Synthesis and thermal decomposition of lanthanide hexacyanochromate(iii) complexes,Ln[Cr(CN)6]·nH2O (Ln=La-Lu; n=3, 4)

New solid complex of nitrilotriacetic acid and bismuth trichloride was synthesized by a solid phase reaction of nitrilotriacetic acid and bismuth trichloride at room temperature. The composition of the sample is BiCl₃[N(CH₂COOH)₃]_2.5. The crystal structure of the complex belongs to triclinic system with the lattice parameters: α=0.7849 nm, β=0.9821 nm, χ=2.0021 nm, α=96.50°, β=98.76° and γ=90.49°. The far-infrared spectra show the bonding between the Bi ion and N atom of nitrilotriacetic acid. The thermal analysis also demonstrates the complex formation between the bismuth ion and nitrilotriacetic acid. The gaseous pyrolysis product and the final residue in the thermal decomposition process are determined to check the thermal decomposition reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sol–gel synthesis and characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> nanocrystalline powder

Al₂O₃–TiO₂ nanocrystalline powders were synthesized by sol–gel process. Aluminum sec-butoxide and titanium isopropoxide chemicals were used as precursors and ethyl acetoacetate was used as chelating agent. Thermal and crystallization behaviors of the precursor powders were investigated by thermal gravimetric-differential thermal analysis, Fourier-transform infrared spectrum and X-ray diffraction. The average crystalline size of heat treated Al₂O₃–TiO₂ powders at 1,100 °C is ~100 nm.     

Analytical Techniques Applied in Optimization of Electrophoretic Deposition of Thin Film YBCO Superconductors

 YBa₂Cu₃O _7−x (x = 0.1–0.2) compounds (YBCO) were produced by the oxalate coprecipitation and the solid state reaction methods. The powders obtained were used for the production of YBCO superconducting coatings on Pt/Si wafers, by the electrophoretic deposition technique. The optimum process conditions for the production of both powders and coatings were found by using a combination of modern analytical techniques. The thermal treatment of the samples was followed by thermogravimetry (TG) and differential scanning calorimetry (DSC). The optimization and characterization of the superconducting properties of the powders and coatings were achieved by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), optical microscopy, magnetic susceptibility and electrical resistivity measurements.     

Synthesis of cyclolinear permethylpolycarbosilanes with oligosilane fragments in the backbone and study of their properties

Cyclolinear permethylpolycarbosilanes were synthesized for the first time by the reaction of 1,3- and 1,4-dihydrodecamethylcyclohexasilanes H₂Si₆Me₁₀ with α,ω-diallylpermethyloligo-silanes All(SiMe₂) _n All (n = 1–6) in the presence of Karstedt’s catalyst. The molecular weight characteristics, thermal and thermooxidative stability, and the spectral properties of the synthesized polymers were studied. The dependence of the yield and the molecular weight of the synthesized polymers on the number of the SiMe₂ units in the linear oligosilane fragment of the main chain was established.     

Thermal transformations of lead oxides

Differential scanning calorimetry, differential thermogravimetry, X-ray analysis and electronic microscopic studies of thermal transformations of PbO₂ were carried out. Formation of fine dispersed (less than 100 nm) particles of α-PbO was observed at PbO₂ thermal decomposition at heating to 580°C. Reverse reaction of Pb₃O₄ formation from PbO was found at cooling and annealing at 400°C in air. At heating of α-PbO to 650°C the particle growth to 1 μm with formation of β-PbO took place. Thermal decomposition with formation of β-PbO particles with size from 0.3 to 1 μm at PbO₂ heating to 650°C was observed. Transition from PbO to Pb₃O₄ at cooling of sample heated to 650°C was not detected. Interpretation of observed phenomena from the point of view of particle size influences on the shift of α-PbO↔β-PbO phase transition temperature and on the chemical activity of phases are presented.     

Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method

Al₂O₃ and Al_2−x Cr _x O₃ (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL^*a^*b^* color data). The obtained results allow to identify the γ-Al₂O₃ to α-Al₂O₃ phase transition. The single-phase α-Al₂O₃ powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al_2−x Cr _x O₃ are related to the γ to α-Al₂O₃ phase transition and the temperature and time range for such transition depends on the chromium content.     

