Viscosity measurements of glass melts - Certification of reference material

Abstract

This work describes the investigation and the results for three glass types for qualification as reference materials. The measurements were carried out by means of a specially designed rotational viscometer in a temperature range from 400 up to 1400 °C and a viscosity range from about 10^2 to 10^14 dPas. Further measurements were performed in a fibre elongation viscometer to compare elongational viscosity and shear viscosity by means of the Trouton ratio. The technical design of the viscometers including calibration by tracing back to national standards is described. The uniformity of the glass types as well as the stability and reproducibility of the viscosity measurements were checked for compliance with the requirements placed on a reference material. The measurements were performed under equilibrium conditions and include the working point and the softening point (Littleton point) according to ISO 7884, part 1, to allow comparisons with techniques often used. The viscosity-temperature relationship is presented, the uncertainty of the measurements and the best-fit polynomial equation are calculated and the results are discussed.