Virgin Samples Research Articles

Effects of gamma irradiation on the properties of Ce2S3 thin films

Cerium sulphide (Ce2S3) thin films were prepared via successive ionic layer adsorption and reaction (SILAR) scheme. The optical, structural, and electrical investigations of both virgin and gamma-exposure samples were conducted, focussing on the gamma irradiation dose. The objective was to examine the impact of gamma irradiation on the characteristics of the Ce2S3 thin films. An X-ray diffraction (XRD) study of the samples established the orthorhombic phase of the Ce2S3 thin films and revealed that the crystallinity was improved with the gamma dose. The Field emission scanning electron microscope (FESEM) images of the virgin thin film detected a smooth surface with spherical grains with distinct grain boundaries. In contrast, after the gamma exposure, the thin film surface revealed a cluster of small particles. Energy dispersive X-ray (EDX) study inveterate the stoichiometry of the prepared Ce2S3 thin films. The gamma exposure dose caused a deviation in the bandgap, which was related to the quantum confinement effect. Photoluminescence (PL) spectra proved that the emission intensity of the Ce2S3 thin films decreased with increasing gamma dosage, and this phenomenon was attributed to the additional crystallites and a smaller number of structural defects. This simple approach to amend the characteristics of Ce2S3 thin films by gamma exposure could become an attractive option to explore this material for dosimetry and radiation sensing.

Understanding intentionally and non-intentionally added substances and associated threshold of toxicological concern in post-consumer polyolefin for use as food packaging materials

The use of post-consumer recycled (PCR) polymers in food contact materials (FCMs) can facilitate achieving a circular economy by reducing environmental waste and landfill accumulation. This study aimed to identify potentially harmful substances, including non-intentionally added substances (NIAS) and unapproved intentionally added substances (IAS), in polyolefin samples from material recovery facilities using gas-chromatography mass-spectrometry. Selected phthalates and bisphenols were quantified by targeted gas-chromatography tandem mass-spectrometry. The analysis detected 9 compounds in virgin polymers and 52 different compounds including alcohols, hydrocarbons, phenols in virgin and hydrocarbons, aromatic, phthalates, organic acids, per- and polyfluoroalkyl substances (PFAS) in PCR polymers. The Cramer classification system was used to assesses the Threshold of Toxicological Concern associated with the detected compounds. The PCR sample showed a slightly higher proportion of Cramer Class III compounds (48.08 %) than the virgin sample (44.44 %), indicating higher toxicity potential. Quantification detected bisphenols only in PCR material including BPA (2.88 ± 0.53 μg/g), BPS (5.12 ± 0.003 μg/g), BPF (3.42 ± 0.01 μg/g), and BADGE (4.638 μg/g). Phthalate concentrations were higher in PCR than virgin samples, with the highest levels detected as DIDP, at 6.18 ± 0.31 μg/g for PCR and 6.04 ± 0.02 for virgin. This study provides critical understanding of the safety and potential risks associated with using PCR polyolefins from different sources in food contact applications.

Determination of NTA and EDTA in authentic water samples by LC-MS/MS combined with precolumn methylation

Nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA), as widely used chelating agents, have created many environmental issues and raised much attention regarding their environmental occurrence. However, the determination of NTA and EDTA in samples of complex solution chemistry remains challenging. Here, we proposed a simple and sensitive method based on liquid chromatography tandem mass spectrometry (LC-MS/MS) to determine NTA and EDTA from aqueous samples without an enrichment step. During the analysis, H+-cation exchange was used to efficiently eliminate interference from metal ions. The intensity of NTA and EDTA with trimethylsilyldiazomethane methylation could be improved hundreds of times that of the virgin samples. To maximize sensitivity, the sample pretreatment methods, the derivatization procedures and the LC-MS/MS conditions were systematically optimized. The validated method showed low limits of quantification (0.4 μg/L for NTA and 1.5 μg/L for EDTA), a wide linear response (up to several mg/L, R2 > 0.998), and good intra- and inter-day precision (relative standard deviation ≤ 11%). The reliability of this method was successfully validated by analysis of authentic water samples collected from three WWTPs and one river with satisfactory recoveries (80–117%). It can be proposed as a powerful analytical method of NTA and EDTA in authentic water samples and could potentially be adapted to detect other chelates and polydentate compounds.

