Pore Size Distribution Measurements Research Articles

Pore Size Distribution Measurements in Small Samples and with Nanoliter Volume Resolution by NMR Cryoporometry

NMR cryoporometry is demonstrated to provide access to pore size and pore size distribution in small amounts of porous materials. With a conventional NMR spectrometer and probe, the detection limit for total pore volume is shown to be on the order of 100 nL with a volume resolution on the order of a few nanoliters.

Microstructure Densification of Geomaterial Chiefly Composed of Fly Ash after Addition of Hydrated Lime

Many researches already concluded that concrete which contains fly ash usually possesses higher rates of pozzolanic reactions with increasing pore sizes of 0.1μm or less. When a pozzolanic reaction evolves, densification of CSH hydrates also starts. This densification process is high in 0.003–0.01μm size of pore and low in 0.01–0.05μm size of pore. The technology described in this paper is related to the microstructure change in granulated foundation materials, which contain primarily fly ash mixed with small amounts of cement. The authors developed a special mixer that can be used to prepare granular foundation materials from mixing of water, fly ash, and cement. This kind of foundation material has many similarities with natural foundation materials like sand and crushed stone, and it can be produced by a single process of mixing in a short time.Similar to the fly ash concrete, the granulated foundation material chiefly composed of fly ash and a small amount of cement contains many pores of sizes 0.1μm or less. Experiments also concluded that when hydrated lime was added into the granulated foundation material to prevent leaching of heavy metals and other substances, CSH hydrates developed in pores of size 0.1μm or less and the material consisted of approximately 50% of the total pore space.The authors also used an electron probe microscope analysis (EPMA) and measured pore size distribution after addition of hydrated lime to the granulated foundation material. It made easier to understand the changes in micro-structure and to explore the causes behind the development of different microstructures in the granulated foundation material after addition of hydrated lime.

Steam Reforming of Dimethyl Ether over Cu/ZnO/ZrO<sub>2</sub> and γ-Al<sub>2</sub>O<sub>3</sub> Mixed Catalyst Prepared by Extrusion

Steam reforming of dimethyl ether, DME, over Cu/ZnO/ZrO2 and γ-Al2O3 mixed catalysts prepared by the extrusion technique was investigated. The catalysts were characterized by BET, pore-size distribution measurements, N2O chemisorption, powder X-ray diffraction, and SEM-EDX analysis. The effect of reaction temperature on catalyst life time was investigated. Steam reforming of DME over the extruded catalyst proceeded above 623 K. The major reaction products were H2 and CO2 with relatively small amounts of CO and CH4. DME steam reforming was not restricted by the equilibrium limitation of DME hydration to CH3OH, suggesting that CH3OH produced was subsequently reformed into H2 and CO2 over the catalyst. The catalyst suffered from thermal deactivation at higher temperatures; mainly caused by a reduction in Cu dispersion in the Cu/ZnO/ZrO2 catalyst. Incorporation of ZrO2 into Cu/ZnO may stabilize Cu dispersion and increase the stability of the extruded catalyst for long-term operation.

Preparation of porous PVdF membrane via thermally induced phase separation using sulfolane

AbstractSulfolane was acted as a kind of diluent to prepared PVdF porous membranes via TIPS process. Its impact on structure and morphology was studied. Phase diagram for this system was determined by different scanning calorimetry (DSC). Not any structure in the region higher than the dynamic crystallization temperature can be found and the temperature at which particle formation was observed by the optical microscope was approximately in agreement with the dynamic crystallization temperature, which revealed that only S–L phase separation happened for PVdF/sulfolane system during TIPS process. It was found that the heat of crystallization increased with the increase of polymer content. The increase of the cooling rate will increase the crystallization rate. SEM, which showed that membranes had symmetrical structure and pores formed between PVdF crystallization, revealed that PVdF will present different crystallization morphology as the cooling rate changed. With the cooling rate decrease, both the size of particles and the channel size of open pores between particles became larger, but more uneven. As the cooling rate increased, the size of particles decreased and pore became well interconnected and uniform, which were confirmed by the measurement of average pore size and pore size distribution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effective Removal of Odorants in Gaseous Fuel for the Hydrogen Station Using Hydrodesulfurization and Adsorption

