Archive for May 15th, 2007

R W Cahn: RIP

May 15, 2007

Materials science lost one of its greatest expositors, historians and practitioner with the passing away of Prof. Robert W Cahn. Be it the commentaries that he wrote for Nature, or the one page essays that he used to write for MRS Bulletin, Prof. Cahn’s writing had always been very enjoyable–see for example this extraordinary book review he  wrote to Sir C Frank’s Eightieth birthday tribute calling him a fox with quills (pdf), and this little piece about his work for Oxford English Dictionary (pdf).

Of course, the multi-volume tome that he edited with Hassen in Physical Metallurgy is something that every materials scientist/metallurgist would have borrowed from the library at least once; and, his Coming of Materials Science is a must-read for anybody who is interested in the subject and its history (An aside: Coming of Materials Science also tells us that Northwestern is the first university to adopt Materials Science as part of the department title). Prof. Cahn recently published his memoir, which I was/am looking forward to reading.

Personally, I have some pleasant memories of Prof. Cahn. He was also the editor and reviewer of my first publication. It so happened that we submitted our paper to Intermetallics in December (of 1999, I think)–those were the days of hard copy manuscript submissions. So, one afternoon in mid-January we received a mail from him–he was on vacation; on his return, he just then saw the submission; he will get it reviewed soon and get back to us. By that evening, we got another mail from him; since he was interested in the subject himself (constitutional vacancies in B2 NiAl), and could manage some time that afternoon, he decided to review the paper himself; he was happy to accept; and, one of the corrections was a typo in one of the authors’ names–he said something about the perils of having a South Indian name with so many A’s in it 🙂

Prof. Cahn visited Indian Institute of Science, Bangalore several times; and so, I had the fortune of attending his lectures and attending lectures along with him. He will be missed by the materials community, and by his friends all over the world; and, his contributions to the subject and its exposition will be remembered for a long time to come.

PS:- Thanks to Gandham for the email alert.

The materials science of earth

May 15, 2007

Today I heard Prof. Steven D Jacobsen on Hydrogen related defects in mantle mineralogy: Oceans in the Earth’s interior? The basic question that he addressed is as follows: Is it possible that the minerals in the earth’s mantle, by virtue of their being at high temperatures and pressures, store water. The answer is that the transition region in earth’s mantle (from 410 kms till 660 kms) can in principle store 2-3 wt. % of water.

In reaching these conclusions, he brought together several interesting materials aspects to the problem. They varied from the physical chemistry of hydrogen under high temperatures and pressures, to high pressure-high temperature infra red spectroscopy and neutron diffraction of silicate minerals, to charge neutrality induced point defects in spinels which lead to changes in elastic properties of these minerals, to crystal growth under high pressure-high temperature conditions.

His talk also showed what a live, heaving mass the earth is. For example, how do we know that the transition region of the earth’s mantle begins at the 410th km? Because, during earthquakes, the shear waves that are generated bounce off from these transition layers. Further, after earthquakes, apparently, the earth vibrates like a bell, the normal modes of which can be measured in the laboratory.

Finally, from a materials point of view, it was also very interesting to see that the conditions at the earth’s mantle a few hundred kilometres from the surface could be simulated so well using a diamond anvil cell  (to pressurise) and laser (to heat); and, the resulting phase transitions could be studied in situ using spectroscopic and diffraction techniques, while the microstructure can then be analyzed using TEM.

A nice talk, and a very interesting field! For those of you who are interested in learning more about this area, his home page has several pointers; for those of you at Northwestern, he is also planning a course on the subject. Have fun!