bluuebunny/crossref_metadata_2025 huggingface dataset:
Recovery evaluation of lipophilic markers from Echinacea purpurea roots applying microwave‐assisted solvent extraction versus conventional methods
Authors: Hudaib Mohammad , Gotti Roberto , Pomponio Romeo , Cavrini Vanni
Published: February 2003

In the present study the recovery from roots of lipophilic markers (mainly alkamides) of Echinacea purpurea (L.) Moench for analysis by GC/MS was evaluated by applying microwave‐assisted solvent extraction (MASE), as a new extraction approach, versus two other conventional methods (Soxhlet and ultrasonic extraction). A preliminary screening of the three methods, using the best‐reported parameters (solvent and extraction time) for Soxhlet (as a reference method) and ultrasonic extraction, showed MASE and ultrasonic extraction (using 70% methanol as the solvent system in both) to be superior methods to Soxhlet extraction in two solvent systems. Both methods, MASE and ultrasound, were further evaluated applying different ratios of methanol‐water (60 to 100% methanol) as the solvent system. In these investigations, MASE showed significantly higher recoveries than the ultrasonic technique over the 70–100% methanol range while comparable values were obtained at 60% methanol. The best recovery of the individual alkamides and the whole lipophilic fraction was obtained at 70% methanol. The MASE method could serve as good alternative procedure for the preparation of more chemically potent samples and/or crude extracts from Echinacea species.
Delamination of polymeric coatings on silidized iron
Authors: Rebhan M. , Rohwerder M. , Stratmann M.
Published: February 2003

The delamination of polymeric coatings (pc) on iron and steel is a phenomena everybody knows e.g. from his rusting car. The damage caused by it costs the Western countries hundreds of millions Euro every year. Hence it is a very important task for the steel industry and also for scientists to improve the stability of the pc on iron and steel.

The authors developed a new corrosion protection of iron by covering it with a thin layer of a‐SiO2:Fe. An adhesion promoter sticks on top of it so that the pc adhers well. The delamination of the pc as function of the surface preparation (roughness, adhesion promoter) is described in this paper. The Scanning Kelvin Prove (SKP) is utilized to detect the delamination.
Photoinduced Refractive Index Change of Polymer Films Containing Mesoionic Sulfur‐Substituted Phenyloxatriazolones
Authors: Kato Yuichi , Horie Kazuyuki
Published: February 2003

We measured photoinduced refractive index changes (see Figure) of polymer films containing various sulfur‐containing mesoionic compounds. PMMA films containing 30 wt.‐% of 3‐phenyl‐1,2,3,4‐thiatriazole‐5‐thione (3PTTT) showed refractive index changes of −0.036 during photoirradiation, at a wavelength far from the resonant region. An increase in the number of sulfur atoms in the mesoionic compounds doped in PMMA films resulted in the increase in refractive index changes during photoirradiation. The estimation and comparison of the changes in specific refraction and densities of the systems suggest that the change in electronic structure mainly contributes to the refractive index changes of the film in the case of 3PTTT, while the changes in both electronic structure and density equally contribute to the refractive index change in the film with 3‐phenyl‐1,2,3,4‐oxatriazole‐5‐thione (3POTT).

Refractive indices, n, of PMMA films containing various weight fractions of 3POTT (square) and 3PTTT (circle). Open symbols are for n before photoirradiation, filled ones are for n after photoirradiation.

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Refractive indices, n, of PMMA films containing various weight fractions of 3POTT (square) and 3PTTT (circle). Open symbols are for n before photoirradiation, filled ones are for n after photoirradiation.
Studies on the Synthesis and Conductivity of a Novel Reactive Ladder‐Like Poly(β‐cyanoethylsilsesquioxane) and Poly[(β‐cyanoethylsilsesquioxane)‐co‐(β‐methylsilsesquioxane)]
Authors: Zhang Yong , Guo Guangqing , Sun Jin , Zhou Xiaoshu , Xie Ping , Zhang Rongben , Fu Pengfei
Published: February 2003

Two novel reactive poly(β‐cyanoethylsilsesquioxane) (CN‐T) and poly[(β‐cyanoethylsilsesquioxane)‐co‐(β‐methylsilsesquioxane)] (CN‐Me‐T) have been synthesized successfully for the first time via stepwise coupling polymerization (SCP). A variety of characterization methods including FTIR, 1H NMR, 29Si NMR, X‐ray diffraction (XRD), differential scanning calorimetry (DSC) and vapor pressure osmometry (VPO) were combined to demonstrate that the structures of the title polymers possess ordered ladder‐like structures. As expected, the ionic conductivity of these polymers mixed homogeneously with lithium perchlorate reached 10−6 S · cm−1 at room temperature and obviously increased with the raise of temperature.

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Anionic Polymerizations of 1‐Adamantyl Methacrylate and 3‐Methacryloyloxy‐1,1′‐biadamantane
Authors: Ishizone Takashi , Tajima Hiroyuki , Torimae Hiroshi , Nakahama Seiichi
Published: February 2003

Anionic polymerizations of 1‐adamantyl methacrylate (1) and 3‐methacryloyloxy‐1,1′‐biadamantane (2) were carried out in THF at −50 to −78 °C for 24 h. The initiator employed was either [1,1‐bis(4′‐trimethylsilylphenyl)‐3‐methylpentyl]lithium (3)/lithium chloride, or diphenylmethylpotassium. The polymerizations of 1 and 2 proceeded quantitatively to afford the polymers having the predicted molecular weights based on the molar ratios of monomers and initiators and the narrow molecular weight distributions (Mw/Mn = 1.05–1.18), indicating the living character of the polymerization systems of 1 and 2. Novel well‐defined block copolymers, poly[2‐block‐(tert‐butyl methacrylate)], poly(2‐block‐isoprene‐block‐2), and poly[[(2,2‐dimethyl‐1,3‐dioxolan‐4‐yl)methyl methacrylate]‐block‐2], were anionically synthesized by the sequential copolymerization of 2 and comonomers. The poly(2) had the significantly higher glass transition temperature (Tg) of 236 °C and decomposed over 370 °C, while poly(1) started to decompose at around 320 °C before its Tg was reached. This thermal stability can be explained by the substituent effects of the bulky adamantyl and 1,1′‐biadamantyl moieties.

