Slag Penetration Research Articles

Controllable Preparation of Al2O3‐MgO·Al2O3‐CaO·6Al2O3 (AMC) Composite with Improved Slag Penetration Resistance

Compact Al2O3‐MgO·Al2O3‐CaO·6Al2O3 (AMC) composite was obtained by melting technology using industrial alumina, light‐burned magnesia, and quick lime as raw materials based on the Al2O3‐MgO‐CaO ternary phase diagram. The results show that the phases of MgO·Al2O3 and Al2O3 are formed as the main framework with plate‐like CaO·6Al2O3 crystals mainly discontinuously embedded in MgO·Al2O3. The bulk density of AMC composite is up to 3.42 g/cm3, equivalent to 90.5% of the theoretical density. The synthesized compact AMC composite in the work also exhibits better slag penetration resistance than the castable based on tabular corundum due to the formation of liquid phase.

Study on a Lime-Fluorite Slag Melting Agent for Ladle Slag Buildup

The Al2O3-MgO-Cr2O3 brick, which is used for wear lining in the ladle slag line, was selected, and the static crucible method was applied to perform a slag sticking test with the refining slag and then investigate the effect of the lime-fluorite slag melting agent with different recipes. The slag corrosion and penetration rate of samples were measured, and the microscopic structure was analyzed through a scanning electron microscope (SEM), the possible slag melting effect and the proportion of active lime and fluorite were discussed. The results show that, with an increase of CaF2 in the slag melting agent, the corrosion and penetration rate rise as well, and a corrosion ring in the sample was observed while the content of CaF2 reached the certain value. The high melting point phases including MA, CA2, CA6, C3T2 and the low melting point phases including C2AS, CAS2, CA were distributed discontinuously. Suitable slag melting agents could reduce the viscosity of the slag, form the discontinuous high melting phases and corrosion ring, so as to achieve the purpose of slag melting for ladle lining.

Corrosion Behavior of Al2O3‐C Refractories with Casting Mould Meniscus Slags at 1 550 °C

The degradation behavior of alumina (10–20 wt%) carbon refractories was investigated during high temperature (1 550 °C) contact with a ternary casting mould meniscus slag containing 50% MnO, 25% SiO2, and 25% Al2O3 and a binary slag containing 40% MnO and 60% SiO2. Using the sessile drop approach, the transient progress of corrosion reactions was investigated as a function of time and refractory composition. An in‐depth characterization and analysis of reacted assemblies was carried out using optical and scanning electron microscopy (SEM). Optical micrographs showed a significant penetration of both slags within the refractory substrate, with very little slag remaining behind after 15 min of contact. The depth of penetration of ternary slag was found to increase with carbon concentration in the refractory. An all‐round corrosion was observed with extensive refractory degradation over a period of time. Corrosion was determined to a great extent by dissolution reactions in the interfacial region; alumina dissolution from the refractory resulted in the formation of needle‐like corundum crystallites which transformed to a cohesive network of faceted corundum crystals on extended contact. A number of reaction products containing Mn and Si were also observed.

(Invited) Refractory Ceramic Sensors for Process and Health Monitoring of Slagging Gasifiers

