Impact of Pb substitution on the formation of high <Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> superconducting phase in BSCCO system derived through sol-gel process

Sol-gel process was employed to synthesize the Pb-BSCCO system having general composition Bi_2−xPb_xSr₂Ca₂Cu₃O_10−δ, where x=0.2, 0.4 and 0.8. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), dilatometry and vibrating sample magnetometer (VSM) were employed to study the materials produced at different stages. Two-stage heating firstly at 300 and then 800°C was adopted in order to avoid the burning of the materials and formation of carbonates. The carbonate formation was avoided by heating the materials firstly at 300°C for 2 h and without intermediate cooling moved to the furnace having temperature 800°C and hold for 2 h. The sintering behaviour of samples was studied by dilatometry and the results revealed that the sample having x=0.4 was stabled up to a temperature of 700°C while samples having x=0.2 and 0.8 to a temperature of 625°C. The maximum shrinkage was observed at 850°C in all the samples. On the basis of dilatometry results, the samples were sintered at 845°C for 60 h to observe the superconducting phases. The highest volume fraction of high superconducting phase (2223) was noticed in the sample containing x=0.4 having onset T _c=110 K.     

A simple non-invasive optical pyrometric method for plotting temperature—Time profiles of high temperature reactions in microwave ovens

A simple optical pyrometric method is described, based on a photocell with red and blue filters calibrated by the disappearing filament technique. The method, which is cheap, non-invasive and reproducible, is used for measurement of the rate of heating of solid materials such as coke, CuO or Fe₃O₄ in a microwave oven. All materials were heated under dinitrogen in a silica reaction vessel over 3 min in a 650 W oven. Coke (which contains graphitic phases) and magnetite heat smoothly to maximum temperatures of 1180 and 1050°C respectively. CuO heats erratically with plasma discharges from the surface, however when covered with a layer of coke the oxide heats smoothly achieving a maximum temperature of 1210°C. The observations are discussed.     

HfB2-SiC (45 vol %) ceramic material: Manufacture and behavior under long-term exposure to dissociated air jet flow

Ultra-high-temperature composite materials HfB₂-SiC containing 45 vol % SiC were prepared by spark plasma sintering. The behavior of a sample of this composition under exposure to a subsonic jet of dissociated air of a high-frequency induction plasmatron was studied; the total time was more than 30 min. Under certain test conditions, some regions of the sample were found to experience a rapid increase in temperature up to 2700°C. So, most of the surface area of the sample experienced exposure to temperatures up to 2500–2700°C for more than 15–18 min, while the rest of the surface had a temperature of 1700–1800°C during almost the entire duration of the experiment. The joint use of optical microscopy, scanning electron microscopy (with EDX analysis), X-ray powder diffraction, and X-ray computed microtomography enabled us to study the microstructure and composition of a structurally complex oxidized layer.     

Improved electrochemical performance of nano-crystalline Li2FeSiO4/C cathode material prepared by the optimization of sintering temperature

Li₂FeSiO₄/C cathode materials have been prepared using the conventional solid-state method by varying the sintering temperature (650 °C, 700 °C and 750 °C), and the structure and electrochemical performance of Li₂FeSiO₄/C materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, respectively. The results show that Li₂FeSiO₄ nano-crystals with a diameter of about 6–8 nm are inbedded in the amorphous carbon, and the Li₂FeSiO₄/C material obtained at 700 °C exhibits an initial discharge capacity of 195 mA?h g^?1 at 1/16 C in the potential range of 1.5–4.8 V. The excellent electrochemical performance of Li₂FeSiO₄/C attributes to the improvement of conductivity and reduction of impurity by the optimization of the sintering temperature.     

