Slag Corrosion Research Articles

Cr7C3: A potential antioxidant for low carbon MgO–C refractories

Magnesia carbon (MgO–C) refractory, one of the most commonly used refractories in the steelmaking system, relies on graphite to improve the thermal shock resistance and slag corrosion resistance. The oxidation of graphite carbon in a MgO–C brick usually leads to the destruction of the carbon network in the brick, which causes the structure of the brick to become loose and easily eroded. At present, metal powders, carbides, and borides are used as antioxidants to prevent the oxidation of carbon in MgO–C bricks. The metal carbide Cr7C3 can be prepared from aluminum chromium slag through a simple synthetic process and at a low cost. In this work, we investigated the oxidation resistance of low carbon MgO–C refractories with different amounts of Cr7C3 powder (1, 2, 3, and 4 wt%). The refractories with 3 wt% Cr7C3 powder showed optimal resistance to oxidation. The microstructure indicated that oxygen reacts with Cr7C3 preferentially over carbon to form chromium oxide and magnesium chromium spinel, blocking the pores and hindering oxygen diffusion. Carbon arising from the reduction of carbon monoxide by Cr7C3 can act as a supplementary carbon source. The better oxidation resistance also contributed to the improvements in slag corrosion and thermal shock resistance of the refractories.

Slag corrosion-resistance mechanism of lightweight magnesia-based refractories under a static magnetic field

Slag corrosion resistance of lightweight magnesia-based refractories with micro/nano-sized pores under a static magnetic field is investigated. They exhibited excellent slag resistance under static magnetic field of 8.5 mT with an isolation layer composed of solid phases formed at the refractory/slag interface. The static magnetic field generated a “magnetic brake effect” that suppressed the infiltrating flow of the molten slag and decreased the dissolution rate of MgO grains. Moreover, it also limited the thickness of the isolation layer by reducing the extent of the refractory-slag interaction, which can be applied to further improve the slag resistance of refractories.

Corrosion Mechanisms of Different Refractory Aggregates in Contact with SiO2-MgO-Based Slag

Abstract: To improve the utilization and evaluation of metallurgical solid waste, the investigation of slag has become a focused research subject in the recent years. However, when slag with various compositions was smelted to produce high value-added products in the slag furnace, the SiO2-MgO based slag caused serious damage to the refractory lining material of the furnace compared to the common CaO-Al2O3-SiO2 based slag. The tabular alumina, lightweight alumina, silicon carbide, mullite and brown fused alumina aggregates were selected for testing. The static crucible method was used to investigate the SiO2-MgO based slag corrosion and comparative analysis was performed. The results show that mullite-silicon carbide or tabular alumina-silicon carbide refractories are promising for the use as lining materials of SiO2-MgO slag smelting furnaces.

Influence of the atmosphere on the mechanical properties and slag resistance of magnesia-chrome bricks

Magnesia-chrome bricks are commonly used as the lining of smelters in copper and lead industry because of their resistance against the thermal, mechanical and chemical loads in the pyrometallurgical production process. In fact, the pyrometallurgical production process of lead-copper matte is generally a reducing process with plenty of coke and iron fillings as reducing agent, which implies that the magnesia-chrome bricks service in stronger reducing atmosphere. In this work, the microstructure, mechanical properties and slag resistance of such materials were investigated in reducing atmosphere to simulate the influence of the atmosphere on the properties of magnesia-chrome refractories. The results show that obvious increase in porosity and decrease in strength occurred to the magnesia-chrome samples after treating in reducing atmosphere. This is related to the structural damage of samples, in which Fe3+/Fe2+ within spinel (Mg, Fe)(Cr, Al, Fe)2O4 were partly reduced to metallic Fe under reducing atmosphere. Consequently, the slag penetrated much easily into the matrix of the samples. Moreover, the slag corrosion also aggravated due to the aggressive FeO in slag and the formation of magnesiowüstite in the penetration layer. Nevertheless, the high melt phases of spinel and forsterite were formed when the slag corrosion test was conducted in air atmosphere, thereby preventing further slag corrosion and penetration.

