Slag Penetration Research Articles

Influence of ZrSiO4-SiC reinforcement on the decarburization and thermal shock behavior of MgO-C refractories

The slag corrosion resistance and thermal shock and of MgO-C refractories are crucial in the steelmaking industry. The current study presents a novel approach to enhance these properties by incorporating reinforcing particles such as zircon and silicon carbide. MgO-C refractories containing various amounts of ZrSiO4 and SiC were prepared and subjected to slag corrosion and thermal shock tests. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to characterize the microstructure and chemical composition of the samples. The findings demonstrated significant improvements in the overall performance of the refractories with the addition of zircon and silicon carbide. Thermal shock resistance increased from 11 cycles for MgO to 18 and 15 cycles due to the increased fracture toughness and altering crack propagation paths with the addition of ZrSiO4 and SiC particles. The formation of a CaZrO3 phase within pores significantly improved slag corrosion resistance. This led to a reduced slag penetration depth and a thinner decarburized layer compared to the unreinforced MgO-C refractory. SiC decomposition formed a protective silica layer, while zircon particles locked MgO grain boundaries, further enhancing corrosion resistance. The study proposes a corrosion mechanism based on the formation of microstructure containing dense and decarburized layers. These findings highlight the potential of reinforcing particles to improve the performance of MgO-C refractories in steelmaking applications.

Dissolution Behaviors of Recycled Cement Paste and Lime in EAF Slag Under Static Conditions

AbstractRecycled cement paste (RCP) is a CaO-rich resource that is recycled from waste concrete and waste cement. For reducing environmental impact and promoting comprehensive resource utilization, RCP could partially replace lime as flux in electric arc furnace (EAF) steelmaking process. In this study, the dissolution behaviors of RCP and lime in EAF slag at 1400 °C and 1500 °C were investigated using static dissolution experiments. The measured dissolution rate constant of lime at 1400 °C and 1500 °C is 3.12×10−5 and 8.42×10−5 m/s, respectively, while that for RCP is 1.37×10−4 and 2.91×10−4 m/s, respectively. For the lime dissolution, a dense dicalcium silicate (C2S) product layer was generated at the dissolution interface, with the diffusion of Ca2+ in the C2S layer being the limiting step for the lime dissolution. However, for the RCP dissolution, no product layer was observed at the dissolution interface. Instead, a dissolution intermediate layer forms due to slag penetration. During the dissolution of RCP, Ca2+ and SiO44− diffuse from RCP layer to slag, while Fe2+ and AlO45− diffuse from slag to RCP layer accumulating in the dissolution intermediate layer. Furthermore, a dissolution model was developed based on current experimental results, which helps to predict dynamic dissolution process of lime and RCP in EAF slag. In general, the dissolution rate of RCP in EAF slag was much higher than that of lime, partially adding RCP as flux in EAF could accelerate the liquid slag formation in EAF steelmaking process.

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.

Corrosion mechanism of postmortem converters slag-blocking ZrO2 sliding gate

The post-service ZrO2 sliding gate for converter slag-retaining was examined by XRD, SEM, EDS and X-CT to investigate its corrosion mechanism. The results show that m-ZrO2 in the hot working layer transform into stable t-ZrO2, and cracks and flaws are generated due to the accompanied volume contraction, leading to severe slag penetration. The CaO in the slag preferentially reacts with ZrO2, forming a CaZrO3 dense layer with a high melting point to prevent slag penetration. While SiO2-Al2O3-FeO component in the slag removes the MgO stabilizer out of Mg-PSZ crystals, causing destabilization and decomposition of the Mg-PSZ grains. The microstructure loses its integrity and is easily spalled. A corrosion model was established.

