Heating In Argon Research Articles

Wall Heat Transfer Coefficient in a Molten Salt Bubble Column: Testing the Experimental Setup

One of the advantages of bubble columns is high heat transfer rates. High heat transfer is important in reactors when high thermal duties are required. An appropriate measurement of heat transfer coefficient is of primary importance for designing reactors that are highly exothermic or endothermic. This paper presents the design and operation of experimental setup used for measurement of the heat transfer coefficient in molten salt media. The experimental setup was operated with tap water, heat transfer oil 32, LiCl–KCl eutectic and argon gas. Tap water was operated at the temperature of 40oC and heat transfer oil was operated at the temperature of 75oC, 103oC and 170oC. There were some challenges when operating the bubble column with molten salt due to leakages on the welds and aggressive corrosion on the column. All the experiments were run at superficial gas velocities of 0.01–0.05 m/s. Three heating tapes, each connected to a corresponding variable AC voltage controller, were used to heat the column media. Heat transfer coefficients were measured by inducing a known heat flux through the column wall and measurement of the temperature difference between the wall and the contents. In order to balance the system, heat was removed by the cooling water flowing through a copper tube on the inside of the column. Temperature differences between the column wall and the liquid were measured at five axial locations. It was found that the heat transfer coefficient increases with superficial gas velocity. The values of heat transfer coefficient for argon–water system were higher than those of argon–heat transfer oil system. Heat transfer coefficient was also found to increase with an increase in temperature.

Studies on U-Zr and U-Pu-Zr alloys for determination of Cl and F using pyrohydrolysis

Abstract Pyrohydrolysis method was studied for the separation of Cl and F from U-Zr and U-Pu-Zr alloy nuclear fuels and determination by ion chromatography. A detailed study was performed on pyrohydrolysed products of U-Zr alloy, obtained on heating in moist argon and oxygen atmospheres using X-ray powder diffraction (XRD) and thermogravimtric methods. Using oxygen as the carrier gas pyrohydrolysis performed at 900 ℃ was complete within 30 min. It was found that, moist oxygen as carrier gas only could open the matrix completely within stipulated time. This was attributed to the formation of α-U3O8, which was not possible in moist argon heating for 30 min. The pyrohydrolysis in moist Ar required 60–90 min for complete removal of halides. The method was then successfully extrapolated to U-Pu-Zr alloys. The results showed recovery up to 90% or above for the optimized conditions.

Carbonitridation of mechanically activated mixtures of zircon and carbon

Abstract Two different stoichiometries of zircon (ZrSiO 4 ) and activated carbon (C:zircon molar ratios of 3:1 and 6:1) were milled together at for 5 h and subjected to thermo-gravimetric analysis (TGA). TGA runs were performed under argon and nitrogen atmospheres. The main mass loss reaction started at around 1200 °C in all samples, but the mass loss was greater in the 6:1 C:zircon ratio samples in nitrogen. X-ray diffraction (XRD) of the residues showed the decomposition of zircon was nearly complete. Traces of ZrN along with monoclinic and tetragonal forms of zirconia were observed in the nitrogen atmosphere, however only zirconia was present after heating in argon. Heating the 6:1 C:zircon molar ratio sample for 1 h at 1400 °C in argon resulted in the formation of ZrC and SiC, in nitrogen ZrN was formed.

Changes in an Australian laterite ore in the process of heat treatment

This paper examines an Australian garnieritic-type ore and changes in phase composition and morphology caused by heating in argon at 400–1000°C using XRF, XRD, DTA/TG, SEM/EDS and BET analyses. The mineral phases detected by XRD in the original ore include chlorite, talc, hematite and quartz. Traces of iron silicate, Fe–Cr spinel and monoxide phase (predominantly manganese oxide) were observed by EDS. Nickel was detected in chlorite, talc, iron silicate and monoxide phase. Heat treatment at 400–500°C did not change XRD patterns. At 600°C, dehydroxylation of the brucitic phase of chlorite occurred. Chlorite was converted into olivine (forsterite) and enstatite at 600–800°C. Upon heating to 900–1000°C, talc was also converted into olivine and enstatite. Ni-bearing phases after heat treatment at 800–850°C were forsterite, enstatite, talc, iron silicate and monoxide.

