Sintering stage

Figure 7.35 Densification behavior of compacts of two alumina powders (0.8- and 1.3 — /rm average particle size), with the sintering stages indicated for the coarser powder. A hot-pressed powder is shown for comparison. From J. S. Reed, Principles of Ceramics Processing, 2nd ed. Copyright 1995 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

The dominant mechanism and transport path—or combinations thereof—depend upon material properties such as the diffusivity spectrum, surface tension, temperature, chemistry, and atmosphere. The dominant mechanism may also change as the microstructure evolves from one sintering stage to another. Sintering maps that indicate dominant kinetic mechanisms for different microstructural scales and environmental conditions are discussed in Section 16.3.5. 

After the sintering stage, electrodes are applied, usually either by electroless nickel plating or by painting or screening on specially adapted silver paint. Leads are then soldered to the electrodes when, for many applications, the device is complete in other cases it may be encapsulated in epoxy or silicone resins. Examples are illustrated in Fig. 4.15. 

It is rather unfortunate that of ail the sintering stages the most important is also the most difficult to model. For example, any intermediate-stage model that does not take into account the details of particle packing has very limited validity. A cursory examination of the results shown in Fig. 10.10 should make this point amply clear. 

These compounds are prepared by the same procedures as titanium carbide. The reaction mixture consists of either ZrOg (or HfOg) + 3 C, or Zr (or Hf) + C the reaction temperatures lie above 2000°C. Since both ZrC and HfC are very sensitive to Ng, die high-temperature sintering stage must be carried out in 99% Ar. 

Preparation of magnetic ceramics Table 3.4. Sintering stages. 

Fig. 3.16. Schematic representation of sintering stages (a) greenbody, (b) initial stage, (c) intermediate stage, and (d) final stage.

To prevent the presence of such a phase on the samples, we proceed to the SO2-treatment just after the sintering stage in order to prevent a weak homogenity for the sodinm sulfate. 

Table 5.4 Parameters related to the three sintering stages of polycrystalline sohds...

In this case, the pores are assumed to have shrunk continuously and most likely disappear altogether. Main parameters of the three sintering stages are summarized in Table 5.4. 

Similar assumptions are made for the final sintering stage, so that nondensifying mechanisms can be neglected, which is similar to that in the intermediate stage model [27, 38]. The procedure to derive the sintering equations for the intermediate... 

Figure 4.1. Schematic showing the densification curve of a powder compact and the three sintering stages.

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