Structural and thermal studies on the solid products in the system MnSeO<Subscript>3</Subscript>-SeO<Subscript>2</Subscript>-H<Subscript>2</Subscript>O

The solubility of MnSeO₃-SeO₂-H₂O system was studied in the temperature region 25–300°C. The compounds of the three-component system were identified by the Schreinemaker’s method. The phase diagram of manganese(II) selenites was drawn and the crystallization fields for the different phases were determined. Depending on the conditions for hydrothermal synthesis, MnSeO₃·H₂O, MnSeO₃·3/4H₂O, MnSeO₃·l/3H₂O and MnSe₂O₅ were obtained. The different phases were proven and characterized by chemical, powder X-ray diffraction and thermal analyses, as well as IR spectroscopy. The kinetics of dehydration and decomposition of MnSeO₃·H₂O was studied under non-isothermal heating. Based on 4 calculation procedures and 27 kinetic equations, the values of activation energy and pre-exponential factor in Arrhenius equation were calculated for both processes.     

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.     

Preparation of nanocrystalline BiFeO<Subscript>3</Subscript> via a simple and novel method and its kinetics of crystallization

The precursor of nanocrystalline BiFeO₃ was obtained by solid-state reaction at low heat using Bi(NO₃)₃·5H₂O, FeSO₄·7H₂O, and Na₂CO₃·10H₂O as raw materials. The nanocrystalline BiFeO₃ was obtained by calcining the precursor. The precursor and its calcined products were characterized by differential scanning calorimetry (DSC), Fourier transform-infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The data showed that highly crystallization BiFeO₃ with rhombohedral structure (space group R3c (161)) was obtained when the precursor was calcined at 873 K for 2 h. The thermal process of the precursor experienced three steps, which involve the dehydration of adsorption water, hydroxide, and decomposition of carbonates at first, and then crystallization of BiFeO₃, and at last decomposition of BiFeO₃ and formation of orthorhombic Bi₂Fe₄O₉. The mechanism and kinetics of the crystallization process of BiFeO₃ were studied using DSC and XRD techniques, the results show that activation energy of the crystallization process of BiFeO₃ is 126.49 kJ mol⁻¹, and the mechanism of crystallization process of BiFeO₃ is the random nucleation and growth of nuclei reaction.     

Hydrothermal synthesis and thermodynamic properties of 2CaO·3B<Subscript>2</Subscript>O<Subscript>3</Subscript>·H<Subscript>2</Subscript>O

2CaO·3B₂O₃·H₂O which has non-linear optical (NLO) property was synthesized under hydrothermal condition and identified by XRD, FTIR and TG as well as by chemical analysis. The molar enthalpy of solution of 2CaO·3B₂O₃·H₂O in HCl·54.572H₂O was determined. From a combination of this result with measured enthalpies of solution of H₃BO₃ in HCl·54.501H₂O and of CaO in (HCl+H₃BO₃) solution, together with the standard molar enthalpies of formation of CaO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of −(5733.7±5.2) kJ mol⁻¹ of 2CaO·3B₂O₃·H₂O was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method.     

Phase formation in the ZrO(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript>-CsF-H<Subscript>2</Subscript>O system at low concentration of the phosphorus-containing component

The ZrO(NO₃)₂-H₃PO₄-CsF-H₂O system was studied at 20°C along the section at a molar ratio of PO₄³⁻/Zr = 0.5 (which is of the greatest interest in the context of phase formation) at ZrO₂ concentrations in the initial solutions of 2–14 wt % and molar ratios of CsF: Zr = 1−6. The following compounds were isolated for the first time: crystalline fluorophosphates CsZrF₂PO₄ · H₂O, amorphous oxofluorophosphate Cs₂Zr₃O₂F₄(PO₄)₂ · 3H₂O, and amorphous oxofluorophosphate nitrate CsZr₃O_1.25F₄(PO₄)₂(NO₃)_0.5 · 4.5H₂O. The compound Cs₃Zr₃O_1.5F₆(PO₄)₂ · 3H₂O was also isolated, which forms in a crystalline or glassy form, depending on conditions. The formation of the following new compounds was established: Cs₂Zr₃O_1.5F₅(PO₄)₂ · 2H₂O, Cs₂Zr₃F₂(PO₄)₄ · 4.5H₂O, and Zr₃O₄(PO₄)_1.33 · 6H₂O, which crystallize only in a mixture with known phases. All the compounds were studied by X-ray powder diffraction, crystal-optical, thermal, and IR spectroscopic analyses.     

