Solid phase sintering

The effect of Co on the process of diamond powder compaction has been studied at the pressure of 8 GPa and temperatures between 1400-2000 °C. It is shown that the interaction between liquid Co and diamond particles speeds up the process if not changes the limiting value of shrinkage as compared with solid phase sintering. The dependences of the rate of diamond powder infiltration with cobalt and Co-WC, Co-Mo and Co-Ti melts on the temperature have been studied experimentally under high pressure. It is shown that the infiltration by pure cobalt occurs quicker as compared with that by cobalt-base alloys. Based on the Einstein equation for the viscosity of mixtures, an equation for the infiltration coefficient is derived which is in good agreement with the experimental data for Co-Ti and Co-WC alloys. 

Thus, sintering diamond powders with the liquid cobalt present considerably speeds up the compaction process, not changing though the limiting value of shrinkage as compared with the solid phase sintering. 

We have established the Kp(t) dependence for diamond powder of 14-20 pm in size at the temperature of 2400 K and the pressure of 7.7 GPa in solid phase sintering. In this case, the Kp(t) becomes constant in 7 s [6]. However, if this powder is cobalt-infiltrated, the Kp(t) becomes constant in 0.5 s. under the same thermobaric conditions. Considering that in our experiments the liquid migration time ranges from 2 to 20 s, let us assume that Kp(t) is constant. Having integrated equation (1) we obtain... 

Some researchers attempted to crystallize IrSbs from a Sb-rich melt[3J. In this method, the IrSb3 ingot contains many Sb inclusions. On the other hand, an attempt was made to form IrSb3 via liquid-solid phase sintering (LSPS) with an Ir and Sb powder mixture. However, the relationship between the fabrication process and the IrSbs thermoelectric properties was not clear. 

In this work, an attempt was made to prepare IrSbs by liquid-solid phase sintering (LSPS) and hot pressing of pulverized LSPS powders. The LSPS powder were characterized by using an X-ray diffractometer. These procedures were also applied to form an IrSbs-CoSba solid solution. The electrical conduction parameters of these materials were examined on the electrical measurement. The thermal stability of the hot-pressed IrSbs was also investigated. 

The diffraction patterns of the IrSbs reacted material taken from the two different regions were identical to each other as shown in Fig.2, and they agreed with the pattern of a skutterudite structure. It is confirmed that a homogenous skutterudite IrSb3 structure was formed by the liquid-solid phase sintering of Ir and Sb powder mixture. 

Haviar M (1985) The mechanisms involved in solid-phase sintering. Silikaty 29 363-377... 

Sintering excludes a complete melting of the material and can therefore occur without any liquid phase. However, it can be facihtated by the presence of a hquid phase, in a more or less abundant quantity. We can thus distinguish solid phase sintering on the one hand and sintering where a hquid phase is present the latter... 

Figure 3.2. Top, vitrification the liquid phase is abundant enougfi to fill the interstices between the particles in the middle, liquid phase sintering the liquid is not suffieient to fill the interstiees bottom, solid phase sintering organization and shape of the partieles are extremely modified. This diagram does not show the grain coarsening in fact, the grains of the sintered material are appreeiably coarser than the starting particles [BRO 91 If...

For solid phase sintering, there are fonr ways of diffusion i) surface diffusion, ii) volnme diffusion (often called lattiee diffusion), iii) vapor phase transport (evaporation-eondensation), and iv) grain boundary diffusion the boundaries are very disturbed areas, which allow diffusion short-circuits . For liquid phase sintering, we must add dissolution-reprecipitation effects or a vitreous flow. Finally, for pressure sintering the pressure exerted allows the plastic deformation of the crystallized phases and the viscous flow of the amorphous phases. 

T able 3.1. Matter transport during a solid phase sintering [ASH 75]... 

Figure 3.4. Matter transport during a solid phase sintering mechanisms I, 2 and 3 are non-densifying mechanisms 4, 5 and 6 are densijying 1 schematizes a dislocation [ASH 75]...

Solid phase sintering 3.5.1. The three stages of sintering... 

Solid phase sintering refers to the case where no hquid phase has been identified (but observations through electronic microscopy in transmission sometimes show the presence of a veiy small quantity of hquid phase, for example due to a... 

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