Preparation and properties of open-cell zinc foams as human bone substitute material

Foamed zinc was prepared by infiltration casting process.The mechanical properties and corrosion resistance of the samples were studied,and the feasibility of the foamed zinc as a bone implant material was discussed.All the compression stress-strain curves of open-cell zinc foams with various cell size(1-4 mm)and porosity(55%-67%)show three stages:elastic stage,plastic stage,and densification stage.The compression strength increases with decreasing density.The smooth stress-strain response indicates a progressively deformation of open-cell zinc foam.In addition,the cell wall or edge bending and fracture are the dominated mechanisms for failure of open cell zinc foam.The immersion test for determining the corrosion rate of open cell zinc foam was conducted in simulated body fluid.It was found that zinc foam with a small cell size and high porosity showed a higher corrosion rate.In addition,open-cell zinc foams can effectively induce Ca-P deposition in immersion tests,showing good bioactivity.Therefore,the open cell zinc foam prepared in this experiment has a good potential application as a human bone substitute material.

Numerical Modeling of the Compression Process of Elastic Open-cell Foams

The random models of open-cell foams that can reflect the actual cell geometrical properties are constructed with the Voronoi technique. The compression process of elastic open-cell foams is simulated with the nonlinear calculation module of finite element analysis program. In order to get the general results applicable to this kind of materials, the dimensionless compressive stress is used and the stress-strain curves of foam models with different geometrical properties are obtained. Then, the influences of open-cell geometrical properties, including the shape of strut cross section, relative density and cell shape irregularity, on the compressive nonlinear mechani- cal performance are analyzed. In addition, the numerical results are compared with the predicted results of cubic staggering model. Nu- merical results indicate that the simulated results reflect the compressive process of foams quite well and the geometrical properties of cell have significant influences on the nonlinear mechanical behavior of foams.

Preparation of open-celled aluminum foams by counter-gravity infiltration casting

A novel counter-gravity infiltration casting device and corresponding fabricating process for producing open-celled aluminum foams were presented. The experimental results show that defects such as insufficient or excessive infiltrating can hardly be found in the foam samples prepared by counter-gravity infiltration casting. The foam materials exhibit excellent mechanical properties. The void content strongly affects the mechanical properties of aluminum foams. The yield stress and plateau stress significantly increase with the decrease of void content. Raising pre-heating temperature and increasing packing pressure are effective to lower the void content in aluminum foams.

Thermal properties of open-celled aluminum foams prepared by two infiltration casting methods

Contrastive research was carried out to study the thermal properties of open-celled aluminum foams prepared by counter-gravity infiltration casting system and the traditional process respectively.The experimental results show that the thermal conductivity coefficients of aluminum foams prepared by two different infiltration methods have similar increasing trend with the increase of particle size;along with the reducing porosity,the thermal conductivity coefficients will be enhanced oppositely.However,with the same particle size,the open-celled aluminum foam prepared by the former method has a higher thermal conductivity coefficient obviously.It is largely because that the sample prepared by counter-gravity infiltration casting has a lower void content and better dense crystallization of metal-matrix after the constant pressure process.

Effects of microstructure on uniaxial strength asymmetry of open-cell foams

Based on the elongated Kelvin model, the effect of microstructure on the uniaxial strength asymmetry of open-cell foams is investigated. The results indicate that this asymmetry depends on the relative density, the solid material, the cell morphology, and the strut geometry of open-cell foams. Even though the solid material has the same tensile and compressive strength, the tensile and compressive strength of open-cell foams with asymmetrical sectional struts are still different. In addition, with the increasing degree of anisotropy, the uniaxial strength as well as the strength asymmetry increases in the rise direction but reduces in the transverse direction. Moreover, the plastic collapse ratio between two directions is verified to depend mainly on the cell morphology. The predicted results are compared with Gibson and Ashby＇s theoretical results as well as the experimental data reported in the literature, which validates that the elongated Kelvin model is accurate in explaining the strength asymmetry presented in realistic open-cell foams.

