Heating In Argon Research Articles

Effect of oxygen and nitrogen sensitization on structural, optical and electrical properties of PbSe thin films

An effective two-step sensitization technique was implemented in PbSe thin films, leading to a remarkable improvement in the optoelectronic performance of PbSe photodetectors. The phase composition, surface and cross-sectional morphology, temperature-dependent carrier concentration and mobility as well as the detectability of PbSe films after sensitization were systematically investigated using characteristic techniques. The optimal PbSe film oxygen sensitized at 450 °C exhibited a room-temperature photodetection with a carrier concentration of 5.31 × 1016 cm−3, carrier mobility of 16.52 cm2/V−1s−1, and detectivity of 2.25 × 109 Jones. High-temperature argon heat treatment and oxygen sensitization of PbSe films are expected to suppress recombination losses and significantly improve the optoelectronic properties of sensitized PbSe films due to enhanced carrier separation and transport. The enhanced photoresponse mechanism of the PbSe films through two-step sensitization method was also discussed. These results suggest that the proposed method can be applied to high-performance lead selenide photodetectors.

Knock control in hydrogen-fueled argon power cycle engine with higher compression ratio by water port injection

Hydrogen-fueled Argon Power Cycle engine is a novel concept for high efficiency and zero emissions, which chooses high specific heat ratio argon‑oxygen mixture as working fluid. However, the low specific heat of argon also increases the in-cylinder temperature, causing severe knock, which limits the efficiency of the engine. A typical knock-limited compression ratio for a hydrogen port-injected Argon Power Cycle engine is about 5.5:1 if no specific method is used. This article presents experimental research on the effect of water port injection under 1000 r/min at a compression ratio of 9.6:1 with IMEP ranging from 0.1 to 0.6 MPa and argon ratios of 79%, 85%, and 90%. The net indicated thermal efficiency peaks at 53.50% without a water injection but the knock intensity reaches 3.4 MPa. With the water injection, 16 mg/cycle water is sufficient to eliminate knock and the maximum net indicated thermal efficiency slightly reduces to 52.41%. With the water increased to 51 mg/cycle, a maximum IMEP of 0.64 MPa is achieved with an argon ratio of 85%. Argon ratio shows a marginal effect on the peak net indicated thermal efficiency, but the diagram factor is lower with higher argon ratios. At peak net indicated thermal efficiency conditions of different argon ratios, the diagram factor of Argon Power Cycle engine ranges from 76% to 80%, while a typical diagram factor of an air-breathing hydrogen engine can reach 90%. Both argon‑oxygen and air-breaching hydrogen engines can currently achieve the indicated thermal efficiency of over 52%, but the Argon Power Cycle engine shows a greater potential for further efficiency improvement. This paper suggests that the water injection is a feasible method for the knock suppression of the Argon Power Cycle engine with a marginal negative effect on efficiencies.

Synthesis and thermal behavior of RAFT-based copolymers of acrylonitrile and 1-vinylimidazole

The copolymers of acrylonitrile and 1-vinylimidazole with a narrow molecular weight distribution (MWD) were synthesized for the first time by the reversible addition–fragmentation chain transfer (RAFT) polymerization in a DMSO solution in the presence of acetic acid. Their thermal behavior difference upon heating in argon and in air along with ability to melt make them promising precursors for carbon fiber production.

