Decomposition of magnesite during heating

Conclusions The rate of decarbonization in magnesite critically depends on the grain size. With an increase in the grain size the process rate diminishes, especially when we change from particles measuring less than 10 mm to particles measuring 30 mm.The retardation in the decarbonization rate is due to the slower heating of the large fractions of magnesite, the formation of low conducting layers, hindering access of heat to the center of the grains, and the enhanced concentration of CO₂ in the gas phase. The relationship between the time for complete decarbonization and the grain size of the magnesite is expressed by a parabolic equation, the numerical coefficients for which vary with temperature change.Translated from Ogneupory, No. 3, pp. 49–52, March, 1973.     

Effect of the decarbonization cycle for dolomite and magnesite on the sintering of powders

Conclusions A study was made of the effect of the decarbonization schedule for dolomite and magnesite on the activity of the powders in relation to sintering. During rapid heating and with the minimum soaking at the final temperature of calcination, in. conditions of complete decarbonization for the original materials, it is possible to obtain caustic powders with a high specific surface and defect concentration in the lattices of MgO and CaO, which predetermines their hydration and sintering activity. With the optimum conditions of decarbonization for the powdered dolomite and magnesite the maximum densities of the fired briquets based on hydrated powders (respectively, 3.34 and 3.42 g/em³) are obtained with moderate firing temperatures (1500 and 1600°C).Translated from Ogneupory, No. 8, pp. 14–22, August, 1979.     

Sintering of caustic magnesite dust over the length of a rotary kiln

Conclusions The intensive formation of the pellets (granules) of caustic magnesite dust commences from the moment of completion of the decarbonization of the particles of raw magnesite. The development of pellets is established at a distance of 29 m from the charging end of the kiln.The formation of grains and their densification and reinforcement occur in the section 29–45 m of the length of the kiln as a result of the compaction of the particles of caustic dust.The recrystallization of the periclase, sintering, and agglomeration of the powder occur mainly in the section 45–75 m of the furnace length in the presence of melt.During the burning in a 90-m rotary kiln of unground caustic magnesite dust, the apparent porosity of the powder resulting from its grains diminishes from 50–60 to 24%.Translated from Ogneupory, No. 8, pp. 52–55, August, 1971.     

The effect of increasing MgO content in dendromass on ash fusibility and corrosion of corundum refractory castable

Low melting temperatures of the biomass ash at the intensive combustion can generate the slag with a portion of unburned fuel. The portion of imperfectly burned fuel reduces the efficiency of its use. An alternative route to solve the problem without changing the combustion condition is a modification of the chemical composition of the ash with the addition of an agent increasing the melting temperature of the ash/slag. In this paper, we report on the impact of adding the magnesite waste sludge to ash on their melting. Three types of ashes with different SiO₂ and K₂O content were selected for the tests. The melting temperatures of ash and ash mixtures with magnesite sludge (mass ratio 0.5–2:1) have been determined. The addition of magnesite sludge to ash increased the temperature of fusibility index of the mixtures by 50–100 °C. The ash fusibility temperature rose with a decrease of the SiO₂ content in the ash. Subsequently, the interaction of the ash/ash mixtures with the refractory corundum castable was monitored at a temperature of 1450 °C using a static crucible corrosion test. The addition of magnesite sludge to ash reduced the aggression of the slags to the refractory corundum materials. The Al₂O₃ concentration in the post mortem slags of the ash mixtures with the magnesite sludge (2:1) was about 20–23 wt% lower in comparison to the slag without magnesite. The evaluation of the effect of magnesite sludge addition to ash and the elements (K, Ca, Mg, Fe, Si) penetration on the extent of corrosion is the subject of further work aimed at analyses of the corrosion interface of the slag – corundum refractory material.     

