Etchant to reveal platinum welds

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Category: Physical Methods

Subject: Etchant to reveal platinum welds

Question

What etchant can be used to reveal welds in platinum group metals?

Answer

Platinum, rhodium, iridium and alloys can be electrolytically etched in a 10% HCl solution saturated with NaCl.

AC current should be used through a platinum wire pin and platinum cathode. We use 2–3 volts and moderate the current appropriately for sample surface area to avoid burning; typically 0.4–1.2 amps should suffice; the bottom end for platinum and rhodium.

It will generally take several minutes and better results are obtained if the sample is etched, re-polished and re-etched.

Answer posted 09 May 2007

Submitted by: Ms Sara Coles

Affiliation: Platinum Metals Review

Answered by: Robert McGrath

Affiliation: Johnson Matthey Noble Metals