Spectroellipsometric Characterization of Multilayer Sol-Gel Fe2O3 Films

Multilayer Fe₂O₃ films were deposited by the sol-gel method on glass substrates using three successive deposition procedures. The films were thermally treated for 1 h at 300°C.The optical and microstructural properties of these films were investigated by spectroscopic ellipsometry (SE) in the 500–1000 nm range. The optical gap was found by fitting the dispersion of the film refractive index (n) with the Wemple-DiDomenico (WDD) formula.The ellipsometric measurements showed also that the Fe₂O₃ films are anisotropic. The birefringence values (n) of the sol-gel films (0.05–0.08) are smaller than the large values of the Fe₂O₃ (which are around 0.28) but increase with the crystalization of the films. AFM mesurements showed that the films treated at 300°C start to crystallize.     

Sol-Gel Preparation of Fast Proton-Conducting P2O5-SiO2 Glasses

We have investigated the proton conductivities of the sol-gel-derived P₂O₅-SiO₂ glass at –50 to 120°C. The obtained glass is porous, where the surface area, pore volume and pore diameter are 740 m²/g, 0.5 cm³/g and <5 nm, respectively. The freezing temperature of water molecules adsorbed in the pores was –20°C, which is much lower than that of free liquid water due to the quantum size effect of the water confined in the pores. The electrical conductivities followed the Arrhenius equation in the temperatures between –20 and 120°C. Below –20°C, the adsorbed-water molecules were frozen, resulting in a rapid decrease of the proton conductivity. Considering the high conductivity, chemical and thermal stability, this oxide glass membranes have potential for the fuel cell membrane.     

Orientation and Surface Properties of Sol-Gel Derived Y2O3 Films

The orientation, surface and optical properties of sol-gel derived Y₂O₃ films have been investigated. Transparent Y₂O₃ films were prepared on quartz glass substrates by sol-gel processes using YCl₃·6H₂O as a starting material. The water droplet contact angles of the films reached constant values between 79° and 90° after the films were left for 8 to 10 days in air at ambient temperature, indicating that the film surface exhibited hydrophobicity. When 2-(2-methoxyethoxy)ethanol (MEE) was added to the sol, yttria in the films crystallized to a strongly oriented cubic phase at firing temperatures between 400°C and 500°C. The intensity of the XRD peaks increased as the firing temperature was increased to 900°C. However, yttria crystallized to a non-oriented cubic phase when MEE was not used. The refractive index and packing density of the Y₂O₃ films increased from 1.55 to 1.68 and from 0.67 to 0.79, respectively, as the firing temperature was raised from 400°C to 900°C, indicating that sol-gel derived Y₂O₃ films are lower in density than evaporated ones.     

Preparation and Characterization of SiO2-MxOy(M = V, Sn, Sb) Thin Films from Silicic Acid and Metal Chlorides

The preparation of SiO₂-M _x O _y (M = V, Sn, Sb) binary oxide thin films by sol-gel method was investigated. The reaction of silicic acid with metal chloride (M = Sn and Sb) or oxychloride (M = V) formed homogeneous solutions. The dip-coating of slide glass and silicon wafer followed by heat treatment gave oxide films having Si—O—M bond. The changes of FT-IR spectra as a function of heat treatment temperature and molar composition confirmed the Si—O—M bonds. The sheet resistance of films increased with an increase on heat treatment temperature and decrease in the content of metal oxide M _x O _y . X-ray diffraction peaks were observed for the SiO₂-V₂O₅ films with high V₂O₅ contents and heat-treated above 250°C, while the others were amorphous. Oxide films heat treated at 500°C had a thickness between 340–470 nm.     

Preparation of spherical spinel LiMn2O4 cathode material for lithium ion batteries

A novel process is proposed for synthesis of spinel LiMn₂O₄ with spherical particles from the inexpensive materials MnSO₄, NH₄HCO₃, and NH₃H₂O. The successful preparation started with carefully controlled crystallization of MnCO₃, leading to particles of spherical shape and high tap density. Thermal decomposition of MnCO₃ was investigated by both DTA and TG analysis and XRD analysis of products. A precursor of product, spherical Mn₂O₃, was then obtained by heating MnCO₃. A mixture of Mn₂O₃ and Li₂CO₃ was then sintered to produce LiMn₂O₄ with retention of spherical particle shape. It was found that if lithium was in stoichiometric excess of 5% in the calcination of spinel LiMn₂O₄, the product had the largest initial specific capacity. In this way spherical particles of spinel LiMn₂O₄ were of excellent fluidity and dispersivity, and had a tap density as high as 1.9 g cm^–3 and an initial discharge capacity reaching 125 mAh g^–1. When surface-doped with cobalt in a 0.01 Co/Mn mole ratio, although the initial discharge capacity decreased to 118 mAh g^–1, the 100th cycle capacity retention reached 92.4% at 25°C. Even at 55°C the initial discharge capacity reached 113 mAh g^–1 and the 50th cycle capacity retention was in excess of 83.8%.     

