Growth of sodiumsulfate heptahydrate crystals

Leo Pel and Eric Doehne
Eindhoven Univerisity of Technology
The Getty conservation institute

The growth of heptahydrate crystals was observed with an optical microscope. The experimental setup is given in figure 1

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Figure 1: The experimental setup for optically following the crystallization of a sodium sulfate solution during cooling
 The sample is cooled down with help of a Peltier element

In this setup setup the sample is cooled down with the help of a Peltier element. Initially a droplet of saturated sodiumsulfate at 40oC  is put on the glass. From that moment on the sample is cooled down upto 5 oC and the crystallization is observed. At picture was taken at a fixed time intervals. At the end of the experiment the solution is touched with a mirabilite crystal forcing the transformation from hepta to mirabilite

RESULTS

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Figure 2: The growth of a single large heptahydrate crystal
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Figure 3: Growth of various heptahydrate crystals. The movie is made with top light.
The point at which the transformation is forced by a mirabilite crystal can clearly be observed
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Figure 4: The growth of a large heptahydrate crystal
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Figure 5: The growth of a large heptahydrate crystal
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Figure 6: The growth of a heptahydrate crystals
in the presence of a ring of thenardite crystals
(thenardite is supersurated with respect to hepta)