Mechanical Stress Tests Research Articles

Comparison of Commercial Collagen and Marine Collagen: Efficiency and Effects on the Formation of EDC/NHS-Crosslinked Membranes

AbstractThis study investigates the extraction and characterisation of collagen derived from fish skin and scales, the collagens obtained were used to produce membranes which were subsequently cross-linked by EDC/NHS. A comprehensive investigation of their microstructure, composition, mechanical properties, swelling, degradation, thermal properties and a 24 h cell viability test was carried out. The results showed that the yields of collagen from skin and fish scales were 25.14 ± 2.90 and 29.26 ± 2.53%, respectively. Mechanical stress tests showed that membranes made from fish skin collagen and commercial collagen had comparable load-bearing capacities before failure. The Young’s modulus of the membranes was 9.45 MPa ± 1.77 for commercial collagen, 5.76 MPa ± 0.74 for fish skin collagen and 2.43 MPa ± 0.78 for fish scale collagen, this similarity was maintained in degradation tests and at denaturation temperature (75 °C).These results demonstrate the viability of collagen derived from marine by-products as an effective and efficient alternative for biomedical and tissue engineering applications.

Acceleration of Service Life Testing by Using Weibull Distribution on Fiber Optical Connectors

The service life assessment of previous fatigue stress has a fundamental role in estimating the reliability of products like fiber optical connectors, and should replicate use in severe environments in telecommunications systems. However, the vibration prediction models used in the literature present limitations in vibration life prediction. In this paper, we propose using the insertion loss fatigue life and including it in the Weibull distribution to determine the Weibull parameters ƞ and β to evaluate fiber optic connector reliability R(t) under environmental and mechanical testing stress. We analyzed the failure data of a standard telecommunication fiber optical connector under a program of service life stress testing against that of a fiber optical connector under only mechanical vibration stress testing. The fiber connectors were monitored during the vibration testing to review the transient change of the optical signal. Their results showed that the reliability of the fiber connectors submitted to the service life program was Rt=0.694, while that of the fiber connectors submitted to mechanical vibration only was Rt=0.970. In addition, the analysis showed that the service life testing consumed 70.2% of the product’s lifetime. We present in Numerical Validation the steps to determine the acceleration factors of the vibration test developed.

Simulation of fuel cell membrane durability under vehicle operation

In this work, a statistical fuel cell chemo-mechanical membrane degradation model is developed based on the ionomer fibrillar morphology as a framework for use-level membrane durability prediction for fuel cell electric vehicles. The mechanical and chemical degradation modes are separately calibrated with pressure differential-accelerated mechanical stress tests and accelerated membrane durability tests, respectively. Finite element simulations are used to estimate the initial stress distribution across the membrane, while the genetic algorithm with the least squares method is employed to calibrate the model parameters with experimental results, thus reaching a good agreement. Next, the validated model is utilized for a case study of fuel cell electric transit bus operation in the city of Victoria, B.C., Canada. The initial cell voltage profile is obtained using a dynamic fuel cell power system model applied to the transit bus drive cycle recorded during real-world operation. According to the model predictions, reducing the stack nominal power from 396 to 132 kW results in a 148% membrane lifetime enhancement, whereas decreasing the cell temperature from 90 to 70°C results in an 11-fold increase in the membrane lifetime under simulated transit bus operation, thereby exceeding the 25,000-h lifetime target for this application.

