Open Pore Volume Research Articles

High Electrocatalytic Activities of the Electrochemically Exfoliated Graphene Deposited Carbon Paper Electrodes for Vanadium Redox Flow Batteries

The cost-effective and process-efficient preparation of highly electrocatalytic carbon electrodes on a large scale is crucial for enhancing the competitiveness of vanadium redox flow batteries (VRFBs). In this work, electrochemically exfoliated graphene oxides (Exf-GOs) are prepared form graphite foil at large scale with a multi-electrodes equipped continuous Exf-GOs production system. The Exf-GOs are deposited on the activated carbon paper (A-CP) substrate by a direct infiltration-deposition approach. Collective electro-kinetics analysis applying cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) revealed that the resulting Exf-GO/A-CP electrodes exhibit two orders magnitude greater intrinsic electrocatalytic activities than the A-CP electrode for the VO2+/VO2 + redox reactions. A trade-off between the Exf-GO deposition amount and the open pore volume through the Exf-GO/A-CP electrodes was found that have critical impacts on the overall electro-kinetic performance of the electrodes. Compared to the A-CP electrode, the Exf-GO/A-CP electrode provided the VRFB with more than two-fold enhancements in the energy storage capacity and at least 10 – 15 % higher voltage and energy efficiencies. The results collectively demonstrate the high effectiveness of the Exf-GO/A-CP electrodes for VRFBs that can be prepared cost and process efficient approach at large scales.

AI-assisted deep learning segmentation and quantitative analysis of X-ray microtomography data from biomass ashes

X-ray microtomography is a non-destructive method that allows for detailed three-dimensional visualisation of the internal microstructure of materials. In the context of using phosphorus-rich residual streams in combustion for further ash recycling, physical properties of ash particles can play a crucial role in ensuring effective nutrient return and sustainable practices. In previous work, parameters such as surface area, porosity, and pore size distribution, were determined for ash particles. However, the image analysis involved binary segmentation followed by time-consuming manual corrections. The current work presents a method to implement deep learning segmentation and an approach for quantitative analysis of morphology, porosity, and internal microstructure. Deep learning segmentation was applied to microtomography data. The model, with U-Net architecture, was trained using manual input and algorithm prediction.•The trained and validated deep learning model could accurately segment material (ash) and air (pores and background) for these heterogeneous particles.•Quantitative analysis was performed for the segmented data on porosity, open pore volume, pore size distribution, sphericity, particle wall thickness and specific surface area.•Material features with similar intensities but different patterns, intensity variations in the background and artefacts could not be separated by manual segmentation – this challenge was resolved using the deep learning approach.

Investigation of key morphological parameters of pores in different grades of asphalt mixture based on CT scanning technology

The internal pore structure of asphalt mixtures directly influences their permeability characteristics. Current research has not yet clarified the quantitative characterization of different types of meso-pore structures and their impact mechanisms on permeability characteristics. Therefore, this study, based on the acquisition of the internal pore structure of asphalt mixtures through CT non-destructive scanning technology, classifies pores according to their characteristics. It conducts a multi-dimensional and multi-scale qualitative and quantitative analysis of the meso-pore structures of asphalt mixtures in terms of pore distribution, equivalent radius of pore throats, inclination angle of pore throats, tortuosity of pore throats, and pore connectivity. The results indicate that the internal pore distributions of AC-16, SMA-16, OGFC-13, and OGFC-16 gradation asphalt mixtures are uniform, without noticeable segregation. The results of porosity obtained through non-destructive CT scanning technology demonstrate good consistency with those of macroscopic experiments. This demonstrates that analyzing CT images can accurately acquire pores and quantify pore characteristics. The number of pores in AC-16 gradation specimens is approximately 3–5 times that of other groups of gradation specimens, but the average volume of the pores is only 0.98 mm3. The average pore volume for SMA-16 gradation is 5.1 mm3, while for OGFC-13 and OGFC-16 gradation, the average pore volumes are 28.3 mm3 and 29.6 mm3, respectively. In SMA-16 grade specimens, the volume of open pores accounts for 95% of the total pore volume, despite the fact that open pores make up only 1% of the total number of pores. In the OGFC-13 and OGFC-16 graded asphalt mixtures, the volumes of interconnected pores account for 88.7% and 88.9% of the total pore volume, respectively. The number and volume proportion of pore throats decrease with the increase in pore throats angle, indicating that there are more pore throats with smaller angles, which are conducive to longitudinal drainage, and fewer pore throats with larger angles, which are conducive to lateral drainage. This suggests that the vertical permeability of samples formed by traditional Marshall compaction is usually greater than their horizontal permeability.

