Spinel-bonded magnesia-based refractory castables with hydratable alumina as binder

This thesis is divided into three sections: MgO-Al{dollar}sb2{dollar}O{dollar}sb3{dollar} Spinel Formation and Characterization; Preparation of Cement-Free Castables and Their Properties; and Estimation of Corrosion Resistance against basic ferritic slags.; The first section is about spinel formation; several mixtures composed of different alumina and magnesia powders are prepared and fired at various temperatures. The physical properties of the mixes as a function of the amount of spinel formed at different firing temperatures are investigated.; The nature and size of raw materials determine strongly the formation of spinel and the properties of mixture. The degree of dispersion of MgO and Al{dollar}sb2{dollar}O{dollar}sb3{dollar} control the amount of spinel produced. The sinterability of raw materials and the quantity of spinel produced determine the ultimate properties of fired mixtures.; In the second section on castables and their properties, the effect of granulometry is studied. Using Andreasen's equation, it has been shown that the optimized compactness is obtained with the exponent of n = 0.37.; Fine alumina in castables leads to a large expansion at 1400{dollar}spcirc{dollar}C and a rapid shrinkage at 1600{dollar}spcirc{dollar}C, and this sudden change will decrease the structural stability. The ultrafine alumina produces a gradual change from expansion at 1200{dollar}spcirc{dollar}C to shrinkage at 1600{dollar}spcirc{dollar}C and this continuous change can decrease the internal stresses.; Alumina has a strong influence on the corrosion resistance of basic castables. When increasing the alumina amount, the erosion increases. The castable containing fine alumina shows less corrosion resistance than those containing ultrafine alumina.; The basic castable shows a deep penetration depth due to the lack of dissolution reaction between the aggregates and the penetrated slag which results in the change of slag properties. The matrix of basic castable is not dense enough to prevent slag penetration, and the grains are hence easily wetted by slag.; In summary, in this thesis it is possible to demonstrate that it will be possible to manufacture castables containing more than 80 weight% magnesia, with an hydraulic binder and without any hydration problem, during drying and at first heat-up. Those are castables with hydraulic binders, without any cement. Their refractoriness are intrinsically higher than the commercially available castables nowadays. This is then a major technological improvement. The binder is an hydratable alumina, called "actibond".; As expected, the corrosion resistance of the new castables which have produced is higher than all the best commercial castables, even in basic slags with 30% iron oxides. However the resistance to penetration is still a weak point. (Abstract shortened by UMI.)...