EFFECT OF TYPICAL SLAGS ON FIRE BRICK WITH A METHOD OF DETERMINATION CORRELATED TO SERVICE1

In an investigation of the problem of producing refractories which would give maximum resistance to slags encountered in service, laboratory slag tests were made in a rotary slagging test furnace. A photograph and sketch of the furnace are given and the method of operation is described. A photograph of a typical test is shown and test data are given for typical high iron oxide, high lime, and high soda slags. These data include the numerical rating of ten test bricks in each case. Ten slag tests have been made with 50 different mixes, all in the field of fireclay and diaspore refractories. Bricks of the brands which give best results in the laboratory were tested in service in malleable iron air furnaces, gray iron cupolas, and “bull” ladles where sodium carbonate purifier is used. Operating conditions are given and chemical analyses of slags presented in several instances. Special firing treatment was given a few bricks prior to service tests. Excellent correlation between laboratory and service tests was obtained in cases where high-temperature abrasion was not severe, demonstrating the reliability of the rotary furnace type of slagging test in predicting service results insofar as slag alone is concerned. Of equal importance with the reliability of the slag test is the need of a reliable high-temperature abrasion test. The data indicate that in many installations high-temperature abrasion is the major cause of failures that are charged entirely to slag erosion.     

Fireclay refractories in pyrometallurgical processes

In primary liquid metal production, the temperature of processing and the composition of the slag phase largely determine the selection of the refractories used to line the furnace. The objective of this work was to study the effect of temperature and FeO content on the dissolution rate of a clay refractory.50-g samples of synthetic, prefused iron oxide and silica were poured into slip cast crucibles of a high-duty fireclay. These were then placed in a preheated silicon carbide-element furnace and held at the required temperatures for known times. The cooled crucibles and their contents were broken and the amount of crucible wall thinning which had taken place at the slag-refractory interface was measured using a low-power microscope and a calibrated graticule.The study of the effect of process temperature was carried out over the temperature range 1100°–1400°C at 50°C intervals. Only two compositions, 65 and 75 wt.% FeO, were chosen for this part of the work.The effect of slag composition was next studied at 1300°C, the range of slag compositions being 60–80 wt.% iron oxide at 5% intervals in the iron oxide-silica system. Only one high-duty fireclay composition was studied throughout the tests.The outcome of the work was to show that for the iron oxide-silica compositions studied a high-duty fireclay refractory can be used to contain the melts if the temperature of the process is maintained below 1300°C and when the slag composition is less than the orthosilicate composition (2FeO.SiO₂).     

Slag resistance of chamotte refractories with particolored clay

A laboratory study of slag resistance of fireclay specimens on substitution for clay DN2 in the binding part of the mixture by a refractory clay is presented. The slag resistance is determined by the crucible method. It is shown that the replacement by the refractory clay for DN2 does not cause a decrease in the slag resistance of refractories of equivalent density. The results of the laboratory study have been confirmed by full-scale tests.     

A STUDY OF CHROME AND DIASPORE MIXES1

The history, development, and properties of chrome and diaspore brick are discussed. The plan for this investigation was the determination of (1) softening points of various mixes, all of which withstood cones 33 to 34, (2) workability of mixtures, wherein it was found that bars of soft mud were workable with difficulty while no trouble was experienced with dry-press, (3) porosity and shrinkage on reheating; slag action and spalling. Increasing the proportion of diaspore increased the shrinkage while the absorption remained about the same in all cases. Various slags from different sources were used in the investigation, and it was found that a small per cent of finely-ground chrome ore cut down slag action on diaspore while the addition of diaspore to chrome increased its resistance to spalling action; conversely, the addition of finely-ground chrome to diaspore increased its resistance to spalling action.     

Constitution of Fireclays at High Temperatures: II, Mineralogical Composition

Quantitative X-ray diffraction analysis of quenched specimens, supplemented by HF solution and X-ray fluorescence, was used to determine the mineralogical composition of three refractory clays after heating at 1150° to 1500°C. The three clays represent a range of purity found in high and superduty fireclay refractories: an impure plastic clay, a flint fireclay, and a kaolin. The results show the percentages of mullite, cristobalite, quartz, and liquid. The quantity and composition of the liquid phase were estimated by difference. Iron and titanium oxide impurities in the mullite decreased with increased firing temperatures.     