Analysis and control of some parameters of the converter lining during firing

Conclusions Experiments showed that firing with isothermic holding by interrupting the oxygen blow for 2–5 min is the most efficient mode of firing a converter lining. In this case the depth of the coked layer of the lining in the top part of the cylindrical section reaches 50–80 mm, the decarbonization of the surface layer of the lining is 5 mm or less, and the lining temperature does not undergo steep fluctuations.A brief (2–5 min) interruption of the oxygen blow and the second batch of coke help to increase the CO content in the converter to 50% and to reduce the O₂ content to zero. The creation of a reducing atmosphere in the converter results in less decarbonization of the surface layer of the lining and in an increase in the carbon content of that layer due to carbon precipitation from the gas phase.Translated from Ogneupory, No. 6, pp. 16–20, June, 1976.     

Use of magnesite refractories in the chequerwork of the air heaters of blast furnaces

Conclusions Magnesite refractories are a promising material for use in the upper rows of the chequerwork, particularly where it is necessary to increase the thermal capacity of the air heaters without increasing their dimensions.When the magnesite refractories are used, the mass of the chequerwork and the unit load on the subchequerwork grid and the lower rows of the chequerwork are increased.The improved efficiency of magnesite refractories in the chequework of air-heaters by comparison with other types of refractory is becouse of their high storage capacity for heat as a result of the increased apparent density and better thermophysical characteristics.The magnesite refractory used in the chequerwork should contain a minimal amount of impurities, particularly of Fe₂O₃.When magnesite refractories are used to replace dinas, the cost per ton of chequerwork increases 50% while for the replacement of mullite by magnesite, the cost per ton of chequerwork is reduced by 16%.Contact between the magnesite refractories and the dinas (without a load) is permissible at a temperature not higher than 1450°C; with sillimanite, at not more than 1350°C.In order to prevent the action of finely dispersed particles of dust and alkali oxides accidentally introduced into the air heaters it is sensible for the upper row of chequerwork to be made from sillimanite or mullite refractories.The theoretical extreme temperature for the use of magnesite refractories in the chequerwork of the air heaters (allowing for creep and the interaction with other types of refractories) is 1650°C for M-I type blocks and for M-II, not more than 1450°C. For greater safety it is recommended that the ultimate working temperatures be reduced by 150°C.Taking into account the favorable experience abroad in using magnesite blocks in the chequerwork of air heaters, it is necessary to carry out industrial tests of the magnesite products in the upper zones of the chequerwork.Translated from Ogneupory, No. 7, pp. 32–36, July, 1982.     

A Study of Magnesites of Provenance from the Goluboe Deposit (Krasnoyarskii Krai) and Their Laboratory Tests for Technological Applications at the Kombinat Magnezit Joint-Stock Co.

Results of a preliminary study of the composition and properties of magnesites of provenance from the Goluboe deposit (Krasnoyarskii Krai, Russia) are reported. All magnesites, irrespective of their varietal, structural, and textural features, can be considered as acceptable raw materials. The concentration of impurities and inclusions in a high-quality magnesite does not exceed 1.5%, whereas in low-quality magnesites (2nd grade) they are within 3 – 8% of the total mineral composition. The heat-assisted beneficiation or calcination of raw magnesite yields a material with 98% MgO and a CaO-to-SiO₂ ratio greater than 3, which provides means for producing high-quality periclase powders. Tests conducted under industrial conditions show that using technologies of fine grinding, pelletizing, and calcination at 2100°C makes it possible to prepare dense periclase clinker. Calcination of lumpy magnesite at still higher temperatures is not an efficient technique for dense periclase powders. Clinker technology is shown to be the best way towards obtaining periclase and periclase-containing powders using raw magnesite from the Goluboe deposit.     

Stabilization of lining elements of the working zone of open-hearth furnaces

Various factors affecting the stability of lining elements of the working zone of the open-hearth furnaces at the Azovstal' Works are studied. The main reasons for damage to the open-hearth furnace tanks are deterioration of the quality (high content of SiO₂ and CaO) of magnesite powders (Satkinskoe deposit) and exclusion of the high-phosphorus cast iron from the conversion process. Damage to the weld bead and charging layer results from formation and modifying transformations of bicalcium silicate. The improvement of the maintenance procedure, production of new bottoms, and charging of the working zone of the open-hearth furnace with magnesite powders imported from Slovakia (the special chemical composition of these powders prevents formation of bicalcium silicate) adopted at the Azovstal' Works make it possible to increase the stability of the lining, substantially decrease the magnesite powder consumption, and reduce the labor input and time for maintenance. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 5, pp. 36–39, May, 1997.     

