Synthesis and thermal decomposition of antimony(III) oxide hydroxide nitrate

The thermal decomposition of the only known antimony nitrate antimony(III) oxide hydroxide nitrate Sb₄O₄(OH)₂(NO₃)₂, whose synthesis routes were reviewed and optimized was followed by TG-DTA under an argon flow, from room temperature up to 750°C. Chemical analysis (for hydrogen and nitrogen) performed on samples treated at different temperatures showed that an amorphous oxide hydroxide nitrate appeared first at 175°C, and decomposed into an amorphous oxide nitrate above 500°C. Above 700°C, Sb₆O₁₃ and traces of -Sb₂O₄ crystallized.Author to whom all correspondence should be addressed     

Phase Equilibria in the System CuO-Fe2O3-Sb2O4-O2

Results of X-ray phase analysis were used to construct the phase diagram of the system CuO-Fe₂O₃-Sb₂O₄-O₂ at 1000°C in air. Two Cu_2x Fe_4-3x Sb _x O₆ solid solutions (0 x 0.154 and 0.923 x 1) of, respectively, hematite and bixbyite structure were identified.     

Thermal characterisation of chemically reduced electrolytic manganese dioxide

Summary Samples of electrolytic manganese dioxide (EMD) were chemically reduced using 2-propanol under reflux (82°C) for 1, 2, 3, 6 and 24 h intervals. XRD analysis showed that the -MnO₂ structure was preserved although the lattice dimensions were observed to increase with increasing degree of reduction to accommodate the intercalation of protons. The exception was the 24 h reduced sample which contained two phases; -MnO₂ and -MnOOH. Three regions of decomposition in the range of 50 to 1000°C were observed using thermogravimetric analysis coupled with mass spectrometry (TG-MS) and were accounted for as water removal below 390°C, reduction of MnO₂ to Mn₂O₃ between 400 and 600°C, and Mn₂O₃ to Mn₃O₄ between 600 and 1000°C. Again the exception proved to be the 24 h reduced sample which was observed to decompose predominantly in one step between 400 and 600°C directly to Mn₃O₄.     

Mössbauer spectroscopic and X-ray diffraction study of the thermal decomposition of Fe(CH3COO)2 and FeOH(CH3COO)2

Thermal decomposition of iron(II) acetate, Fe(CH₃COO)₂, and iron(III) acetate hydroxide, FeOH(CH₃COO)₂, has been studied using⁵⁷Fe Mössbauer spectroscopy and X-ray diffraction. Samples were thermally treated in air atmosphere between 150°C and 1000°C. The formation of maghemite '-Fe₂O₃, and hematite, -Fe₂O₃, is discussed. Hematite appears as the final decomposition product.     

Precursor-Support Interactions in Silica-Supported Manganese Oxide Catalysts

Summary. Catalyst materials investigated in this study were obtained by calcination of impregnated silica with Mn(CH₃COO)₂·4H₂O and MnC₂O₄·2H₂O, so as to yield 10wt% Mn/SiO₂. The precursor compounds as well as pure and impregnated silica support were calcined at 600 and 1000°C in a static air atmosphere for 5h. Structural characteristics of the catalysts thus obtained were investigated by DTA, TG, XRD, IR and DRS. N₂ adsorption at –195°C was used for the assessment of surface texture of the test materials. Results of structural characterisation of catalysts obtained by calcination of manganese acetate-impregnated silica at 1000°C indicated the presence of strong silica-precursor interactions. Species of manganese silicates were detectable. Moreover, the decomposition of manganese acetate enhanced the transformation of amorphous silica into well crystallised -quartz. In contrast, Mn₂O₃, Mn₃O₄, and minor proportions of MnO were detected in the catalysts derived from the manganese oxalate-impregnated silica. This has been ascribed to much weaker precursor/support interactions in the oxalate-impregnated silica than the acetate-impregnated one.     

Thermal dehydration and decomposition of FeCl3·xH2O

Thermal dehydration and decomposition characteristics of Fe(III) chloride hydrate have been studied by both isothermal and non-isothermal methods. After the initial melting at 35–40°C both dehydration and decomposition of the salt proceed simultaneously at temperature above 100°C. At 250–300°C a stable hydrated Fe(OH)₂Cl is formed representing the first plateau region in the TG curve. Around 400°C, a second plateau is observed corresponding to the formation of mostly Fe₂O₃ which however retains some OH groups and Cl^– ions. However, these temperature ranges vary with the TA equipments used. Chemical analysis of the products of decomposition at temperatures above 140°C also gives evidence for the formation of FeOCl which on hydrolysis in water gives FeCl₃ in solution. The FT-IR spectra suggest the presence of structural OH groups even for samples calcined at 300–400°C. The XRD patterns of the products of decomposition in the temperature range 160–400°C indicate the presence of -FeOOH, some unidentified basic chlorides and -Fe₂O₃.The authors wish to thank the Director, R. R. L. Bhubaneswar for his kind permission to publish this paper. One of the authors (SKM) is grateful to the Council of Scientific and Industrial Research (CSIR), New Delhi for the award of a fellowship.     