Oxygen purity effect oxygen deficiency by argon heat treatment on Y:123 superconductors

Argon heat treatments at 450°C for different times of 0, 12, 24, 36, 48 and 60h on the two Y:123 oxygenated samples with different oxygen purity (Hp 99.99% and Lp 93%) are reported. The results of X-ray diffraction, oxygen deficiency and resistivity measurements are presented in details. Furthermore, the superconducting critical temperature Tc, normal resistivity ρ300, residual resistivity ρ0, resistivity slope dρ/dT and width of transition ΔTc are extracted from resistivity data. It is found that both c-parameter and oxygen deficiency increase by increasing annealing time, while OD and effective Cu valance decrease. But, the relative increase/decrease is more in Lp samples than that of Hp samples. Although Tc is decreased by annealing time for the two samples, the relative decrease in Tc is more in Lp samples when compared with those of Hp samples. Our results are discussed in terms of oxygen vacancies and hole carriers which are produced by annealing for the considered samples.

Phase transformation of iron oxide–silica coreshell structure during differential scanning calorimetry and pulsed electric current sintering processes: A comparison

This paper discusses the phase transformation of iron oxide nanoparticles inside the silica spheres during high temperature differential scanning calorimetry (DSC) in argon and pulsed electric current sintering (PECS) compaction in vacuum. The maximum temperature used was 1323K. In both cases it was found that the iron oxide nanoparticles were reduced depending on the heating atmosphere. Results suggested that during DSC heating in argon, the silica matrix acted as a reducing agent for iron oxide nanoparticles, while in PECS, the reduction of iron oxide nanoparticles was caused by the reducing environment created during the sintering at high temperature, and resulted also in crystallization of the silica matrix.

New photo- and electroluminescent conjugated copolyfluorenes with 7,8,10-triarylfluoranthene units in the backbone

A new monomer, the dibromo derivative of fluoranthene 1-[7,10-bis(4-bromophenyl)fluoranthen-8-yl]pyrene, is synthesized and used to prepare three new copolyfluorenes containing 3, 5, and 10 mol % 7,8,10-triarylfluoranthene groups via the Yamamoto reaction. The number-average molecular masses and polydispersities of the polymers vary in ranges 41900–78900 and 2.7–3.5, respectively. All polymers are soluble in common organic solvents, and their glass-transition temperatures are from 95 to 115°C. Temperatures corresponding to a 10% loss in weight during heating in argon and air are in the ranges 420–435 and 405–415°C, respectively. The photoluminescence spectra of the polymers exhibit strong blue emission with a maximum at 418 nm, whereas the absorption spectra show characteristic peaks at 351–357 nm. All polymers possess reversible or partially reversible redox behavior owing to high electric activity and demonstrate redox pairs at 1.51 eV (oxidation) and −2.09 eV (reduction).

The effect of the gas atmosphere on the response of the Al86Ni6Y4.5Co2La1.5 metallic glass powder to heating

The response of nitrogen gas-atomised fully amorphous Al86Ni6Y4.5Co2La1.5 powder (<25 μm) to heating in nitrogen and argon from 5 K/min to 40 K/min was investigated using differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and nano-indentation. The powder showed noticeably lower glass transition temperature, crystallization onset temperature, and peak crystallization temperatures in nitrogen than in argon, particularly at heating rates of ≥30 K/min. The activation energy for the onset of crystallisation of the powder was determined to be 301.58 ± 42.47 kJ/mol in nitrogen compared to 418.18 ± 7.20 kJ/mol in argon. Experimental evidence confirmed the reaction between the amorphous Al86Ni6Y4.5Co2La1.5 powder and nitrogen at ≥360 °C or even from ∼280 °C. The powder that crystallized in nitrogen exhibited slightly but consistently higher hardness and elastic modulus. These results are necessary to inform the selection of the sintering atmosphere and parameters for the fabrication of bulk metallic glass of Al86Ni6Y4.5Co2La1.5 from powder.

