ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
This paper investigated two-dimensional spatial and temporal images of a copper emission line in laser-induced breakdown spectroscopy (LIBS), in order to clarify the excitation/de-excitation processes occurring in a laser-induced plasma. The measurements were carried out under different plasma gases (argon, krypton, helium, and nitrogen), pressure levels (100 - 900 Pa) and delay times (100 - 1000 ns) with the aim of monitoring their effects on the behavior of the copper emission. Depending on the plasma gas type and the pressure level, large differences were found in the plasma shape and temporal intensity evolution of the copper emission profile. Namely, krypton produced the most compact plasma emitting larger intensities, compared to argon and helium, and an increase in the gas pressure made these plasmas to shrink, which could be related principally to the stopping power of the applied gases. Through temporally resolved analysis, the delay profiles could be obtained for each plasma gas, indicating that the helium plasma disappeared more rapidly than the argon and krypton plasmas. It was suggested that the variations in the emission intensity would be determined by interactions between gas particles and highly energetic particles in the plasma breakdown as well as interactions between excited gas particles and copper species during plasma expansion. These insights could prove to be useful in the understanding of the background of LIBS as well as the optimization of its practical applications.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
This paper describes uncertainty ranges of the analytical values by laser-induced breakdown spectrometry (LIBS), in order to realize an element-based sorting of commercial Al alloys whose chemical compositions are varied depending on the kind. For this purpose, calibration factors and their standard errors between the emission intensity and the content of major alloyed elements were estimated using a series of standard reference materials of Al alloys. From the result of LIBS analysis, Al alloy samples, labeled as A1050, A1100, A2017, A2024, A5052, A5083, and A6061, were actually classified into the kinds of Al alloy for which the chemical compositions have been standardized by the Japanese Industrial Standards. The sorting was successfully conducted, although several of them could not be classified into a particular alloy type. This was not due to the analytical precision of LIBS but due to a similarity of the chemical composition between several types of the Al alloy. For comparison, a similar sorting procedure was carried out using the analytical result by ICP-OES, which gave the same conclusion as the LIBS. In fact, ICP-OES requires sample pretreatment and dissolution and thus cannot be applied to on-site/in-line analysis, whereas LIBS can provide a rapid response of analytical values. Accordingly, the LIBS analysis may be actually applied for sorting Al alloy materials in detail.
ABSTRACT
This study describes a direct analysis of oxygenated organic compounds, such as ketones, esters and ethers, rapidly and easily using a soft plasma ionization (SPI) source combined with a Q-mass spectrometer. A related molecular ion, [2M+H]+, in which a sample molecule (M) can undergo protonation via water clusters, such as [(H2O)n+H]+ and [N2(H2O)n+H]+, in an ambient air glow discharge plasma, can be dominantly detected as a base peak with little or no fragmentation at a pressure of several kPa. Oxygenated organic compounds with high proton affinity were found to generate their dimers through the hydrogen bonding interaction at higher pressures. A deuterated solvent was used to examine whether or not the adduct ion of analyte was derived from the solvent. The formation of [2M+H]+ strongly depended on the time. A two-dimensional spectrometer was used to obtain the distribution of several excited species and then to confirm the ionization reactions of the analyte in the SPI source. The sample molecule would be readily ionized through Penning-type collisions with excited N2, which causes fragmentation for oxygenated compounds due to the lower pressures (approx. 1.0 kPa) while it is ionized by an attachment with protons from water clusters at higher pressures (several kPa). The SPI source can be a new and powerful tool for soft ionization in direct analysis of volatile organic compounds (VOCs).
ABSTRACT
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.
