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This study investigates the development and characterization of chitosan, gelatin, and chitosan/gelatin (Chi/Gel) bioaerogel composites through a facile and eco-friendly approach. The goal is to optimize their structural and functional properties for potential environmental and biomedical applications. Direct freezing and lyophilization approach were used to prepare the aerogels, the focus was on investigating the effects of blending ratios on the density, porosity, surface area, and water absorption capabilities of the aerogels. The results show that Chi/Gel 60/40 composition achieved an optimal balance of structural robustness and functional performance, characterized by a moderate density of 74.2 mg/[cm.sup.3], the highest porosity among the samples at 93.5%, an impressive surface area of 184.8 [m.sup.2]/g, and a water absorption capacity of 28.8 g/g. These results suggest that the synergistic effect of chitosan and gelatin at specific ratios significantly enhances the overall properties of the material. Our findings suggest that Chi/Gel bioaerogels, especially the 60/40 composite, hold great promise for diverse applications. Highlights * All Gelatin/Chitosan bioaerogels exhibited high porosity and low density. * The Chi/Gel 60/40 mix achieved the highest porosity and surface area. * Highest water adsorption was observed in the Chi/Gel 60/40 composite. * Synergistic effects enhanced properties of the Gelatin/Chitosan scaffolds. KEYWORDS bioaerogel, biopolymers, chitosan, eco-friendly, gelatin, porose materials, 1 | INTRODUCTION In recent years, the focus has shifted towards developing aerogels from biopolymers due to their biocompatibility, biodegradability, and abundance. (1,2) Bioaerogels, known for their extraordinary lightweight and [...]

Polylactic acid (PLA) is the most widely used material in the fused filament fabrication (FFF) technique, which is a biocompatible thermoplastic. However, PLA's usefulness is limited by its narrow processing window and relatively low mechanical properties. Therefore, PLA composites have been developed to enhance its properties for FFF printing. A key challenge in producing composite parts via this method is to find the correlation between the mechanical properties of the parts and the process parameters. This knowledge is essential for optimizing the printing process to achieve the desired mechanical properties for composite parts industries such as aerospace, automotive, and medical, where high-performance composite materials are crucial. The ability to control and predict the mechanical properties of FFF-printed composite parts is critical for their successful integration into these industries. In this study, the effect of nozzle temperature (NT), printing speed (PS), and nominal porosity (POR) on the impact strength and specific impact strength of PLA/iron composites was examined using FFF. Response surface methodology (RSM) was used to optimize the experimental design. The results revealed that POR had the most significant effect on the impact resistance data, while NT had the least effect. Reducing the POR led to improved impact resistance in the samples. Multi-objective optimization results showed that the lowest NT (190[degrees] C), the lowest POR (30%), and a PS of 50 mm/s were the optimal conditions for multiple objectives. RSM was also utilized to develop mathematical models of impact properties, focusing on varying NT, POR, and PS, which can be used to predict desired impact properties. Highlights * Nominal porosity has the most influence on the impact strength of PLA/iron composites. * Optimum values were temperature of 190[degrees]C, nominal porosity of 30%, and speed of 50 mm/s. * RSM was effective in enhancing the mechanical properties of composite materials. * RSM models provide a predictive tool for future FFF-printed composite parts. * Maximum impact strength of 4.44 kJ/[m.sup.2] was achieved. KEYWORDS 3D printing, composites, impact resistance, mechanical properties, thermoplastics, 1 | INTRODUCTION Time is one of the most important factors during the engineering process, but accuracy is another that must be kept in mind at all times. Due to [...]

Lateritic soil usually contains a large amount of iron and aluminium, which promotes the formation of large-size aggregations and further affects soil fabric. It has been demonstrated that the microstructure of soil influences the hydraulic and mechanical behaviour significantly. As a commonly used filling material with special mineral composition, the microstructure change of lateritic soil under common environment actions, such as wetting and loading, is thus of great importance. In this study, the microstructure properties of a lateritic silt under drying-wetting and one-dimensional compression were investigated using mercury intrusion porosimetry and scanning electron microscopy. Test results show that large-sized aggregates are formed in the compacted lateritic silt with 10% of hematite. These aggregates induce a bi-modal pore size distribution (PSD) which includes both micropore and macropore peaks. The different macropore distributions under various dry densities lead to scattered soil-water characteristic curves in a suction range less than 20 MPa. Changes in volume and pore structure mainly occur in the suction path within the 'transition zone' where the dominant capillarity affects only the macropore. Drying causes an increase in macropores due to the decreased volume of aggregates, while has limited effect on micropores, whereas wetting weakens the bonding between aggregates, and induces a reduction in macropores. The compacted lateritic silt shows obvious collapse upon soaking, in which the collapse grows up to a peak and then turns to decrease with increasing stress level. Both loading and soaking lead to the collapse of macropores, whereas soaking tends to affect a broader range of pore sizes. It is inferred that, the strong particle cementation produced by hematite leads to a strong micropore structure, which is almost unaffected by the suction change under both confined and unconfined conditions. The PSD change due to the variation in suction is different from that observed on other compacted fine- grained soils, which verifies the effects of special mineral composition (iron and aluminium) on microstructure and further the hydro-mechanical behaviour of lateritic soil. Key words: lateritic soil, drying-wetting, collapse upon soaking, microstructure, 1. Introduction Lateritic soil is formed by the weathering of carbonate rocks in tropical region or sub-tropical region, which usually appears red-brown owing to the presence of iron and/or aluminium [...]

