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Thermal Aging (thermal + aging)

Distribution by Scientific Domains

Polymers and Materials Science	82%

Selected Abstracts

Effects of Thermal Aging on the Mechanical Properties of a Porous-Matrix Ceramic Composite

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2002
Eric A. V. Carelli
The present article focuses on changes in the mechanical properties of an all-oxide fiber-reinforced composite following long-term exposure (1000 h) at temperatures of 1000,1200°C in air. The composite of interest derives its damage tolerance from a highly porous matrix, precluding the need for an interphase at the fiber,matrix boundary. The key issue involves the stability of the porosity against densification and the associated implications for long-term durability of the composite at elevated temperatures. For this purpose, comparisons are made in the tensile properties and fracture characteristics of a 2D woven fiber composite both along the fiber direction and at 45° to the fiber axes before and after the aging treatments. Additionally, changes in the state of the matrix are probed through measurements of matrix hardness by Vickers indentation and through the determination of the matrix Young's modulus, using the measured composite moduli coupled with classical laminate theory. The study reveals that, despite evidence of some strengthening of the matrix and the fiber,matrix interfaces during aging, the key tensile properties in the 0°/90° orientation, including strength and failure strain, are unchanged. This strengthening is manifested to a more significant extent in the composite properties in the ±45° orientation, wherein the modulus and the tensile strength each exhibit a twofold increase after the 1200°C aging treatment. It also results in a change in the failure mechanism, from one involving predominantly matrix damage and interply delamination to one which is dominated by fiber fracture. Additionally, salient changes in the mechanical response beyond the maximum load suggest the existence of an optimum matrix strength at which the fracture energy in the ±45° orientation attains a maximum. The implications for long-term durability of this class of composite are discussed. [source]

Thermal aging of a blend of high-performance fibers

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010
Carlos Arrieta
Abstract The focus of this work is the study of the thermal aging of high-performance fibers used in the making of fire protective garments. Accelerated thermal aging tests were carried out on fabric samples made up of a blend of Kevlar® (poly p -phenylene terephthalamide) and PBI (poly benzimidazole) staple fibers, as well as on yarns pulled from this fabric, by means of exposure to elevated temperatures, comprised between 190°C and 320°C. All samples underwent loss of breaking force retention. The material thermal life, defined as the time required for the fibers to attain a 50% reduction of the original breaking force, ranged between a dozen of days at the lowest exposure temperature, to less than an hour at the highest. Breaking force data were fitted using the Arrhenius model following two different approaches, namely the extrapolated thermal life value and the shift factors yielded by the time-temperature superposition (TTS). The Arrhenius model seemed to describe appropriately the overall aging process, as inferred from the excellent fit obtained when using both approaches, although activation energies provided from both approaches are different. To follow the chemical evolution of the material with thermal aging, Fourier-transform infrared (FTIR) analyses were conducted. The qualitative analysis of the FTIR spectra showed little evidence of chemical changes between the aged and the nonaged samples, indicating either that the aging process carries on without significant modification of the chemical structure of the fibers, or that FTIR is not an appropriate method to spot such a modification. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Characterization of reversible permeability in advanced USC steel during thermal aging

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010
Chung Seok Kim
Abstract The effects of microstructure on reversible permeability (µrev) are discussed for thermally aged ultra-supercritical (USC) steel, which is required for the next generation of power plants. Thermal aging was observed to coarsen the tempered carbide (Cr23C6), generate the Laves (Fe2W) phase and decrease the dislocation density. The peak position of the µrev decreased drastically during the initial 1000,h aging period, and was thereafter observed to decrease only slightly. The variation in peak position of µrev is closely related to the decrease in the number of pinning sites, such as dislocations, fine precipitates, and the martensite lath. [source]

Effects of Aging on Interfacial Microstructure and Reliability Between SnAgCu Solder and FeNi/Cu UBM,

ADVANCED ENGINEERING MATERIALS, Issue 6 2010
Qing-Sheng Zhu
Effects of thermal aging on the interfacial microstructure and reliability of the SnAgCu/FeNi-Cu joint are investigated. It is found that aging effects depends strongly on the temperature. Aging at low temperature, e.g., at 125,°C, a submicron meter thick FeSn2 IMC layer formed at the SnAgCu/FeNi-Cu interface during reflowing grows at a rate twenty times slower than the growth rate of the IMC at the SnAgCu/Cu interface. At high temperature, e.g., at 180,°C, the Cu element is found to diffuse through FeNi layer to produce the (Cu, Ni)6Sn5 IMC and this IMC layer grows even faster than the IMC at the SnAgCu/Cu interface. Solder ball shear test results show that the SnAgCu/FeNi-Cu joint has a comparable strength to the SnAgCu/Cu joint after reflowing, and the strength drop after aging at 125,°C is less than that of the SnAgCu/Cu joint. However, after aging at 180,°C, the strength of the SnAgCu/FeNi-Cu joint is degraded to a low value, along with a shift in failure mode from the solder fracture to the brittle intermetallics fracture. [source]

