High-temp Quartz - Characterizing quartz properties predicting high temperature performance in production of ferrosilicon and silicon alloys

Quartz (SiO2) is the silicon source in the production of silicon alloys. Silicon alloys are produced in electric furnaces at very high temperatures, up to more than 2000oC. The High-temp Quartz project in 2016-20 will investigate the behavior of quartz at such high temperatures. High-temp Quartz will investigate how quartz material characteristics affect the production processes for silicon alloys. Based on this new knowledge, the goal is to develop measuring methods that makes it possible to predict how suited a specific quartz will be for a specific silicon furnace operation. The new test scheme included measuring equipment and methods, will be a qualification test for new quartz types prior to industrial use. Based on the new knowledge about how quartz affects the furnace conditions, it will be possible to adapt the way the furnace is operated to the actual quartz properties, which may result in significant improvements in the furnace productivity with reduced energy consumption. New knowledge about the correlation between geological history and the high temperature properties of the quartz will, together with the new quartz test method, be used in exploration of new quartz sources. The quartz investigations will start at laboratory facilities. Later, the test methods and hypotheses will be verified at pilot scale and finally, at tests at industrial silicon furnaces. In parallel, new quartz source will be tested industrially to compare the results with knowledge we will obtain in the project from laboratory- and pilot-scale testing. Elkem Silicon Materials is a major producer of silicon alloys with three plants and two quartz mines in Norway, in addition to international operations. Elkem has a potential profitability improvement of 50-100 MNOK/y by applying the project results. Finally, the project will improve Elkem's competitive position as a quartz supplier and increase the possibility of establishing new quartz production facilities in Norway. Elkem Technology is project manager, with Elkem Silicon Materials, Sintef and NTNU as project partners. The project includes one PhD candidate, four MSc students at NTNU and parts of a Postdoc position at the University of Bilbao, Spain. Elkem has for several years worked closely with a doctoral program at the University of Oxford, Institute for Applied Mathematics. This is included in the project where a DPhil will model the flow of quartz through the furnace. The PhD student at NTNU started her work in August 2016. She investigates how quartz properties change during heating to temperatures found in industrial silicon and ferrosilicon furnaces. The most important properties she is investigating is the phase transformations and the disintegration after shock heating of various quartz types. Some of her work is also focusing on trying new test methods for quartz. Raman spectroscopy, Fourier-transformed infrared spectroscopy (FT-IR), computed tomography (CT) and differential thermal analysis (DTA) been used to see if they could give any new information about the quartz. Her work has so far resulted in three publications in connection with international conferences in South-Africa, Canada and Norway. The candidate has participated and presented the work herself at these conferences. A journal paper about phase transformations in different quartz types is published. She defended her PhD in June 2020. Two MSc students in geology were a part of the project in 2017-18. They used different techniques to describe the different generations of quartz found in the mine and investigated the quartz by micro thermometry, where we can look at the sample in microscopy during heating. One of the MSc students joined Elkem, where she continued the micro-thermometry investigation. We also try to understand why some quarters seem to melt faster than others. Sintef and NTNU have done tests in a small furnace where a quartz piece is heated up to almost two thousand degrees. This is recorded on film, so that we can see what happens to the quartz when the temperature rises. In 2020, Sintef carried out an extensive experimental program in this furnace to study the softening and melting conditions of various quartz. The project has funded parts of a Postdoc. position at the University of Bilbao, Spain. In this work, the history of formation of a quartz mine shall be described and samples examined in the laboratory. Elkem has created a database for various quartz types that includes all measurements, material data, experimental results, petrographic studies and micro thermometry from the project. A multivariate data analysis will now be performed on this quartz database. There is great interest in the project from Elkem's silicon plant and there are several participants from the plants in the project meetings and the project participates in workshops on works. Elkem has started an internal "dissemination project" in 2021.

Prosjektet har resultert i ny kunnskap om hvordan materialegenskaper i ulike kvartstyper endres som følge av oppvarming og hvordan dette vil påvirke grad av oppsprekking, faseomvandling, nedsmelting og flytbarhet til den smeltede kvartsen. Vi har også kunnet etablere sammenhenger mellom kvartstypenes geologiske historie og hvordan de oppfører seg ved oppvarming til høye temperaturer. Det vil ha en stor økonomisk verdi å ta denne nye kunnskapen og etablere driftsstrategier for smelteovnen som tar hensyn til de ulike kvartstypenes egenskaper ved høye temperaturer. Den nye kunnskapen vil også ha en stor økonomisk verdi i søk etter egnede kvartsforekomster. Ved hjelp av de nye testmetodene vil vi nå kunne gi en bedre vurdering av hvordan en forekomst vil kunne egne seg som en smelteovnskvarts.

Quartz (SiO2) is the silicon source in the production of silicon alloys. The High-temp Quartz project in 2016-19 will develop novel knowledge about the high temperature material properties of quartz that enables more energy-efficient production of silicon with reduced raw material consumption. High-temp Quartz will investigate how quartz material characteristics affect the production processes for silicon alloys, and develop measuring methods that makes it possible to predict how suited a specific quartz will be for a specific silicon furnace operation. The new test scheme with measuring equipment and methods will be implemented in Elkem by 2020. This will be a qualification test for quartz prior to industrial use, as well as a tool in exploration for new quartz sources. The knowledge about how quartz affects the furnace conditions will result in significant improvements by adapting the furnace operation parameters to the quartz properties. The project will investigate the material properties of quartz during heating of up to the process temperatures for a silicon furnace, study the interaction with the silicon process conditions and develop a quartz "furnacability" test. Correlation of important properties with geological characteristics will broaden the use to a powerful tool in quartz exploration. Elkem Silicon Materials is a major producer of silicon alloys with three plants and two quartz mines in Norway, in addition to international operations. Elkem has a potential profitability improvement of 50-100 MNOK/y by applying the project results. Finally, the project will improve Elkem's competitive position as a quartz supplier and increase the possibility of establishing new quartz production facilities in Norway. Elkem Technology will be the project manager, with Elkem Silicon Materials, Sintef Materials and Chemistry and NTNU Faculty of Natural Science and Technology as project partners. The project includes one PhD candidate and 3-4 MSc students.