Experimental values for the ionization constant of water, pKw,m, from T = 373 K to T = 674 K and from p = 5.75 MPa to p = 31.15 MPa, have been derived from direct measurements of the electrical conductivity of very pure water at the University of Guelph, the University of Delaware, and the Oak Ridge National Laboratory using high-precision high-temperature flow-through AC electrical conductance instruments based on the design by Wood and co-workers [J. Phys. Chem. 99, 11612 (1995)]. The results compare well with published high-temperature potentiometric and calorimetric studies up to 573 K and are consistent with the 1981 and 2006 IAPWS (International Association for the Properties of Water and Steam) pKw,m formulations to within better than 0.1 pK units up to 598 K and to better than 0.2 pK units at 623 K. Above 623 K, the 2006 and 1981 IAPWS formulations showed systematic deviations from the new results, which reached two and five orders of magnitude near the critical point, respectively. Based on these conductivity studies and critically evaluated literature data, revised parameters for the Marshall–Franck and Bandura–Lvov equations of state are reported, which reproduce the experimental data with standard uncertainties u(pK) = 0.018 and u(pK) = 0.016, respectively, over the experimental temperature range at water densities from 1.00 g cm−3 to 0.20 g cm−3, which corresponds to T = 373 K–674 K from psat to p = 31 MPa, and over the range T = 273 K–373 K at p = 100 kPa. These new experimental conductivity results are the most accurate values to be reported under near-critical conditions for densities between 0.50 g cm−3 and 0.20 g cm−3.

中文翻译：

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高温高压下水的电离常数：直接电导率测量的新数据和修订后的配方从 T = 273 K 到 674 K 和 p = 0.1 MPa 到 31 MPa

水的电离常数 pKw,m 的实验值从 T = 373 K 到 T = 674 K 和从 p = 5.75 MPa 到 p = 31.15 MPa，是通过直接测量极纯水的电导率得出的圭尔夫大学、特拉华大学和橡树岭国家实验室使用基于 Wood 及其同事设计的高精度高温流通式交流电导仪 [J. 物理。化学 99, 11612 (1995)]。结果与已发表的高达 573 K 的高温电位和量热研究相得益彰，并且与 1981 年和 2006 年 IAPWS（国际水和蒸汽特性协会）pKw,m 配方一致，在高达 0.1 pK 单位以内598 K 并且在 623 K 时优于 0.2 pK 单位。高于 623 K，2006 年和 1981 年的 IAPWS 公式显示出与新结果的系统偏差，分别在临界点附近达到了两个和五个数量级。根据这些电导率研究和严格评估的文献数据，报告了 Marshall-Franck 和 Bandura-Lvov 状态方程的修正参数，这些参数再现了标准不确定度 u(pK) = 0.018 和 u(pK) = 0.016 的实验数据，分别在水密度从 1.00 g cm−3 到 0.20 g cm−3 的实验温度范围内，这对应于从 psat 到 p = 31 MPa 的 T = 373 K–674 K，以及在 T = 273 K–在 p = 100 kPa 时为 373 K。这些新的实验电导率结果是在密度介于 0.50 g cm-3 和 0.20 g cm-3 之间的近临界条件下报告的最准确值。