Light and elevated temperature induced degradation (LeTID) can induce high power losses in photovoltaic modules built from various types of silicon wafers. After the industry's rapid transition from ...Boron- to Gallium-doping, it is still unclear how the new dopant atom affects the degradation process and why it entails an apparently higher resistance to LeTID. We treat identically processed Gallium-doped Czochralski silicon wafers at 16 different conditions by screening temperature and minority charge carrier density (in the following “injection”). The illumination source is regulated to keep the injection constant at each condition. This method allows for an improved quantitative analysis of the LeTID kinetics based on effective lifetime measurements. Our results show that Gallium-doping shifts the equilibrium between the formation of LeTID defects and their temporary recovery (TR) to the latter, leading to a reduced degradation extent at temperatures up to 80 °C. The efficacy of this TR-induced LeTID suppression depends delicately on both temperature and injection which explains why Gallium-doped silicon appears to be LeTID-immune at high illumination intensities. By accounting for the influence of TR, we extract activation energies and injection exponents that relate to the dominant defect transitions separately, revealing a large discrepancy to effective values reported in literature. The increased accuracy of our kinetic parameters enhances the reliability of existing efficiency models. Finally, we find that a degradation as expected under field conditions can be probed at a 100-fold accelerated rate in the lab. By shining light on LeTID kinetics in Gallium-doped silicon, we explain the dopant atoms' influence on the degradation behavior, establish a basis for precise yield modelling and formulate guidelines for accelerated test protocols.
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•Gallium doping promotes temporary recovery induced LeTID suppression.•Probing LeTID at constant minority charge carrier density.•Improved determination of kinetic parameters for yield modelling.•100-fold accelerated LeTID testing method proposed.
•Exposure of PLA to PBS solution at elevated temperature led to accelerated hydrolysis degradation.•Hydrolysis-induced chain-scission and morphological damages reduced mechanical properties of ...PLA.•Sorption behavior including double mass increase and subsequent rapid mass loss was physically explained with diffusion-degradation mechanism•Correlations between mechanical property decay, sorption behavior, and the degree of hydrolysis degradation were clearly identified.
For the reliable use of polylactic acid (PLA) materials in the human body for supportive implants, an appropriate accelerated testing method to assess the lifetime of the PLA with an acceptable model that can describe the entire degradation process is required. In this study, accelerated degradation were conducted on the polylactic acid (PLA) exposed to the phosphate buffered saline (PBS) solution at elevated temperatures, 50 ℃, 60 ℃, and 70 ℃. The high level of accelerated degradation was achieved with elevating temperatures. The evolution of surface degradation degree with exposure time was quantified by measuring the molecular end group and modeled by a proper equation. In addition, it was demonstrated that hydrolysis-induced chain-scission is the governing mechanism in the accelerated degradation. The chemi-crystallization behavior with the hydrolysis degradation was also characterized. The morphological observation revealed that the microcracks and pits are pronouncing mechanisms of surface damage. The tensile properties were severely degraded after a certain period of induction time, depending on the temperature. The sorption kinetics were also assessed and explained during the entire lifetime until the severe mass loss, based on the diffusion with degradation behavior, as well as the evolution of the morphological damages. The formation of the surface degradation layer and subsequent damages are suspected to result in early saturation and secondary sorption behavior at the elevated temperature. Finally, the integrated correlations between the sorption behavior, amount of hydrolysis degradation, and mechanical property decrease were physically described, and accurate correspondences were obtained.
