The analysis and minimization of oxygen contamination in the powder processing of molybdenum disilicide (open access)

The analysis and minimization of oxygen contamination in the powder processing of molybdenum disilicide

Problems with MoSi{sub 2} include low-temperature fracture toughness, high-temperature creep resistance, and ``pest`` phenomena. Oxygen introduced by powder processing may be the cause of some of these problems. This study led to the following conclusions: Supplied powders have significant oxygen present prior to processing (up to 2.5 %), in the form of silica on the surface. This oxygen contamination did not increase by exposure to air at room temperature. An improved powder processing method was developed that uses glass encapsulation. Analysis of microstructures created from powders that contained 4900 to 24,100 ppM oxygen showed that the silica was transferred to the fully dense MoSi{sub 2} as SiO{sub 2} inclusions. A method of producing MoSi{sub 2} with less oxygen was attempted.
Date: April 24, 1994
Creator: Shannon, K.
Object Type: Thesis or Dissertation
System: The UNT Digital Library
GPHS-RTGs in support of the Cassini Mission. Semiannual technical progress report, 27 September 1993--27 March 1994 (open access)

GPHS-RTGs in support of the Cassini Mission. Semiannual technical progress report, 27 September 1993--27 March 1994

This report is organized by the program task structure as follows: (1) spacecraft integration and liaison; (2) engineering support; (3) safety; (4) qualified unicouple fabrication; (5) ETG fabrication, assembly, and test; (6) ground support equipment (GSE); (7) RTG shipping and launch support; (8) designs, reviews, and mission applications; (9) project management, quality assurance and reliability, contract changes, non-capital CAGO acquisition, and CAGO maintenance; and (H) contractor acquired government owned property (CAGO) acquisition.
Date: April 24, 1994
Creator: unknown
Object Type: Report
System: The UNT Digital Library
The mechanism of the oligomerization of thiophene-based para-quinodimethanes (open access)

The mechanism of the oligomerization of thiophene-based para-quinodimethanes

For the last decade, the Trahanovsky research group has focused on the study of various reactive molecules such as o-quinodimethanes (o-QDM`s) and p-quinodimethanes (p-QDM`s) derived from benzene, furan, and thiophene. These types of molecules are reactive and dimerize or polymerize at room temperature. One of the group`s interests is to understand the dimerization mechanism of these molecules. Paper 1 describes the preparation and dimerization product analyses of 2-ethylidene-5-methylene-2,5-dihydrothiophene. Insights provided by these results into the mechanism of the dimerization of 2,5-dimethylene-2,5-dihydrothiophene are discussed. In paper 2, a convenient synthesis of cyclooctadecane is presented.
Date: April 24, 1994
Creator: Wang, Yili
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Support minimized inversion of acoustic and elastic wave scattering (open access)

Support minimized inversion of acoustic and elastic wave scattering

This report discusses the following topics on support minimized inversion of acoustic and elastic wave scattering: Minimum support inversion; forward modelling of elastodynamic wave scattering; minimum support linearized acoustic inversion; support minimized nonlinear acoustic inversion without absolute phase; and support minimized nonlinear elastic inversion.
Date: April 24, 1994
Creator: Safaeinili, A.
Object Type: Thesis or Dissertation
System: The UNT Digital Library