Thermal Aging Conditions Research Articles

The Attractiveness of the Ternary Rh-Pd-Pt Alloys for CO Oxidation Process

Ternary alloys of platinum group metals attract a growing interest due to their unique catalytic properties. The present research is aimed to synthesize a series of Rh-Pd-Pt alloys with varied ratios of metals using a single-source precursor approach. Rhodium and palladium are partly miscible metals, while each of these metals is unlimitedly miscible with platinum. Thermolysis of complex salts used as a precursor results in the formation of metastable systems. The 3D nanostructure alloys are being formed after the complete decomposition of the single-source precursor. High-resolution transmission electron microscopic studies have shown that the nanoalloys are composed of interconnected polycrystalline ligaments with a mean diameter of 50 nm. The single-phase composition is confirmed by an X-ray diffraction analysis. The ratio of metals plays an important role in determining the catalytic activity of alumina-supported alloys and their thermal stability. According to UV-vis spectroscopy data, the higher palladium portion corresponds to worse dispersion of initially prepared, fresh catalysts. Treatment of the catalysts under prompt thermal aging conditions (up to 800 °C) causes redispersion of palladium-rich alloyed nanoparticles, thus leading to improved catalytic activity and thermal stability.

Effect of Silver Addition on the Adsorption Properties of Y Zeolite

The present work is aim to study the adsorption/desorption properties of the Ag-modified Y zeolite towards toluene as well as its high temperature behavior under the prompt thermal aging conditions. The Ag/Y samples were obtained by an ion exchange technique and mixed with pure alumina used as a binder. The reference samples were prepared by an incipient wetness impregnation of alumina with a solution of silver nitrate and mixed with pure HY zeolite. The initial and aged samples were characterized by TEM and XRD methods. It was found that the Ag-modified Y zeolite strongly adsorbs toluene. Irreversible sorption of toluene over the most active silver sites was shown to exclude them from the participation in oxidation processes, thus diminishing the overall efficiency of the adsorption-catalytic system.

Effect of thermal ageing on atomic redistribution at the ferrite/ferrite and ferrite/cementite interfaces

The heat-affected zone (HAZ) of the low-alloy steel in dissimilar metal welds has been investigated by electron backscatter diffraction, scanning electron microscopy and atom probe tomography. The welding process generates a temperature gradient, creating two zones in the HAZ: a carbon depleted zone and a carbon non-depleted zone (NDZ). The evolution of the microstructure in the NDZ and the atomic distribution at the ferrite/ferrite and ferrite/cementite interfaces was investigated for different long-term thermal ageing conditions. Many alloying elements segregate to grain boundaries (ferrite/ferrite interfaces) with a different amount in relation to the misorientation of the grain boundaries, but only phosphorus (P) segregates to the ferrite/cementite interface. In addition, the amount of P segregation increases with the increase in temperature and ageing time and depends also on the structural parameters of the interface. The partitioning between cementite and ferrite phases presents a slight evolution with long-term thermal ageing, related to kinetic limitation.

Microstructure evolution and hardness of MWCNT-reinforced Sn-5Sb/Cu composite solder joints under different thermal aging conditions

In this work, multi-walled carbon nanotubes (MWCNTs) reinforced Sn-5Sb/Cu composite solder joints were synthesized and the effects of MWCNTs addition on the microstructure evolution and hardness of the Sn-5Sb solder alloy during various thermal aging conditions were investigated. After conducting a thorough microstructural analysis, the SbSn and Cu6Sn5 intermetallic compounds (IMCs) were observed in the β-Sn matrix of the composite solder joints subjected to reflow soldering while the latter was also present at the solder/Cu interface. However, after subjecting the composite solder joints to isothermal aging, the Cu3Sn IMC emerged between the Cu6Sn5 IMC at the solder/Cu interface and the Cu substrate. With the promising properties exhibited by MWCNTs as a reinforcement material, experimental results showed that MWCNTs refined the bulk solder microstructure and inhibited growth of the interfacial IMC layer in the Sn-5Sb-xCNT/Cu samples. In general, the composite sample reinforced with 0.05 wt% MWCNTs showed the least IMC layer thickness and diffusion coefficient in the ranges of 2.6–11.99 μm and 1.07 × 10−14-14.9 × 10−14 cm2/s respectively. Meanwhile, the strengthening mechanism triggered by MWCNTs addition was clearly evident in the MWCNT-reinforced Sn-5Sb/Cu as superior hardness values within a range of 20.6–15.3 HV were registered for the as-soldered and aged composite solder joints with 0.05 wt% MWCNTs reinforcement.

