Impact Of Thermal Aging Research Articles

The impact of the environment of use on the behavior of polychlorinated (vinyl chloride).

Polymers are omnipresent in our daily life thanks to their low production cost and their ease of implementation, which makes thermoplastics more usable in supplying drinking water, distributing cold and hot water, and transporting hot corrosive fluids and industrial chemicals, including inorganic acids. The material of our study is chlorinated polyvinyl chloride (CPVC); it has better thermal insulation and a wide operating temperature range. This paper deals with the impact of thermal aging over time on the behavior of CPVC by performing two types of tests according to ISO 15877 (EN ISO 15877) two types of tests; the first is thermal aging (Fig.1) at a temperature of 95°C and a pressure of 10 bars for periods of up to 2000h and the second test exposure of the pipeline to pressure until bursting. On the basis of the test results, we can predict the rupture of the pipeline and thus avoid the dangerous accidents due to the bursting under the effect of the pressure and the high temperature; by using the results of this study, the inspectors change CPVC structures at the right time, neither too early when the part is still in good condition nor too late after failure; this will be very useful to save water and money and of course save the environment.

Bending behavior of 3D printed sandwich structures with different core geometries and thermal aging durations

In recent years, the Fused Deposition Modeling (FDM) method has been employed in the production of small-scale structural elements with moderate loads, such as small-unmanned aerial vehicles, sports equipment, dental implant molds, and similar applications. In these cases, the FDM technique can utilize polymers like Polyamide (PA), Polylactic Acid (PLA), and Acrylonitrile Butadiene Styrene (ABS) to manufacture structural components. Lightweight sandwich structures are utilized as structural elements in various industries due to their unique characteristics, high stiffness-to-weight ratio, and energy absorption capabilities. Although the number of studies on the mechanical properties of sandwich structures manufactured with FDM has increased in recent years, experimental data on the mechanical characteristics of sandwich structures manufactured with FDM under different thermal aging durations are still insufficient. Driven by this motivation, the energy absorption capabilities of sandwich structures with different four core geometries (i.e., circular, hexagonal, square, and triangular) were experimentally investigated under different thermal aging durations. The sandwich structures were manufactured from PLA material by the FDM method. Four different thermal aging durations, 0, 15, 30 and 45 days, were considered for environmental conditions. Quasi-static three-point bending experiments were conducted to assess the energy absorption capability of lightweight sandwich structures featuring diverse core topologies. The bending test results demonstrate that the core topology significantly affects the energy absorption abilities of sandwich structures. Moreover, fractographic analysis using scanning electron microscopy (SEM) was conducted to gain deeper insights into the impact of thermal aging on aged specimens. In addition, it was concluded that the energy absorption performances of all sandwich structures with different core structure topologies were adversely affected by increasing the thermal aging time.

CH4 combustion over a commercial Pd/CeO2-ZrO2 three-way catalyst: Impact of thermal aging and sulfur exposure

Thermal aging and sulfur poisoning are major problems influencing the efficiency and lifetime of natural gas three-way catalysts (TWCs) during real-world operation. In the present study, thermal aging and sulfur-induced deactivations on CH4 combustion were investigated over commercial monolithic honeycombs, i.e., Pd/CexZr1-xO2 (CZ)-based TWCs that are thermally aged in the bench (HTA), followed by being operated behind the stoichiometric natural gas engine in high sulfur fuel (HTA + S). Both HTA and HTA + S samples show degraded performance in CH4 combustion relative to the fresh one, which are caused by the reconstruction of Pd species induced by thermal aging and the decreased reducibility of the support. The 18O2 labelling experiments show that in all cases CH4 combustion proceeds via a MvK mechanism in which lattice O (OL) plays a key role. The sulfation aging (HTA + S sample) promotes the activation of CH4 and O2 by forming Pdδ+-(SO42-)δ- and Ce3+-VO couples at the interface as compared to HTA sample. However, such a promotion effect could be compromised by the blocking effect of sulfate on the exchange of OL from the bulk to the surface and across the surface. The fundamental understanding of thermal and S deactivation mechanisms from this study could help to predict a real-world lifetime use curve of natural gas TWCs.

