Effects of Particle Size and Shape

There is no single optimum particle size of molybdenum disulphide powder for lubrication, and the preferred size depends on the application. For example, the finest powders will be more easily dispersed and give more stable dispersions in light solvents, whereas larger particles are more effective for carrying heavy loads. 

More important than the particle size are the purity and the particle shape. The effect of bad milling on a large lamellar particle is a particle having far smaller shape factor or aspect ratio than the original material. Since it is the basal plane surface which provides low friction and the edges which cause abrasion, it is therefore important in milling to maintain the highest possible aspect ratio consistent with the required particle size. 

These effects of particle size and shape have all been described in connection with dispersions, pastes, greases or loose powders, in which particles remain separated. The effects of particle dimensions on the formation and properties of films are far less clear. The process of film formation as described in Sections 6.2 and 6.3, would seem likely to benefit from large particle size, for a number of reasons. Large particles would presumably embed more effectively in substrate surfaces. Subsequently large particles would experience higher rotational couples than small ones during the orientation process. Finally, once the surface is fully oriented, a 

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I Goodarznia, DN Sutherland. Floe simulation Effects of particle size and shape. Chem Eng Sci 30 407-412, 1975. 

Rendon, J.L. Serna, C.J. (1981) IR spectra of powder hematite effects of particle size and shape. Clay Min. 16 375-381... 

Luxon, J. T., D. J. Montgomery, and R. Summitt, 1969. Effect of particle size and shape on the infrared absorption of magnesium oxide powders, Phys. Rev., 188, 1345- 1356. 

Effect of Particle-Size and Shape—The effect of particle-size on consistency is clearly shown in Figures 95 and 96, taken from the investigations of Ward and Kammermeyer (1940) and DeVaney and Shelton, respectively. Note that as the size of the average particle decreases, the consistency of the pulp increases. In other words, pulps composed... 

Celik, M., Ong, J. T., Chowhan, Z. T., and Samuel, G. J. (1996), Compaction simulator studies of a new drug substance Effect of particle size and shape, and its binary mixtures with microcrystalline cellulose, Pharm. Dev. Technol., 1,119-126. 

Swaminathan V. Kildsig D. Polydisperse powder mixtures Effect of particle size and shape on mixture stability. Drug Dev Ind Pharm 2002 28(l) 41-8. 

Foss, C.A. Jr, Hornyak, G.L., Stochkert, J.A. and Martin, C.R. (1994) Template-synthesis nanoscopic gold particles optical spectra and the effects of particle size and shape. J. Phys. Chem., 98, 2963-2971. 

The effect of particle shape on bulk powder properties has been illustrated by Rupp (5). The effect of particle size and shape on the bulk density and flow rate is illustrated in Figures 2 and 3. As illustrated in these examples, packing of powder in the bulk becomes more efficient as the shape factor or loss in sphericity increases. The flow rate becomes worse with loss in sphericity. 

Pilpel, N. Walton, C.A. (1974) The effect of particle size and shape on the flow and failure properties of procaine penicillin powders. J. Pharm. PharacoL, 26, IP-IOP. 

M.C. Bonferoni, S. Rossi, F. Ferrari, M. Bertoni, C. Caramella, A study of three hydroxy-propyl cellulose substitution types Effect of particle size and shape on hydrophilic matrix performance, STP Pharma Sci, 6 277-284,1996. 

Table 4 compares calcium carbonate, hard clay and soft clay in an SBR compound. The effects of particle size and shape are evident. The ealeium carbonate represents large (approximately 2500 nm average) isometrie particles providing little improvement in eompoimd properties compared to the clays. The hard clay provides greater tensile and tear strength than the soft clay. 

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