Microstructural and micromechanical assessment of aged ultra-fast sintered functionally graded iron/tungsten composites

Functionally graded (FG) iron/tungsten (Fe/W) composites are considered for stress-relieving interlayers in tungsten-steel joints, required in future fusion reactors. The macroscopic gradation of the two materials allows relaxation of thermally-induced stresses and hence extend the lifetime of the cyclic-loaded dissimilar materials joints. While many properties, e.g. thermal expansion and strength, of the as-manufactured Fe/W composites are promising with respect to the anticipated application, the temperature-induced microstructural changes and their effect on the material properties remain largely unexplored. Given that the thermodynamic system of FeW contains two types of intermetallic phases, understanding the microstructural changes in the FG Fe/W composites is crucial for long-term operation of fusion reactors.In the present work, the microstructure of ultra-fast sintered Fe/W composites containing 50 and 75 vol% tungsten is studied via electron microscopy (SEM) and X-ray diffraction (XRD) in as-manufactured and thermal aged conditions (300, 500, and 800 °C for up to 72 h). The hardness and modulus of selected composites are measured via nanoindentation, and the fracture toughness of the FeW interfaces is tested via notched micro-cantilever bending tests. The results from microstructural and micromechanical analyses are discussed, and the materials are evaluated for their application in fusion reactors based on the microstructure-to-property relationship.

Identification of the dynamic behavior of epoxy material at large strain over a wide range of temperatures

Adhesively bonded joints using epoxy resin are nowadays often replacing welding in offshore applications for safety reasons. During its lifetime, the bonded joint epoxy is submitted to severe environmental and loading conditions, such as humidity, water uptake, thermal aging, and complex loading conditions affecting its mechanical performance. We investigate here the dynamic mechanical behavior of an epoxy resin at large strain over a wide range of temperatures. Analysis of the elastic modulus, yield strain, yield stress and plastic flow as a function of the temperature and strain rate is carried out. Unlike the elastic modulus and the yield stress showing strong sensitivities to the temperature and the strain rate, the plastic flow appears to have a limited sensitivity to the temperature and the strain rate. Numerical modeling is used to determine the yield stress and elastic modulus variations over the glass transition temperature and good agreement is observed between numerical predictions and experimental results.

Interaction of Pd and Rh with ZrCeYLaO2 support during thermal aging and its effect on the CO oxidation activity

A commercial ceria–zirconia composition modified with yttrium and lanthanum oxides was studied as a support for palladium- and rhodium-containing three-way catalysts. The most attention was paid to an interaction of the supported active metals with the support under high-temperature conditions. It was found that both the metals affect noticeably the porous structure of the support and the loading of metal plays a role in this process. Moreover, oxygen storage capacity of the oxide composition was also influenced by the supported metals. Hydrothermal aging of the metal-loaded samples has decreased the oxygen storage capacity values in more than 2 times. The thermal stability of the monometallic samples was compared with bimetallic Pd–Rh catalysts prepared using a “single-source precursor” approach. The experiments were performed under prompt thermal aging conditions. It was found that monometallic Pd-only samples and bimetallic Pd–Rh samples exhibit excellent stability, while monometallic Rh-only catalysts undergo deactivation being heated up to 800 °C due to diffusion of rhodium into the bulk of the support. All the samples were additionally characterized by a diffuse reflectance UV–vis spectroscopy and a testing reaction of ethane hydrogenolysis. According to the results obtained, the character of the metal-support interaction was found to be strongly affected by the catalyst’s composition. Application of the bimetallic Pd–Rh particles of alloyed type was shown to result in the preferable location of the active components on the support’s surface, thus facilitating high activity and stability of the catalyst.

