An Experimental Investigation of Alumino-Silicate Refractories of High Purity, for Use in Glass Melting. Part II. The Effect of Soda (Na₂O) on Materials of a Sillimanite and Mullite Composition when Fired at Different Temperatures

JSGT 1952 V36 T242-T265

The effects of small additions of soda on the rate of recrystallisation of alumino­silicate mixtures during firing, and on the properties of the fired materials, have been studied. The mixtures consisted of calcined alumina and a specially fine china clay, in proportions corresponding with sillimanite (Al₂O₃.SiO₂) and mullite (3Al₂O₃.2SiO₂), and sodium silicate was added in amounts to give up to 0·5% of soda in the “sillimanite” mixtures and up to 3% in the “mullite” mixtures. Two “sillimanite” mixtures and one “mullite” mixture were made with fired china clay (Malachite) replacing some of the raw china clay. Grogs were prepared from each mixture by firing for 20 hours at 1400°, 1450°, 1510° and 1590° respectively, the linear shrinkages during firing and the apparent porosities of the fired grogs being determined in each case; the true porosities of a number of the grogs were also determined. By X-ray methods determinations were made of the proportions of mullite, corundum and non-crystalline material in a selection of the fired grogs. Refractory mixtures were made by mixing portions of each grog with a suitable proportion of the corresponding “raw mix,” and corrosion tests were carried out on extruded specimens of each mixture after firing for 20 hours at the temperature used in the original firing of the grogs.

R. Heeley & H. Moore