Corrosion of aluminosilicate refractories by molten aluminum and melts based upon it in melting and casting units

Corrosion mechanisms are proposed for aluminosilicate refractories by molten aluminum taking account of new ideas about physicochemical reaction of molten aluminum with refractory.With a negative volumetric effect for aluminum reactions with components of aluminosilicate refractories reaction products will not form a continuous film, and with a positive volumetric effect the reaction products will split pores and cause material cracking. Aporous aluminum oxide film will not be a barrier for the reaction of aluminum with refractory. The possibility for aluminosilicate refractories of wetting by molten aluminum and the size of pores permeable for penetration of molten aluminum in relation to presence or absence of antiwetting additions are determined.     

Effect of light ash of solid fuels on zirconia refractories

Conclusions The action of the melts of the light ash of the Kuznetsk and the Berezovsk coals containing potash additive on zirconia refractories leads to their destruction due to destabilization of the cubic solid solution of CaO in ZrO₂ accompanied by the formation of -ZrO₂, melilites, and a glass phase and the formation of spinellids, pyroxenes, and fayalite if iron-bearing compounds are present in the ash.Intensive destruction of the CaO-stabilized zirconia refractory under the action of a mixture of the Berezovsk ash and potash is due to its low melting point and the high degree of saturation of the refractory with the melt additionally containing iron compounds.The service life of the zirconia refractories subjected to the action of a mixture of the ash of the Kuznetsk coal and potash is longer owing to the smaller degree of melt penetration at a temperature up to 1580°C.Translated from Ogneupory, No. 5, pp. 4–6, May, 1987.     

The influence of impurities in the original materials on the properties of refractories made of zirconia

Conclusions The effects of admixtures of the oxides of iron, aluminum, titanium, silicon and phosphorus on sintering, strength factors, thermal shock resistance, deformation under load, linear expansion and microstructure of articles made from zirconia stabilized with calcium oxide, were studied.According to their influence on the properties of the refractories, the impurities can be divided into three groups:those which prevent stabilization;those which have practically no effect on stabilization;and those which help stabilization.The first group includes P₂O₅, SiO₂, Al₂O₃; the second group includes TiO₂; and the third group includes Fe₂O₃.Oxides preventing stabilization adversely affect deformation of the bodies under load, but increase the compressive strength. No general rale for the influence of these additions on the other properties of the products was evolved, which is probably connected with the different amounts and properties of the new phase which develops.Titania reduces the compressive strength but does not influence the other properties of zirconia.Oxides of iron, although they help stabilization of zirconia, lead to the formation of porous hearts in the products, which very adversely affects all properties of the products.According to the reduction of the working properties of the articles of ZrO₂ the admixtures investigated can be placed in the following order: phosphorus pentoxide, iron oxide, silica, titania and alumina.Commercial zirconia for the production of high-grade refractories should contain the minimum amount of impurities, the presence of phosphorus pentoxide, iron oxide, and silica being particularly undesirable.     

Interaction of Molten Iron with Ceramics Based on Iron and Aluminum Oxides

The interaction of molten iron with a ceramic material based on iron and aluminum oxides taken in equimolar ratio is investigated experimentally. The interaction begins with thermal decomposition of hematite, oxidation of boundary layers of molten iron to wüstite, and the reaction of wüustite with aluminum oxide with the formation of hercynite FeAl₂O₄ (in a surface layer of the melt). The rate of iron oxidation with hematite is relatively low, which is explained by the electrochemical processes at the molten iron–hematite melt interface. The reaction zone involves molten products of the interaction of wüstite with other components of the ceramic material, which are separated from the initial ceramic material by a gas-saturated loose layer. This structure of the reaction zone accounts for the extremely high resistance of the ceramic material under consideration to a thermal shock during contact with overheated melts.     

Slag-resistant products made from stabilized ZrO2

Conclusions The resistance of zirconia refractories to the action of acid slags is determined by the interaction between the added stabilizer and the silica component of the slag and by the rate of formation of the corresponding silicates. Of those materials studied, the most resistant of the action of the more acid slags is ZrO₂ stabilized by Y₂O₃.The rate of wear of the articles made from stabilized zirconia under the action of the more basic of the melts we studied is determined by the diffusion of Ca²⁺ into the structure of ZrO₂ forming CaZrO₃ which leads to the articles becoming less dense. The interaction between the stabilized ZrO₂ and the basic industrial slag, moreover, is accompanied by the intense dissolution of the refractory in the slag as a result of the formation of low-melting melts at the slag-refractory interface.Thus, zirconia refractories have an excellent resistance to the action of an acid multicomponent slag and are intensively damaged by basic slags.Translated from Ogneupory, No. 3, pp. 54–57, March, 1979.     

