Thermal Aging Conditions Research Articles

Formation of separating layers under conditions of the thermal aging of sorbents modified by fluorinated polyimide

Thermogravimetry, elemental analysis, low-temperature nitrogen adsorption, high-resolution electron microscopy, and gas chromatography are used to study the effect of the content of perfluorinated polyimide when used as a stationary phase for modifying Chromosorb P NAW diatomite supports and aluminum oxide, and the effect of thermal aging conditions on changes in their texture and chromatographic characteristics. It is shown that Chromosorb P NAW + 5 wt % of polyimide (PI) adsorbent thermally aged at 700°C in a flow of inert gas exhibits properties of carbon molecular sieves, while aluminum oxide impregnated with 10 wt % of PI and thermally aged at 250°C allows us to selectively separate permanent and organic gases, as well separate saturated and unsaturated hydrocarbons.

전기기기의 발열을 고려한 다단계 가속열노화 방법

Thermal aging test is performed to qualify the life time of equipment in thermally aged condition. Due to long life time more than 10 years like as in power plant, the equipment is subjected to the accelerated thermal aging condition which is able to shorten the long aging test period by increasing aging temperature. Normally, conservatism of thermal aging test causes to impose unbalanced and excessive thermal load on components of the equipment, and deformation and damage problems of the components. Additionally, temperature rise of each component through heat generation of the electric equipment leads to long-term problem of the test period.<BR> Multi-phase accelerating aging test is to perform thermal aging test in multiple aging conditions after dividing into groups with various components of equipment. The groups might be classified considering various factors such as activation energy, temperature rise, glass transition temperature and melting temperature. In this study, we verify that the multi-phase accelerating aging test method can reduce and equalize the thermal over load of the components and shorten aging test time.

Effects of photodegradation and thermal ageing on the scratch behavior of uncoated thermoplastic olefin

This study examined the effects of exposure to thermal ageing and weathering conditions on the scratch resistance of an uncoated thermoplastic polyolefin system over a period of 1800h. A flatbed scanner and scanning electron microscopy were used to observe the surface characterization and morphology for the scratch-induced damage of the aged TPO systems. The number of oxygen containing polar functional groups, amount of talc, crystallinity and discoloration on the TPO surface increase with increasing ageing time. At the same time, the number of hydrocarbon groups decreases. These findings suggest that the hydrocarbon groups locally undergo oxidation on the TPO surface due to thermal ageing and weathering. The abovementioned changes lead to an increase in scratch resistance and performance.

Ultra-High Thermal-Stable Glass Phosphor Layer for Phosphor-Converted White Light-Emitting Diodes

A glass phosphor layer with ultra-high thermal stability appropriate for phosphor-converted white light-emitting diodes (PC-WLEDs) is demonstrated. The results showed PC-WLEDs utilizing the high thermal stable glass phosphor maintained good thermal stability in lumen, chromaticity, and transmittance characteristics under the thermal aging condition up to 350 $^{\circ}{\hbox{C}}$ . This is a considerable high operating temperature for a phosphor layer in the PC-WLEDs. The lumen degradation, chromaticity shift, and transmittance loss in the glass-based PC-WLEDs under thermal aging at 150 $^{\circ}{\hbox{C}}$ , 250 $^{\circ}{\hbox{C}}$ , 350 $^{\circ}{\hbox{C}}$ , and 450 $^{\circ}{\hbox{C}}$ are also presented and compared with those of silicone-based PC-WLEDs under thermal aging at 150 $^{\circ}{\hbox{C}}$ and 250 $^{\circ}{\hbox{C}}$ . The result clearly demonstrated that the glass-based PC-WLEDs exhibited better thermal stability in lumen degradation, chromaticity shift, and transmittance loss than the silicone-based PC-WLEDs. The advantages of glass encapsulation in high-temperature operation of the PC-WLEDs could be explained that the glass transition temperature of the glass phosphor (567 $ ^{\circ}{\hbox{C}}$ ) was much higher than it of silicone (150 $ ^{\circ}{\hbox{C}}$ ). The newly developed ultra-high thermal-stable glass is essentially critical to the application of LED modules in the area where the high-power, high-temperature and absolute reliability are required for use in the next-generation solid-state lighting.

