Simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by slurry-sampling graphite furnace AAS.

A fast and accurate analytical method was established for the simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by graphite furnace atomic absorption spectrometry using a slurry sampling technique and a Hitachi Model Z-9000 atomic absorption spectrometer. The slurry samples were prepared by the ultrasonication of silicon carbide or silicon nitride powders with 0.1 M nitric acid. Calibration curves were prepared by using a mixed standard solution containing aluminum, calcium, iron and 0.1 M nitric acid. The analytical results of the proposed method for aluminum, calcium and iron in silicon carbide and silicon nitride reference materials were in good agreement with the reference values. The detection limits for aluminum, calcium and iron were 0.6 microg/g, 0.15 microg/g and 2.5 microg/g, respectively, in solid samples, when 200 mg of powdered samples were suspended in 20 ml of 0.1 M nitric acid and a 10 microl portion of the slurry sample was then measured. The relative standard deviation of the determination of aluminum, calcium and iron was 5 - 33%.     

粉末压饼LA-ICP-MS测定土壤样品中微量元素

研究了采用粉末压饼制样LA-ICP-MS测定土壤样品中多元素的分析方法.在土壤样品中事先加入已知含量的In,并以聚四氟乙烯(PTFE)为粘合剂,在200 KN的压力下制备用于激光剥蚀的压饼.详细讨论了粉末压饼样品中元素的均一性及元素相对信号响应.所建立的方法用于土壤标准参考物质固体样品的直接分析,测定值与参考值具有较好的一致性.     

Application of glow discharge mass spectrometry to multielement ultra-trace determination in ultrahigh-purity copper and iron: a calibration approach achieving quantification and traceability

A new approach was developed for quantitative calibration in GD-MS which can afford reliable and metrologically traceable results for many trace elements and was exemplified for pure copper and pure iron. It can be assumed that the technique can be further improved and applied to the analysis of other pure metals. Pressed copper and iron powder samples were used to calibrate the glow discharge mass spectrometry applied to the analysis of pure copper and iron. The new type of glow discharge mass spectrometer—the Element GD (Thermo Electron Corporation)—was used with a Grimm-type discharge cell for flat samples. Two series of powder samples were prepared for each of the copper and iron matrixes. The powders were quantitatively doped with solutions of graduated and defined concentrations of 40 or 20 analytes, respectively. The mass fractions of the analytes in the dried and homogenized metal powder samples ranged from μg/kg levels up to 10 mg/kg levels. A special technique was developed to press the samples and to form mechanically stable pellets with low risk of contamination. Ion beam ratios of analyte ions to matrix ions were used as measurands. The calibration curves were determined and the linear correlation coefficients were calculated for different intervals of the curves. The linear correlation coefficients are very satisfactory for most of the calibration curves, which include the higher segments of mass fractions; however, they are less satisfactory for the lower segments of the calibration curves. Nevertheless, in many cases rather acceptable and rather promising values were achieved even for these lower segments, representing mass fractions of analytes at ultra-trace level. The comparison of the certified values of different reference materials with the measured values based on calibrations with the pressed powder samples led to deviations less than 30% for most of the considered examples.      

Investigation of catalytic activity of ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles in the thermal decomposition of ammonium perchlorate

A new powder metallurgy technique was developed in order to increase the reinforcement proportion of aluminum with two different fractions of Al₂O₃. Aluminum powders were mixed with 20 % vol of alumina particles as primarily reinforcement, and additional alumina was produced in situ as a result of reaction between Al and additional 7.5 % vol of Fe₂O₃ powder. The three grades of powders were milled and hot-pressed into small preforms, and differential scanning analysis (DSC) was performed to determine the kinetics of microstructural transformations produced on heating. DSC curves were mathematically processed to separate the superposing effects of thermal reactions. Transformation points on resulting theoretical curves evidenced two distinct exothermal reaction peaks close to the melting point of aluminum that were correlated with formation of Fe–Al compounds and oxidation of aluminum. Microstructural investigations by means of SEM-EDX and XRD suggested that these exothermal reactions produced complete decomposition of iron (III) oxide and formation of Fe–Al compounds during sintering at 700 °C, and therefore, heating at higher temperatures would not be necessary. These results, along with calculation of activation energies, based on Kissinger’s method, could be used to optimize the fabrication of Al-Al₂O₃ composites by means of reactive sintering at moderate temperatures.     

