Abstract
Etching plays an important role in the production of superconducting cavities (SRF). As other laboratories engaged in RF superconductivity R and D did, FNAL is also developing a facility for the chemical etching of niobium (Nb) cavities. Two techniques are common accepted for cavity etching: (1) chemical etching--buffered chemical polishing (BCP); and (2) Electropolishing (EP). Among them, at FNAL it was decided to pursue chemical etching, which is considered a reliable technique tested by several labs for many years. In the past, numerous mixtures of acids have been tested leading to the actual buffered chemical polishing mix (BCP) characterized by the following composition by volume: 1 of HF 49 %wt; 1 of HNO{sub 3} 69.5 %wt; 2 of H{sub 3}PO{sub 4} 85 %wt. Because of the dangerous nature of the chemicals involved, safety considerations require the development of a proper process and a reliable control algorithm. For the post-processing rinsing of the cavities, one needs to know the expected pH of the water used to rinse the cavity. On the other hand, for early detection of leaks in the hydraulic system, which is done by measuring the conductivity of the rinsing water used in the process, one needs to understand the relationship between pH and resistivity of the diluted BCP mix. This report is an attempt to address these issues.
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