Novel Crosslinking of High-order and Multiple Copper Twins in Advanced Microelectronics Packaging,

ADVANCED ENGINEERING MATERIALS, Issue 4 2004
W. Zhang
Novel crosslinking of high-order and multiple copper twins has been formed in the metallization/solder interconnect subjected to the thermal aging. This surprising finding may illustrate a universal metallization failure mode. Meanwhile, many copper nanocrystals in situ originated from those twins crosslinking shed a novel light on the synthesis approach to fascinating nanocrystalline metals. [source]

The classical kinetic model for radical chain oxidation of hydrocarbon substrates initiated by bimolecular hydroperoxide decomposition

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2006
X. Colin
Kinetic modeling of the low-temperature (typically T , 200°C) thermal aging of polymers is a problem of great technological importance, owing to the continuously increasing needs of industry in terms of reliable methods for lifetime prediction. In the temperature domain under consideration, for most hydrocarbon substrates, oxidation proceeds by a radical chain reaction initiated by bimolecular hydroperoxide decomposition. In other words, the reaction generates its own initiator, which explains its strong autoaccelerated character. The most pertinent model is, to our opinion, the model elaborated by Tobolsky et al. (J Am Chem Soc 1950, 72, 1942) in the early 1950s. This model is, however, based on three questionable assumptions: the existence of a stationary state for radical concentrations (hypothesis S), the presence of oxygen in excess (hypothesis E), and the fact that the onset of steady state can be observed in the domain of low conversions, where the substrate consumption can be neglected (hypothesis L). One hypothesis (S) lacks consistency. A sounder alternative, which does not modify significantly the mathematical expressions of the model, will be proposed. The other hypotheses (E and L) can be justified in certain cases, but the limits of their domain of validity were never established to our knowledge. It is tried, here, to express these limits in function of fundamental parameters: rate constants and concentrations of reactants. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38:666,676, 2006 [source]

Thermal aging of a blend of high-performance fibers

Hydrogenated natural rubber blends: Aspect on thermal stability and oxidative behavior

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2009
N. Hinchiranan
Abstract Hydrogenated natural rubber (HNR) prepared from natural rubber (NR) is a new sustainable elastomer with excellent thermal properties. This study reports on the effect of vulcanization system and blend ratio on the thermal and oxidative resistance of HNR/NR vulcanizates. The various HNR/NR ratios vulcanized by peroxide and sulfur donor system exhibited the highest retention of tensile strength after thermal aging due to the formation of zinc-dimethyldithiocarbamate (ZDMDC) which is an efficient antioxidant. The results from thermogravimetric analysis (TGA) indicated that the saturated structure of HNR had higher decomposition temperature and activation energy to enhance the thermal stability of HNR/NR vulcanizates. The initial and maximum decomposition temperatures of NR and HNR phases in vulcanizates were not affected by rubber blend ratio. This suggests that the decomposition pattern of HNR has no influence on another constituent. The increase in HNR content in the blends could retard the ozonolysis resulting in the surface cracking attacked by ozone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

Effects of cyclic compression and thermal aging on dynamic properties of neoprene rubber bearings

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008
Hsoung-Wei Chou
Abstract The dynamic properties of rubber bearings frequently used as isolators in structures could be significantly deteriorated because of the change of microstructure in rubber caused by cyclic compression and thermal aging. As a result, a catastrophic failure of bridges and buildings unexpectedly occurs when they are subjected to earthquake attack. Here, the dynamic properties of neoprene rubber bearings before and after different cycles of compressive loading or various periods of thermal aging were first measured and compared to each other. On the basis of the experimental results, the effects of cyclic compression and thermal aging on the stiffness, energy absorption, and equivalent viscous damping coefficient of neoprene rubber bearings are investigated. It is found that the deterioration of dynamic properties of neoprene rubber bearings caused by either cyclic compression or by thermal aging is significant and should be taken into account in designing rubber bearings. © 2007 Wiley Periodicals, Inc. JAppl Polym Sci, 2008 [source]

Blends of triazine-based hyperbranched polyether with LDPE and plasticized PVC

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007
Jyotishmoy Borah
Abstract Triazine-based hyperbranched polyether was obtained by earlier reported method and blended with low density polyethylene (LDPE) and plasticized poly(vinyl chloride) (PVC) separately to improve some desirable properties of those linear polymers. The properties like processability, mechanical properties, flammability, etc. of those linear polymers were studied by blending with 1,7.5 phr of hyperbranched polyether. The mechanical properties were also measured after thermal aging and leaching in different chemical media. SEM study indicates that both polymers exhibit homogenous morphology at all dose levels. The mechanical properties like tensile strength, elongation at break, hardness, etc. of LDPE and PVC increase with the increase of dose level of hyperbranched polyether. The flame retardant behavior as measured by limiting oxygen index (LOI) for all blends indicates an enhanced LOI value compared to the polymer without hyperbranched polyether. The processing behavior of both types of blends as measured by solution viscosity and melt flow rate value indicates that hyperbranched polyether acts as a process aid for those base polymers. The effect of leaching and heat aging of these linear polymers on the mechanical properties showed that hyperbranched polyether is a superior antidegradant compared to the commercially used N -isopropyl- N -phenyl p -phenylene diamine. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 648,654, 2007 [source]

