Calciothermic reduction of titanium oxide and <Emphasis Type="Italic">in-situ</Emphasis> electrolysis in molten CaCl<Subscript>2</Subscript>

A concept for calciothermic direct reduction of titanium dioxide in molten CaCl₂ is proposed and experimentally tested. This production process consists of a single cell, where both the thermochemical reaction of the calciothermic reduction and the electrochemical reaction for recovery of the reducing agent, Ca, coexist in the same molten CaCl₂ bath. A few molar percentages of Ca dissolve in the melt, which gives the media a strong reducing power. Using a carbon anode and a Ti basket-type cathode in which anatase-type TiO₂ powder was filled, a metallic titanium sponge containing 2000 ppm oxygen was produced after 10.8 ks at 1173 K in the CaCl₂ bath. The optimum concentration of CaO in the molten CaCl₂ was 0.5 to 1 mol pct, to shorten the operating time and to achieve a lower oxygen content in Ti.     

Strengthening of steel by the method of spraying oxide particles into molten steel stream

A new technique, Spray-Dispersion Method, which produces a steel containing homogeneously dispersed fine oxide particles sprayed from outside into the molten steel stream has been developed. The conditions for the distribution of particles in solid steel, and the mechanical properties of A1₂O₃- or ZrO₂-dispersed steels were studied. The homogeneous distribution of fine oxide particles is obtained by the addition of a certain suitable controlling element which lowers the contact angle of molten steel on various oxides and the interfacial tension at the oxide—molten steel interface. Among others columbium (niobium) was found to be the most effective on decreasing the average particle size of sprayed oxides. Because of fine dispersion of particles of less than 120 nm, the strength of steels increased with their volume fractions; for example, 1.15 vol pct ZrO₂ causes an increment of 79 MN/m² in proof strength and 94 MN/m² in tensile strength. For practical applications, the Spray Dispersion Method makes it possible to produce 18 chromium-8 nickel austenitic stainless steels dispersion-strengthened by A1₂O₃ or ZrO₂ particles, and ThO₂-dispersed nickel with an average particle size of 61.4 nm and a volume fraction of 5.1 pct.     

Systematic study of the dependence of magnetic and structural properties of Nd_2Fe_(14)B powders on the average particle size

A systematic study of the magnetic and structural properties dependence on the particle size was realized.For this,commercial NdFeB powder was separated into five different mean particle sizes using sieves.Besides,from the original powder,eleven samples were also produced by mechanical milling assisted by surfactant,using various milling times.A total of sixteen samples were studied by scanning electron microscopy(SEM),X-ray diffraction(XRD),vibrating sample magnetometry(VSM),and Mdssbauer spectrometry(MS).The particle sizes of the samples vary from the micrometer to the nanometer scale.The crystallite size decreases with decreasing particle size.XRD result indicates that the Nd_2Fe_(14)B phase is found in all the samples,and the presence of this phase is also corroborated by MS using six sextets for fitting their spectra,with an additional singlet corresponding to the Nd_(1.1)Fe_4B_4 phase.The mean hyperfine magnetic field increases with increasing particle size because the magnetic dipolar interaction between the magnetic moment of the particles increases with particle size.From the VSM measurements the magnetic energy density(BH)_(max) values were calculated for different particle sizes,and their maximum value of 34.45 MGOe is obtained for the sample with the particle size of 60 μm.     

A fundamental study on the preparation of niobium aluminide powders by calciothermic reduction

Fine niobium aluminide powders such as NbAl₃ were produced directly from mixtures of Nb₂O₅ and aluminum powder by calciothermic reduction. Prior to the reduction experiment, phase equilibria between Nb-Al and Ca-Al alloys were studied. Isothermal annealing of the specimens in the Nb-Al-Ca system at 1273 K showed that NbAl₃ is in equilibrium with CaAl₂ and Al-rich Ca-Al liquid alloys and that Nb₃Al and Nb₂Al equilibrate with Ca-Al alloys containing around 9 to 18 and 18 to 36 mol pct Al, respectively. Based on these experimental phase equilibria and on reported thermodynamic data of the Al-Ca system, the activities of Al in Nb-Al alloys were evaluated. This information is necessary in determining suitable compositions and conditions for the coreduction and ultimate production of single-phase niobium aluminide. The procedure for preparation of niobium aluminide powders by calciothermic reduction of Nb₂O₅ consists of three steps: (1) blending of starting materials (Nb₂O₅ + Al); (2) high-temperature reaction with calcium; and (3) acid leaching. After the reduction of Nb₂O₅ with calcium and aluminum to produce niobium aluminide powders, by-products of Ca-Al alloy, CaAl₂, and CaO were formed. These were removed by leaching in aqueous acid solution. The NbAl₃ particles obtained were a few micrometers in size and contained about 0.15 wt pct oxygen.     

