Thermal Aging Treatment Research Articles

Electrical breakdown mechanism and life prediction of thermal-aged epoxy/glass fibre composites

Epoxy/glass fibre composites possess excellent mechanical and electrical properties and are widely utilised in electrical and electronic power equipment. However, the composites exhibit relatively poor thermal conductivity, causing the temperature of the composites to increase during the operation of power equipment, resulting in a significant reduction in the electrical breakdown strength. Although the effects of thermal aging on polymeric materials have been widely studied, its influence on electrical strength mechanisms has not been investigated at the molecular level. In this study, epoxy/glass fibre composite specimens were subjected to accelerated thermal aging treatment for 360 h at 180 °C. Functional groups, molecular chain dynamics, and electrical breakdown are characterised using infrared spectroscopy, dielectric spectroscopy, and breakdown measurement. Subsequently, electrical breakdown mechanism and life prediction of the thermally aged composites are discussed. During thermal aging, the epoxy resin molecular chains undergo continuous oxidation and chain scission, which generate numerous polar functional groups and short chains and an increase in the free volume. This triggers an enhancement in the chain segmental dynamics, thereby significantly reducing the activation energy of the epoxy resin. After 360 h, activation energy decreased from 0.78 eV to 0.67 eV. The DC breakdown voltages of the specimens decreased from 168.28 kV/mm to 134.91 kV/mm. An insulation life prediction model for thermally aged epoxy/glass fibre composites is established based on the time-temperature equivalence theory. The prediction results indicate that the service life of the operational composites is approximately 11.2 years at 353 K, which is consistent with engineering experience.

Deep Cryogenic and Thermal Aging Treatments of Ti–5Al–5Mo–5V–3Cr Alloy Additively Manufactured by Powder Bed Fusion–Laser Beam

The properties of 3D‐printed components via powder bed fusion–laser beam (PBF–LB) depend strongly on the processing parameters, particularly due to the rapid solidification conditions involved. In this study, an innovative post‐treatment strategy combining deep cryogenic treatment (DCT) and thermal aging treatments are introduced to enhance the properties of Ti–5Al–5V–5Mo–3Cr alloy (Ti‐5553) alloy fabricated by PBF–LB. In the results, it is revealed that DCT of as‐built material can refine the grain size and introduce defects and sub‐grain boundaries, thereby improving strength and ductility without significantly altering the microstructure or phase composition. However, applying DCT after aging can significantly improve ductility and maintain strength, primarily by refining β‐phase grains. Conversely, thermal aging followed by DCT of as‐built materials tends to increase strength at the expense of ductility, due to the formation of the ω phase and defects induced by the cryogenic treatment that in turn promote the development of more abundant and finer α phase within grains during aging. In the findings of this research, significant insights and valuable methodologies are offered for optimizing the mechanical properties of Ti‐5553 alloy manufactured by PBF–LB via an extra DCT following thermal aging.

Molecular dynamics study on the influence of thermal aging on the mechanical properties of epoxy resins for high voltage bushing.

Thermal aging significantly deteriorates the mechanical properties and service performance of epoxy resins used for the high-voltage bushing. Current studies on the thermal aging behavior of epoxy resins mainly focus on experimental observations. However, an in-depth understanding of the mechanism of thermal aging of epoxy resins requires the monitoring of structural evolution of epoxy resins during thermal aging at the molecular level. To thoroughly analyze the intrinsic factors affecting structural evolution and the effect of thermal aging on the mechanical properties of epoxy resin for high-voltage bushing, epoxy resin models with different crosslinking degrees were established and thermal aging treatments at various temperatures and time periods were carried out by molecular dynamics simulation. It was found that the tensile strength of the epoxy resin was enhanced with the increase of the crosslinking degree, which was related to the elevation of the proportion of C-N and O-H bonds in its structure. With the increase of thermal aging temperature, the tensile strength of the epoxy resin decreased, which was related to the formation of weak bonds. At the early stage of thermal aging and after a period of high-temperature thermal aging, the strength of epoxy resin significantly decreases. The thermal aging of the epoxy resin is accelerated under external loading. In addition, the crosslinking degree and curing agent also affect the thermal aging resistance of epoxy resins. The results of this study can provide guidance for predicting and improving the thermal aging resistance of epoxy resins. Materials Studio was used to construct molecular models and complete crosslinking reactions. DGEBA and 44DDS (or 33DDS) were mixed at a ratio of 2:1, followed by crosslinking reaction. During this process, the Nose method was used to control temperature, the Berendsen method was used to control pressure, and the polymer consistent force field (PCFF) was used to control the motion and force of atoms. Isobaric-isothermal ensemble (NPT ensemble) was used to heat up epoxy resin models to various thermal aging temperatures of 400K, 500K, 600K and 700K. The models were maintained at these temperatures for different thermal aging times of 100ps, 200ps, 300ps, 400ps, 500ps, 600ps, 700ps and 800ps. Afterwards, the models were cooled down to 300K and subjected to uniaxial tensile testing at this temperature with a strain rate of 1 × 109s-1. The structural configurations and stress-strain data during the tensile process were recorded. The flow stress of the material was derived by counting the average stress in the 20-50% strain interval.

