Hr In Air Research Articles

Synthesis and characterization of Co 3O 4/RuO 2 composite nanofibers fabricated by an electrospinning method

Co 3O 4–RuO 2 composite nanofibers (NFs) were synthesized by an electrospinning method and were calcinated at 400°C for 1 hr in air. Scanning electron microscopy and high-resolution transmission electron microscopy (HRTEM) examinations show that all the synthesized NFs have uniform surface morphology and their diameters are in the range of ~ 30–~70 nm. X-ray diffraction (XRD) results show that crystalline Co 3O 4 phase and RuO 2 phase coexist in the composite NF matrix which is confirmed by X-ray photoemission spectroscopy. In addition, the HRTEM energy-dispersive X-ray spectroscopy mapping results show that the Co 3O 4 and RuO 2 phases are uniformly distributed across the NF matrix.

Cobalt-Based Alloys for High Temperature Applications

The isothermal oxidation behavior and thermal stability of a cobalt base alloy was investigated up to a period of 312 hr in air from 1000 to 1200°C. A comparison of oxidation behavior of this alloy with a conventional nickel-base superalloy (Inconel 713C) has been conducted in detail. This experimental alloy oxidizes by forming layers of Al2O3, Cr2O3, TiO2, CoO and traces of SiO2 with WO2 oxides on the surface of the specimen in contact with air. Scanning electron microscopy (SEM) was used to study the microstructure, morphology and compositions of oxides formed after the exposure. Thermal stability of the alloy after extended periods of exposures to air at 1000, 1100 and 1200°C was studied using transmission electron microscopy (TEM).

Synthesis and Photoluminescence Properties of InVO4:Eu3+ Phosphors Prepared Using Sol-Gel Method

InVO4 doped with Eu3+ ions had been synthesized at 950° for 6 hr in air using the sol-gel method. XRD results indicate that the crystallinity of InVO4:Eu3+ powders decreases with increasing Eu3+ ion concentrations. From the SEM images, the shapes of the InVO4 particles are uniform and like pebbles. With increasing Eu3+ ion concentrations, the shapes of the InVO4:Eu3+ particles become smaller and irregular. In the PL studies, the sharp excitation peaks between 300 and 600 nm correspond to the Eu3+ intra-4f transitions. For (In1-xEux)VO4 system, excitation at 326 nm shows that the (In1-xEux)VO4 phosphors display bright red luminescence at about 615 nm belonging to the 5D0→7F2 electric dipole transition, and the time-resolved 5D0→7F2 transition presents a single exponential decay behavior. The saturation of emission intensity excited by intra-4f transitions occurs at a concentration of x = 0.3, indicating that the concentration quenching is active when x > 0.3.

Characteristics of IGZO Thin Film Transistor Deposited by DC Magnetron Sputtering

Indium Gallium Zinc Oxide (IGZO) thin films were deposited onto 300 nm-thick oxidized Si substrates and glass substrates by direct current (DC) magnetron sputtering of IGZO targets at room temperature. FESEM and XRD analyses indicate that non-annealed and annealed IGZO thin films exhibit an amorphous structure. To investigate the effect of an annealing treatment, the films were thermally treated at <TEX>$300^{\circ}C$</TEX> for 1hr in air. The IGZO TFTs structure was a bottom-gate type in which electrodes were deposited by the DC magnetron sputtering of Ti and Au targets at room temperature. The non-annealed and annealed IGZO TFTs exhibit an <TEX>$I_{on}/I_{off}$</TEX> ratio of more than <TEX>$10^5$</TEX>. The saturation mobility and threshold voltage of nonannealed IGZO TFTs was <TEX>$4.92{\times}10^{-1}cm^2/V{\cdot}s$</TEX> and 1.46V, respectively, whereas these values for the annealed TFTs were <TEX>$1.49{\times}10^{-1}cm^2/V{\cdot}$</TEX> and 15.43V, respectively. It is believed that an increase in the surface roughness after an annealing treatment degrades the quality of the device. The transmittances of the IGZO thin films were approximately 80%. These results demonstrate that IGZO thin films are suitable for use as transparent thin film transistors (TTFTs).