Thermodynamic evaluation of a pumped thermal electricity storage system integrated with large-scale thermal power plants

The use of renewable energies is an alternative for decarbonizing the electricity generation sector and thus large-scale energy storage systems are required. The purpose of the present study is to assess the performance of the emerging Pumped Thermal Electricity Storage (PTES) systems and their integration with thermal power plants (TPP). A suitable thermal storage system (TES) has been extensively studied and five alternatives for the simulation of two-tank molten salt storage are implemented. Several options for the charge and discharge systems are modeled. The Round-Trip-Efficiency (RTE) is evaluated and accompanied by the power and energy density. A sensitivity analysis is performed by varying the main operational parameters to evaluate different utilization scenarios. The results are compared with the reported performance of commercial systems. The RTE of the integrated PTES configurations is around 50%–65% and high values of energy and power density can be achieved. For Rankine cycle configurations, the argon heat pump is recommended. Reusing old coal power plants, while plausible for reducing costs, results in moderate RTEs. In modern supercritic Rankine cycles, the reachable RTE is greater than 63%. RTE in Brayton and air heat pump configurations is similar, especially over 700°C at the discharge. However, it is highly sensitive to other operational parameters, and the energy density is significantly lower. Therefore, a more suitable TES system is required. Compared to commercial technologies, the system studied has the potential of being implemented if energy and power density are exploited to produce cost-effective systems.

Probing the transient evolution and heat transfer of nascent liquid film during initial condensation

A hybrid theoretical and simulation method is employed to investigate the transient characteristics of heat and mass transfer of nascent liquid film during initial condensation of argon vapor on a subcooled substrate. The method combines a non-equilibrium thermodynamics analysis with molecular dynamics simulations to provide the kinetics and evolution of the atoms. Throughout the evolution process, three different stages can be recognized by the variation of interfacial mass flux. Initially, the solid-vapor interfacial effect is dominated and the argon atoms are adsorbed as clusters and aggregate on the surface. In the transition stage, the mass flux increases and the adsorption behavior almost vanishes, a nascent liquid-like film is formed. When the times exceed a critical value of tc, the condensation process is initiated and the solid-vapor interface is replaced by the vapor-liquid interface. As a result, the mass flux keeps constant. During the adsorption process, the driven force of is theoretical determined through the cluster evolutions. With the decrease of cooling temperature, the mass flux is enlarged and the time for the transition becomes earlier. The mass flux determined from MD simulations coincides well with the theoretical analysis from statistical rate theory. Meanwhile, the spatial evolutions of the atoms are also traced. The atoms in the near wall region present a crystal-like structure. Compared with that in bulk vapor phase, the atoms in the liquid film have a stronger mobility. For the heat and mass transportation, the interfacial temperature jump and the thermal resistance is increased with the increase of cooling temperature. Two independent methods are adopted to obtain the heat and mass fluxes. The slop of the relationship between the heat and mass fluxes shows close agreement with the latent heat of argon, which reveals the occurrence of condensation.

ADSORPTION OF 4-CHLORPHENOL BY BROWN COAL ACTIVATED BY POTASSIUM HYDROXIDE

The purpose of work is to evaluate the 4-chlorophenol (CP) adsorption capacity of brown coal activated carbons (ACs) prepared at different temperature of KOH activation. ACs were obtained in three stages: 1) impregnation of coal with a KOH solution, 2) heating (4 deg/min) in argon to a given temperature t (400-800°C) and exposure for 1 h, 3) cooling, washing from KOH, drying. The samples are designated as AC(t). Based on the N2 adsorption-desorption isotherms, the ACs total pore volume (Vt, cm3/g) and specific surface area (S, m2/g) were determined. The ACs adsorption capacity were measured at 25°С, CP concentration ≤700 mg/L, АC dosage – 1 g/L.
 The alkaline activation temperature was found to be a key factor in forming porosity of ACs and ability to adsorb CP. The CP maximum capacity (ACP(m), mg/g) increases 6.6 times up to 307 mg/g for AC(800) having S=1142 m2/g. The specific adsorption capacity (ACP(S) = ACP(m)/S, mg/m2) sharply decreases in a sample range from AC(400) to AC(550) and weakly depends on temperature at 550-800°C. The kinetics of CP adsorption is best described by a pseudo-second order model. The rate determining stage is the interaction of CP molecules with AC surface. The CP adsorption isotherms are best described by the Langmuir model.
 The dependence of the ACP(m) from S can be approximated by three linear equations that probably correspond to the three regions of forming surface adsorbtion centers (AdCs). The first (S≤370 m2/g) is characterized by a small adsorption capacity increment (kS=0.103 mg/m2), but a significant (16.4 times) decrease in the specific capacity ACP(S). In the second region (S=370-770 m2/g, t=550-750°C), capacity increment is 10 times more (kS=0.985 mg/m2) and in the third region (S≥770 m2/g, t≥750°C) the increase in CP capacity is the smallest (kS=0.067 mg/m2). The thermoinitiated formation of AdCs is assumed to be not proportional to the increase in surface area, and their chemical structure and reactivity is determined by the alkaline activation temperature.