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Synthesis and Characterization of Hyperbranched Polyethylenes Made with Nickel‐α‐Diimine Catalysts
Authors: Kunrath Fábio A. , Mota Fábio F. , Casagrande Osvaldo L. , Mauler Raquel S. , de Souza Roberto F.
Published: February 2003

The polymerization of ethylene in the presence of 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediiminenickel(II) dichloride (1) and methylaluminoxane (MAO) gives hyperbranched polyethylene (HBPE) in appropriate reaction conditions. The system 1/MAO is active in solvents like toluene or hexane at temperatures as high as 80 °C and ethylene pressures ranging from 1 to 15 atm. The polyethylenes obtained show high molecular weights (up to 467 kg · mol−1) and more than 218 branches per 1 000 backbone carbon atoms, qualifying these materials as hyperbranched. Dynamic‐mechanical thermal analysis (DMTA) of these materials shows high β‐transitions, directly related to the branch content of these polyethylenes.

DMTA analysis of polyethylenes obtained with 1/MAO at 0, 30, and 50 °C (corresponding to entries 1, 2 and 3).

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DMTA analysis of polyethylenes obtained with 1/MAO at 0, 30, and 50 °C (corresponding to entries 1, 2 and 3).
Control of In‐Plane and Out‐Of‐Plane Reorientation in Photo‐Cross‐Linkable Copolymer Liquid‐Crystal Films by Irradiation with Linearly Polarized Ultraviolet Light and Annealing
Authors: Kawatsuki Nobuhiro , Furuso Nobuyoshi , Uchida Emi , Yamamoto Tohei
Published: February 2003

This paper describes thermally enhanced in‐plane and out‐of‐plane reorientation of mesogenic groups in copolymer liquid‐crystal (CPLC) films that have a photo‐cross‐linkable 4‐(4′‐methoxycinnamoyl)biphenyl (MCB) side group and a 4‐methoxybiphenyl (4MB) side group. The side groups are cross‐linked by irradiation with linearly polarized ultraviolet (LPUV) light and subsequent annealing. Due to axis‐selective photo‐cross‐linking, a small negative optical anisotropy is observed for all CPLCs after exposure to LPUV light. When the composition of the 4MB comonomer is less than 45 mol‐%, thermal treatment in the liquid‐crystalline temperature range causes in‐plane reorientation of the film and results in an in‐plane order parameter of 0.71. In contrast, when the composition of the 4MB is increased, out‐of‐plane reorientation is generated. Three‐dimensional molecular reorientation and inclined out‐of‐plane reorientation are achieved by adjusting the exposure angle.

Angular dependence of UV absorption spectrum of film 3. The inset shows a conoscope observation of the film. The film was annealed at 130 °C for 10 min.

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Angular dependence of UV absorption spectrum of film 3. The inset shows a conoscope observation of the film. The film was annealed at 130 °C for 10 min.
Specific Roles of Al‐Alkyl Cocatalyst in the Origin of Isospecificity of Active Sites on Donor‐Free TiCl4/MgCl2 Ziegler‐Natta Catalyst
Authors: Liu Boping , Nitta Takashi , Nakatani Hisayuki , Terano Minoru
Published: February 2003

The formation, deactivation and transformation of stereospecific active sites on the donor‐free TiCl4/MgCl2 catalyst induced by short time reaction with triethylaluminium (TEA) cocatalyst (pretreatment time: 0 ∼ 60 s) were investigated by stopped‐flow propylene polymerization combined with temperature rising elution fractionation (TREF) and gel permeation chromatography (GPC) methods. We got the first report that the origin of isospecificity of active sites derived from the catalyst substrate and cocatalyst were individually observed without and with TEA pretreatment, respectively. Based on the three‐sites model of Corradini and Busico et al., a plausible mechanism of the formation and transformation of stereospecific active sites was proposed using active sites models in terms of specified roles of Al‐alkyl cocatalyst. It was demonstrated that the introduction of bulky alkyl groups instead of chlorine atoms into the neighborhood of active sites seems to be crucial for the generation of active sites with the highest isospecificity.

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Chromatic Transitions in Polydiacetylene Langmuir‐Blodgett Films due to Molecular Recognition at the Film Surface Studied by Spectroscopic Methods and Surface Analysis
Authors: Geiger Elisabeth , Hug Paul , Keller Beat A.
Published: February 2003

Langmuir‐Blodgett films of polydiacetylene are used to create a biosensor on the basis of a surface host‐guest recognition process. Functionalizing a 10 wt.‐% fraction of the diacetylene monomer with biotin leads to a visually observable color change in the resulting polymerized film when streptavidin in the molar ratio streptavidin:biotin = 1:2 is added. The chromatic transition, caused by a shortening of the conjugation length of the π‐electron system in the polydiacetylene backbone, is investigated by monitoring the change of visible optical absorption and Raman spectroscopy. Chemical species and to some extent also the presence of surface‐immobilized peptide are identified via time‐of‐flight secondary‐ion mass spectrometry (TOF‐SIMS) signal assignment and XPS studies.

Optical spectra of the blue LB film consisting of two layers PDA 1 and one layer of a mixture containing 10 wt.‐% 7 in 1, the film after 10 min immersion in tris(hydroxymethyl)aminomethane hydrochloride buffer (pH 7.3 at 21 °C) and after 2 h immersion in streptavidin solution (protein:biotin molar ratio = 1:2).