Comparison of corrosion resistance of high chromia brick, high zirconia brick, fused AZS brick and Si3N4 bonded SiC brick against coal slag

Corrosion resistance of four typical refractories against coal-water slurry coal slag, was investigated in laboratory. These typical refractories are high chromia brick (Cr2O3–Al2O3–ZrO2), fused AZS brick (Al2O3–ZrO2–SiO2), high zirconia brick (ZrO2) and Si3N4 bonded SiC brick, respectively. The cup test and micro-structural analysis method were used to evaluate the corrosion resistance and reaction mechanism at high temperature. Meanwhile, potential reactions between refractories and slag are predicted using thermodynamic calculation. The result shows that infiltrated depth increases in following order: Si3N4 bonded SiC brick < fused AZS brick < high zirconia brick < high chromia brick. The ZrO2 dissolution and higher porosity for the high chromia brick synergistically result in the worst corrosion resistance. Whereas, for the high zirconia brick, the continuous slag infiltration accelerate dissolution of ZrO2 grains, which decreases corrosion resistance. Due to the extremely low porosity, slag infiltration can be effectively hindered, and fused AZS brick has better slag corrosion resistance. For the Si3N4 bonded SiC brick, poor wettability, protective SiO2 film and increased slag viscosity synergistically contribute excellent corrosion resistance.

Calculated and Experimental Determination of the Phase Composition of Extra-Furnace Steel Treatment Slags

An experimental assessment of the reliability of a mathematical model and software for calculating the phase composition of steelmaking slags is given. It is established that the model proposed and the software developed may be used during modification of the slag chemical composition after furnace treatment of steel to reduce slag corrosion of a metallurgical unit lining and to suppress the effect of slag silicate decomposition.

MgO Refractory Doped with ZrO2 Nanoparticles: Influence of Cold Isostatic and Uniaxial Pressing and Sintering Temperature in the Physical and Chemical Properties

The chemical environment and the internal conditions of the furnaces and ladles are extremely aggressive for the refractories, so metallurgical industries demand refractory linings with greater durability and resistance to avoid unforeseen stoppages and to reduce the changes of the furnace lining. Therefore, the current work aims to evaluate the impact of the additions of ZrO2-nanoparticles (1, 3, and 5 wt. %) in magnesia-based bricks. A comparative study of the physical and chemical properties in bricks obtained using two cold pressing techniques (uniaxial and isostatic pressing) and two sintering temperatures (1550 and 1650 °C) was carried out. The microstructure and crystalline phase characteristics obtained after the heat treatments and the slag corrosion test was studied using scanning electron microscopy/electron dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). The results reveal that the sample with 5 wt. % of ZrO2 nanoparticles (obtained by cold isostatic pressing and sintering at 1650 °C) has the lowest porosity and greatest resistance to penetration of blast furnace slag.

Steelmaking in India - new evidence from microscopic and archaeometallurgical analysis from middle Ganga plain, Balirajgarh.

The present study deliberates on the archaeometallurgical examination of 2300 years old excavated iron nail from India's middle Ganga plain of Balirajgarh. The nail was subjected to multianalytical investigations in order to determine the raw materials used, manufacturing technology and preservation state. The combined analytical techniques optical microscopy, scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX), Vickers hardness and X-ray diffractometry shed light towards the characterisation and use of the iron artefact. Special attention was paid for qualitative and quantitative analysis of slag inclusions, metal matrix and corrosion products. The presence of heterogeneous microstructure and inclusion of impurities suggests that nail has been produced through the direct process and work hardened. The noncorroded nail is made of hypereutectoid steel and used for building purpose. The study is important to understand the role of technology in the evolution of cultural changes in India that also provides archaeometric data on the method used in the forging work.

