A Rapid Method of Determining Salt Flux Melting Point and Composition

Abstract

Salt fluxes are commonly used in the recycling of dirty or high surface area aluminum scraps and drosses. The salt fluxes perform many functions such as stripping away the oxide films and promoting droplet coalescence, but to be effective they must be in a molten state. The most common class of salt fluxes used in aluminum recycling contain a mixture of sodium chloride (NaCl) and potassium chloride (KCl), and often minor amounts of a fluoride compound such as cryolite. Fluxes are specified to certain chemical compositions to produce a defined melting point of the flux. The NaCl–KCl phase diagram is a simple eutectic system. By measuring the liquidus temperature of the mixture it is possible to accurately back calculate the composition of the blend and verify that the delivered flux matches the desired specifications. This paper describes a practical method for measuring the liquidus temperature and then inferring the flux composition.