Synthesis of lead metaniobate by thermal decomposition of a coprecipitation product

The paper reports a new, nonconventional method for the preparation of oxygen-containing niobium compounds, based upon coprecipitation. The coprecipitation product of niobic acid with lead oxalate was used as precursor. Lead metaniobate was obtained by proper thermal treatment of the coprecipitate. The coprecipitate mechanism was studied and the optimal conditions for quantitative precipitation of niobium and lead were established. The mechanism of thermal decomposition of the coprecipitate was investigated by differential thermal analysis and X-ray powder diagrams. The final product of thermal decomposition, lead metaniobate, is formed at 850°C.     

Thermal synthesis of Barium and barium-strontium metaniobates by using a coprecipitation method

The paper presents a new, non-traditional method for the synthesis of barium metaniobate, BaNb₂O₆, and of a mixed barium-strontium metaniobate, Ba_0.29Sr_0.71Nb₂O₆, through the thermal decomposition of coprecipitation products. The conditions of quantitative precipitation of the metals as niobic acid and barium or barium-strontium oxalate were established. The mechanism of thermal decomposition of the coprecipitate was deduced from differential thermal analysis and X-ray diffraction date. Barium metaniobate forms at 470°C, below the temperature required in the synthesis based upon the solid-state reaction between Nb₂O₅ and BaCO₃ (1100°C). The mixed barium-strontium compound is formed at 700°C, below the 1100°C used in the reaction between Nb₂O₅, BaCO₃ and SrCO₃.     

Thermal and structural investigation of some oxalato-niobium complexes

Strontium tris(oxalato)oxoniobate, Sr₃[NbO(C₂O₄)₃]₂ · 8 H₂O has been synthesized and characterized by elemental analysis, infrared spectroscopy and powder X-ray diffraction. A mechanism of thermal decomposition is suggested on the basis of differential thermal analysis. The conditions of strontium metaniobate formation, as final product of the thermal decomposition, have been established.     

Synthesis of bismuth mixed oxide by thermal decomposition of a coprecipitate precursor

Bismuth mixed oxide powders were prepared by oxalate coprecipitation process. The thermal decomposition behaviour of the coprecipitate precursors has been followed by thermal analysis (TG-DTA) and FTIR spectroscopy. During the decomposition of the precursor, several intermediates species were detected and a mechanism of formation of mixed oxide by this method is proposed. After the thermal treatment, the precursor obtained of suggested formula Ca₃[Bi₆O₆(C₂O₄)₄(OH)₃NO₃]0.5H₂O, has led to the formation of CaBi₂O₄ at shorter reaction time than the traditional ceramic method. In order to consolidate the results, the coprecipitation in absence of oxalic precipitant under the same conditions was examined. XRD and scanning electron spectroscopy were used to study particles sizes and morphology.     

Separation and determination of tantalum and niobium by precipitation from homogeneous solution

An attempt to separate niobium and tantalum by precipitation from homogeneous solution by thermal decomposition of their peroxy complexes, in the presence of tannin and oxalate, has been only moderately successful. A more satisfactory separation of tantalum and niobium for ratios from 50:1 to 1:30 is obtained by extracting the bisulphate melt with ammonium oxalate before adding hydrogen peroxide, hydrochloric acid and tannin. For a tantalum/niobium ratio of 1:1 the niobium coprecipitation is reduced to 5 %. Furthermore, two alternative possibilities are presented: (1) a quantitative recovery of a tantalum precipitate at small oxalate and high tannin concentration, leaving 90% of the tantalum-free niobium in solution; (2) an 85 % recovery of niobium-free tantalum at high oxalate and small tannin concentration. A study of the coprecipitation process of niobium shows that the distribution coefficients follow a logarithmic pattern, true homogeneous mixed crystals being formed.     

Thermal,X-ray. And neutron-activation investigations of compounds of niobium and tantalum

The thermography of the sodium and potassium salts of metaniobate and metatantalate as well as the dichelate of niobium with n-propyl-3,4,5-trihydroxybenzoate (PTB) is investigated in atmospheres of air, nitrogen, and carbon dioxide; and their thermal decomposition products are identified. The niobyl dichelate (dichelate(1)) is isolated and its structure has been shown to be K[NbO(C₆H₂(OH)(O₂)-(COO)C₃H₇)₂]2(PTB)·3H₂O.     

