Understanding Metals

Well, that just about covers the entirety of our metals chapter for both our summer camp and our year-long material science course.

If my students could understand the totality of this seventeen-minute video, they would rock my end of chapter test. It covers...

• BCC/FCC/HCP
• crystalline v amorphous
• slip planes
• defects - point, line, and screw
• grains and grain boundaries
• cold working / work hardening
• alloying - both substitutional and interstitial
• heat treating
• two-phase alloys & precipitation hardening
• the iron/carbon eutectic diagram with ferrite and austenite

Thankfully the video is incredibly well laid out, animated, and presented. This would make a great end of the chapter review for students to watch.

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.

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?

Allotropes of Iron (a phase diagram)

One of our campers, Michael Martin, in Salt Lake City was searching for a phase diagram for iron while my co-master teacher explained the glory that is the iron wire demonstration. See, phase diagrams are comfortable and familiar for we few, we happy few, we chemistry teachers. 

Luckily, he found a really nice one showing the various allotropes of iron at different temperatures (and at really low pressures.)

Not everybody else looks at a phase diagram as familiar, comfortable territory, but we do, and sometimes it helps to put new information (the crystal changes for iron at increasing temperature) in a familiar form.

Where to buy a variac?

The iron wire demonstration is brilliant for showing an application of a solid state phase change, an allatropic phase change, and an real-world application of the idea that different crystal structures do, indeed, affect the properties of a material.

The biggest to that hurdle, however, is finding a way to adjust the AC current traveling through the iron wire, itself. It is possible to do so using very unsafe methods (I've seen it done with a split cord, two copper wires, and a trough of water to which an increasing amount of salt was added, but I do NOT recommend that method), but the best method is a 20-amp variac.

A couple of master teachers swear by the variacs that come from Parts Express, but they're $200, or alltronics, still $170. Recently, however, I found what looks to be the exact, identical variac available for $109 from Circuit Specialists.

Has anybody ever ordered from Circuit Specialists? If so, what was your experience - especially as to the quality of their product?

Making Diamonds with a Blowtorch

This video creates some interesting discussions about how diamonds are made, natural and synthetic, as well as allotropes of carbon.  Its also fun to talk about the cost involved in this experiment and why its not worth running a blowtorch for 8 hours to make tiny diamonds.

NASA: Blacker Than Black

This video gives us a look at how NASA uses carbon nanotubes to produce a surface that reflects an absolute minimum of lightwaves for their optical instruments in space. The video looks at the structure of the nanotubes as well as some of the durability tests that they have conducted to make the nantube coatings more durable.

What is graphene

Graphite is one of the allotropes of carbon - along with diamond and buckminsterfullerenes (buckyballs). Graphite exists as a series of hexagonal-based carbon layers, a single layer of which is known as graphene, the exploration of which lead to the awarding of the 2010 Nobel Prize in Physics.

In this video the structure and electrical properties of graphene are explained in very simple, udnerstandable language.