Outward development of the formed solid

In this case, the internal interface is motionless because no expansion is possible against solid A. This means  

The production of B involves only the displacement of the external interface then. 

If it is a pseudo-steady state mode, taking into account the ejqtression of z (equation [7.36]), we get  

If now the rate of growth is separable (9t = ), the space function e of this 

Therefore, using [9.8], the motion velocity of the external interface becomes  

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