Secondary phases characterization by SANS and XAS of an ODS ferritic steel after thermal aging at 873 K

An ODS steel with nominal composition Fe–14Cr–2W–0.4Ti-0.3Y2O3 (wt.%) was produced by mechanical alloying and compacted by hot isostatic pressing (HIP) followed by hot cross rolling (HCR). To check the effects of thermal aging at relevant temperatures of operation in fusion power plants, the alloy was thermally aged at 873 K for 2000 h. In this work, small-angle neutron scattering (SANS) and X-ray absorption spectroscopy (XAS) techniques are used for the advanced characterization of secondary phases and the oxide nanoparticle dispersion. SANS results show that the oxide nanoparticles remain stable after the thermal aging treatment. Composition of the oxide nanoparticles was identified as Y2TiO5 or Y2Ti2O7 by SANS, while non-stoichiometry was found by XAS analysis. Laves phase precipitation after the thermal aging treatment is further confirmed by SANS, from the magnetic anisotropic contribution to the scattering intensity associated to this metallic phase, and by XANES.

Influence of Thermal Aging Treatments on Intergranular Corrosion and Cyclic Oxidation Behavior of Low Nickel and Nickel-Free Austenitic Stainless Steels

Influence of Thermal Aging Treatments on Intergranular Corrosion and Cyclic Oxidation Behavior of Low Nickel and Nickel-Free Austenitic Stainless Steels

In-situ reconstruction of LaCoO3-Co3O4 hetero-interface over lanthanum modified Co3O4 nanocatalyst for improved catalytic activity and sintering resistance in methane combustion

Nanoparticles-based catalysts still suffer from deactivation due to sintering and structural collapse through long-time running at high reaction temperature. Developing simple strategy for improving the sintering resistance of nanoparticles is of great importance for fabrication of durable heterogeneous catalysts. In this work, lanthanum was used to prevent Co3O4 nanoparticles from sintering with restricting growth of nanocrystals by in-situ generation of LaCoO3 perovskite phase during thermal ageing process, further building LaCoO3-Co3O4 hetero-interface with strong interfacial effect. Specifically, the Co3O4 nanocatalyst was loaded with different amount of La by traditional impregnation method and a series of characterizations were carried out to explore the physical and chemical properties of the as-prepared catalysts, including XRD, Raman, BET, SEM, HRTEM, XPS, H2-TPR and O2-TPD. It was found that 5 wt% La-Co3O4 has the highest catalytic activity in CH4 combustion and the value of T90 (temperature of 90% methane conversion) between fresh and aged was only 9 ºC, while this value was 108 ºC over pure Co3O4 sample. The Raman, XPS, H2-TPR and O2-TPD results exhibited that the synergistic effect between Co3O4 and LaCoO3 could not only induce lattice distortion in Co3O4 with more defects and adsorbed oxygen species, enhanced oxygen mobility and reducibility, but also significantly suppress the growth of Co3O4 nanocrystals during thermal ageing treatment.

