泡沫铝材料制备中孔结构的长大和控制

分析了泡沫铝材料的发泡过程中气泡长大的动力学过程,推导了气泡长大中气泡半径与时间的关系及理论上球形气孔的最大半径,并依据熔体发泡法制备的不同孔径泡沫铝硅材料的实验结果,推导了此材料孔径与发泡过程中所加入增粘剂铝粉体积分数的关系,为泡沫铝材料中孔结构的控制和制备不同孔径的泡沫铝材料提供了理论指导.     

三聚氰胺树脂含水量对泡沫结构的影响

在三聚氰胺树脂的制备终期通过调整减压蒸馏的时间制备含水量不同的树脂。保证树脂中高聚物、发泡助剂的质量比一致,在相同发泡条件下制备泡沫样品。通过固含量、凝胶时间,粘温曲线发现树脂预聚体的含水量越低,则固含量越高,树脂活性越大,固化速度快,制得泡沫的密度较大。SEM照片显示,树脂预聚体固含量越大,泡沫孔径越小,且孔径尺寸分布趋于均匀。此外,含水量也会对泡沫骨架的截面微观结构造成影响,含水量越少,骨架截面上的小气孔越多。     

泡沫铝-聚氨酯静态压缩特性及吸能特性分析

目的研究球形孔开孔泡沫铝相对密度、孔径对泡沫铝-聚氨酯复合材料力学性能的影响,以及对其吸能性能的影响。方法对制备的泡沫铝-聚氨酯复合材料进行准静态压缩实验。结果通过准静态压缩实验,得出分别对应的应力-应变曲线,并通过应力-应变曲线推导出吸能-应变曲线。当泡沫铝孔径一定时,泡沫铝相对密度从35.0%提升到38.4%时,泡沫铝-聚氨酯复合材料的屈服强度增加了6.5 MPa。当泡沫铝相对密度一定时,泡沫铝孔径从5.5 mm增大到9.5 mm时,泡沫铝-聚氨酯复合材料的屈服强度增加了3.38 MPa。结论泡沫铝的相对密度、孔径对泡沫铝-聚氨酯复合材料的性能有很大的影响,泡沫铝的相对密度越大,复合材料的性能越好,泡沫铝孔径越大复合材料性能越好,且泡沫铝相对密度越大,复合材料吸能特性越好,泡沫铝孔径越大,复合材料吸能特性越好。     

泡沫铝累积叠轧制备方法及孔隙结构研究

以L2纯铝为基体金属,TiH2粉末为发泡剂,通过累积叠轧试验,探索泡沫铝制备的新方法。结果显示,叠轧道次对泡沫铝孔隙率与平均孔径影响显著,叠轧道次越多,孔隙率越高,平均孔径越小;TiH2含量与发泡温度是影响发泡驱动力的主要因素,试验温度范围内,发泡剂含量越大,温度越高,发泡驱动力越强,发泡后孔隙率越高,并且平均孔径也越大。叠轧6道次的L2纯铝,发泡剂含量0.5%(质量分数),在670℃条件下发泡5min,可以获得孔隙率61.4%,平均孔径1.6mm的泡沫铝。上述研究表明,累积叠轧焊是一种有效的泡沫铝制备方法,通过工艺参数的优化,可以获得孔隙均匀,高孔隙率的泡沫铝。     

新型泡沫铝制备工艺研究

泡沫金属是近几年发展起来的一种新型结构功能材料。利用粉末冶金法制备的泡沫铝，其相对密度为0.2-0.6，平均孔径为25mm，孔隙率为40%-85%。分析讨论了试验工艺条件和工艺参数如混料条件，铝坯压缩条件以及发泡中的加热温度，加热速度和保温时间等对泡沫铝形成的影响。     

Al-Si闭孔泡沫铝电磁屏蔽效能

通过调整发泡温度、发泡时间、保温时间及发泡剂加入量等工艺参数,采用熔体转移发泡法制备不同相对密度的Al-Si闭孔泡沫铝.利用法蓝同轴法测试其电磁屏蔽效能,结果表明:电磁干扰频率对其屏蔽效能影响显著,在10～600MHz范围内,随着干扰频率增加,泡沫铝屏蔽效能逐渐减小,在600～1500MHz范围内,屏蔽效能又逐渐增加.相对密度对Al-Si闭孔泡沫铝材料电磁屏蔽效能影响不大.     

