Tank waste treatment science task quarterly report, April 1995--June 1995

This report describes the work performed by the Pacific Northwest Laboratory (PNL) during the third quarter of FY 1995 under the Tank Waste Treatment Science Task of the Tank Waste Remediation System (TWRS) Pretreatment Technology Development Project. Work was performed in the following areas: (1) analytical methods development, (2) sludge dissolution modeling, (3) sludge characterization studies, (4) sludge component speciation, (5) pretreatment chemistry evaluation, and (6) colloidal studies for solid-liquid separations

New tight-binding pair potentials for mineral oxides: Application to. beta. -cassiterite (110),. beta. -tridymite (10 1 0) and cristobalite (110)

Tight-binding, total-energy (TBTE) methods have successfully predicted surface atomic geometries for a variety of semiconducting and insulating materials that are well described by a nearest-neighbor model of interatomic interactions. However, little work has been done on distant-neighbor models, which are required to study many important mineral oxides. In this paper we demonstrate one way in which the TBTE methodology can be extended to these materials. To illustrate this approach, we calculate surface atomic structures for cassiterite SnO{sub 2} (110), {beta}-cristobalite SiO{sub 2}(110) and {beta}-tridymite SiO{sub 2} (10T0)

Tank Waste Treatment Science Task quarterly report for January--March 1995

The pretreatment Technology Development Project is one of seven Tank Waste Remediation (TWRS) System projects being conducted at the Pacific Northwest Laboratory. A key objective of this Project, and of the Tank Waste Treatment Science Task within it, is to provide the technical basis and scientific understanding to support TWRS baseline decisions and actions; in particular, TPA Milestone M50-03, the 1998 sludge pretreatment decision regarding the level of pretreatment to be incorporated into the tank waste process flowsheets. Work performed by this task during the second quarter of FY 1995 (January--March 1995) is detailed in this report. Work for the first quarter reported in Tank Waste Treatment Science Task, Quarterly Report for October--December 1994

Tank Waste Treatment Science Task quarterly report for October--December 1994

The Pretreatment Technology Development Project is one of seven Tank Waste Remediation System (TWRS) projects being conducted at Pacific Northwest Laboratory (PNL). A key objective of this project, which includes the Tank Waste Treatment Science Task, is to provide the technical basis and scientific understanding to support TWRS baseline decisions and actions, in particular, the 1998 sludge pretreatment decision regarding the level of pretreatment to be incorporated into the tank waste process flowsheets being developed by Westinghouse Hanford Company. This report details work performed by the Tank Waste Treatment Science Task during the first quarter of FY 1995 (October--December 1994) in support of the project objective. Specific activities discussed in the main text are: analytical methods development; sludge dissolution modeling; sludge characterization studies; sludge component speciation; pretreatment chemistry evaluation; and colloidal studies for solid-liquid separations

Electronic structure and photophysical properties of polyimides

The quantum mechanical AM1 and CNDO/S3 models were used to examine the effect of isoelectronic substitutions on the conformation, electronic structure, and optical absorption spectra for a series of aromatic polyimides. An analysis of the geometric changes at the substitution site and its effect on the electronic structure allowed for the prediction of changes in the ICT band of the optical absorption spectra