ABSTRACT
The ionization source based on glow discharge plasma using ambient air is driven by a pulsed direct-current voltage for soft plasma ionization (SPI). The novelty of this work is that molecular ions [M+13]+ related to the analyte species (M), which may be formed by numerous oxidation, can be dominantly detected as a base peak with little or no fragmentation of them in an air plasma at a pressure of several kPa. The unique ion [M+13]+ was assigned to the oxidation product, [M+O-3H]+, which was confirmed as a deuterated ion [M+O-3D]+ ([M+10]+) by using a deuterated solvent. The ionization reactions were suggested that the product ion [M+O-3H]+ may arise from hydride abstraction reaction of M with O2+â¢, dehydrogenation reaction of [M-H]+⢠and subsequently oxidation reaction of [M-3H]+ with O3. n-Alkane mixtures was also measured to evaluate the intermolecular interaction in this system. The limits of detection (LOD) were in the range of 0.126-1.68 ppmv and the relative standard deviation (RSD) for repeatability was approximately 10.0% at the lowest concentration. To our knowledge, this is the first report demonstrating that the spectrum pattern of saturated hydrocarbons could be directly determined without any complicated fragmentation.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
This paper describes the fundamental process of laser ablation occurring in a laser-induced plasma. The sampling process in laser-induced breakdown plasma spectrometry is very complicated and thus has not been fully understood. Our study focused on a relationship between the composition of ablation amounts and the bulk composition, when Fe-based binary alloys were employed as test samples. For this purpose, the ablation amounts of constituent elements in the alloys were determined by ICP-OES, through a method in which ablated deposits by laser irradiation were collected on a glass plate and then dissolved in an acid solution. In Fe-Ni binary alloys, the Ni content in the ablated deposits was almost the same as the bulk composition, which implied that Ni and Fe atoms evaporated along with the chemical composition of the samples; however, in Fe-Cr binary alloys, the Cr content in the ablated deposits was half of the bulk composition, probably because Cr atoms were difficult to be released from the sample surface. X-ray photoelectron spectra of ablated Fe-Cr alloy samples indicated that the resultant surface layer after laser irradiation comprised a thin oxide layer, consisting of Cr2O3 and FeO, and a relatively thick oxide layer beneath the outermost surface oxide, of which the composition was a complex of Cr2O3, Fe and FeO. The reason for this is that the dissociation energy of Cr2O3 is obviously higher than that of FeO, and thus Cr2O3 decomposed with more difficulty and thus left preferentially in a surface oxide layer of the Fe-Cr alloys. As a result, the Cr2O3 layer could suppress the ablation of Cr.
ABSTRACT
We investigated a simultaneous internal standard method in flame atomic absorption spectrometry (FAAS), in order to better the analytical precision of 3d-transition metals contained in steel materials. For this purpose, a new spectrometer system for FAAS, comprising a bright xenon lamp as the primary radiation source and a high-resolution Echelle monochromator, was employed to measure several absorption lines at a wavelength width of ca. 0.3 nm at the same time, which enables the absorbances of an analytical line and also an internal standard line to be estimated. In considering several criteria for selecting an internal standard element and the absorption line, it could be suggested that platinum-group elements: ruthenium, rhodium, or palladium, were suitable for an internal standard element to determine the 3d-transition metal elements, such as titanium, iron, and nickel, by measuring an appropriate pair of these absorption lines simultaneously. Several variances of the absorption signal, such as a variation in aspirated amounts of sample solution and a short-period drift of the primary light source, would be corrected and thus reduced, when the absorbance ratio of the analytical line to the internal standard line was measured. In Ti-Pd, Ni-Rh, and Fe-Ru systems chosen as typical test samples, the repeatability of the signal respnses was investigated with/without the internal standard method, resulting in better precision when the internal standard method was applied in the FAAS with a nitrous oxide-acetylene flame rather than an air-acetylene flame.
ABSTRACT
This paper describes a plasma-diagnostic method using an enhancement factor on the Boltzmann distribution among emission lines of iron atom in an argon radio-frequency inductively-coupled plasma (ICP). It indicated that Boltzmann plots of the atomic lines having lower excitation energies (3.4 to 4.8 eV) were well fitted on a straight line while those having more than 5.5 eV deviated upwards from a linear relationship. This observation could be explained by the fact that ICP is not in a complete thermodynamic equilibrium between direct excitation to energy levels of iron atom, ionization of iron atom, and radiative decay processes to the ground state. Especially, the recombination of iron ion with captured electron should accompany cascade de-excitations between closely-spaced excited levels just below the ionization limit, the rates of which become slower as a whole; as a result, these high-lying levels might be more populated than the low-lying levels as if a different LTE condition coexists on the high energy side. This overpopulation could be quantitatively estimated using an enhancement factor (EF), which was a ratio of the observed intensity to the expected value extrapolated from the normal distribution on the low energy side. The EFs were generally small (less than 3); therefore, the cascade de-excitation process would slightly contribute to the population of these excited levels. It could be considered from variations of the EF that the overpopulation proceeded to a larger extent at lower radio-frequency forward powers, at higher flow rates of the carrier gas, or at higher observation heights. The reason for this is that the kinetic energy of energetic particles, such as electrons, becomes reduced under all of these plasma conditions, thus enabling the high-lying levels to be more populated by cascade de-excitation processes from iron ion rather than by collisional excitation processes with the energetic particles. A similar Boltzmann analysis using the EF was also carried out in emission lines of nickel atom, which confirmed the conclusion concerning the atomic lines of iron.
ABSTRACT
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.