Effect of binder type and other parameters in synthesis of magnesite chromite refractories from process waste

Recycling of the process waste in basic refractory production will not only make it possible to put the waste substances to use but also help to solve the problems of environmental pollution and storing. This paper is the first part of a study on using the magnesite and chromite dusts in refractory production, accumulated in −10⁻³ m and finer particle fraction as process waste at the Konya Chrome-Magnesite Plant. In this work, three different MgO and Cr₂O₃ compositions were studied. Magnesite ore is added to the mixture without any thermal process. The type and proportion of the bond to be used, particle size distribution of the magnesite and chromite ores and the influence of compaction pressure on the refractory properties were examined. Consequently the influence of the changes in the mixture composition and sintering temperature on refractory properties was studied. The results of the experiments revealed the optimum type and content of the bond as MgSO₄·7H₂O and 8%, and optimum pressing pressure of the materials containing raw magnesite at 250 MPa. It was observed that when the chromite content of the material composition increased from 10 to 28% and 50%, the cold crushing strength (CCS) of the material has decreased, yet its porosity (P%) increased. This improves when the sintering temperature increased from 1450 to 1550 °C and 1750 °C. The optimum sintering temperature was found at 1750 °C     

Properties of refractories produced from synthetic magnesia

Conclusions The sinterability, open porosity, and cold-crushing strength of magnesite and magnesite-chromite specimens processed from magnesia powders (96–97% MgO) are improved with a decrease in the size of the periclase grains in the powder and with an increase in the firing temperature and do not depend on the percent and composition of the silicates and on the B₂O₃ content of the magnesia powder.The high-temperature bending strength of both types of refractories increases with a decrease in the B₂O₃ content of the magnesia powder. The creep resistance of the magnesite specimens increases with the ratio CaO/SiO₂ in the magnesia powder while the creep resistance of the magnesite — chromite specimens does not depend on this index.The indices of the open porosity and strength of the magnesite and magnesite — chromite specimens were optimal when they were produced with magnesia obtained by the bicarbonate method from dolomite.To produce dense and strong magnesite refractories from magnesia, they should be fired at a temperature not below 1700°C. The firing temperature of magnesite — chromite refractories should not be below 1750°C.Translated from Ogneupory, No. 6, pp. 53–57, June, 1978.     

X-ray phase analysis of open hearths

Conclusions After current and capital repairs, the basic phase in the hearths is periclase. Apart from periclase there is also magnesioferrite, monticellite and forsterite.Hearths surfaced with nine layers of a mixture of magnesite and scale and three layers of pure magnesite with slagging of the scale after capital repairs hardly differ at all in phase composition. When surfacing with nine layers, there is a considerably greater amount of forsterite.The basic laws governing the variation in phase composition according to window and layer are manifested both in the hearth surfaced with nine layers of magnesite and scale, as well as in the ones surfaced in three layers with pure magnesite and slagged with scale.During current repairs, the phase composition of the hearth is basically no different from the phase composition which is obtained during capital repairs. Since there is no substantial difference in the phase composition of the hearth surfaced by the high-speed or conventional methods, the strength of the hearth during high-speed surfacing is not inferior.The composition of the hearths after service is characterized by magnesioferrite, periclase, a solid solution of magnesioferrite in periclase, monticellite, forsterite, merwinite, complex spinel MgO·Al₂O₃, dicalcium silicate and braunmillerite.Typical of the phase distribution and lattice parameter of the periclase according to the level of the hearth is a parallel variation in the content of the periclase and monticellite as well as an inverse relationship between the amount of periclase and its lattice parameter.     

