THERMODYNAMICS

The Surface Processing and Mechanics Group has substantial experience and capabilities in chemical thermodynamics. Previous efforts have ranged from determining the chemical state of nuclear fuel to predicting phase assemblages that will deposit during chemical vapor deposition. A variety of chemical thermodynamic calculation packages are available, including SOLGASMIX, ChemSage, FactSage, Thermocalc, and HSC, together with extensive thermochemical databases. Studies can be performed that will provide both equilibrium and quasi-equilibrium results such as include condensed phase and gas compositions, solution behavior including glasses, chemical activities, predominance diagrams, phase diagrams, and others. Capabilities for modeling reacting flow systems are also available.

Research Areas in Thermodynamics:

Thermochemical Modeling of Oxide Glasses

The development and processing of high-level nuclear and transuranic waste in a host glass matrix is an ongoing effort at several national facilities such as Pacific Northwest National Laboratory, Savannah River Laboratory, Idaho National Engineering Laboratory and West Valley.  The glasses developed for such applications have to meet several critical requirements, e.g., they have to be mechanically durable and exhibit a negligible leaching rate on exposure to moisture.  Another goal is to maximize the waste loading of the glass.  Since experimental work in such systems is difficult and tedious to perform, the ability to accurately model the glass stability and corrosion behavior is of vital importance.  Such modeling efforts require reliable information about the phase stability and thermochemical properties of the constituent systems.  As part of a collaborative effort with Penn State and Pacific Northwest National Laboratory, scientists in the Surface Processing and Mechanics Group at Oak Ridge National Laboratory are developing an exhaustive multicomponent thermochemical database for oxide glass systems.

The unique feature of the modeling effort is the utilization of a "modified associate species" approach for describing the thermodynamic properties of liquid oxide solutions. This approach, besides being relatively easy to use for non-specialists in thermochemistry, is attractive in its ability to describe thermodynamic behavior of rather complex oxide glass systems over a wide range of temperatures and compositions and accurately predict activities of components in glasses.   Our current database consists of the SiO2-Al2O3-Na2O-B2O3-CaO-MgO-Cr2O3-ZrO2-MnO-NiO systems.  Experimental determination of liquidus temperatures for several glass compositions in these systems is being conducted at Pacific Northwest National Labs.   Based on these measurements, modifications in the thermochemical models for the relevant systems are performed and the database is improved.  The database is to be periodically updated to include additional glass oxide systems that are usually found in the waste glass formulations.

A typical phase diagram obtained using our glass database is provided below.

Publications:

• T. M. Besmann and K. E. Spear, "Thermochemical Modeling of Oxide Glasses," J. Am. Ceram. Soc., 85 [12] 2887-94 (2002)
• K. E. Spear and M. D. Allendorf, "Thermodynamic Analysis of Alumina Refractory Corrosion by Sodium or Potassium Hydroxide in Glass-Melting Furnaces," J. Electrochem. Soc., 149 (12) B551-B559 (2002).
• M. D. Allendorf and K. E. Spear, "Thermodynamic Analysis of Silica Refractory Corrosion in Glass-Melting Furnaces," J. Electrochem. Soc., 148 (2) B59-B67 (2001).
• T. M. Besmann, K. E. Spear, and E. C. Beahm, "Assessment of Nepheline Precipitation in Nuclear Waste Glass via Thermochemical Modeling," Mat. Res. Soc. Symp. Proc. Vol. 608 (2000).
• T. M. Besmann, K. E. Spear and E. C. Beahm, "Thermochemical Models for Nuclear Waste Glass Subsystems - MgO-CaO and MgO-Al₂O₃," Mat. Res. Soc. Symp. Proc. Vol. 556 (1999).
• K. E. Spear, T. M. Besmann, and E. C. Beahm, "Thermochemical Modeling of Glass: Application to High-Level Nuclear Waste Glass," MRS Bulletin, 24(4) 37-44 (1999).
• K. E. Spear, T. M. Besmann, and E. C. Beahm, "Thermochemical Modeling of Nuclear Waste Glass," Proc. Symp. High Temperature Corrosion and Materials Chemistry, The Electrochemical Society, Pennington, NJ (Fall 1998).

Ted Besmann & Nagraj Kulkarni
Oak Ridge National Laboratory

Karl Spear
The Pennsylvania State University

John Vienna & Pavel Hrma
Pacific Northwest National Laboratory

Dr. Ted Besmann Group Leader
Oak Ridge National Laboratory
P. 0. Box 2008, Oak Ridge, TN 37831-6063
Telephone (865) 574-6852
Fax (865) 574-6918
Email besmanntm@ornl.gov