Search results for "Isothermal process"
showing 10 items of 114 documents
Non-isothermal separation of ferrofluid particles through grids: Abnormal magnetic Soret effect
2013
Abstract Nanoparticle transport through thin non-isothermal ferrofluid layer between permeable walls is investigated. The transient mass flux is determined from measurements of particle concentration changes in two fluid chambers of different temperatures which are attached on both sides of the layer. Experiments are performed employing fluid samples of small ordinary magnetic Soret effect, which is detected by thermal grating technique. The separation measurements say that a magnetic field, aligned along a temperature gradient, causes a remarkable increase in the mass diffusion coefficient and a simultaneous decrease in particle thermodiffusion mobility. It is proposed that the observed ef…
On the origin of the sigmoid shape in the UO2 oxidation weight gain curves
2009
International audience; Cracking and spalling are known to occur during the oxidation of UO2. However, these phenomena are not considered by the existing kinetic models of the oxidation of UO2 into U3O8. In this study the oxidation of UO2 samples of various sizes from the single crystal to nanopowders, has been followed by isothermal and isobaric thermogravimetry, environmental scanning electron microscopy and in situ X-ray diffraction at temperatures ranging from 250 to 370°C in air. It has been shown that cracking occurs once a critical layer thickness of intermediate oxide has been reached, which corresponds to the beginning of the sigmoid kinetic curve. Cracking contribution to the sigm…
High temperature reactivity of nickel aluminide diffusion coatings
2008
Abstract The high-temperature oxidation behaviour of nickel aluminides has been studied at 900 °C in air under atmospheric pressure. Yttria doped and undoped specimens of nickel were aluminised and then oxidised for 100 h under isothermal and cycling conditions. The results showed that when yttria is added by metal-organic chemical vapour deposition technique prior to the aluminisation process, it increased the oxidation rate of aluminised nickel, but improved the oxide scale adherence under cyclic conditions. The effects of yttria on the scale morphology, oxidation behaviour and scale spallation tendency are discussed based on the experimental results, using X-ray diffraction (XRD), scanni…
Viscoelastic Behavior of an Epoxy Resin Modified with Recycled Waste Particles Analyzed through a Fractional Model
2021
It is well-known that the addition of randomly dispersed particles in polymers influences their linear viscoelastic behavior and dynamic mechanical properties. The aim of this study was to describe the viscoelastic behavior of an epoxy resin modified by waste glass and rubber particles using the linear fractional spring-pot model. Unlike complex classical exponential models, fractional models, being only two-parameter dependent, make it easier to characterize the viscoelastic behavior of materials. Isothermal relaxation and single frequency sweep temperature dynamic tests were carried out in a dynamic mechanical analyzer DMA150 by varying the content of the particles from 0 to 20% by weight…
11B-MAS NMR approach to the boron adsorption mechanism on a glucose-functionalised mesoporous silica matrix
2018
[EN] Boron chemistry has raised much interest because, despite the difference between necessities and toxicity being very narrow, it is still widely used in industrial processes. In a previous work we reported an adsorbent for boron extraction from water by the functionalisation of a UVM-7 mesoporous silica matrix with gluconamide moieties. The ability of this material to adsorb boron is based on its well-known affinity for coordinating the cis-diols present in attached saccharide. Although much research on the formation of boron esters with sugars and sugar derivatives in solution has been done, very few reports have dealt with the adsorption mechanism of boron onto functionalised material…
Compensating isothermal calorimeter to investigate the vulcanization of factice
1990
Abstract Sulphur factice is produced from a mixture of a vegetable oil and sulphur for linkage. To start vulcanization, the mixture is heated to temperatures betueen 130 and 150 °C. Within hours or days the temperature increases to about 160 °C and the product solidifies. To investigate the production process and to optimize the reaction, the temperature development was simulated in laboratory-scale experiments and the heat released was measured. In order to investigate the reaction kinetics of the entire vulcanization process, the calorimeter must a11ow the measurement of the mixture in liquid and solid state. The developed compensating calorimeter consists of a hot plate equipped with thi…
The effect of rare earths deposited on steel surfaces, by different processes (sol/gel, electrophoresis, OMCVD), on high temperature corrosion behavi…
1993
Abstract In this paper, different methods of rare earth oxides deposition on the surface of AISI 304 steel are described: sol/gel, electrophoresis in aqueous or organic medium, OMCVD of rare earth β-diketonates. After the deposition, all the samples were reheated. This treatment was absolutely essential for a strengthening effect of the protective oxide scale. Oxidation of coated and non-coated samples was performed under isothermal and cyclic conditions. The effect of rare earth deposition is significant in isothermal conditions. However, in thermal cyclic conditions, the effect of a rare earth deposited on surface is spectacular. Scale spallation is then completely avoided under the chose…
A quantitative electron-microscopic study of a linear polyethylene fraction crystallized at different temperatures
1981
Replica and thin-section electron microscopy was performed on a linear polyethylene fraction (Mw = 1.89 × 105, Mn = 1.79 × 10 5) which was either isothermally crystallized or quenched at difference temperatures. The results are numerically analyzed in such a manner so as to give the distribution of the total long spacing and of the crystallite and amorphous thicknesses. The quantitative information about the maximum and minimum values for these parameters at each crystallization temperature yields important clues as to possible molecular processes involved. Qualitative information regarding general morphology, molecular tilt with respect to the lamellar surface, and possible crystallographi…
A quantitative electron microscopic study of the crystallite structure of molecular weight fractions of linear polyethylene
1984
Utilizing thin-section techniques, transmission electron microscope studies were performed on a series of bulk-crystalized fractions of linear polyethylene covering the range M = 5 × 103−6 × 106. The crystallization conditions were varied from long-time isothermal to rapid quenching. Quantitative analysis could be carried out on such samples crystallized under controlled conditions. The crystallite thickness distributions and long periods are presented in terms of histograms. From these data the degree of crystallinity can be calculated and was found to compare favorably with that from other methods. The amorphous thickness increases significantly with molecular weight for all modes of crys…
Modeling of the hydrogen sorption kinetics in an AB2 laves type metal hydride alloy
2021
Abstract Hydrides of the AB2 Laves type alloys (A=Zr, Ti; B = transition metal – Fe, Co, Ni, Mn, Cr, V) have been extensively studied as materials for the storage of gaseous hydrogen. They contain up to 4 H atoms/formula unit AB2, thus achieving reversible H storage capacities in the range between 1.5 and 2.0 wt% H and offering high rates of hydrogen charge and discharge, thus making them suitable for designing efficient hydrogen stores operating at ambient conditions. In the present study, we performed an experimental study and modeling of the thermodynamics and the kinetics of interaction in the AB2-hydrogen system. The experimental data was collected by studying a model alloy with a comp…