The impact of thermal ageing on sealing performance of HNBR packing elements in downhole installations in oilfield wellhead applications

Hydrogenated nitrile butyl rubber (HNBR) elastomers are highly resistant to chemicals and degradation, and they are good candidates to be adopted in aggressive environmental conditions of high temperature and pressure. As these service parameters are common in oil and gas applications, HNBR is popular in applications such as elastomer packers in wellhead installations. This study investigated the thermal ageing behaviour of HNBR elastomers to better predict the long-term sealing performance of the packers. Elastomer compounds were thermally aged and FTIR-ATR and differential scanning calorimetry techniques were used to indicate dominant chemical reactions during ageing. Furthermore, the mechanical performance of the aged compounds were studied to investigate the effect of dominant ageing reactions on performance. It was indicated that crosslinking reaction was dominant in the ageing process of HNBR compounds up to 150 °C. This resulted in increased stiffness and alleviated elongational strains at the break. However, compounds behaved brittle at ageing temperatures above 150 °C, and from the thermal analysis, it was concluded that at those temperatures chain scission reactions overtook the ageing mechanism. Finally, an approach for life-long prediction of mechanical characteristics of the specimens showed while long-term ageing promotes elastic failure, ageing temperatures above 150 °C facilitate rupture because of the brittle response of the compounds.

Thermal aging behavior characteristics of asphalt binder modified by nano-stabilizer based on DSR and AFM

Abstract In order to clarify the effect of thermal aging on the nano-stabilized modified asphalt binder, TINUVIN 770 (T770) hindered amine light stabilizer of nanoscale was selected as aging modifying agent to prepare modified asphalt. The impact of thermal aging on the rheological properties of T770-modified asphalt was investigated using dynamic shear rheological test of frequency sweep and multiple stress creep recovery test. The surface roughness variation of T770-modified asphalt was characterized by using atomic force microscope throughout the thermal aging process. Furthermore, the typical morphology and parameter features of T770-modified asphalt were identified. The results showed that with the extension of thermal aging time, the high temperature rutting resistance of T770-modified asphalt was improved, while the unrecoverable creep compliance was degraded. When the thermal aging time exceeded 6 h, the bee structure appeared on the surface of T770-modified asphalt. Meanwhile, with the increase in thermal aging time, the special structure formed on the surface of asphalt gradually became smaller. The surface fluctuation difference of T770-modified asphalt reflected the better thermal aging resistance property of T770-modified asphalt than 70# asphalt.

Impact of Aging on Mechanical Properties of Thermally Conductive Gap Fillers

Abstract Thermal interface materials (TIMs) are an important component in electronic packaging, and there is a concerted effort to understand their reliability when used under various environmental load conditions. Previous researchers have investigated gap fillers and other types of TIMs to understand their performance degradation under loading conditions such as thermal cycling and thermal aging. Most of the study in the literature focuses on studying the changes in thermal properties, and there is a lack of understanding when it comes to studying the mechanical behavior of TIMs. Degradation of mechanical properties is the cause for the loss in thermal performance and is critical during TIM selection process. Moreover, mechanical properties such as modulus and coefficient of thermal expansion (CTE) are critical to assess performance of TIMs using finite element analysis (FEA) and potentially save time and money in the evaluation and selection process. Due to the very soft nature of TIMs, sample preparation is a challenging part of material characterization. In this paper, commercially available TIMs are studied using testing methods such as thermomechanical analyzer (TMA), dynamic mechanical analyzer (DMA), and Fourier infrared spectroscopy (FTIR). These methods are used to characterize the material properties and study the changes in properties due to aging. In this work, the followings are presented: impact of filler content on the mechanical properties, sample preparation method for curable TIM materials with specified thicknesses, and impact of thermal aging on mechanical properties.

