Temperature Range Of RT Research Articles

Role of catalyst oxidation states in the selective detection of reducing gases: A comparative study of nanocomposites based on Au and chemically/thermally reduced graphene oxide

Catalyst-loaded reduced graphene oxide (rGO) is a promising material for developing high-performance gas sensors. In this work, surface functionalization is achieved by loading different quantities of nanogold (Au) on chemically and thermally reduced graphene oxide (CRGO and TRGO). These materials showed selective gas response toward reducing gases such as hydrogen (H2), carbon monoxide (CO), and methane (CH4) in the temperature range RT to 150 °C. The quantity of Au catalysts and their oxidation states in the films influenced the selectivity attributes of the studied sensors. The surface oxidation states of the Au catalyst are different for CRGO-Au and TRGO-Au films. It is apparent from the results that the difference in the Au oxidation states is due to the variation in surface oxygen functionalities of the base matrix CRGO and TRGO. The experimental results are tallied with the proposed gas selectivity mechanism of CRGO-Au and TRGO-Au films.Novelty of the Work:In reduced graphene oxide based gas sensors, the combined influence of the graphene oxide reduction method, gold (Au) catalyst quantity, and valence oxidation states (in the Au catalyst) on the gas selectivity is rarely reported. The available reports only focus on examining the metallic gold (Au0) phase of the catalyst. However, it is necessary to note that Au can also exist in various higher oxidation states (Au+1, Au+2, Au+3, etc.), which provide selective gas adsorption sites. Therefore, this work addresses the above issue by employing chemically reduced graphene oxide (CRGO) and thermally reduced graphene oxide (TRGO) decorated with Au nanoparticles (Au wt% = 1 %, 50 % & 90 %) for the selective sensing of reducing gases.

A comprehensive study of dielectric, modulus, impedance, and conductivity of SrCeO3 synthesized by the combustion method

AbstractIn this work, perovskite oxide SrCeO3 was synthesized using the solution combustion method (SCM). Synthesized samples have been characterized using X‐ray diffraction (XRD), Raman, ultra violet (UV)–visible spectroscopy, and scanning electron microscopy (SEM) techniques. The XRD and Rietveld refinement has confirmed the orthorhombic structure with space group Pnma. The average grain size of this ceramic sample is 1.2 µm. The dielectric constant, dissipation factor, modulus, impedance, and alternating current (AC) and direct current (DC) conductivities were analyzed in the temperature range RT to 600°C and frequency range 20 Hz–2 MHz. Further, it was observed that the role of grain boundaries in dielectric and electrical properties is significant, at low temperatures. The origin of the dielectric relaxation and conduction process is the same. The activation energy for DC conduction (Edc) was found to be .79 eV. Electrical conduction/relaxation is assigned to the diffusion of doubly ionized oxygen (Vo··). The value of DC conductivity (1.2 × 10−3 Ω−1 cm−1 at 600°C) and activation energy of .79 eV is very close to the values reported for doped CeO2‐based oxide ion conductors for SOFCs. This study has demonstrated that SrCeO3 can be an alternative candidate for the oxide ion conductor electrolyte application and the potential to be used as a thermally stable capacitor application for microwave dielectric applications.

Characterization of the Aroma Profile of Food Smoke at Controllable Pyrolysis Temperatures

Smoking is used to give food its typical aroma and to obtain the desired techno-functional properties of the product. To gain a deeper knowledge of the whole process of food smoking, a controllable smoking process was developed, and the influence of wood pyrolysis temperature (150–900 °C) on the volatile compounds in the smoking chamber atmosphere was investigated. The aroma profile of smoke was decoded by headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Subsequently, the correlations in the most important substance classes, as well as in individual target components, were investigated by the Pearson test. Phenols and lactones showed an increase over the entire applied temperature range (rT = 0.94 and rT = 0.90), whereas furans and carbonyls showed no strict temperature dependence (rT < 0.6). Investigations on single aroma compounds showed that not all compounds of one substance class showed the same behavior, e.g., guaiacol showed no significant increase over the applied pyrolysis temperature, whereas syringol and hydoxyacetone showed a plateau after 450 °C, and phenol and cyclotene increased linear over the applied temperature range. These findings will help to better understand the production of aroma-active compounds during smoke generation in order to meet consumers preferences.

