Growth radial anisotropic

In the radial anisotropic growth, we distinguish between the normal component and the tangential components of the motion velocity of the interfaces. Taking into account the special character of the tangential components, we assmne that these components are very large compared with the normal component so that the surface of A recovers instantaneously, and an infinitesimal layer of B then grows slowly and normally to the interface. 

Always by preoccupation with a simplification, in the case of radial anisotropic growth, we assume that the surface of the initial solid has a uniform average behavior with respect to the normal component of the velocity and thus the thickness of the layer of B is at any time identical at the various points of surface, as shown in... 

To derive the space function, we assume isothermal and isobaric conditions so that the reactivity of growth remains constant. We will successively study both isotropic and radial anisotropic models of growth. 

In radial anisotropic growth, at time r of nucleation, the surface of the initial grain is completely covered with a layer of the new solid with negligible thickness, and we nornmlly see the development of this layer on the surface of the grain. 

Tables of Appendix 2 give the various expressions of the space function of radial anisotropic growth for various shapes of grains. Examining all these expressions for the space function according to time, we can write this function in a general form, using the initial volume vq and area of grain...

Two-process model with surface nucleation-radial anisotropic growth 10.4.1. Reaction of a single grain... 

Conclusion on Ae surface nucleation and radial anisotropic growth model... 

Even wood that has no discernible defects has extremely variable properties as a result of its heterogeneous composition and natural growth patterns. Wood is an anisotropic material in that the mechanical properties vary with respect to the three mutually perpendicular axes of the material (radial, tangential, and longitudinal). These natural characteristics are compounded further by the environmental influences encountered during the growth of the living tree. Yet wood is a viable construction material because workable estimates of the mechanical properties have been developed. 

In what follows we will stiek to the first ease of inward development with internal interface step as rate determining (the laws that correspond to the other cases were not established). Indeed, the laws that correspond to the isotropic growth are primarily known for reactions in which the initial solid A is the single reactant, that is, for the thermal decompositions and the polymorphic transformations. It is known that in these cases, the essence of chemistry proceeds at the internal interface, and as there is no other reactant, the outward development is not conceivable. In the other cases, if the initial solid is not a single reactant, the experiment shows that we have, in the large majority of the cases, either a one-process model with instantaneous nucleation or a two-process model with surface nucleation and anisotropic radial growth developed earlier. 

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