Magnesia Carbon Research Articles

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.

Chemical degradation of magnesia–carbon refractories by different gaseous atmospheres

In this work, we use a novel methodology to analyse how the critical compositional variables of MgOC bricks affect their chemical degradation by oxygen attack; the study focuses on the effect of the graphite content, the presence of aluminium, and the binder type. Oxidation tests are performed at 1000 °C, a typical preheating condition for steelmaking ladles, under two atmospheric conditions: one simulated the oxygen concentration in air, and the other, with a lower amount of oxygen, reproduces the conditions of the inner part of the brick when liquid steel is present. It was found that: a) the addition of Al reduces the carbon oxidation kinetic, mainly at a low O2 partial pressure, b) increasing the graphite content led to a smaller decarburized area with higher O2 consumption, and c) mixing CarboRes® with phenolic resin resulted in a higher O2 consumption but at a slower oxidation rate.

MgO-based cements – Current status and opportunities

The cement industry is a major contributor to the anthropogenic CO2 emissions, with about 8% of all emissions coming from this sector. The global cement and concrete association has set a goal to achieve net-zero CO2 concrete by 2050, with 45% of the reduction coming from alternatives to Portland cement, substitution, and carbon capture and utilization/storage (CCU/S) approaches. Magnesia-based cements offer a conceivable solution to this problem due to their potential for low-to-negative CO2 emissions (CCU/S) but also being alternatives to Portland cement. The sources of magnesia can come from magnesium silicates or desalination brines which are carbon free for raw-material-related emissions (cf. carbonated rocks). This opens up possibilities for low or even net-negative carbon emissions. However, research on magnesia-based cements is still in its early stages.
 In this paper, we summarize the current understanding of different MgO-based cements and their chemistries: magnesia oxysulfate cement, magnesia oxychloride cement, magnesia carbonate cement, and magnesia silicate cement. We also discuss relevant research needed for MgO-based cements and concretes including the issues relating to the low pH of these cements and suitability of steel reinforcement. Alternatives reinforcements, suitable admixtures, and durability studies are the most needed for the further development of MgO-based concretes to achieve a radical CO2 reduction in this industry. Additionally, techno-economic and life cycle assessments are also needed to assess the competition of raw materials and the produced binder or concrete with other solutions. Overall, magnesia-based cements are a promising emerging technology that requires further research and development to realize their potential in reducing CO2 emissions in the construction industry.

Unveiling the role of reactive magnesia and red mud in CO2-cured aerated concrete

Instead of using ordinary Portland cement (OPC), this study investigated the use of hydrated magnesia carbonates, which is derived from the carbonation of reactive magnesia, as the binding material for the production of aerated concrete, where the impacts of material design (e.g., the Ca/Mg ratio) on the properties of aerated concrete were studied. The results showed that the selection of Ca/Mg and water/binder ratio in raw materials directly determined most properties of the aerated concrete, and the use of reactive magnesia enabled the samples to reveal excellent carbon sequestration and a good pore structure. Further, substituting fly ash with red mud improves early strength by forming small amounts of AFt (3CaO·Al2O3·3CaSO4·32H2O) and hydrotalcite. In view of the above, adopting CO2 curing for aerated concrete involving reactive magnesia and red mud is beneficial when producing high-quality aerated concrete (AC).

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.

Improved thermal shock stability and oxidation resistance of low-carbon MgO–C refractories with introduction of SiC whiskers

This research focuses on the utilization of SiC whiskers synthesized from rice husk powders in low-carbon magnesia–carbon (MgO–C) refractories, and attempts to reduce the flake graphite content in refractories by adding synthesized SiC whiskers. The effect of the addition amount of SiC whiskers on the microstructure, mechanical properties, thermal shock stability and oxidation resistance of MgO–C refractories with different graphite content was studied. The results indicated that the introduction of SiC whiskers facilitated the generation and growth of ceramic phases in MgO–C refractories. By adding 1 wt% SiC whiskers, the graphite content could be reasonably reduced (from 5 wt% to 4 wt%), and the strength, thermal shock stability and oxidation resistance of refractories were enhanced by the synergistic effect of the introduced SiC whiskers and the generated ceramic phases, the CMOR, CCS, residual CCS, and oxidation resistance were increased by 44, 6, 12 and 27% respectively.

Utilization of Recycled Material for Producing Magnesia–Carbon Refractories

The partial replacement of primary raw materials for the production of refractories with recycled ones gains in importance, as it contributes to the conservation of natural resources, energy saving, and reduction in greenhouse gas emissions. In this work, the use of a magnesia–carbon (MgO-C) recyclate in the fractions 3–6, 1–3, and 0–1 mm as a raw material for MgO-C refractories was investigated. The recyclate was examined via optical and scanning electron microscopy. Using mixtures with different recyclate contents up to 82 wt%, MgO-C specimens were prepared to study the influence of the recyclate on their chemical composition, structure, and properties. The substitution of primary raw materials with the recyclate did not cause a decrease in the MgO content analyzed after carbon burnout, but the contents of the individual impurities changed. A comparison of the MgO-C that contains 82 wt% recyclate with the recyclate-free material through computed tomography indicated a change in the size distribution of the MgO grains. The porosity increased, and the cold modulus of rupture decreased with increasing recyclate content, whereas the thermal shock resistance improved. At a recyclate content of 40 wt%, the refractoriness under load was only slightly lower than that of the recyclate-free material.

Oxidation resistance of magnesia carbon bricks and the influence on their performance

ABSTRACT In this paper, the oxidation resistance of magnesia carbon bricks with different compositions was evaluated and the influencing factors were obtained, the influence of oxidation resistance on the performance of magnesia carbon bricks was investigated. The test results showed that for low-carbon MgO-C refractories, the influence of holding time was greater than that of oxidation temperature; for medium and high carbon MgO-C refractories, the influence of oxidation temperature was greater than that of holding times. The oxidation resistance of refractories, especially that of low-carbon MgO-C refractories, improved with the increase of the content of metallic additives. The oxidation resistance improved with the increase of graphite purity, especially in the low-temperature region. It is expected that this study can contribute to the optimal selection of magnesia carbon bricks in the trunnion area of furnace lining and provide a reference for the design of refractories with long overall service life.

The effect of C-coated alumina particles on properties of MgO–C refractories

In this study, carbon-coated α-Al2O3 powder was prepared by two routes: a physical method and a chemical method. The obtained carbon-coated α-Al2O3 powders were adopted to prepare MgO–C refractory materials for the purpose of regulating the in-situ synthesis of MgAl2O4. The effect of the carbon-coating α-Al2O3 powder addition on the service behavior of MgO–C refractories was studied. The results show that both the physical and chemical methods for coating alpha-alumina particles could regulate the solid-phase formation of spinel in the magnesia carbon material, which weakened the solid-phase reaction of the spinel in the magnesia carbon material, thus reducing the volume expansion. Samples containing coated alpha Al2O3 micropowder, prepared by the chemical method, presented the largest bulk density, the minimum apparent porosity, the largest cold and hot modulus of rupture, and the best thermal shock and corrosion resistance.

Basic slag corrosion of alumina–magnesia–carbon refractory bricks containing Al and Si antioxidants

AbstractThe slag‐corrosion behavior of two alumina–magnesia–carbon refractories (AMC) with different antioxidants (Si and Al) has been comparatively studied by means of thermodynamic simulation and laboratory tests. A cup test (static) at 1723 K and 1873 K and dipping test (dynamic) at 1873 K were carried out using a steelmaking ladle slag. An iterative method that considers the change of the liquid's composition while it penetrates the refractory was employed for the thermodynamic calculation. The simulation as well as the static tests showed similar performance between both refractories (5% of wear at 1723 K and 6% at 1873 K). In spite of the type of antioxidant, the material with smaller particles of magnesia exhibited better performance in the dynamic test, with 55% less wear than the other AMC brick. This behavior was attributed to the faster MgAl2O4 spinel formation, which increased the material's cohesion, especially the matrix, during the heating stage. The Si antioxidant improved oxidation resistance, although it did not have a positive effect on the corrosion resistance of the material in any of the performed tests.

Wetting and corrosion behavior between magnesia–carbon refractory and converter slags with different MgO contents

Wetting and corrosion behavior between magnesia–carbon refractory and converter slags with different MgO contents

Microstructural characteristics of refractory magnesia produced from macrocrystalline magnesite in China

Sintered and fused magnesia (FM) produced from the macrocrystalline magnesite in China have attracted attention worldwide for the production of various refractories. Herein, dead burnt magnesia (DBM) with varying compositions was investigated. The results revealed that the periclase crystals of the DBM92 sample were subrounded to rounded euhedral, whereas the periclase crystals of the DBM95 sample were subhedral and idiomorphic. In addition, a significant amount of periclase–periclase bonding with straight boundaries was observed in the DBM97 sample. The periclase crystals of the DBM98 sample with no clear boundaries exhibited the densest packing among the samples. The silicate matrix around the periclase grains of the DBM92 sample contained forsterite and monticellite, whereas that around the periclase grains of the DBM95 sample was mainly composed of monticellite and merwinite. Dicalcium silicate and merwinite were observed in small amounts as interstitial phases in the DBM97 sample. In contrast, only dicalcium silicate, which was concentrated in small triangular pockets, was observed in the densely packed periclase grains of the DBM98 sample. The hot modulus of rupture tests revealed that an alkali-resistant DBM95-based brick can be prepared at a lime–silica ratio of <0.5. The best-quality DBM97-based brick can be prepared at a lime–silica ratio of approximately 2.2, which ensures that dicalcium silicate is the only interstitial phase. The periclase crystals of the two-step FM were significantly larger than those of the one-step FM and exhibited remarkably fewer silicate boundaries. The superior structure and large crystal size of the two-step FM can endow magnesia–carbon bricks with slag corrosion resistance.

