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The aim of this study was to investigate the influence of qualitatively different powder feeder performances on resulting granule size distributions after twin-screw granulation of a highly drug loaded, hydrophobic mixture and a mannitol powder. It was shown that powder feeder related problems usually cannot be identified by trusting in the values given by the feeder. Therefore, a newly developed model for the evaluation of the performance of powder feeders was introduced and it was tried to connect this model to residence time distributions in twin-screw granulation processes. The influence of feeder performances on resulting granule size distributions varied, depending on the applied screw configuration and the used powder. Regarding the hydrophobic and highly drug loaded formulation, which was granulated at an L/S-ratio of 0.5, a pure conveying screw and a medium kneading configuration, consisting of 60° kneading blocks were negatively influenced by poor feeder settings. For optimal settings more narrow distributions could be obtained. For an extensive kneading configuration good and poor settings resulted in mono-modal granule size distributions but were differing in the overall size. Mannitol, a model substance for a liquid sensitive formulation was granulated at an L/S-ratio of 0.075. It was even more important to maintain optimal feeding as mannitol was highly affected by poor feeder performances. Even an extensive kneading configuration could not level the errors in powder feeder performance, resulting in qualitatively different granule size distributions. The results of this study demonstrate the importance of detailed knowledge about applied feeding systems to gain optimal performance in twin-screw granulation. [ABSTRACT FROM AUTHOR]

Abstract: Electroacoustic measurement of the seismoelectric current generated by ultrasound in wetted porous materials yields information on pore size in certain situations. This occurs when electric double layers inside the pore overlap or when the pore size is sufficiently large that for a given frequency the hydrodynamic flow cannot achieve a steady Pousille profile inside of the pores. Indeed, we show experimentally that magnitude and phase of the seismoelectric current become pore size dependent in such systems. Calculations of pore size from such experimental raw data requires information concerning the porosity of the material. We suggest using high frequency conductivity measurement of the porous material to determine a ``formation factor'', which is the ratio of the wetted porous material conductivity to the conductivity of a equilibrium supernate. Porosity calculations from the formation factor can be done by applying the Maxwell–Wagner theory. We provide experimental verification that this theory can be applied for porous materials. [Copyright &y& Elsevier]

The performance of nanoporous carbons, used for hydrogen storage, ionic charge storage, or selective gas separation, is strongly determined by their pore shape and size distribution. Two frequently used experimental techniques to characterize the nanopore structure of carbons are gas adsorption combined with quenched-solid density functional theory and small angle X-ray scattering. However, neither of the two techniques can unambiguously derive a valid pore model for disordered pore structures without making assumptions. Here, we quantitatively compare pore size distributions from X-ray scattering and gas adsorption data. We generate three-dimensional pore models of activated carbons using small angle scattering and the concept of Gaussian Random Fields. These pore models are used to generate pore size distributions inherently containing a slit-pore assumption, making them comparable to pore size distributions obtained from gas adsorption analysis. This is realized by probing the effective adsorption potential via sampling of the three-dimensional pore structure with a probing adsorbate and calculating a "Degree of Confinement" parameter accounting for local pore geometry effects. We also generate pore size distributions with an alternative definition of pore size and discuss intricacies of gas adsorption results, such as the dependence on the underlying pore model in disordered microporous carbons. Image 1 [ABSTRACT FROM AUTHOR]

• A novel evaluation routine for in-depth analysis of radiographic data has been developed and validated. • An evaluation routine for the determination of the dynamic share of the total hold-up is presented and the data show the necessity of a complementary tool to classical computer-tomography. • The presented method is less elaborate, both with regard to experimental effort and evaluation time, thus enabling high-throughput measurement series. Imaging techniques have significantly improved the understanding of fluid dynamics in mass transfer columns over the last decades. In order to detect small-scale and highly dynamic flow phenomena such as droplets, a high spatial and temporal resolution is of crucial importance. One approach is ultrafast electron beam X-ray computed tomography, another is to extend the X-ray computed tomography by a radiographic measuring method. The latter allows a very high spatial and temporal resolution. For example, the X-ray computed tomograph used in the present study allows up to 500 projections per second. This enables the precise detection of highly dynamical effects in the entire column without influencing the flow. A new evaluation routine for radiographic measurements is presented and validated. The procedure enables to measure the liquid hold-up over a wide range with considerable low evaluation times, thus enabling a high experimental throughput. Additionally, a novel method to extract and quantify the dynamic share of the total hold-up is introduced. The possibilities arising from this are then explored utilizing Sulzeŕs structured packing MellapakTM as an example. We compare our findings of the hold-up with published data and discuss how the highly dynamic phenomena affect total flow, its local distribution, and substance dependency. Furthermore, the observations serve as indicator to which extend the computer tomographic method is suited to assess the total hold-up within a structured packing. [ABSTRACT FROM AUTHOR]