Fabrication of Y2O3-doped MgO refractory raw materials based on magnesium hydroxide from salt-lake brine

High-purity magnesia refractories were fabricated by brine magnesium hydroxide from the salt-lake brine (Qinghai Salt Lake) and Y2O3 as an additive at 1780 °C. It avoided the substantial CO2 emissions and ultra high temperature sintering process (＞1900 °C) when compared with the conventional magnesite-calcination technical approach. The results confirmed that Y2O3 was dispersed on the MgO grains boundaries in the fabricated MgO aggregates, resulting in a decrease in apparent porosity and enhancing the grains' boundaries. With 3 wt% addition of Y2O3, the apparent porosity and bulk density of the sample reached to 15.9 % and 3.10 g/cm3 from 37.9 % to 2.30 g/cm3 of blank control group, respectively. Compared to the blank control without Y2O3-adding, the sample with 5 wt% Y2O3 exhibited a 54.17 % increase in the resistance to molten slag. SEM results indicated that the incorporation of Y2O3 in samples increased the porosity of small pores and enhanced grains boundaries, thereby suppressing slag's penetration. Furthermore, the Y2O3-adding was employed to disperse the MgO grains boundaries and existed as separate phases for grains boundaries enhancement. The slag attack of the fabricated MgO–Y2O3 refractory raw materials were controlled by an inter-crystalline corrosion process.

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.

Calculations of Non-Metallic Particles Removal from Liquid Aluminium to Top Slag

In the paper, the results of a numerical analysis of KCl and KF particles present in liquid aluminium assimilation to the slag are presented. The authors analysed particle movement in the slag model, which is based on buoyant, capillary, viscosity, Newton and repulsion forces, interfacial tensions at the interface of phases and surface energy during the particle movement through phases boundary. On the basis of the mathematical model, a computer programme was written to make simulations under different conditions. The results of particle position in the slag are presented for different particle radiuses: 1, 5, 10, 20 μm, and constant viscosity of the slag including velocity evolution of the velocity. Another approach was used to indicate the influence of slag viscosity on particle and slag penetration depth. During computations, selected viscosities of slag of 0.0012, 0.0015, 0.0018 [kg/m·s] were taken into account. Different comparisons were made for the chosen particle sizes. Each examination takes into account the impact of the particle type. The results clearly show that for larger particles the penetration depth is greater and viscosity of the slag has an impact on the velocity evolution during assimilation process.

Comparative analysis on corrosion behavior of lightweight and dense mullite–corundum refractories: Role of Si‐rich phase

AbstractThe corrosion resistance of lightweight and dense mullite–corundum refractories to cement materials was examined. The specimens following static crucible treatment were investigated using phase analysis, microstructure, and thermodynamic simulation. The results reveal that diffusion of the silica‐rich phase enhances alumina saturation solubility in the slag, reducing the corrosion resistance of the mullite–corundum refractories. The large proportion of closed pores and the continuous net‐like structure of anorthite created by the corrosion reaction in the matrix, on the other hand, prevent further slag penetration into the lightweight mullite–corundum refractories. As a result, the presence of the silica‐rich phase assures better slag penetration resistance of lightweight mullite–corundum refractories.

Alternative Industrial Chrome-Free Alumina-Based Bricks for Copper Alloy Melting Furnaces

Abstract In this study, the corrosion resistance of alumina-based bricks against the slag of copper alloy melting furnaces was investigated. Four commercial chrome-free alumina bricks have been studied. Bulk density and apparent porosity measurements and phase analysis of the bricks were performed. The most important property, the slag corrosion resistance, was evaluated at the temperature of 1,200°C for 2 h. The microstructures of the bricks, their penetration depth, and corrosion index were evaluated. The results showed that two bricks showed acceptable corrosion resistance against the slag. The low corrosion index of these bricks was attributed to their aluminosilicate phases (sillimanite, or andalusite) and lower phosphate bonding; however, the problematic matter was the silicate phase, which showed lower resistance against the penetration of slag. It was observed that the aluminosilicate phase can improve the corrosion resistance through the reaction with slag, whereas the presence of large alumina aggregates can restrict the penetration of slag.

