CHARACTERIZATION OF PARTICLE-SIZE BASED ON FINE AND COARSE FRACTIONS

The mathematical modelling and analysis of particle or droplet size di stributions have been extensively investigated in the chemical enginee ring literature. One such mathematical description is the Rosin-Rammle r model that has found extensive application in milling and crushing o perations and size distributions obtained from spray nozzles. The Rosi n-Rammler function is represented by two parameters: mean size and n-v alue (width of distribution) and a goodness-of-fit factor is often als o given. The increasing importance of granulation operations in the ph armaceutical and chemical process industries and the advent of process es other than spray drying have limited the scope of applications of t he Rosin-Rammler function. There is also increasing emphasis on qualit y control, which is expressed as limits on proportions of fines and co arse particles. Therefore it has been postulated that simply measuring the fractions of coarse and fine particles in an assembly can provide the necessary and sufficient data for quality control, without loss o f accuracy with respect to Rosin-Rammler. A sound, mathematically rigo rous, yet simplified and practical approach has been formulated that a ims to address the needs of both powder manufacturers and scientists. This paper shows that for every Rosin-Rammler distribution there is a coarse and fines fraction that maps uniquely to a Rosin-Rammler curve. Consequently, the coarse and fines fractions, which are of main inter est anyway, can be used to describe the Rosin-Rammler distribution wit hout any loss of data integrity. The advantages of the approach may be summarized as follows: (i) a particle size distribution can be expres sed with confidence by using two real, comprehensible numbers; (ii) a particle size distribution as measured by sieving is simplified to the use of two sieves, the coarse and fines sieves; (iii) analysis of dat a is reduced to the calculation of two parameters, the coarse/fines fr action and the coarse + fines fraction; (iv) the approach allows the c onventional Rosin-Rammler parameters d(m) and n to be determined; (v) extremely rapid checks can be made on fines and coarse levels of the p rocess output and whether or not changes in process parameters/conditi ons have led to the required outcomes; (vi) the approach can be adapte d to any mathematical expression that closely describes the particle s ize distribution; (vii) the influence of coarse and fine particles on the Rosin-Rammler mean size and n-value can be comprehended, in partic ular the fact that for any mean size and n there will exist a unique c oarse and fines level.