Abstract
This report presents a characterization of slag samples from three different silicon production studies: an excavation of Wacker Chemicals Norway AS Furnace No. 2 in 2026, an excavation of Elkem Thamshavn Furnace No. 2 in 2023, and tapping slag collected from Finnfjord AS in 2026. Samples were analysed using EPMA and WDS to investigate slag composition, phase distribution, and the occurrence and distribution of SiC within the slag.
The Wacker excavation revealed a well-defined furnace structure with distinct inactive, SiC-rich, and metal-producing zones. Slag compositions varied primarily in SiO2 content and could be grouped into three compositional regions corresponding to different furnace locations. Comparison with previous excavations showed similar slag compositions and distribution patterns.
The Thamshavn excavation revealed a furnace structure different from that observed during the previous excavation in 2013. Large quantities of slag containing smaller SiC particles were found across the furnace bottom, while porous SiC and condensate dominated the upper furnace regions. The slag compositions were primarily within the SiO2-CaO-Al2O3 system and were consistent with both previously excavated samples and tapping slag.
The Finnfjord study showed that high-viscosity tapping slags contain significantly higher SiO₂ contents than normal tapping slags, resulting in approximately twice the calculated viscosity. Although SiC was present in all samples, no direct relationship between SiC content and slag viscosity was observed. The results indicate that slag composition is the primary factor controlling the occurrence of high-viscosity problem slag.