Distinguishing xenotime and zircon in ores and estimating the xenotime content for on-site analysis.

Estimation of the content of the major minerals containing rare earth element (REE) (e.g., xenotime, monazite, and bastnäsite) to extract metal REEs is a critical task for efficient exploration of mines with REE reserves. X-ray-excited optical luminescence (XEOL) imaging is a promising method for estimating the REE-bearing mineral content on-site. However, distinguishing between xenotime and zircon in ores via XEOL imaging is difficult owing to their similar luminescence colors and intensities. This study reveals that XEOL images of ores before and after annealing at 1300 °C can distinguish xenotime and zircon by investigating images obtained via cathodoluminescence (CL), which is the same phenomenon as XEOL except that it used electron bombardment instead of X-ray irradiation. After annealing, zircon exhibits a luminescence intensity stronger than that of xenotime in the CL images. In these images, zircon corresponds to an area with green luminescence whose CL intensity is drastically enhanced by annealing; in contrast, xenotime corresponds to an area with green luminescence whose CL intensity does not change much. The xenotime content in ores can be estimated from the area corresponding to xenotime in the CL images. The exposure time for CL images, which is comparable to XEOL images, is obtained in 30 s. Therefore, the proposed method can be applied to XEOL imaging and used to on-site prescreen ores before precise quantitative analyses, such as inductively coupled plasma mass spectrometry, electron-probe microanalysis, or scanning electron microscopy based on automated mineralogy, which require a large amount of time; thus, the adoption of the proposed method can lead to a drastic reduction in the time required to explore mines reserving REEs.

Rapid determination of the approximate content of bastnäsite in ores using cathodoluminescence imaging.

A rapid determination of the rough content of the major rare earth element (REE)-bearing minerals (bastnäsite, monazite, and xenotime) can lead to a drastic reduction of the time required to analyze mineral ores for the extraction of REE metals, thus enabling the efficient exploration of mines with REE reserves. This study presents a method of using cathodoluminescence (CL) imaging to identify bastnäsite in mineral ores and determine the rough bastnäsite content rapidly. By investigating the luminescence colors in CL images and the peaks in CL spectra emitted by minerals in ores that include bastnäsite, the author found that bastnäsite can be identified by detecting dark red or red-orange luminescence in CL images of the ores in the wavelength range 420-680 nm or by detecting areas that emitted no luminescence in the 420-680 nm CL images but that do emit pale red luminescence in CL images in the broader wavelength range 350-1000 nm. The bastnäsite content in the ores can be estimated roughly from the fractional areas identified as bastnäsite in the CL images. The CL images can be obtained within 30 s. Therefore, CL imaging can prescreen mineral ores for subsequent more precise quantitative analyses (e.g., using inductively coupled plasma mass spectrometry or electron-probe microanalysis) by identifying mineral ores having a probable high bastnäsite content. This approach can drastically reduce the time required to explore mines with potential REE reserves.

Laser-induced breakdown spectroscopy to obtain quantitative three-dimensional hydrogen mapping in a nickel-metal-hydride battery cathode for interpreting its reaction distribution.

We present a method for obtaining a three-dimensional quantitative hydrogen distribution in a Ni-MH battery cathode using laser-induced breakdown spectroscopy (LIBS) and demonstrate that the reaction distribution in the cathode can be interpreted based on a state-of-charge (SOC) distribution converted from the hydrogen distribution. In this method, we measured the hydrogen emission-line intensities at 656.28 nm for a model cathode cycled five times at 2.3 mA cm-2 and a commercial Ni-MH battery cathode cycled 1000 times at 1C under a 3000 Pa helium atmosphere. Our results show that the average SOC in the SOC distributions of the cathodes agreed with those evaluated from X-ray diffraction and charge-discharge curves and that the overcharged areas exhibited SOC values above 100%. The present LIBS method will allow us to understand the deterioration mechanism of a Ni-MH battery and improve its cycle life and capacity.

Effect of Reheating and Quenching on the Cathodoluminescence Intensity of Free Lime in Steelmaking Slag.

Determining free lime content in steelmaking slag is crucial for its safe reuse in road construction. A simple method has been recently developed to rapidly derive this value via cathodoluminescence (CL) imaging of steelmaking slag, previously quenched from 1,000°C to room temperature, according to the illuminated areas corresponding to free lime (luminescence peak at 600 nm). This quenching is required to obtain intense CL from free lime, but the mechanism of such signal enhancement is still unknown. Therefore, the present study investigated the mechanism by comparing the microstructures, CL images, and CL spectra of free lime in quenched and unquenched steelmaking slag. Large amounts of defects, including dislocations, were observed in the free lime emitting intense luminescence at 600 nm, whereas the samples without clear CL exhibited only a few defects. These results and previous studies suggest that the luminescence at 600 nm from free lime is enhanced by the CL originating from oxygen vacancies (380 nm); therefore, the enhancement of the intensity of the free lime CL peak could be attributed to the increase in the oxygen vacancies via quenching from 1,000°C to room temperature.

