An electrostatic levitator for high-temperature containerless materials processing in 1-g

Abstract

This article discusses recent developments in high-temperature electrostatic levitation technology for containerless processing of metals and alloys. Presented is the first demonstration of an electrostatic levitation technology which can levitate metals and alloys (2-4 mm diam spheres) in vacuum and of superheating-undercooling-recalescence cycles which can be repeated while maintaining good positioning stability. The electrostatic levitator (ESL) has several important advantages over the electromagnetic levitator. Most important is the wide range of sample temperature which can be achieved without affecting levitation. This article also describes the general architecture of the levitator, electrode design, position control hardware and software, sample heating, charging, and preparation methods, and operational procedures. Particular emphasis is given to sample charging by photoelectric and thermionic emission. While this ESL is more oriented toward ground-based operation, an extension to microgravity applications is also addressed briefly. The system performance was demonstrated by showing multiple superheating-undercooling-recalescence cycles in a zirconium sample ( T, = 2 128 K) . This levitator, when fully matured, will be a valuable tool both in Earth-based and space-based laboratories for the study of thermophysical properties of undercooled liquids, nucleation kinetics, the creation of metastable phases, and access to a wide range of materials with novel properties.

Noncontact technique for measuring surface tension and viscosity of molten materials using high temperature electrostatic levitation

“…Other details about the HTESL are given in an earlier publication. 7 To excite the drop oscillations a few modifications had to be made to the existing electrostatic levitator. These included the insertion of an ac voltage amplifier between the bottom electrode and the electric ground as schematically shown in Fig.…”

Experimental determination of a time–temperature-transformation diagram of the undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy using the containerless electrostatic levitation processing technique

“…6,7 The sample temperature was measured using an E 2 T pyrometer ͑model 7000ET-1HR͒. Prior to the temperature measurements, the pyrometer was calibrated using the known eutectic temperature of 937 K. Initially, the molten sample was cooled radiatively to a predetermined temperature by blocking the heating source of a xenon arc lamp.…”

“…This lends the material to experimental study of its undercooling and solidification behavior. The containerless high-temperature high-vacuum electrostatic levitation ͑HTHVESL͒ processing technique 6 permits comprehensive studies of thermophysical properties in deeply undercooled liquid metals. By applying the HVHTESL technique to the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 alloy, for example, the authors found that proper thermal treatment during solification results in the ''self-fluxing'' of the melt, allowing it to successfully undercool down to the glass transition with cooling rates of about 1 K/s.…”

Metallic glass formation in highly undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 during containerless electrostatic levitation processing

“…Modest cooling rates of 10 3 K/s or less have been applied to attain deep undercoolings in many binary and ternary alloys such as Pd-Si, 2 Pd-Cu-Si, 3 Au-Pb-Sb, 4 and Pd-Ni-P. 3,5 Very slow cooling rates ͑0.3 K/s or less͒ have resulted in sufficiently large undercooling to form glassy Te-Cu alloys in the form of a fine droplet emulsion. 6 To achieve a deeply undercooled liquid state, high-temperature high-vacuum electrostatic levitation 7 has been developed as a containerless process which eliminates the need for a melt containment vessel that often initiates heterogeneous nucleation. Recently, the undercooled melt of a Zr-Ti-Cu-Ni-Be alloy has been found to exhibit extremely high thermal stability.…”