Changes In Pore Morphology Research Articles

Effects of Rock Water with Different Alkalinity and Pre-Oxidation on Re-Ignition Characteristics of Residual Coal

ABSTRACT To investigate the impact of alkaline rock water (pH = 8, 9) combined with pre-oxidation on changes in pore structure and functional groups of residual coal in goaf, and consequently, on the secondary oxidation and spontaneous combustion characteristics of coal samples, an analysis was conducted. This analysis focused on examining changes in pore morphology and functional group content of pre-oxidized coal (OI0) and water-immersed oxidized coal (OI) through experiments utilizing low-temperature nitrogen adsorption and in-situ diffuse reflectance infrared spectroscopy. Secondary oxidation and spontaneous combustion characteristics of coal samples were analyzed using thermogravimetric differential thermal analysis incorporating oxidation kinetic theory. The findings indicated that after the combined effect of pre-oxidation and alkali leaching, the mesopore volume of the coal decreased, pore complexity increased, oxygen storage capacity was enhanced, and the apparent activation energy of the coal samples was significantly reduced. This reduction in activation energy was pronounced at lower temperatures but less so at higher temperatures. Specifically, the methyl and methylene contents of OI9 were significantly higher than those of other coal samples within the temperature range of 80–160°C. Meanwhile, the heat release of the low-temperature oxidation stages of OI0, OI8, and OI9 increased by 70.82%, 190.25%, and 75.05%, respectively, compared with RC. The study indicates an elevated risk of spontaneous coal combustion following the combined treatment of alkaline leaching and pre-oxidation. This research elucidates the mechanism of spontaneous combustion of water-immersed coal by alkaline rock water and pre-oxidation, providing valuable insights for the control of coal fires in alkaline mine-water environments.

Progressive inhibition of [formula omitted] reaction in wood char packed bed by in-situ evolving [formula omitted]: Experimental insights and theoretical analysis

Previous research on Char reactions with gas phase compounds under micro-thermogravimetry systems shows that hydrogen inhibits heterogeneous char reactions. However, its impact on larger gasification systems with evolving hydrogen profiles remains largely unexplored. This study examines a macro-scale wood char bed to understand the influence of in situ evolving hydrogen on char reactions. When subjected to a specific steam flux, carbon conversion and pore morphology changes are mainly confined to the bed’s upstream, with the downstream char retaining its original characteristics. Numerical investigations reveal over 75 % of species production and consumption occurs within the initial 20 % of bed height. Fourier-transform infrared spectroscopy confirms hydrogen-induced inhibition in downstream segments, showing a shift from C–OH to C–H bonds. Particle-scale analysis indicates significantly higher rates of hydrogen diffusion and adsorption compared to H2O, impeding downstream C+H2O reactions. Increased temperature, higher reactant concentrations, or reduced residence time can overcome this inhibition, enhancing conversion rates. These findings are critical for optimizing steam-to-biomass ratios in oxy-steam gasification systems for generating hydrogen-rich syngas.

Pore morphology changes and quantitative analysis and evaluation of high‐rank coal samples after impact

AbstractThe influencing mechanism of impact loads on the pore morphology of high‐rank coal has been extensively investigated since mining safety is greatly determined by the ensuing state of gas occurrence. In this work, we propose a combined use of a scanning electron microscope and Image Pro Plus software to examine the impact‐induced changes in pore characteristics. Impact loads of 0, 28.46, 51.8, and 58.7 MPa were applied to the coal samples in various directions (parallel/vertical/45° oblique). The results show that the pore connectivity of coal samples is enhanced following the impact load, and the number and diameter of pores are significantly increased on the whole. Surface porosity and roundness of the coal body first rise and then fall as the impact load increases. Following the impact load, surface porosity and roundness of the coal body significantly increase in the vertical and oblique bedding directions, while decreasing in the horizontal bedding direction.

