Interface behaviour and corrosion behaviour of magnesia refractory by alkaline slag in an alkali recovery furnace

The adhesion of Na₂CO₃ slag to the surface of refractories in an alkali recovery furnace can cause corrosion and spall. Magnesia refractories can be used as linings in alkali recovery furnaces owing to their strong corrosion resistance to alkali slag. However, the permeability resistance of magnesia refractories is relatively poor. Hence, the interface and corrosion behaviours of slag cladding on magnesia refractories were studied using sessile drop and static crucible tests. The experimental results showed that an increase in the heating rate positively affected the cladding of the molten column on the refractory surface. The microstructure, element changes, and chemical composition changes of the corroded refractories were analysed using SEM-EDS and XRD. Thermodynamic simulation of the reaction between the slag and refractory was performed using Factsage 7.3. The results indicate that the generated forsterite filled the pores of the magnesia refractories. The microstructure of dense slag-refractory interface layer was formed, which prevented the infiltration of slag phases and alleviated the corrosion of refractories by the slag.     

Formation of liquid-phase isolation layer on the corroded interface of MgO/Al2O3-SiC-C refractory and molten steel: Role of SiC

Formation of a dense layer on corroded interface to suppress corrosion is always desired, but it is controlled by numerous environmental conditions. In this work, corroded microstructures of MgO/Al₂O₃-SiC-C refractories in metal bath area of ladle furnace were investigated after industrial trails. A liquid-phase isolation layer in which MgO islands and liquid phases was established on the corroded interface of refractories with 6 wt% coarse/fine SiC-additive. The formed isolation layer against steel/slag attacks led to an approximate 30% improvement in corrosion resistance than that of refractory with 3 wt% fine SiC-additive. More importantly, the liquid-phase isolation layer blocked the direct mass transfer between molten steel and refractories while it decreased exogenous pollution from refractories. SiC-additive affected the formation process of isolation layer by controlling the generation/migration of Mg(g) on refractory' surface. A further formation mechanism of liquid-phase isolation layer was discussed in detail and role of SiC was elucidated.     

Methods of determining the corrosion resistance of glass-tank refractories

Conclusions When laboratory investigations are being carried out to find resistant refractories for glass tank furnaces it is desirable to make simultaneous use of indirect and direct methods of assessing corrosion resistance.The use of indirect methods for determining corrosion resistance in refractories permits us to explain the nature of the interaction between the refractory and glass, to study the nature and properties of the reaction products, and also to select refractories that form with the glass the most infusible or viscous reaction products for subsequent investigation in molten glass.The direct methods permit direct determination of the rate of corrosion of refractories by glass at working temperatures and allow us to recommend the most corrosion resistant refractories for tests in service conditions.In laboratory conditions we established that the most corrosion resistant refractories in regard to original glass used for obtaining slag sitalls are bakor-33 and dense zirconium refractory. This may be explained by the formation of viscous reaction products in the contact layer which have a protective action on the refractory.Translated from Ogneupory, No. 5, pp. 56–60, May, 1967.     

Electromagnetic field effects on the formation of MgO dense layer in low carbon MgOC refractories

Electromagnetic field (EMF) would speed up the corrosion of low carbon MgOC refractories. Its influence mechanism will be investigated in this paper. The slag-resistance experiments of low carbon MgOC refractories were carried out under the condition of an induction furnace and a resistance furnace, respectively. Low carbon MgOC refractories with carbon of 6% (in mass) and a slag with the basicity (CaO/SiO₂) of around 0.87 were used in the experiments. The slag line of MgOC refractories corroded by the slag under the different conditions were analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results show that in the induction furnace with an electromagnetic field (EMF), no MgO dense layer exists in the interface. However, MgO dense layer could be formed in the interface without any EMF. The formation mechanism of MgO dense layer indicates that the EMF could enhance the solution of MgO and power of Mg (g) discharge. As a result, EMF restrains the formation of MgO dense layer.     

