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A vacuum cell for obtaining clean surfaces on liquid low melting point metals
Vacuum/volume
48/number G/pages 551 to 55211997 0 1997 Elsevier Science Ltd Printed in Great Britain. All riahts reserved 0042-207X/57 $17.00+.00
PII: s0042-207x(97)00016-x
A vacuum cell for obtaining clean surfaces on liquid low melting point metals A Simanovskis,” J Maniks,*” A Bojarevicsb and Yu Gelfgat,b ainstitute of Solid State Physics, University of Latvia, 8 Kengaraga St., Riga LV1063, Latvia; blnstitute of Physics, Latvian Academy of Sciences, Salaspils LV 2169, Latvia received
21 December
7996
Clean oxide film-free surface of liquid gallium was obtained in a sealed vacuum cell with a glass lid for observation. The cell was evacuated to high vacuum f lop4 Pa) before admission of liquid and sealing. The surface contamination was about Z-5% of the free area and did not exhibit noticeable increase during several months of storing and employing the cell. The cell described allows observation of surface flows, capillary phenomena and crystallization processes under different conditions. 0 1997 Elsevier Science Ltd. All rights reserved
Thermocapillary convection on the surfaces of liquid metals is known to play an important role in the processes of crystal growth and fusion welding.‘,2 However, such surface tensiondriven flow can be observed only on clean oxide film-free surfaces. Though there are several ways of obtaining clean surfaces of liquid metals (mechanical or thermal cleaning, ion bombardment in ultrahigh vacuum, etc.)3*4 there is still interest in finding new possibilities in this area. In the present paper a simple method for obtaining clean surfaces of liquid low-melting metals by the use of an autonomous vacuum sealed cell is described. Preparation of the cell has been performed using high vacuum ( 10m4Pa) equipment. The idea of the method is to introduce noncontaminated liquid metal from the bulk of the melt into the vacuum cell and ensure conditions for maintaining surface cleanliness during the experiments: the amount of residual and desorbed gases as well as gases penetrating the cell must be less than is necessary to form a continuous metal oxide film on the melt surface. To put the idea into practice a vacuum cell has been designed as shown in Figure 1. The internal diameter of the cell was 4 cm and its volume was 15 cm3. The cell consists of a stainless steel cup, lead gasket, viewport (glass lid), flange and a pipe for introducing the liquid metal. The elbowed pipe serves as a valve when the trapped melt solidifies. The design of the cell allows a temperature gradient to be created and measured in the melt by locating a heating and cooling system to its bottom wall. The glass viewport ensures visual monitoring of the surface flow velocities and flow-produced surface deformations. The assembly including the cell with a valve 1, pipeline, valves 2 and 3, pool
*To whom all correspondence
should be addressed
with melt and surrounding heater (see Figure 1) was fitted with the vacuum system allowing it to reach 10M4Pa. Liquid gallium as a model object for investigations of thermocapillary flows was used for experiments. The procedure of introducing gallium into the cell includes the following operations. First, the outgassing of the entire set-up is carried out at 550-570 K for 50 h. Then the valve 2 is closed and the required quantity of liquid gallium with initially clean surface is introduced from the bulk of the melt into the cell by opening the valve 3. The excess melt through the valve 2 is allowed to flow out of pipelines. Some of the melt is trapped in valve 1, which seals the cell off from the rest of the vacuum chamber. After solidification of gallium in valve 1 the cell is separated from the vacuum chamber. Our observations have shown that the above described method allows a clean liquid gallium surface to be obtained with only 25% of its area covered with impurity particles. The described cell was used for investigations of capillary flows in liquid layers of
Valve,3
1,
\ Heater
c)
Valve
Figure 1. A schematic view of the cell and the set-up for introducing liquid metal into the cell.
the
551
A Simanovskis
et al: Liquid low melting
point metals
gallium.5,6 Surface velocities were measured by recording the motion of impurity particles used as tracers. Applying thermal gradient to liquid gallium produces surface flows in the melt as indicated by the moving particles (Figure 2). Their independent movement and high mobility (0.5 cm/s at 35 K/cm) give evidence of the absence of a continuous oxide film on surface of the melt. Observed behaviour agrees with that for liquid gallium under the conditions of UHV.3 Figure 3(a) shows oxide particles are gathered by applying a thermal source to the cup bottom. Magnetic field causes their rotation as seen in Figure 3(b). The surface contamination for the melt does not exhibit noticeable increase during several months of storing and employment of the cell. The described cell allows observation of flows on clean surfaces of liquid metals as well as capillary phenomena and crystallization processes under different excitations.
