METALLURGICAL REQUIREMENTS FOR REFRACTORIES IN THE ELECTROTHERMIC METALLURGY OF ZINC1

Refractory brick for lining electrothermic dry distillation furnaces must have a melting point of not less than 1600°C, must retain their strength at temperatures of 1400–1500°C, must be non-porous, and of uniform size. For lining electrothermic smelting furnaces, in which a liquid slag is produced, they must in addition to having these qualities be resistant to the corrosive action of highly heated slags which may be either strongly acid or strongly basic. The condensers are similar for both types of furnace. The brick for lining them need not have a high melting point but must be dense and of uniform size and must be very low in free iron oxide to withstand the disintegrating effect of carbon monoxide in the cooler portion of the condenser.     

SOME EFFECTS OF COAL ASH ON REFRACTORIES1

The action of coal ash on the following types of refractories was studied: (1) high diaspore brick, (2) fireclay refractories with very little quartz, (3) fireclay refractories with considerable quartz, (4) refractories containing a mixture of diaspore and fireclay, and (5) andalusite refractories. The tests were carried out in a rotary test furnace at temperatures ranging from 1500 to 1600°C. The phases present in the coal-ash refractory slag were identified by means of the petrographic microscope and consisted of magnetite, mullite, and glass. The effects of time of slag action and slagging temperature were studied.     

THE PREVENTION OF DISINTEGRATION OF BLAST FURNACE LININGS1

Theories and observations on the causes of disintegration of fireclay refractories in blast furnaces are given and a process is developed for improving high iron clays for this use. The disintegration of refractories in blast furnace linings is initiated by alteration in the iron spots. Ferric oxide is reduced to ferrous oxide at 500°C and hastens the cracking of 2CO to CO₂+C₁ the carbon being retained by the lining. When Fe₂O₂ is converted to Fe₃O₄ the brick will not disintegrate.     

SERVICE FACTORS GOVERNING THE SLAGGING OF BOILERFURNACE REFRACTORIES1

Service factors, dependent on the type of coal burned and the method of burning, that are considered to govern slag erosion directly are: refractories temperatures, furnace gas temperatures, furnace gas compositions, furnace gas velocities, slag composition, and slag quantities. Values determined for part or all of these factors under each of the following sets of conditions are presented and their significance is discussed: eastern bituminous coals on underfeed stokers, powdered eastern bituminous coals in furnaces with extended radiant-heat absorbing surface, high-sulphur Pittsburgh coal on underfeed stokers, low-sulphur Pittsburgh coal on underfeed stokers, high-sulphur Pittsburgh coal on chain-grate stokers, Illinois coal on chain-grate stokers, and powdered Illinois coal.     

低碳MgO-C耐火材料结构和性能优化的研究进展

MgO-C耐火材料作为钢铁冶炼用关键基础材料,被广泛用作转炉衬砖、电弧炉炉壁和钢包渣线用砖。寻求制备高性能低碳MgO-C耐火材料的新方法对耐火材料及冶金行业的发展至关重要,本文从纳米碳源的引入、骨料表面的改性和镁基骨料的引入、酚醛树脂的改性、抗氧化剂的引入及陶瓷相的原位形成角度出发,综述了改善低碳MgO-C耐火材料结构和性能的研究进展,以期为进一步推动低碳MgO-C耐火材料的发展提供参考,并对MgO-C耐火材料未来的研究方向进行了展望。     

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.     

NEW REFRACTORY COMPOSITIONS RESISTANT TO MOLTEN ROCK PHOSPHATE*

The Tennessee Valley Authority has carried out small-scale and large-scale studies during the past five years, directed toward the development of refractories more resistant to corrosion by molten rock phosphate than the present commercial types. Small-scale tests were made on refractories containing varying proportions of zirconium silicate and oxides of aluminum, beryllium, calcium, cerium, chromium, magnesium, thorium, and zirconium. Promising compositions were then tested by fabrication into standard 13l½-in. and 9-in. brick and by determining their resistance to corrosion by molten rock phosphate, basic open-hearth slag, and electric phosphate-smelting furnace slag. The most promising of the compositions tested were (1) Cr₂O₃ 67%, CaO 30%, and Al₂O₃ 3% and (2) ZrO₂ 33.5%, Cr₂O₃ 33.5%, CaO 30%, and Al₂O₃ 3%. A 25-kw. Detroit rocking furnace was lined successively with brick of these two compositions, as well as a commercial superduty firebrick and a commercial unburned magnesite brick, and each lining was tested against molten rock phosphate until failure occurred. The tests show that the two new types of refractories are superior to the commercial refractories and that they may have promising possibilities for use where basic refractories are now extensively used.     

