Ferrosilicon is one of the alloys used in various industries, especially metallurgical industries, and has become relatively important in this regard. How this material is used in industry largely depends on the ratio of iron and silicon in it, as well as conventional impurities. The metallurgical industry is used as an alloying, germinating, deoxygenating, and almost pure silicon element in the electronics industry as a semiconductor and rectifier. In addition, its composite derivatives are used to make silicon resins, glazes, rubbers, etc. It is not possible to obtain ferrosilicon production technology without recognizing the properties of each of the elements of iron or silicon or their composite product. Comments In this chapter, the main issues of ferrosilicon user are discussed according to its properties and characteristics.
Physical and chemical properties of silicon:
Silicon is an element in the fourth period of the table of chemical elements that has 4 electrons in its last circuit and therefore, unlike carbon, it appears in all chemical compounds with a capacity of 4, such as:, the presence of silicon in compounds with a capacity of 2 has also been proven. However, these compounds are unstable and quickly turn into compounds with a capacity of 4 and only act as intermediaries according to the combined conditions.
The formation temperature of one mole of silica “Sio2” varies according to the formation conditions of quartz or carbocytoballite () and is as follows:
While the heat of formation of silicon and silica monoxide is reported as follows:
Sio gas decomposes at less than 1500 ° C to silicon and silica.
The melting point of silicon is degrees Celsius, which is not found freely in nature due to its strong affinity for oxygen and other oxidizing substances. Its main composition is various forms of silica, which are almost pure and with a degree of mixture of more than 98%, and also in the form of spinel (double oxide with aluminum) or silicates in different proportions in nature. Silicon is the most important constituent after oxygen. The Earth’s crust is estimated at 28 percent, while the Earth’s crust is estimated at 49 percent, aluminum at 7.2 percent and iron at 5.6 percent.
Silicon is available in three forms (polymorphs), which are:
A. Amorphous silicon is a brown powder with a density. This substance oxidizes rapidly and is converted to silica in the presence of air. Reduction of silica powder by magnesium powder at a temperature of about 100 to 1200 ° C usually leads to the formation of amorphous silicon or Silicon turns brown.
B. Graphite silica مت is a silicon formed by the reduction of silica by carbon at temperatures above 1400 ° C. It is layered and black and shiny, and more resistance to air and acidic solutions indicates that its density is approximate, and in most cases where it is necessary to add pure silicon to the melt, this type of silicon is not used.
C. “Crystallized” silicon, or piece silicon, also known as metal silicon, is generally produced by increasing the temperature in a silica reduction furnace or by heating graphite silicon indoors. In most cases, in pure silicon applications in In the electronics industry, this type of silicon is used and the density is reported.
Fragmented silicon and graphite silicon are often present together due to similarity in how they are produced. The graphite type is more used in the metallurgical industry due to its better solubility in molten materials, but the fused silicon type can also be used in other purposes. Metallurgical and the main difference is that its reaction rate is slower than the previous type
Crystallized silica is reported in the cubic structure of a diamond with a lattice constant.
3-1- Silicon and industry
Silicon, whether purely or in combination, has found various applications in industry, the most important of which are classified as follows:
Metallurgical industries
A. Deoxygenation: Silicon is more oxidizable than many major metals in industry, metallurgy (iron, copper, nickel, chromium, etc.) (Figure 1-1 – Richardson Table) and hence for many industrial alloys The term deoxygenation is used, including the use of this element in the steel industry and steel casting.
Silicon as a deoxygenator is not generally used in steels in pure form, and most of the alloying compounds are rosilicon, ferrosilicon manganese, ferrosilicon aluminum, or silicon calcium.
The most important factor in choosing silicon (with or without aluminum) as an oxygenator in steels is that:
The density of silica is about 2 to 2.4 and hence according to the stock relationship
It accumulates rapidly on the surface of the melt where:
V: Buoyancy speed
: r The size of the particle or silica formed
Melt density
Density of silica
Melt viscosity
Is .
Silicon residues in amounts less than 0.1% in steel and cast iron have no critical adverse effects, while the amount of aluminum in steels should be controlled at about 0.01%.
The silicon produced at the melting temperature of steel can be formed by the adsorption of other oxides such as iron, calcium and ك silicate compounds, and its slag mode can effectively remove those oxides.
Figure 1-1 Diagram of Richard Sion
The following points can be considered about the deoxidizing effect of silicon in steel and its comparison with other deoxygenating materials.
The deoxygenation limit of silicon is much lower than that of aluminum and several times that of manganese, in which case the Brinel test is used to determine the degree of deoxygenation based on the residual elements.
