Eli Ringdalen

Phase Transformations from Quartz to Cristobalite

Two quartz types used in the silicon and ferrosilicon industry were heated to temperatures of 1600 and 1700 °C. The parameters varied were the temperature and the holding time at maximum temperature. The amount of quartz, cristobalite and intermediate amorphous phase were measured using XRD and the internal standard method. Type P showed a much larger ability to transform to cristobalite at lower temperatures than type A. Type P had a larger amount of alkali and alkaline earth impurities. This could have enhanced the transformation to cristobalite. For quartz type A the amount of cristobalite was larger at 1600 °C than 1700 °C. This can also be seen for some of the samples of type P at shorter holding times.

Softening and Melting of SiO2, an Important Parameter for Reactions with Quartz in Si Production

Quartz (SiO2) is the main silicon source for production of metallurgical grade silicon in submerged arc furnaces. During heating in the furnace, quartz will first transform to other SiO2 polymorphs, then soften and melt. Volume changes during heating and melting are expected to affect for the rate of reactions with SiO2 and gas flow. Industrial quartz sources are investigated here with heating rates relevant for industrial furnaces. A method to study softening and melting of quartz at conditions relevant for Si-production was developed. Both volume expansion and melting properties vary considerably between quartz sources. Theoretical volume expansion is 22 % and melting temperature 1726 °C. Volume increase up to 40 %, softening temperatures in the range 1675 °C to 1800 °C, and melting temperatures in the range 1790 °C to 1900 °C were recorded.

Production of FeMn Alloys with Heat Treated Mn-Nodules

FeMn alloys are typically produced with lumpy ore or sinters. Minara Autlan, the Mexican FeMn producer, is however making Mn-nodules as a raw material for Mn-alloy production. The Mn nodules have been characterized by XRF, XRD, by wet chemical methods and by EPMA. The Mn/Fe ratio is somewhat lower compared to commercial Mn ore on the marked. The basicity of the ore is however close to 1, and additional fluxes may not be used. The Mn-nodules will be in a state of manganosite (MnO), tephroite ((Mn, Ca)2SiO4) and galaxite ((Mn,Mg)Al2O4). This leads to a low melting temperature area. A low porosity and low amount of higher Mn-oxides gives a high thermal strength to the nodules.

Reduction of Agglomerated Manganese Ores in a 150 kW Pilot Scale Furnace

Manganese ore fines cannot be added to the submerged arc furnace directly as they will prevent even gas flow through the burden. Low gas permeability in the burden will lower the degree of pre-reduction of ore subsequently increase the carbon and energy consumption of the process. In order to utilize manganese ore fines in the furnace, they are typically agglomerated into sinter. In this work, the melting and reduction properties of Gabonese sinter and Gabonese ore have been investigated in pilot scale experiments. Two experiments were conducted, one with 100% sinter as manganese source and one with 50/50 sinter and ore. Lime was used to achieve a charge basicity of 0.72 in both experiments. The composition of slag samples from the excavation of the furnace was established using EPMA(WDS), and the composition of the tapped slag and metal was found using XRF. It was found that while the coke-bed size would determine the tapped slag composition, the melting behavior of the Mn source would determine the mixing with lime.

Quartz-Cristobalite Transformation and Its Effect on Reactions in Si Production: Initial Studies

In Si and FeSi production, the main Si source is SiO2, in the form of quartz. Reactions with SiO2 generate SiO-gas that further reacts with SiC to Si. During heating, quartz will transform to other SiO2 modifications with cristobalite as the stable high temperature phase. Transformation to cristobalite has been investigated and shown to be a slow process where the rate varies between the investigated quartz types.