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 around their circumference, 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 all over 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 bricks is attributed to such a bonding structure of whisker-interwoven network, which could reduce slag penetration and facilitate thermomechanical stress resistance.     

Corrosion Resistance Mechanism of Magnesia Zirconia Brick to RH Furnace Slag

Magnesia zirconia brick containing 11 wt% zirconia was prepared with magnesia and monoclinic zirconia as starting materials in order to replace the chrome-containing materials for RH furnace.The corrosion resistance of magnesia zirconia brick and fused rebonded magnesia chrome brick (short for magnesia chrome brick) to high and low basicity slag of RH furnace was comparatively researched by rotary slag method and their slag resistance mechanisms were analyzed.The results show that:(1) because the reaction l...     

The wear of magnesia refractories in electric furnaces for melting cast iron

Conclusions The wear of magnesia refractories, i. e., magnesite, perictase — spinel, and magnesite — chromite bricks and magnesite — phosphate mortar, in the walls of electric furnaces for melting cast iron is the result of the solution predominantly of the periclase crystals and to a lesser extent of the spinel in the lowbasicity ferrosilicate slag melt. Brick of the PShS type proved to be the most durable refractory. The use of high-alumina brick in the roof of the furnaces accelerates the wear of the magnesia bricks in the walls.To increase the durability of the lining of these furnaces trials should be carried out with an all-basic wall lining constructed of high-density PShSP-type brick on MF-1-type magnesite — phosphate mortar and a roof lining constructed of MKhS brick and the same mortar.Translated from Ogneupory, No. 4, pp. 44–49, April, 1976.     

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

Aiming at prolonging the service life of refractories for direct reduction of laterite nickel ores in rotary kilns, the slag resistance of ten materials(corundum bricks, chrome corundum bricks, silicon nitride bonded silicon carbide bricks, high alumina silicon carbide bricks, high alumina bricks, magnesia chrome bricks, magnesium aluminate spinel bricks, spinel chrome corundum bricks, chrome corundum castables and magnesia alumina chrome composite spinel bricks) was evaluated by rotary slag tests, which simulate the service conditions in rotary kilns. The corroded residual bricks were analyzed by SEM and EDS. The results show that the magnesia alumina chrome composite spinel brick possesses the advantages of magnesium aluminate spinel bricks and chrome corundum bricks; MgO-rich spinel can absorb the penetrated ferric oxide, and forms a dense zeylanite layer, which prevents the penetration of the molten laterite nickel ores; therefore, it is an ideal lining of rotary kilns for direct reduction of laterite nickel ores.     

TiO_2对镁铬砖抗渣蚀性的影响

利用XRD分析和光学显微镜等测试手段 ,研究了添加TiO2 对镁铬砖抗渣蚀性的影响。结果表明 :炉渣中的CaO能分解镁铬砖中的二次尖晶石而使镁铬砖损毁 ,但加入TiO2 后 ,TiO2 能优先于尖晶石中的Cr2 O3与渣中CaO反应 ,生成高熔点的CaTiO3,从而抑制CaO对砖中镁铬尖晶石的分解 ,提高了镁铬砖的抗高钙渣渣蚀能力     

Resistance of magnesite refractories to smelting products of blister copper

Conclusions An improved method of assessing the results and testing refractories for slag resistance was described.It was established that the most resistant materials to the action of converter slags are periclase-spinel refractories.Magnesia articles are destroyed at the bond owing to the passage of thin periclase constituent into the fusible magnesia-iron silicates.To reduce the rate of wear and increase the resistance of refractories in these melting conditions for blister copper, it is necessary in the production of magnesia articles to use magnesite and chromite ore with a minimum content of SiO₂ and iron oxides.     