Current sensor technologies for measuring the temperature and health of slagging gasifiers are primarily based on thermocouples that are inserted into the gasifier through open access ports within the refractory. The major disadvantages of this technique include the intrusive nature of the access port that provides a path for slag penetration, and the severe temperature and corrosion limitations of the sensor materials. The current work presents the development of a series of ceramic-based thermistors, thermocouples and strain sensors, which may be used within a variety of refractory brick for the gasifier application. The key aspect of this technology is that these sensors are incorporated and interconnected through the volume of the refractory brick and do not significantly impact the intrinsic properties of the refractory. This technology circumvents the need to insert an isolated monolithic, stand-alone sensor into the refractory via an access port. This insures the integrity of the sensor within the harsh environment and does not introduce flaws or slag penetration pathways within the refractory. These sensors can be used to in situ monitor reaction conditions and degradation within slagging gasifiers and will provide better understanding of the health of the refractory (which is key for planning maintenance schedules and reducing the refractory degradation). The development of such a refractory sensor system concept can be also implemented into other applications, such as conventional coal-fired boiler technology, biomass gasification, and steel and glass manufacturing. As stated above, the objective of our work is to develop high-temperature sensors such as thermocouples, thermistors and strain/stress sensors composed of refractory composite materials that are electrically conductive and chemically stable at high temperatures (750°-1500°C) and high pressures (up to 1000 psi). The high-temperature sensors investigated in this work were composed of intermetallic composites directly embedded into refractory oxides. The composites used for this work were synthesized by a mixed-oxide route. Metal silicides (such as MoSi2, WSi2, ZrSi2, etc.) were inserted within a matrix material composed of refractory oxides (Al2O3, ZrO2, Y2O3, etc.) to form a 3-3 ceramic composite. The physical and electrical properties were specifically manipulated by altering the level of percolation of the conductive species (silicide) within the refractory constituent (refractory oxide). Prior to the development of the high-temperature sensors, the silicide-oxide composites developed in this study were sintered up to 1600°C under argon atmosphere in order to investigate densification, microstructural evolution, phase development, and their thermal and electrical performance as a function of the composition (fraction of silicides) and processing. The 4-point DC conductivity and coefficient of thermal expansion (CTE) measurements were performed between 1000°-1200°C. All results were compared in detail to select compositions that would work as high-temperature sensor materials. The sensors were fabricated from the composite materials by screen-printing, pressing, or casting the sensor design into a monolithic preform and inserting this preform into the refractory brick during the consolidation process. An example of one of these embedded ceramic-based sensors is a thermocouple composed of two separate silicide-alumina composite compositions which were patterned to produce a couple within the interior of a refractory matrix. The thermocouple successfully displayed a predictable thermoelectric voltage trend (as a function of temperature), and the voltage was 11.56 mV at 1000°C. For reference, a high-temperature type-B thermocouple (Pt-Rh) produces a voltage of 4.83 mV at the same temperature. Acknowledgements: This research was funded by the US Department of Energy, National Energy Technology Laboratory under contract no. DE-FE0012383. The authors would like to thank the project monitor, Maria Reidpath, for her insightful discussions and guidance. The authors would also like to acknowledge West Virginia University Shared Research Facilities for support through materials characterization.

Dissolution behaviour of MgO based refractories in CaO–Al2O3–SiO2 slag

Magnesium oxide (MgO) based refractories are widely used in secondary refining processes, and their dissolution into refining slag is the primary cause of their shortened lifespan. The dissolution rate was investigated for sintered MgO and commercial MgO–C and MgO–Cr2O3 refractories in a synthesised 50CaO–45Al2O3–5SiO2 liquid (mass-%) slag. The change in slag composition was measured after a refractory sample was placed into the molten slag that was stirred by flowing argon gas at 1773 K. The dissolution rate of the sintered MgO was above those of the MgO–C and MgO–Cr2O3 refractories under the same gas flowrate, although the dissolution rate of all samples increased as the gas flowrate was increased from 25 to 75 mL·min− 1. The slag containing 5 mass-% FeO considerably promoted the dissolution of the MgO–C refractory because of the oxidation of carbon by FeO. The dissolution of all the refractories was greatly affected by penetration of the liquid slag, with the mass transfer of MgO in the penetrating slag at lower gas flowrates likely being the rate controlling step. At high gas flowrates, Ar bubbles covered the surface and blocked the contact between the liquid slag and the solid phase, reducing the dissolution rate.

