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Degradation Mechanism (degradation + mechanism)
Selected AbstractsGround Water Chlorinated Ethenes in Tree Trunks: Case Studies, Influence of Recharge, and Potential Degradation MechanismGROUND WATER MONITORING & REMEDIATION, Issue 3 2004Don A. Vroblesky Trichloroethene (TCE) was detected in cores of trees growing above TCE-contaminated ground at three sites: the Carswell Golf Course in Texas, Air Force Plant PJKS in Colorado, and Naval Weapons Station Charleston in South Carolina. This was true even when the depth to water was 7.9 m or when the contaminated aquifer was confined beneath ,3 m of clay. Additional ground water contaminants detected in the tree cores were cis,1,2-dichloroethene at two sites and tetrachloroethene at one site. Thus, tree coring can be a rapid and effective means of locating shallow subsurface chlorinated ethenes and possibly identifying zones of active TCE dechlorination. Tree cores collected over time were useful in identifying the onset of ground water contamination. Several factors affecting chlorinated ethene concentrations in tree cores were identified in this investigation. The factors include ground water chlorinated ethene concentrations and depth to ground water contamination. In addition, differing TCE concentrations around the trunk of some trees appear to be related to the roots deriving water from differing areas. Opportunistic uptake of infiltrating rainfall can dilute prerain TCE concentrations in the trunk. TCE concentrations in core headspace may differ among some tree species. In some trees, infestation of bacteria in decaying heartwood may provide a TCE dechlorination mechanism within the trunk. [source] Analysis of electrochemical degradation products of sulphonated azo dyes using high-performance liquid chromatography/tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2006Dana Van, rková Electrochemical treatment of wastewaters containing azo dyes in the textile industry is a promising approach for their degradation. The monitoring of the course of the decomposition of azo dyes in wastewaters is essential due to the environmental impact of their degradation products. In this work, aqueous solutions of a simple azo dye with a low molecular weight (C.I. Acid Yellow 9) and more complex commercial dye (C.I. Reactive Black 5) were electrochemically treated in a laboratory-scale electrolytic cell in sodium chloride or ammonium acetate as supporting electrolytes. Ion-pairing reversed-phase high-performance liquid chromatography coupled with negative-ion electrospray ionization mass spectrometry is applied for the identification of electrochemical degradation products. In addition to simple inorganic salts, the formation of aromatic degradation products obtained due to the cleavage of azo bonds and further degradation reactions is shown, as well as chlorination where sodium chloride is the supporting electrolyte. Degradation mechanisms are suggested for the treatment with sodium chloride as the supporting electrolyte. Copyright © 2006 John Wiley & Sons, Ltd. [source] Analysis of GaInAsP laser diodes degraded by light absorption at an active layer of the facetELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 2 2010Hiroyuki Ichikawa Abstract Electrostatic discharge-induced degradation is one of the serious reliability problems of GaInAsP/InP laser diodes. The authors have conducted an analysis of electrostatic discharge-induced degradation, and have elucidated the principal degradation mechanism. The main cause of degradation is heating by light absorption at the active layer of the facet. This phenomenon is similar to the catastrophic optical damage that occurs in GaAs-based high-power laser diodes. The problem has become more serious with the recent tendency to high power demand. Therefore, technology to suppress against degradation is extremely important. Focusing on facet coating, which is one of the key processes to suppress facet degradation, we demonstrated that facet degradation can be successfully suppressed by inserting an ultrathin aluminum layer between the semiconductor and the dielectric coaling films. This effect is caused by a reduction of surface recombination. This degradation suppression technology has the potential to be applied not only to GaInAsP/InP laser diodes, but to any InP-based laser diodes. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(2): 32,38, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10196 [source] Porous Structures: In situ Porous Structures: A Unique Polymer Erosion Mechanism in Biodegradable Dipeptide-Based Polyphosphazene and Polyester Blends Producing Matrices for Regenerative Engineering (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Mater. Abstract Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in-growth in regenerative medicine. To allow tissue in-growth and nutrient transport, traditional three-dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here we demonstrated for the first time a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure. This polymer system was developed on the highly versatile platform of polyphosphazene-polyester blends. Co-substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4-phenylphenoxy group generated a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permitted the formation of 3D void space filled with self-assembled polyphosphazene spheres. Characterization of such self-assembled porous structures revealed macropores (10,100 ,m) between spheres as well as micro- and nanopores on the sphere surface. A similar degradation pattern was confirmed in vivo using a rat subcutaneous implantation model. 