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The influence of high temperature composition of surface active substances on the performance characteristics of refractories

In metallurgical processes the role of the gas and especially the liquid phase in the reaction between the solids of the lining, as well as in the reaction between lining material and molten metal occurring at the interface of the refractory - molten metal, can be considerable and even decisive. In some cases, the duration of the refractories and their resistance to molten slag and metal differ substantially from generally accepted provisions. Based on our research, we have tried to identify certain patterns, which, in our view, are consistent with the theoretical foundations of the technology of refractories and their service in the steelmaking facilities.

In refractories the thermodynamic equilibrium towards which any system operated by the minimum values of thermodynamic potentials. The interfacial energy is only one of these terms. According to the second law of thermodynamics of the condensed phase are distributed according to the principle of minimising the free energy, the magnitude of which depends on the surface phases, surface energies between the phases and their mutual location [1].

In the considered cases, the liquid phase is concentrated or in the pores between the crystal grains, or distributed between the crystalline phases and envelops them, the crystals do not form crystalline concretion.

It is believed that crystalline phase is more stable and the potential energy it is small, and the glass phase is metastable, and the potential energy she's got a big. However, a decisive influence on the properties of refractories in contact with molten metal and slag has not only a quantitative ratio of the phases, but also their distribution in the refractory[1]. At high temperatures in glinozemservice products under non-equilibrium condition assumes the existence of two liquids: one containing almost no alumina, with a relatively low surface tension, and other containing alumina, and therefore having a higher surface tension.

Of the energy provisions known that liquids with low surface tension is able to spread on the surface of liquids with large surface tension, the opposite is not possible.

To regulate the ratio of the interfacial energies and the distribution of phases in the whole volume of the refractory in the process of operation it is recommended that the introduction of high-temperature surface-active substances - surfactants[2].

The selection of the composition of the liquid phase as to change in the desired direction of interfacial energies, and the temperature coefficient of surface tension is one of the promising areas in the technology of refractories. The liquid phase has a significant impact on the change of structure and properties as in the sintering process, and in further service of refractories. The process of external impregnation of the melt, in our case the metal is always preceded by migration of the liquid phase in the refractory under the influence of the temperature gradient, thus there is a redistribution of the concentration of the high-temperature surface-active substances in the direction of contact with the molten metal.

Migrating the liquid phase, wetting of pore walls of the refractory that fills the pores and prepares the way for the impregnation of external melts. To avoid this mechanism, it is necessary to introduce an additional layer of the liquid phase to prevent direct dissolution of oxides of the refractory metal. In the case of formation of two liquids, a liquid having a greater wetting, tends to displace the less wetting and, thereby, to occupy the pores of the smallest size.

The concentration of the high temperature of the surfactants, depending on their nature, can vary in different limits. In the works of S. I. Popel [3] has had a huge impact intermediate liquid film, changing the viscosity and surface tension which can significantly adjust the properties of oneupornah materials. The concentration of the surfactant in this case can be small.

We have conducted a number of works with the aim of selecting the optimal composition of high-temperature surfactant to provide increased performance characteristics of materials, working in direct contact with the molten metal and, in particular, to monolithic linings of the bottoms of steel-teeming ladles.

Of particular interest is the possibility of making monolithic linings of dry mixtures by ramming or gaskets without the use of liquids for mixing concrete mixtures, and thus the exclusion of such a long, energy-consuming and responsible stage of drying the concrete lining.

Regulation of the quantity and quality of liquid phase needed to ensure a thermoplastic condition of the refractories.

Thermoplastic state accompanied by relieve stresses generated during operation of the refractory, especially in such units as steel casting ladles, which have direct contact with the molten metal and large temperature changes.

In Fig. 1 shows the dependence of the thermal stability aroundspiral samples of the composition of additives selected as the surfactant. All samples were manufactured for cementless technology, pre-termoobrabotki at a temperature of 1100oC and had a porosity in the range of 18-20%. The content of aluminum oxide 94.8 per cent, of magnesium oxide and 3.9%. The amount of the additives was 2% in excess of 100. Supplement number 4 was selected by us based on providing high strength properties for a range of materials alumomagnesium and forsterite compositions. Under Supplement No. 1 to 3 were taken as traditionally used in the production of refractories as sintering additives and at the same time, which is a high-temperature surface-active substances.

