Microcalorimetric study of the effect of manganese on the growth and metabolism in a heterogeneously expressing manganese-dependent superoxide dismutase (Mn-SOD) strain

DSC, SEM–EDS, XRD and high-temperature XRD analysis was used to study thermal and crystallization behaviour of yttrium aluminate glasses prepared in the form of microspheres. The glasses YA-E (eutectic composition from the pseudo-binary system Al₂O₃–Y₃Al₅O₁₂) and YA-G (a composition identical to the stoichiometric Y₃Al₅O₁₂ (YAG) phase) were prepared by combination of the Pechini method with flame synthesis. The resulting microspheres were largely amorphous, but contained traces of yttrium–aluminium garnet as the main crystalline phase embedded in the yttrium aluminate glass matrix. Crystallization of the YAG phase was observed as the dominant exothermic process on DSC curves. From the DSC records, the basic thermal characteristics of the matrix glass, i.e. T _g (glass transition temperature), T _x (onset of crystallization peak temperature), T _f (temperature of the inflection point of the crystallization peak) and T _p (maximum of crystallization peak temperature), were determined. HT XRD experiments in the temperature interval 750–1200 °C and isothermal HT XRD experiments at 932, 998 and 1200 °C with 6-h holding time were also performed. Crystallization experiments at lower temperatures 932 °C (YA-E) and 915 °C (YA-G) were conducted to study phase development in a low-temperature region. Crystallization experiments at higher temperatures (1000, 1300 and 1500 °C) with maximum holding time of 6 h were performed to study crystallization of α-Al₂O₃ in the eutectic system. The SEM and SEM–EDS examination of polished cross sections of crystallized microspheres revealed slow volume crystallization of the YAG phase in the AY-E glass. Eventually, polycrystalline microspheres with fine-grained microstructure were prepared after 6-h treatment at 1500 °C.     

Thermal stability of aluminium hydroxycarbonates with monovalent cations

Dawsonite-type compounds of formula MAl(OH)₂CO₃ (M = Na. K, NH₄) as well as a laminar hydrotalcite-type hydroxycarbonate of composition [Al₂Li(OH)₆]₂CO₃·4H₂O. have been hydrothermally synthesized The thermal decomposition of these compounds was monitored by DTA and TG, and the resulting products have been studied by X-ray and IR techniques. Sodium and potassium dawsonites are destroyed at 335°C. yielding a poorly crystalline compound in which part of the overall carbonate is present; the remaining carbonate is lost between 600 and 700°C, yielding NaAlO₂ and KAlO₂, respectively Ammonium dawsonite and lithium hydrotalcite are less stable, their thermal decomposition occurring at about 240°C. The ammonium dawsonite heated at 680°C shows the presence of A1₂O₃ with a poorly ordered structure, while lithium hydrotalcite yields poorly crystalline γ-Al₂O₃ at 500°C and a mixture of γ-LiAlO₂ and LiAl₅O₈ when the compound is heated at higher temperatures ( ~ 1000°C).     

Preparation of γ-Alumina Membranes From Sulphuric Electrolyte Anodic Alumina and Its Transition to α-Alumina

Gamma-alumina membrane was prepared from anodic (amorphous) alumina (AA) obtained in a sulphuric acid electrolyte. The transformation scheme, i.e., the crystallization to form metastable alumina polymorphs and the final transition to α-Al₂O₃ with heating was studied by TG-DTA and X-ray diffraction (XRD) using fixed time (FT) method. When heating at a constant rate, the crystallization occurred at 900°C or higher and the final formation of α-Al₂O₃ occurred at 1250°C or higher, which temperatures were higher than the case of using anodic (amorphous) alumina prepared from oxalic acid electrolyte. Relative content of S of the products was obtained by transmission electron microscope (TEM)-energy dispersive spectroscopy (EDS). The proposed thermal change of anodic alumina membrane prepared from sulphuric acid is as follows: 1. At temperatures lower than ca 910°C: Formation of a quasi-crystalline phase or a polycrystalline phase (γ-, δ- and θ-Al₂O₃); 2. 910–960°C: Progressive crystallization by the migration of S toward the surface within the amorphous or the quasi-crystalline phase, forming S-rich region near the surface; 3. 960°C: Change of membrane morphology and the quasi-crystalline phase due to the rapid discharge of gaseous SO₂; 4. 960–1240°C: Crystallization of γ-Al₂O₃ accompanying δ-Al₂O₃; and 5. 1240°C: Transition from γ-Al₂O₃ (+tr. δ-Al₂O₃) into the stable α-Al₂O₃. The amorphization which occurs by the exothermic and the subsequent endothermic reaction suggests the incorporation of SO₃ groups in the quasi-crystalline structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rapid crystal phase transformation into hexagonally shaped α-alumina using AlF3 seeds