Segmental bone tissue engineering is a highly effective approach for the repair of large bone defects. In this article, 3D printing was used to fabricate the polycaprolactone (PCL)/NaCl-based cylindrical structures. The effects of the structure's thickness (L) and NaCl concentration on the mechanical properties, degradability, swelling behavior, porosity, and cytotoxicity of the samples were investigated. Response surface methodology was employed to study the mechanical behavior using the central composite design (CCD). Results showed that increasing the NaCl concentration up to 10% wt significantly improved the degradability, swelling, and hydrophilicity of the structures. It was also indicated that the maximum stiffness of the guide structures under vertical loading was almost five times larger than the horizontal loading direction, but the samples showed greater compressive strength and elongation under horizontal compressive loading. Results indicated that the mechanical properties of the structures were more dependent on the structure thickness so the thicker structures with an 800 [micro]m thickness had better mechanical properties in both vertical and horizontal loading. Cytotoxicity assay also approved the nontoxic effect of the PCL structures on the MC3T3 osteoblast cell line. Based on the results, the PCL-based structures were a suitable candidate to act as a guide for segmental bone tissue engineering. Highlights * A 3D-printed conduit was manufactured to guide bone reconstruction * Response surface methodology (RSM) using central composite design (CCD) was employed * NaCl concentration and the diameter of strands were the main parameters * This 3D-printed guiding approach is useful for segmental bone tissue engineering KEYWORDS 3D printing, guide structures, large bone defect, polycaprolactone, segmental bone tissue engineering, 1 | INTRODUCTION Large bone defects are the most common bone fractures caused by trauma, car accidents, and occupational injury. (1) The repair of large bone defects is a major [...]

Abstract Treatment of large bone defects is challenging and requires coordination between cells, cytokines, and mechanical demands. Scaffold for bone tissue engineering should provide mechanical properties and allow cells adherence, [...]

Buffer materials that are used to isolate heat-emitting waste canisters must bear a strong thermal load and have good thermal conductivity and stability. This study investigated the strengthening of internal thermal conduction via bentonite sealing. An admixture of quartz and graphite accelerated the heat transfer into the host rock. Samples containing different bentonite-sand-graphite (BSG) mixtures were prepared. The influence of the volumetric water content, degree of saturation, dry density, porosity, sand content, and particle size on the thermal conductivity of the BSG mixtures was analyzed by conducting a series of thermal needle tests. Electrical resistivity tests were conducted to examine the electrical resistivity of the BSG mixtures, and the dependency of soil thermal conductivity on the volumetric water content based on electrical resistivity data. The results indicated that the dependency of thermal conductivity on the volumetric water content was closely related to electrical resistivity. Based on the thermal conductivity inflection point as determined by the volumetric water content corresponding to the electrical resistivity inflection point, an improved series-parallel thermal conductivity prediction model and the method to determine model parameters for the unsaturated BSG mixtures were proposed. The precision of the proposed prediction model was verified based on laboratory data. Key words: BSG mixtures, buffer material, thermal conductivity, electrical resistivity, prediction model, 1. Introduction and background In the conceptual design of high-level radioactive waste (HLRW) repositories, the thermal performance of the buffer material is one of the key factors considered in the [...]

This study demonstrates the change in porosity of permeable reactive barrier (PRB) material when it reacts with acidic flow. The laboratory column test data obtained over 9 months prove that the porosity of a granular limestone assembly decreases significantly due to bio-geochemical clogging caused by a continuous flow of acidic groundwater. The variations in pH, the pressure measurements, ion concentrations, and the results from X-ray diffraction suggest that clogging at the outlet of the column is much less than at the inlet. About 57% of the total reduction in porosity of the column is attributed to chemical clogging, while the remainder is mainly due to biological clogging. In this paper, a mathematical approach is proposed to estimate the reduction of reactive surface area based on changes in the pore volume. These proposed equations suggest that at the end of experimentation, the dissolution of calcite and bio-geochemical clogging can reduce the total surface area of limestone aggregates by more than 70%. The rigorous approach presented in this paper to determine the dominant clogging component within a granular filter at a given time is vital in estimating the longevity of a PRB and for planning its maintenance. Key words: acidic groundwater, permeable reactive barrier, biogeochemical clogging, porosity, surface area, 1. Introduction Biological and chemical clogging reduces the porosity of granular filters, obstructs the flow, and increases the hydraulic gradients in porous media (Cooke et al. 2005; McIsaac and Rowe [...]

Porous stones are commonly used in geotechnical laboratory testing to provide solid support at the two ends of the tested specimen. Although porous stones can have several advantages, they can induce a hydraulic impedance that might alter the flowrate results. Numerous suggestions and recommendations were issued to avoid some of the problems encountered when using porous stones, such as clogging and stones' low permeability coefficient ([K.sub.p]). However, it is proven in this technical note that the existence of a soil-porous stones interaction prevents the elimination of porous stones' influence, leading to unreliable permeability results. A practical solution based on manufacturing unique porous stones (MS) is suggested in an attempt to eliminate such an influence. The porous stones' influence is highlighted by running excess pore pressure dissipation tests under triaxial conditions with calibrated beads. The results show a soil-porous stones interaction and a flowrate increase up to 700% due to MS. This interaction is addressed through permeability measurements of three soil types in a flexible-wall permeameter using standard porous stones (SS) and the newly manufactured stones (MS). At least one order of magnitude of difference in the soil permeability measurement and a decrease in the dissipation test time are observed with MS. This technical note also validates the limitation of the superposition approach for correcting the soil's permeability ([K.sub.soil]). It is shown that porous stones can induce a signature directly related to the soil type and applied pressure. Key words: porous stones, zero impedance, manufactured porous stones, permeability, pressure dissipation, clogging Les pierres poreuses sont couramment utilisees dans les essais geotechniques en laboratoire pour fournir un support solide aux deux extremites de l'echantillon teste. Bien que les pierres poreuses presentent plusieurs avantages, elles peuvent induire une impedance hydraulique qui pourrait alterer les resultats de debit. De nombreuses suggestions et recommandations ont ete emises pour eviter certains des problemes rencontres lors de l'utilisation de pierres poreuses, tels que le colmatage et le faible coefficient de permeabilite (Itp) des pierres. Cependant, il estprouve dans cette note technique que l'existence d'une interaction sol-pierres poreuse empeche l'elimination de l'influence des pierres poreuses, conduisant a des resultats de permeabilite peu fiables. Une solution pratique basee sur la fabrication de pierres poreuses uniques (MS) est proposee pour tenter d'eliminer cette influence. L'influence des pierres poreuses est mise en evidence en effectuant des essais de dissipation de la pression interstitielle en conditions triaxiales avec des billes calibrees. Les resultats montrent une interaction entre le sol et les pierres poreuses et une augmentation du debit jusqu'a 700% grace au MS. Cette interaction est abordee par le biais de mesures de permeabilite de trois types de sols dans un permeametre a paroi flexible utilisant des pierres poreuses standard (SS) et des pierres nouvellement fabriquees (MS). Une difference d'au moins un ordre de grandeur dans la mesure de la permeabilite du sol et une diminution du temps d'essai de dissipation sont observees avec le MS. Cette note technique valide egalement la limitation de l'approche par superposition pour corriger la permeabilite du sol ([K.sub.soil]). Il est montre que les pierres poreuses peuvent induire une signature directement liee au type de sol et a la pression appliquee. [Traduit par la Redaction] Mots-cles : pierres poreuses, impedance nulle, pierres poreuses manufactures, permeabilite, dissipation de pression, colmatage, 1. Overview Porous stones are required to provide solid support at both ends of the specimens while allowing free water passage. These stones are needed for evenly distributing the water [...]

