High-density periclase clinker: A promising material for refractory production

Data on testing sintered periclase clinker obtained from flotation magnesite concentrate for the production of refractory parts are presented. It is shown that by organizing production of high-density periclase powders in the plant from flotation magnesite concentrate with the minimum possible content of impurity SiO₂ and CaO oxides the quality of the products can be improved with a much longer service life provided for linings of heating installations.     

Structure and properties of fused periclase and periclase-chromite blocks produced from beneficiated starting materials

Conclusions Fused periclase and periclase-chromite blocks containing a high proportion of highmelting oxides of magnesium and chrome were produced from beneficiated starting materials.The structure and properties of the periclase and periclase-chromite were analyzed zonewise in the blocks. The thickness of the block zones with a high content of magnesium oxide and the yield of high-quality periclase and periclase-chromite depend on the degree of purity of the chemical composition of the starting materials.The content of magnesium oxide is highest and the proportion of contaminating oxides low in fused periclase produced from chemically beneficiated Satkin magnesite, and in the monocrystalline subzones of the blocks. An increase in the proportion of chromite in the mix results in a higher porosity and in a higher content of spinel and ferrochrome in the fused material. The properties are optimal in the case of a periclase-chromite material from a mix containing 15–20% chromite.Translated from Ogneupory, No. 3, pp. 37–44, March, 1978.     

Periclase-spinel products based on sintered materials for vacuum treatment of steel outside the furnace

Conclusions A technology was developed for periclass-spinel, low-silica chrome-concentrate (SiO₂ <1.5%) and sintered periclase (MgO 91–92%, SiO₂ < 3%). As regards the resistance in the walls of the metal zone of circulation vacuum equipment, these refractories are not inferior to PKhP periclase-chromite goods made from fused materials.In the production of PShKh articles it is recommended that titanium additives be used to ensure sintering of the chrome-concentrate to a low porosity, and to stabilize the properties of goods made with it.It is desirable to make wider tests of these refractories in vacuum units of different types. The introduction of PShKh articles based on sintered materials in the walls instead of PKhP articles should reduce the consumption of scarce fused materials for vacuum treatment and cut the costs of the linings.Translated from Ogneupory, No. 7, pp. 32–36, July, 1991.Deceased.     

Ways Toward Improving the Technology of Refractories Based on Powdered Periclase

Periclase powders available from domestic (Magnezit JSC) and foreign manufacturers are analyzed for chemical and mineralogical composition. Domestic magnesite is shown to differ from its foreign analogs in smaller values of MgO content, CaO/SiO₂ ratio, and periclase crystal size. A way toward obtaining high-quality powers involves reducing the concentration of SiO₂ in magnesite to 0.2 – 0.5% and increasing the calcination temperature to 2000 – 2100°C to prepare coarse-grained periclase with a crystal size larger than 140 m. The need for developing a technology that would enable fabrication of refractory components with tailored structural properties from periclase powder is emphasized.     

Composition of Periclase and Calcium-Silicate Phases in Magnesia Refractories Derived from Natural Microcrystalline Magnesite

Mineralogical and microstructural properties of sintered and fused magnesia grains and refractory bricks derived from natural magnesite were examined. Although their CaO/SiO₂ ratios can be used to approximate their mineralogical compositions, detailed X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies revealed significant deviations from the expected phase assemblages. Their microstructures vary widely in terms of proportions of direct periclase bonding, amounts and phase constitution of the siliceous bonding, and the size and composition of the periclase crystals. An exceptionally high solid solubility of CaO in periclase crystals was detected. Most of the phases of the siliceous bond exhibit nearly stoichiometric compositions and show intriguing substitutions.     

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.     

