The modern understanding of the glass electrode response
The modern understanding of the glass electrode response
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对玻璃电极响应的现代理解
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
F. Baucke
中科院分区：
文献类型：
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作者：
F. Baucke
电化学实验结合红外光谱和亚表面浓度谱分析得到了玻璃电极膜表面离子过程的信息，并得出了玻璃电极响应的详细机制。这种“解离机制”是基于玻璃表面阴离子基团与溶液中的氢离子或碱离子之间的相边界平衡，它控制着玻璃的电位和附着在表面基团上的离子浓度。由此产生的玻璃表面和大块玻璃之间的浓度梯度导致不同离子的相互扩散，如果它们不受空间阻碍渗透到玻璃中，并且在玻璃表面下产生扩散势。相互扩散决定了玻璃腐蚀的过程，因此取决于质子或碱离子是否附着在玻璃表面并与玻璃的碱离子相互扩散，分别导致稳定的浸出层或不断生长的碱交换层。含有la2o3的膜玻璃的pH电极在中性和碱性磷酸盐和氟溶液中显示出延迟的干扰电位漂移，分别是由LaPO4和LaF3沉积在膜表面引起的（“磷酸盐”和“氟误差”）。在热力学和动力学的基础上推导了相边界势和相边界浓度的方程，并进行了实验验证。研究了玻璃浸出和碱离子的相互扩散，确定了浸出层内的扩散势。解释了pH和pM玻璃电极的形成周期，并检测了钠误差的间接部分和不可逆钠误差。浸出和碱交换层由改性玻璃组成，而不是一般认为的“凝胶”层。相边界平衡的大交换电流密度解释了玻璃电极电位的稳定性。迁移实验和随后的浓度谱分析表明，玻璃可以是碱离子、质子和碱离子-质子混合导体，并且在硅酸锂玻璃中产生了锂离子和替代质子的浓度依赖迁移率。在无碱溶液中，场驱动质子化前后膜的pH响应不变，排除了离子交换理论假设的不同离子交换作为玻璃电极响应的来源，验证了解离机制。
Electrochemical experiments in combination with infrared spectroscopy and subsurface concentration profiling yielded information on ionic processes at the membrane surface of glass electrodes and resulted in a detailed mechanism of the glass electrode response. This “dissociation mechanism” is based on phase boundary equilibria between anionic groups at the glass surface and hydrogen or alkali ions in the solution, which control the potential of the glass and the concentrations of ions attached to the surface groups. The resulting concentration gradients between glass surface and bulk glass cause an interdiffusion of the different ions, if they are not hindered sterically to penetrate into the glass, and a diffusion potential beneath the glass surface. The interdiffusion determines the course of the glass corrosion, which thus depends on whether protons or alkali ions are attached to the surface and interdiffuse with the alkali ions of the glass, leading, respectively, to a steady-state leached layer or a continuously growing alkali-exchanged layer. pH electrodes with La2O3-containing membrane glasses show delayed interfering potential drifts in neutral and alkali phosphate and fluoride solutions caused by LaPO4 and LaF3 deposits, respectively, at the membrane surface (“phosphate” and “fluoride errors”). Equations for the phase boundary potential and phase boundary concentrations are derived on a thermodynamic and kinetic basis and are verified experimentally. Glass leaching and alkali ion interdiffusion are studied, and the diffusion potential within a leached layer is determined. The formation periods of pH and of pM glass electrodes are explained, and an indirect part of the sodium error and an irreversible sodium error are detected. Leached and alkali-exchanged layers consist of modified glass and are not “gel” layers as generally assumed. Large exchange current densities of the phase boundary equilibria explain the stability of glass electrode potentials. Migration experiments with subsequent concentration profiling showed that glasses can be alkali ion, proton, and mixed alkali ion-proton conductors and yielded concentration-dependent mobilities of lithium ions and replacing protons in a lithium silicate glass. The unchanged pH response of membranes before and after field-driven protonation, in alkali-free solutions, excludes the exchange of different ions as the origin of the glass electrode response, as assumed by the ion exchange theory, and verifies the dissociation mechanism.