Structure Design of Long-Life Spinel-Oxide Cathode Materials for Magnesium Rechargeable Batteries.

Development of metal-anode rechargeable batteries is a challenging issue. Especially, magnesium rechargeable batteries are promising in that Mg metal can be free from dendrite formation upon charging. However, in case of oxide cathode materials, inserted magnesium tends to form MgO-like rocksalt clusters in a parent phase even with another structure, which causes poor cyclability. Here, a design concept of high-performance cathode materials is shown, based on: i) selecting an element to destabilize the rocksalt-type structure and ii) utilizing the defect-spinel-type structure both to avoid the spinel-to-rocksalt reaction and to secure the migration path of Mg cations. This theoretical and experimental work substantiates that a defect-spinel-type ZnMnO3 meets the above criteria and shows excellent cycle performance exceeding 100 cycles upon Mg insertion/extraction with high potential (≈2.5 V vs Mg2+ /Mg) and capacity (≈100 mAh g-1 ). Thus, this work would provide a design guideline of cathode materials for various multivalent rechargeable batteries.

Nondestructive thickness measurement of silica scale using cathodoluminescence.

The knowledge of the composition, morphology, and thickness of surface protective scales, such as SiO2 and Al2O3, is important to control the performance of heat-resistant alloys operated at high temperatures above 1000 °C. Cathodoluminescence (CL) analysis is one of the most promising methods to acquire such information nondestructively. Unlike Al2O3 scale, the use of the brightness of CL image to determine SiO2 scale thickness is difficult because the brightness and color of its acquired CL image depend not only on the thickness of the scale but also on its oxygen potential and impurity concentration. In this study, we investigated the CL spectra of SiO2 scales formed on Fe-20%Si alloy, Si, and MoSi2 to present a method for measuring the thickness of SiO2 scale on silica-forming materials from their CL spectra. A linear calibration curve was obtained from the intensity of the CL peak at 445 nm which originated from the intrinsic defects in SiO2 and the thickness of the SiO2 scale for each heat-treatment temperature (1000 °C, 1200 °C, 1300 °C, and 1400 °C). Data in this study can be adequately employed to derive CL calibration curves at different temperatures because the CL intensity and heat-treatment temperature were fitted according to Arrhenius relationship at different SiO2 scale thickness, regardless of the type of base materials. These results indicated that the thickness of the SiO2 scale formed on silica-forming alloys can be determined by acquiring their CL spectra. Therefore, CL analysis has the potential to be employed as a novel analytical method to control the performance of silica-forming alloys.

Quantitative Analysis of Hydrogen in High-Hydrogen-Content Material of Magnesium Hydride via Laser-Induced Breakdown Spectroscopy.

An analytical approach that can rapidly determine a wide range of hydrogen concentration in solid-state materials has been recently demanded to contribute to the hydrogen economy. This study presents a method for estimating hydrogen concentrations ranging from 0.2 to 7.6 mass % via laser-induced breakdown spectroscopy (LIBS) in a few seconds, with an improvement in the upper limit of determination (7.6 mass %) by approximately 1.3 times compared with a previous work (5.7 mass %). This extension of the determinable concentration range was achieved by measuring the emission intensity at 656.28 nm from the sample in a helium atmosphere at 3000 Pa under focused laser irradiation and by reducing the water residues in both the sample and gas line of the LIBS system. The as-determined hydrogen concentrations in magnesium hydride (MgH2) samples agreed well with those estimated through inert gas fusion/gas chromatography. The calibration curve for LIBS analysis was acquired by measuring the emission intensity at 656.28 nm of standard Mg/MgH2 mixtures containing various hydrogen concentrations (0, 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, and 7.6 mass %). Results indicated that the proposed LIBS-based method is applicable to the rapid quantitative analysis of hydrogen in hydrogen-containing material of MgH2.

Effects of divalent-cation iron and manganese oxides on the luminescence of free lime and free magnesia.

