PHYSICAL MODEL FOR ELECTROCHEMICAL OXIDATION OF COMPOSITE CERAMICS 

 
V.A. Lavrenko 1,
 
I.Podchernyaeva 1,
      
V.F. Labynets 2
 

1 I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Omeliana Pritsaka str.,3, Kyiv, 03142, Ukraine
2 National Aviation University, 1, Liubomyra Huzara ave., Kiev, 03058, Ukraine
sirote2910@gmail.com

Powder Metallurgy - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2021, #05/06
http://www.materials.kiev.ua/article/3241

Abstract

The paper examines the corrosion behavior of dense ZrB2-based ceramic samples in simulated seawater (3% NaCl solution) using polarization curves of electrochemical oxidation (ECO). The dense ceramic samples of 3–5% porosity were produced by hot pressing and had the following composition (wt.%): ZrB2, 77 ZrB2–23 SiC, 70 ZrB2–20 SiC–10 AlN, and 60 ZrB2–20 SiC–20 (Al2O3–ZrO2). The main ECO parameters were the conduction current i, corrosion current іcorr (i value at which di/dE decreased through diversion of some oxygen ions to oxidate the material) and anodic potential Ea (E value at which the protective oxide film failed (i > 0)). A two-stage model of the ECO process was proposed upon analysis of the experimental data. At the first stage (E < Ea, i = 0), an oxide film is formed on the working surface: the higher the protective function of the oxide film, the greater its thermodynamic stability. The second ECO stage (E > Ea, і > 0) has two steps of changing the conduction current і, carried by negative oxygen ions. The first step is characterized by an avalanche-like increase in i at E = Ea up to maximum i = icorr, at which the rate of change in i decreases with increasing anode potential (di/dE). At higher icorr (second step), the increase in icorr with greater E slows down through the interaction of oxygen with the test material, i.e., through oxidation. The higher the maximum icorr value, the greater the oxidation resistance of the material. According to the proposed model, the highest values of Ea and icorr in ECO conditions of ZrB2–SiC materials are reached when AlN is added as it promotes the formation of thermodynamically stable mullite in the protective film. An oxide addition, Al2O3–ZrO2, increases the oxidation resistance of the material (high icorr values) but does not change the composition of the outer borosilicate glass film. This explains the close values of the anodic potential of 77 ZrB2–23 SiC (Ea = 0.1 V) and 60 ZrB2–20 SiC–20 (68 Al2O3–32 ZrO2) composites (Ea =  0 V).


ALN, ANODE POTENTIAL, CORROSION CURRENT, ELECTROCHEMICAL OXIDATION, SIС, ULTRAHIGH-TEMPERATURE CERAMICS, ZRB2