Dr. Won-Kyu Rhim

Education and professional history

2001-Present: Senior Research Associate, California Institute of Technology
2000-2001: Visiting Associate, California Institute of Technology
1972-2000: Worked at JPL as a senior scientist, technical staff, and a technical group leader in various tasks.
1971-1972: Presidential Research Fellow, California Institute of Technology.
1969-1971: Post-doctoral Research Fellow, Massachusetts Institute of Technology.
1964-1969: Ph.D. in Physics, University of North Carolina at Chapel Hill, NC
1957-1963: MS and BS in Physics, Seoul National University, Seoul, Korea.

Research Interests:

Dr. Rhim is a senior research associate of Caltech Materials Science Department. He has been using the High Temperature Electrostatic Levitator (HTESL) measuring properties of refractory materials in their molten and undercooled states. Working with Professor William Johnson and his group members he has been measuring various thermophysical properties and solidification processes of bulk glass-forming alloys. Currently he is also a principal investigator of a NASA's microgravity material science program under the title 'Measurement of Thermophysical Properties of Molten Silicon and Germanium'.
Before Dr, Rhim Joined Caltech campus in 2000 he was worked at the Jet Propulsion laboratory for 28 years in areas of technology developments for containerless science, undercooling-nucleation experiments, containerless protein crystal growth experiments, drop dynamics experiments, and the technology development for solid state NMR experiments. Dr. Rhim was instrumental in developing the High Temperature Electrostatic Levitator (HTESL). This device uses controlled electrostatic forces to isolate a molten sample in high vacuum condition allowing the melt to deeply undercool and its thermophysical properties and solidification phenomena are investigated. In addition to Temperature-Time-Transformation (TTT) curves, the HTESL can measure the specific volume, thermal expansion coefficient, the sureface tension, the viscosity, the ratio of specific heat and total hemispherical emissivity, and the electric resistivity of undercooled liquids.
In colaboration with Dr. Eugene Trinh of JPL, an electrostatic-acoustic hybrid levitator was developed. Charged liquid drops were suspended in air by controlled electrostatic forces, and their resonant oscillations and rotations were induced by applying an appropriate acoustic pressure. An extensive experimental investigation of dynamics of freely suspended liquid drops was conducted. Through this experiment, the theoretical results on the shape evolution of rotating drops was confirmed.
A new method of mass-producing monodisperse polymeric microspheres was invented and a US patent was obtained. Monodisperse monomer droplets produced by a specially designed nozzle were captured by a liquid nitrogen bath and vitrified. Monodisperse polymeric microspheres were obtained upon slow-thawing of the frozen particles after ?-ray irradiation.
In cooperation with Dr. Melvin Saffren and Dr. Daniel Elleman, both theoretical and experimental studies of dynamics of simple and compound drops were conducted. Compound drops made out of water and silicon oil were produced in a neutral buoyancy tank and the theoretical results were successfully verified.
Dr. Rhim was instrumental in the development of dipolar line narrowing techniques for the high resolution solid state NMR: The line narrowing pulse sequences known as the Rhim-Elleman-Vaughn 8-Pulse Sequence (REV-8), and the Burum-Rhim 24-Pulse Sequence (BR-24) are being used in the solid state NMR spectroscopy. Using these techniques, the strong dipolar interactions in solid phase can be selectively removed while preserving more interesting interactions such as the anisotropic chemical shifts or the exchange interactions. In cooperation with Professor Robert Vaughn at Caltech, Dr. Rhim helped complete two Ph.D’s from Caltech graduate students.
Dr. Rhim received his Ph.D. from the University of North Carolina at Chapel Hill with the discovery of a new nuclear spin echo that occurs in dipolar coupled solids. Against overwhelming belief at the time that spin-echo phenomena cannot exist in a strongly coupled many body system, existence of a new spin echo phenomena was discovered and it was experimentally demonstrated using 19F spins in CaF2 . This echo, commonly known as 'Dipolar Echo' (or 'Magic Echo'), was the first demonstration of time-reversal phenomena in the many body system..

