"Triax this is Houston, do you read?"

Ted and Heather got a lot of work done on the Triaxial apparatus while I was away. For one thing, they got the pressure vessel all lined up and then set up these two blue mini-versions of the vessel, called intensifiers, that control the confining pressure and the pore fluid pressure (so, one controls the pressure outside the sample and the other, inside). We'll use kerosene for the confining liquid. There's also that row of seven things sitting atop the mini-vessels. I don't know what they do yet but I'm excited to find out.

In addition, there are now big hoses going to and from the vessel and intensifiers and a burly hydraulic fluid pump. The pump is so powerful and loud that it sits in its own insulated doghouse outside the lab, otherwise it would drive us all crazy.

And one very exciting development is that they rewired the old control panel that will be used to communicate with the Triax. Since the rig will get up to very high pressures during experiments, you really don't want to be standing next to it while it is running. Rather, you want to be safely around the corner at this groovy old school station, complete with analogue Heise pressure gauges (on the blue wall panel) and all the digital readings you require.

Research Trip: Edinburgh

For the last 30 days I was in Edinburgh on a research exchange visit. It was an absolutely wonderful time to be visiting Scotland. The days were brisk, but not that cold and somehow I managed to avoid most of the rain. 

The visit was funded by a branch of the European Science Foundation, called MicroDICE. Their purpose is to promote the exchange of science and techniques between Universities and countries, especially if it is concerning the microstructures of Ice. 

I was visiting Jane Blackford, who is in the Materials Science department of the University of Edinburgh.  Here's Jane with the fields of outer Edinburgh below her. Whenever we weren't in the lab, we tried to sneak out to the surrounding hills for a hike or to the local climbing gym for a route or two.

Our research goal was to measure the "dihedral angle" of sulfuric acid and ice, that is, the wetting angle that a liquid acid solution makes in the corners of ice grains, which is determined by the surface energies. Sulfuric acid has been found in polar ice packs and is thought to exist on icy moons in the outer solar system. The reason for measuring the angle is because if the angle is very large (>60 degrees), sulfuric acid would be stuck and confined to the corners of grains, but if the angle is small (<60 degrees) it could travel through interconnected veins of liquid. Traveling liquid acid could really influence the physical properties of ice, so it is an important characteristic to measure. We sprayed a solution of ~5%acid into liquid nitrogen so that it would flash freeze into droplets that we collected and put into these little aluminum containers (right). Then we let the samples "cook" at various temperatures that were below the freezing temperature of ice yet above the freezing temperature for the liquid acid solution. We let them sit like that for about a week and then we quenched them in liquid nitrogen to capture that microstructure.  Then it was off to the Biology department to visit Chris Jeffree and his scanning electron microscope that is specially equipped to handle frozen samples (below).

Chris was an absolute wizard with the SEM and managed to take hundreds of images of dihedral angles. I am now in the process of measuring all those angles, first by hand and then electronically. Publication coming soon!

working on the triax

Now that the biaxial apparatus is ready to run (we're just hammering out some bugs with our National Instrument gear), our attention has turned to the triaxial rig. It applies a confining pressure using either gas or a solid medium. The pressure inside the vessel can really build and if it blows, it could be deadly, so this behemoth sits in its own room in the back of the lab. Our first task was to rotate the steel cylindrical vessel 90 degrees so that it can connect to new gas tubing and then check the integrity and alignment of the vessel. The vessel and attached top plate together weigh almost 1000 lbs, so taking things apart is no small feat. Ted rigged up a pulley system to a beam in the ceiling and we carefully lowered the two parts, which immediately began to swing out on us.

Eventually we got the parts under control, rotated, and back up in place. Next week while I am away, Ted and Heather will make sure the vessel is perfectly centered. They will use a tool that precisely measures the location of the inside wall of the vessel with a needle. Using the machine hydraulics they will raise the needle up the inner length of the vessel. If there is any tilt to the vessel wall, the tool will indicate that and they can shove little wedges of wood or thin steel around the top plate to center it.

a library grows at lamont

Today we cleared some counter space and pulled out all the old dusty reference books out of boxes. Need to know anything about metals, alloys, pressure vessels, analog to digital conversion?....we've got it covered! And nice bookends, don't you think? 

a gaggle of strain gauges

Today we moved another big step closer to running an experiment by connecting strain gauges to the sample. Ted affixed various kinds of gauges along the business edge of the sample in order to measure strain that is parallel, perpendicular, and at 45 degrees to the frictional surface. The gauges are then soldered to a rainbow of wires that lead to that little green breakout box. Coming from the box are wired connectors that will plug into individual signal conditioners.

Each of 10 signal conditioners below are used to zero-out and amplify the response from the gauges and will then send a voltage output to the computer.

We were getting a little interference from the rainbow of wires and the output connections in the back were hard to reach, so Ted reconfigured it as below, with the strain wires now hiding safely inside the silver mesh tube. Although it looks a bit hectic this way, it works really well.

And "how on earth do we plug all those things into the computer?" you may ask. Well they first get connected to this BNC box. Then the BNC box is connected to a thing called a chassis (more on that later) that is, in turn, connected to a card in the back of the PC.

a clean, well-lighted place to talk about rocks

Big addition to the lab yesterday: the facilities folks found us a table! I don't know where they found it, but it's new-ish, relatively clean, and can be wheeled around the lab easily. Today I came in to find a cute little plant in the middle of it. Now we have a place to sit around and plan the next step. Since our housecleaning is generally finished, it is time to start rehabilitating the testing machinery. First on the list is that rig in the center back. It is called a "biaxial" friction apparatus because it applies stress on the top and on one side, but there is no confining pressure.

a little calibrating

Today was a very productive day. While Ted worked on the strain gauges (they each have to be glued onto the side of the sample and then soldered to wires), I calibrated the LVDT. The box on the left provides an excitation voltage to the LVDT, which is a cylinder with a hollow in the middle. Using that little Schaevitz tool in the foreground, I systematically inserted a core piece into the hollow of the LVDT a half millimeter at a time. With each increment, the LVDT puts out a different voltage, which is measured by the box on the right. I make a plot of distance versus voltage that tells us the calibration factor for our experiments. 

Meanwhile, Heather checked the gauges and put a protective coating on the load cells. We use homemade load cells here, which is unusual I think. We will put one on the side of the sample to measure the horizontal load and one on the top to measure the vertical.