This study focused on synthesizing highly crystalline α-Al₂O₃ at low temperatures. We found that when a small amount of hexagonal structured aluminum fluoride seeds (AlF₃) were added to aluminum precursors, the crystal phase transformation temperature required to form α-Al₂O₃ were considerably lowered and the produced α-Al₂O₃ particles showed hexagonal shapes. Furthermore, when 2.0 mol% of hexagonal structured-AlF₃ particles were added as seed to sol-solutions containing various aluminum precursors such as AIP, AlCl₃, Al(NO₃)₃ or AlOOH, rhombohedral α-Al₂O₃ particles were formed at 750 °C regardless of the use of alumina precursors. Scanning electron microscopy photos showed the α-Al₂O₃ particles produced had hexagonal shapes, and that the morphologies of these particles depended on the primitive structures of the AlF₃ seeds added. Based on the relationship between α-Al₂O₃ crystallites sizes and calcination temperatures, crystal growth in α-Al₂O₃ structure was enhanced by adding AlF₃ seeds.     

Determination of the maximum monolayer dispersion and dispersed state for WO3 on γ-Al2O3

The maximum monolayer dispersion (the threshold) for WO₃ on γ-Al₂O₃ calcined at 500°, 550°, 600°, and 640°C has been determined quantitatively by XRD (amount of crystalline phase) and XPS (intensity ratios I_w4f/I_Al2). The results show that if the amount of WO₃ loaded is lower than the maximum monolayer dispersion, WO₃ will react with γ-Al₂O₃ to form surface compound due to mutual ionic interaction, and will be dispersed on γ-Al₂O₃ surface as monolayer then. In case the amount is higher than this value, the residual crystalline WO₃ will remain. The maximum monolayer dispersion (threshold) is 0.21 g and 0.20 g WO₃/100 m² γ-Al₃O₃ by XRD and XPS respectively. It agrees with the value (0.189 g WO₃/100 m² or 4.90 × 10^?18 W atoms/m²) calculated from the model on assumption that the WO₃ is dispersed as a closed-packed monolayer on γ-Al₂O₃ surface. Inasmuch as WO₃/γ-Al₂O₃ system is stable up to higher temperature, e.g. 700°C, than MoO₃/γ-Al₂O₃ system, WO₃ seems unfavorable to form new bulk compound with γ-Al₂O₃ at that temperature. However, Al₂(MoO₄)₃ forms perceptibly in MoO₃/γ-Al₂O₃ system at 500°C. Besides, the size of residual crystalline WO₃ in WO₃/γ-Al₂O₃ is much smaller than that of MoO₃ in MoO₃/γ-Al₂O₃. It might be the reason that WO₃/γ-Al₂O₃ catalyst is superior to MoO₃/γ-Al₂O₃ in hydrodesulfurization (HDS) or hydrodenitrogenation (HDN) in some cases.     

Sol‐Gel Preparation and Characterization of Codoped Yttrium Aluminium Garnet Powders

A sol‐gel method has been developed to prepare lanthanide‐codoped yttrium aluminium garnet (Y₃Al₅O₁₂, YAG) ceramic samples. The XRD patterns of the polycrystalline Y₃Al₅O₁₂:Nd,Ho and Y₃Al₅O₁₂:Nd,Er powders sintered at 1000 °C showed the formation of monophasic garnet materials. A homogeneous distribution of rare‐earth dopants in the YAG lattice was achieved in both cases. The morphological characterization of lanthanide‐codoped YAG by scanning electron microscopy (SEM) showed the formation of highly agglomerated nanocrystalline samples. The luminescence properties of sol‐gel derived doubly activated yttrium aluminium garnet samples were also investigated in the present study.     

Comparison of the thermal stability of β- and β″-alumina at high pressures

The high-pressure thermal stability of Na⁺ β-alumina and magnesium-stabilized Na⁺ β″-alumina was studied from 5 to 50 Kb and from room temperature to 1400°C. Above 5 Kb and 560°C, Na⁺ β-alumina decomposes into α-Al₂O₃ and NaAlO₂. Magnesium-stabilized Na⁺ β″-alumina decomposes at slightly higher temperatures to α-Al₂O₃, MgAl₂O₄, and probably NaAlO₂. Estimates of activation volume and enthalpy support a model for decomposition that depends on cation vacancies and proceeds by sodium diffusion in quasi-liquid conduction planes.     

