bluuebunny/crossref_metadata_2025_split huggingface dataset:
V. Practical applications: PGM‐Alloys as corrosion‐resistant high‐temperature materials
Authors: Kock W. , Lupton D. , Merker J. , Meinhardt J. 
Published: July 2012

AbstractThe available thermodynamic data on the platinum group metals (PGMs) are summarized with reference to the use of these metals and their alloys at high temperatures. The significance of these data with regard to reactions with various environments and resulting corrosion effects are discussed. The influence of solubility limits in platinum solid solutions on achievable strength properties and the importance of oxide dispersion hardening for further improving strength and corrosion resistance are illustrated.
Glass formation in metallic systems
Authors: Clavaguera‐Mora M. T. 
Published: July 2012

AbstractThe aim of the present paper is to analyse the formation and stability of metallic glasses. Attention is focused to the history of the progress on new glassy alloys with specific applications: from soft magnetic Fe‐based ribbons obtained by melt spinning or planar flow casting, through metallic glasses acting as precursors of nanocrystalline precipitates embedded in an amorphous matrix, towards the finding of new multicomponent metallic alloys with large glass‐forming ability that open a new area of development and applications of bulk metallic glasses. The glass formation process is discussed in terms of the structure of the resultant material and in terms of the thermodynamics and kinetics of the process. The development of structural criteria for glass formation is based upon the notion that the free energy of particularly stable glassy structures will be low enough to make the driving force for crystallization negligible. Both structural and energetic criteria point to an enhanced glass‐forming ability in multicomponent alloys. Kinetic criteria allow to differentiate between the ease of glass formation from an undercooled melt (or from a mixture of crystalline grains, as in solid state amorphization) and the stability of the glassy state versus devitrification or crystallization. Key kinetic parameters are viscosity and, more specifically in multicomponent systems, diffusivities of the different elements in the crystalline, glassy and metastable liquid state, respectively. The formation of nanostructured materials from controlled thermal treatment and their temperature stability is discussed in terms of the concentration gradients developing at the interface between the nanocrystals and the amorphous matrix. The qualitative influence of several parameters in the glass‐forming ability and glass‐stability as well as their link to the empirical criteria that have been successfully employed to predict the glass‐forming ability are presented.
Experimental applications of sodium‐containing alloys in molten alkali halides
Authors: Haarberg G.M. , Egan J.J. 
Published: July 2012

AbstractSodium‐bismuth alloys were used as reference electrodes in contact with molten alkali halides to establish sodium activities. Electronic conductivity versus sodium activity was obtained for molten sodium halides using such alloys (ã5 mol% Na) in polarization experiments. Results are presented for molten NaI. Also concentration versus activity data for Na in Na‐Bi alloys were determined as a function of composition (xNa: 0.01–0.15) and temperature (700–900°C) by using a simple coulometric titration technique. Sodium‐lead alloys (ã 8 mol% Na) were used to study the kinetics of the sodium electrode in molten NaCl using ac impedance spectroscopy combined with galvanostatic perturbation. Results from potential measurements between aluminium and a sodium alloy electrode performed in cryolite‐alumina melts to study the effects of electrolyte composition are also presented.
Distribution of elements between liquid alloy and slag phases in extractive metallurgy
Authors: Itagaki Kimio , Hino Mitsuhisa , Pagador Romeo U. , Surapunt Supachai 
Published: July 2012

AbstractThe distribution ratio of the component elements between the liquid Cu‐Zn‐Fe or Cu‐Ni‐Fe alloy and the FeOx‐SiO2‐CaO or MgO‐saturated FeOx‐SiO2‐CaO slag was evaluated thermodynamically based on the activity coefficients of the alloy components determined using a transpiration method and a double Knudsen cell‐mass spectrometer.
Phase relations in the Sn‐Ag‐Sb system at 220°C
Authors: Oberndorff P. J. T. L. , Kodentsov A.A. , Vuorinen V. , Kivilahti J.K. , van Loo F.J.J. 
Published: July 2012

