Thermophysical and optical property measurements of electromagnetically levitated liquid metals

[摘要] Electromagnetic levitation was used in conjunction with drop calorimetry to determine the enthalpy increments and heats of fusion of an Al-Ni bronze and a Ni-based superalloy. The results showed some curvature to the enthalpy data in the two phase region (solid-liquid). Additionally, excellent agreement was seen with the measured specific heats for the liquid, C$sb{m p}$(l), with those calculated with the Neumann-Koop sum rule. Further, a unique multiple-view photographic technique was developed for the determination of liquid metal densities at elevated temperatures.High speed photography utilizing film and video techniques and a technique utilizing laser reflectance were used to study liquid metal droplet dynamics. These included electromagnetic levitation studies of Cu, Ni, and Ni-base alloys. Initial experiments revealed interesting dynamics of the droplets that included axisymmetric oscillation, rotation, and oscillation mode changes. Based on the photographic and FFT information, it was possible to extract liquid metal surface tensions.The development of a unique, non-contact, temperature measurement device utilizing rotating analyzer ellipsometry is described. The technique circumvents the necessity of spectral emissivity estimation by direct measurement concomitant with radiance brightness. Initial studies involved the measurement of the optical properties and spectral emissivities at 633 nm for several resistively heated metals. These metals included Hf, Ir, Mo, Nb, Pd, Pt, V and Ta, and were studied in the temperature range 1000-2500 K. Additionally, the oxidation behavior of iridium was studied.Using this approach, the optical properties of electromagnetically levitated liquid metals Cu, Ag, Au, Ni, Pd, Pt, Zr were measured in situ as a function of temperature and wavelength. These measurements were performed at 1064, 632.8, 514.5 and 488 nm. Temperature dependence was examined up to 600 K superheat in the liquid. Additionally, measurements on the levitated undercooled liquid and solid were also performed.The data suggests an increase in the emissivity of the liquid compared with the incandescent solid. Moderate temperature dependence of the dielectric constants and spectral emissivities were observed for the liquid metals studied. The temperature dependence appeared to be stronger when the wavelength of the light was near an absorption edge. The spectral emissivity of the undercooled liquids were virtually the same as that of the liquid but slighlly lower for moderate undercoolings ($<$50 K). Excellent agreement with available data for dielectric constants and refractive indices was seen.

[发布机构] Rice University

[效力级别] Materials