The manufacture of bricks from semiacid materials by semidry pressing

Conclusions Tests in laboratory and industrial conditions showed the possibility of producing semiacid refractories by the semidry pressing method using Prosyanov kaolin and quartz residues from its enrichment in the batch.The semiacid stopper tubes and ladle brick so made are not inferior in their exploitation potential to standard fireclay products.     

Increasing the life of linings of split steel discharge gutters in open hearth furnaces

Conclusions The protective coating made of air-setting concrete of chrome-magnesite composition protects the lining of forked and single steel-discharge gutters from the effects and penetration of molten metals and slags.The chemical inertness toward basic and fireclay refractories enables us to use the chrome-magnesite coating to protect concrete and brick linings of steel discharge gutters made of basic and fireclay refractories.The capacity of chrome-magnesite concrete based on magnesium-sulfate to become friable at 700–1100°C facilitates easy removal from the gutter of the slag and metal residues built up on the weakened zone of the protective layer.Easy restoration of the protective layer with chrome-magnesite mortar enabled us to introduce protective coatings at the North Steel plant without considerable expense and the use of equipment.Restoration of the concrete coating after each heat increased the life of the firebrick lining.The method proposed for increasing the life of the lining of forked and single gutters can be used in any steel plant.     

Adding combustible liquids to fireclay bodies to regulate the structure and increase spalling resistance

Conclusions A simple method has been discovered and investigated to control the structure of fireclay refractories with the aim of increasing their spalling resistance by creating microcracks on the surface of the grains of grog at the boundary with the bond.The development of microcracks is attained by first coating the grains of grog with a hydrophobic organic liquid (before mixing grog with bond clay). This increases the spalling resistance of fireclay refractories made of plastic and semidry bodies 1.5–2.0 times.When such additives are introduced into the bond part of the batch, the microcracks are situated, not around the grains, but in the main mass and are preferentially oriented parallel to each other. Under these conditions the spalling resistance of the material deteriorates.A reduction in the magnitudes of a number of properties (linear thermal expansion, elasticity, strength, Poisson Ratio, and thermal conductivity) takes place with both methods of treating fireclay bodies with organic liquids (covering the grog-grains or adding it to the bond). This suggests the prevailing positive influence of the structural nature (microcracks at the surface of the grains of grog) on the spalling resistance of the firebrick refractories.It is shown that with an increase in porosity of the fireclay refractories, their spalling resistance increases (to a given level) if the pores are localized chiefly at the surface of the grains of grog and bond; it is reduced when the pores are on the bonding mass of the refractory.     

Increasing the spalling resistance of fireclay refractories by adding combustible organic liquids and m ineral a dditives

Summary The combined addition of hydrophobic organic liquids and mineral (refractory) additions improves the structure and physico-mechanical properties of fireclay refractories. The spalling resistance is greatly increased.The spalling resistance of fireclay specimens assessed by the number of heat cycles before destruction with the combined action of mazut and mineral additives is 2.0–2.8 times greater than with the manufacture of the articles without these additives.The increase in spalling resistance occurs owing to the development of microcracks in the structure around the grains of grog, with a simultaneous reduction in the modulus of elasticity and coefficient of thermal expansion and also an increase in deformation before failure (/E) of the material.The addition to the hydrophobic organic liquid (mazut) of fine powders (magnesite, alumina) permits not only a considerable increase in spalling resistance, but also a certain reduction in the porosity and an increase in the strength of the products.Separate introduction of the additives (mazut on the grog, magnesite and kaolin to the bond) gives worse results compared with the above method (lower spalling resistance, increased expansion).Thus it was shown that the main factor determining the resistance of fireclay refractories against thermal strains is the nature of the contacts of the surfaces of the grains of grog and the bond.Semiplant testing of the method showed that the addition of 5% mazut and 5% calcined kaolin (or magnesite) doubled the life of fireclay saggers.     

