Calculation of viscosity–temperature curves for glass obtained from four wastewater treatment plants in Egypt M. Garcia-Valles • H. S. Hafez • I. Cruz-Matı ´as • E. Verge ´s • M. H. Aly • J. Nogue ´s • D. Ayala • S. Martı ´nez Received: 9 November 2011 / Accepted: 16 January 2012 / Published online: 31 January 2012 Ó Akade ´miai Kiado ´, Budapest, Hungary 2012 Abstract This article establishes the relationship between the chemical composition, temperature and viscosity of glasses obtained from the four sludge treatment plants of urban and industrial wastewater from the Nile Delta in Egypt. In order to determine the working conditions of these glasses and their growth temperature, different techniques have been used: differential thermal analysis, hot stage microscopy and dilatometry. We used a prototype of hot stage microscopy, with the help of an image analysis programme developed in the present study. The chemical composition of major oxides sludge ranging from: SiO 2 (36–48 wt%), Al 2 O 3 (9–16 wt%), CaO (5–25 wt%), P 2 O 5 (1.5–11 wt%), and Fe 2 O 3 (*9 wt%), this composition is close to a basalt rock, being necessary to incorporate some raw materials to adjust it to the basalt rock that has a good viscosity-temperature curve. The glass tran- sition temperatures of the four glasses obtained vary between 650 and 725 °C and the growth occurs between 938 and 1,033 °C. We also obtained the viscosity–temperature curves with the aid of the hot stage microscopy that has allowed us to determine the working temperatures of the four glasses, ranging from 926 to 1,419 °C, depending on the type of forming process used. Keywords Wastewater  Viscosity  Glass  Hot stage microscopy  Dilatometry Introduction Currently, sewage sludge production is constantly increasing in Egypt, as the population has tripled over the last 50 years and the total population is likely to increase to above 96 9 10 6 by 2026 [1]. The limited capacity to stabilise and dispose of these wastes has become a problem of increasing urgency, which will inevitably lead to a further increase in the production of sewage sludge. One of the main applica- tions of such sludge is used in agriculture, either directly or with any previous treatment, such as for pyrolysis with charcoal [2]. Vitrification is a thermal treatment of sludge that leads to the decomposition, destruction or immobiliza- tion of all the contaminant elements contained in the original sludge, and thus solves an environmental problem [3]. Solid waste is transformed into vitrified slag that is not leached. Making glass out of the different Egyptian sludge is an environmentally friendly solution to this problem [4]. However, before this can be done, the physical properties and the commercial applicability of the glass need to be deter- mined. Viscosity is a key property for glassmakers, and determines the melting behaviour, working range and annealing temperature. The viscosity is usually measured at different temperatures to establish the melting behaviour of the glass in relation to temperature. Hot stage microscopy (HSM) is a suitable technique for studying the behaviour of glass viscosity in relation to temperature. We can obtain the necessary viscosity-tem- perature curves by combining HSM with a dilatometric analysis. In addition, differential thermal analysis (DTA) is M. Garcia-Valles (&)  J. Nogue ´s  S. Martı ´nez Departament de Cristallografia, Mineralogia i Diposits Minerals, Facultad de Geologia, Universitat de Barcelona (UB), c/Martı ´ i Franque `s, s/n, 08028 Barcelona, Spain e-mail: maitegarciavalles@ub.edu H. S. Hafez  M. H. Aly Environmental Studies and Research Institute, Minufiya University, Sadat City, Six Zone/n, 328, Minufiya, Egypt I. Cruz-Matı ´as  E. Verge ´s  D. Ayala Departament de Llenguatges i Sistemes Informa `tics, ETSEIB, Universitat Polite `cnica de Catalunya (UPC), Av. Diagonal, 647, 08028 Barcelona, Spain 123 J Therm Anal Calorim (2013) 111:107–114 DOI 10.1007/s10973-012-2232-7