Solidification of Eutectic Alloys in Microgravity

Every group in the PFC project had to plan an own experiment which focuses in some phenomena in weightlessness.

In the beginning we were thinking about two different experiment possibilities: To analyse the chrystal structure of a sample produced in microgravity or the behavior of different liquids in weightlessness.

Now after the project it is good that we chose the first option because all of the groups handling liquids had some problems in the waterproofness in the safety tests done by Novespace. Besides that we got some concrete evidence other than just observations or videomaterial. Also our test was not so complicated and during the microgravity phase we did not have much to do so we could enjoy the microgravity sensation in full.

First we asked a few persons in TUT Institute of Physics some advice and they directed us to the Institute of Materials Science. Professor Veli-Tapani Kuokkala was very interested in the project from the start and together we developed the idea of analysing Eutectic Alloys. We chose the Eutectic alloys because in them the component metals solidify at the same time and also the melting point is the lowest possible. As material we used normal solders and leadless solders. The sample had to be really small so that it would solidify in the twenty seconds time the microgravity lasted.

In the making of the equipment we got help from Protopaja in TUT for the electronics and the rough work was made in the Materials Science workshop. We ourselves did a great part of the work that didn't need any specialisation.

         

The model for developing the sample tube was a fuse. In the sample tube the wire is heated by the current flowing trough it. A spherical sample is attached to it and melts fast. The needed current for a 0.8 mm steel wire was about 15 ampers. This requires much from the power source, because it may not be overheated. Our first version of power source did not stand out the high current and low voltage. We made the stand for the sample tube from car's fuse holders. Another critical thing was the glass of the sample tube that could be broken quite easily. Also the sample had to be attached hard in order to the current to flow easily, but the samples had to be changed easily. We developed special pliers for changing the samples. They staked the sample tube ends so that no exertion was transmitted to the glass tube.

We produced more than one hundred of the samples and that took quite much time. Last of the samples were made during the week before the trip to France.

         

Changing the samples was performed between the parabolas. Two minutes was just enough for that. We had numbered the samples and held notes about how well the melting and solidification seemed to work. In normal conditions on the ground we produced the reference samples, that were later compared with the microgravity samples.

Video: The melting and solidification of a sample. (3.8M)

The premilinary results of our experiment are found here..

Our experiment outline in short can be found here.