Influence Of Hydrothermal Aging Research Articles

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.

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.

Reversible and irreversible effects on the epoxy GFRP fiber-matrix interphase due to hydrothermal aging

Epoxy R-Glass Fiber-Reinforced Polymer (GFRP) composite plates were hydrothermally aged at 60 °C for 23, 75, and 133 days. The water content reached 0.97 wt%, 1.45 wt% and 1.63 wt%, respectively. The studied GFRP matrix was inert to hydrolysis or chain scission, allowing for investigation of irreversible changes in the fiber-matrix interphase due to hydrothermal aging upon re-drying. During each period, a subset of the specimens was removed from the water bath and dried in a chamber. The weight loss upon drying was explained with epoxy leaching (impurities), sizing-rich interphase hydrolysis, glass fiber surface hydrolysis, accumulated degradation products escaping, and water changing state from bound to free. The influence of hydrothermal aging on the fiber-matrix interfacial properties was investigated. Lower interfacial strength of hydrothermally aged (wet) samples was attributed to plasticization of the epoxy, plasticization and degradation of the sizing-rich interphase (including formation of hydrolytic flaws), and hydrolytic degradation of the glass fiber surface. The kinetics of epoxy-compatible epoxysilane W2020 sizing-rich interphase hydrolysis provided an estimate of ca. 1.49%, 4.80%, and 8.49% of the total composite interphase degraded after 23, 75, and 133 days, respectively. At these conditions, the interface lost 39%, 48%, and 51% of its strength. Upon re-drying the specimens, a significant part of the interfacial strength was regained. Furthermore, an upward trend was observed, being 13%, 10% and 3% strength, respectively; thus, indicating a possibility of partial recovery of properties.

Understanding the Catalytic Deactivation upon Hydrothermal Aging at 850 °C of WO3/Fe-Cu-ZSM-5 Catalyst for Selective Catalytic Reduction of NO by NH3

A WO3/Fe-Cu-ZSM-5 catalyst was prepared using the solid state ion exchange method (SSIE) and its performance for the Selective Catalytic Reduction of NO with NH3 (NH3-SCR of NO) was investigated. The study shows that the tungsten addition can slightly improve the high temperature catalytic activity of Fe-Cu-ZSM-5. The influence of hydrothermal aging at 850 °C for 5 h on the structural and textural properties of WO3/Fe-Cu-ZSM-5 was also studied in this paper. The XRD and FE-SEM measurements did not indicate a breakdown of the zeolite structure upon steam treatment for both aged catalysts. The aged W-base catalyst demonstrates a lower deactivation and better catalytic activity for NO reduction than the bimetallic catalyst after hydrothermal aging despite the lower acidic properties as shown by FTIR-Pyr spectroscopy owing to the presence of tungsten oxide crystallites. The “severe” stage of aging occurring in the absence of W led to the formation of copper oxide agglomerates detected using STEM and H2-TPR techniques being responsible for the deterioration of SCR activity of the aged Fe-Cu-ZSM-5.

Effects of Hydrothermal Aging on the Breakdown Voltage of Polyesterimide

Polymers have always played a big role in the insulation of electrical machines and have been the focus of several studies when they are subjected to different stresses. The humidity and temperature are the main constraints that degrade the insulating performance of the materials when they act together causing hydrothermal aging of the polymers. This study deals with the influence of hydrothermal aging on the breakdown voltage of polyesterimide which is known as one of the most important factors which define the electrical insulation performance of the polymer. The breakdown test was executed under AC and DC voltage. A statistical analysis of breakdown data was carried out using the two-parameter Weibull distribution. According to the findings, the breakdown voltage changes with aging time. Its rise is due to a polymer crosslinking by thermal action, causing a reduction of the mean-free path of charge carriers decreasing their mobility. The decline is attributed to the material plasticization after water penetration into the polymer matrix at the beginning of aging, which is a physical effect. Eventually, the chemical effect reflects the hydrolysis reaction, which destroys the hydrogenous links of the polymer. The breakdown voltage under the DC ramp is higher than that obtained under the AC ramp. The DC breakdown voltage depends on the polarity of the applied electrical field. The polymer degradation is characterized by a change in color and the crumbling of samples.

