bluuebunny/crossref_metadata_2025 huggingface dataset:
Rate constants for the gas‐phase reactions of O3 with a series of Terpenes and OH radical formation from the O3 reactions with Sesquiterpenes at 296 ± 2 K
Authors: Shu Yonghui , Atkinson Roger
Published: January 2005

Rate constants for the gas‐phase reactions of O3 with the sesquiterpenes α‐cedrene, α‐copaene, β‐caryophyllene, α‐humulene, and longifolene, and with the monoterpenes limonene, terpinolene, α‐phellandrene, and α‐terpinene, have been measured using a relative rate technique at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained (in units of 10−17 cm3 molecule−1 s−1) are: limonene, 20.1 ± 5.1; terpinolene, 188 ± 67; α‐phellandrene, 298 ± 105; α‐terpinene, 2110 ± 770; α‐cedrene, 2.78 ± 0.71; α‐copaene, 15.8 ± 5.6; β‐caryophyllene, 1160 ± 430; α‐humulene, 1170 ± 450; and longifolene, <0.07, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference organics. Hydroxyl radical formation yields were also determined for the O3 reactions with the sesquiterpenes, of 0.67 for α‐cedrene, 0.35 for α‐copaene, 0.06 for β‐caryophyllene, and 0.22 for α‐humulene, all with estimated overall uncertainties of a factor of ca. 1.5. The tropospheric lifetimes of the sesquiterpenes due to reaction with O3 are calculated. © 1994 John Wiley & Sons, Inc.
Kinetic analysis of reversible thermal decomposition of solids
Authors: Vyazovkin Sergey , Linert Wolfgang
Published: January 2005

The isoconversional method was used to elucidate the kinetics of reversible solid‐state reactions occurring under nonisothermal linear heating. The characteristic dependencies of the effective activation energy (E) on the extent of conversion (W) were established for two model processes: a reversible first‐order reaction and a reversible reaction followed by an irreversible one. For the first process, E is almost independent of W and varies between the activation energy of the direct and inverse reaction. For the second, process with an endothermic reversible step, the dependence of E on W is of decreasing shape. The effective activation energy is limited by the sum of the activation energy of the irreversible reaction and the enthalpy of the reversible reaction, at low conversions, and by the activation energy of the irreversible reaction at high conversions. Analyses of the kinetic data for the dehydration of crystalhydrates, as well as other processes proceeding through a reversible step, show the dependencies of E on W characteristic of a reversible reaction followed by an irreversible one. © 1995 John Wiley & Sons, Inc.
Kinetic study of the reaction of chlorine atoms with CF3I and the reactions of CF3 radicals with O2, Cl2 and NO at 296 K
Authors: Kaiser E. W. , Wallington T. J. , Hurley M. D.
Published: January 2005

The kinetics of the gas‐phase reaction of Cl atoms with CF3I have been studied relative to the reaction of Cl atoms with CH4 over the temperature range 271–363 K. Using k(Cl + CH4) = 9.6 × 10−12 exp(−2680/RT) cm3 molecule−1 s−1, we derive k(Cl + CF3I) = 6.25 × 10−11 exp(−2970/RT) in which Ea has units of cal mol−1. CF3 radicals are produced from the reaction of Cl with CF3I in a yield which was indistinguishable from 100%. Other relative rate constant ratios measured at 296 K during these experiments were k(Cl + C2F5I)/k(Cl + CF3I) = 11.0 ± 0.6 and k(Cl + C2F5I)/k(Cl + C2H5Cl) = 0.49 ± 0.02. The reaction of CF3 radicals with Cl2 was studied relative to that with O2 at pressures from 4 to 700 torr of N2 diluent. By using the published absolute rate constants for k(CF3 + O2) at 1–10 torr to calibrate the pressure dependence of these relative rate constants, values of the low‐ and high‐pressure limiting rate constants have been determined at 296 K using a Troe expression: k0(CF3 + O2) = (4.8 ± 1.2) × 10−29 cm6 molecule−2 s−1; k∞(CF3 + O2) = (3.95 ± 0.25) × 10−12 cm3 molecule−1 s−1; Fc = 0.46. The value of the rate constant k(CF3 + Cl2) was determined to be (3.5 ± 0.4) × 10−14 cm3 molecule−1 s−1 at 296 K. The reaction of Cl atoms with CF3I is a convenient way to prepare CF3 radicals for laboratory study. © 1995 John Wiley & Sons, Inc.
Theoretical analysis of the rate constants for the interstellar reaction N+OH→NO+H
Authors: Cobos C. J.
Published: January 2005

The title reaction, a key elementary process involved in the chemistry of molecular clouds, has been theoretically studied over the 5–600 K temperature range. Rate constants calculations have been carried out using the full version of the statistical adiabatic channel model in conjunction with a potential energy surface that has been derived from recent ab initio quantum chemical data. By using various switching functions, the influence of the attenuation of the bound‐complex bending frequency upon NOH bond elongation on the temperature dependence of the reaction was investigated. The rate constants exhibit a slightly positive temperature dependence with a calculated rate constant value at 300 K in very good agreement with the measured value. A comparison with the available experimental data between 250 and 515 K suggests that recrossing trajectories might occur with increasing importance as the temperature increases. However, the nonstatistical recrossing effects are expected to be of minor importance at interstellar temperatures such that the rate constants over the 5–200 K temperature range are given by k = 8.41 × 10−12 T+0.30 cm3 molecule−1 s−1. The rate constant calculated at 10 K is consistent with that derived in the astrochemical modeling of the L134N dark cloud. Rate constants for individual quantum states are also presented. © 1995 John Wiley & Sons, Inc.
The kinetics of the B2H6/O (3P) system at room temperature
Authors: Gal Gyora , Bar‐Ziv Ezra
Published: January 2005

