Cubic Unit Cells

I'll admit that I posted this video. If you check, it's on the Lonnie Dusch (the actual name of your friendly neighborhood blogger) account.

I didn't make the video. I didn't clip it from whatever its original source it. But I needed it, and I had a downloaded copy that I got somewhere along the way of teaching the material science summer camps.

So I posted it on YouTube so I could stream it from anywhere.

If that's the event that pushes me over the edge into eternal damnation, I really wish I would've known.

But you might as well benefit from me risking my eternal soul.

So, check this video out.

It's a brilliant computer animation showing the main crystal structures that we cover in our material science course - simple cubic, body centered cubic, face centered cubic, and hexagonal close packing. We get the coordination number of each structure, a great animation showing the slicing to find the unit cell, the percent occupied, the 

The animation showing how many total atoms are in the simple cubic unit cell (at 1:35 - and repeated throughout the video for the other crystal structures) is so simple and elegantly shown.

I absolutely show this one in class every year - though I stop at about 5:34 because they start to get into ionic compounds (ceramics) which are beyond where we go with unit cells.

(I do warn you that it looks like the video locks up about 0:15 - 0:45. The audio continue, but the video goes still. Don't freak out. It works fine after that.)

The wonder material of the 21st century | Monica Cracuin & Dimitar Dimov | TEDxTruro

No, I have never wondered why pushing harder on a pencil while I'm writing makes the line darker.

I just assumed that there were more layers of graphite being left behind.

Oh, wait, that's it?

Wow. that's not a great opening question, Dimitar.

Here Dimitar discusses the benefits of adding graphene to concrete to make the concrete even stronger. Then Professor Cracuin steps in and suggests other uses of graphene - electronics integrated into fabrics or even our skin - and graphene-like materials (?). She mentions a material of two layers of graphene sandwiched around iron chloride (a combination she calls graphexeter - after the University of Exeter where she researches) to make incredibly flexible, durable, conductive displays - possibly even 'tatoo'ed onto the skin or integrated into contact lenses.

As an aside, I think this is the first TED talk I've seen that switches presenters partway through.

Self organising steel balls explain metal heat treatment

TL;DW - Top video great, absolutely show in class...second video mathematical diversion, not efficient use of class time, good math...third video between the two - more mathy but more tightly edited and efficient and material-science-course tied)

I'm posting all three of these videos together because they're part of a series that Steve Mould made (with help on the lower two) exploring ball bearings and ball-pit balls as crystalline modeling tools.

In the above one, Mould makes a really fancy version of our ASM BB board (we use CD cases and airsoft pellets - he uses plexiglass and metal bb's, more akin to the Atomix toy of yesteryear). If you want to make something like his fancy version, here are a couple of links to check out.

Mould uses the BB board the same way we use it in class: to discuss grains, grain boundaries, heat treating etc in crystalline metals. He places the BB board on a shaker to model adding energy via heat (and there's a brilliant view of vacancy defects moving through the crystal at 2:27 and again at 2:35). Mould then discusses how the crystalline structure he's modeling affects the macroscopic properties (hardness, toughness, strength, etc) of the metal.

Honestly, it's a great explanation of about half a day of summer camp, even admitting that his model is limited in exactly how accurate it is compared to more complicated reality. He mentions a couple of videos that go further. I've already posted one and will look at the other.



The second video is Mould and Matt Parker going through to find the most efficient packing for spheres - using ball pit balls. They then shift from tetrahedral packing to a more square packing - which turns out to be exactly the same (check the below video to see that they're the same). 

I'll warn you that the second video is a lot less professionally laid out and more heavily math-leaning. (There's a slightly more organized video that shows about the same content.) But Mould and Parker do cut a whole bunch of oranges trying to calculate the percentage of space occupied in the face centered cubic packing. (It an IRL version of a computer animation that we use in class and that I'm STUNNED to see I haven't posted on the blog before - coming in two weeks now.) We include a mathematical version of the proof at 16:55 in our summer camp powerpoint (at least Becky and I do - check slides 85 & 86) and you can find the math laid out here, too.

The last video is back to Steve Mould's channel and shows - using ball pit balls and a cardboard box - hexagonal (and face centered cubic) packing. They use that to demonstrate stacking faults (maybe defects, maybe disolcations, maybe grain boundaries - I need to figure out which term is most correct there), brilliantly shown with the color-coded balls from about 6:00-8:00.

The idea that the face centered cubic lattice is really and A-B-C (repeat) hexagonal arrangement whereas hexagonal close packing is A-B (repeat) is kind of mind blowing and so brilliantly well shown with the ball arrangement. The ABC diagram is a little weird to me and very much a mathematical diagram, something I wouldn't get into in class.

Discover the materials of the future...in 30 seconds or less | Dr. Taylor Sparks | TEDxSaltLakeCity

(Must refrain from making snarky comment about mustache...boots...slacks...)

Wait, the video is fifteen minutes long ( a pretty standard TED talk length, admittedly), but the title says "...in 30 seconds or less"). That feels like a serious disconnect.

I'm also a little disappointed that I don't know Dr Sparks because I've taught a material science camp at University of Utah (where he teaches) a half dozen times. I know a lot of the people on this page - but Dr Sparks seems to have eluded me for some reason.

In the above talk, Dr Sparks goes through the historical model of - as he says - "Edisonian trial and error" and serendipity (a la the discovery of saccharine) discovering new materials. He then transitions to our needs to discover modern materials in a more purposeful way via the Materials Genome Initiative and his research using machine learning to predict properties of materials either not yet created or with ingredients too rare to risk on trial and error experimentation. He refers to this field as materials informatics, a term I've never heard of before.

I think I'm going to hunt Dr Sparks down when I get out to Salt Lake (hopefully) next summer.

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?