Intergranular pressure solution in internally wetted polycrystals: Effect of additives

Wetting of grain boundaries in polycrystalline materials leads to considerable changes in their physicochemical and mechanical properties. Under a constant compressive load, internally wetted materials display an enhanced deformability; creep rate increases sometimes by several orders of magnitude. The dominant creep mechanism is known as dissolution–precipitation or pressure solution; a stress-induced excessive chemical potential provides a driving force for dissolution of material within grain contacts, diffusion through the grain boundary solution film and re-precipitation elsewhere. Sensitivity of pressure solution rate to the chemical composition of the intergranular liquid was reported earlier, but the underlying mechanisms were poorly understood. In the present work, the creep experiments were carried out on poly- or monocrystalline sodium chloride in the presence of NaCl aqueous solution (pure or containing additives such as copper, magnesium and lead chlorides, K₄Fe(CN)₆ and urea). In all cases, pressure solution has been shown to be the main deformation mechanism. Creep rate decreases in the presence of additives which are known to affect the dissolution and growth processes of sodium chloride or its concentration in the brine. Rate-limiting stage (dissolution or diffusion) in various environments has been identified.     

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.     

Treatment of vertigo with betaserk in patients with vascular and traumatic cerebral injuries

Managed care's focus on patient-centered care has made the need for point-of-care (POC) clinical systems more critical than ever. This article examines some of the more common POC options available, explains what nurses need to know to choose among them, and suggests ways to ensure that nursing's needs are addressed in the selection process.     

Hydrogen-induced phase and structural transformations in titanium alloys with β-eutectoid stabilizers

The mechanism of hydrogen-induced structure formation in titanium alloys with β-eutectoid stabilizers is analyzed. Additional hydrogen alloying of Ti-Cr alloys is shown to increase the stability of the β phase with respect to the α phase and to decrease its stability with respect to the intermetallic compound TiCr₂. Hydrogen dissolved in a commercial multicomponent TS6 alloy containing 11.3% Cr is found to favor the precipitation of an intermetallic compound Ti_xCr_y, which also contains other alloying elements present in the alloy. The mechanism and kinetics of the formation of this intermetallic compound during hydrogenation annealing and isothermal heat treatment are considered. Structures with the intermetallic compound Ti_xCr_y can be produced upon low-temperature vacuum annealing of a hydrogen-charged TS6 alloy.