Abstract
Сonten
- Introduction
- 1. Relevance of the topic
- 2. The purpose and objectives of the research, the expected results
- 3. The meaning and use of silica refractories
- 4. The effect of additives on the properties of silica refractories
- 5. Technology of production of silica refractories
- 5.1 Sirevye materials
- 5.2 Preparation of raw materials
- 5.3 Compression of silica products
- 5.4 Drying Dinas
- 5.5 Firing Dinas
- 6. Еxperimental findings
- List of sources
Refractory Industry plays an essential role in the mining and metallurgical complex, which occupies a strategically important position in the economy of Ukraine. But in the process of market reform refractory companies faced with economic problems common to the nature of the crisis. It is the industry desperately needs the introduction of modern technology solutions, providing the competitiveness of refractory products in the global market while reducing the use of energy and raw materials.
The refractory industry occupies an important place among the basic industries of Donetsk region. At present, they account for about 5 percent of the total volume of industrial production in the region and in the future will increase.
The development strategy of the refractory industry is based on innovation and investment model of scientific and technical progress and is a further specification of the relevant sections of the "Program of scientific and technological development" The priority areas are:
- Updated Equipment refractory production, replacing obsolete and worn-out equipment at factories producing refractories;
- Development of new refractory lightweight products with low thermal conductivity for the metallurgical units, in particular for blast furnaces, heaters, slide gates, continuous casting machines;
- Further implementation of the strategy of modernization quarries refractory raw materials;
- Improving the technology of silica refractories, expanding the product range.
Silica called refractory material comprising at least 93% silica. Silica products consist of tridymite, cristobalite, residual quartz, glass, variable composition, crystalline calcium silicates. On the chemical and mineralogical composition of Dinas determines its fire resistance, strength, impermeability. The main raw material for the production of Dinas are crystalline quartzite. As a mineralizer additives commonly used calcium oxide. When roasting raw undergoing complex physical and chemical processes accompanied by a modification transformations of quartz to tridymite and cristobalite, irreversible expansion of silica and other raw. Silica firing feature is that the sintering process takes place without sealing Silica, but rather more often with increasing porosity. Dinas hardened by firing through the transformations occurring during recrystallization (formation of crystalline concretion tridymite), and the reaction of silica with a mineralizer.
Dinas of refractory materials has deservedly take priority because of its best building strength at high temperatures. Dinas – one of the few traditional refractory materials, which retains its strength and fire resistance, softens to a temperature above its melting point of 1700 °C.
1. Relevance of the topic
The environmental situation in the Donetsk region is estimated by experts as critical. Our region is a major industrial center of Ukraine developed heavy industry, which over the years keeps the basic course to receive coal, metal, and other energy and material resources. The environmental situation in the region is complicated by the large amount of waste, especially toxic. Currently, in the Donetsk region has accumulated more than 4 billion tons of industrial waste. The area of land occupied by waste, close to 2% of the territory. The largest suppliers of industrial waste is coal, mining, chemical, metallurgical and energy industries.
On the one hand, these residues are a source of ecological problems, but on the other hand, they contain valuable components can be a potential resource. But because the processes are carried out so as to provide optimum production parameters main product materials are unstable side composition are not sorted, stored and stored without taking into account possible future use. Therefore, the work in which we investigate the possibility of using these as a waste of resources for the production of recycled glass materials, ceramics, construction, refractory products, may be considered relevant. This approach not only enhances the mineral base of the industry, but also allows you to ensure environmental safety.
In the Donetsk region contains most refractory plants in Ukraine. The main objective of the refractory industry today is to improve the quality of domestic materials and products to international standards that will make them competitive.
Nowadays significantly increased requirements for construction, ceramic and refractory materials. Scientific advances requires creation of new products with new properties and high performance that can be achieved by the use of additives.
2. The purpose of the study
The aim of this study was to investigate the possibility of obtaining silica products using differences supplements.
3. The meaning and use of silica refractories
Since the second half of the XVIII century begins the industrial revolution, which was an important result of active development in the field of metallurgy, construction, ceramics, etc.
For lining blast furnaces, glass melting, coke ovens operating at high temperatures required refractories.