Meta-structure enhanced second harmonic S0 waves for material microstructural changes monitoring

Cumulative second harmonic Lamb waves in nonlinear media feature increasing amplitudes with propagation distance, conducive to the monitoring of material microstructural changes in structures. The phenomenon can be readily generated by zero-order symmetric (S0) mode waves in the low-frequency range. However, in a practical piezoelectric-transducer-activated system, both S0 and A0 (zero-order antisymmetric) mode Lamb waves are inevitably excited, while only the former is responsible for cumulative effects. The generation efficiency of the cumulative second harmonics is then affected by the presence of the A0 waves. To tackle the problem, this study develops a metamaterial structure, referred to as a meta-structure, to tactically enhance the cumulative second harmonic S0 Lamb waves by converting the A0 mode components into S0 mode waves. Topology optimization is conducted to design the meta-structure, which is surface-mounted onto the structure under inspection, to achieve high-efficiency A0-to-S0 wave mode conversion. Through tuning the parameters and constraints of the optimization, the designed single-sided meta-structure breaks the structural symmetry in the thickness direction, while facilitating its practical implementation. Typical scenarios with different meta-structure materials are discussed. Numerical simulations demonstrate that the strain amplitudes of the fundamental S0 mode waves can be increased by 60% with the deployment of the meta-structure, alongside an enhancement of the second harmonic S0 mode waves at different sensing distances. Finally, the designed meta-structure is fabricated via 3D printing technique and tested experimentally on an aluminum plate subjected to thermal aging treatment for monitoring the heating-induced microstructural changes inside the structure. Experimental results confirm an increase in the wave amplitudes of the linear S0 mode waves with the assistance of the meta-structure. The developed system improves the sensitivity of nonlinear Lamb wave-based monitoring methods in characterizing material microstructural changes, which shows great promise for detecting incipient damage in practical structural health monitoring applications.

Synthesis of Amphiphilic Block Copolymer and Its Application in Pigment-Based Ink.

Amphiphilic block copolymers-based aqueous color inks show great potential in the field of visual communication design. However, the conventional step-by-step chemistry employed to synthesize the amphiphilic block copolymers is intricate, with low yield and high economic and environmental costs. In this work, we present a novel method for preparing an amphiphilic AB di-block copolymer of PCL-b-PAA by employing a combined polymerization strategy that involves both cationic ring-opening polymerization (ROP) of the ε-caprolactone monomer and the reversible addition-fragmentation chain-transfer (RAFT) polymerization on the acrylic acid monomer simultaneously. The corresponding polycaprolactone (PCL) and polyacrylic acid (PAA) serve as the hydrophobic and hydrophilic units, respectively. The effectiveness of the amphiphilic AB di-block copolymer as the polymeric pigment dispersant for water-based color inks is evaluated. The amphiphilic AB di-block copolymer of PCL-b-PAA exhibits a molecular weight of 1400 g mol-1, which is consistent with the theoretical value and suitable for polymeric dispersant application. The high surface excess (Γmax) of the PCL-b-PAA in water indicates a densely packed molecular morphology at the water/air interface. Additionally, micelles can be stably formed in the aqueous PCL-b-PAA solution at very low concentrations by demonstrating a low CMC value of 10-4 wt% and a micelle dimension of approximately 30 nm. The model ink dispersion is prepared using organic dyes (Disperse Yellow 232) and the amphiphilic block copolymer of PCL-b-PAA. The dispersion demonstrates near-Newtonian behavior, which is highly favorable for the application as inkjet ink. Furthermore, the ink dispersion displays a low viscosity, making it particularly suitable for visual communication design and printing purposes. Moreover, the ink dispersion demonstrates an unimodal distribution of the particle size, with an average diameter of approximately 500 nm. It retains exceptional stability of dispersion and even conducts a thermal aging treatment at 60 °C for 5 days. This work presents a facile and efficient synthetic strategy and molecular design of AB di-block copolymer-based dispersants for dye dispersions.

Methyl Ester-Mineral Oil Mixture under Thermal Aging

Replacement with natural esters (retrofilling) is an alternative solution to extend the life expectancy of an oil-filled transformer containing mineral oil. During the retro-filling process, some portions of the mineral oil remain inside the transformer's tank, forming a mixture between the used mineral oil and the new vegetable oil. In this investigation, methyl ester was mixed with a relatively low percentage of mineral oil to simulate the retro-filling process. The aim is to examine the characteristics of a mixture of mineral and vegetable oils under thermal aging. Thermal aging treatments were carried out at 120°C for 28 days and 140°C for 14 days. Kraft paper and copper wire were incorporated during the aging test. After thermal aging, the characteristics of the oil mixture were evaluated based on electrical, physical, and chemical characteristics. The result shows that physical and chemical characteristics are significantly influenced by the increase in mineral oil content and the temperature of thermal aging. However, the breakdown voltage increased after thermal aging, but at a higher temperature, the breakdown voltage dropped as the mineral oil content increased.

