The influence of the stabilizing agent SDS on porosity development in alkali-activated fly-ash based foams

Alkali activated foams (known also as “geopolymer foams”) are formed by the adding of a foaming agent, such as Al powder or H₂O₂, to an alkali activated matrix which can be based on, for example, fly ash, slag or meta-kaolin. The foaming agent decomposes and reacts inside the matrix, resulting in the release of gasses which form pores within the structure. Such pores have to be created before the alkali activated foams harden. In order to prevent the escape of these gasses from the foam, a stabilizing agent can be added to the foam mixture. This paper presents the results of tests involving the pore-foaming process in the case of highly porous, alkali activated, fly-ash based foams. Between 0.5 and 1.5 mass % of H₂O₂ was added to the fly ash precursor as a foaming agent, as well as different amounts (varying from 0.1 to 4.0 mass %) of the selected stabilizing agent, which is known as SDS - sodium dodecyl sulfate. The physical, mechanical, and microstructural properties of the hardened alkali-activated foams were determined. Their pore structures were characterised by SEM, as well as by a three-dimensional (3D) technique, X-ray computed micro-tomography. The advantage of the latter method is that a better insight can be obtained into the characteristics of the hardened pore structure, including information about its homogeneity and the pore size distribution. The influence of the amount of the added foaming agent, as well as that of the amount of the stabilization agent, was evaluated, and optimal addition mass percentages were determined. In the case of the best mixtures, the investigated hardened pore structures showed relatively good mechanical properties, and could therefore be used for various applications in the building industry.     

Elaboration and characterization of metallic foams based on tin–lead

This study is devoted to the fabrication of metallic foams based on tin–lead of various relative densities and pore sizes by means of the liquid alloy infiltration process and its characterization (mechanical behavior and microstructure). Room temperature uniaxial compression tests were carried out in order to study the influence of the size of cell and of the relative density on the behavior in compression and to interpret these relations within a framework. A characterization on a microscopic scale (metallography and hardness) is achieved in order to link the morphological and mechanical characteristics of the constitutive phases, the parameters of the process and the macroscopic mechanical behavior.     

X-ray characterization of starch-based solid foams

Wide- and small-angle X-ray scattering (WAXS and SAXS) and X-ray microtomography were used to study the structure of brittle, solid foams made by extrusion of whole grain barley flour and additional whey protein isolate (WPI) and polydextrose (PD). The structure of the extrudates was described in a coarse way from nano- to microscale, and the effects of additives were discussed. The additives were observed to affect the structure in many scales, for instance, by inducing differences in the crystal structure of starch and in the microscale pore structure observed with both SAXS and X-ray microtomography. The most significant effects were introduced by WPI, but these were highly reduced in the presence of PD. Differences were also seen in lamellar structures of starch, which were probably formed due to retrogradation and observed with SAXS in powder samples soaked in water before the measurements.     

Morphological characterization of microcellular carbon foams

Microcellular carbon foams have been prepared by the high-temperature carbonization of polyacrylonitrile (PAN) foams in an inert atmosphere. The PAN precursor foams were first prepared by thermally induced phase separation of PAN solutions followed by gelation/extraction or freezing/freeze-drying processes. The resulting carbon foams have low densities and open-celled morphologies. We have developed two complementary techniques to characterize objectively carbon foam morphologies, BET surface area measurements and mercury porosimetry. These two measurement techniques, when used in conjunction with known stereological rules, allow us to calculate densities and average cell sizes or cell size distributions. As a bonus, values of the bulk modulus for low-density carbon foams also can be determined from mercury porosimetry. Unlike other techniques, our determinations do not require carefully prepared surfaces (such as for microscopy) or an assumed morphological model (required for most other techniques).     