Calciothermic reduction of titanium oxide in molten CaCl<Subscript>2</Subscript>

Titanium oxides were reduced to metallic titanium using the liquid calcium floating on the molten CaCl₂. A part of Ca dissolved into CaCl₂ and reacted with TiO₂ settled below CaCl₂. The by-product CaO also dissolved by about 20 mol pct into CaCl₂, which was effective in reducing the oxygen concentration in the obtained Ti particles. The compositional region in the Ca-CaCl₂-CaO system was examined for the less oxygen contamination in Ti and the better handling in leaching. A large amount of the residual calcium oxidized the titanium powder in leaching. The metallic Ti powder less than 1000 mass ppm oxygen could be obtained only for 3.6 ks using 5 to 7 mol pct Ca-CaCl₂ at 1173 K. The powder was slightly sintered like sponge, and contained approximately 1500 ppm Ca. The anatase phae, the intermediate product in the refining process of TiO₂, could be also supplied as raw material as well as rutile.     

Effects of precursor moisture and inert N_2 atmosphere calcinations on structure and properties of alumina modified CeZrLaNd mixed oxides

CeO_2-ZrO_2 mixed oxides are widely used in the three-way catalysts due to their unique reversible oxygen storage and release capacity. Large surface area, high oxygen storage capacity and good thermal stability of cerium zirconium mixed oxides are the key properties for the automotive catalysts so as to meet the strict emission regulations. In this work, alumina modified CeZrLaNd mixed oxides were prepared by a co-precipitation method. The effects of moisture in precursor and inert N2 atmosphere during calcinations on the structure and properties were investigated by Brunauer-Emmett-Teller(BET) surface area measurements, X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), hydrogen temperature-programmed reduction(H_2-TPR), oxygen storage capacity(OSC), Raman spectroscopy, and X-ray photoelectron spectroscopy(XPS). The results show that the moisture in precursor during calcinations increases the crystal grain size of the cerium zirconium mixed oxides, improving the thermal stability. And the aged surface area of sample after being calcined at1000 ℃ for 4 h reaches 68.8 m~2/g(5.7% increase compared with the common sample). The inert N2 atmosphere endows a great pore-enlarging effect, which leads to high fresh surface area of 148.9 m2/g(13.5% increase compared with the common sample) and big pore volume of 0.5705 mL/g. The redox and oxygen storage capacity are also improved by inert N2 atmosphere with high OSC value of 241.06μmolO_2/g(41.3% increase compared with the common calcination), due to the abundant formation of the crystal defects and oxygen vacancies.     

Solidification processing of Al-Al2O3 composite using turbine stirrer

Solidification processing of Al-Al₂O₃ composites involves mixing of nonwetting alumina particles in molten aluminum alloy resulting in a slurry where the particles are often attached to bubbles sucked at the center of vortex below the stirrer. The internal surface of bubbles is eventually oxidized by oxygen from air entrapped in it. These bubble-particle combines may float or settle during casting depending on the overall density influencing the particle and porosity distribution in a cast composite ingot where the performance of a stirrer may be evaluated under a given condition of processing. Particle incorporation is more for turbine stirrers instead of flat blade stirrers, but the porosity also increases. Flotation of bubble-particle combines during casting of ingot results in higher particle content at the top. Microstructure shows clusters of particles along circular boundaries of thin oxides at the top of the ingot and sometimes at the bottom. This may be a consequence of filling of bubbles to different extents by surrounding liquid puncturing the oxide layer, if necessary, during solidification. When the manner of stirring is changed to 2 minutes of stirring of particles into molten alloy with an intermediate 2-minute period of no stirring before stirring the slurry again for 2 minutes, relatively uniform particle incorporation results along the height of cast ingot compared to that obtained by continuous stirring. This difference in particle distribution may be attributed to flotation of bubble-particle combines to release the particles on the top of the slurry when stirring ceases and its remixing into the slurry when it is stirred again. However, an increase in the intermediate period of no stirring and a higher processing temperature result in enhanced porosity and a more inhomogeneous particle distribution along the height of the ingot.     