Intermetallic growth study on SnAgCu/Cu solder joint interface during thermal aging

The intermetallic compound (IMC) growth behavior at SnAgCu/Cu solder joint interface under different thermal aging conditions was investigated, in order to develop a framework for correlating IMC layer growth behavior between isothermal and thermomechanical cycling (TMC) effects. Based upon an analysis of displacements for actual flip-chip solder joint during temperature cycling, a special bimetallic loading frame with single joint-shear sample as well as TMC tests were designed and used to research the interfacial IMC growth behavior in SnAgCu/Cu solder joint, with a focus on the influence of stress–strain cycling on the growth kinetics. An equivalent model for IMC growth was derived to describe the interfacial Cu-Sn IMC growth behavior subjected to TMC aging as well as isothermal aging based on the proposed “equivalent aging time” and “effective aging time”. Isothermal aging, thermal cycling (TC) and TMC tests were conducted for parameter determination of the IMC growth model as well as the growth kinetic analysis. The SnAgCu/Cu solder joints were isothermally aged at 125, 150 and 175 °C, while the TC and TMC tests were performed within the temperature range from −40 to 125 °C. The statistical results of IMC layer thickness showed that the IMC growth for TMC was accelerated compared to that of isothermal aging based on the same “effective aging time”. The IMC growth model proposed here is fit for predicting the IMC layer thickness for SnAgCu/Cu solder joint after any isothermal aging time or thermomechanical cycles. In addition, the results of microstructure evolution observation of SnAgCu/Cu solder joint subjected to TMC revealed that the interfacial zone was the weak link of the solder joint, and the interfacial IMC growth had important influence on the thermomechanical fatigue fracture of the solder joint.

Stability of ITO Thin Film on Flexible Substrate Under Thermal Aging and Thermal Cycling Conditions

Indium-tin-oxide (ITO) is a transparent conductive thin film that is widely used as a top conducive layer in photovoltaic solar cells. However, ITO is sensitive to environmental conditions and the electrical conductivity degrades as a consequence of harsh environmental conditions. Furthermore, the thermal expansion coefficient mismatch between the ITO film and the substrate creates stress/strain on the film when the package is subjected to fluctuating temperatures. This could create micro-cracks and consequently damage the film. Therefore, this study was designed to study the effect of the thermal cycling and thermal aging on the ITO thin films to simulate the effect of continuous high temperatures and fluctuating temperatures that may be applied on the thin films during the usage. In this study, two sets of experiments were conducted on a 60Ω/□square sputter-deposited ITO on 127 μm heat stabilized Poly Ethylene Terephthalate (PET) substrate. The first set of experiments contained four samples which were thermally aged at 100°C for 30 days and the other set of experiments contained another four samples which were thermally cycled for 900 cycles. The thermal profile consisted of a high temperature of 100°C, a low temperature of 0°C, dwell time of 10 minutes, and ramp rate of 10°C/min , as depicted in Fig. 1. The initial results showed that the ITO thin film is not stable in the thermal aging experiment and the electrical resistivity gradually increased for all samples until the end of the 30 days. The degradation happened during the thermal cycling as well. However, SEM images show that the morphology of the ITO surface is stable under both conditions. Energy-dispersive X-ray (EDX) spectroscopy analysis showed stability in the ITO thin film in terms of composition. XRD spectra confirmed the improved crystallinity for the thermally aged films, which corresponded to the increased transmission in the visible region.

Mechanical Properties of Aged Cord-Rubber Composites

Cord-rubber composites are usually subjected to cyclic deformation for the tire applications. Due to the hysteretic nature of the rubber, heat generation in the rubber component under dynamic cyclic loading often causes a rise in temperature, which can deteriorate the physical properties of the composites. Therefore, better understanding of the cord-rubber composites under thermal aging conditions is of great importance for the lifetime prediction. In the present work, the effective modulus of polyester cord- and steel cord-rubber composites at different aging conditions was studied by means of the mechanics of composite materials and the Arrhenius relationship based on the properties of components. It is found that the Halpin-Tsai relation with introducing the effect of thermal aging is also valid for the aged cord-rubber composites.

