Today is the 30th of December, so we are well into the depths of winter, so you might wonder why I would write about something like “heat.” Well, read on and find out…
My beloved and sainted father (glory be unto his name) has been struggling with a sample holder for quite some time now. “Version 1” of the beast required only a bit of adjustment before it worked, but it is a sample holder (and that’s it). It turns out that the sample holder my beloved father needs must also do double-duty as a sample heater as well.
From the “vacuum science” post in October, we discussed that keeping your vacuum system clean is a key part of getting to low pressures. Heating things up in the midst of your system (not during the bake-out process) is NOT a good way to keep things clean. As things heat up, “stuff” (alcohols, water, and then hydrocarbons) boil off of the surface as the thing being heated reaches the boiling point of these materials. The longer you heat something, the more contamination gets into your system. This makes the creation of a sample holder/heater nontrivial.
Now enter “Version 2” — a completely re-designed holder/heater that really was a work of art. The metal was all a special steel alloy that could take lots of heating and cooling in oxidizing atmospheres (like the ones we’ll require) without losing its key properties. The “core” of the heater was a piece of boron nitride — a remarkable material that is a good thermal conductor while also being an electrical insulator. This turns out to be important, because in a vacuum, there isn’t anything (or really much of anything) to “transmit” your heat. That means that the most effective heaters work by conduction (versus radiation or convection); take a look at this:
My beloved father wrapped the boron nitride with kanthal wire (a wire that is designed to have current run through it with the goal of generating heat). If the boron nitride wasn’t an electrical insulator, when the heater was turned on, the entire system would have 20 Amps running through it — not the safest configuration!
Everything was assembled, and initial tests started. And ended. As the kanthal heated up, it expanded off of the boron nitride and ended up doing nothing. The solution is easy then, right? Find a material that will hold the kanthal on the boron nitride. This new material needs to be strong (to resist the kanthal expansion), be an electrical insulator (otherwise the whole thing will short out), and act as a thermal reflector. The answer? Zirconia. After weeks and weeks of waiting (and not a few dollars), “Version 2.1” (held by its inventor) looked like this:
What a thing of beauty! Testing commenced. And then came to a screeching halt. There aren’t a lot of materials that will endure the temperature ramp rate we put into this piece during the second phase of testing, and the zirconia decided it didn’t want to play anymore:
Sigh. The top piece of zirconia (bottom white part) is barely discolored, but the cylinder cracked twice — once around the circumference (creating the piece second from the bottom that separated from the main body just above it) and once vertically (creating the odd black/tan pattern that we still don’t understand).
Bigger sigh. Since then, my beloved and sainted father has been trying to talk to people about custom insulation for furnaces. There are lots of materials that could work, but they have to work in our vacuum (without killing it) and in a partial oxygen atmosphere (without dying). We’re thinking that it’s likely going to be some carbon/zirconia fiber composite, but getting people to return telephone calls or e-mails about this isn’t as easy as it sounds… Stay tuned (hopefully for success!).
What does the microwave have to do with any of this? In a completely different (but kind of related) set of experiments, another of my beloved and sainted father’s students is trying to make thin films of new materials. Daddy’s lab has already produced some very nice thin films; here is an image from the atomic force microscope of a thin vanadium dioxide film on sapphire:
This image is 10 x 10 microns (a human hair is ~90 microns in diameter; wool fibers thinner than 25 microns can be used for clothing); the yellow part of the “step” is vanadium dioxide, and the blue part is the sapphire substrate. The “step” was “engineered in” using the “Version 1” sample holder (see above). Well, these new materials do not like to create solid films — they form patterns that look like tiny little hedge mazes (imagine tiny versions of the maze at Longleat House in Wiltshire, England). That’s interesting, but not what we’re going for. In discussion with some colleagues from the Nano Tech Center at Texas Tech, it became obvious that we needed a plasma etcher (an interesting reference describing plasma etching is here). In short, let’s consider this little gedankenexperiment: you take a drop of water and place it in the center of a normal glass microscope slide. Now, using a clean pair of forceps, try to spread that drop of water out. It turns out that you cannot. The water droplet will follow the forceps around, but it will remain a little droplet. The surface is hydrophobic. Now, put the same plain slide into the plasma etcher for 30 seconds or so and try the experiment again. This time, the drop of water will spread very evenly over the entire surface of the slide. The surface is now hydrophilic — and will hopefully help generate our solid thin film.
Buying a plasma etcher was pretty much out of the question (they cost ~$10k), but my beloved and sainted father found a way to create one using a used microwave oven. To prove it, here is a picture of it working (with argon gas; oxygen will be added later once the pump is made safe for oxygen; the hand is that of the student who is trying to make the films):
Interestingly enough, if you have just a bit too much gas in the system, you get this odd arcing pattern:
Hopefully, when my beloved and sainted father returns from Christmas break in the next day or so, everything will be in its own housing and working properly. Sometimes you just need a bit of help from above. Just to be clear, pyrex can be melted in the microwave:
Before you get all excited and say that the picture is of plain kitchen pyrex and not “science-grade” pyrex, I’ll offer the following:
Broken glass is broken glass, but a working device is a working device — in this case, all for less than $500 (which is, using my mad Pekingese math skills, less than $10,000). Sometimes, you just need some help from above.
Speaking of which, while in Wheelock earlier this month, my mother and my beloved and sainted father (glory be unto his name) went to the St. Francis of Assisi Catholic church in Franklin, Texas (there’s not one in Wheelock). It’s a beautiful church, and the service was very nice (since when is Mass not nice?); there weren’t any screaming children — Deo gratias!
As my parents sat down, they noticed a large stained glass window behind the altar (you cannot possibly miss it) depicting the Holy Spirit as a dove. Now, there are lots of depictions of the Holy Spirit as a dove. I like this one from the Holy Spirit Catholic Church:
These are often serene pictures – the dove is meant to be gentle and comforting; one of my favorite images like this is the dome of St. Peter’s church in Vienna (the dove is actually on stained glass at the very top of the dome):
or this one with the Holy Father:
This image of the Holy Spirit seems different. In fact, I think it’s kind of disturbing. The Holy Spirit isn’t supposed to be mean or vicious. Something tells me that parents might use this image to persuade their children to do whatever they want. I envision something like Luke 10:27 (paraphrased, emphasis mine): “You WILL love the Lord thy God with thy whole heart, and with thy whole soul, and with all thy strength, and with all thy mind, OR I WILL HUNT YOU DOWN AND EAT YOU.” Here’s what it looks like:
I apologize for the distortion of this image. Someone was slightly perturbed that my beloved and sainted father needed to document this “beast” and this is the best he could do from that pew without making a “scene” (according to my mother, anyway). That bird has a serious beak. Put some slightly bigger talons on it, and you have one scary bird.
In any case and wherever you find yourself, Pekingese everywhere hope you had a wonderful Christmas and we wish you a very happy, healthy New Year (complete with more Thoughts from Yours Truly)!