Aggregate Strength—Interparticle Bonding

These can show the actual appearance of the interparticle bonding, especially if the particle diameter is greater than 15-20 nm. This is the case with certain powders but generally not so with conventional gels. 

If the particle diameter, d, can be measured, the theoretical surface area, Se, for spheres can be calculated from the relation 

The method was applied to a precipitate of silica particles about 12 nm in radius. This precipitate had a coalescence of C = 0.47, from which r /rp = 0.19 and 2.3 nm. Additional silica was deposited on the original suspension to the extent of 2 parts of added silica to 1 of original silica, which should increase the particle radius by 3  

It is seen that the increase in particle radius is of the same magnitude as the increase in neck radius. However, the latter should have increased more, rather than less, rapidly than particle radius. Possibly deposition of silica is more rapid on the open surface of the particle than in the crevice at the neck. 

Another typical application was to follow the sintering of relatively large colloidal silica spheres with a radius of 50 nm when heated for 1 hr in air at elevated temperature. 

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