Solid State Electrotransport Research Articles

Impurity Characterization by LA-ICP-MS in Terbium Metal after Solid State Electrotransport Purification

Terbium metal rod with the dimension of 6.8mm in diameter and 150mm in length has been purified by solid state electrotransport (SSE) at 1050°C under a pressure of 10-5Pa for 50h, and the impurity distribution has been determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The research results indicate that, the rare earth impurity migrates from cathode to anode of the rod, and the impurity distribution is relatively uniform in the longitudinal section; low melting point impurity of Al migrates from cathode to anode and the impurity concentration distribution is relatively uniform in the longitudinal section, the segregation degree is about 10% in each sample; the impurity with high melting point, Ta, W, Mo, etc., the distribution of above impurity is very non-uniform, for the impurity of Ta, the mean concentration of sample 7 is only 8.75 ppm, but the local concentration is up to 350 ppm, and it exists in an elementary substance form in the Tb; non-rare earth impurity in Tb metal, such as Ni, Si and Ti, migrates from cathode to anode of the rod significantly; the total impurity content in cathode end is lower than other posion, the impurty content of 22 imputies in sample 6 is 648.47 ppm, is the lowest in the Tb rod, except for the high melting point impurities, the lowest impurity content is 60.05ppm in sample 7.

Migration regularities of impurities C, O, Fe, Co and Ni and effect of crystal transition on C, O and Fe in purification of metal La by solid-state electrotransport

Migration regularities of impurities C, O, Fe, Co and Ni and the effect of crystal transition on C, O and Fe in purification of metal La by solid-state electrotransport (SSE) were studied. The impurity migration direction, removal extent and difficulty were intuitively judged by impurity residual rate distribution curve. It is indicated that major impurities Fe, Co, Ni, C and O in metal La are found to significantly migrate to anode and migration effects are much better with the increase in temperature and prolongation of time in purification of La by SSE. Impurities Fe, Co and Ni in La may be fast diffusion elements, which are very extreme to be removed, and removal difficulty is in the order of Fe < Co < Ni < O < C. When La was migrated for 100 h at 800 °C by SSE, the residual rates of impurity Fe, Co, Ni, O and C are 0.25%, 10.10%, 40.04%, 64.00% and 70.04%, respectively. The crystal transition of La, transformed from fcc crystal to bcc crystal, has significant effect on migration of interstitial impurities, and removal effect of interstitial impurities C and O can be significantly improved when purification was performed above crystal transition temperature of 865 °C of La. However, there is little effect on Fe. When La was migrated at 880 °C for 100 h, residual rates of impurities C and O are, respectively, 19.90% and 32.67% lower than those at 820 °C for 100 h, while that of Fe is lower than 0.25% in both situations. Therefore, more pure metal La can be obtained through further increasing temperature, especially above crystal transition temperature of 865 °C of La.

Nickel in Terbium Metal and Its Characterization by Laser Induced Breakdown Spectroscopy-Original Position Statistic Distribution Analysis

The application of terbium involved in giant magnetostrictive materials, phosphors, magneto-optical storage materials, magneto-optical glass, and so on. The requirement of content of nickel is stringent for most of the materials. The distributions of nickel in terbium by Laser induced breakdown spectroscopy-original position statistic distribution analysis (LIBS-OPA) and the reason of difficult removal of nickel by vacuum distillation but easy removal by SSE had been mainly discussed in this paper. Terbium ingot prepared by electron-beam smelting after vacuum distillation was processed into rod of 0.76 cm in diameter and 15 cm in length. The solid state electrotransport (SSE) experiment was done to the rod at 1100°C and 450 A cm-2 for 100 h under UHV (10-7 Pa) conditions. LIBS-OPA was used to acquire the local distribution of nickel in terbium after SSE purification in this study. The result of this study showed that nickel particles transported by the passing current from anode to cathode. This result was consistent with the result of glow discharge mass spectrometry (GDMS) analysis to the whole rod. LIBS-OPA is a promising approach which could be used to analyze the distributions of micro and trace impurities in other metals and alloys. Highlights: Distribution of Ni in terbium after SSE had been obviously observed by LIBS-OPA. Nickel in Terbium is difficult to be removed by vacuum distillation, but after Solid State Electrotransport (SSE) for relative long time, content of Nickel can be greatly reduced. The main reason of the difficult removal of nickel by vacuum distillation and easy removal by SSE had been discussed in detail in this study.