Analysis and simulation for tensile behavior of anisotropic open-cell elastic foams

Based on the elongated Kelvin obtained to investigate the tensile behavior Kelvin model＇s periodicity and symmetry in model, a simplified periodic structural cell is of anisotropic open-cell elastic foams due to the whole space. The half-strut element and elastic deflection theory are used to analyze the tensile response as done in the previous studies. This study produces theoretical expressions for the tensile stress-strain curve in the rise and transverse directions. In addition, the theoretical results are examined with finite element simulation using an existing formula. The results indicate that the theoretical analysis agrees with the finite element simulation when the strain is not too high, and the present model is better. At the same time, the anisotropy ratio has a significant effect on the mechanical properties of foams. As the anisotropy ratio increases, the tensile stress is improved in the rising direction but drops in the transverse direction under the same strain.

Preparation of open-cell metal foams by investment cast

Metal foams are a new kind of materials with low densities and novel physical, mechanical, thermal, electrical and acoustic properties. They can be divided into closed and open cell structures. In this paper the open cell structures, called sponges, were treated. A new technique to manufacture sponges by plaster investment casting was described. Experimental results show that it is essential to make a sound plaster mould by casting plaster slurry into the polyurethane foams and infiltrate the open channels of the baked plaster mold by molten metal. The optimal processes include plaster slurry preparation, plaster mold baking, and molten metal infiltration. The sponge sample with porosity of 97% is presented.

Fabrication and compressive behavior of open-cell aluminum foams via infiltration casting using spherical CaCl_(2) space-holders

The infiltration casting fabrication process based on spherical CaCl_(2) space-holders and the compressive behavior including the mechanical performance and energy absorption capacity of open-cell aluminum foams were investigated.Open-cell aluminum foams with different porosities in the range of 63.1%to 87.3%can be fabricated by adjusting compression ratios of CaCl_(2) preforms prepared by precision hot-pressing.The compression tests show that a strain-hardening phenomenon always occurs especially for open-cell aluminum foam with low porosity,resulting in the inclining stress-strain curve in the plateau region.The energy absorption capacity of open-cell aluminum foam decreases with increasing porosity when compared at the same strain.However,when compared at a given stress,each foam can absorb the maximal energy among the five foams in a special stress range.Additionally,open-cell aluminum foam possesses the maximum energy absorption efficiency at its optimum operating stress.At this stress condition,the foam can absorb the highest energy compared with other foams at the same stress point.The optimum operating stress and the corresponding maximal energy absorption decrease with increasing the porosity.The optimum operating stress for energy absorption can also be determined similarly when taking into consideration of the lightweight extent of foams.

Bonding effect of liquid magnesium with open-celled carbon foam in interpenetrating phase composite

The issue of bonding formation in liquid metal/open-celled carbon foam(C_(of))systems was examined,taking into account the practical aspects of the synthesis of a new type of Mg-C metal material composite.The problem is complex due to the strong oxidation and intense evaporation of liquid magnesium,as well as the 3D geometry of the carbon component,where metal transport occurred through the foam cells’windows.Laboratory experiments performed at 700℃ in ceramic crucibles showed that spontaneous carbon foam infiltration by liquid metal is impossible under the applied conditions,either in an air atmosphere coupled with flux protection or under argon protection.Comparative tests performed in a UHV chamber filled with static pure Ar by a sessile drop method,coupled with non-contact heating and capillary purification at a test temperature of 700℃ directly in the UHV chamber,showed non-wetting behavior of the Mg/C_(of)couple with a correspondingly high contact angle of about 135°.The graphite capillary was then moved down,the liquid drop being slightly pressed into the foam,but these changes did not induce effective foam penetration.Despite the short contact time for the sessile drop test under an argon atmosphere,SEM+WDS analysis of the solidified Mg/C_(of)couple revealed the formation of an MgO interlayer at the interface,with a thickness of approx.1μm.The experimentally demonstrated presence of oxygen in the carbon foam sample,both before and after its contact with magnesium,points to oxide-type bonding being established between Mg and C_(of).This observation is in a good agreement with previous reports on the interface characterization of magnesium matrix composites reinforced with glassy carbon materials and carbon fibers by stir casting and pressure infiltration.Based on the findings of this study,a general structural scheme of the bonding process between carbon foam and liquid magnesium,as an important stage in the syntheses of Mg-C composites,was proposed.