Influence of Hydrothermal Aging under Two Typical Adhesives on the Failure of BFRP Single Lap Joint

Facing increasingly serious resource crises, energy conservation is becoming the development trend of various delivery vehicles, and lightweight is an important way to achieve energy conservation. In this paper, the basalt fiber-reinforced resin composite material (BFRP) was selected to study the effect of its bonding structure, and it was used to make BFRP-BFRP joints. Two adhesives, Araldite®2012 and Araldite®2015, were used to make single-lap joints and dumbbell-shaped specimens. Aging environments of 80 °C/95% RH and 80 °C/pure water were used for the 0-day (unageing), 10-day, 20-day, and 30-day aging tests, respectively. According to Fick’s second law, the moisture absorption change model of two adhesives was established, and it was found that the water absorption process could be divided into two stages, which explains the precipitation of water molecules and the reaction of water molecules with functional groups. The maximum average failure load and load-displacement curves under different environments and different joints were obtained by using the electronic universal tensile machine, and the exposure time was more important than the effect of humidity. At the same time, the change law of failure strength and ductility were analyzed. The change of Tg (Glass transition temperature) was analyzed by differential scanning calorimetry (DSC) equipment, and the results showed that molecular chain rupture was the reason for the decrease of Tg. It could be seen from the joint failure mode distribution that Araldite®2012 adhesive was easily affected by the environment, and the joint of Araldite®2015 adhesive was affected by the combined effect of the adhesive and BFRP.

Influence of hydrothermal aging on the mechanical performance of foam core sandwich panels subjected to low-velocity impact

Abstract The effect of hydrothermal aging on the impact resistance of foam core sandwich panels is studied in this study. The sandwich panels with glass fiber-reinforced skins and polyurethane foam core were fabricated and then were treated with different hydrothermal aging conditions. The moisture absorption characteristic of the composite skins was evaluated. A modified Fickian formulation was proposed to predict the moisture absorption behavior of composite skins. The low-velocity impact resistance of the aged sandwich panels was determined at three different impact energies. The impact responses including contact force, deflection, and dissipated energy of the sandwich panels with and without hydrothermal aging were analyzed. The macroscopic and microscopic damage morphologies were observed by visual inspection and scanning electron microscope methods, respectively. The damage mechanism of the aged panels was revealed. Results indicate that the impact resistance of aged sandwich panels is degraded, and the performance degradation is larger with increasing aging temperature. Compared to the panel without hydrothermal aging, the reduction of the contact force is 35.69%, and the increase of the deflection is 71.43% for the aged panel at 70°C aging temperature. The fiber/matrix interfacial cohesive performance is degraded resulting from the hydrothermal aging.

Investigation on the stability of copper modification of SAPO-34 catalysts in NH3-SCR reaction after hydrothermal aging

The influence of hydrothermal aging on the structural stability of Cu-modified SAPO-34 prepared by ion-exchange and impregnation methods was studied. XRD, Ar adsorption at −196 °C, solid-state NMR, UV–vis, H2-TPR, and EPR were used to probe the structural properties of the catalysts. It was found that the precipitation of crystalline AlPO4 and SiO2, the appearance of mesopores, the migration of silicon to form siliceous islands, and the formation of copper oxide crystallites occurred in aged catalysts. Furthermore, more siliceous islands and copper oxide crystallites were present in the aged samples prepared by the impregnation method than in those prepared by the ion-exchange method. Therefore, the impregnated catalysts show a much poorer structural stability than the ion-exchanged catalysts, which leads to more serious deterioration in the NH3-SCR reaction after hydrothermal aging.

The Influence of Hydrothermal Aging on the Dynamic Friction Model of Rubber Seals.