Morphology and phosphate distribution in bottom ash particles from fixed-bed co-combustion of sewage sludge and two agricultural residues

The purpose of this study was to provide detailed knowledge of the morphological properties of ash particles, including the volumetric fractions and 3D distributions of phosphates that lay within them. The ash particles came from digested sewage sludge co-combusted with K- and Si-rich wheat straw or K-rich sunflower husks. X-ray micro-tomography were combined with elemental composition and crystalline phase information to analyse the ash particles in 3D.Analyses of differences in the X-ray attenuation enabled calculation of 3D phosphate distributions that showed high heterogeneity in the slag particles. This is underscored by a distinct absence of phosphates in iron-rich and silicon-rich parts. The slag from silicate-based wheat straw mixtures had lower average attenuation than that from sunflower husks mixtures, which contained more calcium. Calculated shares of phosphates between 7 and 17 vol% were obtained, where the highest value for a single assigned phosphate was observed in hard slag from wheat straw with 10 % sewage sludge. The porosity was notably higher for particles from pure wheat straw combustion (62 vol%), compared to the other samples (15–35 vol%). A high open pore volume fraction (60–97 vol%) indicates that a large part of the pores can be accessed by the surroundings. For all samples, more than 60 % of the discrete (closed) pores had an equivalent diameter < 30 μm, while the largest volume fraction consisted of pores with an equivalent diameter > 75 μm. Slag from sunflower husk mixtures had larger pore volumes and a greater relative number of discrete pores >75 µm compared to wheat straw mixtures.

Effect of the combination of 25-hydroxyvitamin D3 and higher level of calcium and phosphorus in the diets on bone 3D structural development in pullets.

Bone issues such as osteoporosis are major concerns for the laying hen industry. A study was conducted to improve bone-health in pullets. A total of 448 one-day-old Hyline W36 pullets were randomly assigned to four treatments (8 rep; 14 birds/rep) until 17weeks (wks). Dietary treatments were: 1) vitamin D3 at (2,760IU/kg) (D), 2) vitamin D3 (2,760IU/kg)+62.5mg 25-(OH)D3/ton (H25D), 3) vitamin D3 (2,760IU/kg) + 62.5mg 25-(OH)D3/ton + high Ca&P (H25D + Ca/P), and 4) vitamin D3 (2,760IU/kg) + high Ca&P (D + Ca/P). The high calcium (Ca) and phosphorus (P) diet was modified by increasing both high calcium and phosphorus by 30% (2:1) for the first 12wks and then only increasing P for 12-17wks to reduce the Ca to P ratio. At 17wk, growth performance was measured, whole body composition was measured by dual energy x-ray absorptiometry (DEXA), and femur bones were scanned using Micro-computed tomography (Micro-CT) for bone 3D structure analyses. The data were subjected to a one-way ANOVA using the GLM procedure, with means deemed significant at p < 0.05. There was no significant outcome for growth performance or dual energy x-ray absorptiometry parameters. Micro-computed tomography results indicated that the H25D + Ca/P treatment had lower open pore volume space, open porosity, total volume of pore space, and total porosity in the cortical bone compared to the D + Ca/P. It also showed that a higher cortical bone volume/tissue volume (BV/TV) in the H25D + Ca/P than in the D + Ca/P. Furthermore, the H25D + Ca/P treatment had the lowest trabecular pattern factor and structure model index compared to the other treatments, which indicates its beneficial effects on trabecular structural development. Moreover, the H25D + Ca/P had a higher trabecular percentage compared to the D and 25D, which suggests the additional high calcium and phosphorus supplementation on top of 25D increased trabecular content in the cavity. In conclusion, the combination of 25D with higher levels of high calcium and phosphorus could improve cortical bone quality in pullets and showed a beneficial effect on trabecular bone 3D structural development. Thus, combination of a higher bio-active form of vitamin D3 and higher levels of high calcium and phosphorus could become a potential feeding strategy to improve bone structural integrity and health in pullets.

