The authoritative public forum
  for Metal Finishing since 1989
-----

Fluoride is getting into etching bath

Hello

Can somebody tell me how fluoride gets into an etching batch in an anodizing line?

Jan de Hoop
- Hoogezand, The Netherlands
June 12, 2009

---

First of three simultaneous responses --

Ammonium Bifluoride and Sodium Fluoride are sometimes added to the alkaline etch to create a finer grain. Maybe some suppliers are now adding it to their product. Some USA municipalities add fluoride to the drinking water.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

June 17, 2009

---

Second of three simultaneous responses --

Jan

Sodium fluoride is added to some (commercially available) etches for whitening and leveling characteristics.

Willie Alexander
- Colorado Springs, Colorado
June 17, 2009

---

Third of three simultaneous responses -- June 18, 2009

Jan,

Can you give us some more details of your process such as the chemistry of the etch tank, the chemistry of the other tanks used in the process, a list of any other tanks in the area.

Some of the proprietary etch salts have what is known as dry acid salts (sodium ammonium bifluoride or ammonium bifluoride). These dissociate when dissolved in water giving a source of hydrofluoric acid for etching.

If you are using a self formulated solution then we really need to know the solution chemistry before we can help.

Brian Terry
Aerospace - Yeovil, Somerset, UK