Hydrothermal Aging Research Articles

Investigation on irreversible deterioration mechanism of CFRP–steel adhesive joint based on the hydrothermal aging behavior of resin matrix

Resin-impregnated carbon fiber fabric reinforced polymer (CFRP) is a novel material for steel structure reinforcement, but its performance is influenced by moisture and temperature. This study investigates the irreversible degradation of CFRP–steel adhesive joints in a hydrothermal setting, focusing on resin hydrothermal aging behavior. Moisture absorption tests, Fourier-transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) were conducted to assess moisture’s impact on resin matrix’s properties. Results indicate that moisture absorption behavior is partially reversible through physical drying, while hydrolysis resulting from moisture absorption is irreversible. The partially reversible aspect of moisture absorption leads to a partial restoration of the thermodynamic properties of the resin matrix. Additionally, the mechanical performance of resin specimens and CFRP-steel adhesive joints in hydrothermal conditions was assessed using tensile and pull-off tests. Findings show that elevated temperatures accelerate the moisture absorption rate of resin while increasing the maximum moisture absorption capacity. The moisture absorption affects the fracture surface morphology of the resin matrix, with aging time negatively correlated with adhesion strength. Compared to the hydrothermally aged state, there is a slight recovery in the mechanical performance of CFRP–steel adhesive joints after drying desorption. The saline environment with no significant promotion aging compared to the distilled water environment. These findings provide insights for evaluating CFRP–steel adhesive joints’ durability in atmospheric or marine environments.

Impact of Oxygen Storage Components in Prototype Pd-Based Three-Way Catalysts under Exhaust Conditions Relevant to Propane Engines

With increasing concerns about global warming, the push for sustainable and eco-friendly fuels is accelerating. Propane, recognized as liquefied petroleum gas or LPG, has garnered research interest as an alternative fuel due to its notable advantages, including a high-octane rating, reduced greenhouse gas emissions, and potential cost-effectiveness. However, to realize its full potential as an alternative fuel it is essential to develop catalysts that efficiently handle emissions at low temperatures. In our research, we investigated three distinct palladium (Pd)-based three-way catalyst (TWC) formulations (PdRh, Pd-only, and Pd-OSC) to investigate the influence of typical TWC components rhodium (Rh) and oxygen storage components (OSC) in exhaust scenarios relevant to propane-fueled engines. Among these, the formulation containing oxygen storage components (Pd-OSC) showed the highest reactivity for both NO and C3H8 while minimizing performance degradation from hydrothermal aging (HTA). Notably, the temperature of 50% conversion (T50) for propane in the Pd-OSC fresh and HTA sample was lower by 30 °C and 13 °C, respectively, compared to the Pd-only sample, highlighting the role of oxygen storage materials in enhancing catalyst performance, even without dithering. Additionally, N2 physisorption showed that the Pd-OSC sample has a higher surface area and increased pore volume. This underscores the idea that OSC materials not only augment the catalyst’s porosity but also optimize reactant accessibility to active sites, thus elevating catalytic efficiency. In addition to evaluating performance, we further explored the performance and characteristics of the catalysts using catalytic probe reactions, such as water–gas shift and steam reforming reactions.

Exploring the Impact of Palladium Loading on Pd-Based Three-Way Catalyst Performance and Propane Reactivity for Emission Reduction in Liquefied Petroleum Gas Engines

To reduce air pollution worldwide, regulations on exhaust gas emissions from ships are becoming increasingly stringent. One fuel that is being considered as an alternative to replace the heavy fuel oil used in existing ship engines and thereby reduce harmful emissions, such as NOx, SOx, and greenhouse gases, is sulfur-free liquefied petroleum gas (LPG). To assess the viability of this alternative, it is necessary to understand propane reactivity, the main component of LPG, and develop after-treatment devices applicable to LPG engines. This research evaluated the performance of three prototype Pd-based three-way catalysts (TWCs) with varying Pd loadings (6.5, 4.1, and 1.4 g/L), focusing on their effectiveness concerning propane reactivity in LPG engines. For the fresh samples, catalysts with 4.1 g/L Pd demonstrated performance that was comparable to, or even surpassed, those containing 6.5 g/L Pd. Notably, the temperature of 50% conversion (T50) for NO and C3H8 in the fresh Pd-4.1 was lower by 14 °C and 10 °C, respectively, compared to the fresh Pd-6.5 sample, despite having 37% less precious-metal loading. However, after hydrothermal aging at 900 °C for 100 h, the performance of the 4.1 g/L Pd catalyst significantly deteriorated, exhibiting lower efficiency than the 6.5 g/L Pd catalyst. The study also delved into various probe reactions, including the water–gas shift and propane steam reforming. Advanced analytical techniques, such as N2 physisorption and scanning transmission electron microscopy, were employed to elucidate the texture and structural characteristics of the catalyst, providing a comprehensive understanding of its behavior and potential applications. Through this research, within the efforts of the maritime sector to address challenges posed by emission regulations and rising costs associated with precious metals, this study has the potential to contribute to the development of cost-effective emission control solutions.