The synthesis and characterization of a heat-resistant Si-containing aryl ether arylacetylene resin

A Si-containing arylether arylacetylene resin, poly(dimethylsilyene-ethynylene-phenyleneetherene-ethynylene) (PSEE), was synthesized from diethynyldiphenyl ether and dichlorosilane through Grignard reactions. The structures and properties of PSEE resin were characterized by NMR, FT-IR, DSC, TGA analysis techniques. PSEE resin can be crosslinked to form a thermoset at a temperature less than 2000C. There is no glass transition in the temperature range of RT~5000C and Td5 is 5680C in N2 for PSEE thermoset. The thermoset shows good dielectric properties and its glass fiber reinforced composite exhibits high mechanical properties. Copyright © 2017 VBRI Press.

Radiation damage of MoAlB at elevated temperatures: Investigating MAB phases as potential neutron shielding materials

A new family of ternary nano-laminated compounds, MAB phases, are studied as a promising class of neutron shielding materials for applications within fusion reactors. The shielding capacity against high-energy neutrons was evaluated, and the damage tolerance of MoAlB against Si+ irradiation was investigated over the temperature range of RT- 600 °C. The linear attenuation coefficients of these materials over wide neutron-energy ranges imply that Mo(W)AlB have a high neutron shielding capacity. MoAlB shows a strong resistance to crack formation and excellent tolerance to amorphization under higher temperatures. The detailed thermal dynamic behaviors (reaction barrier and migration barrier) associated with the defects in MoAlB were studied through DFT calculations. Also, the lattice parameter changes are related to the formation of various point defects and the defect evolution evidenced by Rietveld refinement of the GIXRD and DFT calculations. MoAlB is confirmed to be a great candidate as a neutron shielding material.

Experimental characterization of the short crack growth behavior of a ductile cast iron (DCI GJS-500) affected by intergranular embrittlement at temperatures nearby 400 [formula omitted

In this investigation, the fatigue and crack growth behavior of the ductile cast iron material (DCI) GJS-500 was experimentally characterized by performing isothermal low cycle fatigue (LCF) tests, out-of-phase thermomechanical fatigue (OPTMF) tests as well as low cycle fatigue tests combined with the replica testing method (LCF-R) within the temperature range RT–500 °C. The studied material exhibits an embrittlement at temperatures nearby 400 °C, leading to a significant higher fatigue crack growth rate and a reduced lifetime, when compared with RT and 500 °C. A possible explanation for the observed higher fatigue crack growth rate coupled with a significant lifetime reduction, is intergranular embrittlement.

Electrical transport and thermoelectric study of Ca3Co4O9 ceramics

The study of thermoelectric materials, which convert thermal energy to electrical energy in the solid state, has grown immensely in the past decade. The polycrystalline Ca3Co4O9 powder were synthesized using conventional sold state route by employing double sintering method. Homogeneous mixture in stoichiometric proportion of CaCo3 and Co3O4 powder was ground for 3 hrs and sintered at 1100 °C for 24 hrs with several intermediate grindings. The electrical transport property such as temperature dependent resistivity and thermoelectric seebeck coefficient was measured in the temperature range RT to 623 K. The electrical resistivity decreases with increasing temperature showing the semiconductor behaviour. The resistivity behaviour is fitted and explained using Thermal activation model and small polaron hopping (SPH) model. The value of seebeck coefficient (S) measured from room temperature to 623 K and it is found to be ∼42.7 μV/K. Ca3Co4O9 is thermoelectrically potential material for waste heat retrieval energy applications.

Influence of Temperature on Low Cycle Fatigue and Ratcheting Behavior of SA333 Gr-6 C-Mn Steel

The aim of this investigation is to study the influence of temperature on the cyclic plastic deformation behavior of SA333 Gr-6 steel at two loading conditions. Strain-controlled cyclic loading experiments were carried out at ± 0.5% total strain amplitude, 1×10-3 s-1 strain rate, and temperature varied from RT to 400°C, whereas stress controlled ratcheting experiments were conducted at fixed mean stress (σm) of 50 MPa and stress amplitude (σa) of 400 MPa, 115 MPa s-1 stress rate, and in the temperature range of RT to 350°C. The investigated steel shows cyclic hardening characteristic at DSA temperature regime in both the loading condition. The steel shows lower fatigue lives at 250°C and 300°C temperatures even though plastic strain amplitude is smaller. The ratcheting life of the steel increases and strain accumulation decreases with the increase in temperature up to 300°C and on further increment in temperature ratcheting life get decreased. The steel shows greater cyclic hardening at both the loading conditions at 300°C.

