Volumetric Swelling Research Articles

Physical properties of palmyra palm wood for sustainable utilization as a structural material

Physical properties are major characteristics that validate biomaterials' adaptability to commercial utilization. The moisture content, density, swelling, and shrinkage within male and female Borassus aethiopum were assessed. Green and dry moisture content, and density were tested with the oven-dry method while swelling and shrinkage were evaluated using the water-saturation test and oven-dry methods respectively. Unlike moisture content, density decreased towards the crowns and radially from the peripheries to their cores. Directional swelling decreased as: Radial > Tangential > Longitudinal. Volumetric swelling was greatest at the core of the base (6,99 %) but at least at the periphery within the middle of the male (2,89 %). However, the female recorded much swelling at the core of its mid-portion (6,23 %) and least (4,01 %) at the crown periphery. Directional shrinkage decreased identically as the male variety while the volumetric shrinkage for both varieties was not consistent. The peripheries had less moisture content, better dimensional stability and density (which influences wood strength) at the butt than those of the core indicating the peripheries would maintain its original dimension and strength when subjected to environmental changes and be more viable for structural works than the core.

Improving Hydrophobicity of Tropical Hardwood along Axial Positions

Wood is hygroscopic and is considered dimensionally unstable materials when exposed to wet conditions. To increase the hydrophobicity of wood, this study focused on the modification of tropical hardwood (Triplochiton scleroxylon) along different positions of the stem using acetic anhydride The weight percent gain (WPG) was determined and acetylation reaction was confirmed with FTIR. The dimensional stability of the wood was characterized by water absorption (WA), volumetric swelling (VS), anti-swelling efficiency (ASE), and water repellent efficiency (WRE). Data obtained were subjected to analysis of variance at α0.05. It was observed that the weight gain (WG) by acetylation increases along the axial position (base to top) of T. scleroxylon wood. IR-spectra confirmed properly the substitution of the acetyl group. The treatment resulted in a marked improvement in the WA and VS, ASE, and WRE of acetylated T. scleroxylon wood were also found to improve considerably from base to top of the wood. It could be said that the WPG and hydrophobicity increased, but the percentage of water absorption and volumetric swelling diminished. Hence, the modified wood showed good hydrophobicity and improved dimensional stability.

A mechanistic damage model for solid oxide fuel cell ceramic materials - Part I: Constitutive modeling

A multiscale mechanistic damage model for solid oxide fuel cell (SOFC) ceramics that combines micromechanics of stiffness reduction due to material porosity change and microcracking with a continuum damage mechanics (CDM) description for the evolution of microcracks up to fracture is developed in this work. The model also accounts for volumetric swelling of the anode due to redox cycling. Porosity change and swelling during redox combined with normal operating thermomechanical loads could increase the stress, strain and damage distributions in SOFC stacks leading them to failure. The proposed model involves three governing parameters: (i) the porosity in terms of the pore or void volume fraction, (ii) material swelling magnitude prescribed at a given loading step, and (iii) the damage variable that describes microcracking caused by thermomechanical loads and swelling. Pores and microcracks in the ceramics are modeled as randomly distributed ellipsoidal inclusions with negligible stiffness by an Eshelby-Mori-Tanaka formulation combined with an inclusion orientation distribution method. Microcracking damage evolution is described by a CDM formulation. Volumetric swelling is treated in a similar way to thermal expansion in the constitutive relations. After validation and numerical checks, the damage model is used to analyze a simplified SOFC positive-electrode/electrolyte/negative-electrode (PEN) structure subjected to a redox cycle in addition to thermomechanical loads experienced during normal operation of a SOFC stack.

Simulation and experimental characterization of microporosity during solidification in Sn-Bi alloys

The formation of microporosity during solidification of Sn-Bi alloys is investigated through experiments and simulations. Samples of varying composition with 20, 30, 47 and 58 wt% Bi are solidified in a copper mould and the pore fraction is measured through scanning electron microscopy. Finite element models are derived from X-ray micro computed tomography data and a material model is implemented to capture the effect of liquid pressure and volumetric swelling. The experimental assessment of solidification porosity shows a strong dependency on alloy composition. The round morphology of porosity found in the Sn-20 wt% Bi alloy indicates its formation in the terminal stage of solidification. Microporosity formation is computed by means of Finite Element simulations and the results correlate with experimental findings. The analysis confirms volumetric shrinkage in the liquid state of confined eutectic domains as the mechanism for pore formation and determines the composition dependency of Sn-Bi alloys.

