Simple Binary Phase Diagram without Intermediate Compound or Solid Solution

1 Simple Binary Phase Diagram without Intermediate Compound or Solid Solution 

At any point along the liquidus curves TA-eAB and Te-eAB, there exist two phases-either solid A -i- melt, or solid B -i- melt Consequently, the degree of freedom F is 1 that is, either the temperature or the composition can be altered without changing the number of phases present (univariant equilibrium). At the eutectic point Oab the two solid phases A and B are in equilibrium with the melt Thus, the number of phases is P = 3, and F = 0, since any variation of the temperature or the composition will invariably displace the system from point Oab at which two solubility (liquidus) curves intersect (invariant equilibrium). 

The mechanism of solidification of a homogeneous melt of composition X (75 mass% A, 25 mass% B) is represented by the isopleths, the vertical dashed line Xl-X. If a melt of composition Xl cools it reaches the liquidus curve at X3 and a temperature T3, and small amounts of A start to solidify. Upon further cooling. 

3) Strictly speaking, tridymite does not truly belong to the pure one-component system Si02 as it is considered a stuffed derivative requiring foreign ions for its stabilization (see below). 

A = anorthite, B = diopside. The composition is given in mass%. The eutectic composition Xab is 42% anorthite, 58% diopside the eutectic temperature Te is 1270°C. 

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Figure 3.3 Simple binary phase diagram without intermediate compound or solid solution.

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