Hour In Nitrogen Atmosphere Research Articles

Rate-Limiting Steps Elucidated By Electrochemical Impedance Spectroscopy of a Yttria-Stabilized Zirconia 2-in-1 Temperature and Oxygen Gas Sensor Measured at Extreme Temperatures

Introduction Yttria-stabilized zirconia (YSZ) is known for its good ionic conductivity, essentially being synonymous with the term “lambda sensor”. Automotive lambda sensors have been fabricated with YSZ as the electrolyte for 30+ years and have operated in a temperature region of 600oC to 800oC. There is an increasing demand for higher operating temperature sensors, specifically a 2-in-1 temperature and oxygen sensor which is stable, selective, and sensitive in extreme environments. However, there remains a disagreement among scholars about the effects on oxygen vacancy activation energy at temperatures higher than 800oC. Also, the rate-limiting step of oxygen reduction on the platinum electrode is not inherently clear. A 2-in-1 temperature and oxygen sensor was fabricated and characterized with the analysis of electrochemical impedance spectroscopy (EIS), DC resistance, and open circuit potential measurements at temperatures between 600oC and 1200oC. The temperature dependence on individual activation energies within the sensor was elucidated directly through these techniques. Methods Yttria-stabilized zirconia (MTI Corp) was employed as the solid-state electrolyte in sensor fabrication, with the primary electrode material as porous platinum (ESL 5570). Platinum paste was screen printed onto planar YSZ substrates in an interdigitated electrode configuration, then fired at 1500oC for 2 hours in nitrogen atmosphere (1 atm). The sensor was placed in a ThermoScientific tube furnace capable of reaching 1500oC, with mass flow controllers varying oxygen gas concentration throughout electrical measurements. Platinum foil acted as a Faraday cage around the sensor to shield from furnace inductive fluctuations and minimize noise during low frequency EIS measurements. A thermocouple placed next to the sensor validated furnace operating temperature and cooling endcaps on the furnace tube created a natural temperature gradient between sensor placement and the electrical connections outside of the furnace. Figure 1 displays the environmental testing setup. Results and Conclusions Figure 2a displays an impedance Nyquist spectrum that contains real and imaginary components of impedance measured at 0.21 atm PO2, where electrolyte resistance decreases with an increase in temperature. Figure 2b displays the Arrhenius plot of isolated YSZ electrolytic resistance extracted from figure 2a, where there are distinct activation regions at moderate and high temperatures. In agreement with Badwal [1], the shift to lower EA at higher temperatures was due to a gradual transition between an association region where oxygen vacancies are bound to dopant cations, and a dissociation region where vacancies are free and mobile.At a known temperature, EIS also elucidates oxygen concentration dependence on sensor electrode resistance. Figure 3a shows sensor electrode resistance, fitted from figure 2a, as a function of oxygen concentration. Investigating the oxygen reduction reaction (ORR) variation on platinum at various temperature regions, it is suggested that ORR on platinum is co-limited by oxygen adsorption and by oxygen transport along the surface of the electrode, in agreement with Adler [2]. Figure 3b shows that electrode 2 is dominant at temperatures below 1050oC, indicative of oxygen diffusion limitation on the surface and through platinum. Electrode 1 is dominant at temperatures above 1050oC, where dissociative adsorption of oxygen on the electrode surface is predominant.

