, R 1 = 0.0358, w R 2 = 0.0763, S = 1.140 for 234 parameters.

A co-precipitation technique to prepare BaTa 2O 6

A mixture of ammonium oxalate and ammonium hydroxide was used to co-precipitate barium and tantalum ions as barium oxalate and tantalum hydroxide under basic conditions. On calcination at 750 °C, this precursor yielded BaTa 2O 6 (BT) ceramics. This is much lower temperature as compared to that prepared by traditional solid-state method (1000 °C) as reported for the formation of BaTa 2O 6. Transmission electron microscope (TEM) investigations revealed that the average particle size is 70 nm for the calcined powders. The room temperature dielectric constant at 1 kHz is found to be 100.

A co-precipitation technique to prepare CaNb 2O 6

A mixture of ammonium oxalate and ammonium hydroxide was used to co-precipitate calcium and niobium ions as calcium oxalate and niobium hydroxide under basic conditions. This precursor yielded CaNb 2O 6 (CN) ceramics on calcining at 750 °C, i.e. at a temperature much lower than 900 °C, reported for the formation of CaNb 2O 6 prepared by the traditional solid state method. Transmission electron microscope (TEM) investigations revealed an average particle size 100 nm for the calcined powders. The room temperature dielectric constant at 1 kHz was found to be 100. The ferroelectric hysteresis loop parameters of these samples were also studied.

Preparation of pyrochlore-free PMN powder by semi-wet chemical route

Wet chemical route was used to prepare lead magnesium niobate (PMN) powders by both the direct and the “columbite” methods. The columbite (MgO·Nb 2O 5) phase was prepared by calcining a homogeneous mixture of magnesium oxalate and niobium oxide powder in the temperature range of 1000–1050 °C Three different lead precursors, i.e., lead hydroxide, lead acetate and lead formate were investigated. In some cases, 3% excess MgO was also added. Pyrochlore-free PMN powder was obtained only in the case of formate precursors with 3% excess MgO processed via the columbite route. The phase pure powder was compacted, sintered at 1150 °C for 2 h in a lead rich atmosphere and dielectric constant of the sintered body was measured. The dielectric constant was measured to be 10,335 at room temperature and at a frequency of 100 Hz. The maximum dielectric constant was found to be 79,100 at 4.18 MHz.

A coprecipitation technique to prepare SrNb 2O 6

A mixture of ammonium oxalate and ammonium hydroxide was used to co-precipitate strontium and niobium ions as strontium oxalate and niobium hydroxide under basic conditions. This precursor yielded SrNb 2O 6 ceramics on calcining at 650 °C. This is a much lower temperature compared to preparation of SrNb 2O 6 by the traditional solid state method (900 °C). Transmission electron microscopy (TEM) revealed that the average particle size is 100 nm for the calcined powders. The room temperature dielectric constant at 1 kHz is found to be 550. The ferroelectric hysteresis loop parameters of these samples were also studied.

Photoredox processes in the Cr(VI)–Cr(III)–oxalate system and their environmental relevance

Irradiation of the [Cr(C2O4)3]3− complex or the chromate(VI)–oxalate mixture, or the ternary system composed of Cr(III), Cr(VI) and oxalate, leads to chromium photoreductions in consequence of the ligand to metal charge transfer (LMCT) excitations induced by artificial solar radiation. In the case of the Cr(III) complex, the photoreduction involves the innersphere electron transfer leading to the formation of the Cr(II) species and the C2O4− radicals. On reacting with molecular oxygen, Cr(II) is oxidised to Cr(III) catalysing thereby the oxalate substitution reaction. Moreover, under specific conditions, Cr(II) can be also oxidised to Cr(VI). Chromate(VI) is not photoreducible, but in the presence of oxalate, or other sacrificial electron donor, the outersphere photoinduced electron transfer (PET) produces Cr(V) species and the C2O4− radicals. This initiates a series of thermal reactions leading to the formation of Cr(III) and oxidized oxalate (CO2). In the system composed of [Cr(C2O4)3]3− and chromate(VI), the acidic medium and anoxic conditions favour the Cr(VI) photoreduction, whereas alkaline oxygenated solutions assist the Cr(VI) photoproduction. When an approximately neutral solution equilibrated with the ambient air is irradiated intermittently, Cr(VI) is consumed and/or produced, accordingly to the time sequence of exposure and dark periods. The oscillations of Cr(VI) concentrations are accompanied by continuous oxidation of oxalate, playing the role of the sacrificial electron donor. The effects of solution pH, molecular oxygen, concentrations of reagents and cations on the reaction rates were investigated. The results of this paper revealed that the Cr(III)/Cr(VI) system under environmental conditions behaves as the photocatalytic one catalysing the oxidation of oxalate or other organic matter by molecular oxygen, contributing thereby to the abatement of pollution.

