Hydrogen Plasma Arc Research Articles

Preparation of TiZrHfNbMo refractory high entropy alloy powder via hydrogen plasma-arc melting

Refractory high-entropy alloys (RHEAs) are a new type of metal materials composed of four or more refractory elements. However, the melting point and liquid viscosity coefficient of RHEAs are high, which leads to low fluidity. Therefore, powders of such alloys are difficult to prepare by conventional methods. In this study, a new method called a hydrogen plasma-arc melting has been developed for the preparation of RHEA powders. Results show that the TiZrHfNbMo RHEA powders have single body-centered-cubic (BCC) structures, consisting of a large number of irregularly-shaped powders and small numbers of spherical powders. The average particle size of the powder was 66.97 μm. There is no obvious composition segregation on the surface and inside of the RHEA powders. In addition, this method greatly reduces the oxygen content of the powders.

A Numerical Study on the Influence of External Magnetic field on Hydrogen Electric Arc Flow

We present a 3D numerical model capable of simulating hydrogen electric arc. The numerical model couples the electromagnetic field with hydrogen plasma arc dynamics (flow and heat transfer). Electric arc operates under the conditions of atmospheric pressure using direct current (DC) in the presence of external magnetic field. It is found that arc instabilities emerge spontaneously near the cathode before propagating downwards along the arc jet. Also, spontaneous splitting into several arcs is observed before merging again into one arc. The horizontal magnetic field induces arc skewing and directional flow perpendicular to the applied magnetic field. However, the axial magnetic field induces a rotational flow and arc swirling.

Residual hydrogen reduction and refining effect during two-step hydrogen-argon plasma arc melting of cerium

Herein, the two-step hydrogen-argon plasma arc melting technology (HPAM-APAM) namely hydrogen plasma arc melting (HPAM) followed by argon plasma arc melting (APAM), was put forward to successfully realize the application of HPAM on cerium refining. The residual hydrogen content was significantly decreased to 79 ppm with the increase of APAM time to 40 min. The contents of volatile impurities Li and Mg were greatly reduced to less than 0.1 ppm. Paradoxically, the contents of Ti and W with low vapor pressures could be reduced to 2 ppm, whereas the impurities Fe and Si with high vapor pressures were hardly removed. The analysis indicated that the reduction of W and Ti was ascribed to the formation of volatile WO3 and TiO, while the negligible reduction of Fe and Si was attributed to the strong interaction strength with cerium based on “alloy phase formation theory”. A new kinetic refining mechanism by the activated H during HPAM process was proposed. This work helps to extend HPAM to refine hydrogen absorbing metals and provides new insights into the removal mechanism of metallic impurities.

Hydrogen arc plasma promotes the purification and nanoparticle preparation of tungsten

As an important refractory metal, tungsten (W) has unique physical-chemical properties, and the applications of high-quality tungsten NPs with uniform particle size, high purity, and good particle dispersion in industrial fields are highly desirable. Herein, the integration of tungsten metallurgical purification and nanoparticle preparation is achieved by the hydrogen arc plasma method. In the process of purification, on the condition of arc current of 250 A, hydrogen concentrations of 30 vol%, purification time of 40 min, and gas pressure of 60 kPa, the highest impurity removal rate is achieved. The active H+ is able to react with impurities to generate metal hydride (MH, M = Al, Cr, Mg, and Fe), which promotes the removal rate of impurity elements. During the preparation of nanoparticles (NPs), the as-prepared tungsten NPs with an average particle size of 44.1 nm have a regular spherical structure, high purity, and a relatively uniform particle size distribution. When the hydrogen concentration is controlled at 50 vol%, the extremely high temperature promotes the evaporation of tungsten. Meanwhile, the active H+ reacts with tungsten to form tungsten hydride (WH), further increasing the evaporation rate of tungsten. According to the above results, the hydrogen arc plasma promotes the simplification of the production process steps of high purity tungsten NPs and reduces the industrialized production cost of high-quality refractory metal NPs.

