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To produce high-purity Mg metal directly from MgO, the scale-up of a novel electrolytic process using a metal cathode and vacuum distillation was investigated. The electrolysis of MgO was conducted in MgF2–LiF molten salt using Cu or Ag cathode and graphite anode at 1053 K. The influence of the cathode metal and the concentration of Mg in the Mg alloy on the current efficiency was investigated. In addition, the interaction of Al2O3 in contact with the electrolyte and cathode was studied. When electrolysis was carried out with an applied current of 8.81–9.59 A for 75–95 h, Mg alloys such as Mg2Cu and MgAg were produced with a current efficiency of 82.2–88.0%. In addition, owing to the reaction between the Mg alloy and Al2O3, a dense layer of magnesium aluminum oxide was produced. Afterward, when the vacuum distillation of the Mg alloys was conducted at 1300 K, 99.9997% Mg metal was obtained.

Steel containers and instruments are used to hold and transport Mg melts. Thus, quantitative analysis of the dissolution of metallic elements from the steel materials into the liquid Mg is important for controlling the impurities in processes such as Mg alloy production and Ti smelting. When austenitic stainless steels containing Cr and Ni come in contact with a Mg or Mg alloy melt, a large amount of Ni and limited amounts of Fe and Cr dissolve into the melt. In this study, the composition of a Mg-Ni-based melt in equilibrium with SUS316 was investigated to determine the maximum amounts of impurities dissolved from SUS316 into the liquid Mg. Mg-Ni melts of different compositions were held in a closed crucible of SUS316 at 1073 K (800 °C) to 1273 K (1000 °C), and the compositions of the inner wall of the crucible and the Mg-Ni alloy were evaluated after quenching. Subsequently, the relationships between the solubility limit of element i (i: Ni, Fe, and Cr) in liquid Mg with the coexistence of SUS316, $$ C_{{{\text{sol}},{i}}}^{*} $$ (mass pct), and the temperature, T (K), were determined: $$ \log \,(C_{{{\text{sol}},{\text{Ni}}}}^{*} ) = {{ - 1.40 \times 10^{3} }}/{T} + 2.57 \, ( \pm \,0.12), $$ $$ \log \,(C_{{{\text{sol}},{\text{Fe}}}}^{*} ) = - {{5.20 \times 10^{3} }}/{T} + 3.93 \, ( \pm \,0.16),\;{\text{and}} $$ $$ \log \,(C_{{{\text{sol}},{\text{Cr}}}}^{*} ) = - {{5.96 \times 10^{3} }}/{T} + 3.80 \, ( \pm \,0.05). $$ These solubility limits were compared with those estimated based on the available thermodynamic data for the SUS316 and Mg-i binary systems. The validity of the obtained data and the reliability of the previously reported thermodynamic data were also discussed.

Titanium (Ti) is produced by a multi-step process from Ti ore composed of Ti oxide including chlorination process. However, the smelting cost is a major factor that leads to an increase in the cost of Ti. To lower the cost of Ti, the development of a new technique for the direct production of metallic Ti from an oxide feed material is highly desired. However, owing to the high affinity between Ti and oxygen (O) and the high solubility of O in Ti, it is extremely difficult to produce metallic Ti with low O concentration which meets the level required by the industry. In this study, we developed a new method for producing Ti with a low O concentration directly from TiO2 by using Mg as a reductant, assisted by a rare earth oxychloride formation reaction. The production of Ti with a low O concentration was demonstrated using a magnesiothermic reduction of TiO2 in MgCl2–LaCl3 molten salt via a reduction reaction involving LaOCl formation: (TiO2 (s) + 2 Mg (l) + 2 LaCl3 (l) = Ti (s) + 2 MgCl2 (l) + 2 LaOCl (s)). An electrochemical method that produces metallic Ti from TiO2 with no consumption of rare earth elements and Mg was designed based on the experiment results. This process is expected to replace the current smelting processes of Ti as well as numerous other rare metals produced from raw oxide materials and contribute significantly to a decrease in the price of rare metals.

A novel electrolytic process that uses a liquid–metal cathode was investigated to produce high-purity magnesium (Mg) metal using magnesium oxide (MgO). Electrolysis of MgO in a magnesium fluoride (MgF2)-lithium fluoride (LiF) molten salt was carried out with applied voltages of 2.5 V to 3.0 V at 1053 K to 1083 K using tin (Sn), silver (Ag), or copper (Cu) as the cathode and graphite or platinum (Pt) as the anode. After electrolysis, Mg alloys with Mg2Sn, AgMg, and Cu2Mg phases were produced with current efficiencies of 77.2 to 83.8 pct when the concentration of Mg in the Mg alloys was 11.9 to 12.9 mass pct. For the production of high-purity Mg metal directly from the Mg alloys, vacuum distillation was performed. When vacuum distillation was conducted at 1200 K to 1300 K, the concentration of Mg in the Mg alloys feed decreased from 30.2 to 34.1 mass pct to 0.32 to 1.75 mass pct, and Mg metal with a purity of 99.975 to 99.999 pct was obtained. Therefore, this study demonstrates that the production of high-purity Mg metal through an efficient and environmentally sound method using the electrolysis of MgO is feasible.