Nonlinear creep behaviour of glass fiber reinforced polypropylene: Impact of aging on stiffness degradation

Nonlinear creep behavior of one commercial short glass fiber reinforced polypropylene was investigated using tensile creep tests and stiffness degradation measurements. The impact of thermal aging and following quenching was evaluated on the latter mechanical property. Experimental results were modeled applying nonlinear viscoelastic model used by Pupure et al. (2013) and developed by Lou and Schapery [1,2]. Results showed that this model can describe nonlinear behavior of short glass fiber reinforced polymer composites, where microdamage is given by debonding of fiber-matrix interfaces already at low strains, where cracks propagate and lead to tensile creep fracture.

Impact of Thermal Aging on the SCR Performance of Tungsten Doped CeVO4 Mixed Oxides

The development of more thermally stable vanadia-based SCR catalysts for combined end-of-pipe technologies, i.e. selective catalytic reduction catalysts wash-coated on a particulate filter, has been considered in this study. The impact of thermal aging at 850 °C in wet atmosphere has been investigated on bulk W-doped CeVO4 catalysts. Strong detrimental effect on the specific surface area was observed delayed by the presence of tungsten. However, they preserve a significant selective conversion depending on the surface composition with an optimal tungsten composition.

Impact of thermal aging on the intermetallic compound particle size and mechanical properties of lead free solder for green electronics

The Sn-Ag3.0-Cu0.5 lead free solder (LFS) alloy is mostly used as good alternative as compared to conventional Tin-Lead (Sn-Pb) due to its good mechanical properties and no harmful effect on environment but it stills has some problems to be solved regarding the growth formation of intermetallic compounds (IMCs). The IMCs present inside the bulk tin (Sn) matrix grow at high temperature and hence their impact on mechanical properties becomes more significant. In this work the effects of lanthanum (La) doping of Sn-Ag3.0-Cu0.5 is investigated as function of IMCs growth and mechanical properties including yield strength (YS) and ultimate tensile strength (UTS) under different thermal aging temperatures. The selected La concentration in this study is 0.4wt%. The aging time is 50h and thermal aging temperatures are 60°C, 100°C and 140°C. The microstructure examination before and after thermal aging is observed using scanning electron microscopy (SEM) followed by image analysis to estimate the nature of IMCs. The chemical composition is confirmed with energy dispersive X-ray (EDX). The YS and UTS are also examined before and after thermal aging for the un-doped and doped samples from stress-strain curves using universal testing machine (UTM). It is investigated that inclusion of 0.4wt% La into Sn-Ag3.0-Cu0.5 solder system results in increasing the IMCs growth rate and hence mechanical properties reduced. It is also observed that the microstructure becomes coarsen after thermal aging due to growth of average IMCs particle size with significant decrease in YS and UTS. Further, mathematical relations with minimum error are developed to predict mechanical properties (YS and UTS) at various levels of aging temperature, showing a reciprocal relationship between aging temperature and mechanical properties.

Fracture load and failure types of different veneered polyetheretherketone fixed dental prostheses.

The aim of this study is to investigate the fracture load of different veneered PEEK 3-unit fixed dental prosthesis (FDPs) after different aging regimens. Congruently anatomically shaped 3-unit FDPs were milled using a master stl-data set and randomly divided into four groups (N = 120, n = 30 per veneering group), which were veneered using different veneering methods: (i) digital veneering with breCAM.HIPC, (ii) conventional veneering with crea.lign, (iii) conventional with crea.lign paste, and (iv) using pre-manufactured veneers visio.lign. The FDPs were then adhesively cemented on a metal abutment and fracture loads were measured in a universal testing machine (1mm/min) before and after aging (10,000 thermal cycles, 5/55°C). Two- and one-way ANOVA followed by post hoc Scheffé tests were used for data analysis (p < 0.05). This investigation showed an influence of the veneering method on the fracture load results independent of the aging level. The highest fracture load was measured for the FDPs with digital veneering (1882 ± 152N at baseline, 2021 ± 184N after thermocycling). The remaining groups showed comparable results, and no impact of thermal aging was observed. Digital and conventional veneers showed cracks in the pontic region starting from the connector area as a main failure type after loading, while the pre-manufactured veneers showed predominantly adhesive failures. The digital veneering method showed the highest fracture load resistance. Thermal aging showed no impact on the fracture load of all tested veneered PEEK 3-unit FDPs. According to this study results, reliable veneering of PEEK FDPs can be achieved with digital veneering.

