High-purity Materials Research Articles

Thermal expansion of the V 5Si 3 and T 2 phases of the V–Si–B system investigated by high-temperature X-ray diffraction

The thermal expansion anisotropy of the V 5Si 3 and T 2-phase of the V–Si–B system were determined by high-temperature X-ray diffraction from 298 to 1273 K. Alloys with nominal compositions V 62.5Si 37.5 (V 5Si 3 phase) and V 63Si 12B 25 (T 2-phase) were prepared from high-purity materials through arc-melting followed by heat-treatment at 1873 K by 24 h, under argon atmosphere. The V 5Si 3 phase exhibits thermal expansion anisotropy equals to 1.3, with thermal expansion coefficients along the a and c-axis equal to 9.3 × 10 −6 K −1 and 11.7 × 10 −6 K −1, respectively. Similarly, the thermal expansion anisotropy value of the T 2-phase is 0.9 with thermal expansion coefficients equal to 8.8 × 10 −6 K −1 and 8.3 × 10 −6 K −1, along the a and c-axis respectively. Compared to other isostructural silicides of the 5:3 type and the Ti 5Si 3 phase, the V 5Si 3 phase presents lower thermal expansion anisotropy. The T 2-phase present in the V–Si–B system exhibits low thermal expansion anisotropy, as the T 2-phase of the Mo–Si–B, Nb–Si–B and W–Si–B systems.

Influence of coarse particles on microstructure of aluminum nitride sintered body

Aluminum nitride (AlN) is used for quick diffusion and elimination of heat that is generated from electronic devices, such as power modules used for hybrid cars and micro processing units (MPUs) of computers. AlN provides high thermal conductivity, and it is known that its sintering performance and sintered body characteristics vary with the quality of AlN raw powder. When two types of commercially available AlN raw powder produced by the same reductive nitriding method were compared, the sintering performance and the thermal conductivity of sintered compacts processed from low-price AlN material powder were found to be lower than those of sintered compacts processed from high-price, high-purity, evenly granulated, and fine AlN material powder. As one of the causes of the foregoing, the effect of coarse particles contained in AlN material powder was investigated. The investigation results indicated that the coarse particles were AlN and the powder with the coarse particles removed by sifting out with sieves provided sintering performance and sintering behavior similar to those of high-price and high-purity AlN material powder. It was therefore found that the coarse particle constituted a sintering inhibiting factor. This paper reports the investigation results.

Kinetics of the behavior of photosensitive impurities and defects in high-purity semi-insulating silicon carbide

The kinetics of the behavior of photosensitive impurities and defects in the high-purity semi-insulating material 4H-SiC has been studied both theoretically and experimentally using electron paramagnetic resonance (EPR) under photoexcitation and optical admittance spectroscopy. The rate equations describing the processes of recombination, trapping, and ionization of nonequilibrium charge carriers bound dynamically to shallow donors and acceptors (nitrogen and boron), as well as of charge carrier transfer from the shallow nitrogen donor to deep levels of intrinsic defects, have been solved. A comparison of the calculations with the experimental curves plotting the decay of admittance conductance and EPR signal intensities due to nitrogen and boron after termination of photoexcitation has revealed that the probabilities of hole trapping by an ionized acceptor and the rate of ionization of a neutral boron acceptor are two orders of magnitude higher than those of similar processes in a system of donor levels. The latter is dominated by cascade electron transitions between levels in the band gap, as well as by electron-hole recombination.

Room Temperature Mechanical Properties of Fe3Al Intermetallic Alloys with Li and Ni Additions

This work analyzes the effect of very small additions of Li and Ni on the mechanical properties of the Fe72Al28 intermetallic alloy, close to the Fe3Al ratio. Hardness and tensile strength at room temperature were analyzed for the cast Fe3Al intermetallic alloys as a function of Li and Ni additions. For this purpose, high-purity raw materials were melted in an open induction furnace into a SiC crucible and the liquid alloys were poured into sand moulds to directly get tensile test-shaped specimens to minimize machining. Mechanical tests were carried out in the as-cast condition as well as after a homogenization heat treatment at 400 °C for 120 h. The obtained microstructure was characterized by XRD and SEM. Results show an increase in ductility, particularly when Li was added.