This paper presents a brief review of the history of titanium smelting and the current trends in related research and development. Presently, both electrolytic and metallothermic reduction processes utilizing various feed materials such as titanium oxide are widely studied. However, many challenges remain to be addressed before realizing the practical application of smelting processes utilizing oxide feed. To make titanium a “common metal”, a new reduction process that is high speed, energy-efficient, low cost, and of low environmental impact is required. The current status of titanium recycling is likewise outlined, and the development of the recycling process is discussed. Low-grade titanium scraps heavily contaminated by oxygen and iron are currently used for producing additive alloys (ferro-titanium) in the steel industry. In the near future, if the demand for titanium metal increases dramatically, there could be an oversupply of low-grade titanium scraps in the market. Therefore, the development of anti-contamination and efficient removal processes for oxygen and iron is essential for the efficient utilization of titanium. The development of these technologies is vital for expanding the titanium industry through innovation in both titanium smelting and recycling technologies.

Observation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCu6AlBiO4(SO4)5Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation (μSR), and inelastic neutron scattering (INS) measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state., There exist many theoretical models of frustrated quantum magnetism, most of which lack convincing experimental realisations. Here the authors combine several experimental methods to argue that KCu6AlBiO4(SO4)5Cl behaves as a square-kagome-lattice quantum Heisenberg antiferromagnet.

The development of a new titanium (Ti) smelting process is highly desired to decrease the cost of Ti metal. In this study, a new method to produce a low-oxygen-concentration Ti directly from TiO2 using La as the reductant was developed. First, deoxidation experiments of metallic Ti using La as the deoxidant were conducted, and the ability of La to deoxidize metallic Ti was demonstrated. The oxygen concentrations in Ti were approximately 3900 ± 400 mass ppm O and 120 ± 50 mass ppm O at La/La2O3 and La/LaOCl/LaCl3 equilibria, respectively, at 1200 K (927 °C). Then, TiO2 reduction experiments utilizing La as the reductant were conducted to produce low-oxygen-concentration Ti directly. TiO2 pellets and Ti pieces were held in LaCl3 molten salt with a sufficient amount of La at 1200 K (927 °C) for 86 ks. After the reaction, the TiO2 pellets were reduced to metallic Ti without reaction inhibition by the formation of intermediate products. The oxygen concentration of the Ti pieces, which were placed in the molten salt with the TiO2 pellets, was 100 ± 50 mass ppm O. These results indicate that low-oxygen-concentration Ti containing less than 200 mass ppm O could be produced directly from TiO2 by utilizing La as the reductant in LaCl3 molten salt at 1200 K (927 °C). This new method is expected to lead to the development of a new industrial process for the production of ultra-low-oxygen-content Ti from Ti ore without a chlorination process.

At J-PARC, the MuSEUM (Muonium Spectroscopy Experiment Using Microwave) collaboration aims to precisely measure the ground-state hyperfine splitting of muonium atoms arising from the muon and electron spins. The pulsed muon beam is stopped in a krypton gas cell to form muonium atoms. The transitions of spin states are induced with a microwave cavity, which are then measured by positron counters. After the previously performed successful measurements with a nearly-zero magnetic field, we are currently planning a measurement with the 2.9T magnetic field by measuring two Zeeman-split sub-levels, so that increased statistics will allow us to more precisely determine the transition frequency down to ∼1ppb. Moreover, a new microwave cavity with a unique geometry is being designed to perform the measurement at an even stronger field of 2.9T in the future.

Deoxidation methods of titanium (Ti) scrap and Ti powder have become increasingly important in recent years. Some rare earth (RE) metals with strong deoxidizing capabilities, including Y, La, Ce, and Ho, are candidate agents for the development of a new deoxidation technology. In this study, a new method was developed to directly remove oxygen (O) from Ti using the Y/YOCl/YCl3 equilibrium. According to the calculation based on available thermodynamic data in the literature, the O concentration in β-Ti can be reduced to less than 10 ppm O at 1300 K (1027 °C) in the Y/YOCl/YCl3 equilibrium. To demonstrate the effectiveness of this method using the Y/YOCl/YCl3 equilibrium, the deoxidation limits of Ti samples using Y metal in YCl3 (l) or in YCl3-NaCl-KCl (l) at 1300 K (1027 °C) were experimentally investigated in this study. As a result, the O concentrations in the Ti samples were from 30 to 60 ppm O in YCl3 (l). This result revealed that Ti with extremely low O concentration can be reliably obtained using the RE/REOCl/RECl3 equilibrium for the first time. The establishment of this process will realize efficient recycling of Ti scrap and production of low O concentration Ti powder, which contribute to the large-scale use of Ti products.