High-temperature oxidation of intermetallics formed by group IV transition metals with chromium

We have studied the oxidation resistance of chromium intermetallics: TiCr₂, HfCr₂, and ZrCr₂, in the temperature interval 873–1473 K with isothermal holding of the specimens for up to 20 h. We have shown that the intermetallics TiCr₂ and HfCr₂ are oxidized 2–3 times more slowly than pure titanium and hafnium, but more than 1–2 orders of magnitude faster than chromium at T≤1273 K and 4–6 times faster at 1473 K. In this temperature interval, the intermetallic ZrCr₂ is rapidly oxidized at an increasing rate as the heating temperature rises. The scaling resistance of intermetallics of Group IV d metals with chromium is determined by formation of scales in which the major role is played by the oxides TiO₂, HfO₂, and ZrO₂, with weak protective properties.     

Titanium powder prepared by magnesiothermic reduction of Ti2+ in molten salt

A process to produce titanium powder from Ti²⁺ in the molten salt was confirmed experimentally. It consists of two steps. In the first step, titanium (IV) chloride gas dissolves in the molten salt as the titanium (II) chloride by reacting chemically with the metallic titanium or magnesium. In the second step, this molten salt is exposed to the metallic reductant Mg for the final reduction to the metallic Ti powder. Experimentally, the feed of TiCl₄ gas and the subsequent reaction with Ti prepared the molten salt containing 5 to 10 mass pct Ti²⁺. By Mg reduction of this salt, the well-isolated fine Ti particles were recovered. The powder morphology and particle size depended on the Ti²⁺ concentration, reduction temperature, time, and concentration of the by-product MgCl₂. The stirring by argon gas bubbling effectively grew the fine and round particles to a few tens of microns in size.     

Activity of Chromium Oxide in CaO‐SiO2 based Slags at 1873 K

Thermodynamic properties of chromium oxides in molten slags are very important for optimization of stainless steel refining processes as well as reduction processes of chromium ores. The solubility of chromite into molten slags has been found to vary drastically with oxygen partial pressure and slag composition in the former studies by the authors. In the present study, activity data and redox equilibria of chromium oxides measured under moderately reducing conditions, P_O2= 6.95×10^?11 atm, at 1873 K are summarized. For the CaO‐SiO₂‐CrO_x system, the activity coefficient of chromium oxide increased with increasing basicity and the optimized slag composition for stainless steel refining is assessed as that saturated with CaCr₂O₄ and Cr₂O₃ using the phase relations determined. On the other hand, the presence of MgO and Al₂O₃ brings about different behaviour of chromium oxide activity and redox equilibria and the 44 mass per cent CaO ‐ 39 mass per cent SiO₂ ‐11 mass per cent Al₂O₃ ‐ 6 mass per cent MgO slag is recommended to reduce the chromium oxidation loss in the practical stainless steel refining process at 1873 K.     

Effects of precipitate aging time on the cerium-zirconium composite oxides

Cerium-zirconium composite oxides with high performance were synthesized by a co-precipitation method, using zirconium oxychloride and rare earth chloride as raw materials. The effects of precipitate aging time on the properties of cerium-zirconium composite oxides were investigated. The prepared cerium-zirconium composite oxides were characterized by X-ray diffraction（XRD）, BET specific surface area, pulsed oxygen chemical adsorption, H2 temperature-programmed-reduction（H2-TPR）, scanning electron microscopy（SEM）, etc. The results showed that the precipitate aging time caused great effects on the properties of cerium zirconium composite oxides. With the increase of aging time, the cerium zirconium composite oxides showed enhanced specific surface area, good thermal stability, and high oxygen storage capacity（OSC）. The best performance sample was obtained while the precipitate aging time up to 48 h, with the specific surface area of 140.7 m2/g, and OSC of 657.24 μmolO2/g for the fresh sample. Even after thermal aged under 1000 oC for 4 h, the aged specific surface area was 41.6 m2/g, moreover with a good OSC of 569.9 μmolO2/g.     

