A soft chemistry route is described to obtain glasses in the P 2 O 5 -Na 2 O-ZnO-H 2 O. It is based on the addition of zinc salts to coacervates prepared from sodium polyphosphate. The processing of these coacervates leads to polyphosphate glasses with the same properties as those of glasses prepared in the classical way. So far, little work has been implemented in this system using 'coacervate route'. However, it makes an attractive method for coating and joining processes on the industrial scale. As the anion associated to zinc may take part in the adhesion mechanism, coacervate formation has been studied using zinc chloride, nitrate and sulphate as starting materials. The physical properties of the glasses obtained by this method are reported and potential applications of zinc and silver coacervate are described. To cite this article: G. Willot et al., C. R. Chimie 5 (2002) 899-906 © 2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS glass / polyphosphate / coacervate / coating / sealingRésumé -Nous décrivons une nouvelle méthode permettant d'obtenir par voie douce des verres dans le système P 2 O 5 -Na 2 O-ZnO-H 2 O. Elle est basée sur la formation de coacervats de polyphosphates obtenus par l'action de sels de zinc sur des solutions concentrées de polyphosphate de sodium. Par chauffage, on obtient, à des températures de l'ordre de 400 °C, des phases vitreuses ayant les mêmes propriétés que les verres obtenus par une méthode classique. Cependant, compte tenu des propriétés des coacervats, cette méthode permet de développer des procédés de collage ou de revêtements applicables en milieu industriel. Comme les anions associés aux sels de zinc utilisés peuvent intervenir dans les mécanismes d'adhésion, nous avons étudié plus en détail les mécanismes de formation des coacervats à partir des chlorure, nitrate et sulfate de zinc. Nous donnons les propriétés physiques des verres obtenus par ce procédé, ainsi que les potentialités de verres obtenus à la fois à partir de coacervats de zinc et d'argent.

The coacervation of polyphosphates usually takes place at very low pH value. We show that, in the system Na2O-CaO -P2O5, the decrease of pH is due the hydrolysis of the terminal P-OH groups and that it is a consequence of the coacervation. So a very low pH is not necessary to obtain a coacervate and it is possible to form coacervates in non-acid media (even basic). The same results are obtained with other precursor systems of polyphosphate coacervates. These results may be interesting for the achievement of coacervates as industrial glasses precursors.

We propose a new route to obtain polyphosphate glasses based on silver.by use a soft chemistry route, the coacervation.We precise the obtaining conditions of the silver coacervates. By curing, we obtain glasses. It is possible to induce in these glasses silver particles by the action of a wet atmosphere. These results may present some interests for industrial applications.