The development of refractories was important for many industries, most notably for iron and steel making and glass production. The iron and steel industry accounts for almost two-thirds of all refractories used.
Sidney Gilchrist Thomas (1850-1885)
The discovery by Sidney Gilchrist Thomas and his cousin Percy Gilchrist in 1878 that phosphorus could be removed from steel melted in a dolomite-lined Bessemer converter (and subsequently on a dolomite hearth) was an important development.
They solved a problem that had defeated the leading metallurgists of the day. In addition, what is even more remarkable is that Thomas, who had initially wanted to be a doctor, was a magistrate’s clerk at Thames police court in London.
Out of interest he attended evening classes in chemistry, and later metallurgy, at Birkbeck Mechanics Institute (now Birkbeck College, University of London), where he became aware of the phosphorus problem. It took three attempts (over a 1-year period) by Thomas and Gilchrist to report the successful outcome of their work to the Iron and Steel Institute. A lesson in perseverance! When their paper was finally presented (Thomas and Gilchrist, 1879) the success of their process had become widely known and they attracted an international audience.
Dolomite refractories are made from a calcined natural mineral of the composition CaCO3 ・ MgCO3. The production of magnesite, a more slag-resistant refractory than dolomite, began in 1880. Magnesite refractories consist mainly of the mineral periclase (MgO); a typical composition will be in the range MgO 83–93% and Fe2O3 2–7%.
Historically, natural magnesite (MgCO3) that was calcined provided the raw material for this refractory. With increased demands for higher temperatures and fewer process impurities, higher purity magnesia from seawater and brine has been used.
In 1931 it was discovered that the tensile strength of mixtures of magnesite and chrome ore was higher than that of either material alone, which led to the first chrome– magnesite bricks. Chrome refractories are made from naturally occurring chrome ore, which has a typical composition in the range Cr2O3 30–45% Al2O3 15–33%, SiO2 11–17%, and FeO 3–6%. Chrome–magnesite refractories have a ratio of 70 : 30, chrome : magnesia. Such bricks have a higher resistance to thermal shock and are less liable to change size at high temperatures than magnesite, which they replaced in open-hearth furnaces. The new refractories also replaced silica in the furnace roof, which allowed superior operating temperatures with the benefits that these furnaces were faster and more economical than furnaces with silica roofs.
Finally, not the least important development in refractories was the introduction of carbon blocks to replace fireclay (compositions similar to kaolinite) refractories in the hearths of blast furnaces making pig iron. Early experience was so successful that the “all carbon blast furnace” seemed a possibility. These hopes were not realized because later experience showed that there was sufficient oxygen in the upper regions of the furnace to oxidize the carbon and hence preclude its use there.
As in the history of other ceramics, the great progress in refractories was partly due to developments in scientific understanding and the use of new characterization methods. Development of phase equilibrium diagrams and the use of X-ray diffraction and light microscopy increased the understanding of the action of slags and fluxes on refractories, and also of the effect of composition on the properties of the refractories.