Enhanced performance of low-carbon MgO–C refractories with nano-sized ZrO2–Al2O3 composite powder

Low-carbon MgO–C refractories are facing great challenges with severe thermal shock and slag corrosion in service. Here, a new approach, based on the incorporation of nano-sized ZrO₂–Al₂O₃ composite powder, is proposed to enhance the thermal shock resistance and slag resistance of such refractories in this work. The results showed that addition of ZrO₂–Al₂O₃ composite powder was helpful for improving their comprehensive performances. Particularly, the thermal shock resistance of the specimen containing 0.5 wt% composite powder was enhanced significantly which was related to the transformation toughening of zirconia and in-situ formation of more spinel phases in the matrix; also, the slag resistance of the corresponding specimen was significantly improved, which was attributed to the optimization of pore structure and formation of much thicker MgO dense layer.     

Role of graphite on the corrosion resistance improvement of MgO–C bricks to MnO-rich slag

In order to clarify the effect of graphite content on the corrosion behavior of MgO–C refractories immersed in MnO-rich slag, the MgO–C refractory samples bearing 5 wt%, 10 wt% and 15 wt% graphite were prepared, and exposed in the slag composed of 40 wt% CaO, 40 wt% SiO₂ and 20 wt% MnO. The results show that metallic Mn particles and (Mg,Mn)O solid solution are formed at the slag/refractories interface. Whereas, no dense layer is formed by (Mg,Mn)O solid solution at the interface. The decrease in MnO content of slag is mainly attributed to the reaction with graphite to form liquid Mn. The graphite is found in the slag, and dissolved in the form of oxidation. The poor wetting limits the contact area of graphite and slag, reducing graphite oxidation and decarburized area. The graphite does not become the passage for slag to penetrate into the refractories due to the oxidation. On the contrary, the dissolution of MgO in slag is faster than graphite, thus is mainly responsible for the degradation of refractories. As a result, MnO and MgO contents change less in the slag contacted with the refractories bearing higher graphite content.     

Evolution of in Situ Refractories in the 20th Century

A common theme over the past 100 years in refractories science and technology has been to generate a protective refractories layer in a high-temperature container, often by reaction of the refractory materials with the contents (glass, slag, or atmosphere). The history of refractories during the 20th century is used in this review to illustrate how techniques-such as slag splashing, in situ spinel generation in castables, magnesia dense layer formation in magnesia-carbon brick in steelmaking, clinker adhesion in cement kilns, and viscous boundary layer generation in glass tanks-have evolved to their present status.     

Influence of Additives on Slag Resistance of Al2O3-SiO2-SiC-C Refractory Bond Phases under Reducing Atmosphere

The microstructures of Al₂O₃–SiO₂–SiC–C refractory matrices with aluminum, silicon, Si₃N₄, BN, B₂O₃, and B₄C additives are characterized before and after a crucible slag test, and the phases present are compared to those expected at thermodynamic equilibrium. The carbon content dominates the resistance to CaO–MgO–Al₂O₃–SiO₂ slag penetration, while the viscosity of liquid phases present has a significant influence when the matrix carbon contents are similar. Silicon and Si₃N₄ additives reduce slag penetration resistance because of indirect oxidation of carbon to form SiC. B₄C, in particular, and B₂O₃ also reduce slag penetration resistance because of formation of a more fluid boron-containing liquid, while aluminum and BN addition have no significant effect. Carbon and BN hardly react with the slag, while SiC partially reacts with it, leading to deposition of carbon as a dense layer. Corundum present in the refractories also readily dissolves in the slag. Microstructurally, slag penetration resistance is associated with the dense carbon layer located at the slag-refractory interface.     