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The corrosion of steel in post-tensioned tendons has been associated with deficient grout materials containing high free sulfate ion concentrations. In a Florida bridge in 2011, tendon corrosion ...failures occurred for a prepackaged thixotropic grout that had developed material segregation. However, the available grout and corrosion testing prescribed in material specifications, such as grout bleed water testing, was not able to identify the propensity or modality for the grout deficiencies and the associated steel corrosion that was observed in the field. It was of interest to identify corrosion testing methods that could prescribe grout resistance to segregation-related deficiencies that can form by aberrations in construction. The objectives of the work presented here included (1) characterizing the development of physical and chemical grout deficiencies due to excess mix water and water volume displacement, (2) developing small scale test methodologies that identify deficient grout, and (3) developing test methodologies to identify steel corrosion in deficient grout. The inverted-tee test (INT) and a modified incline-tube (MIT) test were assessed and both were shown to be useful to identify the robustness of grout materials to adverse mixing conditions (such as overwatering and pre-hydration) by parameters such as sulfate content, moisture content, electrical resistance, and steel corrosion behavior. It was shown that the different grout products have widely different propensities for segregation and accumulation of sulfate ions but adverse grout mixing practices promoted the development of grout deficiencies, including the accumulation of sulfate ions. Corrosion potentials of steel < −300 mVCSE developed in the deficient grout with higher sulfate concentrations. Likewise, the corrosion current density showed generally high values of >0.1 μA/cm2 in the deficient grouts. The values produced from the test program here were consistent with historical data from earlier research that indicated corrosion conditions of steel in deficient grout with >0.7 mg/g sulfate, further verifying the adverse effects of elevated sulfate ion concentrations in the segregated grout.
When cement with mineral additions is employed, the carbonation resistance of mortar and concrete may be decreased. In this study, mortars containing mineral additions are exposed both to accelerated ...carbonation (1% and 4% CO2) and to natural carbonation. Additionally, concrete mixtures produced with different cements, water-to-cement ratios and paste volumes are exposed to natural carbonation. The comparison of the carbonation coefficients determined in the different exposure conditions indicates that mortar and concrete containing slag and microsilica underperform in the accelerated carbonation test compared to field conditions. The carbonation resistance in mortar and concrete is mainly governed by the CO2 buffer capacity per volume of cement paste. It can be expressed by the ratio between water added during production and the amount of reactive CaO present in the binder (w/CaOreactive) resulting in a novel parameter to assess carbonation resistance of mortar and concrete containing mineral additions.
•Coupled effects of temperature and water on viscoelastic properties of epoxy nanocomposites.•New methodology for constructing master curves from DMTA temperature scans.•Comparison of master curves ...and shift factors determined by different methods.•High reinforcement efficiency of nanocomposites maintained after hydrothermal aging.•Modelling time and temperature dependences of storage moduli.
Graphene-based fillers are promising candidates for improving the long-term dimensional stability of structural epoxy resins. The development of reliable accelerated test methods is critical to predicting their durability. Herein, the viscoelastic behaviour of the industrial-grade amine-epoxy and corresponding nanocomposites with modified graphene oxide (up to 1.72 wt%) is studied using dynamic mechanical thermal analysis (DMTA) in both temperature and frequency sweep modes. Time-temperature (TTSP), time-water ageing (TWSP), and coupled superposition principles (TTWSP) are used to predict the long-term storage moduli of nanocomposites. The temperature and water shift functions, determined by curve shifting, agree well with the Arrhenius calculations based on data from independent tests. A methodology for constructing master curves from DMTA temperature scans is developed, and the results are well correlated with the predictions made from traditional isothermal multifrequency test data. The temperature and time dependences of the storage moduli are well fitted by known relaxation models, and their parameters are analysed in terms of the filler and water-ageing effects. The results can be applied in the development of the material model and the prediction of macromechanical properties and the service lifetime, which are relevant to examined epoxy/GO composites and other water-sensitive glassy polymers.
•Degradation analysis of PV module after 20 years of exposure in the field.•A methodology designed for the accelerated UV stress test for different climatic conditions.•A procedure proposed to ...estimate the UV radiation for different climatic conditions.•Accelerated UV stress testing condition design for Indian climatic condition.
One of the significant environmental stress factors for degradation in the PV module is UV irradiation exposure in the field during its operational lifespan. In this work, degradation analysis of 20-years field-operated PV modules have been performed. The defects that occurred in those modules are due to the combined effect of environmental conditions like temperature, humidity, soiling, etc., along with UV irradiation. Based on the literature resources, efforts have been made to analyze the role of UV irradiation on the degradations that happened during 20 years of field operation of the PV modules. Average Pmax, Isc and Voc degradation are found to be 1.49 %/ year, 0.59 %/year and 0.29 %/year after 20 years of exposure, respectively. The effect of UV irradiation and temperature in indoor conditions has been analyzed for the 20 years of field-exposed PV modules. The effect of browning in the module is also studied in this research work at the cell level. Since the UV irradiation doses mentioned in IEC 61215 are not sufficient as compared to the amount of UV irradiation faced by the PV modules throughout their lifetime, therefore, a procedure is proposed to estimate the UV irradiation doses for different climatic conditions. The UV radiation data for India's climatic zones have been estimated and analyzed, to design accelerated UV stress test conditions using the procedure reported in this paper. The accelerated testing time equivalent for five years of UV irradiations on PV modules in the field is proposed to be around 40 days.