12 weeks of implantation resulted in an interconnected porous structure with 82,87% porosity. Cell infiltration and collagen tissue in-growth between microspheres observed by histology confirmed the formation of an in situ 3D interconnected porous structure. It was determined that the in situ porous structure resulted from unique hydrogen bonding in the blend promoting a three-stage degradation mechanism. The robust tissue in-growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation. [source] In situ Porous Structures: A Unique Polymer Erosion Mechanism in Biodegradable Dipeptide-Based Polyphosphazene and Polyester Blends Producing Matrices for Regenerative EngineeringADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Meng Deng Abstract Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in-growth in regenerative medicine. To allow tissue in-growth and nutrient transport, traditional three-dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure is demonstrated for the first time. This polymer system is developed on the highly versatile platform of polyphosphazene-polyester blends. Co-substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4-phenylphenoxy group generates a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permits the formation of 3D void space filled with self-assembled polyphosphazene spheres. Characterization of such self-assembled porous structures reveals macropores (10,100 ,m) between spheres as well as micro- and nanopores on the sphere surface. A similar degradation pattern is confirmed In vivo using a rat subcutaneous implantation model. 12 weeks of implantation results in an interconnected porous structure with 82,87% porosity. Cell infiltration and collagen tissue in-growth between microspheres observed by histology confirms the formation of an in situ 3D interconnected porous structure. It is determined that the in situ porous structure results from unique hydrogen bonding in the blend promoting a three-stage degradation mechanism. The robust tissue in-growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation. [source] Origin of Radiation-Induced Degradation in Polymer Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Ankit Kumar Abstract Polymer solar cells have been shown to degrade under X-rays. Here, in situ polymer photovoltaic performance and recombination lifetimes are measured and it is found that charge accumulation is the primary reason for degradation of solar cells. This is affected by the mixing ratio of donor and acceptor in the bulk heterojunction. Both a quantitative understanding and the physical model of the degradation mechanism are presented. Understanding of the degradation mechanism is extended in polymer donor,acceptor bulk heterojunction systems to propose a material combination for making radiation hard diodes that can find important application in fields ranging from memory arrays to organic X-ray detectors for medical imaging. [source] Protein-Release Behavior of Self-Assembled PEG,, -Cyclodextrin/PEG,Cholesterol HydrogelsADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Frank van de Manakker Abstract This paper reports on the degradation and protein release behavior of a self-assembled hydrogel system composed of , -cyclodextrin- (,CD) and cholesterol-derivatized 8-arm star-shaped poly(ethylene glycol) (PEG8). By mixing ,CD- and cholesterol-derivatized PEG8 (molecular weights 10, 20 and 40 kDa) in aqueous solution, hydrogels with different rheological properties are formed. It is shown that hydrogel degradation is mainly the result of surface erosion, which depends on the network swelling stresses and initial crosslink density of the gels. This degradation mechanism, which is hardly observed for other water-absorbing polymer networks, leads to a quantitative and nearly zero-order release of entrapped proteins. This system therefore offers great potential for protein delivery. [source] Friction and degradation of rock joint surfaces under shear loadsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2001F. Homand Abstract The morpho-mechanical behaviour of one artificial granite joint with hammered surfaces, one artificial regularly undulated joint and one natural schist joint was studied. The hammered granite joints underwent 5 cycles of direct shear under 3 normal stress levels ranging between 0.3 and 4 MPa. The regularly undulated joint underwent 10 cycles of shear under 6 normal stress levels ranging between 0.5 and 5 MPa and the natural schist replicas underwent a monotonics