Phase transitions in the Fe/NH3/H2 and Fe-N systems

In the article, based on the literature, the phase changes in iron nitrides on iron powders and on solid samples were discussed. Phase transformations in NH3/H2 atmosphere and in inert atmospheres are discussed. The similarity of phase transformations in different atmospheres used during annealing were indicated. The conditions of phase transformations in iron nitrides during annealing in NH3/H2 atmosphere, argon and vacuum were discussed. Phase transformations occurring during annealing in the NH3/H2 atmosphere are reversible and there is a hysteresis phenomenon. During the phase transformation ɛγ' in the NH3/H2 atmosphere until the transformation is completed, nitrogen emission to the atmosphere takes place. On the other hand, the condition for the course of the transformation of γ'ɛ is the nitrogen flow from the atmosphere to the surface. Phase changes during heating in vacuum and argon are irreversible. During continuous heating at a rate of 30 K / min in vacuum and argon, nitrided iron powders, two phase transformations may occur, which are not accompanied by weight loss, the first (α+γ')γN in the temperature range 540÷550°C in a vacuum and 620÷630°C in argon and the second (γ+γ')ɛ in the range of 610÷620°C in vacuum and 690÷710°C in argon. In the case of heating in argon, the onset of weight loss was recorded at a temperature of about 860°C. Whereas in vacuum the denitration of nitrogen austenite γN ends at this temperature. During annealing at the temperature of 360°C, the phase change ɛγ′ in the ɛ/γ′ layer is accompanied by an increase in the thickness of the γ′ phase, which is at the expense of the thickness of the ɛ zone, while the total thickness of the layer after the transformation is the same as its initial thickness. At the temperature of 420°C, after the completion of the γ′ transformation, the formed monophasic layer γ′ is thicker than the ɛ/γ′ layers in the initial state.

Morphology, Sizes and Oxidation of Composite Copper Nanopowders, Obtained by an Electron Beam with Different Energies

Copper nanopowders were obtained by the gas-phase method under the influence of an electron beam of different powers. Thermodynamic modeling of the phase equilibrium state of the Cu-O2-C system during heating in argon and atmospheric pressure was carried out using the TERRA software package. The obtained nanopowders of copper were studied by X-ray phase analysis and transmission electron microscopy. The morphology, structure, size distribution, and average size of copper nanoparticles are determined. The dependence of the content of copper oxides in a copper-containing nanopowder on the electron beam power has been established. It is shown that copper nanopowders obtained at high power are not oxidized.

Effect of the Phase Composition of a Titanium Nickelide-Based Alloy on the Formation of Liquid in Sintering

The formation of a liquid phase in titanium nickelide–based alloys, which are enriched in nickel (55.8–55.9 wt %) and abundant in Ti2Ni/Ti4Ni2Ox phase intermetallic particles, is studied. The phase transformations in the alloys are investigated during heating in argon and helium atmospheres in a temperature range of 900–1200°C by differential thermal analysis. The cause for the formation of liquid in the alloys in a gas medium is found to be their oxidation. Oxidation results in the redistribution of the main chemical elements of the alloy on its surface and the formation of titanium- and nickel-rich phases. This leads to the eutectic transformation TiNi + TiNi3 → L. On heating in a vacuum, the formation of liquid is possible only in the alloy characterized by a high volume fraction of Ti2Ni/Ti4Ni2Ox phase particles. The precipitation of the particles during melting of the alloy depletes its matrix of titanium; this leads to a substantial increase in the nickel content in the matrix as compared to the total nickel content in the alloy. This effect, likely in combination with oxidation, also initiates the eutectic reaction in heating. Liquid-phase (supersolidus) sintering is shown to be possible for titanium nickelide–based alloys due to the eutectic reaction.