The hydromechanical behavior of compacted clayey soils is significantly influenced by its microstructure. The microstructural void ratio is a key parameter that is strongly associated with the microstructural state. The objective of this study is to provide a practical and reliable estimation approach for predicting the evolution of the microstructural void ratio of compacted clay soils subjected to wetting and drying paths. In this paper, the microstructural evolution of 12 clayey soils was investigated quantitatively using the mercury intrusion porosimetry (MIP) results. Based on this study, a comprehensive criterion has been developed for identifying different pore populations of compacted clayey soils for interpreting the MIP results. The 'as-compacted state line' was proposed to estimate the initial microstructural void ratio of clayey soils at the as-compacted state. An incremental linear constitutive model was proposed for correlating the microstructural void ratio to the 'microstructural average skeleton stress' in compacted clayey soils following monotonic wetting and drying paths. The developed approach is validated by providing comparisons between the predicted and interpreted microstructural void ratios for all the examined soils. The proposed approach can be extended in constitutive modeling of the hydromechanical behavior of compacted clayey soils by incorporating explicitly the microstructural information. Key words: microstructure, compacted clayey soils, microstructural void ratio, microstructural average skeleton stress, mercury intrusion porosimetry (MIP) Le comportement hydromecanique des sols argileux compactes est fortement influence par leur microstructure. Le taux de vide microstructural est un parametre cle qui est fortement associe a l'etat microstructural. L'objectif de cette etude est de fournir une approche d'estimation pratique et fiable pour predire l'evolution du taux de vide microstructurel des sols argileux compactes soumis a des chemins de mouillage et de sechage. Dans cet article, l'evolution microstructurale de 12 sols argileux a ete etudiee quantitativement en utilisant les resultats de la porosimetrie par intrusion de mercure (PIM). Cette etude a permis de developper un critere complet pour identifier les differentes populations de pores des sols argileux compactes afin d'interpreter les resultats du PIM. La << ligne d'etat tel que compacte >> (ACSL) a ete proposee pour estimer le taux de vide microstructurel initial des sols argileux a l'etat tel que compacte. Un modele constitutif lineaire incrementiel a ete propose pour correler le taux de vide microstructurel a la << contrainte moyenne du squelette microstructurel >> dans les sols argileux compactes apres des parcours monotones de mouillage et de sechage. L'approche developpee est validee par des comparaisons entre les taux de vide microstructurels predits et interpretes pour tous les sols examines. L'approche proposee peut etre etendue a la modelisation constitutive du comportement hydromecanique des sols argileux compactes en incorporant explicitement les informations microstructurelles. [Traduit par la Redaction] Mots-cles : microstructure, argileux compactes, rapport de vide microstructural, contrainte moyenne du squelette microstructural, porosimetrie par intrusion de mercure (MIP), 1. Introduction It is widely recognized in the literature that the soil microstructure significantly influences the hydraulic and mechanical properties of compacted clayey soils. The pioneering studies linking the macroscopic [...]

In the preparation of polyethylene (PE) microporous membrane, the stretching process of PE/liquid paraffin (LP) blend is of great significance for improving the mechanical properties and optimizing the pore size and its distribution. In this study, we have adopted a method that combines experimental investigation and numerical simulation to explore crystal structure transformation and residual stress distribution of PE matrix during the stretching process. First of all, the X-ray diffraction, small-angle X-ray scattering test, and tensile strength test are used to analyze these PE/LP blend samples that are processed at different stretching temperatures (110[degrees]C, [15[degrees]C, [20[degrees]C, [25[degrees]C) and different stretching ratios (2 * 2, 3 * 3, 4 * 4, 5 * 5). It is found that a higher temperature or larger ratio is beneficial for crystallizing of PE long chains and affecting the tension strength. After the extraction process, the obtained PE microporous membranes have more uniform pore size distribution and an increased pore diameter according to the results of scanning electron microscopy and porosity test. It is attributed to the fact that residual stress is more easily stored in the amorphous region of PE microporous membrane. PE microporous membranes can have higher crystallinity and welldispersed crystal region by controlling a matched temperature and ratio. It is inspired for optimizing the technological parameters in industrial production. KEYWORDS crystallization, numerical simulation, polyethylene, stretching ratio, stretching temperature, 1 | INTRODUCTION Owing to its high mechanical strength, good uniformity, excellent wettability, strong chemical stability, and many other advantages, polyethylene (PE) microporous membrane prepared by the wet process has [...]