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Optical spectra of the blue LB film consisting of two layers PDA 1 and one layer of a mixture containing 10 wt.‐% 7 in 1, the film after 10 min immersion in tris(hydroxymethyl)aminomethane hydrochloride buffer (pH 7.3 at 21 °C) and after 2 h immersion in streptavidin solution (protein:biotin molar ratio = 1:2).
Amorphous‐Smectic Glassy Main‐Chain LCPs, 1. Poly(ether esters) Derived from Hydroxybibenzoic Acid and (R,S)‐ and (R)‐2‐Methylpropane‐1,3‐diol
Authors: del Campo Aránzazu , Bello Antonio , Pérez Ernesto , García‐Bernabé Abel , Díaz Calleja Ricardo
Published: February 2003

The synthesis and the characterization of main‐chain liquid‐crystalline poly(ether esters), derived from hydroxybibenzoic acid and (R,S)‐ and (R)‐2‐methylpropane‐1,3‐diol, are reported. These polymers show an interesting thermal behavior. They develop mesophases with a slow rate of formation, allowing the easy quenching of the melt into: a) the glassy amorphous state, b) the glassy liquid‐crystalline state, or c) a mixture of both, depending on the thermal treatment. The extent of the transformation and the symmetry of the different phases have been determined by means of calorimetric and X‐ray diffraction methods. Dielectric spectroscopy results provide additional evidence for the detection of distinct glass transitions. The results show that the racemic polymer forms a low‐ordered SmCalt mesophase, while a more ordered phase is obtained in the case of the enantiomerically pure polymer. The comparison of the properties of the different states evidences the special behavior and properties of the glass transition (Tg) in these polymers. Emphasis is paid to the location of the Tg of the liquid‐crystalline state in comparison to the Tg of the amorphous state. It is found that the glass transition of the SmCalt glass in R,S‐PBO3 (the poly(ether ester) derived from hydroxybibenzoic acid and (R,S)‐2‐methylpropane‐1,3‐diol) appears at lower temperatures than the glass transition of the amorphous state. However, in R‐PBO3 (the poly(ether ester) derived from hydroxybibenzoic acid and (R)‐2‐methylpropane‐1,3‐diol), where the more ordered phase is present, the glass transition follows the classical tendency of semicrystalline polymers.

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Bulk and Solution Copolymerization of Butyl Acrylate/Methyl Methacrylate at Elevated Temperatures
Authors: Dubé Marc A. , Hakim Malik , McManus Neil T. , Penlidis Alexander
Published: February 2003

A series of bulk and solution (in toluene) copolymerizations of butyl acrylate/methyl methacrylate were performed independently at two laboratories. The runs were at elevated temperatures ranging from 90 to 140 °C conducted to high conversion levels, and samples were characterized for conversion, cumulative copolymer composition and number‐ and weight‐average molecular weights and distribution. Variation of the comonomer feed composition, temperature, and the solvent, initiator and chain transfer agent concentrations was studied. Using a mechanistic model, conversion data were predicted to high conversions using terminal model kinetics at 90 and 115 °C. The copolymer composition data conformed to the terminal kinetic model over the entire temperature range. Solvent effects were reflected by changes in the butyl acrylate rate constants.

Composition vs. conversion. Effect of feed composition for runs at 140 °C.

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Composition vs. conversion. Effect of feed composition for runs at 140 °C.
Glass‐Transition Temperature (Tg) of Free‐Radically Prepared Polyacrylonitrile by Inverse Gas Chromatography, 1. A Study on Tg of Atactic Monodisperse Polystyrenes
Authors: Minagawa Masatomo , Kanoh Hiroyasu , Tanno Satoshi , Nishimoto Yuhko
Published: February 2003

The glass‐transition temperature (Tg) of several atactic monodisperse polystyrenes (PSt)s was studied by an inverse gas chromatographic (IGC) analysis, as a preliminary study for the detection of the Tg of polyacrylonitrile. The Tg of PSt with different molecular weights was clearly obtained by this method. The agreement in the Tg values obtained by IGC and by differential scanning calorimetry (DSC) was quite good within the molecular‐weight range Mp = 7 600–2 430 000 (where, Mp = (Mn × Mw)1/2). This method has a wide universality for the detection of the Tg of polymers. Several essential factors were extracted for the establishment of the optimum conditions for IGC measurements, such as the concentration of polymer toward a clay matrix (10 wt.‐%), and the type of lower probe, decane. The best probe was determined empirically from the most effective detection in the IGC measurements of PSt.

Molecular‐weight dependence of the Tg of PSt. Experimental data obtained here are indicated by an arrow. Other data was taken from ref.21

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Molecular‐weight dependence of the Tg of PSt. Experimental data obtained here are indicated by an arrow. Other data was taken from ref.21
Synthesis of Silica‐Supported Metallocene Catalysts for Olefin Polymerization
Authors: Bortolussi Frédéric , Broyer Jean‐Pierre , Spitz Roger , Boisson Christophe
Published: February 2003

Four supported metallocene catalysts were synthesized directly on silica [Si(CpZrCp), Si(CpZrInd), Si(IndZrCp), and Si(IndZrInd)]. The first ligand was chemically tethered to silica (internal ligand) while the second was free from silica (external ligand). The polymerization of ethylene and the copolymerization of ethylene with hexene were investigated. The activity of the catalysts and the molecular weights of the polymers were found to depend on the position of the ligands. In all cases, high‐molecular‐weight polyethylene with moderate polydispersity was obtained. Moreover, the copolymerization of ethylene with hexene provided a homogeneous polymer.

Reaction of ZrCl4(OC4H8)2 with modified silica (SiCp).

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Reaction of ZrCl4(OC4H8)2 with modified silica (SiCp).
Cu(S2CNEt2)Cl‐Catalyzed Reverse Atom‐Transfer Radical Polymerization of Vinyl Monomers
Authors: Li Peng , Qiu Kun‐Yuan
Published: February 2003

A new copper catalyst containing chlorine and a photo‐labile diethylthiocarbamoylthiyl group was successfully employed in the reverse ATRP of methyl methacrylate (MMA). The polymeric chains were end‐capped with S2CNEt2, due to pseudo‐halogen atom‐transfer reaction between active and dormant species. Photopolymerization of this PMMA in the presence of fresh MMA and styrene monomers at ambient temperature yielded chain‐extended PMMA and MMA/styrene block copolymers, respectively.

