Vladimir Traskine

The role of intermetallics in wetting in metallic systems

Abstract Formation of intermetallic seems to improve strongly wetting of a solid metal by a liquid one. The aim of this study is to identify the reasons of this improvement. For this purpose, wetting of Fe is determined at the same experimental conditions for two liquid metals, one reactive (Sn), the other non-reactive (Pb).

Single-contact pressure solution creep on calcite monocrystals

Abstract Pressure solution creep rates and interface structures have been measured by two methods on calcite single crystals. In the first kind of experiments, calcite monocrystals were indented at 40 °C for six weeks using ceramic indenters under stresses in the 50–200 MPa range in a saturated solution of calcite and in a calcite-saturated aqueous solution of NH4Cl. The deformation (depth of the hole below the indenter) is measured ex situ at the end of the experiment. In the second type of experiment, calcite monocrystals were indented by spherical glass indenters for 200 hours under stresses in the 0–100 MPa range at room temperature in a saturated aqueous solution of calcite. The displacement of the indenter was continuously recorded using a specially constructed differential dilatometer. The experiments conducted in a calcite-saturated aqueous solution of NH4Cl show an enhanced indentation rate owing to the fairly high solubility of calcite in this solution. In contrast, the experiments conducted in a calcite-saturated aqueous solution show moderate indentation rate and the dry control experiments did not show any measurable deformation. The rate of calcite indentation is found to be inversely proportional to the indenter diameter, thus indicating that the process is diffusion-controlled. The microcracks in the dissolution region under the indenter dramatically enhance the rate of calcite indentation by a significant reduction of the distance of solute transport in the trapped fluid phase. This result indicates that care should be taken in extrapolating the kinetic data of pressure solution creep from one mineral to another.

Grain boundary wetting in polycrystals: wettability of structure elements and liquid phase connectivity (part I)☆

Abstract A model is proposed describing the wetting of internal structure elements of polycrystals (grain boundaries, triple lines and quaternary nodes). The assumption is made that the only driving force for wetting is the minimization of interfacial solid–solid and solid–liquid energies. The former is assumed to be more scattered than the latter, as a function of the grain boundary misorientation. The well known Gibbs–Smith condition for grain boundary wetting is extended to grain edges and vertices, by introducing a parameter defined as the ‘characteristic free energy’ of these elements. Also suggested is a simple method allowing one to find relative amounts of wetted and non-wetted faces, edges and vertices. The percolation theory is employed to evaluate the critical solid–liquid to solid–solid energy ratio at which liquid phase inclusions become interconnected in a polycrystal of any size.

Misorientation Effects on Grain Boundary Grooving of Ni by Liquid Ag

The mechanisms of grain boundary grooving of polycrystalline Ni in cont a t with molten Ag at 1313 K in pure He are studied. Distribution of groove depths over a w ide range of values are observed and explained by misorientation of grain boundaries. A method is proposed allowing to evaluate the anisotropy of grain boundary energy by measuring the angular and li ne r imensions of grooves.

Wetting of Stressed Grain Boundaries in Polycrystals and Rheological Behaviour of Resulting Materials

Orientational patterns of wetted grain boundaries (GBs) in stressed NaCl polycrystals have been used for describing the GB penetration process on the basis of combined interfacial and mechanical energy balance considerations. The response of the internally wetted polycrystals to static loading has been shown to obey “pressure solution” constitutive laws involving dissolution at stressed surfaces, diffusive transport of dissolved matter and precipitation at less stressed surfaces. Direct experimental evidence for pressure solution mechanism is presented.

Inhibiting Effect of Additives on Pressure Solution of Calcite

The task of protection of cultural heritage requires a better understanding of combined effects of mechanical and chemical factors involved in environmental deterioration of monuments. The present paper deals with extending some known physicochemical methods proposed for inhibiting the decay of unstressed materials to their study during water-assisted deformation. The tests have been carried out on natural limestone samples and calcite powders in CaCO3 saturated aqueous solutions under static loads causing measurable pressure solution creep. In the solutions containing 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilotriacetic acid, or ethylenediaminetetraacetic acid, the creep rate decreases considerably with increasing concentration of additives. The extent of creep deceleration has been found to be proportional to the independently estimated calcite surface area occupied by adsorbed species. This fact enables us to discriminate the adsorption-induced effect from other variables controlling the pressure solution rate and may be used in screening of compounds able to minimize the environmental impact on marble and limestone objects undergoing mechanical stresses.