The removal efficiency of dimethyl sulfide (DMS), tert-butylmercapatan (TBM), and tetrahydo thiophene (THT) was investigated for applying to hydrogen station. The sorbents such as Cu/Al2O3, ZnO/Al2O3, Cu/ZnO, and Cu/ZnO/Al2O3 were prepared by the coprecipitation method and characterized by XRD, surface area, and pore size distribution measurements. Among the various sorbents employed for the removal sulfur compounds, the Cu/ZnO/Al2O3 exhibits superior activity compared to the conventional ZnO sorbent (G-72D) as well as the others. The order of sorption capacity for the removal sulfur compounds after hydrodesulfurization (HDS) was found to be Cu/ZnO/Al2O3 > Cu/ZnO > Cu/Al2O3 > ZnO/Al2O3 > G-72D. The BET surface area and pore volume of Cu–ZnO based sorbents were found to be higher than other sorbents, and it suggests that ZnO effectively enhanced the dispersion of Cu in Cu/ZnO/Al2O3 sorbent. In the modified HDS system combining with adsorption of sulfur compounds by Cu/ZnO/Al2O3, the sulfur compounds such a...

Investigation of mechanochemically modified kaolinite surfaces by thermoanalytical and spectroscopic methods

The effect of mechanochemical activation (dry grinding), formamide intercalation, and thermal deintercalation on high- and low-defect kaolinite surfaces was studied by thermogravimetry and diffuse reflectance Fourier transform infrared spectroscopy. These investigations were completed with specific surface area and pore size distribution measurements. The surface acidity of the ground and the ground-and-intercalated kaolinites was probed with ammonia adsorption. The surface area and the pore volume as well as the amount of adsorbed ammonia increased with the rate of mechanochemical activation. At the same time the thermally deintercalated minerals showed increased surface area but decreased pore volume with the time of grinding. Adsorbed ammonia was detected as ammonium ion in the 1400–1500 cm −1 spectral range.

Effect of KCl on selective catalytic reduction of NO with NH3 over a V2O5/AC catalyst

Abstract Deactivation of a low temperature selective catalytic reduction (SCR) catalyst, 1 wt% V 2 O 5 /AC, by potassium chloride (KCl) is studied using BET and pore size distribution measurements, NH 3 sorption and temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR). Results show that KCl deactivates 1 wt%V 2 O 5 /AC’s SCR activity and the deactivation become severer at higher KCl loadings. The deactivation is not caused by pore plugging but by neutralization of acid sites on V 2 O 5 /AC. Weak acid sites are responsible for NH 3 activation and SCR of NO, and are preferentially deactivated by KCl.

Use of Electrospun Nanofiber Web for Protective Textile Materials as Barriers to Liquid Penetration

To examine the potential of electrospun nanofibrous webs as barriers to liquid penetration in protective clothing systems for agricultural workers, layered fabric systems with electrospun polyurethane fiber web layered on spunbonded nonwoven were developed. Barrier performance was evaluated for the layered fabric systems with different levels of electrospun web area density, using three pesticide mixtures that represent a range of surface tension and viscosity. Effects of electrospun web density on air permeability and water vapor transmission were assessed as indications of thermal comfort performance. Pore size distribution was measured to examine the effect of electrospun fiber web layers on pore size. Penetration testing showed that a very thin layer of electrospun polyurethane web significantly improved barrier performance for challenge liquids with a range of physicochemical properties. Air permeability decreased with increasing electrospun web area density, but was still higher than most of protective clothing materials currently available. No significant change was observed in moisture vapor transport of the system from electrospun nanofibrous web layers. Pore size distribution measurements indicated the feasibility of engineering pore size via the level of electrospun web area density, hence, controlling the level of protection and thermal comfort of layered fabric systems depending on their need.

