Stability towards heating and outgassing of activated carbon oxidized in the liquid phase
Abstract
The stabihty of the surface state of activated carbon oxidized in the liquid phase is checked under conditions of heating and outgassing. The oxidation was performed using aqueous solutions of H 2O 2,O 3, ClO 2, H 2SO 4, HNO 3, HClO 4, KIO 4 and KMnO 4. Also, the pH was varied in the case of H 2O 2, KIO 4 and KMnO 4, and the concentration was varied for HNO 3, KIO 4 and KMnO 4. The oxidizing agent strongly influences the thermal stability of the surface oxides that are removed by heat treatment between 35 and 800°C. It is generally higher for the substances with acidic properties; in particular HNO 3, but only when a concentrated solution is used in the oxidation of carbon. The release of surface oxides takes place to a larger extent for O 3 and HNO 3, although for the latter substance it depends on the concentration of the solution. In contrast to these oxidizing agents, thermally unstable oxygen complexes are not formed with ClO 2. In the treatment with a saturated solution of KMnO 4, the formation of insoluble substances which decompose on heating appears probable The thermal stability and the removal of surface oxides or reaction products increases at acidic pH values; this is affected by the concentration of HNO 3 or KMnO 4 but not by the concentration of KIO 4. The results do not always agree with those obtained when the samples are outgassed under vacuum. Thus, discrepancies are observed in the influence of pH and concentration on the stability.
- Publication:
-
Thermochimica Acta
- Pub Date:
- January 1991
- DOI:
- 10.1016/0040-6031(91)80268-N
- Bibcode:
- 1991TcAc..176..129G