Microstructural complexity and dimensional changes in heavily irradiated zirconium

Using atomistic simulations based on the creation-relaxation algorithm, we explore the evolution of microstructure in irradiated zirconium over a broad range of radiation exposure. In agreement with experimental observations, we find that at relatively low temperatures, microstructure evolves towards an asymptotic dynamic steady state forming at doses close to 1 dpa. Simulations show the spontaneous formation of $a$-type interstitial dislocation loops, gradually transforming into an $a$-type extended dislocation network and giving rise to macroscopic anisotropic dimensional changes in a textured material. A fully developed $a$-type interstitial/vacancy and $c$-type vacancy dislocation microstructure corresponds to the highest degree of irradiation growth anisotropy and vanishingly small volumetric swelling of the material.

Damage Modeling of Solid Oxide Fuel Cells Accounting for Redox Effects

This work applies a multiscale mechanistic damage model developed for brittle ceramics and implemented in commercial finite element (FE) packages via user subroutines to study progressive damage in solid oxide fuel cells (SOFC) subjected to thermomechanical loading under normal operating and shutdown conditions including redox effects. The damage model captures the micromechanics of stiffness reduction due to material porosity change and microcracking and integrates the as-obtained stiffness reduction law into a continuum damage mechanics (CDM) formulation for the evolution of microcracks up to fracture. The volumetric “swelling” that occurs during redox is treated in constitutive modeling similarly to thermal expansion, but swelling strains are irreversible. This damage model was first validated through predictions of strength and stress-strain response for the SOFC electrode materials. Next, it has been applied to predict the potential for degradation in a generic planar SOFC stack with large active area cells. Multicell stack models were simulated in both co-flow and counter-flow configurations. In addition, a constant temperature redox cycle was also simulated to capture overall cell electrode damage due to volumetric swelling of the nickel (Ni)-based anode in the anode-supported cells.

Numerical simulation and experimental measurement of pressureless sintering of stainless steel part printed by Binder Jetting Additive Manufacturing

Binder Jetting-Metal Additive Manufacturing (BJ-MAM) is a powder bed-based additive manufacturing technology which deposits liquid binder droplets to join powder particles to form complex shaped structures (i.e., green parts). As the printing process is done around room temperature, BJ-MAM is largely immune to the distortion and cracking issues that can be prevalent in melting based powder bed processes. However, a main issue for BJ-MAM is the part shrinkage and distortion during high-temperature sintering. The densification and deformation behaviors during pressureless sintering of green parts printed by BJ-MAM were studied in this paper. Experimentally, cantilever- and bridge-shaped coupons with varying beam lengths were printed using 316L stainless steel powder; these coupons produced different extents of deformation after sintering. Based on the existing modeling approaches in the powder metallurgy literature, a finite element model was developed incorporating an elastic-viscoplastic constitutive equation for computing both uniaxial equivalent creep strain and volumetric swelling strain. Two methods, a viscosity based and a power-law creep based, were further evaluated for calculating the uniaxial equivalent creep strain. Material property data used in the constitutive equation such as viscosity and creep parameters were collected from the literature, critically reviewed, and then inputted into the model. Other salient features of the model included thermal-mechanical property data that were dependent on both relative density and temperature as well as frictional contact between the part surface and the furnace wall under gravitational load. The calculated quantities such as shrinkage, final relative density, and deformed shapes were compared with the respective experimental data across different part geometries.