Thermal stability of high temperature epoxy adhesives by thermogravimetric and adhesive strength measurements

The thermal degradation of two high temperature epoxy adhesives has been measured in terms of weight loss and adhesion loss and the lifetime predictions are compared for the two independent measurements of thermal degradation. Weight loss measurements were performed at high temperature under accelerated thermal aging conditions. Adhesion loss measurements were performed at lower temperatures closer to typical continuous operating temperatures. An Arrhenius relationship is validated for the thermal degradation of the epoxy adhesives, and the extent of degradation in terms of weight loss and adhesion loss is modelled with an autocatalytic rate expression. The degradation kinetic parameters and models are compared between the two thermal degradation measurements and are found to give similar predictions for the lifetime of the adhesives. In addition, the relationship between network degradation and loss of adhesive strength is discussed.

Effect of thermal aging conditions on the corrosion properties and hardness of a duplex stainless steel

The corrosion properties of a 22.5 wt. (%) Cr duplex stainless steel were investigated after long-term aging of 3000, 5000 and 7000 hours at 300 and 400 ºC. The corrosion resistance was measured based on mass loss in a FeCl3 10 wt. (%) solution and electrochemical measurements in a 0.1 M H2SO4 solution. The results indicate that the corrosion resistance decreased steadily up to 5000 hours of aging. However, the samples subjected to 7000 hours of aging showed better corrosion resistance than those aged for 3000 and 5000 hours. This effect is attributed to the phase transformation that occurs during aging, a finding which was confirmed by hardness, transmission electron microscopy and X-ray photoelectron spectroscopy measurements.

Analysis of aging mechanism of SBS polymer modified asphalt based on Fourier transform infrared spectrum

The aging mechanism of SBS modified asphalt during its aging process was studied. The characterizations of base asphalt, SBS polymer and its modified asphalt were determined in different aging time by Fourier transform infrared spectrum (FTIR). FTIR shows that oxidative dehydrogenation reaction occurs in asphalt, and unsaturated carbon bond is generated under short-term thermal aging condition. Additionally, SBS polymer was aged significantly under that condition, the speed of which was faster than that of base asphalt. The aging laws of both asphalt and SBS polymer during the aging process of SBS modified asphalt were similar to their aging laws respectively. Due to the protective effect between asphalt and SBS polymer, the aging degrees of asphalt and SBS polymer were lower than those aged independently.

Influence of ageing on the quasistatic fracture toughness of an SS 316(N) weld at ambient and elevated temperatures

The leak before break analysis of SS 316L(N) components of the prototype fast breeder reactor requires the elastic plastic fracture toughness parameter J for 0.2 mm crack extension, J 0.2, especially for the welds, at the operating temperatures. The J– R curves for the welds produced using the consumable developed by Indira Gandhi Centre for Atomic Research, were determined in the as-welded condition as well as after thermal ageing (923 K/4200 h) conditions at 298 K and 643 K, using unloading compliance method for 298 K and normalization method for 643 K. The aged material exhibited pop-in crack extensions of magnitudes that, according to ASTM E1820 standard, could be ignored for multi-specimen data analysis for determining J 0.2. Therefore, for this condition, J nom– Δ a curves were established using the multiple specimen method and also single specimen normalization method; for the latter, a modification earlier developed by the authors for accounting for small pop-in crack extensions was used. The value of J 0.2 from both methods showed excellent reproducibility. Ageing is seen to reduce the toughness of this material considerably at both the testing temperatures.

The Effect of Thermal Aging on Tensile Strength of Three-Dimension and Five-Direction Braided Carbon Fiber/BMI Composites

This work aims at investigating the effect of thermal aging on tensile properties of three-dimension (3D) and five-direction braided carbon fiber/BMI resin composites prepared by resin transfer molding (RTM) process. The influence of high temperature on the tensile strength and the failure mechanisms of un-aged and aged composites were studied, respectively. As for the thermal aging condition, 180 for 24h was selected. The tensile strength of both un-aged and aged specimens were tested by SHIMADZU universal material testing machine at room temperature. The fracture modes of specimens were observed by scanning electron microscopy (SEM). It was found that the tensile load at break and tensile strength decreased after ageing. From the SEM views of the failed samples, the fracture surface presented hackles which were specific to the debonding of the interface between fibers and matrix. A lot of fibers were pulled-out in the aged state specimen. It can be confirmed that the failure occurred at the fiber/matrix interface and the fiber/matrix interface seemed to be weak in aged carbon fabrics reinforced BMI composites.