Performance of Na-ion Supercapacitors Under Non-ambient Conditions—From Temperature to Magnetic Field Dependent Variation in Specific Capacitance

Single phase NaFePO4 can works as economically viable cathode material for Na-systems similar to LiFePO4 – a material that led to the commercialization of Li-ion based energy systems. The reported microstructures of hollow NaFePO4 particles, with porous walls, establish their advantages over solid morphologies. The hollow structures deliver stable electrochemical specific capacitance of 115 F g-1 in 2 M NaOH electrolyte, over a large number of cycles. This observation is directly attributed to the increased surface area, transport channels and redox sites, which become available in the porous-hollow particles. Hitherto unreported electrochemical performance under non-ambient environment is discussed. In contrast to recently reported in Fe-based metal oxides, where significant change in specific capacitance has been reported as a function of magnetic field, NaFePO4 can protect itself and suppress modifications. More importantly, NaFePO4 also acts as efficient electrode material in the temperature range RT to 65oC, which makes it useful for automotive industry.

Warm white light emission of apatite-type compound Ca4Y6O(SiO4)6 doped with Dy3+

A series of Ca4Y6O(SiO4)6: x%Dy3+ (x = 1, 3, 5, 7, 9) phosphors were synthesized successfully via a conventional solid-state method at high temperature. The X-ray diffraction results show that all obtained samples are the pure hexagonal crystal structure of the space group P63/m (No.176). The blue (4F9/2 → 6H15/2) and yellow (4F9/2 → 6H13/2) emissions of Ca4Y6O(SiO4)6:7% Dy3+ phosphors are of such a ratio to produce almost perfect white light with CIE coordinates of (0.330, 0.339). The correlated color temperature is about 5600 K, close to that of the midday sunlight (5500 K). In addition, both the emission intensity and the CIE coordinates exhibit an excellent thermal stability in the temperature range of RT ∼ 300 °C. Our study illustrates that Ca4Y6O(SiO4)6:7%Dy3+ may serve as potential warm white lighting phosphors in NUV-based solid state lighting and optical display applications.

Preparation and characterization zirconium and samarium co-doped ceria solid electrolytes for IT-SOFC applications

Zirconium and Samarium co-doped ceria solid electrolyte materials Ce0.8–xSm0.2ZrxO2-δ (x=0, 0.05, 0.10, 0.15 and 0.20) for intermediate temperature-solid oxide fuel cells were synthesized by citrate-nitrate auto combustion synthesis technique. Powder x-ray diffraction results reveal that all the synthesized samples show a single-phase with cubic fluorite structure. The lattice parameter values were calculated from the powder x-ray diffraction data. Samples with high density were obtained by sintering the samples at 1300°C for 4h. The average crystallite sizes were calculated from the Scherer formula. Surface morphologies of all the samples were obtained by using the scanning electron microscope. The total ionic conductivity of all the samples was carried out from impedance analysis in the temperature range RT – 500°C. The highest total ionic-conductivity with lowest activation energy values were observed for Ce0.65Sm0.2Zr0.15O2-δ at 500°C makes it as a useful solid electrolyte material for intermediate temperature-solid oxide fuel cells (IT-SOFCs) applications.

Towards a temperature dependent and probabilistic lifetime concept for nodular ductile cast iron materials undergoing isothermal and thermo-mechanical fatigue

In this investigation, the fatigue behaviour of a ductile cast iron with high content of silicon and molybdenum, was experimentally characterized by performing isothermal low cycle fatigue (LCF) tests as well as out-of-phase thermomechanical fatigue (OPTMF) tests within the temperature range RT – 500 °C. The studied material shows an embrittlement at temperatures nearby 400 °C. A possible explanation for the observed lifetime reduction is intergranular embrittlement (IE). A mechanism based lifetime model is proposed for assessing the lifetime. The model is based on the assumption that the crack advance per cycle is correlated with the cyclic crack tip opening displacement (ΔCTOD) attributed to the crack tip blunting caused by accumulation of plastic and creep deformations ahead of the crack tip. Intergranular embrittlement is accounted for by introducing a temperature and strain rate dependent prefactor in the crack growth law, which only acts in a certain temperature range. The model is calibrated for a GJS material and successfully applied to predict the lifetime of this material when undergoing isothermal and non-isothermal mechanical loadings. A probabilistic interpretation of the scatter of the investigated material is presented in conjunction with the random nature of the initial defect size distribution.