Migration regularities of impurity aluminum and copper in purification of metal lanthanum by solid-state electrotransport

In view of the previous studies on the migrations of impurity aluminum (Al) and copper (Cu) in purification of rare earth metal by solid-state electrotransport (SSE), there are still some questions about that which direction they migrate to and whether there are significant migrations or not. The metal lanthanum (La) was used as research object, and the effects of migration temperature and time on the distributions and migration regularities of impurity Al and Cu were investigated in the present study by increasing concentration of impurity Al and Cu in raw metal La. The impurity migration direction and removal difficulty were intuitively judged by the residual rate distribution curve of impurity. It is indicated that metal impurity Al and Cu in metal La at 800 °C with direct current are found to significantly migrate to anode and their residual rates near cathode decrease with the increase in migration temperature and prolongation of migration time. The relatively large vapor pressure of Al and Cu makes their residual rate distribution curves being low in middle and high in ends. When metal La was continuously purified for 100 h at 800 °C by SSE, the residual rates of impurity Al and Cu at 20 mm from cathode are 68.43% and 57.43%, respectively, showing that Cu is much easier to be removed than Al.

Quantification of oxygen concentration on the purification of Nd metals by Solid-state electrotransport

Neodymium used for permanent magnets was purified through the Solid-state electrotransport (SSE) process that reduced the oxide concentration. Interstitial and transition-metal impurities such as Fe, Al, Ti, Cr, Ni, O, N in the Nd specimen were analyzed via inductively coupled plasma mass spectrometry and time-of-flight secondary ion mass spectrometry. The results revealed that the concentration of oxygen was significantly reduced (by up to 1000 ppm) during the purification. In addition, oxygen atoms in the Nd specimen migrated to each end of the specimen, toward the electrode (anode and cathode). The high temperature by high voltage test condition (> 1.2 V) was sufficient for a phase transformation from the hexagonal close-packed to the body-centeredcubic crystal structure. After the SSE process, the cross-sectional morphology and hardness were examined via field emission scanning electron microscopy and measured with a Vickers hardness tester, respectively. The concentration of oxygen atoms in the Nd specimen was significantly reduced (to 42 ppm), and an optimal condition for purification was determined.

Electrode connection optimization for both temperature difference and purification of lanthanum rod during solid-state electrotransport

In order to solve the problem of large temperature difference between the center and ends of the metallic rod in the purification process of solid-state electrotransport (SSE), three types of electrode connections of tantalum and the corresponding rods of metallic lanthanum were designed, the temperature distributions of three kinds of rod were measured, and the influence of temperature difference on the purification effect of solid-state electrotransport was investigated. The results indicate that the maximum temperature difference of the rod will be significantly reduced through decreasing the cross section of electrode connection to make its unit length resistance close to that of rod, or increasing the unit length resistance of the section at both ends of the rod. When these two measures are adopted at the same time, the effect of decreasing rod temperature difference is the best in the present study, and the maximum temperature difference of the rod can be reduced to 29 °C when the maximum temperature of the rod is 820 °C. The migration velocity of the impurities at rod ends can be obviously improved after the rod temperature difference is reduced, which enables the purification effect and efficiency of solid-state electrotransport to be greatly raised; it is also found that the major impurities iron in metallic lanthanum migrates more easily than oxygen and carbon during the purification of metal lanthanum with solid-state electrotransport.

Composition-tuning in a solid-state electrotransport furnace with active thermal expansion compensation.

A new solid-state electrotransport (SSE) apparatus for refining ultra-pure single crystals of metallic compounds under ultra-high vacuum is described. The setup employs a novel thermal expansion compensation mechanism to minimize mechanical stress on the sample during refinement with cold clamps for contamination-less purification at elevated temperatures. The apparatus is designed to tune the composition of initially slightly off-stoichiometric samples. The expansion compensation and stress-free operation were tested by recording the thermal expansion of elemental cerium in a treatment up to 655 °C. SSE refinement was then performed on a high-quality single crystal of U6Fe resulting in a 50% increase of its residual resistivity ratio to the highest value obtained for a single crystal to date.