Influence of Argon Heat Treatment on Structure, Critical Temperature, Magnetic Shielding and Irreversibility Line of Ln(SrBa)Cu3O6+z(Ln = Y, Eu)

Influence of Argon Heat Treatment on Structure, Critical Temperature, Magnetic Shielding and Irreversibility Line of Ln(SrBa)Cu3O6+z(Ln = Y, Eu)

Lattice Deformation and Improvement Oxidation Resistance of Ti-6Al-4V Alloy Powders Prepared by Hydrogen Added Argon Heat Treatment

In the present work, a new hydrogen added argon heat treatment process that prevents the formation of hydrides and eliminates the dehydrogenation step, is developed. Dissolved hydrogen has a good effect on sintering properties such as oxidation resistance and density of greens. This process can also...

Role of thermal effects in neon and argon constricted discharges

The paper is aimed at investigating the role of inhomogeneous heating of the neutral gas in a constricted glow discharge in neon and argon. It is shown that inhomogeneous heating is not the primary cause of constriction in specified gases at pressures of tens and hundreds Torr cm and reduced currents not exceeding 100–200 mA cm−1. Constriction of the positive column occurs even with an insignificant gas heating in a pulsed regime. An abrupt constriction is caused by the nonlinear dependence of the ionization number on the electron density. In mentioned discharge conditions the frequency of electron–electron collisions is comparable to the electron energy relaxation frequency due to elastic electron-atom collisions. Thermal effects play a secondary role in the formation of a constricted discharge. At the same time, inhomogeneous gas heating in argon is more notable than in neon. Unlike neon, stationary argon discharge loses spatial stability in a vertically oriented tube as the pressure and current increase and a buoyancy effect takes place in a horizontal orientation. Such difference in the behavior of constricted neon and argon discharges is mainly caused by the difference in shape of elastic electron-atom collision cross sections. Interferometric methods allowed to study the temperature field of neutral atoms, dynamics of both gas heating and ascent of constricted cord. Observed effects are interpreted on the basis of the heat equation and the Navier–Stokes equation. Comparison of experimental and theoretical results shows good agreement.

Surface Characterization of Depleted Uranium–Molybdenum to Determine Surface Coating Compatibility

Scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy have been used to characterize the surface of depleted uranium molybdenum (DU-Mo) alloys as a chemical surrogate to determine potential challenges with the surfaces of manufactured and stored U-Mo foils and powders. Even when stored and shipped in an inert atmosphere, U-Mo has a tenacious surface contamination of oxygen and carbon. The 8 at. % molybdenum (DU-8Mo) powder and 10 at. % molybdenum (DU-10Mo) foil samples have surface contamination of oxygen and carbon in different ratios that is hundreds to thousands of nanometers thick. The DU-8Mo powder sample has been stored in an inert atmosphere and as a result has a lower carbon-to-oxygen ratio at the surface than the DU-10Mo foil sample that was stored in air. This surface contamination has not been removed by up to 20 min of argon ion sputtering nor with 5% hydrogen in argon heat treatment for up to 96 h at 950°C.