Thermal decomposition of some metal-organic precursors

In this paper we present a study on the synthesis of Fe(III) oxide, by thermal decomposition of some complex combinations of Fe(III) with carboxylate type ligands, obtained in the redox reaction between some polyols (ethylene glycol (EG), 1,2-propane diol (1,2PG), 1,3-propane diol (1,3PG) and glycerol (GL)) and NO₃ ^– ions (from ferric nitrate). Fe₂O₃ was obtained by thermal decomposition of the synthesized metal-organic precursors at low temperatures. γ-Fe₂O₃ was obtained as nanoparticles at 300°C, while at higher temperatures α-Fe₂O₃ starts to crystallize and becomes single phase at ~500°C. The formation of the metal-organic precursors and their thermal decomposition were studied by thermal analysis and FTIR spectroscopy.     

Preparation of titanium carbide powders by sol–gel and microwave carbothermal reduction methods at low temperature

Titanium carbide ultrafine powders were prepared from tetrabutyl titanate and sucrose by sol–gel and microwave carbothermal reduction. The influences of reaction temperature and molar ratio of Ti to C on the synthesis of titanium carbide were studied. The results show that excess amount of carbon plays a positive effect on the carbothermal reduction of TiO₂ at low temperature. The inceptive carbothermal reduction temperature of TiO₂ and formation of titanium oxycarbide was below 900 °C, and pure TiC can be prepared at 1,200 °C, which was considerably lower compared to that by conventional carbothermal reduction using a mixture of TiO₂ and carbon powders as raw materials. The morphology and particle size of synthesized TiC powder were examined by field emission-scanning electron microscopy (FE-SEM) and the quantities of the phases of the powders were analyzed by Rietveld refinement method, the particle sizes of the TiC powders synthesized at 1,300 °C distribute over 0.1–0.5 μm.     

Synthesis,structure, and third-order nonlinear optical properties of W/S cluster [Fe(DMF)<Subscript>6</Subscript>][W<Subscript>2</Subscript>(μ<Subscript>2</Subscript>-S)<Subscript>2</Subscript>S<Subscript>4</Subscript>]

The homometal cluster [Fe(DMF)₆][W₂(μ₂-S)₂S₄] (I) was successfully synthesized by low-temperature solid-state reactions. X-ray single-crystal diffraction studies suggest that compound I is a dinuclear anion cluster. The compound was characterized by elemental analyses, IR spectra, and UV-Vis spectra. The third-order nonlinear optical (NLO) properties of the cluster were also investigated and exhibited nice nonlinear saturation absorption (α₂ < 0) that is rarer than reverse saturation absorption (α₂ > 0) and self-defocusing property (n ₂ < 0) and self-defocusing performance with modulus of the hyperpolarizabilities (9.547 × 10⁻³¹ esu) for I. The article was submitted by the authors in English.     

Non-isothermal decomposition kinetics of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles synthesized using egg white solution route

The thermal decomposition kinetics of nickel ferrite (NiFe₂O₄) precursor prepared using egg white solution route in dynamical air atmosphere was studied by means of TG with different heating rates. The activation energy (E _α) values of one reaction process were estimated using the methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS), which were found to be consistent. The dependent activation energies on extent of conversions of the decomposition reaction indicate “multi-step” processes. XRD, SEM and FTIR showed that the synthesized NiFe₂O₄ precursor after calcination at 773 K has a pure spinel phase, having particle sizes of ~54 ± 29 nm.     

Modified Pechini synthesis of Na3Ce(PO4)2 and thermochemistry of its phase transition

Effect of the synthesis conditions of Pechini technique on crystallinity and purity of Na₃Ce(PO₄)₂ compound was investigated. Nano-sized cerium-sodium phosphate obtained when EDTA was used as an additional chelating agent for Ln³⁺. The total enthalpy change of Na₃Ce(PO₄)₂ phase transition was determined as 14.2±0.7 kJ mol⁻¹ for sample synthesized by conventional solid-solid reaction. The phase transition process was confirmed to occur at 1060°C or in temperature range 920–1060°C depending on thermal treatment of powders.     

