Diffusive sintering experimental studies

In an early experimental study of sintered monazite, Shestakov (1969) estimated an activation energy of 60 kcal/mol by volatilizing Pb in a stream of nitrogen at temperatures between 800 and 1100°C. Smith and Giletti (1997) measured the tracer diffusion of Pb in natural monazites using ion microprobe depth-profiling and observed Arrhenius parameters o E = 43 11 kcal/mol and Do = 6.6 x 10 mVsec in the temperature range of 1200 to 1000°C (Fig. 4). They found that transport parallel to the c-... 

Experimental Studies of Diffusive Sintering presents the limited data available on the densification kinetics of crystalline gels. A given composition is shown to sinter much more slowly if it is allowed to crystallize first. 

In this paper, we extend the classical 2-dimensional Ostwald ripening model in the light of new theoretical developments, and present novel solutions, compatible with the experimental particle size distributions. A family of solutions is available for each limiting case studied, i.e. when sintering dynamics are controlled by either crystallite-support interface interaction or by the rate of diffusion of adatoms on the support. 

An experimental setup for gaseous systems is shown in Fig. 7. The actual ZLC column consists of a thin layer of adsorbent material placed between two porous sinter discs. The individual particles (or crystals) are dispersed approximately as a monolayer across the area of the sinter. This minimizes the external resistances to heat and mass transfer, so that the adsorption cell can be considered as a perfectly mixed isothermal, continuous-flow cell. The validity of this assumption has been examined in detail [52]. The isothermal approximation is generally valid for studies of diffusion in zeoHte crystals, but it can break down for strongly adsorbed species in large composite particles under conditions of macropore diffusion control. 

Therefore, care must be taken in discussing sintering mechanisms based on previous investigations. Some investigations determined diffusivities from sintering experiments. However, the diffusivities determined in these experiments may have no absolute meaning because of the inherent problems and may imply only that related diffusion mechanisms were operative in the experimental conditions studied. 

---