An experimental study of the kinetics of the B2H6/O (3P) system at room temperature, is presented. Modeling was based on a multiple‐parameter fitting process to a complex kinetic mechanism. The aim of the study was to propose and evaluate a preferred set of elementary reactions which might be important for the oxidation of boron‐hydrides. In this study, relative concentration‐vs.‐time profiles of the radicals OH and BO2 were measured in a low pressure flow reactor, by the technique of laser‐induced‐fluorescence. A range of almost two orders of magnitude in the initial fuel to oxygen ratio was covered, while the residence times of the gases in the reactor were up to 1 s. A comprehensive kinetic mechanism was constructed from the available measured and estimated data in literature. After the fitting process and dropping all of the reactions with negligible contribution, a 46 elementary reactions mechanism was obtained. In this mechanism, 27 reactions are not measured and their rate coefficients were used as the adjustable (within reasonable limits deduced from kinetic and thermodynamic considerations) parameters of the fitting process. Good agreement was obtained between all of the measured and calculated profiles. From sensitivity analysis it was found that only a limited group of these reactions highly contributes to the calculated concentrations of OH and BO2. With only the highly contributing reactions and all the oxygenhydrogen reactions which are measured and relatively well known, a 30 elementary reactions mechanism was obtained. In this mechanism only 13 reactions are not measured and the agreement between the measured and the calculated profiles is still reasonable. To demonstrate the possible usefulness of the proposed mechanism, the rate coefficient of the reaction B2H6 + OH → B2H5 + H2O which was not measured before, was directly measured in our experimental set‐up. The rate coefficient that was obtained in the direct measurement is (3.3 ± 1.1) × 1011 cm3mol−1s−1, in excellent agreement with the predicted one by the multiple‐parameter‐fitting process, which was 2 × 1011 cm3mol−1s−1. © 1995 John Wiley & Sons, Inc.
Thermal decomposition of 1‐butyne in shock waves
Authors: Hidaka Yoshiaki , Higashihara Tetsuo , Oki Takashi , Kawano Hiroyuki
Published: January 2005

1‐Butyne diluted with Ar was heated behind reflected shock waves over the temperature range of 1100–1600 K and the total density range of 1.36 × 10−5−1.75 × 10−5 mol/cm3. Reaction products were analyzed by gas‐chromatography. The progress of the reaction was followed by IR laser kinetic absorption spectroscopy. The products were CH4, C2H2, C2H4, C2H6, allene, propyne, C4H2, vinylacetyiene, 1,2‐ butadiene, 1,3‐butadiene, and benzene. The present data were successfully modeled with a 80 reaction mechanism. 1‐Butyne was found to isomerize to 1,2‐butadiene. The initial decomposition was dominated by 1‐butyne → C3H3 + CH3 under these conditions. Rate constant expressions were derived for the decomposition to be k7 = 3.0 × 1015 exp(−75800 cal/RT) s−1 and for the isomerization to be k4 = 2.5 × 1013 exp(−65000 cal/RT) s−1. The activation energy 75.8 kcal/mol was cited from literature value and the activation energy 65 kcal/mol was assumed. These rate constant expressions are applicable under the present experimental conditions, 1100–1600 K and 1.23–2.30 atm. © 1995 John Wiley & Sons, Inc.
Evidence of protonation during the oxidation of some aryl alcohols by permanganate in perchloric acid medium and mechanism of the oxidation processes
Authors: Sen Pratik K. , Sanyal Ankan , Sen Gupta Kalyan K.
Published: January 2005

The oxidation of benzyl alcohol and methoxy‐, chloro‐, and nitro‐ substituted benzyl alcohols by permanganate has been studied in aqueous and acetic acid medium in presence of perchloric acid. The reaction is first‐order in [MnO4−] and [XC6H4CH2OH], but the order is complex with respect to [H+]. Different thermodynamic parameters have been evaluated. The reaction occurs through the protonation of alcohol in a fast preequilibrium followed by a slow rate‐determining oxidation step. A two‐electron transfer oxidation step has been suggested for benzyl alcohol and chloro‐ and nitro‐ substituted alcohols, while the oxidation of methoxy compounds involves a one‐electron transfer via a free‐radical mechanism. © 1995 John Wiley & Sons, Inc.
Atmospheric chemistry of FCOx radicals: Kinetic and mechanistic study of the FC(O)O2 + NO2 reaction
Authors: Wallington Timothy J. , Schneider William F. , Møgelberg Trine E. , Nielsen Ole J. , Sehested Jens
Published: January 2005

A pulse radiolysis system was used to study the kinetics of the reaction of FC(O)O2 radicals with NO2. By monitoring the rate of the decay of NO2 using its absorption at 400 nm the reaction rate constant was determined to be (5.5 ± 0.6) × 10−12 cm3 molecule−1 s−1 at 296 K and 500–1000 mbar pressure of SF6 diluent. A long path length Fourier transform infrared spectrometer was used to investigate the thermal stability of the product FC(O)O2NO2. The rate of thermal decomposition of FC(O)O2NO2 was independent of the total pressure of N2 diluent over the range 100–700 torr and was fit by the expression k−3 = 6.0 × 1016 exp(−14150/T) s−1. The results are discussed in the context of the atmospheric chemistry of FCOx radicals. © 1995 John Wiley & Sons, Inc.
Kinetic study of the oxidation of L‐phenylalanine by potassium permanganate in acid medium
Authors: Insausti M. J. , Mata‐PÉRez F. , Alvarez‐Macho M. P.
Published: January 2005

The kinetics of permanganate oxidation of L‐phenylalanine in acid medium at a constant ionic strength has been investigated spectrophotometrically. An autocatalytic reaction was observed being autocatalyzed by a soluble form of Mn(IV).

