Synchrotron X-ray tomographic characterization of CVI engineered 2D-woven and 3D-braided SiCf/SiC composites

The properties of ceramic matrix composites strongly depend upon their complex internal structures. To better understand and improve the properties of the silicon carbide fiber-reinforced silicon carbide matrix composites (SiC_f/SiC), we explored the microstructural properties of composites reinforced with either two-dimensional (2D) woven or three-dimensional (3D) braided preforms using synchrotron X-ray computed microtomography. Transects and volumetric images of the composites were reconstructed from objection images and the microstructures were investigated in three spatial directions. The network of void space in a composites was visualized in 3D and quantitative analysis of the porosity was performed to characterize the fiber-tissue structures. 2D-woven SiC_f/SiC composite exhibited important fluctuations of porosity in different directions and the stacking of plies had a significant effect on the porosity distribution. In contrast, 3D-braided SiC_f/SiC composites showed much less variation of porosity. We found the degree of densification of the composite also influenced the porosity distribution.     

Shrinkage of digested sludge from gelatin production

This study evaluated the influence of temperature on the apparent density, porosity and shrinkage of sludge during drying experiments conducted in a drying oven, under three different temperatures. Also, the apparent density behavior and porosity during the drying were evaluated. The influence of temperature was evident in all evaluated parameters. However, the behaviors are distinct for each temperature range due the case hardening phenomenon. The volumetric shrinkage of the dimensions was correlated linearly by Perez and Calvelo modified model. During drying, the apparent density and porosity exhibited variations in behavior, related to drying rates and critical moisture content.     

Effect of PVC resins on multi-screw pipe extrusion

The increased use of multi-screw (twin) extruders by pipe producers brought on this study of available PVC homopolymer “pipe grade” resins. Basic tests on resin were examined via a “Correlation Matrix” computer program. Highly significant test data were determined to be internal pore volume and centrifuge plasticizer adsorption. Additional compound evaluation proceeded via torque rheometer followed by twin-screw extrusion. Significant resin test values affecting extrusion properties are inherent viscosity, apparent bulk density, porosity uniformity and melt viscosity. The work shows that the compounder should know resin properties in order to benefit from processing equipment developments.     

A new approach for the characterization of the pore structure of dual porosity rocks

For the realistic representation of the pore space of dual porosity rocks, a new method of pore structure characterization is developed by combining experimental Hg intrusion/retraction curves with back-scattered scanning electron microscope (BSEM) images and inverse modeling algorithms. The pore space autocorrelation function measured by processing the digitized BSEM images is combined with the surface fractal dimension estimated from the high pressure Hg intrusion (MIP) data to derive a synthetic small-angle neutron scattering (SANS) intensity function, the inversion of which provides a volume-based pore body radius distribution (PBRD). The volume-based PBRD is fitted with a multimodal number-based PBRD consisting of two component distributions: one representing the macroporosity and another one representing the microporosity. Based on arguments of percolation theory, analytical mathematical models are developed to describe the Hg intrusion in and retraction from dual pore networks in terms of the complete PBRD, pore throat radius distribution (PTRD) of macroporosity, drainage accessibility functions (DAFs) of both porosities, and imbibition accessibility functions (IAFs) of both porosities. Inverse modeling of the Hg intrusion data set enables us to estimate the PTRD and DAFs. Inverse modeling of the Hg retraction datasets enables us to estimate a set of primary and secondary IAFs. The method is demonstrated by the pore structure characterization of four outcrop samples of carbonate and sandstone rocks. Analytic approximate equations developed from the critical path analysis (CPA) of percolation theory enable us to calculate explicitly the absolute permeability and the formation factor of the porous rocks using the estimated parameters (PBRD, PTRD, DAF) of the macroporosity. The measured permeability of cores is predicted satisfactorily and observed discrepancies may be attributed to large length-scale macro-heterogeneities which are not evident in BSEM images and Hg porosimetry data.     

Porosity and pore size determination in polysulfone hollow fibers

Average pore sizes and effective porosity of microporous polysulfone hollow fibers were determined by the gas permeability method. Surface structure and porosity were determined by scanning electron microscopy. The values of effective porosity ε/q² (porosity/tortuosity factor) are approximately one order of magnitude lower than those reported previously for flat sheet porous membrane. These lower values are a direct outcome of a higher polymer concentration in the spinning dope. Correlations between the wall void volume, equivalent pore size, and hydraulic permeabilities of the hollow fibers have been determined. Rather low values of ε/q² have been calculated compared to those of the void volume; these effective porosity values indicate either a very high tortuosity factor or a large number of “dead end” pores. Exposure of the fibers to elevated temperature (110°C) for a short period of time drastically reduces the surface pore size and narrows the pore size distributions, whereas overall fiber dimensions are reduced only by 1%, and 85% of the fiber's hydraulic permeability is retained. The scanning electron microscopy study reveals the formation of a relatively dense skin in some spun fibers. For such “skinned” fibers, kinetic (permeability) evaluation of static structure such as mean pore size is not realistic and is further generalized to the term “equivalent pore size.”     

