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The rapid determination of ‘live’ clay in greensand is an essential procedure for the efficient running of a foundry production line, since progressive calcination of the clay binder during casting affects mould competence and quality of finish. A new method for assessing the active fraction of clay in foundry sand is described that is based on the response of an ion-selective electrode (ISE) to sodium ions liberated from the clay by ammonium ions. The method possesses advantages of speed and objectivity over the Methylene Blue titration method presently employed in foundries. Results appear to be unaffected by the presence of coal dust in greensand.
The sample (5 g) was stirred for 2 min with a NH4Cl/NH3 solution. A Na ISE was then immersed in the suspension and the potential was recorded. The ISE response, which was related to the concentration of Na ions displaced from the sample, was used to calculate the amount of live clay present in the greensand. The detection limit was 0.5 ppm Na. The method was faster and gave better accuracy and precision than the methylene blue titration method.
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