A scalable versatile methodology to construct micro/nano open-cell polypropylene foam with high oil adsorption capacity and speed

Oil pollution is a serious environmental and natural resource problem.Traditional adsorption materials for oil–water separation have limitations in terms of their preparation cost,reusability,and mechanical properties.Among the conventional adsorption materials,super-hydrophobic/super-lipophilic materials are easily contaminated by oil.In this study,polypropylene(PP)is used as a foam substrate to prepare an open-cell PP foam via hot pressing,supercritical CO_(2) foaming,and electron beam(EB)irradiation.The impact of EB irradiation dose on the open-cell content of PP foam can lead to cell wall rupture,resulting in an open-cell structure that enhances oil-water separation performance.At an absorbed radiation dose of 200 kGy,the PP foams exhibit optimal oil–water separation performance,cyclic compression stability,heat insulation,and preparation cost.The open-cell content of PP foam is increased to 86.5%,the adsorption capacity for diesel oil is 42.8 g/g,and the adsorption efficiency remains at 99.6%after 100 cycles of oil desorption in a complex pH environment.Meanwhile,cracks and nano-voids simultaneously promote the capillary action of oil,and the oil transport rate is 0.0713 g/(g·s).This study provides a new concept for the preparation of open-cell polymer foams that can meet the demand for high oil-absorption capacity under complex acid-base pH conditions.

Effects of foaming parameters on microstructure and compressive properties of aluminum foams produced by powder metallurgy method

Semi open-cell aluminum foams having channels between individual cells were produced using low cost CaCO3foamingagent and applying the powder compact melting process.To this end,the aluminum and CaCO3powder mixtures were coldcompacted into dense cylindrical precursors for foaming at specific temperatures under air atmosphere.The effects of severalparameters including precursor compaction pressure,foaming agent content as well as temperature and time of the foaming processon the cell microstructure,linear expansion,relative density and compressive properties were investigated.A uniform distribution ofcells with sizes less than100μm,which form semi open-cell structures with relative densities in the range of55.4%-84.4%,wasobtained.The elevation of compaction pressure between127-318MPa and blowing agent up to15%(mass fraction)led to anincrease in the linear expansion,compressive strength and densification strain.By varying the foaming temperature from800to1000°C,all of the investigated parameters increased except compressive strength and relative density.The results indicated theoptimal foaming temperature and time as900°C and10-25min,respectively.

Manufacturing Microporous Foam Zinc Materials with High Porosity By Electrodeposition

In order to get foam zinc materials of porous metal electrode,a novel method for preparing foam zinc was proposed,in which the polyurethane foam with diameter of 0.3 mm as substrate was processed by degreasing,roughening,activating,electroless plating and electrodeposition.The main factors affecting the process,such as ZnSO4 content,temperature,pH value,current density,and electrodes distance,were investigated comprehensively.The optimal process conditions are 250 g/L ZnSO4,20 g/L Al2（SO4）3,40 g/L KAl（SO4）2,30 g/L Na2SO4,pH=3.5,4.0 cm of electrodes distance and 0.04 A/cm2 current density at 30 ℃.The result shows that adding ultrasonic on the process can elevate the deepening plating ability and current efficiency.Foam zinc material with a high porosity of 92.2% and a three-dimensional network structure can be fabricated by electrodeposition.

