Derived Diffusion Coefficients Research Articles

Obsidian hydration dating by infrared transmission spectroscopy

AbstractThe obsidian dating method converts the quantity of diffused molecular water within a near‐surface hydration layer to elapsed time using an experimentally derived diffusion coefficient predicted from the structural water content of the glass. Infrared spectroscopic transmission measurements on transparent archaeological samples record vibrational responses of water bands in the near‐infrared region, permitting determination of structural water content (OH), and the amount of diffused ambient water (H2O). In this application, the H2O water band at 5200 cm−1 is measured directly. The accuracy of the approach is assessed by an evaluation of the precision of each contributing variable. The new protocol is evaluated using obsidian artifacts from radiocarbon‐dated deposits at Salamanca Cave in Argentina.

In situ high-temperature transmission electron microscopy investigation of dynamic element migration for Sm-Co-Fe-Cu-Zr sintered magnets

The investigation delved into the dynamic migration of elements and the evolution of interface structures within the Sm(CobalFe0.09Cu0.09Zr0.03)7.2 magnet as temperature increased, employing high-temperature transmission electron microscopy. Notably, the Cu distribution exhibited temperature susceptibility. Elevating the temperature from room temperature (RT) to 400 °C led to a notable expansion in the distribution width of Cu, ranging from 28.5 to 50.8 nm. Simultaneously, the average Cu content at the cell boundaries decreased from 14.4 to 11.6 at.%. According to the high-temperature in-situ experimental results of the transmission electron microscopy thin-film samples, the derived diffusion coefficients, D300°Cand D400°C, were determined as 0.0525 nm2/s and 1.414 nm2/s, respectively. The significantly higher D400°C compared to D300°C underscores the considerable influence of temperature on Cu element diffusion behavior. The simulation results demonstrate that the trend of magnetic properties variation at different temperatures closely aligns with the observed trend. Subsequent calculation of the temperature coefficient of intrinsic coercivity (β) reveals that |β300–400°C| is notably higher than |βRT-300°C|. This suggests a substantial impact of Cu diffusion-induced deterioration on the β. Moreover, micromagnetic simulation results delineated the reverse magnetization process for magnets at varying temperatures, revealing that the presence of the Cu diffusion region diminished the pinning effect of the cell boundary phase. Furthermore, a wider Cu diffusion region facilitated easier magnetic moment reversal at the cell boundary phase, resulting in a marked deterioration of intrinsic coercivity. This elucidates that the formation of the Cu diffusion region stands as one of the primary reasons for the sharp decline in magnetic properties of Sm2Co17-type magnets under high-temperature conditions.

International Comparative Analysis of Advanced Diagnostic Imaging Equipment Demand Characteristics Using the Bass Diffusion Model

Objectives: This paper proposed the direction of future supply and demand management policies through demand prediction and demand characteristics analysis of advanced diagnostic imaging equipment using new medical technology.Methods: This study used the Bass Diffusion Model to analyze demand characteristics for advanced diagnostic imaging equipment. Derived diffusion coefficients were applied for medium to long-term demand predictions (2021-2050). Parameter estimation employed non-linear regression analysis (SPSS 27.0). Demand characteristics were further analyzed using the ratio of the Bass model’s innovation to imitation coefficients for each country and device.Results: Comparing the imitation coefficients (<i>q/p</i> ratio) for computed tomography (CT) and magnetic resonance imaging (MRI) among South Korea, the United States, and Japan, South Korea has the highest <i>q/p</i> ratio for both CT and MRI. This implies that the influence of opinion leaders and group pressure is relatively more significant in South Korea, particularly in CT purchases. In the demand prediction results, South Korea’s <i>q/p</i> ratio for CT and MRI is notably larger, suggesting that institutional pressures and collective decision-making, rather than individual clinical decisions, play a significant role in the purchase of advanced diagnostic imaging Equipment. The <i>q/p</i> ratio for advanced diagnostic imaging Equipment in South Korea is higher than in other countries, reflecting a large power distance in the adoption of these technologies.Conclusions: This study utilizes the Bass Diffusion Model to predict the demand for advanced diagnostic imaging equipment in South Korea, Japan, and the United States. Findings highlight that imitation, not innovation, is the main driver of diffusion, with South Korea showing a faster adoption rate for CT and MRI. The study identifies factors influencing diffusion in South Korea, noting the impact of the quantity system on CT and the absence of influence on MRI. CT diffusion is positively linked to the quantity-based payment system, while MRI remains unaffected.

