The shapes of a pore resulting from an entrapped bubble by a solidification front for different locations of the bubble below the free surface are predicted in this work. Bubble location is an important factor affecting temperature gradient in liquid, solute gas dissipated into the ambient, heterogeneous nucleation of the bubble and shape of the bubble cap, and subsequent entrapment and the pore shape in solid. The shapes of pores in solid influence not only material properties, but also contemporary issues of engineering, biology, medical technology and science, etc. This study takes into account solute transport across a coupling shape of the pore cap determined by the Young-Laplace equation governing balance of liquid, gas and capillary pressures. The results find that increases in depthwise location of a bubble increase pore radius and time for bubble entrapment as solute transport is from the pore across cap emerged through a concentration boundary layer along the solidification front into surrounding liquid in the early stage. On the other hand, the bubble cannot be entrapped, provided that solute transport in opposite directions across the cap submerged in a concentration boundary layer along the solidification front. The predicted growth and entrapment of a tiny bubble as a pore in solid agree with experimental data. Understanding and controlling of the pore shape via controlling bubble location is of interest and challenging.

The main aim of this research was investigation of the processing-structure-property relationship for polymer blends. The paper presents the results of tests on the structure, basic physical and porous properties of polymer films blend of low density polyethylene (LDPE) with poly(4-methyl-1-pentene) (PMP). Studies utilizing LDPE/PMP blends were undertaken to investigate a three-stage process: melt-extrusion/annealing/uniaxial-stretching (MEAUS), and a two-stage process: melt-extrusion/uniaxial and biaxial stretching (MEUS and MEUBS), used to produce porous films. The permeability and porosity results coupled with small-angle x-ray scattering data provide a direct connection between changes in microstructure to the observed changes in gas transport properties.

Tungsten foams with directional, controlled porosity were created by directional freeze-casting of aqueous WO3 powder slurries, subsequent freeze-drying by ice sublimation, followed by reduction and sintering under flowing hydrogen gas to form metallic tungsten. Addition of 0.51 wt% NiO to the WO3 slurry improved the densification of tungsten cell walls significantly at sintering temperatures above 1250 °C, yielding densely sintered W–0.5 wt% Ni walls with a small fraction of closed porosity (<5%). Slurries with powder volume fractions of 15–35 vol% were solidified and upon reduction and sintering the open porosity ranges from 27–66% following a linear relation with slurry solid volume fraction. By varying casting temperature and powder volume fraction, the wall thickness of the tungsten foams was controlled in the range of 10–50 µm. Uniaxial compressive testing at 25 and 400 °C, below and above the brittle-to-ductile-transition temperature of W, yields compressive strength values of 70–96 MPa (25 °C) and 92–130 MPa (400 °C).

In this paper a second-order two-scale (SOTS) analysis method is developed for a static heat conductive problem in a periodical porous domain with radiation boundary condition on the surfaces of cavities. By using asymptotic expansion for the temperature field and a proper regularity assumption on the macroscopic scale, the cell problem, effective material coefficients, homogenization problem, first-order correctors and second-order correctors are obtained successively. The characteristics of the asymptotic model is the coupling of the cell problems with the homogenization temperature field due to the nonlinearity and nonlocality of the radiation boundary condition. The error estimation is also obtained for the original solution and the SOTS’s approximation solution. Finally the corresponding finite element algorithms are developed and a simple numerical example is presented.

A new structural model is proposed for cubic nitroprussides and the crystal structure for the complex salts of Fe(2+), Co(2+), and Ni(2+) refined in that model. In cubic nitroprussides the building unit, [Fe(CN)5NO]2−, and the assembling metal (M=Fe2+,Co2+,Ni2+), have ¾ occupancy with three formula units per cell (Z=3). This leads to certain structural disorder and to different local environments for the outer metal. The crystallographic results are supported by the Mössbauer and infrared data. The XRD powder patterns, index in a cubic cell (Fm3m space group), show a sinuous background because of diffuse scattering from positional disorder of the metal centers. Because of this, the crystal structures were refined allowing the metal centers to move from the (0,0,0) and (0,0,1/2) positions (away from positional symmetry restrictions). The refinement under these conditions leads to excellent agreement factors (Rwp, Rp, S), good pattern background fitting, and produced a refined structural model consistent with the crystal chemistry of nitroprussides. The studied materials are obtained as hydrates. On heating, the crystal water evolves, and below 100°C an anhydrous phase is obtained, preserving the framework of the original hydrates. The loss of the crystal water leads to cell contraction that represents around 2% of cell volume reduction. On cooling down from room temperature to 77 and 12 K, a slight expansion for the -M-N≡C-Fe-C≡N-M- chain length is observed, suggesting that at low temperature and reduction in the metals charge delocalization on the CN bridges takes place. For M=Fe and Co the crystal structure was also refined for the anhydrous phase at 12, 77, and 300 K.

The crystal structures of Mn, Zn, and Cd nitroprussides in their anhydrous state, M[Fe(CN)5NO] (M=Mn, Zn, Cd), were refined from XRD powder patterns using the Rietveld method. These compounds have a porous framework useful for adsorption and storage of small molecules. Water crystallization can be removed by heating below 100 °C without disrupting the 3D network by introducing certain structural modification mainly around the M site (Mn, Zn, Cd). For M=Mn and Cd, the compounds were found to be orthorhombic with space group Pnma [Mn:a=13.7844(1), b=7.3750(2), c=10.9470(2) Å, V=1112.8(1) Å3, Z=4; Cd:a=13.9566(3), b=7.5040(4), c=11.0230(2) Å, V=1154.4(1) Å3, Z=4]. Anhydrous zinc nitroprusside crystallizes in rhombohedral with space group R3 [a=b=19.2525(1), c=17.7107(2) Å, γ=120.0°, V=5685.1(1) Å3, Z=18]. When exposed to humid air, these anhydrous compounds become hydrated. The XRD powder patterns were recorded under vacuum on samples dehydrated in situ. The structural information from XRD was complemented with thermo-gravimetric, infrared, and Mössbauer data.

Various porous titania photocatalysts are analyzed three-dimensionally in real space by electron tomography. Shapes and three-dimensional (3D) distributions of fine pores and silver (Ag) particles (2 nm in diameter) within the pores are successfully reconstructed from the 3D data. Electron tomography is applied for measuring the specific surface area of the porous structures including open and closed porosity. Calculated specific surface areas of 22.8 m2/g for a conventional sol-gel TiO2 sample and 366 m2/g for a highly porous TiO2 sample prepared using the Pluronic P-123 self-assembly process are compared with those measured by the general BET method. The real-space surface measurement indicates that the highly porous TiO2 produced by the present method using block copolymers has a greater number of effective reaction sites for the degradation of methylene blue. Electron tomography shows a great potential to contribute considerably to the nanostructural analysis and design of such catalyst materials for photocatalysis.

An approximate anisotropic yield function is presented for anisotropic sheet metals containing spherical voids. Hill's quadratic anisotropic yield function is used to describe the anisotropy of the matrix. The proposed yield function is validated using a three-dimensional finite element analysis of a unit cell model under different straining paths. The results of the finite element computations are shown in good agreement with those based on the yield function with three fitting parameters. For demonstration of applicability, the anisotropic Gurson yield function is adopted in a combined necking and shear localization analysis to model the failure of AA6111 aluminum sheets under biaxial stretching conditions.