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Containerless Processing of a Lithium Disilicate GlassGlasses of Li2O.2SiO2 (LS2), and LS2 doped with 0.001wt% platinum (LS2 + 0.001 wt% Pt) compositions were melted, cooled and reheated at controlled rates while levitated (containerless) inside an Electrostatic Levitator (ESL) furnace at the NASA Marshall Space Flight Center, Huntsville, AL. The experiments were conducted in vacuum (approximately 10(exp -5) Pa) using spherical, 2.5 to 3 millimeter diameter, glass samples. The measured critical cooling rate for glass formation, R(sub c), for the LS2 and LS2+0.001 wt% Pt glasses processed at ESL were 14 plus or minus 2 Celsius per minute and 130 plus or minus 5 Celsius per minute, respectively. The values of R(sub c), for the same LS2 and LS2 + 0.001 wt% Pt glasses processed in a container were 62 plus or minus 3 Celsius per minute and 162 plus or minus 5 Celsius per minute, respectively. The effective activation energy for crystallization, E, for this LS2 glass processed without a container at ESL, 392 plus or minus 15 kiloJoules per mole, was higher than that, 270 plus or minus 15 kiloJoules per mole, for an identical glass processed in a container. These results suggest that the glass formation tendency for a containerless LS2 melt is significantly increased compared to an identical melt in contact with a container. The absence of heterogeneous nucleation sites that are inherently present in all melts held in containers, and or a change in the surface composition due to evaporation of Li2O during processing at ESL are likely reasons for the increased glass forming tendency of this containerless LS2 melt.
Document ID
20040085916
Acquisition Source
Marshall Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Ranasinghe, Kisa
(Missouri Univ. Rolla, MO, United States)
Ray, Chandra S.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Day, Delbert E.
(Missouri Univ. Rolla, MO, United States)
Rogers, Jan R.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Hyers, Robert W.
(Massachusetts Univ. Amherst, MA, United States)
Rathz, Thomas
(Alabama Univ. Huntsville, AL, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 2004
Subject Category
Solid-State Physics
Distribution Limits
Public
Copyright
Other

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