Physico-chemical growth models

We will now examine the case of the growth mechanism of uranium reduction reaction by hydrogen [14.R7], which involves interstitial oxygen as a point defect. The physico-chemical modeling of ( ) does not depend on the morphological model as long as both approaches are addressed with the same direction of development of the formed solid and the same location of the determining step  

The reaction takes place in five steps. Three of these steps [14.R7a], [14.R7b] and [14.R7c] occur at the external interface (between hydrogen and uranium dioxide). The fourth step is diffusion [14.R4d] and the last and fifth step is [14.R7e]. 

The first step is the dissociative adsorption of hydrogen on a surface site of the dioxide formed  

The second step is the use of interstitial oxygen coming from the internal interface (see steps [14.R7d] and [14.R7e]) to form hydroxides  

The fourth step is the diffusion of interstitial oxygen ion from the internal interface to the external interface (step [14.R4d])  

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The formation of bubbles and their gradual growth are also Influenced by water physico-chemical properties (Inclusions, surface tensions, and specific viscosity). The modeling of the phenomenon Is not easy, especially In the presence of a free surface. 

With two physico-chemical processes, it is necessary to model the two reaction mechanisms. Hence, the basic steps of nucleation and growth have to be written. 

LEB 05] Lebert L, Dussap C.G., Lebert A., Combined physico-chemical and water transfer modelling to predict bacterial growth during food processes , International Journal of Food Microbiology, vol. 102, pp. 305-322,2005. 

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