shear under 5 normal stress levels ranging between 0.4 and 2.4 MPa. These direct shear tests were performed using a new computer-controlled 3D-shear apparatus. To characterize the morphology evolution of the sheared joints, a laser sensor profilometer was used to perform surface data measurements prior to and after each shear test. Based on a new characterization of joint surface roughness viewed as a combination of primary and secondary roughness and termed by the joint surface roughness, SRs, one parameter termed ,joint surface degradation', Dw, has been defined to quantify the degradation of the sheared joints. Examinations of SRs and Dw prior to and after shearing indicate that the hammered surfaces are more damaged than the two other surfaces. The peak strength of hammered joint with zero-dilatancy, therefore, significantly differs from the classical formulation of dilatant joint strength. An attempt has been made to model the peak strength of hammered joint surfaces and dilatant joints with regard to their surface degradation in the course of shearing and two peak strength criteria are proposed. Input parameters are initial morphology and initial surface roughness. For the hammered surfaces, the degradation mechanism is dominant over the phenomenon of dilatancy, whereas for a dilatant joint both mechanisms are present. A comparison between the proposed models and the experimental results indicates a relatively good agreement. In particular, compared to the well-known shear strength criteria of Ladanyi and Archambault or Saeb, these classical criteria significantly underestimate and overestimate the observed peak strength, respectively, under low and high normal stress levels. In addition and based on our experimental investigations, we put forward a model to predict the evolution of joint morphology and the degree of degradation during the course of shearing. Degradations of the artificial undulated joint and the natural schist joint enable us to verify the proposed model with a relatively good agreement. Finally, the model of Ladanyi and Archambault dealing with the proportion of total joint area sheared through asperities, as, once again, tends to underestimate the observed degradation. Copyright © 2001 John Wiley & Sons, Ltd. [source] The hydroxyl radical reaction rate constant and products of 3,5-dimethyl-1-hexyn-3-ol,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2004J. R. Wells A bimolecular rate constant,kDHO, of (29 ± 9) × 10,12 cm3 molecule,1 s,1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 3,5-dimethyl-1-hexyn-3-ol (DHO, HCCC(OH)(CH3)CH2CH(CH3)2) at (297 ± 3) K and 1 atm total pressure. To more clearly define DHO's indoor environment degradation mechanism, the products of the DHO + OH reaction were also investigated. The positively identified DHO/OH reaction products were acetone ((CH3)2CO), 3-butyne-2-one (3B2O, HCCC(O)(CH3)), 2-methyl-propanal (2MP, H(O)CCH(CH3)2), 4-methyl-2-pentanone (MIBK, CH3C(O)CH2CH(CH3)2), ethanedial (GLY, HC(O)C(O)H), 2-oxopropanal (MGLY, CH3C(O)C(O)H), and 2,3-butanedione (23BD, CH3C(O)C(O)CH3). The yields of 3B2O and MIBK from the DHO/OH reaction were (8.4 ± 0.3) and (26 ± 2)%, respectively. The use of derivatizing agents O -(2,3,4,5,6-pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O -bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible DHO/OH reaction mechanisms based on previously published volatile organic compound/OH gas-phase reaction mechanisms. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 534,544, 2004 [source] Kinetic study of the thermal degradation of poly(aryl ether ketone)s containing 2,7-naphthalene moietiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Si-Jie Liu Abstract The degradation of poly(aryl ether ketone) containing 2,7-naphthalene moieties was subjected to dynamic and isothermal thermogravimetry in nitrogen and air. The dynamic experiments showed that the initial degradation temperature, temperature for 5% weight loss, and temperature corresponding to the maximum degradation rate of poly(aryl ether ketone) containing 2,7-naphthalene moieties were a little higher than those of poly(ether ether ketone) and almost independent of the 2,7-naphthalene moiety content. The thermal stability of poly(aryl ether ketone) containing 2,7-naphthalene moieties in air was substantially less than that in nitrogen, and the degradation mechanism was more complex. The results obtained under the isothermal conditions were in agreement with the corresponding results obtained in nitrogen and air under the dynamic conditions. In the dynamic experiments, the apparent activation energies for the degradation processes were 240 and 218 kJ/mol in nitrogen and air for the second reaction stage as the heating rate was higher than 5°C/min. In the isothermal experiments, the apparent activation energies for the degradation processes were 222 and 190 kJ/mol in nitrogen and air, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Catalytic effects of copper oxides on the curing and degradation reactions of cyanate ester resinJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Shinn-Gwo