熔融还原熔体与镁炭砖的相互作用

采用三维旋转浸渍法研究了铁浴型熔融还原熔体与镁炭砖的相互作用，测试和分析了熔体中氧化铁的浓度、熔池温度、熔体与耐火材料间的相对运动速度、耐火材料的组成等与镁炭砖侵蚀速度的关系及侵性特征。     

Future application of aluminosilicate refractories for aluminum electrolyzers. Part 4. Wettability of aluminosilicate refractories with molten industrial electrolyte and sodium fluoride

Optical microscopy is used to determine wetting angles for aluminosilicate refractories with molten industrial electrolyte and NaF. Kinetic wetting parameters and interaction of electrolyte with refractory are determined. It is shown that removal of silicon from refractory also occurs in the form of silicon monoxide. It is established that aluminosilicate refractories, prepared with addition of mullite-corundum chamotte, are wetted worse by fluoride salts, but the corrosion resistance of them is better than for refractories prepared by normal technology. __________ Translated from Novye Ogneupory, No. 1, pp. 17–21, January 2008.     

耐火材料与洁净钢的关系

从化学热力学分析讨论了耐火氧化物及复合氧化物与钢液中平衡氧含量的关系 ,钢液中氧含量与氧势的关系 ,耐火氧化物与钢中硫含量 ,耐火氧化物及结合剂与钢中磷含量 ,耐火材料中残余水分及有机结合剂与钢中氢含量的关系 ,以及炼超低碳钢时的碳污染等问题。     

Service of zircon-containing nozzles for use in continuous steel casting plant

Summary During service in the casting of killed steel, zirconium containing nozzles took on a zonal structure. The least changed zone of the nozzles is scarcely distinguishable from the refractories before service. The working zones during service are saturated with oxides of iron, manganese, aluminum, silicon and titanium, and their amount is strictly related to the compositon and quantity of deoxidant.Highly refractory nozzles of ZrO₂ and made of a mixture of ZrO₂ and zircon, possessing a higher apparent porosity, acquire a larger working zone than nozzles made of zircon with clay additions.The dense working zone is more rapidly formed in nozzles made of zircon and clay. The oxides adsorbed in the pores of the refractory contribute to the tightening up of the aperture of the nozzles.Zircon nozzles with clay additions used at the Donets Steel Mill proved to have excellent wear resistance and the lowest tendency to closing up when casting low-carbon killed steels and can be recommended for permanent use in continuous steel casting plants.     

Silicon Nitride–Silicon Carbide Refractories Produced by Reaction Bonding

Silicon nitride-silicon carbide refractories have been prepared by reaction bonding. The percentage of silicon nitride in the refractory was varied from 5 to 45 wt%. The modulus of rupture of refractories increases with an increase of temperature, whereas thermal expansion decreases. These refractories are resistant to molten non-ferrous metals but are attacked by molten cast iron.     

Corrosion of oxide bonded silicon carbide refractories by molten salts in solid waste-to-energy facilities

Oxide bonded silicon carbide refractories are used successfully in solid waste-to-energy facilities (WtE). They are submitted to severe thermo-chemical stresses that limit their performance. Even if the corrosion resistance of silicon carbide is high, wear and failure of refractory lining are currently observed.For a better understanding of corrosion mechanisms, oxide bonded silicon carbide refractories, collected in the combustion chamber of several WtE facilities, were examined. The main mechanisms of corrosion, according to the environment of refractories, were determined. The chemical composition and the nature of the corrosive agents were calculated from the thermo-chemical modeling. They are mainly condensed phases of sulfates and chlorides (CaSO₄, K₂SO₄, Na₂SO₄, KCl, and NaCl). In service conditions, these molten salts react with the SiC aggregates and the matrix of the refractories to form low melting compounds.The post-mortem analyses showed the formation of para-wollastonite in the porosity and around the SiC grains, on the hot face of refractory tiles. Other phases such as cristobalite and microline (KAlSiO₈) were also formed down to the core of refractories. The volume expansion created by the formation of new mineral phases (cristobalite, para-wollastonite) causes the formation of micro cracks in the refractory lining.In this paper, the degradation mechanisms of oxide bonded silicon carbide refractories are presented and the main research developments for the future are discussed.     

A study on the wetting behavior of liquid iron on forsterite,mullite, spinel and quasi-corundum substrates

Wetting characteristics of liquid iron on magnesia, alumina and silica mixture substrates were studied by sessile drop experiments. Chromium-free forsterite, mullite, spinel and quasi-corundum phases were selected as alternative refractories in MgO-Al₂O₃-SiO₂. Morphological changes of molten electrolytic iron on the oxide substrates were investigated via apparent contact angle measurements. The results showed that the wetting behavior was significantly influenced by FeO compounds that were formed via oxidation of the liquid iron. Morphologies of the reacted layer were studied by Scanning Electron Microscope (SEM)/EDX analysis. The ternary phases FeO-MgO-SiO₂ and FeO-Al₂O₃-SiO₂ improved the wetting of liquid iron on the forsterite and mullite substrates by providing liquid phases at solid (refractory)–liquid (iron) interfaces. However, corrosion by liquid iron was significantly inhibited at spinel phase which did not feature FeO based compounds at the interface. Quasi-corundum (10MgO-25SiO₂-65Al₂O₃) showed a much enhanced resistance to liquid iron compared to forsterite or mullite refractories.     

