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Hydrogen‐induced damage of lead‐zirconate‐titanate (PZT) Mohammadabadi, Ali Shafiei


Lead-Zirconate-Titanate Pb(Zr,Ti)O₃ (PZT) based actuators are evaluated by automotive industry for advanced fuel-injection systems, including hydrogen injection. However, hydrogen can have deleterious effect on the PZT's functionality and properties. The general objective of this work is to study the interactions between PZT and hydrogen. The results of long-term (200-1200 hours) high-pressure (10 MPa) hydrogen exposure on the PZT microstructure show that hydrogen has only superficial effects on the microstructure of bare PZT. However, when an electrode is attached to PZT, the hydrogen damage increased; a porous layer developed immediately adjacent to the electrodes on the PZT surface due to hydrogen spillover. The kinetics of the PZT structural modifications due to hydrogen was investigated by online monitoring of the electrical properties of PZT above the Curie temperature, up to 650°C. The results show that the structural changes can be described by the classical nucleation and growth theory. The growth of the new structure appears to be limited by the diffusion of protons into PZT, with a calculated activation energy of 0.44± 0.09 eV, at 450-650°C. Two relaxation peaks were observed in the dissipation factor curves of the hydrogen-treated PZT. While the kinetics of one of the relaxation peaks obeys the classical Arrhenius law with the activation energy of 0.66 eV, the other peak shows an unusual relaxation kinetic. The mechanisms for the formation of these relaxation peaks are determined. Low temperature (20°C) diffusion of hydrogen into the PZT was also studied, using the water electrolysis technique. Based on the microstructural observations, the diffusion coefficient of hydrogen in PZT was calculated as 9×10-¹¹ cm²/sec. The Maxwell-Wagner polarization mechanism is determined to be responsible for the changes in the hydrogen-affected PZT capacitance. In the last part of the project, alumina coatings were applied to PZT plates using the sol-gel technique, to explore the possibilities of decreasing H₂ damage to PZT. The functionality of the coating against hydrogen damage was evaluated by the water electrolysis technique. Significant decrease of hydrogen damage was observed even for highly porous coatings. The mechanisms by which the alumina coating decreases the hydrogen damage were tentatively proposed.

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