Slag Resistance Research Articles

Catalytic synthesis of SiC coated graphite and its application in carbon containing castables

SiC coated graphites were prepared via a catalytic conversion method, employing graphite flakes and silicon powder as the starting materials, and Fe, Co and Ni as catalysts, respectively. The effects of firing temperature and various kinds of catalyst on the growth and morphologies of SiC coating on graphite surface were evaluated. Density functional theory (DFT) calculations revealed that the catalytic role of catalysts on the formation of SiC could be attributed to the occurrence of chemisorption between CO (g) molecule and catalysts owing to charge transfer effects. The graphites.coated with SiC displayed better oxidation resistance and water wettability than uncoated graphites. Also, mechanical strength, thermal shock resistance, slag resistance and oxidation resistance of a model of Al2O3-C castables containing coated graphites were better than its uncoated counterparts.

Preparation of MgO-MgAl2O4 refractories doped with La2O3 and the wetting permeation behavior by alkaline slag

Alkaline slags play a crucial role in modern smelting processes, underscoring the necessity for researching novel refractories and their interaction mechanisms concerning wetting and infiltration. This study investigates the influence of La2O3 doping on the wettability and infiltration behavior between MgO-MgAl2O4 refractories and alkaline slag, introducing a theoretical evaluation method. The study explored the effects of La2O3 doping on the physical properties, mechanical properties, and thermal shock resistance of the samples, as well as the interface reactions between the samples and slag. Results indicate that La2O3 doping from 0 to 3 wt% enhances sintering performance by promoting the formation of LaAlO3, thereby reducing the apparent porosity from 18.25 % to 15.01 % and increasing the bulk density from 2.85 g·cm−3 to 3.34 g·cm−3. Cold compressive strength improves from 166.24 MPa to 178.42 MPa, while the residual strength retention ratio after thermal shock rises from 86.57 % to 88.65 %. Regarding the interface reaction between slag and samples, CaO and SiO2 react with internal MgO in the samples to form low-melting compounds and high-melting solid solutions. These compounds block pores, weaken slag erosion, and enhance the slag resistance of the samples. As the La2O3 doping amount increases from 0 to 3 wt%, the contact angle between the samples and slag increases, resulting in a greater residual volume of slag and a reduced depth of the slag infiltration layer. The penetration depth of the slag gradually decreases from 102.54 μm to 47.84 μm. This study offers new strategies for optimizing the manufacturing process and selection of refractories.

Effect of metakaolin on the chloride diffusion properties of alkali-activated slag in an acidic environment

Alkali-activated materials (AAMs) have good resistance to chemical corrosion compared to silicate cements, but the effect of the pH of chloride-containing solutions on the resistance of AAMs to chloride diffusion is not clear. In this paper, the resistance of alkali-activated slag (AAS) with different metakaolin replacement rate to chloride diffusion in HCl/NaCl solution was investigated in terms of mechanical properties, hydration product composition and pore structure. The experimental results show that acidic solutions lead to alkali leaching, and dissolution of gel and hydrotalcite. The capillary pores that appeared in the AAS after the replacement rate of 10% metakaolin resulted in a decrease in the average pore size of the AAS and low depth of chloride diffusion. 30% metakaolin replacement led to a decrease in the diffusion resistance. In HCl solution, the high [AlO4]5− retention corroded layer was observed in the AAS with 30% metakaolin replacement and this layer slowed down the migration rate of [Cl−]. This study shows the promising application of alkali-activated slag/metakaolin in complex chloride solution environments.

Significant improvement of oxidation resistance and slag penetration resistance of MgO-SiC-C refractories with Si3N4-Fe addition

MgO-SiC-C refractories demonstrate distinguished thermal shock resistance and slag resistance, making them a promising alternative to magnesia-chrome refractories in matte smelting furnaces. Herein, we propose a novel approach to enhance both oxidation resistance and slag penetration resistance of such refractories by incorporating Si3N4-Fe powder. The results demonstrated that adding Si3N4-Fe powder effectively enhanced their overall performance. The oxidation resistance of the specimen with 6 wt% Si3N4-Fe was greatly improved because Si3N4 in Si3N4-Fe could promote in-situ reactions to form more forsterite, and the FeO formed by iron oxidation could react with SiC to form Fe-Si alloys; the formed forsterite and Fe-Si alloys worked together to prevent oxygen intrusion. Meanwhile, Si3N4 in Si3N4-Fe promoted the formation of forsterite layer in the corrosion area of refractories, and the reaction of Si3N4 and Fe in Si3N4-Fe formed Fe-Si alloys to prevent slag penetration, which greatly improved the resistance to matte slag penetration of the refractories.