Impurities especially titanium in the rare earth metal gadolinium—before and after solid state electrotransport

Gadolinium was prepared by conventional procedures of fluorination, reduction, distillation and solid state electrotransport (SSE). The electronegativities of the metals were found to have an important influence on the electrotransport process and result of the impurity element. Meanwhile, titanium particles in the distilled gadolinium as major metallic impurities were studied by high resolution transmission electron microscopy (HRTEM) before and after solid state electrotransport. The results showed that impurities especially titanium transported from anode to cathode during SSE. In the metal before SSE, there were impurities of titanium in strip shape or embedded round shape. After SSE processing, titanium particles in the metal smaller than 50 nm in the cathode, but existed 6 to 10 times bigger in the anode.

High purity specimens of URu2Si2 produced by a molten metal flux technique

We report a molten metal flux technique to produce high purity specimens of URuSi. Magnetic susceptibility (), heat capacity () and electrical resistivity () measurements show that the bulk properties of these crystals are similar to those that are produced by the Czochralski technique followed by solid-state electro-transport. In particular, we find residual resistivity ratios RRR / as large as 220.

Influence of Sample Preparation Technology and Treatment on Magnetism and Superconductivity of UCoGe

Ferromagnetic superconductor UCoGe is reported to be a week ferromagnet with Curie phase transition temperature T C ≈2.5 K. The magnetic order coexists with superconductivity that appears below critical temperature T SC ≈0.7 K. Nevertheless, the exotic coexistence of the mentioned physical phenomena is strongly sample dependent and only few samples can take pride in thereby. We have prepared a series of polycrystalline samples and single crystals using Czochralski and floating zone method. The samples were treated by a standard annealing under the vacuum or refined using solid state electrotransport. All samples were carefully characterized by X-ray and neutron diffraction methods and by electron-dispersive X-ray analysis in a scanning electron microscope. They were subsequently also studied with respect to magnetism and superconductivity by electrical resistivity, magnetization, AC susceptibility and specific heat measurements. The results have been analyzed and the relations between the sample quality, ferromagnetism and superconductivity are discussed.

High-quality single crystal growth and Fermi surface properties in f-electron systems

High-quality single crystals of rare earth and actinide compounds were grown by using several kinds of techniques such as the Czochralski method, flux method, chemical transport method and Bridgman method, together with purification of a uranium ingot by the solid state electrotransport method. For these single crystals, the de Haas–van Alphen experiment was carried out to clarify the Fermi surface properties, focusing on the quasi-two-dimensional electronic state of RTX 5 (R: rare earth, T: transition metal, X: In and Ga) and AnTX 5 (An: Th, U, Np and Pu), which were compared with the results of the energy band calculation.

High-quality single crystal growth and physical properties in a ferromagnet UIr

UIr crystallizes in the monoclinic crystal structure without inversion symmetry. The magnetization measurement indicated that UIr is an Ising-type ferromagnet with the Curie temperature T C 1 = 46 K at ambient pressure. We grew a high-quality single crystal by the Czochralski method in a tetra-arc furnace. The ingot was annealed under high vacuum by the solid state electrotransport method. Superconductivity with a transition temperature T sc = 0.14 K was found under pressure.

High-quality single crystal growth of UGe2 and URhGe

Abstract We searched for an experimental condition of crystal growth for a ferromagnetic superconductors of UGe 2 and URhGe. Samples were prepared for both polycrystalline and single crystals, which were arc-melted and grown by the Czochralski-pulling method in a tetra-arc furnace, respectively. Annealing is an important process to enhance sample-quality, namely the residual resistivity ratio. We tried to anneal the samples under various temperatures, which were wrapped by the Ta-foil and vacuum-sealed in the quartz ample, together with the solid state electrotransport method in ultra-high vacuum. The highest residual resistivity ratio was 900 for UGe 2 and 41 for URhGe.

Modeling of solid-state electrotransport for purification of gadolinium

Modeling of solid state electrotransport (SSE) was formulated to understand the transport phenomena of the interstitial impurities in gadolinium, are of the rare earth metals. Through numerical analysis, the optimum conditions for SSE are theoretically predicted. The processing parameters such as pressure, temperature, and reaction time can be determined to attain maximum effectiveness. The concentration profiles of interstitial impurities such as oxygen, nitrogen, and carbon were calculated based on this model. The electromigration of oxygen is faster than nitrogen and carbon because of its greater diffusivity and mobility. When the reaction time was 105 seconds, the oxygen and nitrogen were refined up to 92%–95% at 10−5Pa while carbon was refined to 98% at 10−6Pa. The increase in temperature gives rise to a shorter reaction time, but extremely low pressure is required.

