High temperature and pressure chemical sensors based on Zr/ZrO 2 electrode prepared by nanostructured ZrO 2 film at Zr wire

Abstract

A Zr/ZrO 2 oxidation electrode was fabricated for in situ measurement of pH values of high temperature aqueous solutions. Combined with a Ag/AgCl reference electrode, the Zr/ZrO 2 sensor responded rapidly and precisely to the pH of the solutions over a wide range of temperatures. The Zr/ZrO 2 electrode was made by oxidizing Zr metal wire with a Na 2CO 3 melt to produce a thin film of ZrO 2 on the Zr wire surface. The nanostructure of the ZrO 2 thin film was characterized using high-resolution transmission electron microscopy (HRTEM) observations. The nature of the nanostructured ZrO 2 thin film on the Zr of the Zr/ZrO 2 electrode plays a vital role in the construction of Zr/ZrO 2 chemical sensors, particularly when the electrode is utilized for in situ measurement of the electrochemical parameters of aqueous solutions at high temperatures and pressures. Chemical analyses of the ZrO 2 thin films revealed that the Zr/ZrO 2 interface is divided into five zones from the outermost zone to the center: (1) prismatic and oxygen-rich ZrO 2 zone; (2) ZrO 2; (3) oxygen-rich Zr; (4) oxygen-bearing Zr; and (5) Zr metal. Especially, the outermost oxygen-rich ZrO 2 zone of the films is composed of nanometer-sized monoclinic crystals.