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The soret effect and superstructures in eutectic composites
Journal of Crystal Growth 3, 4 (1968) 679 © North-Holland Publishing Co., Amsterdam
679
THE SORET EFFECT AND SUPERSTRUCTURES IN EUTECT1C COMPOSiTES
R. E. JESSE Philips Research Laboratories, N. V. Philips’ Gloeilampenfabrieken, Eindhoven, The Netherlands
When a two-phase composite is grown from a eutectic melt by the Czochralski technique, one of the phases is found to be ordered in dish-like two-phase regions perpendicular to the direction of growth. These twophase regions, which in the case considered consist of needles directed parallel to the direction of growth in a single-phase matrix, are separated from each other by single-phase regions. This formation of a superstructure is related to ternperature fluctuations in the melt near the solid—liquid interface. These temperature fluctuations result in growth rate fluctuations. It has been shown that in principle the Soret effect must be taken into account
in the considerations ofgrowth kinetics. In single-phase systems with k0 < 1, the contribution of the Soret effect to the composition of the boundary layer is of minor importance. However, in the case of eutectic systems it gives a relatively important contribution to the concentration in the boundary layer. This contribution amounts to 1 % of the concentration CE of the eutectic melt but can be considerably more for systems with a large thermal diffusion coefficient or in cases where the temperature gradient is steep. In cornbination with growth rate fluctuations superstructures as observed in Czochralski-grown eutectics may result.
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679
THE SORET EFFECT AND SUPERSTRUCTURES IN EUTECT1C COMPOSiTES
R. E. JESSE Philips Research Laboratories, N. V. Philips’ Gloeilampenfabrieken, Eindhoven, The Netherlands
When a two-phase composite is grown from a eutectic melt by the Czochralski technique, one of the phases is found to be ordered in dish-like two-phase regions perpendicular to the direction of growth. These twophase regions, which in the case considered consist of needles directed parallel to the direction of growth in a single-phase matrix, are separated from each other by single-phase regions. This formation of a superstructure is related to ternperature fluctuations in the melt near the solid—liquid interface. These temperature fluctuations result in growth rate fluctuations. It has been shown that in principle the Soret effect must be taken into account
in the considerations ofgrowth kinetics. In single-phase systems with k0 < 1, the contribution of the Soret effect to the composition of the boundary layer is of minor importance. However, in the case of eutectic systems it gives a relatively important contribution to the concentration in the boundary layer. This contribution amounts to 1 % of the concentration CE of the eutectic melt but can be considerably more for systems with a large thermal diffusion coefficient or in cases where the temperature gradient is steep. In cornbination with growth rate fluctuations superstructures as observed in Czochralski-grown eutectics may result.
xv-1o