Heating effect on the DSC melting curve of flaxseed oil

Flaxseed oil is rich in the alpha-linolenic acid. The effect of heating on the thermal properties of flaxseed oil extracted from flax seeds has been investigated. The flaxseed oils were heated at a certain temperature (75, 105, and 135 °C, respectively) for 48 h. The melting curve (from ?75 to 100 °C) of flaxseed oil was determined by differential scanning calorimetry (DSC) at intervals of 4 h. Three DSC parameters of exothermic event and endothermic event, namely, peak temperature (T _peak), enthalpy, and temperature range were determined. The initial flaxseed oil exhibited an exothermic peak, two endothermic peaks, and two endothermic shoulders between ?68 and ?5 °C in the melting profile. Heating temperature had a significant influence on the oxidative deterioration of flaxseed oil. The melting curve and parameters of flaxseed oil were almost not changed when flaxseed oil was heated at 75 °C. However, the endothermic peaks of melting curve decreased dramatically with the increasing of heating time when heating temperature was above 105 °C. There is almost no change of melting heat flow of flaxseed oil when heating time exceeded 32 h at 135 °C. The preliminary results suggest that the DSC melting profile can be used as a fast and direct way to assess the deterioration degree of flaxseed oil.     

Behavior of HfB<Subscript>2</Subscript>-SiC (10, 15, and 20 vol %) ceramic materials in high-enthalpy air flows

HfB₂–SiC ceramic samples containing 10, 15, and 20 vol % silicon carbide were prepared by spark plasma sintering. The samples were characterized by X-ray powder diffraction, SEM, and other methods. Their densities and calculated porosities were determined. The behavior of the materials under heating by a subsonic dissociated air flow was studied on a VGU-4 high-frequency inductive plasmatron. The average surface temperatures of the 10 and 15 vol % SiC samples were shown to increase up to 2550–2675°C during heating, due to the generation of surface localities having temperatures of 2600–2700°C (the initial surface temperature was ~1700–1900°C) and the progressive growth of these regions in area. The overall time during which the average surface temperatures of these samples were higher than 2000°C, was about 31–32 min. For the 20 vol % SiC sample, heat removal (when the sample touched a water-cooled holder) was shown to influence the surface temperature and surface temperature distribution. The variation in gas-phase composition over the central area of the sample surface during an experiment was studied using emission spectroscopy. Explanations are proposed to the variation of boron and silicon concentrations in the course of exposure to high-enthalpy flows. The elemental and phase compositions were determined and the microstructures were studied on the surface and sections of samples after long-term (~40-min) exposure to high-enthalpy air flows.     

High-temperature dilatometer with pyrometer measuring system and rate-controlled sintering capability

An optical pyrometer is used to measure and, in conjunction with temperature programmer and controller, control the temperature of the NETSZSCH Dilatometer DIL 402 E/7 up to 2400°C. This instrument is thus suitable to investigate sintering of technical ceramic materials such as SSiC and ZrO₂. Measurements carried out on these materials containing organic additives show that the sintering range of SSiC starts at 1800°C—although its final density is not reached at 2400°C at a heating rate of 20 deg·min^?1—and that the densification of ZrO₂ occurs between 1000° and 1800°C. Using rate controlled sintering (RCS) the sintering process can be extended on a time scale, but the same densities are obtained at the same temperatures when comparing the measurements with and without RCS.     

Some Physico-chemical Properties of Doxazosin Mesylate Polymorphic Forms and its Amorphous State

Seven polymorphic modifications of doxazosin mesylate, designed as forms A, D, E, F, G, H, I, and the amorphous state were studied by thermal methods (TG and DSC), temperature resolved X-ray powder diffractometry, hot stage and scanning electron microscopy and by FT-IR spectroscopy. Amorphous form was obtained either by fast evaporation of the solvent or by fast cooling of the melt in the DSC. Polymorphs A and F were found to be stable in the temperature range from room temperature to their melting points at 277.9 and 276.5°C, respectively. Form G, which melts at 270.8°C, was found to be hygroscopic. Polymorph D undergoes irreversible solid–liquid–solid phase transition at 235.5°C to polymorph I which melts at 274.9°C. Form H, which melts at 258.0°C, was found to be unstable at high temperatures. DSC examinations revealed that form H is irreversibly transformed to polymorph F during heating above the temperature of about 240°C. The amorphous state was found to be stable at room temperature but when heating above the glass transition (T _g=144.1°C) it crystallizes at 221.6°C, what leads into a mixture of polymorphic forms. The new polymorphic form designed as E was identified in the mixture. The polymorph E is converted by heating to the more stable form F. The solubilities at 25°C for forms A, and F in methanol are 3.5 and 7.7 mg mL⁻¹and in water they are 3.8 and 6.2 mg mL⁻¹, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature Dependence in the Synthesis of SBA-16-Type Mesoporous Silica with Pluronic F68 Block Copolymer