ESTIMATING THE SPREADING RATES OF HAZARDOUS MATERIALS ON UNMODIFIED CELLULOSE FILTER PAPER: IMPLICATIONS ON RISK ASSESSMENT OF TRANSPORTING HAZARDOUS MATERIALS

The transportation of hazardous materials (HAZMATs) poses an inherent threat to human health and the environment. To comprehensively grasp the environmental impacts of HAZMAT accidents, it is vital to estimate their potential spread. Although numerous studies have addressed associated risks, there is a need to distinguish the spread area of key HAZMATs. We conducted diffusion tests on an unmodified alpha-cellulose filter paper for four HAZMAT compounds: methanol, ethanol, hydrochloric acid, and sodium hydroxide, at set temperatures. We employed an analytical solution based on an amplitude diffusing mass model to compute the diffusion coefficients for each analyte with respect to temperature. Fick's second law was applied using the derived diffusion coefficient values to determine the maximum spread. A finite element model with a Crank-Nicolson formulation was used to assess the consistency between analytical and numerical models for each analyte. Two-way analysis of variance (ANOVA) and the Kolmogorov-Smirnov (K-S) tests were utilized to validate the model. We can adduce that even HAZMATs with similar functional groups may have different exposure pathway risks with temperature as a key factor. Key parameters, such as spread area, diffusion time, porosity, temperature, and retention factors, may be important spill-site characterization parameters.

Unveiling moisture transport mechanisms in cellulosic materials: Vapor vs. bound water.

Natural textiles, hair, paper, wool, or bio-based walls possess the remarkable ability to store humidity from sweat or the environment through "bound water" absorption within nanopores, constituting up to 30% of their dry mass. The knowledge of the induced water transfers is pivotal for advancing industrial processes and sustainable practices in various fields such as wood drying, paper production and use, moisture transfers in clothes or hair, humidity regulation of bio-based construction materials, etc. However, the transport and storage mechanisms of this moisture remain poorly understood, with modeling often relying on an assumption of dominant vapor transport with an unknown diffusion coefficient. Our research addresses this knowledge gap, demonstrating the pivotal role of bound water transport within interconnected fiber networks. Notably, at low porosity, bound water diffusion dominates over vapor diffusion. By isolating diffusion processes and deriving diffusion coefficients through rigorous experimentation, we establish a comprehensive model for moisture transfer. Strikingly, our model accurately predicts the evolution of bound water's spatial distribution for a wide range of sample porosities, as verified through magnetic resonance imaging. Showing that bound water transport can be dominant over vapor transport, this work offers a change of paradigm and unprecedented control over humidity-related processes.

Determination of Ce3+, Co2+, Mn2+ and Fe2+ diffusion coefficients in Nafion® membrane

Concentration gradient diffusion coefficients for Ce3+, Co2+, Mn2+ and Fe2+ cations are determined in Nafion®211 membranes over a wide range of environmental conditions. Measurements are made using finite-width cation-rich bands introduced to NR211 via a hot-pressing procedure. A robust method of accurate diffusion coefficient determination of the finite-width deposits is developed using a Fick's second law of diffusion solution for one-dimensional systems. The transition metal dications are found to have nearly identical NR211 diffusion coefficients under water saturated conditions over the 22–80 °C range. The powerful chemical mitigant, Ce3+, is about one-half as diffusive as the dications under identical conditions. Derived diffusion coefficients for Ce3+ and Co2+ are found to be independent of initial cation concentration over the range of 12.5–70 mol% exchange level. The diffusion behavior of Ce3+ in 80 °C liquid water and saturated water vapor is identical. The diffusion coefficients of Ce3+ are shown to have a strong dependence on membrane hydration level varying by a factor of more than 30 over the range of 95 to 40% RH. The implications of these new diffusion findings are applied to a discussion of potential guidelines for the development of highly durable fuel cell systems, which employ mobile metal cations as lifetime-extending redox stabilizers.

