Advances in Understanding Damage by Salt Crystallization

摘要

Tnhe single most important cause of the deterioration of mon-numents in the Mediterranean basin, and elsewhere around thenworld, is the crystallization of salt within the pores of the stone.nConsiderable advances have been made in recent years in eluci-ndating the fundamental mechanisms responsible for salt dam-nage. As a result, new methods of treatment are being proposednthat offer the possibility of attacking the cause of the problem,nrather than simply treating the symptoms. In this Account, wenreview the thermodynamics and kinetics of crystallization, thennexamine how a range of technological innovations have beennapplied experimentally to further the current understanding of in-npore crystallization. We close with a discussion of how computernmodeling now provides particularly valuable insight, includingnquantitative estimates of both the interaction forces between thenmineral and the crystal and the stresses induced in the material.nAnalyzing the kinetics and thermodynamics of crystal growthnwithin the pores of a stone requires sensitive tools used in com-nbination. For example, calorimetry quantifies the amount of saltnthat precipitates in the pores of a stone during cooling, andndilatometric measurements on a companion sample reveal thenstress exerted by the salt. Synchrotron X-rays can penetratenthe stone and identify the metastable phases that often appearnin the first stages of crystallization. Atomic force microscopy andnenvironmental scanning electron microscopy permit study of the nanometric liquid film that typically lies between salt andnstone; this film controls the magnitude of the pressure exerted and the kinetics of relaxation of the stress. These experi-nmental advances provide validation for increasingly advanced simulations, using continuum models of reactive transport onna macroscopic scale and molecular dynamics on the atomic scale.