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The calcitic prismatic units forming the outer shell of the bivalve Pinctada margaritifera have been analysed using scanning electron microscopyelectron back-scatter diffraction, transmission electron microscopy and atomic force microscopy. In the initial stages of growth, the individual prismatic units are single crystals. Their crystalline orientation is not consistent but rather changes gradually during growth. The gradients in crystallographic orientation occur mainly in a direction parallel to the long axis of the prism, i.e. perpendicular to the shell surface and do not show preferential tilting along any of the calcite lattice axes. At a certain growth stage, gradients begin to spread and diverge, implying that the prismatic units split into several crystalline domains. In this way, a branched crystal, in which the ends of the branches are independent crystalline domains, is formed. At the nanometre scale, the material is composed of slightly misoriented domains, which are separated by planes approximately perpendicular to the c-axis. Orientational gradients and splitting processes are described in biocrystals for the first time and are undoubtedly related to the high content of intracrystalline organic molecules, although the way in which these act to induce the observed crystalline patterns is a matter of future research.

CET IN SOLIDIFYING ROLL -THERMAL GRADIENT FIELD ANALYSIS KRT W KRYSTALIZUJĄCYM WALCU -ANALIZA GRADIENTOWEGO POLA TEMPERATURYAs the first step of simulation, a temperature field for solidifying cast steel and cast iron roll was created. The convection in the liquid is not comprised since in the first approximation, the convection does not influence the analyzed occurrence of the C → E (columnar to equiaxed grains) transition (CET) in the roll. The obtained temperature field allows to study the dynamics of its behaviour observed in the middle of the mould thickness. This midpoint of the mould thickness was treated as an operating point for the C → E transition. A full accumulation of the heat in the mould was postulated for the C → E transition. Thus, a plateau at the T (t) curve was observed at the midpoint. The range of the plateau existence t C ↔ t E corresponded to the real period of transition, t R C ↔ t R E that occurs in the solidifying roll. At the second step of simulation, the thermal gradients field was studied. Three ranges were distinguished: a/ for the formation of the columnar structure (the C -zone):b/ for the C → E transition (from columnar to fully equiaxed structure):c/ for the formation of the fully equiaxed structure (the E -zone):The columnar structure formation was significantly slowed down during incubation period. It resulted from a competition between columnar growth and equiaxed growth expected at that period of time.≈ 0 relationship was postulated to correspond well with the critical thermal gradient, G crit. . A simulation was performed for the cast steel and cast iron rolls solidifying as if in industrial condition. Since the incubation divides the roll into two zones (columnar and equiaxed) some experiments dealing with solidification were made on semi-industrial scale.A macrosegregation equation for both mentioned zones was formulated. It was based on a recent equation for redistribution after back-diffusion. The role of the back-diffusion parameter was emphasized as a factor responsible for the redistribution in columnar structure and equiaxed structure.Keywords: solidifying roll, thermal gradient field, columnar into equiaxed structure transition, macro-segregation index W pierwszym etapie symulacji wygenerowano numerycznie pole temperatury dla krzepnącego walca staliwnego oraz żeliwnego. Nie uwzględniono konwekcji uznając, że w pierwszym przybliżeniu konwekcja nie wpływa na przebieg transformacji C → E (struktura kolumnowa w równoosiową, CET). Uzyskane pole temperatury pozwala na analizę jego zachowania w środku grubości wlewnicy. Ten punkt wlewnicy zostałpotraktowany jako punkt operacyjny dla transformacji C → E. Postuluje się w tym modelu, że zachodzi pełna akumulacja ciepła we wlewnicy właśnie dla tej transformacji. Stąd, spłaszczenie krzywej T (t) jest obserwowane dla punktu operacyjnego. Zakres tego spłaszczenia oznaczony t C ↔ t E odpowiada rzeczywistemu okresowi transformacji, t Symulacja została przeprowadzona zarówno dla walców staliwnych jak i żeliwnych dla warunków zbl...