GPC traces of (A) PMMA end‐capped with a photo‐labile group (pre‐PMMA), (B) chain‐extended PMMA (post‐PMMA), and (C) PMMA/styrene block copolymer (PMMA‐b‐PSt).

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GPC traces of (A) PMMA end‐capped with a photo‐labile group (pre‐PMMA), (B) chain‐extended PMMA (post‐PMMA), and (C) PMMA/styrene block copolymer (PMMA‐b‐PSt).
Quantifying Polymer Swelling Employing a Linear Variable Differential Transformer: CO2 Effects on SBS Triblock Copolymer
Authors: Shenoy Suresh , Woerdeman Dara , Sebra Robert , Garach‐Domech Alberto , Wynne Kenneth J.
Published: February 2003

A linear variable differential transformer (LVDT) was employed to evaluate CO2‐polymer plasticization. Preliminary results on polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) elastomer are presented. At 22 °C under CO2 pressure, SBS undergoes compression due to hydrostatic pressure. However, sample expansion occurs upon depressurization. At 45 °C, SBS undergoes swelling of 0.7% due to CO2 plasticization, while no post‐pressurization expansion is observed. The contrasting result is explained by change in PS domain mobility and discontinuity in the density‐pressure relationship.

Linear displacement of SBS as a function of time at 56 and 134 bar CO2.

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Linear displacement of SBS as a function of time at 56 and 134 bar CO2.
Living Cationic Polymerizations Utilizing an Automated Synthesizer: High‐Throughput Synthesis of Polyoxazolines
Authors: Hoogenboom Richard , Fijten Martin W. M. , Meier Michael A. R. , Schubert Ulrich S.
Published: February 2003

Living cationic ring‐opening polymerizations of 2‐ethyl‐2‐oxazoline and purification of the resulting polymers were performed utilizing an automated synthesizer. Eight polymers (500 mg scale) as well as 40 polymers (150 mg scale) were synthesized in parallel to investigate the reproducibility and the living character of the polymerizations. The poly(2‐ethyl‐2‐oxazoline)s obtained such were characterized by means of 1H NMR spectroscopy, MALDI‐TOF mass spectrometry and online gel permeation chromatography.

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High‐Throughput Screening of Mechanical Properties on Temperature‐Gradient Polyurethaneurea Libraries
Authors: Sormana Joe‐Lahai , Meredith J. Carson
Published: February 2003

Combinatorial libraries of segmented polyurethaneurea with gradients in curing temperature were prepared and characterized using a novel high‐throughput mechanical instrument. Stress/strain profiles were taken at different temperature positions on the libraries, and a structure/property relationship between microstructure and mechanical properties was established by correlating the measured strength and strain at break to high‐throughput AFM and FT‐IR measurements on the same library. These results demonstrate the feasibility of rapid and accurate screening of mechanical properties, and their correlation to structure, by using gradient combinatorial polymer libraries.

Impact energy/thickness and elongation at break versus cure T for a T‐gradient SPUU library.

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Impact energy/thickness and elongation at break versus cure T for a T‐gradient SPUU library.
The use of Monte‐Carlo simulations to calculate small‐angle scattering patterns
Authors: McAlister Bryan C. , Grady Brian P.
Published: February 2003

Determining the morphology that corresponds to an experimentally observed scattering pattern is a non‐trivial problem in small‐angle scattering. The purpose of this paper is to describe methods to calculate small‐angle scattering patterns from a given morphology via Monte‐Carlo methods. In these methods, scattering intensities are calculated from pairs of randomly selected points. This paper reviews the different formulas and procedures that have been used. Multiple studies have shown that the Monte‐Carlo method gives accurate results for various morphologies having no interparticle interference. In certain cases, these calculations have been used to fit experimental patterns according to a minimization criterion. For morphologies with interparticle interference, these methods have not been very successful for reasons that are not entirely clear.
Monitoring kinetic processes in polymer solutions with time dependent static light scattering (TDSLS)
Authors: Reed Wayne F.
Published: February 2003

An overview of recent developments in TDSLS and auxiliary techniques is given. This includes background theory, and examples of results and applications for online monitoring of polymerization reactions, kinetics and structural determinations from degrading polymers, aggregation, and dissolution of dry polymer powders. Also, automatic dilution techniques allow for continuous characterization of the equilibrium states of multi‐component solutions. Illustrations are given for the case where the change in polyelectrolyte dimensions, interactions and hydrodynamics can be probed.
The effect of water on cellulose solutions in DMAc/LiCl
Authors: Röder Thomas , Potthast Antje , Rosenau Thomas , Kosmsa Paul , Baldinger Thomas , Morgenstern Bernd , Glatter Otto
Published: February 2003

The solution state of cellulose in the system N,N‐dimethylacetamide/lithium chloride (DMAc/LiCl) depends on various factors such as cellulose concentration, provenience (cotton, hardwood, softwood) and chemical history (pulping, pretreatment, bleaching) of cellulose, LiCl concentration, activation method, dissolution conditions (time, shaking), and water content. In particular the influencing of the latter has been intensively investigated in our present studies. Working in anhydrous conditions is not practicable for routine size exclusion chromatography (SEC) analysis. Especially in solutions diluted to SEC levels (0.9 wt% LiCl), an aggregation induced by water was observed. Depending on the time of dissolution and on the amount of water, changes in the solution state were observed. In some cases the amount of aggregates increases within a few minutes. This is reflected by a time‐dependent increase in the scattering intensity and quantitatively proved by an increase in the aggregation peak in the calculated intensity distributions. With less soluble pulps, traces of water (lower than 0.01 M) can already suffice to induce and promote aggregation. To disturb a “good” stock solution, the concentration of water must be higher than 0.05 M. The aggregates formed correspond to the model of the fringed micelle.
Some properties of aqueous xanthan gels formed under the action of aluminium(III) ions
Authors: Rodd Andrew B. , Dustan Dave E. , Boger David V. , Schmidt Juergen , Burchard Walther
Published: February 2003

