[Rutherford]

Spinels are a large group of compounds having the general formula AB₂O₄. The parent compound, the mineral spinel, has the composition MgAl₂O₄. Its noble varieties are used as precious stones. The simplest way of producing spinels is the direct reaction of the single oxides: MgO + Al₂O₃ → MgAl₂O₄.
The reaction proceeds with noticeable speed only at very high temperatures (> 1800 °C), because it is only then that the mobility of the articles in the solid becomes sufficiently high. Two blocks of the metal oxides AO and B₂O₃ are compressed and heated for the determination of the reaction mechanism of spinel formation. The interphase is marked e.g. by a thin wire. The reaction starts by ions diffusing through the interphase. After some time, some spinels have formed. Conclusions about the reaction mechanism can be drawn from the position of the wire (picture attached).

I can't imagine this process. What causes the wire to move? How does it happen?

[UG]

I can't imagine this process. What causes the wire to move? How does it happen?

Have you heard of the Kirkendall effect?

[Rutherford]

Trying to understand it, but it's not that easy. Never mind then, I will leave this for some other time  .