Binder Distribution in Macro-Defect-Free Cements: Relation between Percolative Properties and Moisture Absorption Kinetics

Macro-defect-free (MDF) cement is fabricated from a calcium aluminate cement and a poly(vinyl alcohol-acetate) (PVA) copolymer. For the composites studied, it was determined that the interphase regions comprised 63 voi % of the total binder content, while the bulk PVA regions comprised 37 vol% of this phase. Mercury intrusion porosimetry showed that a bimodal pore size distribution developed as binder was removed in increasing amounts from heat-treated samples. Larger pores with a characteristic diameter above 30 nm resulted from the removal of bulk PVA, whereas smaller pores approximately 5 nm in size resulted from the removal of water and PVA from the interphase regions. Simulation results obtained from a hard-core/soft-shell continuum percolation model of the MDF microstructure indicate that both the bulk PVA and interphase regions form percolative pathways through the system. Dramatic changes in both moisture absorption kinetics and flexural strength were observed only when a percolative network of larger pores was present in these composites. Hence, the bulk polymer regions are the dominant transport pathway for moisture in MDF cement. Based on this knowledge, processing guidelines have been developed to improve the moisture resistance of these materials.     

Processing and microstructure characterization of porous corundum–spinel ceramics prepared by in situ decomposition pore-forming technique

Porous corundum–spinel ceramics were prepared from Al(OH)₃ and basic magnesium carbonate by an in situ decomposition pore-forming technique. Apparent porosity was detected by Archimedes’ Principle with water as medium. Pore size distribution and the volume percentage of micropores were measured by mercury intrusion porosimetry, and the microstructure was analyzed by SEM. The apparent porosity of the sintered sample decreased with increasing the Al(OH)₃ content in the raw mixture. With increasing temperature from 1200 °C to 1300 °C the porosity of the sample increased rapidly, from 1300 °C to 1500 °C the apparent porosity increased slightly, while it decreased rapidly when the temperature increased from 1500 °C to 1600 °C. The pores in the samples consist of two groups. One group is composed of micropores whose diameter is mostly in the range from 150 nm to 300 nm while the other is composed of bigger pores whose diameter is in the range from 0.5 μm to 1 μm. It was found that the composition of the starting powders and the sintering temperature are responsible for the apparent porosity and the pore size distribution of the samples. However the spinel formation and sintering play a more important role on porosity and pore size distribution.     

Effect of Curing Conditions on the Capillary Porosity of Hardened Portland Cement Pastes

The capillary pore structure of hardened portland cement pastes cured by high-pressure steam, chemical acceleration, high-pressure steam with reactive SiO₂, water immersion, water immersion and high-pressure steam, and hot-pressing was measured using mercury porosimetry to 50,000 psi. Differences of > 2 orders of magnitude exist in the average capillary pore diameters of the cement pastes studied. The largest pores (∼1 to 3 μm in diameter) are associated with high-pressure steam-cured pastes. The smallest average capillaries observed were 0.02 μm for pastes steam-cured with reactive SiO₂. Hot-pressed pastes had essentially no porosity accessible to mercury. The application of pore size control to problems of polymer-impregnated concrete is discussed.     

Porous carbon material based on petroleum pitch

The samples of granulated (2–4 mm) porous carbon material with unimodal and bimodal poresize distributions were prepared. The sample with a unimodal porous structure was prepared via the mixing of soot and petroleum pitch followed by carbonization (the first stage). At the second stage, the carbon material obtained was ground to a particle size smaller than 0.2 mm, mixed with petroleum pitch, and also subjected to carbonization. The porous structures of these materials were studied by scanning electron microscopy and mercury porosimetry. It was established that the predominant pore size (20–1000 nm) of the samples with the unimodal structure depends on the used soot grade. At the second stage of the process, a considerable volume of pores in a range of 4–12 μm is formed in the production of bidisperse material. As compared with a sample with the monodisperse structure, porous carbon material with a bimodal distribution of pores was characterized by a lower crushing strength of granules and comparable specific surface areas, total pore volumes, and ash contents.     

