pH Electrode

Porex designs a porous rod, with a consistent structure throughout, for a pH electrode that can be easily machined using standard workshop techniques – while also maintaining exacting tolerances. The company now offers a range of porous rods as custom or stock parts, depending on the customer’s needs.

Design Challenge:
Combination electrodes used in the measurement of pH include both sensing and reference elements in one body. In some designs, the junction separating the reference electrolyte from the sample solution is constructed of a porous material. To work effectively, this junction must consistently provide a defined performance over a wide thermal range and control the interface between the two disparate liquids within the system. Porex was asked to produce a porous shape, exhibiting a consistent structure throughout, for a pH electrode that could easily be machined to exacting tolerances.

Solution:
Porous junctions must securely press-fit into precision glass tubing. Recent designs have specified rods incorporating sealing rings and grooves to accommodate O-rings. Molding does not allow the close tolerances required, which resulted in the preference for precision machining after sintering. Porex engineers solved the challenge by using porous granules from our membrane manufacturing line, comprising 100 percent PTFE. This not only met the chemical and thermal requirements of the application, but it also virtually eliminated the possibility of cross-contamination from lubricants, salts, solvents or other elements. Secondly, a compression process was developed to ensure that uniform pressure was applied across all sections of the component with a consistent, specified porosity. As a result, the Porex PTFE rod has a consistent structure throughout, allowing maximum use of material during the machining process.

Result:
Porex now offers a range of porous rods that can be machined using standard workshop techniques, tool angles, etc., while maintaining exacting tolerances. Customers have the choice of purchasing either custom parts or stock rod depending on their application needs.

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