Orientation parameters for the specification of effective properties of heterogeneous materials

A general formulation is presented for the orientation averaging of the properties of representative volume elements of heterogeneous materials. Approximations are introduced that result in the identification of four independent orientation parameters that are required to specify a general state of three-dimensional orientation. The general relationships are reduced further for the special case of “planar” and “axial” distribution and applied to an aggregate averaging scheme for short-fiber composites.     

Some new operational modes and parameters of stress relaxation for the viscoelastic characterization of solid polymers. II. The “vertical‐shift” mode and intrinsic “time–strain clock”

As in part I of this study, in the same manner in the present part II as well, by the same modus operandi way, an attempt was made to introduce, by means of a given operational mode, some further practical parameters for a “by‐eye” but well‐proven experimental viscoelastic characterization of a polymeric solid. Thus, through consideration of the peculiar vertical shift behavior of the apparent modulus (?) of isotactic polypropylene (iPP) and based on the KWW model, it is shown that, in an empirical and a formalistic sense, a relevant effective or equivalent (single) characteristic relaxation time can be introduced which can give some new interpretations for the linear and nonlinear viscoelastic behavior of a polymeric material, as that of a “time–strain clock,” which, as an intrinsic function, is responsable for a functional time–strain shift of the relaxation time and, at the same time, for a shift toward to a more linear or to a more nonlinear behavior. In the above context of attempts, another functional relationship was shown, the so‐called spectral shift function and its corresponding parameter of nonlinearity strength, through which some further interpretations and characterizations connected with the existence of the permanent internal stress could be made. Finally, the introduction of the so‐called spectral isostrains and their corresponding “spectral inversion point” complete the “set” of the operative parameters proposed for the above‐mentioned purpose. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 138–148, 2003     

Diffusion Profiling of Therapeutic Proteins by Using Solution NMR Spectroscopy

Characterizing changes to structure and behavior is an important aspect of therapeutic protein development. NMR spectroscopy is well suited to study interactions and higher-order structure that could impact biological function and safety. We used NMR diffusion methods to describe the overall behavior of proteins in solution by defining a “diffusion profile” that captures the complexities in diffusion behavior. Diffusion profiles offer a simple means to interpret protein solution behavior as a distribution of sizes and association states. As a characterization method, diffusion profiling is well suited to complement and augment traditional biophysical and NMR methods to probe the solution behavior of therapeutic proteins.     

Study on the mechanical properties of porous tin oxide

Despite the importance of tin oxide (SnO₂) in diverse functional applications, little information is available on the mechanical properties of bulk or porous SnO₂. In this study, porous SnO₂ was synthesized using an ice-templating method to produce a “dual” pore structure that comprises large wall pores (on the order of several micrometers) with small micropores (~2 µm) on their surfaces. The Vickers hardness decreased with increasing porosity and increased with increasing contiguity of struts. The compressive stress–strain curves of porous SnO₂ samples with porosity ranging from 48% to 73% were compared with both the Gibson–Ashby and the cellular-lattice-structure-in-square-orientation models, which generally represent the “lower” and “upper” bounds of yield strength for porous materials, respectively. As expected, the yield strength of the porous SnO₂ samples decreased with increasing porosity, and all the yield-strength values of porous SnO₂ fell between the two extreme prediction models. The sample with the lowest porosity of 48% exhibited sharply increasing elastic behavior followed by sudden rupture, as generally reported for bulk ceramics; however, the other samples with higher porosities ranging from 50% to 73% exhibited “porous-metal-like” behavior at strains of 15% or greater as a result of the fracturing of the solid walls between the pores.     

The limiting residence time distribution of continuous recycle systems

The limiting residence time distribution (RTD) of continuous recycle systems as the recycle ratio approaches infinity is considered. It is shown that the RTD converges to the exponential distribution whenever the system does not consist of a “dead volume” at the limit. This limiting behavior is independent of the system configuration and flow patterns. Issues concerning the proper modeling approach and the mathematical formulation of the condition that the system has no “dead volume” are discussed in detail. Some examples illustrating the importance of selecting the proper modeling approach are also provided.     