AbstractThe isothermal cross‐section through the ternary phase diagram Sn‐Ag‐Sb at 220°C was constructed by means of diffusion couples and equilibrated alloys.It is proposed that only two phases, Sn4Sb3 and Sn3Sb4, exist in the binary Sn‐Sb system, and no equi‐atomic compound SnSb is present as an equilibrium phase at this temperature.No ternary phases were found in the Sn‐Ag‐Sb system at 220°C; the topology of the isotherm is largely determined by the presence of the extended region of solid solution between the ζ‐Ag4Sn and ζ‐Ag4Sb intermetallic phases.
Thermodynamics and kinetics of internal reactions: Nitridation of Ni‐Cr alloys
Authors: Kodentsov A.A. , van Dal M.J.H. , Kivilahti J.K. , van Loo F.J.J 
Published: July 2012

AbstractThe implementation of Wagner's theory of internal precipitation for evaluating nitriding kinetics has been discussed. Nitriding experiments on Ni‐Cr alloys were carried out in the range of 1‐6000 bar of hydrostatic N2‐pressure and under a flowing NH3+H2 gas mixture at 873‐1398 K. When a moderately stable phase is precipitated out during an internal reaction, the behaviour of the penetrating atoms within the diffusion zone can be interpreted based on thermodynamic considerations. The thermodynamic assessment of the Ni‐Cr‐N system was performed using the Thermo‐Calc databank and the results were verified experimentally. However, “uphill” diffusion of the penetrating species through the matrix towards the precipitation front can be predicted in certain cases and then Wagner's treatment cannot be utilised. It was demonstrated that under suitable experimental conditions of solute content, temperature and external activity of the penetrating element, Wagner's analysis can be applied to internal precipitation process in any material system.
Reversible and irreversible biopolymer gels — Structure and mechanical properties
Authors: Ross‐Murphy Simon B. 
Published: July 2012

AbstractThe majority of synthetic polymer gels are formed by the covalent cross‐linking of linear or branched macro‐molecules using multi‐functional cross‐linking agents. Such gels are networks, or true macromolecules with (nominally) infinite molecular weight and consequently they swell rather than dissolve if immersed in a good solvent. However, there are also a whole class of materials called physical gels where non‐covalent crosslinks occur. These show similarities to covalent networks, but because the cross‐links are not permanent, they will show creep behaviour at very long times. Some of these form on cooling a heated solution, such as gelatin gels, while others form only on heating. Also, some gels are thermoreversible, while others are not.Physical gels can be formed from synthetic or biopolymers. In the latter case non‐covalent cross‐links often comprise more specific and complex mechanisms involving, rather than point‐like cross‐links, “junction zones” of known, ordered secondary structure such as multiple helices. Typically there is a specific, and often intricate, hierarchy of arrangements, which are more familiar to molecular biologists than to polymer physical chemists. In this paper we introduce viscoelastic techniques for characteristing physical gels, and then relate the properties to the underlying structure at the macromolecular and junction zone level. The parallels between synthetic and biopolymer gels will also be illustrated. Finally we describe recent work on the heat‐set gelation of globular proteins, and an attempt to relate the important parameter of the gelation time, tc, to both polymer concentration and temperature.
Luminescent inorganic networks
Authors: Bredol M. , Kynast U. , Boldhaus M. , Lau C. 
Published: July 2012

AbstractSilica‐based inorganic networks combined with organic rare earth complexes should lead to a new class of luminescent materials, adding the chemical stability of silica to the strong UV absorption of organic ligands and the emissive properties of rare earth ions. This concept is demonstrated by the preparation of silica xerogels containing benzoic acid in its network and subsequent reaction (ion exchange) of these gels with terbium chloride solution. The product yields green luminescence similar to the one of solid terbium benzoate. Alternatively, complete rare earth complexes (example: europium thenoyltrifluoracetonate) may be immobilized in silica xerogels, yielding luminescent hybrid materials.
Investigations on the organic crosslinking in ORMOCERs by means of Raman spectroscopy
Authors: Riegel B. , Kiefer W. , Hofacker S. , Schottner G. 
Published: July 2012