Templateless Electrosynthesis of Nanostructured PEDOT Films

Conducting polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) have been widely used as electrode materials for supercapacitors. PEDOT is a promising electrode material because of its high electrical conductivity, great environmental stability and high cycling stability. Nanostructuration of the polymers can provide better performances of volumetric swelling and shrinking during charge/discharge processes. We have already described the templatefree electrosynthesis of PPy nanostructures [1-3] but to the best of our knowledge, the easy templateless electrosynthesis of nanostructured PEDOT in aqueous solutions has not been reported yet. This work demonstrates a simple one-step templatefree electrosynthesis method of preparing various structured PEDOT films which show good specific capacitance and cycling stability. By varying some experimental parameters, we have obtained various nanostructures: nanofiber networks, nanorods, nanospheres and nanowires of PEDOT (Figure 1, SEM micrographs of various morphologies of PEDOT obtained using a templateless electrochemical route.). These structures were obtained by simply adjusting the applied potential and the composition of the monomer solution i.e. the concentration of weak-acid anions such as HPO4 2- and the concentration of non-acid anions such as ClO4 -. The growth mechanism of the nanostructured PEDOT films will be discussed. At the very beginning of the process, water oxidation takes place which leads to the formation of hydroxyl radicals and to the evolution of O2. Moreover, the nanostructured PEDOT films show high specific capacitance (~100-200 F/g) and cycling stability (capacitance retention is about 90% after 1000 scans). Therefore, the nanostructured electrogenerated PEDOT films could be used for many applications, such as supercapacitors.

Furfural-based resin for modifying birch wood properties

Furfural (F) cannot be easily polymerized like furfuryl alcohol, but it is an aldehyde that can react with urea (U) to make a polymeric network. The possibility of preparing F/U polymer along with an acidic catalyzer (maleic anhydride; M) was evaluated as a means to improve some selected properties of birch (Betula pendula) wood. The F+U/M resin was introduced into the wood with a double treatment technology. The first step involved dilution of F in water and methanol, and the second step was immersion in a U/M aqueous solution. The color of treated wood was darkened after resin curing from brown to a spectrum of black depending on the amount of loaded resin. The 60 to 80% of materials were converted to a non-leachable polymer based on the different formulations. The water absorption and volumetric swelling of the treated samples decreased with an increase in weight percent gain (WPG). The analysis of mechanical strength showed that treatment with F + U/M reduced to some extent the hardness and the impact bending of wood, while modulus of rupture, modulus of elasticity, and compression parallel to the grain with WPG were increased. The exposure of the samples to the accelerated weathering showed noticeable changes in color and roughness.

Characterization of Mellowing Process to Control Expansion in High-Sulfate-Bearing Soil

Calcium-based stabilizing materials (CBSMs) such as lime and fly ash are extensively used in subgrade primarily to enhance mechanical strength and improve resistance to chemical attack, resulting in more durable roadway. The soluble sulfate phase contained in some soils, however, can react with CBSMs and form ettringite minerals. If the soil is compacted before the end of this reaction, large, unstable, and volumetric swelling can occur. Among several methods to control sulfate-induced swelling, a “mellowing” approach is typically used because of its efficient, economical, and practical benefits when dealing with calcium-based stabilization of soils with significant soluble sulfate contents. Although the mellowing method is one of the frequently used methods, little data is available on the characterization of the specified mellowing process in the high-sulfate-bearing soil during the mellowing period. A research program investigated key factors influencing the mellowing process during the mellowing period, explaining how stabilizer type and content, remixing interval, mellowing period, and temperature play a role in reducing soluble sulfate content. Moreover, for selected mixtures, the 3-dimensional volumetric expansion and retained strength were measured after the mellowing process. Laboratory test results have revealed that a single mellowing process with higher lime content and daily remixing at high temperature leads to the rapid reduction of sulfate content in the soil. Moreover, after the mellowing process, additional soil treatment with fly ash or a combination of lime and fly ash leads to lower expansion and higher retained unconfined compressive strength of the soil mixture.