Mechanism for metal loss in smelting of recycled spent lithium-ion batteries: The overlooked role of refractory materials

The pyrometallurgical process used to recover spent lithium-ion batteries (LIBs) involves high smelting temperatures. During the smelting process, the refractories dissolve into the slag. This can have negative effects on metal recovery. Nonetheless, issues related to the effects of refractories on separation of the slag and metal during smelting of spent LIBs have not received much attention. Therefore, in this study, the effects of refractories (Al2O3 and MgO) on metal recovery rates were investigated. The aim was to reveal the mechanism for metal loss from the slag due to the influence of refractories and the interfacial reactions between the slag and the refractories. The results showed that less MgO dissolved in the slag, and this resulted in a metal recovery rate higher than that seen with Al2O3. The Al2O3 refractory continued to dissolve in the slag so that the crucible matrix was no longer dense. Furthermore, the slag penetrated the crucible, resulting in accelerated dissolution of the Al2O3 refractory. The formation of spinel and transition layers at the interface between the MgO refractory and the slag generated a region of local equilibrium, slowing the penetration of slag into the refractory and reducing the dissolution rate of MgO. The difference in metal recovery rates was attributed to physical losses. Dissolution of the Al2O3 refractory led to an increase in the slag viscosity, which adversely affected settling of the alloy particles in the slag. This led to increased losses of the metal in the slag and reduced metal recovery with the Al2O3 refractory.

The Melting Mechanism of Hydrogen Direct Reduced Iron in Liquid Slag

The heating and melting of hydrogen direct reduced iron (H‐DRI) in liquid slag is investigated experimentally at 1923 K. For the experiments, slags comprising the CaO‐SiO2‐MgO‐FeO‐Al2O3 system are first premelted at 1923 K in alumina crucibles. The molten slag bath is subsequently used to submerge samples of 7 g of H‐DRI with different degrees of reduction (90.4–99.8%). Following the submersion, the slag bath and the H‐DRI sample are quenched at different times (5–10 s). It is found that the liquid slag penetrates the porous network of the H‐DRI. The penetration is found to increase with lower reduction degrees. The reaction‐enhanced capillary action theory is proposed to explain the dependence. The reasoning is validated by a cold model consisting of a quartz capillary, water, and solid sugar. The slag penetration also enhances the heat transfer and the dephosphorization rate. The present findings can, therefore, aid in optimizing the hydrogen‐based steelmaking route.

In-situ visualization of high temperature slag corrosion process for alumina-magnesia refractory

The stringent service environment of refractory, which is composed of complex photo-thermal radiation, limits the evaluation of its corrosion process and corrosion mechanism. The visualization of interaction between refractory and slag at the temperature range of 1350∼1600 °C was realized based on the development of high-temperature resistant speckles combined with digital image correlation technology. The corrosion processes of alumina-magnesia refractories can be divided into three stages: slag penetration, refractory dissolution, and formation of new precipitates. The relationship between corrosion and corrosion processes induced strain was established: the stress caused by slag penetration and refractory dissolution was about 1.29 times that of the formation of new precipitates, such as CA6. With the quantification and identification of slag penetration and corrosion area using the full-field chemo-mechanical strain distribution on the refractory surface, a new method for precise research and real-time evaluation of corrosion behavior of refractory under extreme environment is established.

Performance enhancement of free CaO containing magnesia by in situ intergranular CaAl2O4 and MgAl2O4

Magnesia refractory raw material with free CaO has inherent weaknesses of low resistance to hydration, thermal shock and slag penetration. In this work, micro-sized Al2O3 powder was added into such magnesia with the purpose of improving its comprehensive performances. The results showed that with increasing Al2O3 content, CaAl2O4 and MgAl2O4 phases were sequentially formed at the MgO grain boundaries, which enlarged the MgO grains and reduced the apparent porosity. Owing to the transformation of free CaO to CaAl2O4, reduction of apparent porosity and covering of intergranular MgAl2O4 on MgO grains, hydration of the specimens was inhibited effectively by introducing the Al2O3 addition. The formed CaAl2O4 and MgAl2O4 phases lowered the thermal expansion coefficient and induced crack deflection, and therefore residual flexural strength ratio after thermal shock tests increased remarkably from 15.1% to 33.2% with increasing Al2O3 addition from 0 wt% to 7 wt%. Moreover, slag penetration resistance of the specimens was improved effectively with raising the Al2O3 content to 3 wt%, attributing to the increase in MgO grain size, decrease in apparent porosity and formation of high stable intergranular CaAl2O4 phase. However, further increasing Al2O3 content would dramatically accelerate the slag penetration owing to the decrease in grain size and formation of more unstable intergranular MgAl2O4 phase.

