Influence Of Thermal Aging Research Articles

Influence of thermal aging on decomposition behavior and kinetic mechanism of commercial proton exchange membranes

The aim of this work is to examine the pyrolysis and thermal properties of new and aged membranes. The results showed that the physical/chemical properties of membranes were changed after thermal aging. The onset decomposition temperature of the aged membrane was higher than that of the new one, whereas the maximum mass loss rate was reversed. The predicted thermogravimetric data by the ANN model, coincided well with the experimental data for both new and aged membranes. The average activation energy of the new membrane estimated by isoconversional methods was relatively higher than that of the aged one. A two-stage reaction modeling was employed to describe the degradation of new and aged membranes. The reaction mechanism of each stage was determined by the generalized master-plots method. The significant difference in reaction model between new and aged membranes was observed. Besides, the aged membrane released pyrolysis products later and less but faster than the new one. The burning results indicated that the aged membrane exhibited lower flammability and less heat release compared with the new one. The variation of pyrolysis and thermal behaviors between new and aged membranes was due to the changes of chemical component, molecular structure, and composition proportion.

Influence of Thermal Aging on Space Charge Accumulation and Dissipation of Cross-Linked Polyethylene With Different Cross-Linking Agent Contents

This article presents the influence of thermal aging on space charge accumulation and dissipation of cross-linked polyethylene (XLPE) with different cross-linking agent contents. In this article, dicumyl peroxide (DCP) and low-density polyethylene (LDPE) respectively are used as cross-linking agent and basic experimental material. Additionally, an improved PEA method is used to measure space charge densities during voltage application and removal when thermal aging time respectively is 0, 5, 15, 30 and 80 days due to higher accuracy. And experimental results indicate thermal aging can introduce negative charge traps into pure LDPE and make space charges easier to inject and accumulate in pure LDPE and XLPE, but space charge densities in XLPE increase more rapidly as thermal aging time increases, moreover, thermal aging can simultaneously increase densities of deep and shallow charge traps in pure LDPE and XLPE, etc. And we have also explained the change of space charge accumulation and dissipation of pure LDPE and XLPE after thermal aging from the perspective of micro-structure change of pure LDPE and XLPE through the quantitative analysis of average charge densities. Besides, theoretical model of the average charge decay has also been summed up, and this model can perfectly reflect the dissipation of space charges in pure LDPE and XLPE of different thermal aging time.

Thermal Aging of Menzolit BMC 3100

This paper deals with the influence of thermal aging on physical properties of a composite material, Menzolit BMC 3100. First, we present a number of analysis, FTIR (infrared spectroscopy), DSC (differential scanning calorimetry), TMA (thermomechanical analysis), TGA (thermogravimetric analysis), and HDT (heat deflection temperature), to understand the material performance under heat, and then, we carry out a test of toughness and strength using Charpy impact strength and Brinell hardness. Finally, we present optical surface analysis of the material under investigation by carrying out aging analysis at increments from room temperature up to 300°C. It was observed that above 200°C, the material begins to degrade at the surface, especially its organic component, polyester resin. This type of degradation has a negative impact on a variety of its physical properties. Exposure to temperatures above 200°C reduces the material’s hardness, toughness, and shape stability, likewise, material degradation was found to increase with higher thermal loads almost linearly for all the observed properties.

Investigation on thermal stability and flame spread behavior of new and aged fine electrical wires

Thermal properties and fire propagation performance were studied for the new and aged electrical wires. Two fine electrical wires were tested using the DSC–TG and a flame spread apparatus. The main objective is to understand the thermal aging effect because the aging of electrical wire is inevitable in real service conditions. The significant discoloration occurs for PC sample during the thermal aging, while slightly changes for PN sample. The microstructure of all samples surface presents relatively smooth. The diffusion of metal from inner core to polymer insulation was discovered by the XPS. The change of these parameters including melting temperature, heat of melting, onset temperature of decomposition, mass loss, etc., is observable and complicated. The metal core also has the effect on properties of polymer insulation during the thermal aging. The difference of thermal properties between new and aged electrical wires shows that the chemical composition and structure of polymer insulation change due to thermal degradation and metal catalysis. Finally, the influence of thermal aging on the flame spread rate was also discussed. This study indicates that thermal aging coupled with the metal catalysis can promote the degradation and change the thermal or fire spread properties of polymer materials.

