Moisture-induced caking of boric acid powder

There is a need to establish a caking test that gives a measure of the caking propensity of powders due to the presence of moisture in a relatively short time. A suitable test has been developed for materials that cake by the partial dissolution and recrystallisation of material to form solid bridges between particles. Boric acid (H3BO3) has been used as a candidate material due to its modest tendency to cake. The developed test involves addition of a specific amount of water to a powder, and then subjecting the contained powder to temperature cycling. The amount of water for addition is determined by independent measurement of the equilibrium moisture sorption isotherm. A caking index can be obtained by comparing the mass of cake formed to the mass of original sample.