The library of redox-active organics that are potential candidates for electrochemical energy storage in flow batteries is exceedingly vast, necessitating high-throughput characterization of ...molecular lifetimes. Demonstrated extremely stable chemistries require accurate yet rapid cell cycling tests, a demand often frustrated by time-denominated capacity fade mechanisms. We have developed a high-throughput setup for elevated temperature cycling of redox flow batteries, providing a new dimension in characterization parameter space to explore. We utilize it to evaluate capacity fade rates of aqueous redox-active organic molecules, as functions of temperature. We demonstrate Arrhenius-like behavior in the temporal capacity fade rates of multiple flow battery electrolytes, permitting extrapolation to lower operating temperatures. Collectively, these results highlight the importance of accelerated decomposition protocols to expedite the screening process of candidate molecules for long lifetime flow batteries.
The degradation of cementitious composite materials under chemical sulfuric acid attack has been widely investigated. The agglomeration of a global database of test results is complicated by the ...differing test methodologies employed in each study. As a result it is difficult to isolate the influence of individual test parameters and hence directly compare the relative performance of different cementitious material. In this study the existing accelerated test methodologies including: brushing, wetting and drying cycling, and increased concentration of sulfuric acid are investigated such that the influence of test methodology on degradation rate and microstructural performance can be identified. This approach is taken with the view of developing a common methodology for indicating the susceptibility of a given cementitious material in an aggressive environment. Rather than comparing the performance of individual materials this work aims to compare the influence of test methodology when applied to different materials.
•The main focus is accelerated testing and degradation modeling of Li-ion batteries.•Discharge C-rate variable has been investigated for accelerating the battery testing.•The model is inspired by the ...physics of SEI layer formation.•The model utilizes historical degradation data for better generalization capability.•The non-linear mixed effect regression technique has been used to capture the battery-to-battery variations.
As Li-ion batteries are used in increasingly diverse applications, their performance and reliability become more critical. Reliability testing of Li-ion batteries involves battery capacity fade monitoring over repeated charging/discharging cycles. Cycling at a nominal charge/discharge current requires an extensive amount of time and resources, and hence a battery qualification process based on battery cycle testing may cause delays in time to market. Discharge C-rate variable can be used for accelerating Li-ion battery cycle testing. This paper develops an accelerated capacity fade model for Li-ion batteries under multiple C-rate loading conditions, to translate the performance and degradation of a battery population at accelerated C-rate conditions to normal C-rate conditions. A nonlinear mixed-effects regression modeling technique is used to take into account the variability of repeated capacity measurements on individual batteries in a population. The model is validated using the experimental data from two battery populations that have been fielded.
For battery electrodes, measured capacity decays as charge/discharge current is increased. Such rate-performance is usually characterised via galvanostatic charge-discharge measurements, experiments ...which are very slow, limiting the speed at which rate experiments can be completed. This is particularly limiting during mechanistic studies where many rate measurements are needed. Building on work by Heubner at al., we demonstrate chronoamperometry (CA) as a fast method for measuring capacity-rate curves with hundreds of data points down to C-rates below 0.01C. While Heubner et al. reported equations to convert current transients to capacity vs. C-rate curves, we modify these equations to give capacity as a function of charge/discharge rate, R. We use these expressions to obtain simple equations which can accurately fit data for both capacity vs. C-rate and capacity vs. R at normal rates. Interestingly, at high-rates, the curves obtained from CA deviate from the normal behaviour showing a new, previously unobserved, decay feature. We associate this feature with the very early part of the current transient where electronic motion dominates the current. Using a simple model, we show that the dependence of the high-rate time constant on electrode thickness can be linked to electrode conductivity.
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•Chronoamperometry can yield capacity-rate data much faster than standard methods.•The resultant data sets are much richer than standard capacity-rate data.•This work leads to an equation to fit capacity-rate data.
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