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Lacy, L. L.

Publications and source records attributed to Lacy, L. L..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

High-temperature containerless calorimeter

A high-temperature (greater than 1500 K) containerless calorimeter is described and its usefulness demonstrated. The calorimeter uses the technique of omnidirectional electron bombardment of pendant drops to achieve an isothermal test environment. The small heat input into the sample (i.e., 15-50 W) can be controlled and measured. The apparatus can be used to determine the total hemispherical emissivity, specific heat, heat of fusion, surface tension, and equilibrium melting temperature of small molten drops in the temperature range of 1500 to 3500 K. The total hemispherical emissivity and specific heat of pure niobium and two alloys of niobium-germanium have been measured in the temperature range of 1700 to 2400 K. As reported in the literature, the total hemispherical emissivity varied as a function of temperature. However, specific heat values for both the pure metal and alloys seem to be independent of temperature. Specific heat for the liquid alloy phase was also measured and compared to the solid phase.

Robinson, M. B.↗
NASA NTRS1983

Method and apparatus for supercooling and solidifying substances

An enclosure provides a containerless environment in which a sample specimen is positioned. The specimen is heated in the containerless environment, and the specimen melt is dropped through the tube in which it cools by radiation. The tube is alternatively backfilled with an inert gas whereby the specimen melt cools by both radiation and convection during its free fall. During the free fall, the sample is in a containerless, low-gravity environment which enhances supercooling in the sample and prevents sedimentation and thermal convection influences. The sample continues to supercool until nucleation occurs which is detected by silicon photovoltaic detectors. The sample solidifies after nucleation and becomes completely solid before entering the detachable catcher. The amount of supercooling of the specimen can be measured by knowing the cooling ratio and determining the time for nucleation to occur.

Lacy, L. L.↗
NASA NTRS1982

Optical Studies of model binary miscibility gap system

In order to develop a better understanding of separation processes in binary miscibility gap metal alloys, model transparent fluid systems were studied. The system selected was diethylene glycol-ethyl salicylate which has convenient working temperatures (288 to 350 K), low toxicity, and is relatively easy to purify. The system is well characterized with respect to its phase diagram, density, surface and interfacial tensions, viscosity and other pertinent physical properties. Studies of migration of the dispersed phase in a thermal gradient were performed using conventional photomicroscopy. Velocities of the droplets of the dispersed phase were measured and compared to calculated rates which included both Stokes and thermal components. A holographic microscopy system was used to study growth, coalescence, and particle motions. Sequential holograms allowed determination of particle size distribution changes with respect to time and temperature. Holographic microscopy is capable of recording particle densities up to 10 to the 7th power particles/cu cm and is able to resolve particles of the order of 2 to 3 microns in diameter throughout the entire volume of the test cell. The reconstructed hologram produces a wavefront that is identical to the original wavefront as it existed when the hologram was made. The reconstructed wavefront is analyzed using a variety of conventional optical methods.

Lacy, L. L.↗
NASA NTRS1982

Containerless undercooling and solidification of bulk metastable Nb3Ge alloys

Experiments using containerless undercooling and low-gravity solidification of Nb(1-x)Ge(x) alloys for x=0.13-0.27 have been carried out in a 32-m drop-tube apparatus to study the feasibility of forming metastable Nb3Ge in bulk form. It is found that bulk samples (2-3 mm diam) of Nb-Ge alloys with 18-22% Ge can be undercooled by large amounts (300-500 K) and solidified in a containerless environment. Subsequent quenching of the solidified samples in oil helps preserve the metastable A-15 phase by removing the latent heat of fusion and quickly cooling the samples to a stable temperature below 1000 C. Even at an undercooling of less than 100 K, the superconducting transition temperature of the material is enhanced over the cast material by about 1 K.

Lacy, L. L.↗
NASA NTRS1982

Solidification studies of Nb-Ge alloys at large degrees of supercooling

A 32 meter evacuated drop tube has been used to investigate the solidification of Nb-Ge alloys after deep undercooling. Samples have been supercooled as much as 500 K below the liquidus by using free-fall conditions to eliminate crucible induced nucleation. Final microstructures are dependent on the quenching rates at the bottom of the drop tube with a striking extension of the beta phase solubility limit at the higher quenching rates.