Effect of sintering on stress distribution of thermal barrier coatings for high temperature blade

In the process of long-term high temperature service, thermal barrier coatings (TBCs) will inevitably be sintered, leading to pores healing and porosity decline, which will affect the microstructure and the stability of mechanical properties of TBCs. To understand the relationship between the microstructural changes of sintered TBCs and the mechanical properties, in this work, the cross-sectional microstructure of TBCs at different sintering times were investigated by scanning electron microscopy (SEM). After calculating the porosity and pore size distribution, two-dimensional (2D) numerical models were developed for five different porosities (16 %–12 %) by an improved reconstruction method with layer-by-layer labeling. Based on the results of finite element (FE) analysis after thermal cycling, it was found that the coating's irregular pore structures lead to stress concentration, which affects the mechanical properties of the coating to a great extent. For the whole TC layer, the level of stresses increases and the absolute value of maximum stress augments significantly by 46 % associated with the doubled increase of stress concentration areas with the densification of coating. For the local areas of TC layer, the changes in pore morphology led to a more complex variation in local stress fields. At the TC/BC interface, the Mises stress level tends to increase with decreasing porosity during sintering. At the TC surface, coatings with lower porosities cause higher stresses near this region. The insights gained from the numerical results contribute to a better understanding of the failure behavior of real TBCs systems and help to further remedy the deficiencies and difficulties of the experimental work.

Exploring Carbonate Rock Dissolution Dynamics and the Influence of Rock Mineralogy in CO2 Injection.

Understanding geochemical dissolution in porous materials is crucial, especially in applications such as geological CO2 storage. Accurate estimation of reaction rates enhances predictive modeling in geochemical-flow simulations. Fractured porous media, with distinct transport time scales in fractures and the matrix, raise questions about fracture-matrix interface dissolution rates compared to bulk dissolution rate and the scale-dependency of reaction rate averaging. Our investigation delves into these factors, studying the impact of flow rate and mineralogy on interface dissolution patterns. By injecting carbonated water into carbonate rock samples containing a central channel (mimicking fracture hydrodynamics), our study utilized μCT X-ray imaging at 3.3 μm spatial resolution to estimate the reaction rate and capture the change in pore morphology. Results revealed dissolution rates significantly lower (up to 4 orders of magnitude) than batch experiments. Flow rate notably influenced fracture profiles, causing uneven enlargement at low rates and uniform widening at higher ones. Ankerite presence led to a dissolution-altered layer on the fracture surface, showing high permeability and porosity without greatly affecting the dissolution rate, unlike clay-rich carbonates. This research sheds light on controlling factors influencing dissolution in subsurface environments, critical for accurate modeling in diverse applications.

Changes in mineral fraction and pore morphology of coal with acidification treatment: contribution of clay minerals to methane adsorption.

The accurate calculation of the contribution which provided by clay minerals in coal on methane adsorption not only bares a significant importance for evaluating the effectiveness of acid stimulation in improving permeability and estimating the coalbed methane reserves but also serves a guide for the governance and utilization of methane resources. In this study, hydrochloric acid (HCl) and hydrofluoric acid (HF) were used to remove specific minerals in Qingdong coal samples. We firstly analyzed the mineral compositions of coal samples with different acidification treatments based on the X-ray diffraction (XRD) experiments, together with analysis of the changes in pore morphology and adsorption capacity. The results showed that acidification did not significantly change the shape of the pores, which remained slit-/plate-like pore. However, the altered adsorption capacity of the coal samples was attributed to changes in pore structure and mineral distribution. Acid erosion of mesopores promoted the transition from mesopores to macropores, contributing to an increase of 8.4% and 24.36% in the percentage of macropores in coal samples treated with HCl and HF, respectively. Fractal dimension D1 grew from 2.2193 to 2.3888 and 2.2572, respectively, but D2 decreased from 2.6146 to 2.5814 and 2.5433, indicating an increment in pore surface roughness and a simplification of the pore structure. The mineral richness of the coal seams should be taken into consideration when applying acid stimulation to increase permeability due to that the acidification products may block the passage of gas migration when the mineral content is slight, which can hinder gas extraction. The aim of this study is to quantitatively determine the contribution rate of clay minerals in coal to methane adsorption with a calculation method is provided by combining pore parameters and limit adsorption capacity, resulting in a contribution rate of 15%.

