FLAME GENERATION OF 2 NEW PRECURSORS OF VANADYL PYROPHOSPHATE

Two new vanadyl pyrophosphate precursors were produced in a single ste p operation using a counterflow diffusion flame burner. The technique consists of adding a vanadium and a phosphorus halide to the fuel stre am of hydrogen-oxygen flames. Particles nucleate and grow in the flame to an average diameter between 5 and 30 nm. Upon exiting the flame, p owders are collected on two stainless steel strips and their crystalli ne structures are analyzed by x-ray diffraction and Fourier-transform infrared spectroscopy. A strong effect of flame temperature on the cry stalline structure of the powders produced is observed. When a high te mperature flame is used, the powder collected is a mixture of VOPO4 . 2H(2)O and (VOPO4)(1-x)(VOHPO4)(x) . 2.6H(2)O. This mixture forms gamm a-VOPO4 upon subsequent reheating at 750 degrees C in a oxidizing atmo sphere, and transforms into (VO)(2)P2O7 in an oxygen-free atmosphere a t 700 degrees C. When a lower temperature flame is used, the powder co llected is (VOPO4)(1-x)(VOHPO4)(x) . 2.9H(2)O, which transforms at 750 degrees C into beta-VOPO4 in an oxidizing atmosphere and to (VO)(2)P2 O7 at 700 degrees C in an oxygen-free atmosphere. Structural differenc es between the two vanadyl pyrophosphates are observed. These differen ces are discussed in terms of the ability of (VO)(2)P2O7 to accommodat e various disordered and polytypic structures. (C) 1996 Academic Press , Inc.