Z. N. Skvortsova

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.

Indentation Study of Adsorption Plastification of Sodium Chloride Single Crystals

Rheological behavior of sodium chloride single crystals in various media was studied by a ball indentation method. The method provides for a gradual decrease in applied stress as an indenter penetrates into a crystal. If a stress is higher than 30 MPa, a deformation follows the dislocation glide mechanism. If the stress is lower than the value above, a marked deformation occurs only in the presence of aqueous solutions and follows the recrystallization mechanism through solution (pressure solution), and a deformation rate is determined by a solute diffusion rate.

Transport properties of sodium chloride polycrystals with liquid intergranular interlayers

The diffusion permeability, electric conductivity, and filtration coefficient of water-containing sodium chloride polycrystals have been measured. Based on the measurement results, the dynamic thickness of intergranular interlayers, which determines the transport properties of the material, has been calculated. For samples that are initially continuous, this value (120–130 nm) corresponds to the averaged capacity of the grain boundaries with respect to water independently determined by analytical methods. The dynamic thickness of the interlayers in pellets molded from a wetted NaCl powder under a high pressure is significantly smaller (about 20 nm).

Calcite deformation in the presence of water

The rates of calcite powder compacting and deformation of calcite polycrystals under a punch are measured. The processes occurring upon calcite loading in inert and dissolving media are analyzed, and a scheme is proposed to relate the deformation rate to the parameters characterizing the stressed state, kinetics of dissolution, and mass transfer rate upon a single contact. The validity of the extension of the proposed scheme to the whole polydisperse ensemble of particles in a densified powder is discussed.

Effect of cyclic loading on dissolution-precipitation creep

The recrystallization creep of water-wetted sodium chloride, calcium carbonate, and ammonium nitrate powders is studied under the conditions of static and cyclic loading. For the two former salts, a drastic acceleration of the creep is revealed upon the passage from the static to the cyclic regime; when returning to the static regime, the creep rate appears to be close to the initial one. For ammonium nitrate, no acceleration of the creep is observed. When the samples are tested in nonsolvent media (heptane and Vaseline oil), the effect is not observed. A mechanism is proposed to explain the observed phenomena.

Recrystallization creep of sodium chloride in solutions with different compositions: 2. The effect of urea additives

The study of the recrystallization creep of sodium chloride crystals shows that, beginning with a concentration of 10−2 M, the addition of urea to a solution noticeably decelerates the recrystallization creep of NaCl. It is proven that the deceleration of the creep is due to the passage of the process from a diffusion regime to a kinetic one, which is limited by the rate of salt dissolution.

Recrystallization creep of sodium chloride in solutions with different compositions. 1. The effect of additives of inorganic salts

The deformation of sodium chloride single and polycrystals is investigated in the presence of its own saturated aqueous solution. It is shown that the addition of salts to the solution in a wide concentration range may substantially affect the rate of the recrystallization creep of NaCl. The observed effect is explained by the influence of the additives on the intensity of the diffusion mass transfer in sodium chloride solutions.

Deformation at the contacts of sodium chloride crystals in the presence of water

The processes taking place at the intergrain contacts during powder pressing in dissolving media are studied. The threshold stress corresponding to a change in the mechanism (the transition from the dislocation glide to the recrystallization creep) of sodium chloride deformation in the presence of its saturated aqueous solution is determined. An equation is proposed for describing the variations in the compaction rate of powders in the course of their deformation.

Colloid-Chemical Approach to Methods for Preventing Table Salt from Caking

Communications devoted to analysis of the reasons and mechanisms for the formation of crystallization contacts between particles of disperse systems (primarily, NaCl) upon the removal of water from them and the contemporary methods for controlling this process with the purpose of preventing them from caking (loss of flowability) have been briefly reviewed. The main attention has been focused on works in which such processes are considered with the use of the methods and concepts of modern colloid chemistry and physicochemical mechanics of materials.

Heavy oil as an emulsion: Composition, structure, and rheological properties

Recent works devoted to studying the structure and rheological properties of water/oil disperse systems have been reviewed. Contemporary understandings of crude heavy oil as a water-in-oil emulsion have been discussed. Data on the mechanism of the stabilizing effect of natural lipophilic surfactants and ultradispersed particles of different natures contained in oil have been presented. Methods that are used to improve the transport characteristics of heavy oil—in particular, the formation of low-viscosity oil-in-water emulsions—have been listed. Colloidal and rheological properties of heavy oil-in-water emulsions, which are increasingly applied for pipeline transportation of oil, have been considered.