2887.     ROGINSKIĬ, S. Z., AND TSELLINSKAYA, T. F.  Experimental Investigation of the Role of Supersaturation in the Preparation of Catalysts.  Acta physicochim, U.R.S.S., vol. 19, 1944, pp. 225-247 (in English); Jour. Phys. Chem. (U.S.S.R.), vol. 18, 1944, p. 477-492; Chem. Abs., vol. 39, 1945, p. 2447.

        Pyrolytic decomposition of NiCO₃ is a centripetal topochemical reaction.  The decomposition was affected in an apparatus in which the CO₂ pressure (pT) was controlled by freezing out CO₂ in a cryostat maintained at various temperatures.  the supersaturation (A) of the genetic reaction is defined as A=RT in (pT/pT’), in which pT is the equilibrium pressure of CO₂ at the surface of the solid.  The decomposition of NiCO₃ is autocatalytic; the reaction velocity increases with increasing supersaturation.  This decomposition is extremely rapid at CO₂ partial pressures of 10^-4 to 10^-2 mm. of Hg; near the equilibrium pressure the decomposition is slow.  The rate constant varies exponently with the temperature.  The apparent activation energies for the decomposition are 11,000 cal. per mol. for Δ F=constant, 17,000 for p_co2=3X10^-3 mm., 15,000 for p=2 mm., and 11,000 for p=10 mm.  Up to its maximum, the reaction velocity obeys an approximate quadratic law; hence the process involves primarily the development of formerly existing initiation centers, as is true for the decomposition of Ni formate (abs. 703). The values of the reciprocals of the times needed to attain a definite degree of decomposition increase almost linearly with the supersaturation.  A plot of velocity versus % of decomposition shows a maximum for each temperature and CO₂ pressure; this maximum is at 5-10% decomposition and is only slightly dependent on the experimental conditions.  The H₂O content of the sample of NiCO₃ has a peculiar, and as yet unexplained, effect on the kinetics of the decomposition.

        ROĬTER, V. A.  See abs. 1164, 1165.