Rheological characterization of hydroxypropylcellulose gels

The present paper describes the rheological properties of hydroxypropylcellulose (HPC) gels formulated in propylene glycol (PG), water, ethanol, and mixtures of these components. The effects of molecular weight, polymer concentration, and solvent composition on the apparent viscosity and flow characteristics have been studied by continuous shear rheometry. The HPC gels are shear thinning and do not exhibit significant yield or hysteresis in their rheograms. The apparent viscosity increases with increasing molecular weight and concentration of the polymer, as expected. Although not so pronounced at lower concentrations (≤ 1.5%), HPC gels tend to become increasingly non-Newtonian with increasing molecular weight at higher polymer concentrations (3%). A mathematical model has been proposed for the prediction of viscosities of HPC gels. There exists a high degree of dependence on molecular interactions between various solvent molecules in the prediction of mixture viscosities in ternary systems. The effects of solvent composition on the viscoelastic behavior of these gels have also been examined by dynamic mechanical analysis. The HPC gels are highly viscoelastic and exhibit greater degrees of elasticity with increased PG content in ternary solvent mixtures with water and ethanol. The study also suggests that dynamic mechanical analysis could prove to be a useful tool in the determination of zero-shear viscosities, viscosities that are representative of most realistic situations.     

聚甲基丙烯酰亚胺(PMI)泡沫制备及结构表征

以甲基丙烯酸、甲基丙烯腈和甲基丙烯酰胺为主要单体原料,在适当的发泡剂存在下,以过氧化物为引发剂引发单体共聚,制得甲基丙烯酸-甲基丙烯腈-甲基丙烯酰胺共聚物,并在高温下进行发泡和环化反应,制得聚甲基丙烯酰亚胺(PMI)泡沫,并表征了PMI泡沫的结构.     

POM/PEO共混物中PEO对POM非等温结晶的影响

利用DMA和DSC考察了POM/PEO共混物的相容性及PEO对POM非等温结晶的影响。结果表明,POM/PEO共混物只有一个玻璃化转变温度(Tg),与组分的关系符合Fox方程,POM与PEO在无定形态相容,PEO抑制了POM成核,降低了POM的结晶速度和共混物中POM的相对结晶度。PEO含量较高时POM结晶温度下降。     

溶液插层复合法制备PEO/LixMoO3纳米复合材料的插层过程机理研究

利用溶液插层制备了环氧乙烷（PEO）／LixMoO3纳米复合材料,并对PEO插层过程的机理作了初步探讨。结果说明,PEO插入到LixMoO3片层间的动力一方面来自PEO与Li^ 间的配位能力,另一方面可能与熵的补偿机理有关。     

Rheological characterization and in-situ investigation of the time-dependent cholesteric based lyotropic liquid crystals

The impact of cell culture media on the rheology of liquid crystals is critical to developing liquid crystal (LC) based biosensors. The rheological properties of cholesteryl ester based lyotropic liquid crystals (LLC) were investigated in a rotational rheometer and using in-situ methods after incubation in cell culture media for periods of 24, 48 and 72 h. The results of the rheological experiments indicated that for incubation up to 48 h, LLC exhibited a linear viscoelastic behavior < 10% strain at low angular frequencies < 1 s^? 1 and an insignificant decrease in the complex viscosity. The in-situ experiments involved examining the response of the LLC to stresses generated by keratinocyte. It was found that cells induced deformations in the liquid crystal surfaces could be completely removed by disrupting the actin cytoskeletons of cells with cytochalasin-B after 48 h in culture media, but could only be partially removed after 48 h in culture media. In fixed stress experiments, it was found that LC deformation lengths remained constant over 72 h and exhibited a statistically insignificant decrease after 72 h in culture media. These later results indicate very little time related change of viscosity in the LLC. However, the in-situ rheological behaviors were in good agreement with the rheological results obtained from oscillatory tests for the LLC incubated up to 48 h. These results suggest that LLC coated substrates have viable physical properties within 48 h of incubation that can allow them to monitor cell-generated stresses in culture.     

Elemental and molecular characterization of aged polydimethylsiloxane foams

The application and integration of micro X-ray fluorescence (MXRF) and Fourier transform infrared (FT-IR) imaging to polydimethylsiloxane (PDMS) foam aging issues have been applied to cross-sectional images. Previous work has shown the tin in the stannous 2-ethylhexanoate catalyst to be highly mobile and it typically migrates to the PDMS foam upper surface. The current paper discusses a method for the integration of full spectral MXRF and FT-IR imaging of aged foams. Solvent extractions have also been performed on both fresh and aged foams to further examine aged foam properties. Combining elemental and molecular imaging techniques and applying them to PDMS aging provides synergistic information that aids in understanding the sample composition and distribution of components. Application of chemometric analysis to the full spectral elemental and molecular maps demonstrates correlations within the foams of the residual tin, organo-tin functional group moieties, and the presence of nitroplasticizer from an exogenous source.     