Magnetic Properties of Ball-Milled Nanocrystalline Alloys Fe78B13Si9

 Magnetic properties of nanocrystalline Fe₇₈B₁₃Si₉ alloys are studied for three series prepared by ball milling starting from amorphous ribbons, crystallized ribbons, and elemental powders. Temperature variation of static magnetization results in strong ferromagnetic interaction which is weakly dependent on the initial material. Magnetic hysteresis loops show that saturation magnetization, magnetic remanence, and coercive field increase with frequency for both series of ribbon samples, whereas they decrease for alloys prepared from elemental powders. Power losses raise faster for the alloys prepared from elemental powders than for the two other alloys.     

X-射线荧光光谱法(XRF)测定钼精矿中多种元素

详细论述了压片法及熔融片法测定钼精矿的分析条件。其中压片法通过大量采用同一矿区的生产样品经化学定值后作为校准样品建立校准曲线,因此粒度效应和矿物效应基本上可忽略。详细地讨论了元素之间谱线干扰、背景和脉冲高度选择。使用经验系数法校正基体效应,可准确测定钼精矿中的钼、硫、铁、铜、铅、锌等11种元素。在熔融片法中主要讨论了元素谱线的选择及其相互之间的干扰,经理论α系数校正后,可准确测定不同钼矿中的多种元素,其适用范围更广。     

Magnetic Properties of Ball-Milled Nanocrystalline Alloys Fe78B13Si9

Summary.  Magnetic properties of nanocrystalline Fe₇₈B₁₃Si₉ alloys are studied for three series prepared by ball milling starting from amorphous ribbons, crystallized ribbons, and elemental powders. Temperature variation of static magnetization results in strong ferromagnetic interaction which is weakly dependent on the initial material. Magnetic hysteresis loops show that saturation magnetization, magnetic remanence, and coercive field increase with frequency for both series of ribbon samples, whereas they decrease for alloys prepared from elemental powders. Power losses raise faster for the alloys prepared from elemental powders than for the two other alloys. Received October 5, 2001. Accepted (revised) November 12, 2001     

Composite SiO2—Iron Oxide Materials for Magnetically Intensified Adsorption

Composite SiO₂—iron oxide materials were prepared by three experimental procedures. In the first case, the iron oxides were precipitated during a sol-gel process. In the second case, a SiO₂ matrix was initially obtained, and the iron oxides were formed by thermal treatment after impregnation of a soluble Fe²⁺ salt in the previously processed matrix. In the third method, ferrite powders, prepared by wet chemical method, were embedded into a SiO₂ based sol-gel matrix. Materials with convenient porosity and nano-sized iron oxide content could be prepared using the mentioned methods. The prepared composite has been tested for arsenic(V) removal.     

XPS分析固体粉末时的样品制备法研究

用XPS分析固体粉末样品时通常将粉末直接撒在双面胶带上进行测试.这种方法粉末容易脱落,并导致仪器污染或损坏.本文介绍一种将粉末样品铺在胶带上压成薄层进行测试的制样方法.后一种方法不需模具,简单快捷,实验表明它不仅有利于保护仪器,而且有利于提高XPS分析的灵敏度和分辨率.     

Analysis of organic compounds with SNMS

Summary Plasma-based Secondary Neutral Mass Spectrometry (SNMS) as a depth-resolving technique was examined for the first time as a method for the quantitative analysis of heterogeneously distributed organic compounds in environmental material. Using argon ion bombardment (340 eV, 2 mA/cm²) SNMS was applied to a variety of organic compounds. Aliphatic and aromatic hydrocarbons as well as organic compounds with heteroelements yielded mass spectra with predominant atomic signals of carbon and all other elements composing the organic compound. Except for molecularly bound chlorine and nitrogen these signals were found to be governed primarily by atomic ionization probabilities, a prerequisite for elemental quantitation with low matrix dependence. For oxygen as one of these elements matrix dependent variations of the relative detection factor of ±40% were obtained in agreement with average deviations reported for alloy samples. The organic character of the samples is manifested in the appearance of C_mH_n clusters with relative yields declining with increasing number of atoms. The CH signal turned out to be proportional to the hydrogen content regardless of the molecular structure of the compound. This is of analytical importance because low mass separation usually hampers reliable detection of atomic hydrogen with quadrupole mass filters. Other heteroelemental clusters were not detected in significant amounts.     

