Production and use of forsterite refractories

Abstract

Do!gikh UDC 666.762.34 The importance of magnesia refractories for industries using refractories, and especially ferrous metallurgy, is continuously increasing. The treatment of certain parts of the resources of high-quality magnesite raw materials and the need to find new ways of supplying the raw material for the production of magnesia refractories make it desirable to examine the possibility of economizing on this raw material by using forsterite refractories. The latter may have value also for replacing aluminosilicate refractories, in some cases, with a simultaneous increase in the service life.The USSR possesses a large number of deposits of magnesia-silicate raw materials but the industry prepared only I00,000 tons of various forsterite articles and a small quantity of powders.The causes of this Iie mainly in the inadequate economic incentives for the development of this type of product~ The physicochemical principles of the technology for forsterite refractories have been worked out in the fundamental works, of A. S. Berezhnoi [i]. The constituent components of magnesia-silicate rocks and refractories made from them, in the main, are to do with the system CaO-MgO-FeO-Fe203-AI203-Si02.Examining the separate subsystems in this system it is possible to note that, in combintion with dicalcium silicate and forsterite, the melt develops at 1490~and as a result of the reaction of forsterite with A1203"2Si02 -at 1370~ In the latter case we note the formation of cordierite, with a melting tempreature of 1435~ In a mixture of forsterite and anorthite the melt is formed at 1320~ and the gehlenite at 1390~In the systems forsterite-diopside-anorthite, and forsterite-anorthite-metasilicate of magnesium, the minima on the liquidus surface are observed respectively at 1270~ and 1300~ On the diagram for MgO-FeO-SiO2 the lowest liquidus temperatures approximate to II00~ but ferrous oxide mainly enters into the composition of the solid solutions of substitution. On the MgO-Fe20~-SiO 2 diagram the eutectic temperature equals 1330~The adition to forsterite of 10% Mg2AI4Si~018 , CaMg (Si03)2, CaAl2Si2Os, and Ca2MgSi20 v leads to the formation of 10-20% melt at temperatures from 1360 to 1430~Only the addition of MgO to forsterite does not reduce the temperature of melt formation.The best refractories can be obtained in the system MgO-FeO-Fe2Oa-SiO 2 with an adequate amount of magnesium oxide for bonding the silica and iron oxides respectively into forsterite and magnesioferrite.A useful additive may be chromite, and the region of compositions with a concentration of melt of less than 10% at 1600 ~ in the system MgO-SiO2-Cr20a is somewhat extended, compared with MgO-SiO2- Fe~03.It follows from the above that forsterite refractories are inferior to periclase and periclase-spinel in their refractory properties, and apparently in their resistance to basic slags. At the same time there are a number of applications in which forsterite refractories may be succesful, including those subjected to the action of iron oxides.Natural f...