Mesoporous Nb2O5 Films: Influence of Degree of Crystallinity on Properties

Nanocrystalline Nb₂O₅ films were prepared by an extended sol-gel method. The synthesis is based on the hydrolysis of a modified Nb-alkoxide precursor. Reaction of the modified precursor (Nb(OEt)₅ + 2 2,4-pentanedione) with water in ethanol leads to a homogeneous hydrolyzed solution, which is stable against precipitation of niobium oxide after evaporation of the ethanol and in the whole pH-range investigated (1–10). Autoclaving leads to amorphous gels, from which homogeneous nanocrystalline niobium oxide films of up to 15 m can be made. During annealing crystalline phases are first observed above 500°C with fully crystalline films of orthorhombic T-phase Nb₂O₅ attained at 600°C. The microstructural, crystallographic, optical and photoelectrical properties of the films were characterized by means of SEM, XRD, UV-VIS spectroscopy and surface photovoltage spectroscopy, respectively.     

Studies on hydrolyzable carbides. XXII: The carbothermal reduction of scandium oxide Sc2O3

The composition of the products of carbothermal reduction of Sc₂O₃ is examined by X-ray diffraction and chemical analysis and by the hydrolysis method. At pressures of 10^–2-1 Pa, the reaction starts in the temperature region of 1 000–1 200°C. The first product is Sc₂OC of NaCl type; at 1 Pa and 1 400–1 500°C this substance is formed quantitatively (according to stoichiometry) within 50–100 h, repeated homogenization, however, is necessary, or else Sc₂OC reacts locally with Sc₂O₃ giving Sc₂O_1+x C_1–x . The lattice parameter of Sc₂OC in the presence of Sc₁₅C₁₉ is 457.6₃pm. At temperatures above 1 500°C, Sc₁₅C₁₉ is incompletely formed by subsequent reaction with carbon. The product melts at cca. 1 800°C; carbon dissolves and the final composition approaches ScC₂. Carbon separates during solidification. The phase fractions in the products are affected by evaporation, the vapour pressures above both Sc₂OC and Sc₁₅C₁₉ being comparable with the pressure requisite for the carboreduction process. The results are discussed with respect to the often ambiguous published data.

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Untersuchung hydrolysierbarer Carbide, XXII. Die karbothermische Reduktion von Scandiumoxid

Zusammenfassung Zur Untersuchung von Produkten der karbothermischen Reduktion von Scandiumoxid wurden sowohl röntgenographische und chemische Analyse als auch die hydrolytische Methode verwendet. Bei 10^–2 bis 1 Pa beginnt die Reaktion im Temperaturintervall von 1 000–1 200°C. Das erste Reaktionsprodukt ist das Scandiumoxidcarbid Sc₂OC von NaCl-Typ, das quantitativ (der Stöchiometrie entsprechend) bei 1 400–1 500°C und 1 Pa in 50–100 Stunden entsteht. Eine wiederholte Homogenisierung ist allerdings notwendig, damit es zu keiner lokalen Reaktion zwischen Sc₂OC und Sc₂O₃ kommt, bei der dann die Phase Sc₂O_1+x C_1–x entsteht. In Gegenwart von Sc₁₅C₁₉ ist der Gitterparameter von Sc₂OCa=457.6₃pm. Über 1 500°C führt eine weitere Reaktion mit Kohlenstoff zu einer nicht ganz vollendeten Bildung von Sc₁₅C₁₉. Bei cca. 1 800°C schmilzt das Reaktionsprodukt bei gleichzeitiger Auflösung von weiterem Kohlenstoff und die Zusammensetzung nähert sich der Formel ScC₂, beim Erstarren fällt der Kohlenstoff wieder aus. Die Verteilung der Phasen im Produkt wird von der Verdampfung beeinflußt, da die Dampfdrucke von Sc₂OC und Sc₁₅C₁₉ mit dem zum Karboreduktionverlauf notwendigen Druck vergleichbar sind. Die erhaltenen Ergebnisse werden in Relation mit den nicht eindeutigen Angaben in der Literatur diskutiert.

