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.     

Synthesis,phase formation,and thermal expansion of sulfate phosphates with the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> structure

The NaFeZr(PO₄)₂SO₄ and Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 sulfate phosphates with the NaZr₂(PO₄)₃ (NZP) structure were synthesized and studied using X-ray diffraction, electron microprobe analysis, IR spectroscopy, and simultaneous differential thermal and thermogravimetric analysis. The phase formation and thermal stability of the compounds were studied by powder X-ray diffraction and DTA–TG. The Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 structure was refined by full-profile analysis. The structure framework is composed of randomly occupied (Fe,Zr)O₆ octahedra and (P,S)O₄ tetrahedra; the Pb²⁺ ions occupy extra-framework sites. The thermal expansion of Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 in the temperature range from–120 to 200°C was studied by temperature X-ray diffraction. In terms of the average linear coefficient of thermal expansion (α_av = 1.7 × 10^–6°C^–1), this compound can be classified as having low expansion. The combination of different tetrahedral anions (a phosphorus and a smaller sulfur one) in the NZP resulted in a decrease in the framework size and cavities and enabled the preparation of low-expansion sulfate phosphate with a smaller extra-framework cation (cheap Pb) instead of larger cations (Cs, Ba, Sr) used most often in the monoanionic phosphates.     

Synthesis of LaCoO<Subscript>3</Subscript> from lanthanum trisoxalatocobaltate(III) (LTC) precursor employing microwave heating technique

Lanthanum cobaltite LaCoO₃, an important catalyst and an electronic material used as cathode in solid oxide fuel cells was prepared from lanthanum trisoxalatocobaltate(III) hydrate [LaCo(C₂O₄)₃]·9H₂O (LTC) employing microwave heating technique. It was observed that LTC heated in microwave heating system gives a pure product of LaCoO₃ at 400°C within one hour. Thermogravimetry, differential thermal analysis and X-ray diffraction techniques were used to optimize conditions for microwave processing of the precursor.Authors are thankful to Mr. N. A. Kulkarni and Mr. V. M. Chopade from TIFR, Mumbai for recording the XRD patterns of the sample.     

Nanosized SrTiO<Subscript>3</Subscript> powder from oxalate precursor microwave aided synthesis and thermal characterization

Nanosized strontium titanate (SrTiO₃) was synthesized from strontium titanyl oxalate hydrate, SrTiO(C₂0₄)₂4H₂0 (STO) precursor employing microwave heating technique. STO precursor was characterized by Thermogravimetry (TG) and differential thermal analysis (DTA) techniques prior to the heat treatment in conventional and microwave heating system. STO precursor heated in microwave heating system in air at 773 K for 30 min yielded pure cubic SrTiO₃. The product obtained by heating of STO precursor in the same system at 973 K for same duration was, however, much more crystalline. Experiments repeated in conventional furnace showed that SrTiO₃ was formed above 973 K. SrTiO₃ powder obtained was characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM) techniques. TEM study shows that the particles of SrTiO₃ are nearly spherical in shape and the particle size of SrTiO₃ powder varies between 28 and 68 nm.     

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.     

Zirconium phospho-sulfates with NaZr2(PO4)3-type structure

Two new crystalline zirconium phospho-sulfates, α- and β-Zr₂(PO₄)₂(SO₄) were prepared by the gel method followed by drying and calcining at controlled temperatures. Their X-ray patterns were indexed and their infrared spectra interpreted. They belong to the NaZr₂P₃O₁₂ or [NZP] structural family, and constitute the first example with S⁶⁺ in the tetrahedral site.     

