A study of slag corrosion of oxides and oxide-carbon refractories during steel refining

The use of ceramic material as refractories in the manufacturing industry is a common practice worldwide. During usage, for example in the production of steel, these materials do experience severe working conditions including high temperatures, low pressures and corrosive environments. This results in lowered service lives and high consumptions of these materials. This, in turn, affects the productivity of the whole steel plant and thereby the cost. In order to investigate how the service life can be improved, studies have been carried out for refractories used in the inner lining of the steel ladles. More specifically, from the slag zone, where the corrosion is most severe. By combining thermodynamic simulations, plant trails and post-mortem studies of the refractories after service, vital information about the behaviour of the slagline refractories during steel refining and the causes of the accelerated wear in this ladle area has been achieved. The results from these studies show that the wear of the slagline refractories of the ladle is initiated at the preheating station, through reduction-oxidation reactions. The degree of the decarburization process is mostly dependent on the preheating fuel or the environment. For refractories without antioxidants, refractory decarburization is slower when coal gas is used in ladle preheating than when a mixture of oil and air is used. In addition, ladle preheating of the refractories without antioxidants leads to direct wear of the slagline refractories. This is due to the total loss of the matrix strength, which results in a sand-like product. Thermal chemical changes that take place in the slagline refractories are due to the MgO-C reaction as well as the formation of liquid phases from impurity oxides. In addition, the decrease in the system pressure during steel refining makes the MgO-C reaction take place at the steel refining temperatures. This reduces the refractory’s resistance to corrosion. This is a serious problem for both the magnesia-carbon and dolomite-carbon refractories. The studies of the reactions between the slagline refractories and the different slag compositions showed that slags rich in iron oxide lead mostly to the oxidation of carbon/graphite in the carbon-containing refractories. This leads to an increased porosity and wettability and therefore an enhanced penetration of slag into the refractory structure. If the slag contains high contents of alumina and or silica (such as the steel refining slag), reactions between the slag components and the dolomite-carbon refractory are promoted. This leads to the formation of low-temperature melting phases such as calcium-aluminates and silicates. The state of these reaction products during steel refining leads to an accelerated wear of the dolomite-carbon refractory. The main products of the reactions between the magnesia-carbon refractory and the steel refining slag are MgAl2O4 spinels, and calcium-aluminates, and silicates. Due to the good refractory properties of MgAl2O4 spinels, the slag corrosion resistance of the magnesiacarbon refractory is promoted.

Ceramic coating for refractories protection against carbon oxidation, Part 1: Protection mechanisms

For retarding carbon oxidation in refractories during the preheating of metallurgical furnaces, a ceramic coating, made mainly of sodium phosphosilicate and clay was developed. The coating presents high adherence to the substrate with no swelling. The coating was characterized by thermal analysis, X-ray diffraction at room temperature (XRD) and at high temperature (HTXRD), X-ray fluorescence and scanning electronic microscopy (SEM). The glass transition temperature is reached at 800 °C and only glassy phase is observed above this temperature. Thus the mechanism of protection seems to be the formation of a glassy phase on the surface of the refractory, and the coating tends to be more efficient at temperatures higher than 800 °C.

Key features of alumina/magnesia/graphite refractories for steel ladle lining

The corrosion resistance of resin bonded alumina/magnesia/graphite refractories containing different kinds of aggregates were investigated when submitted to the action of slags of several CaO/SiO2 ratios. The laboratory testing was performed by means of the rotary slag attack test. Specifically evaluated was the influence of alumina/carbon ratio and magnesia and silica contents on the refractories corrosion resistance. It was found that this property could be improved by increasing the refractory Al2O3/SiO2 ratio as well as by choosing the appropriate Al2O3/C ratio. © 2000 Elsevier Science Ltd.

Corrosion behavior in graphite refractories impregnated with ZrO 2 and CeO 2 carrying solutions

This paper investigates corrosion behavior in graphite refractory hot metal impregnated with ZrO 2 and CeO 2 carrying solutions used in Blast Furnace hearth, consisting of 50% graphite and 50% anthracite. Corrosions tests were carried out by means of finger test method in an induction furnace, using bar-shaped 30×30×280 mm test specimens and hot metal from CSN#2 Blast Furnace runner. The temperature chosen for this test was 1520°C and sixty-minute isotherm. Upon test completion, test specimens were characterized by their dimensional variation, X-ray diffractometry and Scanning Electronic Microscopy (SEM).

Refractories,

Bibliography: p. 161-162.

The vaporization and physical properties of certain refractories.

pt. 1. Techniques and preliminary studies, by A. A. Hasapis, M. B. Panish and C. Rosen.--pt. 2. Experimental studies, by A. A. Hasapis and others.

Southern Illinois novaculite and novaculite gravel for making silica refractories /

Includes bibliographical references.

H-W fireclay and high alumina refractories.

Mode of access: Internet.