Sol–gel processing of drug delivery zirconia/polycaprolactone hybrid materials

Poly(epsilon-caprolactone) (PCL 6, 12 and 24 wt%) and zirconium (ZrO(2)) organic-inorganic hybrid materials have been synthesized by the sol-gel method from a multicomponent solution containing zirconium propoxide [Zr(OC(2)H(7))(4)], poly(epsilon-caprolactone) (PCL), water, chloroform (CHCl(3)). Sodium ampicillin was incorporate in the hybrid materials to verify the effect as local controlled drug delivery system. The structure of interpenetrating network is realized by hydrogen bonds between Zr-OH group (H donator) in the sol-gel intermediate species and carboxylic group (H-acceptor) in the repeating units of the polymer. The presence of hydrogen bonds between organic/inorganic components of the hybrid material was proved by FTIR analysis. The morphology of the hybrid material was studied by scanning electron microscope (SEM). The structure of a molecular level dispersion has been disclosed by atomic force microscope (AFM), pore size distribution and surface measurements. The bioactivity of the synthesized hybrid material has been showed by the formation of a layer of hydroxyapatite on the surface of PCL/ZrO(2) samples soaked in a fluid simulating the composition of the human blood plasma. Release kinetics in a simulate body fluid (SBF) have been subsequently investigated. The amount of sodium ampicillin released has been detected by UV-VIS spectroscopy and SEM. The release kinetics seems to occur in more than one stage. HPLC analysis has also been taken to ensure the integrity of ampicillin after the synthetic treatment.

Capillary Pressure Estimation Using Statistical Pore Size Functions

AbstractCapillary pressure curves, which have been employed for a long period of time by researchers interested in pore size distribution, are commonly obtained from experimental measurements. The dynamic capillary pressure that influences the flow is affected by many factors including the pore size characteristics and pore scale dynamics. Hence, it is important to investigate the variation of the estimated pore size distribution with capillary number. In this study, a glass type micromodel is considered as the porous media sample. A parametric probability density function is proposed to express the pore size distribution of the porous model, which is also measured using an image analysis technique. The capillary pressure saturation mathematical model is developed by integrating the pore size distribution function. Model parameters with a physical significance are estimated by fitting the model to the measured capillary pressure data at different capillary numbers. The results of capillary pressure obtained are well matched to the measured values. The results show that the trends of the extracted pore size distribution curves have similar trends, but they are not exactly the same. Therefore, the dynamic capillary pressure data alone are not sufficient for estimation of the pore size distribution. As a related development, the prediction of the capillary pressure curves based on measured pore size distributions is also presented. The proposed probability distribution function has the flexibility of representing a wide variety of pore size distributions.

The preparation and properties of monodisperse core-shell silica magnetic microspheres

The monodisperse core-shell silica magnetic microspheres (MMS) were synthesized by sol-gel method gelling in the emulsion. Optical microscope (OM), field emission scanning electron microscope (FESEM), nitrogen adsorption and desorption Brunauer Emmett Teller Procedure (BET) isotherms and Barrett-Joyner-Halenda (BJH) pore size distribution measurements, X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and vibrating sample magnetometer (VSM) were used to characterize the appearance, size distribution, phase, specific surface area, chemical composition and magnetic property of silica MMS. The results showed that silica MMS prepared through sol-gel method with acid-alkali two-step catalyze and gelling in emulsion exhibited the superior core-shell structure and size distribution of the microspheres concentrated in about 20 mum. The main phase of microspheres was amorphous silica and spinel ferroferric oxide. Meanwhile, the microspheres remained the superparamagnetic behavior and could be used as biomaterials.

The contribution of out-of-plane pore dimensions to the pore size distribution of paper and stochastic fibrous materials

Theory is presented for the distribution of the narrowest dimension of voids encountered in a path through a stochastic fibre network from one side of its plane to the other. Using expressions from the literature we show that the mean out-of-plane pore dimension is always less than half the mean in-plane dimension such that out-of-plane pore dimensions have a controlling influence on the measured pore size distribution. An approximate model is derived which predicts that the overall mean pore dimension of a network of fibres with given dimensions is inversely proportional to its areal density and proportional to a simple function of porosity. Good agreement is demonstrated between this model and experimental data. Regression analysis suggests that out-of-plane pore dimensions account for more than 70% of the measured pore size distribution.