Figure 3. An optical micrograph of the free surface of liquid gallium. (a) the conglomerate of gathered particles is seen in the centre and (b) its rotation under the influence of magnetic field. The soft contrast features are reflections.
References
Figure 2. A view of the free surface of liquid galli& on it. Micrograph has been obtained by computer video images.
552
with moving particles matching the separate
1. Tison, P., Camel, D., Tosello I. and Favier, J.J., Proc. 1st Int. .S.WI~. on Hydromechanics and Heat/Mass Transfkr in MicrograritF, PermMoscow, Russia, eds Gordon and Breach, 1991, p. 121. 2. DebRoy, T. and David, S.A., Recieti’s of ModernPhysics, 1995, 67. 85. 3. Fine, J., Hardy, S.C. and Andreadis, T.D., J. Var. Sci. T&no/., 1981. 18, 1310. 4. Trittibach, R., Griitter, Ch. and Bilgram, J.H., Phys. Rev. B, 1994,50, 2529. 5. Bojarevics, A., Gelfgat, Yu., Gerbeth, G., Proc. 2nd Int. Con/: on Energy Transfer in Magnetohydrodynamic Flows, Aussois, France, Vol. 1, 1994, p. 117. 6. Bojarevics, A., Gelfgat. Yu., Gerbeth, G., Simanovskis, A. and Maniks, J., Abstr of 8th Beer-Sheoa International Seminar on MHD,POWSand Turbulence, Jerusalem, Israel, 1996, p. 13.
48/number G/pages 551 to 55211997 0 1997 Elsevier Science Ltd Printed in Great Britain. All riahts reserved 0042-207X/57 $17.00+.00
PII: s0042-207x(97)00016-x
A vacuum cell for obtaining clean surfaces on liquid low melting point metals A Simanovskis,” J Maniks,*” A Bojarevicsb and Yu Gelfgat,b ainstitute of Solid State Physics, University of Latvia, 8 Kengaraga St., Riga LV1063, Latvia; blnstitute of Physics, Latvian Academy of Sciences, Salaspils LV 2169, Latvia received
21 December
7996
Clean oxide film-free surface of liquid gallium was obtained in a sealed vacuum cell with a glass lid for observation. The cell was evacuated to high vacuum f lop4 Pa) before admission of liquid and sealing. The surface contamination was about Z-5% of the free area and did not exhibit noticeable increase during several months of storing and employing the cell. The cell described allows observation of surface flows, capillary phenomena and crystallization processes under different conditions. 0 1997 Elsevier Science Ltd. All rights reserved
Thermocapillary convection on the surfaces of liquid metals is known to play an important role in the processes of crystal growth and fusion welding.‘,2 However, such surface tensiondriven flow can be observed only on clean oxide film-free surfaces. Though there are several ways of obtaining clean surfaces of liquid metals (mechanical or thermal cleaning, ion bombardment in ultrahigh vacuum, etc.)3*4 there is still interest in finding new possibilities in this area. In the present paper a simple method for obtaining clean surfaces of liquid low-melting metals by the use of an autonomous vacuum sealed cell is described. Preparation of the cell has been performed using high vacuum ( 10m4Pa) equipment. The idea of the method is to introduce noncontaminated liquid metal from the bulk of the melt into the vacuum cell and ensure conditions for maintaining surface cleanliness during the experiments: the amount of residual and desorbed gases as well as gases penetrating the cell must be less than is necessary to form a continuous metal oxide film on the melt surface. To put the idea into practice a vacuum cell has been designed as shown in Figure 1. The internal diameter of the cell was 4 cm and its volume was 15 cm3. The cell consists of a stainless steel cup, lead gasket, viewport (glass lid), flange and a pipe for introducing the liquid metal. The elbowed pipe serves as a valve when the trapped melt solidifies. The design of the cell allows a temperature gradient to be created and measured in the melt by locating a heating and cooling system to its bottom wall. The glass viewport ensures visual monitoring of the surface flow velocities and flow-produced surface deformations. The assembly including the cell with a valve 1, pipeline, valves 2 and 3, pool