Absorption of gaseous oxygen by liquid cobalt, copper, iron and nickel

An experimental investigation of the rates of oxygen solution in molten cobalt, copper, iron and nickel was carried out using pure oxygen and a constant-volume Sieverts' method. It was found that the volume of gaseous oxygen which initially reacted with the inductively stirred metals was strongly dependent on the physical nature of the oxide film which formed during the first stage of reaction. The initial temperature of the molten iron, cobalt, and nickel was 1600‡C, and for copper was 1250‡C. For initial oxygen pres-sures above the melt of about one atmosphere both molten iron and copper, which formed liquid surface oxides, initially absorbed nearly 20 cm³ (STP) O₂/cm² of melt surface area, while molten cobalt and nickel, which formed solid oxides, absorbed about 6 cm³ (STP) 0₂/cm² under the same experimental conditions. For approximately 30 s after the initial reaction between these liquid metals and gaseous oxygen, the oxygen absorption rate was proportional to the square root of the oxygen pressure above the melt, and pro-portional to the melt surface area, but independent of melt volume. The rate-limiting step for oxygen absorption by liquid iron, cobalt and copper can be described by dissocia-tive adsorption of oxygen molecules at the gasJoxide interface. After 30 s of reaction, the rate of oxygen absorption became less dependent on the oxygen pressure above the melt. This indicated that the rate-controlling step was changing from a surface reaction to growth of the oxide layer by cationic diffusion in the bulk oxide. The oxidation rate of liquid nickel appears to be too complex to be described by models for dissociative ad-sorption of oxygen molecules at the gasJoxide interface and parabolic growth of the oxide layer. The formation of a thin layer of nickel oxide which allows oxygen to migrate through cracks or grain boundaries may be responsible for the relatively high oxygen ab-sorption rate compared to that of liquid cobalt. Formerly a Graduate Student at The University of Michigan     

The structure of molten binary silicate systems CaO-SiO2 and MgO-SiO2

The structure of the molten binary CaO-SiO₂ and MgO-SiO₂ was investigated by means of a high temperature X-ray diffraction technique. From an analysis of the X-ray scattering intensity, the radial distribution function was evaluated from which interionic distances and coordination numbers were calculated. The following features emerge from these results: Molten silicates consist mainly of SiO₄ tetrahedral units, up to 57 mol pct alkaline earth metal oxides. The number of oxygens which surround Ca and Mg at the monosilicate composition is 7 and 5 respectively. The structure of molten silicates is insensitive to temperature within the present experimental temperature range. The ionic distribution and structural changes in the molten mixture of alkaline earth silicates are also discussed.     

Optimization of synthesis of upconversion luminescence material NaYF4：Er^3＋,yb^3＋ nanometer-phosphor by low-temperature combustion synthesis method

A kind of Er3+-Yb3+ co-doped natrium yttrium fluoride nanometer-phosphor sensitive to 980 nm was synthesized by the low-temperature combustion synthesis method, which expanded the application range of the low-temperature combustion synthesis (LCS) method which is always used in the synthesis of oxides and compound oxides. The synthesis conditions were optimized with orthogonal experiments and the optimum technological parameters were obtained. Intense upconversion emissions at 522, 540 and 653 nm corresponding to the 2H11/2, 4S3/2, and 4F9/2 transitions to the 4I15/2 ground state were observed when excited by continuous wavelength (CW) laser radiation at 980 nm. The effect of the carbamide amount on the phase formation and the luminescence intensity was analyzed. The average particle size of the sample was 30-40 nm.     

Absorption of gaseous oxygen by liquid cobalt,copper, iron and nickel

An experimental investigation of the rates of oxygen solution in molten cobalt, copper, iron and nickel was carried out using pure oxygen and a constant-volume Sieverts’ method. It was found that the volume of gaseous oxygen which initially reacted with the inductively stirred metals was strongly dependent on the physical nature of the oxide film which formed during the first stage of reaction. The initial temperature of the molten iron, cobalt, and nickel was 1600°C, and for copper was 1250°C. For initial oxygen pressures above the melt of about one atmosphere both molten iron and copper, which formed liquid surface oxides, initially absorbed nearly 20 cm³ (STP) O₂/cm² of melt surface area, while molten cobalt and nickel, which formed solid oxides, absorbed about 6 cm³ (STP) O₂/cm² under the same experimental conditions. For approximately 30 s after the initial reaction between these liquid metals and gaseous oxygen, the oxygen absorption rate was proportional to the square root of the oxygen pressure above the melt, and proportional to the melt surface area, but independent of melt volume. The rate-limiting step for oxygen absorption by liquid iron, cobalt and copper can be described by dissociative adsorption of oxygen molecules at the gas/oxide interface. After 30 s of reaction, the rate of oxygen absorption became less dependent on the oxygen pressure above the melt. This indicated that the rate-controlling step was changing from a surface reaction to growth of the oxide layer by cationic diffusion in the bulk oxide. The oxidation rate of liquid nickel appears to be too complex to be described by models for dissociative adsorption of oxygen molecules at the gas/oxide interface and parabolic growth of the oxide layer. The formation of a thin layer of nickel oxide which allows oxygen to migrate through cracks or grain boundaries may be responsible for the relatively high oxygen absorption rate compared to that of liquid cobalt. R. H. RADZILOWSKI, formerly a Graduate Studient at The University of Michigan     

