Inert Gas Pressure Research Articles

SHS metallurgy of nickel-based alloying compositions for the manufacture of high-temperature steels

The possibility of producing multicomponent master alloys with low-melting-point (Mg) and refractory (Ni, Mo, W) metals, which are used for the manufacture of high-temperature alloys in metallurgy, by SHS metallurgy is studied. The experiments are performed at a high inert gas pressure in a reactor. Highly exothermic powder mixtures of nickel oxide, molybdenum, tungsten, elementary magnesium, and elementary aluminum are used for synthesis. The experimental results demonstrate a strong effect of the ratio of the reagent masses, the gas pressure, and the magnesium and aluminum particle sizes on the laws of synthesis and the formation of the composition and microstructure of the end products.

The transition from spark to arc discharge and its implications with respect to nanoparticle production

The synthesis of nanoparticles by means of electrical discharges between two electrodes in an inert gas at atmospheric pressure, as driven by a constant current ranging from a few milliamps to tens of amps, is investigated in this work. An extensive series of experiments are conducted with copper as a consumable electrode and pure nitrogen as the inert gas. Three different DC power supplies are used to drive electrical discharges for the entire operating current range. Then, three electrical discharge regimes (spark, glow, and arc) with distinct voltage–current characteristics and plasma emission spectra are recognized. For the first time, nanoparticles are synthesized by evaporation of an electrode by atmospheric pressure inert gas DC glow discharge of a few millimeters in size. The discharge regimes are characterized in terms of the mass output rate and the particle size distribution of the copper aerosols by means of online (tapered element oscillating microbalance, TEOM; and scanning mobility particle sizer, SPMS) and offline (gravimetric analysis; small and wide angle X-ray scattering, SWAXS; and transmission electron microscopy, TEM) techniques. The electrical power delivered to the electrode gap and the gas flow rate are two major parameters determining the aerosol mass output rate and the aerosol particle size distribution. The mass output rate of copper aerosols raises from 2 mg h−1 to 2 g h−1 when increasing the electrical power from 9 to 900 W. The particle mean size (SMPS dg) varies between 20 and 100 nm depending upon the electrical power and the gas flow rate, whereas the particle size dispersion (SMPS σg) ranges from 1.4 to 1.7 and is only weakly dependent on the gas flow rate.

Thermodynamic parameters for the Ta–Cr–H solid solution from equilibrium (P–C–T) data

Isothermal pressure–composition–temperature, (P–C–T) equilibrium study for the solubility of hydrogen is investigated over the temperature range of (673 to 873)K to evaluate the relative change in Gibbs energy, enthalpy and entropy for the solution of hydrogen in the Ta–Cr solid solution alloys. The inert gas fusion technique and pressure drop method are used for hydrogen analysis. It is observed that the solubility of hydrogen in tantalum decreases as the Cr content increases. The change in hydrogen solubility in tantalum with increase in Cr content could be explained on the basis of change in strain energy of dissolved hydrogen due to presence of different size interstitial sites around a substituted atom and due to increase in e/a ratio and it may be attributed to repulsive interaction between H and Cr atoms. The exothermic heat of reaction is observed for solution of hydrogen in all the samples.

High-temperature synthesis of cast Cr2AlC at an inert gas overpressure

This paper reports the high-temperature synthesis of cast Cr2AlC from mixtures of chromium(III) oxide, chromium(VI) oxide, aluminum, and carbon at an increased inert gas (Ar or N) pressure in a 3-L self-propagating high-temperature synthesis reactor at an initial argon pressure pi = 5 MPa. The reaction products were characterized by X-ray diffraction and X-ray microanalysis. The results indicate that the ingots obtained under optimized conditions consisted of Cr2AlC and Cr3C2 with a ratio of about 85 : 15.

Terahertz Continuous Wave Detection Using Weakly Ionized Plasma in Inert Gases

A weakly ionized plasma detector was designed for the terahertz (THz) continuous wave detection. The effect of inert gas pressure, components, and discharge current on the detector's responsivity and stability was investigated. Experiment results reveal that the detector's responsivity can be as high as 194.4 V/W and its signal-to-noise ratio can reach 560 at 0.187 THz.