Impact of Multiple Reprocessing on Properties of Polyhydroxybutyrate and Polypropylene.

Biobased plastics have the potential to be sustainable, but to explore their circularity further, current end-of-life options need to be broadened. Mechanical recycling is one of the most accepted methods to bring back plastics into the loop. Polyhydroxybutyrates (PHBs) are biobased and biodegradable in nature with promising properties and varied applications in the market. This study focuses on their potential for mechanical recycling by multiple extrusion cycles (E1-E5) and multi-faceted characterization of the virgin (V) and reprocessed materials from E1 to E5. The behavior is compared to polypropylene (PP) as a reference with a similar property profile, which has also been reprocessed five times. The thermal properties of both series showed a stable melting point and thermal decomposition temperature from thermal analyses (differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)). However, a steady increase in the degree of crystallinity was observed which could counterbalance the decrease in molecular weight due to repeated extrusion measured by gel permeation chromatography and resulted in similar values of tensile strength across the cycles. The strain at break was impacted after the first extrusion, but no significant change was observed thereafter; the same was observed for impact strength. Even in scanning electron microscopy (SEM) images, virgin and E5 samples appeared similar, showing the stability of morphological characteristics. Fourier transform infrared spectroscopy (FTIR) results revealed that no new groups are being formed even on repeated processing. The deviation between the PHB and PP series was more predominant in the melt mass flow rate (MFR) and rheology studies. There was a drastic drop in the MFR values in PHB from virgin to E5, whereas not much difference was observed for PP throughout the cycles. This observation was corroborated by frequency sweeps conducted with the parallel plate method. The viscosity dropped from virgin to E1 and E2, but from E3 to E5 it presented similar values. This was in contrast to PP, where all the samples from virgin to E5 had the same values of viscosity. This paper highlights the possibilities of mechanical recycling of PHB and explains why future work with the addition of virgin material and other additives is an area to be explored.

Experimental study of the effects of initial shear stress on post-liquefaction behavior of submarine liquefiable ground: An energy-based evaluation

In offshore earthquake regions, granular soils are prone to liquefaction and flow failure, resulting in imponderable damage to adjacent structures. When the foundation is constructed on inclined terrains, initial static shear stress induced by the self-weight of slope soils can significantly affect the soil behavior and liquefaction potential. This paper discusses the effects of initial shear stress on the liquefaction and post-liquefaction behavior through an energy-based approach. A series of monotonic and cyclic undrained simple shear tests are performed under various initial shear stress levels. The cumulative dissipated energy is used to evaluate the effects of initial shear stress on typical soil behaviors, including the onset of instability in monotonic tests and the liquefaction in cyclic tests. In monotonic tests, the cumulative energy required for triggering instability decreases with the initial shear stress level at the post-liquefaction stage. Moreover, at the same relative density, a strain-softening response on virgin samples can be transformed into a strain-hardening type at the post-liquefaction stage. In cyclic tests, a unique correlation is found between cumulative energy and pore water pressure and it is closely related to the initial shear stress level. Based on the test results, two relationships are proposed to estimate the cumulative energy required for liquefaction or flow-type failure at the initial liquefaction and post-liquefaction stages.

Thermal degradation of virgin and waste plastics: Estimation of kinetic and thermodynamic parameters using model‐free iso‐conversional methods

