Monday, January 8, 2018

Why Roman Concrete Still Stands Strong While Modern Version Decays



Concrete, strong stuff...

But apparently Roman concrete is among the strongest stuff, and it just got stronger while it was under seawater.
Previous work had revealed lime particles within the cores that surprisingly contained the mineral aluminous tobermorite – a rare substance that is hard to make.

The mineral, said Jackson, formed early in the history of the concrete, as the lime, seawater and volcanic ash of the mortar reacted together in a way that generated heat.

But now Jackson and the team have made another discovery. “I went back to the concrete and found abundant tobermorite growing through the fabric of the concrete, often in association with phillipsite [another mineral],” she said.

She said this revealed another process that was also at play. Over time, seawater that seeped through the concrete dissolved the volcanic crystals and glasses, with aluminous tobermorite and phillipsite crystallising in their place.

These minerals, say the authors, helped to reinforce the concrete, preventing cracks from growing, with structures becoming stronger over time as the minerals grew.
And it looks like the Romans knew what they were doing.
As the authors note, the Romans were aware of the virtues of their concrete, with Pliny the Elder waxing lyrical in his Natural History that it is “impregnable to the waves and every day stronger”.
If you want to read more, check out the original research article...or the Guardian article that's way more readable and that I quoted up above.

Sunday, December 31, 2017

Costa Rica's Turquoise River - A Natural Optical Illusion



That blue water doesn't look too natural to me.

I mean it's a gorgeous blue, but it's a blue that doesn't seem quite right.

Apparently - at least according to this article - there's no copper in the water, so that's not what it's blue.

Instead, the Rio Celeste produces particulates of aluimosilicate of exactly the right size to reflect light in the blue area of the spectrum. Neither tributary contains particles of the right size, but...
[t]here was only one puzzle left to solve, though. If Rio Buena Vista also had an abundance of aluminosilicate, how come its water looked completely transparent, while Rio Celeste appeared to be turquoise? It turned out to be a matter of particle size. Upon analyzing samples from both bodies of water, scientists realized that aluminosilicate particles in Rio Buena Vista measured 184 nanometers (nm), while those in Rio Celeste were much larger at 566 nm

“This increase in size is what causes the scattering of sunlight, such that it occurs principally in the blue region of the visible spectrum. So that’s why we have that spectacular light blue color of the Rio Celeste” said Dr. Max Chavarría Vargas, who lead the scientific investigation into the turquoise waters of Rio Celeste. “It’s one of those quirks of nature where one of the rivers provides mineral material with one size and the other river provides the acidic environment so that those particles grow.”
Who knew that particulate size mattered?


Monday, December 18, 2017

Brad Makes a Knife with Bob Kramer | It's Alive | Bon Appétit



I'm a fan of goofy Brad, the host of the video series, It's Alive. Mostly the show is about cooking in the realm of fermented foods (kombucha, beer, garlic honey, cultured butter, sauerkraut, etc), but this time Brad goes to a small-scale knife shop because, as he says at about 13:10, "this ain't necessarily alive, but it's got energy...watching [the knife-making process] from start to finish, if it don't make you feel alive, I can't help you.

There are a bunch of metal topics covered here...
  • 0:45 - "make some steel from scratch"...they make their steel from powdered ingredients (carbon, iron, manganese) and then melt them together
  • 1:30 - induction heat melting of the steel ingredients
  • 2:20 (and again at 3:00) - forging...the take the fresh, steel 'biscuit', reheat it 
  • 2:45 - heating the steel back up to the plastic state...they don't mention the phase transition from BCC to FCC, but they do explain that hot steel can change it shape more easily...and that they have to reheat the 'biscuit' because it's getting cold
  • 3:30 - rolling mill...a small mill but still far larger than what we show in the summer workshop
  • 4:15 - forge welding different steels together...they only refer to the steels as steel A and steel B...no mention of high- or low-carbon steels
  • 4:40 - iron oxide...the captions explain that, "[t]hose dark flakes are iron oxide. High temperatures accelerate the oxidation process."
  • 6:20 - "quench tank there, Vinnie"...Vinnie is the camera man for all the Bon Appétit videos...no explanation yet as to why you would quench something
  • 6:58 - hardening the knife...molten salt bath for an oxygen-free atmosphere for heating..."dissolving the carbon into the iron" then capturing it during the quench...followed by a tempering bath to, "bring the knife to a working hardness, so it's not too hard...not too brittle"..."when it's hardened, it's under a lot of STRESS...we go in there (the tempering bath) and it just adds some heat, kind of massages it...makes the knife 'happy'...yeah, this is the 'martini' for the knife"...there's a decent graphic summary of this at 7:50
  • 8:40 - acid etching the knife..."the acid eats these layers at a different rate...because we mixed in different things in the steel"
  • 11:20 - nothing curricular, but watching Bob Kramer put a blade on the knife just by eye as stunning...I assume it took a few more passes than what the video shows, but he makes it look so casual and awesome...I'm amazed
Warnings
  • 7:35 - mention of making the steel happy via a 'martini'
  • 10:20 - there's a bleeped, "I always f*#^ that up"
Brad's a goof, but it's loads of fun to watch him make a knife.

Tuesday, November 28, 2017

Prop: Shop - How to Make a Vacuum Forming Machine



This might be a little beyond my skill set at this point, but with the shift of material science from a semester to a full year, this might be in the future.

Gonna need myself a little suctioned viking head.

Wednesday, November 15, 2017

Phase Transition in Steel



That's an interesting addition to the iron wire demo: a glass rod to exaggerate the 'dip'.

The glass rod makes sense because it's non-conductive enough to not be too dangerous, I would think.

The graphing on the video really makes the phase transitions remarkably visible, though.

I like it.

The video's description gives a little more detail as well as the reason for the slow, overall downward slope.
A steel wire is heated up by a current and it expands. When the phase transition temperature is reached the wire takes up additional energy which cools the wire down for a short time and shortens it. 
This step can also be observed in the opposite direction when the current is switched off and the wire cools down. When the phase transition takes place the wire is heated up and it expands for a short time. 
Over three cycles the thin wire gets already worn out. Is is deformed so that the diameter, the heating power and the temperature is not equal along the wire and the phase change occurs more distributed over time.

Thursday, November 9, 2017

Heat treating tool steel -- the phase change



I'm going to trust the video's description (copied below) when it says that the flashes of light at 0:32 are visual indications of the BCC --> FCC phase change that takes place at 910 C.
Visual indication of tool steel phase change to austenite when heat treating. Small pools of iron are forced from the steel as the volumetric change takes place and small amounts of carbon are burned off.
So, my understanding from reading that, is that the BCC (ferrite) --> FCC (austenite) change squeezes some of the carbon out of the structure. That carbon then - because of the high temp and the presence of oxygen around the steel - burns off in the flashes that we see.

Can anybody tell me that I'm reading the situation correctly?

Wednesday, November 1, 2017

The Coolest Way to Open a Bottle of Wine



Yeah, that's one way to open a bottle of wine.

Shatter the glass, yeah.

It causes some secondary challenges (possible shards of glass in the wine, a messy lip of broken glass), all of which seem to have brought about solutions to those challenges.

As neat as the science is (hot glass contracts quickly and unevenly when cooled suddenly, aka thermal shock), the whole process just seems needlessly Rube Goldbergian to me.