Deoxidation Process Research Articles

Dissolution-electrodeposition pathway and bulk porosity on the impact of in situ reduction of solid PbO in deep eutectic solvent

The verification of dissolution-electrodeposition pathway and bulk porosity on the impact of in situ electrochemical reduction of solid PbO in choline chloride-ethylene glycol deep eutectic solvent (ChCl-EG DES) is systematically clarified at cell voltage 2.5V and 353K. Cyclic voltammetry of the microelectrode loaded with PbO powders in PbO-ChCl-EG saturated solution exhibits that an additional reduction peak corresponding to the deposition of [PbO·Cl·EG]− is observed. There is no conspicuous difference in morphologies between the products obtained from saturated PbO-ChCl-EG and ChCl-EG DES. The effects of bulk porosity of PbO pellet on the deoxidation process, phase composition and morphologies of products are investigated. When the adding amount of NH4HCO3 and bulk porosity of PbO pellet are about 50% (in weight) and 54.49% (in volume) respectively, the reaction rate of PbO to lead is the fast in the range of present study. Moreover, the direct electro-reduction models of PbO pellet in dense and porous form in ChCl-EG DES are proposed and it emphasizes that the bulk porosity plays an important role because a larger porosity allows a faster diffusion of ions and a higher solubility of PbO into [PbO·C·EG]− which is strongly in favor of the deposition pathway. This method not only forms the scientific base for a scientifically electrolytic extraction of metallic lead but also opens an avenue to the electrochemical fabrication of other metals and alloys from oxide precursors.

Dilatometry Coupled with Mass Spectrometry as Instrument for Process Control in Sintering of Powder Metallurgy Steels

The production of ferrous powder metallurgical parts by the press-and-sinter route becomes more and more attractive. Today, parts are produced for loading requirements that until now only could be fulfilled by conventional produced steel components. The high mechanical properties that must be attained require the use of alloying elements so far not common in powder metallurgy because of their high affinity for oxygen. The sintering of chromium containing steels is a challenge for the whole production process, because the reduction of the surface oxides is critical for successful sintering.Dilatometry can be a useful instrument to control the sintering behaviour of the materials, especially the combination with mass spectrometry allows analysing the very complex sintering process and simultaneously monitoring the solid-gas reactions. This work shows that the sintering atmosphere plays a major role in the entire process. Degassing and deoxidation processes during sintering are demonstrated for different alloying systems (Fe, Fe-C, Fe-Mo-C, Fe-Cr-Mo-C). Dilatometry coupled with MS is shown to be a very good instrument for process control of the sintering process. The generated analytical data can be related to the mechanical properties of the sintered steels if the size of the specimen is large enough.

Research on the removal of impurity elements during ultra-high purification process of terbium

Ultra-high purification of terbium (Tb) by vacuum distillation and external getter was investigated. More than 20 kinds of impurity elements were analyzed by glow discharge mass spectrometry (GDMS) and inert gas analysis (IGA). The analysis results show that total impurities decrease from 1114 ppm to 63 ppm. High volatile metallic impurities such as Mg, Ca, Mn, Zn, and Tm can be reduced effectively after distillation. The oxygen (O) concentration can be decreased to 1.8 ppm after deoxidation process, which currently is one of the best results in the contemporary studies. The chemical driving force for deoxidation has been calculated in this paper. The different deoxidation results of Tb metal with various purity have been discussed in detail using the secondary ion mass spectroscopy (SIMS). Finally, a ultra-high purity Tb with low concentration of O can be obtained through vacuum distillation and external getter method.

