Slag corrosion of alumina-magnesia-carbon refractory bricks: Experimental data and thermodynamic simulation

Alumina-magnesia-carbon (AMC) bricks are used in steelmaking ladles, where they are part of the bottom and sidewalls working linings. These refractories can be corroded by liquid slag, especially during tapping and casting. In order to contribute with information regarding the reaction mechanisms and the formed phases when they are in contact with a molten slag, the slag corrosion at high temperatures of three AMC refractories is analyzed in this paper. A crucible test was performed at 1600 °C using an industrial basic slag, and the results were compared with those obtained in testing at 1450 °C. In addition, thermodynamic simulations of the slag-refractory contact were performed using FactSage software and a model which considers the global chemical composition of each refractory. Differences in the materials wear associated with differences in composition were predicted by the simulation. Other determining factors, such as microstructure and texture of the evaluated AMC refractories, were also discussed.     

Wetting of aluminosilicate refractories with cast iron

Conclusions The magnitude of the wetting angle of molten cast iron on aluminosilicate refractories depends on the structure, phase composition, and physicochemical properties of the solid material and the melt. An increase in the temperature from 1140 to 1500°C causes the wettability of the refractories by molten cast iron to increase as a result of the increase in the content and chemical activity of the liquid phase in the refractory.An increase in the open porosity of sintered kaolin refractories from 8 to 16% results in a decrease in the wetting angle of cast iron at 1350 and 1500°C from 122 to 108° and from 119 to 102°, respectively; at 1140°C the wetting angle increases with the open porosity.The largest wetting angles of cast iron occur on high-density mullite and kaolin refractories containing a minimum of glass phase.Translated from Ogneupory, No. 5, pp. 35–38, May, 1978.     

Wear of the periclase-lime lining of steel teeming ladles in ladle desulfurization of steel

Conclusions Wear of a periclase-lime steel teeming ladle refractory lining is a complex physicochemical process in which it is practically impossible to distinguish a predominant elementary direction of action of the molten slag and metal.Replacement of liquid synthetic slags with solid slag-forming mixtures in ladle desulfurization of steel does not have a significant influence on wear of the lining working layer.An increase in the amplitude and number of thermal cycles significantly increases formation of cracks in the refractory lining and, consequently, accelerates its wear. An increase in temperature gradient within the refractory layer significantly increases crack formation.The presence of high-temperature contact of the periclase-lime lining working layer with strong deoxidizers accelerates its wear.Reduction of the magnesium and calcium of the refractories by the carbon of the binder under ladle service conditions may occur only with escape of gaseous CO through the reinforcing layer and the joints of the refractory lining in special gas escape holes in the ladle shell.Translated from Ogneupory, No. 3, pp. 33–36, March, 1993.     

Corrosion-erosion behavior of MgAl2O4 spinel refractory in contact with high MnO slag

The corrosion and erosion behavior of spinel refractory of different compressive strength has been investigated for refractories in contact with a high MnO slag for producing manganese ferroalloys. The finger rotating test (FRT) was adopted to evaluate the degradation behavior at 1550 °C under a rotating condition of 150 rpm. The sample with higher compressive strength (Sample C1) showed higher corrosion resistance than Sample C2. In Sample C1, the refractory progressively corroded from the surface to the inner region by chemical corrosion, while mechanical erosion of the refractory suddenly occurred in Sample C2 as a result of the penetration of the slag within the refractory and the rotating energy.     

Interface behaviour and corrosion behaviour of magnesia refractory by alkaline slag in an alkali recovery furnace

The adhesion of Na₂CO₃ slag to the surface of refractories in an alkali recovery furnace can cause corrosion and spall. Magnesia refractories can be used as linings in alkali recovery furnaces owing to their strong corrosion resistance to alkali slag. However, the permeability resistance of magnesia refractories is relatively poor. Hence, the interface and corrosion behaviours of slag cladding on magnesia refractories were studied using sessile drop and static crucible tests. The experimental results showed that an increase in the heating rate positively affected the cladding of the molten column on the refractory surface. The microstructure, element changes, and chemical composition changes of the corroded refractories were analysed using SEM-EDS and XRD. Thermodynamic simulation of the reaction between the slag and refractory was performed using Factsage 7.3. The results indicate that the generated forsterite filled the pores of the magnesia refractories. The microstructure of dense slag-refractory interface layer was formed, which prevented the infiltration of slag phases and alleviated the corrosion of refractories by the slag.     

Effect of Cr2O3 on Slag Resistance of Al2O3–SiO2 Refractories

Refractory bodies of 65 wt% Al₂O₃ were prepared from a mixture of calcined alumina and raw kaolin with the addition of Cr₂O₃ up to 15 wt%. The Cr₂O₃ addition effectively enhances slag resistance and reduces mullite formation. Petrographic analysis of the refractories after the slag test suggests that Cr₂O₃ increases the viscosity of both the glassy phase in the refractory as well as the slag, thereby retarding slag penetration and reaction at elevated temperature.     