Identification of free lime (f-CaO) and free magnesia (f-MgO) is vital for the effective reuse of steelmaking slag in road construction because f-CaO and f-MgO can cause road expansion. In the present study, we present a method to rapidly identify f-CaO and f-MgO likely to cause road expansion by investigating CL spectra of CaO and MgO containing FeO and MnO because MnO and FeO are major components dissolved in f-CaO and f-MgO. The CL peaks related to Mn2+ (600 nm for CaO and 755 nm for MgO) showed the highest intensities. The intensity of the peak at 600 nm for CaO containing 10 mass% MnO was the lowest for f-CaO and was 2.5-times lower than that for f-CaO, whose luminescence was captured in 15 s. MgO with 5 mass% MnO and 20 mass% FeO was found to show the lowest intensity for f-MgO that is responsible for road expansion, and its CL intensity was 10-times lower than that of f-MgO, whose luminescence was captured in 2 s. Therefore, we can identify the f-CaO and f-MgO likely to cause road expansion by capturing CL colors of the peaks related to Mn2+ at the exposure time of approximately 40 s. The method presented here will contribute to the effective reuse of steelmaking.

X-Ray Excited Optical Luminescence and Portable Electron Probe Microanalyzer-Cathodoluminescence (EPMA-CL) Analyzers for On-Line and On-Site Analysis of Nonmetallic Inclusions in Steel.

The potential of the application of an X-ray excited optical luminescence (XEOL) analyzer and portable analyzers, composed of a cathodoluminescence (CL) spectrometer and electron probe microanalyzer (EPMA), to the on-line and on-site analysis of nonmetallic inclusions in steel is investigated as the first step leading to their practical use. MgAl2O4 spinel and Al2O3 particles were identified by capturing the luminescence as a result of irradiating X-rays in air on a model sample containing MgAl2O4 spinel and Al2O3 particles in the size range from 20 to 50 µm. We were able to identify the MgAl2O4 spinel and Al2O3 particles in the same sample using the portable CL spectrometer. In both cases, not all of the particles in the sample were identified because the luminescence intensities of the smaller Al2O3 in particular were too low to detect. These problems could be solved by using an X-ray tube with a higher power and increasing the beam current of the portable CL spectrometer. The portable EPMA distinguished between the MgAl2O4 spinel and Al2O3 particles whose luminescent colors were detected using the portable CL spectrometer. Therefore, XEOL analysis has potential for the on-line analysis of nonmetallic inclusions in steel if we have information on the luminescence colors of the nonmetallic inclusions. In addition, a portable EPMA-CL analyzer would be able to perform on-site analysis of nonmetallic inclusions in steel.

Portable pyroelectric electron probe microanalyzer with a spot size of 40 µm.

We report a method of reducing the spot size of an electron beam in a portable pyroelectric electron probe microanalyzer (EPMA) and its application to on-site microanalysis. An electron beam with a spot size of 40 µm full width at half maximum was achieved by preventing the production of an electric field on the side of a needle tip set on the pyroelectric crystal in the EPMA by coating the side of the tip with an insulating material. This spot size was approximately 10 times smaller than that previously reported. We were able to acquire a line scan profile of a thin copper line sputtered on a silicon substrate using the portable pyroelectric EPMA. The width of the sputtered copper evaluated from the line scan profile (120 µm) corresponded to that from a line scan profile obtained by conventional stationary scanning electron microscope-energy dispersive X-ray spectroscopy equipment.

Scanning Electron Microscope-Cathodoluminescence Analysis of Rare-Earth Elements in Magnets.

Scanning electron microscope-cathodoluminescence (SEM-CL) analysis was performed for neodymium-iron-boron (NdFeB) and samarium-cobalt (Sm-Co) magnets to analyze the rare-earth elements present in the magnets. We examined the advantages of SEM-CL analysis over conventional analytical methods such as SEM-energy-dispersive X-ray (EDX) spectroscopy and SEM-wavelength-dispersive X-ray (WDX) spectroscopy for elemental analysis of rare-earth elements in NdFeB magnets. Luminescence spectra of chloride compounds of elements in the magnets were measured by the SEM-CL method. Chloride compounds were obtained by the dropwise addition of hydrochloric acid on the magnets followed by drying in vacuum. Neodymium, praseodymium, terbium, and dysprosium were separately detected in the NdFeB magnets, and samarium was detected in the Sm-Co magnet by the SEM-CL method. In contrast, it was difficult to distinguish terbium and dysprosium in the NdFeB magnet with a dysprosium concentration of 1.05 wt% by conventional SEM-EDX analysis. Terbium with a concentration of 0.02 wt% in an NdFeB magnet was detected by SEM-CL analysis, but not by conventional SEM-WDX analysis. SEM-CL analysis is advantageous over conventional SEM-EDX and SEM-WDX analyses for detecting trace rare-earth elements in NdFeB magnets, particularly dysprosium and terbium.

