Zirconium propoxide hydrolysis was performed with the help of an esterification reaction using acetic acid. Products, obtained according to the value of hydrolysis ratio, are successively crystals, sols and gels or precipitates. The similarity of FUR and NMR spectra for crystals and gels allows to think that the arrangements of ligands around the zirconium atoms are close. The crystalline structure determination permits to precise the environment : acetate groups are always bridging and propoxy groups can be bridging or terminal. Clusters containing 9 zirconium atoms, bridged by oxygen atoms, exist in the structure. The colloid size growth was performed by light scattering. A discussion of the role of acetic acid and the competition between the possible reactions is given.

A new versatile method to prepare monolithic metal-organic derived gels is presented in which the sol-to-gel transition is achieved through hydrolysis and condensation reactions in a reversed micelles microemulsion. C7 to C10 alkanes were used as solvents for the reaction and water molecules were solubilized using a non ionic surfactant. The general rules governing the sol-to-gel transition for several alkoxides such as Ti (OPri)4, Ti(OBut)4 and Fe(OPri)3 have been laid down and the exchange of water between reversed micelles related to hydrolysis and condensation rates has been investigated. Hydrolysis and condensation kinetics were monitored for different water/surfactant ratio u-sing gas chromatography. At the sol state growing of colloidal particles is mainly affected by the structure of the water inside the reversed micelles. It has been demonstrated using light scattering measurements that gelation times depend on the particle size evolution into the sol.

In separative process, the use of mineral membranes instead of organic ones is more interesting for it offers numerous advantages as follows :

- High temperature and pressure resistant (no compression of the membrane).

- Corrosion and abrasion resistant.

- Not sensitive to bacterial action.

- Steam sterilisable.

- Longer life time.