Study on preparation, compression strength and theophylline/diclofenac sodium release ability of NIPAAm/DMAPMAAm hydrogels

The present study was undertaken to investigate the effect of the composition of the polymerization medium and the type of drug/drug loading process on the mechanical strengths and release profiles of poly(N-isopropylacrylamide-co-N-[3-(dimethylamino)propyl] methacrylamide) P(NIPAAm-co-DMAPMAAm) hydrogels. In line with this goal firstly, the temperature- and pH-responsive hydrogels of NIPAAm and DMAPMAAm were synthesized in three different media at 60 °C: pH 7.4 phosphate-buffered saline (PBS), pH 7.4 phosphate buffer without NaCl/KCl (PB), and distilled-deionized water (pH ≈ 5.5 DDW). The result is that the presence of anionic species such as phosphate (HPO4 2-/H2PO4 -) and chloride (Cl-) ions in the solution affects on their basic network properties such as volumetric swelling ratio and compression modulus. To evaluate their intermolecular interactions with protonated DMAPMAAm units and drug molecules, depending on composition, type of loading process and drug structure, each of the hydrogels was loaded with diclofenac sodium (DFNa) and theophylline (Thp) by using both diffusion and in situ loading methods. DFNa and Thp release profiles in pH 7.4 PBS at 37 °C were analysed by using zero-order, first-order, Higuchi, Korsmeyer-Peppas, and Peppas-Sahlin models. It has been observed that for the first 60% of DFNa and Thp releases from P(NIPAAm-co-DMAPMAAm) hydrogels synthesized in PB at 60 °C, the contribution of the chain relaxation for the copolymer hydrogels loaded during gelation process was higher than the ones loaded by diffusion process.

Human Platelet Lysate-Loaded Poly(ethylene glycol) Hydrogels Induce Stem Cell Chemotaxis In Vitro.

Platelet lysates (PL) contain a selection of proteins and growth factors (GFs) that are known to mediate cell activity. Many of these biomolecules have been identified as chemoattractants with the capacity to induce cell migration. In order to effectively deliver and retain these biomolecules to the site of injury, a scaffold containing PL could be an option. We use poly(ethylene glycol) (PEG) hydrogels consisting of 90 vol % PL to investigate their migratory potential on human mesenchymal stem cells (hMSCs). Cells exposed to these hydrogels were tracked, resulting in cell trajectories and detailed migratory parameters (velocity, Euclidean distance, directness, and forward migration index). Volumetric swelling ratios, hydrogel mechanical properties, and the release kinetics of proteins and GFs from hydrogels were also assessed. Furthermore, hMSC spheroids were encapsulated within the hydrogels to qualitatively assess cell invasion by means of sprouting and disintegration of the spheroid. Cell spheroids encapsulated within the PL-PEG gels exhibited initial outgrowths and eventually colonized the 3D matrix successfully. Results from this study confirmed that hMSCs exhibit directional migration toward the PL-loaded hydrogel with increased velocity and directness, compared to the controls. Overall, the incorporation of PL renders the PEG hydrogel bioactive. This study demonstrates the capacity of PL-loaded hydrogel constructs to attract stem cells for endogenous tissue engineering purposes.