Protonation of Surface Carboxyls on Rice Straw Cellulose Nanofibrils: Effect on the Aerogel Structure, Modulus, Strength, and Wet Resiliency.

Rice straw cellulose nanofibrils from the optimal 2,2,6,6-tetramethylpiperidine-1-oxyl oxidation/blending process carrying 1.17 mmol/g surface carboxyls were protonated to varying charged (COO-Na+) and uncharged (COOH) surfaces. Reducing the electrostatic repulsion of surface charges by protonation with hydrochloric acid from 11 to 45 and 100% surface carboxylic acid most prominently reduced the aerogel densities from 8.0 to 6.6 and 5.2 mg/cm3 while increasing the mostly open cell pore volumes from 125 to 152 and 196 mL/g. Irrespective of charge levels, all aerogels were amphiphilic, super-absorptive, stable at pH 2 for up to 30 days, and resilient for up to 10 repetitive squeezing-absorption cycles. While these aerogels exhibited density-dependent dry [11.3 to 1.5 kPa/(mg/cm3)] and reduced wet [3.3 to 1.4 kPa/(mg/cm3)] moduli, the absorption of organic liquids stiffened the saturated aerogels. These data support protonation as a critical yet simple approach toward precise control of aerogels' dry and wet properties.

Effect of Calcination Temperature on the Properties of Nanotitania-Based Extrudates from an Industrial Raw Material

Titanium dioxide is an important material for catalytic reactions as a promoter, support, catalyst, and additive. In this paper, titania extrudates were prepared from industrial raw material by an extrusion method and then calcined at different temperatures. Results show that there are nanostructures with anatase phase from 450o to 850oC because the presence of SO4 2– delays the formation of rutile nucleation up to 950oC,and the morphology is irregular and smooth at 950oC. The SO4 2– ions and crystallinegrowth affect the properties of titania extrudates at various calcination temperatures. At temperatures below 650oC, the effect of SO4 2–removal is more than the effect of crystalline growth on the properties of the extrudates. But at temperatures above 650oC, the effect of crystal growth is dominant because of mobility of atoms, although more sulfate ions are exited. It decreases open pore volume and increases strength and attrition resistance.

Plastic behaviour of clay materials for the manufacture of fast-drying red ceramics

AbstractFast drying (~60 min) is useful for optimizing production processes by increasing productivity and reducing costs and environmental impacts, especially in red ceramic industries in Brazil. However, suitable clays are necessary and, currently, studies focused on the plastic behaviour of clays with compositions suitable for extrusion, especially for fast drying, are scarce. Therefore, in this study, three different clays from the same mineral deposit were studied for producing clay-based structural products via fast drying. The clays were characterized according to their chemical, mineralogical and thermal properties, particle size, cation-exchange capacity, specific surface area and open pore volume distribution. Ten formulations were developed using a simplex-centroid mixture design of experiments and their plasticity index (PI) values were determined. The response surfaces of the formulations were evaluated according to their PI, while the formation characteristics were determined according to their extrusion workability factor values. Formulations F5 (50.0 wt.% yellow clay and 50.0 wt.% green clay) and F8 (66.6 wt.% yellow clay, 16.7 wt.% grey clay and 16.7 wt.% green clay; PI = 15.5–16.6%) displayed optimal extrusion properties, followed by formulations F7 (33.3 wt.% yellow clay, 33.3 wt.% grey clay and 33.3 wt.% green clay) and F10 (16.7 wt.% yellow clay, 16.7 wt.% grey clay and 66.6 wt.% green clay; PI = 13.8–14.2%), which are within acceptable extrusion index values. Thus, the chosen formulations have significant potential for use in the manufacture of fast-drying red ceramics.