AbstractKinetic triplets—apparent activation energy (Ea), pre‐exponential factor (A), and the reaction model—were estimated for the thermal degradation of three primary virgin and waste plastics, as well as mixed plastics waste. Model‐free iso‐conversional FWO, KAS, Starink, Kissinger and Vyzovkin and Friedman methods were employed for the kinetic analysis. The apparent activation energy was determined by the integral methods as 206.5‐209.1 kJ mol−1 and 195.6‐198.8 kJ mol−1 for the virgin and waste high‐density polyethylene (HDPE), 211.6‐214.1 kJ mol−1 and 183.1‐186.6 kJ mol−1 for the virgin and waste polypropylene (PP), 144.0‐163.1 kJ mol−1 and 159.7‐167.1 kJ mol−1 for the virgin and waste polystyrene (PS), and 173.6‐178.9 kJ mol−1 for the mixed plastics waste respectively. Ea was found to follow the trend HDPE > PP > PS with higher values for HDPE and PP virgin samples than that for their waste and marginally smaller for the virgin PS than its waste. Degradation of all plastic samples followed Avrami‐Erofeev equation with n varying between 1.0 and 1.8. The effect of conversion on Ea suggested the degradation of both virgin and waste HDPE to consist of multiple parallel reactions while that of others to be more complex. FTIR analysis of the evolved gases was used to explain the possible reaction mechanism. A small difference between the enthalpy change and the apparent activation energy (6‐7 kJ mol−1) for all plastic samples indicated favourable pyrolysis reactions. The estimated kinetic parameters and thermodynamic properties showed the stability of different plastics as HDPE > PP > PS.

Crystal Lattice Defects in Deuterated Zr in Presence of O and C Impurities Studied by PAS and XRD for Electron Screening Effect.

Low-energy nuclear reactions are known to be extremely dependent on the local crystal structure and crystal defects of the deuterated samples. This has a strong influence on both hydrogen diffusion and the effective electron mass. The latter determines the strength of the local electron-screening effect and can change the deuteron-deuteron reaction rates at very low energies by many orders of magnitude. In the present study, zirconium samples were exposed to various conditions and energies of deuteron beams using the unique accelerator system with ultra-high vacuum, installed in the eLBRUS laboratory at the University of Szczecin. Irradiated and virgin samples were investigated by means of the X-ray diffraction (XRD) and positron annihilation spectroscopy (PAS). While the first method delivers information about changes of crystal lattice parameters and possible production of hydrides accompanying the formation of dislocations that are produced during irradiation of the samples, the second one can determine the depth distribution of crystal defects, being especially sensitive to vacancies. The studied Zr samples were also implanted by carbon and oxygen ions in order to simulate the real situation taking place in nuclear reaction experiments and to investigate their influence on the kinetic of produced vacancies. The observed enhancement of the electron-screening effect in the deuteron fusion reaction at very low energies could be explained by formation of a high number of vacancies during the deuteron irradiation of samples. Possible carbon and oxygen impurities can affect this process in various ways by changing the depth distribution of vacancies and their diffusion, but they play only a minor role in the strength of the electron-screening effect.

Scott Blair Fractional-Type Viscoelastic Behavior of Thermoplastic Polyurethane.

In this paper, the experimental characterization of the viscoelastic properties of thermoplastic polyurethane (TPU) samples through creep experiments is presented. Experiments were conducted at different constant temperature levels (15, 25, and 35 ∘C), for three different tensile stress levels (0.3, 0.5, and 0.7 MPa), and at different physisorbed water contents, providing access to: (i) the temperature dependency of creep parameters and (ii) the assessment, if behavior is indeed viscoelastic. The physisorbed water content was achieved by exposing virgin samples to environments with relative humidity ranging from 0 to 80 percent until mass stability was reached. Creep tests were conducted immediately afterwards with this particular humidity level. The main results of this study are as follows. The temperature dependency of the obtained creep parameters is well described in Arrhenius plots. With regard to water content, two prototype material responses were observed in the experimental program and accurately modeled using the following fractional-type models: (i) Scott Blair-type (i.e., power-law-type) only behavior, pronounced for the combination of low water content/low temperature; (ii) combined Scott Blair plus Lomnitz (i.e., log-type) behavior for high water content/high temperature. This change in behavior associated with certain thresholds for the specified environmental conditions (temperature and relative humidity) may indicate the initiation of hydrogen bond breakage and rearrangement (carbamate H-bonds and physisorbed water H-bonds). Regarding the short-term or quasi-instantaneous behavior, the Scott Blair element seems highly appropriate and may be better suited than the standard elastic model: the Hookean spring. We associated Scott Blair behavior with the load-induced, quasi-instantaneous re-arrangement of polymer network chains. The secondary viscoelastic mechanism associated with the Lomnitz element, hydrogen bond breakage and rearrangement, comes into play for higher temperatures and/or higher physisorbed water contents. In this case, the contribution of the two constitutive elements is well separated due to the large number of the characteristic time of the Lomnitz element, much larger than the respective value for the Scott Blair element.