Aqueous xanthan solutions form gels when aluminium salts are added and the solutions are heated above 45 °C. The gelation process was followed by dynamic light scattering. Characterization was based on the heterodyne and nonergodic approaches. Both techniques gave the same fast relaxation times, but for the slow motion much larger values were found in the heterodyne than in the nonergodic approach. The heterodyne fraction 1‐X was found to correlate closely with the plateau height of the time correlation function (TCF) at large delay times in the nonergodic experiments. Three methods of gel point determination are demonstrated: (i) onset of heterodyne/nonergodic behavior, (ii) observation of a sharp maximum for the fast relaxation time at the gel point, (iii) observation of power‐law behavior of the TCF. The statistics of nonergodic fluctuations were examined and evaluated. The potential of this procedure for detailed structure evaluation of inhomogeneities in the gel is emphasized.
Phase separation mechanism in gelling aqueous biopolymer mixture probed by light scattering
Authors: Leisner D. , Blanco M.C. , López Quintela M.A.
Published: February 2003

Using time‐resolved static and dynamic light scattering (DLS) we have studied the kinetics of phase separation in an aqueous gelatin/maltodextrin mixture upon fast cooling. The time evolution of the droplet radius is modelled for the monodisperse case under reaction‐limited and diffusion‐limited conditions and compared with the observed evolution of the mode associated with the droplet diffusion. For quenches to above the gelatin ordering temperature, nucleation and rather reaction‐limited than diffusion‐limited growth and late‐stage coalescence of droplets with diameters up to 90 μm were concluded. Quenches to well below the gelatin ordering temperature seem to induce diffusion‐limited growth or (delayed) spinodal decomposition (SD) to a phase‐separated microstructure with slow late‐stage coarsening. In deep quenches, a second slow SD or diffusion‐limited cluster aggregation (DLCA) process becomes apparent from the evolution of the static structure factor; the process seems to be related to the maltodextrin gelation in the composite.
Mechanical properties and creep of Mg – rare earth – Sc – Mn squeeze cast alloys
Authors: Stulíková I. , Smola B. , von Buch F. , Mordike B. L.
Published: February 2003

The microstructure developed during the T5 treatment of squeeze cast magnesium alloys containing rare earth (Gd, Y, or Ce, ≈ 3–10 wt.%), Sc (< 1 wt.%) and Mn (< 1.5 wt.%) is responsible for a reasonable age hardening in MgGdScMn alloys. Moderate age hardening is only possible in MgY4Sc1Mn1 or MgCe3Sc1Mn1 alloys. The c‐based centred orthorhombic phase precipitating as fine prismatic plates in a triangular arrangement is the most effective hardening phase. The stability of yield strength up to 250°C–300°C was confirmed in T5 treated MgGdScMn and MgY4Sc1Mn1 alloys. All alloys exhibit a reasonable ductility at room temperature. The precipitation of very fine basal discs of Mn2Sc phase observed in all T5 treated alloys investigated does not contribute considerably to the hardness, but it is very effective in restricting creep. The creep resistance of all alloys investigated is superior to that of commercial WE54 alloy up to 350°C.
Gefügemäßige Bewertung der Schweißeignung von Stahlgusssorten unter Berücksichtigung der Kaltrissbeständigkeit
Authors: Schelev A.
Published: February 2003

Das Verhalten unterschiedlicher Stahlgusssorten beim Konstruktionsschweißen wird weitgehend von den Gefügebesonderheiten der Wärmeeinflusszone (WEZ) bestimmt. Die Identifizierung der einzelnen Gefügebereiche ist vom Legierungssystem des Gusswerkstoffs abhängig. Bei Bewertung der Schweißeignung höhergekohlter und niedriglegierter Gusssorten muss der Kaltrissanfälligkeit eine besondere Aufmerksamkeit geschenkt werden, die sowohl mit der chemischen Zusammensetzung, als auch mit Inhomogenitäten des Ausgangsgefüges zusammenhängt.
Ermittlung und Beschreibung des Werkstoffverhaltens unter betriebsnaher mehrachsiger Kriechermüdungsbeanspruchung
Authors: Roos E. , Schemmel J.
Published: February 2003

Komponenten, die im Hochtemperaturbereich eingesetzt werden unterliegen einer mehrachsigen Kriechermüdungsbeanspruchung. Für die Beschreibung des Werkstoffverhaltens für diese praxisnahe Beanspruchung wurde ein elastisch‐viskoplastisches Werkstoffmodell ertüchtigt. Zur Ermittlung des Werkstoffverhalten wurden mehrachsige Kriechermüdungsversuche an Hohlzylinderproben durchgeführt. Die Versuche dienten zur Verifizierung des Werkstoffmodells. Das Werkstoffmodell beschreibt das Materialverhalten unter Kriechund Ermüdungsbeanspruchung und erfasst deren Wechselwirkung. Das Schädigungs‐ und Versagensverhalten wird durch implementierte Schädigungsparameter für Kriechen und Ermüden sowie für Versagen erfasst. Dadurch ist das Werkstoffmodell insgesamt in der Lage das Verformungs‐ und Versagensverhalten in guter Übereinstimmung mit dem Experiment zu beschreiben.
Sprühkompaktieren von Halbzeugen unterschiedlicher Geometrie aus unlegierten und niedriglegierten Stählen
Authors: Spangel S. , Schulz A. , Vetters H.
Published: February 2003