Abstract: In order to get more insight into the characterization of nanoporous carbons by gas adsorption, the use of different probe molecules has been compared. A series of activated carbons with ranging porosity (burn-off) have been prepared from olive stones using CO2 as activating agent and characterized using nitrogen and argon adsorption at low temperature (77.4K for N2 and 87.3K for Ar) together with CO2 adsorption at 273K and immersion calorimetry into liquids of different molecular dimensions. Experimental results show that argon adsorption in narrow carbon micropores takes place at a higher relative pressure compared to nitrogen due to a weaker effective adsorption potential (lower strength of dispersion forces), including the absence of specific interactions of argon with the adsorbent surface. We show further that application of advanced theoretical approaches based on the density functional theory (NLDFT and QSDFT) provides an accurate description of the pore-size distribution (PSD). The PSD obtained from the argon adsorption data at 87.3K is in good agreement with immersion calorimetry measurements. Our results demonstrate that argon adsorption at 87.3K in combination with the application of advanced DFT methods (e.g. QSDFT) allows for a reliable characterization of the narrow microporosity in highly heterogeneous activated carbons. [Copyright &y& Elsevier]

Abstract: Due to their network flexibility, metal-organic frameworks (MOFs) may respond to external stimuli such as guest molecules, heat, pressure, humidity and so on by a dynamical transformation of their structure. In this work we present experimental studies by means of nitrogen and argon physisorption at cryogenic temperature concerning the influence of handling and storage on the recently synthesized highly flexible copper-based MOF . Unusual adsorption isotherms with up to three distinct steps in the adsorbed volume have been found substantiating once more: (i) the high sensitivity of flexible network structures for environmental influences, (ii) the high diversity of physisorption isotherm types for flexible materials including isotherms with several steps and large hysteresis loops, and last but not least (iii) that theoretical methods assuming inert solids cannot be applied to highly flexible materials for calculating pore sizes and other solid state parameters. [Copyright &y& Elsevier]

Abstract: The micro-porous layer of gas diffusion layers (GDLs) was fabricated with the carbon slurry dispersed in water containing sodium dodecyl sulfate (SDS), by wire rod coating process. The aqueous carbon slurry with micelle-encapsulation was highly consistent and stable without losing any homogeneity even after adding polytetrafluoroethylene (PTFE) binder for hundreds of hours. The surface morphology, contact angle and pore size distribution of the GDLs were examined using SEM, Goniometer and Hg Porosimeter, respectively. GDLs fabricated with various SDS concentrations were assembled into MEAs and evaluated in a single cell PEMFC under diverse operating relative humidity (RH) conditions using H2/O2 and H2/air as reactants. The peak power density of the single cell using the GDLs with optimum SDS concentration was 1400 and 500mWcm−2 with H2/O2 and H2/air at 90% RH, respectively. GDLs were also fabricated with isopropyl alcohol (IPA) based carbon slurry for fuel cell performance comparison. It was found that the composition of the carbon slurry, specifically SDS concentration played a critical role in controlling the pore diameter as well as the corresponding pore volumes of the GDLs. [Copyright &y& Elsevier]

Abstract: In order to explore the potential of novel open metal organic frameworks (MOFs) with soc topology for gas storage applications, we performed a systematic physical adsorption study with Hydrogen, Methane and Carbon dioxide as adsorptives over a wide range of temperatures (77–323K) and pressures (0–5MPa) by using a volumetric low pressure adsorption analyzer equipped with a cryostat, and a high pressure gravimetric system. The advanced interpretation of our systematic adsorption data in combination with the results from a comprehensive structural and surface characterization allows one assessing the potential of these novel MOFs for gas storage and separation applications. [Copyright &y& Elsevier]

