People said this experiment was impossible, so I tried it

As promised last week, here's the first Veritasium video about thermite. 

I'm not thrilled that Dr Derek's titles seem to be getting more clickbaity and less informative. Again this week, the video's title isn't really what the video is about. It's a minor part of the video - here addressed in about six minutes in the middle of the video - and doesn't really cover the bulk of the video's content.

With that being said, seeing thermite in slow motion and through glass is pretty stunning.

Great video...bad title...

Why don't railroads need expansion joints?

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.

Railroad Thermite Welding: Europe & Russia

(Edit: As of 6/28/21, the old video had disappeared from YouTube, and I wasn't able to find it anywhere. I was able to find the animation, however, and since that's the only really important thing, I'm reposting that video. If you want to find videos of railroad welding, I have others of that, too.)

Yup, dramatic music at the beginning. That's...um...awesome?

In addition to possibly watching this with the sound off, I'd also suggest turning off the annotations because they're just annoying ads for other videos.

There's a pretty stunning, handheld blowtorch at 0:30. All those tiny flames makes me wonder just how frickin' hot the torch gets.

Most of what we get in the video - including the phenomenally bright fire at 1:55 - is pretty standard railroad, thermite welding.

The animation at 2:09, however, isn't standard. It's a great cutout view of what's happening within the thermite weld.

After that, there isn't much more than three barely  different versions of thermite welding. The first ends around 3:05. The second ends around 5:50, and the third wraps up at about 8:25.

Really, the animation at 2:09 is the only new thing to see here.

Cincinnati Streetcar 1/16/14 Liberty St Thermite Weld (night)

This thermite reaction isn't really any better than any of a dozen other ones you can see on YouTube, but it's in my hometown, and I've seen the weld after the fact. My wife and I happened to be down in that area a few days after this was posted online, and I was able to see the weld shown here. To me, that's pretty cool.

I've been curious for a while how these welds worked - not the chemistry of them, that I understand, but rather how the molten iron was finished into the final weld. So I went hunting an explanation and found this animated video of the weld process.

Railroad thermite welding

There are just no words.

I mean, really, this video has no words what so ever.

What it does have is...at 0:15 a thermite mixture placed on a heated form...at 0:23 an ignitor lit and placed in the mixture...at 0:28 a controlled hell breaking loose, peaking at about 0:35...molten iron leaking into the form at 0:45 (I think)...an awesome sound at 0:48...or maybe molten iron leaking at 0:50...I have no idea what the yellow thing does at 2:05...still glowing iron being cleaned up at 2:45...and big grinding at 3:30.

And that's what thermite is used for.