Sub-sampling

Once all of specimen cross sections and internal surfaces were thoroughly examined and all the regions of interest had been identified. The sampling locations were defined and the sampling process was undertaken. This involved cutting further segments to isolate the regions of interest, and each of the resulting segment were subsequently cut in to suitably sized sub-samples. Finally

the samples were cut to a thickness of 3~5mm and no greater than 28mm at the widest point. After a suitably sized and representative sample was obtained, the piece was thoroughly washed with a dilute detergent solution, then with deionised water, and finally with ethanol. The cleaned samples were then oven dried at 100˚C for at least twelve hours.

The samples were subsequently removed from the oven and placed in a desiccator where they were allowed to cool to room temperature. Each sample was then taken from the desiccator and carefully positioned in a 30mm polypropylene mould, and a small amount of cyanoacrylate adhesive was used to fix the sample to the mould to prevent it moving during the next step of resin impregnation.

A colourless, transparent, cold-setting epoxy resin was prepared and poured over each sample to fill the mould to around 15mm, a label was created for each sample bearing its unique sample identification code and placed in the resin alongside the sample. The filled moulds were then transferred to a vacuum desiccator and place under vacuum overnight. This vacuum process aided in the removal of bubbles from the epoxy resin and ensured that the resin penetrated and filled the cracks and vesicles present in this material type, improving structural integrity and reducing friability. Once the resin had hardened, the moulds were removed from the vacuum desiccator and the encapsulated samples were removed from the moulds.

The newly formed 30mm epoxy resin stubs containing the slag samples were then ground using abrasive papers on rotating turntables, lubricated and cooled with water. This step was undertaken to completely expose the slag sample on one surface and to produce a uniformly flat sample. The grinding process was completed in a number of steps using progressively finer grades of silicon carbide abrasive papers. The papers used were 180, 400, 800, and 1200 grit. Periodically the grinding surface was examined using a metallurgical microscope to determine the extent of the slag samples exposure and to ensure sample surface flatness. After grinding, the exposed slag surface was thoroughly cleaned with a dilute detergent solution. If the surface of the sample was

particularly vesicular or cracked the sample was cleaned in an ultrasonic bath using a dilute detergent solution. Each sample was then rinsed with plain tap water, then with ethanol, and then hot-air dried.

After the complete exposure of the slag samples surfaces was achieved, the ground samples were then taken to a further set of dedicated rotating turntables for polishing. As these samples would not be etched or subjected to any significant optical microscopy, a 3μm polish was determined to be sufficient. This was accomplished in two steps, firstly a 6μm polish and then finally a 3μm polish.

Each turntable was equipped with an appropriate size-grade polishing cloth onto which a small amount of diamond paste polishing media was dispensed, a water based lubricant was then sprayed onto the cloth and the samples were polished. Periodically the surface that was being polished was examined using a metallurgical microscope to look for remaining deep scratches from the grinding stage. Once the 6μm polish was completed the sample was thoroughly cleaned with a dilute detergent solution, for particularly vesicular or cracked samples an ultrasonic bath filled with a dilute detergent solution was used. Each sample was then rinsed with plain tap water, then with ethanol, and then hot-air dried. This cleaning process was of particular importance at this stage as cross contamination of 6μm polishing media on to the 3μm polishing cloth would render the cloth useless. After the 3μm polish was completed, a slightly more rigorous cleaning regime was adopted to prepare the final polished surface for carbon coating, this included repeated washing with a detergent solution, then with deionised water, then finally with ethanol. An air duster was used to expel any remaining liquids from cracks and vesicles, and finally the sample was hot-air dried. The polished surface was carefully examined using both a stereo-microscope and a metallurgical microscope, looking for unpolished regions, surface contamination and residues. At this stage any physical contact with the newly cleaned surface was avoided to prevent contamination.

All of the prepared samples were then coated on their polished surface with carbon using a vacuum

evaporation coater. This step would produce a thin conductive coating on the samples surface to prevent charging when placed under the electron beam of the scanning electron microscope. To ensure good conductivity and to complete an electrical circuit with the electron microscopes stage a small strip of aluminium tape was adhered to the sample stub connecting the coated surface to the base of the stub.

A small selection of duplicate samples were also taken, these additional samples would be used for other testing methods. Two additional samples were prepared using the resin encapsulation method described above, however, they did not receive a final carbon coating. These samples would be used for optical microscopic techniques and pXRF. A further two samples of approximately 10g each were used to produce a fine powder for EDXRF and PXRD.

The powder samples were produced by coarse maceration of the as-cut slag samples, using a Dodge-type jaw crusher, into nodules of ≤5mm suitable for crushing in a ring mill. Then a tungsten ring mill was used to crush the coarse nodules into a fine powder with a grain size of ≤10μm. The powders were then transferred to airtight containers for storage. Airtight containers were deemed necessary after the first set of duplicate sample powders exhibited notable changes in appearance after storage in polymer baggies. Initially, the as-crushed samples appeared as a dark orange-brown powder, and upon retrieval for analysis after ten days of storage it was observed that the samples had changed colour, appearing much lighter in colouration. This observed change was explained by the powder samples having a much greater surface area to volume ratio than the intact solid samples, this increases the reactivity potential of the powder allowing it to readily react with atmospheric moisture and oxygen.