Cylinder has become an indispensable and important pneumatic actuator in the development of green production technology. The sealing performance of the cylinder directly affects its safety and reliability. Under the service environment of the cylinder, hydrothermal aging of the rubber sealing ring directly affects the dynamic friction performance of the cylinder. So, the dynamic friction model of the cylinder has been developed based on the LuGre friction model, which considers the influence of hydrothermal aging. Here, the influences of the static friction coefficient and Coulomb friction coefficient on the friction model are analyzed. Then, the aging characteristic equation of rubber is embedded in the model for revealing the influence of aging on the friction coefficient of the model. Results show that the aging temperature, aging time, and compressive stress affects the friction coefficient; the variation of the static friction coefficient is larger than that of the Coulomb friction coefficient. The improved cylinder friction model can describe the influence of the aging process on the cylinder friction characteristics, which is of great significance in the design of the cylinder’s dynamic performance.

Influence of hydrothermal ageing on the mechanical properties of an adhesively bonded joint with different adherends

The effect of hydrothermal ageing on the adhesively bonded joints of similar and dissimilar adherends, namely, aluminium alloy (AA7075) and glass fibre reinforced epoxy (GRE) was investigated. The practicality of the adhesively bonded joint technique was demonstrated using single lap joint (SLJ) configuration. The adhesively bonded SLJ specimens were hydrothermally aged in tap water. In order to estimate their long-term performance, an ageing process was performed on adhesively bonded joints at a constant water temperature of 50 °C with variable immersion periods (20, 40, 60, 80, 100, and 120 days). The mechanical strength of the joints was studied using tensile and fatigue testing with three combinations of materials, similar-AA7075/AA7075, similar-GRE/GRE, and dissimilar-AA7075/GRE, with the adhesive layer of two-part Araldite epoxy of 0.2-mm thickness. The tensile tests were performed at room temperature (RT) with a speed rate of 1 mm/min. The fatigue tests were performed at RT for the prolonged 120-days immersion SLJ specimens. Scanning electron microscopy (SEM) images were observed, and the relationship between the ageing period and strength of the adhesively bonded joint was determined. The comparison between unaged and aged specimens was discussed thoroughly. The results showed that as the exposure time increases, the moisture content of joint material increases. However, the joint strength decreases as the exposure time increases, which can be attributed to the effect of failure modes. Different types of failure modes were observed on the damage failure surface, namely, cohesive failure, adhesive failure, structural failure, and intralaminar failure.

Influence of hydrothermal ageing on single lap bonded CFRP joints

Nowadays adhesive are widely used in structural applications, in particular for assembly composite materials. In fact, this technique allows to obtain a more uniform load in the joint, to realise a joint with an higher specific strength and to avoid drilling parts as in the case of bolted joints. However, the mechanical properties of bonded parts over time are not well understood if they are subjected to a more or less aggressive environment. Generally, the main factors of influence regarding the durability of bonded joints are humidity and temperature, but their effects are not always clear if these two factors act simultaneously. In this work the effect of hydrothermal ageing on the mechanical resistance of single lap bonded CFRP joints has been investigated. In particular two types of adhesives (AF 163-2K film and EA 9309NA paste) and three ageing environments (thermal cycles from -28 °C to 85 °C in air, distilled water and salt water) have been chosen for the activity.

Influence of hydrothermal ageing on the compressive behaviour of glass fibre/epoxy composite pipes

The effects of hydrothermal ageing on the crushing behaviour of glass fibre-reinforced epoxy (GRE) pipes are discussed. Pipes with three different winding angles (±45°, ±55°, ±63°) were manufactured by filament winding process. The pipes were then hydrothermally aged in tap water at a constant temperature of 80°C for periods of 500, 1000, and 1500h. Uniaxial compressive tests were conducted on the virgin and aged samples using a universal testing machine in accordance with ASTM D695-10. The tests were also performed at temperatures ranging from room temperature (RT) at 25°C to 45°C and 65°C to study the response of the pipes at elevated temperatures. Scanning electron microscopy (SEM) images were captured and the relationship between the ageing period and strength of the GRE pipes was determined. The results indicate that the strength of the GRE pipes significantly decreases with increase in the temperature and ageing period. On the contrary, the strength increases as the winding angles decrease. The compressive strength of the pipes was also predicted using a Berbinau’s based model and was found to correlate well with the earlier obtained experimental results yielding a maximum variation of less than ∼25%.

