A study of the thermal decomposition of BaCO 3
- PDF / 784,679 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 35 Downloads / 183 Views
I.
1I.
INTRODUCTION
THE use of BaO in sulfur/phosphorus refining slags in iron- and steelmaking is getting increased attention due to the higher basicity of BaO compared to CaO. Lower sulfur/phosphorus contents and faster refining rates could be achieved by adding BaO to the slag along with CaO.tq By adding barium carbonate to hot metal, the stirring effect will be enhanced due to the evolution of CO z gas. It has also been shown that BaO can be used to remove N in industrial processes, t2] Even in the development of a solidstate reaction method for the synthesis of superconducting ceramics, e.g., YBa~Cu3Ox, BaCO3 is decomposed to form the complex oxide phase. [3J A knowledge of the kinetics of the decomposition of BaCO3 would be helpful in understanding and optimizing these processes. The decomposition of BaCO3 has been studied by several researchers53-~] As early as 1937, Hackspill and Wolfe [71 reported eutectic reaction between BaCO3 and BaO in the BaCO3-BaO system. Lander~41 found that the eutectic reaction occurred at 1303(_ 3) K. BakertS~carried out a phase diagram study for this system at different pressures of carbon dioxide. The phase diagram proposed by Baker is reproduced in Figure 1. According to this phase diagram, the eutectic point is at 1333 K and 0.00661 atm. The formation of the liquid due to the eutectic reaction could complicate the process of decomposition. To the knowledge of the present authors, a systematic study of the kinetics of decomposition of BaCO3 to date has not been carried out. The present investigation seeks to obtain an understanding of the kinetics and mechanism of the decomposition of the BaCO 3 by simultaneous thermogravimetric analysis (TGA) and differential thermal analysis (DTA).
EXPERIMENTAL
A. Materials BaCO3 powder (99.999 pct pure) was supplied by Aldrich Chemic (Steinheim, Germany). In view of the hygroscopic nature of BaCO 3, the powder was first calcined at 673 K for 24 hours and preserved in a desiccator. The calcined powder was well ground in an agate mortar under Ar atmosphere just before being used in the thermal analysis. In some experiments, dense spheres were used. The spheres were prepared by mixing a small amount of acetone in the BaCO 3 powder and pressing the mixture isostatically in silicon-rubber molds. In one of the spheres, a Pt-10 pct Rh/Pt thermocouple was embedded in the center during pressing. These were later sintered in a muffle furnace at 673 K for 24 hours. After sintering, the spheres had a diameter of I. 1 cm and a weight of 2.2 g, which would give a porosity of less than 8 pct. Anhydrous aluminum oxide powder (chloride < 0.02 wt pct, sulfate < 0.05 wt pct, arsenic < 0.0005 wt pct, and iron < 0.02 wt pct) obtained from E. Merck (Darmstadt, Germany) was used as the reference substance in DTA measurements. This was heated up to 1573 K to remove the adsorbates before use. The argon gas (maximum of 2 ppm impurity) and CO2 gas (>99.998 pet pure) used during thermal analysis were supplied by AGA Gas (Stockholm).
B. Apparatus and Procedure Th
Data Loading...