Simulation of Solar Wind Turbulence near Corotating Interaction Regions: Superposed Epoch Analysis of Simulations and Observations

The effect of the turbulence that is associated with solar wind corotating interaction regions (CIRs) on transport of galactic cosmic rays remains an outstanding problem in space science. Observations show that the intensities of the plasma and magnetic fluctuations are enhanced within a CIR. The velocity shear layer between the slow and fast wind embedded in a CIR is thought to be responsible for this enhancement in turbulent energy. We perform physics-based magnetohydrodynamic simulations of the plasma background and turbulent fluctuations in the solar wind dominated by CIRs for radial distances between 0.3 and 5 au. A simple but effective approach is used to incorporate the inner boundary conditions for the solar wind and magnetic field for the periods 2007–2008 and 2017–2018. Legendre coefficients at the source surface obtained from the Wilcox Solar Observatory library are utilized for dynamic reconstructions of the current sheet and the fast and slow streams at the inner boundary. The dynamic inner boundary enables our simulations to generate CIRs that are reasonably comparable with observations near Earth. While the magnetic field structure is reasonably well reproduced, the enhancements in the turbulent energy at the stream interfaces are smaller than observed. A superposed epoch analysis is performed over several CIRs from the simulation and compared to the superposed epoch analysis of the observed CIRs. The results for the turbulent energy and correlation length are used to estimate the diffusion tensor of galactic cosmic rays. The derived diffusion coefficients could be used for more realistic modeling of cosmic rays in a dynamically evolving inner heliosphere.

Non-Arrhenius behaviour of nickel self-diffusion in liquid Ni77Si23

Nickel self-diffusion was measured for a Ni77Si23 alloy in the liquid state over a temperature range of about 400 K through quasielastic neutron scattering. At the two lowest temperature points the derived diffusion coefficients deviate from a high-temperature Arrhenius-type behaviour and indicate a change in dynamics above the liquidus temperature. A fit with a power-law temperature dependence as predicted by the mode coupling theory for the liquid to glass transition can describe the diffusion coefficients quite well over the whole measured temperature range. The obtained results agree with predictions from a classical molecular dynamics (MD)-simulation, which evidenced an increasing glass forming ability with increasing silicon content. A crossover to a super-Arrhenius behaviour was reported for metallic glass formers above the liquidus temperature and the here investigated NiSi alloy demonstrates the same signature.

Electrochemical Modeling of GITT Measurements for Improved Solid-State Diffusion Coefficient Evaluation

Galvanostatic Intermittent Titration Technique (GITT) is widely used to evaluate solid-state diffusion coefficients in electrochemical systems. However, the existing analysis methods for GITT data require numerous assumptions, and the derived diffusion coefficients typically are not independently validated. To investigate the validity of the assumptions and derived diffusion coefficients, we employ a direct pulse fitting method for interpreting GITT data that involves numerically fitting an electrochemical pulse and subsequent relaxation to a one-dimensional, single-particle, electrochemical model coupled with non-ideal transport to directly evaluate diffusion coefficients that are independently verified through cycling predictions. Extracted from GITT measurements of the intercalation regime of FeS2 and used to predict the discharge behavior, our non-ideal diffusion coefficients prove to be two orders of magnitude more accurate than ideal diffusion coefficients extracted using conventional methods. We further extend our model to a polydisperse set of particles to show the validity of a single-particle approach when the modeled radius is proportional to the total volume-to-surface-area ratio of the system.

Comparison between ab initio and polarizable molecular dynamics simulations of 1-butyl-3-methylimidazolium tetrafluoroborate and chloride in water

In this study we compare the results of three different polarizable molecular dynamics force fields with an ab initio trajectory of the aqueous mixture of 1-butyl-3-methylimidazolium tetrafluoroborate and chloride, especially regarding their ability to describe static and dynamic phenomena. The discrepancies are discussed in terms of intra- and intermolecular force field parameters as well as the system size. We report significant differences in the derived diffusion coefficients and attribute them to system size, density and general discrepancies between ab initio and classical molecular dynamics simulations. In most cases, radial distribution functions show qualitative agreement; however, the overpolarization of chloride in the MD trajectories gives rises to unphysical results. Excellent agreement between dipolar distributions point out the importance of explicit polarizability in MD, while the comparison of computational and experimental IR spectra highlights the similarities between classical and ab initio dynamics in the low-wave number region and the differences around 1500 cm−1.

