Particle surface morphology and roughness

The particle surface of mineral fillers can be estimated Ixom a knowledge of the crystal structure, since the milling process cleaves the crystals according to a typical pattern of cleavage for a particular mineral. Many crystals, particularly these of mineral origin, cleave in only one direction and form plate like particles. Table 5.4 summarizes the crystal structure and cleavage pattern of some fillers of mineral origin. 

The information in the table shows that the shape of filler particles is determined by their crystal structure and cleavage. The surface area of crystal is increased by milling but it retains the original features of the mineral. This 

Crystal structure Fillers (typical cleavage is given in parentheses) 

The surface roughness of filled materials is obviously not related to filler surface imperfections but it is very much determined by the shape of filler particles.The effect of glass fibers in plastics and flatting agents are specific examples of the influence of specific shaped particles on surface roughness. 

Specific surface area is a convenient method of characterizing fillers. The results can be correlated to many performance characteristics and to the properties of filled systems. Table 5.5 gives a summary of the specific surface area of some fillers. 

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