The reaction appears to involve a parallel consecutive reaction process in which Mn(IV) is formed as an intermediate and Mn(II) as a reaction product. A tentative mechanism consistent with the kinetics is discussed. © 1995 John Wiley & Sons, Inc.
Kinetic study of the formation of N‐chloramines
Authors: Antelo J. M. , Arce F. , Parajó M.
Published: January 2005

We studied the kinetics of the chlorination of amines by sodium hypochlorite in strongly alkaline aqueous solution. A reaction mechanism compatible with experimental results is proposed and discussed. © 1995 John Wiley & Sons, Inc.
Ionic strength effects in binary aqueous mixtures: Study of the reaction between Co(en)2(2‐pzCO2)2+ and Fe(CN)5H2O3−
Authors: Rodríguez Amalia , Pérez‐tejeda Pilar , Jiménez Rafael , Sánchez Francisco , López Pilar , Calvente Juan José , Moyá Marí Luisa
Published: January 2005

The reaction between Co(en)2(2−pzCO2)2+ (bis‐ethylenediamine (2‐pyrazinecarboxylato)cobalt(III)) and Fe(CN)5H2O3− (aquopentacyanoferrate(II)) to form the binuclear complex [(en)2Co( μ‐pzCO2)Fe(CN)5]− has been studied in several isodielectric binary mixtures at 298.2 K (cosolvents: methanol, ethanol, tertbutyl alcohol, ethyleneglycol, and glycerol). Results were rationalized by using a free energy relationship. The importance of correcting the rate constants obtained in the different mixtures from the ionic strength influence has been shown. © 1995 John Wiley & Sons, Inc.
Approximate analytic solution for the dissociation of molecular iodine in the presence of singlet oxygen
Authors: Perram Glen P.
Published: January 2005

A computational study including sensitivity, nondimensional, and stedy‐state analyses of the gas‐phase kinetics associated with Chemical Oxygen‐Iodine Lasers (COIL) was performed to develop a simplified kinetic model and assess kinetic limitations to laser performance. A minimal set of 13 reactions is developed that adequately describes the time evolution of the major chemical constituents of a COIL device. A characteristic time for the dissociation of molecular iodine by singlet oxygen is established in terms of iodine fraction, water content, yield of singlet oxygen, and rate parameters. Finally, an approximate analytic solution to the iodine dissociation problem is established for a broad range of reagent concentrations. The current study is limited in applicability due to the exclusion of chemical heat release and reactive mixing phenomenon. © 1995 John Wiley & Sons, Inc.
On the application of an oxygen probe in chemical kinetics: The influence of the probe response on kinetic measurement
Authors: Connick Robert E. , Zhang Yi‐xue
Published: January 2005

Membrance covered oxygen probes are frequently used to monitor the progress of chemical reactions involving dissolved oxygen. For reactions that are comparable in rate to the response of the oxygen probe it is difficult to obtain the correct kinetic constants directly from the probe signal with traditional kinetic data manipulation methods. In this article, we apply the method of impulse response function to describe the probe signal of an oxygen probe for three different types of simple chemical reactions. The impulse response function is obtained experimentally. Using the impulse response function we have obtained the relationships between the probe signal and the kinetic parameters of these reactions. The slow response of the probe has two effects on the kinetic curves of the reaction studied: a time‐lag and distortion of the shape of the kinetic curve throughout the reaction. The latter effect becomes significant when the reaction is fast. Procedures to obtain the correct kinetic information from the oxygen probe signal are described. © 1995 John Wiley & Sons, Inc.
The rate constant for aerial oxidation of NADH by methylene blue
Authors: Ševčík Peter , Dunford Brian
Published: January 2005

The second‐order rate constant for the oxidation of NADH by methylene blue at pH 9.0 and 25°C under aerobic conditions is 4.21 M−1 s−1. © 1995 John Wiley & Sons, Inc.
Rate constants for the gas‐phase reactions of cis‐3‐Hexen‐1‐ol, cis‐3‐Hexenylacetate, trans‐2‐Hexenal, and Linalool with OH and NO3 radicals and O3 at 296 ± 2 K, and OH radical formation yields from the O3 reactions
Authors: Atkinson Roger , Arey Janet , Aschmann Sara M. , Corchnoy Stephanie B. , Shu Yonghui
Published: January 2005

Rate constants for the gas‐phase reactions of the four oxygenated biogenic organic compounds cis‐3‐hexen‐1‐ol, cis‐3‐hexenylacetate, trans‐2‐hexenal, and linalool with OH radicals, NO3 radicals, and O3 have been determined at 296 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained were (in cm3 molecule−1 s−1 units): cis‐3‐hexen‐1‐ol: (1.08 ± 0.22) × 10−10 for reaction with the OH radical; (2.72 ± 0.83) × 10−13 for reaction with the NO3 radical; and (6.4 ± 1.7) × 10−17 for reaction with O3; cis‐3‐hexenylacetate: (7.84 ± 1.64) × 10−11 for reaction with the OH radical; (2.46 ± 0.75) × 10−13 for reaction with the NO3 radical; and (5.4 ± 1.4) × 10−17 for reaction with O3; trans‐2‐hexenal: (4.41 ± 0.94) × 10−11 for reaction with the OH radical; (1.21 ± 0.44) × 10−14 for reaction with the NO3 radical; and (2.0 ± 1.0) × 10−18 for reaction with O3; and linalool: (1.59 ± 0.40) × 10−10 for reaction with the OH radical; (1.12 ± 0.40) × 10−11 for reaction with the NO3 radical; and (4.3 ± 1.6) × 10−16 for reaction with O3. Combining these rate constants with estimated ambient tropospheric concentrations of OH radicals, NO3 radicals, and O3 results in calculated tropospheric lifetimes of these oxygenated organic compounds of a few hours. © 1995 John Wiley & Sons, Inc.
Simultaneous laser absorption measurements of CN and OH in a shock tube study of HCN + OH → products
Authors: Wooldridge Steven T. , Hanson Ronald K. , Bowman Craig T.
Published: January 2005

