Contemporary superconducting materials

Superconductors currently under active study are briefly described from a chemical perspective. The author's current views on those superconductors, the role of theory in searching for new superconductors, and possibilities for new superconducting materials that might be found in the future are presented.     

Neutron activation determination of the oxygen factor for high temperature superconducting materials

Due to its precision and sensitivity, activation analysis can be applied in investigating the composition of high temperature superconducting materials (HTSC) including determination of the oxygen factor. When activation is ensured with fast neutrons, it is expedient that the oxygen factor be determined by the ratio of oxygen to one of the elements of the matrix. In case of yttrium-based ceramics the analytical parameter is chosen in the form of a ratio of activities due to oxygen and yttrium. Other types of HTSCs were analyzed in terms of O/Cu ratio. The relative standard deviation rangea from 0.3 to 0.5% for O/Y and O/Cu ratios for 10 replicate analyses of the same sample.     

Characterisation of porous materials for bioseparation

A set of chromatographic materials for bioseparation were characterised by various methods. Both commercial materials and new supports presenting various levels of rigidity were analysed. The methods included size-exclusion and capillary phenomena based techniques. Both batch exclusion and inverse size-exclusion chromatography were used. Gas adsorption, mercury porosimetry and thermoporometry were applied as well as a new method based on water desorption starting from the saturated state. When the rigidity of adsorbents is high enough, the agreement is reasonable between the values of the structural parameters that were determined (surface area, porosity, and pore size) by various methods. Nevertheless, a part of macroporosity may not be evidenced by inverse size-exclusion chromatography whereas it is visible by batch exclusion and the other methods. When the rigidity decreases, for example with soft swelling gels, where standard nitrogen adsorption or mercury porosimetry are no more reliable, two main situations are encountered: either the methods based on capillary phenomena (thermoporometry or water desorption) overestimate the pore size with an amplitude that depends on the method, or in some cases it is possible to distinguish water involved in the swelling of pore walls from that involved in pore filling by capillary condensation.     

Fast multi-element screening of non-digested biological materials by slurry introduction to ICP-AES

A fast method for direct multi-element analysis of non-digested biological samples is presented. The only sample preparation needed is 1 min homogenization with a Polytron mixer in a small volume of neutral phosphate buffer saline solution (PBS). The total time for analysis (sample preparation and measurement) is 4 min only. This “mix and measure” method can handle large sample loads of biological samples and thus minimize dilution of trace elements. For example 100% whole blood was introduced without any clogging of the introduction system or extinguishing of the plasma. In 70% (v/v) whole blood reference material 14 of 16 analytes were quantified within ±10% (Al, B, Ba, Ca, Cu, Fe, Mg, Mn, P, Pb, S, Sr, Ti and Zn) and two semi-quantified within ±20% (Cd and K). Fresh bovine liver was also analyzed with the same method and 7 of 9 analytes were quantified in 5% (w/v) liver slurry. Three different nebulizers were tested, Glass Expansion Concentric (GEC) of Meinhard type, Cross Flow and Burgener T2100 and they performed roughly equally well in giving quantitative results for the slurries but the sensitivity was better with the GEC. The stability of the plasma was studied by evaluating the ratio of Mg 280.270 nm and Mg 285.213 nm lines. When increasing the sample load from 20 to 100% (v/v) of whole blood and from 0.5 to 10% (w/v) of bovine liver the Mg ratio was constant within a few percent for all of the nebulizer tested. The ratio of the sensitivity between GEC and Burgener T2100 was studied and the ratio increased with the energy sum for atomic and ionic lines separately.     