孔径可调的泡沫铝材料制备研究

利用传统熔体发泡法制备泡沫铝,产品的孔径大小很难精确控制.采用金属铝粉这种新型增粘剂,通过对铝粉的含量,发泡剂的含量以及控制发泡剂加入后熔体中的发泡温度,制备出孔结构均匀,不同密度和孔径大小的泡沫铝.整个工艺平稳、易控制和调整.     

泡沫铝-聚氨酯复合材料力学及吸能性能分析

目的 研究泡沫铝相对密度、孔径对泡沫铝-聚氨酯复合材料准静态压缩力学性能、吸能性能、吸能效率和理想吸能效率的影响。方法 将制备的泡沫铝-聚氨酯复合材料试样在万能材料试验机上进行准静态压缩试验,得出对应的应力-应变曲线,由应力-应变曲线分析材料的吸能性能、吸能效率、理想吸能效率。结果 当泡沫铝孔径一定,泡沫铝相对密度由0.350提升至0.384时,泡沫铝-聚氨酯复合材料屈服强度提升了4.38 MPa,而最大吸能效率由0.29下降至0.27,准静态压缩性能有所提高。当泡沫铝相对密度一定,泡沫铝孔径由5 mm增加至9 mm时,泡沫铝-聚氨酯复合材料屈服强度提升了6.16 MPa,而最大吸能效率由0.25升高到0.27,准静态压缩性能有所提高。结论 当进行准静态压缩时,泡沫铝-聚氨酯复合材料压缩性能随相对密度的增大而增大,随孔径的增大而增大;泡沫铝-聚氨酯复合材料的吸能性能随相对密度的增大而增大,随孔径的增大而增大;泡沫铝-聚氨酯复合材料的最大吸能效率随相对密度的增大而减小,随孔径的增大变化微小。     

短纤维对泡沫铝压缩力学性能与吸能特性的影响研究

为探索闭孔泡沫铝加入短纤维后的力学性能和吸能特性变化规律。利用熔体发泡法在铝熔体中加入短碳纤维后制作得到纤维增强泡沫铝,通过万能材料试验机和高速液压伺服材料试验机在常温下分别对泡沫铝、纤维增强泡沫铝进行准静态和中应变率下(0.001~100 s-1)的动态力学性能测试,分析了纤维长度、纤维含量对泡沫铝力学性能和吸能特性变化规律。研究结果表明,纤维在泡沫铝内部主要呈现三种不同的形态模式:穿透模式、贯穿模式和嵌入模式;在平均孔径为2 mm的泡沫铝中加入长度为1 mm的纤维后,大多数纤维呈现穿透模式,泡沫铝整体性能下降,加入等含量长度为3 mm的纤维后,大多数纤维呈现贯穿和嵌入模式,平台应力和吸能效率有所提升;加入纤维后,泡沫铝整体呈现更为明显的应变率效应。     

双氧水对镁系无机泡沫材料性能和孔结构的影响

以镁系胶凝材料为基体,双氧水为发泡剂,采用化学发泡工艺制备了内部含有大量密闭气孔的镁系无机泡沫材料。研究了双氧水添加量对泡沫材料发泡倍率、体积密度、压缩强度、弯曲强度、孔结构参数以及导热系数的影响。研究结果表明:双氧水添加量增加,导致胶凝体中的气泡核增加以及气泡生长的内动力增大,气孔孔径变大,体积密度和力学强度减小;随着双氧水添加量增加,材料的导热系数不断减小,在双氧水添加量大于16‰时增大。镁系无机泡沫材料的压缩强度和弯曲强度与体积密度的回归方程分别为y=-6.06+24.19x,y=-0.64+3.82x,均为密切线性相关关系。且在双氧水添加量为8‰时泡沫材料取得最大力学强度,此时气孔孔径最小,孔结构参数较优,导热系数为0.071 W/(m·K),体积密度仅为0.54g/cm3。     

Fabrication and investigation of influence of CaCO3 as foaming agent on Al-SiCp foam