Effect of the synthesis conditions on the formation of MgSrP2O7 and its characterisation for pigmentary application

In present research, we examined MgSrP₂O₇ as a new pigment with focus on its application as a corrosion inhibitor. The influence of the synthesis’ conditions on the product properties was examined. Samples were obtained by solid-state reaction and various homogenisation methods of initial components were employed (hand-milling, wet (ethanol/acetone) ball-milling and coprecipitation). Thermal behaviour of the reaction mixtures or dried coprecipitate was investigated using differential thermal and thermo-gravimetric analyses. Obtained samples were characterised with X-ray diffraction analysis, scanning electron microscopy and IR spectroscopy. Focusing on pigmentary application, specific properties of the samples were evaluated, such as thermal stability, mean particle size values and colour parameters, and also preliminary anticorrosion tests have been performed. Based on obtained results, MgSrP₂O₇ could be considered as a perspective corrosion inhibitor and homogenisation via coprecipitation can be rated as the best method of preparation of this composition, which provides the best thermal stability, the lowest particle size, the best homogeneity and the most promising corrosion inhibition characteristics (pH and ρ of the pigment aqua suspension) for the final product.     

Gravimetric analysis of tantalocolumbites by precipitation from homogeneous solution

An analysis of complex tantalocolumbites has been carried out by precipitation from homogeneous solutions. A homogeneous precipitation of tungsten, titanium, tantalum and niobium by thermal decomposition of the soluble peroxytungstates, described in previous papers, is used. Corrections for incomplete precipitation and coprecipitation phenomena are applied on the basis of the experimentally found values. Silicon and tin are separated by volatilisation as fluoride and iodide, respectively. Iron is extracted by means of isopropyl ether and the rare earth metals are precipitated homogeneously from an oxalate solution. Manganese is precipitated as the ammonium phosphate. The results are in good agreement with an independent method, the standard deviations being within 1 % for the major constituents.     

Mechanism for hydrotalcite decomposition: a controlled rate thermal analysis study

The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. Hydrotalcites containing carbonate, vanadate and molybdate were prepared by coprecipitation. The resulting materials were characterised by XRD, simultaneous TG-DTG-DTA and controlled rate thermal analysis (CRTA) to determine the stability and thermal decomposition pathway of the synthesised hydrotalcites. For the carbonate intercalated hydrotalcite dehydration takes place in three steps two of which are quasi-isothermal and one non-isothermal. Dehydroxylation and decarbonation occur separately over the 235-330 and 330-370 degrees C temperature range. A second non-isothermal decarbonation step is observed in the 371-541 degrees C range. In comparison the mixed carbonate-vanadate and carbonate-molybdate hydrotalcites show two dehydration steps and the dehydroxylation and decarbonation occur simultaneously. The observation of three dehydration steps is used to support the model of water molecules in three structurally distinct environments in the hydrotalcite interlayer. CRTA technology provides a mechanism for the decomposition of hydrotalcites.     

Isothermal and rising temperature kinetic studies of doped nonstoichiometric basic nickel carbonate

The techniques of thermal analysis are used to determine the mode of decomposition of nickel carbonates doped by the method of coprecipitation. Nickel carbonate prepared by this method is basic in nature with the stoichiometryxNiCO₃·yNi(OH)₂·zH₂O. Isothermal Thermogravimetry was applied to determine the mechanism of decomposition. Rising temperature Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) were used to study the effects of doping on the kinetics of the decomposition. Doping was found to strongly influence the kinetics of the decomposition. The kinetics of thermal decomposition of the doped carbonates were compared with conductivity studies. A compensation effect has been observed and is discussed, in the thermal decomposition of the doped nickel carbonates. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Molecular states of p-dimethylaminobenzonitrile coground with β-cyclodextrin investigated using solid-state fluorescence spectroscopy

