NUCLEATION AND GROWTH OF TA-OXIDE IN NONSTATIONARY THERMAL FIELD .2. SINGLE-LAYER SELF-ORGANIZED STRUCTURE

Oxidation of metals in the non-stationary thermal field generates part icles of micrometre size which grow by local, isolated kinetics, as se lf-organized (SO) structures. At a heating rate 20 K min-1 less-than-o r-equal-to beta less-than-or-equal-to 50 K min-1 the SO structures on Ta appear as clusters of hemispherical particles and also as a single- layer structure with a logarithmic spiral envelope having the volcano type vertical cross-section, with approximately 60-degrees polar segme nts. This particle structure resembles the asymmetric six-petal flower . Particle characteristics are the direct consequence of a two-dimensi onal triangular lattice and the SO structure organization: (a) the cel l organization into triangular segments (petals) ; and (b) organizatio n of triangular segments into hexagonal superstructures (flower). This type of particle with the shrinking spiral envelope, can be generated by gradual stepping from the hexagonal periphery toward the centre in a clockwise direction. Triangular petals, are shown to be commensurat e with the measure forming the 5, 5, 4, 4, 3, 2 staircase.