Simultaneous, quantitative, narrow‐line laser absorption measurements of CN time‐histories at 388.444 nm and OH time‐histories at 306.687 nm have been made in incident and reflected shock wave experiments using dilute mixtures of nitiric acid (HNO3) and HCN in argon. The thermal decomposition of HNO3 serves as a rapid source of OH upon shock‐heating, and the OH subsequently reacts predominantly with the HCN in the test gas mixture. The rate coefficient for the reaction
equation image
was determined in the temperature range 1120–1960 K via detailed kinetics modeling of the simultaneously acquired CN and OH measurements. These data are in good agreement with lower temperature measurements of the rate of the reverse reaction (−1a) when recent values of the heats of formation of CN and HCN are used. The expression

valid for temperatures 500 to 2000 K, effectively represents the experimental measurements. The estimated uncertainty of the expression for k1a is ±30%, based on the experimental uncertainties of the individual rate coefficient studies. Analysis of the decay region of the experimental OH time‐histories yielded the total rate coefficient k1 (all product channels) for the reaction of HCN with OH for temperatures ranging from 1490 to 1950 K. These measurements are consistent with a previous theoretical analysis of the three primary addition‐isomerization‐dissociation processes for the HCN + OH reaction at combustion temperatures when the contribution to k1 from reaction (1a) is included. © 1995 John Wiley & Sons, Inc.
A kinetic model for pyrolysis of CF2HCl
Authors: Zhang Z. , Pollard R.
Published: January 2005

Thermal decomposition of CF2HCl has been modeled using 2,269 thermally activated reactions and 63 chemically activated processes. Thermochemical properties for the species involved are calculated using statistical mechanics and group contribution theory, and reaction rate constants are determined using transition state theory. The theoretical predictions, obtained without fitting any parameter values, afree closely with available experimental data. Also, the reactions that control the distribution of reaction products are identified, and this, in turn, permits simplification of the reaction set. Sensitivity studies show that uncertainties in the calculations do not alter the predicted trends in behavior or the main reaction pathways. © 1995 John Wiley & Sons, Inc.
Kinetics and modeling of the H2O2NOx system
Authors: Bromly J. H. , Barnes F. J. , Nelson P. F. , Haynes B. S.
Published: January 2005

The addition of NO (0 to 400ppm) to mixtures of H2 (ca. 1%) and O2 (0.7 to 22%) has been studied over the temperature range 700 to 825 K, in a flow reactor at atmospheric pressure. The overall effect of NO is to promote the oxidation of H2 but high concentrations of O2 actually inhibit the NO‐promoted oxidation of H2.

A detailed kinetic mechanism has been constructed and found to describe the experimental observations. The promotion of the oxidation of H2 arises through the catalytic cycle
equation image
The ability of R.34 to reactivate chains normally terminated by the formation of HO2 is a key feature of this system.

The predictions are highly sensitive to the rate of the reaction R.5 and the rate constants for this reaction is the only adjustable parameter required in the model. The value of k5,N2 found to describe all the results

has an absolute uncertainty <35%. The uncertainty relative to other important rate constants in the H2O2 system is less than 10%. © 1995 John Wiley & Sons, Inc.
Rod‐Coil Globular Structures – Simple Models for Proteins
Authors: Nowak Christian , Rostiashvili Vakhtang G. , Vilgis Thomas A.
Published: December 2004

Summary: In this article, we discuss the phase behavior of rod‐coil copolymers with two main methods. First, a scaling theory on different conformations is presented, which shows how micelles form. The circumstances of their stability is discussed. In the second part, we have formulated the general self‐consistent field theory (SCFT) for the rod(or helix)‐coil multiblock copolymer globule. This model and both approaches provide a simple description of the interplay between the secondary and tertiary structures in a globule α‐helix proteins.

Pictorial representation of a used series ratio: each bar, zigzag line and fat dot correspond to $\hat G_{{\rm rod}} ,\;\hat G_{{\rm coil}} ,$ and σ1/2, respectively.

magnified image

Pictorial representation of a used series ratio: each bar, zigzag line and fat dot correspond to $\hat G_{{\rm rod}} ,\;\hat G_{{\rm coil}} ,$ and σ1/2, respectively.
Clusters of Optimum Size Formed by Hydrophobically Associating Polyelectrolyte in Homogeneous Solutions and in Supernatant Phase in Equilibrium with Macroscopic Physical Gel
Authors: Zaroslov Yuri D. , Fytas Georgios , Pitsikalis Marinos , Hadjichristidis Nikos , Philippova Olga E. , Khokhlov Alexei R.
Published: December 2004

Summary: The formation of finite‐sized microgel particles was revealed by photon correlation spectroscopy in aqueous solutions of hydrophobically associative polyelectrolyte polystyrene‐block‐poly(sodium methacrylate)‐block‐polystyrene. Starting from the lowest polymer concentration (1 × 10−6 g · L−1) up to 1 g · L−1 a single relaxation process dominates the spectrum of relaxation times of the polymer solutions. This dominant mode was attributed to the diffusive motion of supramolecular microgel particles with a size of about 100 nm. Above a polyelectrolyte concentration of 1.0 g · L−1, the size of the microgel grows up to ca. 300 nm. At a polymer concentration 20 g · L−1, macroscopic phase separation occurs: the liquid phase of the microgel‐cluster solution coexists with the phase of the macroscopic gel.