A combined Fourier transform infrared and Cr K-edge X-ray absorption near-edge structure spectroscopy study of the substitution and diffusion of H in Cr-doped forsterite

Abstract. Single crystals of synthetic Cr-doped forsterite (Cr:Mg2SiO4) containing both Cr3+ and Cr4+ were partially hydroxylated in piston-cylinder apparatuses at 750–1300 ∘C and pressures from 0.5 to 2.5 GPa, with p(H2O) ≈Ptotal. The oxygen fugacity (fO2) was buffered by graphite-water, Ni–NiO, Re–ReO2, Fe2O3–Fe3O4 or Ag–Ag2O, and the silica activity (aSiO2) was buffered by powdered forsterite plus either enstatite (Mg2Si2O6), periclase (MgO) or zircon–baddeleyite (ZrSiO4–ZrO2). Profiles of OH content versus distance from the crystal edge were determined using Fourier transform infrared (FTIR) spectroscopy, and profiles of the oxidation state and coordination geometry of Cr were obtained, at the same positions, using K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The techniques are complementary – FTIR spectroscopy images the concentration and nature of O–H bonds, where Cr K-edge XANES spectroscopy shows the effect of the added H on the speciation of Cr already present in the lattice. Profiles of defect-specific absorbance derived from FTIR spectra were fitted to solutions of Fick's second law to derive diffusion coefficients, which yield the Arrhenius relationship for H diffusion in forsterite: log⁡10D̃[001]=-2.5±0.6+-(224±12+4.0±2.0P)2.303RT, where D̃ is the measured diffusion coefficient in m2 s−1, valid for diffusion parallel to [001] and calibrated between 1000 and 750 ∘C, P and T are in GPa and K, and R is 0.008314 kJK−1 mol−1. Diffusivity parallel to [100] is around 1 order of magnitude lower. This is consistent with previous determinations of H diffusion associated with M-site vacancies. The FTIR spectra represent a variety of Cr-bearing hydrous defects, along with defects associated with the pure Mg–Si–O–H system. It is proposed that all of the defects can form by interaction between the dry lattice, including Cr3+ and Cr4+, and fully hydroxylated M-site vacancies. The initial diffusive wave of hydroxylation is associated with neither reduction nor oxidation of Cr but with Cr4+ changing from tetrahedral to octahedral coordination. Superimposed on the H diffusion and concomitant change in Cr4+ site occupancy, but at a slower rate, producing shorter profiles, is reduction of Cr4+ to Cr3+ and potentially of Cr4+ and Cr3+ to Cr2+. In addition, by comparing FTIR data to trace element contents measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), constraints can be placed on absorption coefficients used for converting absorbance to H2O contents – our data support either wavenumber- or defect-dependent values of absorption coefficients. We estimate absorption coefficients of between 60 200 and 68 200 L mol−1 cm−1 for OH− associated with octahedral Cr3+ and an M-site vacancy and 18 700 to 24 900 L mol−1 cm−1 for two OH− associated with octahedrally coordinated Cr4+ and a Si vacancy (i.e. a “clinohumite-type” point defect).

A molecular model for obsidian hydration dating

Water diffusion in high silica volcanic melts results in the formation of rhyolite glasses where hydroxyls are linked to the silica tetrahedra. Space between these linkages form pathways for the diffusion of molecular water into the glass surface during secondary hydration. The accumulation of water in the near surface forms a water-rich hydration layer that can be converted to time by the application of experimentally derived diffusion coefficients. In this paper, we summarize mechanisms for water diffusion in obsidian and use a diffusion pathway model as the basis for a more detailed understanding of the parameters that control the magnitude of the water diffusion coefficient, its constancy over time, and how the properties of the glass reflect the thermal history experienced during secondary hydration. We evaluate hypotheses about water diffusion in obsidian with new low temperature (140–200 °C) accelerated hydration experiments and present a calibration for the age determination of obsidian artifacts.