Synthesis and characterization of Co<Subscript>0.8</Subscript>Zn<Subscript>0.2</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Cobalt zinc ferrite, Co_0.8Zn_0.2Fe₂O₄, nanoparticles have been synthesized via autocatalytic decomposition of the precursor, cobalt zinc ferrous fumarato hydrazinate. The X-ray powder diffraction of the ‘as prepared’ oxide confirms the formation of single phase nanocrystalline cobalt zinc ferrite nanoparticles. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential thermal analysis. The precursor has also been characterized by FTIR, and chemical analysis and its chemical composition has been determined as Co_0.8Zn_0.2Fe₂(C₄H₂O₄)₃·6N₂H_4. The Curie temperature of the ‘as-prepared oxide’ was determined by AC susceptibility measurements.     

Synthesis of 5-hydroxymethylfurfural from glucose in a biphasic medium with AlCl<Subscript>3</Subscript> and boric acid as the catalyst

In combination with non-corrosive and low-toxic boric acid, AlCl₃ · 6H₂O was found to be effective for the synthesis of 5-hydroxymethylfurfural (5-HMF) from glucose. In this work, a 5-HMF yield of ≈ 60 % was obtained at 170°C for 40 min in a H₂O/THF biphasic solvent mixture. An addition of NaCl not only improved the partition coefficients but also inhibited by-product formation. THF was identified as an ideal extraction solvent in biphasic systems containing C4 solvents. However, low concentration of ZnCl₂, CoCl₂ · 6H₂O, MnCl₂ · 4H₂O, NiCl₂ · 6H₂O, FeCl₃ · 6H₂O were not suitable for the catalyst system, while ZrOCl₂ · 8H₂O, InCl₃ · 4H₂O showed high activity for the reaction. Boric acid increased the amount of Lewis acid sites in the reactive phase and enhanced the isomerization of glucose to fructose. A mechanism of the AlCl₃ · 6H₂O and boric acid catalyzed glucose dehydration reaction was proposed to proceed through the isomerization of glucose to fructose followed by the transformation of fructose to 5-HMF.     

The effect of tin precursors on the formation of Zr<Subscript>0.8</Subscript>Sn<Subscript>0.2</Subscript>TiO<Subscript>4</Subscript> nano-powder by sol gel process

Different precursors can have different effects upon the properties of materials. In this paper, two different tin precursors, i.e., tin (IV) chloride pentahydrate (SnCl₄·5H₂O) and tin (IV) t-butoxide (Sn(OC₄H₉)₄) have been used to prepare Zr_0.8Sn_0.2TiO₄ powders. The dry gel and powder were characterized by Simultaneous DTA/TGA analysis (SDT), X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Accelerated surface area and porosimetry analyzer (ASAP). The results show less weight loss for dry gel from precursor SnCl₄·5H₂O than that of Sn(OC₄H₉)₄. The onset of polycrystalline ZST nano powders occurred at 450 °C from precursor SnCl₄·5H₂O which is 50 °C lower than that of Sn(OC₄H₉)₄. Even though the powders from SnCl₄·5H₂O had a specific surface area of 30.4 m²/g which is higher than that of 28.7 m²/g from Sn(OC₄H₉)₄. The crystallite size of ZST powders were about the same around 15 nm. This may be due to the powders are more aggregated in Sn(OC₄H₉)₄ system. Two major mechanisms are proposed for above differences in morphology and the formation of powders.     

LaCrO<Subscript>3</Subscript> powder from lanthanum trisoxalatochromate(III) (LTCR) precursor

Lanthanum chromite LaCrO₃, an important catalyst and interconnect material used in solid oxide fuel cell was prepared from lanthanumtrisoxalatochromate(III) hydrate [LaCr(C₂O₄)₃]·9H₂O (LTCR) employing microwave heating technique. The compound LTCR heated in microwave heating system gave pure LaCrO₃ at 500°C within one hour. However LTCR heated in silicon carbide furnace yielded LaCrO₃ at 900°C. BET surface area of LaCrO₃ prepared by microwave and conventional heating techniques were found to be 2.8 and 1.2 m² g⁻¹, respectively. Thermogravimetry, differential thermal analysis and X-ray diffraction techniques were used to optimize the conditions for the microwave processing of the precursor.     

Thermodynamic characteristics of double salts crystallizing in LiCl-RbCl-H<Subscript>2</Subscript>O system at 298.15 K

The Pitzer ion-interaction model has been used for calculations of thermodynamic characteristics of double salts 3RbCl · LiCl · 2H₂O and RbCl · 2LiCl · 4H₂O in the ternary system LiCl-RbCl-H₂O at 298.15 K. The standard molar Gibbs energy of formation of the two double salts from the corresponding simple salts LiCl · H₂O and RbCl, as well as the standard molar Gibbs energy of formation have been determined.     

