Effect of melting conditions on striae in iron-bearing silicate melts

Chemical striae are present in a broad range of glass products, but due to their negative impact on e.g., the optical and mechanical properties, elimination of striae from melts is a key issue in glass technology. By varying melting temperatures, retentions times and redox conditions of an iron-bearing calciumaluminosilicate melt, we quantify the effect of each of the three melting parameters on the stria content in the melt. The quantification of the stria content in the melt is conducted by means of image analysis on casted melt samples. We find that in comparison to an extension of retention time an increase of melt temperature and/or a decrease of viscosity play a more important role in decreasing the stria content. We also demonstrate that the extent of striation is influenced by the crucible materials that causes a change of redox state of the melt, and hence its viscosity. We discuss the effect of other factors such as compositional fluctuation of melts and bubbling due to iron reduction on the stria content. During the melting process, striae with a chemical gradient in a more mobile species equilibrate faster than striae caused by a chemical gradient in a less mobile species. The temperature and time effects on melt homogeneity at lower temperatures are larger than at higher temperatures.