Ultrapurification of yttrium metal from oxide to single crystal: results and perspectives

A proposed technique of ultrahigh purity metal single crystal preparation consisting of obtained high purity anhydrous yttrium chloride from its oxide, the reduction of chloride by lithium in gas phase, vacuum remelting and solid state electrotransport (SSE) in UHV is presented and discussed. Data on the behavior of impurities for each stage are listed. It was found that the major limiting impurities are oxygen and carbon. Yttrium single crystals with residual resistance ratio RRR>1200 were obtained by using the proposed technology. An investigation of the behavior of interstitial impurities on the yttrium surface during SSE was performed by Auger electron spectroscopy and a new technique for more efficient and deeper purification using SSE based on consequent ion etching and solid state electrotransport are analyzed and further perspectives for deep purification of Y and other rare earth metals are discussed.

ネオジム中の酸素の固相エレクトロトランスポート

Solid state electrotransport of oxygen in neodymium was studied. The effective valence Z* and the non-dimensional number δ (= uEL/D；u：mobility, E：electric field intensity, L：length of specimen, D：diffu-sion coefficient) of oxygen were measured by the tangent method under the following conditions；electric field intensity = 1.9∼2.5 Vm-1, temperature = 973∼1,223 K, initial oxygen content = 0.01∼0.11 mass %. The results can be summarized as follows： (i) The absolute values of the effective valence and δ of oxygen decrease with increasing either electric field intensity or temperature. (ii) The diffusion coefficient of oxygen in neodymium was determined as follows：DO /m2 s-1 = 0.26 exp (-196000/RT) (Nd(α)：973 ∼ 1,073 K)DO /m2 s-1 = 1.6 × 10-2 exp (-180000/RT) (Nd(β)：1,173 ∼ 1,223 K) (iii)Mobility of oxygen in neodymium increased with increasing temperature.

Purification of Uranium Metal using the Solid State Electrotransport Method under Ultrahigh Vacuum

A uranium ingot was successfully purified using the solid state electrotransport (SSE) method. The concentration of impurities was dramatically reduced after the SSE treatment. In particular, magnetic transition metals such as Fe and Cu were removed almost completely. Impurities with high vapor pressure such as Mn and Zn were evaporated. The mechanism of the impurity-reduction was qualitatively explained by three effects: sweeping out by the flow of the electrical current, diffusion and evaporation. It is very important to hold the uranium ingot at a high temperature just below the melting point.

High-quality single crystal growth of uranium-based intermetallics

Single crystals of various uranium-based intermetallics such as UPt 3, UPd 2Al 3, U 6Fe, URu 2Si 2, etc., were grown by the Czochralski pulling method in a tetra-arc furnace. Subsequent annealing treatment by the solid-state electrotransport (SSE) method under ultra-high vacuum is found to be quite effective for compounds UPt 3 and CeRu 2. The residual resistivity ratio (RRR) of CeRu 2 has been improved from 30 to about 300 after the SSE treatment. In the case of UPt 3, the best annealing temperature is about 900°C, where RRR is increased up to 640.

イットリウム中の酸素の固相エレクトロトランスポート

The solid state electrotransport of oxygen in yttrium was studied and the effective valence Z and the non-dimensional number δ(=uEL/D; u: mobility, E: electric field intensity, L: length of specimen, D: diffusion coefficient) of oxygen were measured by the tangent method under the following conditions; electric field intensity=7.2-10.6Vm-1, temperature=1, 173-1, 563K, initial oxygen content=0.5 mass%. The extraction conditions (analyzing temperature, pretreatment of the specimen, and selection and content of flux) for the accurate determination of oxygen in yttrium was also studied. The results obtained were:(i) For the oxygen analysis of yttrium, platinum was the best flux and should be added more than 0.5 of its molar fraction.(ii) The absolute values of the effective valence and δE-1L-1 of oxygen decreased with increasing either electric field intensity or temperature.(iii) The diffusion coefficient of oxygen in yttrium was determined as follows:Do/m2s-1=3.1×10-8 exp (-68700/RT)(iv) The mobility of oxygen in yttrium increased with increasing temperature.

&amp;gamma;-Fe中のCの固相エレクトロトランスポートに及ぼすグラファイトの析出ならびに析出しているセメンタイトの影響

&amp;gamma;-Fe中のCの固相エレクトロトランスポートに及ぼすグラファイトの析出ならびに析出しているセメンタイトの影響