Kinetics and mechanism of ferrous spinel oxidation studied by electrical conductivity and thermogravimetry

A mechanism of valence transfer between Fe²⁺ and Fe³⁺ ions in the octahedral, as well as the tetrahedral position of the spinel lattice is suggested to account for the electrical behaviour with the number of Fe²⁺-Fe³⁺ pairs in either position for oxidation reactions in finely-grained ferrous spinels. From the =f(t) curves which are identified with those obtained in thermogravimetry, it was established for inverse spinels such as Fe₃O₄ or for normal spinels such as FeCr₂O₄ that the kinetics is governed by a diffusion law under variable working conditions. For more complex spinels such as chromium-or titanium-substituted magnetites which exhibit both Fe²⁺ ions on octahedral and tetrahedral sites, the results are discussed only qualitatively although the profile of the =f(t) curves can also be related to the electronic exchange between the Fe²⁺ and Fe³⁺ ions from the two cation sites.     

Numerical and experimental study of a nonisothermal turbulent jet with a heavy impurity

Temperature and momentum distributions of the carrier phase are determined experimentally and compared to results of numerical calculations using the (k–) model.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 5, pp. 735–743, May, 1986.