A coprecipitation technique to prepare BaNb 2O 6

A mixture of ammonium oxalate and ammonium hydroxide was used to coprecipitate barium and niobium ions as barium oxalate and niobium hydroxide under basic conditions. This precursor on calcination at 750 °C yielded BaNb 2O 6 ceramics. This is a much lower temperature as compared to that prepared by traditional solid-state method (1000 °C), as reported for the formation of BaNb 2O 6. Transmission electron microscope (TEM) investigations revealed that the average particle size is 100 nm for the calcined powders. The room temperature dielectric constant at 1 kHz is found to be 1100. The ferroelectric hysteresis loop parameters of these samples were also studied.

Formate ion decomposition in water under UV irradiation at 253.7 nm.

Formate ion (HCO2-) occurs in natural waters as a result of photooxidation of humic substances. Under UV irradiation, as applied in water purification (253.7 nm), formate ion decomposed following split-rate pseudo-zero-order kinetics (k1 and k2 are initial and final rate constants, respectively). In the presence of dissolved oxygen (DO), it was found that (a) k1 < k2, (b) k1 and k2 increased with initial formate ion concentration ([HCO2-]0 = (1.73-38.3) x 10(-5) mol L(-1)) and absorbed UV intensity (Ia = (1.38-3.99) x 10(-6) mol quanta L(-1) s(-1)), and (c) k1 and k2 were relatively insensitive to initial pH (pHo = 5.41-8.97) in buffer-free solutions. Both rate constants decreased with increasing carbonate alkalinity ((0-1.0) x 10(-3) mol L(-1)) and k1 was virtually unchanged in phosphate buffer at pH0 between 5.25 and 9.92. Carbonate buffer lowered the rate of formate ion decay, possibly due to scavenging of OH* radicals. Initial rate constant k1 slightly increased with temperature (15-35 degrees C), while k2 remained unchanged. The reaction pH increased rapidly during irradiation of buffer-free NaHCO2 solution to approach an equilibrium level as [HCO2-] reached the method detection level (MDL). The pH profile of buffer-free formate ion decay was estimated using closed-system equilibrium analysis. DO utilization during UV irradiation was 0.5 mol of O2/mol of HCO2-, while nonpurgeable organic carbon (NPOC) measurements on kinetic samples closely followed the HCO2- profile, thus strongly suggesting the transformation of HCO2- -C to CO2 in the presence of DO. In DO-free water, k1 > k2 was observed. Furthermore, k(1,DO FREE) > k(1,DO) (k(1,DO) = k1) and k(2,DO FREE) < k(2,DO) (k(2,DO) = k2). The effect of dual acid solutions on HCO2- decay was examined in a mixture of NaHCO2 and sodium oxalate (Na2C2O4). HCO2- decomposed readily until [HCO2-] approximately equal to MDL but at a lower rate than in buffer-free HCO2- solutions, while C2O4(2-) remained virtually unchanged. C2O4(2-) decay commenced following near complete conversion of HCO2-.

Non-isothermal studies for the decomposition course of CdC 2O 4–ZnC 2O 4 mixture in air

The thermal decomposition of cadmium–zinc oxalate (1:1 mol ratios) mixture in air was investigated by non-isothermal thermogravimetric analysis. Intermediates and the final products were characterized by X-ray diffraction and scanning electron microscopy techniques. TG showed that the mixture dehydrated in two steps and decomposed exothermically to CdO–ZnO mixture at 390 °C in a further two steps. The observed increase in the intensity of the X-ray diffraction lines by raising the calcination temperature from 400 to 800 °C is attributed to the grain growth of CdO–ZnO mixture as revealed from SEM experiments. The kinetics of the oxalate decomposition steps was performed using the various reaction interface models and differential techniques of computational analysis of non-isothermal data. The activation parameters, calculated using the integral composite method, showed that the reactions were best described by the random nucleation model characteristic of solid state nucleation growth mechanism. The results of activation parameters for the different decomposition steps are compared and discussed.