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Disappearing platinum coating on alumina

I recently applied platinum to an alumina substrate in hopes of creating a high temperature reflective barrier. However, the previously-reflective platinum coating disappeared on exposure to low temperature (1250 C). Do you think the coating oxidized or diffused into the substrate, and do you have any ideas how to prevent the problem?

Steve Miller
university researcher - Flagstaff, Arizona

Hi, Steve. We may have received that temperature wrong due to the way different internet software interprets symbols like degree marks, but 1250 °C doesn't seem like a low temperature to me. Please clarify. Thanks

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

First of two simultaneous responses --

To answer your questions, we just want to know...

what is the thickness of pt was applied.
what is the surface preparation method you have adopted, before plating.
What is the salt you used for pt plating.
If we know the answer for the above questions, then only it is possible to clarify you the answer.

Vanajambika Jeyakumar
- Chennai, India

Second of two simultaneous responses --

Quoting the CRC Handbook of Chemistry & Physics [adv: on Amazon & AbeBooks & eBay (adv.)] , 64th ed.: " corroded by halogens, cyanides, sulfur, and caustic alkalis...dissolves in 'aqua regia'." Do you have any of those around? By the way Ted, the same source lists melting point as 1772 C.

Tom Gallant
- Long Beach, California, USA

First of two simultaneous responses --

I apologize for any confusion resulting from my editorial comments! I consider the temperature (1250 C) low relative to the melting point of platinum (1768 C). I have since repeated the experiments and found that the same thing occurs at lower temperatures.

Stephen Miller
- Flagstaff, Arizona, USA

Second of two simultaneous responses --

I agree with Ted, 1250 °C doesn't sound low temperature to me! What atmosphere is the reflector being exposed to? Remember that these temperatures, the electromagnetic spectrum could have an effect and if there is anything in the atmosphere that could react with the platinum, it will go like the clappers! Hopefully it is in a vacuum.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

I found this question while seeking the answer to my own, similar issues. It appears that platinum reacts with alumina, in a reducing atmosphere, and melts at less than 1200 C. I have this from direct experience in the last 24 hours.

Steve Taylor
- Manchester, UK
October 11, 2011

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