Structure and properties of H<Subscript>8</Subscript>(PW<Subscript>11</Subscript>TiO<Subscript>39</Subscript>)<Subscript>2</Subscript>O heteropoly acid

Heteropoly acid (HPA) H₈(PW₁₁TiO₃₉)₂O·xH₂O (I) is synthesized by three different ways and studied by chemical analysis, potentiometric titration, mass-spectrometry, IR, ³¹P, ¹⁸³W, and ¹⁷O NMR spectroscopy, thermogravimetry, and transmission electron microscopy. Anion I consists of two subparticles of the Keggin structure bridged by Ti-O-Ti. The dimeric anion exists in HPA aqueous solutions at [I] > 0.02 M. At pH > 0.6 it splits to a [PW₁₁TiO₄₀]⁵⁻ monomer stable up to pH ∼ 6. When heated (150–400)°C, I splits into H₃PW₁₂O₄₀ and, apparently, H₃PW₁₀Ti₂O₃₈ without phase separation. Thermolysis products are soluble and when dissolved in water turn again into I. Complete decomposition of I to oxides occurs at ∼450°C.     

Synthesis of La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> by thermal treatment of mechanically activated salt mixture

A lanthanum zirconate La₂Zr₂O₇ was synthesized by soft mechanochemical method using zirconium oxynitrate ZrO(NO₃)₂·6H₂O and lanthanum carbonate La₂(CO₃)₃·8H₂O as reagents. Mechanical activation of the reagents was carried out in a centrifugal planetary ball mill. The processes occurring during calcination of the jointly and the separately mechanically activated salt mixture were studied using DSC, TG coupled with mass spectrometry, XRD analysis, and FTIR spectroscopy. It was shown that in the course of joint mechanical activation in the mill alongside with intimate mixing of the reagents and their amorphization exchange reaction occurred, producing lanthanum nitrate, basic lanthanum nitrate, basic zirconium carbonate, and hydrated zirconium oxide. The DSC curve of the jointly mechanically activated salt mixture showed a strong exothermic peak at 878 °C which was not associated with mass loss. This peak was attributed to La₂Zr₂O₇ crystallization in agreement with XRD data. Nanocrystalline lanthanum zirconate synthesized by annealing of the jointly mechanically activated salt mixture was characterized using XRD analysis, scanning, and transmission electron microscopy.     

Synthesis of hydroxyapatite by hydrolysis of α-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Conditions for hydroxyapatite (HAP) synthesis in aqueous solutions by hydrolysis of α-Ca₃(PO₄)₂ were studied. Temperature exerts a substantial effect on the rate of α-Ca₃(PO₄)₂ hydrolysis and also changes the morphology of the reaction products. At 40 °C, the plate-like intersecting (perpendicular to the surface of the initial particles) crystals of HAP grow. Their maximum size after the 24-h hydrolysis is 1–2 µm. Needle like HAP crystals are formed upon boiling of the suspension. The morphology observed for the HAP particles agrees well with the conclusions obtained by analysis of the kinetics of tricalcium phosphate hydrolysis.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 78–85, January, 2005.     

Oxonitrates VO(NO<Subscript>3</Subscript>)<Subscript>3</Subscript> and MoO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> and nitronium and nitrosonium nitratometallates as nitrating agents

Dissolution of vanadium in anhydrous HNO₃ followed by exposure of the solution in a dessicator over P₂O₅ gave liquid vanadyl trinitrate (I). The X-ray diffraction analysis of I was carried out for a single crystal grown on cooling the liquid in a sealed capillary. The structure is composed of VO(NO)₃ molecules in which the V atom has an unusually high C.N. 7; it coordinates the terminal O atom and three bidentate nitrate groups to form a distorted pentagonal bipyramid as the coordination polyhedron with the terminal O atom occupying one axial vertex. Using the GAMESS program package, ab initio calculation of the structure of VO (NO₃)₃ in the liquid phase was carried out. It was shown that in all three physical states, vanadyl trinitrate retains its molecular structure almost invariable. Toluene and naphthalene nitration using I and (NO₂)[Fe(NO₃)₄], NO[Cu(NO₃)₃], (NO)_3/4(NO₂)_1/4[Zr(NO₃)₅], and MoO₂(NO₃)₂ proceeds at high rates at low temperatures to give an unusually high para-nitrotoluene percentage in the products as compared with the ortho-isomer. The activity of the studied compounds in the nitration of naphthalene decreases in the series VO(NO₃)₃ > (NO)_3/4(NO₂)_1/4[Zr(NO₃)₅] > MoO₂(NO₃)₂.     

