Why all solar panels are secretly LEDs (and all LEDs are secretly solar panels)

In the fall of 1995, Professor Arthur B Ellis of UWisconsin came to Wabash College - where I was then a senior chemistry major - and gave a presentation about LEDs. At the time I knew of LEDs as the little red or green light bulbs that were pretty much used as power indicators on electronic devices. I didn't - before his talk - have much of an idea how they worked or how important they would come to be in our world now twenty-five years later.

Coincidentally, Dr Ellis had just written Teaching General Chemistry: a materials science companion, a book that my cooperating teacher bought for me after my student teaching semester later that academic year and that I accidentally re-purchased twenty years or so later. (I realize now that I've told this story on the blog before.)

But I digress...I have come to realize that Dr Ellis's lecture at Wabash really laid out the chemistry of LEDs marvelously well because I watched the above video - showing the LEDs and solar panels are of a kind - and the below video - in which Steve Mould explains the science of LEDs and how they turn electricity into light (and the reverse in solar panels) - and realized that I already knew that information...even down to the P- and N-type semiconductor information.

I've never had a chance to thank Dr Ellis for his lecture, so maybe - if I'm lucky - he'll come across one of these blog posts and realize that he's appreciated.

Smart Materials | Anna Ploszajski | TEDxYouth@Manchester

A little while back, I typed in "material science TED" into the YouTube search bar to see what I could learn. It turns out that there's quite a bit I can learn from that search as there are a WHOLE LOT of material science TED talks.

This is the first result of that search, but the material science TED talks will be posting every other week (I'm interrupting them with non-TED talks on the alternating weeks so as not to get too monotonous around the blog) through sometime in March.

This first talk starts with a natural smart material, the pine cone. The material, as Anna related, is hygroscopic, changing its shape as the humidity around them changes, opening as the conditions are right to disperse seeds and closing as the conditions aren't so right.

Her definition of a smart material is "an object that has a property - like its color, its shape, or maybe its magnetism - and this property changes in response to an external stimulus - which might be light levels or moisture levels...temperature, pressure, that sort of thing."

She then gets into some more 'futuristic' materials than the pine cone: self-healing cement in Egyptian pyramids, quartz (piezo electricity - with a bit of crystal basic including why quartz's unit cell yields piezo electricity), photochromic sunglasses, battery gauges on Duracell batteries, color-changing mugs, mood rings (the last four of which she describes as 'quite naff'), DaVinci's flying machine, shape memory alloys (for changing airplane wing shapes), shape memory polymers (to cover that changing wing shape), quantum tunneling composites (???), 

She then covers a few problems with smart materials - slow to react, too delicate, diminishing performance over time, toxicity, cost, issues with upscaling manufacturing - and just handwaves this concerns away saying that you engineers will solve these problems.

My general impression from this is that I want a lot more detail about the 'really cool' smart materials that she mentions instead of so much time spent on the only one she really does explain: piezo electric crystals. The talk is too short for the breadth of materials that she just mentions. It feels very much like a brief survey that might've been better served to condense the intro and spend more time on one or two more cutting edge materials.

ACME corrosion cell on a single piece of metal

Source - https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_-_The_Central_Science_(Brown_et_al.)/20%3A_Electrochemistry/20.8%3A_Corrosion

I took a three-day, corrosion-focused ASM workshop at the University of Akron a few years back. It wasn't necessarily a part of the ASM summer camp world tour, but it was a certainly adjacent to the regular tour. ASM master teachers were teaching it - Andy and Debbie, honestly - and a solid handful of the attendees were ASM master teachers helping out and learning along the way.

That workshop was - I think - the first time that I ever heard the concept of ACME as it relates to corrosion.

By way of introduction, ACME is an acronym for Anode Cathode Metal Electrolyte. In order for corrosion (or oxidation and reduction) to happen, you must have...

• an anode (a more reactive metal)
• a cathode (a less reactive metal)
• a metal (sometimes called a metallic path connecting them)
• an electrolyte (a source of ions that keep the charge of the cell balances)

For example...

Source - https://www.marineinsight.com/tech/understanding-sacrificial-anodes-on-ships/

In the cell there...

• anode - zinc, more reactive than copper, loses electrons, turns from neutral zinc into zinc ions which drift into the solution around the zinc electrode
• cathode - copper, less reactive than zinc, gains electrons, gains mass as copper ions from the solution become neutral copper atoms
• metal - the wire between the zinc and copper electrodes, allows electrons to move from anode to cathode, can involve a thing (light bulb, radio, cell phone) that needs that flow of electrons to opperate
• electrolyte - the solutions around the electrodes and the porous disk that lets the ions move to keep the overall charge on each side of the disk to stay neutral, without it charge would build up and electrons would stop flowing

If this cell is set up, corrosion is going to happen, and the two electrodes don't have to be separated. They can be dissimilar metals abutting each other.

Source - https://pomametals.com/how-to-prevent-galvanic-corrosion/

Here we see two metals joined together (like a copper and a lead pipe connecting) with an electrolyte solution flowing through them. Bad things will happen to the more active (less noble) metal.

If we can break any connection in that cell, corrosion will stop (or at least be drastically arrested).

Source - https://pomametals.com/how-to-prevent-galvanic-corrosion/

After a few years of teaching corrosion in Princeton's material science course and the ASM summer camps and in AP chemistry, I think I'm finally getting to understand the ACME cell.

And I find myself thinking back to what one of the Akron professors said at that workshop when we asked how much of this they wanted us to teach to our students. He said that if students could understand that a single piece of metal could be both anode AND cathode, he would be happy. At the time, I didn't think much about it, but I've come to realize that is a big ask, especially to identify the ACME cell on a single piece of metal.

Thank heaven for that diagram up top (and that I'll repeat here)...

Source - I already told you up top, but since you asked so nicely... https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_-_The_Central_Science_(Brown_et_al.)/20%3A_Electrochemistry/20.8%3A_Corrosion

The ACME cell is still present these on a single piece of iron...

• anode - the bit of iron on the left, for some reason - a crystal defect, a difference in concentration in the electrolyte solution - that site is slightly more likely to release electrons
• cathode - a different part of the iron piece, the part on the right in this diagram
• metal - the two areas of the iron are connected because they're the same piece
• electrolyte - the metal has to be wet with some ions present (keep the metal totally dry, and you prevent corrosion)

At the anode, the iron becomes iron +2...at the cathode, O₂ becomes water (it helps if the solution is slightly acidic)...in between, we have iron ions and oxygen atoms, so we get iron (III) oxide...rust.

See, clear as day, huh?

Hiding a Nobel Prize From the Nazis

This is famous - at least within the science teacher world - story about the hiding of a couple of Nobel prizes (gold medals) won by Jewish scientists by Neils Bohr. 

I've posted the story (from NPR's quoting from The Disappearing Spoon) before, but this goes into the science of the full electron shells (particularly the d-shell) and equilibrium going on a lot more than that other article did.