In-situ pressure differential-accelerated mechanical fatigue testing and modeling of a reinforced fuel cell membrane

Modern polymer electrolyte fuel cells typically use reinforced membranes for improved mechanical durability. Due to costly experimentation, however, the fatigue properties of these membranes remain poorly understood. In this work, we employ the G'Sell-Jonas constitutive material model to investigate the mechanical fatigue response of a reinforced membrane under various environmental conditions in accelerated in-situ test settings. For fatigue evaluation, we utilize a novel pressure differential-accelerated mechanical stress test (ΔP-AMST) of shorter duration (<1 week) than previous AMSTs. The S–N curves constructed from experimental results at variable ΔP and temperature demonstrate inverse linear relationship between logarithmic fatigue lifetime and nominal stress, with greatly enhanced (∼10x) lifetime at reduced temperature. According to the results, a finite element-based fatigue model is developed and validated, which considers the impacts of hygrothermal fluctuations and strain rates. The model shows peak tensile stress during the dry phase at the center of the test section, which is consistent with the expected scenario for in-situ fuel cell membrane fatigue. Through this novel accelerated test and its modeling, it becomes possible to assess the fatigue lifetime of reinforced membranes under variable temperatures, humidity swings, pressure differentials, and swelling properties, in much shorter time than with standard protocols.

Don’t shake it! Mechanical stress testing of mRNA-lipid nanoparticles

Shaking stress studies are typically performed during formulation development to test the liability of a drug product towards interfacial stress occurring during transport, especially if a liquid formulation is desired. We evaluated various shaking procedures using a polyA-surrogate solution and verified our findings by eGFP-LNP cell-expression experiments. Shaking on an orbital shaker in vertical and horizontal orientations at increasing speeds from 300 to 600 rpm resulted in decreasing levels of encapsulated nucleic acid content, larger LNP sizes, and decreasing PDI. We report that vertical and horizontal shaking of both polyA- and eGFP-LNPs led to white deposits on the inner glass vial surface, depending on time, rpm, and temperature. Increasing the fill volume/smaller headspace (0.3 versus 0.9 mL fill) did not mitigate this phenomenon in the studied configuration, and the use of hydrophobic primary packaging even accelerated the formation of white deposits. In contrast, we demonstrated that a lyophilized polyA-LNP dosage form was less susceptible to shaking and maintained cake integrity and product properties. Multiple vortexing steps resulted in an increase in LNP size, PDI, and a decrease in encapsulated polyA content. We conclude that shaking experiments of nucleic acid-loaded LNPs in their final configuration at intended transport conditions need to be considered during technical development.

Development of Chemical and Mechanical Acceleration Stress Test Method for PEMFC Polymer Membranes

Development of Chemical and Mechanical Acceleration Stress Test Method for PEMFC Polymer Membranes

Computer-aided designed 3D-printed polymeric scaffolds for personalized reconstruction of maxillary and mandibular defects: a proof-of-concept study

PurposeTo investigate the potential reconstruction of complex maxillofacial defects using computer-aided design 3D-printed polymeric scaffolds by defining the production process, simulating the surgical procedure, and explore the feasibility and reproducibility of the whole algorithm.MethodsThis a preclinical study to investigate feasibility, reproducibility and efficacy of the reconstruction algorithm proposed. It encompassed 3 phases: (1) scaffold production (CAD and 3D-printing in polylactic acid); (2) surgical simulation on cadaver heads (navigation-guided osteotomies and scaffold fixation); (3) assessment of reconstruction (bone and occlusal morphological conformance, symmetry, and mechanical stress tests).ResultsSix cadaver heads were dissected. Six types of defects (3 mandibular and 3 maxillary) with different degree of complexity were tested. In all case the reconstruction algorithm could be successfully completed. Bone morphological conformance was optimal while the occlusal one was slightly higher. Mechanical stress tests were good (mean value, 318.6 and 286.4 N for maxillary and mandibular defects, respectively).ConclusionsOur reconstructive algorithm was feasible and reproducible in a preclinical setting. Functional and aesthetic outcomes were satisfactory independently of the complexity of the defect.