Study on UV aging characteristics of low-grade asphalt in the desert climate

The Taklamakan Desert in China’s Xinjiang region faces severe heat conditions that cause rutting in asphalt pavements. In order to combat this issue, local construction management has been advocating for the utilization of low-grade asphalt with penetration levels between 20 and 50, to enhance the pavement’s resistance to rutting. However, there is limited research on the durability of low-grade asphalt under intense UV irradiation in the region. To this end, a multiscale investigation was conducted, examining three different types of asphalt (30#, 50#, and 70#), under various conditions such as virgin, UV aging, and Pressure Aging Vessel aging. Analytical techniques such as Atomic Force Microscope, Gel Permeation Chromatography, Fourier Transform Infrared Spectroscopy, Dynamic Shear Rheology, and Bending Beam Rheometer were employed. The results revealed that the surface roughness of the three types of asphalt increased by 15.50% (30#), 5.99% (50#), and 2.70% (70#) after UV aging, compared to the virgin samples. Furthermore, the adhesion properties of lower-grade asphalt were less affected by UV aging. Weight-average molecular weight of the three types of asphalt increased significantly after UV aging, with a 26.96% increase in 30#, 51.92% increase in 50#, and 43.76% increase in 70# compared to the samples prior to UV aging. The 30# asphalt with higher large molecule content exhibited slower UV aging. The 30# asphalt also exhibited the smallest increase of C=O and S=O after UV aging among the three types of asphalt. The study also found that UV aging had a lesser effect on the high- and low-temperature performance of asphalt, compared to PAV aging. Overall, the effects of UV irradiation on various properties of 30# asphalt were less pronounced than those of 50# and 70# asphalt. These findings offer valuable insights into aging resistance in the Taklamakan Desert, benefiting road contractors and the academic community.

Aromatic Fingerprints: VOC Analysis with E-Nose and GC-MS for Rapid Detection of Adulteration in Sesame Oil.

Food quality assurance is an important field that directly affects public health. The organoleptic aroma of food is of crucial significance to evaluate and confirm food quality and origin. The volatile organic compound (VOC) emissions (detectable aroma) from foods are unique and provide a basis to predict and evaluate food quality. Soybean and corn oils were added to sesame oil (to simulate adulteration) at four different mixture percentages (25-100%) and then chemically analyzed using an experimental 9-sensor metal oxide semiconducting (MOS) electronic nose (e-nose) and gas chromatography-mass spectroscopy (GC-MS) for comparisons in detecting unadulterated sesame oil controls. GC-MS analysis revealed eleven major VOC components identified within 82-91% of oil samples. Principle component analysis (PCA) and linear detection analysis (LDA) were employed to visualize different levels of adulteration detected by the e-nose. Artificial neural networks (ANNs) and support vector machines (SVMs) were also used for statistical modeling. The sensitivity and specificity obtained for SVM were 0.987 and 0.977, respectively, while these values for the ANN method were 0.949 and 0.953, respectively. E-nose-based technology is a quick and effective method for the detection of sesame oil adulteration due to its simplicity (ease of application), rapid analysis, and accuracy. GC-MS data provided corroborative chemical evidence to show differences in volatile emissions from virgin and adulterated sesame oil samples and the precise VOCs explaining differences in e-nose signature patterns derived from each sample type.

Study tracking and erosion properties of modified nitrile butadiene rubber with nanoparticles by inclined plane test