Wear-resistant refractories in aluminum pyrometallurgy

Service conditions for refractories and physicochemical processes at their contact with molten aluminum are provided. Thermodynamic calculations establish the relative wear resistance of a number of oxides, silicates, and oxygen-free compounds towards aluminum in the range 700–1200°C (937–1473 K). The role is revealed of contact physicochemical processes at the boundary of a refractory with molten aluminum. The high resistance towards aluminum is demonstrated for high-alumina calcium aluminates, particularly bonite CaO · 6Al₂O₃ and spinel MgO · Al₂O₃. The most practicable wear-resistant fuzed materials for preparing lining of melting furnaces are lime-aluminate slags of OAO Klyuchevsk Ferroalloy Plant. __________ Translated from Novye Ogneupory, No. 9, pp. 15–19, September 2007.     

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.     

Corrosive Interaction between Slags High in Copper and Nickel Oxides and Periclase,Periclase-Chromite,and Chromite Refractories

A mechanism of corrosive interaction between periclase-chromite, periclase, and chromite refractories and molten copper (I) oxide and slag melts containing copper oxide and nickel oxide has been studied. The refractories in question are shown to be insufficiently resistant to slag attack typical of smelting technologies for converting nickel-containing copper sulfide mattes into blister copper. __________ Translated from Novye Ogneupory, No. 8, pp. 41 – 47, August, 2005.     

Service of chamotte articles in furnaces for melting aluminum

Chamotte bricks are studied after service in the tank of a furnace for melting secondary aluminum. The deterioration of the lining is caused by the reducing action of molten aluminum mainly on the silica contained in the refractory. It is inferred that high-alumina refractories are more suitable for such furnaces.     

Resistance of silicon carbide referactories to the effect of aluminum melt and aluminum chloride vapor

Silicon carbide refractories with binders of silicon nitride and silicon oxynitride are compared with dense aluminum silicate refractories. It is shown that silicon carbide refractories possess high stability in aluminum melts and vapors of aluminum chloride, whereas aluminosilicate refractories are severely damaged under these conditions. Silicon carbide refractories with a binder of silicon nitride possess the highest resistance to the effect of the tested aggressive factors and are recommended for operation in aluminum melts and gaseous aluminum chloride media.Translated from Ogneupory, No. 12, pp. 2–5, December, 1995.     

Action of iron and slag on the zirconia coating of the lining of submerged lances

Conclusions As the result of the physicochemical reaction between the zirconia coating applied to the lining of the submergible lances for addition of magnesium to molten iron in desulfurization of it and the molten metal and slag a dense crust of particles of zirconia and the nonmetallic phase formed as the result of the chemical reaction of the zirconia and the binder with the slag contained in the ladle with the molten iron is formed in the layer of coating. This prevents penetration of molten metal into the pores and cracks of the lining, reduces oxidation of its carbon-containing components, and increases life.Application of the zirconia coating to the lance lining eliminates manual coating of it with a refractory compound after treatment of iron.Translated from Ogneupory, No. 5, pp. 46–48, May, 1988.     

Fireclay refractories in pyrometallurgical processes

In primary liquid metal production, the temperature of processing and the composition of the slag phase largely determine the selection of the refractories used to line the furnace. The objective of this work was to study the effect of temperature and FeO content on the dissolution rate of a clay refractory.50-g samples of synthetic, prefused iron oxide and silica were poured into slip cast crucibles of a high-duty fireclay. These were then placed in a preheated silicon carbide-element furnace and held at the required temperatures for known times. The cooled crucibles and their contents were broken and the amount of crucible wall thinning which had taken place at the slag-refractory interface was measured using a low-power microscope and a calibrated graticule.The study of the effect of process temperature was carried out over the temperature range 1100°–1400°C at 50°C intervals. Only two compositions, 65 and 75 wt.% FeO, were chosen for this part of the work.The effect of slag composition was next studied at 1300°C, the range of slag compositions being 60–80 wt.% iron oxide at 5% intervals in the iron oxide-silica system. Only one high-duty fireclay composition was studied throughout the tests.The outcome of the work was to show that for the iron oxide-silica compositions studied a high-duty fireclay refractory can be used to contain the melts if the temperature of the process is maintained below 1300°C and when the slag composition is less than the orthosilicate composition (2FeO.SiO₂).     

Development and Application of Refractory Materials for Molten Aluminum Applications

Two new refractory materials have been developed for use in molten aluminum contact applications that exhibit improved corrosion and wear resistance leading to improved thermal management through reduced heat losses caused by refractory thinning and wastage. The development of these materials was based on an understanding of the corrosion and wear mechanisms associated with currently used aluminum contact refractories through physical, chemical, and mechanical characterization and analysis performed by Oak Ridge National Laboratory (ORNL) and the University of Missouri, Rolla Rolla (UMR), along with their industrial partners, under the ITP Materials project "Multifunctional Metallic and Refractory Materials for Energy Efficient Handling of Molten Metals." Spent castable refractories obtained from a natural gas-fired reverberatory aluminum alloy melting furnace were analyzed, leading to identification of several refractory degradation mechanisms and strategies to produce improved materials. The newly developed materials have been validated through an R&D industrial trial.