Chemical Etching Facility at NSCL

Chemical etching of the 161 MHz quarter-wave resonator.

    After fabrication of an SRF cavity, chemical etching is performed to remove a layer of material and expose a pure metallic surface.  A Buffered Chemical Polish (BCP) solution is used for etching of niobium.  The etching must be done with care in order to make sure that excess hydrogen does not become dissolved in the bulk Nb, as this may lead to the formation of a lossy hydride layer on the cavity surface.  Proper procedures must be followed in order to carry out the etching safely.

    A chemical etching facility has been set up at NSCL for etching prototype cavities.  A closed-loop system is used to pump the acid through the cavity.  A chiller in the loop is used to remove the heat of reaction from the acid.  The gases produced in the reaction are vented through a scrubber.

    The chemistry facility has been used to etch single-cell elliptical cavities, a half-wave resonator, and two quarter-wave resonators.

Related Internal Reports

Etching of Niobium in Buffered Chemical Polish in a Small Ventilated Room

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Abstract:  A small room was designed and built for the etching of niobium in buffered chemical polish (BCP).  The design and operation of the room is described.  The safety precautions used in protecting the operator from the acids used in the etching solution and from the fumes given of during the process are discussed. The quantity of nitrogen dioxide given off during etching in 18°C BCP was found to be 0.14 mg per minute per inch squared of niobium surface exposed.

Non-Temperature Controlled Etching of Niobium in BCP

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Abstract:  The etching of a square 1 inch niobium wafer in BCP solution is described.  The etch rate in a non-agitated solution was found to be 1.4 mm/min with an average temperature of 29°C.  When the wafer was slowly swirled in the solution, the etch rate increased to 3.5 mm/min.  Recommendations for further experiments are included.

Heat of Reaction of Niobium in Buffered Chemical Polish

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Abstract:  The heat of reaction of niobium in BCP was determined by a labscale experiment performed in a vent hood.  The reaction was allowed to occur over a temperature range of 20°C to 25°C over a five to seven minute time scale in a nearly adiabatic container.  One milliliter of BCP was found to heat up 0.37°C for every gram of niobium etched.  This corresponds to an approximate heat of reaction of 770 kJ/mol of niobium etched.