Occurrence of tracking and erosion on surface of polymer insulator leads to breakdown of these materials and has negative impact on their quality. Contaminants forms surface layer on insulators and chemically interact with it. This effect reduces smoothness of surface insulator and forms conducting paths. It allow passage of higher values of leakage current and cause ionization of field around insulator and rise temperature of surfaces, this leads to formation phenomenon of tracking and erosion.it cause deterioration, ageing and collapse of insulator, which affect safety of electric system. How to significantly enhance the tracking and erosion properties of nitrile butadiene rubber (NBR) are a major topic in electric insulators. With a view to enhancing the tracking and erosion properties of NBR used in power systems, nanoparticles are usually added to pure materials to enhance their electrical and physical properties. This work deals with experimental studies on tracking and erosion properties on NBR loaded with [0, 0.5, 1, 1.5, and 3 part per hundred part of rubber (Phr.)] titanium dioxide (TiO2) nanoparticles. Composite materials have been experimentally tested by inclined plane test (IPT) according to the ASTM D2303 standard. When it is necessary to explore a new insulating material, the inclined plane test is used. This is because IPT is used to evaluate the properties of laboratory modified polymers under different voltages. The times to track during the test were recorded. Data processing, analog to digital systems, and data acquisition have been used to measure leakage current passing through samples. When comparing result of leakage current measurements, it was noted that its value was lower for modified samples compared to virgin samples. This positive effect indicates to enhancement of NBR as a result of formation of stable chemical bonds.

Novel epoxy/cyclic olefin copolymer/carbon structural composites with electro‐activated self‐healing properties

AbstractMultifunctional self‐healing composites have great potential in several applications, i.e., from automotive to aerospace. This study examines the self‐healing behavior of carbon fiber reinforced composites by depositing jet‐spun cyclic olefin copolymer (COC) meshes on dry carbon fiber plies before lamination with epoxy resin (EP). Three different laminates were prepared, including neat EP/CF and two composites with 4 wt.% and 8 wt.% of COC in the form of a jet‐spun network as a healing agent. The introduction of COC mesh reduced flexural stress by 26% and interlaminar shear strength by 50%. Mode I interlaminar fracture toughness (GI) was evaluated and specimens were mended at 110°C by resistive heating generated by an electrical current flowing within the samples. The laminates containing 8 wt% COC reported a healing efficiency, evaluated as the ratio between the GI and as the ratio of the maximum load (PMAX) of virgin and healed samples, of 9.4% and 33.7%, respectively. Fractography analysis highlighted the poor adhesion between the COC mesh and EP matrix, and several COC microfibers were trapped inside the epoxy matrix, hindering their diffusion inside the crack zone, which limited the healing capability of the prepared laminates.

Mechanical and Thermoanalytical Study of Polypropylene Geomats Exposed in the Field and the Laboratory.

A Hydroelectric Power Plant (HPP) presents erosion problems on reservoir slopes and margins. Geomats are a biotechnical composite technology increasingly used to protect soils against erosion. Survivability or durability of geomats is essential for successful application. This work analyses the degradation of geomats exposed in the field for more than six years. These geomats were used as erosion-control treatment in a slope at HPP Simplício in Brazil. The degradation of the geomats in the laboratory was also analysed through exposure in a UV ageing chamber for 500 h and 1000 h. Degradation was quantitatively evaluated by testing the tensile strength of the geomat wires and thermal tests such as thermogravimetry (TG) and differential scanning calorimetry (DSC). The results showed that the geomat wires exposed in the field had a greater decrease in resistance compared to the samples exposed in the laboratory. In the samples collected in the field, it could be observed that the degradation of the virgin sample occurred earlier than in the exposed samples, contrary to what was observed in the TG tests carried out with the samples exposed in the laboratory. The DSC analysis showed that the samples had similar behaviours for the melting peaks. This evaluation of the wires of the geomats was presented as an alternative to analysing the tensile strengths of discontinuous geosynthetic materials such as the geomats.

Effects of saliva on additive manufacturing materials for dentistry applications: Experimental research using flexural strength analysis

Accurate and reliable results in orthodontics heavily depend on selecting the right impression materials. With the rise of digital technology and additive manufacturing techniques, it has become necessary to characterize experimentally the materials used to design prosthetic bases. In this study, the mechanical properties of Polyetheretherketone, Nylon6, Nylon12, and Polypropylene are analyzed, as impression materials commonly used in dentistry applications. Specifically, the effect on their flexural elastic modulus of the exposure to working environment conditions is also investigated by means of 3-point bending test performed on virgin materials and samples immersed in saliva for 72 hours. The proposed approach revealed significant behavior in terms of loss in mechanical performances. These findings have significant implications for the proper selection and use of AM materials in dental applications.

Damage and Fracture Mechanics of Porcine Subcutaneous Tissue Under Tensile Loading.