Phase composition,formation parameters,and morphology of precipitates in the LiVO<Subscript>4</Subscript>-VOSO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

The phase and chemical compositions of the precipitates formed in the LiVO₃-VOSO₄-H₂O system at initial pH within 1 ≤ pH ≤ 4 and 90°C were studied. The following phases were prepared: an α phase Li_1.4(VO)_1.3[H₂V₁₀O₂₈] · nH₂O and a β phase Li_{0.6 ? x} H_{1.4 + x} [V₁₂O_{31 ? y/2}] · nH₂O (0 ≤ x ≤ 0.5, 1.3 ≤ y ≤ 2.0) with a layered structure. Li_0.4V₂O₅ · H₂O nanorods with the interlayer distance 10.30 ± 0.08 Å were synthesized at 180°C in an autoclave. The morphology, IR spectra, and main formation processes for these polyvanadates were studied.     

Interactions in the system Mn(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-HCONH<Subscript>2</Subscript>-H<Subscript>2</Subscript>O

Solubilities and solid phases in the system Mn(NO₃)₂-HCONH₂-H₂O were studied by an isothermal method at 25°C. The congruently saturating compound Mn(NO₃)₂ · 2HCONH₂ · 2H₂O was isolated; the concentration conditions for its crystallization in the system were determined. The solid phases of the system were characterized by physicochemical methods (X-ray powder diffraction, differential thermal analysis, IR spectroscopy, and crystal-optical analysis).     

Influence of precursor on the thermally Induced synthesis dysprosium manganite with perovskite structure

The thermal behaviour of two coordination compounds [MnDy(malic)3]· 5H₂O and [MnDy(gluconic)3]·12H₂O has been studied to evaluate their suitability for dysprosium manganese perovskite ;synthesis. A decomposition scheme is proposed leading to perovskites with orthorhombic (malic precursor) and hexagonal (gluconic precursor) structures which were obtained after a heating treatment of 4 h at 1000°C with one-hour plateau at 500°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study on the obtaining of cobalt oxides by thermal decomposition of some complex combinations,undispersed and dispersed in SiO<Subscript>2</Subscript> matrix

In order to obtain cobalt oxides nanoparticles we have used the thermal decomposition of some carboxylate type precursors. These precursors were obtained by the redox reaction between cobalt nitrate and ethylene glycol, either bulk or dispersed in silica matrix. The redox reaction takes place by heating the Co(NO₃)₂·6H₂O-C₂H₆O₂ solution or the Si(OC₂H₅)₄-Co(NO₃)₂·6H₂O-C₂H₆O₂ gels. Thermal analysis of the Co(NO₃)₂·6H₂O-C₂H₆O₂ solution and Si(OC₂H₅)-Co(NO₃)₂·6H₂O-C₂H₆O₂ gels allowed us to establish the optimal value for the synthesis temperature of the carboxylate precursors. By fast heating of the solution Co(NO₃)₂·6H₂O-C₂H₆O₂, the redox reaction is immediately followed by the decomposition of the precursor, which represents an autocombustion process. The product of this combustion contains CoO as unique phase. We have obtained a mixture of CoO and Co₃O₄ by annealing the synthesized carboxylate compounds for 2 h at 400°C. With longer annealing time (6 h), we have obtained Co₃O₄ as unique phase. The XRD study of the crystalline phases resulted by thermal decomposition of the precursors embedded in silica matrix, showed that the formation of Co₂SiO₄ and Co₃O₄, as unique phases, depends on the thermal treatment.     

Influence of heat treatment on the phase transition of ZrMo<Subscript>2</Subscript>O<Subscript>8</Subscript> and photocatalytic activity

ZrMo₂O₇(OH)₂·2H₂O was obtained from ZrOCl₂·2H₂O and Na₂MoO₄·2H₂O by a coprecipitation method. The phase and structural changes occurred during the heat-treatment of ZrMo₂O₇(OH)₂·2H₂O were investigated by XRD, IR and XPS analysis. The sequence of phase transformation can be divided into three stages: (1) transformation of ZrMo₂O₇(OH)₂·2H₂O to orthorhombic LT-ZrMo₂O₈ up to 300°C; (2) obtaining of mixture of both polymorphs of ZrMo₂O₈: cubic and trigonal at 400°C; (3) conversion to single trigonal (α) ZrMo₂O₈ above 450°C. The microstructure of the obtained trigonal (α) ZrMo₂O₈ was observed by scanning electron microscopy (SEM). The particle sizes were below 0.5 μm. The specific surface area was measured by modified BET method. The photocatalytic activity of the obtained trigonal (α) ZrMo₂O₈ powders was investigated by degradation of a model aqueous solution of Malachite Green (MG) upon UV-light irradiation.     

