Bio-silica incorporated barium ferrite composites: Evaluation of structure,morphology, magnetic and microwave absorption traits

A series of bio-silica incorporated barium-ferrite-composites with the composition of (x)Bio-SiO₂:(80-x)γ-Fe₂O₃:(20)BaO, where x = 0, 1, 2, and 3 wt% were prepared using the modified solid-state reaction method. The influence of different bio-silica (extricated from sintered rice husk) contents on the surface morphologies, structures, and magnetic characteristics of these composites were assessed. The relative complex permittivity and permeability were resolved using the Nicholson-Ross-Weir strategy in the frequency range of 8–13 GHz. Meanwhile, the reflection loss was estimated through the transmission/reflection line theory to assess the MW absorption properties of the composites. Incorporation of the bio-silica in the barium ferrite composites generated a new hexagonal phase (Ba₃Fe₃₂O₅₁) and a tetragonal phase (BaFeSi₄O₁₀) which led to a decrease in the saturation magnetization and significant shift in the MW frequency absorption peak positions.     

Determining the permeability of organic solvents through PVC pipes using a direct SPME model

The permeability of aromatic hydrocarbons, i.e. BTEX and styrene, through PVC pipes was investigated using a 6-cm pipe-bottle model with direct solid-phase microextraction (SPME) sampling. It was found that an aromatic hydrocarbon with a large molecular size or low polarity may be less permeable through PVC pipes. In addition, the diffusion coefficients of BTEX and styrene in PVC pipes ranged from 4.87 to 7.64 × 10⁻⁸ cm²/s. According to the simulation results of a one-dimensional diffusion model, it is speculated that diffusion transport of benzene and toluene in PVC pipes may have non-Fickian behavior. The advantage of using the innovated test model is that SPME provides a nondestructive analytical means to monitor the concentrations of organic compounds in pipe-water. Therefore, the pipe-bottle model developed herein has potential applications in determining the resistance of polymeric pipes to permeation by solvents in the aqueous solution.     

Comparison of the accuracy of curve-fitting methods for the determination of gas permeability parameters of sheet polymer samples

Accuracy of the gas permeability parameters (GPPs), i.e. solubility, diffusivity and permeability deduced from permeation measurements, is investigated for the case of homogeneous polymer sheet samples. The widely used time-lag method (TLM) and the recently introduced full curve-fitting method (FCFM) are compared on simulated and on measured permeation curves artificially distorted in various ways in order to mimic potential deficiencies of permeation measurements. Accuracy of the methods is defined as the relative deviation of the calculated from the real GPPs, i.e. those which are deduced from the distorted and the original, non-distorted curves, respectively. The following distortions have been applied: temporal truncation of the permeation curves, increasing the noise level of the measurement and shifting the permeation curve either along the concentration or the time axis. (The latter two transformations correspond to an unnoticed background shift in the readings of the concentration detection unit and an uncertainty in the actual inception of the permeation process, respectively). While all these distortions mimic realistic deficiencies of permeation measurements, the last one is relevant only in case of fast permeation processes through highly permeable membranes. For all but the last transformation, FCFM has been found to yield more accurate GPPs than TLM.     

对岩体加固工程的水文地质条件分析

裂隙岩体的透水性各向异性和透水率大小的随机性,决定着渗控 (加固 )工程钻孔方位、倾角的多样性。它说明渗控工程设计中把裂隙岩体透水性假定成各向同性是不合实际的。应根据岩体的水文地质条件,寻找出裂隙隙宽、透水性和透水率相对较大的方位和倾角作为渗控工程钻孔的矢量。     

Pore space network characterization with sub-voxel definition

Morphological measurements in 3D for pore space characterization (connectivity pore-body/throat classification, shape factors, virtual fluid intrusion) are based on computed intensive digital-thinning operations for skeletonization and medial axis extraction from 3D digital images. We present an alternative method that is measurably faster and allows sub-voxel definition of the pore space network. The method allows extracting—based on morphological considerations only—the centered and shortest stream-lines—i.e., the paths—to follow in order to go through the pore space from one given point to another and to exit. In addition the method penalizes long and narrow pore-throats in favor of short stubby/ones—i.e., it has a built-in exemplification capacity. It exploits well-established mathematical methods successfully applied in medical endoscopy.     