Analytical Techniques Applied in Optimization of Electrophoretic Deposition of Thin Film YBCO Superconductors

 YBa₂Cu₃O _7−x (x = 0.1–0.2) compounds (YBCO) were produced by the oxalate coprecipitation and the solid state reaction methods. The powders obtained were used for the production of YBCO superconducting coatings on Pt/Si wafers, by the electrophoretic deposition technique. The optimum process conditions for the production of both powders and coatings were found by using a combination of modern analytical techniques. The thermal treatment of the samples was followed by thermogravimetry (TG) and differential scanning calorimetry (DSC). The optimization and characterization of the superconducting properties of the powders and coatings were achieved by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), optical microscopy, magnetic susceptibility and electrical resistivity measurements.     

The role of the trivalent metal in an LDH: Synthesis, characterization and fire properties of thermally stable PMMA/LDH systems

Two layered double hydroxides (LDHs), calcium aluminum undecenoate (Ca₃Al) and calcium iron undecenoate (Ca₃Fe), have been prepared by the co-precipitation method. XRD analysis of these LDHs reveals that they are layered materials and FT-IR and TGA confirmed the presence of the undecenoate anions in the material produced. The PMMA composites were prepared by bulk polymerization and the samples were characterized by XRD, TEM, TGA and cone calorimetry. Both additives greatly enhance the thermal stability of PMMA, while the calcium aluminum LDH gives better results when the fire properties were examined using the cone calorimeter.     

Mechanical Activation of Inorganic Powders by vibromilling

Mechanochemical polymerization of vinyl monomers on vibromilled aluminum, iron and silica powders were examined at 293 K. It was found that aluminum and silica powders were effective as an initiator for the polymerization even after milling. The order of the monomer reactivity on the vibromilled silica powder was vinyl acetate < styrene < methyl methacrylate < acrylonitrile and it was in agreement with the order of monomer reactivity in anionic polymerization. The activity of examined powders as the initiator for the polymerization of methyl methacrylate was iron < aluminum ? silica and it was explained by the emission intensities and the kinetic energies of exoelectron emitted from powders.     

Fused glass sample preparation for quantitative laser-induced breakdown spectroscopy of geologic materials

Laser-induced breakdown spectroscopy is a powerful analytical method, but LIBS is subject to a matrix effect which can limit its ability to produce quantitative results in complex materials such as geologic samples. Various methods of sample preparation, calibration, and data processing have been attempted to compensate for the matrix effect and improve LIBS precision. This study focuses on sample preparation by comparing fused glass as a preparation for powdered material to the more commonly used method of pressing powder into pellets for LIBS analysis of major elements in complex geologic materials. Pelletizing powdered material is a common and convenient method for preparing samples but problems with the physical matrix brought on by inconsistencies in the homogeneity, density, and laser absorption, coupled with the chemical matrix problem lead to spectral peak responses that are not always consistent with the absolute concentration of representative elements. Twenty-two mineral and rock samples were analyzed for eight major oxide elements. Samples were prepared under both glass and pellet methods and compared for internal precision and overall accuracy. Fused glass provided a more consistent physical matrix and yielded more reliable peak responses in the LIBS analysis than did the pressed pellet preparation. Statistical comparisons demonstrated that the glass samples expressed stronger separability between different mineral species based on the eight elements than for the pressed pellets and showed better spot-to-spot repeatability. Regression models showed substantially better correlations and predictive ability among the elements for the glass preparation than did those for the pressed pellets.     

Thermal analysis of ammonium,mono-, di- and triethanolammonium alginates

Thermal behaviour of ammonium (NH₄alg), mono- (MEAalg), di- (DEAalg) and triethanolammonium (TEAalg) salts of alginic acid (Halg) was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). Salts were prepared by the direct reaction of alginic acid with the ammonium hydroxide and with the respective ethanolamines. After preparation the compounds were lyophilized during 24 h and characterized by FTIR spectroscopy and elemental analysis (C, H and N). Under air the compounds exhibited three successive thermal decomposition steps: dehydration, decomposition of the polymeric matrix and finally, burning of carbonaceous residue. Under nitrogen two steps (dehydration and decomposition) were observed. The stability order of this series of compounds was: TEAalg this series of compounds was: TEAalg<DEAalg<NH₄alg<Halg≈MEAalg. DSC curves between –50 and 150°C did not show any thermal events suggesting that after lyophilization probably non-freezing type water is present in the system.     