Introducing Ni co-cations to simultaneously maintain a high NOx uptake capacity and improve the hydrothermal stability of Pd/SSZ-13 for low-temperature NO adsorption

The hydrothermal stability of Pd/SSZ-13 needs to be improved, particularly when subjected to hydrothermal aging (HTA) at temperatures exceeding 850 °C. Generally, incorporating co-cations in coordination with thermally stable Al pair sites enhances the Pd/SSZ-13 stability. However, this approach significantly reduces the NO storage capacity of fresh samples due to competition between co-cations and Pd2+ ions, leading to the sintering Pd2+ to PdO. In this study, we demonstrate that the “smart” behavior of Ni2+ breaks this activity-hydrothermal stability trade-off. We discovered that in the as-prepared Pd/Ni/SSZ-13 sample, Ni2+ ions predominantly occupied single Al sites as Z[Ni(OH)]+. The abundant ion-exchange sites (with single Al sites accounting for 70 % of the total framework Al) easily accommodated both Pd2+ and Ni2+ ions, mitigating cation competition. The presence of Ni2+ only marginally reduced the NOx storage capacity of Pd/SSZ-13, with the NOx/Pd ratio decreasing from 0.78 to 0.70. During HTA at 850 °C, Z[Ni(OH)]+ gradually transformed into the more thermally stable Z2Ni2+ coordinated to Al pair sites, effectively limiting dealumination. This well-preserved structure maintained a larger number of ion-exchange sites to accommodate Pd2+ ions while simultaneously facilitating the PdO hydrolysis to Pd2+ ions on Brønsted acid sites in Pd/Ni/SSZ-13 during HTA. Consequently, the NOx storage capacity increased (the NOx/Pd ratio rose from 0.70 for the fresh sample to 0.75 for the aged sample). In contrast, undoped Pd/SSZ-13 experienced nearly complete deactivation after HTA (NOx/Pd = 0.2). These findings offer valuable insights for rationally designing Pd/SSZ-13 materials that exhibit both high NO uptake capacity and robust hydrothermal stability.

Influence of hydrothermal aging on the shear bond strength of 3D printed denture-base resin to different relining materials

ObjectivesThis study evaluated the repairability of three-dimensional printed (3DP) denture bases based on different conventional relining materials and aging. Material and methodsThe groups for surface characterization (surface-roughness and contact-angle measurements) were divided based on the denture base and surface treatment. Shear bond strength test and failure-mode analysis were conducted by a combination of three variables: denture base, relining materials, and hydrothermal aging (HA). The initial characterization involved quantifying the surface roughness (n = 10) and contact angle (n = 10) of denture base specimens with and without sandblasting (SB) treatment. Four relining materials (Kooliner [K], Vertex Self-Curing [V], Tokuyama Rebase II (Normal) [T], and Ufi Gel Hard [U]) were applied to 3DP, heat-cured (HC), and self-cured (SC) denture-base resin specimens. Shear bond strength (n = 15) and failure-mode analyses (n = 15) were performed before and after HA, along with evaluations of the fractured surfaces (n = 4). Statistical analyses were performed using a two-way analysis of variance (ANOVA) for surface characterization, and a three-way ANOVA was conducted for shear bond strength. ResultsThe surface roughness peaked in HC groups and increased after SB. The 3DP group displayed significantly lower contact angles, which increased after treatment, similar to the surface roughness. The shear bond strength was significantly lower for 3DP and HC denture bases than for SC denture bases, and peaked for U at 10.65 ± 1.88 MPa (mean ± SD). HA decreased the shear bond strength relative to untreated samples. Furthermore, 3DP, HC, and SC mainly showed mixed or cohesive failures with V, T, and U. K, on the other hand, trended toward adhesive failures when bonded with HC and SC. ConclusionThis study has validated the repairability of 3DP dentures through relining them with common materials used in clinical practice. The repairability of the 3DP denture base was on par with that of conventional materials, but it decreased after aging. Notably, U, which had a postadhesive application, proved to be the most effective material for repairing 3DP dentures.