Chemical corrosion mechanisms of magnesia–chromite and chrome-free refractory bricks by copper metal and anode slag

The penetration and corrosion resistance to copper and anode slag of six magnesia–chromite and six chrome-free refractory brick types were tested using static finger tests at a typical copper-refining temperature (1300 °C). The microstructures of the as-delivered and tested refractory types were investigated by means of electron-probe micro-analysis (EPMA) and scanning electron microscopy (SEM) techniques. The results showed that the overall wear rate of the fingers was very low, with the exception of the alumina-based brick made of fused corundum and magnesia–alumina spinel, and the magnesia-based brick made of sintered magnesia and zircon addition. In all refractory types new phases were formed as a result of slag-refractory interactions. Apart from the samples recovered from the copper zone of the latest generation of direct-bonded magnesia–chromite bricks, all the rest were completely infiltrated by copper and slag components (copper oxide, iron oxide, alumina and silica). However, the amount of infiltrated liquid in the chrome-free types was higher than in the magnesia–chromite bricks. Explanations are provided for the distinct infiltration behaviour. The results show that economically viable chrome-free refractory alternatives are still elusive for anode furnace linings.     

Chemical Resistance of Refractories to AI and AI-Mg Alloys

The chemistry of the reaction between molten aluminum alloys and some refractory oxides is discussed. High-alumina brick containing 85, 94, and 99% Al₂O₃ periclase brick, and magnesia spinel brick were immersed for 48 hours in three aluminum alloys containing 0, 2.4, and 7.7% magnesium, respectively. All brick were discolored, although most of the discoloration disappeared after reheating at 1000°C in an oxidizing atmosphere. Only the 85 and 94% brick, which contained silica, showed permanently darkened reaction rims. X-ray diffraction analysis of these darkened areas showed that the alloy containing 7.7% magnesium caused periclase formation in the rim whereas the alloy containing 2.4% magnesium produced spinel. Commercial aluminum caused only a decrease in the mullite content of the darkened area. Magnesia spinel and periclase were unaffected by all the alloys tested.     

Technology of Spinel-Bonded Periclase Brick

This study covers the development of a new basic brick with outstanding resistance to load deformation, slagging, and spalling. This brick is made of 92% high-purity periclase and 8% high-purity alumina. During firing for a ceramically bonded brick or in service for a chemically bonded brick, the fine periclase and alumina react to form a spinel (MgO.Al₂O₃) bond. As the magnesia content of the periclase is increased, the properties of this brick become more outstanding.     

Investigation of slag-refractory interactions for the Ruhrstahl Heraeus (RH) vacuum degassing process in steelmaking

In order to determine the effect of slag composition during the RH process on refractory wear, magnesia–carbon and magnesia–chromite refractories were immersed for 10 min at 1600 °C in a ladle slag, two FeO-rich slags (20 and 40 wt% FeO) and two CaO–Al₂O₃ slags. Corrosion of magnesia–carbon refractory by the ladle and CaO–Al₂O₃ slags was limited as the refractory carbon phase efficiently prevented slag infiltration. Severe degradation was observed in contact with FeO-rich slags. FeO oxidized the carbon phase with formation of Fe droplets at the hot face. Regarding magnesia–chromite refractory, the corrosion mechanism consisted of severe slag infiltration, high temperature inactivation of the secondary chromite and primary chromite dissolution in the infiltrating slag. The FeO-rich slags seem to have generated more severe conditions as the infiltrating slag pushed apart the periclase grains, leading to severe refractory erosion. The degradation mechanisms are discussed by combining experimental results and thermodynamic calculations.     

Innovative Lining of Unburnt Al_2O_3-MgO Brick for 300t Steel Ladle in Baosteel

The manufacture of clean steel needs high performance carbon-free bricks for ladle lining.Based on long term application experiences of the prefab Al₂O₃-MgO blocks,unburnt Al₂O₃-MgO brick has been developed by pressing a mix of alumina,spinel and magnesia as major raw materials and Al₂O₃-MgO gel powder as binder.In addition to low open porosity and high strength,the unburnt Al₂O₃-MgO brick shows superior corrosion resistance and thermal shock resistance to the prefab block.Field trials in a 300t steel ladle have indicated the residual lining of unburnt Al₂O₃-MgO bricks showed smooth surface without large spalling and seldom steel infiltration,consequently longer service life than the prefab blocks.The reliable,unburnt Al₂O₃-MgO bricks have more advantages of high efficiency,energy-saving and eco-friendly production.It will be one of the best options for ladle lining in the manufacture of high-purity steel.     

