純鋯金屬於超臨界純水環境的氧化現象

Oxidation Behavior Study of Pure Zirconium under SCW Environments

為進行超臨界狀態下金屬材料的電化學行為分析並獲取相關的電化學參數，除了建立一套適用於溫度374℃以上與壓力22.1 MPa以上的模擬超臨界水循環系統外，穩定且耐用的參考電極是不可或缺的。本研究主要研究目的在於研究純鋯金屬在超臨界環境下的氧化情形，以確定Zr/ZrO2是否適合當作參考電極，用以監測超臨界核反應器中的水化學變化。改變實驗溫度、溶氧條件，以掃描式電子顯微鏡進行氧化層的觀察，發現在100小時的時間實驗下，改變溶氧濃度所造成的氧化層差異並不明顯，而溫度為影響氧化層厚度的重要關鍵。400℃下，調整實驗環境之溶氧濃度及試片放置時間，進行耐久度的測試，發現在長時間1300小時的實驗下，溶氧濃度為8.3 ppm時氧化情況較劇烈，溶氧濃度的影響較顯著。

A lasting and sustainable reference electrode is necessary to analyze the electrochemical behaviors of metal materials under supercritical water (SCW) environment in which the temperature and pressure is greater than 374 ℃ and 22.1 MPa, respectively. In this study we investigate the oxidation behavior of zirconium in SCW environment at 400℃ to 500℃ and deaerated to 8.3ppm dissolved oxygen content to evaluate the performance of the Zr/ZrO2 reference electrode at elevated temperature. Furthermore, the durability of Zr/ZrO2 reference electrode was tested by changing the dissolved oxygen content in the water and immersion time.
The microstructure of the Zr and ZrO2 was characterized by using the scanning electron microscope (SEM). The results of our study show that the thickness of oxide layer is related to the temperature in the short immersion time and is less relevant to the dissolved oxygen content. However, for longer immersion time, the thickness of the oxidation layers is larger under 8.3 ppm of dissolved oxygen water environment at 400℃for 1300 hours.