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  • 1
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    Effect of Residual Accelerations on the Crystal Growth of II-VI Semiconductors in Low Earth Orbit (2002)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The paper compares and summarizes the effects of residual acceleration during crystal growth on the compositional variation of two II-VI solid solution binary alloys (Hg(0.8)Cd(0.2)Te and Hg(0.84)Zn(0.16)Te). The crystals were grown by directional solidification on the second United States Microgravity Payload (USMP-2) and the first United States Microgravity Laboratory (USML-1) missions, respectively. For both alloys, changes in the direction and magnitude of the quasisteady acceleration vector (approximately 0.4- 1 mu g) caused large changes in the radial compositional distribution that demonstrates the importance of residual accelerations, even in the submicrogravity range, for large density gradients in the melt and slow solidification rates. The observed compositional variations will be correlated to changes in the radial flow velocities ahead of the solidification interface.
    Keywords: Space Processing
    Type: Fourteenth American Conference on Crystal Growth; Aug 04, 2002 - Aug 09, 2002; Seattle, WA; United States
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  • 2
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    Joint Launch + One Year Science Review of USML-1 and USMP-1 with the Microgravity Measurement Group (1994)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: On September 22-24, 1993, investigators from the First United States Microgravity Laboratory (USML-1) and the First United States Microgravity Payload (USMP-1) Missions met with the Microgravity Measurement Group (MGMG) in Huntsville, Alabama, to discuss science results and the microgravity environments from the respective missions. USML-1 was launched June 1992, and USMP-1 was launched October 1992. This document summarizes from the various investigations, the comprehensive results and highlights, and also serves as a combined mission report for the two missions. USML-1 was the first totally U.S.-sponsored mission dedicated to microgravity research and included 31 investigations in fluid dynamics, crystal growth, combustion, biotechnology, and technology demonstrations supported by 11 facilities. The papers in these proceedings attest to the wealth of information gleaned from the highly successful mission. On the USMP-1 mission, both the MEPHISTO and the Lambda Point experiments exceeded by over 100% their planned science objectives. The mission also marked the first time that acceleration data were down-linked and analyzed in real-time. The meeting, which concentrated on flight results, brought low-gravity investigators, accelerometer designers, and acceleration data analysis experts together. This format facilitated a tremendous amount of information exchange between these varied groups. Several of the experimenters showed results, sane for the very first time, of the effects of residual accelerations on their experiment. The proceedings which are published in two volumes also contain transcriptions of the discussion periods following talks and also submittals from a simultaneous poster session.
    Keywords: Space Processing
    Type: NASA-CP-3272-Vol-2 , M-750-Vol-2 , NAS 1.55:3272-Vol-2 , Joint Launch + One Year Science Review of USML-1 and USMP-1 with the Microgravity Measurement Group; Sep 22, 1993 - Sep 24, 1993; Huntsville, AL; United States
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  • 3
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    Viscosity Relaxation in Molten HgZnTe (2001)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: Rotating cup measurements of the viscosity of the pseudo-binary melt, HgZnTe have shown that the isothermal liquid with zinc mole fraction 0.16 requires tens of hours of equilibration time before a steady viscous state can be achieved. Over this relaxation period, the viscosity at 790 C increases by a factor of two, while the viscosity at 810 C increases by 40%. Noting that the Group VI elements tend to polymerize when molten, we suggest that the viscosity of the melt is enhanced by the slow formation of Te atom chains. To explain the build-up of linear Te n-mers, we propose a scheme, which contains formation reactions with second order kinetics that increase the molecular weight, and decomposition reactions with first order kinetics that inactivate the chains. The resulting rate equations can be solved for the time dependence of each molecular weight fraction. Using these molecular weight fractions, we calculate the time dependence of the average molecular weight. Using the standard semi-empirical relation between polymer average molecular weight and viscosity, we then calculate the viscosity relaxation curve. By curve fitting, we find that the data imply that the rate constant for n-mer formation is much smaller than the rate constant for n-mer deactivation, suggesting that Te atoms only weakly polymerize in molten HgZnTe. The steady state toward which the melt relaxes occurs as the rate of formation of an n-mer becomes exactly balanced by the sum of the rate for its deactivation and the rate for its polymerization to form an (n+1)-mer.
    Keywords: Inorganic, Organic and Physical Chemistry
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  • 4
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    Gravity Effects in Carbon Nanotube Growth by Thermal Chemical Vapor Deposition (2001)
    In:  Other Sources
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    Publication Date: 2019-07-17
    Description: Carbon nanotubes are synthesized using thermal chemical vapor deposition. The sizes of these carbon nanotubes (CNT) are quite uniform and the length of the tube is up to several tens of micrometers. With the substrate surface normal either along or against the gravity vector, different growth orientations of CNT are observed by scanning electron microscopy although the Raman spectra are similar for samples synthesized at different locations. These results suggest the gravitation effects in the growth of long and small diameter CNT.
    Keywords: Space Processing
    Type: 2nd Pan-Pacific Basin Workshop on Microgravity Sciences; May 01, 2001 - May 04, 2001; Pasadena, CA; United States
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  • 5
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    Technique for Determining the Viscosity and Electrical Conductivity of Semiconducting Liquids (2002)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: A novel apparatus for determining the viscosity and electrical conductivity of semiconducting liquids has been developed at NASA/MSFC. The apparatus is based on the transient torque technique and utilizes a 125 micrometer diameter quartz fiber as a torsion wire and a sensitive angular detector to measure the deflection angle of the crucible containing the liquid. A rotating flow is induced in the semiconducting melt by the application of a rotating magnetic field and measurement of the magnitude and transient behavior of the induced deflection angle allows the simultaneous determination of the viscosity and electrical conductivity of the melt. Measurements at room temperature and up to 900 C were made on high purity melts.
    Keywords: Inorganic, Organic and Physical Chemistry
    Type: (CIMTEC) International Conference on Modern Materials and Technologies; Jul 15, 2002; Florence; Italy
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  • 6
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    Thermophysical Properties of Liquid Te: Density, Electrical Conductivity, and Viscosity (2004)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The thermophysical properties of liquid Te, namely, density, electrical conductivity, and viscosity, were determined using the pycnometric and transient torque methods from the melting point of Te (723 K) to approximately 1150 K. A maximum was observed in the density of liquid Te as the temperature was increased. The electrical conductivity of liquid Te increased to a constant value of 2.89 x 10(exp 5 OMEGA-1m-1) as the temperature was raised above 1000 K. The viscosity decreased rapidly upon heating the liquid to elevated temperatures. The anomalous behaviors of the measured properties are explained as caused by the structural transitions in the liquid and discussed in terms of Eyring's and Bachiskii's predicted behaviors for homogeneous liquids. The Properties were also measured as a function of time after the liquid was coded from approximately 1173 or 1123 to 823 K. No relaxation phenomena were observed in the properties after the temperature of liquid Te was decreased to 823 K, in contrast to the relaxation behavior observed for some of the Te compounds.
    Keywords: Inorganic, Organic and Physical Chemistry
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