Slag Resistance Research Articles

The Effect of the Glass Phase on the Modulus of Rupture of High-Alumina Refractories

Owing to their high refractoriness and slag resistance, high-alumina refractories are widely used in the lining of steelmaking furnaces, glass furnaces and cement rotary kilns in high-temperature industries. The impurities in the raw materials react to form the glass phase, which can melt into liquid at high temperatures. The modulus of rupture of refractories depends intensively on the content and composition of the glass phase. In this work, the cold and hot modulus of rupture for high-alumina bricks were investigated by means of fitting based on different theories. The effect of the glass phase on the modulus of rupture was analyzed by combining the phase composition, morphology of fracture surfaces and porosity for high-alumina refractories.

Evaluation of Sulfate Resistance of Calcined Dolomite Activated Ground Granulated Blast Furnace Slag

Aggressive environments significantly influence the durability and serviceability of hardened cement and concrete. This paper presents an evaluation of the resistance of ground-granulated blast-furnace slag (GGBS) activated with calcined dolomite, as a novel alkali activator, to 5% sodium sulfate attack and 5% magnesium sulfate attack. Two calcined dolomites, D800 and D1000, were prepared in the laboratory at 800°C and 1,000°C, respectively. The results demonstrated the good potential of using calcined dolomite activated slag in resisting sulfate attack. Immersion in Na2SO4 (aqueous) led to an increase in strength in both the D800 (D800S) and the portland cement CEM I 52.5 N (PCS) activated slag with a more pronounced effect in the former and a decrease in the D1000 (D1000S) activated slag. Conversely, calcined dolomite activated slag had less strength loss than PCS after MgSO4 attack. The products of sulfate attack and the deterioration processes are also analyzed by a range of tests, including pH, weight change, corroded depth, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). After Na2SO4 attack, the main product on D800S and D1000S was gypsum with a larger amount in the latter. Gypsum, thaumasite, and M-S-H were the main products of D800S and D1000S after MgSO4 attack. The better resistance of D800S to sulfate attack was attributed to the absence of portlandite in the hydrated paste. Conversely, the presence of portlandite in D1000S led to the inhomogeneous sulfate ions inward progression; hence, the severe deterioration of the sample was observed.

Microsilica influence on the phase consTITUTION and properties of spinel-forming composition

Experience in using low cement alumina-magnesia castables, containing spinel-forming reagents, in monolithic ladle linings identified their significant advantages in terms of thermomechanical properties, corrosion resistance and slag resistance. A particular feature of these castables is the synthesis of «in situ» magnesium aluminate spinel at high operating temperatures, which provides increased operational lifetime of the lining.The microsilica influence on the phase constitution of the composite mixture, containing calcium aluminate cement and spinel-forming reagents - calcined alumina and sintered periclase after firing at 17000C was investigated in the paper. It was found that as a result of the interaction of cement calcium aluminates with microsilica, fusible compounds - anorthite and helenite that, at increased microsilica content, impair physical and technical properties of the composite are formed. It was determined that the ratio of spinel-forming reagents and content of the silica-containing material in a matrix component of alumina-magnesia castables is a more important factor of the synthesis of high-melting-point crystalline phases than the microsilica content. Directed regulation of the phase constitution of the matrix component of alumina-magnesia castables by adjusting the grain-size composition of spinel-forming reagents and their optimal ratio will ensure achieving a set of the given physical and technical characteristics of concrete and increasing the operational lifetime of monolithic ladle linings.

Studying effects of low-reactivity GGBFS on chloride resistance of conventional and high strength concretes

This paper presents the results of an experimental investigation on strength development and chloride resistance of low-reactivity ground granulated blast furnace slag (GGBFS) incorporated concretes. Fine and coarse GGBFS samples were used to replace the Portland cement at 20 %, and a series of tests were conducted to investigate the effects on conventional and high strength concretes. Compressive strength, RCMT, RCPT and electrical resistivity tests were carried out at different ages up to 180 days. Furthermore, half-cell potential test was conducted weekly on steel reinforced specimens exposed to wet–dry cycles for 30 weeks. The results imply that despite the low activity index of the local GGBFS, it could be used at low levels of Portland cement replacement. Of note, however, is that despite its positive effect on the chloride resistance of concrete, a reduction in compressive strength (mainly at early ages and for conventional concrete mixes) should be expected. Furthermore, the test results indicate that increasing fineness of low-reactivity local GGBFS (within the studied range) does not lead to higher resistance of concrete against chloride attack.