A systematic study was carried out in order to identify the optimum processing conditions for the preparation of PLA 3D porous structures applying foaming with supercritical C[O.sub.2] (sc-C[O.sub.2]). Both the depressurization rate and the C[O.sub.2] saturation pressure had a significant effect on the obtained sc-C[O.sub.2] PLA structures. When sc-C[O.sub.2] was instantaneously depressurized, a thin wall pore structure was formed, characterized by anisotropy with pores diameter ranging from 100 to 650 [micro]m, whereas the scaffold porosity varied between 85% and 95%. In this case, a decrease in the porosity percentage was observed with increasing saturation pressure. A trend of increase in the pores' size was recorded from 150 to 200 bar, followed by a decrease at 300 bar. Highly organized pore structures with thicker pore walls and pores with diameters within the range of 10-350 [micro]m and porosity and 74%-77% were fabricated when a slow depressurization rate was applied. An optimum porous structure, with average pore diameter 340 [micro]m and porosity 88% was prepared when [P.sub.sat] was maintained at 200 bar, followed by instantaneous depressurization. Although this scaffold included the biggest number of closed pores in its structure, it presented the highest degree of pore interconnectivity due to C[O.sub.2] bubbles' coalescence. KEYWORDS biodegradable scaffolds, foaming, micr[degrees]CT, poly(lactic acid), scanning electron microscopy, super critical C[O.sub.2], 1 | INTRODUCTION In many tissue-engineering applications, three-dimensional (3D), interconnected porous scaffolds, are broadly utilized as functional replacements for damaged tissues or organs. [1] Those scaffolds are required to be [...]

Physical, chemical, and mineralogical characterisation of as-received rice husk ash (RHA) samples sourced from four rice-growing regions (North, South, East, and West) of India is presented. Valorised RHA was obtained through controlled combustion at two temperature ranges (600-700[degrees]C and 650-700[degrees]C) of husks from the North in an industry set up. Valorisation efficacy has been tested through comparative characterisation of the valorised RHAs with the as-received RHAs from the four regions. Blending of 15% valorised RHA (in the beneficiated state) by weight of cement had no adverse effect on compressive strength even though water-binder ratio of the blended mortar had to be increased by 14% to achieve flow of the control cement mortar. Compared with the control cement mortar, porosity of the mortar blended with the beneficiated RHA measured using mercury intrusion porosimetry (MIP) increased by up to 10% primarily due to an increase in the number of large mesopores (0.01-0.05 [micro]m). Key words: rice husk ash, pozzolans, reactivity, supplementary cementitious material, compressive strength La caracterisation physique, chimique et mineralogique des echantillons de cendres de balle de riz (CBR) telles que recues des quatre regions rizicoles (nord, sud, est et ouest) de l'Inde est presentee. Les CBR valorisees ont ete obtenues par combustion controlee a deux plages de temperature (600-700[degrees]C et 650-700[degrees]C) de balles du nord, et ce, dans une installation industrielle. L'efficacite de la valorisation a ete verifiee par la caracterisation comparative des CBR valorisees avec les CBR telles que recues des quatre regions. Le melange de 15% de CBR valorisees (a l'etat ameliore) en poids de ciment n'a eu aucun effet negatif sur la resistance a la compression, meme si le ratio liant-eau du mortier melange a du etre augmente de 14% pour atteindre la fluidite du mortier de ciment temoin. Comparativement au mortier de ciment temoin, la porosite du mortier melange avec les CBR ameliorees, mesuree au porosimetre a mercure, a augmente jusqu'a 10%, principalement en raison d'une augmentation du nombre de grands mesopores (0,01 a 0,05 [micro]m). [Traduit par la Redaction] Mots-cles : cendres de balle de riz, pouzzolanes, reactivite, matiere cimentaire supplementaire, resistance a la compression, 1. Introduction Estimated annual production of paddy in India is about 169 million tonnes (MT) (FAO RMM 2018) and its processing generates approximately one-fifth the weight of paddy as rice [...]

A purpose-built permeameter was used to explore the transient evolution of porosity during the mixing process in filtration experiments. The experiments considered upward seepage flow and explored the influence of base and filter particle sizes, along with different hydraulic conditions. The permeameter acted as a coaxial transmission line enabling electromagnetic measurements based on spatial time domain reflectometry, from which the porosity profile was obtained using an inversion technique. Quantitative characteristics of the onset and progression of the mixing process were extracted from a porosity field map. The limiting onset condition was influenced by geometric and hydraulic factors, with the critical flow rate exhibiting a strong dependence on the base particle size, while the critical hydraulic gradient exhibited a stronger dependence on filter particle size. The progression of the mixing process was characterised by both the transport of base particles into the filter layer, as well as the settlement of the filter particles into the base layer due to the reduction of the effective stress at the base-filter interface leading to partial bearing failure. The rate of development of the mixture zone was strongly dependent on the hydraulic loading condition and the base particle size, but the final height of the sample after complete mixing was independent of the hydraulic loading path. Key words: spatial time domain reflectometry, filtration, porosity, internal erosion. Un permeametre specialement concu a ete utilise pour explorer l'evolution transitoire de la porosite pendant le processus de melange dans les experiences de filtration. Les experiences ont pris en compte le flux d'infiltration ascendant et ont explore l'influence de la taille des particules de la base et du filtre, ainsi que differentes conditions hydrauliques. Le permeametre a agi comme une ligne de transmission coaxiale permettant des mesures electromagnetiques basees sur la reflectometrie spatiale dans le domaine temporel, a partir desquelles le profil de porosite a ete obtenu par une technique d'inversion. Les caracteristiques quantitatives du debut et de la progression du processus de melange ont ete extraites d'une carte du champ de porosite. La condition limite d'apparition a ete influencee par des facteurs geometriques et hydrauliques, le debit critique presentant une forte dependance par rapport a la taille des particules de base, tandis que le gradient hydraulique critique presentait une dependance plus forte par rapport a la taille des particules du filtre. La progression du processus de melange a ete caracterisee a la fois par le transport des particules de base dans la couche filtrante et par le tassement des particules filtrantes dans la couche de base en raison de la reduction de la contrainte effective a l'interface base-filtre, ce qui a conduit a une defaillance partielle des paliers. La vitesse de developpement de la zone de melange dependait fortement de la condition de chargement hydraulique et de la taille des particules de base, mais la hauteur finale de l'echantillon apres melange complet etait independante du chemin de chargement hydraulique. [Traduit par la Redaction] Mots-cles : reflectometrie spatiale temporelle, filtration, porosite, erosion interne., 1. Introduction Internal erosion occurs when soil particles within the body of a dam or its foundations are detached and transported under seepage flows. Internal erosion is attributed to approximately [...]