Schematic representation of the formation of supramolecular structures in aqueous solutions of hydrophobically associative polyelectrolyte.

magnified image

Schematic representation of the formation of supramolecular structures in aqueous solutions of hydrophobically associative polyelectrolyte.
Cover Picture: Macromol. Rapid Commun. 24/2004
Authors: Simon Carl G. , Eidelman Naomi , Deng Yan , Washburn Newell R.
Published: December 2004

Cover: The upper left panel shows a polymer gradient solution being deposited from a syringe onto a glass slide. The colored panel (FTIR microspectroscopy) depicts the composition of the PLLA‐PDLLA composition gradients that were made (blue corresponds to PDDLA‐rich regions, orange to PLLA‐rich regions). The bottom panels are crossed polar images taken in 10 mm intervals across the gradients showing the change in spherulite morphology as the composition changes from PDLLA‐rich (amorphous) to PLLA‐rich (crystalline).

Further details can be found in the Communication by C. G. Simon, Jr.,* N. Eidelman, Y. Deng, and N. R. Washburn on page 2003.
Die praxisnahe Ermittlung der Anfälligkeit hochlegierter Stähle für chloridinduzierte Spannungsrißkorrosion Neueste Erkenntnisse über die Aussagefähigkeit verschiedener Prüfverfahren
Authors: Krauß H. , Hirth F. W. , Speckhardt H.
Published: December 2004

Prüfverfahren zur Ermittlung der Beständigkeit hochlegierter Cr‐Ni‐Stähle gegen Spannungsrißkorrosion – Vergleich der Aussagefähigkeit verschiedener Methoden – Übertragung auf die Praxis.
Ermittlung des Zeitstandverhaltens einer austenitischen Schweißverbindung
Authors: Kloos K. H. , Granacher J. , Schieblich W.
Published: December 2004

Das Zeitstandverhalten einer Schweißverbindung aus dem Stahl X6CrNi1811 wurde an Proben unterschiedlicher Geometrie und Größe untersucht. Unterschiede im Zeitstandverhalten zwischen Schweißverbundproben und Proben aus den einzelnen Gefügezonen werden diskutiert. Das Plastizitäts‐ und Kriechverhalten der einzelnen Gefügezonen wird durch Gleichungen beschrieben.
Ausscheidung von Hollanditwhiskern in Aluminiumtitanatglaskeramiken
Authors: Peters G. , Jansen M.
Published: December 2004

Die präparativ‐chemischen Voraussetzungen für eine Verstärkung von Aluminiumtitanatkeramiken durch innere Ausscheidung Whiskerförmiger Fremdphasen werden erarbeitet. Der Schwerpunkt der Untersuchunghen liegt bei dem nichtsilicatischen System Ba‐Al‐Ti‐O. Hierin existiert die Hollanditphase Ba1,23Al2,46Ti5,54O16. Solche Hollanditkristalle stellen potentielle neue keramische whisker zum Zwecke der Verstärkung von Keramiken dar. Im Falle von Tialitkeramiken gelingt die Darstellung dieser Whisker „in situ”︁ auf dem Wege eines glaskeramischen Prozesses, dessen abschließender Schritt in der Kristallisation der Tialitmatrix besteht. Man erhält ein dichtes, whiskerdurchdrungenes Gefüge.
Plastographische Werkstoff‐ und Schadensuntersuchung an Kunstststoffbauteilen
Authors: Schwarz M. , Münster R.
Published: December 2004

Licht‐ und rasterelektronenmikroskopische Untersuchungen, energiedispersive Röntgenmikroanalysen an Anschliffen und Dünnschliffen sowie Mikrohärte‐ und DSC‐Messungen ermöglichen die Gefügedarstellung und Werkstoffbeurteilung an Polymerwerkstoffen. Herstellungs‐ und Fertigungsfehler sowie Schädigungen durch Betriebsmedien an Bauteilen aus glasfaserverstärkten Kunststoffen (GFK) und Polypropylen werden dargestellt.
Schwingfestigkeitseigenschaften von Schweißverbindungen hochfester, schweißgeeigneter Baustähle
Authors: Prior F. , Maurer K. L.
Published: December 2004

Die hoch‐ und höchstfesten Baustähle sind vor allem im Falle von Schweißverbindungen, unter ungünstigen Randbedingungen, einem normalfesten Baustahl kaum überlegen. Im Rahmen dieser Untersuchungen soll gezeigt werden, ob durch eine Optimeirung der Schweißnahtgeometrie und durch eine nachträgliche mechanische Behandlung durch Strahlen mit Keramikkugeln bzw. mit Stahlsplitt die Schwingfestigkeitseigenschaften von Stumpfstoß‐und Kreuzstoß‐Proben verbessert werden und welche Schwierigkeiten dabei auftreten können. Die praktischen Versuche werden durch theoretische Berechnung mittels FE‐Methode unterstützt und ergänzt. Ein abschließender Vergleich mit den Regelwerken soll die Schwierigkeiten bei der Festlegung von zulässigen Schwingfestigkeitswerten bei solchen Schweißverbindungen verdeutlichen.
Charakterisierung des Ermüdungszustandes in zyklisch beanspruchten Schweißverbindungen durch röntgenographische und mikromagnetische Kenngrößen
Authors: Lachmann C. , Nitschke‐Pagel Th. , Wohlfahrt H.
Published: December 2004