Lacy, L. L.↗
NASA NTRS1981

Containerless high temperature calorimeter apparatus

A calorimeter apparatus for measuring high temperature thermophysical properties of materials is disclosed which includes a containerless heating apparatus in which the specimen is suspended and heated by electron bombardment.

Lacy, L. L.↗
NASA NTRS1981

Containerless undercooling and solidification in drop tubes

A containerless low-gravity environment, produced within a 32 m drop tube apparatus, has been used to undercool and solidify metals, alloys or glasses by eliminating crucible induced nucleation processes. Niobium droplets with diameters in the range of 2 to 5 mm have been undercooled by 525 K which corresponds to the maximum undercooling reported by Turnbull and others on fine dispersions of low melting point metals. Solidification at large undercooling resulted in single crystalline spheres with the formation of interdendritic shrinkage channels on the sample surface rather than interior shrinkage cavities. The grain refinement as observed for Ni samples undercooled and solidified in fused silica crucibles does not occur in free-falling drops of Nb. A calculated solidification speed of undercooled Nb is compared to Ni. A solidification speed of 320 m/s is found for the Nb drops. This solidification speed is greater than or comparable to the solidification speeds calculated in splat cooled samples. Thus, a drop tube apparatus can be useful in the preparation and study of high temperature metastable compounds or alloys in bulk form.

Lacy, L. L.↗
NASA NTRS1980

Containerless materials processing in the laboratory

Drop tube makes possible preparation of exotic materials. The 100 foot tube is oriented precisely vertical to prevent free-falling drop from hitting tube walls. Inert-gas supply, evacuation pumps, viewing ports, and flexibility in choice of melt technique allow precise control and monitoring of solidification.

Lacy, L. L.↗
NASA NTRS1979

Containerless high-temperature calorimeter

Samples are heated by electron bombardment in high-temperature calorimeter that operates from 1,000 to 3,600 C yet consumes less that 100 watts at temperatures less than 2,500 C. Contamination of samples is kept to minimum by suspending them from wire in vacuum chamber. Various sample slopes such as wires, dishs, spheres, rods, or irregular bodies can be accommodated and only about 100 nq of samples are needed for accurate measurements.

Lacy, L. L.↗
NASA NTRS1979

Gravitational influences on the liquid-state homogenization and solidification of aluminum antimonide

Typical commercial or laboratory-prepared samples of polycrystalline AlSb contain microstructural inhomogeneities of Al- or Sb-rich phases in addition to the primary AlSb grains. The paper reports on gravitational influences, such as density-driven convection or sedimentation, that cause microscopic phase separation and nonequilibrium conditions to exist in earth-based melts of AlSb. A triple-cavity electric furnace is used to homogenize the multiphase AlSb samples in space and on earth. A comparative characterization of identically processed low- and one-gravity samples of commercial AlSb reveals major improvements in the homogeneity of the low-gravity homogenized material.

Ang, C.-Y.↗
NASA NTRS1979

Investigations on transparent liquid-miscibility gap systems

Sedimentation and phase separation is a well known occurrence in monotectic or miscibility gap alloys. Previous investigations indicate that it may be possible to prepare such alloys in a low-gravity space environment but recent experiments indicate that there may be nongravity dependent phase separation processes which can hinder the formation of such alloys. Such phase separation processes are studied using transparent liquid systems and holography. By reconstructing holograms into a commercial-particle-analysis system, real time computer analysis can be performed on emulsions with diameters in the range of 5 micrometers or greater. Thus dynamic effects associated with particle migration and coalescence can be studied. Characterization studies on two selected immiscible systems including an accurate determination of phase diagrams, surface and interfacial tension measurements, surface excess and wetting behavior near critical solution temperatures completed.

