Solute distribution in KNbO3 melt-solution and its effect on dendrite growth during rapid solidification |
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Authors: | Pan Xiu-Hong Jin Wei-Qing Liu Yan and Ai Fei |
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Institution: | Shanghai Institute of Ceramics, Chinese Academy of
Sciences,
Shanghai 200050, China |
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Abstract: | This paper reports that the rapid solidification of mixed
Li2B4O7 and KNbO3 melted in a Pt loop heater has
been performed experimentally by the method of quenching, and
various morphologies of KNbO3 crystals have been observed in
different regions of the quenched melt-solution. Dendrites were
formed in the central region where mass transfer is performed by
diffusion, whereas polygonal crystals with smooth surface grew in
the marginal region where convection dominates mass transport. Based
on measurement of KNbO3 concentration along crystal interface
by electronic probe analysis, it finds the variety of crystal
morphologies, which is the result of different solute distributions:
in the central region the inhomogeneity of solute concentration is
much sharper and morphological instability is easier to take place;
nevertheless in the marginal region the concentration homogeneity
has been greatly enhanced by convection which prevents the
occurrence of morphological instability. Additional solute
distribution in the melt along the primary dendrite trunk axis as
well as that in mushy zones has also been determined. Results show
that the solute concentration in the liquid increases linearly with
distance from the trunk tip and more solutes were found to be
concentrated in mushy zones. The closer the mushy zone is to trunk
tip, the lower the solute concentration will be there. |
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Keywords: | rapid solidification KNbO3
melt-solution solute distribution dendrite growth |
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