Microstructure Of Porous Materials Research Articles

Quantitative analysis of micro-porosity of eco-material by using SEM technique

Microstructure of the eco-material combining vegetation recovery with slope protection is important for determining plant-growing properties. Several techniques for analyzing the eco-material microstructwe are presented, including the freeze-cut-drying method of preparing samples for scanning electronic microscopy (SEM), the SEM image processing technique and quantifying analysis method of the SEM images, and etc. The aggregates and pores in SEM images are identified using the different mathematics operators, and their effects are compared. The areas of aggregates and pores are obtained using the operator of morphology, and the influences of different thresholds in image segmentation are also discussed. The results show that the method, in which the variation of non-maximum grey-level gradient is limited, improves the effect of edge detections due to a weak distinction existing at the edge between the aggregates and pores in image. The determination of the threshold should combine the image characteristic with filling operation, so as to assure the precision of the image analysis, in which the contact-segmentation is the simplest and most effective method. The results also show that the pore areas in eco-materials are generally larger than those in the correlative soils, and their increment is large as soil fabric being fine. These differences are related to admixture of expansive perlitic. The operator of morphology provides a new method for the image analysis of other porous material microstructure such as soils and concretes.

Study of production route for titanium parts combining very high porosity and complex shape

The production of highly porous titanium parts of complex shape by powder metallurgical technology is described. Well defined porosity and pore sizes were achieved using a pore forming additive. This additive also enhances the strength of unsintered compacts, allowing machining in the green state. The requirements of the initial powders and pecularities of each production step are discussed in detail. The microstructure of porous materials and examples of net shape parts are given, aiming preferentially at biomedical applications. The impurities of the obtained titanium parts are compared with the requirements of the ISO standard for titanium implants.

A Constructive Approach for Heterogeneous Material Modeling and Analysis

AbstractIn this paper, we apply the Constructive Solid Analysis (CSA) method developed recently to heterogeneous material modeling and analysis. The key idea in the methodology is that the hierarchy in the description of the geometry is mirrored by an identical hierarchy in the analysis fields guided by the appropriate governing equations. It is shown that the method is ideal for handling the multi-phases in the heterogeneous material microstructure, especially when the microstructure is subject to iterative change which, arises during microstructure design. The effective elastic properties of various 2D composites and porous material microstructures, including random microstructures, are evaluated to verify the procedure. The results are in good agreement with those obtained using the finite element method.

Computational Modeling of Phase Connectivity in Microstructures of Porous Materials during Sintering and Grain Growth.

A Monte Carlo simulation method using a three dimensional lattice was developed to analyze the connectivity of pores in sintered materials. The changes in porosity (fV), mean grain diameter (DS), intercept length of pores (DV), contiguity of the solid phase (C) and fraction of connected pores (fV, C) with the number of Monte Carlo steps (MCS) were analyzed as a function of initial porosity (fV, 0) and initial grain diameter (DS, 0). In many cases, fV, C decreased with MCS down to 0%, particularly at small and intermediate values of fV, 0 and DS, 0. However, in some cases of large fV, 0 and DS, 0, an fV, C of 100% was maintained irrespective of MCS, which means that all pores may remain connected in the material. Systematic plots of DV, DS and C vs fV, 0×fV, C, which indicate the amount (%) of connected pores, are found to be useful for designing sintering and grain growth processes of porous materials.

Lattice model of adsorption in disordered porous materials: mean-field density functional theory and Monte Carlo simulations.

We present mean-field density functional theory calculations and Monte Carlo simulations for a lattice model of a fluid confined in a disordered porous material. The model is obtained by a coarse graining of an off-lattice model of adsorption of simple molecules in silica xerogels. In some of our calculations a model of a porous glass is also considered. The lattice models exhibit behavior that is qualitatively similar to that of their off-lattice counterparts but the computations required are much more tractable and this makes it feasible to investigate the effects of porous material microstructure at longer length scales. We focus on exploring in detail the behavior in the adsorption/desorption hysteresis region for these models. In agreement with recent results for a model that uses a random distribution of solid sites on the lattice [Kierlik et al., Phys. Rev. Lett. 87, 055701 (2001)] we show that the disorder of the solid matrix induces multiple metastable states within the hysteresis region, which are evident in both the mean-field theory calculations and the Monte Carlo simulations. These multiple metastable states can be connected by scanning curves that are very similar to those seen in experimental studies of adsorption hysteresis. The results from mean-field theory predict that while there is hysteresis in the adsorption/desorption isotherms it is not possible to locate a condition of phase equilibrium that satisfies thermodynamic consistency. A wider significance of these results is discussed.

Advances in computational design and optimization with application to MEMS

AbstractIn this paper, we will highlight the current research which employs the topology optimization to find the optimal configuration of various smart structures and microstructures, specifically, pressure actuated compliant mechanisms, flextensional transducers, and porous material microstructures with unusual thermoelastic properties. These examples demonstrate that the topology optimization problem involving multiple physics domain is a viable direction for future research, in particular, for sensor and actuator design. Copyright © 2001 John Wiley & Sons, Ltd.