Investigation of the fundamental assumptions relating compression-permeability data with filtration

A recently reported investigation indicates several inaccuracies in the methodology of compression-permeability (C-P) testing which suggest that previously reported agreement between C-P and filtration data may be fortuitous. Until now, there has been no separate and direct confirmation of each of the two assumptions necessary to obtain a unique correspondence between C-P and filtration data. The first assumption that the specific filtration resistance is a function solely of cumulative-drag-stress is generally accepted. Direct proof requires that the parabolic filtration equation, which is derived primarily on this assumption, describes both incompressible and compressible cake behavior. Most materials produce compressible cakes and “a priori” screening to find an incompressible cake requires identification of a material (Geon) that produces a cake with a linear axial pressure distribution. Results show that the parabolic filtration equation fits both types of cake behavior but an equation based on constant filtration resistance describes only incompressible cake behavior. To engineering accuracy and for dilute slurries, the assumption is verified. The second assumption that the cumulative-drag-stress equals the cake pressure drop is a macroscopic force balance and experimental verification requires a filter chamber designed to measure both of these quantities. A theoretical development, based on integral averaging, and experimental results both indicate that the ratio of cumulative-drag-stress to cake pressure drop correlates extremely well with cake porosity. A unique one-to-one correspondence between C-P and filtration data is not possible without “a priori” knowledge of filter cake porosity. Previously reported agreement between C-P and filtration data can probably be attributed to the L/D dependence of C-P specific filtration resistances. Consequently, C-P data can be used as a research tool to simulate filtration data but predicted filtration times based solely on C-P data can be in considerable error.     

Synthesis and simple method of estimating macroporosity of methyl methacrylate–divinylbenzene copolymer beads

Macroporous methyl methacrylate–divinylbenzene copolymer beads having diameter ～ 300 μm were synthesized by free radical suspension copolymerization. The macroporosity was generated by diluting the monomers with inert organic liquid diluents. The macroporosity was varied in the range of ～0.1 to ～ 1.0 mL/g by varying a number of porosity controlling factors, such as the diluents, solvent to nonsolvent mixing ratios when employing a mixture of the two diluents, degree of dilution, and crosslinkage. Increase in pore volume from 0.1 to 0.45 mL/g resulted in a sharp increase in mesopores having diameters in the range of 3–20 nm whereas the macropores remained negligible when compared with mesopores. Increase in pore volume from 0.45 to 1 mL/g resulted in a sharp increase in macropores, whereas mesopores having diameters in the range of 3–20 nm remained almost constant. The mesopores having diameters in the range of 20–50 nm showed an increase with the increase in pore volume throughout the whole range of pore volume studied. Macroporosity characteristics, i.e., pore volume (V_m), surface area (SA), and pore size distributions were evaluated by mercury penetration method. Statistical analysis of the data obtained in the present study shows that the macroporosity characteristics can be estimated with a reasonable accuracy from the pore volumes, which in turn are determined from the densities of the copolymers. These results are explained on the basis of pore formation mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of thermal treatment on the tensile and in‐plane shear behavior of carbon fiber‐reinforced poly(phenylene sulfide) composite specimens

The effect of PPS matrix evolution occurring during thermal treatment of carbon fiber‐reinforced PPS plies prior to their consolidation to laminates on the mechanical behavior of the composite material has been investigated. The thermal treatments were performed at temperatures and times, which are relevant for processing PPS composites. All thermal treatments were carried out in an oven in air to facilitate the presence of oxygen, while the subsequent consolidation was performed in an autoclave. The tensile and in‐plane shear behavior of both, thermal‐treated and untreated materials, was investigated. Differential scanning calorimetry and microscopy analyses were made to evaluate the effect of the performed thermal treatments on degree of crystallinity and porosity of the laminates. The mechanical tests carried out have shown an appreciable degradation of the mechanical properties investigated. The observed degradation increases with increasing thermal treatment temperature and time when thermal treatments were carried out on each single composite ply prior to the consolidation. On the other hand, when, prior to the consolidation, the whole set of plies was subjected to thermal treatment, improved mechanical properties were observed. The results were discussed under the viewpoint of PPS matrix evolution during processing of the composite plies in the presence of oxygen. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of the compaction and sintering of hydroxyapatite powders by mercury porosimetry

Mercury porosimetry was used to measure the bulk and real densities, pore volumes and pore size distributions of compacts of hydroxyapatite before and after sintering. The hydroxyapatites were prepared by two different methods and had widely different surface areas. The properties were determined as a function of compaction force and sintering temperature. Densities from porosimetry were in good agreement with geometric densities. A linear relation was found between pore volume and log of the applied force. There was also a linear relationship between bulk volume and pore volume of the compacts. A bimodal pore size distribution was observed for the high surface area hydroxyapatite which disappeared with increasing compaction loads. Pressurization and depressurization measurements indicated that the main body of the pores in the compacts attained a more regular “spherical” shape with increasing compaction force than did the “necks”. The pore volume, percent porosity, and bulk density of the compacts remained unchanged up to 600°C; however, the surface area and the average pore diameter changed at 400°C. The distribution of pores became more uniform, narrower in distribution, and larger in size as the sintering temperature increased. The change in pore area with pore volume indicated that two mechanisms were operating during sintering. The pore area proved to be the most sensitive indicator of changes during sintering.     