Hong Abstract The catalytic effect of copper oxides on the curing and degradation behaviors of the cyanate ester resin is studied with infrared spectroscopy, attenuated total reflection infrared spectroscopy (ATR), differential scanning calorimetry (DSC), and thermogravimetry analysis (TGA). The result of infrared spectroscopy and DSC analyses indicates that accelerated curing effects from different additives are in the order of zinc octoate > cuprous oxide > cupric oxide. The exothermic characteristics of the cyanate ester resin during cure are drastically affected by the presence of the copper oxides. In addition, it is obtained from TGA analyses that the thermal stability and degradation mechanism of cyanate ester resins are also significantly affected by the addition of copper oxides whereas the extent of degradation from the cupric oxide is greater than that from the cuprous oxide. These results are attributed to the differences in catalytic effects and surface areas of two copper oxides on the cyanate ester resin in contact during the thermal exposure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 442,448, 2007 [source] Multiscale approach to investigate the radiochemical degradation of epoxy resins under high-energy electron-beam irradiationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2006N. Longiéras Abstract A multiscale investigation of the degradation mechanism of two epoxy systems exposed to electron-beam irradiation under a helium atmosphere was carried out with a variety of analytical methods, including high-resolution solution- and solid-state NMR spectroscopy, NMR relaxometry, infrared spectroscopy, sterical exclusion chromatography, and differential scanning calorimetry. As a first step, we studied a linear phenoxy polymer, poly(2-hydroxyether of bisphenol A), which provided a basis for the investigation of the degradation of a more complex, insoluble epoxy,amine network, diglycidyl ether of bisphenol A/triethylene tetramine. Among different structural modifications, the main degradation process was shown to produce in both cases a chain scission. For the phenoxy resin, the hydroxypropylidene moiety was identified as the fragile site leading to the formation of two phenolic chain ends and acetone and isopropyl alcohol as low-molecular-weight products. All methods, ranging from molecular to supramolecular scales, were shown to correlate both qualitatively and quantitatively. Experimental results obtained with diglycidyl ether of bisphenol A/triethylene tetramine evidenced a different degradation scheme occurring at the ethylene amine part and producing a dangling vinyl amine as the major degradation product. A selective increase in the molecular mobility at this site was confirmed by a two-dimensional, local-field wide-line separation experiment. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 865,887, 2006 [source] Microarray Analysis of Ethanol-Treated Cortical Neurons Reveals Disruption of Genes Related to the Ubiquitin-Proteasome Pathway and Protein SynthesisALCOHOLISM, Issue 12 2004Ramana Gutala Background: Chronic ethanol abuse results in deleterious behavioral responses such as tolerance, dependence, reinforcement, sensitization, and craving. The objective of this research was to identify transcripts that are differentially regulated in ethanol-treated cortical neurons compared with controls by using a pathway-focused complementary DNA microarray. Methods: Cortical neurons were isolated from postconception day 14 C57BL/6 mouse fetuses and cultured according to a standard protocol. The cortical neuronal cells were treated with 100 mM ethanol for five consecutive days with a change of media every day. A homeostatic pathway-focused microarray consisting of 638 sequence-verified genes was used to measure transcripts differentially regulated in four ethanol-treated cortical neuron samples and four control samples. Quantitative real-time reverse transcriptase-polymerase chain reaction analysis was used to verify the mRNA expression levels of genes of interest detected from the microarray experiments. Results: We identified 56 down-regulated and 10 up-regulated genes in ethanol-treated cortical neurons relative to untreated controls at a 5% false-discovery rate. The expression of many genes involved in ubiquitin-proteasome and protein synthesis was decreased by ethanol, including ubiquitin B, ubiquitin-like 3, ubiquitin-conjugating enzyme E3A, 20S proteasome ,- and ,-subunits, and members of the ribosomal proteins. Furthermore, the mRNA expression of heat shock proteins, myristoylated alanine-rich protein kinase C substrate, phosphatase and tensin homolog deleted on chromosome 10, and FK506 binding protein rapamycin-associated protein (FKBP) (mTOR) was also decreased in ethanol-treated cortical neurons. Quantitative real-time reverse transcriptase-polymerase chain reaction analysis of genes involved in the ubiquitin-proteasome cascade revealed a down-regulation of these genes, thereby corroborating our microarray results. Conclusions: Our results indicate that chronic ethanol