Abstract

Five refractory cement mixes were prepared from different proportions of barite, zirconia and calcined alumina by sintering at 1500– ۱۵۵۰ ۸C for 3 h. The obtained cements were composed of barium aluminate and barium zirconate minerals in addition to comparable proportions of di-barium silicate. Cement mix prepared from 70 wt.% barite, 10 wt.% zirconia and 20 wt.% alumina and containing comparable proportions of barium aluminate and barium zirconate minerals (
۳۸ and
۲۹ wt.%, respectively) shows a comporomise between good cementing, sintering and refractory properties. Refractory concretes prepared from 20 wt.% of this cement and 80 wt.% of either bauxite or fused spinel aggregate are composed mainly of mullite, barium aluminate, barium zirconate and a-corundum in case of bauxite aggregate or magnesium aluminate spinel in addition to barium aluminate and barium zirconate in case of fused spinel aggregate. These assemblages of minerals exhibit compact and homogenous microstructure and results in outstanding technological properties that meet the requirements of international standard specifications, i.e., good volume stability (permanent linear change is only 0.62 and 0.28%, respectively) good mechanical properties (680 and 610 kg/cm2 ), high spalling resistance (>30 cycles), high refractoriness (>1700 8C) as well as high load bearing capacity (ta: 1560 and 1590 8C). The combination of these advantages in such refractory concretes makes them suitable for use in severe conditions at high temperature applications especially in steel-making industries.

Introduction

The progress of high temperature industrial technology resulted in a substantial advances in monolithic refractories over the last decades. This has led not only to important innovations in castable preparation and application processes but also to significant improvement in product performance, in response to the constantly increasing service conditions imposed mainly by the steel and foundry industries [1,2]. The concretes based on alumina and magnesia are the most widely used high temperature materials. It has been reported that the refractoriness of refractory concretes can be increased substantially, without adversely affecting their compressive strength, when CaO in the cement clinker is partially substituted by MgO [3]. This is due to the formation of magnesium aluminate spinel which results in improved slag resistance and high hot sagging under load. Therefore, they are being used increasingly in steel-making applications such as lining of steel ladles, continuous casting tundishes and degasser snorkels and lancers [4,5]. However, their working temperatures are significantly lower and amount to 1800– ۱۹۰۰ ۸C [6]. Under the service conditions involving temperatures close to 2100 8C, barium aluminate–barium zirconate cement forms the promising materials.