Microstructural Evaluation of High Oxidation Resistant CrAlSiN Hard Coating at Elevated Temperature in Air Atmosphere

CrAlSiN hard coatings were fabricated on the Si substrate from metallurgical Cr0.45Al0.45Si0.10 alloy target by reactive r.f. magnetron sputtering. The oxidation resistance of CrAlSiN coatings was investigated after annealing at temperatures between 900 and 1100°C for 1 hr in air. The phase identification and microstructure of CrAlSiN coatings after heat treatment were analyzed by X-ray diffraction (XRD). The hardness of CrAlSiN coating after heat treatment at 900oC for 1hr in air is slightly decreased from 30.2GPa to 28.3±1.3GPa, which was caused by the thin oxide formation on the surface of the film. The microstructure of CrAlSiN coating after heat treatment at 1000oC from 1 hr analyzed by TEM revealed two types of layer feature, including the nanocrystalline grain embedded in the Al-riched amorphous layer and reaction interface with relative high content of Si.

Sintering and Dielectric Properties of Nano-BaTiO&lt;sub&gt;3&lt;/sub&gt; Powder Synthesized by High-Gravity Reactive Precipitation

The dielectric properties and sintering activity of nano-BaTiO3 powders synthesized by HGRP method were investigated. The starting BaTiO3 powders were calcined at different temperatures from 700 to 900°C to improve their crystallinity and the mean particle size of BaTiO3 powders obtained increased from 40nm to 80nm. After being formed by conventional dry pressing the green bodies were sintered at 1100°C and 1200°C for 2hr in air. The effects of both calcinating and sintering temperatures on the sinterability, dielectric property and microstructure of BaTiO3 ceramics were discussed. The experimental results showed that the BaTiO3 powders have high sintering activity and the highest dielectric constant of this material at room temperature may reach 2880.

Thermal Stability and Oxidation Resistance of Pt–10 Al–4Cr Alloy at Super-High Temperatures

The isothermal-oxidation behavior of refractory superalloy Pt–10Al–4Cr (in at.%) was investigated up to a period of 312 hr in air from 1200 to 1400°C. A comparison of the oxidation behavior of this alloy with a conventional Ni-base superalloy (Inconel 713C) shows an order of magnitude higher oxidation resistance. This experimental alloy oxidizes by forming Al2O3 and Cr2O3 (and perhaps trace amounts of PtO) with Al2O3 as the oxide layer in contact with air. Optical and scanning-electron microscopy (SEM) were used to study the microstructure, morphology, and composition of the scale formed after oxidation. The thermal stability of the alloy after extended periods at 1200, 1300, and 1400°C was studied using transmission-electron microscopy (TEM).

Cyclic-Oxidation of Ti&lt;sub&gt;3&lt;/sub&gt;SiC&lt;sub&gt;2&lt;/sub&gt; and Ti&lt;sub&gt;3&lt;/sub&gt;AlC&lt;sub&gt;2&lt;/sub&gt; between 900 and 1200°C in Air

Using the hot pressing method, the Ti3SiC2 materials having fine and coarse grains were synthesized from TiC0.6 and Si powders, and the Ti3AlC2 materials having fine and coarse grains were also synthesized from TiC0.6 and Al powders. The cyclic oxidation between 900 and 1200oC for 40 hr in air resulted in the formation of an outer TiO2 layer and an inner (TiO2+ amorphous SiO2) mixed layer for Ti3SiC2, and the formation of an outer TiO2 layer and an inner (TiO2+ Al2O3) mixed layer for Ti3AlC2. The effect of the grain size on the cyclic oxidation resistance was not significant.

Adhesion of glass to steel using a geopolymer

Many potential and actual uses for geopolymers (GPs) have been listed, such as waste encapsulation, refractories, fire resistant paneling, sewer pipes, building products, and acid-resistant coatings [1]. Other proposed technical uses include fire protection coatings as applied to concrete [2]. Understanding the nature of bonding of GPs to other materials is desirable if GPs are to be applied as protective coatings or adhesives. Two common methods of making GPs are to add fly ash or metakaolinite (MK: kaolinite heated to ∼750 ◦C to render it amorphous) to concentrated alkali solutions for reaction and subsequent polymerization to take place. The GPs produced consist of amorphous to semi-crystalline three-dimensional aluminosilicate networks [3]. For industrial applications, the use of fly ash as a precursor gives a cost advantage over MK. However to understand the science of the polymerization process, the use of the latter is preferred. It has been reported that ball milling the aluminosilicate precursors up to 4 hr improves the compressive strength of GPs [4]. In the present work, we attrition-milled the MK, which is a more effective method of milling than ball milling, to determine the effect on the compressive strength. Furthermore, we examined the adhesion of stainless steel to glass using GPs derived from the milled MK and determined the interfacial fracture energy by a fracture mechanics approach. The MK was produced by heating kaolinite (Kingwhite 80, Unimin, Australia) at 750 ◦C for 15 hr in air. An MKwater slurry was attrition-milled at 300 rpm with 5 mm zirconia balls for 30, 60 and 120 min. The milled slurry was dried in a stainless steel pan at 40 ◦C for 5 days. The particle size distributions of each batch, including the unmilled sample were determined using laser diffraction techniques (Mastersizer 2000, Malvern Instruments Ltd., UK) and are shown in Fig. 1. The MK exhibits a bimodal distribution and the amount of fines (∼0.18 μm) increased with milling time. The 30 min milling time reduced the coarse particle size from 8.7 to 4.4 μm and doubled the volumes of fines. A further 30 min again reduced the coarse particles to 2.9 μm and increased the fines. Additional milling for 60 min did not