ABSTRACT
This paper suggests a correction-free calibration method in wavelength dispersive X-ray fluorescence analysis in order to determine tungsten as a major alloyed element in high-speed steels accurately. Matrix effects on fluorescent X-ray intensity of tungsten Lα line were minimized by borate fusion, and the total amount of tungsten in the glassy matrix could be quantified. Glass bead specimens were prepared with 10 to 12 mg of the steel sample and 4.0 g of lithium tetraborate as a flux agent. Without untraceable X-ray intensity correction, a linear calibration curve was obtained by measuring synthesized calibration standards prepared by using standard solutions. As compared with fundamental parameter calculations, the present method gave more accurate results of tungsten in certified reference materials of high-speed steel.
ABSTRACT
This paper describes several interesting excitation phenomena occurring in a microwave-induced plasma (MIP) excited with Okamoto-cavity, especially when a small amount of oxygen was mixed with nitrogen matrix in the composition of the plasma gas. An ion-to-atom ratio of iron, which was estimated from the intensity ratio of ion to atomic lines having almost the same excitation energy, was reduced by adding oxygen gas to the nitrogen MIP, eventually contributing to an enhancement in the emission intensities of the atomic lines. Furthermore, Boltzmann plots for iron atomic lines were observed in a wide range of the excitation energy from 3.4 to 6.9 eV, indicating that plots of the atomic lines having lower excitation energies (3.4 to 4.8 eV) were well fitted on a straight line while those having more than 5.5 eV deviated upwards from the linear relationship. This overpopulation would result from any other excitation process in addition to the thermal excitation that principally determines the Boltzmann distribution. A Penning-type collision with excited species of nitrogen molecules probably explains this additional excitation mechanism, in which the resulting iron ions recombine with captured electrons, followed by cascade de-excitations between closely-spaced excited levels just below the ionization limit. As a result, these high-lying levels might be more populated than the low-lying levels of iron atom. The ionization of iron would be caused less actively in the nitrogen-oxygen plasma than in a pure nitrogen plasma, because excited species of nitrogen molecule, which can provide the ionization energy in a collision with iron atom, are consumed through collisions with oxygen molecules to cause their dissociation. It was also observed that the overpopulation occurred to a lesser extent when oxygen gas was added to the nitrogen plasma. The reason for this was also attributed to decreased number density of the excited nitrogen species due to collisions with oxygen molecule.
ABSTRACT
When a nitrogen microwave-induced plasma produced with an Okamoto-cavity was employed as a source for the nitridation of steel samples, the characteristics of the plasma were investigated by analyzing a spatially-resolved emission image of nitrogen excited species obtained with a two-dimensionally imaging spectrograph. Our previous study had reported on an excellent performance of the Okamoto-cavity microwave-induced plasma (MIP), enabling a nitrided layer having a several-micrometer-thickness to form on an iron substrate, even if the treatment is completed within 1 min, which is superior to a conventional plasma nitriding using low-pressure glow discharges requiring a prolonged treatment time. In this paper, the reason for this is discussed based on a spectrometric investigation. The emission images of band heads of nitrogen molecule and nitrogen molecule ion extended toward the axial/radial directions of the plasma at larger microwave powers supplied to the MIP, thus elevating the number density of the excited species of nitrogen, which would activate any chemical reaction on the iron substrate. However, a drastic increase in the growth rate of the nitrided layer when increasing the microwave power from 600 to 700 W, which had been observed in our previous study, could not be explained only from such a variation in the excited species of nitrogen. This result is probably because the growth process is dominantly controlled by thermal diffusion of nitrogen atom after it enters into the iron substrate, where the substrate temperature is the most important parameter concerning the mobility in the iron lattice. Therefore, the Okamoto-cavity MIP could contribute to a thermal source through radiative heating as well as a source of nitrogen excited species, especially in the growth process of the nitrided layer.
ABSTRACT
For the rapid and precise sorting of steel scrap with relatively high contents of copper, laser-induced breakdown spectroscopy (LIBS) is a promising method. It has several advantages such that it can work under ambient air atmospheres, and specimens can be tested without any pretreatment, such as acid digestion, polishing of the surface of the specimens, etc. For the application of LIBS for actual steel scrap, we obtained emission spectra by an LIBS system, which was mainly comprised of an Nd:YAG laser, an Echelle-type spectrometer, and an ICCD detector. The standard reference materials (SRMs) of JISF FXS 350-352, which are Fe-Cu binary alloy and have certified concentrations of copper, were employed for making calibration lines. Considering spectral interferences from the emission lines of the iron matrix in the alloys, Cu I lines having wavelengths of 324.754 and 327.396 nm could be chosen. In five replicate measurements of each SRM, shorter delay times after laser irradiation and longer gate widths for detecting the transient emission signal are suggested to be the optimal experiment parameters. In the determination process, utilizing the calibration line from Cu I 327.396 nm was better because of less spectral interference. By using 200 pulsed laser shots for the measurement sequence, a limit of detection of 0.004 Cu at% could be obtained.