Corrosion Behavior of Alumina Containing Refractory in Blast Furnace Hearth by CaO–SiO&lt;sub&gt;2&lt;/sub&gt;–MgO–Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;–Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Slags

The corrosion behaviors of corundum brick and carbon composite brick used in blast furnace hearth by CaO-SiO2-MgO-Al2O3-Cr2O3(-CaF2) slags were studied in the present work. The degradation of the corundum brick in slag was a result of slag infiltration and brick dissolution, and the corrosion of the brick became more serious with the addition of CaF2 due to the decrease of slag viscosity. The disintegration of carbon composite brick in CaF2-containing slag was caused by the combination of slag penetration, brick dissolution and reaction between slag and brick. By comparing the corrosion behavior in CaF2-containing slag between the corundum brick and carbon composite brick, the corrosion degree of the corundum brick was greater than that of the carbon composite brick. To the blast furnace operation in which a low grade iron ore such as laterite ore and CaF2 containing slag (about 2 wt%) are used, it was found that the carbon composite brick with better slag corrosion resistance can be selected as a hearth refractory so as to improve the operation performance and ensure the longer campaign life of blast furnace.

The Behavior of Slag Resistance of MgO-C Refractory Prepared by Sucrose as Binder

The harmful components such as formaldehyde and phenolic compounds released during the development, production and use of MgO-C refractories prepared by using phenolic resin as a binder can cause serious harm to the environment and human health. In this paper, MgO-C refractory material with sucrose as binder and metal aluminium powder as antioxidant is prepared. Different slag temperature and time factors have a largely influence on the slag corrosion resistance of as-prepared samples. By analyzing the microstructure and composition of the samples, it is found that under the condition of constant time, the higher the temperature, the more obvious the slag corrosion phenomenon; under isothermal conditions, the longer the time, the more obvious the slag corrosion phenomenon. At the same time, it is revealed that the main corrosion process of MgO-C refractories prepared by adding sucrose as a binder is carbon oxidation and slag corrosion, which provides a theoretical basis for optimizing the slag resistance of MgO-C refractories.

Research on Corrosion Resistance of Al2O3-MgAl2O4 Refractories and SiC-MgAl2O4 Refractories to Gasifier Slag

Spinel-containing refractory is a kind of potential chromium-free refractory for coal gasification because MgAl2O4 spinel has good slag resistance. Corundum-spinel refractories with w(Al2O3)=94%, w(MgO)=5% and SiC-spinel refractories with w(SiC)=64%, w (Al2O3)=5% were prepared. The crucible specimens were tested for slag corrosion with commercial gasifier slag at 1 500°C for 1 h in reducing atmosphere. XRD analysis were researched on the sidewall of the crucible after slag test. Microstructure and chemical composition of samples in slag corrosion zone were analyzed by SEM and EDS. The results show that the slag resistance of SiC-MgAl2O4 refractory was significantly better than Al2O3-MgAl2O4 refractory. The corundum particles were decomposed into fine particles by the slag, and the microstructure was destroyed. The oxidation of the surface of the silicon carbide particles formed a high-viscosity glass phase with the infiltrated slag, which was benefit to prevent the slag penetration into the interior. And a solid solution of (Mg, Fe)O·Al2O3 composite spinel was formed in matrix of the sample after slag penetration because MgAl2O4 absorbed FeO in the slag. It is speculated that the spinel solid solution repairs and strengthens the structure of the matrix, which improves the slag resistance.

Estimated and experimental determination of the phase composition of out-of-furnace steel processing slags

An experimental assessment of the reliability of the mathematical model and software (software) for calculating the phase composition of steelmaking slags is given. It is established that the proposed model and the developed software can be used to modify the chemical composition of slag after furnace treatment of steel to reduce slag corrosion of the lining of metallurgical units and suppress the effect of silicate decomposition of slag. Ill. 3. Ref. 7. Tab. 3.