Sintering of MgO made from MgCl2

Conclusions The production parameters for a densely sintered magnesite powders made from MgO obtained from the thermal decomposition of MgCl₂ have been established. It is shown that the mechanical activation of MgO can be carried out in a vibromill for 10–20 min with an addition of a surface-active material (distillery waste or C₇-C₉ (fatty acids).Under pilot-plant conditions, using the process which has been developed, we obtained an MgO briquette of apparent density 3.20–3.33 g/cm³, an open porosity of 1.6–4.6%, and a MgO concentration of 97.9%. The magnesite and magnesite-chrome articles based on this briquette have excellent properties.Deceased.Translated from Ogneupory, No. 7, pp. 41–45, July, 1979.     

Magnesite refractory with a high CaO content

Conclusions Chromite, added in amounts of 10% to dolomitic magnesite containing 8.35% CaO by bonding with it completely during firing, is an effective stabilizer.An increase in the chromite content of the batch of more than 10% lowers the quality of the refractory.The hydrothermal treatment of the calcined dolomitic magnesite with 10% chromite accelerates the process of hydrating the free CaO and disperses the material, which helps the refractory to sinter during firing.The proposed technique provides for combined grinding and firing of a mixture of dolomitic magnesite with chromite, excludes aging of the body, reduces the firing temperature of the body and increases the quality of the refractory compared with the periclase-spinel technique.The calcium oxide in dolomitic magnesite with the addition of 10% chromite is bonded mainly with theCr₂O₃ into calcium oxychromite 9CaO · 4CrO₃ · Cr₂O₃ and the ferric oxide is introduced into the lattice of the periclase with the formation of a solid solution. With 30% chromite in the batch 3CaO · 2CrO₃ · 2Cr₂O₃ is formed, and the ferric oxide enters the magnesio-ferrite.Calcium oxychromite, existing in the refractory with 10% chromite and being a secondary phase, at its fusing temperature (>1250–1290°C) reversibly converts to calcium monochromite with a fusing temperature of 2170°C, which explains the increase in the refractoriness under load.     

Microstructures and strengths of microporous MgO-Al2O3 refractory aggregates using two types of magnesite

Six microporous MgO-Al₂O₃ refractory aggregates were prepared with Al(OH)₃ and two different types of magnesite powders via an in-situ decomposition pore-forming technique. One magnesite powder contained more CaO (Magnesite C), the other one contained more SiO₂ and Al₂O₃ impurities (Magnesite SA). Effects of magnesite powder type and content (11 wt.%, 36 wt.% and 77 wt.%) on the phase compositions, microstructures and mechanical strengths of the prepared microporous aggregates were investigated by X-ray diffractometry (XRD), mercury porosimetry measurements, and scanning electron microscopy (SEM), etc. With the addition of 11 wt.% and 77 wt.% magnesite, the type of magnesite had only a small effect on the microporous corundum-spinel and periclase-spinel aggregates, while great influence on the microporous spinel aggregates was observed with 36 wt.% addition. This was mainly because of the sintering process with liquid phase. The best microporous MgO-Al₂O₃ refractory aggregates, which had an apparent porosity of 39.1%, a median pore size of 3.38 μm and a compressive strength of 66.3 MPa, were prepared by using 36 wt.% Magnesite C. This work has practical significance for the efficient utilization of magnesite and the development of energy-saving lightweight MgO-Al₂O₃ refractories.     

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.     