Synthesis of an aluminum nitride–yttria (AlN–Y2O3) composite from nano-sized porous AlN and YCl3

In order to enhance the thermal conductivity of aluminum nitride (AlN) with sintering additives including yttria (Y₂O₃), it is necessary to form yttrium aluminate garnet (YAG) and secondary phases both within and around the boundaries of AIN drains. Nano-sized porous AlN particles were produced to form YAG and secondary phases within AlN grains, after which a AlN–Y₂O₃ nano–nano composite was formed from AlN and amorphous Y₂O₃. Porous AlN powders were first successfully synthesized by the chemical vapor synthesis (CVS) method. Highly crystalline and nano-sized porous AlN powders were synthesized at 1,200 °C. Brunauer–Emmett–Teller (BET) analysis showed that these powders had very large surface areas, suggesting that the particles approached nano-scale sizes with very small pores. To form composites of Y₂O₃ and AlN, we prepared a yttrium source solution that infiltrated the nano-sized pores of the AlN particles. Such an infiltration of AlN with amorphous Y₂O₃ was expected to effectively reduce the residual oxygen content by facilitating the formation of YAG and secondary phases during the sintering process. We characterized the composite powders of AlN–Y₂O₃ and the sintered bodies using BET, XRD, SEM, TEM, and thermal conductivity analyses.

     

Investigation of thermal decomposition of yttrium–aluminum-based precursors for YAG phosphors

Three types of precursors were prepared using the wet-chemical synthesis route, starting from yttrium?Ceuropium?Caluminum nitrate solution and different precipitating agents (urea, oxalic acid, and ammonium carbonate). The precursors were fired at 1200?°C in nitrogen atmosphere in order to obtain europium-doped yttrium aluminate Y₃Al₅O₁₂:Eu³⁺ phosphor with garnet structure (YAG:Eu). The processes involved in the thermal decomposition of precursors and their composition were put in evidence using thermal analysis (TG?CDTA) and FT-IR spectroscopy. The GA?CDTA curves possess typical features for basic-oxalate, -nitrate, and -carbonates as formed with oxalic acid, urea, and ammonium carbonate, respectively. Correlation between the thermal decomposition steps, mass loss, and composition of gases evolved during the thermal treatment was established using TG?CDTA?CFT-IR coupling. It was found that the different composition of precursors reflects on the luminescent characteristics of the corresponding phosphors. Urea and ammonium carbonate lead to the formation of YAG type phosphors, with garnet structure and specific red emission. As for the oxalic acid, this precipitating agent generates a non-homogeneous powder that contains yttrium oxide as impurity phase. This phosphor is a mixture of Y₂O₃:Eu³⁺, Y₄Al₂O₉:Eu³⁺, and Y₃Al₅O₁₂:Eu³⁺ that explain the relative higher emission intensity.     

Study of CuCl2 Supported on SiO2 and Al2O3

The nature and stability of surface species of CuCl₂ supported on α-Al₂O₃, γ-Al₂O₃, and SiO₂ were investigated by using X-ray diffraction techniques and reflectance spectroscopy. No specific chemical interaction of CuCl₂ is observed on an inert α-Al₂O₃ support, as opposed to hydrated carriers as SiO₂ and γ-Al₂O₃. On these supports the coordination sphere of Cu²⁺ consists of surface groups (OH^? or O^? at drying and activation, resp.), H₂O and Cl^?, with the H₂O ligands decreasing in concentration in the process of impregnation, drying and calcination. γ-Al₂O₃ samples, calcined at 400°C, show γ-Cu₂(OH)₃Cl as opposed to CuAl₂O₄ at higher temperatures. The absence of Cu₂(OH)₃Cl on SiO₂-supported samples is related to the acid-base characteristics of the carriers. The various supports can be arranged in the following order of stability of the complexes formed: γ-Al₂O₃ > SiO₂ ? -Al₂O₃.     

Effect of silica on the stability of the nanostructure and texture of fine-particle alumina

The effect of the modification of aluminum oxide with silicon oxide on the stability of fine-particle Γ- and δ-Al₂O₃ phases upon heat treatment in the wide temperature range of 550–1500°C was studied. It was found that the Γ- and δ-Al₂O₃ phases modified with silica are thermally stable up to higher temperatures than pure aluminum oxide. This is due to changes in the real structure of the modified samples, specifically, an increase in the concentration of extensive defects stabilized by hydroxyl groups bound to not only aluminum atoms but also silicon atoms. It is likely that Si-OH groups, which are thermally more stable than Al-OH groups, stabilize the microstructure of Γ- and δ-Al₂O₃ to higher temperatures, as compared with aluminum oxide containing no additives. Simultaneously, an increase in the thermal stability of the modified samples is accompanied by the retention of a high specific surface area and a developed pore structure at higher treatment temperatures.     