A new mechanism for the magnetic enhancement of hematite during heating: the role of clay minerals

The magnetic properties of loess, lake, and ocean sediments are often used as indicators for paleoclimatic/paleoenvironmental changes. Thermomagnetic analysis is a conventional approach for identifying magnetic phases and thermal alteration of samples. Magnetic concentration parameters are often enhanced after thermal treatment. In this study, the role of clay minerals in magnetic enhancement at elevated temperatures is systematically investigated. The results indicate that the clay minerals (saponite, Ca-montmorillonite, kaolinite, and chlorite) are dominated by paramagnetic behaviour and that the magnetic properties remain relatively stable after heating to 700°C in argon. In contrast, mixtures of hematite and chlorite have a high degree of magnetic enhancement after heating in argon, which indicates that clay minerals play important role in magnetic enhancement. These results improve our understanding of the processes involved in complicated mineral transformations, which is important for retrieving paleoclimatic/paleoenvironemntal signals from magnetic proxies.

Packing effects on argon and methanol adsorption inside graphitic cylindrical and slit pores: A GCMC simulation study

Using Grand Canonical Monte Carlo simulation, we have studied the effects of confinement on argon and methanol adsorption in graphitic cylindrical and slit pores. Linear chain, zigzag and incomplete helical packing are observed for argon adsorption in cylindrical pores. However, for methanol adsorption different features appear because the electrostatic interactions favour configurations that maximize the hydrogen bonding among methanol molecules. We have found zigzag chains with hydrogen-bonded structures for methanol adsorption in cylindrical and slit pores. To investigate how dense the adsorbed phase is and how many molecules could be packed per unit physical volume of the solid, we consider two different definitions of pore density; one based on the physical volume and the other on the accessible volume. That based on accessible volume gives a measure of the fluid density, while that based on the physical volume gives a measure of how much adsorbate can be stored per unit volume of the adsorbent. It is found that the adsorbate is denser in cylindrical pores, but that slit pores can pack more molecules per unit solid volume. We also discuss the effects on the isosteric heat of argon and methanol of pore size, pore geometry and loading.

Enhancement of Tc, orthorhombicity and AC magnetic shielding in argon preheated HTC superconductor (Y1−xSmx)(SrBa)Cu3O6+z

We report in this paper on the preparation, X rays diffraction, AC magnetic compound measurements and the effect of heat treatments in (Y1−xSmx)(SrBa)Cu3O6+z (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1). Each sample was subjected to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. For each x value, the [AO] treatment increases the orthorhombicity ϵ = (b−a)/(b+a) (for 0≤ x ≤ 1), Tc (for x ≥ 0.4) and the distance d[Cu(1)-(Sr/Ba)] for x < 0.5. When x increases from 0 to 1, ϵ decreases with Tc[O]. However, Tc[AO] decreases with ϵ until x = 0.2 and after it increases by 6 K to 85 K for x = 1 [AO]. A remarkable improvement in the shielding effect S, in the case of the samples [AO] at all T < Tc and for any applied field, was observed for x > 0.5 indicating an improvement in the pinning properties. Remarkable correlation was observed between Tc(x) and the number psh(x) of holes by Cu(2)-O2 superconducting planes. So the structural, magnetic and superconducting properties are correlated with the effect of argon heat treatment. A combination of several factors such as decrease in d[Cu(1)-(Sr/Ba)]; increase in cationic and chain oxygen ordering; psh and in-phase purity for the [AO] samples may account for the observed data.