Effect of La2O3 addition on the microstructural evolution and thermomechanical property of sintered low-grade magnesite

The rich mineral resources of magnesite have been decreasing rapidly, while the low-grade magnesite is abandoned, and the requirement on utilization of low-grade magnesite is causing much attention. La₂O₃ has been introduced as an additive in this study, considering its positive role in the modification of the magnesia matrix. Low-grade magnesite containing 0–3 wt% La₂O₃ was fired at 1550 °C for 3 h. The effect of La₂O₃ on the microstructural evolution and thermomechanical property of sintered low-grade magnesite was investigated. The results showed that La₂O₃ markedly improve the microstructure of sintered low-grade magnesite. The distribution state of the low melting monticellite phases among the periclase grains evolved from distribute continuously to concentrate in isolation at the triple-point junction of the periclase grains, and the generated CaO·3SiO₂·2La₂O₃ based dendrites phases interlaced in the magnesia matrix. The hot modulus of rupture (HMOR) was significantly enhanced with increasing addition of La₂O₃ due to the low-melting monticellite phases were transformed to CaO·3SiO₂·2La₂O₃ phases based dendrites with large aspect ratio, effectively reducing the availability of monticellite. Besides, the bridging phenomenon resulting due to the dendritic phase exhibited an optimal toughening effect, attributing to the increase in crack deflection and resistance to crack propagation.     

Industrial production of dense powder from Satkinsk magnesite beneficiated by flotation

Conclusions The beneficiation by flotation of Satkinsk magnesites of the fourth grade with fine mutual growth of minerals allows us to obtain from them a product containing (calculated on the calcined substance) 94.0–96.5% MgO, 0.3–0.4% SiO₂, and 1.40–2.87% CaO.A technology was developed for producing dense powder from the magnesite beneficiated by flotation, specifying combined fine grinding of it with caustic magnesite in a tube mill, briqueting on smooth roller presses, and burning the briquet in a rotary kiln.In industrial conditions using the beneficiated (flotation) and briqueted Satkinsk magnesite, firing in a rotary kiln, we obtained high-quality powder with an apparent density of 3.13–3.32 g/cm³, with a developed direct bond in the periclase crystals. The powder of all fractions is homogeneous in chemical composition, does not contain free calcium oxide, and may be used completely without aging for producing magnesite refractories for critical locations in furnaces.Translated from Ogneupory, No. 2, pp. 5–11, February, 1972.     

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.     

Magnesite-Spinel products from fused materials with by-products from chemical processes

Conclusions The feasibility was demonstrated of producing chrome-containing magnesia spinel from a mixture of the by-products of chemical processes and magnesite. The composition of this spinel is similar to that of spinel fused from a mixture of commercial alumina, magnesite, and chromite. The fused spinel from the by-products contains a large proportion of SiO₂ and correspondingly less FeO + Fe₂O₃ than spinel fused from commercial alumina.The properties of magnesite-spinel refractories based on fused and sintered spinels from the by-products were investigated and compared with those of specimens based on fused and sintered spinels from alumina. The properties of the products containing fused spinels from the by-products proved to be good and similar to those of products containing fused spinel from alumina.Fused spinel from the by-products can be used also as starting material for the production by the ceramic method of spinel brick with good properties.Translated from Ogneupory, No. 6, pp. 33–39, June, 1974.     

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.     

Reversible phase transformation in the system calcium oxide-chromium sesquioxide-oxygen

Further studies were carried out on the reversible phase transformation of the low melting (1228°c) calcium chromate chromite (941) into the high melting (2170°c) monocalcium chromite (CK) with the liberation of free CaO and oxygen. The investigation of specimens of synthesised 941, calcium chomate (CK₁), and 941-bearing samples with a high content of periclase (as in dolomitic magnesite chrome refractories) cooled from different temperatures showed the presence of transformation products of 941 phase under different conditions of its formation, and thermogravimetric analysis and complex differential thermal analysis confirmed the reversible nature of this phase transformation. Irrespective to the method of formation of 941 or the existence of a high periclase content and a solid solution of 2CaO.SiO₂ with it, 941, at its melting point, starts to undergo a reversible phase transformation according to the equation: 9CaO.4CrO₃.Cr₂O₃.3CaO.Cr₂O₃+6CaO+3 O₂. The presence of 941 phase in basic refractories produced from raw materials with a high CaO content, should be considered to be a secondary phase, re-formed during the cooling process. Beta-alpha polymorphism of the liberated CK was exhibited above 1600°c during this phase transformation.     

