Slag Resistance Research Articles

Enhanced slag resistance of magnesia refractory castables with addition of BaSO4

The present study aims to clarify the influence of BaSO4 on composition, microstructural evolution and properties of magnesia refractory castables. Castables with different BaSO4 contents were prepared using calcined magnesia, microsilica, and BaSO4 as raw materials. The results show that introducing BaSO4 can significantly enhance slag resistance of magnesia refractory castables. Castables presented high compactness and mechanical properties with 0–3 wt% BaSO4 for the liquid sintering process and formation of BaMgSiO4 at high temperature. Then compactness of castables decreased when BaSO4 content increased from 5 wt% to 10 wt% for its decomposition and a subsequent increase in the pore content. BaSO4 presented minor effects on the low temperature (1100 °C) structure of castables and played an important role in enhancing high temperature slag resistance, owing to its high structural stability till 1550 °C. The slag resistance mechanism of castables with BaSO4 is that Al3+ in slag was incorporated into periclase intergranular to form BaAl2O4 phases during corrosion process, resulting in the increased slag viscosity and suppressed continuing penetration. The research of this work provides a new insight into microstructure and properties enhancement of magnesia refractory castables used in metallurgical field.

Slag Resistance of Refractories for Direct Reduction of Laterite Nickel Ores in Rotary Kilns

Slag Resistance of Refractories for Direct Reduction of Laterite Nickel Ores in Rotary Kilns

Comparison study of slag corrosion resistance of MgO–MgAl2O4, MgO–CaO and MgO–C refractories under electromagnetic field

To illuminate the corrosion behavior of MgO-based refractories under electromagnetic field (EMF), herein, the slag corrosion and penetration resistance of MgO–MgAl2O4, MgO–CaO, and MgO–C refractories were investigated using the rotary immersion slag resistance test at 1873 K for 1 h. The results showed that the order of the good slag resistance of as-tested refractories was MgO–C > MgO–CaO > MgO–MgAl2O4. The EMF accelerated the corrosion and penetration of slag to the refractories, which caused the molten slag to be easier into the refractories by natural convection and Marangoni effect. In addition, the MgO–C refractories did not show an overwhelming advantage in slag resistance because EMF impeded the formation of the dense protection layer. Consequently, in view of the present results, the MgO–C refractories are still the most promising slag line material for refining furnace among MgO–MgAl2O4, MgO–CaO, and MgO–C refractories.

Moisture stability improvement of asphalt mixture considering the surface characteristics of steel slag coarse aggregate

Weathering treatment is a necessary operation to ensure the volume stability of steel slag coarse aggregate (SSCA) in service. Some previous research proved that the surface of weathered SSCA can significantly affect the moisture resistance of steel slag based asphalt mixture. In this research, the surface characteristics of weathered SSCA and its effect process on the moisture stability of asphalt mixture were first determined. Then two corresponding measures, strengthening the surface of weathered SSCA by an improved organic modification method and enhancing the bonding performance between SSCA and asphalt mastic by adjusting the composition of asphalt mastic, were taken to improve the moisture stability of weathered SSCA based asphalt mixture. Results suggested that weathered SSCA was sensitive to freeze–thaw cycle damage, and the fracture of calcium carbonate product layer coating the surface of weathered SSCA should be responsible for it. The proposed two measures both play a positive role in raising the freeze–thaw cycle damage resistance of weathered SSCA based asphalt mixture. Considering the asphalt pavement may be faced to serious freeze–thaw damage environment in service, weathered SSCA or organic modified weathered SSCA was suggested to prepare asphalt mixture with SBS modified asphalt and some Portland cement. The recommended dosage of Portland cement was 50% of the total filler volume after considering the technology solutions commonly adopted in the actual construction of asphalt pavement in China.