Physico-chemical studies on the thermolysis of strontium and barium ferrimaleates

The thermolysis of strontium and barium tris(maleato)ferrates(III), M₃ [Fe(C₂ H₂ C₂ O₄ )₃ ]₂ ·x H₂ O has been investigated from ambient temperature to 800 °C using simultaneous TG-DTG-DTA, XRD, Mössbauer and IR spectroscopic techniques. After dehydration the anhydrous complexes undergo decomposition to yield an iron(II)maleate/oxalate intermediate in the temperature range of 240-280 °C. An oxidative decomposition of iron(II) species leads to the formation of -Fe₂ O₃ and respective alkaline earth metal carbonate in the successive stages. Finally at 540-590 °C, a solid state reaction occurs between -Fe₂ O₃ and strontium/barium carbonate resulting in the formation of SrFeO_2.5 and BaFe₂ O₄ , respectively.     

Preparation and performances of nanosized Ta2O5 powder photocatalyst

Nanosized-Ta₂O₅ powder photocatalyst was successfully synthesized by using sol-gel method via TaCl₅ butanol solution as a precursor. Ta₂O₅ species can be formed under 500 °C via the decomposition of the precursor. The crystalline phase of Ta₂O₅ powder photocatalyst can be obtained after being calcined above 600 °C for 4 h. The crystal size and particle size of Ta₂O₅ powder photocatalyst was about 50 nm. A good photocatalytic performance for the degradation of gaseous formaldehyde was obtained for the nanosized-Ta₂O₅ powder. The Ta₂O₅ powder formed at 700 °C for 4 h and at 650 °C for 12 h showed the best performance. The calcination temperature and time play an important role in the crystallization and photocatalytical performance of nanosized-Ta₂O₅ powder.     

Flavonoids of inflorescences of Calendula officinalis

By column chromatography on polyamide sorbent, the inflorescences of pot marigold calendula have yielded eight substances of flavonoid nature: two aglycons — quercetin (C₁₅H₁₀O₇, mp 309–311°C) and isorhamnetin (C₁₆H₁₂O₇, mp 314–316°C); six glycosides, of which three have been identified as isoquercetin (C₂₁H₂₀O₁₂, [] _D ²⁰ –36° in methanol, mp 218–220°C), isorhamnetin 3-O--D-glucoside (C₂₂H₂₂O₁₂, [] _D ²⁰ –59° in dimethylformamide, mp 193–195°C), narcissin (C₂₈H₃₂O₁₆, [] _D ²¹ –28° in dimethylformamide, mp 180–182°C), and three substances that have proved to be new and have been called calendoflaside (C₂₈H₃₂O₁₅, [] _D ²¹ –85° in methanol, mp 192–195°C; calendoflavoside (C₂₈H₃₂O₁₆, [] _D ²⁰ –106° in methanol, mp 189–192°C), and calendoflavobioside (c₂₇H₃₀O₁₆, [] _D ²⁰ –105° in methanol, mp 194–197°C).All-Union Scientific-Research Institute of Drug Chemistry, Khar'kov. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 795–801, November–December, 1988.     

Ionic conduction of a high-temperature modification of Lu<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

A nanoceramic product of the composition Lu₂Ti₂O₇ is synthesized by a coprecipitation method with a subsequent sublimation drying and an annealing at 650–1650°C. The conduction of Lu₂Ti₂O₇ synthesized at 1650°C is ionic (10^–3 S cm^–1 at 800°C). Thus, a new material with a high ionic conduction has been discovered. The ordering in Lu₂Ti₂O₇ is studied by methods of RFA, RSA, IK spectroscopy, electron microscopy, and impedance spectroscopy. The existence of a low-temperature phase transition fluorite-pyrochlore at 800°C and a high-temperature conversion order-disorder at 1650°C are established.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 298–303.Original Russian Text Copyright © 2005 by Shlyakhtina, Ukshe, Shcherbakova.     

