Dielectric loss in heterogeneous model systems

1965 ◽  
Vol 12 (1) ◽  
pp. 57-64 ◽  
Author(s):  
L. K. H. Beek ◽  
J. Booy ◽  
H. Looyenga
Keyword(s):  
Dielectric Loss ◽  
Model Systems ◽  
Heterogeneous Model

Employing Exfoliated Graphite as Novel Support Material for Heterogeneous Model Catalysts

2019 ◽  
Author(s):  
Moritz Wolf ◽  
Nico Fischer ◽  
Michael Claeys
Keyword(s):  
Surface Area ◽  
Graphite Powder ◽  
Model Catalysts ◽  
Model Systems ◽  
Exfoliated Graphite ◽  
Support Material ◽  
Heterogeneous Model ◽  
Support Materials ◽  
Metal Support Interaction ◽  
Catalyst Systems

<p>The inert nature of graphitic samples allows for characterisation of rather isolated supported nanoparticles in model catalysts, as long as sufficiently large inter-particle distances are obtained. However, the low surface area of graphite and the little interaction with nanoparticles result in a challenging application of conventional preparation routes in practice. In the present study, a set of graphitic carbon materials was characterised in order to identify potential support materials for the preparation of model catalyst systems. Various sizes of well-defined Co<sub>3</sub>O<sub>4</sub> nanoparticles were synthesised separately and supported onto exfoliated graphite powder, that is graphite after solvent-assisted exfoliation <i>via</i> ultrasonication resulting in thinner flakes with increased specific surface area. The developed model catalysts are ideally suited for sintering studies of isolated nano-sized cobaltous particles as the graphitic support material does not provide distinct metal-support interaction. Furthermore, the differently sized cobaltous particles in the various model systems render possible studies on structural dependencies of activity, selectivity, and deactivation in cobalt oxide or cobalt catalysed reactions.</p>

Électrons en excès dans les milieux polaires homogènes et hétérogènes

1996 ◽  
Vol 74 (1) ◽  
pp. 1-23 ◽  
Author(s):  
Annette Bernas ◽  
Christiane Ferradini ◽  
Jean-Paul Jay-Gerin
Keyword(s):  
Physicochemical Characteristics ◽  
Molecular Clusters ◽  
Model Systems ◽  
Micellar Solutions ◽  
Solvated Electron ◽  
Heterogeneous Model ◽  
Polar Media ◽  
Excess Electrons ◽  
Solvation Mechanisms ◽  
Homogeneous Media

A review of our present knowledge concerning the solvation of excess electrons e−exc → e−solv produced by photoionization or radiolysis in polar media has been attempted. Various properties of the solvated electron (proposed solvation mechanisms, structure, physicochemical characteristics) are considered. In spite of some similarities, e−solv does not seem to be a good prototype for solvated halide anions. The behavior of e−exc in heterogeneous model systems, such as micellar solutions and molecular clusters, is described and correlated with that observed in homogeneous media. Key words: excess electrons, homogeneous and heterogeneous polar media, photoionization, radiolysis, solvation, charge transfer to solvent, properties of the solvated electron, micellar solutions, molecular clusters, comparison with the solvation of anions.

scholarly journals Determining calcium concentration in heterogeneous model systems using multiple indicators

Cell Calcium ◽  
2007 ◽  
Vol 42 (6) ◽  
pp. 576-589 ◽  
Author(s):  
Krzysztof L. Hyrc ◽  
Ziemowit Rzeszotnik ◽  
Bryan R. Kennedy ◽  
Mark P. Goldberg
Keyword(s):  
Calcium Concentration ◽  
Model Systems ◽  
Heterogeneous Model ◽  
Multiple Indicators

scholarly journals Improving Microwave Heating using Polysaccharides as Thickeners

2009 ◽  
Vol 27 (Special Issue 1) ◽  
pp. S342-S345
Author(s):  
L. M Guardeño ◽  
M. Hernández-Carrión ◽  
J. M Catala-Civera ◽  
P. Plaza ◽  
I. Pérez-Munuera ◽  
...  
Keyword(s):  
Dielectric Loss ◽  
Electric Field ◽  
Microwave Heating ◽  
Penetration Depth ◽  
Loss Factor ◽  
The Other ◽  
Model Systems ◽  
Starch Concentration ◽  
Modified Starches ◽  
Kappa Carrageenan

The aim of this work was to improve microwave heating in white sauces using different polysaccharides in their formulation; &iota;-, &lambda;- and &kappa-carrageenan and native and modified starches were used as thickeners. Five model systems were prepared, each one with a different polysaccharide, salt, and water. Dielectric loss factor (&epsilon;'') was measured and penetration depth of the electric field was calculated at 20 and 40°C at 2450 GHz. The results showed that &epsilon;'' increased significantly (<I>P</I> < 0.05) when temperature rose in all the model systems. Moreover, &epsilon;'' decreased significantly (<I>P</I> < 0.05) when the polysaccharide concentration rose in the systems elaborated with starch (both native and modified). The penetration depth increased significantly at 40°C when native starch concentration rose. Not significant differences due to the thickener concentration were found in the depth penetration values in the other model systems, both at 20 and 40°C.

scholarly journals New insights into atmospherically relevant reaction systems using direct analysis in real-time mass spectrometry (DART-MS)