Frost resistance of fiber-reinforced blended slag and Class F fly ash-based geopolymer concrete under the coupling effect of freeze-thaw cycling and axial compressive loading

The poor frost resistance of low-calcium geopolymer concrete is an urgent problem that needs to be solved before its application in practice. In this study, polypropylene (PP) fiber, polyvinyl alcohol (PVA) fiber and steel (S) fiber were added to enhance the frost resistance of blended slag and Class F fly ash-based geopolymer concrete (SFGPC). More importantly, to evaluate the frost resistance of fiber-reinforced SFGPC under axial compressive loading, a coupling experiment with 20 MPa of compressive stress and 125 freeze-cycles was conducted. It was found that the addition of fibers did not inhibit the initiation of microcracks but could suppress their propagation. The water penetration depth and mercury intrusion porosimetry (MIP) test results verified that the applied compressive loading further compacts the concrete, which significantly improves the frost resistance. In comparison, the S fiber-reinforced SFGPC exhibited an inconsistent frost resistance with and without compressive stress due to the extremely high elastic modulus of the S fiber. Overall, 0.3% vol PVA fiber had the best effect on improving both the mechanical properties and the frost resistance of SFGPC.

An investigation on alkali-activated slag pastes containing quartz powder subjected to elevated temperatures

In this work, the opportunity of employing crystalline silica in the form of quartz powder (QP) to increase the fire resistance of alkali-activated slag (AAS) has been explored. The ground granulated blast-furnace slag (designated as slag) was partially replaced with QP at levels changed from 5% to 30% with a step of 5%, by weight. After curing for 28 days, the specimens were subjected to elevated temperatures varying from 400 oC to 1000 oC with a step of 200 oC for 2 h. The compressive strength before and after heating was measured. The new formed phases were evaluated by using X-ray diffraction (XRD), whilst the decomposition phases were evaluated by using thermogravimetric (TGA). The changes in the microstructures were monitored by using scanning electron microscopy (SEM). The results showed a positive effect of incorporation of QP, up to 30%, in AAS system before and after exposure to elevated temperatures.

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.

Effect of n-CaCO3 on fresh, hardened properties and acid resistance of granulated blast furnace slag added mortar

Nano size CaCO3 (n-CaCO3) particles were used as an additive into the Ground Granulated Blast Furnace Slag (GGBS) added mortar to investigate their effects on fresh, hardened properties and acid resistance. Setting time, normal consistency, flow diameter, volume stability, flexural and compressive strengths tests were performed in the present study. In addition, to see how n-CaCO3 and GGBS affect the acid resistance of the mortars, the produced mortar samples were stored in the acid solution and their mass losses were determined. Mortars including 20% GGBS (replaced with cement by weight) with 0%, 1% and 2% n-CaCO3 (added by weight of cement) and a control mortar which has no GGBS and n-CaCO3were produced. Experimental results showed that addition of 1% n-CaCO3 were helpful to increase the both flexural and compressive strength and resonance frequency of mortars 11.54%, 11.9% and 10%, respectively and the setting period was shortened, 7.4% according to control sample. XRD analysis showed that the chemical structure of the mortar samples before and after acid attack did not change, significantly.

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.

Formation mechanism of MgSrAl10O17 and its effect on the mechanical performance of lightweight Al2O3–MgAl2O4 refractories

Lightweight Al2O3–MgAl2O4 refractories can be achieved by producing a density gradient structure which guarantees good slag resistance and low thermal conductivity. To further improve the mechanical properties of this material, in this study, in situ platelike structure was developed by adding different amounts of SrCO3 in the matrix. The phase composition, microstructure, physical and mechanical properties of the obtained lightweight refractories were characterized and evaluated. The results showed that besides corundum and spinel, platelike MgSrAl10O17 phase was also formed during reactive sintering. The well-developed MgSrAl10O17 phase possessing an interlocking structure formed grain-grain bridging with MgAl2O4, which significantly improved the mechanical performance of lightweight Al2O3–MgAl2O4 refractories. Although no obvious changes occurred in apparent porosity and bulk density of the specimen, the compressive strength and refractoriness under load were significantly improved after SrCO3 addition, which increased from ~50 MPa to ~80 MPa and 1589 °C–1656 °C, respectively. To better understand the relationship between microstructure evolution and improvement in performance, the formation mechanism of the MgSrAl10O17 phase and its reinforcement mechanism in the material were described in detail.