Effect of Cr2O3 additive on alumina-spinel and alumina-magnesia castable

Alumina-spinel and alumina-magnesia castables are important for steel ladle applications primarily for the bottom and side wall areas respectively. Presence of spinel in alumina castables enhances the resistances against corrosion and thermal shock and improves the performance and service life of the steel ladles. Development of these type of castables is planned in the present study in presence of Cr2O3 as an additive using high alumina cement as binder. Variation in spinel (10 and 20 wt%) and MgO (2.8 and 5.6 wt%) content was also explored, along with two different particle size distributions (q value 0.21 and 0.29) for different flow consistencies. The castable compositions were processed conventionally and evaluated for various refractory properties after heat treatments at 110, 1000 and 1550 °C. Both the castables showed well developed refractory properties with alumina-magnesia castable having better slag resistance due to greater extent of calcium hexa aluminate phase formation protecting the refractory.

Weak magnetic effect and free radical reaction mechanism on the dissolution of lightweight magnesia in CaO–Al2O3–SiO2 melts

Lightweight magnesia-based refractories play a crucial role in achieving energy savings and carbon reduction in steelmaking furnaces. The primary requirement is to make lightweight magnesia refractories with high corrosion resistance. The introduction of a weak static magnetic field is also a promising way to improve the slag resistance of lightweight refractories in addition to optimizing the composition and structure of the refractories. In this paper, the dissolution behavior of the lightweight magnesia in CaO–Al2O3–SiO2 molten slags at and above 1600 °C under weak static magnetic field is presented. The influence of the weak static magnetic field on the dissolution rate was analyzed, the behavior from the perspective of free radical and kinetics was discussed, and the influence of different calcia–silica weight ratios (C/S) on slag, magnetic flux density and the reaction mechanism are revealed. The results show that the dissolution rate of the lightweight magnesia in the molten slag presents a significantly weak magnetic effect, with a reaction inhibition interval of 2–4 mT in the range of 0–16 mT magnetic field intensity, and the key inhibition threshold surpasses that of alumina. The mechanism of the free radical formation and reaction during magnesia dissolution in high-temperature slag is explained and illustrated. The relationship between the magnetic flux density, superoxide radical content, and dissolution rate is presented, providing theoretical guidance for developing magnetic combined magnesia refractories.

Effect of ferrotitanium slag particle size on properties of Al2O3–SiC–C castables

Ferrotitanium slag can be used to replace bauxite to fabricate refractories owing to its high refractoriness (>1790 °C) and Al2O3 content (≥70 wt%). However, impurities in the ferrotitanium slag is harmful to the materials. In this paper, the mechanical properties and molten slag resistance of Al2O3–SiC–C castables were improved by replacing part of bauxite with large size ferrotitanium slag (8-5 mm). The large size ferrotitanium slag contained a small amount of impurities, which reacted with SiO2 at high temperature to form CaO–Al2O3–SiO2–TiO2 liquid layer on the surface of particles. Under the action of the liquid phase, the ferrotitanium slag particles and the matrix were combined more closely. With the decrease of the particle size of ferrotitanium slag, the slag resistance of the castables began to decrease. This was because the specific surface area of the particles with smaller particle size was relatively larger, large contact area with molten slag resulted in worse slag resistance. Meanwhile, decreasing ferrotitanium slag particle size brought the increase of apparent porosity of Al2O3–SiC–C castables, resulting in weak mechanical properties.