The effect of the oxidizer present in the etching solution on the surface morphology and microstructure obtained after porosifying a p-type silicon wafer using metal-assisted chemical etching was studied. The morphologies of Si wafers porosified using two different solutions, HF/[H.sub.2][O.sub.2] and HF/[KMn0.sub.4], were compared to establish how either of the oxidizers ([H.sub.2][O.sub.2] or [KMn0.sub.4]) should be chosen depending on the desired application. A comparative study revealed that parallel pores with wire-like structures or interconnected pores with cheese-like structures can be obtained when [H.sub.2][O.sub.2] or [KMn0.sub.4] are chosen, respectively. Careful analysis of the SEM images was carried out using ImageJ to establish that the samples prepared using [KMn0.sub.4] are more porous due to aggressive etching. Additionally, experimental and theoretical Raman spectroscopic studies have been utilized to study the presence of low-dimensional Si nanostructures, which are a few nanometers in size, at the microscopic level in porosified silicon. Key words: porosity, silicon nanostructures, oxidation, etching, Raman spectroscopy. Nous avons etudie l'effet de l'agent oxydant present dans la solution de gravage sur la morphologie de surface et la microstructure de gaufres de silicium de type p apres porosification par gravure chimique assistee par un metal. Nous avons compare la morphologie des gaufres de Si porosifiees a l'aide de deux solutions differentes, a savoir HF/[H.sub.2][O.sub.2] et HF/[KMn0.sub.4], afm d'etablir les facteurs qui doivent dieter le choix de l'oxydant ([H.sub.2][O.sub.2] ou [KMn0.sub.4]) en fonction de l'application souhaitee. L'etude comparative revele qu'il est possible d'obtenir des pores paralleles de structure semblable a des fils ou des pores interconnected de structure ressemblant a un fromage, selon que l'on choisit l'[H.sub.2][O.sub.2] ou le [KMn0.sub.4]. Nous avons effectue une analyse minutieuse des images de microscopie electronique a balayage a l'aide du logiciel ImageJ pour etablir que les echantillons prepares a l'aide du [KMn0.sub.4] sont plus poreux en raison d'un decapage agressif. De plus, nous avons fait appel a des analyses experimentales et theoriques par spectroscopic Raman pour etudier a l'echelle microscopique la presence de nanostructures Si de faible dimension, soit de quelques nanometres, dans le silicium porosifie. [l'raduit par la Redaction] Mots-cles: porosite, nanostructures de silicium, oxidation, gravure, spectroscopic Raman., 1. Introduction Silicon (Si) and its nanostructures (NSs), including porous silicon (p-Si), have been widely used for decades, playing an important role in the field of electronics, energy conversion and [...]

In this study, the onset of convection in a rotating horizontal porous layer saturated by a binary nanofluid was theoretically investigated under the influence of thermodiffusion and nanoparticles. To study the onset of convection, the Darcy-Brinkman model was employed for the porous medium, and the thermal Rayleigh number was derived analytically using linear stability analysis. Water-ammonia-based silver, copper, and alumina, three binary nanofluids, were considered, and the effect of nanoparticles on the stability of the system was analysed using addition factor analysis. The Brinkman model for viscosity and Bruggeman model under the mean field approach for thermal conductivity were used to study the impact of nanoparticles. Heat transport was examined by calculating the heat transfer coefficient. The effects of nondimensional parameters involved in binary nanofluids on the onset of convective instabilities are depicted pictorially. The dependence of the size of the convection cells on nondimensional parameters is also discussed. The Darcy-Taylor number decreases the size of convection cells, whereas the Darcy number increases the size of convection cells. The size of the convection cells is independent of the porosity of the medium, Lewis number, volume fraction of nanoparticles, Soret effect of nanoparticles, and the solute in binary nanofluids. Furthermore, the Darcy-Taylor number and porosity have stabilising effects, whereas the Darcy number, volume fraction of nanoparticles, and Lewis number have destabilising effects on the system. Soret effects of nanoparticles and solutes exhibit dual consequences on stability. They stabilise the binary nanofluid layer if [[delta].sub.4] < -1 and destabilise when [[delta].sub.4] > -1. Their effect is immaterial if [[delta].sub.4] = -1. Key words: binary nanofluid, convection, porous medium, rotation, thermodiffusion. Nous presentons ici une etude theorique de l'apparition de la convection dans une couche poreuse horizontale en rotation saturee par un nanofluide binaire, sous l'influence de la thermodiffusion et des nanoparticules. Afin d'etudier l'apparition de la convection, nous utilisons le modele de Darcy-Brinkman pour le milieu poreux et le nombre de Rayleigh est donne analytiquement par analyse de stabilite lineaire. Nous considerons, sur une base d'eau-amoniaque, l'argent, le cuivre et l'alumina, nos trois nanofluides binaires et l'effet des nanoparticules sur la stabilite du systeme est verifiee par analyse factorielle d'addition. Nous utilisons le modele de Brinkman pour la viscosite et le modele de Bruggeman en approche de champ moyen pour la conductivite thermique, afin d'etudier l'impact des nanoparticules. Le transport de chaleur est examine en calculant le coefficient de transfert de chaleur. L'effet des parametres sans dimension impliques dans les nanofluides sur l'apparition de la convection est presentee graphiquement. Nous discutons la dependance de la grandeur des cellules de convection sur les parametres sans dimension. Il est rapporte que le nombre de Darcy-Taylor diminue la grandeur des cellules de convection, alors que le nombre de Darcy l'augmente. La grandeur des cellules est independante de la porosite du milieu, du nombre de Lewis, de la fraction volumique des nanoparticules, de l'effet Soret des nanoparticules et du solute dans les nanofluides binaires. De plus, le nombre de Darcy-Taylor et la porosite ont un effet stabilisant, alors que le nombre de Darcy, la fraction volumique des nanoparticules et le nombre de Lewis ont un effet destabilisant sur le systeme. L'effet Soret des nanoparticules et le solute ont une consequence duale sur la stabilite. Ils stabilisent le nanofluide si [[delta].sub.4] < -1 et le destabilisent si [[delta].sub.4] > -1. Ils n'ont aucun effet si S4 > -1. [Traduit par la Redaction] Mots-cles : nanofluide binaire, convection, milieu poreux, rotation, thermodiffusion., 1. Introduction In recent times, nanofluids have been an active field of research because of their greatly enhanced thermal properties and numerous significant applications in many fields, such as heat [...]