202 クエン酸洗浄による籾殻中のセルロース系有機物の加水分解挙動と高純度シリカ焼成灰の作製(循環型廃棄物処理技術(1))

A rice husk is one of agricultural wastes, but useful non-eatable biomasses because it contains 70〜75 mass% organics and about 15 mass% amorphous silica. The objective in the present study is to fabricate high-purity amorphous silica materials originated from rice husks by using citric acid leaching process, not employing the conventional strong mineral acid solutions. The GCMS analysis indicated the citric acid solution was effective for the hydrolysis reaction of cellulose and hemi-cellulose contained in rice husks, and the reactivity increased with increase in the aid concentration of the solution used in leaching. At the same time, the metal impurity contents, such as K, Ca, Mg, Al, were also reduced after citric acid leaching process due to the chelate reaction between their impurities and the carboxyl group (-COOH) of the citric acid solution. As a result, the silica materials with high-purity of 99% or more were obtained from the rice husks.

An international comparison of mass fraction purity assignment of theophylline: CCQM Pilot Study CCQM-P20.e (Theophylline)

Under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a laboratory comparison, CCQM-P20.e, was coordinated by the Bureau International de Poids et Mesures (BIPM) in 2006/2007. Nine national measurement institutes, two expert laboratories and the BIPM participated in the comparison. Participants were required to assign the mass fraction of theophylline present as the main component in two separate study samples (CCQM-P20.e.1 and CCQM-P20.e.2).CCQM-P20.e.1 consisted of a high-purity theophylline material obtained from a commercial supplier. CCQM-P20.e.2 consisted of theophylline to which known amounts of the related structure compounds theobromine and caffeine were added in a homogenous, gravimetrically controlled fashion. For the CCQM-P20.e.2 sample it was possible to estimate gravimetric reference values both for the main component and for the two spiked impurities.In addition to assigning the mass fraction content of theophylline for both materials, participants were requested but not obliged to provide mass fraction estimates for the minor components they identified in each sample.The results reported by the study participants for the mass fraction content of theophylline in both materials showed good levels of agreement both with each other and with the gravimetric reference value assigned to the CCQM-P20.e.2 material. There was also satisfactory agreement overall, albeit at higher levels of uncertainty, in the quantification data reported for the minor components present in both samples. In the few cases where a significant deviation was observed from the consensus values reported by the comparison participants or gravimetric reference values where these where available, they appeared to arise from the use of non-optimal chromatographic separation conditions.The results demonstrate the feasibility for laboratories to assign mass fraction content with associated absolute expanded uncertainties in the range 0.05% to 0.5% for solid organic compounds of high purity (mass fraction of main component >995 mg/g) and in the range 0.1% to 1% for compounds of lower purity (mass fraction of main component >980 mg/g).Main text.To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM Working Group on Organic Analysis.

Conditions for CeS Formation During Manufacturing of Ce–S–Al Based Grain Refiners for Steels

In the present investigation the phase relations within the Ce–S–Al system have been clarified, using a combination of optical microscopy and WDS microprobe analyses. As a starting point high-purity charge materials of cerium, aluminium and Ce2S3 were melted and superheated to about 2000°C within small tantalum crucibles inside a dedicated laboratory furnace filled with cleaned argon. The main constituent phases detected in the as-solidified samples are CeS, Ce3Al, CeAl and γ-Ce, where the CeS phase constitutes a discontinuous dendritic network within the grain refiners. The melting experiments show that pure cerium can dissolve about 6 wt% of sulphur at 2000°C, which drops to approximately 1.8 wt% at 1500°C. The measured sulphur solubility is considerable lower than that inferred from the existing binary Ce–S phase diagram, which therefore should be revised to comply with these new measurements. Because alloying with aluminium reduces the sulphur solubility in liquid cerium, the addition of this element should be restricted if a high volume fraction of CeS is desired in the grain refiners. At the same time the use of Ce2S3 as a sulphur source in replacement of pyrite (FeS2) means that aluminium is not actually needed to prevent the grain refiners from disintegrating in contact with air due to internal oxidation.

