Vibrational analysis of iron and zinc phosphate conversion coating constituents

The FT-MIR/FT-FIR and NIR-FT-Raman spectra of orthorhombic alpha -Zn-3(PO4) (2). 4H(2)O (alpha -hopeite) and monoclinic Zn2Fe(PO4)(2). 4H(2)O (phosphop hyllite), including deuterated samples, have been measured in the polycryst alline state at room temperature and below. The distribution of vibrational levels was related to the results of complete unit-cell group analyses. Th e number of uncoupled OD stretching modes of alpha -hopeite (isotopically d ilute samples) strongly exceeds that expected from the number of hydrogen p ositions of the structure reported. In contrast, unequivocal assignment of the four hydrogen bonds of phosphophyllite has been performed. The distorti on of the phosphate tetrahedra, as revealed from both site group and unit-c ell group splitting of the PO stretching modes, is found to be almost equal in both compounds, in accordance with the identical tetrahedral linkage sc heme. (C) 2001 Elsevier Science B.V. All rights reserved.