Perovskite evolution on La modified Mn1.5Co1.5O4 spinel through thermal ageing with enhanced oxidation activity: Is sintering always an issue?

Non-precious metal oxides have great potential in catalytic deep oxidation of emitted hydrocarbons to help address various environmental pollution concerns. However, sintering issue is a stumbling block in practical application upon long-term high-temperature operation or thermal shock experience. Herein, La was applied to modify Mn1.5Co1.5O4 spinel to get a highly active oxidation catalyst with exceptional stability against high-temperature thermal ageing treatment. With thermal ageing at 750 °C for 100 h, the La modified Mn–Co composite reached 90 % conversion in toluene oxidation at 265 °C under the high WHSV of 120,000 mL g−1 h−1, while this value increased to 312 °C over blank Mn–Co spinel. The addition of La not only inhibited the growth of spinel nanocrystals, but also brought about perovskite formation through sintering, generating perovskite-spinel interfaces, thus enhancing both activity and stability. Meanwhile, the La modified Mn–Co spinel exhibited superior performance in presence of water or sulfur dioxide after thermal ageing treatment. This work offers a versatile strategy to design anti-sintering and active oxidation nanocatalysts based on non-precious metal oxides for industrial applications.

Improved high-temperature sintering resistance and light alkanes oxidation activity by La modification on Co3O4 nanocatalyst

In order to improve low-temperature activity and high-temperature sintering resistance of cobalt-based catalyst in catalytic degradation of emitted light alkanes, a strategy of lanthanum modification on Co3O4 nanocrystalline is proposed in this work, aiming at efficiently degrading methane emitted from the oil and natural gas industry. The La-Co3O4 nanocatalysts were prepared by co-precipitation method, and the effects of La-doping on the structural features and catalytic activity of Co3O4 catalyst for methane oxidation were investigated. The results show that the addition of lanthanum forms a composite catalyst containing La2O3 phase and Co3O4 phase, and the interaction increases the active species, which can significantly improve the low-temperature activity of the catalyst. Among them, 5 % La-Co3O4-F catalyst shows the best catalytic activity with 48 °C decrease of the temperature of 90 % methane conversion (T90) compared with pure Co3O4. Furthermore, with thermal ageing treatment at 750 °C for 100 h, Lanthanum modification can significantly slow down the agglomeration growth and the decrease of specific surface area of cobalt oxide in long-term running, and the formation of perovskite structure (LaCoO3) on Co3O4 nanocrystal surface increases the mobility of lattice oxygen, further inhibiting the sintering deactivation of Co3O4 catalyst. The catalyst doped with 5 % La still showed better performance after thermal ageing, which is 127 °C lower than T90 of pure Co3O4. Moreover, this advantage of La doping can also be observed in the catalytic oxidation of other typical hydrocarbons such as ethane and propane. This work provides a promising strategy toward the design of advanced non-precious metal oxide catalysts for practical catalytic oxidation application with excellent high-temperature sintering resistance.

Increasing the Resistance to Cavitation Erosion of 6082 Aluminum Alloys through Thermal Aging Treatments at 140°C and Holding Time of 12 Hours

The use of aluminum alloys in the manufacture of hydropneumatic systems components is very known. However, the knowledge of their behavior under cavitational demands, determinated of flow of the working liquid, is limited. For this reason, in recent years, the older research, carried out on this type of material and on some of its alloys, regarding the resistance to cavity erosion, has been resumed, especially since the mechanical properties and reduced mass are an advantage for the parts that work in this conditions (ship propellers, pumps and bodies of hydraulic devices, etc.). Therefore, the results of this paper are in step with the new researches, highlighting the behavior and resistance to the erosion produced by vibrating cavitation on the aluminum alloy 6082 subjected to the thermal aging treatment at 140 °C, with a holding time of 12 hours. The performance evaluation is based on the characteristic curves of the cavity, the specific parameters and the macro and microstructural investigations. The comparison with the delivered state shows a double increase in resistance from the cavitational erosion created by the shock waves and microjets.

