Making amorphous slag

Work Packages 1 and 2 of the SOCRATES project are working on the extraction and recovery of critical and economically important metals that are present in the investigated tailings, sludges, slags and ashes. This leaves behind residual mineral matrices that can be used in our Work Package 3: “Residual matrix valorization”, possibly requiring prior treatment processes. By activating these (treated) residues with alkaline solutions (i.e. solutions with high pH) a 3D network consisting of inorganic (e.g. Si, Al, Fe) elements is formed, which is called an inorganic polymer (IP).

a beautiful shiny amorphous slag obtained after quenching

a beautiful shiny amorphous slag obtained after quenching

In my thesis we focus on the production of IPs from amorphous synthetic slags, resembling these residual mineral matrices. More specifically, the focus lies on iron-rich residues mainly originating from the non-ferrous industry. The structure and the chemistry of the slags, that are used as precursors for the synthesis of the IPs, are of great importance, which is why I am studying the compositional dependence of reactivity and strength development. Previous studies have shown that by increasing the amorphous fraction of the slags, the reactivity can be boosted drastically, leading to a more suitable precursor for inorganic polymers.

The most common method of producing an amorphous solid is to rapidly cool the molten form of the material, i.e. quenching, which is also employed here. More precisely, quenching is a multi-step process, beginning with heating of the sample up to a temperature which is some hundreds degrees above the liquidus (lowest temperature at which a material is completely liquid), in order to assure that the material is completely molten. Careful attention must be paid on keeping the temperature throughout the material uniform. When the material (slag) is completely molten, is then quenched into water, for which I will let the video speak for itself! (the most interesting bit starts at 32″!) After quenching, a beautiful shiny amorphous slag is obtained, which can then be used as precursor for the synthesis of  inorganic polymers.



About The Author

ESR 12, Christina Siakati grew up in a beautiful small village, called Emporio, situated near Kozani in north Greece. There, she spent all her school years, till she went to university to become a physicist. Now, she is doing her PhD at the Materials Engineering department of KU Leuven in Belgium on “Iron-rich inorganic polymers derived from residual matrices”, deepening the knowledge of the structure and formation mechanism of Fe-rich inorganic polymers, following experimental and computational approaches. If you are interested in her topic and you wish to learn more about it, please don’t hesitate to get in contact with her at


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