Microstructure of Periclase

The microstructure of magnesia grains obtained from coarse crystalline and cryptocrystalline magnesites and from seawater and brines is illustrated and the influence of the amount and type of impurities on the development of periclase is discussed. The factors which affect direct peri-clase-periclase bonding in basic brick are reviewed; the microstructural effects of additions of sesquioxides are shown. The complex reactions between periclase and chromite spinel are considered with reference to direct periclase-chromite bonding. The formation of secondary periclase is briefly described.     

水煤浆加压气化炉用高铬耐火材料的显微结构及损毁机理

采用扫描电镜和能谱分析方法 ,分析了水煤浆加压气化炉用高铬砖渣蚀前后的显微结构和相组成 ,探讨了主要损毁机理。结果表明 :煤熔渣与砖反应和渗透引起砖组成的改变 ,从而导致砖的结构剥落和强度弱化是砖损毁的主要原因 ;LIRR -HK90砖的显微结构呈网络状镶嵌结构 ,直接结合程度高 ,与渣反应可生成 (Mg ,Fe) (Al,Cr,Fe) 2 O4 复合尖晶石致密带 ,阻止了渣的进一步渗透 ,减缓渣蚀速度和结构剥落 ,其使用效果优于进口的同类产品     

Study of magnesite-chromite brick after service in a tunnel kiln roof

Conclusions During the service of magnesite-chromite brick in constant temperature conditions (1700°C) and an oxidizing gaseous atmosphere in the absence of corrosive agents in the furnace space (silicates, iron oxides), fusion melts developed in the brick migrate to the colder sections, forming dense silicate-iron subzone.The hot end of the brick is enriched with magnesia and consists of coarse grains of recrystallized periclase. The grains of chromite in these sections have a direct bond with the grains of periclase, as a result of which the thermal properties of the hot section on the whole are improved [4] despite the high porosity of the brick in the subzone.Investigation of the structure of the pores confirms the capilliary mechanism of migration of melts. Recrystallization of periclase in the subzones adjacent to the hot zone is accompanied not by sintering and shrinkage but by coalescence (coarsening) of the pores.Movement of the melts over the pore channels is accompanied by corrosion of the walls of the pores.Translated from Ogneupory, No. 8, pp. 36–41, August, 1966.     

Effects of different additives on properties of magnesium aluminate Spinel–Periclase castable

Bauxite- and alumina-based spinels were employed as refractory aggregates, and sintered magnesia fine powder, calcium aluminate cement, microsilica, and activated α-Al₂O₃ were utilized as matrices. The effects of alumina powder, analytically pure zinc oxide, and analytically pure zirconia on the properties of magnesium aluminate spinel–periclase castables were studied. The results demonstrated that the addition of the three additives promoted the sintering of magnesium aluminate spinel–periclase castables. Simultaneously, the three additives significantly improved the high-temperature properties of the samples. The thermal shock resistance of the alumina powder sample increased by 200%, that of the pristine zinc oxide sample by 75%, and that of the zirconia sample by 125%. The additives effectively improved the thermal shock resistance of the magnesium aluminate spinel–periclase castable. In addition, the slag resistance depths of the samples with alumina powder and zirconia were 41% lower than that of the sample without additives, which significantly improved the slag resistance of the magnesium aluminate spinel–periclase castable.     

