Thermally Induced Nano-Structural and Optical Changes of nc-Si:H Deposited by Hot-Wire CVD

We report on the thermally induced changes of the nano-structural and optical properties of hydrogenated nanocrystalline silicon in the temperature range 200–700 °C. The as-deposited sample has a high crystalline volume fraction of 53% with an average crystallite size of ~3.9 nm, where 66% of the total hydrogen is bonded as ≡Si–H monohydrides on the nano-crystallite surface. A growth in the native crystallite size and crystalline volume fraction occurs at annealing temperatures ≥400 °C, where hydrogen is initially removed from the crystallite grain boundaries followed by its removal from the amorphous network. The nucleation of smaller nano-crystallites at higher temperatures accounts for the enhanced porous structure and the increase in the optical band gap and average gap

Optical emission spectroscopy as an online analysis method in industrial electric arc furnaces

Abstract The development of online analysis methods for industrial electric arc furnaces (EAFs) has been a major research topic in recent years. Process control becomes even more important in the future due to the increase in both the usage of recycled metal as charge material and the metal recycling rate. For the industry to keep up with the pace, reliable chemical analysis of the slag together with online information about the furnace operation status is essential. Herein, optical emission spectroscopy is used to obtain the information about the electric arc together with radiative properties and surface temperature of the molten bath in an industrial EAF. The arc is visible for high alloyed steel grades within 5–30 min before tapping and the arc spectra are dominated by the optical emissions from the slag components. The plasma properties of the electric arc are determined with emission lines from atomic chromium, iron, and calcium. The time evolution of the spectra for high alloyed and carbon steel grades are compared with each other to provide a better understanding of the differences in the spectra between these two steel grades

Industrial ladle furnace slag composition analysis with optical emissions from the arc

Abstract With the strict standards for steel quality and high production rates, the demand for faster and more convenient slag composition analysis for both electric arc and ladle furnaces has become a major issue in industrial steel plants. To overcome the time-delay between slag sampling and results of the slag composition analysis, an on-line slag composition analysis is required. Such a method that can be used in on-line analysis and is also chemically sensitive to the slag composition is optical emission spectroscopy. In this work, the optical emissions from the arc have been measured in an industrial ladle furnace and used for slag composition analysis. This article focuses on CaF₂ and MgO, since the CaF₂ is a common additive material in the ladle treatment and high MgO content means that the ladle refractory lining is dissolving into the slag. The analysis has been carried out by comparing emission line ratios to the XRF analyzed ratios of CaF₂/MgO and MnO/MgO, respectively. The results show that several atomic emissions lines of calcium, magnesium, and manganese can be used to evaluate the CaF₂/MgO and MnO/MgO ratios in the slag. It was found out that the plasma temperature derived from Ca I emission lines has a non-linear relation with the CaF₂ content of the slag. Additionally, the dissociation pathways of molecular slag components were determined and studied in different plasma temperatures with equilibrium composition computation in order to determine the relations between the slag and plasma compositions

Improving energy and resource efficiency of electric steelmaking through simulation tools and process data analyses

The European Steel industry is ever more committed to improve the socio-economic and environmental sustainability of its processes by promoting any development, which can increase resource efficiency and lower the environmental footprint of the steel production. The European Steel Technology Platform gives the highest priority to the topic of Sustainable Steel Production within its Strategic Research Agenda since 2013. Several projects have been developed both at corporate level, as well as by associations of companies and research institutions in order to investigate new processes, retrofit actions and apply innovative combinations of existing technologies that can allow to improve the energy and resource efficiency and the management of by-products, waste and wastewater. However, it is still difficult for process managers and plant engineers to find accessible tools to both analyze the process data and to perform scenario analyses aimed at evaluating in a practical and understandable manner the effect of innovations in terms of new technologies or novel procedures and operative practices. Within the research RFCS project entitled ”Environmental Impact Evaluation and Effective Management of Resources in the EAF Steelmaking – EIRES” (where EAF stands for Electric Arc Furnace), an integrated tool has been developed, which allows to evaluate the environmental impact of current operating practices, modified operating conditions and major process variations and innovations, thanks to process simulation models for both production processes and auxiliary equipment. Also a dedicated Life Cycle Assessment (LCA) is linked to the simulation models in order to provide a further evaluation from the specific LCA perspective. The paper is focused on the description of the developed integrated scenario analysis tool, which includes both process modelling and metrics tools, and to depict some examples of its application for process data analyses and scenario simulations