2017 ◽  
Vol 10 (4) ◽  
pp. 1373-1386 ◽  
Author(s):  
Yue Zhao ◽  
Michelle C. Fairhurst ◽  
Lisa M. Wingen ◽  
Véronique Perraud ◽  
Michael J. Ezell ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Real Time ◽  
Atmospheric Chemistry ◽  
Chemical Reactivity ◽  
Direct Analysis ◽  
Model Systems ◽  
Laboratory Model ◽  
Vapor Pressures ◽  
Heterogeneous Model ◽  
Ionization Region

Abstract. The application of direct analysis in real-time mass spectrometry (DART-MS), which is finding increasing use in atmospheric chemistry, to two different laboratory model systems for airborne particles is investigated: (1) submicron C3–C7 dicarboxylic acid (diacid) particles reacted with gas-phase trimethylamine (TMA) or butylamine (BA) and (2) secondary organic aerosol (SOA) particles from the ozonolysis of α-cedrene. The diacid particles exhibit a clear odd–even pattern in their chemical reactivity toward TMA and BA, with the odd-carbon diacid particles being substantially more reactive than even ones. The ratio of base to diacid in reacted particles, determined using known diacid–base mixtures, was compared to that measured by high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), which vaporizes the whole particle. Results show that DART-MS probes  ∼  30 nm of the surface layer, consistent with other studies on different systems. For α-cedrene SOA particles, it is shown that varying the temperature of the particle stream as it enters the DART-MS ionization region can distinguish between specific components with the same molecular mass but different vapor pressures. These results demonstrate the utility of DART-MS for (1) examining reactivity of heterogeneous model systems for atmospheric particles and (2) probing components of SOA particles based on volatility.

scholarly journals Employing Exfoliated Graphite as Novel Support Material for Heterogeneous Model Catalysts

2019 ◽  
Author(s):  
Moritz Wolf ◽  
Nico Fischer ◽  
Michael Claeys
Keyword(s):  
Surface Area ◽  
Graphite Powder ◽  
Model Catalysts ◽  
Model Systems ◽  
Exfoliated Graphite ◽  
Support Material ◽  
Heterogeneous Model ◽  
Support Materials ◽  
Metal Support Interaction ◽  
Catalyst Systems

<p>The inert nature of graphitic samples allows for characterisation of rather isolated supported nanoparticles in model catalysts, as long as sufficiently large inter-particle distances are obtained. However, the low surface area of graphite and the little interaction with nanoparticles result in a challenging application of conventional preparation routes in practice. In the present study, a set of graphitic carbon materials was characterised in order to identify potential support materials for the preparation of model catalyst systems. Various sizes of well-defined Co<sub>3</sub>O<sub>4</sub> nanoparticles were synthesised separately and supported onto exfoliated graphite powder, that is graphite after solvent-assisted exfoliation <i>via</i> ultrasonication resulting in thinner flakes with increased specific surface area. The developed model catalysts are ideally suited for sintering studies of isolated nano-sized cobaltous particles as the graphitic support material does not provide distinct metal-support interaction. Furthermore, the differently sized cobaltous particles in the various model systems render possible studies on structural dependencies of activity, selectivity, and deactivation in cobalt oxide or cobalt catalysed reactions.</p>

scholarly journals New insights into atmospherically relevant reaction systems using direct analysis in real time-mass spectrometry (DART-MS)

2016 ◽  
Author(s):  
Yue Zhao ◽  
Michelle C. Fairhurst ◽  
Lisa M. Wingen ◽  
Véronique Perraud ◽  
Michael J. Ezell ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Real Time ◽  
Atmospheric Chemistry ◽  
Chemical Reactivity ◽  
Direct Analysis ◽  
Model Systems ◽  
Laboratory Model ◽  
Vapor Pressures ◽  
Heterogeneous Model ◽  
Ionization Region

Abstract. The application of direct analysis in real time mass spectrometry (DART-MS), which is finding increasing use in atmospheric chemistry, to two different laboratory model systems for airborne particles is investigated: (1) submicron C3-C7 dicarboxylic acid (diacid) particles reacted with gas phase trimethylamine (TMA) or butylamine (BA); (2) secondary organic aerosol (SOA) particles from the ozonolysis of α-cedrene. The diacid particles exhibit a clear odd-even pattern in their chemical reactivity toward TMA and BA, with the odd-carbon diacid particles being substantially more reactive than even ones. The ratio of base to acids in reacted particles, determined using known acid-base mixtures, was compared to that measured by high resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), which vaporizes the whole particle. Results show that DART-MS probes mainly surface layers, consistent with other studies on different systems. For α-cedrene SOA particles, it is shown that varying the temperature of the particle stream as it enters the DART-MS ionization region can distinguish between specific components with the same molecular mass but different vapor pressures. These results demonstrate the utility of DART-MS for (1) examining reactivity of heterogeneous model systems for atmospheric particles and (2) probing components of SOA particles based on volatility.

Penetration rates into heterogeneous model systems and soluble food material

2018 ◽  
Vol 339 ◽  
pp. 765-774 ◽  
Author(s):  
J. Kammerhofer ◽  
L. Fries ◽  
T. Dymala ◽  
J. Dupas ◽  
L. Forny ◽  
...  
Keyword(s):  
Model Systems ◽  
Food Material ◽  
Heterogeneous Model
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