Swertia Chirata: A Comprehensive review of its abundant medicinal properties

Swertia chirata (S chirata), (Family Gentianaceae) is a well-known herbaceous plant. It is very popular in traditional systems of medicine like Unani, Ayurveda, and Siddha. It is commonly used in Unani medicine, for several pharmacological effects including Musaffi-i-Dam (blood purifier), Muqawwi-i-Mida (stomachic), Muhallil-i-Awram (anti-inflammatory), Muqawwi-i-Qalb wa Jigar (tonic to heart and liver), Mulattif (demulcent), Mudir (diuretic), Mulliyin (laxative) properties. It is used for chronic fever, malaria, anemia, liver disorders, hypertension, dyspepsia, gastritis, ulcers, constipation, and skin diseases, and is included in many pharmacopoeial and non-pharmacopoeial preparations. The entire plant contains ophelic acid, two bitter glycosides chiratin, and amarogentin. It also contains resins, tannin, gum, carbonate, and phosphate of potash, lime, and magnesia. Extensive studies on S. chirata have been carried out by various researchers and a wide spectrum of its pharmacological actions have been explored which includes anti-inflammatory, anti-diabetic, antimicrobial, and antioxidant properties. The present review is an effort to provide a detailed survey of the literature, scientific researches of pharmacognostical characteristics, chemical composition, and pharmacological activities of this plant.

Fundamental Study on the Re-utilization of Waste Magnesia-Carbon Bricks as MgO Additive for Iron Ore Sintering

Waste magnesia-carbon bricks (MCB) exhibit great potential for being reutilized as MgO additive for iron ore sintering due to their main composition of high activity magnesia and extra carbon content. In this paper, the combustion characteristics of the carbon component of waste MCB were first studied by thermogravimetric, derivative thermogravimetric and differential scanning calorimetry thermal analysis. The influence of waste MCB utilization as MgO additive on the mineralization of sinter raw materials was also systematically investigated. The main conclusions are shown as below: (1) Compared with anthracite, the carbon component of waste MCB has relatively worse flammability and combustibility, and its combustion heat per unit mass is less; (2) As the MgO content of sinter increases from 2.0 to 3.0 wt%, the advantage of using waste MCB, compared with dolomite, as MgO additive in the crystallinity degree of sinter gradually appears; (3) At the MgO content of 3.0 wt%, the sinter using the combination of waste MCB and dolomite as MgO additive has higher content of calcium ferrite, and the distributions of main mineral compositions and pores are more uniform than the sinter totally using dolomite or waste MCB as MgO additive.

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

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

Hydraulic conductivity characteristics of carbonated reactive magnesia-treated silt

Carbonation of reactive magnesia (MgO) has recently received increasing attention in the area of soil stabilization and ground improvement. However, as a critical parameter in terms of long-term seepage behavior in the geotechnical analysis, the hydraulic conductivity of carbonated reactive MgO-stabilized silt has not been fully studied. In this context, the effect of water-MgO ratio (ratio of initial water content to MgO content, w0/c) and carbonation time on hydraulic conductivity (or permeability) characteristics was systematically investigated. Serial microstructural tests including mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses were applied to elucidate the intrinsic mechanisms. The obtained results indicate that as the initial water-MgO ratio decreases, the void ratio gradually decreases and the reduction of hydraulic conductivity becomes less prominent because of the little presence of flow paths. The hydraulic conductivity of carbonated MgO-admixed silt similar to that of PC-treated silt is mainly governed by the porosity, and its correlation with void ratio is proposed in the article. The variations of permeability with void ratio are consistent with those of the cumulative pore volume from MIP results in general, and the medium pores (3–30 μm) are substantiated to be the primary contributor in controlling the permeability. SEM and DSC analyses reveal that the cementation of soil particles and filling of hydrated magnesium carbonates marginally reduce the voids and permeability. The reasons for changes of permeability behaviors have been confirmed by the pore-size distribution and microstructure characteristics.