Selected ESL Related Publications

W. K. Rhim, M. Collender, M. Hyson and D. D. Elleman, "Development of an Electrostatic Positioner for Space Materials Processing," Rev. Sci. Instrum. 56(2): 307, 1985

W-K. Rhim, M.T. Hyson, S.K. Chung, M.Colvin , M. Chang, "Containerless Polymeric Microsphere Production for Biomedical Applications," Mat. Res. Soc. Proc. 87: 225, 1987.

W-K. Rhim, S.K. Chung, and D.D. Elleman, "Experiments on Rotating Charged Liquid Drops," Proc. 3rd International Colloquium on Drops and Bubbles, AIP Conf. Proc. 197: 91, 1988.

Won-Kyu Rhim and Sang K. Chung, “Isolation of Crystallizing Droplets by Electrostatic Levitation,” METHODS: (A Companion to Methods in Enzymology) 1(1): 118-127, 1990.

G. Sridharan, W. K. Rhim, D. Barber, and S. K. Chung, “Axial-Gap Induction Motor for Levitated Specimen,” NASA Tech Briefs 16: 32, 1992.

W. K. Rhim, S. K. Chung, D. Barber, K. F. Man, Gary Gutt, A. Rulison, R. E. Spjut. "An Electrostatic Levitator for High Temperature Containerless Materials Processing in 1-g," Rev. Sci. Instrum .64: 2961, 1993.

A. Rulison and W. K. Rhim, "Containerless Measurements of Specific Heat and Hemispherical Total Emmissivity of Refractory Materials" Rev. Sci. Instrum. 65, 695-700, 1994

A. Rulison and W. K. Rhim, "Constant Pressure Specific Heat to Hemispherical Total Emissivity Ratio for Undercooled Liquid Nickel, Zirconium and Silicon" Metall. & Mat. Trans. 26B: 503-508, 1995

R. Busch, Y. J. Kim, W. L. Johnson, A. J. Rulison, W. K. Rhim, and D. Isheim, "Hemispherical total emissivity and specific heat capacity of deeply undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 melts", Appl. Phys. Letts. 66: 3111-3113, 1995

S. K. Chung, D. Thiessen, and W. K. Rhim, "A Non-Contact Measurement Technique for the Density and Thermal Expansion of Molten Materials,” Rev. of Sci. Instrum. 67(9): 3175-3181, 1996. S. K. Chung, D. Thiessen, and W. K. Rhim, Erratum on "A Non-Contact Measurement Technique for the Density and Thermal Expansion of Molten Materials,” Rev. of Sci. Instrum., 68, 2597, 1997

Y. J. Kim, R. Busch, W. L. Johnson, A. J. Rulison, and W. K. Rhim, "Metallic Glass Formation in Highly Undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 during Containerless Electrostatic Levitation Processing", Appl. Phys. Letts. 68: 1057, 1996

Y. J. Kim, R. Busch, W. L. Johnson, A. J. Rulison and W. K. Rhim, "Experimental determination of a time-temperature-transformation diagram of the undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy using the containerless electrostatic processing technique" Appl. Phys. Lett. 68, 1057-1059, 1996

A. J. Rulison, W. K. Rhim, R. Bayuzick, W. Hofmeister, and C. Morton, "Containerless liquid to solid nucleation pathway in two representative grades of commercially available zirconium", Acta Materialia 45(3): 1237-1245, 1997

W. K. Rhim, S. K. Chung, A. J. Rulison, and R. E. Spjut, "Measurements of Thermophysical Properties of Molten Silicon by a High Temperature Electrostatic Levitator", Int. J. Thermophysics 18(2): 459-469, 1997

W. K. Rhim, "Present Status of the Electrostatic Levitation Technology for Containerless Materials Processing", Microgravity Quarterly 6: 79-83, 1997

K. Ohsaka, S. K. Chung, and W. K. Rhim, A. Peker, D. Scruggs, and W. L. Johnson, "Specific volumes of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy in the liquid, glass, and crystalline phases", Appl. Phys. Lett. 70 (6), 726-728, 1997.

