Zhang R H, Zhang X T, Hu S M
Open Research Laboratory of Geochemical Kinetics, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Baiwanzhuang Road 26, Beijing 100037, PR China.
Anal Chem. 2008 Apr 15;80(8):2982-7. doi: 10.1021/ac070684u. Epub 2008 Mar 18.
The aim of this study is to develop new pH sensors that can be used to test and monitor hydrogen ion activity in hydrothermal conditions. A Zr/ZrO2 oxidation electrode is fabricated for in situ pH measurement of high-temperature aqueous solutions. This sensor responds rapidly and precisely to pH over a wide range of temperature and pressure. The Zr/ZrO2 electrode was made by oxidizing zirconium metal wire with Na2CO3 melt, which produced a thin film of ZrO2 on its surface. Thus, an oxidation-reduction electrode was produced. The Zr/ZrO2 electrode has a good electrochemical stability over a wide range of pH in high-temperature aqueous solutions when used with a Ag/AgCl reference electrode. Measurements of the Zr/ZrO2 sensor potential against a Ag/AgCl reference electrode is shown to vary linearly with pH between temperatures 20 and 200 degrees C. The slope of the potential versus pH at high temperature is slightly below the theoretical value indicated by the Nernst equation; such deviation is attributed to the fact that the sensor is not strictly at equilibrium with the solution to be tested in a short period of time. The Zr/ZrO2 sensor can be calibrated over the conditions that exist in the natural deep-seawater. Our studies showed that the Zr/ZrO2 electrode is a suitable pH sensor for the hydrothermal systems at midocean ridge or other geothermal systems with the high-temperature environment. Yttria-stabilized zirconia sensors have also been used to investigate the pH of hydrothermal fluids in hot springs vents at midocean ridge. These sensors, however, are not sensitive below 200 degrees C. Zr/ZrO2 sensors have wider temperature range and can be severed as good alternative sensors for measuring the pH of hydrothermal fluids.
本研究的目的是开发新型pH传感器，用于测试和监测热液条件下的氢离子活性。制备了一种Zr/ZrO₂氧化电极，用于高温水溶液的原位pH测量。该传感器在很宽的温度和压力范围内对pH响应迅速且精确。Zr/ZrO₂电极是通过用Na₂CO₃熔体氧化锆金属丝制成的，其表面生成了一层ZrO₂薄膜。由此，制成了一个氧化还原电极。当与Ag/AgCl参比电极一起使用时，Zr/ZrO₂电极在高温水溶液中很宽的pH范围内具有良好的电化学稳定性。Zr/ZrO₂传感器相对于Ag/AgCl参比电极的电位测量结果表明，在20至200摄氏度之间，其电位随pH呈线性变化。高温下电位对pH的斜率略低于能斯特方程所示的理论值；这种偏差归因于传感器在短时间内与待测溶液并非严格处于平衡状态这一事实。Zr/ZrO₂传感器可在天然深海海水存在的条件下进行校准。我们的研究表明，Zr/ZrO₂电极是适用于大洋中脊热液系统或其他具有高温环境的地热系统的pH传感器。氧化钇稳定的氧化锆传感器也已用于研究大洋中脊热泉喷口处热液流体的pH值。然而，这些传感器在200摄氏度以下不敏感。Zr/ZrO₂传感器具有更宽的温度范围，可作为测量热液流体pH值的良好替代传感器。