Modeling of the Mass Transport during Homo-Epitaxial Growth of Silicon Carbide by Fast Sublimation Epitaxy

Ballistic and diffusive growth regimes in the Fast Sublimation Growth Process of silicon carbide can be determined using suggested theoretical model for the mean free path calculations. The influences of temperature and inert gas pressure on the mass transport for the growth of epitaxial layers were analyzed theoretically and experimentally.

Pressure-induced evaporation dynamics of gold nanoparticles on oxide substrate

Here we report thermal evaporation dynamics of Au nanoparticles on single crystal oxide substrates, including MgO, SrTiO(3), and Al(2)O(3). The size reduction rate of Au nanoparticles via thermal treatments is strongly dependent on not only temperature but also pressure. Lowering the pressure of inert Ar gas from 10(5) to 10 Pa increases the size reduction rate over 30 times in the temperature range 800 °C-950 °C. The temperature dependence is solely due to the variation of saturated vapor pressure of Au, whereas the pressure dependence of the surrounding inert gas can be interpreted in terms of a pressure dependence on a gas-phase diffusion of evaporated Au atoms into the surroundings. We present a simplified model to explain an evaporation dynamics, which well describes the pressure dependence on a size reduction rate of Au nanoparticles. By utilizing this useful pressure-induced evaporation dynamics, we succeeded in manipulating a size reduction of Au nanoparticle arrays down to -10 nm diameter range from -300 nm initial size by programming sequentially a surrounding pressure.

A Study of Mass Transfer Kinetics of Carbon Dioxide in (Monoethanolamine + Water) by Stirred Cell

The gas phase resistance in a stirred cell was investigated to understand and avoid its influence on the measurement of the reaction kinetics. To validate the influence of gas phase resistance and the experimental conditions of pseudo first order reaction for Monoethanolamine (MEA) + CO2 system, low CO2 partial pressure under various inert gas pressure were employed for CO2 the absorption into 0.5, 1, 3 and 3.6M MEA solutions with H2O and ethyleneglycol as solvents, respectively. The absorption was investigated with the stirred cell based on a fall-in-pressure technique.

Elevated Temperature Forming of Titanium Aircraft Hardware

Titanium is difficult to fabricate into complex aircraft configurations. There is several elevated temperature forming techniques that are available to produce titanium components for aircraft, two of which will be discussed here: Superplastic Forming (SPF) and hot forming. SPF is used when complex shapes are required, for example, tight radii, and uses a tool that contains the required configuration and seals around the periphery so inert gas pressure can be used to form the material. Since SPF is a process where the material is stretched, the part is not a uniform thickness when completed. A variation of the process combines SPF with diffusion bonding (SPF/DB) of two or more pieces of titanium together to produce integrally stiffened structure containing very few fasteners. The hot forming process uses matched metal tools, offset by the thickness of the starting material, are used to form the part contour at elevated temperature. The required part geometry usually contains no sharp features that have to be formed. Since the material is free to move as the die is closed, the part is fairly uniform in thickness when completed.

SAW sensor based on highly sensitive nanoporous palladium thin film for hydrogen detection

Graphical abstractDisplay Omitted Highlights? SAWS with Pd nanoporous sensing material were investigated for H2 detection at RT. ? The sensitivity and LOD at RT was 0.31Hz/ppm and 48ppm respectively. ? Sensor response is proportional to the concentration and is reversible. ? For a concentration of 0.2-0.8H2 in air the response times were 15-44s. ? The sensors performance was improved using a nanoporous Pd layer deposited by PLD. Surface acoustic wave sensors (SAWSs) with nanoporous palladium (Pd) sensing material for hydrogen (H2) detection are reported. We fabricated sensors with a stable and fast response and with a high sensitivity for detecting H2 even at room temperature (RT). The fabricated sensors were 'delay line' type (quartz substrate, ~70MHz central frequency). The nanoporous sensitive layer was directly deposited onto a quartz substrate using the picosecond laser ablation method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to investigate the influence of different experimental conditions, such as laser power density and inert gas pressure, on the morphological proprieties of Pd thin films. The sensor performance (sensitivity, detection limit, and response time) at RT, for H2 concentrations in synthetic air between 0.008% and 2% were studied. We obtained a sensitivity and detection limit of 0.31Hz/ppm and 48ppm, respectively, for RT operation. The response time was between 15 and 44s for H2 concentrations between 0.2% and 0.8% in synthetic air.