The influence of ZnO in fayalite slag on the degradation of magnesia-chromite refractories during secondary Cu smelting

In order to study the role of ZnO in the degradation of magnesia-chromite refractories, the chemical corrosion behaviour in a ZnO-containing fayalite slag (FeO–SiO2–ZnO–Al2O3) is investigated using a rotating magnesia-chromite refractory finger corrosion test under a reducing atmosphere at 1200°C. The results show that, likewise to ZnO-free fayalite slag, periclase is predominantly corroded. Both ZnO and FeO diffused into the original periclase and chromite grains thereby forming, respectively, (Zn,Fe,Mg)O solid solution and (Zn,Fe,Mg)[Cr,Al,Fe]2O4 spinel. Concurrently, ZnO and FeO were also incorporated into the (Zn,Fe,Mg)2SiO4 olivine during its formation. None of these phase formations resulted in new crack generation in the refractory. Considering the infiltrated slag is almost completely depleted in ZnO at 4mm from the hot face, the severe slag penetration up to the centre of the refractory sample is not caused by the ZnO presence in the initial slag.

Improvement of Resistance of MgO-Based Refractory to Slag Penetration by In Situ Spinel Formation

MgO-in situ spinel substrate was prepared at 1773 K (1500 °C) using colloidal alumina suspension and coarse MgO as raw materials. While the addition of 10 mass pct colloidal alumina had limited effect, addition of 20 mass pct colloidal alumina into the MgO matrix improved greatly the resistance of the substrate against the slag penetration at 1873 K (1600 °C). The improvement was found to be mainly related to the formation of solid phases, CaO·Al2O3 and CaO·MgO·Al2O3 at the grain boundaries due to slag-spinel reaction. Putting the reacted substrate into contact again with new slag revealed no appreciable new slag penetration. The results showed a potential solution to improve the resistance of MgO-based refractory to slag penetration and to improve steel cleanness.

Influence of β-Sialon/Ti(C, N) Powders on the Corrosion and Oxidation Resistance of Zero-Cement Al2O3-SiC-C Refractory Castables

Al2O3-SiC-C refractory castables added with β-sialon/Ti(C, N) powders were prepared with silica sol and phenolic resin as binding agents at room temperature. The effects of β-sialon/Ti(C, N) powders, silica sol and phenolic resin on slag penetration and corrosion resistance as well as oxidation resistance of the refractory castables were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscope. Corrosion resistance and oxidation resistance mechanisms of the Al2O3-SiC-C refractory castables were also discussed. The results showed that the castables obtained with silica sol as the binding agent at a temperature of 1450oC presented better oxidation resistance. The oxidation resistance and slag erosion resistance of the refractory castables could be improved by adding Ti(C, N)/β-sialon powders. Static crucible method and fractal dimension calculation result showed that the prepared castables possessed excellent slag erosion resistance.

The Slag Resistance of Al<sub>4</sub>SiC<sub>4</sub>-Al<sub>4</sub>O<sub>4</sub>C Composite Refractories

The effect of phase composition and microstructure of Al4SiC4-Al4O4C composite refractories after sintered and immersion in the slag on its slag resistance was preliminary investigated. The penetration layer in refractories synthesized at 1700 °C resulted from loose microstructure led to worse slag resistance. While the refractories synthesized at 1800 °C presented better slag resistance because the dense microstructure and higher Al4SiC4 content inhibited the slag penetration and corrosion.

Influence of thermal equilibrium and microstructure of dense zircon-doped dolomite refractories on rate of hydration and slag attack