RH-Degasser Refractory Corrosion Mechanism by Lime-Silica Slags of Different Basicity

Results are provided for a laboratory study of the reaction of industrial self-dissociating slag after steel treatment in an OAO NTMK furnace-ladle unit and synthetic slag of the system CaO–SiO2–Al2O3 with five forms of periclase-spinelid refractories produced by enterprises of Gruppa Magnezit in Russia and Slovakia (Slovmag), and also two Chinese producers. Refractory slag resistance is compared, and their mineral and phase compositions are studied before and after testing.

Degradation of MgO–C refractories corroded by SiO2–Fe2O3–V2O5–TiO2–MnO–MgO slag

The properties and degradation of resin bonded MgO–C bricks corroded by SiO2–Fe2O3–V2O5–TiO2–MnO–MgO slag were investigated by dynamic induction slag test. Carbon oxidation by oxygen and/or reducing slag and corrosion of MgO grains attacked by corrosive vanadium containing slag are the main degradation mechanism. High temperature and long exposure time lead to more serious corrosion. Marangoni convection at the three phase boundary steel–slag–refractory is observed. Oxidation of carbon is observed which affords pores, cracks and voids for the vanadium containing slag corrosion and penetration. Periclase grains are seriously infiltrated by the slag, leading to the disintegration and the removal of MgO subgrains into the slag. Complex forsterite and spinel solid solution with FeO and MnO, sometimes V2O5 are confirmed by EDS. EDS also confirms the presence of corrosive low melting point species vanadate in the slag or as the result of reaction of slag and refractory components, which is deleterious to the slag resistance of the brick. Furthermore, diffused FeO content in periclase gradually decreases when going deeper into the refractory. However MnO is found difficult to diffuse into periclase.

Impact of Nano-Cr2O3 Addition on the Properties of Aluminous Cements Containing Spinel

In this paper, the effect of nano-Cr2O3 addition on the properties of aluminous cement containing MgAl2O4 spinel was investigated. For this reason, the raw dolomite was used as raw material along with calcined alumina for the preparation of the aluminous cement. Then, the compositions containing different amounts of nano-Cr2O3 particles were fired at 1450 °C and their mineralogical compositions and microstructures were investigated. The setting times of prepared cements were measured after grounding and ball-milling. Besides, the slag resistance of refractory castables containing prepared cements was evaluated. The results showed that nano-Cr2O3 addition has effect on the increasing of spinel and CA2 and decreasing of CA and C12A7 phases in the cement composition. The decreasing of C12A7 leads to increasing of setting times of cement. Besides, the slag resistance of refractory castables containing prepared cements is improved due to increasing of spinel and decreasing of C12A7 amount in the cement composition.DOI: http://dx.doi.org/10.5755/j01.ms.21.1.5211

Slag Resistance Mechanism of Lightweight Microporous Corundum Aggregate

The microstructures of the reaction interfaces between slag and corundum aggregates, microporous corundum produced in the laboratory and tabular corundum were observed after slag resistance experiments, and their associated slag resistance mechanisms were investigated. A continuous isolation layer was observed around the microporous corundum, which showed a significantly better slag resistance than tabular corundum. The formation of columnar crystals of CaAl12O19 (CA6) and CaAl4O7 (CA2) in the isolation layer was the main reason for the difference in slag resistance. With respect to the nucleation and growth of second phase, the slag resistance mechanism of lightweight microporous corundum was explored by thermodynamic and kinetic analysis. Due to its smaller pore size, the second phase is more likely to achieve supersaturation, and large quantities of crystal nuclei are generated for microporous corundum. The critical dissolved depths of the microporous and tabular corundum in saturated slag were calculated to be 0.14 and 0.27 μm, respectively. Additionally, the small pore sizes lead to an increase in the Ostwald ripening rate of the second phase, and the Ostwald ripening rate of microporous corundum was 12 times that of the tabular corundum based on Ardell's theory.