Electrochemical Metallurgy in CaCl2-CaO Melts on the Basis of TiO2·RuO2 Inert Anode

Molten CaCl2 has been considered as significant electrolyte for novel electrochemical metallurgy processes due to high solubility of oxygen anions. Some novel processes based on molten-salt electrolysis of oxides in molten chlorides have been proposed, typically including FFC process and OS process. An inert anode capable of sustained oxygen evolution is crucial for a green and efficient electrochemical de-oxidation process. Herein we report the results of a promising inert anode candidate, who shows an excellent performance. Several techniques including anodic polarization, cyclic voltammetry, Tafel polarization and electrochemical impedance have been performed to evaluate the anode behavior of the TiO2·RuO2 anode, revealing that the anode is quite stable during anodic polarization and has a more positive corrosion electrode potential. An in situ analysis of anode gases using the mass spectra proved the capability of the sustained evolution of oxygen at the TiO2·RuO2 anode during electrolysis, meaning that this oxides anode could be a potential candidate as inert anode in calcium chloride–calcium oxide melts for green metallurgical processes, as it showed a nearly negligible solubility of ruthenium dioxide when immersed in the melt and a low rate of corrosion even after long time electrolysis.

Mechanistic insight of in situ electrochemical reduction of solid PbO to lead in ChCl-EG deep eutectic solvent

ABSTRACT The in situ electroreduction mechanism of solid PbO in choline chloride-ethylene glycol deep eutectic solvent (ChCl-EG DES) is preliminarily clarified through systematical investigations at cell voltage 2.5 V and 353 K. Cyclic voltammetry of the cavity microelectrode loaded with PbO powders exhibits that solid PbO can be direct electrochemically reduced to metallic lead and increasing scan numbers is beneficial to the deoxidation process. Potentiostatic electrolysis with an assumed cathode of PbO pellet and a graphite anode shows that generated numerous gases are mainly composed of O 2 with small amounts of Cl 2 at anode whereas H 2 is released and preferentially adsorbed on the surface of reduced metallic lead at cathode. Parts of Cl 2 can remain in the electrolyte and react with it to form oxidizing Cl − 3 ions. Besides, the dissolution-electrodeposition of PbO(s) → [PbO·Cl·EG] − → Pb(s) exists simultaneously with the direct deoxidation of PbO(s) → Pb(s) during the electrolysis process. ESI-MS analysis implies that complex anions [PbO·Cl·EG] − and [ChCl·O·EG] 2− are formed in ChCl-EG-PbO solution before and after the deoxidation process, respectively. Furthermore, a reduction mechanism model of PbO bulk to metallic lead in ChCl-EG DES is proposed. The in situ electrolysis process takes place initially at the current collector/PbO/electrolyte 3PIs and then new formed Pb/PbO/electrolyte 3PIs expands until the whole bulk are metallized. These findings provide a basis for scientifically in-depth discussion on the implication and optimization of the electrochemical production of metals and alloys from metal oxides.

Effect of Deoxidation Process on Distribution Characteristics of Inclusions in Silicon Steel Slabs

The cleanness and usability of silicon steel are seriously affected by the type, number, size of the non-metallic inclusions. The evolution behaviors of the type, number, and size of inclusions in the non-oriented silicon steel slabs, which were subjected to different deoxidation processes (Si or Al deoxidation), were systematically investigated by using industrial testing and sampling analysis. The results indicate that the number and size of the inclusions are over larger during the starting-cast stage, and the reasonable cutting length for the first casting slab is 6 m. During steady-casting stage, the main types of the inclusions in Al deoxidization slab are Al2O3, Al2O3-MnS, Al2O3-MgO, Al2O3-AlN and their complex inclusions, and the main types of the inclusions in Si deoxidization slab are Al2O3, SiO2, Al2O3-SiO2 and a small amount of Al2O3-MnS, Al2O3-MgO complex inclusions. The number density and the occupation area fraction of inclusions in Al deoxidization slab are less than that in Si deoxidization slab. However, the stability of slab cleanliness in Al deoxidization process condition is inferior to that in Si deoxidization process condition.

INFLUENCE OF HYDROGEN ON PROCESS OF IRON DESULFURIZATION BY POWDERED FLUX

Abstract. The process of liquid iron desulfurization was investigated in the processing by powdered fl ux (20 % CaO – 60 % Al2O3 – 20 % CaF2 ) with simultaneous hydrogen blowing. The presence of hydrogen, dissolved in the melt, has a positive effect on the desulfurization process, because the process of hydrogen deoxidation of liquid metal increases the completeness of desulfurization process. Desulfurization of liquid iron by slag-forming mixture and hydrogen blowing of melt should be carried out simultaneously.

