Low-permeability microporous ceramic electrode rod

Core value and advantage of low permeability

1、 The connotation and physical mechanism of low permeability of microporous ceramics

Low permeability "has a precise definition here: it refers to the microporous ceramic membrane that allows ions to make small, controlled electrical contacts to maintain the conductivity of the electrochemical circuit, but at the same time greatly hinders rapid, high flow bidirectional convection and diffusion between the electrode filling solution (usually saturated KCl solution) and the external test solution.

The implementation of this characteristic relies on the precise physical structure of microporous ceramic materials. Ceramic materials (such as alumina, zirconia, etc.) undergo special formulations and high-temperature sintering processes to form a rigid, robust, and porous structure with a large number of interconnected pores at the nanometer or submicron level. These pores constitute the electrochemical "liquid interface".

• *Ionic conductivity: These tiny pore channels are filled with electrolyte, forming miniature "salt bridges". Ions in the solution can migrate through these channels, ensuring the integrity of the measurement circuit and establishing a stable electrochemical potential.
• *Solution Barrier: Due to the extremely small pore size, according to the principles of fluid mechanics, solutions in such narrow channels will experience significant capillary resistance and viscous forces. This effectively suppresses the overall flow (convection) of the solution caused by concentration differences (permeation), static pressure differences, or temperature fluctuations. The transport of matter mainly relies on slow ion diffusion processes.

In short, microporous ceramic membranes play a role as "ion sieves" and "flow limiters" in physics, achieving a delicate balance between "conducting electrical signals" and "blocking solution exchange".

2、 The core advantage brought by low permeability

• 1. Extraordinary long-term stability and ultra long lifespan: This is the most significant advantage of low permeability. In complex media such as concrete, soil, groundwater, or industrial wastewater, there are high concentrations of ions (such as Cl ⁻, SO ₄² ⁻) or chemicals present. If the permeability of the liquid interface is too high (such as using porous ceramics or fiber filaments), KCl inside the electrode will quickly dissipate, and harmful external components will reverse infiltrate, contaminating the Ag/AgCl filaments and electrolyte inside, causing irreversible drift of the reference potential and rapid electrode failure. The low-permeability characteristics of microporous ceramics slow down the harmful substance exchange process to the extreme, extending the stable working time of electrodes from days or weeks to months, years, or even decades, making them particularly suitable for long-term embedded or online monitoring scenarios that cannot be replaced.
• 2. Excellent anti pollution and anti clogging ability: When measuring in solutions containing proteins, oils, colloids, or suspended particles, traditional porous ceramic liquid interfaces are prone to blockage or contamination by these substances due to their large pores. Once blocked, the resistance of the liquid junction will increase sharply, and the liquid junction potential will become extremely unstable, leading to measurement signal drift or complete failure. The nanoscale pores of microporous ceramics can effectively physically block the invasion of these large molecules and particles, like a sturdy filter, ensuring the long-term cleanliness and functional stability of the liquid interface.
• 3. Stable liquid junction potential with good reproducibility : The liquid junction potential is an inherent and primary source of error for the reference electrode itself. When two solutions of different components meet at the liquid interface, a potential difference will occur due to the different ion migration rates. The low permeability of microporous ceramics makes the ion exchange process very slow and controlled, which helps to form a stable liquid interface potential with minimal temporal variation and good reproducibility, thereby fundamentally improving the accuracy and comparability of potential measurement.

3、 Application and necessary trade-offs

Due to the above advantages, microporous ceramic reference electrodes have become the preferred solution for pH/potential measurement in easily contaminated media such as civil engineering (concrete and steel corrosion monitoring), geological exploration, environmental science (long-term water quality monitoring), as well as food and biotechnology.

However, every technology has its trade-offs. Low permeability brings an inherent technical challenge: high liquid interface resistance. The narrow pores mean that the ion migration path is obstructed, resulting in a high resistance value of the ceramic membrane itself (usually tens of thousands to hundreds of thousands of ohms). Therefore, when using such electrodes, it is necessary to use an electrochemical workstation or high impedance potentiometer with extremely high input impedance (usually requiring>10 ¹² Ω) for measurement, otherwise the signal will be severely attenuated, resulting in inaccurate readings, slow response, or even complete data failure.

In summary, the low permeability characteristics of microporous ceramic reference electrodes are not simply "non permeability", but a precise and controlled "limited permeability". Through its unique microstructure, it sacrifices some conductivity in exchange for unparalleled long-term stability, anti-interference ability, and measurement accuracy, becoming an indispensable technical guarantee for reliable electrochemical monitoring in harsh environments.



Technical Parameters Table