Closed cell aluminum foams have been used in various disciplines of engineering. Aluminum foams provide high strength with the advantage of low weight. In the current research, CaCO₃ is used as a foaming agent for producing closed-cell aluminum foams. For the fabrication of homogenous foam, optimization of process parameters was done. The effect of SiC as a thickening agent on structural property of foams viz. density and porosity have been inspected. Foams with density 0.40–0.86 g/cm³ were produced. The produced foams were studied under axial compression tests for evaluating mechanical properties. It can be inferred from the results that by adding 3 wt.% CaCO₃, the uniform viscosity of melt was achieved and a homogeneous foam structure is achieved with optimum porosity. Also, 5 wt.% addition of CaCO₃ in melt and stirring speed at 1400 rpm tend to increase porosity and decrease cell wall thickness. The optimum values for thickening agent SiC, foaming agent CaCO₃ at stirring speed 1400 rpm were found out to be 15 wt.%, 3 wt.%. The effect of relative density, the addition of thickening and foaming agent is studied.     

Effect of processing parameters on cell structure of an aluminum foam

A closed cell aluminum foam with the same composition but different cell sizes and structures was prepared by changing air injection rate and impeller speed during foaming process to study the influence of air injection rate and impeller speed on cell structure. The foams prepared under the foaming conditions are characterized as roughly equiaxed polyhedral cells with density range of 0.1–0.22 g/cm³ and cell diameter of 4–11 mm with different cell wall thickness and Plateau border size. Cell size of the aluminum foam is increased with increasing air injection rate, and higher impeller speed results in a much smaller cell size at given air injection rate. Cell wall thickness and Plateau border size of the aluminum foams are decreased with the increase in cell size. Moreover, the higher impeller speed produces smaller size of the foam cells with thicker cell wall and Plateau border size, resulted in higher density foam in contrast to the foam with the same cell size prepared at lower impeller speed.     

Closed cell ZA27–SiC foam made through stir-casting technique

Closed cell zinc aluminum alloy (ZA27)–SiC composite foam has been synthesized using conventional stir-casting technique and CaH₂ as foaming agent. The synthesized foams are characterized in terms of its micro-architectural characteristics and deformation responses under compressive loading. It is observed that ZA27–SiC foams could be easily foamed without any difficulty. The density of the developed foam ranges from 0.25 gm/cc to 0.45 gm/cc due to the variation of CaH₂ percentage. The plateau stress and energy absorption of these foams follow power law relationship with relative density. Wherein, the densification strain follows a linear relationship with the relative density.     

Compressive properties of aluminum foam produced by powder-Carbamide spacer route

Effects of cell shape and size, and relative density of aluminum foam on its compressive behavior have been investigated. Aluminum foams were produced via aluminum powder-Carbamide spacer route. The results show that angular cells significantly reduce mechanical properties of the foam. They also indicate that compressive properties of the foams, including plateau stress (σ_pl), densification strain (ε_D), and energy absorption, increase by cell size and relative density of the foams. Experimental results were compared with theoretical predictions; they were fairly corresponded to theoretical conceptions; this arises from near-ideal architecture of the foams with almost spherical cells, in this study. Constant values of C, n and α in theoretical modulus and densification strain equations wear calculated as 1.22, 2.09 and 0.95, respectively. The values indicate compressive behavior approaches to ideal morphology foam via employing spherical space holder.     

Thermal conductivity anisotropy in polypropylene foams prepared by supercritical CO2 dissolution

Different relative density polypropylene foams were prepared by means of two foaming processes: chemical foaming by compression moulding and physical foaming by high pressure CO₂ dissolution. By controlling the foaming parameters, such as blowing agent concentration, foaming temperature, pressure drop and pressure drop rate, it was possible to regulate the cellular structure, foams showing from markedly isotropic-like cellular structures to ones with highly-elongated cells in the vertical foam growth direction (honeycomb-like cell orientation). The thermal conductivity was measured using the transient plane source method. Using this technique, it was possible to measure the global conductivity and the thermal conductivity in both the axial and radial directions of a given sample. Results show that the global thermal conductivity of foams was mainly regulated by their relative density. In addition, the honeycomb-like cell orientation of the CO₂ dissolution foams resulted in considerably higher values in axial direction when compared to radial, demonstrating that there was a direct influence of cellular structure on the thermal conduction behaviour of these foams, enabling the development of new polypropylene foams with direction-dependent thermal properties.     