Na Cocations and Hydrothermal Aging Cooperatively Boost the Regeneration of Phosphorus-Poisoned Pd/SSZ-13 for Passive NOx Adsorption.

Pd/SSZ-13 has been proposed as a passive NOx adsorber (PNA) for low-temperature NOx adsorption. However, it remains challenging for Pd/SSZ-13 to work efficiently when suffering from phosphorus poisoning. Herein, we report a simple and efficient strategy to regenerate the phosphorus-poisoned Pd/SSZ-13 based on the cooperation between hydrothermal aging treatment and Na cocations. It was found that hydrothermal aging treatment enabled the redispersion of Pd and P-containing species in phosphorus-poisoned Pd/SSZ-13. Meanwhile, the presence of Na cocations significantly reduced the formation of AlPO4 and retained more paired Al sites for highly dispersed Pd2+ ions, which was of great importance for the recovery of adsorption performance. To our satisfaction, the restoration ratio of the adsorption capacity of poisoned Pd/SSZ-13 was >90% after regeneration. Strikingly, the NOx adsorption activities of phosphorus-poisoned Pd/SSZ-13 with phosphorus loadings of 0.2 and 0.4 mmol g-1 almost completely recovered upon regeneration. This study demonstrates the promoting effect of Na cocations on the regeneration of phosphorus-poisoned Pd/SSZ-13 by hydrothermal aging treatment, which provides useful guidance for the design of PNA materials with excellent durability for cold-start application.

In Situ Synthesis of Encapsulated Pd@silicalite-2 for Highly Stable Methane Catalytic Combustion.

Methane emissions from vehicles have made a significant contribution to the greenhouse effect, primarily due to its high global warming potential. Supported noble metal catalysts are widely employed in catalytic combustion of methane in vehicles, but they still face challenges such as inadequate low-temperature activity and deactivation due to sintering under harsh operating conditions. In the present work, a series of encapsulated structured catalysts with palladium nanoparticles confined in hydrophobic silicalite-2 were prepared by an in situ synthesis method. Based on various characterization methods, including XRD, HR-TEM, XPS, H2-TPR, O2-TPD, H2O-TPD, CH4-TPR, Raman, and in situ DRIFTS-MS, it was confirmed that PdOx nanoparticles were mainly encapsulated inside the silicalite-2 zeolite, which further maintained the stability of the nanoparticles under harsh conditions. Specifically, the 3Pd@S-2 sample exhibited high catalytic activity for methane oxidation even after harsh hydrothermal aging at 750 °C for 16 h and maintained long-term stability at 400 °C for 130 h during wet methane combustion. In situ Raman spectroscopy has confirmed that PdOx species act as active species for methane oxidation. During this reaction, methane reacts with PdOx to produce CO2 and H2O, while simultaneously reducing PdOx to metallic Pd species, which is further reoxidized by oxygen to replenish the PdOx catalyst.

Fracture toughness, work of fracture, flexural strength and elastic modulus of 3D-printed denture base resins in two measurement environments after artificial aging

