A binary phase diagram is expected to be of isomorphouse type
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Answer:
The following points highlight the four main types of binary diagrams. The types are: 1. Solid Solution Systems 2. Insoluble in the Solid State 3. Soluble in the Solid State 4. Peritectic Reaction.
Binary phase diagrams are based on two component systems. Here, the two components may be mixed in an infinite number of different proportions, that is, composition also becomes a variable, apart from pressure and temperature. Binary diagrams are usually drawn at one atmospheric pressure, i.e., pressure is made constant, because the variation in pressure results in insignificant effect on the equilibrium. Moreover, it helps to obtain the binary diagram as a convenient two- dimensional figure.
When the pressure variable and the vapour phase are ignored, then the phase rule for the condensed phases (solid and liquid phases only) is modified to the following form, which is more commonly used for metallic systems as alloys are normally made under normal atmospheric condition, i.e., at constant one atmosphere:
In binary diagrams, temperature is plotted as the ordinate and the composition as the abscissa. Thus, the phase diagram is a map which shows at a glance the phases which exist in equilibrium for any combination of temperature and alloy composition.
When three phases are in equilibrium in a binary system, (P = 3, C = 2), F = 0, the degree of freedom is zero. In other words, three phase equilibrium is characterised by a fixed composition and temperature, and it is invariant. Two phase equilibrium means (P = 2, C = 2), F = 1, that is, when the temperature is fixed, the compositions of the phases are also fixed, however, the temperature can be varied within certain limits.
When only one phase is present, (P = 1, C = 2), F = 2, i.e., the composition and the temperature can be varied independently without disturbing the number of phases. In the phase diagram, one phase equilibrium is shown as an area (one phase field).
Explanation: