Polycrystalline diamonds aren't nearly as pretty as monocrystalline ones are, but they seem to be much easier to produce - especially if you're trying to grow them onto a computer chip.
...which I would never have thought to do but which seems to be really desirable because diamond is a phenomenal conductor of heat, seemingly an improvement on aluminum as a heat sink for electronics on a massive scale.
...but the Nova episode tends to appear and disappear from YouTube and DailyMotion with fair frequency, so you might need another video that goes through the ancient art of creating samurai swords from the initial collecting and smelting of iron-rich sand through to the slicing of tatami mats to demonstrate the sword's quality and the sword wielder's technique.
This video's contents...
2:00 - why bronze was used for sword and was eventually replaced
3:00 - cyanobacteria creating oxygen that precipitated iron from ancient oceans
6:30 - carbon + iron = steel, initial interstitial positions shown...why alloys are harder than pure metals
10:30 - slag formation and removal from the 'ancient' forge
13:30 - forging the steel by master swordsmiths
14:30 - folding the steel - how and why
16:15 - how carbon atoms migrate to different positions and form ferrite, cementite, perlite, and martensite
18:30 - differential cooling rates via clay thickness creating different steel types and the distinct blade shape
Another great video from Veritasium and one that shows that he's got a team of folks making videos with/for him at this point...and it's short enough at about half an hour - to get through in a single class period, unlike the Nova episode.
...but this video also goes through the specific math required to calculate the packing factor - the percent of occupied space - for each of the crystal structures.
Plus it has a Pokemon analogy - which the computer animation video doesn't have.
To paraphrase Corey Petersman, an AP chemistry and material science student during our first year of teaching matsci at Princeton, "vaporeon, witches!"
The topic are largely the same, though this one goes more deeply into how NiTiNOL works on the stress-strain curve and how the deformation of NiTiNOL is an autenite to twinned martensitic crystal transformation - complete with some nice animations.
It does also mention that the crystal transformation are exo- and endothermic (17:05), something that I don't think I've seen mentioned in other videos. I admit that if hot water is necessary for the martensite to austenite transition, it must be endothermic, but I haven't seen anything demonstrating that transition being both noticeable with bare hands - and a large enough NiTiNOL sample - or via thermal imaging camera. Neat detail there, doctor Derek.
The title of this video - which might change since I'm writing this up just a day after it was posted to YouTube - is a bit misleading. The actual question in the title - why don't railroads need expansion joints - is only answered in the last half minute or so of the video and is answered more thoroughly in a Practical Engineering video that I'll post after a jump.
The bulk of the video is spent explaining how railroad welds using thermite work. The video explains the nuances far better than other thermite videos I've posted before, explaining why the rails must be aligned and peaked, why the rails must be preheated (including a nice demonstration of heat treating), how the crystal structure changes as a result of the weld, and eventually why the rails don't need expansion joints.
This is the second of at least three thermite videos from Dr Derek. I thought I'd posted the first video to both blogs, but I can't seem to find it, so it'll likely show up next week.
"Well, contrary to what you might think, it's not a chemical reaction." ~ 2:17
I'll readily admit that I assumed it was based on a chemical reaction rather than what this video suggests - just after the above quote - the gallium seeps into the grain boundaries between the aluminum crystals and prevents them from holding together as they normally would.
In our material science class at Princeton - and in most of the matsci classes that originated from the ASM summer camps, I would imagine - we grow copper (II) sulfate crystals from solution.
It's a fairly easy lab to do, and the students have a high success rate.
For most students, that crystal growing experience is an end, but for others it's just a beginning, a taste of a much richer world of crystal growth.
In every case, the procedure is largely the same - make a solution, let the solution cool and evaporate to form seed crystals, continue to let the solution evaporate to grow the seed crystals larger. The great things about the crystalverse website is that it has loads of tips and faqs to help you troubleshoot your growing.
Today you get a whole bunch of videos about making salt (all different from previous salt making videos.)
It seems like such a simple thing - talk salt water from the ocean and boil it down - but there's a lot more to the science of making salt including removing the calcium and magnesium impurities, allowing the crystals to grow to the desired size, and sorting those different crystal sizes.
