Equilibrium oxygen pressures of the univariant systems
normalNi‐normalNiO‐NiAl2O4
, and
normalNi‐NiAl2.54O4.81‐Al2O3
were determined between 1123 and 1423 K using galvanic cells with calcia‐stabilized zirconia as the solid electrolyte. Slipcast tubes of a two‐phase mixture of
β‐normaland α‐Al2O3
were used as electrolyte in cells to determine the equilibrium oxygen pressures of the univariant
normalNi‐NiAl2.54O4.81‐Al2O3
between 923 and 1173 K and the dissociation pressure of
Al2O3
equilibrated with (Ni‐Al) alloys containing 0.17, 1.19, and 2.36 atomic percent Al at 1213 K. The free energy of formation of
NiAl2.54O4.81
was determined between 923 and 1423 K. An electron probe microanalyzer was used to determine the composition of oxides and alloy phases of the ternary Ni‐Al‐O system that coexist with each other at 1273 K. The Ni‐Al‐O isotherm at 1273 K and Ni‐Al‐O equilibrium oxygen pressure diagrams at 1213 and 1273 K are presented.
OXYGEN
SummaryIncremental growth rates in dry oxygen of oxides on silicon in the same furnace are found to differ by more than two. These rates are directly related to the index of refraction of the initial oxide film and thus to the original growth temperature. Therefore, there seems to be a change in diffusion rate because of a change in the oxide structure with growth temperature. This structure factor when added to the activation energy for the diffusion of oxygen through fused quartz could account for the higher effective activation energy of the parabolic rate constants usually observed. The activation energy for growth of oxide on <100> silicon should be higher than that on <111> silicon.
AcknowledgmentI should like to express my thanks to H. R. Philipp for his encouragement in the course Of this work.
The sodium oxide activity in the a-A1203 + ~-A1203 coexistence was determined between 823 and 1198 K by relating measured values of the electromotive force of cells of the type Pt[M, MX2, NamX[~-and a-AI~O~[M', M'nO[Pt and the Gibbs energy change of the cell reaction which can be written as M + 2Na~X + taM'nO = mNa20(~) + MX2 + mnM' where X refers to halide or sulfide anion. The dependence of activity, aNa~o, On temperature, T (K), is 16,400 log aNglO = --+ 3.60 (823--~-T --1198 K) * Electrochemical Society Active aMember.
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