Processes and products
Elkem's core expertise includes knowledge of controlling processes that involve very high temperatures and accurately determining the chemical content of materials so that they precisely match customer needs. Additionally, Elkem is a world leader when it comes to the production of carbonaceous materials, which is crucial when silicon is to be extracted from quartz. Elkem's processes are energy intensive and efficient operations require a continuous focus on energy efficiency.
Since the company was formed in 1904 Elkem has developed a production technology for the purpose of improving operations. The most renowned invention is the Söderberg electrode from 1917. The electrode revolutionised the global smelting plant industry and provided Elkem with substantial patent revenue for a number of years.
Silicon is extracted from quartz rock, which consists of silicon and oxygen. It is extracted in a chemical process at high temperatures in which the oxygen in the quartz is bound to carbon, thus freeing the silicon from the oxygen. The smelting furnace is fed with quartz and various types of carbonaceous materials: coke, coal, charcoal and wood chippings. Electrodes made from a carbonaceous material are lowered into this mixture. Elkem Carbon is the world's leading producer of such electrodes and supplies Elkem's silicon plants. When the current is turned on a powerful electric arc is formed between the electrodes. This causes the oxygen in the quartz to react with the carbon in the carbonaceous material and form CO₂ gas. The CO₂ gas rises and the silicon can be tapped from the bottom of the furnace. CO₂ is therefore always formed when silicon and ferrosilicon is produced.
Silicon is a semiconducting material suitable for use in electronics. Other important areas of application include aluminium alloying and as factor input for silicone.
Elkem also manufactures ferrosilicon, a material which is alloy of iron and silicon. The ferrosilicon is divided in different classes or families of materials based on their silicon content and types of additional alloying elements (magnesium (Mg), aluminum (Al), calcium (Ca), barium (Ba), strontium (Sr), cerium (Ce), zirconium (Zr), manganese (Mn)). Ferrosilicon is produced in a furnace similar to a silicon furnace, but with iron containing raw materials as part of the charge mix added in the smelting furnace.
The main ferrosilicon based products from Elkem Foundry Products are called nodularisers and inoculants. These products are used in the production of cast iron in order to achieve the required properties in the end product. Cast iron is an iron-carbon alloy where the carbon is primarily precipitated in the form of graphite. The two main types of cast irons are referred to as grey and ductile.
Nodularisers are a family of Mg-containing ferrosilicon alloys which are used in the production of ductile iron. The purpose of the addition of nodulariser is to tie up elements like S and O and create a basis for the carbon in the cast iron alloy to come out in the form of nodules.
Inoculants are a family of ferrosilicon alloys containing alloying elements like aluminium (Al), calcium (Ca), barium (Ba), strontium (Sr), cerium (Ce), zirconium (Zr), manganese (Mn), sulphur (S) and oxygen (O). Type of inoculant used depends on the application area. The purpose of the inoculants is to form suitable substrates from where the graphite can grow. This ensures that the iron solidifies in the desired manner and obtain the desired structure and properties.
Inoculants are used in all cast irons, while nodularisers are only used to make ductile iron. In the production of ductile iron nodulariser is added first to control the sulphur and oxygen content followed by addition of the most suitable inoculants.
Elkem's products enable cast iron to compete with aluminium when it comes to energy efficiency and power to weight ratio in a number of products such as engine blocks.
When silicon is produced, around 15 percent will exit the pipe in the form of dust. This was previously considered a pollution issue. Elkem has developed a method to collect the dust and sells it as a product called Elkem microsilica® with a number of applications. Several of the plants have specialised in the production of microsilica with defined properties. In addition to its own production Elkem also buys and processes microsilica for resale.
Among other applications, microsilica is used to make concrete more dense and thus also solid and water-resistant and to make ceramics more heat-resistant.
Elkem obtains quartz from its own mines which ensures that it has complete control of the quality of the quartz used in Elkem's processes. Quartz occurs in large quantities but good quality is necessary for efficient production of silicon.
The crucial carbon material
Elkem is also a world leader in the production of carbon material used in furnaces and Elkem Carbon supplies plants across the globe. This concerns both the paste that is baked to the electrode and creates the electric arc in the furnace and the paste used to line and insulate the furnaces as well as other equipment to prevent it from melting.
The electrode paste consists of calcined anthracite coal and coal tar pitch. Calcination is a thermal treatment process applied to solid raw materials. The heat processing turns the anthracite into an electrically conductive, clean and resistant material. Electrodes are also needed where production is based on smelting electrolysis, which is a chemical process created using electricity, with the production of aluminium being a prime example.
Ramming paste, consisting of the same materials, seals joints and prevents the furnace from being damaged by liquid metal. The paste is installed by ramming, i.e. using vibration and pressure. The ramming paste is then 'baked' at 960°C so that it becomes hard and fully sealed.
The actual production of ramming paste and electrode paste involves an initial heat processing of the anthracite, which is coal with a carbon content of 92-98 percent. This is ground and then mixed with coal tar pitch, which binds the paste together. This is then cast using suitable moulds.
Elkem is now researching the use of biological material as an alternative binding agent instead of coal tar pitch.