Phase Relations in Ce–Al–Fe–S Based Grain Refiners for Steels

In the present investigation the phase relations within the Ce–Al–Fe–S system have been clarified, using a combination of optical microscopy and WDS microprobe analyses. As a starting point high-purity charge materials of cerium, aluminium and FeS2 are melted and superheated to about 2000°C within small tantalum crucibles inside a dedicated laboratory furnace filled with cleaned argon. The phases detected in the as-solidified samples were CeS, Ce3Al, Fe2Ce and γ-Ce, along with Ce2O2S, which is an undesirable microconstituent in CeS-based grain refiners. It is concluded that FeS2 can be used as a sulphur source for addition up to about 4 wt% sulphur. At higher levels the Fe–Ta interaction becomes so vigorous that tantalum no longer acts as an inert refractory metal and wetting becomes a major problem. In contrast, aluminium is an essential alloying element in the sense that it prevents the grain refiners from disintegrating in contact with air due to internal oxidation of free cerium by promoting the formation of Ce3Al.

The Challenge for Large-scale Vapor-phase Growths of Not-catalyzed ZnO Nanostructures: Purity vs. Yield

AbstractLarge-scale growth capability is a general requirement for any reliable and cost-effective device application. Catalyst-free vapor-phase growth techniques generally let obtain high purity materials, but their application in large-scale growths of zinc oxide (ZnO) nanostructures is not trivial, because the lack of catalysts makes the control of these process rather difficult. Three different optimizations of the basic vapor phase growth have been studied and performed to obtain selected and reproducible growths of three different ZnO nanostructures with improved yield, i.e. nanotetrapods, nanowires and nanorods. No precursor or catalyst has been used in order to reduce contamination sources as more as possible.

Improved Plasma Synthesis of Si-nanopowders by Quenching

Silicon nanopowders are investigated intensively for application in microelectronics and energy among them.[1–3] However, for the moment the control of the product high quality and the processing costs are limiting their breakthrough. RF-thermal plasmas could respond to both criteria as it is a continuous process achieving high production volume while ensuring a good synthesis control from the gaseous phase. The absence of electrodes for igniting the plasma and the controlled process atmosphere of RF-plasmas are beneficial for producing high purity materials. Typically a supersaturated gaseous phase containing the precursor is condensed rapidly after nucleation took place. The nanoparticles grow then subsequently by coagulation and coalescence.[4] This rapid condensation is achieved either by natural thermal gradients in the plasma or by quenching using a cold source (gas or cold surface) or by using an expansion.[5–8] This paper addresses the development of a specific quenching nozzle design combining rapid cooling with an expansion for controlling the size of silicon nanopowders processed by an inductively coupled plasma (ICP). The design of the quenching device has been supported by computational fluid dynamic (CFD) calculations aiming at modelling the plasma properties like among them the temperature and the velocity of the powderfree plasma. The modelling has been validated by in-situ plasma characterization using an enthalpy-probe coupled to a mass spectrometer. The produced nanopowders were collected either on a filter membrane, or directly in the gas phase using an on-line and in-situ sampling system made of a TEM-grid fixed on a moveable support and then ex-situ characterized by XRD, Raman, microscopy and surface specific area measurement using the BET technique.