The rate of densification of 0.0-2.0 wt.% zircon-doped calcined dolomite samples (CaO-MgO) was studied by means of linear shrinkage and bulk density as a function of firing temperature (1400-1700 � C) and soaking time (1-4 h). The resistance to hydration and to slag attack of selected dense samples were investigated in relation to their thermal equilibrium and microstructure. The nature, chemical composition and zonation of the phases and the microstructure of the products were characterized by X-ray fluorescence (XRF) and X-ray diffraction (XRD), as well as scanning electron microscopy (SEM) and energy-dispersive spectro- scopy (EDS). A mercury intrusion porosimeter was also used to investigate pore-size distribution. The modular system of the quaternary phase diagram MgO-CaO-C2S-C4AF was used in the determination of the thermal equilibrium data, and the solid and liquid phases that coexist at � 1300 and 1400 � C. The rates of hydration and attack by steel-slag were also measured using steam- curing under atmospheric pressure and pill-test. The studied Egyptian dolostone is composed mainly of dolomite with minor amounts of calcite, while the dopant zircon sand is contaminated with rutile grains. The 0.5 wt.% zircon-doped dolomite sample gives maximum bulk density and linear shrinkage after firing for 4 h at only 1400 � C. This is attributed to enhancement of homogeneous discontinuous grain growth of the main free CaO and MgO phases, achieved by crystallization of a Ca-zirconate (s.s) along grain boundaries and at grain triple points. The Ca-zirconate crystallizes by cooling of an evolved liquid phase, together with ZrO2-bearing Ca-silicate and Ca,Mg-alumino-titanate solid solutions. The crystallization of these phases in a matrix of CaO and MgO grains leads to decreased penetration of the viscous ZrO2-rich molten slag through the doped sample, compared to un-doped one. The dense doped sample also gives relatively higher hydration resistance than the un-doped sample on steam curing under atmospheric pressures up to 8 h. The addition of 0.5 wt.% zircon, slightly contaminated with rutile, is therefore sufficient to enhance the densification parameters as well as the slag and hydration resistance of the dolomite-based refractories.

Estudio a nivel laboratorio de la Degradación atípica en un refractario tipo SiO2 utilizado en hornos de inducción

En este trabajo de investigación se realizó un estudio de la degradación atípica que se produce en las paredes de los hornos de inducción. Para esto, se utilizó un material refractario base - SiO2 (98.8%) con dos escorias de composición química diferente y se analizó su comportamiento mediante las pruebas experimentales del método de copa o crisol y el de inmersión, así como por un modelado asimétrico del metal líquido en el horno de inducción. La escoria, la estructura del material refractario y el mecanismo de penetración de la escoria fueron caracterizados por microscopia óptica, utilizando la técnica de luz reflejada. Los resultados demostraron que, con valores altos de frecuencia (240 Hz), para la operación del horno, se obtiene una fuerza de Lorentz muy alta (14.26 N) pero con una velocidad del metal liquido baja (6 m/s) la cual tiene un vector de dirección perpendicular a las paredes del horno, provocando presión sobre la escoria incrustada en los poros del refractario favoreciendo el proceso de degradación del material.

Kinetics and Thermodynamics of Carbon Isothermal and Non-isothermal Oxidation in MgO-C Refractory with Different Air Flow

Today, MgO-C bricks are widely used in steel industry due to their excellent resistance to slag corrosion and thermal shock increased particularly by the carbon content. The presence of carbon makes these bricks very susceptible to oxidation, leading to a reduction of the strength and to the penetration of metal and/or slag. The aim of this paper is to investigate the processes of carbon oxidation of MgO-C commercial bricks containing 7 and 14 pct C by both isothermal and non-isothermal methods. The results show that carbon oxidation of the samples is limited by diffusion through the pores only. If the carbon content does not have a greater influence on the oxidation process at lower temperatures, then at higher temperatures the weight loss increases with increasing carbon content. Both types of commercial bricks oxidize directly in a lower temperature range and indirectly at higher temperatures. That means that the indirect oxidation does not exist alone, but is initiated by direct oxidation of carbon. Activation energy and diffusion coefficient for different bricks have been determined and compared with literature data. The results of the investigation of the non-isothermal carbon oxidation show that for one and the same final thermal state of the refractory the carbon oxidation can be essentially minimised by choosing specific heating-up rates.

Corrosive Interaction between MgO-C Refractories and Vanadium-Recovery Slag

The interaction mechanisms between resin-bonded MgO-C bricks and vanadium-recovery slag by a static crucible slag test are investigated. Oxidation of carbon is observed, which results in pores, cracks and voids for the penetration of the vanadium-recovery slag. Periclase grains are seriously infiltrated by the slag, which leads to the disintegration and removal of MgO subgrains from the slag. Forsterite is formed and EDS confirmed that it has some FeO and MnO content. EDS confirms that there are few vanadium-containing compounds, and most vanadium exists in the form of glassy phases, which are liquid at high temperature. More low-melting point species are formed in the slag or as the result of the reaction of slag and refractory components, which is deleterious to slag resistance. Furthermore, the diffused FeO content in periclase gradually decreases from the hot face into the inner area. No diffused MnO is detected in periclase.