Structural investigation of mechanically activated nanocrystalline BaTiO3 powders

In this article, in order to obtain tetragonal nanocrystalline BaTiO₃, structural investigations of mechanically activated BaTiO₃ powder have been performed. A mercury porosimetry analysis and scanning electron microscopy method have been applied for determination of the specific pore volume, porosity and microstructure morphology of the samples. The lattice vibration spectra of nonactivated and activated powders, their phase composition, lattice microstrains and the mean size of coherently diffracting domains were examined by Raman spectroscopy and the X-ray powder diffraction method. The average crystal structure of obtained nanocrystalline powders, estimated from X-ray diffraction data, gave evidence of retained, but slightly sustained tetragonality of powders, even for particles as small as ∼30 nm. Raman spectroscopy also gave clear evidence for local tetragonal symmetries, in particular through the presence of a band at ∼307 cm⁻¹.     

Extraction and characterization of cellulose nanocrystals from cotton fiber by enzymatic hydrolysis-assisted high-pressure homogenization

Cellulose nanocrystals (CNCs) have attracted increasing attention in the field of nanomaterials because of its high aspect ratio, good structure, and high thermal stability. In this study, enzymatic hydrolysis-assisted high-pressure homogenization was applied as an environmentally friendly technique to extract CNCs from cotton-derived microcrystalline cellulose (MCC). The overall optimization of enzymatic pretreatment was conducted by response surface methodology, and the maximum CNCs yield was 40.09% under the optimized experimental conditions. The extracted CNCs under the optimal conditions showed needle-like shape with a length of 100–250 nm and a width of 5–10 nm and exhibited an overall particle size range of 3–80 nm. The basic chemical structure of cellulose was not changed after enzymatic hydrolysis and high-pressure homogenization. The CNCs exhibited slightly lower crystallinity and higher thermal stability than MCC. High aspect ratio CNCs extracted in this present study have great potential as a reinforcing agent in biodegradable packaging materials.     

Analysis of variations in porosity of metal crosslinked collagen matrix

The fundamental knowledge of the porous nature of crosslinked collagen matrix such as tanned leather is an aid to design appropriate chemicals for leather making. It would also help to target a particular area of matrix to improve its uniformity and other functional properties. The purpose of this study is to analyze the variations in pore sizes of chromium crosslinked collagen matrix, chrome tanned leather, from different animal species and different areas of the same species. In this study, chrome tanned leather from goat and sheep were investigated for surface area, pore size, and distribution. Thermoporometry results show that average pore radius of goat leather is around 2–30 nm and that of sheep is 2–20 nm. Nitrogen adsorption result shows that average surface area of goat (8.24 m²/g) leather is higher than sheep (6.73 m²/g), but the average pore diameter of goat (289 nm) is smaller than sheep (385 nm) leather. It has been found that more numbers of smaller pores are present in goat than sheep leather and all the leather samples including goat and sheep obeyed type‐III adsorption isotherm. Capillary flow porometry analysis gives the smallest, largest, and mean‐flow‐diameter of through‐pores. The average size of largest throat pore diameter of sheep (1313 nm) is smaller than that of goat (1385 nm) leather. In general, the pore volume distribution of sheep leather is higher than that of goat leather. Morphological analysis using scanning electron microscopy shows that pore mouth of goat is deeper than that of sheep. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40835.     