Rheological phase synthesis and electrochemical performances of LiVMoO6 as a high-capacity anode material for lithium ion batteries

Research for new anode materials has been stimulated by the development of lithium ion batteries since the introduction of carbon as a negative material in 1990 by Sony Energetics Inc. Some metal oxides and metalbased composite oxides [1, 2], nitrides [3, 4] and intermetallics [5, 6], which capacities are comparable or superior to those of graphitized carbon (theoretical maximum capacity of 372 mA hr g−1 [7, 8]), were considered as possible candidates for next generation of anode materials. Recently, several vanadium composite oxides exhibited their high-capacity and high-rate performance as negative electrode materials due to their open structure and interesting characteristics from a standpoint of the variety of oxidation states [9–12]. LiMoVO6 crystallizes with the ThTi2O6 branneritetype structure [13] and its electrochemical properties as a positive electrode material for lithium secondary batteries have been investigated [14–16]. But the performance of LiMoVO6 as negative electrode material was seldom reported. In this work, brannerite-type LiMoVO6 powder was obtained by rheological phase reaction method [17]. The result of electrochemical tests showed that the obtained LiMoVO6 as a novel anode material was also feasible and demonstrated very high energy density. The precursor was prepared by rheological phase reaction method. Analytical reagent grade chemicals, LiOH·H2O, NH4VO3 and (NH4)6Mo7O24·4H2O, were used as the starting materials and fully mixed by grinding in a 1:1:1 molar ratio. A proper amount of water was added to get a rheological body and the mixture was sealed in a closed container for 8 hr at 80 ◦C. After drying under vacuum at 80 ◦C for several hours, the precursor was pyrolyzed at 550 ◦C for 10 hr in air, and soft yellow powder LiMoVO6 was obtained. Thermogravimetry and differential thermal analysis (TG/DTA) of the precursor were performed by the Netzsch STA 449 thermal analysis system at a heating rate of 10 ◦C/min in air. The X-ray diffraction (XRD) measurements of the sample were carried out by Shimadzu XRD-6000 diffractometer with CuKα1 radiation (λ = 1.54056 A). The particle sizes and morphological features were observed by a scanning electron microscope (Hitachi SEM X-650).

Rheological phase synthesis and electrochemical performances of LiVMoO6 as a high-capacity anode material for lithium ion batteries

Research for new anode materials has been stimulated by the development of lithium ion batteries since the introduction of carbon as a negative material in 1990 by Sony Energetics Inc. Some metal oxides and metalbased composite oxides [1, 2], nitrides [3, 4] and intermetallics [5, 6], which capacities are comparable or superior to those of graphitized carbon (theoretical maximum capacity of 372 mA hr g−1 [7, 8]), were considered as possible candidates for next generation of anode materials. Recently, several vanadium composite oxides exhibited their high-capacity and high-rate performance as negative electrode materials due to their open structure and interesting characteristics from a standpoint of the variety of oxidation states [9–12]. LiMoVO6 crystallizes with the ThTi2O6 branneritetype structure [13] and its electrochemical properties as a positive electrode material for lithium secondary batteries have been investigated [14–16]. But the performance of LiMoVO6 as negative electrode material was seldom reported. In this work, brannerite-type LiMoVO6 powder was obtained by rheological phase reaction method [17]. The result of electrochemical tests showed that the obtained LiMoVO6 as a novel anode material was also feasible and demonstrated very high energy density. The precursor was prepared by rheological phase reaction method. Analytical reagent grade chemicals, LiOH·H2O, NH4VO3 and (NH4)6Mo7O24·4H2O, were used as the starting materials and fully mixed by grinding in a 1:1:1 molar ratio. A proper amount of water was added to get a rheological body and the mixture was sealed in a closed container for 8 hr at 80 ◦C. After drying under vacuum at 80 ◦C for several hours, the precursor was pyrolyzed at 550 ◦C for 10 hr in air, and soft yellow powder LiMoVO6 was obtained. Thermogravimetry and differential thermal analysis (TG/DTA) of the precursor were performed by the Netzsch STA 449 thermal analysis system at a heating rate of 10 ◦C/min in air. The X-ray diffraction (XRD) measurements of the sample were carried out by Shimadzu XRD-6000 diffractometer with CuKα1 radiation (λ = 1.54056 A). The particle sizes and morphological features were observed by a scanning electron microscope (Hitachi SEM X-650).