Comparative method to evaluate reliable kinetic triplets of thermal decomposition reactions

Reliable kinetic information for thermal analysis kinetic triplets can be determined by the comparative method: (1) An iterative procedure or the KAS method had been established to obtain the reliable value of activation energy E _a of a reaction. (2) A combined method including Coats-Redfern integral equation and Achar differential equation was put forward to confirm the most probable mechanism of the reaction and calculate the pre-exponential factor A. By applying the comparative method above, the thermal analysis kinetic triplets of the dehydration of CaC₂O₄·H₂O were determined, which apparent activation energy: 81±3 kJ mol^-1, pre-exponential factor: 4.51·106-1.78·10⁸ s^-1, the most probable mechanism function: f(α)=1 or g(α)=α, which the kinetic equation of dehydration is dα/dt=Ae^-E _a ^/RT. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preparation of bimetallic CoO-MoO3/γ-Al2O3 and NiO-MoO3/γ-Al2O3 hydrodesulfurization catalysts by deposition of Co, Ni and Mo onto α-AlOOH during paste processing

CoO-MoO₃/γ-Al₂O₃ and NiO-MoO₃/γ-Al₂O₃ catalysts were prepared by the reaction of α-boehmite (α-AlOOH) with MoO₃ in an aqueous paste, followed by the reaction of the MoO₃/α-AlOOH catalyst with Co(OH)₂·CoCO₃ or 2NiCO₃·3Ni(OH)₂·4H₂O in an aqueous paste, and by subsequent drying and/or calcination. The deposited MoO₃ functioned as a thermal stabilizer inhibiting the sintering of the Al₂O₃ phase during calcination. The deposited Co and Ni were efficient activity promoters in benzothiophene hydrodesulfurization.     

Preparation of nanocrystalline CuAlO<Subscript>2</Subscript> through sol–gel route

Nanocrystalline powders of CuAlO₂ were synthesized through sol–gel method using nitrate-citrate route and also through solid state reaction method. We used a new set of precursor materials for the synthesis of CuAlO₂ through sol–gel route which were not reported in the past. A little lowering of the synthesis temperature (1,000 °C) was observed in case of sol–gel process compared to the solid state reaction method (1,100 °C) and also at shorter time duration. The particle size of the synthesized powders was determined through small angle X-ray scattering. It has been observed that the particle size prepared by nitrate-citrate technique is less than the particle size prepared by the solid-state reaction method. Chemical states of the atomic species were determined by X-ray photoelectron spectroscopy. The formation of phase pure CuAlO₂ were also confirmed by Fourier transformed infrared spectroscopy. A number of solvents were also used for finding the best possible combinations for obtaining phase pure CuAlO₂ at 1,000 °C and it was observed that only the combination of nitrate salts, citric acid and ethanol resulted phase pure CuAlO₂.     

Synthesis and thermal behaviour of silicon containing poly(ester imide)s

A series of silicon containing poly(ester imide)s [PEIs] were synthesized using novel vinyl silane diester anhydride (VSEA) and various aromatic and aliphatic dimines by two-step process includes ring-opening polyaddition reaction to form poly(amic acid) and thermal cyclo-dehydration process to obtain poly(ester imide)s. VSEA was synthesized by using dichloro methylvinylsilane and trimellitic anhydride in the presence of K₂CO₃ by nucleophilic substitution reaction. The PEIs were characterized by FTIR spectroscopy. The thermal properties of PEIs were investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) methods. The prepared PEIs showed glass transition temperatures in the range of 320–350°C and their 5% mass loss was recorded in the temperature range of 500–520°C in nitrogen atmosphere. These had char yield in the range of 45–55% at 800°C.     

Picoline as ligand with antimony trichloride and triiodide adducts

Solid adducts SbX₃·L-pic (X=Cl, I and L=α-, β- and γ-picolines) were synthesized and characterized by elemental analysis, ¹H and ¹³C NMR, IR spectroscopy and thermal analysis. The infrared spectroscopy and the magnetic resonance for ¹H and ¹³C nuclei of these compounds suggest that the ligands coordinate through nitrogen atom. Kinetic studies were accomplished by means of thermogravimetric data, through isothermal and non-isothermal techniques. The best adjusting models for adducts thermal decomposition were R¹ for isothermal and R₁ and R₂ for the non-isothermal methods. The energy of activation values obtained by isothermal method indicate the following orders of thermal stability for adducts: i) SbCl₃·α-pic>SbCl₃·β-pic>SbCl₃·γ-pic and ii) SbI₃·β-pic>SbI₃·γ-pic>SbI₃·α-pic. The activation energy values obtained by non-isothermal were higher than those from isothermal methods, showing the order of stability:iii) SbCl₃·α-pic<SbCl₃·β-pic<SbCl₃·γ-pic and iv) SbI₃·β-pic>SbI₃·α-pic=SbI_3··γ-pic. These obtained data through R₁ model presented the kinetic compensation effect for trichloride adducts, which could be associated to both isothermal and non-isothermal processes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of non-agglomerated Ba<Subscript>0.77</Subscript>Ca<Subscript>0.23</Subscript>TiO<Subscript>3</Subscript> nanopowders by a modified polymeric precursor method

