Risks

Hydrofluoric acid (HF) is a corrosive chemical that is extremely toxic to human tissue that will dissolve glass.

Industrial process streams must be treated to reduce fluoride concentrations to meet mandated waste discharge limits.

HF Uses

HF is used in many industrial processes including: to make refrigerants, as a metal cleaner and stainless steel pickling agent, aluminum can etching, to remove silicon dioxide in semiconductor wafer production, to etch glass, chrome and enamel products.

Problems for Electrodes

Low pH in the presence of high HF levels destroys general purpose fluoride and pH sensors.

HF dissolves the glass in most commercial pH sensors. Etching solutions drain the sensor's reference  of its internal salts, which causes drifting.

In treatment, fluoride is converted to calcium fluoride salt for removal, but also precipitates onto the sensing element and reference surface, reducing sensor response.

Most fluoride ion selective electrode sensing elements and reference junctions are destroyed by the low pH solution being measured.

A Better Fluoride Electrode

The fluoride electrode's sensing element is protected from acidic solutions by a special seal.

The solid state polymer reference junction is engineered to resist acid, fluoride and shifting that can occur in high ionic strength solutions.

The reference surface surrounding the sensor tip can withstand cleaning with concentrated or dilute hydrochloric acid as well as abrasive removal, even scraping with a razor knife, of hardened deposits.

The sensor is fully submersible due to chemical resistant materials used for waterproofing.

A Better pH Sensor

pH sensors feature specially formulated, true HF resistant, thick wall low profile parabolic break resistant glass.

Deposits can be removed from the solid state reference surface with concentrated or dilute hydrchloric acid and by abrasive scrubbing or scraping to produce a clean "new" surface.

Thicker pH glass used with some sensors doesn't offer true HF resistance, it only slows the rate of degradation.

ISFET and antimony based pH sensors have HF resistance but lack the stability and accuracy of a glass element sensor.

Cable and sensor waterproofing is provided with chemical resistant flexible tubing and sealant to allow full submersion into the process fluid.

System Summary

Concentration range: 0.019 - 19,000 ppm, possibly to saturation in select applications

pH range: 0 - 9.5 pH continuous

Standard System Results: free fluoride, pH, pH compensated total free fluoride

Available with analog or smart digital pH sensors