Thermal analysis of CsH<Subscript>2</Subscript>PO<Subscript>4</Subscript> nanoparticles using surfactants CTAB and F-68

A study concerned to thermogravimetric analysis is performed in cesium dihydrogen phosphate (CsH₂PO₄) that was synthesized, using cetyltrimethylammonium-bromide (CTAB), polyoxyethylene-polyoxypropylene (F-68) and mixture of (F-68:CTAB) with two mole ratio 0.06 and 0.12 as surfactant. The dehydration behavior of particles was studied using thermal gravimetric analysis and differential scanning calorimetric. Subsequently, the experimental results indicated that the first dehydration temperature in the range of 237–239 °C upon heating, the second peaks occur at temperature range 290–295 °C and overlapping in the thermogravimetric events is observed. The mass loss values are obtained in the range of 6.62–6.97 wt% that is less than reported theoretical value 7.8 wt%. These values show well compatibility of reaction CsH₂PO₄ to Cs₂H₂P₂O₇ with 3.92 wt% whereas mass loss value of CsH₂PO₄ to CsPO₃ is less than theoretical value 7.8 wt%. The activation energy of two steps dehydration are calculated using Kissinger equation for the samples synthesized via CTAB and (F-68) with minimum value mass loss 6.62% and maximum value mass loss 6.97%, respectively. The calculation results reveal that the reaction rate in the first step (CsH₂PO₄ → Cs₂H₂P₂O₇) is faster than the second step (CsH₂PO₄ → CsPO₃). The weight loss values of the samples demonstrate that existence of CTAB can be considered as effective factor which prevents more weight loss during the dehydration process.     

Some properties of rhodium thioselenochloride RhCl<Subscript>4</Subscript>Se<Subscript>6</Subscript>S<Subscript>9</Subscript> and its thermal conversion products

The structure of rhodium thioselenochloride RhCl₄Se₆S₉ and the products of its thermal decomposition are studied by X-ray photoelectron and IR spectroscopies, X-ray powder diffraction, thermal, and elemental analyses. The thermal decomposition of RhCl₄Se₆S₉ was found to occur with a loss of weakly bonded chloro-, sulfur-, and selenium-containing fragments (at 100°C); at the higher temperatures, chlorine is lost and rhodium thioselenides are obtained (Rh₄Se₄S₅ at 490°C and Rh₄Se₃S₅ at 665°C). These changes are attended by the formation of the cluster nucleus [Rh₄(µ_3-Se)₃(µ₃-S)].Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 12, 2004, pp. 910–914.Original Russian Text Copyright © 2004 by Pekhno, Stepanenko, Volkov, Fokina, Korduban.     

Aggregates of the [GaCl<Subscript>4</Subscript>]<Superscript>−</Superscript> anion and the [Ga(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>(NCS)<Subscript>3</Subscript>] complex with 18C6

The complex formation in the system GaCl₃-ROH-MNCS-18K6 is considered (ROH = MeOH, EtOH; M = Na, K; 18C6 is 1,4,7,10,13,16-hexaoxocyclooctadecane). Two modifications of [Na(18C6)][GaCl₄], namely, aggregates [Na(18C6)][GaCl₄](MeOH)_0.9(EtOH)_1.1 and [Ga(H₂O)₃(NCS)₃] · 18C6, are synthesized and identified. The ⁷¹Ga NMR (solutions) and X-ray diffraction studies showed that the compositions and structures of the title compounds are determined by the ratio of the competing acido ligands (Cl^? and NCS^?) in the reaction solution.     