Silica bricks appeared in 1820 in England (of Wales), thanks to developments B. Young, who added a small dose of lime sand, which contributed to a sintering process. Since 1899 actively began to develop the production of siliceous (Dinas) on a bunch of lime and bauxite bricks.
Dinas got its name from pure quartz rock from which it was first made. The binder for the quartz grains was then applied lime.
Dinas of refractory materials has deservedly predominant importance, thanks to his best building strength at the temperatures high.
Dinas – one of the few traditional refractory materials, which retains its strength and ogneuponost not soften to a temperature above its melting point of 1700 °C.
It is quite widely used (Figure 3.1) in the non-ferrous metallurgy furnaces in the glass industry, where it is used for bonding of glass-top structure, as well as pottery kilns [9].
Figure 3.1 – Silica refractories
Silica is widely used for the construction of coke oven [11]. No additional shrinkage, high temperature deformation and sufficient thermal stability lightweight Dinas allow you to use it for the masonry wall and floor rider arches spans large furnace high temperature furnaces. Also lightweight dynasties used for lining covers heaters. He works in a variety of furnaces for heat metal and crucible for melting non-ferrous metals mashinostroitelnyh plants. It is used for laying a small workspace, and heavy furnace chamber for heating large silicates.
4. The effect of additives on the properties of silica refractories
Renowned scientists conducted a series of studies on the choice of mineralization. Tsigler et al [2] in their work to increase the phase tridymite used gypsum, waste burning pyrite and converter slag. Turchinova and others [3] pyrite ash used in the study of their impact on the silica brick. Bulakh and others. [6] to improve the thermal stability and increase the size of the crystals used tridimits hromivuyu ore, chromite pereklazovy fight and silicon carbide. The researchers also used a dry additive [4] of the limestone powder with iron oxide for the clean production of silica brick. Khonchik et al [5] used limestone, blast furnace slag and waste phosphogypsum, which led to a reduction of the residual quartz, tridymite content increased.
Work carried out by known researchers in the past, according to a study of the various types of mineralization. However, studies of the impact of the introduction of metallic additives on silica brick was little. Mineralizer in metallic form have not been studied at all.
The article VJ Greenberg, EA Gimpelmana [2] presents the results of study of the effect of additives on the strength of mineralizyuchy dynasty. Samples used for the manufacture of crystallinity quartzite with 98.1% SiO2, which is used to Pervouralskiy Silica plant for the production of coke dynasty.
In the experiments, the search variables were additive: lime-ferrous mixtureTiO22, Al203, MgO, S. These additives were selected in order to obtain sitalloobrazoi communication structure, which has improved the mechanical properties of the dynasty. As a result of these experiments revealed that when the content is less than 2.2% TiO and more than 3.2% (as CaO) Dinas strength decreases, and to this extent has virtually no effect on her. Therefore, in further experiments TTO content was constant (2.6% CaO).
In laboratory experiments, the main additions were investigated TiO2, Al203, MgO, S. As an indication of the strength of Dinas taken compressive strength.
After studies we can conclude that the introduction of impurities in TiO2 and S quartz base can increase the strength of silica products, while administering Al203 MgO and reduces it.
Maximum compression strength is reached when the content of TiO2 additives 1.5% S 0,5% and equal to 75.9 MPa.
Launched the industrial batch of coke silica products with the addition of portland cement and TiO2. Compressive strength was 80 MPa products.
5. Technology of production of silica refractories
5.1 Raw materials
The main raw material for the production of Dinas are quartzites and quartz sandstones.
The most important raw material, which is used in mass production of crystalline silica refractories is quartzite.
In the manufacture of silica mass they added small amounts of mineralizing agents.
Mineralizer – Additives that are specifically introduced into the batch, which serve to bind the quartz grains manufacturing monolithic mass to accelerate regeneration of quartz and cristobalite, tridymite, for influencing the mineralization process in the desired direction.
Often used as a mineralizer lime, ie calcium ions.
Second mineralizer - iron supplements, such as iron oxide (80% FeO, 10-11% Fe2O3, 6-7% SiO2 and Al2O3 impurities) or pyrite cinder pyrites (50% Fe2O3 27-28% FeO, 13-14% SiO2, 7-8% Al2O3).