Über basische Aluminiumsalze und ihre Lösungen. (XIII). Kristalline basische Aluminiumchloride als Produkte der Rehydratisierung und Hydrochlorierung von Übergangstonerden

Basic Aluminum Salts and their Solutions. XIII. Crystalline Basic Aluminum Chlorides Formed as Products of Rehydration and Hydrochlorination of Transition Aluminas By reaction of transition aluminas with hydrochloric acid in sealed tubes at temperatures above 100°C crystalline basic aluminum chlorides were prepared. From the aluminum oxides used (χ-Al₂O₃, χ-Al₂O₃, and χ-Al₂O₃) χ-Al₂O₃ was most suitable for preparation. The homogeneous basic salts are characterized by a certain variability in composition as phases. After a treatment with water vapor there is a remarkable change in the X-ray diagrams of the compounds. It is shown, that at this alteration the lattice was only changed unessentially. Therefore the existence of intercalation compounds with a 3D host lattice is assumed; the water molecules are located at defined positions in the voids.     

Effects of doping with CeO2 and calcination temperature on physicochemical properties of the NiO/Al2O3 system

The effects of doping with CeO₂ and calcination temperature on the physicochemical properties of the NiO/Al₂O₃ system have been investigated using DTA, XRD, nitrogen adsorption measurements at −196°C and decomposition of H₂O₂ at 30–50°C. The pure and variously doped solids were subjected to heat treatment at 300, 400, 700, 900 and 1000°C. The results revealed that the specific surface areas increased with increasing calcination temperature from 300 to 400°C and with doping of the system with CeO₂. The pure and variously doped solids calcined at 300 and 400°C consisted of poorly crystalline NiO dispersed on γ-Al₂O₃. Heating at 700°C resulted in formation of well crystalline NiO and γ-Al₂O₃ phases beside CeO₂ for the doped solids. Crystalline NiAl₂O₄ phase was formed starting from 900°C. The degree of crystallinity of NiAl₂O₄ increased with increasing the calcination temperature from 900 to 1000°C. An opposite effect was observed upon doping with CeO₂. The NiO/Al₂O₃ system calcined at 300 and 400°C has catalytic activity higher than individual NiO obtained at the same calcination temperatures. The catalytic activity of NiO/Al₂O₃ system increased, progressively, with increasing the amount of CeO₂ dopant and decreased with increasing the calcination temperature.     

Investigation of the state of palladium in the potassium palladium-11-tungstosilicate/alumina system by diffuse-reflectance IR spectroscopy

The influence of redox treatments on the state of palladium in the K₆[SiW₁₁PdO₃₉]·11H₂O/γ-Al₂O₃ system was investigated by diffuse-reflectance IR (DRIFT) spectroscopy using CO as a probe molecule. The K₆[SiW₁₁PdO₃₉]·11H₂O heteropoly-compound (HPC) and starting γ-Al₂O₃ support were studied for comparison. It was shown that palladium is present in HPC mainly in the form of Pd²⁺ ions. Treatment of HPC in an H₂ flow results in complete reduction of palladium to Pd⁰. The HPC is unstable in redox cycles at temperatures above 373 K. When the HPC was supported on alumina, the Keggin units were stabilized on the support surface and Pd⁺ formed in the oxidized sample. The supported K₆[SiW₁₁PdO₃₉]·11H₂O/γ-Al₂O₃ catalyst displays higher thermal stability and does not decompose during redox treatments at temperatures up to 723 K. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 7, pp. 1271–1275. July, 1999.     

Determination des Transitions Vitreuses et Locales de PMMA/Al2O3 Par des Methodes Thermiques et Chromatographiques

Differential thermal analysis (DTA) technique was used to determine the glass transition temperatures of polymethyl methacrylate (PMMA). When PMMA was adsorbed on α-alumina, DTA could not use to obtain the glass transition temperatures of the system PMMA/α-Al₂O₃. Inverse gas chromatography at infinite dilution proved to be an excellent technique to highlight glass transitions and local transitions of PMMA adsorbed on α-Al₂O₃, at various covered surface fractions.     