Based on Swidem tests; The effect of silicon residue on deoxygenation of steel and removal of co-porosity due to CO gas is reported as follows.
Percentage of silicon 12 / 0-15 / 0 15 / 0-18 / 0 18 / 0-2 / 0 2>
Percentage of 100 pieces 8/57 8/13 0
In this experiment, the amount of carbon was 0.55 and the amount of manganese was 0.7%
According to the above explanations, it is clear that the application of silicon in the form of ferrosilicon and ferrosilicon aluminum compounds and the like is one of the most important uses in the metallurgical industry. The amount of silicon used for this purpose is usually more than 0.3%. Pay attention to 75% ferrosilicon (average 0.4% ferrosilicon) for each ton of steel produced, the amount of ferrosilicon consumed is about 4 to 5 kg.
In addition, silicon is used as an oxygenator in steel casting in larger quantities (the critical limit of the presence of silicon in the casting steel is higher and in addition there should be no gas and cavities) in this case, the amount of silicon consumption between 0.3 to 0.6 percent has been reported.
B – Germination: Silicon is a highly graphitic element, so that the formation of graphites in all types of cast iron in the presence of silicon as an alloy element and capacity graphites, to inoculate silicon (as ferrosilicon in the final stages of smelting and before load It depends on the detail.
The germination capacity of silicon depends on the amount of silicon present in the compound or mixture. On the other hand, if pure silicon is used for this purpose, it is possible that it will not dissolve completely, and for this purpose, in most cases, iron and silicon alloys with combined ratios of 70 to 90% silicon are used. Consumption of silicon as a germinating element in all graphite cast irons is reported to be about 0.6 to 1%, if this ratio is measured with 75% ferrosilicon, about 1 to 1.5%, in other words, the amount of germination material is about 10 to 15 kg. Ferrosilicon is used to produce any ton of graphite cast iron
In addition, silicon is used as a germinator in the form of silicon-calcium, in which the presence of calcium is also used to desulfurize and intensify deoxygenation.
Magnesium inoculation to graphite sphericity is often done by mixtures of iron-silica-magnesium to germinate and modify graphite simultaneously.
Alloy element: Silicon is one of the alloying elements in the family of ferrous and non-ferrous alloys. The most important industrial alloys containing silicon are:
Cast irons, silicon is one of the main elements and in fact the second alloying element of all ordinary cast irons. The amount of silicon in these cast irons is usually 1 to 2.7 percent. Silicon In the smelting operation of these ingots, an increase of 1 to 1.5% of silicon is required in the form of ferrosilicon alloys. On the other hand, due to the production of cast iron through scrap iron in induction furnaces or the use of a percentage of scrap in other methods, the supply of necessary silicon deficiency is usually 2.5 to 3.5 percent. The increase of this silicon is usually done in the form of ferrosilicon with different composition ratios. Silver cast irons containing 10% to 22% silicon, which are generally anti-acid, are produced by melting in blast furnaces or melting in electric furnaces by adding crystallized silicon. .
Steels usually contain less than 0.3% silicon, which is obtained from the deoxygenation waste, but silicon-containing steels also contain 3 to 5% silicon and are commonly used as transformer steels. It is done by inoculating ferrosilicon mixtures.
Bronzes and brass; Copper-tin and copper-zinc alloys with an increase in silicon in the amount of 0.2 to a maximum of 3% in special application conditions such as high strength, corrosion resistance, acid resistance in bearings and…. Used Silicon is known as a harmful element in most copper alloys, but it is added to the melt as crystallized silicon in special brass and bronzes.
Copper-silicon alloys have not been produced yet due to lack of consumption and iron-silicon compounds can not be used except in cases where iron is one of the alloying elements. Calcium silicon is also used in copper alloys due to its calcium deoxygenation , Can be used, but this is possible in cases where the required amount of silicon is less than 0.5%.
Aluminum Most aluminum alloys contain 0.1 to 0.5 percent silicon as an impurity that enters the melt under production conditions and through raw materials. But silicon is used as an alloying element in casting and rolling alloys 6000.4000.400.300 as the second element and in other alloy families as the third and fourth elements. The amount of silicon in different aluminum alloys is from 1 to more than 13 percent and in addition to alloys A new one with about 16 to 20% silicon is also used in the manufacture of pistons. Addition of silicon to alloys or aluminum is done through the use of crystalline silicon as well as a variety of alloys such as aluminum-silicon alloys. . While this value is reduced to less than 4% for climbing alloys, silicon in these alloys increases the strength and improves the casting conditions.