Besides mineralizing additives in the silica weight enter LST, calculated on the dry LST – 0.5-1%).
In eksperimentalnoy studied the effect of silica fume on the properties of silica refractories.
5.2 Preparation of raw materials
Quartzites usually come on Silica Plant in pieces the size of 50-300 mm in diameter.
To crush quartzite stage I used crusher jaw size 1200 × 1500 × 150 mm, at the II stage of crushing jaw crusher is used or cone. After crushing quartzite at the greatest pieces of 60 mm contains 10-20% fraction of less than 10 mm. With the increase in the hardness of quartzite content of these fractions decreased. The crushed quartzite arrives on screening.
The silica blend consists of a mixture of dry powders quartzite various factions. The composition of the charge is sometimes administered as Dinas fight. Addition of silica reduces growth combat products at firing and, hence, reduces the stresses arising therein during firing. However, Dinas fight fire resistance decreases, so it is administered only to the charge of coke fittings, fire resistance which may be lower. The silica mass consists of a mixture of wet batch with a mineralizer and other additives.
Lime is introduced into the mass typically in the form of lime milk, which comes from the entire water necessary for humidifying [7].
Weight of silica and non-plastic raw strength derived from it, even at high pressures, low. Lime binds grain quartzite slow and sufficient strengthening of raw occurs only after its drying. In order to increase the strength of raw svizhesformovanogo injected adhesive organic additives, burn out during firing and do not adversely affect the properties of the finished products.
As such additives may wake of sulfite-alcohol bard.
As an adhesive additives can be used molasses (sugar syrup) 0.2-0.5%. The disadvantage of molasses is its ability to thin the svizhesformovanu the silica mass.
5.3 Compression of silica products
Dinas formed only semi-dry pressing on mechanical presses under pressure of 25-60 MPa.
The degree of compressed body affects the composition of mineralizing agents. With the decrease in the mass content of milk of lime, pressing worse. Improved compression is observed with the introduction of lime-mud additives (1.5% CaO 0.5 Al2O3). Maturing of silica mass impairs their pressing.
Dimensions of press forms as a result of the growth of Dinas take on firing at 2-3.5% smaller than the finished products.
5.4 Drying Dinas
Silica raw dried in tunnel driers. Serve as a source of heat or hot flue gases are air, which is taken from the oven, or obtained from the calorimeter.
5.5 Firing Dinas
Upon firing, the following dynasties most important processes:
- 1. reacting SiO2 and CaO form calcium silicates which form silicate to FeO iron oxide solid solution;
- expansion of the silica raw as a result of polymorphic transformations of silica;
- melt formation of complex composition, the dissolution of quartz in it, and dropping out of the supersaturated melt (recrystallization) Tridymite;
- changes in the mechanical strength of the dynasty.
6. Experimental
For research on samples produced on the factory mass of silica fume added to the spent graphite electrodes and quartz sand with high silica content. As the additives used mineralizing calcium oxide in the form of milk of lime and iron oxide in the form of iron ore concentrate. Quartz sand is added in order to improve the chemical composition of Silica, i.e. increasing silica content.
Attempt was made to introduce extra carbon in the form of spent graphite electrodes in order to create the reducing environment during calcination, which in turn promotes more intensive formation of tridymite, elevated content of which is the preferred product.
The paper also studied in order to obtain light-weight of silica refractories with the addition of silica fume, which was produced by burning out of additives. As the latter used coke (30% in the blend).
Samples were formed from a wet mass 7.5-8% dry pressing in metal molds of diameter 30 mm and height of 25-30 MPa pressure. Calcination was carried out in an electric laboratory furnace at a maximum temperature of 1430 °C for firing curve, different from those of the higher production speed and reduce the temperature rise. After roasting samples of Silica tested by standard methods to determine the water absorption, density and open porosity in between the compressive strength. Table 6.1 shows the results (each value is the arithmetical mean value from three parallel).
Technological process of experimental samples is shown in figure 6.1
Figure 6.1 – Manufacturing process of the experimental samples (animation, 8 frames, 154 KB, 10 cycles)