Effect of pore structure on the compressive property of porous Ti produced by powder metallurgy technique

Porous Ti with an average macro-pore size of 200–400 μm and porosity in the range of 10–65% has been manufactured using polymethyl methacrylate (PMMA) powders as spacer particles. The compressive strength and elastic modulus of resultant porous Ti are observed in the range of 32–530 MPa and 0.7–23.3 GPa, respectively. With the increasing of the porosity and macro-pore size, the compressive strength and modulus decrease as described by Gibson–Ashby model. The failure due to cracking (complete fracture) of the struts on porous Ti is controlled primarily by macro-pores. Fractography shows evidence of the brittle cleavage fracture mainly, but containing a few fine shallow dimples and a small amount of transcrystalline fracture of similarly oriented laths. The failure mechanism has been discussed by taking the intrinsic microstructural features into consideration.     

Effect of solid content on pore structure and mechanical properties of porous silicon nitride ceramics produced by freeze casting

Porous Si₃N₄ ceramics were prepared by freeze casting using liquid N₂ as refrigerant. The pore structure, porosity, α → β-Si₃N₄ transformation and mechanical properties of the obtained materials were strongly affected by the solid contents of the slurries. Increasing the solid content would reduce the porosity, decrease the pore size and change the pore structure from the aligned channels with dendrites to the round pores with decreased pore size. The formation of this round pores impeded the α → β-Si₃N₄ phase transformation, but was beneficial to the mechanical properties of the obtained porous Si₃N₄ due to its unique pore structure.     

Synthesis,characterization and mechanism of porous spherical nesquehonite by CO2 biomimetic mineralization

Mineralizing CO₂ is an effective way to reduce the greenhouse effect. Due to the high cost, most CO₂ mineralization projects are basically difficult to be commercialized. Mineralizing CO₂ with magnesium salt is an effective and achievable method. The hydrated magnesium carbonate prepared by this method can be used as a functional material, which has great economic benefits. Inspired by biomineralization, nesquehonite (MgCO₃·3H₂O) was prepared by indirect CO₂ mineralization of MgCl₂ and (NH₄)₂·CO₃ under the regulation of biosugars. Porous spherical nesquehonite with complex hierarchical structure was synthesized with the addition of 10.5 % dextran at the pH value of 9.5 ± 0.05. The formation mechanism of nesquehonite with different morphologies was further revealed. Under the regulation of dextran, 3D porous nesquehonite spheres are formed by the epitaxial growth of 2D-2D nanoarrays assembled and arranged by nanosheets. This work will provide references for further preparation of hierarchical nesquehonite by CO₂ biomimetic mineralization, and give new insights into the formation mechanism of porous spherical nesquehonite.     

Monodisperse porous pod-like hematite: Hydrothermal formation, optical absorbance, and magnetic properties

Uniform monodisperse porous silk-worm pod-like hematite (α-Fe₂O₃) superstructures were efficiently obtained via a facile hydrothermal route. This was realized via the co-precipitation of FeCl₃ and NaOH solutions at room temperature in the presence of H₃BO₃, followed by a mild hydrothermal treatment (150 °C, 12.0 h). The UV-vis band is mainly located in the far-UV region, with one intense broadband from 260 to 290 nm. The porous pod-like superstructures exhibit special magnetic properties with a remnant magnetization of 0.22 emu g^− 1 and a high coercivity of 3315.5 Oe at room temperature, indicating the as-obtained porous pod-like superstructures of a promising candidate for gas sensors, lithium ion battery, photocatalysis, and water treatment.     

Preparation and properties of a new porous ceramic material used in clean energy field

At high temperature, the oxide redox reactions of ceria can split H₂O and CO₂ to produce H₂ and CO, so porous ceria with high temperature resistance and high specific surface area has an important foreground in clean energy applications. In this work, a reticulated porous ceria ceramic material with interconnected porous structure was prepared by the impregnation technique using organic polyurethane sponges as template. The influences of pretreated sponge, dipping time length, pore size and sintering temperature on the porosity and strength of the porous ceria ceramics were systematically studied. With the increasing sintering temperature, the glass phase occurred and led to an increase in strength, but an decrease in porosity. Eventually, we analyzed the relationships between porosity and strength of these porous materials, aiming to provide theoretical and practical references for its application in clean-energy field.     