In-Situ Fatigue Lifetime Modeling of a Reinforced Membrane by Projecting Critical Accumulated Plastic Dissipation Energy from Pressure Differential-Accelerated Mechanical Stress Tests

Polymer electrolyte fuel cells (PEFCs) have become increasingly appealing over internal combustion engines because of their high efficiency, low operating temperature, and zero CO2 emissions. Nevertheless, the transportation sector necessitates high durability and reliability, which may be difficult to predict for emerging technologies. A crucial aspect is the ability of the thin membranes that conduct ions in PEFCs to endure the chemical and mechanical stresses that arise during dynamic operations. For mechanical fatigue, temperature and relative humidity (RH) fluctuations induce dynamic stresses that lead to the formation and propagation of microcracks in the membrane. As the membrane is confined by other components in the membrane-electrode assembly (MEA), changes in temperature and humidity can generate thermal and swelling strains in the membrane, leading to dynamic and residual stresses [1].The US Department of Energy sets a passing criterion of 20,000 RH cycles for mechanical fatigue assessment. However, many modern reinforced membranes have already passed this threshold without failing [2]. Therefore, Ref [3] introduced a pressure differential between the cathode and anode sides of the membrane at 80°C to speed up the testing. In this research, the pressure differential-accelerated mechanical stress test (ΔP-AMST) method was applied to a reinforced membrane at two different temperatures and with four times faster humidity cycles in a wider range of ΔPs. This objective is to project the mechanical fatigue lifetime from the ΔP-AMST to the membrane under its in-situ conditions by using the critical accumulated plastic dissipation energy (CAPDE) in ΔP-AMSTs and the plastic dissipation energy (PDE) during a single cycle of humidity that the membrane experiences under complete fuel cell settings. The first step involves performing a series of ∆P-AMST, and in the second step, a finite element model (FEM) for ∆P-AMST based on the developed constitutive model for the tensile tests that covers temperature, humidity, and swelling strain impacts is built, and therefore its S-N curve is extracted. Next, a FEM model for a complete fuel cell is created, and the mechanical fatigue life is estimated by dividing the CAPDE in ∆P-AMST by the PDE in one cycle of the in-situ modeled membrane by considering amplitude stress as a link between the full fuel cell model and ∆P-AMST, as illustrated in Figure 1 and verified by previous studies [4,5]. In the final step, we will also discuss opportunities to integrate the present mechanical fatigue model with a chemical degradation module to simulate its impacts on fatigue lifetime. This integration includes the two main effects of chemical degradation, which are reflected in the thickness of the reinforced membrane [6] and its updated CAPDE [7]. Acknowledgments The authors gratefully acknowledge AVL Fuel Cell Canada and Mitacs for supporting this project. The authors also thank Roger Penn and Amy Nelson for technical advice.

Simulation of Proton Exchange Membrane Durability Under Fuel Cell Vehicle Operation – a Fundamental Study