Waste rice husk ash derived sol: A potential binder in high alumina refractory castables as a replacement of hydraulic binder

This work provides a new source of binder system, i.e., waste rice husk ash (RHA) derived sol for unshaped refractories. A facile (alkali extraction) route is used to synthesize the sol from the waste RHA. The sol consists of single phase amorphous silica with average particle size around 22 nm. The estimated cost of 30 wt% solid containing RHA derived sol per litre is around 9.35 $. The temperature of mullite (3Al2O3·2SiO2) formation from waste derived sol and reactive alumina containing system is 1250 °C or higher. The sol (30 wt% SiO2) and the dry sol (99.32 wt% SiO2) is used to formulate the high alumina castable samples. The sintering is performed at 1400 °C, 1500 °C and 1550 °C. The different physico-mechanical characterizations and blast furnace slag (BFS) corrosion test at 1500 °C are comprehensively investigated with the prepared castables. The properties of 5 wt% silica (3 wt% from sol and 2 wt% dry sol) containing castable specimens are also equated with the commercially available different silica containing high alumina castable systems. The obtain results are good agreements with the source data. These promising characteristic confirms the possibility of using waste RHA derived sol for manufacturing of cement free high alumina castable and leads to the economic and ecological benefits in the refractory industries.

Corrosion modeling of magnesia aggregates in contact with CaO–MgO–SiO2 slags

AbstractLadle refining is an efficient process for improvement of quality of steel on secondary metallurgy under harsh conditions. Magnesia refractories with high purity are important raw materials for ladle lining in high‐quality steel production. However, the penetration by CaO–MgO–SiO2 slags damages magnesia refractories, which considerably limits their service life. Abundant grain boundaries in magnesia create channels for slag penetration and lead to the destruction of the structure. The effect of the microstructure on the slag corrosion behavior of magnesia aggregates requires further systematic investigation. In this study, a corrosion model was established to describe the slag penetration process of magnesia aggregates. The effects of the grain‐boundary size and slag CaO/SiO2 mass ratio (C/S ratio) on slag penetration were investigated, and the possibility of the microstructure optimization of magnesia aggregates was discussed. The results indicated that magnesia aggregates exhibited excellent slag resistance for slag with a C/S ratio above 1.5 or even 2.0. When the slag C/S ratio was lower than 1.5, the dissolution rate of magnesia decreased more rapidly with the increase in the slag C/S ratio. In addition, the much smaller grain‐boundary size increased the slag penetration resistance by promoting the formation of a dense isolation layer and inhibiting further penetration processes. The calculation results agreed well with the experimental results, suggesting that the corrosion model is promising for predicting slag corrosion.

Fabrication of CaO–MgO–Al2O3 materials from metallurgical waste industrial residue and their potential usage in MgO–C refractories

In this study, CaO–MgO–Al2O3 materials were fabricated from metallurgical industrial waste residue and industrial alumina as raw materials via solid sintering method, and their effects on the properties of low carbon MgO–C refractories were investigated. The fabricated CaO–MgO–Al2O3 materials are mainly composed of MA, CA2 and CA6 phases. The CA2-MA materials can potentially be used in low carbon MgO–C refractories. Despite a slight increase in slag corrosion and a minor reduction in the high-temperature modulus of rupture due to their low thermal expansion coefficient, the introduction of CA2-MA materials leads to improved volume stability, higher cold crushing strength, superior oxidation resistance, a lower thermal expansion coefficient and significantly enhanced thermal shock resistance.

Enhanced corrosion resistance through the introduction of fine pores: Role of nano-sized intracrystalline pores

Lightweight materials containing nano-sized intracrystalline pores are reported, and their slag reaction behaviours are described. The introduction of nano-sized intracrystalline pores favouring the supersaturation of molten slag and the precipitation of solid phases at the reaction interfaces, and the isolation layer can prevent lightweight materials from further slag corrosion and penetration. Because the alumina materials have higher purity and a tight grain-bonding, they show the highest slag resistance. The impurities located between the grains are responsible for the deeper slag penetration of bauxite and magnesia materials. Moreover, the intergranular phases in the magnesia materials are interconnected, resulting in severe slag corrosion.