Composition and formation of fusions of metallurgical magnesite powder

Conclusions In metallurgical magnesite (periclase) powder obtained in rotary kilns of length 50, 75, 90, and 170 m one encounters no less than eight structural genetic types of granules (fusions) in which are selectively concentrated the impurities CaO, SiO₂, etc. The commonest are diabase and dolomite granules.The formation of diabase and clayey (aluminous) fusions is due to the cementation of periclase particles by the melts, formed deposited from the mechanical impurities in the raw material. Morphologically and genetically similar chamotte, and frequently ferruginous, fusions develop as a result of the granulation of aggregate periclase grains of fusible products from the breaking up of the lining in the rotary kilns.The formation of dolomite and diabase-dolomite fusions with an internal core from the products of the decomposition of the broken primary dolomite is connected with the power of the latter to be preserved during firing in the form of lumps, and not subjected (in contrast to magnesite) to self-dispersion.In the formation of granules chemical reactions occur between the periclase, lime, and molten fusible impurities in the magnesite raw materials. The products of the reaction are spinel, magnesioferrite, forsterite, monticellite, merwinite, cordierite, and silicates and ferrites of calcium. In connection with the increase in the concentration of fusible impurities the fusions (granules) are poor quality constitutents of the magnesite powder.Translated from Ogneupory, No. 5, pp.47–54, May, 1971.     

Analysis of corrosion of corundum refractory castables in relation to increased MgO content in dendromass ashes

Biomass ash has a significantly lower proportion of Al₂O₃ and higher proportions of K₂O, CaO and SiO₂ than coal ash. Biomass combustion in power plants increases demands on refractory linings and metal fittings in boilers. Grates and linings of combustion chambers in furnaces and boilers are more susceptible to clogging and are degraded by bio-ash slag. The results of this study suggest that the addition of approximately 2% of powder magnesite waste to the wood-chip fuel can significantly mitigate ash slagging and also corrosion of the corundum refractory material. With regard to the resulting increased MgO content in the dendromass ash, the corrosion of corundum refractory material was studied. The MgO content in the ash was increased by adding powder magnesite waste to ash samples. The results of corrosion tests (1450 °C/7 h) showed that ash slag with MgCO₃ addition corroded the corundum material less. Analyses of the post-mortem slag and corrosion interface confirmed: (i) higher K₂O concentration in the ash caused increased corundum material corrosion by both vapours (g-s) and melt (l-s); (ii) K₂O reacted with Al₂O₃ at the corrosion interface and also penetrated intensively into the fine-grain matrix by surface diffusion; (iii) MgO remained in the slag; (iv) increased Al₂O₃ content in the molten slag initiated a liquation of MA-spinel. These results (especially MA spinel liquation from the slag and K₂O diffusion through the matrix followed by micro-grain dissolution) indicate that replacing the mullite binder phase in the matrix with MgO and/or spinel could lead to improved resistance of the refractory material to biomass ash slag.     

菱镁材料改性研究进展

从菱镁材料成型机理入手,分析了菱镁材料改性外加剂的改性原理及其改性方法,介绍了改性后的菱镁材料具有的各种优异的性能,指明了菱镁材料改性的应用研究方向。     

Erosion Effect of Molten Steel on Carbon Containing Refractories for Continuous Casting

The erosion resistance of carbon containingrefractories for continuous casting to molten steel wasinvestigated by means of simulative erosion test and examining used refractories. Decarbonization and reaction between molten steel and decarbonization layer are main erosion process of carbon containingrefractories by molten steel. The reactions between molten steel and oxide in refractories determine thethickness of decarbonization layer. A dense layer formation on the working surface contacting withmolten steel during casting will suppress decarbonization and erosion process.     

Obtaining dense powder from Satkinsk magnesite beneficiated by flotation

Conclusions Enrichment of Satkinsk magnesite by flotation yields a product containing (calculated on the calcined substance) 94.2–96.5% MgO, 0.3–0.4% SiO₂ and 1.4–2.8% CaO.Enriched magnesite consists of dispersed powder with a relatively narrow particle-size range. A large quantity of particles have dimensions of 0.2–0.063 mm. The concentration of particles measuring less than 0.063 mm did not exceed 55%.In order to obtain dense powder it is necessary to carry out additional fine grinding of the enriched magnesite, ensuring a concentration of fractions less than 0.063 mm of at least 95%, reducing the average particle size by a factor of 4–6 (down to 10) and followed by briquetting of the milled material.Translated from Ogneupory, No. 7, pp. 1–5, July, 1970.