Periodic microstructure of Al–Mg alloy fabricated by inter-layer hammering hybrid wire arc additive manufacturing: Formation mechanism, microstructural and mechanical characterization

Inter-layer plastic deformation is an effective method to improve the mechanical properties of wire arc additive manufacturing (WAAM) components. In this study, the inter-layer hammering hybrid WAAM process was applied, and a periodic microstructure composed of alternate coarse and fine grain regions was obtained. These regions were defined as the work hardening region (W region) and recrystallization region (R region) according to the respective formation mechanism. The grain size, texture intensity, grain boundary misorientation angle, phase structure, and dislocation density in these two regions were systematically investigated, and their contributions to the mechanical properties were analyzed. The results show that hammering, especially with increase of hammering times, maintains the depth of recrystallization of each layer at 1.0 mm and increases the ratio of the R region. The grain size in the R region was significantly refined, and the dislocation density in the R region was lower than that in the W region due to the dislocation release by recrystallization caused by subsequent deposition heat, and sub-grains were formed in the W region. The best tensile properties were achieved in the horizontal direction when the inter-layer region was hammered 3 times. The ultimate tensile stress (UTS) exceeded 400 MPa and the elongation exceeded 13%. However, the change in pore morphology caused anisotropy in hammered samples.

Pore structure evolution during lean-oxygen combustion of pyrolyzed residual from low-rank coal and its effect on internal oxygen diffusion mechanism

The lean-oxygen combustion of incompletely pyrolyzed char dominates at the combustion front of coalfield fires. Using non-local-density functional theory (NLDFT) and Barrette-Joynere-Halenda (BJH) analysis based on N2 and CO2 composited adsorption isotherms, the pore (0.4–300 nm) structure characteristics of pyrolyzed char during lean-oxygen combustion were obtained. The results indicate that the main pore morphology changes from irregular ink-bottle shape of raw coal to cylindrical shape of pyrolyzed char, then to slit-shaped and wedge-shaped pores under the effect of oxidative expansion, and finally coalesce into amorphous macropores during combustion. For the weak-caking coal, softened colloids diffuse and block the mesopores, leading to the reverse development of mesopores into smaller-sized pores. The pore development changes from the generation of secondary micropores in pyrolysis stage to the progressive expansion mode of mesopores in initial combustion stage, then to the free coalescence mode of macropores in late combustion stage. The dominant internal oxygen diffusion mechanism transforms from Knudsen diffusion to transition diffusion at 650 °C, and the carbon-oxygen reaction interfaces shift from the inner surface of deep micropores to the shallow mesopores and macropores. Finally, 650 °C is determined as the early-warning temperature for the accelerating spread of coalfield fires.

Real-time imaging of optic nerve head collagen microstructure and biomechanics using instant polarized light microscopy

Current tools lack the temporal or spatial resolution necessary to image many important aspects of the architecture and dynamics of the optic nerve head (ONH). We evaluated the potential of instant polarized light microscopy (IPOL) to overcome these limitations by leveraging the ability to capture collagen fiber orientation and density in a single image. Coronal sections through the ONH of fresh normal sheep eyes were imaged using IPOL while they were stretched using custom uniaxial or biaxial micro-stretch devices. IPOL allows identifying ONH collagen architectural details, such as fiber interweaving and crimp, and has high temporal resolution, limited only by the frame rate of the camera. Local collagen fiber orientations and deformations were quantified using color analysis and image tracking techniques. We quantified stretch-induced collagen uncrimping of lamina cribrosa (LC) and peripapillary sclera (PPS), and changes in LC pore size (area) and shape (convexity and aspect ratio). The simultaneous high spatial and temporal resolutions of IPOL revealed complex ONH biomechanics: i) stretch-induced local deformation of the PPS was nonlinear and nonaffine. ii) under load the crimped collagen fibers in the PPS and LC straightened, without torsion and with only small rotations. iii) stretch-induced LC pore deformation was anisotropic and heterogeneous among pores. Overall, with stretch the pores were became larger, more convex, and more circular. We have demonstrated that IPOL reveals details of collagen morphology and mechanics under dynamic loading previously out of reach. IPOL can detect stretch-induced collagen uncrimping and other elements of the tissue nonlinear mechanical behavior. IPOL showed changes in pore morphology and collagen architecture that will help improve understanding of how LC tissue responds to load.