Influence of thermal aging on mechanical properties of fiber metal laminates hybridized with nanoclay

One of the main problems of polymer matrix composites in critical applications is their high sensitivity to thermal conditions. Therefore, an experimental study was performed to evaluate the thermal durability of traditional plain weave E-glass/epoxy as well as fiber metal laminates as a possible alternative in this case. In this way, both the laminate types were exposed to thermal aging at 130 ℃ for five weeks, and the plausible degradation is investigated through weight loss analyzes and mechanical testing. The possibility of improving the mechanical behavior of the studied laminates by nanoclay was also studied. The results demonstrated that the weight loss and mechanical degradation were more pronounced in thermally aged plain weave E-glass/epoxy composites. The results also indicated that nanoclay could enhance the mechanical properties of both laminates. On the basis of the results, the shielding role of aluminum layers and thermal resistance of nanoclay can synergistically offer a novel class of nano-fiber metal laminates with high thermal tolerance in thermo-oxidative conditions.

Influence of Thermal Aging in Oil on the Friction and Wear Properties of Nitrile Butadiene Rubber

An experimental study on the influence of thermal aging on the friction and wear properties of a nitrile butadiene rubber (NBR)–steel pair was carried out. Rubber specimens were aged in hydraulic oil at 60 °C and 90 °C for 0–70 days. The Shore hardness, Young’s modulus, rebound resilience, and other mechanical properties were measured. The friction coefficient and wear volume were tested to evaluate the tribology performance. To investigate the mechanism of NBR thermal aging, the molecular structure and crosslinking degree were analyzed. Crosslinking with rubber aging in oil led to differences in the physical and mechanical properties. The Shore A hardness decreased initially and then increased. The Young’s modulus increased and the rebound resilience decreased. The friction coefficient increased but the wear volume decreased with aging time. These differences affected the friction and wear behavior of the NBR against the steel shafts and resulted in sealing-ring degradation and failure.

Effect of Thermal Aging on Local Structure and Three-Way Catalysis of Cu/Al2O3

Cu supported on Al2O3, prepared by impregnation, was thermally aged at different temperatures, and the influence of thermal aging on the local structure, redox behavior of Cu, and catalytic activity for a stoichiometric NO–CO–C3H6–O2 reaction was investigated. Crystalline CuO was mainly formed on Al2O3 after thermal aging at ≤700 °C, whereas aging at higher temperatures induced Cu2+ incorporation into tetrahedral (Td-Cu2+) rather than octahedral (Oh-Cu2+) sites of γ-Al2O3. Despite its lower surface area, thermally aged Cu/Al2O3 with Td-Cu2+ sites showed higher catalytic performance for the stoichiometric NO–CO–C3H6–O2 reaction compared with the as-prepared catalyst, especially for NO reduction. Td-Cu2+ was reduced to Td-Cu+ during reaction with CO and/or C3H6, and NO could be reduced in subsequent reoxidation of Td-Cu+ to Td-Cu2+ by NO. This redox behavior is more probable on Td-Cu rather than crystalline CuO, resulting in enhancement of NO reduction during the three-way catalyst reaction.

Interfacial microstructure evolution of gold alloy/Sn-based solder under different thermal aging conditions

Sn-based solder is used for soldering a gold alloy and a brass sheet. Subsequently thermal aging tests are performed. The influence of thermal aging on the interfacial microstructure evolution of gold alloy/Sn-based solder and its mechanical properties was analysed. The results show that the aging time and aging temperature have large influence on the growth of interfacial compounds, and the interfacial compounds show a multiply-sublayers structure, the main components are AuNi2Sn4, AuSn4, Ni3Sn4 and Ni3Sn. The hardness of the interfacial compounds show a distinct layered phenomenon, in which the hardness of the first layer is the highest. Shear tests indicated that the failure happened at the gold alloy/Sn-based solder interface close to the gold alloy, showing obvious brittle fracture features. Shear strength decreases with increasing aging time at the aging temperature of 150°C and 175°C.