Hydrogels are promising materials for biomedical applications due to highly hydrated, porous, permeable structure with possibility to accommodate living cells, drugs, or bioactive factors. In this paper, we reported poly(methacrylic acid) (PMAA)/gelatin IPN hydrogels, synthesized by free-radical polymerization, with adjustable mechanical, structural, physicochemical, and biological characteristics. The influence of methacrylic acid (MAA), gelatin, and cross-linker in the precursor solution on hydrogels properties was investigated. The increasing concentration of MAA, gelatin, and cross-linker led to better mechanical properties, lower porosity, and water content. The compressive mechanical properties of hydrogels were significantly better in comparison to a single-network PMAA hydrogel, while the obtained compressive strength values up to 16 MPa were comparable with tough hydrogels. The increasing concentration of MAA and cross-linker reduced fatigue resistance and degradability, while the increase in gelatin content acted in the opposite way. Swelling tests in different pH conditions demonstrated strong pH-sensibility of the hydrogels, which was more pronounced as MAA concentration was higher, and gelatin and cross-linker concentrations were lower. In addition, the hydrogels strongly promoted the proliferation of human periodontal ligament stem cells and MRC-5 cells as assayed by MTT assay. KEYWORDS gelatin, IPN hydrogel, poly(methacrylic acid), tissue engineering, 1 | INTRODUCTION Hydrogels are three-dimensional hydrophilic networks of polymers capable of retaining large amounts of water or biological fluids. A highly hydrated, porous structure of hydrogels resembles the structure [...]

Cellular concrete is a lightweight solid cementitious foam that is used mainly for thermal insulation and sound absorption. Either partially or wholly, when the Portland cement in the binder is replaced with ash, the environmental impact of the material is reduced. However, the resulting changes in the cell structure and their subsequent impact upon the physical properties of the material have not been well examined. In this study, cellular concrete was prepared from alkali activated fly ash binders and separately, from Portland cement binders blended with wood ash. The cell structure was photographed using laser confocal microscopy and the images were analyzed to quantify the cellular network in terms of the porosity and the fractal dimension of the porous phase. Alongside, the cellular concrete specimens were tested for their thermal constants and sound absorption. The results show that there was an increase in the fractal dimension and an associated drop in thermal conductivity for an increase in the porosity. Key words: alkali-activation, fly ash, foamed concrete, fractal dimension, sound absorption, thermal conductivity, wood ash. Le beton cellulaire est une mousse cimentaire solide et legere qui est principalement utilisee pour l'isolation thermique et l'absorption acoustique. Lorsque le ciment Portland dans un liant est remplace partiellement ou totalement par des cendres, l'impact environnemental du materiau est reduit. Cependant, les changements dans la structure cellulaire et leur impact subsequent sur les proprietes physiques du materiau n'ont pas ete bien examines. Dans cette etude, le beton cellulaire a ete prepare a partir de liants alcalins a cendres volantes et separement, a partir de liants de ciment Portland melanges avec des cendres de bois. La structure cellulaire a ete photographiee a l'aide de microscopie confocale laser et les images ont ete analysees pour quantifier le reseau cellulaire en termes de porosite et de dimension fractale de la phase poreuse. Parallelement, les specimens de beton cellulaire ont ete mis a l'essai pour leurs constantes thermiques et leur absorption acoustique. Les resultats montrent qu'il y a eu une augmentation de la dimension fractale et une baisse associee de la conductivite thermique pour une augmentation de la porosite. [Traduit par la Redaction] Mots-cles : activation alcaline, cendres volantes, beton de mousse, dimension fractale, absorption acoustique, conductivite thermique, cendres de bois., Introduction Foam concrete is a lightweight cementitious composite, cast to densities ranging from 300 kg/[m.sup.3] to 1900 kg/[m.sup.3] (Fouad 2006). An optimal balance between the mechanical strength and requirements of [...]

In this work, the flexibility of polycarbonate (PC) membrane was improved by using polyurethane (PU) additive. However, due to the hydrophobic nature of the PU polymer, alumina ([Al.sub.2][O.sub.3]) nanoparticles were incorporated to PC-PU blend membrane. The prepared membranes have been used in a submerged membrane system to eliminate humic acid molecules from polluted water in both the presence and absence of coagulant (polyaluminum chloride). The obtained results showed that introduction of PU into PC membrane diminished hydrophilicity and enhanced porosity. Moreover, the flexibility of the PC membrane remarkably improved. Introduction of 1.5 wt % [Al.sub.2][O.sub.3] to the PC-PU blend membrane led to enhancement in both porosity and hydrophilicity. Results of morphological studies showed that in the presence of [Al.sub.2][O.sub.3] nanostructures, finger-shaped voids seemed to elongate across the entire thickness of the prepared membrane. Atomic force microscopy images showed that incorporation of PU and [Al.sub.2][O.sub.3] to the PC membrane resulted in a smoother surface. The antifouling performance of membranes revealed that the PC-PU/[Al.sub.2][O.sub.3] nanocomposite membrane possessed the most favorable antifouling features owing to its lowest surface roughness as well as highest hydrophilicity. For all membranes utilizing coagulant (PAC), the irreversible fouling ratio and the flux recovery ratio significantly diminished and increased, respectively. KEYWORDS alumina nanoparticles, antifouling, coagulant, flexibility, polycarbonate membrane, polyurethane, 1 | INTRODUCTION Rapid growth in human population and industries in the world has caused water scarcity, thereby requiring a solution to overcome this challenge. Today, water reuse is one [...]