Effects of different particle size of spinel and Y2O3 additive of the periclase-spinel refractory on the sintering densification and corrosion resistance to copper smelting slag

In order to analyze the sintering densification and copper smelting slag corrosion resistance of periclase-spinel refractories, the periclase-spinel refractories were prepared with fused magnesia, magnesia-rich spinel, industrial alumina, and yttrium oxide as the main raw materials. The different particle sizes of spinel in material and with or without Y₂O₃ additive were studied. The study demonstrated that: (1) The different particle sizes of spinel in periclase-spinel refractories can result in different effects. Adding particle spinel to the refractory can improve the strength and corrosion resistance of the periclase-spinel refractories. The addition of spinel and magnesia powders in the matrix resulted in cracks due to the great difference of coefficient of thermal expansion between magnesia and spinel. The reduction in bulk density and strength of the material decreased slag penetration resistance because of its poor sintering properties. While adding the alumina in the matrix can further fill the crack and prevent slag penetration by the volume expansion of in-situ reaction to form spinel. (2) The periclase-spinel refractories can be reacted with Cu slag to form a Mg₂FeO₄ insulating layer as the iron ion becomes oxidized. Adding Y₂O₃ in periclase-spinel refractories can result in grain boundary phase reconstruction, which can promote sintering densification, improve the slag physical infiltration resistance, and improve the chemical corrosion resistance of materials.     

含碳耐火材料的电化学侵蚀

为了说明碳或含碳耐火材料在熔渣-金属熔体交界处局部侵蚀的原因,测定了不同熔渣与碳及纯铁构成的高温电池:C|熔渣|Fe的电动势,其值在250至450mV。在这些高温电池中,碳电极皆为阳极(负极),Fe电极皆为阴极(正极)。发现当对此高温原电池外加一反电动势时,碳电极的侵蚀即被抑制。根据这些实验结果,认为含碳耐火材料在熔渣-金属交界处局部侵蚀的主要原因是由于电化学侵蚀机理造成的。文中还拟出了可能发生的电化学反应,并提出了抑制和减轻含碳耐火材料局部侵蚀的措施。     

微孔镁尖晶石碳耐火材料的抗渣性能研究

以方镁石-尖晶石微孔陶瓷、电熔镁砂为骨料,以电熔镁砂细粉、鳞片石墨、金属铝粉为基质材料,以酚醛树脂为结合剂制备了含微孔陶瓷骨料的镁尖晶石碳试样.采用感应炉浸渍法对试样进行了抗渣试验,并对渣蚀后的试样进行了SEM和EDAX分析.结果发现:熔渣和熔钢冲刷是损毁的主要原因,熔损并不显著.显微结构分析表明,在侵蚀层和原质层之间可以发现MgO致密层的形成,MgO致密层的形成可抑制渣对试样进一步的侵蚀和渗透.渣对MSO颗粒的侵蚀主要是FeO和MnO等在方镁石中的固溶,导致MgO颗粒出现结构剥落;方镁石-尖晶石微孔陶瓷骨料的蚀损主要是尖晶石被渣中的CaO和SiO2所侵蚀,而渣对微孔骨料渗透并不严重.     

Synthesis of Al2O3-SiC powder from electroceramics waste and its application in low-carbon MgO-C refractories

Composite additives are an efficient means to improve the high-temperature stability and slag resistance of low-carbon MgO-C refractories. In this work, Al₂O₃-SiC powder was firstly synthesized from electroceramics waste by carbon embedded method at 1500°C, 1550°C, and 1600°C for 4 h, and then the as-synthesized Al₂O₃-SiC powder was used as an additive to low-carbon MgO-C refractories. The effects of its addition amounts of 0, 2.5 wt.%, 5.0 wt.%, and 7.5 wt.% on the properties of the refractories were investigated in detail. It was found that increasing the heat treatment temperature is beneficial to the phase conversion of mullite and quartz to alumina and silicon carbide in the electroceramics waste. Furthermore, the addition of Al₂O₃-SiC powder effectively improves the performance of low-carbon MgO-C samples, and the formation of spinel dense layer and high-viscosity isolation layer is the internal reason for the improvement of the oxidation resistance and slag resistance of low-carbon MgO-C samples. This work provides ideas for the reuse of electroceramics waste and presents an alternative strategy for the performance optimization of low-carbon MgO-C refractories.     

