I arrived in Hannover, Germany, just over a week ago to do high pressure/high temperature experiments at Leibniz University. I’ll be in Hannover for the next two months to hopefully get all the experiments finished I need for my first PhD project. I’m using the amazing experimental facilities and collaborating with geologists who have done these types of experiments for their entire careers, and I’ve already learned a lot in my first week. I came to Germany with everything I need to load capsules for experiments: cutting tools, extra capsules, starting materials and rock powders, polishing equipment, and pre-prepared capsules ready for test runs.
Specifically, I’m doing experiments at high temperature and pressure in Internally Heated Pressure Vessels (IHPVs) to study the behavior of sulfur when a liquid magma has apatite crystallizing from it deep in the Earth. The process for doing these experiments requires a lot of planning and knowledge about the melting temperature of the rock powder and the amounts of water and sulfur to add. After those details have been figured out the experimental capsules are prepared by adding certain amounts of starting materials to a gold capsule and welding it shut. The weld has to be very good – any tiny hole or weakness will cause the capsule to explode and the experiment to fail because of the high temperatures (over 1,400 degrees F) and pressure (more than 43,000 psi) conditions in the vessel.
Once the capsules are made, welded shut, and checked for leaks they are wrapped together with platinum wire and hung by a ring in a ceramic tube. This tube is then inserted into the IHPV and the temperature/pressure conditions are set on the computer. It takes about 45 minutes to reach the run conditions inside the vessel, and then the clock starts for the experiment. My capsules are in the IHPVs at run conditions for 3 days, so once they are set up and going my job is pretty easy just watching to make sure nothing catastrophic happens with the temperature and pressure.
Once the time is up the capsule package is dropped to the bottom of the ceramic tube by applying a voltage across the platinum wire, where it cools to room temperature instantly. The pressure takes longer to pump down, around 4 hours, as releasing it too quickly would damage the vessel. The capsules are taken out and I carefully cut open the gold capsule to retrieve the run product inside – the magma glass with apatite crystals! I mount the run products in epoxy, polish them flat, and examine them under the microscope to see what we have. I need to analyze apatite crystals for my project, so growing apatites large enough to analyze is key these experiments. I’ve done two test runs with capsules I prepared in Michigan: the first had apatite crystals, but they were much too small to analyze. The 2nd test run will finish tomorrow and I will hopefully find big crystals this week in the run products! To try to grow bigger apatites, we tried temperature cycling in the 2nd experiment. This means that instead of holding the temperature constant at 1000 C for the entire experiment we cycled the temperature between slightly higher (1020 C) and slightly lower (980 C) temperatures. This should promote the growth of larger crystals because the smallest apatite should melt at the lower temperature and add to the large apatites that don’t melt over time. I’m very excited to see what apatites we’ve grown after we end the experiment tomorrow. If they’re big enough, I can start running my actual experiments for real!
I’m also planning some travel in Europe while I’m here — find those posts under Travel!