Cryst. Res. Technol. 35 2000 8 969–977 The amorphous sodium disilicate transformation into a crystallized product proceeds on several paths, finally resulting a mixture of crystalline α, β, δ , γ polymorphs. The identification of individual crystalline phases is impaired by the overlapping of X-ray patterns corresponding to various polymorph species. A quite different way from the classical Rietveld method of X-ray diffraction data analysis is proposed: qualitative and quantitative identification of polymorph phases is approached as a classification problem with satisfactory results using two types of neural nets. A backpropagation network with post-processing of the outputs and a neural net based on the adaptive resonance theory have been applied with equivalent results. In comparison with Rietveld method, this original approach can be considered a short-cut technique requesting no fundamental data. The reason of this work is to be a background support in assessment procedures concerning the quantitative evaluation of interdependence between the crystallization parameters and the desired composition of the solid phase mixture. Keywords: XRD analysis, DSC analysis, Na 2 Si 2 O 5 , neural nets, pattern recognition, pattern classification (Received November 12, 1999; Accepted August 11, 2000) 1. Introduction The sodium disilicate can be amorphous or crystallized in one of the four polymorphs known as α, β, γ, δ-Na 2 Si 2 O 5 . Beside δ -Na 2 Si 2 O 5 , which is a genuine layered silicate, β and γ- Na 2 Si 2 O 5 are approaching layered silicates crystal structure and properties [GRUND]. The thermodynamically stable polymorph, α-Na 2 Si 2 O 5 , differs in all the aspects from the other polymorphs [PANT et al.]. The interest in layered and unlayered sodium disilicates raised since they proved to be valuable co-builders minded to substitute tripolyphosphates (mainly responsible for the so called “eutrophication” process) in detergent formulations. A wide range of sodium silicates, with general formula (Na 2 O) x (SiO 2 ) y (H 2 O) z , have been tested and developed to full commercial scale as multifunctional builders [RIECK, BOITTIAUX et al., SOERENSON et al., BAUER, WILKENS]. The sodium disilicate polymorphs are fairly characterized, but the recrystallization kinetics of the metastable phases from the amorphous is not well known. Some attempts to obtain a single enriched β, γ or δ phase have been carried out. The first step of crystalline sodium disilicates preparation consists in drying out the silicate solution to amorphous product, followed by a second step which imply a thermal processing of the amorphous phase to one of the stable or metastable Na 2 Si 2 O 5 polymorphs. A.WOINAROSCHY, R. ISOPESCU, L. FILIPESCU Department of Chemical Engineering, ”Politehnica” University of Bucharest; Romania X-Ray Patterns Identification of Crystallized Sodium Disilicates Mixtures