Characterisation of ash particles from co-combustion of bark and sludges from pulp and paper industry

Recycling phosphorus from waste streams for fertilization purposes could contribute to a sustainable society. The production in the pulp and paper industry results in several waste streams, among others nutrient-rich sludges in different forms. This study presents a detailed chemical and 3D characterization of ash from co-combustion of bark and two types of sludges from a paper mill; mixed sludge and biosludge. The combustion performance was investigated for these experiments and advanced analysis methods were used to characterise the ashes to correlate chemical and physical properties relevant for nutrient recycling. The elemental composition was determined by energy-dispersive X-ray spectroscopy; dominating crystalline phases by X-ray diffraction; and morphology, porosity, pore size distribution and active surface area of the slag were analysed with synchrotron-based X-ray micro-tomography and image analysis. Slag was formed in all combustion experiments to a large extent with increasing amounts with a higher proportion of sludge. Nutrient amounts indicate that slag particles from co-combustion of both biosludge and mixed sludge can be useful either as a soil improvement directly or for recovery processes. Slag from combustion of 30 wt% biosludge and 70 wt% bark contained the highest amount of phosphorus, 9 at% on a C and O free basis. Evaluation of tomography data showed that discrete and open pores could be distinguished on a micrometre scale. The porosity of the slag varied between the replicates and fuel mixtures, on average between 17 and 23 vol% for the bark and sludge mixtures. Open pore volume displayed large variations, on average 39–56 vol% of the pores were open pores connected to the surrounding volume. For all samples, 90 % of the pores were small, with an equivalent diameter under 30 μm, but the largest pore volume (80–90 %) consists of pores with an equivalent diameter over 75 μm. In soils, pores with a minimum equivalent diameter over 30 μm generally transmit water and the smaller pores store water. The slag particles have relatively thick walls, with few pore openings to the surroundings, indicating that the slag needs to be pre-treated by milling or crushing before application in the soil.

Chemical-Physical Properties and Bioactivity of New Premixed Calcium Silicate-Bioceramic Root Canal Sealers.

The aim of the study was to analyze the chemical-physical properties and bioactivity (apatite-forming ability) of three recently introduced premixed bioceramic root canal sealers containing varied amounts of different calcium silicates (CaSi): a dicalcium and tricalcium silicate (1-10% and 20-30%)-containing sealer with zirconium dioxide and tricalcium aluminate (CERASEAL); a tricalcium silicate (5-15%)-containing sealer with zirconium dioxide, dimethyl sulfoxide and lithium carbonate (AH PLUS BIOCERAMIC) and a dicalcium and tricalcium silicate (10% and 25%)-containing sealer with calcium aluminate, tricalcium aluminate and tantalite (NEOSEALER FLO). An epoxy resin-based sealer (AH PLUS) was used as control. The initial and final setting times, radiopacity, flowability, film thickness, open pore volume, water absorption, solubility, calcium release and alkalizing activity were tested. The nucleation of calcium phosphates and/or apatite after 28 days aging in Hanks balanced salt solution (HBSS) was evaluated by ESEM-EDX, vibrational IR and micro-Raman spectroscopy. The analyses showed for NeoSealer Flo and AH Plus the longest final setting times (1344 ± 60 and 1300 ± 60 min, respectively), while shorter times for AH Plus Bioceramic and Ceraseal (660 ± 60 and 720 ± 60 min, respectively). Radiopacity, flowability and film thickness complied with ISO 6876/12 for all tested materials. A significantly higher open pore volume was observed for NeoSealer Flo, AH Plus Bioceramic and Ceraseal when compared to AH Plus (p &lt; 0.05), significantly higher values were observed for NeoSealer Flo and AH Plus Bioceramic (p &lt; 0.05). Ceraseal and AH Plus revealed the lowest solubility. All CaSi-containing sealers released calcium and alkalized the soaking water. After 28 days immersion in HBSS, ESEM-EDX analyses revealed the formation of a mineral layer that covered the surface of all bioceramic sealers, with a lower detection of radiopacifiers (Zirconium for Ceraseal and AH Plus Bioceramic, Tantalum for NeoSealer Flo) and an increase in calcium, phosphorous and carbon. The calcium phosphate (CaP) layer was more evident on NeoSealer Flo and AH Plus Bioceramic. IR and micro-Raman revealed the formation of calcium carbonate on the surface of all set materials. A thin layer of a CaP phase was detected only on AH Plus Bioceramic and NeoSealer Flo. Ceraseal did not show CaP deposit despite its highest calcium release among all the tested CaSi-containing sealers. In conclusion, CaSi-containing sealers met the required chemical and physical standards and released biologically relevant ions. Slight/limited apatite nucleation was observed in relation to the high carbonation processes.