BF slag resistance of β-Si3Al3O3N5 material derived from Al salt cake

Abstract In the process of recycling of salt cake from secondary aluminium smelting, it was shown that a significant value addition can be made as β-Si 3 Al 3 O 3 N 5 could be successfully synthesized from the rest product after water-leaching by silicothermal reduction method. In order to evaluate its refractory application, the corrosion behavior in blast furnace slag was investigated under static condition at 1400–1480 °C in the present work. The results show that the β-Si 3 Al 3 O 3 N 5 material has good slag resistance. The apparent activation energy obtained for corrosion process is −388.7 kJ/mol, revealing a more complicated dissolution mechanism. The corrosion process is started with the dissolution of intergranular phase including the iron silicides and glassy phases in the specimens, which is aided by the softening at high temperature and the continuous attack from slag, then followed by the dissolution of β-Si 3 Al 3 O 3 N 5 grains in the slag.

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

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

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

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

Possible improvements of alumina–magnesia castable by lightweight microporous aggregates

This paper focuses on the properties of lightweight alumina–magnesia castable prepared with homemade microporous corundum aggregate, as well as on the investigation of the effects due to the introduction of microporous corundum aggregate on alumina–magnesia castable. The results showed that, in comparison to common alumina–magnesia castable, due to the small pore size and low apparent porosity of microporous corundum aggregate, its introduction leads to an improvement in volume stability, strength, heat insulation and thermal shock resistance of alumina–magnesia castable. The slag resistance of lightweight alumina–magnesia castable is significantly better than that of common alumina–magnesia castable. Microstructure and energy dispersive analyses show that the formation of conically crystallizing CA2 and CA6 is the main reason for the difference in slag resistance. The conical crystals, interlaced and distributed around the aggregate, prevent the sample from further corrosion and penetration of the slag. In addition, since the CaO content of the slag is largely absorbed by the refractory, the viscosity of slag increases, and a solidified layer is formed and adhered on the hot face of sample, thus further deterring the penetration of the slag.

Performance Evaluation of Refractory Bricks produced from locally sourced Clay Materials

The performance evaluation of refractory bricks produced from some local clay deposits in Delta State, Nigeria was investigated. Four major sites in Delta State renowned for abundant clay deposits were selected, namely; Oghara, Ekpan, Ubeji and Jeddo. The clay samples were crushed, milled (pulverised) and sieved to produce very fine grains of less than 250 μm particle size distribution for all samples. They were then tested for shrinkage, bulk density, Loss on ignition , cold compression strength, apparent porosity, and thermal shock resistance. Also, their mineralogical composition and fusion temperatures were examined. The results shows that kaolin deposit at Oghara was found to be the best material suitable for the lining of the walls of most high thermally operated equipment as the expected operational temperatures of most of them are below 1200°C. It had a bulk density, porosity,cold compressive strength,shrinkage,loss of ignition,slag resisance of 1.74g/cm3 ,31.44%,100kg/cm2 ,5% and 12.18% respectively. Oghara clay was found to be less dense, contains more porosity, and possesses low iron content and higher refractoriness with fusion temperature above 1200°C. Ekpan clay is also suitable for medium thermal application in furnaces, kilns and stoves, while the rest could be beneficiated to improve on their insulating properties.Keywords: Refractory bricks, clay material, performance evaluation, porosity, slag resistance.

Slag Resistance of MgO-Based Refractories with MgO-SiC-C Powder

The slag resistance of MgO-based refractory samples with different synthesized MgO-SiC-C powder contents was investigated by a dynamic testing method via an induction furnace; the microstructure and chemical compositions of the corroded samples were analyzed by SEM and EDS. It can be seen from the results that the slag resistance of MgO-based refractories with more MgO-SiC-C powder content, with smaller particles and higher fixed carbon content was better.

