SEE behind the scenes – Studying crystal formation

SEE behind the scenes is a bi-annual event during which undergraduates can visit different labs within the School of Earth and Environment. As members of the Cohen group, Daniela, Tomasz and I thought that this would be a good chance for us to introduce the laboratories we work in and to show the undergraduates some simple but exciting experiments on how to make crystals.

In my opinion, visiting scientific laboratories can help undergraduates to see a different aspect of the subject they chose to study. It also helps them to decide if they want to pursue an academic career or not. I remember when I was an undergraduate student, I was always curious to find out what researchers do in their labs and how (and what for) they use their fancy instruments.

We planned to talk to the undergraduates about calcium sulphate minerals (CaSO4 ∙ x H2O), as they are common minerals in nature and important for industry (e.g. building materials and plaster). Ever since the discovery of the giant crystals in the Cave of the Crystals (Naica, Mexico), calcium sulphates have been quite well known. My interest for these minerals is derived from a less spectacular point of view (but more important). I study the formation of calcium sulphates scales in industrial systems and the effect of additives on their growth during my PhD. Therefore, I had lots of materials and experiments ready to show to the undergraduates!

1Impressive example of naturally formed gypsum crystals from the Cave of the Crystals, Naica, Mexico (source: National Geographic)

Together with Daniela and Tomasz, I prepared some background information on the formation, mining and usage of calcium sulphates that we then used to give an introduction to the students. The most interesting part of our demonstration however was three experiments to show the students calcium sulphate precipitation in front of their eyes. I had prepared 200 mM Na2SO4 (the source of the sulphate ions) and 200mM CaCl2∙2 H2O (the source of the calcium ions) solutions. Upon mixing of these solutions, calcium sulphate precipitates, producing a turbid solution. In the pure system this took about 90 seconds.  By adding additives we could speed up the process (oxalic acid → instantaneous turbidity) or slow it down (NTMP, a complex organic acid → several hours). I also showed the students how to filter the solutions to separate the crystals that formed and to then use them for further analysis.

2 3

Showing the calcium sulphate precipitation experiments to a group of undergraduates.

In a next step, Daniela explained to them that researchers have to use scientific instruments to quantify their observations in order to publish their data and findings. As an example, she explained the use of the UV-Vis spectrophotometer. This instrument measures the intensity of a light beam before and after the sample and therefore can quantify the turbidity of a solution. She also explained how the Fourier Transform Infrared (or FTIR) Spectrometer can be used to identify different components in the precipitates as they each produce a typical, fingerprint-like signal. We also showed the students some of my high resolution microscope pictures (taken with an SEM) so they would believe us that we actually made tiny crystals of calcium sulphate during the experiments. The pictures also show that the additives do not just affect the reaction rate but also the shape of the crystals formed.

During the 2.5 hours of the event, we had five groups of two to six students visiting our lab. For me this activity was my first time doing outreach and it was really unforgettable. Firstly, I enjoyed the collaborations that I had with my colleagues Daniela and Tomasz. Secondly we could show the visitors some new and interesting things they had never seen before. It was obvious that they enjoyed this experience as they could actually see something happening in the experiments. I hope to have more activities like this in future as I really enjoyed it!

4High resolution microscopy (SEM) images of gypsum precipitates (left) gypsum precipitated in the presence of NTMP (right).


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