三乙醇胺和硬脂酸锌对泡沫混凝土性能的影响

为解决泡沫混凝土存在的高吸水率问题,本文研究了三乙醇胺(TEA)和硬脂酸锌(ZS)对泡沫混凝土孔隙特征、力学性能和防水性能的影响,同时结合接触角测试仪、扫描电子显微镜-能谱仪和X射线衍射仪等微观分析手段,研究了TEA和ZS对泡沫混凝土的改性机理。结果表明,加入1.6%(质量分数)TEA和0.4%(质量分数)ZS可以增大泡沫混凝土直径小于500μm孔隙的占比,使泡沫混凝土28 d抗压强度提升到1.66 MPa。加入0.4%(质量分数)TEA和1.6%(质量分数)ZS能够将泡沫混凝土1、2、3 d吸水率降至2.8%、7.9%和10.5%,接触角最高达134.9°,使泡沫混凝土表面呈现疏水特征。TEA和ZS复掺能够增强泡沫在固化水泥浆体中的稳定性,细化孔隙结构,减少连通孔数量,提升泡沫混凝土的力学性能和防水性能。

有机改性蒙脱土/硼酸锌/硅橡胶泡沫复合材料制备及阻燃抑烟性能

为提高硅橡胶泡沫材料(SRF)的阻燃抑烟性能,采用室温硫化法制备了长链季铵盐(CTAB)有机改性蒙脱土(OMMT)/硼酸锌(ZB)/SRF复合材料。通过极限氧指数(LOI)、水平-垂直燃烧试验(UL-94)、锥形量热分析和热重-差热分析研究了复合材料的阻燃抑烟性能。结果表明,添加2%OMMT和1%ZB的SRF阻燃性能明显提高,LOI为29.5%,阻燃等级达到V-0等级,热释放速率峰值(PHRR)和总热释放量(THR)较纯SRF分别降低26.6%和27.0%,烟释放速率峰值(PSPR)和烟总释放量(TSP)比纯SRF分别降低67.8%和66.5%。添加OMMT和ZB之后,SRF表现出了良好的热稳定性和更致密的炭层,OMMT和ZB存在一定的气相协同阻燃效应。研究结果为阻燃复合材料的研发提供了数据参考。

改性蒙脱土/硼酸锌/硅橡胶泡沫复合材料的阻燃性能及热降解动力学

为提高硅橡胶泡沫(SRF)阻燃性能,将有机改性后的蒙脱土(MMT)和硼酸锌(ZB)作为阻燃剂添加到硅橡胶泡沫中,采用室温硫化法制备了有机改性蒙脱土(OMMT)/硼酸锌(ZB)/硅橡胶泡沫(SRF)复合材料,通过极限氧指数(LOI)、水平-垂直燃烧试验(UL-94)、烟密度测试研究了SRF复合材料的阻燃性能,通过热重-红外联用分析其热稳定性以及热解气体成分,并采用非等温法开展了复合材料热降解热动力学分析。结果表明:添加2wt%的OMMT和1wt%的ZB时复合材料的LOI最高达到29.5%,比纯SRF提高了11.3%;最大烟密度(MSD)和烟密度等级(SDR)较纯SRF分别降低了32.9%、34.1%,延缓了SRF复合材料的热分解进程,残炭量提高;2wt%OMMT/1wt%ZB/SRF复合材料的活化能在热解后期明显提高,说明OMMT和ZB复配可以有效协同提高SRF复合材料的阻燃抑烟性能,阻燃作用主要体现在热解第2阶段。

Fabrication,properties,and applications of open-cell aluminum foams:A review

Open-cell metallic foams or porous metals have a distinctive combination of excellent structural performance and superior functional characteristics,such as their light weight,energy absorption,sound absorption,heat dissipation,and electromagnetic shielding.As a primary representative of metallic foams,aluminum foam has developed into a new engineering material with many unique applications in the fields of aerospace,automotive industry,petrochemical industry,building materials,and etc.This paper summarizes the fabrication methods,properties,and applications of open-cell aluminum foams.The current status and development trends are also introduced.

Analysis and simulation of high strain compression of anisotropic open-cell elastic foams

By elongating the regular Kelvin model in one direction and keeping unchanged in the other two directions,the anisotropic model was constructed.Then,the simplified periodic structural cell was obtained according to the periodicity and symmetry of the model in the whole space.Using the half-strut element and elastic deflection theory to analyze the mechanical behavior as were adopted in the previous studies,this paper obtained the theoretical expressions for the compressive stress and strain as well as the corresponding curves in the rise and transverse directions.In addition,the theoretical results were examined by the finite element simulation.Results indicated that the theoretical analysis was very close to the finite element simulation when the strain was not too high,which confirmed the validity of theoretical analysis.At the same time,the anisotropy was shown to have a significant effect on the mechanical properties of open-cell foams.As the anisotropy ratio increased,the compressive stress was improved in the rise direction but dropped in the transverse direction under the same strain.