Comparison of action of mixed permanent chemical modifiers for cadmium and lead determination in sediments and soils by slurry sampling graphite furnace atomic absorption spectrometry

Slurry sampling atomic absorption spectrometry with electrothermal atomization was used to the determination of cadmium (Cd) and lead (Pb) in soils and sediments using permanent modifiers. Comparison of action of mixed permanent modifiers niobium (Nb)/iridium (Ir) and tungsten (W)/iridium (Ir) were studied in detail. The effect of amount of Ir, W and Nb on analytical signals of Cd and Pb was examined. The optimal amounts of modifiers for Cd and Pb determination were stated. Niobium carbide formation on graphite surface was studied for different pyrolysis temperatures. Finally for Cd determination in sediments and soils 200 μg of Nb mixed with 5 μg of Ir was used as permanent modifiers and 15 μg of Nb mixed with 200 μg of Ir for Pb determination. Suspensions were prepared in 5% HNO₃. The analytical procedure was optimized carefully basing on data from pyrolysis and atomization curves studies. Ammonium dihydrogen phosphate was used additionally as matrix modifier during Cd determination in samples in order to prevent interferences coming from matrix components. The analysis of CRMs confirmed the reliability of the proposed approach. The precision and accuracy of Cd and Pb determination by the described method for soils and sediments were acceptable.     

Magnetic properties of lanthanum orthoferrite fine powders prepared by different chemical routes

Fine powders of lanthanum iron oxide, LaFeO₃, have been prepared by solid state reaction as well as sol-gel synthesis and nebulized spray pyrolysis. Structures, morphologies and magnetic susceptibility measurements of these powders have been examined. The powders prepared by all the three low-temperature routes contain nearly spherical particles with an average diameter of 40 nm. These samples show a lower Neel temperature than the powder prepared by solid state reaction besides showing much lower magnetic susceptibility at low temperatures. Dedicated to Professor C N R Rao on his 70th birthday     

Identification of sulfur interferences during organotin determination in harbour sediment samples by sodium tetraethyl borate ethylation and gas chromatography-pulsed flame photometric detection

Because of the high toxicity of organotin compounds and the current regulation about their applications, analytical method usable in routine analysis is required. A speciation procedure based on NaBEt4 ethylation and GC-PFPD analysis has shown to be suitable for the organotin determination. Unfortunately, some matrix effects were observed during the analysis of harbour sediments from Chile. These effects were identified as the alkylation of elemental sulfur and the coelution between the organotin compounds and some dialkylsulfides. The re-optimization of GC parameters and application of solid phase microextraction (SPME) were proposed to solve these analytical problems. Certified reference materials and different harbour sediment samples were analysed in order to evaluate the suitability of the methods for organotin control in complex environment samples.     

Joint reduction of Fe(III), Ni(II), and Co(II) ions in solution in contact with aluminum

Joint reduction of iron group metals in aqueous solutions on a dispersed aluminum matrix was studied. The powders obtained were examined by X-ray phase analysis and electron scanning microscopy.     

Insight of solvent extraction process: Reassessment of trace level determinations

Solvent extraction is hoary yet modern technique with great scope of research due to the various intriguing phenomena in the system. Tri-n-butyl phosphate (TBP) is a well known extractant which has been extensively used for separation of uranium matrix prior to elemental profiling. In this paper, one of the impurities namely Fe is being considered as it posed a challenge to the separation due to its co-extraction with TBP along with uranium. In these studies, for the first time, the existence of cation-cation inner sphere complexes between the UO₂²⁺and Fe³⁺ ions in both aqueous and organic phases have been establisted in addition to the selective separation of iron from uranium sample matrix using only TBP. The data from both spectrophotometric and thermophysical studies corroborated one another confirming the presence of cation-cation interactions (CCIs). The developed solvent extraction with only TBP showed almost no interferences on the iron extraction from matrix uranium and other co-ions like aluminum and copper. This has been the first time application of pure TBP for selective removal of iron from uranium samples. The procedure possessed excellent reproducibility and robustness.