Who knew that the rate of crystal growth would affect the size of the crystals?
There is no freezing happening. There is recrystallization happening from sodium acetate dissolved in solution.
That's not freezing - a pure liquid turning into a solid like ice turning into water. The host seems to understand that distinction, but he's sloppy on using the term freezing and freezing point somewhat misleadingly. He also is sloppy on liquid versus solution and melted versus dissolved.
Most of this video is an explanation and comparison of the two types of hand warmers - the reusable sodium acetate solution and the single-use iron rusting type. The video host explains the science behind what's happening and judges the single-use to be the better choice - something that I'll leave up to you.
I use both in class for different purposes and different chapters.
The linked article - including the above graphic - used a computer simulation of 'atoms' of two distinct sizes - the ratio of those sizes being the primary variable in the various digital experiments - being vibrated at a constant speed until they organized themselves into a crystalline arrangement. This spontaneous generation of crystals is something I have posted about in the past, particularly in an interesting, large-scale demonstration from Alpha Phoenix.
Following the digital experiments, the scientists made real world, physical experiments with non-magnetic spheres set to vibrate at a constant rate of 120 times per second and found that spheres of 2.4mm diameter and 1.2mm diameter (I think 1.2mm - the article says "the other half that size" in reference to the 2.4mm diameter spheres) and found that the mixture of spheres didn't form a crystal but rather formed what they refer to as a quasicrystal - which sounds to me like a heterogeneous mixture of different crystalline regions.
The article also mentions that this has been found IRL in, "an alloy of aluminum and manganese revealed the undeniable hallmarks of an ordered material that lacked the infinite periodic patterns of a crystal." I'm going to have to read more about this because while it's interesting, I'm not entirely sure I understand the quasicrystals just yet.
Some explanations are so remarkably simply that I never would've thought of them.
I've heard of hopper crystals in bismuth for years. I always assumed that they were studied by a scientist named Hopper. In this video, Adam Ragusea explains that they're actually called hopper crystals (not Hopper crystals) because they resemble the shape of a hopper that feeds ingredients into a production line.
And that's just the surface level of new knowledge that I got from this video. Adam spends much more time trying to explain why making hopper crystals of salt - the ones he shows and that I have in my cabinets at home as Maldon salt - is hard to do. Apparently they only form in super-saturated salt solutions and then only stay hopper-shaped pyramids until they either bump into other crystals to form a raft or get heavy enough to sink to the bottom of the solution and in-fill with more salt.
If only they could get them to grow in space - as an International Space Station experiment shown in the video recounts...
The above video is a very quick, fairly vague explanation of the difference between tempered and untempered chocolate.
Dan Souza, the editor of Cooks Illustrated magazine, illustrates tempered chocolate as a rigid, highly structured stacking of kitchen chairs as compared to an 'untempered', random arrangement of the same chairs.
I would appreciate a little more detail, maybe a micrograph or two, but what you see above is all Dan's giving us this time. Dan has, however, given a little more detail about chocolate in the video after the jump which includes a recipe for millionaire shortbread that requires tempering of the chocolate topping, something Dan shows how to do using a microwave.
Warning: NSFW words (mostly starting with f's) at 0:45...and at 3:43...and at 4:39...and at 4:57...and at 5:33...and at 7:26 and 7:31...and at 7:44...and at 8:42...and at 9:10...and at 10:45...and at a14:10
Ok, so maybe this shouldn't be shown in class.
I've long wondered how single crystal turbine blades are grown to be single crystals. We mimic this is far less complicated ways with our copper (II) sulfate crystal growth lab in our matsci class at Princeton (and in many other ASM-born matsci classes).
...but I knew that simplistic method clearly wasn't going to work for the cast metal structures for metallic crystals.
Thankfully this video's foul-mouthed Yorkie host explains how we go from molten metal to single crystal, grain-boundary-less macrostructures. It's not a very thrilling video as it's just a knowledgeable guy explaining things in his garage with a white board to show what he's talking about. I respect the knowledge and appreciate his explanation about something I've wanted to know for a while now.
Maybe just watch it and explain things to your students rather than showing the video itself.
...because the video itself is absolutely fandabidozi.