Novel model for the sintering of ceramics with bimodal pore size distributions: Application to the sintering of lime

A mathematical model for the sintering of ceramics with bimodal pore size distributions at intermediate and final stages is developed. It considers the simultaneous effects of coarsening by surface diffusion, and densification by grain boundary diffusion and lattice diffusion. This model involves population balances for the pores in different zones determined by each porosimetry peak, and is able to predict the evolution of pore size distribution function, surface area, and porosity over time. The model is experimentally validated for the sintering of lime and it is reliable in predicting the so called “initial induction period” in sintering, which is due to a decrease in intra‐aggregate porosity offset by an increase inter‐aggregate porosity. In addition, a novel methodology for determination of mechanisms based on the analysis of the pore size distribution function is proposed, and with this, it was demonstrated that lattice diffusion is the controlling mechanism in the CaO sintering. © 2016 American Institute of Chemical Engineers AIChE J, 63: 893–902, 2017     

Random stacking template of polymer spheres and water soluble particles to fabricate porous hydroxyapatite with interconnected pores

Particle stacking simulation is applied in the fabrication of porous hydroxyapatite (HA) ceramics to predict the relationship between the template preparation process and the porosity of porous ceramics. The stacking of multi-diameter spherical particles, such as polymer spheres and NaCl particles, in three-dimensional space is simulated by using continuous generation method. The porosity of porous HA is predicted by calculating the stacking density of large spheres (the ratio of large sphere volume and container volume). The model of three-dimensional random stacking spheres is implemented by using the C++ program. Porous HA ceramics with interconnected spherical pores were fabricated by slipcasting which the use of a polymer template. Templates were produced by randomly stacking polymer spheres and NaCl particles. The arithmetic average error between the porosity of porous HA ceramics and the stacking density of polymer spheres (large spheres) is 3.52%. Simulation results obtained by using the proposed method are consistent with the experimental results.     

Firing behavior of argillites from northern Tunisia as raw materials for ceramic applications

This study reports the firing properties of clayey materials from northern Tunisia to evaluate their possible use as raw material in ceramic. Physical, chemical, and mineralogical characterization and thermal behavior were carried out by inductively coupled plasma atomic emission, X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal analysis, particle size distribution, and Atterberg limits tests. Firing properties were evaluated by color, firing shrinkage, water absorption, bulk density, apparent porosity, and flexural strength. Studied clayey materials are made up mainly by kaolinite and illite and are rich in iron. The main transformations after thermal analysis were identified from 500°C to 1000°C subsequent to the dehydroxylation of clay minerals, calcite decomposition, and the recrystallization process. Fired samples up to 1100°C showed better physical and mechanical properties related with a great densification resulting in a significant increase in linear shrinkage, bulk density, and flexural strength and a decrease in apparent porosity and water absorption up to 1100°C. This behavior is due to a crystalline and liquid phases formed at low firing temperature associated with a high content of fluxing agents. The fired ceramic materials exhibited low water absorption up to 2.26% and high flexural strength up to 32.6 MPa, which makes their potential use for some earthenware and stoneware products.     

水泥颗粒分布对水泥颗粒堆积状态的影响

用不同组分、不同颗粒组成的水泥标准稠度用水量近似计算水泥颗粒的堆积孔隙率,分析研究了水泥颗粒组成对水泥颗粒堆积状态的影响规律和贡献。分析结果表明,水泥颗粒堆积孔隙率与水泥的颗粒组成具有良好的相关性,呈线性关系;在通常水泥的颗粒分布参数中,水泥颗粒的堆积状态与80 μm筛余、45 μm筛余最为相关,均匀性系数次之,而与3 μm筛余的相关性最差;在水泥颗粒分布参数中,均匀性系数对水泥颗粒堆积程度的影响最大,80 μm筛余次之。即水泥颗粒的堆积程度主要受颗粒分布宽窄、水泥中的粗颗粒粒径及含量的控制。在水泥整体粗细程度相近或相同的情况下,水泥颗粒分布越宽、水泥中的粗颗粒越大以及含量越高,水泥颗粒堆积的越紧密。