In this work, we have studied the influence of the pH on the synthesis and structural properties of the Ba_0.77Ca_0.23TiO₃ nanopowders synthesized by a modified polymeric precursor method, in order to achieve non-agglomerated powders. Synthesis, morphology, thermal reactions, crystallite and average particle size of the synthesized powders were investigated through thermal analysis (DTA/TG), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and Infrared spectroscopy. In summary, Ba_0.77Ca_0.23TiO₃ nanopowders were synthesized for the first time at a relative low temperature (500 °C). It was also found that the alkalinity and acidity of the solution presented a great influence on the powder properties. The best results were obtained from solutions with pH = 8.5 and 11 whose nanopowders presented weakly agglomerate, with homogeneous particle size and a narrow size distribution (30–40 nm). This behavior could be explained based on the FT-IR results in which it was possible to see the increased of the chelation in higher pHs.     

Synthesis of corundum doped with cerium in supercritical water fluid

The properties of fine crystalline corundum doped with cerium (α-Al₂O₃: Ce³⁺) during synthesis in a supercritical fluid have been studied. The synthesis of corundum has been carried out by the thermal treatment of hydrargillite, Al(OH)₃, at T = 415°C and {ie290-1} MPa in reaction media that contained from 0.001 to 0.25 wt % of cerium. Cerium ions are incorporated into the boehmite lattice during the transformation of hydrargillite into boehmite, which forms fine monocrystals of the doped corundum with a size from 20 to 50 μm. The size of the corundum crystals increases with increasing pressure and increasing concentration of cerium. The synthesized α-Al₂O₃: Ce³⁺ reveals a luminescent band in the UV region at 352 nm and a blue band at 421 nm. The intensity of the cerium ion luminescence in corundum increases with an increase in the water fluid pressure during synthesis. The follow-up annealing of α-Al₂O₃: Ce³⁺ at 1400°C in a vacuum leads to a decrease in the luminescence. It has been concluded that spectrally active complex structures that include cerium ions, oxygen vacancies, and hydroxyl groups are produced in the media of a supercritical water fluid upon the synthesis of boehmite and corundum. Exposure to high temperatures causes their transformation.     

Synthesis of nanocrystalline nickel ferrite by thermal decomposition of organic precursors

Nickel ferrite powders were synthesized by thermal decomposition of the precursors obtained in the redox reaction between the mixture of Ni(NO₃)₂·6H₂O and Fe(NO₃)₃·9H₂O with polyalcohol: 1,4-butanediol, polyvinyl alcohol and also with their mixture. During this reaction the primary C?COH groups were oxidized at ?CCOOH, while secondary C?COH groups at C=O groups. The carboxylic groups formed coordinate to the present Ni(II) and Fe(III) cations leading to carboxylate type compounds, further used as precursors for NiFe₂O₄. These precursors were characterized by thermal analysis and FT-IR spectrometry. All precursors thermally decomposed up to 350?°C leading to nickel ferrite weakly crystallized. By annealing at higher temperatures, nanocrystalline nickel ferrite powders were obtained, as resulted from XRD. SEM images have evidenced the formation of nanoparticulate powders; these powders present magnetic properties characteristic to the oxidic system formed by magnetic nanoparticles.     

Carbothermal synthesis of ultra-fine zirconium carbide powders using inorganic precursors via sol–gel method

Ultra-fine zirconium carbide (ZrC) powders have been synthesized by carbothermal reduction reactions using inorganic precursors zirconium oxychloride (ZrOCl₂ · 8H₂O) as sources of zirconium and phenolic resin as the carbon source. The reactions were substantially completed at relatively lower temperatures (∼1400 °C/1 h) and the synthesized powders had a small average crystallite size (<200 nm) and a large specific area (54 m²/g). The oxygen content of the powder synthesized at 1400 °C/1 h was less than 1.0 wt%. The thermodynamic change process in the ZrO₂–C system and the synthesis mechanism were studied.