     

Synthesis of nano-sized crystalline oxide ion conducting fluorite-type Y2O3-doped CeO2 using perovskite-like BaCe0.9Y0.1O2.95 (BCY) and study of CO2 capture properties of BCY

Formation of nano-sized Y₂O₃-doped CeO₂ (YCO) was observed in the chemical reaction between proton conducting Y₂O₃-doped BaCeO₃ (BCY) and CO₂ in the temperature range 700-1000 °C, which is generally prepared by wet-chemical methods that include sol-gel, hydrothermal, polymerization, combustion, and precipitation reactions. BCY can capture CO₂ of 0.13 g per ceramic gram at 700 °C, which is comparable to that of the well-known Li₂ZrO₃ (0.15 g per ceramic gram at 600 °C). Powder X-ray diffraction (PXRD), energy dispersive X-ray analysis (EDX), laser particle size analysis (LPSA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ac impedance spectroscopy were employed to characterize the reaction product obtained from reaction between BCY and CO₂ and subsequent acid washing. PXRD study reveals presence of fluorite-like CeO₂ (a=5.410 (1) Å) structure and BaCO₃ in reaction products. TEM investigation of the acid washed product showed the formation of nano-sized material with particle sizes of about 50 nm. The electrical conductivity of acid washed product (YCO) in air was found to be about an order higher than the undoped CeO₂ reported in the literature.     

Sol-Gel Poly-Component Nano-Sized Oxide Powders

Nano-sized, amorphous and monodispersed poly-component powders in the Al₂O₃–TiO₂–MgO and Al₂O₃–TiO₂–SiO₂ systems have been obtained by the sol-gel method. These powders have been characterized by XRD, IR spectroscopy, DTA/TGA and EDAX spectrometry. This last method confirmed the composition of the ternary powders, which are formed during the gelation process.The powders were tested as precursors for obtaining advanced ceramics, as tialite, Al₂TiO₅. The samples prepared with powders obtained by sol-gel method have shown a high reactivity, and the formation of tialite was improved.     

Thermal behaviour of high surface area V2O5/TiO2 catalysts

Thermal analysis (TG and DTA) was employed for the characterization of V₂O₅/TiO₂ catalysts supported on high surface area TiO₂. The results obtained are consistent with a uniform spreading of vanadium oxide on TiO₂ surface for V₂O₅ content less than 15% by weight.The presence of V₂O₅ on the surface of TiO₂ affects the anatase-rutile phase transition lowering the temperature at which it occurs.DTA measurements, performed on catalysts after many months from the preparation, show the appearance of an exothermic peak in the range 280°–340°C. This signal has been related to the oxidation of V(IV) to V(V) on the catalyst surface.Catalysts characterization, performed by chemical analysis and FT-IR spectroscopy, has confirmed this interpretation.It has been suggested that a slow modification of the catalyst occurs, leading to an increase of the V(IV) content during the time.

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Zusammenfassung Zur Charakterisierung von V₂O₅/TiO₂-Katalysatoren auf hochoberflächigem TiO₂ Trägermaterial wurde die Thermoanalyse (TG und DTA) angewendet. Für einen V₂O₅-Gehalt von weniger als 15 Gew.% entsprechen die erhaltenen Ergebnisse einer gleichmäßigen Verteilung des Vanadiumoxides an der TiO₂-Oberfläche.Die Gegenwart von V₂O₅ an der Oberfläche von TiO₂ beeinflußt die Anatas-Rutil-Phasenumwandlung, indem sie die zugehörige Temperatur verringert.DTA-Messungen an Katalysatoren mehrere Monate nach ihrer Herstellung zeigten das Auftreten eines exothermen Peaks im Bereich 280°–340°C. Dieses Signal wurde der Oxidation von V(IV) zu V(V) an der Katalysatoroberfläche zugeschrieben.Diese Interpretation konnte durch eine Charakterisierung des Katalysatoren durch chemische Analyse und FT-IR-Spektroskopie bestätigt werden.Es wurde angedeutet, daß der Katalysator mit der Zeit einer langsamen Modifikation unterliegt, die zu einem Ansteigen des V(IV)-Gehaltes führt.

     

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.     

Studies on synthesis, characterization and thermochemistry of Mg2[B2O4(OH)2]·H2O

A new magnesium borate Mg₂[B₂O₄(OH)₂]·H₂O has been synthesized by the method of phase transformation of double salt at hydrothermal condition and characterized by XRD, IR, TG and DSC. The enthalpy of solution of Mg₂[B₂O₄(OH)₂]·H₂O in 0.9764 mol L^–1 HCl was determined. With the incorporation of the enthalpies of solution of H₃BO₃ in HCl (aq), of MgO in (HCl+H₃BO₃) (aq), and the standard molar enthalpies of formation of MgO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of –(3185.78±1.91) kJ mol^–1 of Mg₂[B₂O₄(OH)₂]·H₂O was obtained.This revised version was published online in November 2005 with corrections to the Cover Date.     