"cellpadding="5"> Зависимость металлоустойчивости корундошпинельных образцов от состава высокотемпературных поверхностно активных веществ Figure 1. The dependence of the thermal stability aroundspiral samples from the composition of the high temperature surfactant

As can be seen from the figure, pavilion # 4 provides a significantly higher metallabstudios during the whole time of the experiment in comparison with other additives.

Based on these results we decided to test the influence of additives we have developed high temperature saw-slag and metallabstudios aroundspiral samples with different contents of Al2O3 and MgO. The most illustrative examples is shown in Fig. 2 and Fig. 3. Graphs 1, 2 and 3 in both figures differ in the content of magnesium oxide, MgO, where respectively 10, 4 and 2 percent.

Зависимость металлоустойчивости от количества высокотемпературных ПАВ в образцах
Figure 2. The dependence of the thermal stability of the number of high temperature surfactant in the samples
Зависимость шлакоустойчивости от содержания жидкой фазы в образцах. 1 - Al2O3 - 90%, MgO - 10%; 2 - Al2O3 - 98%, MgO - 2%; 3 - Al2O3 - 95%, MgO - 5%
Figure 3. The dependence of lacoustics from the content of the liquid phase in the samples. 1 - Al2O3 - 90%, MgO - 10%; 2 - Al2b>O3 - 98%, MgO - 2%; 3 - Al2O3 - 95%, MgO - 5%.

The increase in the content of magnesium oxide of more than 5% significantly reduces metal - lacoustics. In addition, with increasing the content of MgO and an increase in contact time pricesordering materials from the melt is markedly reduced mechanical strength of the contact liquid metal - refractory, leading to erosion of the lining. This is clearly seen in Fig. 4, where the graphs shows the dependence of the thermal stability and the content of magnesium oxide in aljumokalievyh samples. These results are also quite understandable from the point of view of the theory of refractory materials and are confirmed in a number of publications on the service of refractories. The effect of high-temperature surface-active substances of periclase refractories, in the quantities in which they are considered to be additives (to 5%), not significantly, because the liquid phase is almost not formed.

The reaction in the solid phase occur reversible volumetric change, leading ultimately to the destruction of the refractories. When this liquid phase is not formed. This is especially true for basic refractories - magnesia, dolomite, forsterite and periklazokhromntovykh.

Зависимость металлоустойчивости образцов с различным содержанием Al2O3 и MgO от времени контакта с расплавленным металлом при t 1650oC. 1 - MgO - 95%; 2 - MgO - 80%; 3 - MgO - 20%; 4 - MgO - 10%; 5 - MgO - 3%.
Figure 4. The dependence of the thermal stability of samples with different contents of Al2O3 and MgO from the time of contact with the molten metal at t 1650oC. 1 - MgO - 95%; 2 - MgO - 80%; 3 - MgO - 20%; 4 - MgO - 10%; 5 - MgO - 3%.</td>

Solid-phase reactions in the system iron oxide - periclase - spinellids so is accompanied by significant changes in the amount that the destruction of magnesia refractories prolonged their interaction with metal and slag is much more intense than high-alumina and corundum, in spite of a considerable difference in the melting point. In magnesia refractories volume changes increase with increasing the number and degree of recovery (oxidation) of iron oxides [4].

Magnesia products provide with iron oxides are the most refractory compounds and have minimal solubility in iron oxides.

Mullite-alumina, and corundophilite-resistant alumina-mullite products with a content of Al2O3 , more than 85% have almost the same lacoustics to ferrous slags as magnesite, but is much less prone to chipping.

The works performed with the use of as additives to aroundspiral-resistant alumina-mullite refractories and high temperature surfactants allow currently talking about the possibility of the manufacture of monolithic linings of the bottoms of stankovska "dry", i.e. without the use of hydraulic binders and liquids in General. Moreover, performance in this case is not only deteriorating, but also on a number of criteria are superior to the flood.

In conclusion, we note the prospect of work on the selection of the high-temperature surface-active substances to impart specific properties of refractory materials under specific operating conditions.

References:

1. K. K. Strelow, Structure and properties of refractories. M. metallurgy, 1972-93, 110C.with.

2. K. K. Strelow, Refractories, 1968, No. 5 - 43 S.

3. S. I. Popel', Surface phenomena in melts. M. Metallurgy, 1994 - 254, 375 S. C.

4. K. K. Strelow, Theoretical foundations of refractory materials. M. Metallurgy, 1985. - 374с.

Published in the journal "New Ogneupory", No. 1, 2005