Yu. D. Kuznetsov

Effect of reaction of periclase and iron-chrome spinel on the properties of periclase-spinel refractories

ConclusionsUsing a typical composition of the type MgO-Mg(Al1−x−yCrxFey)2O4 a study was made of the effect of the processes involved in the processing and decomposition of solid solutions of periclase and spinels on the technical properties of the fired products.During cooling from 1600–1750°C decomposition occurs in the solid solutions of periclase and spinel; the crystals of spinel separating under these conditions are able to grow to large sizes which inevitably should lead to the development of stresses inside the periclase grains.The decomposition of the solid solution of periclase and spinel adversely affects the strength and thermal-shock resistance of the fired specimens.The best technical properties are possessed by combinations of periclase with small (up to 15%) quantities of high-alumina (x=0.16 and 0.46) spinels.The use of compositions of periclase with high-alumina spinels of the type x=0.16 and 0.46 enables us to obtain denser and more thermal-shock resistant refractories.

Unfired periclase-chromite refractories based on periclase and periclase-chromite shells (a discussion)

Etude de la preparation de refractaires non cuits de periclase-chrome, de leur composition et de leurs proprietes physiques, mecaniques et thermiques

A study of the slag-induced wear of the refarctories made from magnesia-spinellid bodies with an argillaceous binder

ConclusionsAmong the experimental additives introduced into the composition of the magnesia-spinellid bodies, the highest resistance to the synthetic slag is exhibited by the fused and the sintered spinels and electrocorundum, and the least resistance is shown by the tricalcium and dicalcium silicates. Forsterite is the most stable silica-bearing phase.The plasticizer additions (refractory clays or bentonite) that ensure satisfactory shaping properties of the bodies are found to have an adverse effect on the slag-resistance of the systems: the interaction period required for the initiation of erosive wear decreases with increasing plasticizer content. The bentonite content in the body must not exceed 3% and the refractory clay content must not exceed 5–6%.A direct correlation with a correlation coefficient of 0.94–0.99 was established between the amount of the direct bonds existing in the refractory and the interaction period up to the initiation of erosive wear; this fact indicates the significant effect of the refractory structure and the phase distribution on the erosive wear. When the refractory clay amounts to 7–10%, erosive wear is observed within the very initial stage of interaction.Under the action of the molten synthetic slag, one does not observe much difference in the destruction of the systems containing the Latnensk and the Novoraisk clays; on the other hand, the systems containing the Latnensk clay possess a high resistance to the molten mixture of the synthetic and the converter slags. The mixture of the synthetic and the converter slags has a significant destructive action.We showed that it is advisable to introduce fused spinel and electrocorundum additives into the composition of the magnesia-spinellid based ramming bodies.

Plastic refractory mixtures for lining the combustion chambers of ship steam boilers

ConclusionsThe use of plastic refractory mixtures for lining ship steam boiler combustion chambers is promising. Plastic mixtures based on an aluminosilicate filler, an inorganic plasticizing component, and special additions have been developed. The method of preparation of the mixtures includes mixing of the constituents and preliminary tamping under a pressure of 10–30 MPa. Types MMKR-58 and MMK-72 mixtures were tested in the linings of operating KAV 16/16 and KVVA 12/28 boilers. The linings operated for about 4000 and 3740 h, respectively.Technical Specification 14-8-342-80 has been approved for supply of a plastic refractory mixture with a minimum content of 72% alumina oxide. Work is being done on the introduction of the plastic mixture.

Volume changes and the technical properties of composites in the spinel-manganese oxide system

ConclusionsThe volume changes during the oxidation-reduction process of the manganese oxide in the Mg(Al, Cr)2O4-Mn2O3-Mn3O4 system have been studied. The volume changes of the solid phase in this case are not great and are less than those observed in the formation and decomposition of the solid solutions of spinels and hausmannite. In composites of spinels and manganese oxide, the liberation of oxygen on reduction and the separation of Mn2O3 from the spinel phase on oxidation are important in the redox processes. In this case three factors appear to destroy the refractory: the liberation and absorption of oxygen; the volume changes undergone by the spinel phase; and the separation of the Mn2O3 phase.The effect of manganese oxide on the technical properties of the products of firing the composites based on spinels of the Mg(Al, Cr)2O4 is complex and depends on the concentration of manganese oxide and the firing temperature. At temperatures of 1473 and 1673°K there is a reduction of the ultimate compressive strength and increase in porosity as the concentration of manganese oxide is increased in the composites with x=0, 0.2, and 0.5. Only in the composites with magnesium chromite is the increase in the concentration of manganese oxide accompanied by an increase in the mechanical strength. When the firing temperature is increased to 1873 and 2023°K, only small (5%) additions of manganese oxide have a beneficial effect on the technical properties of the sinters based on high-alumina spinels.During the slow cooling from 2023°K, the oxidation of hausmannite and the separation of Mn2O3 was observed; this causes a sharp reduction in the mechanical strength and microhardness. The most marked oxidation occurs in composites based on magnesium chromite.The factors destroying the refractory caused by the oxidation-reduction processes of the manganese oxides appear in composites containing high-chromite spinels. Therefore this study makes it possible to recommend as refractories to be in contact with manganese-type material those in which the spinel part consists of high-alumina spinels.