Changes in molecular states of p-dimethylaminobenzonitrile (DMABN) coground with β-cyclodextrin (β-CD) were examined using solid-state fluorescence measurements. Formation of a DMABN/β-CD inclusion complex by coprecipitation was confirmed by powder X-ray diffraction measurement. The powder X-ray diffraction pattern of the ground mixture was a halo pattern and differed from the pattern of the mixture prepared by coprecipitation. Solid-state fluorescence measurements revealed emission by DMABN crystals in a twisted intermolecular charge-transfer state at 473 nm. DMABN in the DMABN/β-CD coprecipitate had a fluorescence emission peak at 393 nm due to its planar structure. In contrast, DMABN in a DMABN/β-CD ground mixture had an emission peak at 473 nm due to its twisted structure. Grinding time-dependent structural changes in DMABN were evaluated using fluorescence lifetime and relative quantum yield measurements. Structural changes in DMABN in the DMABN/β-CD coprecipitate from a planar to a twisted structure were observed with grinding. DMABN, dispersed in microcrystalline cellulose (CC) molecules in a DMABN/CC ground mixture, had a fluorescence emission peak at 473 nm. However, the excitation spectrum of a DMABN/β-CD ground mixture differed from that of DMABN in CC. These results indicated that the molecular state of DMABN accommodated in the β-CD cavity differs between the coprecipitate and the ground mixture.     

The thermal decomposition of calcium,sodium, silver and copper(II) acetates

The thermal decomposition of the acetates of calcium, sodium, silver and copper(II) have been investigated using thermogravimetry and differential thermal analysis, together with analysis of the gaseous products formed during the decomposition process. The results indicate that the major organic product formed is either acetone or acetic acid, depending on whether the final solid product is the oxide or the metal.     

Thermoanalytical investigations of niobium(V) complexes of 4-isopropylphenol

Thermal behaviour of newly synthesized niobium(V) aryloxides of composition [NbCl_5−n (OC₆H₄CH(CH₃)₂-4) _n ] (where n = 1 → 5) synthesized by the reactions of niobium pentachloride with 4-isopropylphenol in predetermined molar ratios in carbon tetrachloride has been studied by thermogravimetric (TG) and differential thermal analysis (DTA) techniques. The results showed that thermal decomposition of complex of composition [NbCl₄(OC₆H₄CH(CH₃)₂-4)] resulted in the formation of NbOCl₃ as the ultimate decompositional product while all other complexes yielded Nb₂O₅ as the final product of thermal decomposition. From the mathematical analysis of TG data, the kinetic and thermodynamic parameters viz. energy of activation, frequency factor, entropy of activation, etc. have been evaluated using Coats–Redfern equation.     

Study of Fe Addition on the Thermal Decomposition of Coprecipitated Oxalates for the Bi-based Superconductor Synthesis

This work introduces results obtained during the preparation of a Bi-based material with superconducting properties by oxalate coprecipitation. The influence of Fe presence on the precursors thermal stability and on the superconducting phases formation mechanism are presented. The thermal decomposition and the stability in air of FeC₂O₄×2H₂O and also of the components mixture were studied by DTA/TG. It was evidenced that iron oxalate decomposes at the lowest temperature compared to the decomposition temperatures of the individual oxalates. XRD, IR and TEM/ED studies were approached to investigate the individual oxalates and the mixture coprecipitates for the high-T _c superconducting material synthesis. This revised version was published online in August 2006 with corrections to the Cover Date.     

XAFS analysis of coprecipitation of zinc by sulfide ions in an acidic solution

The fluorescence XAFS (X–ray absorption fine structure) technique using synchrotron radiation was applied to characterize zinc in the Hg–Zn, Cd–Zn, and Bi–Zn coprecipitates, and to elucidate the reaction mechanism of the coprecipitation of zinc from a strong acidic solution. Hg L_II–, Cd K–, and Bi L_III–edge XAFS spectra suggested that the respective host materials of the coprecipitates listed above are metacinnabar (HgS), greenockite (CdS), and bismuthinite (Bi₂S₃) and that existence of zinc has not affected the local structure of the host metal sulfides in each system. On the other hand, the Zn K–edge XAFS spectra of each coprecipitate indicated that the chemical forms of zinc compounds are controlled by the crystal structure of the host sulfides.The shapes of the Zn K–XAFS spectra of the Hg–Zn and Cd–Zn coprecipitates showed a strong resemblance to those of crystalline standards ZnS, wurtzite and spharelite. It was suggested that the two coprecipitated phases (HgS, ZnS) and (CdS, ZnS) may form a solid solution in the Hg–Zn and Cd–Zn coprecipitates. The local structure around the zinc(II) ion in the Bi–Zn coprecipitate is the same as that around hexaaqua–zinc(II) ions, and adsorption of soluble ions or mechanical occlusion from the mother liquor is regarded as a driving force of coprecipitation in the Bi–Zn system.     