Multi-element analysis by portable total reflection X-ray fluorescence spectrometer.

Multi-element solutions containing the 11 elements S, K, Sc, V, Mn, Co, Cu, Ga, As, Br and Y were analyzed by a portable total reflection X-ray fluorescence (TXRF) spectrometer. The excitation parameters (glancing angle, operational voltage and current) and sample amount were optimized for the portable TXRF in order to realize the smallest possible detection limits for all elements. The excitation parameter dependencies of the fluorescence signal and background for the detected elements are explained in detail. Background contributed by the sample carrier is also discussed. Consequently, nine elements were detectable at sub-nanogram levels in a single measurement of 10 min under the optimal experimental conditions. The portable TXRF spectrometer was found to be suitable for simultaneous multi-element analysis with low detection limits. The features of high sensitivity, small sample amount required, and fast detection of a wide range of elements make the portable TXRF a valuable tool in various applications, such as field studies in environmental and geological investigations.

Focused electron beam in pyroelectric electron probe microanalyzer.

We report a method to focus the electron beam generated using a pyroelectric crystal. An electron beam with a spot size of 100 µm was achieved by applying an electrical field to an electroconductive needle tip set on a pyroelectric crystal. When the focused electron beam bombarded a sample, characteristic X-rays of the sample were only detected due to the production of an electric field between the needle tip and the sample.

Note: Portable rare-earth element analyzer using pyroelectric crystal.

We report a portable rare-earth element analyzer with a palm-top size chamber including the electron source of a pyroelectric crystal and the sample stage utilizing cathodoluminescence (CL) phenomenon. The portable rare-earth element analyzer utilizing CL phenomenon is the smallest reported so far. The portable rare-earth element analyzer detected the rare-earth elements Dy, Tb, Er, and Sm of ppm order in zircon, which were not detected by scanning electron microscopy-energy dispersive X-ray spectroscopy analysis. We also performed an elemental mapping of rare-earth elements by capturing a CL image using CCD camera.

Possibility of scanning electron microscope observation and energy dispersive X-ray analysis in microscale region of insulating samples using diluted ionic liquid.

The possibility of scanning electron microscope (SEM) observation and energy dispersive X-ray (EDX) spectrometry analysis in microscale regions of insulating samples using diluted ionic liquid was investigated. It is possible to obtain clear secondary electron images of insulating samples such as a rock and mineral at 5,000 times magnification by dropping 10 µL of 1 wt% of 1-ethyl-3-methylimidazolium acetate (EMI-CH3COO) diluted with ethanol onto the samples. We also obtained EDX spectra of the samples in microscale regions (~5 µm²) without overlapping EDX spectra of other minerals with different composition. It might be possible to perform quantitative analysis of the samples if a method that does not need standard samples is applied or an X-ray detector sensitive for light elements was attached. The method of dropping 1 wt% EMI-CH3COO diluted with ethanol onto insulating samples is useful for SEM observation, EDX analysis in microscale regions, and the preservation of scarce rock and mineral samples because ionic liquid can be easily removed with acetone.

Note: Development of target changeable palm-top pyroelectric x-ray tube.

A target changeable palm-top size x-ray tube was realized using pyroelectric crystal and detachable vacuum flanges. The target metals can be exchanged easily by attaching them on the brass stage with carbon tape. When silver and titanium palates (area: 10 mm(2)) were used as targets, silver Lα and titanium K lines were clearly observed by bombarding electrons on the targets for 90 s. The intensities were the same or higher than those of previously reported pyroelectric x-ray tubes. Chromium, iron, nickel, copper, and zinc K lines in the x-ray tube (stainless steel and brass) disappeared by replacing the brass stage and the stainless steel vacuum flange with a carbon stage and a glass tube, respectively.

Development of miniaturized electron probe X-ray microanalyzer.

A miniaturized electron probe X-ray microanalyzer (EPMA) with a small chamber including the electron source and the sample stage was realized using a pyroelectric crystal as an electron source. The EPMA we propose is the smallest reported so far. Performance of the EPMA was evaluated by investigating energy of obtained continuous X-rays and lower detection limits of transition metals (titanium, iron, and nickel). End point energy (Duane-Hunt limit) of continuous X-rays of 45 keV was obtained. However, it is expected that the EPMA can analyze characteristic X-rays with energy less than 20 keV. The EPMA was able to measure titanium, iron, and nickel wires whose projected areas were more than 0.03 mm(2).