GITT Analysis of Lithium Insertion Cathodes for Determining the Lithium Diffusion Coefficient at Low Temperature: Challenges and Pitfalls

Understanding the diffusion of lithium ions in electrode materials for lithium ion batteries is of great importance for their knowledge-based optimization and development of novel materials and cell designs. The galvanostatic intermittent titration technique (GITT) is widely applied in battery research to study the diffusion of lithium in anode and cathode materials depending on the degree of lithiation. While transport properties of electrode materials at high and ambient temperatures are largely available, low temperature diffusion and rate coefficients are hardly reported in the literature and vary by orders of magnitude for identical active materials. Herein, we demonstrate and discuss several challenges and pitfalls in the application and evaluation of GITT measurements for determining the effective chemical lithium ion diffusion coefficient in lithium insertion electrodes, which become especially important at low temperature. This includes theoretical considerations and an experimental analysis of the promising cathode material LiNi0.5Co0.2Mn0.3O2 (NCM523) in the wide temperature range of −40 °C to 40 °C. We show how the choice of experimental conditions for the GITT measurements and of the subsequent mathematical evaluation significantly influence the derived diffusion coefficient. The results suggest that the large scattering of reported values of the diffusion coefficient could be caused by the use of different evaluation procedures. Simple calculation methods appear to be less suited the lower the temperature is. It is shown that the complementary use of GITT and EIS supplemented by detailed knowledge of the microstructure of the electrode significantly improves the accuracy of determining the diffusion coefficient.

Investigation of Ce3+ Mobility in NR211 Under RH Gradients

A proton exchange membrane fuel cell (PEMFC) is an attractive candidate for use in transportation and stationary applications as a clean energy source. A key component of a PEMFC is the polymeric ionomer membrane that serves as a proton conductor and prevents reactant gas crossover and electrical shorting. A widely used class of polymeric ionomers are perfluorinated sulfonic acid (PFSA) type ionomers because of their overall superior chemical and mechanical properties. The primary product of an operating fuel cell is water, but there are also small quantities of hydroxyl radical (•OH) and hydrogen peroxide (H2O2) produced from chemical and electrochemical reactions. These species react with non-fluorocarbon atoms or the sulfonic acid moiety to degrade the polymeric ionomer. To mitigate the chemical degradation of the polymeric ionomer, redox active cations such as Ce3+ and Mn2+ can be incorporated in membrane electrode assemblies (MEAs). These cations react at kinetically sufficient rates with •OH to form water. The resulting oxidized cation is subsequently reduced by H2O2 to complete the redox cycle. Within the polymeric ionomer, these cations associate (ion pair) with negatively charged sulfonate (SO3 -) groups. At the same time, cation complexation of the SO3 - groups modulates the local water content (l = nH2O/SO3 -) in the membrane. During fuel cell operation over a period of ten to 100 hours, cations are observed to diffuse on a centimeter length scale. The redistribution of cations can impact the fuel cell performance and mitigation of chemical degradation reactions. The movement of cations within an MEA is dictated by water content (l), water content gradients (Dl), and potential gradients. Therefore, the optimization of fuel cell performance and durability requires understanding how these factors impact cation movement. In this presentation, we will report isotropic diffusion coefficients of Ce3+ and Co2+ within a NR211 membrane over an array of uniform temperature and relative humidity values. The cation concentrations were monitored using FTIR, x-ray fluorescence, and UV-vis spectroscopies. The derived diffusion coefficients from these data show a strong dependence on relative humidity and temperature. These mobility rates are also consistent with redistribution of cations in operating fuel cells. In addition, cation movement under RH gradients will be presented. In this work, a dual-RH chamber apparatus was employed to study cation mobility rates over a range of RH chamber values and temperatures. For example, uniformly Ce3+-doped NR211 membranes clearly exhibit cation migration from the high to the low RH chamber (Figure 1a) and the mobility of cations in the low RH chamber is greatly reduced. Much additional experimentation with Ce3+ patch-doped NR211 strips (Figure 1b) has been conducted to elucidate the influence of water gradients on the rate and extent of cation mobility. Finally, a 1-D in-plane Ce3+ transport model that was developed from these data will be discussed. Figure 1