By adjusting the local effective surfactant packing parameter through synthesis temperature, highly ordered SBA-16-type mesoporous silica materials have been synthesized by templating with a nonionic triblock copolymer Pluronic F68 in strongly acidic conditions at temperature 30～40°C with the addition of K₂SO₄. The prepared SBA-16-type mesoporous silica materials having Im3m cubic mesostructure were proved by the well-defined x-ray diffraction patterns combined with transmission electron microscopy. Scanning electron microscopy indicated that a transformation from faced-sphere to faced-polyhedron shape morphologies could be induced with increasing of the synthesis temperature. The nitrogen adsorption–desorption analysis revealed that the mean pore size (5.50～6.13 nm) of the prepared materials increased with increasing synthesis temperature. However, when the synthesis temperature exceeded 46°C, only disordered mesoporous silca was obtained. Our synthesis strategies by adjusting the local effective surfactant packing parameter through synthesis condition, even in a narrow range, would be used not only to optimize the synthesis conditions of reported mesoporous silca, but also to fabricate new mesoporous silica materials with well-ordered channel and anticipated morphologies.     

Electrical transport properties of a nonstoichiometric rare earth sulfide,EuGd2S4

The electrical transport properties of nonstoichiometric EuGd₂S₄ prepared by heating under a high vacuum have been investigated. The samples heated were classified into two groups on the basis of their electrical transport behavior. One group comprised semiconducting materials heated at 1500 and 1600°C, for which the transport mechanism was found to be via electron hopping with activation energies ranging from 0.013 to 0.027 eV. Another group comprised metallic materials heated at 1700 and 1800°C. Their electrical transport was carried out through ordinary band conduction over the measured temperature range except at temperatures lower than 120°K, where hopping with a very small activation energy (～0.0035 eV) occurred predominantly.     

Electronic Structure and Size of TiO2 Nanoparticles of Controlled Size Prepared by Aerosol Methods

Summary.  A complete characterization of nanostructures has to deal both with electronic structure and dimensions. Here we present the characterization of TiO₂ nanoparticles of controlled size prepared by aerosol methods. The electronic structure of these nanoparticles was probed by X-ray absorption spectroscopy (XAS), the particle size by atomic force microscopy (AFM). XAS spectra show that the particles crystallize in the anatase phase upon heating at 500°C, whereas further annealing at 700°C give crystallites of 70% anatase and 30% rutile phases. Raising the temperature to 900°C results in a complete transformation of the particles to rutile. AFM images reveal that the mean size of the anatase particles formed upon heating at 500°C is 30 nm, whereas for the rutile particles formed upon annealing at 900°C 90 nm were found. The results obtained by these techniques agree with XRD data. Received October 5, 2001. Accepted (revised) December 6, 2001     

Synthesis of CuO nanoparticles via one-pot wet-chemical method and its catalytic performance on the thermal decomposition of ammonium perchlorate

Sphere-like CuO products aggregated by numerous nanoparticles were fabricated by a low-temperature (50°C) wet chemical method using CuSO₄·5H₂O as precursor. The possible formation processes of CuO were investigated by a series of single-factor experiments. The CuO was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, selectedarea electron diffraction. Furthermore, the application of CuO nanoparticles on the thermal decomposition of ammonium perchlorate was studied with 2 wt % CuO nanoparticles at heating rates of 10, 15, 20, and 25°C min^–1 from 35 to 500°C.     