Supercritical CO2 Assisted Preparation of Open-cell Foams of Linear Low-density Polyethylene and Linear Low-density Polyethylene/Carbon Nanotube Composites

The open-cell structure foams of linear low-density polyethylene（LLDPE） and linear low-density polyethylene（LLDPE）/multi-wall carbon nanotubes（MWCNTs） composites are prepared by using supercritical carbon dioxide（sc-CO2）as a foaming agent. The effects of processing parameters（foaming temperature, saturation pressure, and depressurization rate） and the addition of MWCNTs on the evolution of cell opening are studied systematically. For LLDPE foaming, the foaming temperature and saturation pressure are two key factors for preparing open-cell foams. An increase in temperature and pressure promotes both the cell wall thinning and cell rupture, because a high temperature results in a decrease in the viscosity of the polymer, and a high pressure leads to a larger amount of cell nucleation. Moreover, for the given temperature and pressure, the high pressurization rate results in a high pressure gradient, favoring cell rupture. For LLDPE/MWCNTs foaming, the addition of MWCNTs not only promotes the cell heterogeneous nucleation, but also prevents the cell collapse during cell opening, which is critical to achieve the open-cell structures with small cell size and high cell density.

Mechanical behaviors and energy absorption properties of Y/Cr and Ce/Cr coated open-cell nickel-based alloy foams

In this study, Y-and Ce-modified Cr coatings applied by pack cementation method were prepared on the surface of open-cell nickel-based alloy foam. The morphologies and microstructures of Y- and Ce-modified Cr coatings with various Y and Ce contents were investigated in detail. Then, the effects of Y and Ce addition on the mechanical properties of open-cell nickel-based alloy foams were analyzed and compared. Simultaneously, the energy absorption capacity and energy absorption efficiency of the Y- and Ce-modified Cr coated alloy foams were discussed and compared at the room and high temperatures. The results show that Cr coatings containing minor amounts of rare earth element （Y and Ce） are well adhered to the nickel-based foam struts. Especially, the microstructure of the 2 wt% Ce-modified Cr coating is denser and uniform. In addition, the compressive strength and plateau stress of Y- and Ce-modified Cr coated alloy foams firstly increase and then decrease by increasing the Y and Ce contents at room and high temperatures. The energy absorption capacity of Y/Cr and Ce/Cr coated alloy foams increases linearly with the strains increasing. The Ce/Cr coated alloy foams can absorb more energy than Y/Cr coated alloy foams in the plateau and densification regions at room temperature. Compared to those at room temperature, the Y- and Ce-modified Cr coated alloy foams show higher energy absorption efficiency when deforma- tion within 10%-30% at high temperature.

Polylactic Acid (PLA) Foaming: Design of Experiments for Cell Size Control

In this study, a design of experiments (DoE) approach was used to develop a PLA open-cell foam morphology using the compression molding technique. The effect of three molding parameters (foaming time, mold opening temperature, and weight concentration of the ADA blowing agent) on the cellular structure was investigated. A regression equation relating the average cell size to the above three processing parameters was developed from the DoE and the analysis of variance (ANOVA) was used to find the best dimensional fitting parameters based on the experimental data. With the help of the DoE technique, we were able to develop various foam morphologies having different average cell size distribution levels, which is important in the development of open-cell PLA scaffolds for bone regeneration for which the control of cell morphology is crucial for osteoblasts proliferation. For example, at a constant ADA weight concentration of 5.95 wt%, we were able to develop a narrow average cell size distribution ranging between 275 and 300 μm by varying the mold opening temperature between 106°C and 112°C, while maintaining the foaming time constant at 8 min, or by varying the mold foaming time between 6 and 11 min and maintaining the mold opening temperature at 109°C.