*To whom all correspondence
should be addressed
with melt and surrounding heater (see Figure 1) was fitted with the vacuum system allowing it to reach 10M4Pa. Liquid gallium as a model object for investigations of thermocapillary flows was used for experiments. The procedure of introducing gallium into the cell includes the following operations. First, the outgassing of the entire set-up is carried out at 550-570 K for 50 h. Then the valve 2 is closed and the required quantity of liquid gallium with initially clean surface is introduced from the bulk of the melt into the cell by opening the valve 3. The excess melt through the valve 2 is allowed to flow out of pipelines. Some of the melt is trapped in valve 1, which seals the cell off from the rest of the vacuum chamber. After solidification of gallium in valve 1 the cell is separated from the vacuum chamber. Our observations have shown that the above described method allows a clean liquid gallium surface to be obtained with only 25% of its area covered with impurity particles. The described cell was used for investigations of capillary flows in liquid layers of
Valve,3
1,
\ Heater
c)
Valve
Figure 1. A schematic view of the cell and the set-up for introducing liquid metal into the cell.
the
551
A Simanovskis
et al: Liquid low melting
point metals
gallium.5,6 Surface velocities were measured by recording the motion of impurity particles used as tracers. Applying thermal gradient to liquid gallium produces surface flows in the melt as indicated by the moving particles (Figure 2). Their independent movement and high mobility (0.5 cm/s at 35 K/cm) give evidence of the absence of a continuous oxide film on surface of the melt. Observed behaviour agrees with that for liquid gallium under the conditions of UHV.3 Figure 3(a) shows oxide particles are gathered by applying a thermal source to the cup bottom. Magnetic field causes their rotation as seen in Figure 3(b). The surface contamination for the melt does not exhibit noticeable increase during several months of storing and employment of the cell. The described cell allows observation of flows on clean surfaces of liquid metals as well as capillary phenomena and crystallization processes under different excitations.
Figure 3. An optical micrograph of the free surface of liquid gallium. (a) the conglomerate of gathered particles is seen in the centre and (b) its rotation under the influence of magnetic field. The soft contrast features are reflections.
References
Figure 2. A view of the free surface of liquid galli& on it. Micrograph has been obtained by computer video images.
552
with moving particles matching the separate
1. Tison, P., Camel, D., Tosello I. and Favier, J.J., Proc. 1st Int. .S.WI~. on Hydromechanics and Heat/Mass Transfkr in MicrograritF, PermMoscow, Russia, eds Gordon and Breach, 1991, p. 121. 2. DebRoy, T. and David, S.A., Recieti’s of ModernPhysics, 1995, 67. 85. 3. Fine, J., Hardy, S.C. and Andreadis, T.D., J. Var. Sci. T&no/., 1981. 18, 1310. 4. Trittibach, R., Griitter, Ch. and Bilgram, J.H., Phys. Rev. B, 1994,50, 2529. 5. Bojarevics, A., Gelfgat, Yu., Gerbeth, G., Proc. 2nd Int. Con/: on Energy Transfer in Magnetohydrodynamic Flows, Aussois, France, Vol. 1, 1994, p. 117. 6. Bojarevics, A., Gelfgat. Yu., Gerbeth, G., Simanovskis, A. and Maniks, J., Abstr of 8th Beer-Sheoa International Seminar on MHD,POWSand Turbulence, Jerusalem, Israel, 1996, p. 13.