Phase changes of newly synthesized Co-coated Ni cathode in MCFC cathodic conditions

A molten carbonate fuel cell (MCFC) is expected to provide high efficiency generation of electricity and an environmentally clean means of power generation [1, 2]. However, the durability of the MCFC experiences difficulties at over 40 000 hr of operation. One of the lifetime limiting problems of a MCFC is the slow dissolution of the state of the art cathode material NiO into the electrolyte [3]. Two main methods have been adopted to solve this problem. One method is to use an alternative electrolyte. More basic molten carbonate melts adopting Li/Na eutectic carbonates instead of Li/K eutectic carbonates have been used to decrease the Ni dissolution rate in the electrolyte [4]. The other method is to develop alternative cathode materials. Among cathode materials, LiCoO2 seems to be one of the best candidates because of its higher stability in the molten carbonate, and the rate of dissolution is slower than that of the NiO cathode. However, application of LiCoO2 as a new cathode material has problems in scaling up the electrode area and a relatively higher manufacturing cost than that of the NiO cathode. Therefore, recently many investigators have attempted to resolve the problem by developing new cathode materials in which NiO grains have been coated with a small amount of LiCoO2 or CoO by various coating techniques to reduce their dissolution [5, 6]. In this study, we have tried to prepare a new candidate cathode material of Co3O4-coated Ni powders using the Pechini method [7] as a new coating technique. In addition, we report on the phase changes of the Co-coated Ni cathode in MCFC cathodic conditions. The Co3O4-coated Ni powders were prepared by the following method. A stoichiometric amount of cobalt acetate (Aldrich, USA, purity of 98+%) and citric acid (CA) (Aldrich., USA, purity of 99.5+%) were dissolved in distilled water and thoroughly mixed with an aqueous solution of ethylene glycol (EG) (CA:EG:cobalt ions = 2:1:1). After that, the solution was adjusted by adding NH4OH until pH 8 was achieved and Ni powder (filamentary nickel 255, Inco, USA) was immersed in the solution. The resultant solution was heated to 80 ◦C while being stirred until a gel precursor was produced. The gel precursor was calcined at 350 ◦C for 3 hr in air.

Preparation of low–power loss MgCuZn ferrites using the microwave sintering method

Preparation of low–power loss MgCuZn ferrites using the microwave sintering method

Oxidation of (Al+8%Mn)&lt;sub&gt;3&lt;/sub&gt;Ti Intermetallics Synthesized by Mechanical Alloying

The oxidation behavior of (Al+8 at.%Mn)3Ti alloys prepared by mechanical alloying followed by cold isostatic pressing and sintering at high temperatures was investigated at 1000 and 1100°C up to 300 hr in air. Since the Al2O3 barrier layer having some dissolved ions of Ti, and Mn formed, the oxidation resistance of the prepared alloys was excellent.

Air oxidation of SiC fibers prepared from carbon fibers and SiO vapor

Activated carbon fiber composite (ACFC) was reacted with SiO vapor to prepare SiC fibers containing nanopores. The SiC fibers obtained were not oxidation resistant, showing nearly complete oxidation at 1000°C after about 25 hr in air, though the oxidation product was amorphous silica which was generally considered to be oxidation resistant. The poor oxidation resistance was attributed to highly porous, amorphous SiO2 formation on the inherently highly porous SiC fibers. Interconnected micropores inside the fibers rendered the fibers easily oxidizable.

