Rheological properties of calcium metaphosphate melts during extrusion

An extrusion method to determine viscosities is described. Here, different stages of the response on the load applied are observed and the viscous heating effect caused by the mechanical deformation work is taken into account. The method enables the determination of viscosities in the range of 10(6) to 10(8.5) dpa s. The values obtained are in good agreement with interpolated ones determined by beam bending and cylinder rotation. During extruding of calcium metaphosphate melts, the viscositiy decreases with increasing shear rate. This shear-thinning effect (or non-Newtonian behaviour) is attributed to the orientation of flow units of the dynamic melt network. It is found that both Newtonian and non-Newtonian flow behaviour of calcium metaphosphate melts was largely influenced by adding a small amount of SiO2. However, the introduction of a small amount of SiO2 into calcium metaphosphate melts is beneficial to study the now behaviour, since by that the crystallization of melts is avoided, which hinders the continuation of extruding processes.