Microwave assisted extraction for trace element analysis of plant materials by ICP-AES

Application of microwave assisted extraction for the decomposition and dissolution of plant samples for trace metal determination by ICP-AES was examined. Dried onion, leaves of spinach beet and three reference materials CTA-OTL-1, CTA-VTL-2 and CL-1 were analyzed. Water, EDTA and hydrochloric acid (0.01, 0.10 and 1.0 M, respectively) were used as leaching solutions. The extraction efficiency was investigated by comparison of the results with those obtained after microwave wet digestion. HCl was found to be very suitable for quantitative extraction of B, Ba, Cd, Cu, Mn, Ni, Pb, Sr and Zn from the samples. For reference materials, the measured concentrations are well consistent with the certified values. The use of EDTA led to a complete extraction of B, Cd, Ni, Pb, Sr and Zn. Water was found to be a good leaching solution for boron. For extraction with HCl and EDTA, the RSD values for the concentrations measured were below 8% for most of the elements. Received: 4 May 2000 / Revised: 20 June 2000 / Accepted: 22 June 2000     

Microwave assisted extraction for trace element analysis of plant materials by ICP-AES

Application of microwave assisted extraction for the decomposition and dissolution of plant samples for trace metal determination by ICP-AES was examined. Dried onion, leaves of spinach beet and three reference materials CTA-OTL-1, CTA-VTL-2 and CL-1 were analyzed. Water, EDTA and hydrochloric acid (0.01, 0.10 and 1.0 M, respectively) were used as leaching solutions. The extraction efficiency was investigated by comparison of the results with those obtained after microwave wet digestion. HCl was found to be very suitable for quantitative extraction of B, Ba, Cd, Cu, Mn, Ni, Pb, Sr and Zn from the samples. For reference materials, the measured concentrations are well consistent with the certified values. The use of EDTA led to a complete extraction of B, Cd, Ni, Pb, Sr and Zn. Water was found to be a good leaching solution for boron. For extraction with HCl and EDTA, the RSD values for the concentrations measured were below 8% for most of the elements.     

Characterisation of raw materials for production of ceramics

The aim of this paper is to characterize some raw materials used for ceramics material production. Five samples of clay have been analyzed. It has been carried out a patterned sampling in a quarry in Rosarno (South Italy). Chemical-physical properties on clay samples are determined. Test pieces have been prepared and physical properties after firing are determined by DSC thermal analysis, XRD analysis and X-ray fluorescence. It is important to note the high amount of Fe₂O₃. The mixture principally contains quartz, illite and oligoclase. It has been observed the colour and the shape after firing: predominant colour is red. In this case the clay has been used in mixtures covered with glazes. The colour of internal clay is hidden by opaque of glazes. The analysed raw materials can be used in a slip for single fired red tiles. The A2sp clay produces best ceramics at 1000°C.     

Quantitative electron probe microanalysis of Y-Ba-Cu-O superconducting materials

The high temperature superconductor YBa₂Cu₃O_7–x has been studied by quantitative electron probe microanalysis (EPMA). After investigation of appropriate standards and choice between three different matrix correction methods this technique provides very accurate analytical results including those for oxygen. The quantitative results even allow the determination of the stoichiometry with deviations less than 2% relative. The application of computercontrolled EPMA is demonstrated by the characterization of the microstructure of a ceramic Y-Ba-Cu-O sample. Finally the properties of copperL ₂ andL ₃ valence band spectra are presented for compounds with copper in different valence state.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Studies of polycrystalline materials by Pseudo Kossel technique

In contrast to the Kossel Technique the Pseudo Kossel Technique (PKT) is mainly used for investigations of single crystals to determine the crystal structure, the crystallographic orientation and lattice parameter of the specimens so far. Though the PKT has yet large possibilities and is well-suited also for micro range investigations, the application for the characterization of polycrystalline materials is not common. The complicated configuration of the reflex sections in polycrystals, caused by grain boundary effects, usually makes it very difficult to evaluate them. The studies have been carried out at Al and BaTiO₃ polycrystals. Thus, for the first time the successful application of the technique to a ceramic was demonstrated. The dependence of the reflex length on the grain size was investigated by simulation. It is shown that this technique allows precise determination of correlation between neighbor grains, since one diffraction pattern contains contributions from several grains. As a result one obtains for example the relative orientations of neighbor grains, which influence among other things the electrical and mechanical properties. Received: 5 November 1998 / Revised: 26 March 1999 / Accepted: 3 April 1999     

