Structure and simple principle of electroplated glass electrodes for electric heating tubes223 semiconductor electrode

Structure and simple principle of electroplated glass electrodes for electric heating tubes223 semiconductor electrode

The semiconductor junction of semiconductor field-effect transistors is sensitive to H+and can be made into semiconductor electrodes with small volumes. The author developed a portable pH timer for a friend in the 1980s and experimented with it. However, due to the high temperature coefficient of semiconductors (about 2mv/℃ for silicon semiconductors), although a temperature automatic compensation circuit was designed on the circuit to eliminate its impact, it was necessary to simultaneously measure the liquid temperature, which was complex and ultimately abandoned. It is used in medical practice to measure the pH value of blood.

224 antimony electrode

Antimony electrodes are sensitive to H+and are not easily broken. Industrial measurement and control wastewater has been sold as a product. But later it was found that it was also sensitive to chloride ions. It can be used in standard buffer solutions without Cl -, but the actual measurement system often contains Cl -, so it has little practical value.

225 glass electrode

In the 1980s, during a discussion with Japanese electroplating experts, the author was very concerned about the measurement and control of pH and sought advice. The answer was: "So far, only glass electrodes are practical electrodes that are sensitive to H+and have good selectivity." The actual usage situation is also the same, and almost all use this type of electrode.

Structure and Simple Principles of Glass Electrodes

To use glass electrodes correctly, one should have a minimum understanding of their structure and principles.

The glass electrode is a glass ball (or column) with a thickness of approximately 02mm and is filled with 01NHCl, followed by the insertion of a silver chloride electrode (which needs to be grounded with a metal spiral tube to prevent electrostatic effects). Namely:

ＡｇＡｇＣｌ,01ＮＨＣｌ

When the film of the glass electrode is between two different solutions, a potential difference will occur on both sides of the film Φ G (glass electrode membrane potential). The reason for its occurrence is still unclear, and a reasonable view is that H+in the solution can diffuse through the membrane, resulting in potential differences. It can be inferred that Φ There is a linear relationship between g and pH:

Φ ｇ= Φ ｇｏ-ＫｇｐＨ

In the equation Φ Go is the electrode potential of the glass electrode in a solution of aH+=1, and Kg is the electrode function of the glass electrode. Theoretically, it is 2303 RTF (R is the gas constant, F is the Faraday constant, and T is the open temperature), but in practice, it is often less than this value. Theoretically, when the pH values on both sides of the glass electrode are equal (placed in 01NHCl solution), there will be no difference in hydrogen ion concentration, which will cause H+to diffuse inward or outward, and the membrane potential should be equal to zero. But in reality, there is still a potential difference of around (0-30) mv, known as its asymmetric potential. Different electrodes of the same model have different values, so the first use must be corrected using a pH meter with standard buffer solution.

The actual measured pH range of the glass electrode should be between 1 and 90.

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