Improved slag resistance of ferrotitanium slag based Al2O3-SiC-C castables: The effect of reaction between SiC and TiO2

Ferrotitanium slag is a kind of waste slag produced by smelting ferrotitanium alloy. It has high refractoriness (>1790 ℃) and Al2O3 content (≥70 wt%), which can be used to replace bauxite to prepare Al2O3-SiC-C castables. However, excessive substitution will lead to the decrease of slag resistance of Al2O3-SiC-C castables because of impurities in the ferrotitanium slag. In this paper, the slag resistance of ferrotitanium slag based Al2O3-SiC-C castables was improved by increasing the SiC content. The results showed that the castables with 13 wt% SiC had good mechanical properties. Increasing the amount of SiC was beneficial to improve the slag resistance. SiC content increased from 5 wt% to 22 wt%, the erosion index of dynamic slag resistance decreased from 17.05 % to 11.18 %. During the dynamic slag resistance, the TiO2 in the ferrotitanium slag dissolved in the slag, then the SiC reacted with TiO2 in the slag to form TiC coating on the surface of SiC particles. SiC particles wrapped by TiC widely existed in the reaction layer, which prevented further erosion of the slag. Further, the reaction of SiC with TiO2 to consume TiO2 and generate SiO2 increased the viscosity of the slag in the reaction layer, thus hindering slag penetration.

From hydratable alumina bonded high chrome castables to shaped product for coal water slurry gasifier

The gasifier is a key equipment of coal gasification technology, enabling efficient and clean utilization of coal resources. However, the aluminum phosphate bonded high chrome brick lining in the gasifier experienced premature failure due to the migration of phosphate in reducing gases such as H2 and CO, as well as increased slag penetration and thermal spalling. In this study, a high chrome castable was prepared using hydratable alumina as a binder and fired at 1600 ℃ to replace the traditional phosphate bonded high chrome brick. The impact of curing temperatures (25℃, 40 ℃, and 60 ℃) on the properties of the high chrome castable was investigated, with corresponding hydrates examined through XRD, FTIR, TG-DSC, and SEM analyses. Results revealed that higher curing temperatures accelerated the hydration process of hydratable alumina. At higher curing temperatures, more well-developed micro-nano sized boehmite and bayerite phases were formed within the castables, filling their pores effectively and enhancing their properties after drying at 110 ℃. Moreover, during heat treatment these micro-nano sized hydrates decomposed into submicron/nano sized alumina which readily reacted with Cr2O3 to form (Cr-Al)2O3 solid solution. This phenomenon facilitated the sintering of castables fired at 1600 ℃ and optimized internal structure, ultimately leading to the enhanced mechanical properties and improved slag resistance.

A comparative study on the slag resistance of MgO–C, low‐carbon MgO–C, and MgO–SiC–C refractories

AbstractThe corrosion of slag on refractories usually starts from the matrix, so improving the slag resistance of the matrix is of great significance for the slag resistance of the refractories. To clarify the influence of matrix on the slag resistance of magnesia–carbon refractories, the slag corrosion experiments were conducted at 1873 K on MgO–C refractories, low‐carbon MgO–C refractories, and MgO–SiC–C refractories. The results showed that the slag resistance of MgO–C refractories was higher than that of low‐carbon MgO–C refractories, and the slag resistance of MgO–SiC–C refractories was superior to that of low‐carbon MgO–C refractories. The interaction between MgO–SiC–C refractories and slag generated high melting point phases such as forsterite and spinel, reducing the routes for the slag to infiltrate the inside of the refractories. MgO–SiC–C refractories reacted with slag to increase the viscosity of the slag, the viscosity being 86.3% and 51.9% higher than in the case of low‐carbon MgO–C and MgO–C refractories, respectively. Compared with MgO–SiC–C refractories, MgO–C refractories did not exhibit overwhelming advantages in slag resistance. Due to the low‐carbon content and good slag resistance, MgO–SiC–C refractories were promising low‐carbon magnesia‐based refractories for high‐temperature industries.