3D Printing of Carbides Using Renewable Resources

Here we present preliminary results on fabrication of 3D complex shapes of porous carbide material by additive manufacturing. Porous carbides feature unique properties such as high melting point, high chemical stability, low thermal expansion coefficient, low density, high surface area and high specific strength [1]. The current state of the art for fabrication of carbide parts includes incomplete sintering and templating method. However, these methods use non-renewable carbon precursors, which is a matter of concern for the sustainability of the Earth. Furthermore, the shape of the carbide parts strongly depends on the use of mold and making of a 3D complex shape is challenging in these methods. Here we postulate the fabrication of 3D complex shapes of porous carbide material by 3D printing of a biopolymer composite followed by carbothermal reduction reaction. Recently we reported an environment friendly and sustainable approach for synthesis of tungsten carbide using a renewable biopolymer composite [2], which resembles a gel material. The renewable biopolymers eliminate the use of non-renewable carbon precursors and the Bingham plastic nature of the composite allows for layer-by-layer fabrication. The additive manufacturing will eliminate the dependence of mold and it can be possible to fabricate 3D intricate shapes, which are challenging in current methods. The potential application of such 3D printed carbide shapes includes lightweight structural material, catalysts supports, high temperature filters and insulations. The biopolymer composite we used here was composed of iota-carrageenan (IC) and chitin. The IC powder was mixed to chitin in a 1:4 weight ratio. As our initial target was to fabricate 3D printed shapes of tungsten carbide (WC), we mixed tungsten trioxide (WO3) nanoparticles with the biopolymer powders such that a molar ratio of WO3:C equal to 1:6 was achieved. Ultrapure water was added to the biopolymer-WO3 nanoparticle mixture and stirred with a homogenizer to obtain the gel-like composite. The gel composite was loaded into a syringe and extruded into 3D shapes using a paste extruder (Discov3ry) coupled with a 3D printer (LulzBot TAZ 5). Figure 1a shows such a 3D printed shape of the polymer composite. Once the printing was done, the 3D printed composite was dried overnight to obtain a 3D shape of xerogel (Figure 1b). The 3D shape of the xerogel was heat treated at 1300 °C for 3 hours in nitrogen atmosphere to obtain 3D shapes of WC (Figure 1c). The composition of the heat-treated sample was confirmed by the x-ray diffraction (XRD) spectroscopy, as only peaks of WC were observed in the XRD pattern. Ongoing work is 1) characterizing of the shrinkage of the 3D printed parts during drying and heat treatment; 2) implementing a design of experiments to obtain different dimensions of cellular architectures and understanding the effect of printing on those cellular architectures; 3) characterizing the mechanical properties of the 3D printed cellular architectures of WC.

Conversion of SILAR deposited Cu3Se2 thin films to Cu2−xSe by annealing

Thin films of copper selenide were deposited onto glass substrates using SILAR method at room temperature and annealed at 573K for an hour in nitrogen atmosphere. As-deposited and annealed films were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, Raman spectroscopy, and optical absorption measurements. X-ray diffraction studies revealed that annealing the films in nitrogen atmosphere led to conversion of the tetragonal Cu3Se2 phase to cubic Cu2−xSe phase. Scanning electron microscopy images showed a considerable change in the morphology of the films and energy dispersive X-ray analysis demonstrated a reduction in selenium content with annealing. Typical Raman spectra of copper selenide thin films were obtained from the as-deposited and annealed films. Using optical absorption measurements, direct band gap energies of Cu3Se2 and Cu2−xSe phases were found to be 2.72eV and 2.15eV, respectively.

Interstitial oxygen related defects and nanovoids in Au implanted a-SiO2 glass depth profiled by positron annihilation spectroscopy

Samples of amorphous silica were implanted with Au ions at an energy of 190 keV and fluences of ions cm−2and ions cm−2 at room temperature. The damage produced by ion implantation and its evolution with the thermal treatment at 800 °C for one hour in nitrogen atmosphere was depth profiled using three positron annihilation techniques: Doppler broadening spectroscopy, positron annihilation lifetime spectroscopy and coincidence Doppler broadening spectroscopy. Around the ion projected range of nm, a size reduction of the silica matrix intrinsic nanovoids points out a local densification of the material. Oxygen related defects were found to be present at depths four times the ion projected range, showing a high mobility of oxygen molecules from the densified and stressed region towards the bulk. The 800 °C thermal treatment leads to a recovery of the silica intrinsic nanovoids only in the deeper damaged region and the defect distribution, probed by positrons, shrinks around the ion projected range where the Au atoms aggregate. Open volume defects at the interface between Au and the amorphous matrix were evidenced in both the as implanted and in the thermal treated samples. A practically complete disappearance of the intrinsic nanovoids was observed around when the implantation fluence was increased by two orders of magnitude ( ions cm−2). In this case, the oxygen defects move to a depth five times larger than .