Research on the Influence of the Heat Treatment Temperature on the Cavitation Behavior of the Aluminum Alloy 2017 A

The good mechanical properties of aluminum alloy 2017 A have determined its use in a wide range of applications in which cavitational solocitations occur, such as hydraulic actuation installations, heat engine blocks, boat propellers and sloops, pumps in the cooling system of thermal engines, wings and ogives of airplanes. Currently, research is focused on the development of procedures for improving the resistance to cavitational erosion of these materials. This paper presents the results of the research on the cavitation erosion behavior of the material subjected to thermal aging treatment at different temperatures of 140 °C and 180 °C respectively and a constant holding time of 12 hours. The research was carried out according to the ASTM G32-2016 norms, on a vibrating device with piezoceramic crystals from the Cavitation Laboratory of the Polytechnic University of Timisoara. The research results, based on characteristic curves, mechanical properties, micro and macro structural images, showed that the sample kept for 12 h at a temperature of 180 °C is weaker than the control sample, during the sample time kept for 12 h at a temperature of 140 °C, has a small increase, even if, compared to the control sample (without heat treatment), the hardness is lower.

Widening the operating window of Pt/ZSM-5 catalysts for efficient NOx removal in H2-SCR: Insights from thermal aging

NOx emissions from various sources cause serious environmental problems and harm human health. The selective catalytic reduction of NOx by hydrogen (H2-SCR) using Pt/ZSM-5 catalysts has attracted significant attention due to its effective removal of NOx at low temperatures. However, Pt/ZSM-5 has a narrow operating window because of the excessive oxidation of NO to NO2 at high temperatures. In this study, Pt/ZSM-5 catalysts were prepared by thermal aging treatment of fresh Pt/ZSM-5 at various temperatures to prevent the excessive oxidation of NO to NO2 at high temperatures, and these catalysts were applied to the H2-SCR reaction. The fresh Pt/ZSM-5 catalyst showed high NOx conversion at low temperatures, reaching 93% at 75 °C. However, the conversion rapidly declined as the temperature increased, dropping to 50% at 200 °C. In contrast, when the catalyst was thermally aged, the NOx conversion increased at all temperatures, and the operating window was significantly widened. Especially, Pt/ZSM-5 aged at 850 °C, maintained 84% NOx conversion even at 200 °C. Various characterizations, including XRD, NH3-TPD, STEM, CO-DRIFTS, and probe reactions revealed that the oxidation ability of the thermally aged catalysts decreased due to the sintering of Pt, resulting in widen operating windows. This study provides insights into the development of Pt-based catalysts for H2-SCR applications that can improve NOx reduction efficiency over a wide temperature range.

The impact of thermal aging on the degradation of technical parameter of a dynamic latent thermal storage system

A dynamic latent thermal storage (DLTS) system operates at elevated working temperatures to maximize the operation of the thermal system. It potentially deteriorates the phase change material (PCM) after specific cycles due to thermal aging. The present work assesses the impact of thermal aging of wax-based PCM (paraffin and beeswax) toward the technical parameter of a DLTS system. After thermal aging treatment, the charge and discharge performance for both PCM are degraded. The discharge rate of beeswax (BW) decreases by 23.2%, reducing the effective power rate and storage efficiency by more than 50%. The aged paraffin wax (PW) also experiences performance degradation, where the discharge and power rates decrease around 14.7% and 18.7%, respectively. However, the aged PW maintains sufficient efficiency (67.2%) compared to BW (41.1%), implying that the aging effect can vary for different PCM. Surface observation for the aged PCM demonstrates a fracture profile and microvoids which are probably affected by thermal stress that leads to physical deformation at the molecular level. The decomposition curve is also changed for the aged PCM, making thermal stability an important parameter in choosing a suitable PCM for long-term operation. The study demonstrates the urgency to consider suitable PCM and adjustment on the operation protocol of the DLTS system after a certain cycle operation to minimize the degradation of performance parameters of the thermal system.