Orthorhombic YBCO-123 ceramic oxide superconductor: Structural, resistive and thermal properties

Two YBa2Cu3O7-x materials (YBCO-I sintered at 1000 °C, and YBCO-II sintered at 960 °C and following special cooling programs) belonging to the orthorhombic system were obtained. YBCO-I has a complete volume texture, while for YBCO-II it is only on sample surface. On heating in air (with 10 K min−1 in the temperature range 20–1000 °C), two endothermic processes are recorded on DSC curves (of YBCO-II) and they are due to oxygen diffusion from O1 to O5 sites, and then to the release into the environment; second endothermic effect is attributed to the decomposition reaction. Different behaviour is encountered on heating in argon: an endothermic process in two steps; continuous mass decrease (oxygen loss) during argon cooling is recorded on the thermogravimetric curve. In argon atmosphere, the obtained material shall correspond to the chemical composition: YBa2Cu3O6.77, while in air atmosphere, the maximal composition than may be obtained is: YBa2Cu3O6.88. The barrier energies from Arrhenius plots of resistivity vs. temperature (91–93 K) show 2D (YBCO-I) and 3D (YBCO-II) behaviour for the thermally activated flow of melted vortex lattice, below the critical temperature.

Features of the Interaction and Phase Formation in the WC–Fe2O3–C System When Heated in Vacuum and in Argon

Special features of the interactions and phase formations in carbide-oxide mixture WC 33.5 wt % Fe2O3 and in the WC–Fe2O3–C system when heated in vacuum and in argon have been studied. To add free carbon into carbide-oxide mixture, the K354 soot and saccharose, which dissociated when heated to high-clean carbon. It is established that at the absence of free carbon in the carbide-oxide system the active interaction between carbon of tungsten carbide and oxygen of iron oxide takes place that shows up in the weight loss of the samples. As a results there form the phase of the intermetallide Fe7, W6, the phase with a structure of the FeWO4 and W. The addition of free carbon allows keeping tungsten carbide partly or completely and reducing iron from oxide. At the lack of free carbon some part of the tungsten carbide carbon starts to interact with oxygen and the Fe3W3C complex carbide forms in the system, at the excess of carbon the tungsten carbide retained and the bcc-iron forms. The heating in vacuum differs from the heating in argon by two indications: to remove the same amount of oxygen is spent more carbon than in heating in argon; the temperature of the active interaction of carbon with oxygen decreases. The largest (by 300°C) decrease of the temperature is observed when the saccharose is used as the source of free carbon.

Thermal behavior and decomposition of cerium(III) butanoate, pentanoate and hexanoate salts upon heating in argon

The thermal behavior and decomposition of Ce-butanoate monohydrate (Ce(C3H7CO2)3·H2O), Ce-pentanoate (Ce(C4H9CO2)3) and Ce-hexanoate (Ce(C5H11CO2)3) were studied in a flow of argon while heating at 5°C/min. By means of several techniques such as simultaneous TG-DTA, FTIR evolved gas analysis, in-situ x-ray diffraction using a synchrotron source and hot-stage microscopy, it was found that all three compounds undergo melting transitions prior to decomposition and that decomposition involves intermediate stages including at least a Ce2O(CnH2n+1CO2)4 intermediate (n=3, 4 or 5 for Ce-butanoate, pentanoate or hexanoate respectively). The final decomposition product consists of CeO2, which is formed through a Ce-oxycarbonate. The Ce3+→Ce4+ oxidation seems to proceed via Ce2O3 that first results from the decomposition of the oxycarbonate phase. During the whole decomposition process, the evolved gas species consist of CO2 and symmetrical ketones.