Subcutaneous injection, which is a preferred delivery method for many drugs, causes deformation, damage, and fracture of the subcutaneous tissue. Yet, experimental data and constitutive modeling of these dissipation mechanisms in subcutaneous tissue remain limited. Here we show that subcutaneous tissue from the belly and breast anatomical regions in the swine show nonlinear stress-strain response with the characteristic J-shaped behavior of collagenous tissue. Additionally, subcutaneous tissue experiences damage, defined as a decrease in the strain energy capacity, as a function of the previously experienced maximum deformation. The elastic and damage response of the tissue are accurately described by a microstructure-driven constitutive model that relies on the convolution of a neo-Hookean material of individual fibers with a fiber orientation distribution and a fiber recruitment distribution. The model fit revealed that subcutaneous tissue can be treated as initially isotropic, and that changes in the fiber recruitment distribution with loading are enough to explain the dissipation of energy due to damage. When tested until failure, subcutaneous tissue that has undergone damage fails at the same peak stress as virgin samples, but at a much larger stretch, overall increasing the tissue toughness. Together with a finite element implementation, these data and constitutive model may enable improved drug delivery strategies and other applications for which subcutaneous tissue biomechanics are relevant.

Readily Recyclable, Auto-Catalyzed Tung Oil-Derived Vitrimers and Carbon Fiber-Reinforced Composites

The high strength and durability of carbon fiber-reinforced composites (CFRCs) have made them a popular choice in aerospace, civil engineering, and sports equipment. However, the non-degradable resin matrix and non-destructive recycling of carbon fibers present a challenge for their sustainability. To address this issue, we have developed a new type of CFRCs that are readily recyclable and high-performing, using an auto-catalyzed tung oil-derived vitrimer and acid curing agents (TTMA) in combination with bisphenol A epoxy resin (DGEBA) or 4,4′-methylene bis (N,N-di glycidylaniline) (TGDOM). The DGEBA/TGDOM-TTMA networks contain abundant ester bonds, hydroxyl groups, and tertiary amine, which can undergo dynamic transesterification reactions (DTER) at high temperatures, leading to topological rearrangement of cross-linked networks. This results in an epoxy resin matrix with excellent mechanical properties, thermostability, and easy reprocessing, self-healing, and degradation at elevated temperatures. Moreover, the TGDOM-TTMA exhibits good stress relaxation properties due to the high concentrations of hydroxyl and tertiary amine. Additionally, we have found that carbon fibers can be completely recycled from CFRCs using ethanolamine via amidation reaction, with the recycled carbon fibers maintaining nearly 100% of the mechanical properties of the virgin samples. This study offers a sustainable and convenient strategy for designing readily recyclable and high-performance CFRCs, with important implications for the future of composite materials.

Optical spectroscopy study of damage in ion-irradiated 3C-SiC epilayers on a silicon substrate

Epitaxial cubic (100) 3C-SiC films on a (100) silicon wafer were irradiated at room temperature with 2.3-MeV Si+ or 3.0-MeV Kr+ ions up to a fluence of 1 × 1016 cm−2. The evolutions of the epilayer and the substrate were followed as a function of ion fluence by using micro-Raman spectroscopy, optical absorption, and diffuse reflectance spectroscopy in the UV-visible and near infrared range. Raman spectra evidence the amorphization of SiC films at an estimated dose of about 0.1 displacement per atom (dpa) for both ion irradiations. The narrow peaks of the Raman-allowed TO and LO modes of SiC and Si are recorded in the virgin sample, together with few peaks assigned to zone-edge modes of SiC arising from the intrinsic disorder in the strained films. Those crystal phonon peaks broaden or disappear with increasing fluence. The spectra finally exhibit broad extra peaks assigned to the formation of Si–Si and C–C wrong homonuclear bonds in the local order of the amorphous phase. The optical transmission and diffuse reflectance spectra feature interference fringe patterns in the SiC film that are smoothened out with irradiation due to the matching of refractive indices of the amorphous SiC film and Si substrate. The evolution of the refractive index of SiC and optical gap of Si are deduced from those spectra. The respective roles of ballistic effects and electronic excitations in the radiation damage of both SiC and Si are discussed for those two ions with about the same electronic stopping power and about one order-of-magnitude difference in nuclear stopping power. The damage is dominated by the nuclear collision processes and rather well correlated with the estimated irradiation dose in dpa. Optical spectra show that electronic excitations induce damage recovery of the amorphized substrate below the SiC/Si interface. Raman spectra and optical absorption/reflection spectra yield complementary pictures of the radiation damage.