The structure of molten binary silicate systems CaO-SiO2 and MgO-SiO2

The structure of the molten binary CaO-SiO₂ and MgO-SiO₂ was investigated by means of a high temperature X-ray diffraction technique. From an analysis of the X-ray scattering intensity, the radial distribution function was evaluated from which interionic distances and coordination numbers were calculated. The following features emerge from these results: Molten silicates consist mainly of SiO₄ tetrahedral units, up to 57 mol pct alkaline earth Met.al oxides. The number of oxygens which surround Ca and Mg at the monosilicate composition is 7 and 5 respectively. The structure of molten silicates is insensitive to temperature within the present experimental temperature range. The ionic distribution and structural changes in the molten mixture of alkaline earth silicates are also discussed.     

Thermodynamics of lead and bismuth in CaO–CaF2 melts

In order to understand a new refining process for removing tramp elements from alloy steels under strongly reducing conditions, the authors previously reported the thermodynamic behaviour of P, Sn, Sb, As and Cu in CaO–CaF₂ melts. In this investigation, the thermodynamic behaviour of Pb and Bi in CaO–CaF₂ melts under oxygen partial pressures from 10^?16 to 10^?20 atm was studied at temperatures ranging from 1360 to 1550°C, using a similar technique. It was shown that Pb and Bi exist in slag mainly as Ca₂Pb and Ca_1.5Bi, respectively, under very low oxygen partial pressure although a part of Pb is soluble in slags as metal. The obtained results were extrapolated to lower oxygen partial pressures to investigate the possibility of removing these tramp elements from molten iron, causing Bi to be removed from molten iron below an oxygen partial pressure of 10^?23 atm, whereas Pb is removed under higher oxygen partial pressures.     

Synthesis and photocatalytic property of Ce-doped SnO2

Pure SnO₂ and Ce-doped (1%, 4%, 7%, 10% in mass ratio) SnO₂ powders were prepared by a simple sol-gel method. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) specific surface area analyzers. Results showed that the 7% Ce-doped sample has a particle size of 0.1-0.3 μm with a narrow particle size distribution while the pure SnO₂ was consisted of large agglomerated particles with a diameter up to several micrometers. When used as the catalyst to degrade methyl orange (MO), the 7% Ce-doped sample showed best photocatalytic property. These properties can be attributed to the large surface area and small particle size of the 7% Ce-doped sample.     

The Thermodynamics of Some Transition Metals in Molten Slags

In the present paper, the thermodynamic behaviour of transition metals, such as Cr, Ti, Nb and V in molten slags is systematically analysed based on a literature survey. These metals exist in molten slags with multi valences. Oxygen partial pressure, slag basicity, total content of each transition metal, content of each component in slag, and temperature are the influential factors on their thermodynamic properties in molten slags. Higher basicity and strong oxidative atmosphere are generally favourable for the stable existence of transition‐metal ions with higher oxidation states. Temperature is a factor that is less influential than the above‐mentioned ones. For a transition metal in molten slag, the concentration ratio of ions of different valences depends on the activity coefficient ratio of their oxides. The present paper summarizes the activity studies regarding the transition metal oxides in various molten slags. For chromium and titanium oxides, information on CaO? SiO₂ based systems is involved. For titanium oxides, its thermodynamic behaviour in MnO? SiO₂ based slags is introduced. For niobium and vanadium, the information in Na₂O? SiO₂, CaO? CaF₂? SiO₂ systems is provided. Thermodynamic studies are described for Nb₂O₅? MnO? SiO₂ molten slag equilibrated with liquid iron at 1828 K.     

Deoxidation of Liquid Copper with Reducing O<Subscript>2</Subscript>/CH<Subscript>4</Subscript> Flames

The rate of deoxidation of molten copper during top blowing with various reducing gases has been investigated using thermogravimetry. It was observed that the rate of deoxidation increases with an increasing flow rate of H₂ or CO and that H₂ is a more effective reducing reagent than CO. The rate of deoxidation using methane was measured for O₂/CH₄ ratios from 1.5 to 2.0. As expected, the deoxidation rate decreased with an increasing O₂/CH₄ feed ratio because the flame became less reducing. For all tests, initially there is a linear decrease in mass as oxygen is removed. However, for some experiments, after some time, a sudden acceleration in the rate of mass loss occurs. Using video and X-ray imaging, it was found that this pattern corresponded to gas evolution from within the molten copper. This finding can be explained by the sudden water vapor evolution because the hydrogen dissolved in the copper reacts with the remaining oxygen, and “boiling” takes place, leading to an enhanced stirring of the copper.