Corrosion of phosphate added high-chrome refractory materials in an entrained-flow gasifier

Durability of the refractory liner located in an entrained-flow gasifier is one of the main factors affecting the efficiency and cost of gasification process. This study investigates the corrosion mechanism of phosphate added high-chrome refractories in a commercial entrained-flow gasifier and the effect of phosphate additives on the improvement of service life combining thermodynamic simulation calculations. The microstructures, chemical compositions, and mineral phases of the corroded samples were analyzed by scanning electron microscopy (SEM and EDS) and X-ray powder diffraction (XRD). The results demonstrated that chemical corrosion mainly occurred at the slag-matrix interface and the junction of aggregates and matrix regions. Complex spinel solid solutions were formed at the slag-refractory interface. Phosphate additives decomposed into gaseous products (such as O₂, P₂O₃) and diffused into the interior of refractories at or close to the slag-refractory interface, not only causing an oxidizing environment but also increasing the phosphate contents in the interior of refractories. Phosphate additives in the infiltration layer occupied the gaps between crystal grains of (Cr, Al)₂O₃ solid solutions, reduced the infiltration of silicate phases, and absorbed Ca and Na in the slag, which subsequently increased the viscosity of the slag.     

有色金属火法冶炼用耐火材料及其发展动向

根据近些年来有色重金属与轻金属火法冶炼工艺技术的发展,从有色重金属与轻金属火法冶炼条件的特点分析与阐述了所用耐火材料发展的动向,着重介绍了有色金属冶炼炉如:闪速炉、澳斯麦特炉、艾萨炉、诺兰达炉、转炉、连续炼铜炉、氧气底吹熔池直接炼铅炉(QSL炉)、铅锌密闭鼓风炉(ISP炉)、粗锌精馏炉、锌浸出渣挥发回转窑、碱石灰法回转窑、焙烧炉、铝电解槽、铝熔化炉以及硅热还原法制原镁等窑炉关键部位所用的耐火材料。另外,为了给上述冶炼炉的关键部位选择合适的耐火材料,还对一些耐火材料组元的抗FeO-SiO2渣侵蚀,抗炉渣与锍的渗透以及在炉衬工作面形成保护层等方面进行了分析与论述。此外,化学热力学计算与现场试验结果表明,含碳耐火材料不适宜用在重有色金属冶炼炉。还介绍了不同品种的镁铬耐火材料与碳化硅质耐火材料以及Al2O3-Cr2O3-尖晶石材料,并对含Cr2O3耐火材料存在的问题与解决途径做了分析与建议。     

Slag Corrosion Resistance of MgO-ZrO2 Refractories

Slag corrosion resistance of MgO ZrO2 refractories was investigated in this work. The results indicate that in a non-oriented electric steel slag system with a high ratio of calcia to silica,the slag resistance of MgO ZrO2 refractories can be described as follows: ZrO2 reacts with CaO forming calcium zirconate compound which strengthens the material and blocks the channel of the slag infiltration; however,in an oriented electric steel slag system with a high concentration of silica and the low ratio of calcia to silica,the slag corrosion resistance of MgO ZrO2 refractories is different; ZrO2 reacts with CaO forming the calcium zirconate and simultaneously one more product C2S as well; C2S can improve corrosion resistance by blinding pore and enhancing slag viscosity; therefore,it is expected to be the major reason for the enhanced corrosion resistance observed for MgO ZrO2 refractories.     