Effects of molecular weight,heating rate,synthetic temperature and sintering duration on electrochemical properties of a LiFePO<Subscript>4</Subscript>/C cathode material pyrolyzed from lithium polyacrylate

A LiFePO₄/C composite was obtained by a polymer pyrolysis reduction method, using lithium polyacrylate (LiPAA) as carbon source and fractional lithium source, and FePO₄·2H₂O as iron and phosphorus source. The structure of the LiFePO₄/C composites was investigated by X-ray diffraction (XRD). The micromorphology of the precursors and LiFePO₄/C powders was observed using scanning electron microscopy (SEM). Laser particle analyzer and BET were also used to characterize the materials. It was found that the micromorphology, particle size distribution and specific surface area of LiFePO₄/C composites were greatly influenced by the molecular weight of LiPAA. The electrochemical properties of the LiFePO₄/C composites were evaluated by cyclic voltammograms (CVs), electrochemical impedance spectra (EIS) and constant current charge/discharge cycling tests. The results showed that the molecular weight of LiPAA, heating rate, synthetic temperature and sintering duration directly affected the electrochemical properties of LiFePO₄/C composites. The sample with the optimized electrochemical properties were obtained in the following conditions, i.e., LiPAA with the molecular weight of 20,000, heating rate of 10 °C min⁻¹, synthetic temperature of 700 °C and sintering duration of 15 h.     

Thermal decomposition of the carbon nanotube/SiO<Subscript>2</Subscript>precursor powders

Summary TG-DSC-MS (thermogravimetry-differential scanning calorimetry-mass spectrometry) coupling techniques were used to make a simultaneous characterizing study for the thermal decomposition process of the carbon nanotube (CNT)/SiO₂precursor powders prepared by rapid sol-gel method. The thermal stability of the CNT and the SiO₂pure gel were investigated by TG-DSC. The results showed that the oxidation of CNT began from 530 and combusted at about 678°C at the heating rate of 10°C min^-1in air. Moreover, the faster the heating rate, the higher the temperature of CNT combustion. The appropriate calcinations temperature of the CNT/SiO₂precursor powders should be held for 1 h at 500°C.     

High temperature properties of MDF composite based on calcium aluminate cement and polyvinyl alcohol

The macro-defect-free composites belong to the well-known group of promising materials consisting of inorganic binder and organic polymer. MDF composites exhibit unusual mechanical properties, especially the flexural strength that can reach over 200 MPa. Moreover, the MDF composites based on calcium aluminate cement have a good temperature resistance because of the Al₂O₃ content in the cement. This paper deals with the preparation and high temperature characterization of MDF composite based on calcium aluminate cement combined with polyvinyl alcohol that could enable its utilization as a refractory material in industrial kilns. The composition of the MDF mixture has been optimized for an easy high-shear processing and flexural strength of the resulting 7-days cured material has been studied under laboratory condition and after heating at 240, 300, 600, 1,000, and 1,500 °C. The structure changes during the heating have been observed by SEM and the course of processes during the heating has been investigated by TG–DTA–EGA, TMA and heating microscopy.     

Regeneration of C4H10 dry reforming catalyst by nonthermal plasma

Carbon deposition via coke formation is one of the critical problems causing catalyst deactivation during the reforming of hydrocarbons. An effort was made to regenerate the catalyst (Ni/γ-alumina) by oxidation methods. Two approaches were carried out for the regeneration of the deactivated catalyst. The first one involves the plasma treatment of the deactivated catalyst in the presence of dry air over a temperature range of 300～500 °C, while the second one only the thermal treatment in the same temperature range. The performance of the regenerated catalyst was evaluated in terms of C₄H₁₀ and CO₂ conversions and the physicochemical characteristics were examined using a surface area analyzer, an elemental analyzer, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was observed that the carbon deposit (coke) on the catalyst was about 9.89 wt% after reforming C₄H₁₀ for 5 h at 540 °C. The simple thermal treatment at 400 °C reduced carbon content to 6.59 wt% whereas it was decreased to 3.25 wt% by the plasma and heat combination. The specific surface area was fully restored to the original state by the plasma-assisted regeneration at 500 °C. As far as the catalytic activity is concerned, the fresh and regenerated catalysts exhibited similar C₄H₁₀ and CO₂ conversion efficiencies.     