Hydrogen Arc Plasma Promotes the Purification and Nanoparticle Preparation of Tungsten

Hydrogen Arc Plasma Promotes the Purification and Nanoparticle Preparation of Tungsten

The influence of a magnet field on sulfur removal from liquid iron by hydrogen plasma arc melting

In this work, the static magnetic field was applied to plasma arc melting (PAM) method. The influence on sulfur removal from iron by Ar-20%H2(PAM) was investigated experimentally. The results show that, sulfur content decreases more noticeably with the magnet field. The mechanism of sulfur removal by hydrogen plasma arc melting (HPAM) was found to obey a first-order rate law. From kinetic analysis, the adoption of magnet field enhanced purification efficiency about 45% under the same conditions. The numerical simulations were necessarily carried out to investigate the fluid flows of the melt. The results show that the magnet field changes the flow regime and strengthens the flow velocity of the melt. Moreover, the dead zone in melt by typical HPAM was eliminated. It is reasonable that dissolved sulfur atoms transferring to the top interface to react with active hydrogen atoms was promoted. In addition, during solidification process, thermoelectric magnetic (TEM) flows promote solute atoms that discharged from the solid–liquid interface moving to the upside of specimen. As a consequence, iron with much lower sulfur content could be obtained at the bottom of specimens, and sulfur removal was enhanced further during solidification under a static magnetic field.

Effect of hydrogen on interfacial reaction between Ti-6Al-4V alloy melt and graphite mold

In this paper, the effect of hydrogen on the interfacial reaction between Ti-6Al-4V (Ti64) alloy and graphite casting mold was studied by argon and hydrogen plasma arc melting. The experimental results showed that the thickness and the hardness of the interfacial reaction layer decreased with increasing hydrogen partial pressure. The interaction of activated H atoms in the titanium alloy melt and carbon on the interface, [C] + 4[H] = CH4, could be taking place.

Impurity Removal and Microstructural Analysis of Inconel 718 Refined by Hydrogen Plasma Arc Melting

The high-temperature melting and the removal of gaseous and metallic impurities from Inconel 718 by hydrogen plasma arc melting (HPAM) were investigated. Solid-type Inconel 718 scraps were used as raw material. The concentrations of oxygen, nitrogen, and metallic impurities in the scraps were simultaneously decreased by HPAM. The refined ingot satisfied the recommended criteria for commercial Inconel 718. Following the melting of Inconel 718 by HPAM, the microstructure of the as-cast depended on different parts of the ingots, due to the different cooling rate of each part.

Refining effect of TiAl intermetallic compounds prepared by hydrogen plasma arc melting from scraps of Ti–Al mixture

TiAl intermetallic compounds were prepared using scraps of a Ti-40at%Al mixture via hydrogen plasma arc melting (HPAM) and the refining effect was investigated. HPAM was performed under atmospheric pressure condition, which was satisfied by introducing an Ar + 20 vol%H2 gas mixture in a vacuum atmosphere. The mixture scraps and the prepared TiAl intermetallic compounds ingots were analyzed using X-ray diffraction analysis, oxygen/nitrogen analyzer, and glow discharge mass spectrometry. As a result of the study, the separated Ti and Al were dissolved and only γ-TiAl phase was observed. The oxygen concentration of the TiAl intermetallic compounds decreased with the increase in melting time. The plane spacing and lattice parameter decreased owing to the oxygen reduction from the γ-TiAl phase in the refined TiAl intermetallic compounds. The concentration of impurities of the refined TiAl intermetallic compounds for 30 min was 49.35 ppm, which showed a removal degree of 65.52% compared with that of the mixture scraps.

Application of hydrogen for rare-earth gadolinium purification and thermodynamic simulation of system

Due to the extremely high chemical reactivity of gadolinium (Gd), especially the removal difficulty of trace impurities, preparation of ultra-high purity Gd is challenging. Herein, we introduce H2 into Ar plasma arc, building a reductive gas flow with high-density thermal energy. H2 + Ar plasma arc melting performs a wonderful refining effect despite of high initial concentrations. Migration ways and removal mechanism of various impurities have been systematically analyzed. Electromagnetic driving force and turbulence thermal flow of the hydrogen plasma arc are numerically simulated. Results show that activated hydrogen ions, dissociated in plasma arc and bringing special physical and chemical interactions, are supposed to be the cause for the excellent refining effect.

Manganese Removal from Liquid Nickel by Hydrogen Plasma Arc Melting.