New developments in fracture of rubbers: Predictive tools and influence of thermal aging

In this work, the influence of thermal oxidative aging on the ultimate mechanical properties of rubbers is investigated. Two new approaches to predict failure properties are proposed. The first one is the stress limiter approach that uses a “damage” parameter allowing determination of the failure stress and strain of an aged material knowing both the mechanical properties and macromolecular network characteristics of an as-received material. The second one is an extension of the energy limiter approach that suggests capturing the drop of the stress at failure by replacing the strain energy density function of an as-received elastomeric material by a function expressed in terms of an energy limiter. The predictive capabilities of these two approaches are validated using experimental results for two elastomeric materials: an EPDM and a polychloroprene (CR), both of which exhibit a largely predominant post-crosslinking (over chain scissions) during aging. Comparison between the predictions and the experimental results in terms of failure stresses and strains under uniaxial tension showed a good agreement. Consequently, these two approaches are promising tools for designing elastomeric parts subjected to thermal oxidative aging.

Study on Electrical Aging Characteristics of Fiber Sheath Materials in Power Transformer Oil

Optical fiber has great potential in the development of online monitoring for trans-formers. In this paper, the electrical aging test of fiber sheath material based on a gradual voltage-rising method was performed and the influence of thermal aging on electrical aging was determined. Compared to the oil-paper insulation performance of traditional transformers, it was found that ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE) and Polyamide 12 (PA 12) were better than oil-paper. Statistical analysis of the ETFE material and oil-paper test data was conducted using double-parameter Weibull distribution. The inverse power and exponential functions were used to fit the experimental data and voltage tolerance coefficients of the ETFE material were obtained. Experimental results show the parameters of the ETFE model in the inverse power function and exponential function model are better than those of the oil paper insulation, and the sheathed fiber is ETFE that can be stably operated in the transformer.

Influence of Thermal Aging on Microstructure and Property of Gold Alloy Joint Soldered by Sn-based Solder

As an undisputed material of choice to guarantee reliability in a broad range of high performance and safety-critical applications in the electrical contacts and connectors, AuAgCu alloy was soldered with Ag-plated Cu wire using Sn-based solder. To clarify the embrittlement and strength reduction of the gold soldered joint, the microstructure and its influence on the macroand micro-mechanical properties of the soldered joint under various thermal aging conditions were studied. The result indicated that, taking the mechanical property consideration alone, Sn-based solder could be used to join AuAgCu alloy. Different from the embrittlement and strength reduction of the soldered joint of pure gold, although the brittle fracture features appeared in mechanical test of the soldered joints, the shear strength of soldered joint after thermal aging at 125 °C almost did not decrease in comparison with that before thermal aging. Nevertheless, too high temperature and long time still had bad influence on mechanical properties. Otherwise, thermal aging had a large effect on the IMCs layer, as aging temperature elevated and aging time increased, IMCs layer became thicker, more complex components and multiply-sublayers structure with different microhardness. The study provides a fundamental understanding for gold alloy soldering.

Influence of Thermal Aging on Tensile and Low Cycle Fatigue Behavior of Type 316LN Austenitic Stainless Steel Weld Joint

Influence of short-term thermal aging on the low-cycle fatigue (LCF) behavior of 316LN austenitic stainless steel weld joint with 0.07 wt pct N has been investigated. Prior thermal exposure was found to improve the fatigue life compared with the as-welded condition. Besides, the treatment also imparted a softening effect on the weld metal, leading to an increase in the ductility of the weld joint which had a bearing on the cyclic stress response. The degree of cyclic hardening was seen to increase after aging. Automated ball-indentation (ABI) technique was employed toward understanding the mechanical properties of individual zones across the weld joint. It was observed that the base metal takes most of the applied cyclic strain during LCF deformation in the as-welded condition. In the aged condition, however, the weld also participates in the cyclic deformation. The beneficial effect of thermal aging on cyclic life is attributed to a reduction in the severity of the metallurgical notch leading to a restoration of ductility of the weld region. The transformation of δ-ferrite to σ-phase during the aging treatment was found to influence the location of crack initiation. Fatigue cracks were found to initiate in the base metal region of the joint in most of the testing conditions. However, embrittlement in the weld metal caused a shift in the point of crack initiation with increasing strain amplitude under LCF.