Synthesis and Characterization of Nanocrystalline MoSi2 by Mechanical Alloying and Heat Treating

In order to synthesize nanocrystalline MoSi₂, pure molybdenum and silicone powders were milled using an attritor mill with the molar ratio of Mo:Si being equal to 1:2. Mechanically alloyed (MAed) powders were heated in an atmosphere controlled furnace at various temperatures and holding times. The nanopowder characteristics were evaluated by field emission scanning electron microscopy, X-ray diffraction technique, and differential thermal analysis. The obtained results were compared for all prepared samples. The results did not confirm the presence of any related intermetallics after MA. However, Mo₅Si₃ was formed during heating at 900 °C. An increase in temperature caused the enhancement of the volume fraction of Mo₅Si₃ and formation of MoSi₂. Further heating at 1,100 °C caused the enhancement of the volume fraction of MoSi₂, while that of Mo₅Si₃ was decreased, as during heating at 1,100 °C for 7 h the volume fraction of Mo₅Si₃ was negligible.     

Insertion of iron oxide in calciumsilicate gel-derived materials

Samples of the composition of 10Fe₂O₃·10CaO·80SiO₂ were prepared by the sol-gel method and heat-treated in different atmospheres. They were investigated by X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy. In the heat-treated samples in air iron is present up to 1000 °C in form of hematite and as Fe³⁺ in the tetrahedral sites. A wide range of hematite particle sizes was observed, the average size increased with heating temperature. At 1000 °C wollastonite was observed, at 1200 °C tridymite was formed and all the iron was incorporated in hematite. A heat-treatment at 500 °C under reducing conditions led to poorly crystallized maghemite and at 700 °C to metallic iron and fayalite formation.     

Characterization and evaluation of the photocatalytic properties of wormhole-like mesoporous silica incorporating TiO2, prepared using different hydrothermal and calcination temperatures

TiO₂?CSiO₂ mesoporous materials were synthesised by deposition of TiO₂ nanoparticles prepared by the sol?Cgel method on to the internal pore surface of wormhole-like mesoporous silica. In this work we synthesised wormhole-like mesoporous silica of different surface area by changing the hydrothermal temperature (70, 100, or 130?°C). Subsequent to this, titania solution was deposited on to the inner surface of the pores and this was followed by calcination at different temperatures (400, 600, or 800?°C). The effect of different hydrothermal and calcination temperature on the photocatalytic properties was evaluated. The samples were characterized by N₂-sorption, X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The effect of different hydrothermal and calcination temperatures on the photocatalytic properties was evaluated by measuring the degradation of methylene blue in aqueous solution under UV light irradiation (mercury lamp, 125?W). The results indicated that appropriate surface area and degree of crystallinity are two important factors for obtaining high photocatalytic efficiency. Samples prepared at a hydrothermal temperature of 100?°C and calcined at 800?°C had the best photocatalytic performance, because of the highest surface area and high crystallinity.     

Preparation of two-dimensional molybdenum disulfide for NO2 detection at room temperature

In this work, the two-dimensional MoS₂ film was prepared by sulfuring the molybdenum atomic layer on SiO₂/Si substrate. The reaction temperature, heating rate, holding time and carrier gas flow rate were investigated comprehensively. The quality of MoS₂ film was characterized by optical microscopy, atomic force microscopy, Raman and photoluminescence spectroscopy. The characterization results showed that the optimum synthesis parameters were heating rate of 25 °C/min, reaction temperature of 750 °C, holding time of 30 min and carrier gas velocity of 100 sccm. The MoS₂ gas sensor was fabricated and its gas sensing performance was tested. The test results indicated that the sensor had a good response to both reducing gas (NH₃) and oxidizing gas (NO₂) at room temperature. The sensitivity to 100 ppm of NO₂ was 31.3%, and the response/recovery times were 4 s and 5 s, respectively. In addition, the limit of detection could be as low as 1 ppm. This work helps us to develop low power and integrable room temperature NO₂ sensors.