Anorthite insulating refractory

Conclusions A technology was developed for manufacturing heat-insulating refractories with an anorthite composition and an apparent density of 0.3–0.4 g/cm³ or more using kaolin, semihydrated gypsum and stabilized foam. The proposed method guarantees a reduction in the production cycle, yielding cheap insulating brick, and the possibility of mechanizing the production processes.Anorthite ultralightweight refractories in terms of their basic factors correspond to insulating products made by foreign concerns for service at 1100–1260°C.Translated from Ogneupory, No.5, pp. 36–40, May, 1970.     

Investigation of slag-refractory interactions for the Ruhrstahl Heraeus (RH) vacuum degassing process in steelmaking

In order to determine the effect of slag composition during the RH process on refractory wear, magnesia–carbon and magnesia–chromite refractories were immersed for 10 min at 1600 °C in a ladle slag, two FeO-rich slags (20 and 40 wt% FeO) and two CaO–Al₂O₃ slags. Corrosion of magnesia–carbon refractory by the ladle and CaO–Al₂O₃ slags was limited as the refractory carbon phase efficiently prevented slag infiltration. Severe degradation was observed in contact with FeO-rich slags. FeO oxidized the carbon phase with formation of Fe droplets at the hot face. Regarding magnesia–chromite refractory, the corrosion mechanism consisted of severe slag infiltration, high temperature inactivation of the secondary chromite and primary chromite dissolution in the infiltrating slag. The FeO-rich slags seem to have generated more severe conditions as the infiltrating slag pushed apart the periclase grains, leading to severe refractory erosion. The degradation mechanisms are discussed by combining experimental results and thermodynamic calculations.     

Use of fireclay dust from rotary furnaces

Conclusions Dust removed by electric filters from the gases of rotary furnaces can be used for the preparation of firebrick articles. The composition of the bodies recommended is as follows; for standard brick 45% grog, 35% dust and 20% kaolin; for lightweight insulating brick 30% dust, 35% thermal-anthracite, 17.5% kaolin, and 17.5% Chasov-Yar clay.With combined firing into grog of kaolin and dust in the briquette it is possible to add not more than 20% dust; with an increase in the content the water absorption of the grog increases.When designing refractory factories in the complex of which we introduce rotary furnaces with electric filters, it is necessary to specify equipment for transporting dust into the body-preparation section with the aim of using it.The use of dust from rotary furnaces for the production of refractories will be a useful innovation for refractory workers in completing the directives of the 23rd congress of the party aimed at improving use of raw materials.The work was shared by L. S. Shchetina and S. D. Svidlo.     

The action of slags of varied basicity on spinel - Periclase refractories

Conclusions In the action of slags of the Fe₂O₂-CaO-SiO₂ system on spinel-periclase refractories consisting of a filler and a binder the mechanism of erosion depends on the composition of the slag and the degree of erosion on the composition of the spinel party of the binder of the refractory.The essence of the chemical interaction of the refractory with the penetrating melt consists in the formation of solid solutions of periclase and spinels with the ferric component of the slag, and in the interaction of the periclase and silica in the presence of acid slags which results in the formation of forsterite; in the presence of basic slags it is primarily the spinel which is eroded and interacts with the calcium oxide, the result being the formation of calcium monoaluminate and chromite, and periclase.The erosion of the refractory depends largely on the stability of its bond; the periclase grains are affected only superficially by the processes of the interaction.When slags of different basicity act by turns on spinel-periclase refractories, the nature of the processes developing in the refractory as a result of the penetration of the melt is quite different. The chemical compounds formed in the interaction with the previous slag are dissolved in the melt penetrating into the refractory, i.e., the forsterite in the subsequent interaction with basic slag and the alumino- and chromocalcium compounds in the subsequent interaction with acid slag. The result is that the ratio CaOSiO₂ in the melt approaches two so that the chemical activity and solution capacity of the melt decrease. In this case the principal product of the crystallization of the melt is represented by monticellite.This investigation showed that in contact with melts in the Fe₂O₃-CaO-SiO₂ system a marked advantage lies with compositions which contain high-alumina spinels, the reason being the volumetric stability of these spinels to iron oxides.Translated from Ogneupory, No. 2, pp. 39–47, February, 1977.     

