Superequilibrium atomic hydrogen

It is well known that superequilibrium atomic hydrogen (SAH denoted by H ) produced by hot filament or plasma activation, as shown in Figure 1 (a) and (b), plays an important role during the diamond growth. Based on modern thermodynamics, the activated low-pressure vapor deposited diamond process can be regarded as a coupled reaction [13-19], consisting mainly of two simultaneous reactions. 

Table 1. Thennodynamic Data of Activated Graphite (gra ) during the Existence of Superequilibrium Atomic Hydrogen (Hot filament 2400 K, Ref. Temp. 298 K, Pressure range O.OIO-lOO kPa, x 0-28).

Figure 2. Nonequilibrium (stationary) phase diagrams for C-H system with the existence of superequilibrium concentration atomic hydrogen (O, CJ and A are experimental data reported by Matsumoto [6], Sato[10], and Southworth [11] etc.).

Figures 2 and 3 demonstrate calculations of the chemical-equilibration process in the detonation products of a stoichiometric acetylene-oxygen mixture at T = 3160 K and density equal to 0.11 kg/m (this point lies on the isentropic line passing through the C3 point of detonation in a mixture at the initial pressure 0.1 MPa and temperature 298 K). As seen from the figures at the first state CO2 forms by reaction CO-I-OH— C02+H since CO and OH are in superequilibrium concentrations. This increases rapidly the hydrogen atom concentration (Fig. 2) so that it reaches a superequilibrium value and then drops to the equilibrium level. Concentrations of the components involved in all the bimolecular reactions satisfy the detailed balance conditions after 1 fis (Fig. 3). At later states, recombination reactions with he rate limiting step CO-j-O-l-M—> C02+M start to be prevailing.

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