Pore scale modeling and evaluation of clogging behavior of salt crystal aggregates in CO2-rich phase during carbon storage

The optimal CO2 storage operation requires high permeability in the near-well region in order to keep it safe and cost-efficient. Nucleation and growth of salt crystals driven by the evaporation of formation water into under-saturated (dry) super-critical CO2 streams result in the changes in porosity and permeability of the near well-bore area. Permeability reduction is one of the main reasons for injectivity losses in the context of CO2 storage in saline aquifers. According to recent studies, during CO2 storage, salt crystals grow in two different forms: 1) single, large crystals in the aqueous phase, and 2) aggregates of micro-meter size salt crystals in the CO2-rich vapor phase. All previous numerical studies at pore-scale have addressed the formation of single, large crystals in the aqueous phase. In this work we have developed a 3D pore-scale reactive transport solver based on a D3Q19 advection-diffusion Lattice-Boltzmann model. The model takes for the first time salt nucleation into consideration via a new probabilistic approach to simulate the formation of micro-meter size salt crystal aggregates in the CO2-rich phase and their effect on changes in pore morphology and permeability. Comparing the results of porosity-permeability relations with some of the well-known clogging models, confirms the need for a new clogging model to capture the permeability reduction caused by salt aggregates.

Porous Ti6Al4V alloys with high strength-to-modulus ratio fabricated by unidirectional freeze casting of SiC fiber-containing slurry

Porous titanium alloys with high strength-to-modulus ratio are one of the promising materials for bone implants. In the present work, porous Ti6Al4V alloys with SiC fiber bridges and fiber reinforced wall structure were obtained by unidirectional freeze casting of SiC fiber-containing slurry. The effect of SiC fiber content on the pore structure, microstructure, interface and compressive properties was systematically investigated. The formations of fiber bridges and fiber reinforced wall structure were elaborated through analyzing the interaction between fibers and ice front. Addition of SiC fibers has significant effects on the porosity, structural wavelength, and pore morphology of porous alloys. Porosity increases with the increase in fiber content, and pore morphology changes from lamellar to dendritic. Porous Ti6Al4V alloys mainly contain equiaxed α and β phase. Crystalline phases of Ti5Si3 and TiC are present at the interface. Micropores are also observed on the fiber side close to the interface due to the Kirkendall effect. Both Young's modulus and yield stress increase with the increase in SiC fiber content, while they dramatically decrease at higher fiber content of 10 vol%. SiC fiber bridges and fiber reinforced wall structure have synergetic strengthening effects for suppressing buckling deformation of lamellar walls and thus for improving the strength of porous titanium alloys. Porous Ti6Al4V alloys fabricated by 2 vol% SiC fibers possess high porosity of 67% and high strength-to-modulus ratio of 0.027.