AbstractFT‐Raman spectroscopy was used together with supplementary 13C‐NMR measurements to analyze the reaction of the epoxy moieties of 3‐glycidoxypropyltrimethoxysilane and 5,6‐epoxyhexyltrimethoxysilane during sol‐gel processing. The corresponding reactions of the model compounds epoxypropane and epoxyhexane were analyzed to obtain the necessary Raman assignments of the resulting products. Based on these results the formation of the β‐hydroxy methyl ethers could be derived for the silanes. An additional polyaddition of the epoxy rings yielding a mixture of oligo ethers is also consistent with the Raman measurements.
Effect of synthesis conditions on properties of covalently cross‐linked thermosensitive hydrophilic gels
Authors: Groß Hans‐Jürgen , Wack Holger , Althaus Wilhelm 
Published: July 2012

AbstractGel synthesis conditions have a considerable influence on the characteristic properties of the polymerized gel system. Under variation of total amount of monomer, cross‐linker concentration and synthesis temperature, different covalently cross‐linked hydrophilic gels based on N‐isopropylacrylamide were synthesized.The shear modulus, the phase transition temperature and ‐enthalpy and the swelling degree of the hydrophilic gels were measured. Synthesis conditions had a significant influence on the shear modulus and the swelling degree. An influence on the phase transition temperature and ‐enthalpy could only be found in some special cases.
Effect of connectivity and charge density on the swelling and local structural and dynamic properties of colloidal PNIPAM microgels
Authors: Kratz Karl , Hellweg Thomas , Eimer Wolfgang 
Published: July 2012

AbstractThe structural and dynamic properties of thermosensitive neutral and partially charged colloidal microgels of poly(N‐isopropylacrylamide‐co‐acrylic acid) (PNIPAM/AAc) have been investigated by neutron and light scattering techniques. Introduction of cross‐linker induces topological constraints into the polymer network, and hence reduces the swelling capability of the particles as expressed in the variation of their hydrodynamic radii. Small‐angle neutron scattering experiments reveal that below the transition temperature the inhomogeneous structure of the microgel consists of local solid‐like frozen regions and solution‐like regions where the polymer chain behaves as in semidilute polymer solution. The temperature‐induced collapse leads to a strongly segregated micro‐phase separated particle. The swelling of charged microgels is determined by their charge density, controlled through the amount of acrylic acid comonomer, the pH, and the salt concentration.
Praktische Anwendungen von quervernetztem Polyvinylpyrrolidon
Authors: Feifel Klaus , Zeiler Martin , Oechsle Dietmar 
Published: July 2012

AbstractQuervernetztes Polyvinylpyrrolidon (PVPP) ist ein inertes, toxisch unbedenkliches Popkornpolymerisat auf der Basis von N‐Vinylpyrrolidon. PVPP bildet mit Gerbstoffen reversibel Komplexe und kann aufgrund dieser Eigenschaft zur Stabilisierung von Bier und anderen Getränken eingesetzt werden. Ein Komplex von PVPP mit Iod, PVPP‐Iod, kann in einem neu entwickelten Verfahren, der „Bioziden Filtration”︁, zur Inaktivierung von Mikroorganismen in empfindlichen Flüssigkeiten genutzt werden. Der Einsatz des Polymers zur Getränkestabilisierung und in der “Bioziden Filtration” wird in der folgenden Publikation beschrieben.
Fibers and wires in organogels from low‐mass compounds: Typical structural and rheological properties
Authors: Terech P. 
Published: July 2012

AbstractAn overview is given of the special class of thermoreversible organogels and jellies formed with low‐mass compounds. Two distinct rheological behaviors can characterize these binary systems: (1) viscoelastic liquids which develop an elasticity over short times, (2) viscoelastic solids which are constituted on long‐lived 3‐d networks at a temperature T in the gel domain of the phase diagram. Entangled, breakable giant micelles (molecular wires) are opposed to fibers interconnected through crystalline‐like microdomains. Certain thermal and rheological properties are presented as well as the detailed structural context at different scales of the fibrillar networks. A brief review of the different chemical classes of organogelators illustrates the growing development in the field. The class of viscoelastic liquids (jellies) is illustrated with the special category of monomolecular organometallic wires.
Gels of semifluorinated alkanes: Structural investigations by small angle X‐ray scattering
Authors: Lang P. , Marczuk P. , Lermann E. , Möller M. 
Published: July 2012