Molten salts electrochemical synthesis of Cr2AlC

The unique combination of electrical, mechanical and chemical properties of MAX phase ceramics makes them attractive for energy and structural industrial applications. Here, an inexpensive and simple electrochemical deoxidation process is used to produce high quality, homogeneous micron-size particles of one of the most widely studied MAX phases, Cr2AlC. The process used cathode precursors made of cheap and available oxides of both chromium and aluminum and applied a constant potential difference in molten NaCl–CaCl2 as the electrolyte. It was found that the reduction mechanism took an unusual pathway through the formation of sub-stoichiometric oxides and oxycarbide phases that did not necessarily involve reactions between the cathode and the electrolyte. The Cr2AlC powder produced could be easily pressed into a monolithic bulk that have 4.8±0.8GPa hardness and showed excellent oxidation resistance at temperatures below 1100°C. The method is quite generally applicable to the preparation of other MAX phases. Implications are drawn considering the industrial scale-up of this method for the low-cost production of MAX ceramics.

A comparison study on the deoxygenation of coal mine methane over coal gangue and coke under microwave heating conditions

Microwave heating has great advantages in saving energy and time; in this study, it has been first successfully applied in the deoxidization process of coal mine methane (CMM), where carbon in coal gangue reacts with oxygen in CMM. Compared with traditional heating, microwave pretreatment resulted in rapid heating of coal gangue in CMM deoxygenation, which was attributable to the graphitization of carbonaceous materials. This prominent advantage of microwave heating can contribute to deoxygenation. In addition, deoxygenation effectiveness for both coke and coal gangue under microwave heating was investigated. It was discovered that coke acted as a catalyst to some extent to accelerate methane decomposition. However, this effect could be greatly restricted when coal gangue was used in the deoxygenation process because of its chemical inertness. Under optimal conditions (650°C and 300mL/min), there was no residual oxygen in the outlet gas, and methane loss was less than 2.2%.

Preparation of Ti-Mo-Si alloy powders with enhanced high-temperature oxidation resistance using Ti-10Mo scraps

To recycle Ti alloy scraps and enhance the functionality of the recycled scraps, we manufactured low-oxygen contented Ti-Mo-Si powders using two types of ternary Ti alloy ingots which were prepared by vacuum arc melting of Ti-Mo scrap with different amounts of Si. The weight ratio of Ti-Mo scrap was Ti:Mo=9:1 and Si contents in two alloy ingots were 1 and 2 wt%. The alloy powders were prepared by the hydrogenation-dehydrogenation process and the oxygen atoms were removed by the deoxidation in solid state method. We confirmed that the deoxidation process effectively reduced the oxygen content of Ti-Mo-Si alloy powder from 3,350 ppm to 1,700 ppm. In addition, we confirmed that the high-temperature oxidation resistance was increased by adding Si to Ti-Mo alloys. Thermal gravimetric analysis showed that the weight gain of powders by the oxidation was reduced from 8.85% for Ti-Mo to 7.5% for Ti-Mo-Si at 1,500 °C.

THERMODYNAMICAL ANALYSIS OF OXYGEN BEHAVIOR DURING LADLE TREATMENT OF HIGH ALLOYED CORROSION RESISTANT STEEL 08Х18Н10Т

The actual activities of oxygen in liquid metal during ladle treatment high alloyed steel have been determined with using oxygen sensors. Activities of components of liquid steel and slag with using pseudosubregular solution for liquid metal and psevdoregular ion solution for liquid slag have been calculated. An equation has been obtained and used to calculate the oxygen activity in equilibrium with components of liquid steel Fe–Cr–Ni–Mn–Si–C–Al–Ti, slag FeO–MnO–CaO–MgO–SiO2–CrO1.5–AlO1.5–TiO2 and gas phases. The study showed that the system “metal–slag–gas phase” at the end of the process of deoxidation of the metal is much closer to equilibrium than at the end of the oxidation process.