Oxidation Resistance of Ion-Implanted γ -TiAl-Base Intermetallics

A series of alloy elements, including the detrimental, neutral, and beneficial elements for bulk alloying into gamma -TiAl base intermetallics, i.e., V, Cr, Y, Er, Nb, and W, has been implanted into a gamma -Ti-50Al intermetallic in order to explore the mechanism of high-temperature oxidation resistance for the ion-implanted intermetallic. The oxidation resistance was investigated under cyclic-oxidation conditions at oxidation temperatures from 800 to 1000degreesC for 200 hr in air. At a lower oxidation temperature of 800degreesC, the V-ion implantation has a detrimental effect on the oxidation resistance of Ti-50Al, while a neutral and beneficial effect was observed for Er-, Y- and Cr-, Nb-, W-ion implantation, respectively. At 900degreesC, V-, Er-, Y-, and Cr-ion implantation all showed a neutral effect, whereas Nb- and W-ion implantation apparently improved the oxidation resistance. With increasing oxidation temperature to 1000degreesC, Y- and Cr-ion implantation kept the neutral effect, and the beneficial effect of Nb-ion implantation disappeared gradually. The oxidation behavior of ion-implanted gamma -TiAl base intermetallics is different from that of bulk-alloyed materials due to the two alloying methods, although the effect of the alloy elements on the oxidation resistance has not essentially changed in the gamma -TiAl base intermetallics.

Synthesis and characterization of poly(dimethylsilylene-diphenylsilylene) as a precursor to silicon carbide

Poly(dimethylsilylene-diphenylsilylene) copolymer, [(SiMe2 x(SiPh2)]n, where x=1.0 to 8.0, was synthesized by condensation polymerization of dimethyldichlorosilane and diphenyldichlorosilane in xylene. In the thermogravimetric analysis of the copolymer, weight loss started at 170‡C and the weight residue at 1,000‡C was 32%. The copolymer was stabilized by thermal oxidation at 80 to 110‡C for 5 hr in air, and its thermal stability increased as the temperature increased. The copolymer heat treated above 700‡C showed no organic bonds of C-H and Si-CH3, while Si-C and Si-0 bonds were observed. Amorphous SiC was obtained by pyrolysis at 1,000‡C and β-SiC at 1,200 to 1,400‡C, in which better crystallinity of β-SiC was observed at a higher temperature.

Noncontact Determination of Antisymmetric Plate Wave Velocity in Ceramic Matrix Composites

A 13 mJ NdYAG 1064 nm, 4 ns, laser pulse was employed to produce ultrasonic plate waves in 20 percent porous SiC/SiC composite tensile specimens of three different architectures. An air coupled 0.5 MHz transducer was used to detect and collect the waveforms which contained first antisymmetric plate wave pulses for determining the shear wave velocity (VS). These results were compared to VS values determined on the same specimens with 0.5 MHz ultrasonic transducers with contact coupling. Averages of four noncontact determinations on each of 18 specimens were compared to averages of four contact values. The noncontact VS's fall in the same range as the contact. The standard deviations for the noncontact VS's averaged 2.8 percent. The standard deviations for the contact measurements averaged 2.3 percent, indicating similar reproducibility. Repeated laser pulsing at the same location always lead to deterioration of the ulu-nic signal. The signal would recover in about 24 hr in air however, indicating that no permanent damage was produced.

高純度ムライトの泥しょう鋳込成形とその焼結体の特性 （第１報） 泥しょう調製条件の検討

Slip casting of high-purity mullite powder produced by coprecipitation method was studied to fabricate mullite engineering ceramic parts with complicated shapes. The characteristics of the slurries were examined by zeta-potential and viscosity measurements. The preparation conditions of well-dispersed slurries were determined using an organic polymer deflocculant. The most suitable deflocculant content was 0.2wt% of the solid. High-density green bodies (relative density=59.2%) were prepared by vacuum filtration with a polymer resin mold. High-density mullite ceramics (3.12-3.13 g/cm3) were obtained by sintering at 1650°C for 3hr in air.

Homogenization and Particle Size Reduction of PbTiO3 by Ball-Milling of Precursor Gels

Ball-milling of mixed gel derived from a simple mixing of component alkoxides increased the compositional microhomogeneity, judged quantitatively by high-resolution microprobe chemical analysis. At the same time, the particle size of PbTiO3 obtained after calcination at 1023 K for 2 hr in air decreased, approaching those of oxide fine particles delivered from a bidentate alkoxide through an identical thermal treatment.