Thermal ageing effect on solute segregation and precipitation in the heat-affected-zone of dissimilar metal welds for nuclear power plants

Solute segregation in the carbon-depleted (CDZ) heat-affected zone of dissimilar metal welds (DMW) designed for nuclear power plant EPRTM reactors has been investigated by atom probe tomography (APT) and related to the mechanical properties (toughness test). The analysis of grain boundaries (GBs) by APT allowed the quantification of the P segregation and other solute elements, in all the analyzed samples, before and after long-term ageing heat treatments. The post-weld stress-relief heat treatment applied to the samples before the ageing heat treatments leads to important GBs segregation levels. Following thermal ageing treatments allow a relative increase of GB segregation. P segregation increases with the various thermal ageing conditions. The experimental data were used to model P segregation in high-angle GBs. The simulations show that P segregation is kinetically limited by bulk diffusion, explaining the observed P segregation increase with temperature. P segregation in GBs in the CDZ of the DMW should remain low compared to the expected equilibrium segregation level during the entire reactor service. In addition to solute segregation in extended defects, APT measurements revealed the presence of Cu-rich clusters in GBs, dislocations, and grains in all the aged samples. These clusters were not observed in the sample before ageing.

Effects of thermal cycling on bonding properties of novel low-shrinkage resin adhesive.

The current study aimed to investigate the bonding properties of a novel low-shrinkage resin adhesive containing expanding monomer and epoxy resin monomer after thermal cycling aging treatment. Expanding monomer of 3,9-diethyl-3,9-dimethylol-1,5,7,11-tetraoxaspiro-[5,5] undecane (DDTU) as an anti-shrinkage additive and unsaturated epoxy monomer of diallyl bisphenol A diglycidyl ether (DBDE) as a coupling agent were synthesized. A blend of DDTU and DBDE at a mass ratio of 1∶1, referred to as "UE", was added into the resin matrix at the mass fraction of 20% to prepare a novel low-shrinkage resin adhesive.Then, the methacrylate resin adhesive without UE was used as the blank control group, and a commercial resin adhesive system was selected as the commercial control group. Moreover, the resin-dentin bonding and micro-leakage testing specimens were prepared for the thermal cycling aging treatment. The bonding strength was tested, the fracture modes were calculated, the bonding fracture surface was observed by scanning electron microscope (SEM), and the dye penetration was used to evaluate the tooth-restoration marginal interface micro-leakage. All the data were analyzed statistically. After aging, the dentin bonding strength of the experimental group was (19.20±1.03) MPa without a significant decrease (P>0.05), that of the blank control group was (11.22±1.48) MPa with a significant decrease (P<0.05) and that of the commercial control group was (19.16±1.68) MPa without a significant decrease (P>0.05). The interface fracture was observed as the main fracture mode in each group after thermal cycling by SEM. The fractured bonding surfaces of the experimental group often occurred on the top of the hybrid layer, whereas those of the blank and commercial control groups mostly occurred on the bottom of the hybrid layer. Micro-leakage rating counts of specimens before and after thermal cycling were as follows: the experimental group was primarily 0 grade, thereby indicating that a relatively ideal marginal sealing effect could be achieved (P>0.05); meanwhile, the blank control group was primarily 1 grade, and the penetration depth of dye significantly increased after thermal cycling (P<0.05); the commercial control group was primarily 0 grade without statistical difference before and after thermal cycling (P>0.05), while a significant difference was observed between the commercial control group and experimental group after thermal cycling (P<0.05). The novel low-shrinkage resin adhesive containing 20%UE exhibited excellent bonding properties even after thermal cycling aging treatment, thereby showing a promising prospect for dental application.