Improvement in Slag Resistance of No-Cement Refractory Castables by Matrix Design

The corrosion resistance of spinel containing cement bonded castables has been extensively investigated in the past. However, corrosion of no-cement refractory castables (NCC) has not been widely studied since the use of NCC has been relatively limited up till now. This paper focuses on the slag resistance of NCCs, and the often-used spinel containing low cement castable (LCC) is used as the reference. Three different NCC binders were designed: (i) Al2O3 + MgO (alumina bond), in situ spinel formation; (ii) Al2O3 + SiO2 (microsilica-gel bond), mullite formation; and (iii) Al2O3 + MgO + SiO2 (MgO-SiO2 bond). Slag resistance tests were conducted using the static crucible method with ladle slag. The corrosion mechanisms were studied by means of Scanning Electron Microscopy (SEM/EDS), X-ray Diffraction (XRD), and thermodynamic simulations. The results confirmed that the mineral phases, microstructure, and liquid formation at a high temperature of the refractory materials had a strong impact on the corrosion resistance. The slag resistance was significantly improved when the cement was replaced by the cement-free binders.

APPLICATION OF SLAG FILLERS IN THE ASPHALT CONCRETE COMPOSITION FOR INCREASING THE ROAD COATING’S DURABILITY

Introduction. The paper presents the research results of the metallurgical slag characteristics on the example of metallurgical waste of Novokuznetsk in the Kemerovo region. Moreover, the paper demonstrates the ways of metallurgical waste’s usage in the asphalt mixes’ composition for the road construction and shows design methods and features of the asphalt concrete on slag aggregates. The aim of the research is to substantiate the possibility of using steelmaking slags of the Novokuznetsk Metallurgical Plant as a mineral skeleton of asphalt concrete pavement to increase its operational reliability. Basing on the research of the physicomechanical properties of asphalt binder and testing of prototypes, the authors confirm the increased shear strength of asphalt concrete on slag aggregates and resistance to cracking in comparison with traditional mixtures. The issue under consideration is relevant by finding more efficient building materials in the context of the development of resource-saving technologies and increasing environmental requirements in the Russian regions.Materials and methods. The authors carried out investigations of metallurgical slag by determining their physical and mechanical characteristics in accordance with the existing regulatory and technical base using modern measuring instruments and testing equipment.Results. As a result, the authors selected compositions of slag asphalt concrete mixtures that satisfied the requirements of the existing regulatory and technical base across the entire spectrum of physical and mechanical parameters and operational characteristics.Discussion and conclusion. The use of metallurgical slags of the Novokuznetsk Metallurgical Plant as a filler for asphalt concrete increases its operational characteristics, especially those, which are important in conditions of intense traffic load and sharply continental climate and those, which reduce the cost of such mixtures compared to traditional ones due to the use of industrial waste in them. Therefore, the metallurgical slag seriously competes with natural building materials in the preparation and laying of asphalt mixtures for streets and roads of various categories.The authors have read and approved the final manuscript. Financial transparency: the authors have no financial interest in the presented materials or methods. There is no conflict of interest.

Immobilization of cesium with alkali-activated blast furnace slag

Alkali-activated binders (AABs), as a promising alternative to Portland cement, are now being used on a commercial scale in various applications around the world, including hazardous and radioactive waste immobilization. In this paper, the leaching resistance, strength, and nanostructural alteration of alkali-activated blast furnace slag (AABFS) doped with 2 % and 5 % cesium were investigated. The addition of cesium caused a significant increase in the compressive strength of AABFS, followed by mild strength reduction after leaching. AABFS can be considered a potentially efficient matrix for cesium immobilization, since the mean leachability index in both cases (2 % and 5 % of Cs added) was above the threshold value of 6. Both doping with Cs and leaching caused the transformation of the AABFS nanostructure. The majority of the aluminum that was released from the C-A-S-H gel due to leaching remained within the AABFS matrix, initiating gel reconstruction: the C-A-S-H gel was converted to C-S-H gel, and an additional N-(C)-A-S-H gel was also formed. Cesium was preferentially associated with the N-(C)-A-S-H gel rather than with the C-A-S-H gel. The results of this research seem to be in good agreement with the Cross-linked Substituted Tobermorite Model (CSTM).

Properties of a Steel Slag-Permeable Asphalt Mixture and the Reaction of the Steel Slag-Asphalt Interface.