The thermomechanical behavior of ethylene propylene diene monomer (EPDM) foams produced with the salt leaching method has been investigated and compared with the behavior of EPDM foams obtained from conventional blowing agents. Moreover, the salt-leaching process has been optimized to minimize salt residues and the influence of different parameters (such as average particle size and particle size distribution) has been investigated. Scanning electron microscopy and density measurements highlighted that salt-leaching leads to the formation of open-cell porosity with cell dimensions of around 60 to 80 [micro]m, while foams obtained with the two traditional foaming agents lead to closed-cell porosity. Compression set values indicate that the behavior of the foams produced with salt leaching are more similar to the unfoamed rubber, characterized by higher elasticity and low residual deformation. Two theoretical models were successfully applied to the compression curves (Mooney-Rivlin and Exponential-Logarithmic) and they highlighted the effect of foaming on the properties of EPDM rubber and in particular the higher chain extensibility obtained through the salt leaching foaming method. KEYWORDS blowing agents, density, foams, mechanical properties, model, processing, rubber, 1 | INTRODUCTION In the last few years, polymer foams have gained great interest due to their unique features. Due to the combination of low density and low thermal conductivity, [...]

Infrared (IR) spectroscopy has been used to characterize clay and clay-sized minerals present in drill cores that are associated with unconformity-related uranium deposits. Physical properties have been measured on samples to gain empirical data about the rock types and associated relationships with geophysical survey data. These data can be used to build three-dimensional geological models and constrain geophysical inversions. The objective of this study is to verify whether a relationship exists between rock physical properties and IR spectral mineralogy. Physical properties were measured on 427 core samples collected from the Martin Lake project, which is located in the southeastern Athabasca Basin (Saskatchewan, Canada). Results indicate that resistivity, density, and porosity are correlated to each other, especially within basement units. A comparison of their distribution with the IR spectral mineralogy demonstrates a relationship for each altered and unaltered samples. The samples with low resistivity and density, and high porosity are characterized by the presence of a di-trioctahedral (Al--Mg) chlorite (sudoite) due to the hydrothermal alteration processes. The unaltered samples with higher resistivity and density, and low porosity contain a tri-octahedral (Fe--Mg) chlorite as a result of metamorphic processes. Eleven mineralogical classes can be established based on IR spectroscopy. A percentile-based approach has been proposed and tested to define physical property ranges for each of the classes to predict resistivity and density values downhole. Key words: physical properties, density, resistivity, infrared spectroscopy, prediction, uranium, alteration, Athabasca Basin, Saskatchewan, Canada. La spectrométrie infrarouge (IR) est utilisée pour caractériser les phases argileuses des halos d'altération associées aux gisements d'uranium detype discordance. Les propriétés physiques sont mesurées pour déterminer l'emprunte géophysique des gisements mais aussi pour contraindre les modèles géophysiques et produire des modèles géologiques en trois dimensions. L'objectif de cette étude est de déterminer si des relations existent entre les propriétés physiques et la minéralogie déduite par spectrométrie IR. Des propriétés physiques ont été mesurées sur 427 échantillons prélevés sur des sondages carottés provenant du projet Martin Lake. Celui-ci se situe dans la partie sud-est du bassin d'Athabasca (Saskatchewan, Canada). Les résultats ont mis en évidence des corrélations entre la résistivité, la densité et la porosité, notamment dans le socle. La comparaison de leur distribution avec la minéralogie spectrale montre une étroite relation pour chaque type d'échantillon qu'il soit altéré ou non. Les échantillons présentant une résistivité et une densité faibles, ainsi qu'une porosité élevée sont caractérisés par une chlorite (Al--Mg) de type di-trioctaédrique (sudoite). Celle-ci est issue de processus d'altération hydrothermale. Les échantillons non altérés présentant une résistivité et une densité plus élevées, ainsi qu'une faible porosité sont caractérisés par une chlorite trioctaédrique (Fe--Mg). Celle-ci s'est formée lors de processus métamorphiques. Onze classes minéralogiques sont établies par spectroscopie IR. Une approche basée sur des percentiles est proposée pour définir des intervalles de propriétés physiques pour chacune de ces classes, qui peuvent être utilisées pour prédire la résistivité et la densité en forages. Mots-clés : propriétés physiques, densité, résistivité, spectrométrie infrarouge, prédiction, uranium, altération, bassin d'Athabasca, Saskatchewan, Canada., Introduction Igneous, hydrothermal, and sedimentary processes are ultimately responsible for the formation of ore deposits on Earth (Robb 2005). Features and results of these processes (e.g., lithologies, fluid circulation, and [...]

Metal-organic frameworks (MOFs).sup.1-3 are known for their specific interactions with gas molecules.sup.4,5; this, combined with their rich and ordered porosity, makes them promising candidates for the photocatalytic conversion of gas molecules to useful products.sup.6. However, attempts to use MOFs or MOF-based composites for CO.sub.2 photoreduction.sup.6-13 usually result in far lower CO.sub.2 conversion efficiency than that obtained from state-of-the-art solid-state or molecular catalysts.sup.14-18, even when facilitated by sacrificial reagents. Here we create 'molecular compartments' inside MOF crystals by growing TiO.sub.2 inside different pores of a chromium terephthalate-based MOF (MIL-101) and its derivatives. This allows for synergy between the light-absorbing/electron-generating TiO.sub.2 units and the catalytic metal clusters in the backbones of MOFs, and therefore facilitates photocatalytic CO.sub.2 reduction, concurrent with production of O.sub.2. An apparent quantum efficiency for CO.sub.2 photoreduction of 11.3 per cent at a wavelength of 350 nanometres is observed in a composite that consists of 42 per cent TiO.sub.2 in a MIL-101 derivative, namely, 42%-TiO.sub.2-in-MIL-101-Cr-NO.sub.2. TiO.sub.2 units in one type of compartment in this composite are estimated to be 44 times more active than those in the other type, underlining the role of precise positioning of TiO.sub.2 in this system. Investigation of a chromium-based metal-organic framework shows that the location of added TiO.sub.2 inside specific mesopores strongly affects the ability of the material to catalyse photoreduction of CO.sub.2., Author(s): Zhuo Jiang [sup.1] , Xiaohui Xu [sup.1] , Yanhang Ma [sup.2] , Hae Sung Cho [sup.2] , Deng Ding [sup.1] , Chao Wang [sup.1] , Jie Wu [sup.1] , [...]