treatment of cortical neurons resulted in decreased mRNA expression of genes involving the ubiquitin-proteasome pathway and ribosomal proteins together with mTOR expression leading to disruption of protein degradation mechanism and impairment of protein synthesis machinery. [source] Ni,YSZ Solid Oxide Fuel Cell Anode Behavior Upon Redox Cycling Based on Electrical CharacterizationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Trine Klemensø Nickel (Ni),yttria-stabilized zirconia (YSZ) cermets are a prevalent material used for solid oxide fuel cells. The cermet degrades upon redox cycling. The degradation is related to microstructural changes, but knowledge of the mechanisms has been limited. Direct current conductivity measurements were performed on cermets and cermets where the Ni component was removed. Measurements were carried out before, during, and after redox cycling the cermet. The cermet conductivity degraded over time due to sintering of the nickel phase. Following oxidizing events, the conductivity of the cermets improved, whereas the conductivity of the YSZ phase decreased. An improved model of the redox degradation mechanism was established based on the measurements. [source] The role that bond coat depletion of aluminum has on the lifetime of APS-TBC under oxidizing conditionsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 7 2008D. Renusch Abstract Bond coat oxidation as well as bond coat depletion of Al are still believed to be a major degradation mechanism with respect to the lifetime of thermal barrier coating (TBC) systems. In this study the top coat lifetime is described as being limited by both bond coat depletion of Al and mechanical failure of the top coat. The empirical results are introduced by considering three spallation cases, namely, Al depletion failure, thermal fatigue failure, and thermal aging failure. Al depletion failure occurs when the Al content within the bond coat reaches a critical value. In this paper bond coat depletion of Al is modeled by considering the diffusion of Al into both the thermally grown oxide (TGO) and substrate. The diffusion model results are compared to Al concentration profiles measured with an electron beam microprobe. These measured results are from oxidized air plasma sprayed TBC systems (APS-TBC) with vacuum plasma sprayed (VPS) bond coats for exposures up to 5000 h in the temperature range of 950,1100,°C. This paper focuses on the Al depletion failure and how it relates to top coat spallation. [source] Field study on superheater tubes in the loop seal of a wood fired CFB plantMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2004A. Nafari Abstract Two full scale superheaters were exposed in the loop seal of a 30 MW wood-fired CFB plant in Nässjö, Sweden, for one firing season each. Some austenitic steel tubes from the first tube bundle were reinstalled in the second superheater. The superheater tubes were made from one ferritic steel, X10 (Fe8.8Cr) and three austenitic steels; Esshete 1250 (Fe15Cr9Ni6Mn), 347H (Fe17Cr11Ni) and AC66 (Fe27Cr32Ni). Commercial coatings mainly on iron, nickel and carbide base were deposited on some of the X10 and 347H tubes. The material wastage kinetics was non-linear showing that pure corrosion and not erosion-corrosion is the major degradation mechanism in the loop seal. It is however clear that the environment is not very aggressive and the corrosion attack on the uncoated tubes is very small. The largest oxide thickness was only about 150 ,m recorded on the X10 alloy. The austenitic steels mainly suffered from internal corrosion and grain boundary corrosion, the extent and distribution of which strongly depended on the alloy composition. Generally, it was more pronounced in the regions with the thinnest deposit layers. Eight out of 17 coating qualities tested were unaffected by the exposure. Corrosion was only recorded on the lowest alloyed iron based coatings. The only coatings which could not resist the conditions in the loop seal were the carbide containing Metco 3006 and Metco 3007, where severe oxidation and delamination took place. Also the thermally sprayed Inconel 625 coating delaminated, but this was rather due to a mechanical failure resulting from thermal expansion. [source] Reliability and degradation mechanism of AlGaAs/InGaAs and InAlAs/InGaAs HEMTsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003M. Dammann Abstract The long-term stability of AlGaAs/GaAs and InAlAs/InGaAs high electron mobility transistors (HEMTs), tested under high drain voltage and/or high temperature operation is reported. HEMTs with high In content in the active channel, alternatively fabricated on InP substrates and on GaAs substrates covered by a metamorphic buffer (MHEMT), are compared. Despite the high dislocation density in the buffer layer MHEMTs and InP based HEMTs exhibit comparable reliability. AlGaAs/GaAs HEMTs are more reliable than their InAlAs/InGaAs counterparts, especially when operated at high drain voltage. Failure mechanisms are thermally activated gate sinking, Ohmic contact degradation and hot electron induced