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.     

THE USE OF SILICON-CARBIDE REFRACTORIES IN BOILER FURNACES1

The chief causes of failure of refractories in boiler furnaces are slag adhesion, erosion, and failure of structure, dependent on the type of coals and feeds used. Some of the physical and chemical properties of different types of refractories are given. The development of bonded silicon carbide brick is mentioned. Clinker trouble is eliminated by use of these brick in furnaces using all kinds of present day stoker equipment. Failures due to chemical reaction between iron and silicon carbide, and torch action on a wall produced by a blast of flame under pressure together with medium amounts of iron in the ash are discussed. Air cooling of walls is taken up. Installations of air-cooled silicon-carbide blocks are listed and discussed. Water cooling, the use of preheated air, and conditions of use of the water wall are taken up.     

FIRE-CLAY BRICK FOR THE OPEN HEARTH1

Fire-clay brick in the open hearth are normally subjected to medium temperatures and to the action of slag containing high percentages of iron and lime. Temperatures near the maximum of the open hearth itself may exist due to failure to reverse the draft and for that reason brick of high refractoriness are used. Resistance to spalling action is not of primary importance because the temperature change is small. The indications obtained from a laboratory test were that brick having a high alumina content would resist the slag action better than ones higher in silica.     

Life of refractories made of Tal'skiy magnesite

Conclusions Magnesite brick made of Tal'skiy magnesite serves somewhat better than standard magnesite brick and can be used for lining open-hearth furnaces.Magnesite brick with the addition of scale and chrome-magnesite brick made from Tal'skiy magnesite serve just as well as the corresponding refractories from the Satka material, and can be used to line the walls of open-hearth furnaces.Magnesite-chrome brick made with Tal'skiy magnesite serves just as well as standard magnesite-chrome brick and can be used to line the roofs of open-hearth furnaces.Metallurgical powder made from Tal'skiy magnesite serves just as well as Satka magnesite powder and can be used both as a weld-on and as a servicing material for open-hearth furnace hearths.Tal'skiy magnesite of the experimental type is an industrial raw material for making high-grade magnesian refractories.     

Use of dense magnesite-chrome brick in roof of rocking open-hearth furnace

Conclusion The use of dense magnesite-chrome brick for the basic roof of rocking open-hearth furnaces processing high-phosphorous pig irons increase the wear resistance of the roofs by 7–17%, which makes it possible to intensify the operation of the furnaces.The nature of the wear and tear in the dense magnesite-chrome brick in the roof of a rocking furnace does not differ from that of normal magnesite-chrome brick and shows up as the splitting of the working zone.The slighter wear and tear in dense magnesite-chrome brick is due to reduction in the rate of formation of zones on account of retarded migration of the melts into the brick.To increase the wear-resistance of magnesite-chrome roof refractories, they have to be pressed at a greater specific pressure and at optimum grain composition.     

REQUIREMENTS OF REFRACTORIES FOR ELECTRIC FURNACES1

This article is essentially a survey, giving, however, not generalized statements, but a definite discussion of the refractories problems now existing in the important electric furnace processes. After summarizing some of the general refractory requirements of electric furnace work, the author discusses the specific conditions and refractory requirements in steel, iron, and non-ferrous metal melting, smelting furnaces for producing iron, ferro-alloys and calcium carbide, anti in furnaces for melting refractory materials. The article closes with a summary of outstanding present developments. Varied conditions probably make an ideal, universal refractory almost impossible of attainment. The relatively cheap refractories standardized in fuel-fired furnaces have been very largely used in electric furnaces. There is, however, a growing use for specialized “super-refractories,” even at greatly increased cost, that will stand various especially severe conditions in certain kinds of work. Important recent developments are higher firing temperatures, the use of high aluminous fire clays, and increased experimental work on fused refractories. The commercial production of sufficiently high firing temperatures, and the development of satisfactory bonds for special refractories are at present perplexing problems.     