Proton exchange membrane fuel cells (PEMFCs) have been proven to be a promising candidate to replace combustion engines due to their zero-carbon emission and high power densities. Despite the recent success in PEMFC commercialization, a number of challenges such as high cost and difficulty in lifetime estimation still hinder their further development. PEMFC durability tests require a long time to complete; therefore, durability predicting models are increasingly important as a supporting tool for further development and implementation.Fuel cell membranes undergo a variety of dynamic conditions during regular operation such as varying temperature, humidity, current density, and cell potential. The cyclic variations of humidity and temperature (hygrothermal variations) during dynamic operation lead to swelling and contraction of the membrane. The fluctuating stress caused by the continuous expansion and contraction of the membrane when confined within the cell leads to mechanical membrane degradation. The recurring swelling and contraction of the membrane which stem from water content changes in the membrane cause fatigue and creep and ultimately the formation of pinholes, cracks, and tears [1-2].Chemical membrane degradation occurs when radicals such as hydroxyl and hydroperoxyl are formed and attack the membrane and is escalated by high operating cell potentials. Chemical degradation results in decay in the ionomer chemical structure, membrane thinning, increased gas crossover, and potential electrode shorting [3]. The outcomes of such degradation are aggravated in the presence of mechanical degradation [4]. Hence, the study of combined chemo-mechanical membrane degradation is crucial for overall fuel cell membrane durability [5].The objective of the present work is to establish a predictive membrane lifetime simulation tool designed to represent chemo-mechanical membrane degradation under various operating conditions for automotive fuel cell applications. To this end, a statistical model is developed based on the membrane fibrillar morphology presented by El Hannach et al. [6-7]. A network of fibre bundles is generated to represent the membrane structure where any bundle is assumed as the primary building block of the membrane [8-10]. Each bundle contains an aggregate of backbone chains with typical mechanical and chemical properties. Mechanical and chemical degradation rates are separately studied and coupled in the model. The thermally activated breaking rate of each fibre is calculated to evaluate the mechanical degradation rate at any given time. In order to calibrate the mechanical degradation rate in the model, the mechanical degradation of a reinforced membrane under cross-pressure accelerated mechanical stress tests ( p-AMST) [11] is investigated to obtain the membrane fatigue lifetime for a variety of cross pressures and temperatures. Then, the genetic algorithm is successfully applied to optimize the experimental parameters considering the least squares method. Furthermore, accelerated membrane durability tests (AMDT) carried out by Macauley et al. [12] are considered to calibrate the chemical degradation rate parameter in the model. Finally, the fully calibrated model is used to estimate the membrane lifetime under realistic fuel cell vehicle operating conditions (e.g. drive cycles).Fuel cell components experience different degradation mechanisms. In this regard, this modelling framework on the membrane lifetime can be used in conjunction with other methodologies on the cathode catalyst lifetime such as [13-14] to scrutinize the key factors and their impacts on fuel cell durability under similar operating conditions. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Research Chairs, and Simon Fraser University Community Trust Endowment Fund.

Embryonic development and sensitive stages of Atlantic salmon (Salmo salar) eggs

The normal embryonic development of Atlantic salmon eggs was described and illustrated from fertilization to hatching. Additionally, sensitivity based on acute mortality 7 days after mechanical stress exposure was recorded from fertilization to hatching. A mechanical shock device was used for the mechanical stress test, where eggs were dropped from different predetermined heights, and the heights corresponding to 10% and 50% mortality were estimated (LD10 and LD50). The sensitivity was observed to increase from fertilization until gastrulation, where maximum sensitivity occurred, before decreasing throughout late gastrulation and until the “eyed” stage where no mortality was observed at any height. This information may be important for hatchery managers in the decision-making process regarding optimal handling routines.

Ultra-thin polymer foil cryogenic window for antiproton deceleration and storage.

We present the design and characterization of a cryogenic window based on an ultra-thin aluminized biaxially oriented polyethylene terephthalate foil at T < 10 K, which can withstand a pressure difference larger than 1 bar at a leak rate <1×10-9 mbar l/s. Its thickness of ∼1.7 μm makes it transparent to various types of particles over a broad energy range. To optimize the transfer of 100keV antiprotons through the window, we tested the degrading properties of different aluminum coated polymer foils of thicknesses between 900 and 2160nm, concluding that 1760nm foil decelerates antiprotons to an average energy of 5keV. We have also explicitly studied the permeation as a function of coating thickness and temperature and have performed extensive thermal and mechanical endurance and stress tests. Our final design integrated into the experiment has an effective open surface consisting of seven holes with a diameter of 1mm and will transmit up to 2.5% of the injected 100keV antiproton beam delivered by the Antiproton Decelerator and Extra Low ENergy Antiproton ring facility of CERN.

