30 Sep 2010

Inorganic Chemistry of Organ Pipes: Composition and Corrosion

Five Slides About

Submitted by Catherine Oertel, Oberlin College

This presentation provides an inorganic chemist's perspective on metals used to make organ pipes and their corrosion and conservation.  The slides highlight my own research in this area as well as work being done by other scientists around the world.  The purpose of this learning object is to show students an application of inorganic chemistry that they probably have not encountered before and show an example of how analytical methods of materials chemistry can be used in conservation science.   

The Power Point presentation contains nine slides, including the title slide and a slide with additional references.  The Word file containing accompanying notes provides background information corresponding to each slide.

Learning Goals: 

1.  A student should be able to identify the material that is most commonly used to make organ pipes.

2.  A student should be able to describe the chemical process through which atmospheric corrosion occurs.

3.  A student should be able to give examples of experimental methods that are used to study organ pipe corrosion. 

Implementation Notes: 

This learning object is part of a lecture I have developed on inorganic chemistry in art conservation.  Each year, I devote the final class of the semester in my sophomore/junior-level inorganic chemistry course to this topic.  I briefly introduce some ideas about conservation science and then present several case studies showing questions about artifacts or problems of deterioration that have been addressed through scientific analysis.  These include studies of paint discoloration on a portrait and the conservation of a wrecked ship as well as my work on organ pipe corrosion.  I intend this last-class lecture to be interesting and enjoyable, and I let students know that I don't expect them to take in all the details as they might in a normal lecture.  I do point out that during the lecture, we'll briefly touch on and review many inorganic chemistry topics from the semester.

Information about the other case studies and the introduction to conservation science are to come in future "Five Slides" installments!

Evaluation Methods: 

Because of the recreational nature of my last-class lecture, I have not created a problem set to accompany it.  As an exam question, I have asked students to identify the redox reactions involved in atmospheric corrosion.

Creative Commons License: 
Creative Commons Licence


I've frequently mentioned the gray to white tin transistion that occurs somewhat below room temperature and which I understand gives rise to the "tin disease" that organ pipes suffered in Northern Europe before churches were heated. Perhaps this would be an approriate inclusion in future slides?

Catherine, I was preparing my notes for class tomorrow and was also going to use John's example of "tin disease" for phase transformations (we just finished talking about metallic structures).  Can you comment on the validity of these stories?  Has the phase change from beta to alpha tin actually been documented in cold Northern European churches or is this an "urban myth" of chemistry?

Maggie, I didn't see your comment until today.  I'll have to check on how I am receiving updates from VIPEr.  Anyway, I'd say that the tin phase transition is more than an "urban myth", but at the same time, it's hard for researchers to show definitively that it is taking place.  There are examples of tin-rich pipes that have blister-like areas of decomposition where the metal has become flaky and dull.  The appearance is quite different from what is seen in areas of damage due to atmospheric corrosion.  The blisters are consistent with what is seen when higher-density beta-tin converts to lower-density alpha-tin.  However, XRD analysis of the damaged pipes shows tin oxide and beta-tin but not alpha-tin.  This could be because the tin converts back to the beta phase upon warming but of course does not go back to the smooth appearance of the original tin sheet.  The damage is done, but unless the pipe were kept at low temperature continuously, including in the XRD experiment, it's hard to catch the alpha phase "in action."  There is, incidentally, quite an amazing YouTube video showing the beta to alpha transformation: http://www.youtube.com/watch?v=sXB83Heh3_c      

You can see how a metal object would never regain its original form even if the transition were reversed! 

I've been intending to add some images of this type of damage on organ pipes to my "five slides".  Your question reminded me to work on that! 


That YouTube video is AWESOME!!  Thanks for sharing, and I am definitely going to show that one to my class.

I use this example frequently in talking about phase transitions.  At the intro level, I find it useful to let students know that the S, L, V perspective on the world actually leaves out a lot of interesting phase transition behavior, and a very rich morpohology found in many condensed phases.  The tin pest videos are a great addition - and this is also one of the (many) issues that faced Napoleon's army on the Russian steppes - their uniform buttons were made of tin.

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