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The definition of structure primary crystallized from melt of a firm phase

Is primary dropping out at crystallization by a phase there will be crystals of that connection, in a field primary crystallization which the point of structure initial melt lays.

In a fig.1 is represented the type of three-component diagram of a condition with binary chemical connection АС melting congruous. From melt of structure а₁ by first at appropriate temperature (in this case 1300 °С) the crystals of connection АС will drop out, as the point of this structure lays in a field primary crystallization of this connection.

If the point of structure initial melt (for example, а₂) gets on congruous boundary curve (for example, Е₁е₃), at appropriate temperature (1400 °С) simultaneously will begin crystallization of two connections A and АС, the fields primary crystallization which are divided by this curve. If the point of structure initial melt gets on incongruous boundary curve, the way of crystallization from it at once will leave and will begin to drop out crystals of one connection, in which field after that the point of structure of a liquid phase gets.

Figure 1- The diagrams of a condition of three-component system with double (binary) chemical connection AC congruous melting

Definition of final phases and final point of crystallization on the diagrams of a condition

At the given structure initial melt the diagram of a condition allows even without construction of a way of crystallization to define structure of final crystal phases after end of crystallization of melt. On final phases it is possible to define on the diagram a final point of crystallization, which characterizes temperature, at which comes to an end of crystallization and structure of a liquid phase at last moment of crystallization. At job with the diagrams of a condition it is recommended to do it before construction of a way of crystallization, that allows limiting this way initial and final points and by that to avoid mistakes at definition of a sequence of phase changes. The structure of final crystal phases after end of crystallization three-component of melt is defined by a rule of an elementary triangle.

Final products of crystallization are those three connections, the points of which structures lay in tops of an elementary triangle, inside which there is a point of structure initial melt. A final point of crystallization three-component melt is that threefold point, in which the fields of primary crystallization of final phases of crystallization converge.

For example, the diagram of three-component system with binary connection АС, melting incongruous (fig. 2), contains two elementary triangles A-B-AC and АС-В-С. For all three-component melts, the points of which structures get in an elementary triangle A-B-AC, final phases of crystallization according to the stated rule will be connections A, B and АС, forming this elementary triangle, and final point of crystallization - point of double lowering G, in which the fields of primary crystallization of these connections converge. Precisely as all melts, the points of which structures get in an elementary triangle АС-В-С, finish to crystallize in eutectic Е with allocation of connections АС, B and C as final phases of crystallization.

Figure 2- The diagrams of a condition of three-component system with double (binary) chemical connection AC incongruous melting

It is necessary to specify, that at job with the diagrams of a condition there can be so-called special cases, at which some general rules are not always applicable. It, for example, concerns to definition of final phases of crystallization, when the point of initial melt gets on a connecting straight line or precisely corresponds to a point of structure any of connection in the given system. If the point of initial structure gets on a connecting straight line (for example, a point a, fig. 2), final phases of crystallization will be those two connections (B and АС), the points of which structures are connected by this connecting straight line (in similar cases initial structure it is necessary to consider as belonging private to two-component system formed by these connections). If the point of structure of initial melt precisely corresponds to structure of any connection, a final product of crystallization will be one phase - crystals of this connection.

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