SURFACE MODIFICATION STUDY OF BORATE MATERIALS FROM B K-EDGE X-RAY-ABSORPTION SPECTROSCOPY

The B K-edge X-ray absorption near-edge structure (XANES) spectra of t wo berates with tetrahedrally-coordinated B [B-[4]; natural danburite (CaB2Si2O8) and synthetic boron phosphate (BPO4)] have been recorded i n total electron yield (TEY) and fluorescence yield (FY) modes to inve stigate the surface and bulk structure of these materials. The TEY XAN ES measurement shows that danburite is susceptible to surface damage i nvolving conversion of B-[4] sites to B-[3] sites by reaction with moi sture and/or mechanical abrasion (grinding, polishing, etc.). The bulk of the mineral is essentially unaffected. Commercial boron phosphate powder exhibits more extensive surface and bulk damage, which increase s with air exposure but is recovered on heating at 650 degrees C. In c ontrast to ELNES, the XANES technique is not affected by beam damage a nd when collected in the FY mode is capable of yielding meaningful inf ormation on the coordination and intermediate-range structure of B in berate and borosilicate materials.