Impact of UV-absorber and photo-sensitizer on the irradiated waste polyethylene hoses

Composite films of waste polyethylene (WPE) hoses containing carbon black (CB) as UV-stabilizer, and benzophenone (BP) as UV-absorber and photo-sensitizer were prepared. The effect of both CB and BP on the WPE hoses has been studied under the influence of thermal aging. Prepared composites before and after aging were subjected to gamma radiation at 50 kGy and characterized by determining the carbonyl index derived from FTIR, mechanical parameters, DSC, TGA, and SEM. Remarked improvement in the mechanical and thermal parameters were generally determined by the incorporation of CB and BP. Furthermore, melting temperature of composites after aging did not change with CB/BP loaded and reduces the effectiveness of the biodegradability of the films. The mechanism suggested that biodegradation rates were reduced with incorporation of both CB/BP and the composites become more resists to photo-degradation.

Effect of thermal aging on microstructure, hardness, tensile and impact properties of Alloy 617

Influence of thermal aging on microstructural evolution and its effect on hardness, tensile and impact properties have been studied for Alloy 617. Aging was carried out at 1023K up to 20,000h duration on a solution annealed as-received alloy. Detailed microscopic investigation of the alloy revealed the precipitation of γ´ phase (rich in Al and Ti) along with M23C6 carbides during aging treatments. Thermal aging has imparted increased hardness and strength, however with decreased ductility and toughness. Yield stress (YS), though initially increases up to 5000h of aging, and has shown a decreasing trend from 5000 to 10,000h. Further aging up to 20,000h has shown an anomalous increase in YS. Charpy impact test for 20,000h aged sample showed a reduction in fracture energy (~ 85%) w.r.to as-received material along with a shift in fracture mode from transgranular ductile to intergranular brittle. The change in hardness and YS in aged Alloy 617 has been attributed to the aging-induced evolution of γ´ precipitates. The intergranular fracture associated with lower impact energy, as observed after prolonged aging duration, has been attributed to the grain boundary embrittlement originating from precipitation of M23C6 carbides at the grain boundaries.

The influence of thermal aging on absorption phenomena in cross-linked polyethylene cable insulation

Absorption-controlled charge and discharge currents in cross-linked polyethylene (XPE) cable insulation before and after thermal aging have been measured. The experimental dependences were analyzed in terms of the equivalent Voigt scheme. Known parameters of the Voigt scheme were used to calculate the frequency dependences of relative dielectric permittivity, loss factor, and loss tangent of XPE films in the region of low frequencies (ω = 10–3–1 s–1) at high temperatures. Results of analysis of the absorption characteristics of XPE were applied to modeling of the process of thermal aging of cable insulation.

Influence of thermal aging on the breakdown characteristics of transformer oil impregnated paper

For a long time, thermal effect, as a major factor for insulation aging, is a great challenge to the safe operation of power transformers. During the decades-long operation, cellulose fibers contained in the oil-paper insulation, break and deform, accompanied by the generation of new chemical products and variation of mechanical/electrical properties. Therefore, in this work, the influence of thermal aging on the electrical performance of the transformer oil paper insulation was investigated. 50% breakdown voltage and average AC breakdown voltage of oil impregnated paper were experimentally determined, and the water content measurement, surface morphology observation and frequency domain spectroscopy measurement were carried out on the oil impregnated paper samples with different aging degrees. The test results indicate that the electrical performances of aged oil impregnated paper improved during the aging process, which could be attributed to the forming of micro globules caused by the effect of thermal aging.