Sprühkompaktieren bietet die Möglichkeit in einem Prozeßschritt Halbzeuge, sogenannte Deposits, unterschiedlicher Geometrie herzustellen. Die große Anzahl von Prozeßparametern in den Bereichen Schmelzeerzeugung, Zerstäubung und Kompaktierung gewährleistet die hohe Flexibilität des Verfahrens, erfordert jedoch gleichzeitig die genaue Kenntnis der Zusammenhänge zwischen Ausgangswerkstoff, Prozeßparametern und den resultierenden Werkstoffeigenschaften. In der vorliegenden Arbeit wird über grundlegende Untersuchungen an unlegierten bzw. niedriglegierten Stahlsorten (C15, C105, 100Cr6) berichtet, die durchgeführt worden sind, um den Einfluß des Kohlenstoff‐ bzw. Chromgehaltes sowie wichtiger Prozeßparameter auf die Gefügeentstehung beim Sprühkompaktieren von Flachprodukten und zylindrisch geformten Deposits zu ermitteln. Innerhalb der Deposits sind mittlere Austenitkorndurchmesser von bis zu 500 μm nachgewiesen worden, wobei ein enger Zusammenhang zwischen der Korngröße und dem Auftreten von Poren besteht.

Durch eine Klassifizierung unterschiedlicher Porentypen konnte entsprechend ihrer Erscheinungsform unterschieden werden, ob eine unvollständige Kompaktierung, Schwindung bzw. Ausscheidung von Stickstoff vorgelegen hat. Als maßgebliche Einflußfaktoren wurden der Zerstäubergasdruck sowie der Kohlenstoffgehalt ermittelt.
Numerical calculation of the main factors on cold cracking
Authors: Stadtaus M. , Michailov V. , Wohlfahrt H.
Published: February 2003

Low alloy high‐strength steels are nowadays very common in industrial application offering a number of favourable characteristics. However, cold cracking is an increasing problem concerning the weldability of these materials. For the prediction of cold cracking susceptibility many different tests exist. The most important ones are the Tekken‐(Y‐groove restraint test), the controlled‐thermal‐severity test (CTS) and the implant test. But in spite of the same or similar welding conditions, one gets different minimum preheat temperatures dependent on the used test procedure. Therefore, a better evaluation of these tests seems to be necessary.

Based on the commercial FEA‐tool SYSWELD three main factors influencing cold cracking were investigated for MAG‐welded Tekken specimens: the distribution of microstructure, the stress‐strain state and the hydrogen concentration. The analysis was performed for S690 low alloy high‐strength steel. Also, welding experiments were carried out to determine temperature field and microstructure.
Modellierung des Langzeit‐Verformungsverhaltens von Kunststoffen
Authors: Dallner C. , Ehrenstein G. W.
Published: February 2003

Das Verformungsverhalten der Kunststoffe lässt sich durch das Auswerten von Kriechkurven mittels praktikabler mechanisch‐rheologischer Modelle in geschlossener Form mit differenzierter Darstellung der elastischen, viskosen und viskoelastischen Verformungsanteile berechnen. Die dargestellten Möglichkeiten ergeben sich aus der Fortführung der Ansätze von Dr. Bahman Sarabi, der vor allem nachgewiesen hat, dass bereits sorgfältig durchgeführte Kriechversuche bis 1000 h Belastungsdauer eine vollständige Beschreibung des Langzeitverformungsverhaltens ermöglichen.
Die Entwicklung von Strukturmaterialien für die Kernfusion
Authors: Ehrlich K.
Published: February 2003

Werkstoffe der Ersten Wand und von Brutblankets sind intensiver Neutronenbestrahlung und hoher thermischer Belastung ausgesetzt. Fusionsspezifische Auswahlkriterien sind sog. primäre Schädigungsparameter, die Forderung nach einer niedrigen Aktivierbarkeit (Low activation materials) und konventionelle Eigenschaften wie Festigkeit, Korrosionsbeständigkeit und andere. Aus der Vielzahl von Werkstoffgruppen haben sich aufgrund dieser Auswahlkriterien und der Erfahrung beim Einsatz in konventionellen und Kernkraftwerken ferritisch‐martensitische 7–12% Chromstähle, mit SiC‐Fasern verstärkte SiCf/SiC Verbundwerkstoffe sowie spezielle Vanadiumlegierungen herauskristallisiert. Über den Stand der Kenntnisse für diese Werkstoffe wird berichtet und ein Überblick über die mittelfristigen Entwicklungsziele gegeben. Dabei wird die Notwendigkeit für den Bau einer intensiven Neutronenquelle als Testbett für die Werkstoffentwicklung betont.
Neutron Stress Measurement of W‐Fiber Reinforced Cu Composite
Authors: Nishida M. , Hanabusa T. , Ikeuchi Y. , Minakawa N.
Published: February 2003

Stress measurement methods using neutron and X‐ray diffraction were examined by comparing the surface stresses with internal stresses in the continuous tungsten‐fiber reinforced copper‐matrix composite. Surface stresses were measured by X‐ray stress measurement with the sin2ψ method. Furthermore, the sin2ψ method and the most common triaxal measurement method using Hooke's equation were employed for internal stress measurement by neutron diffraction. On the other hand, microstress distributions developed by the difference in the thermal expansion coefficients between these two phases were calculated by FEM. The weighted average strains and stresses were compared with the experimental results. The FEM results agreed with the experimental results qualitatively and confirmed the importance of the triaxial stress analysis in the neutron stress measurement.
Einsatzhärten: Untersuchungen zur Änderung der Härteannahme nach isothermischer Umwandlung
Authors: Clausen B. , Hoffmann F. , Mayr P.
Published: February 2003