用超临界二氧化碳技术制备硅橡胶/碳纳米管/炭黑复合导电泡沫材料

以超临界二氧化碳为物理发泡剂,制备出一种具有良好导电性能的硅橡胶/碳纳米管/炭黑多相复合泡沫材料。系统研究了不同碳纳米管含量及不同加工参数对硅橡胶发泡行为和最终硅橡胶泡沫材料导电性能的影响。实验结果表明,碳纳米管和炭黑在硅橡胶基体中分散良好,无明显团聚体出现。均匀分散的碳纳米管能够提高发泡时的成核密度,从而得到具有较小泡孔尺寸和较高泡孔密度的泡沫材料。研究发现随着饱和温度升高,泡孔尺寸变大,泡孔合并现象明显;随饱和压力增加,泡孔尺寸变小,泡孔密度增加,泡孔合并现象减少。不同泡孔形态对应其导电性能也有所不同,当泡孔尺寸较小,泡孔分布均匀的泡沫材料导电性能较好。     

Manufacturing of Al/SiCp composite foams using calcium carbonate as foaming agent

Abstract

The aluminium composite foams reinforced by different volume fractions of SiC particles were manufactured with the direct foaming route of melt using different contents of CaCO₃ foaming agent. The density of produced foams changed from 0·43 to 0·76 g cm^?3. The microstructural features and compressive properties of the Al/SiC_p composite foams were investigated. Compressive stress–strain curve of Al/SiC_p composite foams is not smooth and exhibits some serrations. At the same relative density of composite foams, the plateau stress of the composite foams increases with increasing volume fraction of SiCp and decreasing weight percentage of CaCO₃. The relation between plateau stress, relative density, weight percentage of CaCO₃ and SiCp volume fraction of Al/SiCp composite foams with a given particle size was investigated.     

煤基炭泡沫孔结构调控

以肥煤镜质组富集物为前驱体, 采用高压渗氮法制备煤基炭泡沫, 研究了发泡温度、发泡压力和发泡时间对炭泡沫孔结构的影响。利用SEM观察炭泡沫的孔胞形貌, 同时利用Nano Measurer分析软件统计SEM照片孔胞直径分布和孔喉直径分布以及平均孔径。结果表明: 微孔塑料成核理论可以定性解释炭泡沫的孔结构变化趋势。发泡温度的升高导致成核密度增加, 同时导致气体在胶质体的溶解度降低, 不利于孔胞长大。发泡压力的增大导致炭泡沫的孔胞密度增加, 临界成核半径降低, 同时加剧了热聚合反应, 导致胶质体的粘度增大, 不利于孔胞长大。发泡时间的延长会使热聚合更加充分, 影响胶质体粘度, 进而影响孔结构。     

Effect of cell shape anisotropy on the compressive behavior of closed-cell aluminum foams

The closed-cell Al–Si foams have been prepared by molten body transitional foaming process using TiH₂ foaming agent. The cell shape anisotropy ratio of specimens with various relative densities was measured. The quasi-static compressive behavior of Al–Si foams in both longitudinal and transverse directions were investigated. The results show that Al–Si foam loaded in the transverse direction exhibits a lower stress drop ratio. The relationship between plastic collapse stress ratio and cell shape anisotropy is in accordance with Gibson and Ashby model. The plastic collapse stress and the energy absorption property of Al–Si foams increase following power law relationship with relative density. Moreover, Al–Si foams exhibit higher plastic collapse stress and the energy absorption property in the longitudinal direction than that in the transverse direction.     

Effect of Porosity and Cell Size on the Dynamic Compressive Properties of Aluminum Alloy Foams

The dynamic mechanical properties of open-cell aluminum alloy foams with different relative densities and cell sizes have been investigated by compressive tests.The strain rates varied from 700 s^-1 to 2600 s^-1.The experimental results showed that the dynamic compressive stress-strain curves exhibited a typical three-stage behavior:elastic,plateau and densification.The dynamic compressive strength of foams is affected not only by the relative density but also by the strain rate and cell size.Aluminum alloy foams with higher relative density or smaller cell size are more sensitive to the strain rate than foams with lower relative density or larger cell size.