In this work, the removal of manganese from nickel melts by Ar and (10%, 20% and 40%) H2 plasma arc melting under various pressures (0.01–0.02, 0.04–0.05 and 0.09–0.1 MPa) was investigated experimentally. The results show that only a slight reduction in the manganese content is obtained by Ar plasma arc melting (PAM). By contrast, the manganese content of liquid nickel decreases noticeably upon the addition of hydrogen to plasma gas, and the rate of manganese removal increases with increasing hydrogen volume fraction. In addition, the reduction in the pressure enhances the efficiency of manganese removal from liquid nickel by hydrogen plasma arc melting (HPAM). The process of manganese removal by HPAM was found to obey a first-order rate law. From kinetic analysis, the rate of reduction in the manganese content increases proportionally to the 0.73–0.75th power of the hydrogen volume fraction in the plasma gas. However, the rate of the manganese content reduction increases proportionally to approximately 0.88th power of %H2 in the plasma gas for the initial manganese content of 0.89 mass%, which is slightly higher than that for the initial manganese concentration of 0.45 mass%. Thermodynamic analysis indicates that the volatilization of manganese benefits from negative pressure and the presence of active hydrogen atoms that act as the transfer media of the metal vapor in the gas boundary layer.

Thermodynamic of Liquid Iron Ore Reduction by Hydrogen Thermal Plasma

The production of iron using hydrogen as a reducing agent is an alternative to conventional iron- and steel-making processes, with an associated decrease in CO2 emissions. Hydrogen plasma smelting reduction (HPSR) of iron ore is the process of using hydrogen in a plasma state to reduce iron oxides. A hydrogen plasma arc is generated between a hollow graphite electrode and liquid iron oxide. In the present study, the thermodynamics of hydrogen thermal plasma and the reduction of iron oxide using hydrogen at plasma temperatures were studied. Thermodynamics calculations show that hydrogen at high temperatures is atomized, ionized, or excited. The Gibbs free energy changes of iron oxide reductions indicate that activated hydrogen particles are stronger reducing agents than molecular hydrogen. Temperature is the main influencing parameter on the atomization and ionization degree of hydrogen particles. Therefore, to increase the hydrogen ionization degree and, consequently, increase of the reduction rate of iron ore particles, the reduction reactions should take place in the plasma arc zone due to the high temperature of the plasma arc in HPSR. Moreover, the solubility of hydrogen in slag and molten metal are studied and the sequence of hematite reduction reactions is presented.

Mechanism of Desulfurization from Liquid Iron by Hydrogen Plasma Arc Melting

In this study, desulfurization from liquid iron by Ar and (10 to 40 pct)H2 + Ar plasma arc melting (HPAM) was examined. The experimental results show that the rate of desulfurization increases as hydrogen is added proportionally to plasma gas. The thermodynamic analysis suggests that the interaction of activated atomic hydrogen and dissolved sulfur in liquid iron, $$ \left[ {\text{S}} \right] + 2{\text{H}} = {\text{H}}_{ 2} {\text{S}}, $$ could be taking place. The kinetic analysis confirms that the desulfurization from liquid iron obeys a first-order rate law.

Deep deoxidization from liquid iron by hydrogen plasma arc melting

In the present study, removal of oxygen from liquid iron by Ar and (10%–40%) H2 plasma arc melting have been investigated experimentally. It is shown that the reduction of oxygen content is slight when the plasma gas was argon only. However, the oxygen content of the iron melt decreases sharply when adding hydrogen in plasma gas, and the rate of deoxidization increases with the hydrogen content. The final oxygen content can be as low as 1 ppm after hydrogen plasma arc melting (HPAM) with 40% H2 in plasma gas. The deoxidization from the iron melt by HPAM was a two-steps process: the fast 1st step and the slow 2nd step. From kinetic analysis, the oxygen removal by HPAM was found to obey a first-order rate law. In the 1st step, the reduction rate of oxygen increases proportionally to the approximately 0.44th power of the hydrogen volume proportion in plasma gas. The deoxidization process can be expressed as the following reaction: [O]+2H=H2O. The thermodynamic analysis indicates that deoxidization power of atomic H is higher than that of molecular H2.

A simplified model for the determination of current-voltage characteristics of a high pressure hydrogen plasma arc

This paper focuses on the modeling of a hydrogen arc column at very high pressure (20 bar). The problem is solved from Elenbaas-Heller equation where the radiation is carefully considered with the net emission coefficient. The absorption spectrum requires the integration of background continuum, molecular bands, and line spectra. This work directly aims to predict the electric current-voltage characteristics which is key for the design of new processes. We propose also a new analytic solution which generalizes the channel model of electric arc to the case when the volume radiation makes a significant contribution to the energy balance. The presented formalism allows a better determination of the plasma thickness parameter Rp for net emission coefficient method in cylindrical arcs and gives satisfactory results in comparison to earlier experimental works on high pressure hydrogen plasma.