High-purity amorphous silica originated in rice husks via carboxylic acid leaching process

The environmentally benign, harmless to human, and economically effective process to produce high-purity amorphous SiO2 materials from rice husks has been established by using a carboxylic acid leaching, not the conventional strong acids. TG-DTA measurement and GCMS analysis indicated that the leaching was effective for the hydrolysis of celluloses and hemicelluloses contained in rice husks at 473–873 K, which produced the same results in using the conventional sulfuric acid. In particular, the formation of furfurals and levoglucosans occurred via the hydrolysis at 473 K and 673 K, respectively, when using rice husks leached by citric acid solutions. The metallic impurities could be also removed from the husks via a chelate reaction between carboxyl groups (–COOH) and the metal elements. Concerning the burning conditions of rice husks after the acid leaching, it was necessary to supply a suitable amount of air to completely combust organics; for example, it required air supplement of 50 mL/min or more. High-purity amorphous silica materials with 99 wt% or more were prepared from rice husks by applying the citric acid leaching treatment and burning process at 1073 K in air.

Scanning electron microscopes Microscan of the MS20 series

A new series of scanning electron microscopes Microscan (MS20) has been developed at the Institute of Microelectronics Technology and High-Purity Materials, Russian Academy of Sciences. The main distinctive feature of these instruments is the modular design of all units and systems, which ensures a high level of unification.

Oxidation Behavior of Mo Containing Alloys

In this study, high temperature (T>500oC) oxidation behavior of two commercial Ni-base alloys and two experimental alloys, all containing more than 10% Molybdenum, is investigated. Experimental alloys were prepared from high purity materials using an arc-melting furnace under a protective environment. During tests, samples were exposed to the stagnant air environment of a high temperature furnace for predetermined times. Extent of oxidation was determined from sample mass change measurements as well as morphological and chemical analyses of the oxidation products. For analyses, a scanning electron microscope (SEM) equipped with backscattered electron (BE) and energy dispersive spectroscopic (EDS) detectors was used. Crystalline phases formed in the product scales over the alloy samples were identified by an x-ray diffractometer (XRD). Preliminary results indicate that although Mo in the alloy prevents the development of a protective oxide scale at the alloy surface, presence of alloying elements such as Cr or Al can decrease this negative effect of Mo on oxide scale formation.

Influence of surface properties of ceramic particles on their incorporation into cobalt electroless deposits

The purpose of this work was to elucidate factors affecting electroless codeposition of metal with ceramic particles. Codeposition of various particles with Co-P in an alkaline solution was compared. Powders of SiC, Al 2O 3 and SiO 2 were used. It was found that surface properties of the technical powders were different from that reported for materials of high purity. Codeposition of SiC was favored by a positive surface charge of the particles, while negative surface charges of alumina and silica inhibited their embedding. The positive surface charge of SiC particles corresponded to low adsorption of cobalt ions and increased adsorption of hypophosphite anions, while opposite dependencies for alumina and silica were observed.

Thermodynamics of electrolyte solutions

The theoretical description of the thermodynamic properties of electrolyte solutions is of great importance for predictions and practical calculations related to the production of high-purity chemical compounds and materials with preset properties. In the present study, the general principles of the construction of electrolyte solution models are developed on the basis of the general statistical approach to the description of interactions in solutions. Let us consider dilute solutions (without loss of generality, aqueous solutions) containing N particles of the

Adiabatic Calorimetry as Support to the Certification of High-Purity Liquid Reference Materials