Recent progress in porous TiNb-based alloys for biomedical implant applications

ABSTRACT

Porous TiNb-based alloys have attracted considerable attention in the medical field of orthopedic applications because of excellent biocompatibility, porous architecture, appropriate mechanical property, etc. The literature reviews the current progress of fabrication methods, porous structure, mechanical properties, corrosion resistance, bioactive hydroxyapatite surface modification, in vitro and in vivo biocompatibility of porous TiNb-based alloy. Moreover, future research directions are pointed out to expand its possible biomedical applications.     

Effects of acid solution of different components on the pore structure and mechanical properties of coal

To explore the influence of acid solution with different components on the pore structure and mechanical properties of coal, nuclear magnetic resonance (NMR), scanning electron microscope (SEM), energy dispersion spectrum (EDS) and uniaxial compression experiments were used to analyze the acid-treated coal samples. The results show that acid treatment can obviously improve the connectivity of coal, increase the porosity of coal, and is conducive to the circulation and diffusion of gas, but the promotion effect of acid solutions of different components on pores with different pore sizes is different. After acid treatment, the number of mineral particles on the surface of the coal samples are obviously reduced, and the space filled with mineral particles is gradually exposed, thus increasing the density of pores and fractures of the coal samples. The energy spectrum analysis shows that acid solution added HF has a good removal effect on kaolinite minerals, iron minerals and calcite minerals. For the mechanical properties of the coal samples, acid treatment can reduce the strength and elastic modulus of coal samples, but increase its toughness. In addition, the fracture evolution of the acid-treated coal samples mainly goes through four stages: initial stage, transition stage, expansion stage and destruction stage. Because most of the energy accumulated in the acid-treated coal samples is used to damage the coal body, the acid-treated coal samples are easy to form fracture network, and is mostly broken in blocks when unstable.     

Effects of local thermal non-equilibrium on the pore pressure and thermal stresses around a spherical cavity in a porous medium

In this paper, we use a local thermal non-equilibrium (LTNE) thermo-poroelasticity theory to investigate temperatures, pore pressure and thermal stresses around a spherical cavity in an infinite fluid saturated porous medium. In the LTNE theory, the solid and fluid phases undergo different temperature variations which induce additional pore pressure and thermal stresses. The asymptotic short time solutions of temperature, pore pressure and thermal stresses are obtained using the Laplace transform technique. Numerical results for two porous materials (clay and sandstone) are presented to examine the effects of LTNE on the temperature, pore pressure and thermal stresses around the spherical cavity. The results show that for the clay, the LTNE radial stress has a significantly larger peak value (magnitude) than that of the classical radial stress. The influence of LTNE on the pore pressure and tangential stress, however, are marginal. For the sandstone, both the radial stress (magnitude) and pore pressure are significantly increased by the LTNE effect.     

Improving strength, drying shrinkage, and pore structure of concrete using metakaolin

This paper presents the results of an investigation on the use of metakaolin (MK) as a supplementary cementing material to improve the performance of concrete. Two MK replacement levels were employed in the study: 10% and 20% by weight of the Portland cement used. Plain and PC-MK concretes were designed at two water–cementitious materials (w/cm) ratios of 0.35 and 0.55. The performance characteristics of the concretes were evaluated by measuring compressive and splitting tensile strengths, water absorption, drying shrinkage, and weight loss due to the corresponding drying. The porosity and pore size distribution of the concretes were also examined by using mercury intrusion porosimetry (MIP). Tests were conducted at different ages up to 120 days. The results revealed that the inclusion of MK remarkably reduced the drying shrinkage strain, but increased the strengths of the concretes in varying magnitudes, depending mainly on the replacement level of MK, w/cm ratio, and age of testing. It was also found that the ultrafine MK enhanced substantially the pore structure of the concretes and reduced the content of the harmful large pores, hence made concrete more impervious, especially at a replacement level of 20%.     

无机多孔基复合相变材料的热湿性能研究进展

无机多孔基复合相变材料兼具调温调湿性能,能够减少室内温度波动,调节室内湿度平衡,既提高了环境的舒适度,又减少了建筑能耗,是近几年建筑材料领域的研究热点。介绍了相变材料的分类及优缺点,并总结了不同种类相变材料的性能优化措施;简述了常用的无机多孔材料,分析比较了其对相变材料的强化导热效果和定形效果;分析了无机多孔基复合相变材料的热湿综合性能,并讨论了材料的不足之处。最后,提出了优化材料性能的措施以及研究方向,为深入研究调温调湿材料提供帮助。     

Control of molecular packing structure of a derivative of vanadyl-phthalocyanine using pore wall of porous alumina and/or magnetic field

We filled one-dimensional alumina pores with a molten derivative of vanadyl-phthalocyanine (VOPcHt) and evaluated the effect of the surface of pore wall on the molecular packing structure of VOPcHt. We also evaluated the effect of a magnetic field of 5.0 T on the packing structure of VOPcHt that was solidified on a flat substrate. X-ray diffraction measurements revealed that both the surface effect as well as the magnetic field controlled the packing structure of VOPcHt. When both the pore wall and the magnetic field existed, the surface effect was dominant in the control of the packing structure. These results provide practical methods to fabricate nanostructures of organic molecules with a controlled molecular packing structure.     

