In-plane boundary description method of the agglomerative structure of molybdenum organometallic precipitate

Understanding the formation and the destruction of large organometallic aggregates obtained by precipitation first requires a description, at each step of the precipitate evolution, of the mode of filling space by aggregates. This evolution results (for example, in a precipitate flotation) in opposite processes of packing and breaking; thus, the description needs to be precise in time and space. Unless there are proofs of 3D anisotropy, the description is made in two dimensions so that it consists in the geometric characterization of a plane-closed boundary. The planar description leads to two series of parameters: micromorphologic and macromorphologic, both being computed from a standard descriptor, which is the polygonal finest vector chain called Freeman chain. The first series intend to find some possible scaling process on the whole boundary or only on sampled arcs characterized by fractal invariants. The scaling laws thus yielded can be stated “fractal” only over a limited scale range included in the size interval between the body size and the resolution threshold of the measurement device. This invariant was studied on organometallic molybdenum aggregates. An analysis of the particle morphology puts in evidence at least two populations of flocs in the Mo precipitate in addition to the genuine germs whose structure is regular. The fractal dimension variations prove the structure heterogeneity of the aggregates. Large flocs with Df in the interval from 1.20 to 1.25 are formed either with more compact microflocs (Df=1.10–1.15) or with regular elementary germs (Df=1.02–1.05). The coincidence between morphologic features and physicochemical properties is obvious and interesting.