Thermoanalytical characterization of epoxy matrix-glass microballoon syntactic foams

Syntactic foams are finding new applications where their thermal stability and high temperature response are important. Therefore, the high temperature response of these advanced composites needs to be characterized and correlated with various material parameters. The present study is aimed at evaluating the effect of microballoon (hollow particle) volume fraction (Φ) and wall thickness (w) on thermoanalytical characteristics of epoxy matrix syntactic foams containing glass microballoons. These composites are characterized to determine the glass transition temperature (T _g), the weight loss, and the char yield. It is observed that T _g decreases and the char yield increases due to the presence of microballoons in the resin. The T _g is increased with an increase in Φ but is not significantly affected by w. The thermal stability is increased by increasing w and is relatively less sensitive to Φ. Understanding the relations between thermal properties of syntactic foams, the microballoon wall thickness, and microballoon volume fraction will help in developing syntactic foams optimized for mechanical as well as thermal characteristics. Due to the increased interest in functionally graded syntactic foams containing a gradient in microballoon volume fraction or wall thickness, the results of the present study are helpful in better tailoring these materials for given applications.     

低密度TMPTA泡沫的制备及表征

低密度聚合物泡沫在惯性约束聚变靶及电磁内爆靶中应用十分广泛。以三羟甲基丙烷三丙烯酸酯(TMP-TA)为聚合单体,安息香甲基醚为引发剂,通过紫外光引发生成凝胶,经超临界干燥得到TMPTA泡沫材料。通过红外光谱仪和元素分析仪确定了TMPTA单体中官能团转化率及泡沫纯度的表征。实验结果表明,聚合反应过程中,在1636cm-1附近碳碳双键(C=C)的转化率为40.48%,泡沫为高纯度的低密度TMPTA泡沫,机械强度可满足核磁内爆靶(Z-pinch)靶装配的需求。     

水铝英石/PEO/LiClO4复合固态聚合物电解质中组分相互作用对PEO结晶的影响

为解决现有锂离子电池的安全性问题,固态电解质的研究备受关注。以Na2SiO3和AlCl3·6H2O为原料,采用溶胶-凝胶法制备出水铝英石(AL);通过溶液共混法将其与聚环氧乙烷/高氯酸锂(PEO/LiClO4)复合得到复合固态聚合物电解质。利用X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FTIR)、差示扫描量热分析仪(DSC)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)以及光学显微镜(OM)对样品进行结构分析及形貌表征。结果表明:水铝英石和LiClO4与PEO间的非价键力相互作用(络合、氢键及Lewis酸-碱作用)显著抑制PEO的结晶。随着水铝英石含量的增加,PEO的结晶度呈现出先降低后增加的趋势;而随着锂盐含量的增加,PEO的结晶度持续降低,当EO/Li+摩尔比为10∶1,水铝英石的含量为5%(质量分数)时,复合固态聚合物电解质的结晶度最低,仅为4.12%。     

Permanently magnetic BaFe12O19 foams: Synthesis and characterization

In the present study, permanently magnetic barium ferrite foams synthesized using a replication technique were characterized. Structural analysis have shown that the products are single phase of BaFe₁₂O₁₉ and pore sizes reach up to 1 mm in diameter with a significantly uniform distribution. Magnetic properties were examined and compared with that of a sintered compact sample. It was observed that magnets become slightly harder with porosity. Our findings reveal that these materials may be applied to different technologies and can be used for understanding the physical interactions of hybrid structures.     

Rheological characterization and thermal degradation of PTFE

PTFE (¯M _n=5×10⁶), when heated near the melting temperature (335 to 337 C) while in contact with carbon black, is characterized by an effective viscosity and a thermal stability which are orders of magnitude lower than those found in the absence of the contacting high surface area material. The penetration of the PTFE into the porous carbon black occurs by the spreading of a very thin polymer film followed by a thickening of this film with time at temperature until a limiting concentration is reached. The lower the average molecular weight of the PTFE, the more rapidly it penetrates into the porous material. Similar phenomena have been observed with high molecular weight PTFE heated near the melting temperature while contacting high surface area metal blacks or porous sintered metals.     