I'm not teaching material science this year (2022-23), but my neighboring chemistry teacher is.
He taught the class a decade or so ago when it was just a semester, and he's never taught it as a year-long course before.
As such, he's been coming to me quite often for help in understanding the concepts, explaining them, and practicing the labs and demonstrations. It's been kind of rewarding to help him understand things better - and in a few cases it's forced me to understand the material science concepts better so I can explain them to him, something I'm used to in teaching students but that isn't as familiar to me in teaching my fellow teachers in a longer form than our week-long summer camps.
Recently, my neighbor came to me asking about slip planes, so I went looking for a video that would directly and clearly label the slip planes in face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close packed (HCP) crystal structures. I wanted a shortish video that would use computer animation to highlight the slip planes and give me a concise, clear marking of where the slip planes are in each type of crystal.
Much to my chagrin, such a video doesn't seem to exist - at least not that I could find with a few days of searching on YouTube.
What I did find, however, was a much deeper understanding of what slip planes and - possibly more appropriately - slip systems are.
In this first video, I found a very helpful quote as written in the notes...
"Slip plane will be most densely packed highest planar density"
So the slip plane is the plane with the highest packing. For FCC that's the diagonal labeled as (1,1,1) because it connects the vertices of the crystal structure and is the 'triangular' plane that we show with our tennis balls in class. For HCP it's any of the 'horizontal' layers that we show with our tennis balls. For BCC, it's the diagonal from edge to edge in the crystal - but it's not very closely packed, making it a crappy slip plane.
"Slip direction is the one most closely packed with atoms (linear density)"
That means FCC structures have three slip directions for every one of their four slip planes. That give them twelve (4x3) slip systems.
But HCP crystals have only three slip systems - one slip plane times three slip directions.
...however, unlike fcc, there are no truly close-packed planes in the bcc crystal structure. Thus, a slip system in bcc requires heat to activate.
I still want a nice, succinct video that shows all that, but I'll take this combination that has helped me understand slip planes way better than I did before my neighbor asked me to explain them to him.
This is NOT another post about Naica's crystal cave in Mexico. I've already posted a few of those.
This post is about the Pulpà Geode, supposedly the world's largest geode, found near the town of PulpÃ, Spain.
The crystals are - like those in Naica's cave - gypsum, and they're admittedly not as large as those in Naica's cave. In the above video, they refer to the Naica crystals as being up to 15m in length and those in the Pulpà Geode as being up to 2m in length. In the video, however, they state - without much explanation - that the Pulpà Geode is a geode - a cavity in rock completely covered with crystals - and the Naica cave as not a geode.
I don't know if that means the Naica cave just has some un-covered surfaces or what, but the video above doesn't go into that detail, admittedly.
But this cave is available for people to walk through - for now, anyway - whereas Naica is flooded again. You just need to get to PulpÃ.
At this point, I'm fully in any time AlphaPhoenix releases a video. He explains material science beautifully.
In today's video he explains the differences between crystalline and amorphous (2:30), shows crystalline aluminum under an SEM (3:45), shows how 2-d magnetic discs when agitated spontaneously produce order (5:00-10:30 - the real money portion of the video), and uses a computer simulation to extend this into the third dimension (11:45).
This is a wonderful exploration of how crystals grow - whether they're our copper (II) sulfate crystals in class or cooling aluminum crystals or any other crystals.
I am coming to love Alpha Phoenix's videos more and more with each video. He explores concepts that are often ridiculously subtle until you think about them a little more deeply, and he uses them to explain the details of the materials around us.
In this video he asks how long it would take for a force - a hammer hit in this case - on one end of a bar of steel to be felt on the opposite end of the bar. It's something that seems obvious at first because a push on one end of a steel bar is 'immediately' felt at the other end of the bar. That's true on the scale of a bar a couple of feet long and with the time scale that you and I notice things, but Alpha Phoenix uses far faster measurements than his eyes and proves that the force isn't felt 'immediately' on the other end.
And then he explains why this happens using magnets and springs representing the particles within a solid and does it brilliantly.
Now I just want him to make more of his videos. At his current pace, he's putting out a video a month or so which leads to high quality videos, but I just want more of them.