Preparation and characterization of poly(vinyl alcohol) nanocomposites made from cellulose nanofibers

A method using a combination of ball milling, acid hydrolysis, and ultrasound was developed to obtain a high yield of cellulose nanofibers from flax fibers and microcrystalline cellulose (MCC). Poly(vinyl alcohol) (PVA) nanocomposites were prepared with these additives by a solution‐casting technique. The cellulose nanofibers and nanocomposite films that were produced were characterized with Fourier transform infrared spectrometry, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Nanofibers derived from MCC were on average approximately 8 nm in diameter and 111 nm in length. The diameter of the cellulose nanofibers produced from flax fibers was approximately 9 nm, and the length was 141 nm. A significant enhancement of the thermal and mechanical properties was achieved with a small addition of cellulose nanofibers to the polymer matrix. Interestingly, the flax nanofibers had the same reinforcing effects as MCC nanofibers in the matrix. Dynamic mechanical analysis results indicated that the use of cellulose nanofibers (acid hydrolysis) induced a mechanical percolation phenomenon leading to outstanding and unusual mechanical properties through the formation of a rigid filler network in the PVA matrix. X‐ray diffraction showed that there was no significant change in the crystallinity of the PVA matrix with the incorporation of cellulose nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Evaluation of microcrystalline cellulose. I. Changes in ultrastructural characteristics during preliminary acid hydrolysis

Several microcrystalline celluloses prepared from viscose staple, bagasse, ramie, and cotton were evaluated by viscosimetry, X-ray diffraction and scanning and transmission electron microscopies. The changes in crystallinity, size of crystallites, grain-size distribution, morphological features, and degree of polymerization were found to be dependent on and greatly limited by the polymorphic conformations of cellulose. These changes were more conspicuous in cellulose II than in cellulose I. The coexistence of a two-phase system still remains in all the specimens of microcrystalline cellulose powders. Combining the findings with respect to the extent of the changes in the size of crystallites, it appears inevitable that recrystallization in some of the defective crystallites and degradation in the disordered areas of cellulose occurs simultaneously in the preliminary hydrolysis process during the production of microcrystalline cellulose. © 1996 John Wiley & Sons, Inc.     

Control of Phase and Pore Structure of Titania Powders Using HCl and NH4OH Catalysts

Porous titania powders were prepared by hydrolysis of titanium tetraisopropoxide (TTIP) and were characterized at various calcination temperatures by nitrogen adsorption, X-ray diffraction, and microscopy. The effect of HCl or NH₄OH catalysts added during hydrolysis on the crystallinity and porosity of the titania powders was investigated. The HCl enhanced the phase transformations of the titania powders from amorphous to anatase as well as anatase to rutile, while NH₄OH retarded both phase transformations. Titania powders calcined at 500°C showed bimodal pore size distributions: one was intra-aggregated pores with average pore diameters of 3–6 nm and the other was interaggregated pores with average pore diameters of 35–50 nm. The average intra-aggregated pore diameter was decreased with increasing HCl concentration, while it was increased with increasing NH₄OH concentration.     

纳米纤维素超微结构的表征与分析

采用场发射环境扫描电镜(FEGE-SEM)、场发射透射电镜(FETEM) 和原子力显微镜(AFM)等仪器对硫酸水解法制备的纳米纤维素(NCC)进行超微结构的表征与分析。结果表明: NCC在水分散体系中可形成非常稳定的胶状溶液。由FEGE-SEM观察到微晶纤维素(MCC)呈不规则形状,直径约为15 μm。通过硫酸水解制得形状较规整的短棒状NCC,直径范围在2～50 nm之间。FETEM观察结果与AFM成像基本一致,FETEM观察大多数NCC直径约2～24 nm,长度为50～450 nm。AFM观察样品尺寸与FETEM观察相比所测得的样品尺寸偏大,这与其质地较软有关。X射线衍射(XRD)图谱表明NCC属于纤维素Ⅰ型,与MCC相比,结晶度由72.25%增大到77.29%。     

粉煤灰-水泥浆体的孔体积分形维数及其与孔结构和强度的关系

采用压汞法对不同龄期粉煤灰-水泥浆体的孔分形结构进行了实验研究，测定了复合浆体孔体积分形维数，探讨了孔体积分形维数与孔隙率，孔表面积、平均孔径、孔分布及宏观力学性能的关系。实验结果表明：粉煤灰-水泥浆体的孔结构具有明显的分形特征，孔体积分形维数在3．3～3．5之间；孔体积分形维数越大，浆体的孔径越小、孔隙率越低，孔表面积越大，小于20nm的微孔越多，大于100nm的大孔越少，而且复合体系的抗压及抗折强度也越高。     