Effect of Acid and Thermo-Mechanical Attacks on Compressive Strength of Geopolymer Mortar with Different Eco-Friendly Materials

This research examined how changing the ratios of certain substances affected the strength and durability of a specific type of building material when exposed to acid and heat. This study used various combinations of zeolite, metakaolin, slag, and Portland cement as primary materials. It also used different amounts of potassium hydroxide (KOH) to make the geopolymer mortar. The concentrations of KOH used were 8 M, 12 M, 14 M, and 16 M. The cement-based material had the highest water absorption. A total of 240 tests were conducted, including 20 samples for each mix design tested at curing times of 7, 14, 21, 28, and 90 days. The results showed that the samples made with slag base material and 8 M mixing design had the highest average compressive strength at 28 and 90 days in the acidic environment test, and the zeolite and metakaolin base material samples had the highest corrosion and weight loss, possibly due to their high specific surface and aluminosilicate origin. The samples made with slag-based material had better resistance and the highest average compressive strength in the 300 °C and 500 °C thermo-mechanical tests. The lowest average compressive strength in the thermal and mechanical stress test was related to the samples made with a metakaolin base material. The tests performed on the samples made with slag base material had better compressive strength than the three other base materials in the acid and heat tests. The zeolite-based mortar lost the most weight under 30% acidic sulfuric water. The findings suggest that changes in the molar ratios of alkaline activators can significantly affect the durability properties and strength of geopolymer mortar, and the slag-based material with an 8 M mixing design had the best performance; also, SEM analysis verified this mechanism.

Improvement of the Mechanical Properties of Mortars Manufactured with Partial Substitution of Portland Cement by Kaolinitic Clays

Presently, the search for urgent solutions to mitigate climate change has become a global priority. One of the most important challenges is the characterization, standardization, and technology of sustainable natural raw materials, which will significantly improve the quality of common types of cement, the production process of which emits large amounts of greenhouse gases into the atmosphere. This work is focused on the study of natural kaolinitic clays (NKC) from the eastern part of the Iberian Peninsula and its main objective is to define and normalize their properties as natural pozzolanic materials. This research consists of an initial study to determine the morphological and chemical properties using SEM and XRF. Furthermore, the physical properties of the samples were studied, such as thermic treatment (TT), Blane particle finesse (BPF), real density (RD) and apparent density (AD), porosity (P), volume stability (VS) and start and final setting time (SFST). On the other hand, technological analyses were carried out as follows: chemical analysis (CATQ), pozzolanicity (CAP), mechanical compression strength tests at 7, 28, and 90 days (MCST) as well as the ultrasonic pulse velocity (UPV). XRF results indicated that the SiO2 content (49.9–51.0%) of kaolinitic clay in its natural state (NKC) increases to 57.41 and 58.10%, respectively, when calcined (CKC). The chemical analysis of pozzolanicity established that the NKC does not show pozzolanic activity during the first 8 and 15 days; however, once calcinated, its pozzolanic reactivity increases substantially. On the other hand, the results of the mechanical stress tests (MCST) indicate an exponential increase in mechanical resistance from 7 to 90 days, which is higher in mortars made with CKC; similarly, and according to the results of the calculation of the Resistant Activity Index (RAI), it shows that the substitutions of Portland cement (PC) by NKC are effective between the ranges of 10 and 25%, while in the case of the substitution of PC by CKC, all formulations (10, 25 and 40%) are effective. This research establishes that the kaolinitic clays of the east of the Iberian Peninsula can be considered quality pozzolanic materials, capable of partially replacing Portland cement. The results presented here could be used as guidelines for the understanding and application of natural pozzolanic materials contributing to the improvement of types of cement, mortars, and concretes, which would positively affect the quality and preservation of the environment as well as the sustainability of eco-efficient construction materials.

