This paper presents an innovative approach to determine and model the kinetics of the catalytic o... more This paper presents an innovative approach to determine and model the kinetics of the catalytic oxidation of urea in alkaline medium on nickel(III) sites. Firstly, the kinetic law is established by considering two types of active sites, either from a chemically synthesized Ni-based powder or from a massive nickel electrode. Thus, the electrochemical regeneration kinetics of nickel(III) can be differentiated from the kinetics of the purely chemical pathway of NiOOH solid particles consumption by urea. Secondly, a mechanism for the urea indirect oxidation mediated by the nickel(III)/nickel(II) system is proposed to predict the formation of all the by-products, contained in the liquid phase that have been experimentally identified in our previous work. Finally, a model combining kinetic laws with diffusive and convective transport phenomena is constructed. The robustness and relevance of the latter are proven by comparing the experimental results obtained during laboratory-scale electr...
This work deals with the formation of dendritic structures by electrodeposition of Cu2+ and Ag+ w... more This work deals with the formation of dendritic structures by electrodeposition of Cu2+ and Ag+ without supporting electrolyte in Hele-Shaw cells. The transition between the two main patterns, ramified branches and dendrites, is specifically addressed at the scale of branch microstructure using careful SEM observations. Ramified branches, composed only of grain assemblies, are obtained at low current densities because of a re-nucleation process induced by space charge dynamics (Fleury, Nature, 1997). For current densities higher than a given threshold, ramified branches are also formed by re-nucleation but another growth mode, the dendritic growth, is also observed while, at the macro-scale, the pattern remains fractal and isotropic. This shows that 1) pattern transition originates from a morphological transition at microstructure scale and 2) the re-nucleation process enables a freedom in local growth direction allowing the pattern to be fractal at the macro-scale. The onset of the...
We explore an alternative synthesis of colloidal metal nanoparticles (cMnP) by electrocrystalliza... more We explore an alternative synthesis of colloidal metal nanoparticles (cMnP) by electrocrystallization. The principle is to make grow long metallic ramified branches by galvanostatic electrolysis of a stagnant metal salt aqueous solution inside a Hele-Shaw (thin gap) cell. In the absence of supporting electrolyte, the constraint of electroneutrality forces the deposit to grow as ramified branches. These branches grow by successive nucleation / growth events that leads to a fine branches structure made up of metal crystals whose size can be lower than 100 nm. The objectives of this work are to study the formation mechanism of such metal nanocrystals assemblies and elaborate a device able to dissociate and release them to propose an alternative synthesis of cMnP.
The ohmic process uses alternating current to heat rapidly and uniformly samples of food to be st... more The ohmic process uses alternating current to heat rapidly and uniformly samples of food to be sterilized, but this process must not modify the organoleptic properties of the food. The aim of this work is to examine whether reactions occur between the electrodes and the various food compounds. The redox behaviour of several commercial foods in contact with various electrodes
This paper presents an innovative approach to determine and model the kinetics of the catalytic o... more This paper presents an innovative approach to determine and model the kinetics of the catalytic oxidation of urea in alkaline medium on nickel(III) sites. Firstly, the kinetic law is established by considering two types of active sites, either from a chemically synthesized Ni-based powder or from a massive nickel electrode. Thus, the electrochemical regeneration kinetics of nickel(III) can be differentiated from the kinetics of the purely chemical pathway of NiOOH solid particles consumption by urea. Secondly, a mechanism for the urea indirect oxidation mediated by the nickel(III)/nickel(II) system is proposed to predict the formation of all the by-products, contained in the liquid phase that have been experimentally identified in our previous work. Finally, a model combining kinetic laws with diffusive and convective transport phenomena is constructed. The robustness and relevance of the latter are proven by comparing the experimental results obtained during laboratory-scale electr...
This work deals with the formation of dendritic structures by electrodeposition of Cu2+ and Ag+ w... more This work deals with the formation of dendritic structures by electrodeposition of Cu2+ and Ag+ without supporting electrolyte in Hele-Shaw cells. The transition between the two main patterns, ramified branches and dendrites, is specifically addressed at the scale of branch microstructure using careful SEM observations. Ramified branches, composed only of grain assemblies, are obtained at low current densities because of a re-nucleation process induced by space charge dynamics (Fleury, Nature, 1997). For current densities higher than a given threshold, ramified branches are also formed by re-nucleation but another growth mode, the dendritic growth, is also observed while, at the macro-scale, the pattern remains fractal and isotropic. This shows that 1) pattern transition originates from a morphological transition at microstructure scale and 2) the re-nucleation process enables a freedom in local growth direction allowing the pattern to be fractal at the macro-scale. The onset of the...
We explore an alternative synthesis of colloidal metal nanoparticles (cMnP) by electrocrystalliza... more We explore an alternative synthesis of colloidal metal nanoparticles (cMnP) by electrocrystallization. The principle is to make grow long metallic ramified branches by galvanostatic electrolysis of a stagnant metal salt aqueous solution inside a Hele-Shaw (thin gap) cell. In the absence of supporting electrolyte, the constraint of electroneutrality forces the deposit to grow as ramified branches. These branches grow by successive nucleation / growth events that leads to a fine branches structure made up of metal crystals whose size can be lower than 100 nm. The objectives of this work are to study the formation mechanism of such metal nanocrystals assemblies and elaborate a device able to dissociate and release them to propose an alternative synthesis of cMnP.
The ohmic process uses alternating current to heat rapidly and uniformly samples of food to be st... more The ohmic process uses alternating current to heat rapidly and uniformly samples of food to be sterilized, but this process must not modify the organoleptic properties of the food. The aim of this work is to examine whether reactions occur between the electrodes and the various food compounds. The redox behaviour of several commercial foods in contact with various electrodes
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