Das Ermüdungsverhalten von Schweißnähten wird durch den Werkstoffzustand, die Gefüge‐und Mikrostruktur und Eigenspannungen beeinflußt. Mit Hilfe des mikromagnetischen Meßverfahrens in Verbindung mit röntgenographischen Verfahren wurde das Werkstoffverhalten von zyklisch beanspruchten Schweißnähten des Baustahls S355 mit der Absicht einer Restlebensdauervorhersage untersucht. Die Vorliegenden Ergebnisse bestätigen die Auffassung, daß hierbei Makro‐ und Mikroeigenspannungen, magnetische Kennwerte und Dehnungskennwerte eng miteinander verknüpft sind. Die bei zyklischer Beanspruchung mit hinreichen großen Spannungsamplituden in Naht, WEZ und Grundwerkstoff eintretenden mikostrukturellen Veränderungen kamen einerseits in starken Veränderungen der Makroeigenspannungen zum Ausdruck und in Bereichen stärkerer Plastizierungen auch in Veränderungen der Mikroeigenspannungen, die sich aus der Röntgeninterferenzlinien‐Profilanalyse ergaben. Andererseits waren die Mikrostrukturänderungen schon frühzeitig im Verlauf der zyklischen Beanspruchungen anhand z.T. sehr ausgeprägter Veränderungen der mikromagnetischen Kennwerte nachweisbar. Diese Ergebnisse lassen erwarten, daß sich die mit den mikrostrukturellen Werkstoffveränderungen verknüpfte fortschreitende Schädigung bis zur Entstehung von Makrorissen mit Hilfe des mikromagnetischen Meßverfahrens nachweisen läßt und so Aussagen über den Ermüdungszustand schwingbeanspruchter Bauteile möglich werden.
Thermoplastic aromatic polyimide composites
Authors: Johnson Robert O. , Teutsch Eric O.
Published: December 2004

ULTEM® polyetherimide resin is characterized by a combination of high performance mechanical, thermal, flammability, and electrical properties. The exceptional mechanical properties are typified by a 15,000 psi tensile strength and 480,000 psi flexural modulus. Because of its amorphous structure and outstanding adhesion to glass, ULTEM® proves to be a very desirable matrix material for glass fiber reinforcement. Addition of fiber glass enhances most mechanical properties and provides a readily processible reinforced thermoplastic.
Macrocomposites made by injection molding
Authors: Hecht James L.
Published: December 2004

Macrocomposites can be prepared by injection molding an engineering resin into a mold which contains an insert of a different engineering resin. Using 3/8‐inch beams and 1/4‐inch disks as model systems, we have shown that macrocomposites give parts with combinations of stiffness and toughness far superior than can be made by conventional injection molding of a single material. The key to making macrocomposites with good properties is to have the insert sufficiently hot so that the surface is melted during the second molding step. The toughness of a macrocomposite can be derived not only from proper positioning of a tough material and a stiff material, but also from more effective orientation of glass fibers resulting from the alteration of the mold cavity caused by the insert. Before macrocomposites can be commercialized, significant technical obstacles with respect to both molding equipment and part design procedures must be overcome.
Thermoplastic matrix sheet composites
Authors: Bigg D. M. , Hiscock D. F. , Preston J. R. , Bradbury E. J.
Published: December 2004

Until recently, most high performance composites have been made with low‐viscosity thermosetting polymers. These polymers are ideally suited for producing composites in low production quantities because a wide variety of custom shapes can be manufactured without a high degree of mechanization. As the demand for composites increases, there is a need to develop high‐volume production techniques. Thermoplastic polymer‐based composites are better suited to high‐volume production than thermoset‐based composites because only heat and pressure are needed to form parts; no chemical reaction is required. Thermoplastic matrix composites are not well suited for low‐volume production runs because the need to handle high temperatures and pressures demands equipment that is best utilized for large production runs. In addition to processing advantages, thermoplastic matrix composites exhibit improved impact strength and chemical resistance over most thermoset‐based composites. In the course of this work, composites reinforced with long and continuous glass fibers were produced that had tensile strengths as high as 270 MPa, tensile moduli of 16.2 GPa, and notched Izod impact strengths of 11.1 J/cm.
Thermal expansion of polyurethane reinforced with continuous glass fibers
Authors: Kia Hamid G.
Published: December 2004

This paper is concerned with the study of the thermal expansion properties of polyurethanes which are reinforced with randomly oriented continuous glass fibers. The thermal expansion of reinforced polymers is of prime importance since it has a significiant effect on the overall dimensional stability of molded products. In this work the coefficient of linear thermal expansion (CLTE) is measured for both soft and rigid polyurethane containing various amounts of glass fibers. The experimental results show that: (1) there exists a maximum in the CLTE‐temperature curves, the position of which depends on the type of resin and not on the glass content; (2) over the range of 0 to +70°C for rigid polyurethane, and –30 to +70°C for soft polyurethane, the CLTE decreases with temperature. The existence of a maximum in the above findings is confirmed with computations from a theoretical expression which was modified by the introduction of an efficiency factor. In applying this expression, parameters such as the Poison's ratios, elastic moduli, and the CLTe's of the resins had to be evaluated at various temperatures. Based on these results, the CLTE‐temperature curves were obtained and found to be in agreement with the experimental observations.
Some remarks on acoustic emission measurements and the single‐fiber‐composite test
Authors: Netravali A. N. , Sachse Wolfgang
Published: December 2004

We compare two methods for carrying out single‐fiber‐composite tests in which acoustic emission (AE) data are used to monitor the progression of fiber fracture. The AE measurements include event count or arrival‐time data. While the former is more easily instrumented, the latter provides additional information related to the location of fiber flaws and the progression of the fiber fracture process.
Mechanical properties of nickel‐powder–filled polypropylene composites
Authors: Maiti S. N. , Mahapatro P. K.
Published: December 2004

Mechanical properties such as tensile and flexural properties as well as impact behavior of nickel‐powder–filled isotactic polypropylene composites were investigated in the composite composition range 0–3.5 volume % Ni. Tensile modulus, strength, and elongation‐at‐break decreased with increase in Ni content, which is attributed to the introduction of discontinuity in the structure. Analysis of tensile strength data indicated the introduction of stress concentration consequent upon addition of Ni into polypropylene. Izod impact strength at first increased up to a critical Ni content beyond which the value decreased inappreciably while flexural modulus and strength increased with filler concentration.
Aging behavior of optically transparent poly (methyl methacrylate) composites
Authors: Lin Hongy , Day Delbert E. , Stoffer James O.
Published: December 2004

