Abstract
A thorough study was made of the effect of temperature on the chemical combination of lime and silica in their mixtures.
Chemically pure calcium carbonate and sillca were proportioned in the molecular ratios of 3:1, 2:1, 3:2 and 1:1, and the mixtures were heated at temperatures ranging from 600° to 1800°C for 30 to 120 min. The products were analyzed for calcium carbonate, free lime and free silica, and the amounts and molecular ratios of combined lime and silica were calculated; also their true specific gravities were determined.
Some difficulties were encountered in the determination of free silica in those samples which had been heated at comparatively low temperatures, since it was more or less soluble in 5% aqueous solution of sodium carbonate. Therefore the silica ignited at 1350°C was used for their these samples.
Rathke's method of determining free lime was improved and the vessels containing the samples and grycerine were heated on a mechanical shaker in an electric oven of a constant temperature; the requisite temperature and time were also determined.
The authors succeeded in obtaining 100.00% pure 3CaO·SiO2, 100.00% pure 2CaO·SiO2, 99.80% pure 3CaO·2SiO2 and 99.72% pure CaO·SiO2 by heating corresponding raw mixturea at 1800°C (2hr.), 1700°C (1hr.), 1475°C (0.5hr.) and 1540°C (0.5hr.) resp.
The reaction between CaCO3 and SiO2 began already at 600°C, the velocity rising suddenly at 800° to 900° and being retarded at about 1200° and up.
The processes in the molecular ratios of combined lime and silica with the rise of temperature are discussed for the four mixtures.