Exploring skid resistance over time: Steel slag as a pavement aggregate—comparative study and morphological analysis

Steel slag has been investigated as a potential aggregate for pavement-wearing courses in road engineering. The volume stability, resistance to high and low temperatures, and water stability for asphalt mixtures containing steel slag have been widely studied. As for the skid resistance, previous studies have primarily focused on the initial performance. The relationship between the steel slag's appearance morphology and skid resistance during the wearing process remains to be further explored. It is essential to undertake a comparative study on the long-term skid resistance of steel slag and conventional aggregates to address the differences. This research picked two steel slags and two types of conventional aggregates (granite and limestone) as research samples. The chosen aggregate samples underwent various degrees of wear treatment with the Los Angeles abrasion machine, and their angularity was examined utilizing an aggregate image measurement system (AIMS). Based on the polishing pre-treatment, the micro-texture of the aggregates was observed with the assistance of a laser confocal microscope, and its correlation with skid resistance was determined. British pendulum number (BPN) tests were also conducted and analyzed at various polishing durations. The results show that steel slag has a low abrasion rate and higher initial angularity and abrasion resistance compared to natural stones. The micro-texture analysis demonstrates that steel slags have a coarser roughness, more contact points, and more durable abrasion resistance. Additionally, the fluctuations in BPN further prove that steel slag has superior initial and sustained skid resistance. Overall, steel slag can be a promising alternative for pavement-wearing course aggregate due to its superior long-term skid resistance.

Impact of basalt fiber reinforced concrete in protected buildings: a review

This study investigates on the impact of basalt fiber reinforcement concrete in protected building and structures. Basalt fibers, derived from the melting of basalt rock at temperatures ranging from 1,500 to 1700°C, are recognized as sustainable and environmentally friendly fiber materials. Various studies have revealed differing optimal percentages of basalt fibers for enhancing the mechanical and chemical properties of concrete. The objectives of this paper are to investigate the effects of basalt fibre reinforcement on mechanical properties like tensile, compressive, and bending strengths. Additionally, performance indicators like void content, water absorption, chloride ion permeability, alkali and slag resistance, temperature stability, shrinkage characteristics, and abrasion resistance will be evaluated. Basalt fibre is typically utilised to increase the mechanical properties and durability of concrete, which has an impact in the effect on protected buildings and structures. The findings indicate that the most effective percentage range for improving mechanical properties lies between 0.1% and 0.3% of basalt fibers. Notably, concrete reinforced with basalt fibers demonstrates superior mechanical and chemical performance in alkaline environments compared to other fiber types. Moreover, the addition of 0.5% basalt fibers to concrete has been shown to significantly reduce chloride ion penetration, as evidenced by a decrease in RCPT load from 2,500 (C) to 1900 (C), indicative of enhanced chloride resistance. Reinforced concrete containing basalt fibers exhibits remarkable temperature resistance, withstanding temperatures exceeding 800°C due to its high-water absorption capacity. Additionally, basalt fibers exhibit resilience at temperatures up to 200°C. However, it is noted that the introduction of 0.14% basalt fibers leads to a slight increase in water absorption from 4.08 to 4.28. In general, basalt fibres are beneficial to many aspects of concrete; they strengthen resistance to temperature, alkali, acid exposure, and chloride while also improving mechanical qualities such as bending and tensile strength. The development of basalt fibres that extend building lifespans and improve concrete quality for structural engineering applications is making encouraging strides, according to all the results.

How does carbonation of alkali-activated slag and Portland cement systems impact steel corrosion differently?

Carbonation of cementitious materials, associated with neutralization of pore solution, is one of the prevalent reasons for inducing corrosion of steel in concrete. Compared with ordinary Portland cement (OPC) concrete, the poorer carbonation resistance of alkali-activated slag (AAS) concrete leads to serious durability concerns of a higher risk of steel corrosion. This work investigates the corrosion behaviors of steel embedded in intact and carbonated AAS and OPC mortars exposed to various relative humidity conditions, with the aim of fostering a better understanding of how carbonation impacts steel corrosion differently in these two cementitious systems. The results show that uncarbonated AAS mortars have better protective ability against corrosion than OPC counterparts; however, poorer performance after complete carbonation. It is mainly attributed to the combined effect of severe deterioration and coarsening of pore structure and increased ratio of chloride ion concentration to hydroxide ion concentration ([Cl−]/[OH−]) in pore solution, resulted from the consumption of hydroxide ions and release of bound chloride after carbonation. Besides, the different shifts of R-C (material resistivity versus corrosion rate) relationship lines in AAS and OPC mortars after carbonation are observed, which is ascribed to the different compositional and microstructural evolutions induced by carbonation in these two cementitious systems.