Microstructure and phase evolution of Indian magnesite‐derived MgAl2O4 as a function of stoichiometry and ZrO2 doping

To aid development of cost‐effective sintered spinel as a refractory raw material, this paper presents an extensive analysis of microstructure and complex phase evolution of Al‐rich, Mg‐rich, and stoichiometric spinel aggregates derived from Indian magnesite and calcined alumina. Pore morphology in Al‐rich spinel was transformed upon sintering at 1650°C and corundum laths embedded in porous Al‐rich spinel matrix was formed. Stoichiometric spinel sintered at 1600°C consisted of mostly direct bonded angular equiaxed spinel grains which incorporated the impurities in solid solution. Mg‐rich spinel was composed of spinel grains with reduced angularity along with intergranular amorphous phase, small round monticellite grains, and periclase. EDS line scan revealed impurity‐free joins existed between direct bonded spinel grains. Mg‐rich spinel containing 0.65 wt% ZrO₂ formed cubic ZrO₂‐CaO‐MgO solid solution located along spinel boundaries, which reduced both intergranular amorphous phase and monticellite. This increased SiO₂ and MgO content in spinel solid solution triggering exsolution of metastable cubic forsterite manifested as split spinel peaks in XRD pattern. A 14.7% reduction in slag penetration was exhibited upon doping Mg‐rich spinel with 0.21% ZrO₂. Stoichiometric and Mg‐rich spinels attained 0.35% and 0.54% apparent porosity at 1600°C, which is better than most commercial sintered refractory spinels.     

RH插入管用优质镁铬砖的开发

以国产优质菱镁矿和铬精矿为主要原料，采用电熔和烧结预合成料并用工艺，研究了不同添加剂对优质镁铬砖性能的影响。结果表明，添加剂可富化方镁石固溶体的晶内尖晶石，促进晶间尖晶石的形成，赋予制品高强度和优良的抗渣性；电熔和烧结料并用工艺．可控制显微结构，改善其抗热震性。本制品在引进RH和RH－OB炉括入管上使用，侵损速度和使用寿命均优于引进同类产品。     

Obtaining magnesia and periclase refractories from bischofite from the volgograd deposits

Conclusions Experimental work was carried out to obtain from bromine liquors of bischofite of the Volgograd deposits magnesium oxide, using low capacity industrial equipment for chemical purification of magnesite, including a recuperator, a tank-collector, a spray-reactor, a cyclone, an absorption column, spray traps, a vacuum pump, and a filter press.We worked out the parameters for the processes of boiling off the liquor, thermohydrolysis of the magnesium chloride, absorption of the hydrogen chloride with the production of hydrochloric acid, washing and leaching the hydrolytic magnesium oxide, and filtration of the resulting magnesium hydroxide. During the reprocessing of the liquor containing the bischofite, using this technology, without preliminary purification to remove boron and sulfates, we obtained magnesium hydroxide with a high purity level (98.5–99.5% MgO on the calcined weight).It is shown that the magnesium hydroxide thus obtained is a high-quality raw material for the production of fused and sintered periclase with a purity of 98–99.5% MgO. The technology of sintering, including carbonization of the magnesium hydroxide, hot palletizing without bond, and firing at moderate temperatures, ensures the production of densely sintered periclase. Tiles with inserts made from fused periclase of high purity with a clear anisotropic structure facilitate the casting of two heats through the gate valves.The results obtained can serve as the starting data for the development of specifications (TLZ) and planning the production of magnesium oxide from the debrominized bischofite liquors at the Volgograd site using the thermohydrolysis method. We need to solve the problem of the use of the 20% HCl that is obtained.Translated from Ogneupory, No. 1, pp. 27–30, January, 1988.     

