Studying Deliquescent Relative Humidity Lowering in Mixtures of Five Fertilizer Ingredients Using Mixture Experiments and a Special Cubic Equation

Abstract

The lowering phenomenon of deliquescent relative humidity (DRH) in the binary to the quinary systems was studied. Gravimetric moisture sorption isotherm experiments were employed to obtain data for estimating DRH. A special cubic model was constructed for the purpose of predicting DRH. The predictive equation described the significant factors which were all the ingredients, all the binary interactions, and one of their ternary interactions. It gave accurate predictions with an average relative deviation of 1.8% compared to the values between 2.3% and 32.4% produced by equations reported elsewhere. DRH lowering occurred in all possible combinations of the ingredients, and the magnitudes of DRH lowering were exceptionally high when urea and one or more deliquescent ingredients were present together. Despite its insoluble nature, kaolin-based filler also caused DRH lowering. However, its presences in the quaternary and quinary systems alleviated the DRH lowering that was caused by other ingredients.