TEMPERATURE OSCILLATIONS IN EUTECTIC ALLOY MELT FOR THE BRIDGMAN-STOCKBARGER CONFIGURATION

The characteristics of the temperature field in AlZn, AlGe, PbSn, and Sb-InSb low-melting alloy eutectics were determined by means of the Br idgman-Stockbarger method of directional solidification with a specime n fixed in a graphite ampoule and a moving furnace. The device could b e rotated in such a way, that an arbitrary angle alpha between the axi al temperature gradient in the melt and the gravity field vector could be set. Periodic and/or nonperiodic temperature fluctuations indicati ng periodic and/or nonperiodic turbulent convection up to an angle alp ha = 80 degrees were studied in the individual systems. At larger angl es laminar convection can be expected. The frequency of the temperatur e oscillations is the same along the entire length of the specimen, wh ilst the amplitudes of the temperature oscillations depend on the situ ation of the measurement in the specimen. It has been found that the z one of unstable periodic convection is reduced with an increase of the axial temperature gradient and a decrease of the H/d ratio for a cyli ndrical ampoule. The convection instability threshold in the ampoule i ncreases with the deviation of the ampoule axis from the axis of the v ertical unstable arrangement, i.e. from the direction of the gravity v ector. The threshold of the laminar now instability and the onset of t urbulent flow increases with the H/d ratio, i.e. an ampoule with a hig her H/d ratio stabilizes laminar flow.