Reaction mechanism of MgO–ZrO2 refractory with CaO–SiO2–Al2O3–FetO slag

In order to understand the reaction mechanism of MgO–ZrO2 refractory with molten slag and to expand the application of MgO–ZrO2 refractory, the reaction process of MgO–ZrO2 refractory with CaO–SiO2–Al2O3–FetO slag was investigated and the mechanism of corrosion resistance was discussed. Results showed that the CaO–SiO2–Al2O3–FetO slag first penetrated into the MgO–ZrO2 refractory and reacted with MgO and ZrO2 components to form Mg(Al, Fe)2O4 and CaZrO3, respectively, decreasing the open porosity of the refractory and forming a dense layer, which could prevent the penetration of the molten slag into the MgO–ZrO2 refractory. Meanwhile, the viscosity of the molten slag in the refractory was increased, leading to the decrease in the penetration ability. Because of the reaction between the MgO–ZrO2 refractory and the CaO–SiO2–Al2O3–FetO slag, the slag corrosion resistance of the MgO–ZrO2 refractory was improved. Compared with the MgO–Cr2O3 refractory, the corrosion parameter and penetration parameter of the MgO–ZrO2 refractory after reaction with slag are only 4·9% and 17·0%, respectively.

Effect of TiO2 addition on Al2TiO5 (tialite) phase evolution of in situ MgAl2O4 formation zero cement castable (ZCC)

In this study, densification behaviour of the in situ MgAl2O4 formation zero cement castable (ZCC) in the presence of TiO2 was analysed. Using a 2 wt-% content of TiO2 increased the bulk density of the brick to 3·10 g cm−3 and decreased the porosity to ∼15·7%. Alternatively, a 2 wt-% TiO2 addition modified the firing shrinkage. X-ray diffraction (XRD) analysis of the fired samples demonstrated that MgAl2O4 spinel and Mg2TiO4 inverse spinel structures also formed, as well as the formation of Al2TiO5 in 2 wt-% TiO2 addition of castables. The SEM investigations of fired samples were carried out to compare the effect of TiO2 addition and in situ phase formation on the physicomechanical properties of castables. The effect of TiO2 content on the mechanism of the slag penetration of ZCC for a steel ladle was examined, and the penetration layer was chemically analysed.

Fate of inorganic matter in entrained-flow slagging gasifiers: Pilot plant testing

The focus of this paper is on the behavior of inorganic fuel components since the end goal is to develop a CFD model which includes inorganic matter transformations. Using CanmetENERGY's 1 MWth gasifier, five gasification tests have been completed with three different coal fuels and a limestone as fluxant. The refractory liner from the upper section of the gasifier was removed for analysis after each test. The liners were made of sintered alumina or castable alumina–chromia refractory. Carbon conversions and cold gas efficiencies for the gasification tests ranged within 97.0–99.6% and 33.7–61.9%, respectively. Solid samples from the refractory liners, in-situ gas sampling probe sheaths and impingers, the slag tap, the slag pot, quench discharge water and scrubber water were collected and characterized. Char and fly ash samples indicate that most of the inorganic matter melted and formed spheres. Devolatilization and interaction with the gasifier refractory affected the composition of slag collected from the gasifier. Signs of refractory spalling/erosion were detected. The slag layers formed on the alumina liners are smooth with some rivulets and spotting. The slag layers formed on the alumina–chromia liners are rough and bubbly. Slag penetration fractions were determined for all liners.