Pt/Zeolite Catalysts for Soot Oxidation: Influence of Hydrothermal Aging

Developments in diesel engines and gasoline direct injection (GDI) engines have spawned the requirement of soot oxidation catalysts that work well in both NO + O2 and O2. In this study, we found that supporting Pt on zeolites such as H-ZSM5 and USY may receive better soot oxidizers than commercial Pt/Al2O3 catalyst. Durability tests indicate that, even after the hydrothermal aging at 800 °C, the aged Pt/H-ZSM5 is still a better soot oxidizer than Pt/Al2O3 in NO + O2, and the aged Pt/USY exhibits the best activity in O2. Further explorations reveal that the NO2 preferential adsorption on soot is dependent on acid sites both inside and outside micropores of zeolites, while the decomposition of surface oxygenated complexes (SOCs) can be promoted by strong acid sites on the external surface. These two factors contribute mainly to the high activity of the Pt/zeolite catalysts in NO + O2 and O2, respectively. Considering a relatively high external surface area is always essential to inhibiting the severe sinter...

Investigation of the Effect of Accelerated Hydrothermal Aging on the Cu Sites in a Cu-BEA Catalyst for NH3-SCR Applications

The influence of hydrothermal aging between 500 and 900 °C for 3 h, on the structure of a Cu-Beta catalyst was studied in this work. The XRD measurements indicated a structural breakdown of the zeolite upon 900 °C hydrothermal aging. This was confirmed from the loss of surface area as measured by BET method. The temperature for the zeolite structure break down was different between the powder bed as opposed to the sample that was washcoated on a cordierite monolith, which was most likely due to slightly different aging conditions and the presence of binders. The strong increase in the intensity of the Cu2p XPS peak indicated that the surface is enriched of copper at higher temperatures due to the zeolite structure collapse. The presence of CuO is usually accompanied by a satellite peak, which was clearly observed at higher binding energies for the catalysts aged at 800 and 900 °C. The XPS results are in good agreement with the UV–Vis experiments, which also point to the formation of copper oxide after high temperature aging.

Mechanisms of Interfacial Degradation of Epoxy Adhesive/Galvanized Steel Assemblies: Relevance to Durability

This study reports on the durability of galvanized steel joints bonded with toughened epoxy adhesive formulations under the influence of temperature and moisture aging. The influence of hydrothermal aging on the substrate and adhesive properties was first determined and then correlated to the durability of bonded joints. The mechanical properties of the adhesively bonded joints were assessed by a shear stress-strain analysis on single lap joints. Experimental results have shown a loss of adherence during aging. Scanning electron microscopy, fourier transform infra-red spectroscopy, and differential scanning calorimetry were conducted to analyze precisely the locus of failure and the failure faces after separation of the interface. Consequently, physical and chemical modifications of the adhesive and surface corrosion of the substrate were observed. A three-step mechanism has been proposed to explain the loss of adhesion during aging. The first step was attributed to adhesive and interface hydrolysis of the lap-shear sample's Highly stressed zones, the second step to hydrolysis of the centre of the bonded joint and initiation of corrosion. The last one is due to an important growth of corrosion products which favours rupture in a weak boundary layer at the metal/polymer interphase. The aging model proposed bears out that the higher the corrosion resistance of the metal surface the lower the loss of adhesion under a wet environment.

Influence of hydrothermal aging on the catalytic activity of sulfated zirconia

The use of reflux aged zirconia gel in the synthesis of sulfated zirconia catalysts for isomerization of short paraffins and isomerization-cracking of long paraffins was assessed. It was found that reflux aging greatly improved zirconia textural properties. The growth of the monoclinic phase was greatly suppressed and the initial area and sintering resistance were increased. The specific surface area of reflux aged material with no sulfate was almost 75 m2 g−1 after calcination at 800 °C. Sulfate promotion of aged materials further increased the tetragonal/monoclinic ratio and the area of sulfated catalysts was 220 m2 g−1 after calcination at 600 °C.