Determination of the partition and diffusion coefficients of five chemical additives from polyethylene terephthalate material in contact with food simulants

Abstract An investigation on the migration of five chemical additives from polyethylene terephthalate (PET) into food simulants was undertaken to determine the partition and diffusion coefficients between PET/food simulants. The migration tests were carried out using three simulants (20%, 50% ethanol and isooctane) in contact with PET samples at different time-temperature conditions, the concentration of additives in polymer matrix and food simulants were analyzed by high-performance liquid chromatography (HPLC). The results confirmed that the partitioning of plastic additives was affected significantly by the temperature and simulants’ properties, the polarity and molecular weight of substances can also have influence. The diffusion coefficients of plastic additives were spread between 9.8 × 10-15 and 1.4 × 10-8 cm2 s-1, which deviated from the calculated values by Piringer model and Welle model. The obtained activation energies of five additives were close to or smaller than 100 kJ mol-1. It indicated that the PET samples in the experiments were influenced (swelling for example) by the food simulant, especially at high temperature. In this situation, the derived diffusion coefficients might be greater than the actual values. The influence of food substance on plastic additives’ partition and diffusion should be pay more attention in future work.

Transport consistent diffusion coefficient for CMFD acceleration and comparison of convergence properties

ABSTRACT A diffusion coefficient for the coarse mesh finite difference (CMFD) acceleration is derived from the semi-analytic solution of one-group, one-dimensional, even-parity transport equation. The derived diffusion coefficient, i.e., the transport consistent diffusion coefficient (TCD), depends on the optical length of a mesh and shows similar behavior with the artificial grid diffusion (AGD) and the effective diffusion (EffD) coefficients for an optically thick mesh. Convergence properties of typical diffusion coefficients are evaluated using the linearized Fourier analysis. Analyses of the C5G7 3D benchmark problems with and without voided region are carried out to compare the convergence properties. The number of transport sweeps to reach convergence using TCD is smaller than that using EffD or AGD.

Variability in obsidian structural water content and its importance in the hydration dating of cultural artifacts

The process of dating ancient obsidian artifacts converts the quantity of surface diffused molecular water to a calendar age using an experimentally derived diffusion coefficient predicted from glass composition. The internal structural water content of rhyolitic obsidian has been identified as a highly influential variable that controls the rate of water diffusion at ambient temperature. We demonstrate through the use of infrared spectroscopy and specific gravity (density) measurements on samples from 34 obsidian sources that total structural water (H2Ot) concentrations between sources can range from 0.07% to 1.66%. Structural water concentration within individual sources may also vary significantly and impact the accuracy of estimated ages for artifact manufacture if not properly monitored. A calibration for the water determination on individual samples by density measurement is developed here and the impact of structural water variation on obsidian chronometric dates is discussed.