CMAS deposition rate and sequence effects on cyclic life in gradient testing

Thermal barrier coating (TBC) resistance to varied CMAS deposition rates was experimentally assessed using a temperature gradient rig using a CMAS precursor spray. TBCs were composed of EB-PVD YSZ. Five different deposition rates were tested quantifying life versus deposition rate. A high deposition rate and low deposition rate were selected from those tests for sequence testing. For sequence effect testing CMAS deposition occurred at the initial rate until the expected half-life and then switched to the other rate until failure, in the order of high deposition rate first followed by low deposition rate and vice versa. The results suggest that the order of deposition rates can affect ultimate failure behavior. Specifically applying the CMAS at the low deposition rate extended the life of the sample by a nearly a factor of 2 compared to a virgin sample. At the high deposition rate, the CMAS infiltrated all the way to the bond coat past the estimated freeze line. Data showing the coating life versus CMAS deposition rate and the existence of sequence effects in CMAS dosing are fundamentally important to coating life prediction.

Experimental and numerical studies of the mechanical properties of nitrile-butadiene rubber exposed to gamma radiation

In this study, the effects of gamma radiation on the mechanical properties of nitrile-butadiene rubber (NBR) samples are examined employing experimental tensile and hardness tests. The NBR is exposed to different doses of gamma radiation (0, 30, 45, 60, 75 and 90 kGy) at room temperature. The obtained results indicate an improvement in the elastic behavior of NBR specimens and a diminution of their plastic behavior with the increase in the absorbed dose. The morphology properties of pristine and irradiated NBR were evaluated by scanning electron microscopy (SEM). A numerical simulation is performed by using five hyperelastic models included in Abaqus: Mooney Rivlin model, Ogden model, Yeoh model, Arruda-Boyce model and Neo-Hookean model. The input data utilized in the conducted simulation are taken from experimental tensile results. The validation of the five hyperelastic models shows that they are stable in tension for both virgin and irradiated samples. The stress-strain curves of both virgin and gamma-irradiated NBR rubber samples are presented and the coefficients of the hyperelastic strain energy function are calculated for all models. The comparison of the simulated results with the experimental measurements demonstrates that the Ogden model provides the best fitting curvature of the stress-strain curves for virgin and irradiated samples. It gives the lowest mean square error. The latter decreases with the rise of the absorbed gamma dose and it is in all cases less than 0.51%. Thus, this model is appropriately applied to better simulate the mechanical behavior of the unirradiated and irradiated NBR. Experimental and numerical results are promising for predicting the behavior of NBR rubber exposed to gamma radiation.

Investigation of charge dynamics in the corona‐aged silicone rubber alumina nanocomposite

AbstractThe effect of corona aging on the surface potential dynamics and charge trap characteristics of silicone rubber alumina nanocomposite are examined using surface potential decay measurement. The aging was carried out by exposing the specimens to corona stress generated by a high‐frequency AC multi needle‐plane electrode system. The results show that the addition of alumina filler increases the surface potential decay time and maximum trap energy. A reduction in trap depth is observed with the corona aging, and the addition of alumina filler limits the degradation and change in charge trap distribution. The results of an analysis of the space charge behavior of different nanocomposites and their comparison are presented. The space charge variation analysis was carried out under the applied electric field of 20 kV/mm at room temperature using the pulsed electro‐acoustic technique (PEA). Based on the results, the charge density, electric field, and charge trap distribution were deduced. It is concluded that the space charge concentration and enhancement in the electric field of the aged material increases with aging duration and it is maximum in the case of 60 min corona‐aged pure silicone rubber. Analysis of the recovery of the charge dynamics of the sample after corona discharges at the different time intervals shows that the recovery of trap distribution is faster for a virgin sample and slower for the sample with 5 wt% of alumina.