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

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

Preparation and blast furnace slag corrosion behavior of SiC–Sialon–ZrN free-fired refractories

Sialon–ZrN powders were synthesized from low-grade bauxite using a zirconite additive by carbothermal reduction nitridation (CRN). The as-synthesized Sialon–ZrN powders were subsequently used as SiC-based free-fired refractories. Their phase compositions and microstructures of the powders were determined using X-ray diffraction and scanning electron microscopy. The physical properties and blast furnace (BF) slag resistance of the SiC–Sialon–ZrN free-fired refractories were also studied. The results show that the low-grade bauxite and zirconite powders were transformed to β-Sialon and ZrN by the CRN process at 1600°C. The phenolic resin provided a strongly bonded interface between the Sialon–ZrN matrix and SiC particles and thus enhanced their combined strength after drying at 150°C. The strength increased as the temperature was elevated from 1000°C to 1500°C. As the ZrN content increased, the slag erosion rate of the SiC–Sialon–ZrN free-fired refractories initially decreased and then increased after being heated at 1500°C. The presence of ZrO2 in the slag (oxidized from ZrN) revealed that the ZrO2 did not react with other oxides in the BF slag to form low melting point phases. This may play a crucial role in its BF slag erosion resistance. The corrosion mechanism of the BF slag towards the as-prepared SiC–Sialon–ZrN free-fired refractories was determined to be oxidation-erosion-dissolution-penetration.

Fe–Sialon–Ti(C,N) composites from carbothermal reduction–nitridation of low-priced minerals and their application in taphole clay refractories

Fe–Sialon–Ti(C,N) composite materials were first synthesized via carbothermal reduction–nitridation reaction with low-priced mineral materials, such as ilmenite, quartz, aluminum dross and coke powders, as starting materials. Effects of temperatures on the phase compositions and microstructures of products were investigated. The investigation results indicated that the optimal synthesis temperature was 1550°C. Rise in synthesis temperature was beneficial for the synthesis of Sialon and Ti(C,N). The as-fabricated Fe–Sialon–Ti(C,N) composites were used as additives to produce taphole clay refractories, and the bending strength and erosion resistance against blast furnace slag of taphole clay refractories were studied. Taphole clay refractories with 20wt% Fe–Sialon–Ti(C,N) composite materials still owned good slag resistance. Bending strength of taphole clay refractories increased with the addition of Fe–Sialon–Ti(C,N) composite materials; when 15wt% Fe–Sialon–Ti(C,N) composite materials were added, bending strength reached its highest value of 13.36MPa.

Evaluation of polishing and degradation resistance of natural aggregates and steel slag using the aggregate image measurement system

Aggregate resistance to polishing and degradation can be related to the change in some of those aggregates particles’ characteristics. Polishing resistance can be related to the loss of surface texture, and it can affect asphalt pavements’ microtexture, influencing its skid resistance. Degradation resistance is related to the loss of angularity and to the aggregates’ breakage. It affects pavement distresses’ resistance and aggregate gradation. The methodologies used to evaluate these characteristics produce results that are mostly not representative. This paper aims to present a digital image processing (DIP) technique to evaluate aggregates’ resistance to polishing and degradation, along with the use of the Los Angeles abrasion equipment. The aggregate image measurement system was used to analyse the aggregates mainly not only with respect to angularity and surface texture, but also with respect to sphericity and flatness/elongation particle percentage, before and after the polishing and the degradation processes. Three natural aggregates (granite, gneiss and phonolite) collected from Brazilian quarries, and one by-product (steel slag) were evaluated. The findings from this study can be used to rank aggregates with respect to their shape properties. With the results obtained for the steel slag, it can be concluded that this material was the most resistant to polishing when compared with the natural aggregates.

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

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

Functionalized Cellular Carbon‐MgO Composites: From Interface Processing to Thermal Shock Resistant Low‐Carbon MgO‐C Refractories

Carbon‐containing refractories have received great attention over the last years, as they are widely used in steel making industry due to their superior properties, such as high thermal shock resistance, high fracture energies in the high‐temperature range, and high slag resistance. However, their main disadvantage is the carbon oxidation associated with considerable CO2 emissions. Aiming to improve carbon oxidation resistivity whilst maintaining improved thermomechanical characteristics, reinforced, and functionalized cellular carbon MgO‐C (FCC‐MgO‐C) refractories are investigated. Experimentally determined thermomechanical data are used to model final crack density characteristics based on an extended Hasselman's thermal shock theory approach. Data calculated are compared with those of pitch‐bonded MgO‐C refractories. The dominant influence of functionalization and tailoring of microstructural phase constitution is reflected in increased fracture energies during crack propagation after thermal shock treatment.