나노섬유 제작기술을 적용한 저온형 고체산화물 연료전지 이중층 페로브스카이트 나노섬유 공기극의 특성 분석

In this study, linear typed nanofibers were fabricated by controlling the variables with the great effects on nanofiber fabrication and the microstructural properties of fabricated nanofibers were investigated as a preliminary step to serve as a carrier, including SmBaSUB0.5/SUBSrSUB0.5/SUBCoSUB2/SUBOSUB5+d/SUB (SBSCO) cathode materials for low temperature-operating solid oxide fuel cells (LT-SOFCs). Beadless nanofibers were produced at a nozzle to substrate distance of at least 9 cm when using the electrospinning process. The diameter of the nanofibers increased with increasing flow rate, and the diameter of the nanofibers also increased at a nozzle to substrate distance of 9cm or more. As the humidity increased, collapse of the nanofibers was observed. The fabricated nanofibers, as a carrier for SBSCO, were decomposed in three parts: a temperature range of RT~340°C, 340°C~454°C, and higher than 454°C. No further weight losses were observed at temperatures higher than 625°C. The lowest area specific resistance (ASR) was observed when SBSCO was used in the nanofiber type and the SBSCO nanofiber exhibited an ASR value of 0.85 Ω.cmSUP2/SUPat 550°C.

Theoretical and experimental study on effective thermal conductivity of pebble bed for fusion blanket

The effective thermal conductivity of breeder pebble bed as an important thermal physical parameter directly affects the thermal and mechanical properties of solid blanket. Theoretical and experimental studies on effective thermal conductivity of Li4SiO4 pebble bed were introduced in this paper. First, a theoretical model coupling the contact areas with bed strains was presented to predict the effective thermal conductivity of mono-sized pebble bed. Taken into account in this theoretical model is the influence of factors, such as properties of pebbles and gas, bed porosity, pebble size, gas flow, contact areas, thermal radiation and contact resistance. Second, experimental platforms were built up to measure the effective thermal conductivity of Li4SiO4 pebble bed. One is based on transient thermal probe method and the other is based on transient plane source method. The effective thermal conductivity of Li4SiO4 pebble bed with pebbles in a diameter of around 1mm were measured in the temperature range of RT∼550°C. The helium at 0.1MPa and air at atmospheric pressure were used as filling gas respectively to assess the influence on effective thermal conductivity of pebble bed. The comparison between the experimental results and calculation results by theoretical model was also discussed.

Effective thermal conductivity of advanced ceramic breeder pebble beds

As the knowledge of the effective thermal conductivity of ceramic breeder pebble beds under fusion relevant conditions is essential for the development of solid breeder blanket concepts, the EU advanced and reference lithium orthosilicate material were investigated with a newly developed experimental setup based on the transient hot wire method. The effective thermal conductivity was investigated in the temperature range RT–700°C. Experiments were performed in helium and air atmospheres in the pressure range 0.12–0.4MPa (abs.) under a compressive load up to 6MPa. Results show a negligible influence of the chemical composition of the solid material on the bed’s effective thermal conductivity. A severe reduction of the effective thermal conductivity was observed in air. In both atmospheres an increase of the effective thermal conductivity with the temperature was detected, while the influence of the compressive load was found to be small. A clear dependence of the effective thermal conductivity on the pressure of the filling gas was observed in helium in contrast to air, where the pressure dependence was drastically reduced.

Microstructure And Thermoelectric Properties Of Tags-90 Compounds Fabricated By Mechanical Milling Process

Abstract TAGS-90 compound powder was directly prepared from the elements by high-energy ball milling (HEBM) and subsequently consolidated by a spark plasma sintering (SPS). Effect of milling time on the microstructure and thermoelectric properties of the samples were investigated. The particle size of fabricated powders were decreased with increasing milling time, finally fine particles with ~1μm size was obtained at 90 min. The SPS samples exhibited higher relative densities (>99%) with fine grain size. X-ray diffraction analysis (XRD) and energy dispersion analysis (EDS) results revealed that all the samples were single phase of GeTe with exact composition. The electrical conductivity of samples were decreased with milling time, whereas Seebeck coefficient increased over the temperature range of RT~450°C. The highest power factor was 1.12×10−3W/mK2 obtained for the sample with 90 min milling at 450°C.