Effect of Layer and Film Thickness and Temperature on the Mechanical Property of Micro- and Nano-Layered PC/PMMA Films Subjected to Thermal Aging

Multilayered polymer films with biomimicking, layered structures have unique microstructures and many potential applications. However, a major limitation of polymer films is the deterioration of mechanical properties in working environments. To facilitate the design and development of multilayered polymer films, the impact of thermal aging on the mechanical behavior of micro- and nano-layered polymer films has been investigated experimentally. The composition of the polymer films that have been studied is 50 vol% polycarbonate (PC) and 50 vol% poly(methyl methacrylate) (PMMA). The current study focuses on the effect of film and layer thickness and temperature on the mechanical properties of the materials subjected to thermal aging. To study the effect of film and layer thickness, films with the same thickness, but various layer thicknesses, and films with the same layer thickness, but various film thicknesses, were thermally aged at 100 °C in a constant temperature oven for up to six weeks. The results show that as the layer thickness decreases to 31 nm, the film has a higher stiffness and strength, and the trend of the mechanical properties is relatively stable over aging. The ductility of all of the films decreases with aging time. To study the effect of temperature, the films with 4,096 layers (31 nm thick for each layer) were aged at 100 °C, 115 °C and 125 °C for up to four weeks. While the 100 °C aging results in a slight increase of the stiffness and strength of the films, the higher aging temperature caused a decrease of the stiffness and strength of the films. The ductility decreases with the aging time for all of the temperatures. The films become more brittle for higher aging temperatures.

Effect of Hydrothermal Aging on Physical and Chemical Properties of a Commercial NOx-Storage Catalyst

Fuel consumption for NOx trap regeneration depends on the regeneration frequency, which is a function of NOx trap performance parameters. Hence, the impact of thermal aging must be considered in the operation strategy. For this purpose, the effect of thermal aging on the physical and chemical properties of a commercial NOx storage/reduction catalyst containing Pt/Pd/Rh has been investigated. After thermal treatment under various conditions, the samples were characterized using CO chemisorption measurements, X-ray diffraction (XRD), N2 physisorption, and electron microscopy. It is shown that the major impact of lean hydrothermal treatment on the catalyst activity is the continuous decrease of the specific surface area with aging temperature due to collapse of smaller pores. The noble metal nanoparticles remained highly dispersed, even after lean aging at 800 °C. In contrast, noble metal sintering represents the main aging effect of lean/rich cycling at elevated temperatures. Furthermore, XRD and selected area electron diffraction revealed a significant loss of crystallinity for the barium component in consequence of lean/rich aging treatment. However, independent from the aging treatment, no formation of mixed oxides could be observed.

Impact of Thermal Aging on the Microstructure Evolution and Mechanical Properties of Lanthanum-Doped Tin-Silver-Copper Lead-Free Solders

An extensive study is made to analyze the impact of pure lanthanum on the microstructure and mechanical properties of Sn-Ag-Cu (SAC) alloys at high temperatures. Different compositions are tested; the temperature applied for the isothermal aging is 150°C, and aging times of 10 h, 25 h, 50 h, 100 h, and 200 h are studied. Optical microscopy with cross-polarized light is used to follow the grain size, which is refined from 8 mm to 1 mm for as-cast samples and is maintained during thermal aging. Intermetallic compounds (IMCs) present inside the bulk Sn matrix affect the mechanical properties of the SAC alloys. Due to high-temperature exposure, these IMCs grow and hence their impact on mechanical properties becomes more significant. This growth is followed by scanning electron microscopy, and energy-dispersive spectroscopy is used for elemental mapping of each phase. A significant refinement in the average size of IMCs of up to 40% is identified for the as-cast samples, and the coarsening rate of these IMCs is slowed by up to 70% with no change in the interparticle spacing. Yield stress and tensile strength are determined through tensile testing at 20°C for as-cast samples and after thermal aging at 150°C for 100 h and 200 h. Both yield stress and tensile strength are increased by up to 20% by minute lanthanum doping.