Surface and pore structure characterisation by neutron scattering techniques

Neutron scattering techniques can provide extensive information about the microstructure of porous materials and the properties of adsorbates within the pores. This information is obtained from measurements of both coherent and incoherent scattering. Coherent scattering comprises diffraction and small angle scattering (SAS) and has a counterpart in X-ray scattering. Incoherent scattering arises from a unique interaction of the neutron with the atomic nucleus and has no equivalent with either X-ray or light radiation. Here the application of small angle neutron scattering (SANS) is reviewed with particular emphasis on two recent developments. The first concerns contrast variation methods to investigate adsorption mechanisms, which include the capillary condensation of benzene in a mesoporous silica gel. The second concerns the examination of oriented anisotropic porous microstructures, as can occur in microporous carbon fibres. The applications of incoherent inelastic and quasielastic scattering together with neutron diffraction are also described. Here the investigation of the state of water in micro and mesoporous silica gels with a model pore structure is illustrated. It is shown that these techniques give evidence of a perturbed H-bonded structure of water due to confinement in pores. This affects both the diffusional behaviour and freezing properties of the water.

Sound propagation in gas-filled rigid-framed porous media: General theory and new experimental and numerical data

The acoustic properties of gas-filled porous media have been the subject of extensive theoretical and experimental work. However, even in the simplest case of rigid-framed materials, most of the theoretical developments found in the acoustical literature remain largely empiric or semiphenomenologic. This is due to the complicated microstructure of porous materials in general. Starting with first principles and using a simple two-scale analysis, a general formulation of the problem of (linear) long-wavelength sound propagation in gas-filled media is provided in terms of two independent permeabilities. One of these—the viscous dynamic permeability—is well known. Its thermal analog, the thermal dynamic permeability, is new in the acoustical context. It can be related to a notion of ‘‘mean survival time’’ in diffusion-controlled reactions. The exact connection between the microgeometry and the frequency-dependent dynamic permeabilities is obtained in terms of independent geometrical distribution functions. Useful analogies with the dispersion of electric and magnetic permeabilities are noted. New experimental and numerical data demonstrate the usefulness of the scaling functions proposed by Wilson et al. and Pride et al. Different limitations of the general modeling and the mentioned scaling functions are also noted.

The use of 129Xe NMR exchange spectroscopy for probing the microstructure of porous materials

The phenomenon of adsorption and desorption of xenon in an inorganic aluminium/zirconoxide fibre, in silica gel and in an organic polymer blend is compared by 129Xe 2D-exchange NMR experiments. A fast chemical exchange between adsorbed, liquid and free xenon gas occurs in the case of the alumina/zirconia fibre. In contrast to this, for the polymer blend, exchange between different adsorption sites in the blend is observed, but no exchange between adsorbed xenon and xenon gas. Hardly any exchange of xenon between adsorbed and free gas occurs in silica gel even at larger time scales. We conclude that the inorganic fibre has an open pore structure, in contrast to the examined copolymer.

Application of A.C. impedance techniques in studies of porous cementitious materials: (II): Relationship between ACIS Behavior and the Porous Microstructure

The relationship between A.C. impedance parameters and the structure of porous cementitious systems was investigated. Theoretical equations relating the high frequency semicircle diameter to the descriptors of ionic concentration in the pore solution have been derived from the application of electrochemical and surface chemical principles to these systems. It is apparent that there is a linear relation between the semicircle diameter and the reciprocal of the square root of ionic concentration. The semicircle diameter was also found to be inversely proportional to the product of porosity and mean pore size. These equations have been confirmed by experiment with porous cementitious systems. It is concluded that the microstructure of porous materials can be characterized by parameters determined by application of A.C. impedance techniques.

Fabric dependence of an anisotropic strength criterion

A strength criterion with a dependence on fabric is developed. A fabric tensor is a symmetric second rank tensor which characterizes the geometric arrangement of a porous material microstructure, or the local spatial distribution of one phase of a multiphase material relative to the other phases. The development of the strength criterion follows the method of Malmeister and of Tsai and Wu. A formula for the stress interaction coefficients introduced by Tsai and Wu is obtained. This formula relates the stress interaction coefficient to the tensile and compressive strengths in two directions, to the shear strength in the plane of the two directions, and to the fabric tensor. Heretofore there has a theoretical representation of the stress interaction coefficient in terms of other physical parameters.

The relationship between the elasticity tensor and the fabric tensor

An algebraic relationship between the fourth rank elasticity tensor of a porous, anisotropic, linear elastic material and the fabric tensor of the material is considered. The fabric tensor is a symmetric second rank tensor which characterizes the geometric arrangement of the porous material microstructure. In developing this result it is assumed that the matrix material of the porous elastic solid is isotropic and, thus, that the anisotropy of the porous elastic solid is determined by the fabric tensor. It is then shown that the material symmetries of orthotropy, transverse isotropy and isotropy correspond to the cases of three, two and one distinct eigenvalues of the fabric tensor, respectively.