Optimization of matrix pore structure and its effects on physicochemical properties of corundum castables

In this paper, the effects of the matrix pore structure on the strength and corrosion resistance of corundum castables are reported. Pore diameters of castables fired at 110 °C could be decreased from 550 nm to 72 nm when 4% Al2O3-SiO2 gel powder was added. The pore diameter of the castables decreased from 850 nm to 500 nm after firing at 1100 °C, but increased from approximately 2 μm–8 μm after firing at 1500 °C. The strength of castables fired at 1500 °C increased remarkably with the addition of Al2O3-SiO2 gel powder. A maximum cold modulus of rupture (CMOR) of 62.34 MPa was obtained when 4% Al2O3-SiO2 gel powder was added. After slag corrosion, the penetration index fell from 16.6% to 4%, suggesting that a homogeneous pore size distribution and a smaller pore size played an important role in improving the penetration resistance.

High temperature mechanical and corrosion resistance of Fe-containing MgO-C refractory in oxidizing atmosphere

Abstract Addition of iron powder is found to be a promising solution to the structure degradation of MgO–C refractory during oxidation, but it may reduce the high temperature properties. To clarify this issue, the influence of Fe addition on the refractoriness under load, creep behavior and slag corrosion resistance in oxidizing atmosphere was investigated. MgO–C refractory exhibited a high maximum working temperature (T0.5, 1720 °C). However, its creep rate at 1550 °C increased rapidly with time because of severe oxidation, causing a failure at an earlier stage. The Fe-containing refractory showed a bit lower refractoriness (T0.5, 1698 °C), while its creep resistance has been greatly improved (1.0% deformation after 50 h duration). The remarkable increase in the bonding degree during oxidation is considered as the main mechanism for the long-term structural stability. Both type of refractories showed good corrosion resistance to oxidized slag due to the presence of graphite and dense MgO layer, but the Fe-containing refractory was more difficult to be penetrated by the slag after graphite oxidation.

Catalytic Fabrication of SiC/SiO2 coated graphite and its behaviour in Al2O3–C castable systems

Abstract SiC/SiO 2 coated graphite was prepared via a combined sol-gel coating and catalytic conversion route, using graphite flake and tetraethyl orthosilicate as the starting materials, and Fe(NO 3 ) 3 ·9H 2 O as the catalyst precursor. X-ray diffraction analysis and microstructural examination revealed that a homogeneous coating comprising SiC and cristobalite (SiO 2 ) and covering the whole surface of graphite was formed. As prepared SiC/SiO 2 coated graphite exhibited better oxidation resistance and water wettability than its uncoated counterpart. Also, oxidation resistance and slag corrosion resistance of a model Al 2 O 3 –C castable using coated graphite as a carbon source were better than in the case of its counterpart using uncoated graphite.

Preparation and application of ZrC-coated flake graphite for Al2O3-C refractories

In the study, ZrC-coated flake graphite was prepared by molten salt synthesis and added to the Al2O3-C refractory. The effects of the molar ratio of Zr/C and the graphite particle size on ZrC-coated flake graphite were investigated. Moreover, the oxidation resistance of the prepared ZrC-coated flake graphite was evaluated. Finally, the effect of ZrC-coated flake graphite on the properties of the Al2O3-C refractory was investigated. The results indicated that Zr and C reacted completely as the Zr/C molar ratio decreased. Furthermore, with a decrease in the graphite particle size, the reaction between Zr and C was more complete and the size of the peeling layer decreased. When compared with natural flake graphite, ZrC-coated flake graphite exhibited better oxidation resistance. The Al2O3-C refractory with 3 wt% ZrC-coated flake graphite exhibited optimal oxidation resistance and that with 1 wt% ZrC-coated flake graphite exhibited optimal slag corrosion resistance ability.