Tests on clay materials available in Illinois coal mines . sts, trials l-)4x 1-Hx 3V? were hand molded andrepressed. For determining tempering water, volume shrinkage, lineardrying and burning shrinkages, porosity, tempering range, and color,briquets lx lx 3J4 were also hand molded and repressed. Allbriquets were dried in the open air at room temperature (about 70° F ). ( )xidation Tests During the process of burning red and buff clays, it is necessaryto burn out the carbon and sulphur and to convert the ferrous iron tothe ferric form before the temperature can be raised safely and theware vit
Tests on clay materials available in Illinois coal mines . sts, trials l-)4x 1-Hx 3V? were hand molded andrepressed. For determining tempering water, volume shrinkage, lineardrying and burning shrinkages, porosity, tempering range, and color,briquets lx lx 3J4 were also hand molded and repressed. Allbriquets were dried in the open air at room temperature (about 70° F ). ( )xidation Tests During the process of burning red and buff clays, it is necessaryto burn out the carbon and sulphur and to convert the ferrous iron tothe ferric form before the temperature can be raised safely and theware vitrified. This process is called oxidation and should be carried 20 CLAY MATERIALS IN ILLINOIS COAL MINES out within a temperature interval in which the ware is at its maximumporosity so as to allow the ingress of oxygen from the kiln atmosphereand the egress of gases due to distillation and combustion. If thetemperature of the kiln is raised to the vitrification stage before oxida-tion is complete, a black-cored or even bloated product will be Fig. 4.—A clay high in pyrite and carbon showing progress of diminishingblack core during oxidation. The trials were drawn from the kiln at one-hourintervals. Under practical working conditions it has been found that thebest range in which to hold the kiln until oxidation is complete liesbetween 600° C and 900° The most troublesome materials duringoxidation are bituminous matter, sulphur in the form of pyrite, ferrousoxide, and ferrous carbonate. As long as any carbon or combustiblesulphur is present, the iron remains in the ferrous form and is evi-denced by the resulting black core surrounded by an oxidized outershell of light salmon or buff color (fig. 4). According to Wells5 pyrite is dissociated at two different tempera-tures one molecule of sulphur coming off at 400° C, and the second re-maining until about 900° C. In the tests of the following shales itwas observed that the pyrite could be completely dissociate
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcoalmin, bookyear1917