Study the Removal of Fluoride from Aqueous Medium by Using Nano-Composites

Endemic fluorosis disease has become a major geo-environmental health care issue caused by fluoride ion. High-efficiency and low-cost materials to uptake fluoride from water have been a chal-lenge for scientists and engineers. Here, we report a low-cost process by utilising low-cost starting materials to develop nanocomposite adsorbents for fluoride uptake from water. Bermuda grass as a starting source material converted into nanocomposite carbon fibers upon heat treatment at 800°C for one hour in Nitrogen atmosphere in the presence of metal oxides. Iron oxide-based nanocomposite (IBNC) is performing high (≈97%) removal of fluoride ion at a contact time of 60 minutes (pH 4) followed by titania-based nanocomposite (TBNC) (≈92%) and micro carbon fiber (≈88%) respectively. The phenomenon of fluoride ion uptake is realised by Freundlich adsorption model, and both adsorption capacity and adsorption intensity for IBNC are higher than those for TBNC and micro carbon fiber.

Annealing Effect on Synthesis of VO<sub>2</sub> (M) Nanopowders by a Novel Solution-Based Process

This paper describes a novel and simple method to preparing monoclinic VO2 (M) nanopowders via the reaction of ammonium meta-vanadate (NH4VO3) and oxalic acid dihydrate (C2H2O4•2H2O). The products were characterized by means of methods. XRD results show that well crystallized nanopowders of the monoclinic VO2 (M) were successfully synthesized, while the molar ratio between NH4VO3 and C2H2O4•2H2O was kept at 1:0.5~2.5, and the annealing temperature was 350~750 °C for 2~10 hour in nitrogen atmosphere. The spherical morphology of the samples is characterized by SEM. The crystallization temperature of the desired M/R-phase VO2 is lower than 387 °C in this work. And the phase transition temperature is determined by differential scanning calorimetry (DSC).

IMPROVEMENT IN HARDNESS AND CORROSION RESISTANCE OF STEEL THROUGH RED MUD COATING

Red mud is a waste product produced during alumina extraction from bauxite by the Bayer’s process and has become a major issue in connection with its disposal. As the aluminum demand in the world is increasing, the disposal of red mud waste into the environment also increases, bringing with its environmental issues coupled, however, a potential for the waste to generate a huge amount of unutilized resources still contained in the red mud, such as Fe2O3, Al2O3, SiO2, and others. As a possible useful utilization of the disposable waste, red mud can be used as a fine ceramic coating material onto metal substrates. For a fine ceramic coating, fine red mud powder was mixed with other substances to form a non-aqueous coating slurry with toluene as the solvent, PEG 6000 as the binder and plasticizer, and sesame oil as the dispersant. The coating process was performed by a dip-coating method onto ST-37 steel with a withdrawal speed of 0.23 mm/sec. The densification of coating material took place after calcinations at 900 °C, 1100 °C, and 1300 °C for 2 hours in nitrogen atmosphere. This treatment evinced an improvement of the surface hardness from 146.2 HV to 1738.8 HV for the sample calcined at 1100°C and the corrosion resistance by 4.14 times, for the sample calcined at 1300°C.

Synthesis of boron nitride nanolayers encapsulating iron fine particles and boron nitride nanotubes

ABSTRACTBoron nitride (BN) nanolayers encapsulating iron (Fe) fine particles have been synthesized by annealing mixtures of hematite (α-Fe2O3) and boron powders at 1373 K for 2 hours in nitrogen atmosphere. The Fe particles had an average diameter of ∼300 nm with BN nanolayers coating of ∼10 nm. The α-Fe2O3 was transformed into Fe and then Fe-B on a process of annealing. The Fe-B was decomposed into Fe and BN, and consequently Fe particles coated with BN nanolayers were synthesized. They showed soft magnetic properties with coercivity of 1.5 kA/m. The BN nanolayers encapsulation was effective on improving oxidation resistance. BN nanotubes with diameter of ∼100 nm were also synthesized as a resultant product by this method.

