Chemical quasi-equilibria: a new concept in the description of reactive plasmas

Non-isothermal plasma chemical reactors are plasma sources of high complexity. This paper reviews some new aspects for a generalized overall description of such reactors. The main point of this concept consists in chemical quasi-equilibria, which, under some conditions, characterize the reactor state by an electronically modified mass action law. The existence of quasi-equilibria reflects the basic role of gross reactions even for non-isothermal plasma chemical conversions. From this, a foundation of the so-called method of macroscopic kinetics is possible which allows a very compact description of different plasmachemical reactors. We try to give a clear definition of the term chemical quasi-equilibrium and show the appearance of two types: CEEC (chemical equilibrium of electronic catalysis) and CECD (chemical equilibrium of complete (electronic) decomposition). The very important case of identical compositions (CEEC = CECD) is discussed as the starting point of the method of macroscopic kinetics. Within the bounds of this method the plasma chemical action of the reactor is governed by the specific energy (i.e. the physical work invested in the reaction mixture per unit volume during its passage through the plasma zone), and for different reactor conditions the chemical changes of the mixture can be described by only one kinetic curve in which the specific energy acts as a similarity parameter. Experimental results on the existence of plasma chemical quasi-equilibria are given, together with some first hints of their significance and possible applications.