Fractal ceramic powders

The properties of fractal ceramic powders depend on their fractal dimensions. The density, p, of a fractal particle depends on its radius, R, and the fractal dimension ... 

The processing of fractal ceramic powders is severely complicated by the evolving nature of the microstructure throu out the covuse of sintering. Changes in microstructure are influenced by a host of factors. 

If the power of R is negative, the probability of intersection decreases as the size of the fractal, R, increases. For this reason, two fractals with the same fractal dimension will have a low intersection probability ifZ>i = D2 > 1.5. As a result, fractals with fractal dimensions greater than 1.5 act as individual spheres in dilute solution. In concentrated solution, fractals with a fractal dimension less than 1.5 can be forced to interpenetrate strongly, unlike hard spheres, during settling and dewatering of fractal sol-gel ceramic powders. 

Reaction-bonded titanium nitride (RBTN) ceramics are like RBSN made from a porous green shape of titanium powder that is reacted with nitrogen to titanium nitride (TiN) at temperatures up to 1000°C. Here the titanium hardly increases in molar volume when nitrided and the initial porosity remains the same but the gas permeability of a pressed titanium tablet is increased after it has been converted to titanium nitride. If the titanium powder particles are too large, the reaction stops after passivation of the metal surfaces the TiN formed at the surface is a diffusion barrier that stops the reaction. A fractal powder morphology of the starting metal (such as can be obtained from gas-phase preparation) is a very suitable reactant for complete reaction at modest temperatures. 

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