Separating Technology of Pure Zirconia from Zircon-Sand by the Ar-H<sub>2</sub> Arc Plasma Fusion and the Microwave Leaching

Zirconia (ZrO2) has excellent properties such as high toughness, high strength, thermal stability and high corrosion resistance. Thus, recent zirconia has been spotlighted as a dental material. Most of pure zirconia has been separated from zircon sand (ZrSiO4) by wet refining process which is very complex and not an environmental. The arc plasma fusion method has the advantages as a sustainable process that can easily and quickly get very good fine and high pure powders from the original materials compared with traditional wet method. In this study, zircon sand is separated into zirconia and silica by using the Ar-H2(hydrogen) arc plasma refining. And then silica is removed from it by the microwave leaching method to produce a high pure zirconia. Argon gas, hydrogen gas, copper anode and tungsten cathode are used for the plasma arc generation. To facilitate zirconia and silica separation, carbon of 1-3molar ratios are added with zircon sand. Plasma melting were sequentially conducted two processes. After a reduction process using Ar gas only, it was refined using a mixed gas of Ar-H2. After melting and water cooling in chamber, the solid phases composed with zirconia and silica were obtained at 240 ̊C, and 20% sulfuric acid solution was used as the leaching materials to obtain a high purity zirconia (more than 99%).

A New Process of Manufacturing “Oxygen-free” Gd

“Oxygen-free” Gd was fabricated by hydrogen plasma arc melting (HPAM). The HPAM is more different than the traditional Ar plasma arc melting (PAM) in Oxygen removal. It is attributable to the hydrogen atoms dissociated and activated in high temperature HPAM. In addition an increased diffusion of oxygen in Gd-O solid solution to the surface also plays an important role in removal of oxygen. The substances are confirmed by optical emission spectroscopy (OES), which are involved in the plasma like Ar I, Ar II and H I and some possible reactions. The effect of H with thermodynamic estimation was discussed in detail.

Optimization of the plasma parameters for the high current and uniform large-scale pulse arc ion source of the VEST-NBI system

A large-scale hydrogen arc plasma source was developed at the Korea Atomic Energy Research Institute for a high power pulsed NBI system of VEST which is a compact spherical tokamak at Seoul national university. One of the research target of VEST is to study innovative tokamak operating scenarios. For this purpose, high current density and uniform large-scale pulse plasma source is required to satisfy the target ion beam power efficiently. Therefore, optimizing the plasma parameters of the ion source such as the electron density, temperature, and plasma uniformity is conducted by changing the operating conditions of the plasma source. Furthermore, ion species of the hydrogen plasma source are analyzed using a particle balance model to increase the monatomic fraction which is another essential parameter for increasing the ion beam current density. Conclusively, efficient operating conditions are presented from the results of the optimized plasma parameters and the extractable ion beam current is calculated.

Purification of terbium by means of argon and hydrogen plasma arc melting

The refining of terbium (Tb) by plasma arc melting using pure Ar and Ar + H2 mixture was examined, respectively. The temperature distribution and gas flow of the plasma arc during the melting process were simulated. The residual metallic impurities were examined by inductively coupled plasma-atomic emission spectrometer. Experimental results show that both methods of argon plasma arc melting (APAM) and hydrogen-argon plasma arc melting (HAPAM) can lead to a good removal of metallic impurities despite of high initial concentrations. HAPAM displays a better refining effect of Tb metal. Activated hydrogen atoms dissociated in high temperature plasma arc, bringing on special chemical interactions, are supposed to be the cause for the wonderful refining effect. The detailed behaviors of impurities and hydrogen atoms are discussed systematically in this study.

Preparation of 6N grade silicon ingot by combined purification processes from waste silicon cutting sludge

Abstract This study is aimed at fabricating ultrahigh-purity silicon ingots from silicon cutting sludge – a byproduct of the ingot for solar cells cutting process. Firstly, silicon powder from the silicon cutting sludge was recovered by 1st purification, such as ultrasonication, centrifugation, and acid treatment before preparation of the silicon ingots. After the 1st purification, the silicon cutting sludge yielded silicon powder with a purity of 99.7612 %. The 1st-purified silicon powder was subjected to 2nd purification – 3 cycles hydrogen plasma arc melting (HPAM), resulting in ultrahigh-purity silicon ingot with a purity of 99.9999 %. HPAM has been verified to be an effective process for removal of B and P – the major impurities of silicon for semiconductors and solar cells – to levels of total ≤ 0.3 ppm.