Analysis of Diffusion Reactions in Spinel

There are two (2) different cases that we can distinguish, both of which represent possible diffusion mechanisms in spinel. These are Ion diffusion or Gaseous. Let us consider the ion-diffusion mechanism first. This is shown in the following diagram. 

we have shown a2+ and B + diffusing through AB2O4. The actual reactions involved are  

Notice that the partial reactions in 3.1.81. are balanced both as to material and charge. There are at least two other possible mechanisms, as shown in the following diagram  

In one case, the diffusion of a2+ is much faster than b3+ and in the other the opposite is true. Note that charge-compensation of migrating species is maintained in aU cases by the diffusion of oxide species. 

We can also illustrate gaseous transport reaction in the same manner, as shown in 3.1.83., given on the next page. The partial reactions are  

---