A novel and effective approach to improve the oxidation resistance and slag corrosion resistance of Al2O3–SiC–C castables

The present study aims to clarify the role of ball pitch in Al2O3–SiC–C (ASC) refractory castables and investigate the influence of low temperature treatment on the composition, microstructural evolution, and properties of ASC refractory castables. By utilizing the expansion properties of ball pitch during heating, the castables undergo a low temperature treatment to induce the flow and expansion of ball pitch within the castables. This, in turn, fills the surrounding pores and enhances the physical properties of the castables. The results of this study demonstrate that low-temperature heat treatment of the castables at temperatures at 350 °C significantly improves the hot modulus of rupture, oxidation resistance, and slag resistance after sintering. This improvement is attributed to the optimized microstructure. In comparison to the corresponding samples without low temperature treatment, the high temperature modulus of rupture (HMOR) of the calcined castables treated at 350 °C increases by 33.3%. Additionally, the oxidation index and slag corrosion index after sintering at 1500 °C decrease by 39.6% and 87.31% respectively for the samples low temperature treated at 350 °C, as compared to the samples low temperature treated at 110 °C. This study provides a fresh perspective on the production of ASC castables with exceptional high temperature performance.

Wetting Behavior of High Alumina Slags on the Fused Magnesia under Different Atmospheres and Low Static Magnetic Field

With the growing demand for high‐aluminum steel, there is an urgent need to enhance the slag resistance of magnesia‐based refractories. The wettability of high‐alumina slag on magnesia‐based refractories serves as a crucial indicator of the refractory's slag resistance. In this study, the influence of atmosphere and magnetic flux density on the wetting behavior between the slags with different basicity (CaO wt%/SiO2 wt%) and fused magnesia is explored using a high‐temperature visualization device with a controllable static magnetic field. Compared to air and argon atmospheres, the apparent contact angle of the slag on the fused magnesia decreases significantly in a vacuum environment as the violent interfacial radical reaction. The static magnetic field of 0.5 mT can regulate the spin state of a single electron in the free radical pair, resulting in an increase of the apparent contact angle by 21.1% in a vacuum atmosphere. It provides new thoughts on the development of external field protection technology for the corrosion resistance of magnesia‐based refractories.

Ash melting and slagging and residual K ion content in biomass pellet combustion

ABSTRACT Combustion of biomass pellets is an effective way to reduce greenhouse gas emissions and achieve carbon neutrality. However, the alkali metal content (represented by K) in ash directly affects its slagging behavior, which can corrode the reactor and shorten its service life. In this study, the ash fusion slag and residual K ion contents were investigated at different combustion times (2, 5, 10, 20, 30 and 60 min) and temperatures (600, 700, 800, 900 and 1000°C). At the same combustion temperature, the residual content of K ions in ash decreases as the combustion time increases; at the same combustion time, the residual content of K ions decreases as the combustion temperature increases. The addition of 5% CaO promotes K precipitation, but at 10% CaO addition, the K precipitation rate is less than that at 5% CaO addition, indicating that the addition of CaO is beneficial to K ion precipitation only within a certain range. Adding CaO also generates high-melting-substances, such as CaSiO3 and calcite, which improve the overall slag resistance of the fuel.

Effects of Al–Si alloy powders on mechanical properties and slag resistance of unfired magnesia refractories: In air and carbon-embedded atmospheres

