
Structure of alloys 59
0 Time
(b)
Figure 3.21 Peritectic reaction (a) Thermal equilibrium diagram, (b) Cooling curve
for composition X
Eutectoid reaction
A eutectoid reaction is said to occur if, during the cooling process in the solid
state,
a reaction occurs and one phase of
a
solid is replaced by a mixture of two
other phases. An example of this is shown in the iron-carbon thermal
equilibrium diagram (see Figure 11.1, page 191).
3.4 Precipitation
If a solution of sodium chloride in water is cooled sufficiently, sodium chloride
precipitates out of the solution. This occurs because the solubility of sodium
chloride in water decreases as th ...