L. Pastero

Bio: L. Pastero is an academic researcher. The author has contributed to research in topics: Halide & Formamide. The author has an hindex of 1, co-authored 1 publications receiving 3 citations.

A three-modal epitaxial adsorption of formamide (HO–C–NH2) on the {111} surfaces of f.c.c. alkali halide crystals growing from aqueous solutions

Abstract: The whole series of the face-centered cubic (fcc) alkali halides, from LiF to RbI, has been crystallized from aqueous solutions in the presence of variable amounts of formamide (HO–C–NH2) Scanning electron microscope images show that the corresponding morphology of the grown crystals is not homogeneous within the whole crystal series, and that the {111} octahedron does appear and compete with the {100} cube only in three separated crystal domains: (NaF), (LiBr, RbF, NaCl) and (KCl, NaI, RbCl, KBr) Starting from our preceding finding about the formation of NaCl/formamide anomalous mixed crystals and recollecting the peculiar {100} + {111} habit change of NaCl growing from pure aqueous solution, we propose that formamide can be adsorbed as a 2D epitaxial layer on the {111} surfaces of the fcc alkali halides according to a three-modal distribution

Morphology of crystals

Abstract: -- Part C: 1. The continuum approach to crystal interfaces: basics. I: Theoretical framework. 2. Operators for orientation-dependent parameters. 3. Mechanics and thermodynamics of interfaces. 4. Equilibrium structures of junctions, edges and vertices. 5. Growth: kinematic wave theory revisited. 6. Kinetic behaviour of junctions, edges and vertices. 7. Structural phase transitions of a crystal surface as a branch of soliton physics. 8. Miscellaneous topics. II: Growth rate functions. 9. Analytic representations of R(n,A) functions. 10. Nonlinear networks and the 'assembled function' notation. 11. Physical aspects of assembling operations. 12. The systematic construction of R(n,A) functions by a sequence of assembling steps. 13. Notes on sphere-growth experiments. 14. Summary: Conclusions and outstanding questions. References. List of symbols, abbreviations and notations.

Habit Change of Monoclinic Hydroxyapatite Crystals Growing from Aqueous Solution in the Presence of Citrate Ions: The Role of 2D Epitaxy

Abstract: Calcium hydroxyapatite (HAp) has been crystallized from aqueous solutions in the presence of citrate ions, in two temperature intervals. At lower temperature, where citrate could form the stable 3D-ordered phase Ca-citrate-tetrahydrate (Ca-Cit-TH), only the monoclinic (P21/c) HAp polymorph occurs and assumes the shape of fence-like aggregates, built by sharply [010] elongated lamellae dominated by the pinacoid {001}. This pronounced anisotropic growth habit is compared with the usually considered rod-like pseudo-hexagonal occurring in pure aqueous solution growth. The habit change is interpreted by assuming that 2D islands of Ca-citrate-tetrahydrate can be adsorbed as epi- monolayers of thickness d001 onto the different growth forms: {001}, {100}, {102¯}, {010}, and {101¯} of HAp. A comparison is made among the corresponding coincidence lattices, in order to explain on reticular basis the selective adsorption of citrate on the {001} HAp form. The role exerted by the 2D-epitaxially adsorbed Ca-Cit-TH as a “mortar” in the monoclinic HAp “brick” assembly is outlined as well.

Impurity Effects on Habit Change and Polymorphic Transitions in the System: Aragonite-Calcite-Vaterite

Abstract: Crystal growth experiments carried out in aqueous solutions, supersaturated with respect to calcite (CaCO3) at room temperature and pressure, show that the lithium ion added to growth solutions not only acts as a habit modifier of calcite, but promotes the nucleation and growth of the two other CaCO3 polymorphs: aragonite and vaterite. This behavior is interpreted on the grounds of foreign adsorption going beyond Langmuir’s isotherm model: two-dimensional (2D)-adsorbed nuclei of Li2CO3 (mineral zabuyelite) can change, under varying Li+ concentrations in solution, the growth habit of calcite, promoting as well both nucleation and growth of aragonite and vaterite, through the mechanism of 2D-epitaxy. Calculation proves how the epitaxy aragonite/2D-zabuyelite reduces the average value of the specific surface energy of aragonite, allowing the nucleation of aragonite and then the coexistence of calcite and aragonite in the same batch. Finally, it is outlined that the 2D lattices fulfilling the epitaxy constraints for the couples calcite/zabuyelite and aragonite/zabuyelite show, as a common feature, a remarkable pseudohexagonality.