Chemical, structural, and thermal properties of Zn(II)-Cr(III) layered double hydroxides intercalated with sulfated and sulfonated surfactants

Zn(II)-Cr(III)-LDHs (layered double hydroxides) containing sulfated or sulfonated surfactants as the interlamellar anion were synthesized by the coprecipitation method. The syntheses were conducted under various different experimental conditions, such as the Zn : Cr ratio, pH, and aging time. In each of the prepared materials, unlike previously reported data, the interlayer anion arrangement did not change, being consistent with a perpendicular monolayer. The thermal decomposition process of the prepared materials was studied by a set of analysis methods, such as TG/DTA, TG/MS, PXRD, and FT-IR. From the results obtained it was possible to conclude that, in an air atmosphere, the anions decomposed by a partial combustion, leading to the formation of sulfide. The results also showed that sulfonated surfactants containing LDHs are much more stable than those containing sulfated surfactants. A mechanism was proposed for the thermal decomposition of such LDHs based on the experimental results.     

Mechanism of thermal decomposition of thiourea derivatives

The thermal decomposition of a series of compounds has been studied by thermogravimetry, mass spectrometry, nuclear magnetic resonance and elemental analysis. The combined use of mass spectrometry and thermogravimetry (MS and TG) in the analysis of these compounds has allowed characterization of the fragmentation pattern which was the objective of this research. The gaseous products, volatile condensed products and solid residues were identified by NMR and MS. Based on the product of thermal decomposition, the mechanism of thermal decomposition has been derived.     

Mechanochemical synthesis and some properties of dispersed lithium niobate

Interactions in the lithium carbonate-niobium pentoxide system upon mechanochemical treatment (MChT) in air and in water are studied. The products are examined using differential thermal and X-ray diffraction analyses; IR, Raman, and electron spectroscopy; nitrogen adsorption; and electron micros-copy. Activation of the reagents and direct mechanochemical synthesis of lithium metaniobate (LMN) were found to occur at 600–850 and 1000 rpm, respectively. Lithium metaniobate prepared by MChT has high dispersion, defect structure, and increased photocatalytic activity.     

Studies on the thermal decomposition kinetics and mechanism of ammonium niobium oxalate

Ammonium niobium oxalate was prepared and characterized by elemental analysis, XRD and FTIR spectroscopy analysis, which confirmed that the molecular formula of the complex is NH₄(NbO(C₂O₄)₂(H₂O)₂)(H₂O)₃. Dynamic TG analysis under air was used to investigate the thermal decomposition process of synthetic ammonium niobium oxalate. It shows that the thermal decomposition occurs in three stages and the corresponding apparent activation energies were calculated with the Ozawa–Flynn–Wall and the Friedman methods. The most probable kinetic models of the first two steps decomposition of the complex have been estimated by Coats–Redfern integral and the Achar–Bridly–Sharp differential methods.     

Ce-Zr-O固溶体的制备和表征

采用硝酸盐直接分解法、共沉淀法、苹果酸溶胶 凝胶法和柠檬酸溶胶 凝胶法制备了Ce Zr O复合氧化物并进行了表征。溶胶 凝胶法制得的Ce Zr O为立方的Ce0 .5Zr0 .5O2 复合氧化物 (其中少量具有立方性质的t″相 ) ,而直接分解和共沉淀法制得的是由立方Ce0 .8Zr0 .2 O2 和四方Ce0 .2 Zr0 .8O2 固溶体组成的复合氧化物。不同制备方法制得的样品由于物相组成不同 ,还原性能也有较大差别。差热分析和X射线衍射分析结果表明 ,凝胶在燃烧的同时生成了Ce0 .5Zr0 .5O2 固溶体。