Slag erosion-resistant coating for periclase-magnesia-aluminum spinel brick

The magnesia-carbon bricks are used at the ladle slag line adds carbon to molten steel and thus has an adverse effect on the smelting process. Steel production enterprises hope to remove carbon from the ladle slag line. This study presents a Silica sol (SS)–magnesium aluminate spinel(MA) coating that can be applied to the surfaces of periclase–MA spinel brick (spinel brick) to improve their slag erosion resistance, facilitating the elimination of carbon from the ladle slag line. The slag corrosion resistance mechanism of a spinel brick covered with the SS–MA coating was analyzed through scanning electron microscopy and simulation using FactSage software. The results show that increasing the SS content (C_SS) led to the formation of fine cracks during the coating-drying process and was detrimental to the slag erosion resistance of the coating. The optimum C_SS was 20%. In the high-temperature slag erosion experiment, the MA in the coating was capable of forming solid solutions with Fe and Mn in the slag, and the nano-SiO₂ in the coating interacted with the slag, increasing the viscosity of the slag and reducing its penetration. In addition, the presence of the coating extended the penetration path of the slag and reduced the contact area between the slag and the spinel brick and their chances to undergo chemical reactions, thereby protecting the spinel brick from slag erosion. The coated spinel bricks outperformed the magnesia-carbon brick in terms of slag erosion resistance, providing a basis for selecting carbon-free refractory materials for the ladle slag line.     

A Retrospective Review of Alumina-magnesia-carbon Refractories

The residual expansion of in-situ spinel formation in using of alumina-magnesia-carbon(AMC)bricks monolizes the lining of steel-making ladles with the closure of their joints,which has been an effective solution avoiding washing out of the joints in ladle lining by the reduction of the penetration of liquid slag and molten steel.Alumina-magnesiacarbon refractories are overall reviewed,in terms of major raw materials,thermal evolution,corrosion and oxidation,and thermomechanical behavior,as well as type,addition and fraction of magnesia used.General commercial products contain 5%-10%MgO and 5%-10%C with a certain amount of metallic aluminum powder,which is believed to facilitate spinel formation at early stage of heating-up,although high magnesia containing AMC bricks are studied and used sometimes.With low ratio of Al₂O₃/C=12.9 and the carbon content of 6.4%C,AMC brick exhibits the highest corrosion resistance.It is important to determine the type,addition and fraction of magnesia used in AMC refractories for demonstrating high corrosion resistance and superior thermomechanical behavior.     

Improvement of Durability of Purging Plugs Using MgO Micropowder for Refining Ladles

To modulate the matrix of purging plugs, MgO micropowder was introduced as a replacement to magnesia powder in alumina–magnesia castables, and the effect of MgO micropowder on the properties of alumina–magnesia castables and the possibility of developing chrome‐free castables were investigated. Experimental results showed that the introduction of MgO micropowder resulted in an improvement in the volume stability, strength, and thermal shock resistance of alumina–magnesia castables due to its high surface energy and small particle size. However, excessive amounts of MgO micropowder led to a lower densification, and there was a slight degradation in the performance of the alumina–magnesia castables. The slag resistance of the prepared alumina–magnesia castables was significantly better than that of the alumina–chrome castables. Microstructure and energy spectrum analysis showed that the formation of a solidified reaction layer, mainly consisting of spinel and CaAl₁₂O₁₉, was the major cause of the observed difference in slag resistance. In addition, the alumina–magnesia castables had a lower linear thermal expansion coefficient than that of the alumina–chrome castables at each experimental temperature, which effectively decreased the thermal stress during its service period, thus exhibiting good thermal shock resistance.     

玄武岩熔液对耐火材料的侵蚀

为深入了解玄武岩高温熔体对耐火材料的侵蚀行为,参照ASTM C621—1984(2001)分别对致密氧化铬砖、致密锆英石砖和熔铸锆刚玉砖(AZS-33)进行了1 500℃72 h的玄武岩熔液侵蚀试验,并对侵蚀后试样进行了显微结构对比分析。侵蚀试验结果表明,致密氧化铬砖的抗熔融玄武岩侵蚀性最好,其次是致密锆英石砖,最差的是熔铸AZS-33砖,其在液面线处出现严重剥落现象。显微结构分析表明:致密氧化铬砖结构均匀,与玄武岩熔液反应性小,同时与玄武岩渣中的成分形成尖晶石致密层阻止了渣的进一步渗透;致密锆英石砖表面与玄武岩熔液反应产生很薄的脱锆层和玻璃相,并且其致密均匀的结构也阻止了渣的进一步渗透;熔铸锆刚玉砖的显气孔率虽然很低,对玄武岩熔液有较好的抗渗透性,但其液相量较多,因此抗侵蚀性相对较差。     

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.