Engineering topics

Weber, J. K. R.

Publications and source records attributed to Weber, J. K. R..

6 records

NASA NTRS1994

Containerless liquid-phase processing of ceramic materials

Containerless melting and solidification provides a powerful tool for investigation and synthesis of ceramic and glass materials. The work described in this article explored and extended the limits of ground-based experimentation by using aero-acoustic and aerodynamic levitation in combination with laser beam heating and melting to investigate ceramic and glass processing. Results of liquid-phase processing experiments on calcia-gallia and calcia-gallia-silica glass-forming mixtures, aluminum oxide, and ceramic superconductors are summarized. The work is discussed in the context of low gravity experimental and materials synthesis requirements and opportunities.

Weber, J. K. R.↗

NASA NTRS1993

Optical properties and spectral emissivities at 632.8 nm in the titanium-aluminum system

Optical properties (including spectral emissivity, refractive index, and extinction coefficient) of liquid Ti-Al alloys were measured as functions of temperature (including temperatures up to 350 K below the equilibrium liquidus temperatures), using laser ellipsometry at 632.8 nm. The experiments were conducted under containerless conditions, using electromagnetic levitation and heating supplemented by CO2 laser beam heating. It is shown that the emissivities of liquid Ti-Al alloy vary with temperature in a manner that can be understood by the same theories which are applicable to solid metals, for regions near to and above the liquidus temperature. At temperatures below the liquidus temperature, the optical properties of highly undercooled liquid Ti-Al alloys are not dependent on temperature.

Krishnan, S.↗

NASA NTRS1991

The use of containerless processing in researching reactive materials

It has recently become possible to perform containerless, high-temperature liquid-phase processing of many nonvolatile materials without resort to orbital microgravity, thereby facilitating the conduct of materials research in conjunction with noncontact diagnostic instruments. The melt-levitation techniques are electromagnetic, aerodynamic, acoustic, aeroacoustic, and electrostatic; nonorbital microgravity conditions are obtainable aboard NASA's KC-135 aircraft on parabolic flight paths, as well as in drop tubes and towers. Applications encompass the purification of metals and the creation of nonequilibrium and metastable structures. Process control and property measurements include optical pyrometry and emissivity, laser polarimetry, and drop calorimetry.

Weber, J. K. R.↗

NASA NTRS1991

Non-contact temperature measurement

Three methods for noncontact temperature measurement are presented. Ideal gas thermometry is realized by using laser-induced fluorescence to measure the concentration of mercury atoms in a Hg-Ar mixture in the vicinity of hot specimens. Emission polarimetry is investigated by measuring the spatially resolved intensities of polarized light from a hot tungsten sphere. Laser polarimetry is used to measure the optical properties, emissivity, and, in combination with optical pyrometry, the temperature of electromagnetically levitated liquid aluminum. The precision of temperature measurements based on the ideal gas law is + or - 2.6 percent at 1500-2000 K. The polarized emission technique is found to have the capability to determine optical properties and/or spectral emissivities of specimens over a wide range of wavelengths with quite simple instruments.

Nordine, Paul C.↗

NASA NTRS1991

Optical and thermodynamic property measurements of liquid metals and alloys

Optical properties and spectral emissivities of liquid silicon, titanium, niobium, and zirconium were investigated by HeNe laser polarimetry at 632.8 nm. The metals were of a high purity and, except for zirconium, clean. The more demanding environmental requirements for eliminating oxide or nitride phases from zirconium were not met. Containerless conditions were achieved by electromagnetic levitation and heating. CO2 laser beam heating was also used to extend the temperature range for stable levitation and to heat solid silicon to form the metallic liquid phase. Corrections to previously reported calorimetric measurements of the heat capacity of liquid niobium were derived from the measured temperature dependence of its spectral emissivity. Property measurements were obtained for supercooled liquid silicon and supercooling of liquid zirconium was accomplished. The purification of liquid metals and the extension of this work on liquids to the measurement of thermodynamic properties and phase equilibria are discussed.

Weber, J. K. R.↗

NASA NTRS1991

Stabilised electromagnetic levitation at 2-13 MHz

SEL, the Stabilised Electromagnetic Levitator, has been developed to exploit the unique design opportunities available in containerless microgravity experiments. Efficiency and versatility are obtained with multiple coils driven by individual broadband amplifiers whose phase and frequency are controlled. The heating and positioning fields are decoupled. Specimen translation, spin, and for liquids, shape may be adjusted. An open coil structure provides access for optical and diagnostic probes. Results of experiments with a prototype device are discussed. Levitating and heating materials on earth were demonstrated at frequencies up to 13 MHz.

Danley, T. J.↗