degradation. [source] Deterioration in mechanical properties of glass fiber-reinforced nylon 6,6 composites by aqueous calcium chloride mixture solutionsPOLYMER COMPOSITES, Issue 4 2009D. Manjula Dhevi In this article, nylon 6,6 (NY66) and glass fiber-(30 wt%) reinforced NY66 (GFNY66) specimens were immersed in various aqueous calcium chloride (aq. CaCl2) mixture solutions at different thermal conditions for varying intervals of time, and analyzed using attenuated total reflection-infrared (ATR-IR) spectroscopy, inductively coupled plasma (ICP), energy dispersive X-ray (EDX), gel permeation chromatography (GPC), and mechanical studies. ICP data revealed increasing concentration of absorbed Ca2+ ions with increasing immersion time resulting in disruption of intra- and intermolecular H-bonding as confirmed using ATR-IR results. From EDX data, the ratio of Ca2+ and Cl, ions absorbed by NY66 was calculated and found to follow its stoichiometric equivalence. GPC data exhibited less reduction in Mn and Mw for aq. CaCl2 -treated NY66 specimens suggesting the absence of any significant chemical degradation, but the occurrence of only physical changes involving H-bond breakage and the formation of new CO···Ca2+ dative bond in NY66 matrix. The mechanical properties of GFNY66 samples treated with various types of aq. CaCl2 solutions exhibited pronounced deterioration, possibly due to the interfacial failure between glass fiber and NY66 matrix. The results obtained from this study were quite useful toward understanding the degradation mechanism in NY66 and GFNY66 caused by various aq. CaCl2 mixture solutions, and will be helpful in improving the mechanical properties of recycled NY66. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Effect of an epoxy octasilsesquioxane on the thermodegradation of an epoxy/amine systemPOLYMER INTERNATIONAL, Issue 1 2010Belén Montero Abstract Polyhedral oligomeric silsesquioxanes (POSS®) can be added to thermoplastic and thermostable polymers to obtain hybrid materials with only a minor tendency to suffer ignition. The aim of the work reported was to analyse the influence of an octafunctional POSS® in the pyrolysis of an epoxy/amine system as well as during the combustion process. Thermal degradation of the modified materials, with respect to the unmodified ones, was analysed using thermogravimetric analysis. As the content of POSS® increased the stability improved and the char/ceramic yields were higher. The Kissinger,Akahira,Sunose method was applied to the modified blends and it showed a decrease in the activation energy with POSS® content. Empirical kinetic models, as well as generalized master plots, were applied to explain the degradation mechanism for ternary blends. The limiting oxygen index parameter was measured to analyse the fire retardancy effect of POSS®: it increased from 24.3 to 25.4% with the addition of 2.5 wt% of POSS®. The mechanism of thermal degradation of the hybrid materials based on an epoxy resin is affected by the presence of the octaepoxy POSS®. Only small amounts of POSS® are necessary to enhance the combustion resistance of the system. Copyright © 2009 Society of Chemical Industry [source] An Investigation of Composite Propellant Accelerated Ageing Mechanisms and KineticsPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 3 2003Michael Abstract The ageing kinetics and mechanisms of a composite solid rocket propellant were investigated by monitoring unstressed propellant samples during prolonged storage at elevated temperatures. For samples confined under air during ageing, it was determined that oxidative cross-linking of the propellant binder was the main degradation mechanism over time. Plasticizer loss was a significant ageing mechanism only for those samples aged unconfined. In addition, there was an indication that ambient humidity had a significant but reversible effect on propellant mechanical properties. Arrhenius mathematical relationships were derived in order to ascertain the extent to which ageing was accelerated by increased propellant temperature. An activation energy for binder oxidation of between 71 and 74,kJ/mol was determined. [source] Deamidation of a model hexapeptide in poly(vinyl alcohol) hydrogels and xerogelsCHEMICAL BIOLOGY & DRUG DESIGN, Issue 2 2000M.C. Lai Abstract: Polymeric controlled release systems have been proposed to prolong the half-lives of protein and peptide drugs in vivo and to deliver active drug at a controlled rate. These systems are ineffective, however, if the drug is not stable during storage and release. This study addresses the effect of poly(vinyl alcohol) on the stability and release of an incorporated hexapeptide, VYPNGA, which undergoes deamidation. Two types of peptide-loaded poly(vinyl alcohol) matrices were formed, a semisolid hydrogel and a lower water content ,xerogel', and stored at 50°C for up to 122 days. The hexapeptide was less stable in both poly(vinyl alcohol) matrices than in aqueous buffer or lyophilized polymer-free powders. The type of poly(vinyl alcohol) matrix appeared to influence the degradation mechanism, since