Microencapsulated phase change materials (PCMs) are being increasingly employed as functional fillers in polymer matrices for thermal management. Therefore, the effect of PCM microcapsules on the rheological, microstructural, thermal and mechanical properties of the host polymer matrices must be understood. This work concerned the preparation of epoxy polymers filled with PCM microcapsules (MC) in various concentrations and their subsequent characterization. The MC phase increases the viscosity of epoxy before curing, thereby reducing castability and hindering elimination of air bubbles. The latter was reflected in an increase in porosity for highly filled compositions, as elucidated by density measurements and microscopic investigation. SEM micrographs showed that the adhesion between the capsule shell and the epoxy matrix was not optimal. The interfacial weakness and the intrinsic low Stiffiiess and strength of MC caused a reduction in mechanical properties, as evidenced by the Nicolais-Narkis and Pukanszky models. On the other hand, at zero or low deformation levels, the interface presents no gaps and is able to transfer load and heat, as demonstrated by the data of elastic modulus, modeled with the Halpin-Tsai and Lewis-Nielsen models, and those of thermal conductivity, in excellent agreement with the Pal model. KEYWORDS interfaces, mechanical properties, microencapsulation, thermal properties, thermosets, 1 | INTRODUCTION Organic phase change materials (PCMs) are the most commonly employed materials for thermal energy storage (TES), particularly at 0 to 100[degrees]C. [1] PCMs represent an innovative, renewable [...]

The flow and heat transfer of [Al.sub.2][O.sub.3]-water nanofluid in a channel partially filled with porous media is investigated numerically. The turbulence effect in the porous media is taken under consideration in this article. A simple case is simulated first to evaluate the accuracy of the results in comparison with the available data. The turbulent kinetic energy profile is investigated at a flow cross section. The results show that the maximum turbulent kinetic energy occurs in the clear fluid region in the vicinity of the porous media region. The turbulent kinetic energy is a decreasing function of the porosity of the porous medium. The effect of porosity on the variation of turbulent kinetic energy decreases with the increase in the porosity of the porous medium. The turbulent kinetic energy in clear fluid and porous media regions decreases with the increase in nanofluid concentration from 0.01 to 0.03, and it increases with the increase in nanofluid concentration from 0.03 to 0.05. The temperature of the nanofluid increases with the increase in the nanofluid concentration and decrease in the porosity of porous media. It is shown that for this case, with the increase in nanofluid concentration and porosity of porous media, the skin friction coefficient increases and the Nusselt number decreases. Key words: porous media, nanofluid, turbulence modelling, heat transfer, computational fluid dynamics. Nous etudions numeriquement le flot et le transfert de chaleur du nanofluide [Al.sub.2][O.sub.3]-eau dans un canal partiellement rempli d'un milieu poreux. Nous tenons compte ici de la turbulence dans le milieu poreux. Nous simulons d'abord un cas simple pour evaluer la precision des resultats en les comparant avec des donnees disponibles. Nous examinons le profil d'energie cinetique turbulente a une section transversale du flot. Les resultats montrent que le maximum de l'energie cinetique turbulente se produit dans la region du liquide coulant pres du milieu poreux et qu'elle est une fonction decroissante de la porosite du milieu poreux. L'effet de la porosite sur la variation de l'energie cinetique turbulente diminue avec l'augmentation de la porosite du milieu poreux. L'energie cinetique turbulente dans la region d'interface liquid-milieu poreux diminue avec l'augmentation de la concentration de nanoparticules de 0.01 a 0.03 et augmente ensuite avec l'augmentation de concentration de 0.03 a 0.05. La temperature du nanofluide augmente avec la concentration en nanoparticules et diminue avec la porosite du milieu poreux. Nous montrons que dans ce cas, avec l'augmentation de la concentration de nanoparticules et de la porosite du milieu, le frottement superficiel augmente et le nombre de Nusselt diminue. [Traduit par la Redaction] Mots-cles: milieux poreux, nanofluide, modelisation de la turbulence, transfert de chaleur, dynamique computationnelle des fluides., 1. Introduction The flow and heat transfer of fluid in porous media has many applications in several engineering processes, such as microelectronic cooling, chemical reactors, energy storage units, and heat [...]

Multilayered films made with at least two different electroactive polymers, in which the least conducting one acts as a dielectric and separates the layers made with the other, behave as efficient electrodes for electrochemical supercapacitors. In this work, we present a simple strategy to develop improved multilayered electrodes with structured interfaces by enhancing the porosity of the dielectric. This has been achieved by growing sodium chloride crystals onto a conducting polymer layer and, after generation of all required layers using the layer-by-layer electrodeposition technique, salt crystals have been eliminated by water etching. Results from morphological and topographical studies on single-layered poly(3,4-ethylenedioxythiophene) (PEDOT), poly(N-methylpyrrole) (PNMPy), and poly(3,4-ethylenedioxythiophene-co-/V-methylpyrrole) (COP), as well as electrochemical investigations on bi-layered films with enhanced porosity at the interface between the two layers, have been used to design new four-layered electrodes. These consist in two layers of PEDOT separated by two layers of nanosegregated COP with a porous interface in the middle. Although the properties of the new four-layered electrodes improve due to the porous interface, the highest specific capacitance corresponds to the two-layered electrode in which two PEDOT layers are separated by an ultra-porous interface., INTRODUCTION Supercapacitors have attracted a great interest over the past decade because of their high power capacity, fast energy uptake and delivery, long cycle life, simple principles, and low sensitivity [...]

Rotational molding allows the production of seamless, hollow parts with a high degree of design flexibility. Nevertheless, the process has limitations such as long cycle times as long holding times are necessary to produce components free of air inclusions. Within the scope of this article, an experimental setup was developed to evaluate the possibility and resulting effects of using vacuum in the rotational molding process. For this purpose, trials with different vacuum pressure levels and holding times were carried out and the resulting porosity and surface quality as well as the mechanical properties of the specimens were determined. The investigations showed that the use of vacuum allows a significant reduction in porosity even at low holding times, which can considerably reduce the cycle time of the process. However, the extent of possible time saving is limited by the requirement of a good surface quality, on which the vacuum application shows no effect. Furthermore, the mechanical properties of the parts could be slightly improved by using vacuum., INTRODUCTION Rotational molding is a polymer processing technology for the creation of seamless, hollow parts, which excels by a high degree of design flexibility and the ability to create parts [...]