A study of the effect of structure on the thermal stability of fireclay refractories

Conclusions A study of the thermal stability of refractories has demonstrated a regularity in the change in thermal shock resistance with the reorientation of microcracks in the structure of the material.The values of the thermal stability of fireclay refractories, obtained by the disruptive temperature gradient method, are in qualitative agreement with the results of the commercial testing of bottom ware having an increased concentration of microcracks oriented along the boundaries of the coarse fireclay grains.Determination of the thermal stability of inhomogeneous refractories using known calculated criteria must be made by considering the structural properties of the material.Translated from Ogneupory, No.4, pp. 56–59, April, 1969.     

Effect of carbon and silicon carbide on the properties of carboxylated refractories

The interrelation between the content of carbon and silicon carbide and the properties of carboxylated refractories (porosity, mechanical strength, heat resistance, resistance to the action of blast-furnace slag) is studied. Dependences of the properties of carboxylated refractories on their material composition are plotted. __________ Translated from Novye Ogneupory, No. 4, pp. 35–37, April, 2007.     

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.     

Al2O3-ZrN-Sialon-C复相耐火材料抗渣侵性能研究

以板状刚玉、石墨、α-Al2O3、金属铝粉、单质硅粉为主要原料,ZrN-Sialon复相粉体为添加剂,采用酚醛树脂结合制备了Al2O3-ZrN-Sialon-C复相耐火材料.采用静态坩埚法研究了ZrN-Sialon复相粉体加入量对材料抗渣侵蚀性能的影响,借助SEM与EDS面扫描对渣蚀后材料的结构和成份进行分析,并探讨了Al2O3-ZrN-Sialon-C复相耐火材料的抗渣侵蚀机理.结果表明:ZrN-Sialon复相粉体加入量为9wt％时,材料表现突出的抗钢渣侵蚀性能.研究表明材料中Sialon氧化后生成的SiO2能形成致密的氧化保护层,同时ZrN氧化后形成的ZrO2有利于提高抗钢渣的浸润,阻止钢渣的渗透与侵蚀.分析认为Al2O3-ZrN-Sialon-C复相耐火材料的钢渣侵蚀机理为氧化-熔蚀-渗透.     

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.     

Hot slag resistance of refractories

Conclusions It is proposed to test refractories for hot-slag resistance by which is meant the complex property typifying the wear resistance of refractories with the single-sided action of high temperature and slags and subsequent sharp cooling.A laboratory gas-oxygen furnace design was developed for testing the slag resistance with one-sided heating with the aim of forming zones in the specimens.The spalling resistance of zonal magnesite-chromite and periclase-spinel goods was determined.According to the slag resistance and operating spalling resistance the periclase-spinel refractories are better than the spalling-resistant magnesite-chromite.     

AN INVESTIGATION OF THE ACTION OF COAL-ASH SLAGS ON FIRE BRICK BY MICROSCOPIC METHODS*

The action of coal-ash slags on firebrick refractories was studied by microscopic examination of thin sections prepared from quenched samples of ash and refractory heated together. The eight refractories used varied as to clays, method of fabrication, grind, and firing treatment. Six different coal ashes varied from highly corrosive to noncorrosive ashes. Samples were quenched at intervals in the range of 2200 to 2800°F and the critical temperature or maximum safe operating temperature of all combinations of slag and refractory was determined. These values are presented together with a discussion of the various minerals formed.     

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.     

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.     

Unfired light-weight fireclay refractories produced by active synthesis of high-temperature structural elements in a hydrothermal-force field

The theoretical views underlying the manufacture of unfired light-weight fireclay refractories are set forth. It is hypothesized that fireclay mixes should include a chemically active ingredient to act as a catalyst and an electrolyte and to promote the active synthesis of high-temperature structural elements in the course of molding in a heat-and-force field, short-term drying, and service. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 1, pp. 3–11, January, 1998.