Synthesis, characterization, and catalytic application of titanium–cryptomelane nanorods/fibers

One-dimensional titanium–cryptomelane manganese oxide nanomaterials were successfully synthesized and characterized by TEM, SEM, XRD, XPS, and BET surface area and pore size distribution measurements. Nanosizes of titanium–cryptomelane nanomaterials were effectively controlled by the synthesis routes, and uniform nanorods were obtained by the reflux method and nanofibers by the hydrothermal one. HRTEM, XRD and N 2 adsorption–desorption analyses revealed that the materials exhibited the cryptomelane crystal structure with the pore diameters of about 0.5 nm. XPS studies demonstrated that Ti 4+ cations of titanium–cryptomelane materials were located at the octahedral coordinated environments, and that the average oxidation states of manganese species were about 3.9. These materials showed high catalytic activities toward CO oxidation at ambient temperature, and catalytic behaviors showed a correlation with the surface area, the morphology and the titanium content.

Improved Halbach sensor for NMR scanning of drill cores

A lightweight Halbach magnet system for use in nuclear magnetic resonance (NMR) studies on drill cores was designed and built. It features an improved homogeneous magnetic field with a strength of 0.22 T and a maximum accessible sensitive volume. Additionally, it is furnished with a sliding table for automatic scans of cylindrical samples. This device is optimized for nondestructive online measurements of porosity and pore size distributions of water-saturated full cylindrical and split semicylindrical drill cores of different diameters. The porosity of core plugs with diameters from 20 to 80 mm can be measured routinely using exchangeable radiofrequency coils. Advanced NMR techniques that provide 2D T(1)-T(2) correlations with an average measurement time of 30 min and permeability estimates can be performed with a special insert suitable for small core plugs with diameter and length of 20 mm.

Sol-gel synthesis, characterization and bioactivity of poly(ether-imide)/TiO2 hybrid materials.

Novel organic-inorganic hybrid materials were synthesized by the sol-gel method from a multicomponent solution containing titanium butoxide, 6 weight % (wt%) or 12 wt% poly(ether-imide) (PEI), water and chloroform. The structure of the interpenetrating network is realized by hydrogen bonds between the Ti-OH group (H-donator) in the sol-gel intermediate species and the carboxylic group (H-acceptor) in the repeating units of the polymer. By Fourier transform infrared (FTIR) analysis the presence of hydrogen bonds between organic-inorganic components of the hybrid materials were proved. The morphology of the hybrid materials was studied by scanning electron microscopy (SEM). The structure of a molecular level dispersion was disclosed by an atomic force microscope (AFM), pore size distribution and surface measurements. The AFM and SEM analyzes confirmed that the PEI/TiO2 samples can be considered homogenous organic/inorganic hybrid materials because in both the compositions studied the average domains were less than 400 nm in size. The bioactivity of the synthesized hybrid materials was demonstrated by the formation of a layer of hydroxyapatite on the surface of the PEI/TiO2 samples soaked in a fluid simulating the composition of human blood plasma (SBF), demonstrated by SEM and energy dispersive spectroscopy (EDS) microscopy.

Processing and Characterization of Porous Structures from Chitosan and Starch for Tissue Engineering Scaffolds

Natural biodegradable polymers were processed by different techniques for the production of porous structures for tissue engineering scaffolds. Potato, corn, and sweet potato starches and chitosan, as well as blends of these, were characterized and used in the experiments. The techniques used to produce the porous structures included a novel solvent-exchange phase separation technique and the well-established thermally induced phase separation method. Characterization of the open pore structures was performed by measuring pore size distribution, density, and porosity of the samples. A wide range of pore structures ranging from 1 to 400 microm were obtained. The mechanisms of pore formation are discussed for starch and chitosan scaffolds. Pore morphology in starch scaffolds seemed to be determined by the initial freezing temperature/freezing rate, whereas in chitosan scaffolds the shape and size of pores may have been determined by the processing route used. The mechanical properties of the scaffolds were assessed by indentation tests, showing that the indentation collapse strength depends on the pore geometry and the material type. Bioactivity and degradation of the potential scaffolds were assessed by immersion in simulated body fluid.

