Dispersant selection for aqueous medium pressure injection moulding of anhydrous dicalcium phosphate

Injection moulding is an extremely versatile method for producing ceramic parts with complex shapes. However, there are many disadvantages associated with conventional injection moulding methods, which may include the requirement of high viscosity polymers, toxic solvents, high temperatures and pressures. In recent years, considerable attention has been directed towards the development of low/medium pressure injection moulding which is an alternative low-cost forming method using water and low melting point gelling food binders. The basic requirement for injection moulding is the preparation of a stable, well-dispersed slip, which is achieved by the selection of an effective dispersant. This paper details an investigation into the dispersing abilities of sodium citrate, sodium pyrophosphate and sodium carbonate in different concentrations (0.01, 0.1, 0.3, 0.5, 1 and 1.5 wt.%) in anhydrous dicalcium phosphate (DCPA) slips by studying the two main interlinking properties: electrophoretic mobility and rheology. Furthermore, the effects of temperature on the behaviour of the dispersants are also investigated. The results obtained showed that the optimum dispersant was sodium citrate at a concentration of 0.3 wt.% which yielded the greatest viscosity decrease (95.6%) relative to the slip without dispersant and showed the best stability over the injection temperature range.