K. Ohsaka, S. K. Chung, W. K. Rhim, and J. C. Holzer "Densities of Si determined by an image digitizing technique in combination with an electrostatic levitator", Appl. Phys. Lett. 70,423-425, 1997

X. H. Lin, W. L. Johnson, and W. K. Rhim, "Effects of Oxygen Impurities on Crystallization on Undercooled Bulk Glass Forming Alloys", Materials Transactions, JIM. (Japanese Institute of Metal), 38, 473-477, 1997.

K. Ohsaka, S. K. Chung, and W. K. Rhim, "Specific volume and Viscosity of the Ni-Zr alloys and their influence on the undercooling and glass forming capability of the alloys", Acta Materialia 46, 4535-4542, 1998

W. K. Rhim and T. Ishikawa, "Noncontact Measurement of Resistivity of Molten Material", Review of Scientific Instruments, Vol. 69, page 3628-3633, 1998.

W. K. Rhim and T. Ishikawa, "Thermophysical Properties of Molten Germanium Measured by a High Temperature Electrostatic Levitator", Int. J. Thermophysics. 21, 429, 2000.

W. K. Rhim, K. Ohsaka, P-F. Paradis, and R. E. Spjut, "A Non-Contact Technique of Measuring Surface Tension and Viscosity of Molten Materials using Electrostatic Levitation", Rev. Sci. Instrum. 70, 2796-2801, 1999

P-F. Paradis and W. K. Rhim, "Thermophysical Properties of Zirconium at high temperatures", J. Mat. Research 14(9), 3713-19, 1999.

W. K. Rhim and P-F. Paradis, “Laser Induced Rotation of a Levitated Sample in Vacuum”, Rev. Sci. Instrum. 70, 4652-4655, 1999.

W. K. Rhim and K. Ohsaka, "Thermophysical Properties of Molten Silicon Measured by High Temperature Electrostatic Levitation" J. Crystal Growth 208, 313-321, 2000.

P-F. Paradis and W. K. Rhim, " Non-Contact Measurements of Thermophysical Properties of Titanium at High Temperature” J. Chem. Thermodynamics 32, 123-133, 2000.

W. K. Rhim and T. Ishikawa, “Noncontact surface tension measurement by drop rotation” Rev. Sci. Instrum 72,3572-3575, 2001.

Z. Zhou, S. Mukherjee, and W. K. Rhim, “Measurement of thermophysical properties of molten silicon using an upgraded electrostatic levitator” J. Crystal Growth 257, 350-358, 2003

Mukherjee, Z. Zhou, W. L. Johnson, and W. K. Rhim, “Thermophysical properties of Ni-Nb and Ni-Ni-Sn bulk-glassforming melts by containerless electrostatic levitation processing” J. Non-Cryst. Solids (accepted for publication)

Mukherjee, Z. Zhou, J. Schroers, W. L. Johnson, and W. K. Rhim, “Overheating threshold and its effect on Time-Temperature-Transformation diagrams of zirconium based bulk metallic glasses” Appl. Phys. Letts. (submitted)

Mukherjee J. Schroers, , Z. Zhou, W. L. Johnson, and W. K. Rhim, “High temperature viscosity and specific volume of bulk metallic glasses and their correlation with glassforming ability” Acta Met. Materialia (to be submitted)

W. K. Rhim, J. Schroer, S. Bossuyt, J. Li, Z. Zhou, and W. L. Johnson, “Achievement of uniform temperature of a levitated spherical sample by tetrahedral laser heating” Rev. Sci. Instrum. (to be submitted)

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