Toward Probabilistic Modeling of Halite Nucleation and Growth during Carbon Storage Process: Pore Scale Modeling

To maximize safety and cost-efficiency of CO2 storage, it is necessary to understand how a high permeability in the near-well region is maintained. Nucleation and growth of salt crystals driven by the evaporation of formation water into under-saturated (dry) super-critical CO2 stream results in the changes in the porosity and permeability of the near well-bore area. Permeability reduction is the main reason of the injectivity loss in the context of CO2 storage in saline aquifers. According to recent studies, during CO2 storage, salt crystals form in two different forms: 1) single, large crystals in the aqueous phase, and 2) aggregates of micrometer size salt crystals in the gas phase. All the previous numerical studies at pore-scale addressed the formation of single, large crystals in the aqueous phase. In this work, we developed a 3D pore-scale reactive transport solver (a D3Q19 advection-diffusion Lattice-Boltzmann model) and took nucleation process into account via a new probabilistic approach to simulate the formation of micro-meter size salt crystals in the gas phase and their effect on changes in pore morphology and permeability for the first time. Comparing the results of porosity-permeability relation with some of the well-known clogging models, confirms the need for a new clogging model to capture the permeability reduction caused by salt aggregates.

An investigation into the relationship between saturated permeability and microstructure of remolded loess: A case study from Chinese Loess Plateau

Understanding the permeability law of remolded loess is important for engineering construction in the loess area. To gain insights into the changes of saturated permeability and microstructural evolution of remolded loess for different dry densities, the loess from the Chinese Loess Plateau was used as a test material and was remolded as samples with different dry densities at the optimum water content state. The saturated seepage test and scanning electron microscopy (SEM) imaging were conducted on the remolded loess samples. The microscopic properties of the loess pores in the SEM images were identified using Image-Pro Plus software. The relationship between the micro-parameters of the pores and permeability were explored using multivariate statistical analysis. Results from this study highlight that the dry density of samples can be classified into three categories: Group I (1.30 and 1.35 g·cm−3) shows permeability decreasing with seepage time, Group II (1.40 g·cm−3) shows permeability initially increasing and then decreasing with seepage time, and Group III (1.45–1.65 g·cm−3) shows permeability increasing with seepage time. Correspondingly, the dry densities of these groups were found to be unsuitable, doubtful, and suitable, respectively, for laboratory study on the saturated permeability of remolded loess. In addition, the evolution mode of remolded loess structure is basically overhead-interlocking-matrix with increasing compactness. In this process, the macropores transform into mesopores and then to small pores, while the change in micropore content is weak. Also, the directional distribution of the pores weakens, while the pore morphology changes little. Furthermore, the contents of macropores and mesopores, as well as the pore diameters, play a positive role in permeability, while the contents of small pores and micropores, and directional probability entropy have a negative impact on permeability.

Stress Sensitivity of Fractured and Vuggy Carbonate: An X‐Ray Computed Tomography Analysis

AbstractFractures, vugs, and pores constitute the main pore space in carbonate reservoirs. The associated pore structure—which is of key importance in terms of hydrocarbon production and fluid flow—varies with effective stress. However, there is a serious lack of data with regard to how precisely the pore morphology changes as a function of effective stress; we thus carried out in situ loading‐unloading experiments (up to 20 MPa effective stress) where two carbonate samples (fractured and vuggy) were examined with X‐ray computed tomography at high resolution in 3‐D. The results showed that after loading, porosity decreased exponentially, followed by an increase during unloading where it did not recover to its initial value. This was mainly because of the stress effect on large pore space (i.e., fractures and vugs). For fractured carbonate, the unrecovered porosity can be linked to similar reduction of the surface area and the average aperture of the fracture. Clearly, the changes in pore morphology were more significant in the fractured carbonate (including extension, connection, and disconnection of fractures) during both loading and unloading, while the vuggy carbonate experienced irreversible structural damage. The vuggy carbonate has bigger porosity variation than fractured carbonate to the mechanical loading‐unloading cycle. This work thus demonstrates how carbonate pore morphology changes with depth (higher effective stresses are encountered deeper in the reservoir) or during production (with hydrocarbon depletion the effective stress increases).