Resistance evaluation of electrical insulating polymer materials used in flexible cables to operational impact

The article presents the test results of polymer material properties taking into account the possibility of their application for flexible cables insulation. The main types of cable constructions and their operation features are considered. Existing test determination methods of insulation resistance to thermal, mechanical, electrical and environmental conditions are analyzed. Requirements for laboratory equipment and test conditions are given. Evaluation criteria of test results are noted. Experimental evaluation was carried out for change degree in the properties of the main types of electrical insulation materials used currently during the flexible cable production: polyvinyl chloride compound (PVC), rubber, ethylene propylene rubber (EPR), thermoplastic elastomer (TPE), fluoropolymer. Tests were carried out under the influence of high and low temperatures, aggressive environments, ozone, mechanical loads. The main processes that determine the changes in electrophysical, physical and mechanical properties of the studied materials are described. Resistance of EPR, TPE and fluoropolymer insulation to a wide range of temperatures, mechanical loads, diesel fuel and transformer oil are shown. An increased resistance of EPR to ozone was also noted. Rubber and PVC compound did not pass the tests under the influence of low and high temperatures, showed "poor" resistance to aggressive environments, but passed the mechanical stress tests. Recommendations on tests and application of polymer insulation taking into account the specifics of flexible cables working are presented.

Effect of current density on membrane degradation under the combined chemical and mechanical stress test in the PEMFCs

This study elucidates the effects of current density on membrane degradation under combined mechanical and chemical stress tests. Relative humidity (RH) cycling tests using hydrogen gas and air are conducted on a polymer electrolyte membrane fuel cell based membrane NRE211 at the open circuit voltage (OCV), 0.05 and 0.3 Acm−2 conditions. The different current density conditions result in different in-plane membrane stresses and H2O2 formation rates during the test. After every 200 RH cycles, membrane integrity is assessed via the hydrogen crossover rate and OCV. Furthermore, catalytic combustion is analyzed during OCV measurement using a thermal imaging method employing high-transmittance glass at the cathode side. The membrane failed after 1600, 1800, and 2200 RH cycles under the OCV condition, 0.05 of 0.3 Acm−2, respectively. The vigorous membrane degradation under OCV conditions can be attributed to higher mechanical stress and H2O2 formation rate. Hotspots created owing to the combustion between the crossover hydrogen and air were successfully captured, with a maximum temperature rise ranging from 15 to 16 °C compared with a given cell temperature of 80 °C. Moreover, a post-mortem analysis (SEM imaging) revealed the presence of pinholes, through-membrane cracks, and membrane thinning at the hotspot locations.

Stability and Application Properties of Surfactant-Free Cosmetic Emulsions: An Instrumental Approach to Evaluate Their Potential

Technological innovation in the cosmetic field must necessarily consider not only the safety and efficacy requirements but also the growing attention to environmental issues and the need for sensory pleasure during application to satisfy the consumers’ expectations. This work aimed to formulate an oil-in-water fluid emulsion stabilized by the combination of organic and inorganic powders, namely Zea mays starch and zinc oxide associated at different ratios in presence of a polysaccharidic rheological modifier. After verifying the physical stability of the prototypes with a mechanical stress test in a centrifuge, the rheological analyses were conducted in continuous and oscillatory flow conditions, and the immersion/de-immersion test, conducted using a texture analyzer, allowed identifying the system with the viscoelastic characteristics and the parameters of textures, such as firmness, consistency, and adhesiveness, more suitable for the formulation of skin-care products with low viscosity and high spreadability. Finally, we studied the compatibility of the powders with sunscreen filters and pigments, to optimize the systems and assess their potential use in finished products.

Oxygen Plasma-Mediated Microstructured Hydrocarbon Membrane for Improving Interface Adhesion and Mass Transport in Polymer Electrolyte Fuel Cells.

Developing a method for fabricating high-efficient and low-cost fuel cells is imperative for commercializing polymer electrolyte membrane (PEM) fuel cells (FCs). This study introduces a mechanical and chemical modification technique using the oxygen plasma irradiation process for hydrocarbon-based (HC) PEM. The oxygen functional groups were introduced on the HC-PEM surface through the plasma process in the controlled area, and microsized structures were formed. The modified membrane was incorporated with plasma-treated electrodes, improving the adhesive force between the HC-PEM and the electrode. The decal transfer was enabled at low temperatures and pressures, and the interfacial resistance in the membrane-electrode assembly (MEA) was reduced. Furthermore, the micropillar structured electrode configuration significantly reduced the oxygen transport resistance in the MEA. Various diagnostic techniques were conducted to find out the effects of the membrane surface modification, interface adhesion, and mass transport, such as physical characterizations, mechanical stress tests, and diverse electrochemical measurements.