ObjectivesTo investigate the fracture toughness (KIC), work of fracture (WOF), flexural strength (FS) and elastic modulus (E) of four additively manufactured denture base resins in two different measurement environments after artificial aging. MethodsRectangular specimens in two different dimensions (n = 480) were 3D-printed with four denture base resins: Denture 3D+ (DEN; NextDent), Fotodent Denture (FOT; Dreve ProDiMed), Freeprint Denture (FRE; Detax), V-Print dentbase (VPR; VOCO)). KIC, WOF, FS and E were measured after (1) water-storage (37 °C; KIC = 7 d; FS = 50 h); (2) water-storage + hydrothermal-aging (20 min, 0.2 MPa, 134 °C); (3) water storage + thermocycling (10,000 cycles, 5/55 °C) in two measurement environments (i) air-23 °C and (ii) water-37 °C. For FS, fracture types were classified, and relative frequencies determined. Univariate ANOVA, Kruskal–Wallis, Mann–Whitney U, and Spearman’s correlation were calculated (p < 0.05, SPSS V.27.0). Weibull modulus (m) was calculated using the maximum likelihood estimation method. ResultsDEN showed the highest KIC (5/6 groups), WOF and highest corresponding m (1/6 groups), while FRE presented the highest FS (2/6 groups) and E values. Hydrothermal-aging and thermocycling reduced KIC and WOF, FS and E, and the number of FS fracture pieces. For 6/8 groups, hydrothermal aging resulted in lower FS than thermocycling. Measurement in air-23 °C led to higher FS for 7/12 groups and a more brittle fracture behavior. A positive correlation between KIC and FS was observed. SignificanceWith measurements in air-23 °C resulting in higher FS than reported in water-37 °C, the measurement environment should be adapted to the clinical situation to allow valid predictions on the mechanical behavior of denture base resins when in situ.

Improving catalytic performance of Cu-SSZ-13 for NOx abatement via in-situ introduction of La and Ce from spent catalyst

Designing a cost-effective and fast fabrication Cu-SSZ-13 with improved selective catalytic reduction of NO by ammonia (NH3-SCR) performance remains an open question. Here we report that LaCe-SSZ-13 zeolites were synthesized from spent fluid catalytic cracking catalyst within 12 h. After ion-exchanging with CuSO4 solution, the obtained LaCeCu-SSZ-13 catalysts exhibit significantly higher catalytic activity and hydrothermal stability than conventional Cu-SSZ-13. Various characterizations reveal that La and Ce modification not only facilitates the disperse of isolated Cu2+ species, but also effectively mitigates dealumination and inhibits copper species aggregation after hydrothermal aging. In-situ diffuse reflection infrared Fourier transform spectrum analyses demonstrate that La and Ce modification can accelerate the adsorption capacity for NH3 and NOx and promote the decomposition of NH4NO3 intermediate species on the catalyst, benefiting the improvement of low-temperature activity. The combination of experiments and theoretical calculations further demonstrate that the most stable positions of La and Ce are on different eight-membered rings in SSZ-13, and then Cu2+ ions tend to enter eight-membered rings to enhance the NH3 adsorption capacity and decrease the H2O adsorption capacity, which results in higher low-temperature activity and hydrothermal stability than Cu-SSZ-13. Our work provides a feasible strategy for preparing the efficient rare-earth-modified Cu-zeolite based NH3-SCR catalyst for nitrogen oxide abatement.

Enhancing the NOx storage and hydrothermal stability of Pd/SSZ-13 passive NOx adsorbers by regulating the Al distributions

Pd/SSZ-13 with different Al distributions were hydrothermally synthesized and utilized as passive NOx adsorbers (PNA). The characterization results indicated that more concentrated Al distribution can not only improve the ion-exchanged level of Pd but also generated more Z2Pd2+ sites at six-member rings. Thus, as revealed by NOx adsorption experiments, samples with more Z2Pd2+ sites showed high NOx storage capacity as well as stronger water resistance. Besides, 84.8 % adsorption capacity of this sample was retained after hydrothermal aging treatment. On the other side, Pd existed as [Pd(OH)]+ sites on SSZ-13 with isolated Al as the majority. These sites were vulnerable to H2O and less stable. Seriously Pd agglomerated was observed on the aged Pd/SSZ-13 with less paired Al. This study revealed that proper Al distribution on SSZ-13 could significantly improve the performance and stability of the catalyst and provided a new direction for the design of PNA catalysts.