Phase formation and thermal stability of the compounds in the Bi2O3-PbO system

The scientific interest for the Bi₂O₃-PbO system has increased due to the importance of the PbO in the high-T _c superconducting phase formation in the Bi₂O₃-SrO-CaO-CuO system. Also Bi₂O₃-PbO system contains compounds with some specific semiconductor and dielectric properties and Bi₂O₃-based solid solutions are well known as high oxygen ion conductors.Previously, several low melting defined compounds have been identified in the system: 6Bi₂O₃·PbO; 3Bi₂O₃·2PbO; 4Bi₂O₃·5PbO; 4Bi₂O₃·6PbO and Bi₂O₃·3PbO.This work deals with the phase formation and thermal stability of these compounds. Under non-isothermal conditions, in all mixtures regardless of the Bi₂O₃/PbO ratio, the compound 6Bi₂O₃·PbO is preferentially formed, followed by the compound 4Bi₂O₃·5PbO. The formation of the compound 4Bi₂O₃·6PbO was not confirmed while the formation of the compound Bi₂O₃ 3PbO occurs through a complex mechanism which includes an intermediate step in which a solid solution with the litharge structure was identified. Under isothermal conditions in the same temperature range the tendency to form the stoichiometric compounds increases. All compounds form, decompose and melt at temperatures between 530–780°C.     

UV-Visible and IR Spectroelectrochemical Properties of V2O5 Crystalline Films Charged/Discharged in Extended Potential Range

Electrochemical properties of amorphous and crystalline V₂O₅ films, dip-coated from V-oxoisopropoxide sols and thermally treated at various temperatures (100, 150, 200 and 300°C), have been studied in extended potential range, i.e. from 1.4 to –1.6 V vs. Ag/AgCl in 1M LiClO₄/propylen carbonate (PC) electrolyte. The formation of various lithiated (-, -, - and -Li _x V₂O₅) phases was correlated with the values of insertion coefficient x obtained from cyclic voltammograms (CV) of crystalline V₂O₅ films (300°C). Reversible charging was observed when films were cycled up to –1.0 V vs. Ag/AgCl, while the extension of the potential to –1.3 V vs. Ag/AgCl change the CV of films irreversibly. Charging of crystalline V₂O₅ films was followed by the help of in-situ UV-visible spectroscopy, that revealed the intensity variations of the polaron absorption above 600 nm and the presence of the absorbing V³⁺ species between 550 and 650 nm. Ex-situ IR spectra of the crystalline films charged/discharged at –1.6V/1.4V vs. Ag/AgCl confirmed the amorphisation of the films' structure.     

Improvement of the Pd/Al2O3 Catalyst by the Control of the Sol-Gel Preparative Parameters

In this work, the metal dispersion of the Pd/Al₂O₃ catalyst prepared by sol-gel method is improved by an adequate optimisation of the preparative variables. First, the gelation temperature and the ageing time are selected, in order to avoid the reduction of the metal precursor (palladium acetylacetonate, Pd(acac)₂) by the solvent (sec-butanol, sB). The metal sintering effect on the catalysts treated in oxygen at 500°C is then minimized when the alumina pore size is controlled by the variation of the alumium alkoxide (AsB) concentration and the acetic acid amount ([AcA]/[AsB]). The appearance of new palladium particles on the alumina surface and the matching between the particle diameters and the pore sizes were also effective for the metallic surface area improvement on the samples treated in oxygen at 800°C. Compared to the reference catalysts, the higher metal dispersion obtained on the sol-gel ones was the determinant factor for their higher catalytic activity in methane combustion.     

Phase transfer catalyzed oxidation of ketones with borax-H2O2

Summary Borax forms peroxy species when dissolved in 30% hydrogen peroxide which can be transferred into the organic phase when biphase mixtures are agitated. The addition of a catalytic amount ofBTEAC promotes the transfer. This biphase system was used for theBaeyer-Villiger oxidation of several ketones insoluble in water. Effects of changing various parameters,e.g. temperature, time, amount of H₂O₂ etc. were investigated. At higher temperature (ca. 80°C), 100% conversion could be achieved in 2–4h. The results show that under appropriate conditions this reaction is of synthetic value for the oxidation of acid-sensitive ketones using inexpensive and easily available reagents.