the product distributions differ in the hydrogel and the xerogel. The results suggest that, rather than stabilizing this peptide, incorporation in poly(vinyl alcohol) matrices reduces stability relative to solution and lyophilized controls. [source] Review: Durability and Degradation Issues of PEM Fuel Cell ComponentsFUEL CELLS, Issue 1 2008F. A. de Bruijn Abstract Besides cost reduction, durability is the most important issue to be solved before commercialisation of PEM Fuel Cells can be successful. For a fuel cell operating under constant load conditions, at a relative humidity close to 100% and at a temperature of maximum 75,°C, using optimal stack and flow design, the voltage degradation can be as low as 1,2,,V·h. However, the degradation rates can increase by orders of magnitude when conditions include some of the following, i.e. load cycling, start,stop cycles, low humidification or humidification cycling, temperatures of 90,°C or higher and fuel starvation. This review paper aims at assessing the degradation mechanisms of membranes, electrodes, bipolar plates and seals. By collecting long-term experiments as well, the relative importance of these degradation mechanisms and the operating conditions become apparent. [source] Chemical modification of polystyrene by low-energy (<100 eV) electron irradiation studied by mass spectrometryJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008S. Massey Abstract Dip-coated thin films of polystyrene were chemically modified (degraded) by low-energy electron irradiation (0,100 eV). The resulting degradation was studied by mass spectrometry with variable electron energy. In the negative-ion mode, H, was observed and was associated with two phenomena. The resonant structure at 9.1 ± 0.4 eV was associated with dissociative electron attachment. The energy of the resonance peak agreed with the results obtained for organic molecules. At a higher energy, a monotonic rise of the emission yield was observed and was associated with nonresonant dipolar dissociation. More mass fragments were observed in the positive-ion mode. The predominant ion was H+ at 100 eV of electron irradiation, and alkyl ions were detected at higher masses. Emission thresholds were measured for the most predominant positive ions. The shape of the emission curve showed that there was no resonant process in the formation of these ions. The energy threshold was measured at about 20 eV, and this meant that the carbon structure of the polymer broke with a recombination of the degradation products with hydrogen atoms before the emission occurred. Below 19 eV, there was only hydrogen loss; this implied that the possible degradation mechanisms did not break the general carbon structure of the material, leading to crosslinking. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Water absorption properties of phosphate glass fiber-reinforced poly-,-caprolactone composites for craniofacial bone repairJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Levent Onal Abstract The moisture uptake of polymers and composites has increasing significance where these materials are specified for invasive, long-term medical applications. Here we analyze mass gain and the ensuing degradation mechanisms in phosphate glass fiber reinforced poly-,-caprolactone laminates. Specimens were manufactured using in situ polymerization of ,-caprolactone around a bed of phosphate glass fibers. The latter were sized with 3-aminopropyltriethoxysilane to control the rate of modulus degradation. Fiber content was the main variable in the study, and it was found that the moisture diffusion coefficient increased significantly with increasing fiber volume fraction. Diffusion, plasticization, and leaching of constituents appear to be the dominant aspects of the process over these short-term tests. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Low-Temperature Aging of Zirconia Ferrules for Optical ConnectorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Michael J. Lance Zirconia ferrules for optical connectors were examined after aging at 85°C and 95% relative humidity. Two degradation mechanisms were the roughening and the deformation of the zirconia ferrule surface. Raman microscopy revealed that this relatively low-temperature degradation of zirconia ferrules is caused by the tetragonal to monoclinic transformation of zirconia, and is accelerated by stress relief during polishing. The surface upheavals associated with low-temperature aging may significantly degrade the performance of optical connectors over time. [source] Fretting behaviour of low-friction coatingsLUBRICATION SCIENCE, Issue 3 2005C. Langlade Abstract The choice of an appropriate low-friction coating for an industrial application is generally a difficult task. As many parameters are involved and are often unknown, selection criteria are hard to define. In order to elucidate the case of fretting conditions, a simulator has been used to reproduce the degradation mechanisms observed for real situations. Numerous experiments performed with this machine permit one to define endurance