열시효가 Mod.9Cr-1Mo강의 재료강도 및 파괴 거동에 미치는 영향

발전소 내열강의 물성치는 고온 가동시간이 누적됨에 따라 열시효의 영향을 받는다. 본 연구에서는 제 4 세대 원자력시스템의 재료로 널리 채택되고 있는 Mod.9Cr-1Mo (ASME Grade 91)강을 대상으로 항복강도, 인장강도 및 파괴거동에 열시효가 미치는 영향에 대해 조사 및 분석하였다. 국내에서 가동 중인 초초임계(USC) 화력발전소의 배관계통에서 채취한, 73,716 시간의 가동 이력을 겪은 Gr.91 강 재료가 재료 실험을 위해 사용되었고, 동 시험결과와 가동 이력을 겪지 않은 신재의 시험결과를 비교 분석하였다. 또한 ASME 코드의 물성치와 RCC-MRx 의 물성치와 비교 분석하였고, 이들 설계기술기준 물성치의 보수성은 신재 및 가동 이력을 겪은 재료의 시험결과와 비교 분석을 통해 정량화하였다.

Preliminary thermal annealing tests of OLED glass samples

Purpose – The purpose of this paper was to determine the influence of thermal aging on the stability of organic light-emitting diode (OLED) glass samples made in ambient condition. Design/methodology/approach – The samples with yellow emitting layer (named as ADS5) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) hole transport layer were examined. Some of the devices were ultraviolet-curable epoxy encapsulation directly after performance. All samples were thermally annealed at 70°C for 1, 2, 3 and 4 hours. The characteristics current–voltage for fresh and aging samples in the range of voltage from 0-15 V were made. The temperature of OLEDs samples in real-time with a thermographic camera was measured too. Additionally, scanning electron microscope image of surface Al cathode immediately after OLED performance and after annealing tests was made. Findings – The authors stated, that irrespective of the type, the samples were undergoing the degradation. The decrease in value of the current density was registered. That were about 44 per cent and about 24 per cent after thermally annealing the samples with and without encapsulation, respectively (at tension 13 V). Additionally, there were observed massive delamination of the metal cathode. Originality/value – Influence of thermal annealing and encapsulation on the dynamic characteristics of the OLED devices fabricated in ambient condition was analyzed. There are not many papers in the literature describing examinations of OLED samples which were made in environmental conditions.

Influence of thermal aging on the SCC susceptibility of wrought 316LN stainless steel in a high temperature water environment

Influence of thermal aging at non-sensitized temperature on the SCC susceptibility of wrought 316LN at high temperature water was investigated. The SCC susceptibility increases with increasing of aging time, especially over 1000h. The fracture surface for aged samples shows a mixed mode. In particular, the intergranular attack (IGA) has been found in brittle surface of the long-term aged material (5000h). Kinks and dislocations at the grain boundary (GB) have been found as well as aging-induced hardening. Carbon enrichment on the GB is believed to be an important cause of IGA and higher SCC susceptibility in aged materials.

Aging behavior of cellulosic materials in presence of mineral oil and ester liquids under various conditions

This paper is aimed at the study of aging behavior of cellulosic materials in different dielectric liquids under air and nitrogen atmospheres. Paper for copper conductor and high density transformer board were aged at 130°C up to 1128 h in sealed vessels in presence of mineral oil (MO), natural ester (VO) and synthetic ester (SE). The influence of thermal aging on cellulose and oil characteristics are investigated and compared. It's observed that the paper degradation is associated with the generation of CO2 and CO gases. Whatever the type of oil, this generation is more important with vessel under air atmosphere than that under nitrogen gap indicating a protective effect of nitrogen. In mineral oil, the degree of polymerization (DPv) reaches the end of life criteria at around 200 whereas it remains around 400 with ester oils. This is mainly due to the higher water solubility of esters compared to mineral oil. The measured degree of polymerization in MO is comparable to that calculated through 2-FAL (Furanic compounds) content using Vuarchex equation whereas for esters oil, there is no agreement between the measured and calculated DPv through 2-FAL content. This can constitute a limitation in the use of 2-FAL for the diagnosis of ester-filled transformers. Overall, the insulation cellulose/oil behavior seems better under nitrogen atmosphere.