Features of the lining wear of tunnel kilns in firing of periclase parts

Conclusions Features of the mass transfer of substances and of the wear of a tunnel kiln lining as the result of occurrence of processes of dissociation, evaporation, condensation, recrystallization, thermal filtration transfer of the silicates, and also corrosion of the periclase and chromospinellide in firing of periclase parts at 1600–1650°C are considered.It is shown that the condensate deposits formed on the lining are primarily sodium and potassium sulfates while chromates are not detected in them.The mechanism of failure of periclase-chromite refractories in a tunnel kiln lining in firing of chrome-free parts was revealed. The indices of the structure of the zones of the parts formed in the refractories in service of them in the kiln firing zone were determined.Taking into consideration the wear mechanism revealed, the use of high-temperature fired periclase-chromite parts based on enriched magnesite and chrome concentrate introduced simultaneously in the granular and finely ground forms is recommended in the kiln linings.Translated from Ogneupory, No. 4, pp. 52–56, April, 1985.     

Development of a resistant spherical packing for service in nitrogen at 1650°C

Conclusions The action of scale on periclase, spinel, corundum, periclase-chromite, and chromite-periclase specimens (production and laboratory) at 1650°C in commercially pure nitrogen was investigated.A method was developed for production of periclase, spinel (aluminomagnesia), and periclase-chromite spherical packings by the pelletizing method. It was shown that pelletizing of fused periclase and of mixtures based on it is possible only with the addition during vibrogrinding of a surface-active hydroxylated alcohol-base alkyl phosphate paste in a quantity of 0.1% and alternate moistening of the powder being pelletized with a suspension of glycerine residue in silica sol and a solution of lignosulfonate and methyl cellulose.Tests were made of the action of scale on pellets of all of the compositions at 1650°C in commercially pure nitrogen under load and without load. The preferable spherical packing materials for service under such conditions are periclase with a density of not less than 3.12 g/cm³, corundum with zero porosity, and spinel of stoichiometric composition with a density of not less than 3.36 g/cm³. In addition, the use of periclase-chromite with a density of not less than 3.32 g/cm³ is possible.Translated from Ogneupory, No. 3, pp. 5–10, March, 1989.     

Formation of scawtite from mixtures of CaO,magnesite and quartz under hydrothermal conditions

The phase composition of samples prepared under hydrothermal conditions at 200°C from a suspension of mixtures of CaO, quartz and magnesite has been studied. When 10, 20, 30 and 50 wt % of CaO were substituted by magnesite, the mole ratio CaO/SiO₂ being 0,83 and 1,20 - chiefly tobermorite, gyrolite and calcite or scawtite and tobermorite were formed, and the strength of the tested materials was observed to decrease.     

Wear of magnesia spinel refractories in portion vacuum-processing steel plant

Conclusions The processes of wear in the lining of vacuum chambers of outdoor-furnace vacuum-treatment plants (UPVS) are due to the simultaneous action of high temperatures, deep vacuum, gaseous medium, molten metal, and slag. The corrosion and erosion of aggressive melts of slag and metal are the decisive forms of wear.Laboratory investigations established the relationship between slag resistance in vacuum and the ratio of corrosive and erosive constituents in the wear of different magnesia-spinel refractories and their phase composition, structure, and properties.Refractories obtained from fused periclase-chromite material with a low content of fusible silicates showed that in laboratory vacuum equipment and during service in the linings of the vaccum chamber of industrial plant they have higher slag resistance and lower wear than refractories based on sintered magnesite, spinel, and chromite ores.Translated from Ogneupory, No. 3, pp. 14–21, March, 1980.     

Periclase-chromite refractories from fused materials

Conclusions Experiments were carried out to obtain high-grade fused chromite-periclase. It is shown that during the melting of batch consisting of raw magnesite and chromite ore we eliminate the process of reducing the chromite ore to metallic ferrochromium, which adversely affects both the content of Cr₂O₃ in the fused material, and also the commerical appearance of the resulting refractories. We developed a technology for preparing periclase-chromite refractories with chromite-periclase constituents. The goods obtained possess good physicoceramic properties and a low content of silicates.The articles thus prepared were used to make the linings of the most critical parts of converters, Kivset unit in PZhV furnaces, which allowed an increase to be made in the duration of campaigns for these units of 1.5–2 times.Translated from Ogneupory, No. 3, pp. 41–44, March, 1985.