Elastic Sintering of Fine Particles

The question of what happens when a bunch of particles comes together was asked by Newton, who found the process diffieult. Yet if aU particles adhere strongly as described above, they should leap into contact, then deform and squash closer to each other as a result of molecular adhesion. It is a paradox that particles which adhere sttongly do not do this. Instead they form weak, loose treelike structures because each particle sticks where it touches, as shown in Fig. 9.19(a). This instant adhesion therefore prevents good compaction, which can only be achieved if the particles do not adhere strongly but can wander around to find dense close-packing positions. Fig. 9.19(b). 

If the agglomeration process has been allowed to proceed to close-packing then there are twelve such contact spots on each sphere, Fig. 9.20(b), so that the sintered fraction is 12 times that of Equation (9.18). Putting in numbers shows that 1 pm particles of 1 GPa modulus will be about 1% sintered when close-packed under a work of adhesion 1 Jm.  

This sintering idea was first proposed to account for the coalescence of 

The JKR explanation of latex coalescence was proposed in 1982. Padget had observed the hexagonal structure of coalesced rubber latex (Fig. 9.21 (a)) and Kendall had measured the contact spot sizes between latex particles using electron microscopy (Fig. 9.21(b)). When the results were plotted in Fig. 9.21(c), they fitted the JKR equation and macroscopic observations, taking the elastic modulus to be 5.64MPa and the work of adhesion to be 26.5 Jm  

The theory of coalescence required two stages the first was an agglomeration step which was driven by drying of the latex film, allowing the particles to be pushed together into close-packed adhesive contact, but with small adhesion because of the presence of water the second was a sintering step in which the work of adhesion increased as the last water was removed and elastic deformation occurred with shrinkage. 

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