Electromigration in Bi-crystal pure Sn solder joints: Elucidating the role of grain orientation

Intermetallic compound (IMC) and void growth are electromigration (EM) damage mechanisms that are controlled by the anisotropic diffusion of Cu in β-tetragonal Sn solder joints. Single crystal fast diffusion, slow diffusion, and bicrystal solder joints were fabricated and tested under thermal aging and EM conditions to investigate the effect of grain orientation on microstructure evolution including IMC growth, void growth and grain structure. Sample and testing geometry ensured there were no effects from current crowding or joule heating so that crystallographic effects could be isolated. Microstructure characterization by scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and X-ray microtomography revealed interface-nucleated and bulk-nucleated IMC growth, particle stimulated nucleation (PSN) of recrystallized grains, and two unique voiding behaviors, void faceting and void burrowing. The relationship between these features and β-Sn grain orientation and implications for EM damage mitigation are discussed.

Nonlinear Resonant Ultrasound Spectroscopy for Predicting Sensitivity to Initiation in Granular High Explosives

AbstractNonlinear Resonant Ultrasound Spectroscopy (NRUS) is a technique that can measure bulk nonlinear coefficients of the nonlinear elastic modulus for a material. NRUS has been used to identify damage in a variety of granular materials including rocks and concrete. Some energetic materials, such as Pentaerythritol Tetranitrate (PETN), are commonly fielded as pressed granular compacts. It is well known that the sensitivity to initiation of these materials is heavily dependent on their microstructure, and that microstructure changes naturally (becomes damaged) over time. In this study, we examine the use of NRUS to identify changes in microstructure between pristine and thermally aged PETN pellets. In particular, we examine the relationship between the bulk hysteretic nonlinearity, α, of the pellets and time spent at temperature, powder specific surface area (SSA), and sensitivity to initiation. We find that, in general, α does not increase uniformly for all pellets within a single thermal aging condition. However, when the pellets are test fired to determine sensitivity to initiation, there is a strong correlation between α and firing voltage threshold. NRUS‐measured α has the added benefit that the measurements can be made in situ and on benchtop scales.

Compressive Behaviour of Laminated Neoprene Bridge Bearing Pads under Thermal Aging Condition

The present study was conducted to obtain a better understanding of the variation rule of mechanical properties of laminated neoprene bridge bearing pads under thermal aging condition using compression tests. A total of 5 specimens were processed in a high-temperature chamber. After that, the specimens were tested subjected to axial load. The parameter mainly considered time of thermal aging processing for specimens. The results of compression tests show that the specimens after thermal aging processing are more probably brittle failure than the standard specimen. Moreover, the exposure of steel plate, cracks and other failure phenomena are more serious than the standard specimen. The compressive capacity, ultimate compressive strength, compressive elastic modulus of the laminated neoprene bridge bearing pads decreased dramatically with the increasing in the aging time of thermal aging processing. The attenuation trends of ultimate compressive strength, compressive elastic modulus of laminated neoprene bridge bearing pads under thermal aging condition accord with power function. The attenuation models are acquired by regressing data of experiment with the least square method. The attenuation models conform to reality well which shows that this model is applicable and has vast prospect in assessing the performance of laminated neoprene bridge bearing pads under thermal aging condition.

Cross-linking density and aging constitutive model of HTPB coating under prestrain thermal accelerated aging

In order to study the cross-linking density and aging constitutive relationship of HTPB coating during storage, the thermal accelerated aging tests at 0%, 3%, 6% and 9% prestrains were carried out. The cross-linking density of HTPB coating at different aging stages were tested using low-field 1H NMR and the variation of cross-linking density was analyzed. The aging model of cross-linking density considering the chemical aging and the physical stretching factors was established. The uniaxial tensile tests were carried out on HTPB coating at different aging stages and the cross-linking density was introduced into Ogden hyperelastic constitutive model as a characterization parameter of correction coefficient. Combined with uniaxial tensile test results, a prestrain aging constitutive model of HTPB coating was established. The results show that the cross-linking density of HTPB coating increases rapidly at first and then slowly with the increase of thermal accelerated aging time without prestrain. Under prestrain conditions, the cross-linking density of HTPB coating decreases at the early stage, and increases rapidly at first and then slowly at the middle and late stages of thermal accelerated aging. The correlation coefficients of aging model of cross-linking density and aging constitutive model with test results are R > 0.9500 and R > 0.9900 respectively, which can be used to accurately describe the cross-linking density and aging constitutive relationship of HTPB coating under prestrain accelerated thermal aging conditions.

