The driving force for sintering

The vapour pressure over a curved surface, p, is related to the vapour pressure over a flat surface, po, by the Kelvin equation  

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In die operation of die first source, the driving force for sintering is the difference in curvature between the neck and the surface of the sphere. The curvature force A l, is given by... 

The values of m given above conform to Hemng s scaling law (1950) which states that since the driving force for sintering, the transport length, the area over which uansport occurs and the volume of matter to be transported are proportional to a, and respectively, the times for equivalent change in two powder samples of initial particle size ai q and 2,0 are... 

This experiment is discussed here in some detail both beeause it casts light on the driving force for sintering and because it is a beautiful example of the ingenious... 

The driving force for sintering is the reduction in the total free energy of the particulate system, AG, which is composed of free energy changes of volume, AGy, boundaries, AGb, and surfaces, AGt. 

Commonly, the applied pressure is much greater than the driving force for sintering, and as a result, equation (e) of (17.2.3.5.1) becomes ... 

External pressure can be applied to provide the driving force for sintering in addition to surface curvature, which could be comparatively smaller in this case. The pressure should be applied during the key state of sintering. There are two ways to apply pressure hot pressing and hot isostatic pressing. By applying an external... 

Figure i.5. Basic phenomena occurring during sintering under the driving force for sintering, A(yA). 

In what follows surface is defined as the plane between condensed matter and a vapour phase or vacuum, such as solid/vapour and liquid/vapour interfaces. In a broader sense, the term interface is used for the dividing plane between any two different phases. The existence of an interface means, by itself, the presence of an excess interface energy over the bulk energy. Since the driving force for sintering is the reduction of the total interfacial energy of the system concerned, it will be useful to understand the thermodynamic characteristics of interfacial energy. 

In the absence of an external stress and a chemical reaction, surface curvature provides the driving force for sintering (Fig. 7.1). To see why this is so, let us... 

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