Designing ultrastable Pt/CeO2-Al2O3 nanosheet catalysts for three-way catalysts applications

Designing Rh-free, especially Pt-only, three-way catalysts with improved low-temperature activity/stability is highly desirable. Herein, we demonstrate that ultrastable Pt/CeO2-Al2O3 nanosheet catalysts can be obtained based on a Sabatier principle of metal-support interaction. Tuning the surface coverage of penta-site rich γ-Al2O3 nanosheets (AlNS, weak adhesion to Pt) by CeO2 “nano-islands” (strong adhesion to Pt) can lead to the synthesis of Pt/60 wt.%CeO2-AlNS that have lower light-off temperatures for CO, hydrocarbons, and NO compared to conventional Pt/CeO2 and Pt/Al2O3 catalysts by 100–200 °C and a similar performance with the state-of-the-art Rh-based catalyst. Incorporating CeO2 on the surface of AlNS can retard the sintering of CeO2 during harsh redox hydrothermal aging, associate with the strong interaction between CeO2 “nano-island” and penta-site rich γ-Al2O3 nanosheets. Moreover, the improved activity/stability of Pt/CeO2-AlNS catalysts can be attributed to tuning of the Pt detachment and migration from and back to the CeO2 “nano-islands”, respectively, that keeps Pt as nanoclusters on CeO2, the most active species for three-way catalyst applications.

Effect of Sn(II)/Sn(IV) additive on the catalytic combustion of diethylamine and N2 selectivity over CeZrOx catalyst

The synthesis of CeZrSnOx by co-precipitation with different valence-state of Sn for diethylamine combustion is novel and intriguing. In this research, the Sn(II)/Sn(IV)-doped CeZrOx catalysts (CeZr(Sn)Ox-(Sn2+) and CeZr(Sn)Ox-(Sn4+)) were facilely prepared using the co-precipitation method, and their catalytic activities on destruction of diethylamine were evaluated. Detailed characterizations of the catalysts were conducted using X-ray photoelectron spectrometer (XPS), X-ray powder diffraction (XRD), hydrogen-temperature programmed reduction (H2-TPR), temperature programmed ammonia desorption (NH3-TPD) and so on. For diethylamine combustion, CeZr(Sn)Ox-(Sn2+) showed higher activity and nitrogen selectivity than other catalysts, and a high conversion of diethylamine (>90 %) at 250 °C was obtained. After hydrothermal aging treatment, a high conversion (>90 %) and high N2 selectivity maintained over CeZr(Sn)Ox-(Sn2+)-H at 280 °C, indicating high hydrothermal stability of CeZr(Sn)Ox-Sn2+. Owe to the large specific surface area (SSA), high oxygen mobility and strong redox performance, and the synergy between metal elements in CeZr(Sn)Ox-Sn2+ catalysts, the catalytic properties were enhanced. Moreover, Sn2+/Sn4+ ratio in the catalyst and strong acidic sites on the surface of the catalyst both had significant impacts on the catalytic activity and N2 selectivity of the catalyst. Finally, the mechanism of diethylamine combustion over CeZr(Sn)Ox-Sn2+ was obtained by analyzing the reaction through in-situ diffuse reflection infrared Fourier-transform spectrum (in situ DRIFTS) test.

Effect of Hydrothermal Aging Behavior on Surface Treated Kevlar Fiber Laminated Composites

The water sorption characteristics of Kevlar fiber–reinforced epoxy composites were studied by immersion in water at 80 degrees Celsius. The hydrothermal aging process was conducted on treated and untreated Kevlar/epoxy composites; also, the composite was evaluated by the three-point bending test. The phosphoric acid (PA) pretreated with epichlorohydrin (ECH) was used for the surface modification of Kevlar. In the case of chemically modified fiber composites, water uptake was found to be dependent on the chemical treatment done on the fiber surface. The lowest water uptake was observed for composites treated with PA with ECH. The effect of thermal aging on the flexural strength of the treated Kevlar composite was 20.42% higher than the untreated composite. Consequently, the flexural modulus was 13.9% higher than the untreated Kevlar composite. Moreover, the water diffusion coefficient of treated composite 23.19% higher with untreated composite. It was concluded that fiber/matrix degradation time at the interface region was increased in the case of treated composite

Influence of hydrothermal ageing on CFRP single lap bonded joint pre-treated by laser texturing

In this work, the influence of hydrothermal ageing on performances of CFRP single lap bonded joints subjected to two types of pre-treatments was investigated. The first is a degreasing pre-treatment, while the second if a laser texturing pre-treatment through a CO2 laser system. The study considered the influence of an aggressive environment on geometrical deviations and mechanical performances of the bonded joints. Measurements showed that adherends were more susceptible to water uptake after ageing, allowing an increase in laminate thickness of about 2.5%. Lap shear tests were carried out and a decrease in obtained mechanical performances was observed only for the degreased specimens, confirming the effectiveness of the adopted laser texturing to reduce ageing effects. Moreover, the proposed laser texturing pre-treatment for bonding is a sustainable process too because reduces the volume of the removed material efficiently with reduced costs.