Effect of the Starting Microstructure on the Thermal Properties of As-Sprayed and Thermally Exposed Plasma-Sprayed YSZ Coatings

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2009
Yang Tan
Thermal barrier coatings (TBCs) experience thermal gradients, excessive temperature, and high heat flux from hot gases in turbines during service. These extended thermal effects induce sintering and significant microstructure changes, which alter the resulting thermal conductivity of the TBCs. To study the effects of different starting microstructures on the sintering behavior, plasma-sprayed yttria-stabilized zirconia (YSZ) TBCs produced from different starting powders and process parameters were subjected to thermal aging at several temperatures and time intervals, after which their thermal conductivity was measured at room temperature. The thermal conductivity results were analyzed by introducing the Larson,Miller parameter, that describes the creep-like behavior of thermal conductivity increase with annealing temperature and time. One set of coatings was also annealed under the same conditions and the thermal conductivities were measured at elevated temperatures. The temperature-dependent thermal conductivity data were analyzed and used to predict the long-term thermal property behavior for a general YSZ coating design. [source]

Crystallization of Lead Niobate Glass by Mechanical Activation

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001
Junmin Xue
Mechanical activation-triggered crystallization in PbNb2O6 -based glass was dependent on the initial presence of nuclei. The crystallization cannot be initiated by mechanical activation in a highly amorphous glass composition quenched from 1350°C where PbNb2O6 nuclei did not exist. The steady growth of nanocrystallites of PbNb2O6 was observed with an increasing degree of mechanical activation in the glass quenched from 1300°C, where a density of PbNb2O6 nuclei existed before mechanical activation. The inability to nucleate in the highly amorphous oxide glass by mechanical activation is consistent with the much higher structural stability as compared with that of metallic glasses, such as Fe-Si-B. The mechanical activation-grown PbNb2O6 nanocrystals were 10,15 nm in size as observed using HRTEM and their crystallinities were further improved by thermal aging at an elevated temperature in the range of 550° to 650°C. [source]

Characterization of reversible permeability in advanced USC steel during thermal aging

Effect of thermal aging on the crystal structural characteristics of poly(tetra fluoro ethylene)

POLYMER ENGINEERING & SCIENCE, Issue 11 2007
Anjana Jain
The residual effects of cumulative thermal aging on the crystal structural characteristics of the fluoro carbon poly(tetra fluoro ethylene) (PTFE) have been studied by X-ray diffraction methods. The initial hexagonal arrangement of the PTFE chains in a 157 helical conformation is left unaffected by the exposures to temperatures (T), up to and beyond its melting point, Tm. The unit cell registers a residual anisotropic volume expansion. The anisotropy arises from the enhanced enlargement of the basal plane dimension a compared with the axial dimension c. Conformational changes contributing to the observed increase in the chain length have been examined. Enhancement of residual crystallinity of samples aged at T's < Tm suggests that the selective thermal aging could be used as an effective tool to improve the initial crystallinity of commercially available PTFE. The activation energy for 50% enhancement in initial crystallinity has been estimated as 53.9 kJ mol,1. Aging at 400°C, a temperature above Tm, is accompanied by markedly different features viz., deterioration in crystallinity and other structural characteristics. The overall behavior of thermally aged PTFE bears a marked similarity to many polyamides. POLYM. ENG. SCI., 47:1724,1729, 2007. © 2007 Society of Plastics Engineers [source]

Reinforcement of compatibilized NR/NBR blends by fly ash particles and precipitated silica

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2009
C. Kantala
Abstract Effects of precipitated silica (PSi) and silica from fly ash (FA) particles (FASi) on the cure and mechanical properties before and after thermal and oil aging of natural rubber (NR) and acrylonitrile,butadiene rubber (NBR) blends with and without chloroprene rubber (CR) or epoxidized NR (ENR) as a compatibilizer have been reported in this paper. The experimental results suggested that the scorch and cure times decreased with the addition of silica and the compound viscosity increased on increasing the silica content. The mechanical properties for PSi filled NR/NBR vulcanizates were greater than those for FASi filled NR/NBR vulcanizates in all cases. The PSi could be used for reinforcing the NR/NBR vulcanizates while the silica from FA was regarded as a semi-reinforcing and/or extending filler. The incorporation of CR or ENR enhanced the mechanical properties of the NR/NBR vulcanizates, the ENR being more effective and compatible with the blend. The mechanical properties of the NR/NBR vulcanizates were improved by post-curing effect from thermal aging but deteriorated by the oil aging. Copyright © 2008 John Wiley & Sons, Ltd. [source]