Preparation and characterization of protein imprinted agarose microspheres

Agarose hydrogel microspheres imprinted with bovine serum albumin (BSA) were prepared by inverse suspension gelating method. The experimental conditions related with beads’ shape and uniformity were studied, including temperature, surfactant content, and stirring speed. The size and distribution of the pores were found related with porogen and surfactant content. Rebinding properties were influenced by the diameter and porosity. The beads with the smallest diameter exhibited the greatest rebinding capacity, rebinding speed, and imprinting efficiency (IE). Smaller pores provided higher rebinding capacity and IE, but lower rebinding speed. Imprinted microspheres showed good specificity toward templating protein compared to others.     

Morphology of microporous neosepta ion-exchange membranes and its effect on separation of biological mixtures

Specially prepared microporous Neosepta ion-exchange membranes were investigated to establish a correlation between their structural characteristics (pore-size distribution, porosity) and permeability to components of immunoglobulin (Ig) fractions of mouse ascitic fluids. The solutions to be separated contained IgG₁ with specificity to horseradish peroxidase or to the heavy chain of human IgM, some other proteins, and a large amount of ammonium sulfate (0.22–0.35M). Analysis of the membrane morphology carried out by scanning electron microscopy and mercury porosimetry showed that the membranes possess a polymodal pore-size distribution. There are large open pores (400–600 and 200–300 nm in diameter) on the membrane surfaces, but the void volume of the membranes is a system of connected pores of smaller diameters (from 60–100 to 7–10 nm). The main part of the pores in the membranes displaying the best separation ability was 8–17 nm in diameter. It was found that highly porous charged membranes (relative porosity 58–60%) with low ion-exchange capacity (0.02–0.1 meq/g) made it possible to achieve the desired desalination degree of protein mixture (80–83%) within 5–7 h instead of 5 days needed in the traditional dialysis. Moreover, the amount of separated accompanying proteins reached 25–30% depending on membrane porosity and the quality of specific IgG₁ was considerably improved. © 1995 John Wiley & Sons, Inc.     

High-Temperature Reactions of Clay Mineral Mixtures and Their Ceramic Properties: IV, Dimensional and Weight Changes on Refiring and the Pore-Size Distribution of Fired Kaolinite-Muscovite-Quartz Mixtures with 25 Wt% Quartz

Dimensional and weight changes on refiring of clay mineral mixtures were used as a measure of moisture expansion and moisture uptake, respectively. Pore-size distributions were measured by the mercury penetration method. With specimens containing more than 15% muscovite, the moisture expansion had a peak value when fired between 1000° and 1050°C. At 1050° the magnitude of moisture expansion and moisture uptake was approximately linear with the muscovite content. For specimens with less than 15% muscovite, the variation of moisture expansion with mica content was complex and this was ascribed to the fact that muscovite particles coated with kaolinite behaved differently from bulk mica in the original firing treatment and on subsequent exposure to moisture. The volume percentage of pores greater than 0.2μ in diameter increase as the muscovite content and firing temperature increased and reached a maximum when moisture expansion was at a maximum. The volume percentage of pores less than 0.2μ in diameter decreased under the same conditions but increased slightly in specimens of low muscovite content because the kaolinite reacted on firing with the mica which it coated.     

Wood's metal porosimetry and its relation to mercury porosimetry

Wood's metal porosimetry permits the determination of the frequency distribution α(D, D_e) of the volume of pores having diameters in the range D → D + dD whose penetration by Wood's metal (or mercury) is controlled by pores having diameters in the range D_e → D_e + dD_e. The results obtained in sandstone samples indicate that the volume of the entry pores is very small in comparison with the volume of the much larger (up to four times) pores which are penetrated through the entry pores. The accessibility of pores of a wide diameter range is controlled by pore necks of diameters which are distributed over a narrower range. The accessibility function α(D, D_e) has been the starting point of a great deal of in-depth research of pore structure.     