Zur Steigerung der Wirtschaftlichkeit von Einsatzhärtungsprozessen gibt es ein großes Bestreben, die Temperatur im Aufkohlungsprozeß anzuheben. Eine Möglichkeit, das bei Hochtemperaturaufkohlung entstehende grobe Gefüge zu beseitigen, ist die Integration einer isothermischen Umwandlung in den Prozeßablauf. Neben einem feinen Härtungsgefüge treten bei Anwendung dieses Verfahrens zwei Nebeneffekte auf, die Anlaß zu weiterer Forschungstätigkeit geben. Zum einen reduziert sich die Härtbarkeit des untersuchten Werkstoffs. Zum anderen wird eine Steigerung der Biegefestigkeit gegenüber herkömmlich einsatzgehärteten Proben festgestellt.
Schäden durch kerbinduzierte Schwingbrüche
Authors: Lange G.
Published: February 2003

Kerben bewirken örtliche Spannungsspitzen und fördern damit nachhaltig die Entwicklung von Schwingungsrissen. Charakterische Formen von Kerben durch Konstruktion, Fertigung und Betrieb werden vorgestellt und Abhilfemaßnahmen diskutiert. Beispiele zeigen die Auswirkungen verschiedener Kerbarten an diversen Bauteilen.
Über den Zusammenhang zwischen dem Kohlenstoffgehalt in Stählen und der Härte des Martensits
Authors: Liedtke D.
Published: February 2003

Die Aufhärtbarkeit der Stähle, gekennzeichnet durch den Zusammenhang zwischen Kohlenstoffgehalt und erreichbarer Höchsthärte in einem voll martensitischen Gefüge ist für die Stahlauswahl und die optimale konstruktive Auslegung von Bauteilen ein wichtiges Entscheidungskriterium. In der industriellen Praxis werden in diesem Zusammenhang Rechenformeln benutzt, die von der “klassischen” Darstellung von Hodge/Orehoski bzw. Burns/Moore/Archer abgeleitet wurden aber signifikant unterschiedliche Ergebnisse liefern. Eine genauere Betrachtung, zu der Daten aus dem “Atlas zur Wärmebehandlung der Stähle” herangezogen wurden, zeigen, daß die Formel von Just die treffsichereren Resultate liefert. Die Anwendung ist ebenso relevant für das Einsatzhärten. Die Betrachtung ergibt, daß ein geringerer als der bisher üblicherweise benutzte Wert von 0,35 Masse‐% Kohlenstoff ausreicht, um eine Grenzhärte von 52,5 HRC bzw. 550 HV zur Bestimmung der Einsatzhärtungstiefe zu erreichen. Dies steht in Einklang mit entsprechenden Untersuchungen des AWT‐Fachausschusses 5/AK4, der für den funktionellen Zusammenhang zwischen Kohlenstoffgehalt und Martensithärte eine Regressionskurve ermittelt hat, die praktisch mit der Kurve von Burns/Moore/Archer identisch ist.
On a new integration scheme for von‐Mises plasticity with linear hardening
Authors: Auricchio Ferdinando , Beirão da Veiga Lourenço
Published: February 2003

Limiting the discussion to an associative von‐Mises plasticity model with linear kinematic and isotropic hardening, we compare the performance of the classical radial return map algorithm with a new integration scheme based on the computation of an integration factor. The numerical examples clearly show the improved accuracy of the new method. Copyright © 2003 John Wiley & Sons, Ltd.
A LATIN computational strategy for multiphysics problems: application to poroelasticity
Authors: Dureisseix D. , Ladevèze P. , Schrefler B. A.
Published: February 2003

Multiphysics phenomena and coupled‐field problems usually lead to analyses which are computationally intensive. Strategies to keep the cost of these problems affordable are of special interest. For coupled fluid–structure problems, for instance, partitioned procedures and staggered algorithms are often preferred to direct analysis. In this paper, we describe a new strategy for solving coupled multiphysics problems which is built upon the LArge Time INcrement (LATIN) method. The proposed application concerns the consolidation of saturated porous soil, which is a strongly coupled fluid–solid problem. The goal of this paper is to discuss the efficiency of the proposed approach, especially when using an appropriate time‐space approximation of the unknowns for the iterative resolution of the uncoupled global problem. The use of a set of radial loads as an adaptive approximation of the solution during iterations will be validated and a strategy for limiting the number of global resolutions will be tested on multiphysics problems. Copyright © 2003 John Wiley & Sons, Ltd.
Implicit individual differences: relationships between implicit self‐esteem, gender identity, and gender attitudes
Authors: V. Aidman Eugene , M. Carroll Steve
Published: February 2003

The study examined whether the magnitude of same‐sex‐favouring implicit gender bias depends on individual differences in self‐esteem and gender identity as theorized by Greenwald et al. The Implicit Association Test (IAT) was used to measure implicit self‐esteem, gender identity, and gender attitudes. Explicit self‐esteem and gender identity were measured with questionnaires. The IAT revealed a strong automatic preference for female words in 34 female undergraduates but, surprisingly, no significant gender bias in 32 males. Individual levels of this gender bias were predicted in both sexes by IAT‐derived implicit measures of self‐esteem and gender identity, as well as by their interaction. Neither declared gender identity nor explicit self‐esteem added to the prediction. The results are discussed in terms of balanced identity design and the potential influence of method effects on the findings. Copyright © 2002 John Wiley & Sons, Ltd.
Light emission versus energy gap in group‐III nitrides: hydrostatic pressure studies
Authors: Suski T. , Teisseyre H. , Łepkowski S. P. , Perlin P. , Mariette H. , Kitamura T. , Ishida Y. , Okumura H. , Chichibu S. F.
Published: February 2003