Diesel Lean NOx-Trap Thermal Aging and Performance Evolution Characterization

The work described in this paper focuses on the impact of thermal aging on NOx trap structure and functions. They were evaluated on a Synthetic Gas Bench (SGB) and correlated with the analysis of the structural and chemical evolution of the catalyst. A FTIR Operando study allowed to further analyse the mechanisms occurring on the catalyst surface and highlight the most critical points. NOx trap samples were hydrothermally aged in a furnace up to 900°C under an oxidising flow. The main following impacts on the material were highlighted: reduction of the surface area, sintering of Pt yielding a decrease of the NO oxidation efficiency and hence of the NOx storage capacity, and a loss of CO and HC conversion, barium structural evolution into BaAl2 O4 also being partly responsible for the loss of NOx storage capacity. Other possibilities for loss of NSC are: the transition of -Al2 O3 to -Al2 O3 and the evolution of Ba crystalline structure which needs further analysis. Both XRD and surface IR Operando studies show that hydrothermal aging has a rather homogeneous impact on all materials: alumina phase transition and BaAl2 O4 production, which all lead to a partial decrease of all storage sites.

Thermal ageing induces drastic changes on mechanical and damage behavior of Sn3.0Ag0.5Cu alloy

For the SnAgCu alloys, previous hardness test results suggested that high temperature thermal ageing causes a quick and significant drop in the mechanical properties. However, to date, the acceleration law of thermal ageing and the relationship between thermal ageing and fatigue mechanical behavior of SnAgCu alloys are still unknown. The aim of this paper is to understand the mechanical changes during thermal ageing of Sn3.0Ag0.5Cu alloy and their impact on solder joint reliability under mechanical stresses. In a first part, influence of thermal ageing on mechanical behavior is analyzed by means of hardness tests, reversed tensile tests on dog-bone specimens and compression test on solder balls used for electronic components. In the second part, the impact of thermal ageing on the solder joint reliability is analyzed thanks to torsion tests on assembled boards. The results show systematically a decrease of 20–60% of the mechanical properties or of the number of cycles to failure (in the case of torsion test). These results lead to enlarge tests conditions in order to define the fields where the influence of thermal ageing cannot be neglected.

Impact of Thermal Aging on the Kinetic Parameters of the NO/H2 Reaction on Pd/LaCoO3

This paper deals with the kinetics of the reduction of NO by H(2) on Pd supported over reducible supports, such as LaCoO(3). An extensive kinetic investigation was performed on aged catalysts after exposure to successive reductive and oxidative atmospheres at a high temperature (T = 500 degrees C). Typically, Pd/LaCoO(3) was reduced in pure H(2) and then aged under reactive conditions in the presence of an excess of O(2). Both thermal treatments are accompanied by significant bulk and surface reconstructions characterized by X-ray diffraction and X-ray photoelectron spectroscopy. Pd/LaCoO(3) is extensively reducef to Pd(0)/CoO(x)/La(2)O(3) after H(2) exposure. It was previously found that the NO/H(2) reaction on Pd(0)/CoO(x)/La(2)O(3) involved the Pd/support interface. This study reports that subsequent thermal aging under oxidative conditions leads to the restoration of the perovskite structure with parallel changes in the chemical environment of oxidic palladium species. The NO reduction by hydrogen was used as a probe reaction to investigate related modifications of the surface properties. It was found that significant changes in the kinetic features of Pd/LaCoO(3) occur after thermal aging, compared to the prereduced catalyst, because of surface modifications that might alter the adsorptive properties of Pd and more significantly the nature of the dissociation step of NO. These surface modifications induce a selectivity enhancement to the formation of nitrogen.