AbstractThe gels of perfluorododecylalkanes F12Hn in dodecane were investigated with small angle x‐ray scattering (SAXS). These gels can be categorised into three groups according to their stability and optical appearance. The short chain samples with n≤6 form highly turbid gels which eventually undergo a phase separation, the samples with 8≤n≤12 form opaque stable gels and the long chain homologues form stable gels which are transparent. This categorisation is also reflected in the SAXS patterns which show that the F12H6 gel has a monolayered lamellar structure, while the SAXS data from the gels with 8≤n≤12 have to be interpreted in terms of double layered undulating stacks. The structure of the gels formed by the long chain members could not be clarified yet.
Network formation in water‐in‐oil microemulsions stabilised by the amphiphilic triblock‐copolymer PEO13PPO30PEO13 in p‐xylene
Authors: Mays Holger , Almgren Mats , Brown Wyn 
Published: July 2012

AbstractThe properties of pseudo‐ternary mixtures of p‐Xylene, PEO13PPO30PEO13 (Pluronic L64) and aqueous phase in water‐in‐oil microemulsions (L2‐phase) have been studied by electric conductivity and viscosity measurements, and by the methods time‐resolved luminescence quenching and dynamic light scattering. Varied system parameters were the content of aqueous phase in the mixture and the temperature. An increase of the water content leads to a swelling of the spherical reversed micelles. An aggregate shrinkage is observed upon temperature decrease. The microemulsion with the largest water amount exhibits a percolative transition of the electric conductivity upon decreasing temperature, which is accompanied by a strong viscosity increase and a fast inter‐droplet exchange. The time‐resolved decay curves from luminescence quenching experiments prove that the droplet‐structure is maintained in the highly conducting state. Viscosity and dynamic light scattering data suggest a gradual network build‐up of physically connected reversed micelles when the temperature is lowered. The observations are interpreted in a self‐consistent picture by temperature induced changes in the solvent quality with regard to the amphiphile.
Molecular simulation: Understanding polymer gels at the molecular level
Authors: Müller‐Plathe Florian 
Published: July 2012

AbstractIt is shown how insight into fundamental atomistic processes in water‐swollen poly(vinyl alcohol) can be obtained from molecular simulation. Molecular dynamics is used both to calculate quantitatively diffusion coefficients and to examine the qualitative concepts of different states of water in such systems. While concentration‐dependent diffusion coefficients are useful quantities in their own right, here they are also being used to validate the simulations. With confidence in the simulated dynamics established, the distribution of re‐orientational correlation times of water molecules is calculated. It shows that, above the freezing point of water, there is only a single, albeit broad, distribution of correlation times, whereas at 250 K the distribution becomes bimodal. The concept of different dynamical states of water in this hydrogel, therefore, makes sense at low temperatures but not at room temperature or above. Moreover, contrary to the purported picture of “free” and “bound” water in hydrogels, at all temperatures the re‐orientation of a water molecule is faster if it is surrounded by other water molecules than if it is close to the polymer.
Determination of hydrodynamic properties in colloidal systems by static and dynamic light scattering
Authors: Härtl W. , Beck Ch. , Hempelmann R. 
Published: July 2012

AbstractThe structure and dynamics of silica hard spheres and charged colloidal systems has been investigated at high concentrations by means of light scattering. The index of refraction at these high volume fractions was matched using a mixture of water/isopropanol for the Yukawa particles and toluene/ethanol for the hard spheres. By simultaneously measuring the dynamic and static properties of the colloidal systems we were able to extract the hydrodynamic function H(Q) at different concentrations. Our results are in good agreement with theoretical calculations over a large concentration range.
Properties of differently charged poly(N‐isopropylacrylamide) Latex dispersions in alcohol‐water mixtures
Authors: Mielke Mark , Zimehl Ralf 
Published: July 2012