Fundamental Investigations on the Corrosion of ZrO2–CRefractories during Interaction with a Casting Mould Meniscus Slag

AbstractThe degradation behavior of Zirconia – 20% carbon refractory was investigated during high temperature (1550 °C) contact with a casting mould meniscus slag containing 50% MnO, 25% SiO2, and 25% Al2O3. Using the sessile drop approach, the transient progress of corrosion reactions was investigated as a function of time; in‐depth characterization and analysis of reacted assemblies was carried out using optical and scanning electron microscopy. Optical micrographs showed a significant penetration of slag within the refractory substrate, with very little slag remaining behind after 15 min of contact. In situ carbothermic reduction of zirconia and the presence of reducible oxides in the slag significantly depleted carbon from the substrate further aiding the penetration of slag. Interaction between slag and zirconia resulted in the depletion of phase‐stabilizing Y2O3from zirconia granules resulting in their fragmentation and subsequent diffusion in slag rich regions. An aggressive all‐round corrosion was observed with extensive refractory degradation over a period of time; a number of reaction products such as Mn5Si3were also observed. These experimental investigations were supplemented with thermodynamic investigations using FactSage.

Effects of MgO micropowder on microstructure and resistance coefficient of Al2O3–MgO castable matrix

Development of lightweight refractories has been in high demand and the matrix of these materials is crucial for its slag resistance. This paper focuses on the relationship between the microstructure and the resistance coefficient of the Al2O3–MgO castables matrix. The permeability experiments were carried out, and the porous media model was adopted to describe both the viscous and inertial resistance. In addition, the effect of the MgO micropowder content is also discussed. Results indicate an improvement in the properties influenced by sintering such as bulk density and apparent porosity. Further, the pore size distribution range becomes narrower and the average pore size decreases when MgO micropowder content is fixed in the range 3–4.5wt%. Moreover, the pore size is more crucial than the apparent porosity for the penetration resistance of the matrix. The relationship between the viscous resistance coefficient of the matrix and the microstructure parameters, fluid properties, and flow has been established to gain a better understanding of the slag penetration process.

Dissolution mechanism of dolomite in converter slag at 1873 K

The mechanism of dolomite dissolution in converter slag was studied and found to proceed by two steps: decomposition of dolomite into CaO and MgO and dissolution of the product into the slag. The first step was found to be controlled by heat transfer, which was confirmed by theoretical calculation. The decomposed dolomite had many pores, which allowed easy slag penetration. A discontinuous 2CaO.SiO2 layer along with MgO.Fe2O3 particles was found on the surface of the samples. Some 2CaO.SiO2 islands were found in the vicinity of the samples in the slag, revealing that the dissolution was dominated by peeling-off of the layer of 2CaO.SiO2–MgO.Fe2O3 mixture. 2CaO.SiO2, (Mg, Fe)Oss along with super cooled liquid phases were found inside dolomite samples close to the surface. 2CaO.SiO2 phase was replaced gradually by 3CaO.SiO2 towards the centre of the decomposed sample. While addition of small amounts of dolomite directly into the slag could be considered in steelmaking converter, too much would result in slow dissolution and waste of the raw materials.

Effect of component variation in CaO–SiO2–MgO–Al2O3 slags on controlling corrosion of olivine based disposable tundish lining material

This study concerns the chemical reactions involved and the phases formed during penetration of slags of variable compositions into porous tundish disposable lining material. The liner is mainly composed of a mixture of MgO and olivine with an organic binder. Slags of different compositions were formulated and indicated a variable composition of CaO (12–20%), SiO2 (44–55%), Al2O3 (4–16%), MgO (10–20%), MnO (9–12%) and FeO (2–3%). Experimental work indicated that when slag penetrated into pores of the refractory, the porosity was reduced depending on the penetration depth. It was observed that the lower the melting point of the slag, the higher the depth of slag penetration by capillary action. The phases of forsterite (Mg2SiO4), magnesiowustite (MgO.FeO) and monticellite (CaO.MgO.SiO2) were formed in the bulk refractory by the slag, and the chief component of the refractory responsible for the formation of those phases is the periclase.