Preparation and characterization of ultra-low density porous gold foams

We present a simple approach to generate ultra-low density porous gold foams with the density as low as 0.519 gcm^-3. In our work, gold nanoparticles with small grain sizes and good solubility were prepared and used as starting building blocks; afterwards, the freeze-dry technique was employed to prepare gold compound foams. Finally the gold compound foams were sintered to obtain porous gold foams with ultra-low density. The results show that the content of gold element in the foams is close to 99.2%. Even though the density is as low as 0.519 gcm^-3 the foams still have good intensity and can be machined to simple regular shapes. The microstructure analysis results indicate that the gold foams have continuous open structure, the average pores size is about 1-2 μm, and the framework of the gold foams is piled up with gold particles of different sizes. Our approach might give a way to produce low-density gold foams with simple fabrication procedures.     

Quasi-static uni-axial compression behaviour of hollow glass microspheres/epoxy based syntactic foams

Hollow glass microspheres/epoxy foams of different densities were prepared by stir casting process in order to investigate their mechanical properties. The effect of hollow spheres content and wall thickness of the microspheres on the mechanical response of these foams is studied extensively through a series of quasi-static uni-axial compression tests performed at a constant strain rate of 0.001 s^?1. It is found that strength of these foams decreases linearly from 105 MPa (for the pure resin) to 25 MPa (for foam reinforced with 60 vol.% hollow microspheres) with increase in hollow spheres content. However, foams prepared using hollow spheres with a higher density possess higher strength than those prepared with a lower one. The energy absorption capacity increases till a critical volume fraction (40 vol.% of the hollow microspheres content) and then decreases. Failure and fracture of these materials occur through shear yielding of the matrix followed by axial splitting beyond a critical volume fraction.     

Rheological characterization of dry-formed networks of rayon fibres

The viscoelastic properties of low-density dry-formed fibre networks have been evaluated by dynamic mechanical measurements in shear. The fibres used were rayon fibres of different diameters (13, 30 and 60 m) and lengths (2, 4 and 6 mm). The effects of network density and grammage on the viscoelastic properties of the network were demonstrated. An important objective of this study was to assess relations between mechanical properties and fibre or network characteristics. The primary mechanical parameters used to describe the networks were the storage modulus G ₀ measured at very low imposed strain amplitudes (in the linear region) and the critical strain _C at which the network yields significantly. It was noted that if the network is to be able to withstand high deformations it should exhibit a high value Of _C, which in turn, is promoted by a short free segment length between fibre crossings and a large number of contact points per fibre in the network. Long and thin fibres provide an advantage in this context. The modulus G ₀ appeared to be related to the ratio of the free segment length to the fibre diameter. A lower value of this ratio corresponds to a higher G ₀ value and an improved load transfer through the network structure. The networks studied here should in general be regarded as weak compared with other types of networks, e.g. paper.     

Microstructural characterization of metal foams: An examination of the applicability of the theoretical models for modeling foams

Establishing the geometry of foam cells is useful in developing microstructure-based acoustic and structural models. Since experimental data on the geometry of the foam cells are limited, most modeling efforts use an idealized three-dimensional, space-filling Kelvin tetrakaidecahedron. The validity of this assumption is investigated in the present paper. Several FeCrAlY foams with relative densities varying between 3 and 15% and cells per mm (c.p.mm.) varying between 0.2 and 3.9 c.p.mm. were microstructurally evaluated. The number of edges per face for each foam specimen was counted by approximating the cell faces by regular polygons, where the number of cell faces measured varied between 207 and 745. The present observations revealed that 50-57% of the cell faces were pentagonal while 24-28% were quadrilateral and 15-22% were hexagonal. The present measurements are shown to be in excellent agreement with literature data. It is demonstrated that the Kelvin model, as well as other proposed theoretical models, cannot accurately describe the FeCrAlY foam cell structure. Instead, it is suggested that the ideal foam cell geometry consists of 11 faces with 3 quadrilateral, 6 pentagonal faces and 2 hexagonal faces consistent with the 3-6-2 Matzke cell.