			Home About us Contact

Desorption Kinetics (desorption + kinetics)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Desorption kinetics of model polar stratospheric cloud films measured using Fourier Transform Infrared Spectroscopy and Temperature-Programmed Desorption

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2001
Birgit G. Koehler
This study combines Fourier transform infrared (FTIR) spectroscopy and temperature-programmed desorption to examine the evaporation kinetics of thin films of crystalline nitric acid hydrates, solid amorphous H2O/HNO3 mixtures, H2O,ice, ice coated with HCl, and solid HNO3. IR spectroscopy measured the thickness of each film as it evaporated, either at constant temperature or during a linear temperature ramp (temperature-programmed infrared, TPIR). Simultaneously, a mass spectrometer measured the rate of evaporation directly by monitoring the evolution of the molecules into the gas phase (temperature-programmed desorption, TPD). Both TPIR and TPD data provide a measurement of the desorption rate and yield the activation energy and preexponential factor for desorption. TPD measurements have the advantage of producing many data points but are subject to interference from experimental difficulties such as uneven heating from the edge of a sample and sample-support as well as pumping-speed limitations. TPIR experiments give clean but fewer data points. Evaporation occurred between 170 and 215 K for the various films. Ice evaporates with an activation energy of 12.9 ± 1 kcal/mol and a preexponential factor of 1 × 1032±1.5 molec/cm2 s, in good agreement with the literature. The beta form of nitric acid trihydrate, ,,NAT, has an Edes of 15.6 ± 2 kcal/mol with log A = 34.3 ± 2.3; the alpha form of nitric acid trihydrate, ,,NAT, is around 17.7 ± 3 kcal/mol with log A = 37.2 ± 4. For nitric acid dihydrate, NAD, Edes is 17.3 ± 2 kcal/mol with log A = 35.9 ± 2.6; for nitric acid monohydrate, NAM, Edes is 13 ± 3 kcal/mol with log A = 31.4 ± 3. The ,,NAT converts to ,,NAT during evaporation, and the amorphous solid H2O/HNO3 mixtures crystallize during evaporation. The barrier to evaporation for pure nitric acid is 14.6 ± 3 kcal/mol with log A = 34.4 ± 3. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 295,309, 2001 [source]

Tailoring Hydrogen Storage Materials Towards Application

ADVANCED ENGINEERING MATERIALS, Issue 5 2006
M. Dornheim
Abstract A breakthrough in hydrogen storage technology was achieved by preparing nanocrystalline hydrides using high-energy ball milling and the use of suitable catalysts/additives. These new materials show fast or in case of Mg-based hydrides very fast absorption and desorption kinetics within minutes, thus qualifying lightweight Mg- or Al-based hydrides for storage applications. This article summarizes our current understanding of the kinetics of Mg-based light metal hydrides, describes an approach for a cost-effective processing technology and highlights some promising new developments in lightweight metal hydride research. [source]

Sorption kinetics of ethanol/water solution by dimethacrylate-based dental resins and resin composites

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2007
Irini D. Sideridou
Abstract In the present investigation the sorption,desorption kinetics of 75 vol % ethanol/water solution by dimethacrylate-based dental resins and resin composites was studied in detail. The resins examined were made by light-curing of bisphenol A glycol dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), bisphenol A ethoxylated dimethacrylate (Bis-EMA), and mixtures of these monomers. The resin composites were prepared from two commercial light-cured restorative materials (Z100 MP and Filtek Z250), the resin matrix of which is based on copolymers of the above-mentioned monomers. Ethanol/water sorption/desorption was examined in both equilibrium and dynamic conditions in two adjacent sorption,desorption cycles. For all the materials studied, it was found that the amount of ethanol/water sorbed or desorbed was always larger than the corresponding one reported in literature in case of water immersion. It was also observed that the chemical structure of the monomers used for the preparation of the resins directly affects the amount of solvent sorbed or desorbed, as well as sorption kinetics, while desorption rate was nearly unaffected. In the case of composites studied, it seems that the sorption/desorption process is not influenced much by the presence of filler. Furthermore, diffusion coefficients calculated for the resins were larger than those of the composites and were always higher during desorption than during sorption. Finally, an interesting finding concerning the rate of ethanol/water sorption was that all resins and composites followed Fickian diffusion kinetics during almost the whole sorption curve; however, during desorption the experimental data were overestimated by the theoretical model. Instead, it was found that a dual diffusion,relaxation model was able to accurately predict experimental data during the whole desorption curve. Kinetic relaxation parameters, together with diffusion coefficients, are reported for all resins and composites. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source]

Root cadmium desorption methods and their evaluation with compartmental modeling

NEW PHYTOLOGIST, Issue 1 2010
Wayne T. Buckley
Summary ,Desorption of plant roots is often employed in studies of plant physiology and nutrition; however, there have been few studies on the validity of desorption procedures. ,Branched and in-line kinetic models with five compartments , cadmium (Cd)-chelate, Cd2+, root apoplast, root symplast and vacuole , were developed to evaluate the efficacy of diethylenetriaminepentaacetic acid (DTPA) and CaCl2 methods for the desorption of Cd from roots of durum wheat seedlings. Solution Cd2+ could exchange with apoplast and symplast Cd simultaneously in the branched model and sequentially in the in-line model. ,A 10-min desorption with 1 × 10,6 M DTPA at room temperature or cold (0°C) 5 × 10,3 M CaCl2 was required to achieve 99% recovery of apoplast-bound 109Cd when experimental results were interpreted with the branched model. However, when the same data sets were analysed with the in-line model, only partial desorption was achieved. Arguments are presented that suggest that the branched model is correct. ,It is suggested that compartmental modeling is a suitable tool for the study of plant root uptake and desorption kinetics, and that there are advantages over more commonly used calculation procedures. [source]