钢包粘渣与包衬耐火材料

阐明了钢包粘渣与包衬耐火材料存在一定的关系 ,抗渣渗透性差、容易出现开裂的包衬耐火材料容易粘渣。为防止钢包粘渣 ,适于采用抗侵蚀性和抗渣渗透性优良的尖晶石砖、铝尖晶石 (或铝镁 )浇注料、低密度浇注料以及抗剥落性好的刚玉 -锆英石浇注料作包衬耐火材料     

Slag-resistant products made from stabilized ZrO2

Conclusions The resistance of zirconia refractories to the action of acid slags is determined by the interaction between the added stabilizer and the silica component of the slag and by the rate of formation of the corresponding silicates. Of those materials studied, the most resistant of the action of the more acid slags is ZrO₂ stabilized by Y₂O₃.The rate of wear of the articles made from stabilized zirconia under the action of the more basic of the melts we studied is determined by the diffusion of Ca²⁺ into the structure of ZrO₂ forming CaZrO₃ which leads to the articles becoming less dense. The interaction between the stabilized ZrO₂ and the basic industrial slag, moreover, is accompanied by the intense dissolution of the refractory in the slag as a result of the formation of low-melting melts at the slag-refractory interface.Thus, zirconia refractories have an excellent resistance to the action of an acid multicomponent slag and are intensively damaged by basic slags.Translated from Ogneupory, No. 3, pp. 54–57, March, 1979.     

Al2O3-SiC-C耐火材料抗CaO-SiO2-K2O渣侵蚀性能研究

研究了Al2O3-SiC-C耐火材料的抗CaO-SiO2-K2O渣侵蚀性能,以及添加Cr2O3对Al2O3-SiC-C材料抗渣侵蚀性能的影响.研究结果表明CaO-SiO2-K2O熔渣对Al2O3-SiC-C材料具有明显的侵蚀作用;在Al2O3-SiC-C材料中添加适量的Cr2O3可以有效地抑制CaO-SiO2-K2O熔渣向耐火材料内部的渗透,降低耐火材料的侵蚀速度.     

Comparative study of B4C,Mg2B2O5, and ZrB2 powder additions on the mechanical properties,oxidation, and slag corrosion resistance of MgO–C refractories

Boron-containing additives are used to improve the oxidation resistance of carbon-containing refractories; however, their effects on the mechanical properties and slag corrosion resistance of the refractories have rarely been studied. In this work, B₄C, Mg₂B₂O₅, and ZrB₂ powders were incorporated into low-carbon MgO–C refractories to study their effects on the mechanical properties, oxidation resistance, and slag corrosion resistance of the refractories. The relationships between these properties and the microstructure and phase evolution were also studied. The results show that the flexural strengths of the MgO–C refractories at high temperatures are closely related to the apparent porosity and formation of an Mg₃B₂O₆ phase. The oxidation resistances are greatly improved after the introduction of boron-containing additives into the MgO–C refractories in terms of both thermodynamical aspects and the filling of voids and pores. The most effective antioxidant is B₄C, followed by the ZrB₂ and Mg₂B₂O₅ powders. The mechanisms through which the vanadium-containing slag attacks the MgO–C refractories mainly include the dissolution of magnesia to form melting phases, penetration through pores, and redox reaction with carbon.     

影响镁碳耐火材料表面MgO致密层形成的因素

研究了镁碳耐火材料中镁砂原料的种类和碳含量 ,渣剂的有无及碱度 ,炉内气氛以及是否加铝脱氧等因素对镁碳耐火材料表面MgO致密层形成的影响。结果表明 :(1)在w(C) =10 %～ 2 0 %范围内 ,随着碳含量的降低 ,形成的MgO致密层越完整 ,且厚度增加 ;(2 )Mg(g)氧化形成MgO致密层的氧是由熔渣通过熔融金属提供的 ,凡是影响熔渣和熔融金属中氧活度的因素 ,都会对MgO致密层的形成产生影响 ;(3)炉内气氛对MgO致密层的形成没有明显的影响 ;(4)与电熔镁砂相比 ,使用烧结镁砂为原料时 ,耐火材料表面更容易形成MgO致密层。