The thermal aging between 25 and 115°C of hot pressed glass fiber reinforced poly (methy1 methacrylate)(PMMA) transparent composites was studied as a function of the temperature and time of hot pressing. Thermal aging at near the Tg of the PMMA matrix caused dimensional changes and a reduction in optical transmission and clarity. The reduction in transmission was attributed to gas bubbles that formed in the matrix, which may be due to the evaporation of residual MMA monomer or low Tg (∼ 75°C) polymer in the composites during aging. Thermal cycling between 25 and 100°C by eliminating low Tg of the PMMA matrix establishes the upper temperature limit to which the composite can be exposed without seriously damaging its optical properties.
Consolidation of advanced composites having volatile generation
Authors: Upadhyay Ram K. , Liang Erwin W.
Published: December 2004

Processing polyimide‐based thermosetting matrix composites is complicated because of gaseous volatiles produced during the polymerization and crosslinking reactions. This process involves complex interactions between part geometry, temperature and force cycles, and matrix/fiber properties. A simple model for the consolidation process that treats these composites as a three‐phase system consisting of fiber, resin, and volatile has been developed. This model has been applied to compression molding process for constant thickness laminates and the predictions agree well with experiments. Further extension to handle three‐dimensional parts and the required numerical techniques have also been developed.
Imidazole and chromium acetylacetonate as additives for the cure and fracture toughness of epoxy resins and their composites
Authors: Lin King‐Fu , Wang Wen‐Hsien
Published: December 2004

The effects of additives such as 2‐undecyl‐imidazole (C11Z) and chromium acetylacetonate (Cr(acac)3) were examined on the curing behavior and fracture toughness of tetraglycidyldiaminodiphenyl methane/diaminodiphenyl sulphone (TGDDM/DDS) epoxy resins and their composites. The C11Z additive alone reacted with TGDDM epoxy resins at about 127°C and increased the resin viscosity, resulting in an acceptable resin content for composite processing. Further addition of Cr(acac)3 to TGDDM/DDS/C11Z formulation increased the fracture toughness 5.7 times compared to the typical TGDDM/DDS/BF3MEA epoxy formulation used for the preparation of laminates. The interlaminar fracture toughness of the laminates prepared by TGDDM/DDS/C11Z/Cr(acac)3 formulation was only twice as much as that prepared by typical TGDDM/DDS/BF3MEA. This was due to the fiber bridging contribution to the interlaminar fracture toughness. Based on the experiment, this fiber bridging contribution was only dependent on the fiber content. Thus, the interlaminar fracture toughness is approximated by the sum of the fracture toughness of epoxy matrix and the estimated fiber bridging contribution.
Gas permeation and viscoelastic deformation of prepregs in composite manufacturing processes
Authors: Nam J.‐D. , Seferis J. C. , Kim S.‐W. , Lee K.‐J.
Published: December 2004

Gas permeation and creep deformation of a commercial prepreg, which exhibits viscoelastic characteristics, were investigated as a function of time, temperature, and consolidation pressure. Experiments using a prepreg stack demonstrated that the material exhibited a linear viscoelastic bulk deformation under vacuum/autoclave pressure and furthermore, the in‐plane gas flow exhibited non‐Darcian flow behavior with a permeation hysteresis. This behavior was viewed and analyzed by two viscoelastic relaxation processes: (1) bulk dimensional relaxation, and (2) microscopic pore structure rearrangement. A modified standard linear solid (SLS) viscoelastic model was used to interpret the creep compliance and dynamic gas permeability utilizing two independent relaxation parameters. By visual investigation of pore sizes and their distribution, air permeation was found to take place mostly through the interlaminar porosity network for the prepreg system examined.
Development of an electrically conductive fiber reinforced plastic pipe
Authors: Pang Su‐Seng , Van Beek Gerald A. , Lea Richard H.
Published: December 2004

Fiber‐reinforced plastic (FRP) pipe has much lower density and better corrosion resistance characteristics than currently used alloy pipe, but it generally does not conduct electricity as well as steel pipe. In this study, an FRP pipe was made conductive by doping the inner liner vinyl ester resin with milled carbon fibers. The joints were also made conductive using the same resin, thus allowing the pipe to be electrically grounded. The result was a pipe having a surface resistivity of less than 125 Ω/□ using current manufacturing processes.
Microhardness of carbon fiber reinforced epoxy and thermoplastic polyimide composites
Authors: Paplham W. P. , Seferis J. C. , BaltáCalleja F. J. , Zachmann H. G.
Published: December 2004

We have examined the micro indentation hardness of a series of carbon fiber reinforced epoxy and thermoplastic polyimide (TPI) composites. In the epoxy systems, the influence of Nylon particles was studied. The effect of crystallization of the thermoplastic polyimide upon the microhardness values of the resin was also investigated. The microstructure of the TPI‐composites was characterized by X‐ray diffraction. The results show that the addition of carbon fibers to the neat resins greatly increases the microhardness and thus the yield stress of the composite. The value of the microhardness technique is highlighted in emphasizing the heterogeneity of the CFRC.
Estimation of molecular weight distribution of poly(vinylpyrrolidone) from diaphragm‐cell diffusion measurements
Authors: Comelli Fabio , Francesconi Romolo , Lanzi Eugenio
Published: December 2004

Viscometry, gel permeation chromatography (GPC) and diffusion measurements on three samples of poly(vinylpyrrolidone) (PVP) were made. The diffusion measurements were carried out by means of a Stokes cell. An equation with five parameters was derived, linking the difference in PVP amount between the two compartments of the cell to the time of the experiment: three parameters are related to the diffusional behavior of the macromolecules and the other two define the molecular weight distribution (the Tung expression has been chosen). A least‐squares procedure allowed us to obtain the five parameters and the calculated weight average molecular weights agree with the ones evaluated by viscometry and GPC. The ratio Mw/Mn (heterogeneity of the polymer) calculated from the parameter z of the Tung expression is very different from the one obtained from GPC.
Dielectric behavior of polystyrene foam at microwave frequency
Authors: Bandyopadhyay Pranab C. , Chaki Tapan K. , Srivastava Srinath , Sanyal Gitindra S.
Published: December 2004