Carbon nanotube‐supported bimetallic palladium–gold electrocatalysts for electro‐oxidation of formic acid

AbstractIt is known that palladium‐based catalysts are initially very active in direct formic acid oxidation but they suffer from fast deactivation caused by a strongly adsorbed CO intermediate. Reactivation of the catalysts involving application of anodic potential may cause palladium dissolution. The aim of the present study is to increase the stability and performance of palladium‐based catalysts in direct formic acid fuel cells (DFAFCs). Preparation and characterization of palladium/multiwalled carbon nanotubes (Pd/MWCNTs) and towards formic acid oxidation via different treatments are described. The catalysts were characterized by thermogravimetric analysis (TGA), X‐ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry (CV). It was shown that the Pd and Pd–Au MWCNTs supported catalysts after reduction in H2–Ar at 200 °C (R200 treatment) were highly active in formic acid electro‐oxidation, whereas the catalysts after heating in argon at 250 °C (C250 treatment) were inactive. The catalysts after hydrogen treatment have smaller metal particles and better contact with MWCNTs support. CV, simulating reactivation of the catalysts, showed that the Pd catalyst suffers from severe Pd dissolution, whereas for the Pd–Au selective leaching of Pd is considerably slower.

Magnetic enhancement upon heating of environmentally polluted samples containing haematite and iron

SUMMARY Pollution has become an increasing problem during the last several decades. Environmental magnetism provides a useful method for detecting and monitoring soil and sediment pollution. Thermomagnetic analysis is a conventional approach for identifying magnetic phases or possible thermal alterations in samples. Magnetic properties of samples are often enhanced after thermal treatment of environmentally polluted samples. In this study, we investigated the possible role of metallic iron for magnetic enhancement due to interaction between iron and haematite at elevated temperature. Our results show that synthetic samples containing both haematite and iron show significant magnetic enhancement upon heating in argon due to the neo-formation of magnetite. Moreover, magnetite formed during heating in argon is rather stable, whereas that produced upon heating in air is oxidized to haematite at higher temperatures. We found that a small amount of iron can induce significant transformation of haematite into magnetite upon heating in argon. Therefore, such a mechanism has to be considered for magnetic enhancement when conducting thermomagnetic analyses of environmentally polluted samples.

VO2(B) nanorods: solvothermal preparation, electrical properties, and conversion to rutile VO2 and V2O3

The solvothermal reduction of V2O5 by formaldehyde or isopropanol yields nanorods of the metastable, monoclinic VO2(B) phase. The structural transition in VO2(B), which occurs near room temperature, has been monitored using electrical resistivity measurements, performed both on pressed pellets of the nanorods as well as on nanorods dispersed on patterned contacts. A sudden, 105 increase in the electrical resistivity upon cooling below 290 K is seen in measurements on VO2(B) samples. Such a transition in the electrical resistivity has not previously been reported in this material. The transition is reminiscent of the metal-to-insulator transition observed in the case of pressed pellets of polycrystalline rutile VO2 upon cooling below 340 K. The metastable VO2(B) nanorods are converted to rutile VO2 by heating in argon, and to corundum V2O3 by reducing in 5%H2:95%N2. In both transformations, the structural integrity of the nanorods is compromised, with large, dense, rutile VO2 crystallites and less well-defined nanorods of V2O3 being formed.

Nickel Ferrite Aerogels with Monodisperse Nanoscale Building Blocks—The Importance of Processing Temperature and Atmosphere

Using two-step (air/argon) thermal processing, sol-gel-derived nickel-iron oxide aerogels are transformed into monodisperse, networked nanocrystalline magnetic oxides of NiFe(2)O(4) with particle diameters that can be ripened with increasing temperature under argon to 4.6, 6.4, and 8.8 nm. Processing in air alone yields poorly crystalline materials; heating in argon alone leads to single phase, but diversiform, polydisperse NiFe(2)O(4), which hampers interpretation of the magnetic properties of the nanoarchitectures. The two-step method yields an improved model system to study magnetic effects as a function of size on the nanoscale while maintaining the particles within the size regime of single domain magnets, as networked building blocks, not agglomerates, and without stabilizing ligands capping the surface.