Preparation and properties of ternary rare earth co-stabilized zirconia ceramics for dental restorations

High fracture toughness and excellent hydrothermal aging resistance are the characteristics required for dental ceramic materials, but the widely used dental ceramic currently (3Y-TZP) does not exhibit. Aiming to solve this problem, a ternary rare earth co-stable zirconia ceramic (1.5Y5.5Ce0.3La-ZrO2) was prepared by a coating method based on a co-doping strategy. The sintering process, densification evolution, mechanical properties, resistance to hydrothermal aging and biocompatibility of 1.5Y5.5Ce0.3La-ZrO2 ceramic were studied. The results show that 1200 °C is the best pre-sintering temperature, and the machinability and controllability of shrinkage can meet the needs. When the final sintering temperature is 1600 °C, it has the best performance. Compared with 3Y-TZP, the bending strength is about 8.7% higher (912.48 MPa), and the fracture toughness is about 76.6% higher (10.49 MPa m1/2). Furthermore, its resistance to hydrothermal aging is significantly enhanced, greatly extending the service life of the material. The biosafety of 1.5Y5.5Ce0.3La-ZrO2 ceramics was evaluated, and the results showed that the material had no cytotoxicity. To sum up, 1.5Y5.5Ce0.3La-ZrO2 ceramics is a promising dental biomaterial, which has a broad application prospect in oral restoration.

Transferability of the Structure–Property Relationships from Laser-Pretreated Metal–Polymer Joints to Aluminum–CFRP Hybrid Joints

The transferability of structure–property relationships for laser-pretreated metal adhesive joints to laser-pretreated metal–carbon-fiber-reinforced plastic (CFRP) bonds was investigated. Single-lap shear tests were performed on hybrid AW 6082-T6–CFRP specimens pretreated with the same pulsed laser surface parameter sets on the metal surface as previously tested, AW 6082-T6–E320 metal adhesive joints. The fracture surfaces were characterized to determine the type of failure and elucidate differences and commonalities in the link between surface structures and single-lap shear strengths. Digital image analyses of the hybrid specimens’ fractured surfaces were used to quantify remaining CFRP fragments on the metallic joint side. The results indicate that high surface enlargements and the presence of undercut structures lead to single-lap shear strengths exceeding 40 MPa and 35 MPa for unaged and aged hybrid specimens, respectively. Whereas for the metal–polymer joints, the trend from high strength to weakly bonded specimens is largely continuous with the degree of surface structuring, hybrid metal–CFRP joints exhibit a drastic drop in joint performance after aging if the laser-generated surface structures are less pronounced with low surface enlargements and crater depths. Surface features and hydrothermal aging determine whether the specimens fail cohesively or adhesively.

Hydrothermal aging effect on crushing characteristics of intraply hybrid composite pipes

In this study, the crushing properties of hybrid glass, basalt, and carbon fiber-reinforced composite pipes under a hydrothermal aging environment were investigated. Hybrid and non-hybrid composite pipes manufactured by filament winding technique were immersed in distilled water and seawater at 30 °C for four months. The water sorption parameters of the samples were calculated theoretically and weighed experimentally. Dry and aged pipes were subjected to quasi-static axial compression to examine aging effects on the crushing properties. The experimental weighing results showed that all composites exhibited a Fickian-like water absorption line. The non-hybrid basalt pipes were the most water-absorbing among all groups. In addition, the results proved that the hybridization effect in pipes is highly effective on water absorption parameters. In line with the results of non-hybrid pipes, hybrid pipes containing basalt fiber absorbed more water than other hybrid ones. Additionally, pipes aged in different environments showed that composite pipes absorbed more distilled water compared to seawater. Also, it was found that hydrothermal aging having adverse effects on the crushing characteristics of the pipes led to significant decreases. This can be explained by the degradation of the fiber–matrix interphase due to aging. However, maximum specific energy absorptions were achieved from non-hybrid carbon pipes regardless of environmental conditions. Also, the hybridization enhanced the crushing properties of the non-hybrid pipes that have lower characteristics. Additionally, it can be said that hybrid samples providing better stability in crushing showed better mean crushing load values since they mostly had a progressive crushing mode. The maximum mean crushing loads were obtained from the unconditioned hybrid GC samples as 36.2 kN which was 9.5 % and 34 % higher than unconditioned hybrid CB and BG samples. In conclusion, the study proved that the samples with low crushing properties can be improved by hybridization even if they are subjected to harsh environmental conditions.