Comparison of sodium zirconium phosphate and calcium zirconium phosphate structures for the retention of fluoride

Fluoride anion interaction has been explored for the first time to investigate how the structure of sodium zirconium phosphate (NZP) and calcium zirconium phosphate (CZP) can be altered in its presence. Different compositions were made by adding NaF and CaF₂ in CZP and NZP matrices respectively. Fluoride interaction differs with NZP and CZP structure as suggested by F-NMR data. The addition of fluoride to the NZP or CZP structure enables to stabilize the structure at a low temperature of 600–700 °C under microwave conditions.     

Phase formation in the InPO<Subscript>4</Subscript>-Na<Subscript>3</Subscript>PO<Subscript>4</Subscript>-Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> ternary system

The 950°C isothermal section of the InPO₄-Na₃PO₄-Li₃PO₄ ternary system was studied and constructed; one-, two, and three-phase fields are outlined. Five solid-solution regions exist in the system: solid solutions based on the complex phosphate LiNa₅(PO₄)₂ (olympite structure), the indium ion stabilized high-temperature Na₃PO₄ phase (Na_{3(1 − x)}In _x (PO₄); space group Fm [`3]\bar 3 m), the complex phosphate Na₃In₂(PO₄)₃, and the α and β phases of the compound Li₃In₂(PO₄)₃. A narrow region of melt was found in the vicinity of eutectic equilibria. All the phases detected in the system are derivatives of phases existing in the binary subsystems. Isovalent substitution of lithium for sodium in Na₃In₂(PO₄)₃ leads to a significant increase in the region of a NASICON-like solid solution.     

Microstructure and Conduction of Composites Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> Near the Eutectic Melting Point

Microstructure and conduction of ceramic composites Bi₂CuO₄ + xBi₂O₃ (x = 5, 10, 15, 20 wt %) near the eutectic melting point (770°C) are studied. Bismuth oxide, initially randomly distributed over the ceramics bulk, after quenching from temperatures exceeding the eutectic melting point, becomes localized at triple junctions and grain boundaries in Bi₂CuO₄, which is caused by wetting grain boundaries and forming a liquid-channel structure. The jumpwise change in the composites’ conductivity near 730 and 770°C caused by polymorphic transformation of Bi₂O₃ and the eutectic melting with simultaneous formation of a liquid-channel structure. Transport numbers of the oxygen ion are measured at 770°C by coulomb-volumetric method. The conduction by oxygen ions increases in the composites with decreasing average size of Bi₂CuO₄ crystallites.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 596–601.Original Russian Text Copyright © 2005 by Lyskov, Metlin, Belousov, Tret’yakov.     

Microstructure and electrical properties of lead zirconate titanate thin films deposited by sol-gel method on La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrate

(La_0.7Sr_0.3)MnO₃ thin films were deposited on SiO₂/Si substrates by a metal-organic decomposition (MOD) method, and then Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were grown on (La_0.7Sr_0.3)MnO₃-coated SiO₂/Si substrates by a sol-gel method. The effects of annealing temperature on the crystalline phases, microstructures and electrical properties of the PZT films were investigated. X-ray diffraction analysis results indicated that the PZT films with a perovskite single phase could be obtained by annealing at 650°C. The dielectric constant and the remnant polarization of the PZT films increased with increasing annealing temperature. The remnant polarization and the coercive field of the films annealed at 650°C were 18.3 μC/cm² and 35.5 kV/cm, respectively, whereas the dielectric constant and loss value measured at 1 kHz were approximately 1100 and 0.81, respectively.     

Synthesis and speciation of zirconium tetrafluoride complexes with phosphoryl-containing bases Ph<Subscript>3</Subscript>PO,Bu<Subscript>3</Subscript>PO and (Me<Subscript>2</Subscript>N)<Subscript>3</Subscript>PO in solutions