Effect of Different Parameters on Synthesis of MoO3 Nanopowder by the Evaporation–Condensation Technique

In the present study, MoO3 nanopowder was produced by evaporation of molybdenum oxide powder at high temperature (around 1,000°C) and its subsequent cooling in inert gas. The effect of different parameters such as pressure, temperature, and type of inert gas on the morphology and particle size were examined. The samples were characterized in terms of structure, morphology, particle size, and surface area using complementary techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Brunauer–Emmett–Teller (BET) method. Particles of the synthesized nanopowder had spherical shape with specific surface area of 18.64 m2g−1 and the average diameter of about 31 nm in optimum conditions.

Effect of Ar Gas Pressure on Phase Separation of Tungsten Silicides Intermetallic Compound <i><i>In Situ</i></i> Self-Propagating High Temperature Synthesis-Casting Process

Tungsten silicides intermetallic compound (WSi2) was synthesized in-situ by self-propagating high temperature synthesis-casting of WO3-Si-Al system in Ar gas environment. It is proposed that the extent of phase separation between oxide ceramic and intermetallic compound depends on the reaction temperature that made a lower viscosity and longer lifetime of the melted. The effects of inert gas pressure on densification of the intemetallic product were investigated.

Burn-in and thermal cyclic tests to determine the short-term reliability of a thin film resistance temperature detector

In this paper, experimental data and theory are presented for two methods of the thermal failure of a multi-layer, thin film resistance temperature detector (RTD). The methods are: (i) while placed in a low pressure inert gas atmosphere, the temperature of the RTD was increased incrementally by means of joule heating until failure (burn-in test), and (ii) the RTD was thermally cycled in both a low-pressure inert gas atmosphere as well as in air at atmospheric pressure. The performance of the RTD was analyzed with respect to three factors: (i) changes in electrical resistivity with respect to temperature of the Ti–Cu–Ti trace that forms the conductive path of the RTD, (ii) degradation of the encapsulation layers, especially the Benzocyclobutene (BCB) with emphasis on its impact on radiation, and (iii) failure of the trace due to crack formation. Environmental effects on performance and probable causes of failure are discussed.

Pressure effects on HiPIMS deposition of hafnium films

High power impulse magnetron sputtering (HiPIMS) was studied during the growth of hafnium films at argon pressures ranging from 0.80 to 5.33Pa with a fixed pulse length (50μs) and frequency (200Hz). The effect of inert gas pressure on the plasma conditions and film structure was investigated. The peak target current increased with pressure, but its sensitivity decreased above 2.00Pa, which corresponded to an increased ratio of ions to neutrals in the plasma. A comparison of plasma characteristics between Hf and Ti HiPIMS growth was made. In addition to pressure, the target currents were affected by the physical properties of the target material, particularly the secondary ionization energy and atomic mass. Sputtering gas rarefaction phenomena were found to be more pronounced for Hf, and as a result, the process characteristics and film properties had a strong interdependence on argon pressure discussed in this study. The microstructure of the hafnium films was analyzed with scanning electron microscopy and X-ray diffraction. When compared to Hf films deposited by dc magnetron sputtering, the HiPIMS process resulted in a decreased grain size and promoted the growth of the (100) orientation in the Hf films. These results demonstrate that Hf HiPIMS sputtering regimes have much stronger dependence on the working gas pressure compared to titanium, and these need to be taken into account to ensure that films are dense and have the desired morphology and crystallographic orientation.