Highly Effective GeNi Alloy Contact Diffusion Barrier for BiSbTe Long-Term Thermal Exposure.

A GeNi alloy diffusion barrier for contacts on bismuth antimony telluride is proposed. Multiple gold contact diffusion barriers were tested at different thermal aging conditions in air and reducing atmospheres. Among all diffusion barriers, the GeNi alloy barrier shows the best performance for bulk samples with no substantial degradation of the contact resistance, no contact color change, and no change of thermoelectric properties. We observed DAu–GeNi = (9.8 ± 2.7) × 10–20 m2/s within the GeNi alloy barrier, which is 4 times smaller than DAu–BiSbTe. The presence of the initial Ge layer also proves to be effective in reducing nickel diffusion yielding DNi–BiSbTe = (8.57 ± 0.49) × 10–19 m2/s. During GeNi alloy formation, Ge diffusion into BiSbTe produces GeTe, which apparently blocks the van der Waals gaps eliminating Au and Ni fast diffusion pathways. Thermal aging of BiSbTe nanowires shows that Au and Ni diffusion degrades the thermoelectric power factor, whereas the GeNi alloy barrier sample is mostly preserved. The GeNi alloy barrier is a reliable solution to long-term thermal applications of BiTe-based materials.

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.

Synthesis of bimetallic AuPt/CeO2 catalysts and their comparative study in CO oxidation under different reaction conditions

In the present work, ceria-supported Au–Pt catalyst with metal ratio 3:2 was prepared using a “single-source precursor” concept. The double complex salt [AuEn2]2[Pt(NO2)4]3·6H2O was used as such precursor. CeO2 of unique morphology with developed surface area (120 m2/g) obtained by urea precipitation technique was used as a support. According to XRD data, size of the alloyed Au–Pt particles was estimated to be less than 3 nm. It was shown that bimetallic Au–Pt system intensifies release of oxygen from the CeO2 lattice. The 0.5%Au2Pt3/CeO2 catalyst was comparatively studied in low temperature CO oxidation (simplified model reaction mixture) and under prompt thermal aging conditions (complex reaction mixture) with regard to monometallic reference samples 0.2%Au/CeO2 and 0.3%Pt/CeO2. The catalytic performance of the samples was found to be significantly dependent on the reaction and pre-treatment conditions. In the case of the bimetallic catalyst, reversible redistribution and enrichment of the nanoparticle surface with Pt or Au were shown to be the key factor defining the activity.

Impact Toughness, Fatigue Crack Growth and Corrosion Behavior of Thermally Aged UNS S32205 Duplex Stainless Steel

The aim of the present work was to study the impact, fatigue crack growth and corrosion behavior of 2205 duplex stainless steel (DSS) when subjected to one of the most influential thermal aging condition that promotes deleterious secondary precipitation. Formation of Cr- and Mo-rich σ-phase was confirmed by EDX analysis which deteriorated impact toughness causing the material to fail following quasi-cleavage mode of fracture. Susceptibility of DSS 2205 to pitting corrosion assessed though Potentiodynamic polarization technique was enhanced by thermal aging, but sensitization performance evaluated via double-loop electrochemical potentiokinetic reactivation (DLEPR) technique did not show much degradation. However, fatigue crack growth behavior testing divulged drastic enhancement in impediment to crack propagation by the matrix after thermal aging.

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.