Synthesis and structural control of Fe-based porous layer on Fe substrate for joining with resin parts using combustion reaction

A porous Fe/TiB2 composite layer was synthesized on an Fe substrate by a powder metallurgy process using combustion reactions among Fe, Ti, and B to achieve Fe/resin joints through interpenetrating phase layers. The effects of Fe particle size and the blending ratio of the raw powder mixture on the porous structure, roughness of the top surface of the porous layer, and adhesiveness between the porous layer and Fe substrate were investigated. The peak temperature measured with a thermocouple increased with increasing Fe particle size and blending ratio of Ti and B. An increase in the peak temperature does not affect the porosity of the porous layer. Higher peak temperatures increase the pore size and change the pore morphology from open to semi-closed (although pores are not completely isolated). The change in pore morphology prevents the exposure of pores on the top surface of the porous layer, resulting in decreasing surface roughness. Moreover, an increase in the maximum temperature promotes bonding between the Fe substrate and porous layer. These results are discussed in view of the thermodynamic assessment using the calculated equilibrium phase diagram.

Effect of swelling agent on the pore structure of SBA-15 studied by positron annihilation

Porous silica SBA-15 was synthesized using triblock copolymer P123 as structure template and tetraethyl orthosilicate (TEOS, C8H20O4Si) as silicon source. The pore structure was adjusted by using swelling agent 1,3,5-trimethylbenzene (TMB). Small angle X-ray scattering (SAXS) and high resolution transmission electron microscopy (HRTEM) indicate that the pore morphology changes in three stages with increasing TMB/P123 ratio. In the first stage (TMB/P123 < 0.2), the pore type is a typical cylindrical hole. When TMB/P123 is 0.2–0.5, the pore morphology is a curved cylinder. In the final stage when TMB/P123 ratio is higher than 0.5, the ordered mesoporous silica is converted into mesoporous silica foam. The average pore size estimated from N2 adsorption measurements increases from 6.5 nm to 17.2 nm with increasing TMB/P123 ratio from 0 to 2. Positron lifetime measurements indicates two long lifetime components τ3 and τ4, which are due to o-Ps annihilation in micropores and mesopores, respectively. It was found that the mesopores are open pores and the micropores are closed pores. With the increase of TMB ratio, the number and size of micropores show nearly no change, but the mesopore size increases gradually with increasing TMB/P123 ratio up to 0.5, which are in agreement with the results of the N2 adsorption/desorption measurements. However after the pores evolves into mesoporous foam, the pore size obtained from o-Ps lifetime is less than that of N2 adsorption/desorption measurements.

Investigations on neutron irradiated 3D carbon fibre reinforced carbon composite material

As against conventional graphite materials carbon-carbon (C/C) composite materials are now being contemplated as the promising candidate materials for the high temperature and fusion reactor owing to their high thermal conductivity and high thermal resistance, better mechanical/thermal properties and irradiation stability. The current need is for focused research on novel carbon materials for future new generation nuclear reactors. The advantage of carbon-carbon composite is that the microstructure and the properties can be tailor made. The present study encompasses the irradiation of 3D carbon composite prepared by reinforcement using PAN carbon fibers for nuclear application.The carbon fiber reinforced composite was subjected to neutron irradiation in the research reactor DHRUVA. The irradiated samples were characterized by Differential Scanning Calorimetry (DSC), small angle neutron scattering (SANS), XRD and Raman spectroscopy. The DSC scans were taken in argon atmosphere under a linear heating program. The scanning was carried out at temperature range from 30 °C to 700 °C at different heating rates in argon atmosphere along with reference as unirradiated carbon composite. The Wigner energy spectrum of irradiated composite showed two peaks corresponding to 200 °C and 600 °C. The stored energy data for the samples were in the range 110–170 J/g for temperature ranging from 30 °C to 700 °C. The Wigner energy spectrum of irradiated carbon composite did not indicate spontaneous temperature rise during thermal annealing. Small angle neutron scattering (SANS) experiments have been carried out to investigate neutron irradiation induced changes in porosity of the composite samples. SANS data were recorded in the scattering wave vector range of 0.17 nm−1 to 3.5 nm−1. Comparison of SANS profiles of irradiated and unirradiated samples indicates significant change in pore morphology. Pore size distributions of the samples follow power law size distribution with different exponent. Narrowing of SANS profile of the irradiated sample indicates creation of significant number of larger pores due to neutron irradiation.