THERMODYNAMICS OF OXYGEN SOLUTIONS AT COMPLEX DEOXIDATION OF THE Fe-Co MELTS

A method for thermodynamic analysis of complex deoxidation process of metallic melts is proposed. This method allows to determine the effect of a weaker element-deoxidizer on increasing deoxidizing ability of a stronger element-deoxidizer. Oxygen solubility curves pass through a minimum. Analysis of the equation of dependence of the concentration of oxygen in the melt on the elements-deoxidizers contents for the presence of extremum possible to obtain an equation for determining the content of a stronger element-deoxidizer, wherein the oxygen concentration is the lowest. A thermodynamic analysis of the joint infl uence of aluminum and silicon on the solubility of oxygen in the melts of Fe – Co system has been performed. Deoxidation reaction products may be formed as mullite (3Al2O3·2SiO2 ) and kyanite (Al2O3·SiO2 ). The presence of silicon in the melt enhances the deoxidizing ability of aluminum: insignificantly in the case of formation of compound 3Al2O3·2SiO2 and significantly in the case of formation of compound Al2O3·SiO2 . Oxygen solubility curves in the case of formation of compound Al2O3·SiO2 pass through a minimum, the position of which depends on the content of aluminum in the melt and is not dependent on the silicon content. The aluminum content in the minimum points is insignificantly reduced from iron to cobalt as in the case of melts of Fe – Co – Al. Further additives are aluminum leads to an increase in oxygen concentration. Areas of compounds Al2O3 , 3Al2O3·2SiO2 , Al2O3·SiO2 and SiO2 depending on aluminum and silicon contents in the melt are determined.

Effect of nanoparticles formed in liquid melt on microstructure and mechanical property of high strength naval steel

Fe-based Ni–Cr–Mo high strength low alloy (HSLA) naval steel B was cast by feeding titanium wire in the melt and simultaneously controlling oxide reaction and solute concentration distribution during deoxidization process, and was then hot-rolled and tempered at temperatures ranging from 450°C to 700°C. Steel A was produced for comparison without titanium wire feeding process. Microstructure and mechanical properties of these two materials were investigated to clarify the interrelations of composition, process, microstructure and mechanical properties. It was found that, titanium oxide (Ti3O5) nanoparticles produce grain refinement as well as inclusion refinement during casting, and can act as nucleation site of carbide precipitation to make finer and denser precipitates during hot-rolling with a slight increase in strength, elongation and toughness compared to steel A in rolling condition. The effect of tempering temperatures on precipitates of steel B indicates that Ti3O5 can restrict growth of carbonitrides and most precipitates coarsen slightly without decreasing elongation and toughness.

Ti-6Al-4V 및 Ti-8Al-1Mo-1V 합금 스크랩을 이용한 저산소 분말 제조와 탈산방법 비교

Ti-6Al-4V 및 Ti-8Al-1Mo-1V (AMS 4972) 합금 스크랩을 대상으로 수소화-탈수소화(HDH) 기술로 분말을 제조하고 칼슘 접촉식과 비접촉식 방법으로 탈산을 실시하여 탈산효과를 비교하였다. 타이타늄을 대상으로 한 이전 연구결과에서는 비접촉식 탈산법이 탈산 효과가 더 크다고 보고되었으나 산소함유량을 분석한 결과 Ti-6Al-4V 및 Ti-8Al-1Mo-1V 합금 분말 모두 비접촉식으로 탈산한 분말의 산소함유량이 더 높은 것으로 밝혀졌다. 따라서, 본 연구에서는 XRD와 가스분석기를 이용하여 합금 내에 가장 많이 함유되어 있는 알루미늄이 비접촉식 탈산 공정 중 탈산에 미치는 영향을 조사하였다. The present study describes the process of producing low oxygen content alloy powder from Ti-6Al-4V and Ti-8Al-1Mo-1V (AMS 4972) alloy scraps using hydrogenation-dehydrogenation (HDH) and deoxidation in solid state (DOSS) processes. Each prepared powder was deoxidized with Ca contact and non-contact method to compare the deoxidation capability. It is known that the non-contact deoxidation method, using Ca vapor above the melting temperature <TEX>$T_m$</TEX> of Ca, has greater deoxidation capability. However, Oxygen contents in Ti-6Al-4V and Ti-8Al-1Mo-1V powder after non-contact deoxidation method were higher than those after contact deoxidation method. Therefore, we investigate the effect of Al - the richest alloy element in theses Ti based metals - on the deoxidation processes.

