25 Jun 2011

Understanding phase diagrams of solid state alloys: Application to archeological studies

Literature Discussion

Submitted by Lee Park, Williams College
This paper from the Journal of Archeological Science describes the analysis of silver-copper artifacts found in Machu Picchu.  The archeological samples were compared to various control samples prepared from different compositions and under varying processing (thermal treatment) conditions.  Using analytical methods (mechanical hardness testing, micrographic analysis of microstructure and morphology, elemental analysis), researchers were able to offer hypotheses concerning the source materials and fabrication methods used by Inca artisans.

This paper has been used in a materials chemistry course in the context of a section on phase morphologies/microstructures of solids.  It’s not a difficult paper and is a good introduction to reading the literature for students who have not yet had a lot of experience with this.  It also illustrates the use of various types of analytical techniques not usually encountered in earlier courses and encourages students to consider the choice of analytical technique used (the need for non-destructive methods in the study of archeological artifacts, for instance.)  It’s also a good introduction to how these kinds of physical studies can provide valuable context to a broad range of fields of study, as well as to a historical perspective on materials properties.

Learning Goals: 
A student should be able to:
  • Articulate the underlying problem and motivations driving the research presented in the paper
  • Understand the types of experiments carried out and explain why these were appropriate experiments given the types of samples the authors had to work with
  • Understand and explain the individual figures presented, and how those lead to the conclusions drawn by the authors
  • Understand how to read a solid state phase diagram, and understand the role of thermal processing in preparing samples with particular microstructures (these were presented in class)

Implementation Notes: 

Students in an upper level materials course (~12 students, juniors and seniors) were asked to read this paper, discuss the paper amongst themselves, and  answer the problem set question given below.  The problem was intended to be a means of guiding them through the paper and relate it to topics that had been covered in class (for instance, the morphologies/microstructures and phases present at a given point in a solid state phase diagram and what changes in the microstructure with fast vs slow cooling from the melt)  I found that the students worked readily together (probably about half the class or more at a time), and were able to work through the concepts in the paper on their own. The paper could also certainly work well as part of a guided in-class discussion.

Problem set question:

Based on J. Archaeol. Sci. 2007, 34, 38-47 (the Peruvian artifact paper), from section 4.1:
(a) how are different lamellar spacings in the eutectic achieved?
(b) what is the relationship between lamellar spacing and hardness?
(c) describe the microstructure shown in Fig. 7 (note: I am not asking you to simply copy out what’s in the text associated with the figure, but to describe what you see.)  You might be better able to make out the details if you look at the pdf available on Glow than in the printout I provided in class.
(d) what is the point (in the context of the artifacts being examined) of the experiments carried out in sections 4.2 and 4.3 of the paper?
Evaluation Methods: 
The students were asked a question on a problem set (see implementation notes above).
Evaluation Results: 
They were able to see that by studying the microstructure and physical properties (hardness, optical properties) of the artifacts researchers are able to draw conclusions about the fabrication methods (and therefore draw conclusions about technological sophistication, for instance) available to ancient artisans.


Creative Commons License: 
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