Sintering effect, with small

Fig. 9. Influence of local temperature T and varying catalyst structure on the CO oxidation effectiveness factor . Each Pt/y-Al203 catalyst was reconstructed by packing of y-Al203 particles of two different sizes with small-to-large particles number 16. Small particles size d = 1 pm was kept constant, while large particles size <72 and particles fractional overlap (level of sintering) were varied. Gas concentrations the same as in Fig. 8 (Koci et al., 2007a).

Sintering with small amounts of melt involving substantial densification is possible when the solid particles are dissolved at the points of contact as a result, the particles come closer together, being attracted by the effect of surface forces acting in the melt surface. This phenomenon requires a certain solubility of the solid phase in the melt (so-called sintering with a reactive liquid) ... 

The recently developed materials of pure SiC can be manufactured by pressure sintering or reaction sintering of a mixture of SiC powder with graphite in silicon vapour. High-dcnsity SiC (98% of theoretical density) can also be prepared by sintering submicron powdered j3-SiC with small additions of boron and carbon at 2000 "C in an inert atmosphere. The effect of these additions is explained by surface effects (Prochazka, 1975). 

The level of loading is important to the role of the support in maintaining dispersion of the active component. Crystallites, even though isolated from each other on the support surface, may sinter. For very small crystallites. sintering occurs through migration over the surface followed by coalescence. Important faaors, besides temperature, are crystallite concentration, interaction with the support, and atomic mobility/ The effect of concentration is shown in Fig. 2.6. ... 

Lubricants protect die and punch surfaces from wear and bum-out of the compact during sintering without objectionable effects or residues. They must have small particle size, and overcome the main share of friction generated between tool surfaces and powder particles during compaction and ejection. They must mix easily with the powder, and must not excessively impede powder flow (see Lubrication and lubricants). 

---