Mechanistic study of plastic layer permeability during coking of Australian metallurgical coals

The plastic layer permeability of five Australian coals was analyzed using two permeability measurement apparatuses operating under isothermal and thermal gradient induced coking conditions. In addition, the microstructure transitions across the plastic layers of the coals were analyzed using Synchrotron micro-CT. The permeability results and pore structure parameters derived from those analyses were correlated to better understand the mechanisms of plastic layer permeability. The high-rank coking coal with low fluidity showed a low plastic layer permeability over a wide temperature range and the generation of high internal gas pressure (IGP). Among all samples tested, the high-rank coal formed an intermediate plastic layer with the lowest number of isolated pores and the smallest size of open pores. This suggests that the lower deformability of the pore structures brought about by the low fluidity prevented additional pore growth and thus hindered pore interconnectivity. Additionally, it is possible that the low permeability in the resolidfied layer lends to pore expansion due to the difficulty of volatile release, evidenced by the larger volume of open pores within a larger size range of 50–100 µm. It appears that the intermediate plastic layer with less interconnectivity solidified into the expanded open pore structures in the resolidified layer through the driver of high IGP, thus contributing to the low permeability. In addition, the formation of the low permeable barrier seemed to redirect the volatiles evolved from the plastic layer toward the loose coal side, which dramatically reduced the temperature range of the plastic layer during its progression from the wall to the center. These results suggest that the plastic layer permeability is influenced by several factors which affect mass transfer in the plastic layer. As such, various approaches were used in this study to observe phenomena of plastic layer permeability.

Changes of Physical and Mechanical Properties of Coral Reef Limestone under CO2–Seawater–Rock Interaction

Large amounts of anthropogenic CO2 in the atmosphere are taken up when the ocean alters the seawater carbonate system, which could have a significant impact on carbonate-rich sediments. Coral reef limestone is a special biogenic carbonate, which is mainly composed of calcium carbonate. When carbonate-rich rocks are brought into contact with a CO2 weak acid solution, they will be dissolved, which may affect the physical and mechanical properties of the rock. In this paper, the physical and chemical interactions between CO2, seawater and the framework structure reef limestone were studied based on an experiment conducted in a hydrothermal reactor. The solution was analyzed for dissolved Ca2+ concentration during the reaction, and the rock mass, effective volume (except for the volume of open pores), permeability, images from electron microscopy and X-ray microtomography were contrasted before and after immersion. The uniaxial compressive and tensile strength tests were conducted, respectively, to clarify the mechanical response of the rock after the reaction. The results indicate that dissolution occurred during the reaction, and the calcium ions of the solution were increased. The physical properties of the rock were changed, and the permeability significantly increased. Because the rocks were soaked for only 15 days, the total cumulative amount of calcium carbonate dissolved was less, and the mechanical properties were not affected.

Morphological characterisation of ash particles from co-combustion of sewage sludge and wheat straw with X-ray microtomography.

Combustion of phosphorus-rich residual streams can produce nutrient-rich ashes and these can be used either in further processing or as materials for direct nutrient recycling. The latter requires knowledge on morphological parameters of such ash particles that may impact plant growth, nutrient availability, and soil physical properties. The present work aims to determine the porosity, pore size, and specific surface area of ash particles, and discuss these properties in light of literature concerning interaction with soil water and plant roots. Bottom ash particles from combustion of sewage sludge and wheat straw and their co-combustion were analysed with X-ray microtomography. Image analysis provided information on morphology, specific surface area, porosity, and pore structure on a micrometre scale resolution. Co-combusting sewage sludge with wheat straw resulted in differences in ash particles' porosity and pore structure compared to combustion of pure fuels. Pure wheat straw ash displayed 62vol% porosity while there was no apparent difference between 10wt% or 30wt% mixtures of sewage sludge, with a porosity of 29-31vol%. Open pore volume comprise the largest part of the porosity (72-99vol%) enabling interaction between surrounding pore water and nutrients. Overall, the ash particles display large open volume fractions and thin particle walls which may lead to rapid weathering and extensive interaction with soil water. The particles generally contained pore openings over 200µm towards the surroundings, which provide opportunities for interaction with microbes and roots from a variety of plant species in addition to nutrient transport by soil water.