The influence of the admixture to the Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;‒MgO‒MnO system and of the firing temperature on the electro-fused corundum composite ceramics sintering

The influence of the eutectic composition addition to the Al2O3‒MgO‒MnO system on the structural ceramics' sintering was investigated in the article. The initial material was the electro-fused corundum F-1000 with the average particle size of 10 microns. The additive powder have been prepared in course of the thermolysis of the alumina hydroxyl together with the manganese carbonate and magnesia carbonate salts. The spinel MgO· Al2O3and MnO· Al2O3have been synthesized separately. It was established that when the addition contents was equal 15 weight percent after the burning at 1550 °С the ceramics density achieved 3,86 gram/cm3 the open porosity being 0,3 %, and the ultimate bent strength achieved 211 MPa.Ill.3. Ref. 8. Tab. 1.

Slag – Refractory Interactions During Ilmenite Smelting: Thermodynamic Simulation and Experimental Data

The interaction of four types of commonly used refractories (i.e., burned magnesite brick, magnesia carbon brick, corundum castable, and SiC castable) with slag formed in the smelting of titanium (wt. [TiO2] = 80%) in an electric furnace at the Panzhihuan Iron and Steel plant was studied. Erosion of refractories by titanium slag was calculated using the FactSage software program. The experiment was carried out in an electric furnace based on calculation results. Meanwhile, the results of the thermodynamic simulation showed that the interaction of SiC castable with titanium slag formed TiC with a high melting point, which can prevent the slag from penetrating more deeply into the refractory and exhibits good erosion resistance. In terms of erosion resistance to titanium slag, different refractory materials can be arranged in order from most to least erosion resistant as follows: SiC castable → magnesia carbon brick → magnesite brick → corundum castable. The results of theoretical calculations are in good agreement with the experiment results.

Raw materials for manufacturing of Superior quality MgO-C bricks

In SAIL Plant, Magnesia carbon (MgO-C) bricks are used as lining material for Metallurgical Vessels like Steel ladles as well as Basic Oxygen Furnaces (BOF). MgO-C bricks are the most suitable refractory in these conditions for slag line as they possess superior slag penetration resistance and excellent thermal shock resistance at elevated temperature. In Iron & Steel Industry, manufacturing processes has changed significantly due to the rising demand of quality steel in the market. Furnace capacities have increased & technological parameters have changed. Plants have been modernized with addition of secondary steel making facilities to meet the stringent quality requirement of newer grades of steel.Refractories in steel ladle are subjected to severe operating conditions like high temperature (1670-1700°C) tapping of liquid steel from BOF, thermal shock, abrasion with molten metal due to stirring during gas purging, localized heating in slag zone due to arcing, corrosion with slag, thermo mechanical stress etc. Hence, use of superior quality refractory material with evenly distributed impurities is essential to get an end product of very high corrosion and spalling resistance and high thermo-mechanical properties. Easier application technique is also required for higher lining life with less down time. Various qualities of magnesia carbon refractories are used in different zones of steel ladles & BOF. Magnesia carbon refractories are essentially constitute of two highly refractory components i.e. magnesia and graphite.Sea water magnesia is mainly used in SAIL as the main raw material for manufacturing of magnesia carbon bricks. Fused magnesia has also been tried by partially mixing with sea water magnesia. Although MgO content in magnesia is important up to a certain level, but the type of impurities and their relative proportions plays vital role in achieving good performance. Besides chemical purity, bulk density and crystal size are considered to be very important properties of magnesia for application in BOF and steel ladles. Beside magnesia, graphite of both indigenous and import sources were used in different occasions. Purity of graphite has been reported to have great influence on slag corrosion resistance and hot properties of magnesia carbon bricks. Particle size distribution of graphite influences porosity and thermal shock resistance properties of magnesia carbon bricks.This paper deals with the properties of different raw materials for making of superior quality MgO-C bricks for improved performance in Metallurgical vessels of SAIL plants.

In-situ development of carbon nanotubes network and graphitic carbon by catalytic modification of phenolic resin binder in Al2O3–MgO–C refractories

In-situ formation of cross-linked carbon nanotubes network reinforced the refractory matrix and helps to improve the mechanical properties at elevated temperature. In this paper, the effect of modified phenol-formaldehyde (PF) resin binder on the various mechanical properties of alumina–magnesia–carbon (AMC) refractories was investigated. Initially, PF resin was modified by adding a different proportion of nickel catalyst. The AMC specimens (with the 7% carbon) were prepared by using 5% of modified PF resin. The pressed samples were cured at 180 °C for 24 h and characterized by XRD, Raman spectroscopy, and FE-SEM. The characterisation shows that, in-situ formation of graphitic carbon and carbon nanotubes network in the specimens due to modification of PF resin. In-situ formation of phases leads to enhancement of density and mechanical properties of refractory at elevated temperature due to the reinforcing effect.