Formation of a strontium buffer layer on Si(001) by pulsed-laser deposition through the Sr/Si(001)(2 × 3) surface reconstruction

The formation of a ½ monolayer (ML) of strontium (Sr) on Si(001) represents the most widely used and effective passivation procedure for the epitaxial growth of strontium titanate (SrTiO3) on Si with molecular beam epitaxy (MBE). In the present study, we demonstrate experimentally the possibility of preparing such a buffer layer with the pulsed-laser deposition (PLD) technique. In-situ analysis using reflection high-energy electron diffraction (RHEED) showed surface structure evolution from two-domain (2 × 1) + (1 × 2), exhibited by the bare silicon surface, to a (3 × 2) + (2 × 3) structure at 1/6 ML Sr coverage, which is then replaced by (1 × 2) + (2 × 1) structure at ¼ ML and maintained up to ½ ML coverage. In addition, two different processes for the removal of native silicon dioxide (SiO2) layer were studied: thermal and Sr-induced deoxidation process. Annealing above 1100 °C proved to be the most efficient in terms of carbon contamination. The results highlight the possibilities of using the PLD technique for the synthesis of an epitaxial SrTiO3 layer on Si, needed for the integration of different functional oxides with a Si platform.

A Multi-step Thermodynamic Model for Alumina Formation during Aluminum Deoxidation in Fe–O–Al Melt

Based on the two-step nucleation mechanism, a multi-step thermodynamic model for alumina inclusion formation during aluminum deoxidation process was proposed in Fe–O–Al melt. Thermodynamic properties of metastable intermediates including (Al2O3) n clusters for prenucleation and α-Al2O3 nanoparticle for growth process were calculated using density functional theory. Furthermore, Gibbs free energy change of forming the intermediate by reaction between the dissolved aluminum (Al) and oxygen (O) in the melt was calculated. The results indicated that the thermodynamics of (Al2O3) n at steelmaking temperature are dependent on their structures, while that of α-Al2O3 nanoparticle are dependent on their size. The nuclei of α-Al2O3 which was originated from (Al2O3) n aggregated under a high supersaturation ratio of Al and O(R s) in the melt. There existing excess oxygen because of the low R s, but the secondary inclusions will be formed during the cooling process due to the excess oxygen. The nuclei lager than 20 nm can grow up spontaneously and instantaneously into primary inclusions because of thermodynamic drive. It is difficult to control the size of α-Al2O3 to be less than 20 nm, in the aluminum deoxidation process of the current conditions of steelmaking.

Preparation of low oxygen content alloy powder from Ti binary alloy scrap by hydrogenation–dehydrogenation and deoxidation process

The present study describes the process of producing low oxygen content alloy powder from β titanium alloy scrap using hydrogenation–dehydrogenation (HDH) and deoxidation in solid state (DOSS) processes. β titanium alloys Ti–Mo and Ti–V with weight ratios of 9:1 and 8:2, respectively, were used to carry out the experimental work. In cases of both the Ti–Mo and the Ti–V alloys, high-quality alloy powders were produced by the HDH process, and it was confirmed that the hydrogenation process of titanium alloy showed lower exothermal temperatures than that of commercially pure (CP) titanium. The oxygen content of the manufactured Ti–Mo and Ti–V alloy powders were 3230 and 3090ppm, respectively. Subsequently, low oxygen Ti–Mo and Ti–V alloy powders were produced by the DOSS process; the oxygen content of these powders was 1000 and 870ppm, respectively. These concentration levels were confirmed to be considerably low as compared to those of commercial Ti–Mo and Ti–V alloy powders with oxygen content of 2750 and 3340ppm, respectively.

