The crystals growth (Part 4).

The heat released during solidification is removed and the liquid crystal phase, and at a high rate of heat dissipation is high rate of crystal growth. In all cases, the melt from the crystallization front is maintained in a supercooled state, and this supercooling ΔТ determines the rate of crystal growth.

Let’s say that the side grows at the s area of the normal in the direction x with Up speed. During dt the side will promote in the direction of liquid on distance

dx = Up*dt.

The crystal weight will increase on

dF = p*dV = ps*dx,

where р — crystal density.

Having designated through λ — the specific heat of crystallization, we will define the marked-out heat:

dQ = λ dF = λ ps dx.

The crystals speed growth is more at those metals which have large heat conductivity and small warmth of the crystallization.

When hardening of strongly overcooled fusion the surface of a crystal is distorted, on it ledges are created. They get to more favorable conditions for growth as here warmth of crystallization dissipates better: the bigger volume of liquid is the share of the convex surface unit. The crystal surface becomes wavy, the stronger the super cooled liquid.

Exert impact on growth of crystals to impurity. Superficially active impurity dissolved in fusion can selectively be adsorbed on crystal sides. As a result of, for example, the adsorption of the impurity atoms on step ledges filling of layers with atoms of metal will slow down (≪stage positioning≫) because of what growth of all side will be slowed down. On another, slowly growing sides having low superficial energy, impurity can promote formation of screw dislocations thanks to what growth accelerates.

The impurities can change and faceted crystals. The technique is widely used by modifying the shape of crystals, the effect of impurities.

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