Thermal aging and oxygen permeation of nylon‐6 and nylon‐6/montmorillonite composites

AbstractNylon/clay nanocomposites are expected materials for the great improvement of various properties with small percent addition of clay; however, the degradation behavior and the long term stability of nanocomposites have been insufficiently studied. During the thermal aging in air atmosphere, Nylon is ordinarily affected by oxygen gas; therefore, the oxygen permeation under thermal aging condition is an important factor for considering the thermal degradation of Nylon. Moreover, to examine the relationship between the thermal degradation and the oxygen permeation, the oxygen permeation should be measured at the temperature higher than the temperature of respective Tg. According to the oxygen permeation measurement at the temperature of 65°C, the Nylon‐6/MMT nanocomposites indicate lower permeability coefficient than that of neat Nylon‐6 and Nylon‐6/MMT composites. On the other hand, the solubility coefficients of the MMT contained Nylon‐6 were similar to each other and the solubility coefficients were significantly higher than that of the neat Nylon‐6. This characteristic is presumable to be closely related with the thermal degradation of Nylon‐6. In case of the MMT contained Nylon‐6, the permeation of oxygen gas is slower than the case of neat Nylon‐6; however, it is conceivable that the oxygen gas permeates with some interactive influences on Nylon‐6 matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

A Study of Delamination Mechanism of Thermal Barrier Coating under Thermal Cycling and Aging Condition by Residual Stress History

Thermal barrier coatings (TBCs) have been employed for the insulation of substrates from high temperature in gas turbine plants. The TBC system consists of ceramic top coating, metallic bond coating and substrate. Delamination of the ceramic coating is important problem in TBC systems. In this paper, the delamination mechanism was studied by residual stress history under thermal aging and thermal cycle conditions. In-plane residual stress histories of ceramic coating and bond coating after thermal aging and cycling were measured by X-ray diffraction method. The residual stress under thermal cycling was also calculated by FEM analysis. The results obtained were as follows: (1) in-plane surface residual stresses of the coatings scarcely changed regardless of the increase of thermally grown oxidation (TGO). (2) high compressive thermal stress, residual stress at room temperature, in ceramic coating induced by thermal stress did not occur. It was found that stress of ceramic top coating was relaxed by micro cracks and driving stress of delamination was in-plane high compressive stress.

Estimation of thermal acceleration factors of ageing epoxy insulation using thermogravimetry and intuitive kinetic model

The long term performance of epoxy resin compounds intended to be applied as electric insulating materials in nuclear equipment has been assessed using an accelerated thermal ageing technique. Conventional bisphenol-A-diglycidyl ether- and cycloaliphatic epoxy resin-based formulations (both crosslinked by anhydrides) have been compared using dynamic and isothermal thermogravimetry. Tests were performed on both virgin samples and on samples exposed to gamma-irradiation. A simple intuitive consecutive thermal decomposition model was suggested and fitted to the isothermal decomposition data. Using the fitted parameters the thermal acceleration factor was established for both kinds of materials. Under practically available thermal conditions radiation ageing had a negligible effect on the decomposition. The bisphenol-A-diglycidyl ether type material proved to be more stable under thermal ageing conditions.

Monitoring of the physical aging of radiation cross-linked conductive rubber blends containing clay nanofiller

Polymeric materials are widely used as insulation and jacketing materials in wire and cable. When such materials are used for long-term applications, they undergo thermal oxidation aging in the environment. It is necessary to develop an in situ and non-destructive condition monitoring (CM) method to follow the aging of cable materials. The main objective of this work was to investigate polymer composites as potential sensor materials for this purpose. Rubber/carbon black composites with a carbon black loading below the percolation threshold underwent accelerated thermal oxidation aging experiments. The results indicated that the substantial resistivity decreases of the composites could be directly related to the increases in volume fraction of the conductive carbon black, which was mainly caused by the mass loss of polymer matrix and sample shrinkage during the thermal oxidation aging process. Compared to existing CM method based on density change, the electrical resistivity is more explicit regarding its absolute changes throughout the thermal oxidation aging. The change in resistivity spanned over two orders of magnitude, whereas the composite density only increased 5%. The results offer strong evidence that resistivity measurements, which reflect property changes under thermal aging conditions, could represent a very useful and non-destructive CM approach as well as a more sensitive method than density CM approach.