Guniting of the monolithic lining of steel-teeming ladles

ConclusionsThe authors have developed the principles of guniting the monolithic lining of steel-teeming ladles with semidry masses. Determination of the wetting of a vitrified siliceous monolithic lining with aqueous solutions of additives and suspensions of these solutions, plasticizing additives, and refractory filler has shown that a coating can be deposited onto the surface of a monolithic lining. Formation of a ceramic bond between the coating and the vitrified surface of a monolithic lining takes place at high temperatures (900°C or above). Masses of siliceous, aluminosilicate, and periclase-chromite compositions have been developed for guniting the monolithic lining of steel-teeming ladles.A procedure for guniting the monolithic lining of 180- and 350-ton steel-teeming ladles has been developed and tested. The best results have been obtained with use of gunite masses of periclase-chromite composition.

Slag corrosion of silicic tamped masses

ConclusionsThe slag erosion of silicic masses in contact with ferrous slags of basicity 3.0, 2.5, and 1.0 has been studied. The wear is determined by the predominant dissolution of the refractory in the slag melt. The phase transformations occurring in the slag-encrusted and slag-free zones of the refractory include the degeneration ofα-quartz into cristobalite.

Influence of the aluminum oxide content of chamotte gunite masses on their slag resistance

ConclusionsThe authors investigate the influence of the aluminum oxide content of chamotte gunite masses on their slag resistance in contact with converter and synthetic slags. The refractory undergoes wear by dissolution of its surface in the fused slag; the slag does not penetrate very deeply into the refractory.A significant increase in slag resistance is observed only when the aluminum oxide content of the slag is 40% or more. An increase in the aluminum oxide content from 34–35 to 37–39% is not accompanied by a marked increase in the slag resistance. Linear regression equations with high correlation coefficients (0.70–0.98 in absolute value) have been constructed for different aluminum oxide content ranges.A more significant decrease in slag corrosion can be attained by introducing special additives into the chamotte mass composition.

Quartz-clay ramming compounds with quartz sand from the Latnensk deposits

ConclusionsRamming compounds based on Latnensk clay-containing quartz sand and intended for the monolithic lining of steelcasting ladles were developed and tested and are now in production.The average durability of the lining of the 180-ton steelcasting ladles of converter section No. 1 of the Novolipetsk Metallurgical Plant is 9–10 melts when it consists of a ramming compound produced from Latnensk quartz sand. The lining becomes unserviceable owing to the low durability of the working layer of the bottom. When using a ramming compound based on Chasov-Yar semifatty sand, the lining of the lateral parts of the ladle bottom and that of the slag zone are severely eroded after 7–8 melts.

The action of slags of varied basicity on spinel - Periclase refractories

ConclusionsIn the action of slags of the Fe2O2-CaO-SiO2 system on spinel-periclase refractories consisting of a filler and a binder the mechanism of erosion depends on the composition of the slag and the degree of erosion on the composition of the spinel party of the binder of the refractory.The essence of the chemical interaction of the refractory with the penetrating melt consists in the formation of solid solutions of periclase and spinels with the ferric component of the slag, and in the interaction of the periclase and silica in the presence of acid slags which results in the formation of forsterite; in the presence of basic slags it is primarily the spinel which is eroded and interacts with the calcium oxide, the result being the formation of calcium monoaluminate and chromite, and periclase.The erosion of the refractory depends largely on the stability of its bond; the periclase grains are affected only superficially by the processes of the interaction.When slags of different basicity act by turns on spinel-periclase refractories, the nature of the processes developing in the refractory as a result of the penetration of the melt is quite different. The chemical compounds formed in the interaction with the previous slag are dissolved in the melt penetrating into the refractory, i.e., the forsterite in the subsequent interaction with basic slag and the alumino- and chromocalcium compounds in the subsequent interaction with acid slag. The result is that the ratio CaO∶SiO2 in the melt approaches two so that the chemical activity and solution capacity of the melt decrease. In this case the principal product of the crystallization of the melt is represented by monticellite.This investigation showed that in contact with melts in the Fe2O3-CaO-SiO2 system a marked advantage lies with compositions which contain high-alumina spinels, the reason being the volumetric stability of these spinels to iron oxides.