Damage Modeling of Solid Oxide Fuel Cells Accounting for Redox Effects

This paper applies a multiscale mechanistic damage model developed for porous brittle ceramics and implemented in finite element analysis (FEA) packages [1] to study progressive damage in solid oxide fuel cells (SOFC) subjected to thermomechanical loading under operating and shutdown states. The damage model captures the micromechanics of stiffness reduction due to material porosity change and microcracking and integrates the as-obtained stiffness reduction law into a continuum damage mechanics (CDM) formulation for the evolution of microcracks up to fracture. An Eshelby-Mori-Tanaka approach (EMTA) [2-3] is first used to model the ceramic containing pores and aligned microcracks regarded as inclusions with negligible stiffness. The stiffness of the actual porous ceramic is obtained from the EMTA solution averaged over all possible microcrack orientations using an orientation averaging method. The evolution of microcracking damage is described by a CDM formulation derived from our previous model [4]. Apart from the operating and shutdown states, additional damage that may occur due to reduction and re-oxidation (redox cycling) of Ni/YSZ anodes is also studied. The reduction of NiO into Ni leads to changes in volume and porosity of the anode layer that consequently change its physical and thermomechanical properties. The volume change or volumetric “swelling” during redox cycling may affect the structural integrity of the anode and may cause fracture of the electrolyte under high tensile stresses leading to operational failure for SOFCs. In the constitutive relations, volumetric swelling is treated in a similar way to thermal expansion using the models developed in Refs [5-6] for fusion energy ceramic materials. However, while thermal expansion vanishes if temperature change tends to zero, swelling is irreversible and significantly contributes to degrade SOFC stacks during redox cycling.This damage model was implemented in the commercial FEA software ABAQUS© and ANSYS© via user subroutines. First, it has been validated through predictions of strength and stress-strain response for the typical SOFC ceramic materials. Figs 1(a) and 1(b) show the predicted stress-strain responses as a function of temperature for dense NiO/YSZ and Ni/YSZ, respectively. These figures also illustrate the predicted responses at 750°C with prescribed initial values of porosity. The damage model predicts significant reductions in strength and elastic modulus with higher initial porosity and higher temperatures, and the predicted trends are in good agreement with the experimental findings [7-8].Next, the damage model was applied to predict the potential for degradation in a generic planar SOFC stack with large active area cells modeled in ANSYS. Stack models with single and multi-cells were simulated in both co-flow and counter-flow configurations. The thermomechanical loads representing the operating and shutdown conditions were simulated. The realistic thermal gradients that occur in an operating stack were imposed in the models by solving the electrochemistry under various operating conditions using the in-house SOFC multiphysics code (SOFC MP-3D) [9-10]. In addition to the operating and shutdown conditions, a constant temperature redox cycle was also simulated to capture overall cell electrode damage due to volumetric swelling of the Ni/YSZ anode in the anode supported cells. The results from single cell stack models showed little damage at operating and shutdown conditions which could be attributed to enough out-of-plane support for the PEN assembly. The results from the multicell stacks (Fig. 2) showed higher damage in counter-flow configuration. Within the stack, the top cells experienced the highest damage and the middle cells experienced the lowest. Overall, no significant damage that may lead to total failure of the cells was observed in the multicell stack models with the operating conditions considered in this study.

FIBER MORPHOLOGY AND PHYSICAL PROPERTIES OF BRANCH AND STEM WOOD OF HAWTHORN (CRATAEGUS AZAROLUS L.) GROWN IN ZAGROS FORESTS

This study aims at investigating the effect of three altitude levels (below 1800 m, 1800-2000 m and above 2000 m) on the physical and biometric properties of stem-wood and branch-wood of hawthorn species. Moreover, the relationship between wood dry density and volumetric swelling, fiber length, fiber diameter, cell wall thickness were studied. Results indicated that altitude had significant effects on the dry density, volumetric swelling and fiber length of stem wood while did not significant effects on the density of branch wood. Additionally, some physical and biometric properties had relatively greater correlation coefficients in branch wood than in stem wood whereas others had higher coefficients in stem wood compared to branch wood. Deep understanding of properties this wood species will provide a fresh insight into the relationship between wood properties and environmental factors.

Economically Feasible Wood Biopreservation Platform in Lannea coromandelica (Houtt.) Merr. Against Wood Rotting Fungus Through Bio-Prospecting Weed Extracts.

As an alternative to synthetic preservatives, the use of plant-based, environmentally sustainable preservatives for wood protection has tremendous potential. The current research analyzed the dimensional stability and longevity of Lannea coromandelica wood using weed extracts viz. Lantana camara L. and Ageratum conyzoides L., respectively. Petroleum ether (PE) and methanolic weed extracts were used to treat wood blocks (5 cm × 2.5 cm × 2.5 cm) at varying concentrations ranging from 0.25 to 2.00%. The PE extract of A. conyzoides resulted in maximum swelling (tangential plane, 6.30%) at 2.00%, volumetric swelling coefficient (13.17%) at 1.50%, and volumetric shrinkage coefficient (7.71%) at 1.00% concentration, while maximum shrinkage (tangential plane, 4.10%) in methanol (M) extract was observed. In L. camara methanolic extract (1.00%), maximum anti-shrink efficiency (37.01%) was recorded. In vitro mycelial growth of the wood-rotting fungus was completely inhibited by PE extract from both weeds. However, the methanolic extract of A. conyzoides resulted in maximal inhibition (75.93%) at a concentration of 2.00%. Also, PE extract (2.00%) of A. conyzoides reduced the fungal colonization to 50%, as compared with control. The lowest weight loss (decay test, 12 weeks) was observed at a 2.00% concentration of L. camara PE extract. The present research highlighted that both A. conyzoides and L. camara could be used as an environmentally sustainable wood preservative substitute that will encourage the utilization of L. coromandelica in wood-based industries.

