Search results for "POROSITY"
showing 10 items of 599 documents
Novel pathways for the preparation of mesoporous MCM-41 materials: control of porosity and morphology
1999
Two novel synthesis routes for the preparation of mesoporous MCM-41 materials are introduced. Both methods use tetra-n-alkoxysilanes such as tetraethoxysilane (TEOS) or tetra-n-propoxysilane (TPS) as a silica source which are added to an aqueous solution of a cationic surfactant in the presence of ammonia as catalyst. In this study, n-alkyltrimethylammonium bromides and n-alkylpyridinium chlorides were employed as templates. The addition of an alcohol (e.g. ethanol or isopropanol) leads to a homogeneous system which allows the formation of spherical MCM-41 particles. The main advantages of these methods are short reaction times, excellent reproducibility and easy preparation of large batche…
POROSITY DETERMINATION WITH HELIUM PYCNOMETRY AS A METHOD TO CHARACTERIZE WATERLOGGED WOODS AND THE EFFICACY OF THE CONSERVATION TREATMENTS
2012
The helium pycnometer allows us to measure the cell-wall density of dry woods and the basic density of wood samples soaked with water and/or a consolidant solution if a non-volatile solvent is used. These parameters were correlated to the porosity, which for degraded waterlogged wood is related to the maximum water content. Moreover, this has revealed the possibility of investigating, by means of accurate cell-wall density determination, the efficacy of several consolidants in the treatment of waterlogged woods.
Pore-space characterization of an altered tonalite by X-ray computed microtomography and the14C-labeled-polymethylmethacrylate method
2012
[1] The structure of geological materials strongly affects migration processes that take place in them and are also important in their weathering and alteration processes. Further information of that structure will also be important for many applications that involve geological materials. The emphasis of this study was thus to characterize the pore structure and porosity of altered tonalite by combining different measuring techniques: X-ray tomography, the14C-polymethylmethacrylate method, electron microscopy, and argon pycnometry. Intragranular porosities were determined using chemical staining of rock surfaces. Three-dimensional distributions of minerals and porosities were evaluated with…
3-D imaging and quantification of graupel porosity by synchrotron-based micro-tomography
2011
The air bubble structure is an important parameter to determine the radiation properties of graupel and hailstones. For 3-D imaging of this structure at micron resolution, a cryo-stage was developed. This stage was used at the tomography beamline of the Swiss Light Source (SLS) synchrotron facility. The cryo-stage setup provides for the first time 3-D-data on the individual pore morphology of ice particles down to infrared wavelength resolution. In the present study, both sub-mm size natural and artificial ice particles rimed in a wind tunnel were investigated. In the natural rimed ice particles, Y-shaped air-filled closed pores were found. When kept for half an hour at −8 °C, this morpholo…
Porous aerosol in degassing plumes of Mt. Etna and Mt. Stromboli
2016
Abstract. Aerosols of the volcanic degassing plumes from Mt. Etna and Mt. Stromboli were probed with in situ instruments on board the Deutsches Zentrum für Luft- und Raumfahrt research aircraft Falcon during the contrail, volcano, and cirrus experiment CONCERT in September 2011. Aerosol properties were analyzed using angular scattering intensities and particle size distributions simultaneously measured with the Polar Nephelometer and the Forward Scattering Spectrometer probes (FSSP series 100 and 300), respectively. Aerosols of degassing plumes are characterized by low values of the asymmetry parameter (between 0.6 and 0.75); the effective diameter was within the range of 1.5–2.8 µm and the…
Functionalization using biocompatible carboxylated cyclodextrins of iron-based nanoMIL-100
2021
9 pags., 7 figs., 1 tab.
Template electrodeposition and characterization of nanostructured Pb as a negative electrode for lead-acid battery
2019
Abstract Despite Lead Acid Battery (LAB) is the oldest electrochemical energy storage system, diffusion in the emerging sectors of technological interest is inhibited by its drawbacks. The principal ones are low energy density and negative plate sulphating on high rate discharging. In this work, it is shown the possibility of overcoming such drawbacks by using nanostructured lead as a negative electrode. Lead nanowires (NWs) were fabricated by electrochemical deposition in template, which is an easy, cheap, and easily scalable process. Their morphology and crystal structure have been characterized by electron microscopy and X-ray diffraction, respectively. An electrochemical cell simulating…
The Relevance of Kneading and Extrusion Parameters in the Manufacture of Active Porous Aluminas from Pseudoboehmites
1987
In order to study the effect-on crushing strength, attrition resistance, specific pore volume, and pore volume distribution of extrudates-of kneading and extrusion parameters in the manufacture of active porous aluminas, a commercial pseudoboehmite (Pural SB from Condea Chemie, Brunsbuttel, FRG) was employed. A minimum kneading torque was required to prepare an extrudable paste, predetermined by extrusion conditions. The torque had an upper limit with respect to certain extrudate properties. The amount of water and the concentration of nitric acid as binder solutions were found to have a decisive bearing on the mechanical properties and the distribution of the pore volume. Crushing strength…
Demixing time and temperature influence on porosity and interconnection of PLLA scaffolds prepared via TIPS
2009
Scaffolds suitable for tissue engineering applications were prepared by Thermally Induced Phase Separation (TIPS) starting from a ternary solution PLLA/ dioxane/water. The experimental protocol consisted of three consecutive steps, a first quench from the homogeneous solution to an appropriate demixing temperature (within the binodal region), a liquid-liquid demixing stage for a given time and a final quench from the demixing temperature to a low temperature (within the spinodal region). A large variety of morphologies, in terms of average pore size and interconnection were obtained upon modifying the demixing time and temperature, owing to the interplay of nucleation and growth processes d…
Temperature-induced microstructural changes in shells of laboratory-grown Arctica islandica (Bivalvia).
2021
Bivalve shells are increasingly used as archives for high-resolution paleoclimate analyses. However, there is still an urgent need for quantitative temperature proxies that work without knowledge of the water chemistry–as is required for δ18O-based paleothermometry–and can better withstand diagenetic overprint. Recently, microstructural properties have been identified as a potential candidate fulfilling these requirements. So far, only few different microstructure categories (nacreous, prismatic and crossed-lamellar) of some short-lived species have been studied in detail, and in all such studies, the size and/or shape of individual biomineral units was found to increase with water temperat…