Ageing effects in a compacted bentonite: a microstructure approach

It is suspected that the as-compacted state of heavily compacted clays used as possible engineered barriers for nuclear waste disposal is time dependent, and that further change may occur in the material, even at constant water content and density. This paper presents an investigation of the time-dependent microstructure changes of an MX80 clay bentonite compacted at various dry densities and water contents. Microstructure investigation is based on mercury intrusion pore size distribution measurements and scanning electron microscopy (SEM). Results obtained by other researchers by using X-ray diffraction at low angles are also used. Statically compacted samples of MX80 were kept at constant volume and water content for various periods of time (1, 30 and 90 days) prior to mercury intrusion and SEM micro-structure investigation. A significant change in micro-structure with time was observed, characterised by a decrease in the inter-aggregate porosity and an increase in the very thin porosity not intruded by mercury (r < 3·7 nm). The former observation is related to the filling of inter-aggregate larger pores by exfoliation, and the latter observation is related to changes that occur in the aggregates within the smectite particles when suction is reduced. These changes are interpreted in the light of an investigation carried out on similar samples using low-angle X-ray diffraction. Changes inside the aggregates are governed by the progressive placement of interlayer water molecules inside the particles together with the subdivision of particles, which gives rise to an interparticle porosity that develops inside the aggregates.

Calcium Oxide Based Sorbents for Capture of Carbon Dioxide at High Temperatures

Calcium oxide is a promising sorbent for the capture of carbon dioxide. In this work, CaO sorbents were prepared using different precursors, including Ca(NO3)2·4H2O, CaO, Ca(OH)2, CaCO3, and Ca(CH3COO)2·H2O. Of these, the sorbent prepared from calcium acetate (CaAc2−CaO) resulted in the best uptake characteristics for CO2. This sorbent had a higher BET surface area and larger pore volume than the other sorbents. According to SEM images, this sorbent exhibits a “fluffy” structure, which probably contributes to its high surface area and large pore volume. This sorbent also showed almost 100% carbonation, at temperatures between 550 and 800 °C. Moreover, the carbonation progressed dominantly during an initial short period. Under numerous carbonation/decarbonation cycles, the CaAc2−CaO sorbent demonstrated the best reversibility, even in the presence of 10 vol % water vapor. During a 27-cycle operation, the sorbent maintained fairly high conversion of 62 mol % at 700 °C. Pore size distribution measurements in...

The investigation of adsorptive performance on modified multi-walled carbon nanotubes by mechanical ball milling

Different lengths of short multi-walled carbon nanotubes (MWNTs) were prepared by mechanical ball milling over 12 h. TEM observation indicated that the extent of shortening and opening of MWNTs increased on prolonging the milling time. The short nanotubes with length of 100–200 nm were obtained after ball milling for 30 h. The adsorptive performance for aniline in aqueous solution indicated that the adsorptive capacity of short open-ended MWNTs increased obviously from 15 to 36% compared to the unmilled MWNTs. The measurements of pore size distribution proved that the inner pore diameter of 3 nm remains constant and the aggregated pore diameter decreased obviously after ball milling. The increasing and expanding of hystersis loop in N 2 adsorption–desorption isotherms confirmed that the capillarity plays an important role in adsorption on the milled short MWNTs.

Preparation of SiC Nanoporous Membrane for Hydrogen Separation at High Temperature

Nanoporous SiC membrane was developed on the porous alumina plate for the hydrogen separation using preceramic polymers such as polyphenylcarbosilane. The prepared preceramic polymers were characterized with FT-IR, TGA, GPC and XRD. Nanoporous SiC membrane was derived from the preceramic polymer using a spin coating method. The SiC membrane spin coated using 20 wt.% of polyphenylcarbosilane solution in cyclohexane does not show any cracks on the surface after heat treatment at 800oC. The average thickness of the SiC membrane is about 1µm. SiC coated porous alumina possesses asymmetric pore size distribution. There are micropores that originated from porous alumina substrate, and nanopores that derived from amorphous state of SiC membranes. The pore size distribution measurement showed that the sample contains 1-3 nm sized nano pores.