Radiation effects on stress evolution and dimensional stability of large fusion energy structures

We assess the effects of neutron irradiation on the deformation and stress evolution of large-scale fusion energy structures. This is accomplished through non-linear finite element structural analysis of the coupled thermal and mechanical fields at the Beginning-Of-Life (BOL), at 45 dpa, and at 90 dpa. Radiation effects include volumetric swelling and the influence of radiation on the mechanical properties. The system studied here is a large section of a full inboard module of an integrated structure comprising the First Wall and Blanket (FW/B) of a Dual Cooled Lithium-Lead (DCLL) energy conversion unit in the Fusion Nuclear Science Facility (FNSF). The structural material is the ferritic/martensitic steel F82H. We analyze several radiation effects phenomena that can lead to significant impact on the mechanical design and lifetime of the structure. These include volumetric swelling effects on the assembly and disassembly of modules and the impact of spatial gradients in neutron damage and helium generation on deformation, stress evolution, and plastic strain accumulation. We show that the stress state is strongly influenced by the accumulation of swelling strains, radiation hardening and softening, and by spatial gradients in displacement damage and helium gas generation. Several key regions in the FW/B structure are identified where severe plastic strains accumulate and may be potential sites for failure, especially during cyclic reactor operations. We finally show that minimum gaps between Inboard (IB) blanket sectors must be present during assembly so as to avoid excessive stress and strain in FW/B modules critical regions and raising chances of failure. A range of structural displacements are shown, from as low as 4 mm at BOL for free side walls to as high as 46 mm at 90 dpa for fully constrained side walls.

Precipitation characteristics and distributions of subsurface hydrides in zirconium

Hydride precipitates that develop in Zr after absorbing hydrogen can impart significant material hardening and embrittlement. Here, we use electrolytic hydrogen charging to synthesize Zr samples with different subsurface hydride aging times and transmission electron microscopy to understand the mechanisms underlying hydride precipitation and their distributions across the microstructure of pure Zr. Subsurface hydride formation involves volumetric swelling, causing the sample surface to produce bumps. Analysis of the morphologies and spatial distributions of these bumps can reveal several important characteristics of hydrides below. The analysis indicates that subsurface hydrides first form by isolated nucleation followed by coalescence. The shape of the hydride bump is found to be determined by the angle between the basal plane of the subsurface hydride and the sample surface. We reveal that, at room temperature, the hydride phase transition sequence follows γ-ZrH→δ-ZrH1.66→ε-ZrH2. The two main α-Zr/hydride orientation relationships are 1) (0001)α||(111¯)δ with [211¯0]α||[011]δ or 2) (0001)α||(001)γ/δ with [12¯10]α||[110]γ/δ. Last, we show that the orientation of the basal plane plays a decisive role in the formation of both intragranular and intergranular subsurface hydrides. Statistical analysis of several hundred grain boundaries reveals that grain boundaries with c-axis misorientation of <15°, =55°-60° and >85° are preferential sites for subsurface hydride formation, while those with c-axis misorientations higher than 15° and one grain's basal plane nearly perpendicular to the grain boundary plane resist hydride precipitation. These findings can guide grain boundary engineering efforts for controlling hydrogen damage in Zr.