Structural and dielectric properties of BaTiO3–Bi(Mg1/2Ti1/2)O3 thin films fabricated by chemical solution deposition

Thin films of the BaTiO3–Bi(Mg1/2Ti1/2)O3 (BT–BMT) solid-solution system were fabricated with the aim of achieving a stable temperature coefficient of capacitance (TCC) favorable for high-temperature electronics. A single perovskite phase with pseudocubic symmetry was obtained for the films fabricated by chemical solution deposition on (111)Pt/TiO2/(100)Si substrates in the composition range of x = 0–0.80 for (1 − x)BT–xBMT. BMT added to the BaTiO3-based films enhanced the crystallinity of the perovskite phase and resulted in saturated P–E hysteresis behavior with remanent polarization of up to 13 µC/cm2. BMT addition led to gradual dielectric relaxation, which also resulted in stable TCC behavior with a relative dielectric constant of approximately 400 in the temperature range of RT − 400 °C, especially for the BT–BMT films with x = 0.20–0.40.

Temperature dependence of tensile properties and fracture behavior of as rolled TiB/Ti composite sheet

In this paper, the tensile properties and fracture behavior of 7.5vol% TiB/Ti composite sheet were studied in the temperature range RT–900°C. The results show that the TiB/Ti composite sheet exhibits much higher ultimate strength in RT to 700°C temperature range compared to matrix alloy sheet while a comparable strength at temperature above 700°C. The ductility of the composite is much lower than that of the matrix alloy at all temperatures. The strengthening mechanism of the composite and strengthening effect of TiB varying with temperature are investigated. In addition, the softening behavior of the composite with the increasing temperature is discussed. Fractograph characteristic of the composite reveals that fracture of TiB whiskers followed by the ductile failure of the matrix is the main failure mechanism of the composite below 700°C while interfacial debonding dominates the fracture mechanism of the composite sheet above 700°C.

Conductivity and electrical modulus studies of La2−x Nd x Mo1.7W0.3O9−δ oxygen ion conductor

La2−xNdxMo1.7W0.3O9−δ (x = 0 − 0.5) and, for comparison, La2Mo2O9 compounds have been synthesized following solid state reaction technique. Temperature-dependent electrical conductivity of La2−xNdxMo1.7 W0.3O9−δ reveals suppression of the phase transition as compared to parent La2Mo2O9 compound. Partial substitution of Nd at the La site of La2Mo1.7W0.3O9−δ increases the conductivity of La2Mo1.7W0.3O9−δ in the entire temperature regime. In the intermediate temperature region (405 °C ≤ T ≤ 570 °C), the overall conductivity of La2−xNdxMo1.7W0.3O9−δ (0.1 ≤ x ≤ 0.5) is higher than that of the parent compound, and the conductivity of the compound with x = 0.1 is almost same with the La2Mo2O9 in the high temperature region (T ≥ 640 °C). Arrhenius to Vogel–Tamman–Fulcher (VTF) transition is observed in all doped specimens above 460 °C. Ion relaxation mechanism has been discussed in the framework of electrical modulus analysis in the temperature range RT–530 °C and is found to be non-Debye type of conductivity relaxation with the distribution of transition rates for hopping ions in the range of 0.60–0.70.

Electron Transport Properties of Rapidly Solidified (GeTe)x(AgSbTe2)1-x Pseudobinary Thermoelectric Compounds

(GeTe)x(AgSbTe2)1−x(x=80, 85) compounds were fabricated by melting-hot press and RSP-hot press processes. The (GeTe)85(AgSbTe2)15 compound, which composed of mainly crystalline and partly amorphous structures, was produced in part by rapid solidification. X-ray diffraction analysis showed that the (GeTe)x(AgSbTe2)1−x compounds represented a single phase of GeTe. The electron transport properties were evaluated over the temperature range of RT∼773K, and then systematically changed with compositions x in (GeTe)x(AgSbTe2)1−x compounds. The maximum Seebeck coefficient was 227 μV/K at 673K in the (GeTe)80(AgSbTe2)20 compounds fabricated by melting and hot-press process. The minimum resistivity was shown in the (GeTe)85(AgSbTe2)15 by melting and hot-press process.