Thermodynamic Analysis of Hardening Paste- and Liquid-Like Elements of Museum Exhibits under the Influence of Microclimatic Conditions in a Room

Abstract

The process of restoration of museum exhibits is associated with the forming of various structural media, for example, drying of paints layers, varnishes and hardening of gypsum and concrete solutions during the restoration of statues, elements of room decor. The mechanics of such media is characterized by spectra of viscous, plastic and elastic properties in their various combinations. The forming of these substances is influenced by the microclimatic conditions of the premises, in which these processes take place. In technological operations, as a rule, large shear deformations take place, which greatly exceed the elastic limit. Thus, the most significant for technological calculations are viscoplastic properties, which reflect the relationship between the existing shear stresses and the rate of irreversible shear deformation. For a qualitative description of this relationship, it is customary to use consistency curves that relate shear stresses to the rate of irreversible shear deformation or the dependence of the effective viscosity on the rate of irreversible shear deformation. Structure formation is one of the main processes in the technology of processing solidifying paste-like and liquid-like media when their characteristics approach those inherent in the corresponding capillary-porous bodies. The properties of such media depend on the type and nature of the structure. The study and control of the process of structure formation to obtain a medium with desired properties is an important technological task, which can be solved, in particular, by microclimate systems. The change in the structural state of the solidifying medium can be estimated from the corresponding changes in plastic and conventional mechanical strength, degree of hydration, heat release, elastic modulus, etc. In this work, structure formation is understood as a process, as a result of which the characteristics of the material approach the characteristics of the corresponding capillary-porous body (CPB). The main parameter that determines this approximation is the degree of completeness of structure formation. Analysis of the hardening process of the considered pasty and liquid-like media on the basis of the moisture state diagram makes it possible to fix the structural state of the capillary-porous structure of these media and to evaluate the interaction of chemical reactions and the process of structure formation. And the resulting changes in the rate of structure formation allows to identify and evaluate the destructive processes that occur during solidification of the substance.