Fabrication and Properties of Aluminum-Containing Silicon Carbide Fibres

By introducing hetero-element aluminum into ceramic precursor and then sintering, polycrystalline, stoichiometric SiC fibres can be prepared. Two types of aluminum-containing SiC fibres were fabricated by the use of aluminum-containing polycarbosilane (Al-PCS). The air-cured Al-PCS fibres were pyrolyzed in inert gas up to 13 50 °C to obtain SiC(OAl) fibres, which were converted into SiC(Al) fibres by heating in argon up to 1800 °C. The properties and performances of SiC(OAl) and SiC(Al) fibres were studied by chemical element analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), tensile strength test, heat resistance and creep resistance. These results show SiC(Al) are polycrystalline SiC fibres, have a near stoichiometric composition. The tensile strength, Young's modulus and diameter of the SiC(OAl) fibres are 2.6 GPa, 210 GPa, 12 μm, respectively. The tensile strength, Young's modulus and diameter of the SiC(Al) fibres are 2.1 GPa, 405 GPa, 10 μm, respectively. The SiC(Al) fibres have higher thermal stability, and better creep resistance than the SiC(OAl), the Nicalon and the Hi-Nicalon fibres.

Gas Chromatographic Analysis of Degassing of Aluminum and Aluminum Alloy Powders

Gas release behavior from aluminum and Al 7075 alloy powders during heating in argon was investigated by in-situ gas chromatography. Water vapor, hydrogen, carbon mono-oxide were detected as individual evolution spectra against heating temperature and time. The mechanisms of water and hydrogen evolutions were studied in detail for the determination of effective degassing condition. The adsorbed water and aluminum hydrate on the particle surfaces were considered to be the sources for the released water. Hydrogen peaks were formed from released gases through the reaction of aluminum and magnesium with adsorbed and hydrated water, and from liberated hydrogen that would have been excessively occluded during atomization. For the alloy powder magnesium was found to lower the hydrogen evolution temperature to enhance overall hydrogen release.

A thermogravimetric study of copper chlorination

The chlorination of metallic copper has been studied by thermogravimetry in the range of temperatures between 100 and 800 °C. The starting temperature for the reaction of copper with chlorine is determined at about 150 °C by non-isothermal measurements. For temperatures above 400 °C a methodology of heating in argon has been applied to decouple two processes taking place: decomposition of CuCl 2 and volatilization of CuCl. These experiments allow to determine the amounts of CuCl, CuCl 2 and Cu 3Cl 3(g) formed at each temperature. The activation energies for volatilization are obtained in chlorine and argon atmospheres. Finally, for temperatures below 250 °C the amounts of CuCl and CuCl 2 formed are calculated with mass balances. Observations in scanning electron microscopy (SEM) reveal that the different chlorides are formed in layers. A possible mechanism for the low temperature reaction is presented.

Molecular modeling and adsorption properties of porous carbons

In this work, we calculate the adsorption isotherms and isosteric heat of argon in molecular models of saccharose coke obtained via the Hybrid Reverse Monte Carlo method. In the first route (method A), the molecular models were built by considering only carbon atoms, and all other heteroatoms present were neglected. In the second route (method B), the molecular models were built by considering carbon and hydrogen atoms. We find that the models obtained via method B have smaller pores as compared to the models obtained via method A. This is reflected in the adsorption properties. The amount adsorbed is less in models obtained via method B as compared to method A. We also find that the isosteric heat calculated in the models obtained via method B match the experimental data more closely as compared to models obtained from method A.

Products of CuO heating in argon

Thermodynamic modeling is used to determine the composition of condensed products of CuO heating in argon at a pressure of 9.8066 × 10−2 MPa in the temperature range 300–1900 K. The formation of solid and liquid solutions with the participation of CuO, Cu2O, Cu2O3, Cu3O2, and Cu4O3 is analyzed.