Critical WIP loops: a mechanism for material flow control in flow lines

Critical WIP loops (CWIPL) is a proposed material flow control mechanism for a balanced flow line environment aiming at improving throughput and lead time. The mechanism establishes critical loops which their WIP identifies the time of releasing raw material to the line. So, through control of WIP level of critical loops the material flow is managed. The proposed mechanism releases the raw material to the line if the ‘total WIP of the line’ or ‘the WIP of the last machine’ is less than the limit. Besides the aforementioned condition, the necessary condition for releasing the raw material to the line is ‘idleness of the first machine’. Simulation is used to compare the performance of the CWIPL, CONWIP and G-MaxWIP. Different line characteristics such as number of machines, processing time distributions and the maximum WIP level of the line are considered in numerical examples. The results show that CWIPL improves both throughput and lead time compared with CONWIP, while CWIPL has better results than G-MaxWIP with respect to both throughput and lead time in the flow line that has less than nine machines.     

Effect of particle size and adsorption equilibrium time on pore structure characterization in low pressure N2 adsorption of coal: An experimental study

This study examined the influence of particle sizes and adsorption equilibrium time (AET) on pore structure characterization using low pressure N₂ adsorption (LPGA-N₂) method. The results demonstrate that pore structures change with progressive crushing. The increase in pore volume in the minipore and mesopore with decreasing coal particle sizes was caused by creating additional large pores during the crushing. The tendency of decreasing at first and then increasing was observed for both the specific surface area (SSA) and micropore volume, demonstrating that the micropore structure was primarily damaged and then followed by additional micropores being created when the sample was broken down smaller than 80 mesh. It is difficult to choose a suitable coal particle size for LPGA-N₂ measurement to yield pore structure parameters closest to the “real” values due to the difficulty in evaluating the compound effect of crushing on pore structures. To make testing results closer to the coal structure under in situ conditions, we propose 1∼3 mm as the preferred coal particle size. Additionally, many replicate experiments were performed by adjusting the AET to ensure LPGA-N₂ isotherms in equilibrium states. The results indicate that a decrease in particle size did not reduce the time for reaching N₂ adsorption equilibrium. Comparison of pore size distributions under different AETs shows that the AETs' increase has a little influence on the measurement of minipore and mesopore but has a positive correlation with micropore, revealing that N₂ adsorption equilibrium is mainly influenced by the micropore whose volume is underestimated at small AETs. The optimal AET for LPGA-N₂ measurement was 8 min and its yielded data can more accurately characterize the pore structure parameters.     

Effects of scan line spacing on pore characteristics and mechanical properties of porous Ti6Al4V implants fabricated by selective laser melting

The use of porous structures is gaining popularity in biomedical implant manufacture fields due to its ability to promote increased osseointegration and cell proliferation. Selective laser melting (SLM) is a metal additive manufacturing (MAM) technique capable of producing the porous structure. Adjusting the parameter of scan line spacing is a simple and fast way to gain porous structures in SLM process. By using the medical alloy of Ti6Al4V, we systematically study the influence of the scan line spacing on pore characteristics and mechanical properties of porous implant for the first time. The scanning electron microscope (SEM) results show that the porous Ti6Al4V implants with interconnected pore sizes which ranges from 250 to 450 μm is appropriate for compact bone. The compression strength and modulus of the porous Ti6Al4V implants decrease with the increase of the scan line spacing, and two equations by fitting the data have been established to predict their compression properties. The compressive deformation of the porous Ti6Al4V implants presented an adiabatic shear band (ASB) fracture, which is similar to dense Ti6Al4V owing to the dense thin wall structures. The ability to create both high porosity and strong mechanical properties implants opens a new avenue for fabricating porous implants which is used for load-bearing bone defect repair and regeneration.     

