Plasma

I may have mentioned before that I love my job. One of the things that I love most about my job is that being such a small company we get the chance to try all sorts of different things. A large company has many specialists and you become quite confined but with only a dozen employees, if you want something done you pretty much have to do it yourself. As you probably know, I do research and development in thermoelectrics. Since the first half of that name is "thermo" you may have guessed that we do a lot of work at high temperatures.

One of the machines that is key to my work is a large machine called a vacuum hot press. This machine can heat a sample to over 2,000°C (for those of you who haven't made the switch to the metric system that is nearly 3,700°F) and while it is hot it can pull a hard vacuum. The vacuum we use removes 99.99999% of the air, that means that if you have 10 million molecules we remove all but one of them. While hot and in the vacuum we can then press the sample with 23,000 kgs of force (for you non-metric types that is 50,000 pounds). You can do amazing things under those conditions. We actually have two vacuum hot presses, one is heated with graphite heating elements and the other one is inductively heated. Induction coils are very cool things. If you take a coil of wire and pass a high frequency electric current through it, it will create an electromagnetic field. If you expose an electrically conducting material to the electromagnetic field it will generate electric current in that material. The induced electrical currents will then heat the part up. Our induction furnace has water cooled copper tubing wound in a coil and when we put a molybdenum die inside the coil we can heat it to 600°C in about one minute.

An electromagnetic field will try and ionize any gas that is in the area. While the electromagnetic field we use doesn't have a high enough voltage to ionize a normal atmosphere we typically heat our parts up in a reducing atmosphere and then once it is hot we start to pull a vacuum. As the pressure of the gas drops it is easier to ionize it and if you watch the induction coil you will gradually see a plasma form around it. As the pressure drops further the plasma gradually disappears as the gas is all evacuated. A plasma is just another name for an ionized gas. A plasma is actually the forth state of matter. The other states that you're probably more familiar with are solid, liquid and gas. It really is a beautiful sight to behold. Our technician took some pictures and a short video on his I-phone. I begged him to share it with me so I could share it with you. I hope you enjoy it as much as I do.