Ageing by UV radiation of an elastomer modified bitumen

Laboratory methods to simulate the short- and long-term ageing occuring during the service life of pure and polymer modified bitumens in a pavement are standardized but none of them takes into account the influence of UV radiations. If the impact of thermal ageing on the degradation of SBS elastomers in bitumens has been extensively studied, there is not study dealing with the photo-oxidation of these copolymers in a bituminous matrix. So, the aim of our study was to investigate, by FTIR spectrometry and SEC chromatography, whether the architecture of elastomers (linear or radial) might have any influence on their ageing by UV radiation in a bituminous matrix. The results show that the elastomers oxidation kinetic, unlike the disappearance kinetic of trans-butadiene double bond, does not depend on their architecture. But, when putted into the same base bitumen, the two copolymers show exactly the same oxidation kinetic and the same decreasing kinetic of trans-butadiene double bond. So, this study has revealed that inside the bituminous matrix, on the one hand, the elastomers architecture does not influence on its degradation when submitted to UV radiation and, on the other hand, there is a “protection” of the elastomers by the studied bitumen towards UV radiation.

Impact of thermal ageing on sorption and diffusion properties of PTMSP

Gas and vapour permeability in both freshly cast and aged poly(1-trimethylsilyl-1-propyne) (PTMSP) membranes were investigated in terms of solubility and diffusion coefficients for two probe molecules, a permanent gas (nitrogen) and an organic vapour (dichloromethane). To get reliable data for this study, we set up a fast and reproducible ageing procedure consisting of thermal treatment of the polymer films (100 °C during 24 h under vacuum). As expected, measurements recorded from time-lag experiments and isothermal sorption showed strong variations of the PTMSP transport properties before and after the thermal ageing procedure. Freshly cast membranes exhibited high permeability, whereas after ageing a 40–45% decrease of the permeability was recorded for both probes. The results demonstrated that only the glassy physical microstructure of PTMSP was affected by the ageing procedure, while the chemical structure was unchanged. Based on a dual-mode model for sorption and a Long's model for diffusion, the analysis of the data showed that the solubility and diffusion coefficients of the gas and the vapour were not affected in the same way. For nitrogen, only the diffusion coefficient decreased, whereas for dichloromethane, the thermal treatment mainly influenced the sorption coefficient. The lower permeability due to the combination of sorption and diffusion parameters could be attributed to a change of the PTMSP hole geometry or the hole connections.

Impact of thermal ageing on the tin catalyst species in room temperature vulcanised polysiloxane rubbers

Tin 2-ethylhexanoate is used as a catalyst in the synthesis of room temperature cured polysiloxane rubbers. The catalyst has the potential to influence the important load bearing and ageing properties of the rubber. In this study, the structure of the catalyst and the nature of the tin species in both fresh and thermally aged polysiloxane samples (RTV5370) have been investigated. Infra-red and 13C NMR of the catalyst confirms the presence of 2-ethyl hexanoate ligands on the tin. Mössbauer Spectroscopy of the catalyst shows that the tin exists predominantly in the tin(II) oxidation state with some residual tin(IV) impurities. The tin(IV) phase predominates in the as-synthesised rubber, representing some 67% of the total tin signal, with the remainder being unreacted tin(II) species. The tin(IV) phase in the catalyst and that in the rubber are different. Overall, our observations suggest that the catalyst has taken part in the cure reaction and has been chemically modified as a result. The isomer shift (IS) and the quadrupole splitting (QS) from Mössbauer Spectroscopy suggests that the tin (IV) phase in the rubber is most probably SnO2 (stannic oxide). Toluene extraction studies show that this phase is not extractable from the rubber network, whereas the tin(II) species is easily removed. Both high temperature and room temperature ageing increase the proportion of the tin(IV) in the rubber.