Simultaneous enhance of the thermal shock resistance and slag-penetration resistance for tundish flow-control refractories: The role of microporous magnesia

As the low thermal shock and slag-penetration resistance of the magnesia castables cause the premature failure of tundish flow-control devices leading to the pollution of steel, the microporous magnesia with high closed porosity and intergranular CaZrO3 phase was utilized for simultaneously enhancing the high-temperature performance. The thermomechanical stress and slag corrosion tests indicated that since the micro-closed pores effectively relieved the thermal stress and CaZrO3 absorbed massive crack-propagation energy, the cold modulus of rupture and residual strength ratio respectively reached 14.4 MPa and 73.4% after thermal shock cycles, nearly half higher than that of the fused magnesia based castables. Meanwhile, the synergistic effect of micro-closed pores and intergranular CaZrO3 phase significantly reduced the slag-wettability, improved the interfacial energy and dihedral angle, leading to the decline of slag penetration indice (decreased by ∼34.8%). This study suggests a potential approach to generate new magnesia based castables in tundish for making clean steel.

Improved properties of in-situ MgAl2O4-TiO2 dense layer reinforced low-carbon MgO-based refractories

With the increasing severity in the service environment of secondary refining furnaces, traditional refractories cannot meet the high requirements. MgO-based fired refractories are subject to the thermal shock effect and slag penetration which are detrimental to their performance. In this study, low-carbon MgO-based refractories are reinforced by an in-situ MgAl2O4(MA)-TiO2 dense layer with the addition of low-cost self-prepared titanium carbonitride [Ti(C, N)]. The influence of the addition of as-prepared Ti(C, N) on the properties of low-carbon MgO-based refractories was investigated. The reinforced refractories had no cracks after 190 thermal shock cycles, demonstrating the highest hot modulus of rupture (HMOR) with excellent thermal shock resistance (TSR). After 2.5 h of rotary immersion in a steel slag, the corrosion depth of the composites was only 26.3% of that of commercial MgO-CaO refractories. Based on the thermodynamic analysis, the Ti(C, N) reinforcement mechanism for the low-carbon MgO-based refractories was studied. A MA-TiO2 dense layer formed during the oxidation process of the composites which enhanced the oxidation resistance. The volume expansion caused by the partial oxidation of Ti(C, N) prevents the penetration of the molten slag to refractories and Ti(C, N) powders forming a protective layer to further effectively protect the composites from slag corrosion owing to its high surface area. In addition, 3CaO·2TiO2 formed by the reaction between the steel slag and Ti(C, N) further increased the slag corrosion resistance (SCR) of the composites. This research offers a new idea for the material selection for secondary refining furnaces to achieve a green and effective steel-making production route and enriches the understanding of the phase behaviour in the Mg-Al-Ti-C-O-N system under high temperatures.

Effect of MgO on wetting and corrosion behaviour of corundum substrate by CaO–SiO2–MgO (–Al2O3) slags

ABSTRACT Effect of MgO content on wetting and corrosion behaviour of corundum substrate by CaO–SiO2–MgO (−15%Al2O3) molten slags was investigated at 1450°C via joint application of a sessile drop technique, SEM–EDS detection and FactSage thermodynamic software. All slags exhibit good wettability on the substrate, and the contact angle values are small. Increasing MgO content from 7% to 9% in CaO-SiO2-MgO slags can increase the contact angle between the droplet and the substrate, while the substrate dissolution thickness and the slag penetration depth tend to decrease. Increasing MgO content from 8% to 15% in CaO-SiO2-MgO-15% Al2O3 slags can also increase the contact angle, but significantly decrease the slag penetration depth. The indirect dissolution thickness increases instead due to the formation of a large amount of MgAl2O4 by the interface reaction. The wettability can give an indication of the slag penetration depth in the substrate but not the dissolution thickness of the substrate.