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Oxidation von Ketonen mit Borax-H₂O₂ unter Phasentransferkatalyse

Zusammenfassung In Wasserstoffperoxid (30%) gelöstes Borax bildet Peroxyverbindungen, die durch Schütteln in die organische Phase zweiphasiger Systeme übergeführt werden können. Der Transferprozeß wird durch die Zugabe von katalytischen MengenBTEAC gefördert. Die zweiphasigen Systeme wurden zurBaeyer-Villiger — Oxidation einiger in Wasser unlöslicher Ketone eingesetzt und die Auswirkung der Variation verschiedener Parameter (z.B. Temperatur, Zeit, Menge an H₂O₂ etc.) untersucht. Unter dem Einfluß höherer Temperature (ca. 80°C) wurde vollständige Umsetzung innerhalb von 2–4 h erreicht. Die Ergebnisse zeigen, daß die genannte Reaktion unter geeigneten Bedingungen von synthetischem Wert zur Oxidation säureempfindlicher Ketone unter Verwendung billiger und leicht verfügbarer Reagenzien ist.

     

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.     

IR-spectral investigation of the structure of glasses in the Fe2O3-V2O5 system

The structure of glasses in the Fe₂O₃-V₂O₅ system in the 0–50 mol% Fe₂O₃ range is studied by IR-spectroscopy. It is found that the introduction of Fe₂O₃ favours the transformation of the VO₅-groups into VO₄ ones. This effect may be shown with the aid of IR-spectra, owing to the fact that these glasses are characterized by two high-frequency bands at 1020 and 930 cm^–1. The first is determined by the vibrations of the short V=O nonbridging bonds in the VO₅-groups, while the second is assigned to the vibrations of the V—O-bonds in deformed VO₄-tetrahedra.

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IR-spektroskopische Strukturuntersuchung von Gläsern des Systems Fe₂O₃-V₂O₅

Zusammenfassung Die Struktur von Gläsern des Systems Fe₂O₃-V₂O₅ in dem Bereich von 0–50 Molprozent Fe₂O₃ wurde mit Hilfe der IR-Spektroskopie untersucht. Zusatz von Fe₂O₃ begünstigt die Umwandlung der VO₅- in VO₄-Gruppen. Das kann in den IR-Spektren durch zwei Banden bei 1020 und 930 cm^–1 festgestellt werden. Die erste wird durch Schwingungen der kurzen V=O-Nichtbrücken-bindungen in den VO₅-Gruppen verursacht, die zweite wird auf Schwingungen der V—O-Bindungen in dem deformierten VO₄-Tetraeder zurückgeführt.

     

Fabrication of Single-Phase BaTi4O9 Nanocrystalline Powder by Sol-Gel Process

BaTi₄O₉ nanocrystalline powder was prepared by sol-gel method using Ti(OC₄H₉)₄ and Ba(CH₃COO)₂ as raw materials. The optimum process was obtained by analyzing the synthesis condition of the single-phase BaTi₄O₉ nanocrystalline powder as follows: the content of acetyl-Titanium = 1 mol/L. pH = 4.2, molar ratio of water/alkoxide = 15, and the powder is kept at 1200°C for 2 h. The XRD and TEM analysis showed that the single-phase BaTi₄O₉ nanocrystalline powder of 30 nm in size was well prepared.     

The thermal dehydration and decomposition of Ba[Cu(C2O4)2(H2O)]·5H2O

The thermal behaviour of Ba[Cu(C₂O₄)₂(H₂O)]·5H₂O in N₂ and in O₂ has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively low temperatures (about 80°C), but continues until the onset of the decomposition (about 280°C). The decomposition takes place in two major stages (onsets 280 and 390°C). The mass of the intermediate after the first stage corresponded to the formation of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The enthalpy for the dehydration was found to be 311±30 kJ mol^–1 (or 52±5 kJ (mol of H₂O)^–1). The overall enthalpy change for the decomposition of Ba[Cu(C₂O₄)₂] in N₂ was estimated from the combined area of the peaks of the DSC curve as –347 kJ mol^–1. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly deceleratory and the -time curves could be described by the three dimensional diffusion (D3) model. The values of the activation energy and the pre-exponential factor for the dehydration were 125±4 kJ mol^–1 and (1.38±0.08)×10¹⁵ min^–1, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry model withn=5. The other process was slow and could also be described by the contracting-geometry model, but withn=2.The values ofE _a andA were 206±23 kJ mol^–1 and (2.2±0.5)×10¹⁹ min^–1, respectively, for the fast process, and 259±37 kJ mol^–1 and (6.3±1.8)×10²³ min^–1, respectively, for the slow process.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday