Structure of zirconium phosphate gels produced by the sol-gel method

Several zirconium phosphate (ZrP) gels of various water contents produced by a sol-gel method were investigated. They were found to be the polymer-class gels using the method of small-angle neutron scattering. X-ray diffraction analysis revealed that their solid-phase framework was formed from branched fragments (layers and blocks) of alpha-ZrP crystal structure. These gels are strongly fluctuating systems when they are on the scale of r < xi. Their fluctuation character is shown to be described by two parameters: a correlation radius xi and a fractal dimension D. It was found that xi approximate to 2.5 nm and almost did not depend on the water content and that D increased from 1.4 +/- 0.25 to 2.6 +/- 0.20 when the water content decreased from 50% to 0% as the gels were dried to a temperature of 105 degrees C. Simultaneously, substantial shrinkage of granules, a decrease in porosity and ion-exchange capability, and formation of blocks from alpha-phosphate layers occurred with alpha decrease in the water of the hydrogel as it dried. A probable description of the evolution of the ZrP-gel structure with variation in the water content during drying is suggested on the basis of the data obtained.