Prospect of Using Nanoalloys of Partly Miscible Rhodium and Palladium in Three-Way Catalysis

Alloys of partly miscible metals attract a growing attention due to their unique physicochemical properties. Palladium–rhodium solid solution was synthesized using a multi-metal single precursor concept. Pd–Rh/γ-Al2O3 catalyst was prepared by an impregnation of the support with a solution of a precursor containing organic ligand. The Pd:Rh ratio in the alloy was 3:2. The samples were characterized by a powder X-ray diffraction analysis, a transmission electron microscopy, electron paramagnetic resonance and photoluminescence spectroscopies. The catalytic behavior of the samples was examined in CO oxidation reaction under prompt thermal aging conditions. The stability of the bimetallic catalyst was found to be improved if compare with monometallic reference samples. Mutual anchoring of palladium and rhodium prevents both the surface migration of Pd particles followed by their agglomeration and the diffusion of rhodium ions into the bulk of alumina support. Improved metal-support interaction for the studied system was found to be facilitated by presence of electron donor sites on the surface of the support.

Optical spectroscopy of Rh3+ ions in the lanthanum-aluminum oxide systems

A series of the Rh-containing samples supported on pure γ-Al2O3, La-doped γ-Al2O3, LaAl11O18 and LaAlO3 was prepared and characterized. Diffusion of Rh3+ ions from the surface of the support into its bulk causing the rapid deactivation of the catalyst in a model reaction of CO oxidation under the prompt thermal aging conditions was shown to be accelerated by a presence of lanthanum. The amount of rhodium disappeared from the surface during the high temperature treatment was estimated by a testing reaction of ethane hydrogenolysis and an electron paramagnetic resonance spectroscopy with spin probe. In order to characterize rhodium ions diffused into the bulk of the support at different calcination temperatures, the optical spectroscopic methods (diffuse reflectance UV–vis and photoluminescence spectroscopies) were applied. Rh3+ ions were shown to be applicable as a luminescence probe to follow the process of their bulk diffusion and localization within the matrix of the support, as well as for the structure identification of the La-containing sites responsible for the alumina thermal stabilization. The obtained data on luminescence of Rh3+ ions indicate that already at 800 °C the oxygen octahedrons corresponding to LaAl11O18 structure are being formed in the local coordination surroundings of isolated La ion in the 4%La2O3-Al2O3 support. It is important to notice that the structures of such kind can be formed in La-doped aluminas only. There are no octahedron positions with sufficient values of the crystal field for the formation of luminescence centers of Rh3+ ions in pure γ-Al2O3.

Influence of Initial Shear Strength on Time-to-Failure of Copper (Cu) Wire Bonds in Thermal Aging Condition

Abstract Copper (Cu) wire bond is used in a majority of microelectronic devices but has not been fully accepted by all industries due to potential reliability issues. Good quality bond is believed to provide high reliability. Shear strength and intermetallic (IMC) coverage are being used as indicators, however there is no developed model. High shear strength is a result of large IMC coverage laterally under the ball, but the reliability of the bond is also related to IMC longitudinal growth (thickness). This work involves studying effect of shear strength on reliability of a variety of experimental Cu ball bonds by performing temperature aging experiments on test devices, in QFN packages. The ball bonds are made by altering ultrasonic power and time to obtain different IMC coverage. All test packages are monitored for resistance change at specific intervals by performing four point resistance measurement. Resistance increase is analyzed with initial shear strength to determine whether “good quality” bonds always lead to high reliability.

Microstructural and tensile properties of Fe and Bi added Sn-1Ag-0.5Cu solder alloy under high temperature environment

In this work, the iron (Fe) and bismuth (Bi) added (0.05 wt% Fe and 1 wt% or 2 wt% Bi) Sn-1Ag-0.5Cu (SAC105) lead-free solder alloys were prepared and their microstructure and tensile properties under severe thermal environments were extensively investigated and compared with the base alloy SAC105. The isothermal aging was done at 200 °C for 100 h, 200 h, and 300 h. Fe/Bi added SAC105 showed a significant reduction in the IMCs size (Ag3Sn and Cu6Sn5), especially the Cu6Sn5 IMCs and a refinement in the microstructure, which is due to the existence of Bi in the alloys. Moreover, the existence of Fe and Bi gives the microstructure better stability under severe thermal aging conditions. The tensile testing results showed that the addition of Fe and Bi to SAC105 greatly improves yield stress and tensile strength, but decreases ductility level, which is because of the Bi solid solution strengthening mechanism. Under severe thermal aging, the Fe/Bi added SAC105 showed more stable tensile properties, because of the existence of both Fe and Bi in the alloys.