Determination of Ce3+ and Co2+ Diffusion Coefficients in NR211 Membrane

The proton exchange membrane fuel cell (PEMFC) is a promising clean energy propulsion system for automobiles and other vehicles. A critical component of the PEMFC is the polymeric ionomer membrane which enables proton conduction and provides a crucial barrier to both reactant gas crossover and electrical shorting. Many fuel cell systems employ thin (12-25 µm) perfluorosulfonic acid (PFSA) based membranes due to their superior mechanical and chemical stability properties. The primary product of a PEMFC is water, generated via the four-electron oxygen reduction reaction. However, smaller amounts of highly oxidizing species such as hydroxyl radical (•OH), and hydrogen peroxide (H2O2) are generated either chemically or electrochemically. These, and other, oxidizing species can react with non-fluorocarbon end groups or with acid side chain functional groups to degrade and weaken the polymeric membrane until causing a physical breach. In the absence of effective chemical mitigation, proton exchange membranes will survive no more than a few hundred hours of operation under typical automotive duty cycles involving large humidity and potential variations. Fortunately, PFSA lifetimes can be extended up to and beyond 10,000 hours of operation using •OH redox quenchers such as Ce3+ and Mn2+ that efficiently reduce •OH to H2O. The remarkable effectiveness of these redox quenchers is due to their high competitive activity toward •OH reduction and the rapid and benign reduction of the oxidized metal to the reduced form via reaction with ubiquitous H2O2. Within an ionomer, cations, including Ce3+, associate (ion pair) with the negatively charged sulfonate groups to varying degrees and have been observed to diffuse in-plane on the centimeter length scale during ten to100 hours of fuel cell operation. More rapid migration of cations into the electrode layers has been observed over the µm length scale of MEA thickness. The movement of cations within the MEA is governed by local water content (λ = n H2O/-SO3 -), water content gradients (Δλ) and electrical potential gradients. The observed in-plane movement of Ce3+ and other cations such as Co2+ can lead to large cation concentration gradients within a fuel cell MEA. This redistribution of cations can have a significant impact on cell performance and mitigation of chemical degradation processes. Accordingly, there is great interest in understanding and quantifying the factors that govern cation movement to optimize fuel cell efficiency and durability. We will report the in-plane isotropic diffusion coefficients of Ce3+ and Co2+ within NRE211 membrane over a wide range of uniform temperature and relative humidity values. The cation concentrations have been monitored using a variety of analytical techniques including FTIR, x-ray fluorescence and UV spectroscopy (Figure 1). The derived diffusion coefficients show a strong dependence on both temperature and relative humidity value (water content) and are consistent with the macroscale redistribution of cations seen in operating fuel cells. Quantitative structure activity relationships and cation movement under RH gradients will also be discussed. Figure 1

The frequency dependence of hygro-expansive scaling of oak

ABSTRACTFluctuations in the ambient relative humidity are often cyclic of nature, composed of a wide variety of frequencies. Variations may be as fast as one minute or as slow as a complete season. A wooden object exposed to these fluctuations exchanges moisture with the air, resulting in a change in the local moisture content of the wood. Since moisture penetration is affected by the timescale of the changes in ambient conditions, so are processes caused by moisture content variations. Moisture content variations cause dimensional changes of a wooden object, which, if mechanically restrained, lead to a buildup of stresses and ultimately to damage. It is therefore important to predict the frequency behavior of moisture content and expansion in wood. In the presented study, experiments are conducted in which the moisture content and expansion of oak cubes with different sizes is measured during sinusoidal relative humidity fluctuations with different frequencies. The amplitude in moisture content and expansion is shown to be simply scalable based on sample size only. Derived diffusion coefficients are in agreement with literature values, although the experimental frequency behavior is shown to deviate qualitatively from diffusive frequency behavior.

Side leakage into the organic interlayer of unstructured hybrid thin-film encapsulation stacks and lifetime implications for roll-to-roll produced organic light-emitting diodes

Side leakage experiments have been performed on the organic interlayer, so-called organic coating for planarization (OCP), in a hybrid thin-film encapsulation (TFE) stack based on two silicon nitride (SiN) barrier layers that was developed for organic light-emitting diodes (OLED). To measure the side leakage into OCP, a metallic Ca thin-film monitor can be used. However, the water uptake capacity of the Ca monitor affects the measurements. Here, we eliminated the contribution of the Ca layer from the measurement by variation of the Ca thickness and by measuring the side leakage until it reaches the Ca layer. For OCP with a water getter inside (5% CaO) the side leakage can be monitored by the loss of scattering of the CaO when it reacts with water to Ca(OH)2. This work describes measurements of the rate of side leakage into the OCP layer of the TFE stack, both for plain OCP and for OCP with CaO getter inside. The side leakage curves are used to derive diffusion coefficients. Performing measurements at various climates provides acceleration factors that are relevant for the performance quantification of the TFE stack. The limiting factors on the performance of an unstructured TFE stack as produced in a roll-to-roll (R2R) process are presented. For small OLED devices side leakage would drastically reduce the shelf lifetime but for larger devices the permeation properties of the TFE stack determine the shelf lifetime.