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Water Adsorption (water + adsorption)
Selected AbstractsSurface Enthalpy, Enthalpy of Water Adsorption, and Phase Stability in Nanocrystalline Monoclinic ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009A. V. Radha A fundamental issue that remains to be solved when approaching the nanoscale is how the size induces transformation among different polymorphic structures. Understanding the size-induced transformation among the different polymorphic structures is essential for widespread use of nanostructured materials in technological applications. Herein, we report water adsorption and high-temperature solution calorimetry experiments on a set of samples of single-phase monoclinic zirconia with different surface areas. Essential to the success of the study has been the use of a new ternary water-in-oil/water liquid solvothermal method that allows the preparation of monoclinic zirconia nanoparticles with a broad range of (BET) Brunauer,Emmett,Teller surface area values. Thus, the surface enthalpy for anhydrous monoclinic zirconia is reported for the first time, while that for the hydrous surface is a significant improvement over the previously reported value. Combining these data with previously published surface enthalpy for nanocrystalline tetragonal zirconia, we have calculated the stability crossovers between monoclinic and tetragonal phases to take place at a particle size of 28 ± 6 nm for hydrous zirconia and 34 ± 5 nm for anhydrous zirconia. Below these particle sizes, tetragonal hydrous and anhydrous phases of zirconia become thermodynamically stable. These results are within the margin of the theoretical estimation and confirm the importance of the presence of water vapor on the transformation of nanostructured materials. [source] Structural characterization and dynamic water adsorption of electrospun polyamide6/montmorillonite nanofibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Qi Li Abstract A facile compounding process, which combined nanocomposite process with electrospinning for preparing novel polyamide6/organic modified montmorillonite (PA6/O-MMT) composite nanofibers, is reported. In this compounding process, the O-MMT slurry was blended into the formic acid solution of PA6 at moderate temperatures, where the nanosized O-MMT particles were first dispersed in N,N -dimethyl formamide solvent homogeneously via ultrasonic mixing. Subsequently the solution via electrospinning formed nanofibers, which were collected onto aluminum foil. The O-MMT platelets were detected to be exfoliated at nanosize level and dispersed homogeneously along the axis of the nanofibers using an electron transmission microscope. Scanning electron microscope and atomic force microscope were used to analysis the size and surface morphology of polyamide6/O-MMT composite nanofibers. The addition of O-MMT reduced the surface tension and viscosity of the solution, leading to the decrease in the diameter of nanofiber and the formation of rough and ridge-shape trails on the nanofiber surface. The behavior of the dynamic water adsorption of composite nanofibers was also investigated and discussed in this article. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effects of Water-Glycerol and Water-Sorbitol Interactions on the Physical Properties of Konjac Glucomannan FilmsJOURNAL OF FOOD SCIENCE, Issue 2 2006Lai Hoong Cheng ABSTRACT Konjac glucomannan (KGM)-edible films were prepared with different amounts of glycerol or sorbitol as a plasticizer. Films were characterized by moisture sorption isotherm, and following conditioning at different relative humidities, by differential scanning calorimetry and tensile tests. Moisture and polyols (sorbitol and glycerol) were found to plasticize KGM-based films with respect to their tensile properties. However, thermal properties and water sorption capacity (WSC) of polyolplasticized KGM films were found to vary with water activity (aw), namely at low aw (< 0.6), WSC and melting enthalpy were decreased with increasing in polyol content and the opposite was true at higher aw (>0.6). This was attributed to extensive interactions between plasticizer and KGM that reduced the available active site (-OH groups) for water adsorption. The presence of polyols at low aw appeared to suppress crystalline structures due probably to restricted molecular mobility. These effects were diminished when the moisture content was >20%. [source] Sorption Isotherm and Calorimetric Behavior of Amorphous/Crystalline Raffinose-Water SystemsJOURNAL OF FOOD SCIENCE, Issue 4 2000H.A. Iglesias ABSTRACT: The water adsorption and desorption isotherms at 27 °C of initially amorphous raffinose over a range of relative humidity of 11% to 97% have been determined. Upon adsorption, the isotherm exhibited a "quasi" plateau, and the moisture content at this plateau was found to be very close to the amount required to form the crystalline raffinose pentahydrate (R.5 H2O). Crystallization of raffinose (R.5 H2O) during water adsorption at 52% and 58% RH was indicated by differential scanning calorimetry (DSC); both thermograms showed an endothermal peak of melting corresponding to R.5H2O. The results of the crystallization kinetics at 52% and 58% RH indicated that the time to assess the stable physical state in a sugar system for a given external condition has to be properly defined and depends on the (T-Tg) value. [source] Surface Enthalpy, Enthalpy of Water Adsorption, and Phase Stability in Nanocrystalline Monoclinic ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009A. V. Radha A fundamental issue that remains to be solved when approaching the nanoscale is how the size induces transformation among different polymorphic structures. Understanding the size-induced transformation among the different polymorphic structures is essential for widespread use of nanostructured materials in technological applications. Herein, we report water adsorption and high-temperature solution calorimetry experiments on a set of samples of single-phase monoclinic zirconia with different surface areas. Essential to the success of the study has been the use of a new ternary water-in-oil/water liquid solvothermal method that allows the preparation of monoclinic zirconia nanoparticles with a broad range of (BET) Brunauer,Emmett,Teller surface area values. Thus, the surface enthalpy for anhydrous monoclinic zirconia is reported for the first time, while that for the hydrous surface is a significant improvement over the previously reported value. Combining these data with previously published surface enthalpy for nanocrystalline tetragonal zirconia, we have calculated the stability crossovers between monoclinic and tetragonal phases to take place at a particle size of 28 ± 6 nm for hydrous zirconia and 34 ± 5 nm for anhydrous zirconia. Below these particle sizes, tetragonal hydrous and anhydrous phases of zirconia become thermodynamically stable. These results are within the margin of the theoretical estimation and confirm the importance of the presence of water vapor on the transformation of nanostructured materials. [source] PAUL-LOUIS CYFFLÉ'S (1724,1806) TERRE DE LORRAINE: A TECHNOLOGICAL STUDYARCHAEOMETRY, Issue 5 2010M. MAGGETTI Fragments of four Terre de Lorraine biscuit figurines were subjected to porosity analysis, X-ray fluorescence analysis, X-ray diffraction analysis, backscattered-electron image analysis,coupled with energy dispersive spectrometry,and electron backscatter diffraction analysis to determine the porosity, bulk, major, minor and trace element compositions, and the composition and the proportion of their constituent phases. Cyfflé's Terre de Lorraine wares embrace two distinct types of paste, a calcareous and an aluminous,siliceous one. Both are porous (9,25% water adsorption). The former consists of a mixture of different proportions of ground quartz or calcined flint, ground Pb-bearing glass and calcium carbonate with a refractory clay. The firing temperature was between 950 and 1050°C. For the latter, Cyfflé mixed ground pure amorphous SiO2, ground quartz or calcined flint, ground porcelain, ground Na,Ca-glass and coarse-grained kaolinite with a fine-grained kaolinitic clay. The figurines were fired below 1000°C. The result was a porous, hard paste porcelain-like material. Cyfflé's recipes for both pastes can be calculated from the chemical and the modal analyses. [source] | ||||||||||