Resumo

TEIXEIRA, Clementina; ANDRE, Vânia; LOURENCO, Nuno  e  RODRIGUES, Maria José. Crescimento de cristais por nucleação heterogénea: "On the Rocks" revisited . C.Tecn. Mat. [online]. 2007, vol.19, n.1-2, pp.66-77. ISSN 0870-8312.

Crystals are of an increasing importance in our Society. In the beginning of the XXI century, Crystal Engineering started to develop, emerging from the main area of Crystallography. In spite of the dominating Bio- and Bio-logical trends in modern Technology, we cannot ignore our life on Earth (and other planets?) surrounded by natural crystals, in the composition of rocks, minerals, metals, and as the basic units of solids, a lot of them being inorganic. Therefore we must understand them, improving our knowledge on them. We can’t afford to neglect the classical Sciences like Inorganic and Analytical Chemistry related to their studies: they seem as if they became out of fashion (at least in our country!), but we cannot deny their importance for understanding Mineralogy, Geology, Materials Sciences, Environmental studies, Bioinorganic Sciences (the role of metals in our bodies as active centres of enzymes…) etc.. If we neglect and dismember Chemistry, the future generations will very fast loose the skills to understand our surroundings and furthermore, their own bodies!   On the Rocks is a research project for inorganic chemical education, consisting on crystal growth on rough surfaces, (rocks, minerals, shells, metallic wires, etc.)[1-10].These substrates, acting as "hosts", are introduced in supersaturated solutions of chemicals, promoting a faster nucleation and strongly stimulating crystal growth. Only substances that can afford large single crystals easily are chosen. Mainly ionic salts fairly soluble in water have been studied, a few of them here described. The technique requires inexpensive glassware and is feasible in schools poorly equipped, under close surveillance and strict safety rules. The large single crystals embedded on the host rocks look like "minerals" (synthetic!), and their beauty is a powerful tool to attract students for Chemistry and other Sciences sharing a common interest on crystals. Many concepts can be introduced during and after the preparation of the samples, especially those regarding group chemistry, and no background on crystal growth is required. The diversity of compounds and hosts one might choose, plus the reactions and interactions that might occur between them turns the method very interesting and creative. This research project started in 1993 and two years later a large network started as a co-operative project between our University Research Centre, Industry, and many Portuguese schools with very interesting results.

Palavras-chave : Crystal growth on rocks; synthetic "minerals"; heterogeneous nucleation; group chemistry; scientific photography.

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