One-pot synthesis of supported hydrogel membranes via emulsion templating

Supported hydrogel membranes were produced by one-pot synthesis by polymerisation of suitable emulsion templates. High internal phase emulsions (HIPEs) with styrene (St), divinylbenzene (DVB) and ethylhexyl acrylate (EHA) in the continuous phase and methacrylic acid (MAA) in the internal phase were polymerised to prepare poly(MAA) hydrogel grafted poly(St-co-DVB-co-EHA) poly(merised)HIPEs. By changing the concentration of the crosslinker, N,N′-methylenebisacrylamide, in the internal phase of the emulsion template the crosslinking density of the grafted poly(MAA) was tuned. The presence of the hydrogel was indicated by a change in pore morphology, e.g. coverage of the pore throats and the wrinkled pore wall surface, and the increase in the density of the composite polyHIPEs as compared to control polyHIPEs. Moreover, the increase in foam density and reduction of porosity were related to the crosslinking degree of the hydrogel. The water uptake of the composite polyHIPEs exceeded the pore volume of the polyHIPE scaffold supporting the grafted hydrogel. The permeability and rejection of aqueous solutions of polyethylene glycol (PEG) by the hydrogel grafted polyHIPE membranes were strongly pH dependent, the permeability decreased and the rejection of PEG increased with increasing pH due to the increased swelling of the hydrogel. A 91% rejection of 50kDa PEG for polyHIPE supported hydrogel membranes has been identified, which qualifies such membranes for ultrafiltration applications.

Pore morphology and temperature dependence of gas transport properties of silica membranes derived from oxidative thermolysis of polydimethylsiloxane

Transport properties of silica membranes derived from the oxidative thermolysis of crosslinked polydimethylsiloxane (PDMS) were studied between 35–100°C. Changes in pore morphology and transport properties were investigated for varying thermolysis and crosslinking treatments. Permeation and pressure-decay sorption measurements were made for CO2, H2, He, O2, N2, and CH4. Physisorption data for CO2 and N2 were also analyzed to characterize the pore size distributions of these materials. The activation energies of permeation and diffusion were measured along with the enthalpies of sorption to compare the effects of varying fabrication methods. All samples showed similar enthalpies of sorption. Regular and extended-thermolysis heat treated silica showed similar permeabilities and diffusion coefficients, but the heat treated silicas showed an average increase of 2.3kJ/mol in their activation energies of permeation. The permeation, sorption, and diffusion selectivities of various gas pairs were compared. The silicas showed high sorption selectivity in gas pairs with large differences in critical temperature, but showed low diffusion selectivity due to low entropic selectivity. Overall, the PDMS-derived silicas show promise, but require further tuning to improve the entropic selectivity of penetrants.

Fabrication and characterization of porous Ti–4Mo alloy for biomedical applications

Porous Ti–4Mo alloy was prepared by indirect selective laser sintering and investigated with focuses on its porous structure, microstructural characteristic, mechanical properties and corrosion behavior. The results indicate that as the porous alloy is sintered from 1000 to 1200 °C, the pore morphology changes gradually from interconnected to closed pores, meanwhile the porosity level and pore size reduce in the ranges 54–20 % and 103–35 μm, respectively. A laminar microstructure composed of dominant α and minor β phases is observed in pore walls together with slight α precipitations. Elastic modulus and yield strength increase with decreased porosity in the ranges 2.56–10.8 GPa and 47.0–162.4 MPa, respectively. The relationship between the relative mechanical properties and relative density obeys a power law relation. All the polarization curves exhibit an obvious passive characteristic despite different pore features, and the passive film could protect the porous alloy against corrosion in simulated body fluids. Overall, the porous Ti–4Mo alloy may be a potential candidate material for biomedical implants.