Polystyrene foams have been generated and fabricated into differently shaped structures', by change of steaming period under constant impregnation time and solvent‐nonsolvent composition. Optical photomicrographs of samples both plain and wax‐copper‐coated reveal uniform appearance, distinct grain‐boundaries, and random cell size distribution. Dielectric measurements have been made on test specimens cut according to wave‐guide size at 9.375 GHz X‐band microwave frequency by short‐circuited wave‐guide method of Smith and Hippel modified by Dakin and Works. Dielectric constants are linear, on direct and semi‐log scales in bulk‐density and volume‐fraction, obeying Weiner's inequalities. Formulae of Landau‐Lifshitz, Beer, Maxwell‐Wagner, Odelevsky, etc. have been tried. Data fit best with the logarithmic law of Lichtenecker and Rother. Specific polarization is also a true function of density. Dielectric constant vs bulk‐density plots of foams resemble dielectric‐constant vs fractional‐density plots based on the theoretical derivation by Smith for polystyrene compacts, signifying that compacts containing closely‐spaced oblong‐spherical particles arc physically similar to foams having spherical gas inclusions in plastic structures. Tan δ lying in the range 0.002–0.0038 results from conformational polarization (β‐relaxation at room‐temperature for wide‐angle torsional oscillations of side‐groups with co‐operative motion from wriggling chains). It is therefore possible for low‐loss foam dielectrics suitable for micro‐wave applications to be made by this method.
Lithographic technique using radiation‐induced grafting of acrylic acid into poly(methyl methacrylate) films
Authors: Gazard M. , Duchesne C. , Dubois J. C. , Chapiro A.
Published: December 2004

A lithographic process is described which increases the sensitivity of polymers to electron beam irradiation. The free radicals and peroxides produced in a film of polymer by irradiation are used to initiate the grafting of a monomer to form a graft copolymer, the solubility of which may be higher or lower than that of the initial polymer. Acrylic acid has been grafted into poly(methyl methacrylate) films to produce a copolymer which is insoluble in the solvents of PMMA. The sensitivity of this negative system depends on the conditions of grafting and on the conditions of development. A sensitivity of 2.8 10−8 C.cm−2 at 20 keV has been obtained.
Limiting regimes of deformation of polymers
Authors: Vinogradov G. V.
Published: December 2004

The relaxation transition of polymers under the influence of deformation from the fluid to the forced high‐elastic (rubbery) and leathery states has been studied. It has been shown that the investigation of the polymers in question under the conditions of uniaxial extension allows one to estimate the properties of polymers at deformation rates exceeding by 4‐5 decades the rates of deformation at which simple shear can be realized. A set of critical parameters has been found for the polymers investigated which determines the regimes of their transition from the fluid to the forced rubbery and leathery states and also their fracture properties. These parameters are subdivided into two groups. The parameters of the first group refer to critical values of stress and deformation. They are invariant to temperature and molecular mass. For different polymer‐homologous series the critical stresses vary by more than 10‐20 times; as regards the values of strains, they vary by more than several times. The parameters of the second group define the rates of strain which bear a simple relation to the initial viscosity and can be changed within many decades. This determines the success of the procedure of reduction of fracture properties to temperature and molecular mass.
Competitive equilibria in miscible polymer blends and low molecular weight analogues: A fourier transform infrared study
Authors: Garton Andrew
Published: December 2004

The relative magnitudes of specific interactions are compared by setting up competitive equilibria in mixed solvent systems. The positions of the equilibria are determined spectroscopically by resolving the overlapping absorptions of the two solvation states. This technique is applied to the study of interactions between polyesters (or model compounds) and a variety of solvents which mimic possible interacting centers in halogenated polymers. Using the same technique of resolving overlapping bands, it is also demonstrated that in a miscible blend of polycaprolactone and Phenox (a polyhydroxyether of bisphenol A) only a relatively small proportion of the carbonyl groups of polycaprolactone are involved in specific interactions with the Phenoxy.
Fourier transform infrared studies of poly(vinyl chloride) blends with ethylene Co‐ and terpolymers
Authors: Iskandar M. , Tran C. , Robeson L. M. , McGrath J. E.
Published: December 2004

The miscibility of poly(vinyl chloride) (PVC) with various ethylene copolymers and terpolymers were investigated using FT‐IR spectroscopy. All blends reported were 50/50 by weight. In blends of PVC with ethylene/dimethyl acrylamide copolymer (E/DMA), frequency shifts were observed in the amide carbonyl (proton acceptor) and the α‐hydrogen of PVC (proton donor) characteristic bands. In blends of PVC with ethylene/ethyl acrylate/carbon monoxide terpolymer (E/EA/CO), both the ester carbonyl and the ketone carbonyl characteristic frequencies showed mutual shifts and appeared as if they merged together. Small frequency shifts were also observed in the α‐hydrogen of PVC characteristic bands. In blends of PVC with ethylene/vinyl acetate/carbon monoxide terpolymer (E/VA/CO), the ester carbonyl frequency showed a shift while that of the ketone carbonyl was essentially unchanged. On the other hand, in PVC blends with ethylene/vinyl acetate copolymer (E/VA), the ester CO frequency did not show any shift, which is consistent with their observed immiscibility. Thus, it is clear that incorporating a ketone CO in ethylene/ester copolymers to form the corresponding terpolymers enhances their miscibility with PVC as earlier proposed on the basis of dynamic mechanical studies. Similar results were shown for blends of PVC with ethylene/2 ethyl hexyl acrylate/carbon monoxide terpolymer (E/2EHA/CO). Frequency shifts imply specific interactions which suggest polymer‐polyer miscibility on a molecular scale.