Battery Separator Characterization Strategy via Electron Microscopes

Lithium Ion (Li-ion) batteries store energy and power billions of devices globally, so manufacturers face pressure to ensure high energy density while maintaining safety. Among a battery’s components, a thin separator material prevents physical contact between electrodes while directing ion transport within a cell. Both processes impact cell rate performance, cycle life, and safety [1]. Therefore, an in-depth understanding of separator structure is essential to improving batteries [2-4]. 2D and 3D electron microscopy (EM) effectively characterize separator structure; however, due to intrinsic beam sensitivity to most separators, care is needed to accurately characterize separator structure in its native state. Our work tested 2D scanning EM (SEM) and 3D DualBeamTM (Focused Ion Beam-Scanning Electron Microscope, FIB-SEM) imaging conditions to understand their effect on recovered separator structure.We investigated battery separator structure using a Thermo Scientific ApreoTM SEM and Thermo Scientific DualBeam systems equipped with CryoMAT. The SEM assisted with understanding surface-level electron beam damage in 2D and the DualBeam uncovered 3D structure using FIB milling. In the 2D case, we found the accelerating voltage could warp the separator. Low kV imaging is thus recommended to minimize structure damage.Additionally, in 2D SEM cross-section studies, sample preparation could affect separator structure. We tested an Al2O3-coated composite separator by FIB milling at three different temperatures (Figure 1). We found that cryogenic temperatures (-80° C; i.e., cryo-FIB) achieved the highest quality cross-section (Figure 1). FIB milling at either room temperature (25° C) or ultracold temperature (-180° C) both introduced defects on the microstructure.Finally, given the previous result, we collected 3D separator structure via cryo-FIB. With the 3D image stack, we used Thermo Scientific Avizo™ Software to recover structural parameters: open pore volume fraction, closed pore count and volume fraction, pore connectivity, tortuosity, and permeability. Such information should be useful for understanding battery separator performance. It is expected the strategies discussed in this talk will facilitate separator technology development.

3D-printed multisampling holder for microcomputed tomography applied to life and materials science research

The aim of this work was to design, fabricate, test and validate a 3D-printed multisampling holder for multi-analysis by microcomputed tomography. Different raw materials were scanned by microcomputed tomography. The raw material chosen was used to fabricate the holder by 3D printing. To validate the multisampling holder, five teeth were filled with a high density-material and scanned in two ways: a single and a multisampling scan mode. For each tooth, the root canal filling volume, porosity volume, closed pore volume, and open pore volume were calculated and compared when the same tooth was scanned in the two sampling scan mode. ABSplus P430™ allowed a high transmission value (84.3 %), and then it was the polymeric material selected to fabricate the holder. In a single sampling scan mode, the scan duration for scanning five teeth was 87.42 min, contrasting with 21.51 min for a multisampling scan mode, which scanned five teeth at the same time. The scan duration time and the cost using a multisampling holder represented a reduction of 75 % and the data volume generated represented a reduction of 60 %. Comparing the two scan modes, the results also showed that the difference of root canal filling volume, porosity volume, closed pore volume, and open pore volume was not statistically significant (p > .05). The multisampling holder was validated to do multi-analysis by microcomputed tomography without significant loss of quantitative accuracy data, allowing a reduction in scan duration time, imaging cost, and data storage.

Variety of structure and changes in the properties of building composites over time

The potential possibility of increasing the level of mechanical properties of composites on mineral binders remains during the long period. The initial structures hereditarily determine the change of the properties of the finished material in time. It can be assumed that an increase in the structural diversity of concretes should lead to such the organization of a structure that will guarantee the preservation or increase of the level of quality indicators at long terms of hardening (up to 720 days). The conducted researches showed that concrete of long hardening with the structure organized at selective adhesion of a cement matrix to the surface of dense or porous aggregates differed are more resistant to external influences. That is, those concretes, organization of structure which happened under the conditions of diversity of interphase interactions at the level of a macrostructure. This was ensured by the use of aggregates with various condition of a surface. The directed change of a ratios of adhesive-cohesive bonding forces at the surfaces of partition between a cement part and the surface of an aggregates provided structures, which caused increase the compressive strength of concrete by 18% and the module of elasticity by 24% at reducing the water by 29-36% and the open capillary pore volume by 44%. The structure of concrete organized at selective adhesion was the densest in comparison with of concrete of other structures. At the same time, the damage of material by technological cracks and inner surfaces of partition has grown more for concrete, the structure of which was provided by a variety of conditions of interactions between the cement matrix and aggregates. Favourable change of the parameters of these elements, along with the processes of hydration of relict binder grains, causes an improvement in time of indicators of the mechanical and deformative properties of concrete. Thus, structural diversity determines the potential changes of the concrete structure at long-hardening that must be taken into account at designing compositions and technology of the concrete, intended for difficult operating conditions.