SOME WOOD PROPERTIES OF MELIAa AZEDARACH L. TREES GROWN IN DUHOK PROVINCE

Melia azedarach L. was introduced into Kurdistan region and planted as an ornamental tree at the nurseries, parks and streets. This study investigated the quality of wood of 9 year old M. azedarach trees grown in Duhok province. Samples of wood from five trees were taken at breast height diameter; and their wood quality was studied in terms of morphological, physical and anatomical properties. Results revealed that the values of morphological properties were: the Heartwood percentage (69.01%), Sapwood percentage (12.93%), Bark percentage (8.06%) and Annual Ring Width (7.74mm). While, the values of the physical properties were: specific gravity (0.42), basic density of wood (0.36g/cm3), annual ring growth width (7.74cm), moisture content (44.46%), maximum moisture content (208.36%), volumetric shrinkage (13.18%), volumetric swelling (16.25%), fiber saturation point (36.34%), cell wall (28.05%) and porosity (71.94%). The values of anatomical properties were: fiber length (0.792 mm), fiber diameter at the mid- point of the fiber (17.75 μm), fiber double cell wall thickness (9.67 μm), fiber lumen width (8.07μm), runkel ratio (1.55), flexibility ratio (47.17), slenderness ratio (47.58), vessel length (241.57μm), vessel diameter at the mid- point of the vessel (169.09μm), and vessel lumen diameter (158.26μm). All properties showed a significant variation from pith to bark and between the trees. The results equip a basis for determining management planning opportune to production wood of M. azedarach plantation trees in Kurdistan region. Also M. azedarach is characterized by low strength resistance and perhaps low pulping production too, therefore according to its low wood quality for some properties, is not recommended for structural purposes. While anatomical properties, showed medium values of fiber dimensions which could be used for production of special type of paper

Assessment of anion exchange membrane selectivity with ionic membrane conductivity, revised with Manning's theory or the Kohlrausch's law

The evaluation of anion exchange membrane (AEM) selectivity towards different anions requires facile characterization methods. The anion selectivity of membranes could principally, but practically not easy to, be extracted from the measured anion transport selectivity in electrodialysis (ED), which is a parameter closely related to the process conditions. According to the classical solution-diffusion model, the membrane anion selectivity could be decoupled into two parts: the partitioning selectivity factor of anions between the membrane and the solution phase; the mobility ratio of anions in the membrane. Alternatively, based on the relationship between the anion composition in the membrane and the mixed-ionic membrane conductivities, these two parts can be calculated from the volumetric swelling ratios and ionic conductivities when the AEMs are in pure and mixed-anion forms, respectively. This relationship is proved to be linear in two commercial AEMs (ASE and ACS) for the NO3−/Cl− and SO42−/Cl− pairs. Further, it is possible to obtain the anion selectivity directly for the ASE membrane from corresponding membrane ionic conductivities, with Manning's counter-ion condensation theory to account for the anion activity coefficients in the membrane. While for the NO3−/Cl− pair in the monovalent-anion selective ACS membrane, the selectivity thus calculated is very different from that obtained in ED. For the nonlinear anion composition-conductivity relationship observed in the commercial FAA membrane, the Kohlrausch's parameter (σ) is successfully introduced to describe the mutual influence of anions in the membrane. In this case, it is also possible to obtain the anion selectivity with the proposed approach. This work provides a different perspective to study the selectivity and conductivity of AEMs.

Gas Bubble Evolution in Polycrystalline UMo Fuels Under Elastic-Plastic Deformation: A Phase-Field Model With Crystal-Plasticity

In monolithic UMo fuels, the interaction between the Al cladding and large gas bubble volumetric swelling causes both elastic-plastic and creep deformation. In this work, a phase-field model of gas bubble evolution in polycrystalline UMo under elastic-plastic deformation was developed for studying the dynamic interaction between evolving gas bubble/voids and deformation. A crystal plasticity model, which assumes that the plastic strain rate is proportional to resolved shear stresses of dislocation slip systems on their slip planes, was used to describe plastic deformation in polycrystalline UMo. Xe diffusion and gas bubble evolution are driven by the minimization of chemical and deformation energies in the phase-field model, while evolving gas bubble structure was used to update the mechanical properties in the crystal plasticity model. With the developed model, we simulated the effect of gas bubble structures (different volume fractions and internal gas pressures) on stress-strain curves and the effect of local stresses on gas bubble evolution. The results show that 1) the effective Young’s modulus and yield stress decrease with the increase of gas bubble volume fraction; 2) the hardening coefficient increases with the increase of gas bubble volume fraction, especially for gas bubbles with higher internal pressure; and 3) the pressure dependence of Xe thermodynamic and kinetic properties in addition to the local stress state determine gas bubble growth or shrinkage. The simulated results can serve as a guide to improve material property models for macroscale fuel performance modeling.