High-Speed Cyclic Bend Tests and Board-Level Drop Tests for Evaluating the Robustness of Solder Joints in Printed Circuit Board Assemblies

This paper presents a comprehensive study of the resistance of solder joints to failure when subjected to strain rates that simulate the conditions of drop impact experienced by a portable electronic product. Two test methods are used in this study: the board-level drop-shock test (BLDST) and the board-level high-speed cyclic bend test (HSCBT). The performance of (i) 12 material combinations consisting of six solder alloys and two pad finishes, and (ii) 11 manufacturing variations covering three vendors, two finishes, three immersion gold thicknesses, and three thermal aging conditions were investigated using these two test methods. Correlations between the two test methods were performed. Quantitative correlation and sensitivity coefficients for the failure modes and the measured characteristic parameters—number of drops to failure for BLDST and number of cycles to failure for HSCBT—were evaluated. Finally, the potential of HSCBT as a test method for material selection and for bridging board-level and product-level tests was demonstrated through generation of board strain versus number of cycles to failure (S–N) curves of solder joints for six material systems, four bending frequencies, and two test temperatures.

Comparison of recovery behaviors of thermally aged SBR composite from compressed and circular deformations

Recovery behaviors of the SBR composite from the compressed and circular deformations after thermal aging were compared. Instantaneous recovery and target recovery time to describe the sealing properties of a sealant were obtained from the recovery variation with the measuring time. For the compressed deformation, the recovery decreased at the initial measurement time and then increased. Since the recovery from the compressed deformation showed a local minimum and the minimum point varied in accordance to the thermal aging conditions, the linearity of the recovery variation was very low. For the circular deformation, the recovery continuously increased as the measurement time elapsed, the linearity was very high, and the instantaneous recovery of less than 0.1 s could be obtained from the extrapolation method. The circular deformation method was found to be suitable for study of recovery behaviors of a rubber article. The recovery behaviors varied with the thermal aging conditions and the difference was explained with the crosslink density change by the thermal aging.

First Stage of Thermal Aging under Oxidizing Conditions of a Ce0.62Zr0.38O2 Mixed Oxide with an Ordered Cationic Sublattice: A Chemical, Nanostructural, and Nanoanalytical Study

After being heated in a flow of 5% O2/He, at 1073 or 1123 K for 30 min, a Ce0.62Zr0.38O2 sample showing an ordered cationic sublattice had very subtle surface nanostructural changes induced on it. In parallel with them, a significant loss of low-temperature (T ≤ 773 K) oxygen storage capacity (OSC), with no modification of its high-temperature (T ≥ 973 K) redox response, was observed. These nanostructural and chemical features characterize the very first stage of the process leading to the destruction of the ordered Ce−Zr sublattice, a structural phenomenon playing a key role in the control of redox behavior of ceria−zirconia mixed oxides. The reported results, including OSC, hydrogen chemisorption, and nanostructural and nanoanalytical data, lend further support to a model providing a comprehensive interpretation of the complex relationship linking thermal aging conditions, nanostructural properties, surface chemistry, and redox behavior in these materials.

Correlation studies for component level ball impact shear test and board level drop test

This paper presents a comprehensive study of the resistance of solder joints to failure when subjected to strain rates that simulate the conditions of drop-impact on a portable electronic product. Two test methods are used in this study: the board level drop/shock test (BLDT) and the component level ball impact shear test (BIST). The performance of (i) 12 material combinations consisting of six solder alloys and two pad finishes; and (ii) 11 manufacturing variations covering three vendors, two finishes, three immersion gold thicknesses and three thermal aged conditions, were investigated using these two test methods, and analysis of correlations between the methods was performed. Quantitative correlation and sensitivity coefficients for the failure modes and the measured characteristic parameters – number of drops to failure for BLDT and peak load, total fracture energy, and energy-to-peak load for BIST – were evaluated. The lack of universal correlations between the two test methods has ruled out the use of BIST for evaluating solder joint materials, but BIST is recommended as a test method for quality assurance in view of the strong correlation between the measured parameters and the failure mode. The total fracture energy parameter is preferred over the peak load and energy-to-peak load due to its higher sensitivity and reduced susceptibility to measurement error.