Steel slag is an industrial solid waste with the largest output in the world. It has the characteristics of wear resistance, good particle shape, large porosity, etc. At the same time, it has good adhesion characteristics with asphalt. If steel slag is used in asphalt pavement, it not only solves the problem of insufficient quality aggregates in asphalt concrete, but can also give full play to the high hardness and high wear resistance of steel slag to improve the performance of asphalt pavement. In this study, a steel slag aggregate was mixed with road petroleum asphalt to prepare a permeable steel slag–asphalt mixture, which was then compared with the permeable limestone–asphalt mixture. According to the Technical Regulations for Permeable Asphalt Pavement (CJJT 190-2012), the permeability, water stability, and Marshall stability of the prepared asphalt mixtures were tested and analyzed. In addition, the high-temperature stability and expansibility were analyzed according to the Experimental Regulations for Highway Engineering Asphalt and Asphalt Mixture (JTG E20-2011). The chemical composition of the steel slag was tested and analyzed by X-ray fluorescence spectrometer (XRF). The mineral composition of the steel slag was tested and analyzed by X-ray diffractometer (XRD). The asphalt was analyzed by Fourier transform infrared spectroscopy (FTIR). The results show that the steel slag asphalt permeable mixture had good permeability, water stability, and Marshall stability, as well as good high-temperature stability and a low expansion rate. The main mineral composition was ferroferric oxide, the RO phase (RO phase is a broad solid solution formed by melting FeO, MgO, and other divalent metal oxides such as MnO), dicalcium silicate, and tricalcium silicate. In the main chemical composition of steel slag, there was no chemical reaction between aluminum oxide, calcium oxide, silicon dioxide, and asphalt, while ferric oxide chemically reacted with asphalt and formed new organosilicon compounds. The main mineral composition of the steel slag (i.e., triiron tetroxide, dicalcium silicate, and tricalcium silicate) reacted chemically with the asphalt and produced new substances. There was no chemical reaction between the RO phase and asphalt.

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.

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.

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.

Effect of Carbonation on Abrasion Resistance of Alkali-Activated Slag with Various Activators.

The effect of carbonation on the abrasion resistance of alkali-activated slag (AAS) was investigated. Various activator sets were selected for synthesizing AAS specimens, and the compressive strength was measured before and after carbonation. The abrasion resistance of the specimens was measured in accordance with the ASTM C944 test method. The relationship between the mass loss caused by abrasion and compressive strength was analyzed to understand the effect of matrix strength on abrasion resistance. Test results showed that the decrease in compressive strength of AAS specimens by carbonation reduced their abrasion resistance. In addition, the abrasion resistance of AAS before and after carbonation was sensitively influenced by activator type. It can be concluded that additional caution is required when using AAS where abrasion may have occurred.

Improved properties of low‐carbon MgO‐C refractories with the addition of multilayer graphene/MgAl2O4 composite powders

AbstractThe paper investigated the effects of different amounts (0%, 3%, 6%, 9%) of in situ multilayer graphene/MgAl2O4 composite powders on the slag resistance, thermal shock resistance, and oxidation resistance of low‐carbon MgO‐C refractories. Comparing with commercial MgAl2O4, the MgAl2O4 in in situ multilayer graphene/MgAl2O4 composite powders has higher lattice strain of crystal, which can trap more Mn and Fe ions, resulting in the better slag resistance. The oxidation decarbonation layer of MgO‐C specimen with 3% composite powders is 9.71 mm, which is lower than not only the specimen with other contents but also specimen containing carbon black/MgAl2O4 powders. Moreover, the residual strength ratio of the specimen C/MA‐3 was 47.47%, which is 28.5% and 8.08% higher than specimens with no additive and with carbon black/MgAl2O4 powders, respectively. Both improving thermal shock and oxidation resistance properties are related with the unique nano structure, multilayer graphene in situ formed between MgAl2O4 grains, of added composite powders. The former is due to higher strain energy consumed by multi‐deflection of cracks inside the multilayer graphene/MgAl2O4 composite powders. And the latter is due to the higher energy of oxidation activation of multilayer graphene/MgAl2O4 composite powders due to effective protection of multilayer graphene by MgAl2O4.

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.