Space-holder effect on designing pore structure and determining mechanical properties in porous titanium

The present work studied the effect of space holders on pore structure and mechanical properties in porous titanium. Four types of space holders (sodium chloride, starch, and urea with different size and morphology) were utilized to fabricate porous titanium. The space holders played a key role in the pore structure as confirmed by microstructural observations and three-dimensional computed tomography technique. Mechanical properties of each sample were investigated and discussed on the basis of the tomography results and finite element method. It is concluded that the porosity determines the elastic modulus regardless of the type and morphology of space holders, whereas both porosity and type of space holder affected strength.     

Assessment of pore structure evolution in the limestone calcined clay cementitious system and its implications for performance

Use of limestone and calcined clay together for clinker substitution makes an effective low clinker cement blend, which shows promising mechanical properties at early ages. The performance of these cementitious systems strongly depends on the pore structure, which is a dominant factor governing the durability characteristics because of its direct influence on the transport properties. The experimental study described in this paper on three different binder systems including Ordinary Portland Cement, Portland Pozzolana Cement - with 30% Type F Fly Ash (designated FA30) - and Limestone Calcined Clay Cement (LC³) pastes shows that the LC³ system attains greater refinement of the pore structure as early as 3 days, as seen from mercury intrusion porosimetry. Electrical measurements also reveal lower conductivity in the system, which suggests better resistance to ionic transport in the binder phase. The results of hydrate phase assemblage studied by X-ray diffraction also indicate that greater amount of hydrates contribute in a major way to the reduction in the (water-filled) porosity in all the systems. This change occurs at varying rates for the different systems due to the difference in hydration characteristics. The estimated permeability suggests that the LC³ binder system attains much lower permeability compared to the ordinary Portland cement and FA30. A comparison of the formation factor shows distinct differences in the microstructural development and suggests a more durable binder with LC³ cementitious system.     

A review of Fe3O4 thin films: Synthesis,modification and applications

Magnetite (Fe₃O₄) has been used for thousands of years as one of the important magnetic materials. The rapid developments of thin film technology in the past few decades attract the attention of material scientists on the fabrication of magnetite thin films. In this article, we present an overview of recent progress on Fe₃O₄ thin films. The widely used preparation methods are surveyed, and the effect of substrates is discussed. Specifically the modified Fe₃O₄ thin films exhibit excellent electrical and magnetic properties compared with the pure films. It is noteworthy that modified Fe₃O₄ thin films can be put into two categories: (1) doped films, where foreign metal ions substitute iron ions at A or B sites; and (2) hybrid films, where magnetite phases are mixed with other materials. Notably, Fe₃O₄ thin films show great potentials in many applications such as sensors and batteries. It is expected that the investigations of Fe₃O₄ thin films will give us some breakthroughs in materials science and technology.     

New ternary intermetallics RE5Ru3Al2 (RE = La, Ce, Pr): Synthesis, crystal structures, magnetic and electric properties

Intermetallics RE₅Ru₃Al₂ (RE = La, Ce, Pr) were prepared by arc melting of the elemental components with subsequent annealing at 820 K. The crystal structures were determined from single-crystal (Ce₅Ru₃Al₂, Pr₅Ru₃Al₂) and powder (La₅Ru₃Al₂) X-ray diffraction at room temperature. The compounds belong to new structural types: space group R3, Z = 6, a = 13.9270(3) Å, c = 8.3260(2) Å for Ce₅Ru₃Al₂ and space group I2₁3, Z = 4, a = 9.95419(6) Å and 9.8084(3) Å for La₅Ru₃Al₂ and Pr₅Ru₃Al₂, respectively. The trigonal structure of Ce₅Ru₃Al₂ is a distorted variant of the cubic La₅Ru₃Al₂ and Pr₅Ru₃Al₂ structures. An interesting feature of the Ce₅Ru₃Al₂ are the short (2.5299(16) Å and 2.5969(15) Å) Ce-Ru distances. Magnetic measurements revealed the Pauli paramagnetic behavior in La₅Ru₃Al₂ and the Curie-Weiss paramagnetism in Pr₅Ru₃Al₂. The latter compound likely exhibits a kind of magnetically ordered state below 24 K. In turn, Ce₅Ru₃Al₂ remains paramagnetic down to 4.2 K and shows signs of mixed valence states of Ce ions. Electrical resistivity measurements indicated simple metallic conductivity in La₅Ru₃Al₂ and Pr₅Ru₃Al₂, and a more complex metallic behavior in Ce₅Ru₃Al₂.