life criteria. The evolution of the life observed has been analysed as a function of the contact pressure and the film thickness. Using a Wöhler approach, endurance curves have been plotted that give useful information for selecting appropriate coatings. As other parameters may be of some interest, performance indices have been associated with them, and the results can be presented on a multi-axis (polar) diagram. [source] Current collapse and reliability of III-N heterostructure field effect transistorsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 3 2007A. Koudymov Abstract Measurements of GaN HFET lifetime as a function of temperature show that different degradation mechanisms are involved at low temperatures (close to room temperature) and high temperatures (above 150 °C). The degradation at low temperatures is linked to the trap generation and can be explained using the current collapse model. At higher tempe- ratures, other degradation mechanisms become important or even dominant. The current collapse related degradation can be diminished by using improved device design, which will greatly increase the overall lifetime (up to long lifetimes obtained by extrapolating high temperature data to room temperature). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Performance of thin-film transistors fabricated by sequential lateral solidification crystallization techniquesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2008M. A. Exarchos Abstract The performance of Excimer Laser Annealed (ELA) Thin-Film Transistors (TFTs), in terms of drain current behaviour in unstressed as well as in DC stressed devices, is presented. The transistors studied were fabricated under different irradiation schemes of a novel Sequential Lateral Solidification (SLS) process. As far as unstressed transistors concerned, drain current transients relaxed through stretched exponential law. Fitting results disclosed that both gate dielectric polarization and carrier recombination mechanisms occurred through transient relaxation. Deep Level Transient Spectroscopy (DLTS) technique was called forth in order to investi- gate the origin of carrier recombination mechanisms. DC hot carrier stress measurements, under "worst ageing condition" regime, were conducted in order to probe degradation mechanisms and device reliability standards. Crystal domain size significantly affects threshold voltage degradation. The latter increases with decreasing crystal domain size, due to increased concentration of protrusions in the polysilicon film. Transconductance degradation also depends on crystal domain size, attributed mainly to bulk polysilicon trap generation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Polydimethylsiloxane,cristobalite composite adhesive system for aerospace applicationsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2009Seema Ansari Abstract The effect of phase-pure cristobalite (a high temperature crystalline polymorph of silica) on the adhesive characteristics of hydroxyl terminated polydimethylsiloxane (PDMS) was studied. The potential advantages of PDMS/cristobalite composite system as an adhesive for aerospace applications are also discussed. A PDMS/cristobalite composite adhesive system containing different filler contents (0,46 volume percentage, vol%) was prepared. The filler material, phase-pure cristobalite, was synthesized by the pyrolysis of fused silica at 1400°C. The mechanical, rheological, and thermal characteristics of the composites were studied. A high yield stress (0.151,Pa), shear-thinning index (1.051), and fast recovery rate were observed for ,34,vol% cristobalite loading, which indicate that PDMS retains its excellent adhesive and flow characteristics even at high filler loading with enhanced mechanical characteristics. Thermal analysis shows the onset of degradation of PDMS shifts to higher temperatures, 372,438°C and 317,417°C in nitrogen and air atmosphere respectively, which shows excellent thermal stability. The residual component yields after thermal degradation of PDMS/cristobalite composite system in nitrogen and air atmosphere show different degradation mechanisms. Copyright © 2008 John Wiley & Sons, Ltd. [source] Identification of degradation mechanisms in field-tested CdTe modulesPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 3 2006Thomas Carlsson Abstract Field tests and accelerated ageing tests were conducted on CdTe photovoltaic modules with Sb-based back contacts. Significant performance degradation was observed during one and a half years of outdoor exposure. Small-area samples were prepared from field tested modules and characterized with current,voltage, capacitance,voltage and resistance measurements. Results show that module performance degradation in the field can be partly attributed to a decrease in doping concentration close to the CdS/CdTe junction and an increased resistance in the transparent front contact. A comparison with results in the literature indicates that bias voltage may play a role in the degradation process. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||