A new electrochemical deoxidation process for Ti, where a mixture of magnesium chloride and yttrium chloride (MgCl2–YCl3) is used as flux, was developed. In the new process, Ti and carbon were used as the cathode and anode, respectively. By elucidating the system using an E-pO2− diagram and the experimental results, the reaction mechanism was proposed. Mg is deposited on the Ti cathode and reduces the oxygen in Ti to oxide ions (O2−). The activity of the generated O2−, $$a_{\text O^{2-}}$$ , in the system is effectively kept at a low level by the formation of yttrium oxychloride, and is further decreased by the electrochemical oxidation reaction on the anode. The process effectively deoxidizes Ti to the level of 100 mass ppm of oxygen concentration at 1200 K. In addition, the oxygen concentration in the Ti sample was maintained at the level of 500 mass ppm O even with the addition of O2− sources. Furthermore, a new concept of the industrial Ti-recycling process based on this new deoxidation process was depicted. The obtained results indicate that this new deoxidation technique can be applied in the recycling process of Ti scrap containing a large amount of oxygen.

Muon spin rotation has long been recognized as one of the few methods for experimentally accessing the electronic state of dilute hydrogen (H) in semiconductors and dielectrics, where muon behaves as a pseudo-H (designated by the elemental symbol Mu). Meanwhile, predictions on the electronic state of H in these materials by density functional theory (DFT) do not always agree with the observed states of Mu. Most notably, Mu frequently occurs in wide-gap oxides simultaneously in a neutral ([Formula: see text]) and a diamagnetic state ([Formula: see text] or [Formula: see text]), which DFT calculations do not explain; they predict that H is stable only in a diamagnetic state with the polarity determined by the equilibrium charge-transition level ([Formula: see text]) vs the Fermi level. To address this issue, we developed a semi-quantitative model that allows a systematic understanding of the electronic states reported for Mu in the majority of oxides. Our model assumes that muons interact with self-induced excitons to produce relaxed-excited states corresponding to donor-like ([Formula: see text]) and/or acceptor-like ([Formula: see text]) states and that these states correspond to the non-equilibrium electronic level ([Formula: see text] or [Formula: see text]) predicted by DFT calculations for H. The known experimental results are then explained by the relative position of [Formula: see text] and [Formula: see text] in the host’s energy band structure. In addition, the model sheds new light on the polaron-like nature of the electronic states associated with shallow donor Mu complexes.

Intermetallic silicide compounds, LaScSi and Y$_5$Si$_3$, known for being hydrogen (H) storage materials, are drawing attention as candidates for electrides in which anions are substituted by unbound electrons. It is inferred from a muon spin rotation experiment that the local field at the muon site (which is the same site as that for H) in these compounds exhibits a large negative shift under an external magnetic field, which is mostly independent of temperature. Such anomalous diamagnetism signals a unique property of electride electrons associated with transition metals. Moreover, the diamagnetic shift decreases with increasing H content, suggesting that the electride electrons existing coherently in the hollow interstitial positions are adsorbed by H to form hydride ions (H$^-$), 6 pages, 5 figures

The electronic and magnetic states of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{MnO}}_{2}$ in terms of hydrogen impurities have been investigated by the muon spin rotation technique combined with density-functional theory (DFT) calculations for muon as pseudohydrogen. We found that 85% of implanted muons are localized in the oxygen channels of the rutile structure and behave like interstitial protons (${\mathrm{Mu}}^{+})$ except those (7.6%) forming a charge-neutral state (${\mathrm{Mu}}^{0})$ at 2.3 K, which indicates that interstitial hydrogen acts like a shallow donor within less than 0.1 meV of ionization energy. The residual 15% of muons are attributed to those related to lattice imperfection as Mn vacancies. Detailed analyses combined with the DFT approach suggested that the muon is localized at the center of the oxygen channel due to its large zero-point vibration energy.

A neutron decays into a proton, an electron, and an anti-neutrino through the beta-decay process. The decay lifetime ($\sim$880 s) is an important parameter in the weak interaction. For example, the neutron lifetime is a parameter used to determine the |$V_{\rm ud}$| parameter of the CKM quark mixing matrix. The lifetime is also one of the input parameters for the Big Bang Nucleosynthesis, which predicts light element synthesis in the early universe. However, experimental measurements of the neutron lifetime today are significantly different (8.4 s or 4.0$\sigma$) depending on the methods. One is a bottle method measuring surviving neutron in the neutron storage bottle. The other is a beam method measuring neutron beam flux and neutron decay rate in the detector. There is a discussion that the discrepancy comes from unconsidered systematic error or undetectable decay mode, such as dark decay. A new type of beam experiment is performed at the BL05 MLF J-PARC. This experiment measured neutron flux and decay rate simultaneously with a time projection chamber using a pulsed neutron beam. We will present the world situation of neutron lifetime and the latest results at J-PARC., Comment: 8 pages, 6 figures, Proceedings of J-PARC Symposium 2019

The neutron lifetime has been measured by comparing the decay rate with the reaction rate of $^3$He nuclei of a pulsed neutron beam from the spallation neutron source at the Japan Proton Accelerator Research Complex (J-PARC). The decay rate and the reaction rate were determined by simultaneously detecting electrons from the neutron decay and protons from the $^3$He(n,p)$^3$H reaction using a gas chamber of which working gas contains diluted $^3$He. The measured neutron lifetime was $898\,\pm\,10\,_{\rm stat}\,^{+15}_{-18}\,_{\rm sys}\,$s., 28 pages, 20 figures, will be submitted to PTEP