Evolution of microstructure, mechanical and corrosion properties of Fe–13Cr–4Al-1.5Nb alloy aged at 450 °C

In the present work, the microstructure evolution, mechanical and corrosion properties of Fe–13Cr–4Al-1.5Nb alloys were systematically studied after the long-term thermal aging treatment. After aging, the Fe–13Cr–4Al-1.5Nb alloys are still mainly composed of α-Fe phase and a small amount of Fe2Nb-type laves phase, but the preferred orientation almost disappeared. With the increase of aging time, the average grain size of Fe–13Cr–4Al-1.5Nb alloy increased obviously and the amount of Fe2Nb-type laves phase also increased significantly. After aging at 450 °C for 2000 h, some coarse grains were observed in the Fe–13Cr–4Al-1.5Nb alloy and it exhibited much coarser grains with an average grain size of 19.7 μm than unaged Fe–13Cr–4Al-1.5Nb alloy due to the incomplete recrystallization. With the increase of aging time, the tensile strength was almost unchanged while the ductility decreased significantly. Due to the incomplete recrystallization, the Fe–13Cr–4Al-1.5Nb alloy exhibited the highest tensile strength of 670.5 MPa but the worst elongation of 3.9% after aging at 450 °C for 2000 h. In addition, the electrochemical corrosion test results showed that the unaged Fe–13Cr–4Al-1.5Nb alloy has better comprehensive corrosion resistance than the aged Fe–13Cr–4Al-1.5Nb alloy in 3.5wt.%NaCl solution.

Confinement effect and Hetero-interface enable High-Performing MnOx/CeO2 oxidation catalysts with exceptional sintering resistance:Morphology effect of ceria support

Combining both low-temperature activity and sintering resistance to meet practical requirements is still a great challenge for the most of effective catalysts. Herein, nano ceria with different morphologies (nanosphere, nanorod, nanocube) were applied to construct novel MnOx/CeO2 catalysts by post impregnation method for catalytic combustion of carcinogenic benzene. Detail structural/physio-chemical characterizations and activity measurements were conducted to investigate the structure-dependent behavior and interfacial effect on catalytic performance and sintering resistance properties. Compared to blank ceria supports, the low-temperature activities of all MnOx/CeO2 catalysts are significantly improved, and the T90 of best-performed MnOx/CeO2 nanorods composite is only 225 °C which is 197 °C lower than that of pure ceria nanorods. Experimental studies indicate low-temperature reducibility, oxygen mobility and surface defects could be greatly promoted by introducing hetero-interface with synergistic effects between ceria and MnOx nanocrystals. Moreover, the morphology-effect on sintering resistance is dramatically different, and the T90 of spherical MnOx/CeO2 increased to only 270 °C from 245 °C after thermal ageing at 750 °C for 100 h while this value raised to 507 °C from 256 °C on MnOx/CeO2 nanocube catalyst. This exceptional sintering resistance over spherical MnOx/CeO2 can be attributed to confinement effect of Ceria nanosphere where the supported MnOx nanoparticles is trapped in the nanopores so that it’s difficult for MnOx particles to aggregate through thermal ageing treatment. In addition, due to the small contact area between the spherical particles, there is no obvious sintering phenomenon such as growth, aggregation and collapse of the spherical particles after thermal ageing, further leading to enhancement of sintering resistance. This work provides a versatile strategy for designing highly active thermal combustion catalysts with good low-temperature activities and sintering resistance for industrial applications.

Influence of Thermal Aging on Dielectric Properties of High Voltage Cable Insulation Layer

Thermal aging is one of the main reasons for the degradation of insulation properties of high voltage cable. Dielectric properties and breakdown strength are important parameters to reflect the insulation performance of the cable insulation materials. In the work, the influence of thermal aging on dielectric and breakdown performance of the cable insulation layer was studied. Firstly, XLPE cable insulation samples were prepared and the thermal aging treatment was carried out. Secondly, the microstructure and molecular structure of XLPE samples under different thermal aging time were analyzed. The dielectric properties and breakdown characteristics of XLPE samples under different thermal aging times were characterized in macro aspect. Finally, the effects of different temperatures on the molecular microstructure of XLPE were studied. The results show that with the extension of thermal aging time, the microstructure of XLPE molecule is destroyed, the macromolecular chain is gradually cleaved, and the carbonyl absorption intensity increases. At power frequency, the breakdown strength decreases from 75.37 kV/mm to 62.18 kV/mm, the relative permittivity increases from 2.44 to 2.51, and the dielectric loss increases from 1.47 × 10−4 to 3.10 × 10−3. The free volume rate of XLPE molecules increases with the increasing temperature, and the mean square displacement gradually increases. The work has good guiding significance for the safe operation and condition assessment of high-voltage cables.