SYNTHESIS AND CHARACTERIZATION OF (CdSe)1-X(ZnS)x MIXED POLYCRYSTALLINE SEMICONDUCTORS BY CO-PRECIPITATION METHOD

The polycrystalline (CdSe)1-x (ZnS)x semiconductor powder with (0 ≤ x ≤ 1) has been prepared by controlled co-precipitation method from an alkaline medium using thiourea as a sulphide ion source. Pellets are made out of these powders under 10 tonnes/sq.cm pressure and are sintered at 800°C for 2 hours in nitrogen atmosphere. X-ray studies have indicated that the compounds are polycrystalline in nature with mixed hexagonal structure of CdSe with x = 0-0.3 and cubic structure of ZnS with x = 1. The chemical homogeneity of the samples was observed from the EDAX and also noted that the atomic contents present were as per the constituents taken in the solution. Lattice parameters (a and c) of all the compounds are determined from the X-ray data and are found to decrease with the increase in ZnS content. It is also observed that the grain size decreases with the increase in x from 0-0.6 and later it remained almost the same till x reaches 0.9. Optical studies indicated that the energy gap was as high as 5.2 eV and remained almost same throughout the composition range x = 0-1. Scanning electron micrographs have shown platelet like structure in CdSe and mixed compounds where as a mixed Cubic and Hexagonal structure in ZnS. The results are explained based on different phases present in the compounds.

Preparation of alumina–silica–nickel nanocomposite by in situ reduction through sol–gel route

Ceramic based composites with dispersion of nano sized metal/metal carbide particles have generated wide technological interest for their improved mechanical properties — hardness, fracture strength as well as fracture toughness, superior electrical properties and magnetic properties. In the present investigation alumina–silica gels have been prepared along with nickel chloride and dextrose distributed in the nanometric pores of the gel. The gels are prepared with different molar proportions of alumina and silica containing 5 wt% of nickel chloride and 50 wt% excess dextrose. During heat treatment at a temperature of 9008C for half an hour in nitrogen atmosphere, nickel chloride is reduced to metallic nickel by in situ generated hydrogen in the silica–alumina matrix. X-ray analyses indicate that no nickel chloride reduction is possible upto 50 mol% silica in alumina–silica matrix. Beyond this range, higher the silica content, higher is the reduction of nickel chloride. The presence of metallic nickel has been substantiated further by SAD analysis. Particle size analysis based on X-ray diffraction as well as transmission electron micrograph shows the presence of nickel particles of size ,20 nm distributed in the alumina–silica nanocomposite.

シナジー磁石と磁性材料 針状α‐ＦｅＯＯＨを用いたＭｎ‐Ｚｎフェライトの配向性および磁気特性

Crystal oriented manganese zinc ferrites were made from acicular α-FeOOH, Mn(C5H7O2)3 and Zn(C5H7O2)2 as raw materials. The materials were mixed and calcined at 800°C for 4 hours in nitrogen atmosphere. The calcined acicular manganese zinc ferrite fine particles were formed into a thin troidal cores, consist of multi-layered. The green bodies were sintered at the range of 1100 to 1250°C for 4 to 8 hours in air, thereafter cooled in nitrogen atmosphere.The crystals of sintered manganese zinc ferrites were strongly oriented to the direction of {111} plane of the spinel, which was all formed along the upper plane of troidal cores. The behavior of crystal growth was similar to that of manganese zinc ferrite single crystal. The initial permeability of crystal oriented manganese zinc ferrites was 1380 at 0.1MHz and it was not allowed to decay up to 2.2 MHz at the operating condition of the 3dB decrease of the initial permeability. The high crystal orientation and suitable grain size has greatly contributed to the improvement of magnetic properties.

In situ Preparation of SiO2-WC Nanocomposites through Sol-Gel Route

SiO2-WC nanocomposites have been prepared by in situ reduction of (NH4)2WO4 with dextrose in the SiO2 gel matrix by heating within the temperature range of 1250°-1300°C for half an hour in nitrogen atmosphere. The average particle size of WC formed is about 24 nm.

Volatile Compounds Formed on Roasting DL-α-Alanine with D-Glucose

The mixture of dl-α-alanine and d-glucose was roasted at 250° for about an hour in nitrogen atmosphere. From the volatile condensates were isolated and identified alkyl and acyl pyrroles, alkyl pyrrole-2-aldehydes, furfuryl pyrroles, alkyl pyrazines and furanic compounds. The identification of these compounds was based on the spectroscopic methods (MS, GC-MS and IR) and gas chromatographic analysis.