Use of X-ray tomography to study the porosity and morphology of granules

X-ray computed tomography (XRCT) is a technique that uses X-ray images to reconstruct the internal microstructure of objects. Known as a CAT scan in medicine, it has found wide application for whole-body and partial-body imaging of hard tissues (e.g., bone). A modern tabletop XRCT system with a resolution of about 4 μm was used to characterize some pharmaceutical granules. Total porosity, pore size distribution, and geometric structure of pores in granules produced using different conditions and materials were studied. The results were compared to data obtained from mercury porosimetry. It was found that while XRCT is less precise in the determination of total porosity in comparison to mercury porosimetry, it provides detailed morphological information such as pore shape, spatial distribution, and connectivity. The method is nondestructive and accurate down to the resolution of the instrument.Tomographic images show that the pore network of individual granules comprises relatively large cavities connected by narrow pore necks. The major structural difference between granules produced at different conditions of compaction and shear is a reduction in the pore neck diameter; the cavity size is relatively insensitive to these conditions. Comparison of pore size distributions determined from tomographic images and mercury porosimetry indicates that mercury intrusion measures the pore neck size distribution, while tomography measures the true size distribution of pores ca. 4 μm or larger (the instrument resolution).     

Use of mercury porosimetry for characterization of poly(vinyl chloride) suspension grades with regard to particle type,particle heterogeneity,and surface area

The correction for polymer and mercury compressibility is essential to the use of mercury porosimetry for the evaluation of the porosity of poly(vinyl chloride) (PVC) suspension granules. The polymer compressibility, however, varies with the morphology type of the granules. The technique outlined in this paper allows the appropriate correction to be made without the need for the prior determination of the polymer compressibility. Bulk-compressibility factors for the polymer samples are derived from the porosimetry data. Surface areas of PVC granules, as derived from porosimetry data using two fundamentally different techniques, are in error because of the presence of “ink-bottle” shaped pores.     

喷雾造粒粉制备ZTM陶瓷的结构缺陷与强度研究

结合喷雾料浆,造粒颗粒的相关工艺控制,对喷雾造粒粉制备的ＺＴＭ陶瓷的结构缺陷及强度进行了研究。结果发现：较低固相含量的料浆易形成具有坚硬外壳的空心颗粒,这种颗粒在成型过程中难以破坏,以坯体中形成结构缺陷;颗粒的残余水分对颗粒的变形性具有重要作用,随残余水分的增加,坯体的断裂从沿颗粒向穿过颗粒的形式过渡。研究还表明：较大颗粒间的气孔,如在成型过程未被完全破坏和变形,则会遗留在烧结体中,导致材料强度的     

Determination of Both Mesopores and Macropores in Three-Dimensional Ordered Porous Materials by Nitrogen Adsorption

Three-dimensionally ordered silica structures containing both mesopores and macropores are created using polystyrene coacervate spheres with a diameter of ca. 146 nm. The close-packed polystyrene coacervate spheres are intercalated with tetraethyl orthosilicate. The spheres are removed by calcination leaving an inverse silica replica with a spherical macropore cavity diameter of 110 nm. Due to the nature of these porous structures, pores leading into the macropore cavity are in the mesopore regime, 40 nm in diameter. The nitrogen adsorption data described in the following paper gives a pore size for both the macropore cavity and the mesopore openings leading into the cavity. The pore sizes as determined by nitrogen sorption are in good agreement with the pore sizes observed by scanning electron microscopy. Mercury intrusion porosimetry results confirm the size of the mesopore openings leading into the macropore cavity, however due to destruction of the sample upon intrusion, extrusion results can not be obtained to determine main cavity diameters. As a result, nitrogen sorption may be a viable option for determining pore sizes with these three-dimensionally ordered materials containing both mesopores and macropores.