Transformation toughening of Na Beta'' alumina

Technical Report · Wed May 01 04:00:00 EDT 1985

OSTI ID:5277200

Olson, D A

The search for alternate energy storage systems has uncovered the potential of the sodium-sulfur battery. The major obstacle to its immediate use is limited battery lifetime and power density due to the degradation of the solid electrolyte: sodium beta'' alumina. The critical current density for initiation of degradation of the electrolyte depends on the fracture toughness of the material raised to the fourth power. Transformation toughening, commonly used in other ceramic systems, has been suggested as a possible means for increasing the fracture toughness of the electrolyte, therby extending the lifetime of the batteries. The effectiveness of a 15 volume % zirconia dispersion in pure beta'' alumina was studied. The problem of producing an acceptable dispersion of zirconia in pure beta'' alumina has not been solved. Microhardness testing of the electrolytes showed that the zirconia toughening resulted in a significant increase in the fracture toughness of the material. Microstructural studies, however, found that irregularities in the surface and bulk of the composite electrolyte material existed which would impair the toughening capabilities of the second-phase dispersion. Acoustic emission studies supported this conclusion in the case of comparisons of as-sintered material. Polishing the electrolyte surface yielded a significant result: composite electrolytes were strengthened by this procedure, while their pure counterparts were weakened. The varying responses to the surface damage associated with polishing arise from the toughening transformation. Under the application of the mechanical stress associated with polishing, metastable zirconia particles transform to the lower density form. The compressive stresses introduced heal the surface damage, and generate an improvement in performance.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 5277200
• Report Number(s): LBL-19896; ON: DE85017671
• Country of Publication: United States
• Language: English

Related Subjects

25 ENERGY STORAGE
250903* -- Energy Storage-- Batteries-- Materials
Components
& Auxiliaries
ACOUSTIC EMISSION TESTING
ACOUSTIC TESTING
BETA-W LATTICES
CHALCOGENIDES
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DISPERSION HARDENING
ELECTRIC BATTERIES
ELECTROCHEMICAL CELLS
ELECTROLYTES
FRACTURE PROPERTIES
HARDENING
HARDNESS
MATERIALS TESTING
MECHANICAL PROPERTIES
METAL-NONMETAL BATTERIES
MICROHARDNESS
NONDESTRUCTIVE TESTING
OXIDES
OXYGEN COMPOUNDS
POLISHING
SODIUM-SULFUR BATTERIES
SOLID ELECTROLYTES
SURFACE FINISHING
TESTING
TRANSITION ELEMENT COMPOUNDS
ZIRCONIUM COMPOUNDS
ZIRCONIUM OXIDES