Characterisation of stabilizers in polyamide using DSC technique

Antioxidants are added to the polymers to suppress oxidation during the service life. The paper deals with determination of stabilizer (VANOX-SKT) antioxidant in polyamides using a differential scanning calorimeter. Normally the amount of antioxidants is determined using HPLC method which takes more than 48 hours for sample preparation. A series of polyamide samples with known content of antioxidants (0.0–0.8%) are analysed using DSC form –50 to 350 °C in oxygen atmosphere keeping Al-crucibles open. For all the compositions a linear relationship was found forH (heat of degradation) and induction time under isothermal conditions at 220 °C which enables the antioxidant VANOX-SKT to be determined in unknown samples.

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Zusammenfassung Zur Unterdrückung der Oxydation von Polymeren während der Nutzungsdauer werden diese mit Antioxydationsmitteln versetzt. Die vorliegende Arbeit beschäftigt sich mit der Bestimmung von Stabilisatoren (VANOX-SKT Antioxydans) in Polyamiden mit Hilfe eines Differential-Scanning-Kalorimeters. Auf herkömmliche Art und Weise wird der Antioxydansgehalt mittels HPLC bestimmt was jedoch wegen der Probenvorbereitung mehr als 48 Stunden dauert. Mittels DSC von –50 bis 350 °C in Sauerstoffatmosphäre in offenen Aluminiumtiegeln wurde eine Reihe von Polyamidproben mit bekanntem Antioxydansgehalt (0,0–0,8%) untersucht. Für alle Zusammensetzungen konnte zwischen der ZersetzungswärmeH und der Induktionszeit unter isothermen Bedingungen bei 220 °C ein linearer Zusammenhang festgestellt werden, welcher die Bestimmung des VANOX-SKT Antioxydansgehaltes von unbekannten Proben erlaubt.

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. ( -) . , 48 -. (0–0,8%) – 50 + 350 °C. 220 °C H ( ) , - .

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One of the authors (PSJ) is thankful to Perkin-Elmer AG,Switzerland and Jnuig Berchtotd, EMS-Chemie AG, for supporting the above work.     

Characterisation of the chemical homogeneity of solid-state materials by chemometric methods: Further multivariate aspects

Some further possibilities of widespread multivariate methods are checked for usefulness in chemometrical characterising the inhomogeneity of solid materials. The methods are applied to data of ten elements obtained by spark source mass spectrometric milliprobing along radial and azimuthal co-ordinates on the surface of a copper disc sample. Special multivariate control charting reveals locations with significant concentration deviations. Two-factor analysis of variance can distinguish very sensitively between radial and azimuthal contributions. Principal components analysis and hierarchical cluster analysis need three or four main components to explain sufficiently some groups of chemical elements with similar behaviour. Factor analysis clearly confirms four element groups as background factors causing inhomogeneity in a different manner. An extended strategy is proposed how to use which chemometrical method in which sequence for characterising the inhomogeneity.Dedicated to Professor Dr. K. Doerffel on the occasion of his 70th birthday     

Separation and determination of Cd in biological materials by continuous-flow fluid extraction coupled to flow-injection ICP-AES

An FI-ICP-AES method for the determination of trace levels of cadmium in biological samples is described based on the complexation of the metal ion with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide (DPTH) and its subsequent on-line extraction into isobutyl methyl ketone (IBMK). The detection limit for cadmium is 8.7 ng/ml and the calibration is linear at least from 10 to 2000 ng/ml. The relative standard deviation for 7 replicate measurements is 3.4% for 100 ng/ml of cadmium. Results from the analysis of some certified biological reference materials are given.     