Influence of the aluminum oxide content of chamotte gunite masses on their slag resistance

Conclusions The authors investigate the influence of the aluminum oxide content of chamotte gunite masses on their slag resistance in contact with converter and synthetic slags. The refractory undergoes wear by dissolution of its surface in the fused slag; the slag does not penetrate very deeply into the refractory.A significant increase in slag resistance is observed only when the aluminum oxide content of the slag is 40% or more. An increase in the aluminum oxide content from 34–35 to 37–39% is not accompanied by a marked increase in the slag resistance. Linear regression equations with high correlation coefficients (0.70–0.98 in absolute value) have been constructed for different aluminum oxide content ranges.A more significant decrease in slag corrosion can be attained by introducing special additives into the chamotte mass composition.Translated from Ogneupory, No. 6, pp. 30–32, June, 1980.     

A PETROGRAPHIC STUDY OF SOME SLAGS FROM BOILER FURNACES1

Observations are based on a microscopic study of the effect of slags, particularly those of an Illinois coal, on refractories. A mineralogical relation is shown between the slag and the refractory used. The principal phases present in a cooled slag are: (1) a plagioclase feldspar, (2) magnetite or hematite, (3) mullite with iron oxide in solid solution, (4) glass. The so-called “interface” between slag and refractory is largely crystalline upon cooling and consists principally of mullite which, surrounded by the slag, has grown from fine needles in the refractory to larger ones. In high alumina refractories where diaspor is present, the stained interface is much thicker and grains of corundum are formed. This zone of crystallization may be conducive to spalling. The effect of slags on various refractories is discussed.     

Methods of determining the corrosion resistance of glass-tank refractories

Conclusions When laboratory investigations are being carried out to find resistant refractories for glass tank furnaces it is desirable to make simultaneous use of indirect and direct methods of assessing corrosion resistance.The use of indirect methods for determining corrosion resistance in refractories permits us to explain the nature of the interaction between the refractory and glass, to study the nature and properties of the reaction products, and also to select refractories that form with the glass the most infusible or viscous reaction products for subsequent investigation in molten glass.The direct methods permit direct determination of the rate of corrosion of refractories by glass at working temperatures and allow us to recommend the most corrosion resistant refractories for tests in service conditions.In laboratory conditions we established that the most corrosion resistant refractories in regard to original glass used for obtaining slag sitalls are bakor-33 and dense zirconium refractory. This may be explained by the formation of viscous reaction products in the contact layer which have a protective action on the refractory.Translated from Ogneupory, No. 5, pp. 56–60, May, 1967.     

Some properties of refractories based on clinkers with various concentrations of calcium oxide

Conclusions We have studied the properties of the refractories prepared from periclase-lime clinkers with a CaO concentration of 2 to 60%. It is established that as the concentration of CaO is increased, the rate also increased at 1500–1650°C; the degree of dissolution of the refractories in slag is reduced; and in connection with this, their wear resistance is also lowered when tested under conditions simulating, in a first approximation, normal production conditions.The wear-resistance of the fired, pitch-impregnated refractories is higher than for the resin-bonded refractories of the same composition; this is the result of their greater density and strength at the test temperatures. The stability of the resin-bonded refractories made from synthetic clinker with 20% CaO is roughly 20% higher and that of the pitchimpregnated fired refractory 40–50% higher than the resistance of the resin-magnesite refractories normally used in production.Translated from Ogneupory, No. 5, pp. 43–48, May, 1981.     

Role of graphite on the corrosion resistance improvement of MgO–C bricks to MnO-rich slag

In order to clarify the effect of graphite content on the corrosion behavior of MgO–C refractories immersed in MnO-rich slag, the MgO–C refractory samples bearing 5 wt%, 10 wt% and 15 wt% graphite were prepared, and exposed in the slag composed of 40 wt% CaO, 40 wt% SiO₂ and 20 wt% MnO. The results show that metallic Mn particles and (Mg,Mn)O solid solution are formed at the slag/refractories interface. Whereas, no dense layer is formed by (Mg,Mn)O solid solution at the interface. The decrease in MnO content of slag is mainly attributed to the reaction with graphite to form liquid Mn. The graphite is found in the slag, and dissolved in the form of oxidation. The poor wetting limits the contact area of graphite and slag, reducing graphite oxidation and decarburized area. The graphite does not become the passage for slag to penetrate into the refractories due to the oxidation. On the contrary, the dissolution of MgO in slag is faster than graphite, thus is mainly responsible for the degradation of refractories. As a result, MnO and MgO contents change less in the slag contacted with the refractories bearing higher graphite content.     