Ultra-low carbon magnesia refractories used in working lining of ladle are crucial components to meet the smelting requirements for producing purity steel. However, the decreased carbon content weakened thermal shock resistance and slag resistance of refractories, resulting in the hampered practical applications. To resolve the mentioned problems, Al–Si alloy powders were introduced into unfired magnesia refractories with glucose and citric acid as binders to form combination of oxides and non-oxides, and performances of refractories were researched systematically in air and carbon-embedded atmospheres according to different service conditions, respectively. The results show that reaction mechanisms in 2 atm led to different effects on microstructure of refractories with added Al–Si alloy powders. The formation of AlN whiskers and plate-shaped MgAl2O4 and Mg2SiO4 with intersecting structure resulted in higher mechanical strength, fracture surface energy and thermal shock resistance of refractories in air atmosphere than that in carbon-embedded atmosphere. The in-situ formed ceramic phases (AlN, MgAl2O4 and Mg2SiO4) in pores led to enhanced slag resistance for refractories. Meanwhile, in carbon-embedded atmosphere, the reduced reactions of Fe2O3 in molten slag increased slag viscosity, presenting higher slag penetration resistance for refractories than that in air atmosphere. Considering the lowered compactness of refractories with excessive alloy powders by large volume expansion from the formation of ceramic phases, refractories with 3 wt% alloy powders showed high mechanical properties, thermal shock resistance and slag resistance. This study provides a reference for the development of ultra-low carbon magnesia refractories used in working lining of ladle, and the research results also indicated that the evaluation of different atmosphere conditions is important for the design of high performance refractories.

Improved oxidation resistance while maintaining slag corrosion resistance of MgO–SiC–C refractories with moderate amounts of liquid phase

AbstractMgO–SiC–C refractories with superior hot strength, oxidation resistance and slag resistance have potential to become substitute refractories for matte smelting furnace. In the present work, the influence of glass powder addition on phase compositions, hot strength, oxidation resistance, and slag resistance of MgO–SiC–C refractories was investigated. The liquid phase introduced by glass powder filled the pores, blocking the channel for the ingress of the oxygen and thus improving the oxidation resistance. Although the oxidation resistance of such refractories was improved with 1–3 wt% glass powder addition, their hot strength and slag corrosion resistance decreased when the glass powder content was 2–3 wt%. To balance the mechanical properties, oxidation resistance and slag resistance, low amount glass powder addition (1 wt%) was considered better choice.

Comparison of the moisture resistance of a steel-slag stone mastic asphalt mixture modified with Ca(OH)2

Stone mastic asphalt is a type of hot mix asphalt that requires much coarse aggregate, so substitution waste aggregate, such as steel slag, will be an economic reason. The problem is that there are still many things that have not been consistent in various studies related to the moisture resistance of steel slag. The study aimed to compare the effect of Ca(OH)2 on the moisture resistance of the steel-slag stone mastic asphalt mixture and to determine the optimal Ca(OH)2 dosage for improving the mixture resistance. This study employs basalt aggregate, steel slag from Krakatau Steel Company, 60/70 penetration asphalt, a stabilizing substance made of bamboo fiber, and Ca(OH)2. The Texas boiling and the static immersed methods are used to test the adhesion on a loose mixture. The retained Marshall stability and indirect tensile strength are used to test the adhesion on the compacted mix. Testing result of Krakatau steel slag shows that steel slag has a much higher Fe2O3 content than steel slag in general and has low water absorption; a poor affinity for asphalt results from this. The result of the Texas boiling method showed a decrease in the percentage adhesion value between steel slag and asphalt compared to natural basalt aggregates and asphalt. Marshall Stability Ratio and Tensile Strength Ratio increased after mixing the asphalt with Ca(OH)2. Marshall test results show decreased stability in mixtures with steel slag substitution. Adding Ca(OH)2 increased stability and resistance to moisture significantly. This indicated that Ca(OH)2 enhances moisture resistance on stone mastic asphalt with modified steel slag. Stability, Marshall stability ratio, indirect tensile strength ratio, particle loss, and Texas boiling test significantly improved with adding Ca(OH)2

Development of composite boron-containing SHS antioxidants for carbon-oxide refractories

Increasing the service life and reducing the cost of refractories remains an actual task for metallurgical production. One of the ways to solve it is the use of new composite materials in the production of modern refractories. The paper presents the test results of the alloying of ladle products PUPK-SH by composite boron-containing antioxidants, obtained by the SHS method. As a result of laboratory tests, it was established that PU-products contained SHS-antioxidants NITRO-BORAL NB-1 (BN·Al2O3) and BorTiX® MM (2TiB2·TiC) grades, instead or together with current antioxidant additive (aluminum powder APV-P grade), has the better characteristics of slag resistance, oxidation and physical and mechanical properties after firing. Based on the results of laboratory tests the products PUPK-SH grade, containing boron-containing SHS-antioxidants, were recommended for pilot industrial testing.