Models for Changes in Properties with Time

An autocatalytic reaction exhibits an increasing rate of aging after a certain time period. Furthermore, cyclic property changes can occur, caused by the superposition of several reactions [94]. 

A general relation for property changes with time can be expressed as  

This equation describes a change in property P which, starting from Pg, deteriorates in the course of time to zero at time to [94]. 

If the final value of P is not zero, the actual value can be entered on the right-hand side of the equation [94]. When 

In practice, this law cannot describe all aging reactions. However, it shows that aging does not necessarily have to progress continuously, but may take place dis-continuously, e.g., after an induction period [94]. 

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