Structure of С@Al<Subscript>2</Subscript>O by multinuclear solid-state NMR spectroscopy

The ²⁷Al, ¹H MAS NMR method is used to study initial nanosized metastable aluminum oxides of a pseudoboehmite series (γ- and δ-Al₂O₃) after being coated with graphene (С@Al₂O₃) and annealed in the air (С@Al₂O₃-Т). It is demonstrated that aluminum nanoparticles coated with graphene and annealed at high temperatures (to 750°C for γ and 1180°C for δ) preserve their phase composition but differ from initial oxides by a very low concentration of defects (ОН groups). After the annealing of the graphene coating the hydroxyl cover of oxides is reduced, however, the set of ОН groups differs greatly from that of the initial oxides. Only one type of terminal ОН groups with a ~0.2 ppm shift and one type of bridging μ²-ОН groups with a 1.8 ppm shift for γ-Al₂O₃ from OH-μ²-AlVAl_n and 2.1 ppm for δ-Al₂O₃ OH-μ²-AlIVAl_n are observed. The data obtained make it possible to characterize in detail the δ-Al₂O₃ pure phase.     

Partial Oxidation of Ethane to Syngas over Supported Metal Catalysts

The reaction performance for C₂H₆-O₂ to syngas over different supported metal catalysts was investigated in a flow-reactor. The activated behavior of ethane is different from that of methane over the supported nickel catalysts. Although there may exist a gas phase reaction at high temperatures, over a Ni (or Rh)/-Al₂O₃ catalyst, the partial oxidation of ethane to syngas is a heterogeneous process, while over a Pt (or Pd)/-Al₂O₃ catalyst, it may be a homo-heterogeneous process. The Ni/-Al₂O₃ and Rh/-Al₂O₃ catalysts are suitable for partial oxidation of ethane to syngas at high temperatures.     

Kinetic Analysis Crystallization of α-Al2O3 by Dynamic DTA Technique

The phase transformation of seeded (5 mass% Fe₂O₃ as a Fe(NO₃)₃ solution) boehmite derived alumina gel to α-Al₂O₃ was studied with DTA technique and compared with unseeded and α-Al₂O₃ seeded boehmite gels. Data for kinetic analysis of α-Al₂O₃ crystallization were obtained from quantitative DTA curves. The kinetic parameters were analysed by traditional Kissinger analysis and Friedman and Ozawa-Flynn-Wall methods using the Netzsch Thermokinetics program. Results of the comparison of values of activation energies for all three gels and methods are the process of α-Al₂O₃ transformation for originally γ-AlOOH/Fe(NO₃)₃ gels goes like that of unseeded boehmite gels,only under lower temperatures (lower about 200°C). This revised version was published online in July 2006 with corrections to the Cover Date.     

KF promoted mesoporous γ-Al2O3 with strong basicity: Preparation,characterization and catalytic activitiy for transesterification to biodiesel

The present paper describes the preparation of KF/M-γ-Al₂O₃, efficient mesoporous solid bases. The procedure involves loading KF into a crystalline mesoporous γ-Al₂O₃ that was synthesized by the self-assembly of poly-4-vinylpyridine (P4VP) with Al³⁺ species. The synthesis is based on the strong acid-base interaction, hydrothermal treatment at 180°C and calcination at 550°C. Characterizations using XRD analysis and low temperature N₂ adsorption indicated that different amounts of KF could be introduced into crystalline mesoporous γ-Al₂O₃ to obtain catalysts with high BET surface areas, large pore volumes and uniform pore size distribution. Based on SEM images, KF/M-γ-Al₂O₃ catalysts have rough surface character and a large nanopore volume. CO₂-TPD curves registered for KF/M-γ-Al₂O₃ contain high temperature peaks, indicating strong basicity of the catalysts. Under the same reaction conditions KF/M-γ-Al₂O₃ catalysts exhibit much better activities for transesterification to biodiesel than KOH, NaOH, H₂SO₄, hydrotalcite and CaO. Enhanced activities appear to arise from strong basisity and large BET surface areas.     

FTIR study of CO adsorption on molybdena-alumina catalysts for surface characterization

CO adsorption at low temperature has been used to probe Lewis acid sites created upon dehydroxylation of γ-Al₂O₃ and reduction of Mo/Al₂O₃ catalysts, using Fourier Transform Infrared spectroscopy (FTIR). Carbon-monoxide adsorption on γ-Al₂O₃ and Mo/Al₂O₃ catalysts dehydroxylated and reduced at different temperatures was studied at 78 K by IR spectroscopy. However, our results indicate that there is an approximately linear correlation between the increase either of dehydroxylation or the extent of reduction of the catalysts and the increasing absorbance of CO due to CO adsorption on Lewis acid sites created upon dehydroxylation of γ-Al₂O₃ and reduction of Mo/Al₂O₃.