High-Temperature Proton Conductors Based on Strontium and Barium Cerates: The Content, Interphase Exchange, and Diffusion of Hydrogen

The hydrogen content and hydrogen exchange kinetics of doped cerates of strontium and barium are studied in a reducing environment by the isotope balance and isotope exchange techniques. The measurements are performed at 500-840°C and hydrogen pressures of 2.7-16 gPa. The interphase exchange of hydrogen is found to occur at high speed via dissociative mechanisms. The effective activation energy for the hydrogen heteroexchange is determined. The diffusion coefficient for hydrogen in BaCe_0.95Nd_0.05O_3- is computed. The hydrogen content per formula unit appears to equal 0.48 ± 0.05 in SrCe_0.95Y_0.05O_3- and 0.60 ± 0.05 in BaCe_0.95Nd_0.05O_3- at 550 and 720°C, respectively, and a hydrogen pressure of 6.7 gPa. This is much greater than in an oxidizing environment, where the hydrogen content in an oxide is approximately proportional to the doping level of sublattice B. A possible explanation is connected with the presence of Ce³⁺ ions in the oxides or the dissolution hydrogen in a neutral form.     

Polarization and ESR studies of thermally pretreated γ-irradiated TiO2

Pellets of TiO₂ thermally pretreated at 450 and 540°C and -irradiated were polarized by d. c. field. The depolarization curves were resolved into different first order components having two and three depolarization constants. By heating the polarized pellets the Current Glow Peak curves were recorded where there were only two peaks around 65 and 400°C in case of pellets heated at 450°C and heated at 540°C and irradiated; and one more additional peak around 20°C in case of pellets heated at 540°C and heated at 450°C and irradiated thereon. In addition to those signals of O ₂ ^– and Ti³⁺ reported earlier there were distinctly four more, signals at g 1.933 and g 2.03, 2.036 and 2.043 appeared in case of samples heated at 540°C and heated at 450°C and irradiated thereon. The signal at g1.933 is attributed to Ti³⁺ ions in new phase Ti₄O₇ developed in heating at 540°C or due to irradiation and the rest of the signals are due to O _2ad ^– or O _ad ^– over the new phase near anion vacancy created.     

Immobilization of yttrium over crystalline titania

A co-precipitation method was adopted for the immobilization of yttrium radioactive waste over crystalline titania. A high uptake of⁹¹Y was observed over the preformed hydrous titania. Weighable quantity of Y was coprecipitated with Ti(IV) hydroxide and a maximum of 38 wt% was found to be adsorbed. Mixed masses were calcined separately at 800 and 1000°C for 20 hours, and soxhlet leach tests at 97°C, repeated 7 times at an interval of 24 hours, showed the release of yttrium in the order of 10^–1 and 10^–2 g·m^–2·d^–1, respectively. X-ray powder diffraction analysis revealed that the yttrium was immobilized in the titania crystal lattice which suffered some structural changes with the formation of new mineral phase Y₂Ti₂O₇ which is accompanied by rutile and little quantity of anatase form of titania at 800°C, and only rutile form of titania at 1000°C.     

The Effect of Precursor Chemistry on the Crystallisation and Densification of Sol-Gel Derived Mullite Gels and Powders

Stoichiometric and silica-rich mullite gels and powders were prepared using four different sol-gel methods. Thermal analysis, X-ray powder diffraction and dilatometry techniques were used to investigate the thermal decomposition, crystallisation and sintering of these mullite precursor gels. The method of preparation, by controlled hydrolysis of various mixtures of tetraethylorthosilicate, aluminium sec-butoxide and aluminium nitrate, affected the texture of the gels, producing single-phase or diphasic samples.The crystallisation sequence of the gels depended on the composition and method of preparation. Single phase mullite crystallised from homogeneous gels at 980°C, while diphasic gels initially formed of a mixture of -Al₂O₃ spinel and mullite, or simple -Al₂O₃ spinel, which subsequently transformed to mullite at 1260°C.Dilatometry and density measurement were used to investigate the sintering of compacts formed by pressing powders prepared from gels precalcined at 500°C. Varying the heating rates from 2 to 10°C min^-1 had little effect on the densification to 1500°C. However, the densification rate was sensitive to the degree of crystallinity and the amount and type of phases present at the sintering temperature. The presence of -Al₂O₃ spinel in the structure initially promoted densification, but the sintering rate was reduced considerably after mullite crystallised. Diphasic materials, especially those with an excess amount of silica in the original gel, sintered to higher densities due to the presence of excess silica promoting densification by viscous phase sintering.     

First and second thermodynamic mixing properties of ethylbenzene +n-alkanes: Experimental and theory

Isobaric expansibilities _P and isothermal compressibilities _T have been determined at 25 and 45°C for binary mixtures of ethylbenzene + n-tetradecane and + n-hexadecane and the corresponding excess functions (V ^E /T)_P and (V ^E /P)_T have also been obtained. With these data and supplementary literature values, the following second order mixing properties are also reported at 25°C: _S ^E , (V ^E /P)_T, C_V and (VT). All mixing quantities have been compared with the results obtained at 25°C by using the Prigogine-Flory-Patterson theory of liquid mixtures. The predicted values suggest that the ability of ethylbenzene as a breaker of the pure n-C_n orientations is similar to what we found for toluene and higher than for p-xylene.     

On the identification of interface oxides and interface serration by ARXPS

Summary Oxidized surfaces show smeared out XPS lines which cannot be fitted by bulk compounds and by lateral growth. By simultaneously fitting XPS spectra obtained for take-off angles between 5 ° and 80 ° the resolution is enhanced. Thus small amounts (<0.5 nm) of interface oxides are identified in level shift, stoichiometry and spatial distribution, i.e., serration and protrusion of interfaces are revealed. The ARXPS-analysis of oxidized (<100 °C) NbN, NbC and Nb shows that the metal surface is serrated by metallic ( 1 nm) and dielectric ( 1 nm) interface oxides, where Nb₂O₅ forms the outermost layer. The serration is deeper for Nb than for NbN, because Nb is weaker and dissolves more O. In contrast, in high temperature oxidation (900 °C) of a clean Si single crystal (100) surface, less interface oxides (<1 nm) have been found which grow laterally.

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Über die Identifizierung von Interface-Oxiden und der Interface-Verzahnung durch ARXPS

     

Studies on styrene phosphonic acid

Some properties of styrene phosphonic acid (SPA) were studied. The crystals were triclinic, witha=0.6434 nm,b=0.5842 nm,c=2.0338 nm, =96.17°, =97.33°, =79.65° andZ=4. SPA underwent a change in crystal structure at 78.8°C, the hydrocarbon network became disordered (liquid-like) at 138.5°C. Crystals melted at 148.6°C giving a cubic mesophase, then changed to an isotropic liquid at 155.6°C and at 162.13°C SPA underwent decomposition. Values for pK₁=2.15 and pK₂=7.66 were obtained at 25°C. The water solubility of SPA at several temperatures, and its interaction with surfactant micelles were determined.     

Phase equilibria in the Ag4SSe-SnTe system

The phase diagram of the system Ag₄SSe-SnTe is studied by means of X-ray diffraction, differential thermal and metallographic analyses and measurements of the microhardness and the density of the material. This diagram is divided into two eutectic-type subdiagrams by the composition Ag₄SSe·2SnTe. The unit-cell parameters of the intermediate phases 3Ag₄SSe·SnTe (phase A) and -Ag₄SSe·2SnTe (phase B) are determined as follows: for phase A: a=0.7851 nm, b=0.7196 nm, c=0.6296 nm, =101.32°, =85.90°, =111.36°; for phase B: a=0.3662 nm, b=0.3303 nm, c=0.3343 nm, =90.74°, =108.94°, =91.91°. The phase Ag4SSe·2SnTe melts congruently at 615°C and a polymorphic transition of the phase takes place at T _- =110°C.This revised version was published online in November 2005 with corrections to the Cover Date.     

Synthesis of MgNb<Subscript>2</Subscript>O<Subscript>6</Subscript> nanocrystalline powders by an improved citrate sol–gel technique

MgNb₂O₆ nanocrystalline powders have been synthesized at a low temperature by improved citrate sol–gel method in this paper. The high quality solution of Nb⁵⁺ was prepared using Nb₂O₅ as the starting material. The crystal structure and microstructure of MgNb₂O₆ powders were characterized by XRD and SEM techniques, and the effects of preparation craft including pH value and the proportion of citric acid to the niobium ions on the crystal structure and microstructure of powders were also investigated. XRD and TG/DTA results show that the single phase of MgNb₂O₆ for synthesized powders can be obtained by calcining the precursor at 700 °C. SEM results indicate that the average particle size of MgNb₂O₆ exhibits a significantly dependence on the pH values and the proportion of citric acid to the niobium ions, where it was found that particle size of a 20 nm can be obtained for the MgNb₂O₆ powders by sol–gel process.