The service of regenerator checkers in open hearth furnaces

Summary An effective way of increasing the life of checkers is to increase the height of the structure made of chrome-magnesite brick to 10–12 courses. This reduces the average melting time, increases furnace output by 5–7%, and reduces the oil consumption by 7%.The dust settling on the refractory has a typically high content of iron oxides. At normal checker temperatures (not above 1400°C) the surface of the refractories forms friable, dusty deposits. With a rise in temperature in the regenerator the dust sinters, partly fuses, and sticks to the refractory. This cake is removed by blowing the checkers.Investigation of the refractories after service confirms that the phase changes,in the reaction layer of the brick, take place mainly owing to the action of iron oxides of the dust on the refractory. Fusing of firebrick is also intensified by oxides of iron contained in the dust.The mineral formation and destruction processes are greatly affected by the changing composition of the gaseous atmosphere, which is confirmed by the formation of mixed crystals of magnetite and haematite in the crusts and reaction zones of the refractory.Of the refractories tested in the checkers, the best was chrome—magnesite.To explain the possibility of increasing the life of checkers, experiments should be made using forsterite brick of high quality in the 15 top courses of the checkers using the Cowper system of building the checkers.     

Study of the service of high-alumina and kaolin refractories in the checkers and structure of blast-furnace stoves

Conclusions The structure of kaolin brick in the high-temperature zone of the stove after 6.7–7.2 years service at subcupola temperatures of 1300°C underwent substantive external and structural changes.In the structure of the stove made from high-alumina brick VGO-62 after six years service we detected substantially less change.In the kaolin brick of the upper rows of the checker three clearly defined zones are formed: working (slag), impregnated with alkalis, the transition zone (porcelain-type), and the least-changed zone. During the service of high-alumina refractories mullite crystallizes, which confirms the results of work carried out previously.Owing to the creep of kaolin and high-alumina refractories 4–5% shrinkage of the brick occurs in the upper rows of the checker, and at a depth of 2.5–6.0 m — 1.5–2.0%. The height of the checker diminishes under these conditions by 0.8–1.0 m.The densification of the structure of the upper rows of the checker corresponds to a reduction in porosity and an increase in the density of the brick.The temperature of initial deformation under load of 2 kg/cm² of the slagged kaolin refractories taken from the upper rows of the checker diminishes by 150–200°C, and in the lower layers of the checker it does not alter. This factor for high-alumina refractories in service increases by 160–190°C. In the high-temperature zone of the stoves it is desirable to test dense, high-alumina refractories containing 72–75% Al₂O₃.Translated from Ogneupory, No. 5, pp.14–19, May, 1972.     

SOME EFFECTS OF COAL ASH ON REFRACTORIES1

The action of coal ash on the following types of refractories was studied: (1) high diaspore brick, (2) fireclay refractories with very little quartz, (3) fireclay refractories with considerable quartz, (4) refractories containing a mixture of diaspore and fireclay, and (5) andalusite refractories. The tests were carried out in a rotary test furnace at temperatures ranging from 1500 to 1600°C. The phases present in the coal-ash refractory slag were identified by means of the petrographic microscope and consisted of magnetite, mullite, and glass. The effects of time of slag action and slagging temperature were studied.     

Al2O3-ZrN-Sialon-C复相耐火材料抗渣侵性能研究

以板状刚玉、石墨、α-Al2O3、金属铝粉、单质硅粉为主要原料,ZrN-Sialon复相粉体为添加剂,采用酚醛树脂结合制备了Al2O3-ZrN-Sialon-C复相耐火材料.采用静态坩埚法研究了ZrN-Sialon复相粉体加入量对材料抗渣侵蚀性能的影响,借助SEM与EDS面扫描对渣蚀后材料的结构和成份进行分析,并探讨了Al2O3-ZrN-Sialon-C复相耐火材料的抗渣侵蚀机理.结果表明:ZrN-Sialon复相粉体加入量为9wt％时,材料表现突出的抗钢渣侵蚀性能.研究表明材料中Sialon氧化后生成的SiO2能形成致密的氧化保护层,同时ZrN氧化后形成的ZrO2有利于提高抗钢渣的浸润,阻止钢渣的渗透与侵蚀.分析认为Al2O3-ZrN-Sialon-C复相耐火材料的钢渣侵蚀机理为氧化-熔蚀-渗透.     

Service of the magnesia-spinellide lining of a melting furnace roof

Conclusions On the basis of a study of the magnesia-spinellide roof of a melting furnace it was established that the refractory consists of four zones, the least changed, the working, the zone of contact with the lining slag, and in the lining slag. A nonuniform distribution of the components in specimens of lining slag taken from different portions of the roof was observed.The lining slag and the zone of contact with the lining slag consist of crystals of picrochromite, ferrite, and magnesioferrite, between which there is located a silicate binder including forsterite, hedenbergite, and the impurity phases bunsenite, hematite, and magnetite. The working zone consists of chromite, picrochromite, monticellite, and the introduced melting products copper, chalcosite, and cuprite.On the basis of analysis of the data on failure of refractories as the result of chemical interaction with the melting products, penetration of the low-melting components, and thermomechanical cracking at the boundaries of the zones it was established that one of the methods of protection of the roof is cooling.Translated from Ogneupory, No. 2, pp. 51–55, February, 1989.