Hydrothermal aging behavior and effects on carbon fabric/polyphenylene sulfide composite

AbstractCarbon fabric/polyphenylene sulfide (CF/PPS) composite has been used in the aircraft industry, which might suffer moisture and high temperature in service, leading to degradation and even failure. Therefore, knowledge of hydrothermal aging behavior and effects is needed to ensure service life. This work explores the water diffusion behavior, crystallization, and interfacial properties of CF/PPS composite under hydrothermal aging in continuous 3 months and periodical cycles. Diffusion coefficients were calculated through the Fickian model, crystallization behaviors were measured through differential scanning calorimetry and polarized optical microscope, and interfacial properties were characterized by interfacial shear strength, and interlaminar shear strength. The results demonstrate the crystal morphology transforms from transverse crystals to spherulites at the CF/PPS interface after recrystallization through hydrothermal aging, revealing water has a significant impact on the nucleation performance of T300 carbon fiber in the PPS matrix. Hydrothermal aging affects the crystallinity and crystal morphology of CF/PPS composite after recrystallization, and impacts the micro and macro interfacial properties.Highlights Transverse crystals transform to spherulites at CF/PPS interface after water uptake. Water impacts on nucleation performance of T300 carbon fiber in PPS matrix. Hydrothermal aging effect can be accumulated and promotes water uptake. ILSS drop is related to water uptake content, crystallization and IFSS changes.

Fabrication of hydrothermal ageing resistant of 3 mol % yttria‐stabilised tetragonal zirconia polycrystalline via microwave sintering

AbstractThe influence of microwave sintering on the densification, mechanical performances, microstructure evolution and hydrothermal ageing behaviour of pure 3 mol % yttria‐stabilised tetragonal zirconia polycrystalline (3Y‐TZP) ceramics was compared with conventional sintered samples. Green bodies were sintered via conventional pressure‐less and microwave sintering method between 1200 °C to 1400 °C with dwelling time and firing rate at 120 min, 10 °C/min and 1 min, 20 °C/min. Result showed that reduced processing temperature and holding time is possible with microwave sintering technique for fabricating good resistant zirconia sample with bulk density, Young's modulus, and Vicker's hardness that are comparable to samples sintered with conventional method. However, the microwave sintered samples suffered from hydrothermal ageing where their average grain size is above critical size. The enhancement of hydrothermal ageing resistance of the sintered samples is associated with the decreasing grain size of the sintered samples instead of sintering method.

Investigation of MQ Resin Enhanced Material Used for On-Site Insulating Bare Conductors

Bare conductors were widely used in the early power distribution system. However, without an insulation layer, it can pose unexpected safety issues. To solve this problem in an effective and economical way, on-site insulating the bare conductors is highly desirable. Unlike the traditional silicone insulating material loaded with high content of inorganic fillers, silicone material reinforced by MQ resin has suitable viscosity to satisfy the requirement of on-site insulating. Benefiting from MQ resin, the formula proposed has excellent mechanical, electrical, and aging properties. It can be observed that the presence of MQ resin is beneficial for mechanical properties because of its core-shell double-layer spherical structure. Furthermore, owing to this special structure, it improves the dispersion of alumina trihydrate (ATH) and enhances the electrical properties of the composites. Although the presence of MQ resin may lead to a slightly negative effect on the thermal property, it can greatly improve flame retardancy by the compounding of a novel Pt catalyst system and ATH. As for the hydrothermal aging performance, the elongation at break of the sample is greatly improved by the addition of MQ resin. Meanwhile, a feasible measure is also proposed to solve the lightning-induced breakage problem of insulated conductors. The results of this paper are helpful for the investigation and application of on-site insulating material for bare conductors.