Bonding phase formation in eco-friendly periclase−spinel−Al bricks used in RH degassing process

Mere unburnt periclase–spinel–Al bricks have been accepted by steel mills in the chromium-free campaign of the lining materials for Ruhrstahl ̶ Heraeus (RH) degassers, in terms of comparable/optimistic performance to traditional material, low carbon emission due to unburnt manufacturing process and chromium-free material for eco-friendly steel-making process. Investigations are made on the used periclase–spinel–Al bricks for the thermal evolution of their components and the formation of novel phase and bonding structure. Under the working atmosphere of RH degasser, metallic Al particles got molten above its melting point, leaving Al rim at their surroundings, and AlN formed in the gaseous state dispersing into overall matrix of periclase–spinel–Al bricks with rising temperature. AlN formed and Mg reduced in their gaseous state germinated MgAlON whisker initially in the original space of metallic Al particles, and MgAlON whisker grew further everywhere in the matrix. A whisker interwoven network has been full of the matrix behind the hot face and toward the cold face of the used bricks, which is a completely novel type of bond and distinguished from traditional ceramic one. The whisker-interwoven network is somewhat like the stripe graphite containing microstructure of magnesia–carbon brick, which results in low wettability and high flexibility. The superior performance of periclase-spinel-Al brick is attributed to such a bonding structure of whisker-interwoven network, which could reduce slag penetration and facilitate thermomechanical stress resistance.

Role of self-disintegrating effect produced by decomposition of limestone core on accelerating dissolution of lime in CaO–SiO2–FeOx slag

ABSTRACT The dissolution behaviours of lime, limestone and lime sample with limestone core-lime shell structure in CaO–SiO2–FeOx slag were investigated. The results show that dissolution of lime slows down once 2CaO·SiO2 layer is formed at slag/lime interface. Self-disintegrating effect produced by decomposition of limestone core can accelerate dissolution, but dissolution rate firstly increases, and then decreases with the CaCO3 content of samples increasing. Limestone must decompose to form lime before dissolution, and too much CO2 generated by decomposition of limestone bearing 98.9 wt% CaCO3 blocks the contact between molten slag and lime layer. Thus, limestone hardly dissolves after 60s contacted with molten slag. For lime sample with core–shell structure, the surface of sample is lime layer that can be directly dissolved in molten slag. Meanwhile, self-disintegrating effect produced by decomposition of limestone core enhances slag penetration, and accelerate dissolution. The optimum CaCO3 content in lime sample is 22.7 wt%.

Three bond modes of basic refractories used for Ruhrstahl Heraeus degassing process

AbstractMagnesia–spinel brick and unburnt periclase–spinel–Al brick are being employed as a substitution of traditional magnesia–chrome brick in the chromium‐free campaign of lining materials in Ruhrstahl Heraeus (RH) degasser. These three materials are investigated, in terms of physical properties, corrosion resistance and flexibility by wedge splitting test. Tracking their physical alterations and chemical reactions through burning or heating, three bond modes are discovered. Magnesia–chrome brick is subject to a series of phase transformation with rising temperature to yield a liquid envelop around chromite‐ore particles, to further form porous rim while liquid is gradually absorbed by surrounding magnesia and eventually to precipitate secondary chromite spinel lied between magnesia particles by thoroughly dissociating chrome ore. The precipitated chromite spinel functions as the featured bond that enhances hot strength and corrosion resistance to slag, and additionally liquid coexistence improves the flexibility. The direct bond mode of magnesia particles in magnesia–spinel brick endures slag penetration by immanent character of MgO. Spinel incorporation in magnesia effectively improves thermal shock resistance. Due to minor negative value of permanent linear change after reheating, further sintering (densifying) in using at high temperature would bring a risk of loosening and open joints of magnesia–spinel lining. While used in RH degasser, unburnt periclase–spinel–Al bricks undergo a miraculous process of metallic Al melting, gaseous AlN and AlON formation, MgAlON whiskers germination combined with gaseous Mg reduced, and micron‐size whisker network bond domination in their matrix. Such a whisker‐network bond renders the material a successful eco‐friendly alternative to magnesia–chrome refractory.