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[...]The discovery that under certain conditions electrically-heated silicate glass defies a long-accepted law of physics known as Joule's first law should be of interest to a broad spectrum of scientists, engineers, even the general public, according to Himanshu Jain, Diamond Distinguished Chair of the Department of Materials Science and Engineering at Lehigh University.
[...]He and his colleagues -- which includes Nicholas J. Smith and Craig Kopatz, both of Corning Incorporated, as well as Charles T. McLaren, a former Ph.D. student of Jain's, now a researcher at Corning -- have authored a paper published today in Scientific Reports that details their discovery that electrically-heated common, homogeneous silicate glasses appear to defy Joule's first law.
[...]"In our experiments, the glass became more than a thousand degrees Celsius hotter near the positive side than in the rest of the glass, which was very surprising considering that the glass was totally homogeneous to begin with," says Jain. "The cause of this result is shown to be in the change in the structure and chemistry of glass on nanoscale by the electric field itself, which then heats up this nano-region much more strongly."
Jain says that the application of classical Joule's law of physics needs to be reconsidered carefully and adapted to accommodate these findings.
[...]The researchers believe that this work shows it is possible to produce heat in a glass on a much finer scale than by the methods used so far, possibly down to the nanoscale. It would then allow making new optical and other complex structures and devices on glass surface more precisely than before.
"Besides demonstrating the need to qualify Joule's law, the results are critical to developing new technology for the fabrication and manufacturing of glass and ceramic materials," says Jain.
(Score: 3, Interesting) by EvilSS on Saturday March 02 2019, @02:41AM (1 child)
(Score: 5, Informative) by AthanasiusKircher on Saturday March 02 2019, @03:52PM
Yeah, this is typical in such posts of the form about scientific research: "Huh, did the researchers consider some bleedingly obvious explanation, phenomenon, or related possibility that I (likely much less knowledgeable on this topic) came up in a half-assed post where I can't even be bothered to read what the researchers wrote?"
About 98% of the time, the answer is, "Yes, the smart researchers did consider your obvious idea -- and it was either wrong/irrelevant, or it at least doesn't completely explain the issue." (Perhaps there is a name for this common posting practice here, as on the other site and in most tech forums. If not, can I humbly propose the name Athanasius's Law? :) Because I'm tired of such things.)
Actually, I'm not so much tired of such posts, which often are legitimate wondering of the form: "Did they consider it? If so, why isn't this applicable?" What causes me to release a sigh is when such posts are aggressive while displaying ignorance ("those morons!") or when such posts get modded up as informative or insightful, generally with none of the modders bothering to actually read the material and see whether the complaint is valid.
Anyhow...
To the present case: Yes, the researchers did consider this. And yes, in some sense, "Joule's Law" is still valid on a micro-scale. It's just that the deviations in behavior in this case were somewhat unexpected and require significantly different modeling from traditional Joule's Law scenarios.
Here's the paper [nature.com], which could be found in literally 15 seconds with a search engine and a couple clicks. Here's what they say in the very first introductory paragraph:
Note what I bolded in the last sentence. The "fundamental Joule effect at the local level remains unquestioned," thereby clarifying that they agree completely with the AC post.
What's less typical here is that the effect itself causes modifications in the material over time, which then alters the electrical fields and the responses to it. It thus requires a much more complex model that doesn't really obey the "classical" version of Joule's Law. As the authors note in discussion:
This is relevant because other recent research has seen problems of this time-dependent effect and alteration of homogeneous samples to non-homogeneous behavior. This leads to their conclusion:
In other words, you start with homogeneous materials, but as they get altered, weird effects happen. Some are relatively predictable, some unexpected in this situation and not really conforming with the traditional Joule's Law (but now capable of being modeled, like thin layers of ion depletion that differ significantly from the bulk glass), and some that are seemingly more random (e.g., localized heating that "meander[s] around randomly") and difficult to model.
Bottom line is that while Joule's Law may still work if one knows exactly what the characteristics of a substance are at a particular time, in situations like this, it can become very difficult to have that time-dependent info continuously to create an accurate model. Meaning that classical Joule's Law can't really work here by itself -- it needs more complex models to predict how the substance will respond (and where and when).