AbstractResults of size control experiments, TEM and viscosity measurements on both negatively and positively charged poly(N‐isopropylacrylamide) (PNIPAAM) latex dispersions are reported. In alcohol‐water mixtures containing low weight fractions of alcohols higher than methanol, negatively and positively charged PNIPAAM particles exhibit both opposite swelling behaviour and flow characteristics at 20°C. Negatively charged particles shrink due to cononsolvency. Shrinking leads to a decreased viscosity. Conversely, positively charged particles swell dramatically and exhibit an increased viscosity. At 40°C, the negatively charged particles collapse and show a similar behaviour to those with positive charge. We observed with TEM that positively charged particles form random flocks after drying on the grid whereas negatively charged ones form arrays of separated particles. This underlines our general concept that the positively charged particles are in general more hydrophobic.
On electric field induced processes in ionic compounds
Authors: Schmalzried H. , Smolin S. 
Published: July 2012

AbstractWith the help of the solid solution (Mg,Fe)O, where Fe‐ions are the dilute species, we investigate the behaviour of a ternary ionic crystal under a d.c. electric current load. The transport equations of the ions and the electronic defects predict that even with reversible electrodes demixing, and in particular decomposition of the compound will occur if the applied d.c. current density is sufficiently high. These predictions are illustrated by appropriate experiments. In this context several additional phenomena are discussed: The internal oxidation of AgBr and the internal reduction of yttria stabilized zirconia. All the compounds mentioned were placed in a galvanic cell, and the internal reactions which then could be observed were driven by the electric field in this cell.
High temperature point defect equilibria in iron‐doped MgO: An in situ Fe‐K XAFS study on the valence and site distribution of iron in (Mg1‐xFex)O
Authors: Hilbrandt N. , Martin M. 
Published: July 2012

AbstractThe point defect structure of a doped (oxide) system was quantitatively studied by applying in situ X‐ray absorption spectroscopy in the vicinity of the absorption edge of the dopant at high temperature (T>270 K) and under defined oxygen activity. Based on refined phase diagrams of second kind (oxygen activity vs. composition x, at constant T), the nearest neighbour dopant‐oxygen bond distances, the corresponding coordination numbers and intensity changes in the near K‐edge structure of iron in (Mg1‐xFex)1‐δO were analysed in terms of the iron oxidation degree at various compositions, x = 0.011–0.106, varying the oxygen activity within the stability field of the mixed oxide (T = 1273–1468 K). At low oxygen activities, near the metal 1 mixed oxide phase boundary (a10−12), iron was found to be divalent and octahedrally coordinated by oxygen. Over a wide range of higher oxygen activities, however, the EXAFS is predominated by two iron species. Identified via the bond length and confirmed by XANES analysis of the pre‐edge region, one species is attributed to Fe2+ (FeO bond distance R = 215.8 pm), the other to Fe3+ (R = 205.0 pm) (averaged over T and x), both occupying magnesium lattice sites. The obtained dependencies of the oxidation degree of iron can be described consistently within a point defect model in which divalent iron ions are randomly distributed within the cation sublattice and trivalent iron ions form defect associates involving two Fe3+ and a cation vacancy. Near the phase boundary to MgFe2O4, indications for trivalent iron ions dissolved in the interstitial sublattice of the NaCl type structure were found.
The density of toluene at high pressures to 673 K and 300 MPa
Authors: Franck E. U. , Kerschbaum S. , Wiegand G. 
Published: July 2012

AbstractThe molar volume and density of pure toluene has been determined from 323 K to 673 K and from 5 to 300 MPa. An autoclave is described which has a variable internal sample volume. 16 different constant volumes have been used and with stepwise increasing temperatures, pairs of temperature and pressure values have been taken along isochors. For the pressure range of 5 to 300 MPa and for 8 isotherms a Tait equation of state is adapted and the calculated data are given. The Tait parameters are presented. The average deviation between experimental and calculated data is below 0.15%. Up to 100 MPa, comparison with recent NIST calculations and other literature data is made. The data are in good agreement.
Photoelectron spectra of toluene rare gas and toluene diethylether 1:1 complexes
Authors: Eisenhardt C. G. , Baumgärtel H. 
Published: July 2012

AbstractThe photoelectron spectra of van der Waals dimers of toluene with rare gases or diethylether have been measured using resonant two‐photon laser ionization and a magnetic bottle spectrometer.