The certification of high-purity liquid reference materials is supported by several analytical techniques (e.g., gas chromatography, liquid chromatography, Karl Fischer coulometry, inductively coupled plasma mass spectrometry, differential scanning calorimetry, adiabatic calorimetry). Most of them provide information on a limited set of specific impurities present in the sample (indirect methods). Adiabatic calorimetry [1] complementarily provides the overall molar fraction of impurities with sensitivity down to few μmol · mol−1 without giving any information about the nature of the impurities present in the sample (direct method). As the combination of adiabatic calorimetry with one (or more than one) indirect chemical techniques was regarded as an optimal methodology, NMi VSL developed an adiabatic calorimetry facility for the purity determination of high-purity liquid reference materials [2]. Within the framework of collaboration with NMIJ, a benzene-certified reference material (NMIJ CRM 4002) from NMIJ was analyzed by adiabatic calorimetry at NMi VSL. The results of this measurement are reported in this paper. Good agreement with the NMIJ-certified purity value (99.992 ± 0.003) cmol · mol−1 was found. The influence of different data analysis approaches (e.g., extrapolation functions, melting ranges) on the measurement results is reported. The uncertainty of the measured purity was estimated.

Heterogeneous nucleation in a glass-forming alloy

Nucleation in the undercooled liquid state in the bulk metallic glass-forming composition Zr52.5Cu17.9Ni14.6Al10Ti5 (VIT-105), produced using high purity (PA) and commercial purity (CA) raw materials was investigated using electrostatic levitation and ex situ neutron diffraction. The CA material was observed to have a lower density than the PA sample and crystallized at relatively shallow undercooling. The densities of the samples at temperatures above the solidus showed an oxygen-dependent hysteresis associated with the state change, indicating the presence of oxygen-stabilized intermetallics. The PA alloy exhibited three distinct crystallization modes dependent on the thermal history of the melt, one of which showed a net volume expansion.

Depth resolved Doppler broadening measurement of layered Al–Sn samples

The accumulation of positrons in a two-dimensional layer of tin embedded in aluminum is examined by Doppler broadening spectroscopy (DBS). For this purpose samples are grown out of high purity materials consisting of a step-shaped layer (0.1–200 nm) of tin on a substrate of aluminum and covered by an aluminum layer of constant thickness (200 nm). The positron implantation profile is varied by different positron acceleration energies of up to 15 keV. The pre-thermal implantation profile of the monoenergetic positron beam is examined since the effect of thermal positron diffusion is less significant at tin layers thicker than 50 nm. At thin layers (<50 nm), the positrons greatly accumulate either at the aluminum–tin interface or in the tin layer due to its higher positron affinity compared to aluminum. Thus a very high sensitivity of the measurement for low densities of tin is observed. Consequently from the experimental results, a sensitivity threshold for the detection of a low amount of tin in an aluminum matrix with DBS is determined. The DB results are compared to theory by an approximation for pre-thermal implantation in layered materials.

Development of certified reference materials of high-purity volatile organic compounds: purity assay by the freezing-point depression method

For accurate measurement of concentrations of substances by instrumental analysis, reliable calibration standards are needed. In Japan, national reference materials are supplied under the national standards dissemination system named the Japan Calibration Service System (JCSS). In JCSS, calibration standards for the analysis of environmental pollutants are supplied. For the traceability to the SI of reference materials for calibration in JCSS, the National Metrology Institute of Japan (NMIJ) is developing high-purity reference materials of volatile organic compounds (VOCs) as NMIJ CRMs. The freezing-point depression method, which has potential as a primary method of measurement, is employed for the determination of property value. In this paper, a development scheme of certified reference materials of high-purity VOCs is described.

EDTA assisted sol–gel synthesis of ZrW2O8

A novel sol–gel synthetic route using water-soluble precursor salts is presented as a synthetic path for a high-purity negative thermal expansion material, ZrW2O8. This synthetic route involves a sol–gel method with the use of EDTA as complexing agent. The aqueous solution is transformed into a ceramic material after a two-step heat treatment: gelation at 60 °C and reactive sintering at 1,180 °C. The decomposition of the gel is monitored with infrared spectroscopy and TGA. The high-temperature heat treatment results in ZrW2O8 with its characteristic negative thermal expansion behaviour α[75–130 °C]: −9.8 ± 1.6 μm/m °C and α[175–300 °C]: −1.2 ± 0.2 μm/m °C.