Cell shape anisotropy contributes to self-organized feather pattern fidelity in birds.

Developing tissues can self-organize into a variety of patterned structures through the stabilization of stochastic fluctuations in their molecular and cellular properties. While molecular factors and cell dynamics contributing to self-organization have been identified in vivo, events channeling self-organized systems such that they achieve stable pattern outcomes remain unknown. Here, we described natural variation in the fidelity of self-organized arrays formed by feather follicle precursors in bird embryos. By surveying skin cells prior to and during tissue self-organization and performing species-specific ex vivo drug treatments and mechanical stress tests, we demonstrated that pattern fidelity depends on the initial amplitude of cell anisotropy in regions of the developing dermis competent to produce a pattern. Using live imaging, we showed that cell shape anisotropy is associated with a limited increase in cell motility for sharp and precisely located primordia formation, and thus, proper pattern geometry. These results evidence a mechanism through which initial tissue properties ensure stability in self-organization and thus, reproducible pattern production.

Optimization and formulation of Conjugated Linoleic Acid (CLA) oil-in-water beverage emulsion stabilized in whey protein isolate using response surface methodology

The present work was carried out to develop and optimize the functional lipid Conjugated Linoleic Acid (CLA) as beverage emulsion stabilized with whey protein isolate using response surface methodology. The effect of three independent variables Conjugated Linoleic Acid (CLA; 5–15% (v/v)), whey protein isolate (WPI; 4–6% (w/v)) and pressure cycle (1–3) on dependent variables creaming index (CI%) and emulsion stability (ES%) were studied. Box Behnken Design (BBD) generated 16 factorial runs with 4 center points. Stress tests such as freeze-thaw test, mechanical stress test, and particle size characterization were analyzed. Under the optimized conditions, CLA beverage emulsion with 10% (v/v) CLA, 6% (w/v) WPI with 3 pressure cycle (T8) have 98% CI and ES 30th day of refrigerated storage was considered as an optimized emulsion for incorporation into dairy products. In conclusion, it is possible to utilize whey protein isolate as a sole emulsifier in formulation of CLA beverage emulsion using Response Surface Methodology-Box Behnken Design (RSM-BBD) method with reproducible results.

Investigation of in-situ catalytic combustion in polymer-electrolyte-membrane fuel cell during combined chemical and mechanical stress test

This study is focused on elucidating the catalytic combustion phenomenon in proton-exchange-membrane fuel cells. A visualization cell and an infrared (IR) camera are used to capture the thermal behavior under combined chemical and mechanical accelerated stress conditions in situ. Catalyst coated membrane (CCM) embedded in the cell is subjected to a relative humidity (RH) cycling test under open-circuit voltage (OCV) conditions at atmospheric pressure and at a cell temperature of 80 °C. The temperature distribution on the gas diffusion layer surface at the cathode is captured through a high-transmittance glass window (ZnS window). Continuous IR imaging revealed a hot spot at ca. 500 RH cycles, suggesting the existence of a pinhole in the degraded CCM and the occurrence of catalytic combustion there. The occurrence of the hot spot coincides with the time at which the electrochemical indicators detect membrane failure, i.e., hydrogen crossover rate, OCV. Furthermore, a post mortem analysis revealed a 105-μm diameter pinhole, the position of which matched that of the hot spot. This pinhole is responsible for the rapid increase in the hydrogen crossover rate as well as the significant decrease in the OCV at 500 RH cycles until the end of the durability test.