In this work we review studies of the pressure dependence of the light emission from quantum structures and thick epitaxial layers of hexagonal and cubic group‐III nitrides. In these semiconductors, an association of the band gap magnitude with the energy of light emission should be treated with caution. Usually, anomalously large Stokes shifts between light emission and absorption are observed, which can reach a value of 0.5–1.0 eV. Two effects are taken into account to explain this phenomenon: (i) in the hexagonal (wurtzite) nitride quantum structures large built‐in electric fields caused by spontaneous and piezoelectric polarization dominate their optical properties; (ii) in hexagonal as well as in cubic nitrides In‐distribution fluctuations lead to a strong Stokes shift effect, too. We show that both effects influence the pressure coefficient of the emitted light energy, dEE/dP, making it different from dEG/dP. In the final part we show that the built‐in biaxial strain caused by a lattice mismatch can also lead to a reduction of dEE/dP.
Nonlinear polarization in nitrides revealed with hydrostatic pressure
Authors: Vaschenko G. , Menoni C. S. , Patel D. , Tomé C. N. , Clausen B. , Gardner N. F. , Sun J. , Götz W. , Ng H. M. , Cho A. Y.
Published: February 2003

We use hydrostatic pressure as an instrument to reveal a strong nonlinearity of the electrical polarization in group‐III nitride quantum well structures. From the photoluminescence peak energies of the quantum well emission at different applied pressures we obtain the values of the built‐in electric field in the wells and the corresponding well‐barrier polarization difference. We found that in both the InGaN/GaN and GaN/AlGaN systems the field and the polarization difference increase with pressure much faster than expected from the conventional (linear) model of polarization. This behavior is explained by the dramatic strain dependence of the piezoelectric coefficients of the group‐III nitrides, which constitutes the nonlinear piezoelectric effect.
Pressure dependent phonon properties of cubic group III‐nitrides
Authors: Talwar D. N.
Published: February 2003

By constructing rigid‐ion models (RIMs) at ambient and high pressures we present a comprehensive study of lattice‐dynamics and thermodynamical properties in cubic III‐nitrides. Murnaghan's equation of state is adopted for relating the volume dependence to pressure. The force constants in the RIM scheme are optimized using non‐linear least square fitting procedures with constrained parameters and weighting of the data on critical‐point phonons, lattice and elastic constants. Theoretical results for the phonon dispersions, density of states, mode Grüneisen parameters, specific heat, and thermal expansion coefficients are compared and discussed with the existing experimental and ab initio data.
Dependence of phonon widths on pressure and isotopic mass: ZnO
Authors: Serrano J. , Widulle F. , Romero A.H. , Rubio A. , Lauck R. , Cardona M.
Published: February 2003

Considerable attention has been devoted recently to the dependence of the widths of the Raman phonons of semiconductors on pressure and on isotopic mass. The dependence on pressure is usually small and monotonic unless the phonon happens to be close to a singularity of the two‐phonon density of states (DOS) which determines its width. In the latter case, strong nonmonotonic dependences of the phonon width on pressure and on isotopic mass can appear. We have investigated the E2high phonons of ZnO crystals with different isotopes and observed a wide range of FWHM depending on isotopic masses. Ab initio calculations of the two‐phonon DOS provide an explanation for this variation of the FWHM: the E2high frequency falls on a sharp ridge of the 2‐DOS corresponding to combinations of TA and LA phonons. Changes in isotopic mass result in a motion of the E2high frequency up and down that ridge which produces the changes in FWHM. These phenomena suggest a decrease of the FWHM with pressure which seems to be present in existing data obtained at 300 K. Similar phenomena are discussed for the E2low phonons. Applications of the isotope and pressure techniques to the elucidation of two‐phonon spectra will be presented.
Specific features of the electronic structure of III–VI layered semiconductors: recent results on structural and optical measurements under pressure and electronic structure calculations
Authors: Segura A. , Manjón F. J. , Errandonea D. , Pellicer‐Porres J. , Muñoz V. , Tobias G. , Ordejón P. , Canadell E. , San Miguel A. , Sánchez‐Portal D.
Published: February 2003

In this paper we review some recent results on the electronic structure of III–VI layered semiconductors and its dependence under pressure, stressing the specific features that differentiate their behaviour from that of tetrahedrally coordinated semiconductors. We will focus on several unexpected results that have led to changes in the image that was currently accepted a few years ago. Intralayer bond angles change under pressure and the layer “thickness” remains virtually constant or increases. As a consequence, models based in intra‐ and inter‐layer deformation potentials fail in explaining the low pressure nonlinearity of the band gap. Numerical‐atomic‐orbital/density‐functional‐theory electronic structure calculations allow for an interpretation of the evolution of the absorption edge under pressure. In particular, they show how the structure of the non‐degenerated valence band maximum in InSe becomes more complex under pressure leading to a non‐conventional direct‐to‐indirect crossover. The valence band maximum in InSe above 4 GPa exhibits a quite singular feature: a “ring‐shaped” constant energy surface and, consequently, a density of states depending on energy as in 2D electronic systems.
Photoluminescence studies of GaAs/partially ordered GaInP quantum wells grown by metalorganic vapor phase epitaxy
Authors: Kobayashi T. , Tomoda H. , Prins A. D. , Homma Y. , Uchida K. , Nakahara J.
Published: February 2003

We report the results of a study on GaAs/partially ordered Ga0.5In0.5P quantum wells using up‐converted photoluminescence (UPL), in which a sample emits photons with an energy (1.89 eV) higher than that of the excitation photon (1.58 eV), together with the normal photoluminescence (PL) excited at a photon energy higher than that of the GaInP band gap and at high pressures up to ∼5 GPa. Both the ∼1.46 eV emission and the UPL observed in this work provide new evidence of a type II band alignment.
Pressure dependence of the natural birefringence in the II–IV–V2 chalcopyrite CdGeP2
Authors: Choi In‐Hwan , Yu P. Y.
Published: February 2003

Chalcopyrite semiconductors are birefringent as a result of their tetragonal crystal lattice structure. The dispersion of this birefringence contains contributions from the near‐bandgap transitions and also from higher energy band‐to‐band transitions. We report the effect of pressure on the dispersion of the natural birefringence in CdGeP2. We found that pressure tends to decrease both contributions. The pressure effect on the near‐bandgap contribution results mostly from an increase of the bandgap with pressure.