Zirconium fluoro complexes with phosphoryl-containing bases (L) have been synthesized by the reaction of a suspension of ZrF₄(dmso)₂ in toluene with an excess of Ph₃PO or Bu₃PO, as well as (Me₂N)₃PO in CH₂Cl₂. The composition and structure of the complexes in CH₂Cl₂ solutions have been studied by ¹⁹F NMR in the temperature range 293–203 K. Phosphine oxides are substituted for dmso to form mainly cis-tetrafluoro species, insignificant amounts of trans-tetrafluoro species, and mer- and fac-[ZrF₃L₃]⁺ complexes. In addition to these species, the reaction with Bu3PO yields the dimeric oxo complex (µ-O)[ZrF₃(Bu₃PO)₂]₂. Hydrolysis of fluoro complexes in CH₂Cl₂ with the use of an NBu₄OH solution in iso-PrOH does not lead to oxo and hydroxo complexes: first, the [ZrF₅L]^– complex is formed, and the final hydrolysis product is ZrF₆^2-. The fine structure of ¹⁹F NMR resonance lines for the zirconium fluoride compounds [ZrF5L]^–, cis- [ZrF₄L₂], dimeric oxo complex, and mer-[ZrF₃L₃]⁺ in organic solvents has been observed for the first time, which makes it possible to reliably identify the composition and structure of the zirconium coordination polyhedron in the complexes under consideration.     

Hydrothermal preparation of CuO-ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> catalyst for phenol <Emphasis Type="Italic">ortho</Emphasis>-alkylation with methanol: effect of the calcination temperature on the catalytic performance

The effect of heat-treatment on 10 wt% CuO-ZnAl₂O₄ catalytic activity in methylation of phenol and the degree of interaction of CuO active phase with support spinel phase were investigated. The CuO-ZnAl₂O₄ sample was subjected to heat-treatment up to 1000°C. The thermal products were characterized by X-ray diffraction (XRD) analysis, nitrogen adsorption-desorption at -196°C and temperature-programmed desorption (TPD-MS) of CO₂. Additionally, the reducibility of copper phases was investigated by temperature-programmed reduction (TPR). XRD patterns of the fresh catalyst sample (calcined at 600°C) indicated the presence of a mixture of poorly crystallized CuO and ZnAl₂O₄ spinel phase. The presence of two reducible copper species has been found on fresh CuO-ZnAl₂O₄ catalyst by TPR analysis. After subsequent calcinations in air at elevated temperatures some CuO disappeared with appearance of CuAl₂O₄ phase. The catalytic results revealed that the CuO addition to ZnAl₂O₄ increases the activity in ortho-methylation of phenol. Subsequent heat-treatment up to 900°C causes partial deactivation of copper centers, which is the result of transformation of CuO to the inactive CuAl₂O₄ phase.     

Electrochemical Synthesis of Co-intercalation Compounds in the Graphite-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript>System

Anodic oxidation of highly oriented pyrolytic graphite in an electrolyte containing concentrated sulfuric and anhydrous phosphoric acids is studied for the first time. The synthesis was carried out under galvanostatic conditions at a current I = 0.5 mA and an elevated temperature (t = 80°C). Intercalation compounds of graphite (ICG) are shown to form at all concentration ratios of H₂SO₄ and H³PO⁴ acids. The intercalation compound of step I forms in solutions containing more than 80 wt % H₂SO₄, a mixture of compounds of intercalation steps I and II forms in 60% H²SO⁴, intercalation step II is realized in the sulfuric acid concentration range from 10 to 40%, and a mixture of compounds of intercalation steps III and II is formed in 5% H₂SO₄ solutions. The threshold concentration of H₂SO₄ intercalation is ∼2%. With the decrease in active intercalate (H₂SO₄) concentration, the charging curves are gradually smoothed, the intercalation step number increases, and the potentials of ICG formation also increase. As the sulfuric acid concentration in the electrolyte changes from 96 to 40 wt %, the filled-layer thickness d _i in ICG monotonously increases from 0.803 to 0.820 nm, which apparently is associated with the greater size of phosphoric acid molecules. With further increase in H₃PO₄ concentration in solution, d _i remains unchanged. According to the results of chemical analysis, both acids are simultaneously incorporated into the graphite interplanar spacing and their ratio in ICG is determined by the electrolyte composition.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 651–655.Original Russian Text Copyright © 2005 by Leshin, Sorokina, Avdeev.