Selective catalytic reduction of NO under lean conditions by methane and propane over indium/cerium-promoted zeolites

The potential of zeolites MFI and MOR promoted by In and Ce as catalysts for the SCR of NOx by methane and propane was studied, particularly considering their stability in the presence of water vapour. A preparation route for a zeolite-based Ce/In composite catalyst was developed and the influence of several reaction conditions was studied to optimise the catalyst performance. TPR and FTIRS were used to check the preparation steps and to investigate the catalyst structure. These data were used together with results from characterisation by X-ray-based techniques to describe the generation and catalytic function of different indium species ((InO)+, In2O3 cluster) and their co-operation with ceria in the composite catalyst. The primary role of the CeOx promoter is to catalyse the oxidation of NO to NO2. Probably, NO2 reacts with methane on Lewis-acidic and redoxactive (InO)+ species, but the further reaction of the intermediate formed needs the presence of residual Brønsted-acid sites. SCR of NOx by methane or propane is still partially inhibited by adsorption competition between water and the hydrocarbons on the (InO)+ species. Higher SCR activity could be achieved by increased hydrocarbon partial pressure in the feed, shifting presumably the competitive adsorption to enhanced adsorption of methane and propane, respectively. Furthermore, combining of methane and propane as reductants opens an opportunity to broaden the ‘temperature window’ for the SCR of NOx. Different influence of hydrothermal ageing was obtained with methane and propane, respectively, as reducing agent.

Influence of hydrothermal ageing and thermal treatments on the viscoelastic behavior of DGEBA-MCDEA epoxy resin

The influence of both hydrothermal and physical ageing on the viscoelastic behaviour of an epoxy resin (DGEBA-MCDEA) was investigated. The samples were first immersed in distilled water and then tested on dynamic mechanical analyser all along thermal treatments. Three relaxations of epoxy networks were observed on mechanical spectra: the main relaxation (α) at higher temperatures, the secondary relaxation (β) at lower temperatures, and the intermediate ω-relaxation. As a result of the plasticization effect of water on DGEBA-MCDEA network, all viscoelastic characteristics (width, magnitude, and temperature location) of both β- and ω-relaxations were shown to be enhanced. It was also observed that bimodal β-relaxation appears unconcerned about the structural recovery following physical ageing. On the opposite, it was concluded that each step of the thermal ageing treatment induce several changes in the viscoelastic characteristics of the ω-relaxation.

Effects of hydrothermal aging on the dielectric properties of epoxy molding compounds

ABSTRACTWe studied the influence of hydrothermal aging on the dielectric properties of epoxy molding compounds used for integrated circuits packaging. Samples were subjected to two different aging (JEDEC 1 and JEDEC 3 procedures, followed by a thermal stress at 240°C for a few minutes). Resistance to aging was studied as a function of crosslinking density. Water uptake increases with crosslinking. Aging leads to a reduction in the dielectric constant and to an increase in the loss factor. Post-mold curing is found to slightly enhance the resistance against hydrothermal aging.

Durability of sheet molding compounds: Influence of hydrothermal aging on morphology and molecular mobility at microscopic scale

AbstractThe physicochemical aging for parts of Sheet Molding Compound should be considered for their lifetime management and reusability. This material has a complex morphology and contains porosity due to the process and to shrinkage compensation. This SMC study has two complementary approaches. One describes the morphological consequences of water uptake, showing the decrease in the total amount and the fractal dimension of micro‐voids by scanning electron microscopy and image processing. The other shows, by mechanical spectrometry, the effect of water on physical or chemical bonds. In both cases, the “low profile agent” in SMC plays an important role. The molecular mobility was taken as a sensor parameter for the structural changes at the molecular scale, highlighting and quantifying the first steps of the aging. The loss factor level increases, and the activation energies are modified, even for the first aging days. The analysis shows recovery for the material near the relaxation peak of the low profile agent, since the curve recovers its initial shape.