Direct Electro-deoxidation of Ilmenite Concentrate to Prepare FeTi Alloy in CaCl2 Molten Salt

Abstract In order to prepare FeTi alloy using ilmenite concentrate in molten salt by electrolytic method, the electrochemical deoxidation process was studied by cyclic voltammetry and AC impedance spectroscopy. The electrolytic experiments at different time verified the electrochemical behavior. It is shown that the electrodeoxidation process for ilmenite concentrate mainly consists of two steps. Fe is reduced firstly from the ilmenite concentrate. The second step is the reduction of titanium dioxide with an intermediate product perovskite. At low voltage, the speed of electro-deoxidation process is mainly dependent on the electrochemical reaction. As the potential increases, the diffusion of ion becomes the main rate-controlling step for the electro-deoxidation of ilmenite concentrate.

Comparison of deoxidation capability for preparation of low oxygen content powder from TiNi alloy scraps

Low oxygen content TiNi alloy powder was produced from TiNi alloy scraps by three types of deoxidation after the hydrogenation–dehydrogenation (HDH) process. The TiNi alloy scrap had a Ti:Ni weight ratio of 7:3. After the HDH process, the TiNi alloy powder was found to comprise α-Ti and Ti2Ni phases. It was also confirmed that the hydrogenation process of Ti–Ni alloy showed lower exothermal temperatures than that of pure Ti. After the process of contact deoxidation in the solid state, the oxygen content of the TiNi alloy powder was 1980ppm. This deoxidized powder was treated again by the non-contact deoxidation process as a result of which the oxygen content decreased further to 1260ppm. Applying only non-contact deoxidation after the HDH process allowed us to obtain an oxygen content of 1280ppm, which is the same as that of the TiNi alloy powder obtained by both the contact and the non-contact deoxidation.

XAFS Study on the Specific Deoxidation Behavior of Iron Titanate Catalyst for the Selective Catalytic Reduction of NOx with NH3

AbstractThe environmentally friendly catalyst iron titanate (FeTiOx) was reported to be very active for the selective catalytic reduction of NOx with NH3 (NH3‐SCR), with high N2 selectivity and H2O/SO2 durability in the medium temperature range, and the specific microstructure of iron titanate crystallites as the active phase was determined. In consideration of the probable existence of a redox cycle between Fe3+ and Fe2+ species in the NH3‐SCR reaction, the deoxidation behavior of the FeTiOx catalyst in an H2 temperature‐programmed reduction process was studied extensively by X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine‐structure (EXAFS) methods. Owing to the presence of an electronic inductive effect between Fe and Ti species in the unique edge‐shared Fe3+(O)2Ti4+ structure, the reducibility of Fe3+ species in the FeTiOx catalyst was greatly enhanced compared with that in pristine Fe2O3, leading to the higher oxidation ability of Fe species in FeTiOx. In the H2 temperature‐programmed reduction process, the well‐dispersed Fe3+ species in iron titanate crystallites could be totally converted into Fe2+ in the form of ilmenite FeTiO3 below 500 °C, whereas pristine Fe2O3 could only be reduced to Fe3O4 up to this temperature point. The typical NH3‐SCR reaction is usually conducted below 500 °C, and the enhanced oxidation ability of Fe3+ species in FeTiOx catalyst is responsible for its excellent catalytic NOx reduction performance at low temperatures. Based on XANES linear fitting and EXAFS curve‐fitting results, the specific deoxidation process of the FeTiOx catalyst was proposed, which can provide useful information for the characterization of the microstructure and redox ability of active sites simultaneously in mixed oxide catalysts for certain catalytic reactions.