Determination of yttrium, scandium and other rare earth elements in uranium-rich geological materials by ICP-AES

A rapid method is described for the determination of yttrium, scandium, and other rare earth elements (REEs) in uranium-rich geological samples (containing more than 0.1% U) and in pitch blende type of samples by inductively coupled plasma atomic emission spectrometry (ICP-AES) after separation of uranium by selective precipitation of the analytes as hydroxides using H(2)O(2)/NaOH in the presence of iron as carrier. Uranium goes into solution as soluble peruranate complex. The precipitated rare earth hydroxides (including Y and Sc) are filtered and dissolved in hydrochloric acid prior to their aspiration into plasma for their individual estimation after selecting interference free REE emission lines. The method has also been applied to some international reference standards like SY-2 and SY-3 (by doping a known amount of uranium) along with one in-house pitch blende sample and the REE values were found to be in agreement with the most usable values, offering an R.S.D. of 1-8.8% for all the REEs', Y and Sc. The method compared well, with the well- established cation exchange separation procedure.     

Determination of the REE and Y in silicate materials with ICP-AES

Summary An ICP-AES method for the determination of 12 rare earth elements and Y is described. Following a Na₂O₂-sinter dissolution of silicate materials the REE and Y were separated and concentrated using ion-exchange chromatography. The dissolution and separation procedures are described in detail. Numerous tests show good recovery of the REE. Spectral interferences were quantified and discussed. The precision is better than 5% (r.s.d.) for all measured REE, except Pr. The accuracy was tested by analyzing more than 30 international reference samples, the results are in good agreement with published data. In this paper we present our latest data from 6 new reference samples.

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Bestimmung der Seltenen Erden und Yttrium in silikatischem Material mit ICP-AES

     

Characterisation of different inulin samples by DSC: Influence of polymerisation degree on melting temperature

Melting behaviour of powder inulin has been studied by differential scanning calorimetry. DSC curves show two endothermic peaks, relative to water elimination and to inulin melting, respectively. The second peak is dependent on inulin type and a shift to a higher temperature is observed with increasing average polymerisation degree (DP) of the sample. For similar crystallinity index, linear relations have been underlined and so predicting inulin mean DP can be done by DSC analysis. The study shows that a relatively high heating rate (25°C min^–1) can be used and brings a supplementary interest by an important reduction of analysis time.This revised version was published online in November 2005 with corrections to the Cover Date.     

Precision analysis of Nb−Ti ratio in a superconducting alloy by NAA-PIXE combined technique

A NAA-PIXE combined analysis has been applied to the precise measurement of the concentrations of Nb and Ti in Nb–Ti alloy ingot. The ingot is used in the production of superconductors and the concentration should be controlled very strictly. The ingot cross section could be analyzed with an accuracy of better than 1% by the use of NAA for the preparation of standard samples and PIXE for the nondestructive rapid scan of the surface. The radial and azimuthal concentration profiles of the ingot could be obtained.     

Titrimetric determination of the stoichiometric composition of ceramic high-temperature superconducting materials

 To characterize the real stoichiometry of ceramic high-temperature superconductors of the Y-Ba-Cu-O type and the Bi(Pb)-Ca-Sr-Cu-O type complex, chemical methods including digestion, separation and subsequent titrimetric determination of the elemental components were investigated. Using optimized automatic titration procedures with photometric, potentiometric or voltametric equivalence point detection, a high accuracy of the analytical results could be achieved. The random as well as the systematic errors are less than 0.5%. The exact stoichiometric coefficients of the components and thereby the phase compositions or the single phase character of the materials were determined and compared with the results of X-ray diffraction measurements. Received : 27 November 1995/Revised: 5 February 1996/Accepted: 10 February 1996     

Titrimetric determination of the stoichiometric composition of ceramic high-temperature superconducting materials

 To characterize the real stoichiometry of ceramic high-temperature superconductors of the Y-Ba-Cu-O type and the Bi(Pb)-Ca-Sr-Cu-O type complex, chemical methods including digestion, separation and subsequent titrimetric determination of the elemental components were investigated. Using optimized automatic titration procedures with photometric, potentiometric or voltametric equivalence point detection, a high accuracy of the analytical results could be achieved. The random as well as the systematic errors are less than 0.5%. The exact stoichiometric coefficients of the components and thereby the phase compositions or the single phase character of the materials were determined and compared with the results of X-ray diffraction measurements. Received : 27 November 1995/Revised: 5 February 1996/Accepted: 10 February 1996