Resistance of blast furnace refractories to the action of aggressive reactants under conditions of an oxidizing gaseous atmosphere

Conclusions Investigations have been made of the resistance of ShPD-41, ShPD-39, and ShUD-37 chamotte refractories to the action of K₂CO₃, Fe₂O₃, blast furnace dust, and initial and final blast furnace slags under conditions of an oxidizing atmosphere. The investigation results showed that iron oxides and slag break down these refractories at 1400–1500°C. Dense ShPD-41 refractory is more resistant to the action of the reactants.The most resistant to the action of slags and iron oxides at 1400–1500°C are silicon carbide refractories with binders of silicon nitride and oxynitride.Translated from Ogneupory, No. 7/8, pp. 24–27, July–August, 1992.     

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).     

Elastic and thermal properties of magnesite-chrome brick which has been used in open-hearth furnace roofs and artificially saturated with iron oxide

Conclusions The elastic and thermal properties of roof basic refractories which have been artifically saturated with iron oxide and have served in a roof do not reveal any great changes, compared with the initial brick; hence it should be considered the importance attributed to the differences in the properties of zones of chrome-magnesite refractories, forming through the action of iron oxides as the dominating factor in cracking bricks during temperature variations is an exaggeration.     

The service of regenerator checkers in open hearth furnaces

Summary An effective way of increasing the life of checkers is to increase the height of the structure made of chrome-magnesite brick to 10–12 courses. This reduces the average melting time, increases furnace output by 5–7%, and reduces the oil consumption by 7%.The dust settling on the refractory has a typically high content of iron oxides. At normal checker temperatures (not above 1400°C) the surface of the refractories forms friable, dusty deposits. With a rise in temperature in the regenerator the dust sinters, partly fuses, and sticks to the refractory. This cake is removed by blowing the checkers.Investigation of the refractories after service confirms that the phase changes,in the reaction layer of the brick, take place mainly owing to the action of iron oxides of the dust on the refractory. Fusing of firebrick is also intensified by oxides of iron contained in the dust.The mineral formation and destruction processes are greatly affected by the changing composition of the gaseous atmosphere, which is confirmed by the formation of mixed crystals of magnetite and haematite in the crusts and reaction zones of the refractory.Of the refractories tested in the checkers, the best was chrome—magnesite.To explain the possibility of increasing the life of checkers, experiments should be made using forsterite brick of high quality in the 15 top courses of the checkers using the Cowper system of building the checkers.     

Periclase-forsterite refractories from silica magnesite

Conclusions Periclase-forsterite refractories from silica magnesite of Beloretsk deposits are endowed with excellent properties.The density of periclase-forsterite brick is subject to a wide range of changes depending on the grain distribution of the mixture, molding pressure, sintering temperatures and the introduction of additives. The effect of additives on the sintering of periclase-forsterite mixtures from silica magnesite has the same pattern as in the sintering of pure magnesium or regular magnesite. The most effective sintering additives are titanium and zirconium dioxides. Additions of ZrO₂ produces a higher refractoriness-under-load of periclase-forsterite brick.Periclase-forsterite brick is highly-resistant in regenerator checkers of open-hearth furnaces. This is caused by peculiar changes in its mineralogical structure which occur during service, i.e. recrystallization of periclase in top layers which brings about higher density instead of looseness as in forsterite refractories bonded with unite.The forming and the properties of periclase-forsterite refractories as they depend on such factors as basic raw material, manufacturing methods and phase composition need further studies and large-scale testing in order to determine the rational areas of application.     

Development and Application of Al_2O_3-Si_3N_4 Refractories Used in Blast Furnace

Newly developed Al2O3-Si3N4 composite refractories used for blast furnace is introduced in this work. Al2O3-Si3N4 composite refractories attacked by alkali vapor and blast furnace slag was investigated. High performance Al2O3-Si3N4 composite refractories was produced and used at both 2560m^3 blast furnaces of Tan-gsteel and No. 5 blast furnace of Shaosteel.