Preparation of nanocrystalline BiFeO3 and kinetics of thermal process of precursor

The Bi₂Fe₂(C₂O₄)₅·5H₂O was synthesized by solid-state reaction at low heat using Bi(NO₃)₃·5H₂O, FeSO₄·7H₂O, and Na₂C₂O₄ as raw materials. The nanocrystalline BiFeO₃ was obtained by calcining Bi₂Fe₂(C₂O₄)₅·5H₂O at 600 °C in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, FT-IR, X-ray powder diffraction, and vibrating sample magnetometer. The data showed that highly crystallized BiFeO₃ with hexagonal structure [space group R3c(161)] was obtained when the precursor was calcined at 600 °C in air for 1.5 h. The thermal process of the precursor in air experienced five steps which involved, at first, the dehydration of an adsorption water molecule, then dehydration of four crystal water molecules, decomposition of FeC₂O₄ into Fe₂O₃, decomposition of Bi₂(C₂O₄)₃ into Bi₂O₃, and at last, reaction of Bi₂O₃ and Fe₂O₃ into hexagonal BiFeO₃. Based on Starink equation, the values of the activation energies associated with the thermal process of Bi₂Fe₂(C₂O₄)₅·5H₂O were determined. Besides, the most probable mechanism functions and thermodynamic functions (ΔS ^≠, ΔH ^≠, and ΔG ^≠) of thermal processes of Bi₂Fe₂(C₂O₄)₅·5H₂O were also determined.     

Dehydration of the Sorel Cement Phase 3Mg(OH)2·MgCl2·8H2O studied by in situ Synchrotron X‐ray Powder Diffraction and Thermal Analyses

Dehydration is an important process which affects the chemical, physical and mechanical properties of materials. This article describes the thermal dehydration and decomposition of the Sorel cement phase 3Mg(OH)₂ · MgCl₂ · 8H₂O, studied by in situ synchrotron X‐ray powder diffraction and thermal analyses. Attention is paid on the determination of the chemical composition and crystal structure of the lower hydrates, identified as the phases 3Mg(OH)₂ · MgCl₂ · 5.4H₂O and 3Mg(OH)₂ · MgCl₂ · 4.6H₂O. The crystal structure of 3Mg(OH)₂ · MgCl₂ · 4.6H₂O is solved and refined by the Rietveld method and a structural model for the 3Mg(OH)₂ · MgCl₂ · 5.4H₂O phase is given. These phases show statistical distribution of water molecules, hydroxide and chloride anions positioned as ligands on the magnesium octahedra. A structural scheme of the temperature induced transformations in the thermal range from 25 to 500 °C is presented.     

Thermal Decomposition of the System CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript> in the Presence of Nitrate Compounds

Chemical, derivatographic, IR spectral, and X-ray diffraction analyses were used to study thermal transformations in the system CO(NH₂)₂-H₃PO₄ and in the same system with addition of KNO₃, CsNO₃, LiNO₃ · 3H₂O, and NH₄NO₃ salts in the temperature range 20–600°C. The influence of the chosen nitrate compounds on the process of reorganization of the constituent ingredients, evolution of nitrogen into the gas phase, yield of the solid residue, and preservation of nitrogen and phosphorus was revealed.     

A new method of synthesis of BiFeO<Subscript>3</Subscript> prepared by thermal decomposition of Bi[Fe(CN)<Subscript>6</Subscript>]·4H<Subscript>2</Subscript>O

In order to investigate the formation of the multiferroic BiFeO₃, the thermal decomposition of the inorganic complex Bismuth hexacyanoferrate (III) tetrahydrate, Bi[Fe(CN)₆]·4H₂O has been studied. The starting material and the decomposition products were characterized by IR spectroscopy, thermal analysis, laboratory powder X-ray diffraction, and microscopic electron scanning. The crystal structures of these compounds were refined by Rietveld analysis. BiFeO₃ were synthesized by the decomposition thermal method at temperature as low as 600 °C. There is a clear dependence of the type and amount of impurities that are present in the samples with the time and temperature of preparation.     

Effect of cerium dioxide on the properties of monolithic CuO-ZnO-CeO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite catalysts in methanol decomposition

Cerium dioxide as a component of CuO-ZnO-CeO₂/Al₂O₃/cordierite catalysts stabilizes their action in the decomposition of methanol by preventing carbon deposition on the surface and facilitating hydrogen formation with selectivity and yield in the range 85–96%. The optimal indices for this reaction are obtained for a CeO₂-CuO/Al₂O₃/cordierite sample prepared using an ammonium precursor for cerium, (NH₄)₂Ce(NO₃)₆. This catalyst displays enhanced reductive capacity relative to the analogous CeO₂-CuO composition prepared using Ce(NO₃)₃·6H₂O.