Electrical characterization of nanocrystalline zinc selenide thin films

In the present paper, we have studied the effect of photo-illumination on electrical properties of nanocrystalline ZnSe thin films. The ZnSe thin films with different grain sizes (coherently diffracting domains) have been prepared. The semiconducting material with the composition Zn25Se75 has been prepared using melt-quenching technique. Thermal evaporation technique has been used to prepare nanocrystalline ZnSe thin films on highly cleaned glass substrates at different partial pressures of Ar gas. The grain size has been controlled by the partial pressure of inert gas. The grain size has been calculated using X-ray diffraction plots. Mobility activation has been studied from the photocurrent decay curves. The effective density of states (Neff), frequency factor (S), and trap depth (E) have been calculated for all the films having different grain sizes. Three different types of trap levels have been found in these films. There is a linear distribution of traps having different energies below the conduction band. The increase in photoconductivity is explained in terms of built in potential barriers (ϕb) at the grain boundaries.

The effect of the operation modes of a gas discharge low-pressure amalgam lamp on the intensity of generation of 185 nm UV vacuum radiation

The effect of the discharge current, mercury vapor pressure, and the inert gas pressure on the intensity and efficiency of the 185 nm line generation are considered. The spectra of the UV radiation (vacuum ultraviolet) transmission by protective coatings from the oxides of rare earth metals and aluminum are investigated.

Deoxification of Liquids for Advanced Semiconductors Processing

Deoxification offers new opportunities in Back End Of Line (BEOL) and also in Front End Of Line (FEOL) to optimize transistor performance. This work presents how to treat ultra pure water (UPW), with and without chemistry, to decrease oxygen concentration to reach ultra low levels. A new approach for a deoxification system will be discussed to meet these upcoming requirements. By creating a semi-empirical model considering the permeation of oxygen through tubes back into the liquid, the necessary dimensions of the deoxification system can be predicted and the final concentration at the point of use (POU) calculated. Parameters like gas flow and liquid flow rate, material, grade of inert gas and system pressure were varied. The efficiency of measures to avoid oxygen permeation after the deoxification step is evaluated as well.

Combustion synthesis of lithium cobaltate

A feasibility of combustion synthesis of lithium cobaltate powders using oxide sources was investigated. Cobalt oxide Co3O4 and lithium carbonate Li2CO3 were used as starting reactants. Two different oxidizers were explored: (i) ammonia nitrate NH4NO3 and (ii) lithium nitrate LiNO3. Some organic reducers (ORs)—such as CH-polymers, melamine, urotropine, etc.—were used as a fuel. Investigated was the effect of green composition/density and inert gas pressure on combustion parameters (burning velocity and combustion temperature) and product micro structure/composition. Best results were obtained for LiNO3-Co3O4-OR blends. Relative green density ρ was found to have a crucial effect: good results might be obtained only for ρ > 65%. XRD data testified that the combustion products obtained in optimized conditions contained pure lithium cobaltate LiCoO2. According to SEM data, the obtained powders had a mean particle size of 20 μm.

Chemically activated combustion synthesis of MoSi 2/Al cermet foams

In this work the feasibility of synthesizing MoSi 2/Al cermet foam under the combustion mode was studied. A halogen containing organic polymer, namely, polytetrafluoroethylene (PTFE) was used as foaming agent. It was shown that the target product reached the maximum porosity, up to 70%, when amount of the foaming agent was 0.04 mol. SEM analyses have shown there are two types of pores (macro and micro) in the products with diameter 0.2–1 mm and 0.01–0.05 mm, respectively. It was established that the portion of macro- and micro-pores depends on the amount of foaming agents and the inert gas pressure. It was established that increase of the metal amount leads to the decrease of the porosity while the toughness increases.

Direct reduction of ammonium molybdate to elemental molybdenum by combustion reaction

Self-sustaining reduction of ammonium molybdate tetrahydrate (AMT) by mixture of zinc and magnesium is investigated. It is shown that utilizing mixtures of metallic reducers is an attractive methodology to control the reduction conditions and product characteristics. Optimal intervals of key parameters, e.g. composition of reducing mixtures and pressure of inert gas are determined. Analysis of combustion temperature profiles, XRD, SEM/FESEM, DTA, microanalysis, and quenching techniques are applied to investigate the reduction mechanism. Based on the obtained fundamental knowledge, for the first time, highly crystalline molybdenum powder with particle sizes in the range 0.1–1 μm is produced by direct reduction of AMT in a single-stage and energy saving process. Proposed combustion-based approach of Mo production has high potential to become an alternative to the conventional hydrogen reduction processes.