Preparation and characterization of the n-HA/PVA/CS porous composite hydrogel

In this paper, a new method combines chemical/physical crosslinking, and emulsification-foaming porogenic was adopted to prepare n-hydroxyapatite (n-HA)/polyvinyl alcohol (PVA)/chitosan (CS) porous composite hydrogel using artificial cornea scaffold materials. The fabricate conditions, including the type and amount of emulsification-foaming porogen, mixing time and speed etc. were researched. The results showed the optimal condition that the alkylphenol polyoxyethylene ether (OP) acted as emulsification-foaming porogen, with the ratio of W_PVA/W_OP as 3.75, and mixing 15 min with a stirring speed of 800 r·min^-1. Additionally, the fabricated composite hydrogel scaffold materials possessed interconnected internal holes, a moisture content of above 65%, and tensile strength of above 6 MPa. In vitro cytotoxicity and acute systemic toxicity assay confirmed that the scaffolds did not show any cytotoxicity. The as-prepared hydrogel could be a promising candidate for artificial cornea scaffold material.     

Hydrodynamic and heat transfer properties of magnetic fluid in porous medium considering nanoparticle shapes and magnetic field-dependent viscosity

The purpose of this paper is to study the characteristics of the combined convection heat transfer and a micropolar nanofluid flow passing through an impermeable stretching sheet in a porous medium. The nanofluid flow field is affected by a magnetic field perpendicular to the sheet. The dynamic viscosity of the micropolar nanofluid changes under the influence of the magnetic field. The continuity, linear momentum, angular momentum, and energy equations are first simplified using the order of magnitude technique that, along with the applied boundary conditions and the definition of the appropriate parameters, are transferred to the similarity space using the similarity analysis. Then the resulting equations are solved using the Runge–Kutta method.The distinction of the macroscale and microscale flow fields and temperature fields resulting from different nanoparticle shapes was clarified. Increasing the Hartmann number, the vortex viscosity parameter, the magnetic parameter, the nanoparticle volume fraction, and the permeability parameter of the porous media increased the surface friction on the sheet. Increasing the vortex viscosity parameter, the magnetic parameter, and the volume fraction of the nanoparticles increases the Nusselt number.     

Egg shell waste as an activation agent for the manufacture of porous carbon

Egg shell waste was used as an activation agent directly for the manufacture of a biomass-derived porous carbon,which possessed a surface area of 626 m~2·g~(-1) and was rich in nitrogen, sulfur and oxygen functionalities. The activation mechanism was proposed, and the carbon showed its potential to act as an adsorbent for the adsorptive removal of various contaminants from both aqueous and non-aqueous solutions, possessing maximum adsorption capacities of 195.9, 185.1, 125.5 and 44.6 mg·g~(-1) for sulfamethoxazole, methyl orange, diclofenac sodium and dibenzothiophene, respectively. Through the utilization of egg shell waste as a sustainable activation agent, this work may help to make the widely applied biomass-derived porous carbons more economical and ecological.     

Pore structure of reactively synthesized nanolaminate Ti3SiC2 alloyed with Al

Ti₃SiC₂ has the unique properties integrating the advantages of metals and ceramics, and good open pore structure when alloyed with Al. In this work, porous Ti₃SiC₂ compounds with different Al/Si atom ratios were prepared through the reactive synthesis of elemental powders at 1300 °C. The results indicate that the phase compositions are determined by Al element mole number, and that the pore structure can be controlled through varying Ti particle size. The MAX phase transits from Ti₃SiC₂ with Al element mole number no more than 0.6 to Ti₃AlC₂ with Al element mole number in the range of 0.8–1.2. When Al element mole number is 0.6, the porous compound has a single MAX phase of Ti₃SiC₂ with uniform microporous structure and high bending strength. Porous Ti₃SiC₂ alloyed with 0.6Al has a slow linear increase rate of 0.0083%/μm in open porosity with increasing Ti particle size, and a strict linear relationship between the maximum aperture and Ti particle size with the increase rate of 0.0342 μm/μm. The pore structure formed by the phase transition mechanism for porous MAX phase has the smallest tortuosity factor compared with that formed by the clearance mechanism and the Kirkendall effect.     

Fabrication of porous titania sheet via tape casting: Microstructure and water permeability study

In this article, we report the effects of slurry formulation and sintering conditions on the microstructure and permeability of porous titania sheets prepared by tape casting. It was found that solid concentration and binder content in the titania slurry play a vital role in the porosity and microstructure of the sintered titania sheets. Solid concentration and binder content were optimized based on the green tape quality and open porosity of the sintered titania sheets. The optimum solid concentration with the lowest surface roughness was obtained at 0.61 g/cm³. The effects of temperature and sintering time on the open porosity and crystal structure of the final product were also investigated. Increasing the sintering temperature from 1000 to 1100 °C resulted in increasing the pore size from 170 to 264 nm and decreasing the open porosity. Finally, water permeability of the porous titania sheets was studied to evaluate the permeation flux and maximum operating pressure. The results revealed that the permeability of the porous titania sheet is increased not only by increasing the open porosity but also by increasing the pore size.     

