Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Transformations in the Si-O-Ca system: Silicon-calcium via solar energy D. Fernández-González a, ⁎ , J. Prazuch b , I. Ruiz-Bustinza c , C. González-Gasca d , J. Piñuela-Noval a , L.F. Verdeja a a Department of Materials Science and Metallurgical Engineering, School of Mines, Energy and Materials, University of Oviedo, Oviedo, Asturias, Spain b Department of Physical Chemistry and Modelling, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Krakow, Poland c Department of Geological and Mining Engineering, Polytechnic University of Madrid, Madrid, Spain d European University of Madrid-Laureate International Universities, Villaviciosa de Odón, Madrid, Spain ARTICLE INFO Keywords: Concentrated solar energy Silicon-calcium Environment Alloying elements Solar energy ABSTRACT The production of silicon-calcium alloy is energy intensive (> 10,000 kWh/t). This means that energy cost has a relevant influence in the price of the alloy. The utilization of concentrated solar energy in the synthesis of silicon- calcium alloy is proposed in this paper. Metallurgical quality silicon and limestone are used as starting materials (25 wt.%, 50 wt.% and 75 wt.% Si). After a 12 min treatment under power values of around 1 kW and without using special atmosphere, silicon-calcium was detected in all samples, although mixed with the products of reaction (Ca 3 Si 2 O 7 , Ca 10 O 25 Si 6 , SiO 2 ). This last question means that there was not proper separation metal-slag, and it should be improved in future investigations. However, the basic knowledge presented in this paper could be of great interest for an industrial process based on the solar energy. This way, the energy costs could be reduced, the pollutant emissions could be minimized, and the competitiveness of the ferroalloys industry could be increased. 1. Introduction Solar energy, when properly concentrated, offers a great potential in high temperature applications, and therefore its use in the field of materials has been studied for many years (Fernández-González et al., 2018a). These applications include metallurgy, materials processing (welding and cladding; surface treatments; coatings and surface hard- ening; and, powder metallurgy), and non-metallic materials (ceramics, fullerenes, carbon nanotubes, and production of lime) (Fernández- González et al., 2018a). In the case of the research group that signs this manuscript, different processes were studied using concentrated solar energy: in the synthesis of calcium aluminates (Fernández-González et al., 2018b), in the indirect reduction of mill scale to produce high quality magnetite (Ruiz-Bustinza et al., 2013), in the direct reduction of iron oxides (laboratory quality reagents, Mochón et al., 2014; Fernández et al., 2015; Fernández-González et al., 2018c; real iron ore sinter, Fernández-González et al., 2018c); and in the treatment of BOF (Basic Oxygen Furnace) slag (Fernández-González et al., 2019). Silicon-calcium is a strong deoxidizing and desulphurizing element that is used in the production of high-quality steels (Pero-Sanz, 2004; Pero-Sanz et al., 2018). The alloy is used in quantities ranging from 0.5 to 3 kg/ton of steel, with 1–2 kg being the average. The world production of this alloy is very limited because only 150,000 tons of silicon-calcium are produced worldwide. The production of the silicon- calcium is distributed into few plants, for instance, FerroGlobe (one of the biggest producers of ferroalloys) produces approximately 30,000 tons of silicon-calcium alloys in Chateau Feuillet (France) and Mendoza (Argentina). Apart from being a strong deoxidizing and desulphurizing alloy, silicon-calcium alloys allow controlling the shape, size and dis- tribution of the oxides and sulfides inclusions (Sancho et al., 2003). In this way, the fluidity, machinability, ductility and properties of the final product are improved: reduction in the number of inclusions and im- provement in their shape, reduction of blowholes during the solidifi- cation, improvement in the toughness, etc. Silicon-calcium alloys are usually produced in submerged arc elec- tric furnaces, which have energy consumptions higher than 10,000 kWh (Robiette, 1973). Mixtures used in the manufacture of silicon-calcium alloys usually comprise quartz/quartzite, lime, fine coke, charcoal and coal. Lime must contain at least 90% CaO because poorly burned lime increases power consumptions, reduces the efficiency of the furnace, implies a non-smooth process and shortens the life of the furnace. Concerning the quality of the different cokes used in ferroalloys in- dustry, their main characteristics can be found in Rodero et al. (2015). Three industrial methods have been developed to produce silicon- https://doi.org/10.1016/j.solener.2019.02.026 Received 20 November 2018; Received in revised form 7 February 2019; Accepted 12 February 2019 ⁎ Corresponding author. E-mail address: fernandezgdaniel@uniovi.es (D. Fernández-González). Solar Energy 181 (2019) 414–423 Available online 16 February 2019 0038-092X/ © 2019 International Solar Energy Society. Published by Elsevier Ltd. All rights reserved. T