Abstract: Gas diffusion layers (GDLs) were fabricated using non-woven carbon paper substrates with various thicknesses developed by Hollingsworth & Vose Co. Highly consistent carbon slurry containing Pureblack carbon and vapor grown carbon fiber (3:1 ratio) with 25wt.% Teflon was prepared by using a dispersion agent, Novec-7300 in isopropyl alcohol. Micro-porous layer was coated by using a fully automated Coatema coating tool with a uniform carbon loading of 2.6–3mgcm−2 using carbon slurry. The surface morphology, contact angle and pore size distribution of the GDLs were examined using SEM, Goniometer and Hg Porosimeter, respectively. Various cathode GDLs assembled into MEAs were evaluated in a single cell PEMFC under various operating relative humidity (RH) conditions using H2/O2 and H2/air as reactants. The peak power density of the single cell using the optimum carbon paper substrate thickness was about 1400 and 700mWcm−2 with H2/O2 and H2/air at 60% RH, respectively. It was found that the pore diameter as well as the corresponding pore volumes of the GDLs played a key role in exhibiting the optimum fuel cell performance. [Copyright &y& Elsevier]

Abstract: Prompted by our earlier study that fumed silica on gas diffusion layer (GDL) favored a performance improvement of the single fuel cell at lower RH conditions, the present study has been carried out with inorganic oxides in the nanoscale such as TiO2, Al2O3, commercially available mixed oxides, hydrophilic silica and aerosil silica. The structure of each of the oxide coating on the GDL surface has resulted in refinement with graded pore dimension as seen from the Hg porosimetry data. The fuel cell evaluation at various RH conditions (50–100%) revealed that the performance of all the inorganic oxides loaded GDL is very high compared to that of pristine GDL. The results confirm our earlier observation that inorganic oxides on GDL bring about structural refinement favorable for the transport of gases, and their water retaining capacity enable a high performance of the fuel cell even at low RH conditions. [Copyright &y& Elsevier]

Abstract: Synthetic saponite-like materials were prepared by traditional hydrothermal crystallisation at 513K of 1 SiO2; 0.835MgO; 0.056Al2O3; 0.056Na2O; nH2O gel with variable amount of H2O. The obtained layered materials were submitted to a systematic study of textural properties, morphology, thermal behaviour of the produced materials by combining different experimental techniques (XRD, SEM, TEM, N2 physisorption, Solid State MAS NMR). For the first time, a fine characterisation of the surface acidity of the produced saponites performed by FTIR spectroscopy of CO probe molecule (complemented with NH3) was given. The dilution (H2O/Si ratio) of the synthesis gel played a significant role in determining the physico–chemical properties of the final products, the higher the gel dilution, the smaller the platelets determined by TEM analysis. Moreover, specific surface area of saponite samples increased with decreasing the lamellae dimensions. NLDFT and BJH approaches applied to nitrogen adsorption and desorption branches were used to define the porosity of the samples. Both micro- and mesopores were found, the latter being much more abundant on the saponite prepared at the highest gel dilution (SAP50, H2O/Si=50). A combined XRD and IR study performed at variable temperature showed that the materials were stable up to 773K and that thermal stability is not dependent on the dilution of the synthesis gel. 27Al-MAS NMR indicated that SAP50 sample contained a higher concentration of octahedral Al species than SAP20 (H2O/Si=20). These species were mainly located in the octahedral sheets as a result of isomorphous substitution of AlIII with MgII ions, and this consequently reduced the cation exchange capacity (CEC) of the material. FTIR of CO adsorption was used to monitor, beside surface protons, interlayer cations. Both magnesium and sodium ions were found in the interlayer space, and their distribution varied from one sample to another. Magnesium, for instance, was more abundant in SAP50 than SAP20. Protons located on bridged hydroxyls [Si–O(H)–Al] of the tetrahedral silica sheets displayed acidity similar to the most acid H-ZSM-5 zeolites. [Copyright &y& Elsevier]

Hydrogen adsorption data on as-grown and heat-treated single walled carbon nanotubes (SWNTs) obtained by a volumetric procedure using a Quantachrome Autosorb-1 equipment are presented. The amounts of hydrogen adsorbed at atmospheric pressure reach approximately 0.01 wt.% at 298 K and 1 wt.% at 77 K. The isosteric heat of adsorption has been calculated for both samples from H2 equilibrium adsorption data at three temperatures, having initial values of 7.42 and 7.75 kJ mol−1. Studies in porous structure by N2 adsorption and density measurements in helium pycnometer are reported. [Copyright &y& Elsevier]