Oxidation mechanism of Si3N4-bonded SiC ceramics by CO, CO2 and steam

This paper presents a theoretical and experimental investigation into the oxidation reactions of Si3N4-bonded SiC ceramics. Such ceramics which contain a small amount of silicon offer increased oxidation and wear resistance and are widely used as lining refractories in blast furnaces. The thermodynamics of oxidation reactions were studied using the JANAF tables. The weight gain was measured using a thermogravimetric analysis technique to study the kinetics. The temperature range of oxidation measurements is from 1073 to 1573 K and the oxidation atmosphere is water vapour, pure CO and CO-CO2 gas mixtures with various CO-to-CO2 ratios. Thermodynamic simulations showed that the oxidation mechanism of Si3N4-bonded SiC ceramics is passive oxidation and all components contribute to the formation of a silica film. The activated energies of the reactions follow the sequence Si3N4>SiC>Si. The kinetic study revealed that the oxidation of Si3N4-bonded SiC ceramics occurred in a mixed regime controlled by both interface reaction and diffusion through the silica film. Under the atmosphere conditions prevailing in the blast furnace, this ceramic is predicted to be passively oxidized with the chemical reaction rate becoming more dominant as the CO concentration increases. (C) 1998 Chapman & Hall.

Temperature and common-ion effect on magnesium oxide (MgO) hydration

MgO based refractory castables draw wide technological interest because they have the versatility and installation advantages of monolithic refractories with intrinsic MgO properties, such as high refractoriness and resistance to basic slag corrosion. Nevertheless, MgO easily reacts with water to produce Mg(OH)(2), which is followed by a large volumetric expansion, limiting its application in refractory castables. In order to develop solutions to minimize this effect, a better understanding of the main variables involved in this reaction is required. In this work, the influence of temperature, as well as the impact of the chemical equilibrium shifting (known as the common-ion effect), on MgO hydration was evaluated. Ionic conductivity measurements at different temperatures showed that the MgO hydration reaction is accelerated with increasing temperature. Additionally, different compounds were added to evaluate their influence on the reaction rate. Among them, CaCl(2) delayed the reaction, whereas KOH showed an opposite behavior. MgCl(2) and MgSO(4) presented similar results and two other distinct effects, reaction delay and acceleration, which depended on their concentration in the suspensions. The results were evaluated by considering the kinetics and the thermodynamics of the reaction, and the mechanical damages in the samples that was caused by the hydration reaction. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

A GUI for online presentation of steel and steelmaking ladle temperature data and simulation.

Continuous casting is a casting process that produces steel slabs in a continuous manner with steel being poured at the top of the caster and a steel strand emerging from the mould below. Molten steel is transferred from the AOD converter to the caster using a ladle. The ladle is designed to be strong and insulated. Complete insulation is never achieved. Some of the heat is lost to the refractories by convection and conduction. Heat losses by radiation also occur. It is important to know the temperature of the melt during the process. For this reason, an online model was previously developed to simulate the steel and ladle wall temperatures during the ladle cycle. The model was developed as an ODE based model using grey box modeling technique. The model’s performance was acceptable and needed to be presented in a user friendly way. The aim of this thesis work was basically to design a GUI that presents steel and ladle wall temperatures calculated by the model and also allow the user to make adjustments to the model. This thesis work also discusses the sensitivity analysis of different parameters involved and their effects on different temperature estimations.

Influência de defeitos e diferentes processos de fabricação nas propriedades mecânicas finais de cerâmicas

Os materiais cerâmicos são atualmente cada vez utilizados como opção na engenharia mundial. Por se tratar de materiais com alta resistência mecânica, possuem muitas aplicações em diversas áreas, como por exemplo a de mancais, a automotiva (sensores, isoladores, catalisadores, pistões, válvulas, revestimentos), a de implantes biocompatíveis (dentário, substituição óssea, válvulas cardíacas), a de produtos sujeitos ao desgaste (guias), a de refratários (revestimento de equipamento bélico, componentes de fornos), a eletrônica, e outras. Nos processos de fabricação da cerâmica há uma gama de fatores que contribuem para as características do produto final. Devido a isso, muitos pesquisadores têm trabalhado no estudo da influência de determinados defeitos e técnicas de produção de cerâmicas nas características do produto final. Este trabalho tem como objetivo fazer uma revisão bibliográfica de recentes artigos que analisam a influência de fatores como velocidade de queima, surgimento de trincas, porosidade, fases cristalinas, e tamanho de partículas, nas propriedades mecânicas finais das cerâmicas. Pode-se concluir que é possível aperfeiçoar o processo de fabricação da cerâmica a fim de promover as melhores propriedades mecânicas possíveis, conhecendo-se fatores prejudiciais e métodos adequados para se obter o melhor produto final.

Nationalization of the carbonaceous mortar for injection in the CNS's blast furnaces hearths

The consumption of the carbonaceous mortar for injection in the CSN's blast furnaces hearth has increased in the last years, as a function of the modern situation of the blast furnaces com paign. Allied to the growing consumption background, the devaluation of the Brazilian currency stroke hardly the importation costs of this product.

Innovaciones en la gestión y calidad de los revestimientos refractarios en la Compañía Sideŕurgica Nacional (Brasil)

The work describes actions carried out in colaboration among the National Steel Company - (CSN)-Brazil and the Interdisciplinary Laboratory of Electrochemistry and Ceramic - LIEC of the Federal University of Sao Carlos Brazil (UFSCar-Brazil), in the area of I&D, for integral management and improvement of the quality and performance of the refractory linings in the sintering areas, blast furnace, hot air pipe lines transferency to the blast furnace, pig-iron ladles, running channels, blast furnaces hearths, torpedo car, etc., as well as, the economic impact generated by the installation of the adopted measures.