Preparation of biphasic hydroxyapatite/ β-tricalcium phosphate foam using the replication technique

Biphasic hydroxyapatite/β-tricalcium phosphate foams were prepared using the replication technique starting from a precipitated hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂: HAP) powder, and sodium glycerophosphate (GP). The effect of the grinding time, solid loading, dispersant amount, and etching, replication, and sintering processes were investigated. The SEM, OEM and FTIR analyses proved that the surface of the polyurethane template must be treated with NaOH solution to make it more hydrophilic prior to the coating process. With a solid loading of 40 wt-%, the slurries prepared from the precipitated hydroxyapatite presented a shear thinning behavior, which was useful for the coating process. The SEM analysis of the foams showed that the optimum number of coating layers to obtain foam with an identical structure with the template was limited to three. The use of GP and the optimized preparation parameters helped to decrease the consolidation temperature of the ceramic foams to 1000 °C. The XRD and FTIR analyses of the prepared foams showed that the thermal treatment of the GP and the HAP mixture led to a partial decomposition of the HAP to tricalcium phosphate. The fitting of the XRD patterns and the obtained lattice parameters proved that the decomposition was accompanied by the insertion of sodium from GP toward the lattice of tricalcium phosphate and the formation of Na-β-tricalcium. The results of the SEM analysis, the pore size distribution and the mechanical strength showed that the presence of the Na-β-tricalcium reduced the pore size distribution from 500-2700 to 100–1700 μm, decreased slightly the total porosity from 80 vol-% to 70 vol-%; and improved the mechanical strength of the obtained foam from 1.56 MPa to 2.60 MPa.     

Fabrication of porous (Ba,Sr)(Co,Fe)O3-δ (BSCF) ceramics using gelatinization and retrogradation phenomena of starch as pore-forming agent

Porous (Ba,Sr)(Co,Fe)O_3-δ (BSCF) ceramics with high open porosity and good electrical conductivity was fabricated using Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF), which shows a high mixed ionic-electronic conductivity. In general, during the fabrication of porous ceramics by the sacrificial template method using pore former particles, closed pores are easily formed unless sufficient pore former particles are added. In this study, we have devised a method using the gelatinization-retrogradation phenomena of starch for producing a porous body with an excellent percolated pore network structure. By dispersing BSCF and starch in an aqueous slurry (0–50% by weight) and heating, gelatinization of the starch occurred and the starch particles adhered to each other. Furthermore, in order to retain the percolated structure, the water solvent was removed by freeze-drying without heating to obtain a dried green body. The sintering behavior of the porous BSCF bodies prepared under various conditions was characterized by microstructural observations and relative density measurements. By optimizing the process conditions of the gelatinization and retrogradation, a porous body having an open porosity of 48.3%, and with 99% of the total pores open, was obtained. The matrix was also well connected and showed a sufficiently high conductivity which was similar to the porous bodies made by the traditional sacrificial template method.     

骨架发热多孔介质方腔内非达西自然对流的数值研究

本文利用局部非热平衡模型,对骨架发热多孔介质方腔内的非达西自然对流进行了数值研究.方腔上下壁面绝热、左右壁面维持恒温T0.采用Brinkman-Darcy-Forchheimer模型来描述多孔介质内的流动,当有效导热系数比(0.001≤γ≤1.0)和无量纲容积换热系数(1.0≤H≤1000)在较宽的范围内变化时,计算研究了不同的有效导热系数比和无量纲容积换热系数对方腔内流动换热的影响.数值模拟结果表明:在有效导热系数比γ=1.0和无量纲容积换热系数H=1000时,局部热平衡模型是成立的;而对其他情形,必须采用局部非热平衡模型才能准确地预测出方腔内的流动换热特性.     

Effective elastic properties of randomly distributed void models for porous materials

Many 2D analytical models are available for estimating the effective elastic properties of porous materials. Most of these models adopt circular voids of a uniform diameter in superlattice arrays, such as unit void or periodically positioned models. There are two principal issues in a realistic representation of porous materials: the random distribution of a statistically sufficiently large number of voids in the model, and the random distribution of the size and position of the voids. Numerical schemes such as the FEM or the BEM have also been presented to cater for regular patterned circular voids. However, due to the large number of elements needed to produce sufficient accuracy for the curved boundary of circular voids or modelling a statistically sufficient number of voids with a random distribution in both the void size and the position, no such model has yet been produced.Modelling based on an FEM approach using a simplified approximation for void geometry is proposed here for the calculation of the effective elastic properties of porous solids. A plane strain model of a square geometry is adopted for a 2D array of voids. This simplified square shape allows a large number of voids to be simulated with a random distribution for both void sizes and their locations. The problem of anisotropy, which arises from the square shape, is discussed. It is verified that along the two principal directions (parallel to the sides of the square voids), the elastic properties remain the same as those predicted by using a circular void geometry. This square-shaped approximation, with its reduced requirement for FE analysis, has the potential to be extended to 3-dimensional modelling for a realistic simulation of engineering materials.     

Mathematical modeling of ammonia-fed solid oxide fuel cells with different electrolytes

An electrochemical model was developed to study the ammonia (NH₃)-fed solid oxide fuel cells with proton-conducting electrolyte (SOFC-H) and oxygen ion-conducting electrolyte (SOFC-O). Different from previous thermodynamic analysis, the present study reveals that the actual performance of the NH₃-fed SOFC-H is considerably lower than the SOFC-O, mainly due to higher ohmic overpotential of the SOFC-H electrolyte. More analyses have been performed to study the separate overpotentials of the NH₃-fed SOFC-H and SOFC-O. Compared with the NH₃-fed SOFC-H, the SOFC-O has higher anode concentration overpotential and lower cathode concentration overpotential. The effects of temperature and electrode porosity on concentration overpotentials have also been studied in order to identify possible methods for improvement of SOFC performance. This study reveals that the use of different electrolytes not only causes different ion conduction characteristics at the electrolyte, but also significantly influences the concentration overpotentials at the electrodes. The model developed in this article can be extended to 2D and 3D models for further design optimization.