Lacy, L. L.↗
NASA NTRS1978

Determination of liquid-phase immiscibility in the lead-zinc system

A number of different techniques in the past have yielded inconsistent equilibrium measurements of immiscibility in the Pb-Zn system above 600 C. Accurate differential thermal analysis (DTA) measurements were performed on well-homogenized samples of high-purity Pb-Zn, and they indicate that the immiscibility curve is higher than previously accepted for Zn compositions between 20 and 70 at. %. The maximum deviations observed correspond to about 20 C. Below 600 C the DTA results agree with previous results.

Trahan, J. F.↗
NASA NTRS1977

Monotectic and syntectic alloys. Experiment MA-044

The flight test furnace run of the monotectic and syntectic alloys experiment was successfully performed during the Apollo-Soyuz Test Project mission in July 1975. Examination of the returned sample cartridges and the formal comparative characterization of the low-g and one-g processed samples of lead-zinc and aluminum antimonide were completed. The results for aluminum antimonide show that polycrystalline and multiphased material can be homogenize in space under low-g conditions. Microstructural study on the lead-zinc flight samples shows that complete interdiffusion of lead and zinc had not been achieved, even though the flight data indicated a soak temperature in the miscible region that was 40 K above the published consolute temperature.

Lacy, L. L.↗
NASA NTRS1976

Low-gravity homogenization and solidification of aluminum antimonide

The III-V semiconducting compound AlSb shows promise as a highly efficient solar cell material, but it has not been commercially exploited because of difficulties in compound synthesis. Liquid state homogenization and solidification of AlSb were carried out in the Apollo-Soyuz Test Project Experiment MA-044 in the hope that compositional homogeneity would be improved by negating the large density difference between the two constituents. Post-flight analysis and comparative characterization of the space-processed and ground-processed samples indicate that there are major homogeneity improvements in the low-gravity solidified material.

Ang, C.-Y.↗
NASA NTRS1976

Monotectic and syntectic alloys experiment MA-044

The flight test furnace run of the monotectic and syntectic alloys experiment was successfully performed during the Apollo Soyuz Test Project mission. All three experiment cartridges were returned intact. A second ground based test was conducted after the mission to provide one g samples with an equivalent thermal history. The examinations of all flight and ground based cartridges and ampoules have been completed. Encouraging results have been obtained in the preliminary analysis of one flight aluminum antimonide sample as compared to ground based and prototype test counterparts. In terms of reduction of the unwanted second phase, the low g sample shows a homogeneity improvement by a factor of 5 to 20. Preliminary examination of one lead zinc flight sample shows a dispersion of lead in the zinc matrix. However, complete homogenization of the material did not occur. A thermal analysis of flight data shows that the average soak temperature for the head zinc ampoules was 20 C lower than planned but 35 C above the published consolute temperature..

Ang, C. Y.↗
NASA NTRS1975

Monotectic and syntectic alloys: ASTP experiment MA-044

A postflight preliminary technical evaluation is presented of the returned samples of aluminum antimonide (AlSb) syntectic compound and lead-zinc (PbZn) monotectic immiscible processed during the Apollo-Soyuz Test Project (ASTP) mission. The returned cartridges, extracted ampoules, and removed samples were examined in detail. A genesis of the experiment is given along with a summary of the efforts and various scheduled tests up to the ASTP mission. A tentative characterization plan is developed from the postflight preliminary examination which makes use of the limited number of available samples and is based on the initial observations. It is indicated that a higher degree of compositional homogeneity in aluminum antimonide was achieved under flight test conditions.

Ang, C. Y.↗
NASA NTRS1974

The stability of liquid dispersions in low gravity

The stability of three different dispersions of oil and water prepared on Skylab 4 is compared with the same dispersions made on earth. The stability of the emulsions has been studied by two independent optical techniques. An analysis of the data indicates that all the investigated emulsions were stable over a period of 10 hr, whereas the fluids separated completely on earth in 10 sec. This experiment indicates that the rate of coalescence in low gravity is at least 3 millionths times that on earth. A knowledge of the coalescence rate in low gravity is important in the solidification of immiscible alloys in space. The parameters obtained for this experiment are compared with those of liquid metals to determine if the same stability could be achieved with immiscible alloys.

Lacy, L. L.↗