Impedance and Resistivity of Low–Pt Cathode in a PEM Fuel Cell

Analysis of impedance model for the low–Pt cathode catalyst layer (CCL) in a PEM fuel cell is reported. The CCL is modeled as a cylindrical pore with the Nafion film separating the open pore volume from the Pt/C surface. In the limit of fast oxygen transport through the open pore, analytical expressions for the CCL impedance, Nafion film impedance and for the ohmic CCL resistivity R ccl (Ohm cm2) are derived. The characteristic frequency of film impedance is independent of film oxygen transport parameters and it is only 1.73 times less than the frequency of faradaic process in the CCL, which impedes separation of these processes by impedance spectroscopy. A fast version of algorithm for distrubution of relaxation times calculation is developed and used to illustrate the problem. R ccl exhibits rapid growth in the vicinity of limiting current density in the Nafion film, manifesting “overlinear” oxygen transport loss reported in experiments. For typical low–Pt cell parameters, this growth occurs at the cell current around 1 A cm−2. The model leads to a simple relation for the Nafion film transport resistivity (s cm−1); this relation is compared to semi–empirical and model relations available in literature.

Капиллярный подсос стенового керамического материала в зависимости от поровой структуры кирпича

The article presents the results of the study by the method of mercury porosimetry of pore structure of ceramic samples formed in the factory, obtained by plastic molding and semi-dry pressing, as well as samples of bricks selected from structures built in the XIX century. It is shown that materials with a larger volume of open large pores have increased frost resistance. There has been established dependence of the capillary suction of ceramic materials on the size of the pores, taking into account the penetration of salt solutions (nitrates, sulfates, chlorides and carbonates) into the brickwork. There has been studied the efficiency and expediency of the introduction of microsilica (terra silicea) into the clay mass from the point of view of the possible effect on the pore structure and strength of the ceramic material. The results of the research will certainly contribute to the development of effective methods related to the preventing the formation of salt deposits (salt efflorescence) violating the aesthetics of the brick building facades, and will allow developing the methods for the restoration of brick structures destroyed as a result of erosion, salt corrosion and biodegradation.

Densification behaviour and three-dimensional printing of Y2O3 ceramic powder by selective laser sintering

The selective laser sintering (SLS) of an yttria (Y2O3) ceramic powder was studied to understand both the effects of i) the initial yttria particle characteristics on the powder bed behaviour and ii) the process conditions (laser power, scanning speed, hatching space) on the sintering/melting of three-dimensionally printed objects. The roughness of the powder bed, a sensitive indicator of the layer bed quality, was determined through three-dimensional optical profilometry and the powder bed packing density was modelled using the discrete-element method. Complex shaped objects including spheres and open rings were successfully fabricated by the SLS three-dimensional printing. In addition, SLS cube-shaped samples were characterized by X-ray diffraction and scanning electron microscopy. The open pore volume fraction significantly decreased from 41% without a post-SLS heat treatment to 31% with a post-SLS heat treatment at 1750 °C for 20 h under secondary vacuum. Finally, an anisotropy in elastic properties has been highlighted, Young's modulus reaches 11 GPa in the stiffest direction.

Production Conditions of Nanoporous Ceramics Based on Mullite

A technology for producing nanoporous ceramics based on mullite (3Al2O3 ⋅ 2SiO2) is developed. The mechanochemical activation of oxides involved in the synthesis of mullite (γ-Al2O3 and amorphous SiO2) makes it possible to obtain single-phase 3Al2O3 ⋅ 2SiO2 and to reduce its sintering temperature to 1300°С. The effect of the pressing pressure and the amount of pore-forming additive (ammonium carbonate) on the value of open porosity, pore volume, and pore size distribution in sintered ceramics 3Al2O3 ⋅ 2SiO2 is established. Mullite nanoceramics with open porosity of 42–47%, pore size <200 nm, and compressive strength 50–65 MPa is obtained.