Mechanical and Transport Properties of Argon Annealed Y1 − x Ca x :123 Superconductors

We report here the effects of argon heat treatment at 450 ∘C for 12 h on two similar sets of oxygenated Y1 − xCax:123 superconducting samples prepared by two different heat treatments and oxygen purity as reported by Sedky and Abu-Ziad (Physica C 470, 659; 12). The oxygenated samples are called ssqHp, sssHp, ssqLp, and sssLp, and the Ar annealed samples are called ssqHpAr, sssHpAr, ssqLpAr, and sssLpAr. It is found that the c parameter of annealed samples is gradually increased with Ca addition for all samples, while orthorhombic distortion (OD) is decreased. It is also noted that Ar heat treatment decreased the link between superconducting grains for all samples, and a linear decrease in microhardness (Vickers hardness number (VHN)) with Ca addition is obtained. But the rate of increase/decrease of the c parameter, OD, and VHN against Ca content is different in ssqHpAr and sssLpAr samples as compared to sssHpAr and ssqLpAr samples. Interestingly, the sssHpAr and ssqLpAr samples show a considerable loss of oxygen and small decrease in Tc. While the ssqHpAr and sssLpAr samples show much smaller loss of oxygen and a gradual increase in Tc up to 16 and 17 K, respectively. These results are discussed in terms of the mechanism of oxygen loss by Ca in addition to ssqHpAr and sssLpAr samples as compared to sssHpAr and ssqLpAr samples.

Phase Transformations in Nitrided Iron Powders

Phase transformations in nitrided iron powders are studied under heating in vacuum and argon by the methods of thermal x-ray imaging and synchronous thermal analysis. The ranges of thermal stability of the nitride phases and nitrous austenite are determined.

Thermal analysis of heat and power plant with high temperature reactor and intermediate steam cycle

Abstract Thermal analysis of a heat and power plant with a high temperature gas cooled nuclear reactor is presented. The main aim of the considered system is to supply a technological process with the heat at suitably high temperature level. The considered unit is also used to produce electricity. The high temperature helium cooled nuclear reactor is the primary heat source in the system, which consists of: the reactor cooling cycle, the steam cycle and the gas heat pump cycle. Helium used as a carrier in the first cycle (classic Brayton cycle), which includes the reactor, delivers heat in a steam generator to produce superheated steam with required parameters of the intermediate cycle. The intermediate cycle is provided to transport energy from the reactor installation to the process installation requiring a high temperature heat. The distance between reactor and the process installation is assumed short and negligable, or alternatively equal to 1 km in the analysis. The system is also equipped with a high temperature argon heat pump to obtain the temperature level of a heat carrier required by a high temperature process. Thus, the steam of the intermediate cycle supplies a lower heat exchanger of the heat pump, a process heat exchanger at the medium temperature level and a classical steam turbine system (Rankine cycle). The main purpose of the research was to evaluate the effectiveness of the system considered and to assess whether such a three cycle cogeneration system is reasonable. Multivariant calculations have been carried out employing the developed mathematical model. The results have been presented in a form of the energy efficiency and exergy efficiency of the system as a function of the temperature drop in the high temperature process heat exchanger and the reactor pressure.

Metal-Based Iodine Bearing Materials Prepared by Mechanical Milling

ABSTRACTRecent research has demonstrated that ternary aluminum-boron-iodine (Al-B-I2) materials prepared by mechanical milling are effective in generating biocidal combustion products. Such reactive materials are of interest for the munitions aimed to defeat stockpiles of biological weapons. In this research, ternary Mg∙B∙I2 composites were synthesized using two-stage milling. The first stage consisted of a binary B∙I2 powder prepared by mechanical milling, followed by addition of magnesium for iodine stabilization. Specific compositions for each ternary material were varied. Stability of the samples was assessed by their heating in argon at a constant rate using Thermo Gravimetric Analysis (TGA) and observing weight loss. Oxidation of the prepared powders was also studied by TGA. Ternary Mg∙B∙I2 composite powders prepared by two-stage milling were more stable than any of the previously prepared iodine-bearing materials with the same concentration of iodine (20 wt %). Particle size distributions were measured using low-angle laser light scattering. Powders were ignited using in an air-acetylene flame and in a constant volume explosion apparatus. Particle burn times and temperatures were measured optically. Substantially longer burn times and lower temperatures were observed for the prepared materials compared to the reference pure Mg powder.