Sinter-neck growth

When diree spherical particles are sintered together, die volume between them decreases as the necks increase until a spherical cavity is left. The source of material to promote further neck growth is now removed by die coalescence of... 

Figure 16.6 Model sintering experiment demonstrating neck growth during sintering...

Data for the neck growth of polymethyl methacrylate (PMMA) during sintering is plotted in Figure 14.10. 

Equations for neck growth in the initial stage have been derived for each mechanism. While the neck growth equations were critical to the early development of sintering theory, their usefulness in practical sintering is limited. The predicted dependence of the... 

Figure C2.11.6. The classic two-particle sintering model illustrating material transport and neck growth at the particle contacts resulting in coarsening (left) and densification (right) during sintering. Surface diffusion (a), evaporation-condensation (b), and volume diffusion (c) contribute to coarsening, while volume diffusion (d), grain boimdaiy diffusion (e), solution-precipitation (f), and dislocation motion (g) contribute to densification.

Mo + 2 Fb2B —> Mo2FeB2 -1- 3 Fe Solid state reaction, enhanced growth of sinter necks, formation of spherical particles and clusters... 

Because amorphous materials, such as glasses, have no grain boundaries, their neck growth and densification are caused by viscous flows and the deformation of the particles. In practice, the paths of matter flows are not clearly defined. The geometrical changes caused by the viscous flow could be complex, in which the equations for matter transport can only be established with significantly simplified assumptions. The sintering mechanisms of polycrystalline and amorphous solids are summarized in Table 5.2. 

Equations for initial stage of sintering have been intensively studied in the open literature [20, 21, 29-32]. With the equations for neck growth and the densifying mechanisms, shrinkage can be expressed in the following general forms ... 

Fig. 5.43 The three mechanisms of grain-shape accommodation and neck growth during solution reprecipitation controlled densification of liquid-phase sintering a contact flattening, b dissolution of small grains, and c solid-state bonding. Reproduced with permission from [73]. Copyright 2009, Springer...

The viscous flow mechanism, which was first proposed by Frenkel," can be operative in the sintering of viscous materials like glass. If the material follows the behaviour of a Newtonian fluid, the neck growth and shrinkage kinetics are expressed as follows. 

As the evaporation or condensation of material is basically controlled by reactions of atoms at the surface, the kinetics of sintering by the evaporation/ condensation mechanism is also determined by either evaporation or condensation of atoms. The kinetics of neck growth by this mechanism was derived from the Langmuir equation, a gas adsorption equation. The use of the Langmuir equation means that the condensation of atoms controls the neck growth. 

Sintering mechanism Neck growth Shrinkage Scale exponent a... 

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