A dual-porosity model for gas reservoir flow incorporating adsorption behaviour—part I. Theoretical development and asymptotic analyses

In this paper a rigorous dual-porosity model is formulated, which accurately represents the coupling between large-scale fractures and the micropores within dual porosity media. The overall structure of the porous medium is conceptualized as being blocks of diffusion dominated micropores separated by natural fractures (e.g. cleats for coal) through which Darcy’s flow occurs. In the developed model, diffusion in the matrix blocks is fully coupled to the pressure distribution within the fracture system. Specific assumptions on the pressure behaviour at the matrix boundary, such as step-time function employed in some earlier studies, are not invoked. The model involves introducing an analytical solution for diffusion within a matrix block, and the resultant combined flow equation is a nonlinear integro-(partial) differential equation. Analyses to the equation in this text, in addition to the theoretical development of the proposed model, include: (1) discussion on the “fading memory” of the model; (2); one-dimensional perturbation solution subject to a specific condition; and (3) asymptotic analyses of the “long-time” and “short-time” responses of the flow. Two previous models, the Warren-Root and the modified Vermeulen models, are compared with the proposed model. The advantages of the new model are demonstrated, particularly for early time prediction where the approximations of these other models can lead to significant error.     

Coupled modeling of damage growth and permeability variation in brittle rocks

This paper presents a coupled model for anisotropic damage and permeability evolution by using a micro–macro approach. The damage state is represented by a second order tensor. The evolution of damage is determined from a crack propagation criterion. The free enthalpy function of cracked material is obtained by using micromechanical considerations. It is assumed that cracks exhibit normal aperture which is coupled with the crack growth due to asperities of crack faces. By using Darcy’s law for macroscopic fluid flow and assuming laminar flow in microcracks, the overall permeability of the RVE is obtained by a volume averaging procedure taking into account crack aperture in each orientation.     

SYNTHESIS AND PROPERTIES OF COPOLYMERS FROM 1-[3,5-BIS(TRIMETHYLSILYL)PHENYL]-2-PHENYLACETYLENE

Copolymerization of 1-[3,5-bis(trimethylsilyl)phenyl]-2-phenylacetylene (m,m-(Me₃Si)₂DPA) with other diphenylacetylene derivatives and their copolymer properties were investigated. Homopolymerization of m,m-(Me₃Si)₂DPA by TaCl₅─n-Bu₄Sn (1:2) did not give the polymer due to steric hindrance. However, m,m-(Me₃Si)2DPA copolymerized with diphenylacetylene (DPA), 1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene (p-Me₃Si DPA), and 1-phenyl-2-[m-(trimethylsilyl)phenyl]acety-lene (m-Me₃SiDPA) in the presence of TaCl₅─n-Bu₄Sn at various feed ratios to give copolymers in moderate yields. The formed copolymers were yellow to orange solids, which were soluble in common organic solvents such as toluene and CHCl₃. The highest weight-average molecular weights (M_w) of these copolymers reached ca. 6 × 105 and tough films could be obtained by solution casting. Their onset temperatures of weight loss in air were observed around 400°C, indicating high thermal stability. The oxygen permeability coefficients at 25°C of copoly(m,m-(Me₃Si)₂ DPA/DPA) (feed ratio 1:1) and copoly(m,m-(Me₃Si)₂DPA/p-Me₃SiDPA) (feed ratio 1:2) were 21 and 100 barrers, respectively, medium in magnitude among polymers from substituted acetylenes.     

Cross‐linked Multilayer Polymer‐Clay Nanocomposites and Permeability Properties

Abstract

Electrostatically layered aluminosilicate nanocomposites have been prepared by the sequential deposition of poly(allylamine hydrochloride)/poly(acrylic acid)/poly(allylamine hydrochloride)/saponite (PAH/PAA/PAH/saponite)₁₀ on poly(ethylene terephtalate) (PET) film. Exfoliated saponite nanoplatelets were obtained by extensive shaking, sonication, and centrifugation of a water suspension. To minimize permeability and improve the mechanical integrity, cross‐linking of composite films was carried out at different temperatures. The formation of amide linkage induced through heating was observed by Fourier Transform Infrared (FT‐IR) and x‐ray photoelectron spectroscopy (XPS). The cross‐linking of nanocomposites (PAH/PAA/PAH/saponite)₁₀ showed 60% decrease in permeability of oxygen when compared with the pristine PET substrate film. In contrast, water permeability of the nanocomposite membrane was not affected by heating temperature and deposition cycles.     

Synthesis and Characterization of the Titanium Containing Mesoporous Molecular Sieve MCM-48

Ti-MCM-48 mesoporous materials have been synthesized by sequential addition of alkoxides. The atomic ratio of Si and Ti in the synthesis gel was 40 and 5, respectively. The materials were characterized by means of powder XRD, N₂ adsorption-desorption measurements. HREM, ²⁹Si MAS NMR, diffuse reflectance FT-IR spectroscopy, electrophoretic mobility measurements and electron probe microanalysis.