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International Journal of Energetic Materials and Chemical Propulsion
ESCI SJR: 0.142 SNIP: 0.16 CiteScore™: 0.29

ISSN Imprimir: 2150-766X
ISSN On-line: 2150-7678

International Journal of Energetic Materials and Chemical Propulsion

DOI: 10.1615/IntJEnergeticMaterialsChemProp.v2.i1-6.110
pages 211-217

A SIMPLE MODEL OF THE OXIDATION KINETICS OF BORON IN A MEDIUM CONTAINING WATER VAPOR

R. Sontgen
DLR-Institute for Chemical Propulsion and Engineering, D-7101 Hardthausen a.K., Germany
A. Friedrich
DLR-Institute for Chemical Propulsion and Engineering, D-7101 Hardthausen a.K., Germany

RESUMO

The oxidation behavior of elementary boron in humid atmospheres is studied in the temperature range between 973 and 1373 К by thermoanalytical methods. In the absence of water vapor, boron forms protective surface layers of B2O3 following a parabolic rate law. In pure oxygen at temperatures above the melting point of B2O3, after an induction period of about 8 min a spontaneous ignition is observed. In air as in a pure oxygen atmosphere, the oxidator is oxygen.
Water vapor changes the reaction mechanism. The oxidator oxygen is substituted by gaseous H2O at temperatures above 810 K, consuming the whole boron by formation of boron oxide and hydrogen. The reaction rate depends only slightly upon the water content of the surrounding atmosphere. Hydrogen is detected by gaschromatography in the exhaust gas. In addition, the oxide layer is diminished due to an enhanced evaporation of metaboric acid formed at the outer sphere of the coated boron grain.


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