Controlling gelation kinetics is an important objective for several applica
tions (ceramic and thin film syntheses, reduction in permeability of porous
rock, etc). There is a growing interest in studying the gelation of polyme
rs by zirconium, a crosslinker of lower toxicity than the chromium which is
still commonly used. XAS at the Zr K-edge was performed at the European Sy
nchrotron Radiation Facility (ESRF) on the BM32 beamline. The fluorescence
detection was used to carry out successful in situ speciation at concentrat
ions as low as 36 ppm. The Zr speciation was determined both in ZrLa (where
La stands for lactate) aqueous solutions and in gels of a terpolymer of ac
rylamide having 2% of zirconium reactive acrylate side groups and 2% of sul
fonate groups introduced to prevent syneresis. XANES results show that Zr i
s always in a dodecahedral geometry. In ZrLa solutions, EXAFS results indic
ate that Zr species grow from a dimer Zr-2(La)(6) to a tetramer (Zr-4(La)(x
)) and then to larger polymers resulting from tetramer associations, as the
Zr concentration decreases from 51840 ppm to 36ppm. In polymer gels, Zr sp
ecies appear to be dimers at pH 6 while tetramers are found when gelation o
ccurred at pH 7. Calculations taking into account multiple scattering effec
ts as well as dynamic molecular calculation confirmed conclusions derived f
rom conventional EXAFS analysis.