Desorptions- und Reaktionskinetik der Erdalkalien Calcium und Strontium mit Chlor an Wolfram. Teil I: Chemisches Gleichgewicht der Oberflächenreaktion M + Cl = MCl im stationären Zustand (M = Ca,Sr)

Desorption- and Reactionkinetics of the Alkaline Earth Elements Calcium and Strontium with Chlorine on a Tungsten Surface — Part I: Chemical Equilibrium of the Surface Reaction M + Cl ? MCl in the Steady State (M = Ca, Br) Utilizing positive and negative surface ionization the reaction M + Cl = MCl (M = Ca, Sr) was studied at a hot tungsten surface under steady state conditions. Comparing the results obtained either by simultaneous M- and Cl₂ -exposures or by MCl₂ -exposure the existence of chemical equilibrium could be confirmed for the reaction in the temperature interval 1600 K.2000 K; at higher temperatures this equilibrium can be disturbed considerably by the desorption of the reacting components. From the experimental results we obtained under conditions of chemical equilibrium the energy of dissociation of MCl-molecules in the gasphase (D = (3.9 ± 0.15) eV, D = (4.2 ± 0.15)eV) and in the case of a strong disturbance of the equilibrium the difference between the activation energies of desorption and of dissociation of MCl-molecules on the surface (? - D? = (1.6 ± 0.2) eV, ? - D? = (1.4 ± 0.2) eV).