Dispersions of Surface Modified Calcium Hydroxide Nanoparticles with Enhanced Kinetic Stability: Properties and Applicat
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Dispersions of Surface Modified Calcium Hydroxide Nanoparticles with Enhanced Kinetic Stability: Properties and Applications to Desalination and Consolidation of the Yungang Grottoes Ya Xiao1,2, Feng Gao1,3, Yun Fang4, Youdan Tan5, Kaiyu Liu5, Shaojun Liu1,5, * 1
State Key Laboratory for Powder Metallurgy, Central South University, Changsha, China, 410083 2 Cultural Relics and Archaeology Institute of Hunan Province, Changsha, China, 410083 3 Chinese Academy of Cultural Heritage, Beijing 100029, China 4 China University of Geosciences (Wuhan), Wuhan, 430074, China 5 School of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China ABSTRACT Calcium hydroxide (Ca(OH)2) is one of the most interesting materials used to consolidate stone sculptures, monuments, mortars or wall paintings. In this study, we reported on the synthesis and characterization of surface modified Ca(OH)2 nanoparticles as a dispersion with enhanced kinetic stability and the applications for the conservation of sandstone monuments. Uniform hexagonal Ca(OH)2 nanoparticles (~35nm) were obtained by mixing NaOH and NaCl aqueous solutions at 100~175oC using homogeneous-phase reactions. It was further demonstrated that 3-(Methacryloyloxypropane oxygen) trimethoxysilane surfactant agent can significantly reduce agglomeration and simultaneously improve specific surface area of assynthesized Ca(OH)2 nanoparticles. Brunauer-Emmett-Teller (BET) measurement showed that specific surface area of modified Ca(OH)2 nanoparticles reaches up to ~48.78m2/g, about 2.5 and 3.4 times higher than that of unmodified and commercial ones, respectively. The kinetic stability of Ca(OH)2 despersion can be further enhanced and its viscosity can be decreased by optimizing the ratio of ethanol and n-propanol. Especially, a technique, which combined the Ferroni-Dini method and dispersion of Ca(OH)2 nanoparticles with enhanced kinetic stability, was proposed to effectively desalinate and consolidate the decayed stone, as evidenced by significant decreases of the porosity and concentration of detrimental Cl- and SO42- ions in the severely decayed sandstone samples from the Yungang grottoes. INTRODUCTION Several nanostructured materials and their applications in the field of cultural heritage conservation have been reported [1-3]. Calcium hydroxide (Ca(OH)2) is one of the most interesting materials used to perform consolidation of stone sculptures, monuments, mortars or wall paintings [4]. Calcium hydroxide reacts with carbon dioxide in the air, producing calcium carbonate that is highly compatible with the inorganic original substrate. However, direct use of aqueous Ca(OH)2 solutions is limited by its low solubility in water [5]. Moreover, commercially *
Email: [email protected] (S.J. Liu)
available Ca(OH)2 particles have a broad size distribution and large range of mean dimensions. This usually results in a formation of white coating on the surface of artifacts because of small surface pore size. In contrast, a nanometric size of Ca(OH)2 particles
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