Synthesis Of Calcium Hydroxide Nanoparticles For Stone Heritage Conservation And Its Application In Yungang Grottoes

With a civilization more than5000years, there is plenty of cultural heritages inChina, including some valuble stone heritages. As the most representativeimmovable stone relics, the conservation state of the Yungang Grottoes has beenpaid so much attention. Although the heritage coservation reseachers made a lot ofefforts to protect the Yungang Grottoes, its weathering problem is still concerning.According to the weathering mechanism, this study prepared a alchoholic ofnanosized calcium hydroxide despersion. With a good compatibility andweatherability, the dispersion will have a prospective application in stone heritageconservation.The Ca（OH）₂nanoparticles was synthesied in diols. With controlling thereactants’ mole ratio and concentration, the reaction temperature and the aging time,the uniform hexagonal calcium hydroxide partcles about35nm were successfullysynthesized. Further study of surface modification were carried out to reduce there-aggregation effects of the nanoparticles. To characterize and analysis the crystalstructure, the surface morphology, the molecular structure, the surfactant and thedespersion performance of the synthesized particles before and after modified,X-rays diffraction （XRD）, scanning electron microscopy （SEM）, fourier transforminfrared spectroscopy （FT-IR）, surficial area analyses （BET） and volumesedimentation methods were applied. The results showed that the particles werehexagonal whether modified or not. What’s more, the average size of the particleswere increased to50nm, but the surfactant and the despersion stability wereenhanced. It was demonstrated that the KH-570showed the best modification effectamong the different agents. FT-IR showed that the KH-570modified the particleswith some organic groups in the surface wich can improve the despersion stability alot. BET also showed that the surface area of the modified particles reached to48.78m²/g, which is about2.5times of the particles before modified and3.4times ofcommercial ones.The despersion kinematic viscosity of different medium was tested withsimulating the capillarity action inside the pores, and the Nuclear MagneticResonance Apparatus （NMR） was used to analysis the internal pore distribution inthe samples with Transverse relaxation time T2. And through a series screening tests,a kind of despersion medium with good stability and low viscosity was abtained toprepare the alchoholic of nanosized Ca（OH）₂despersion. The samples showed asmall color difference, a lower surface free water absorbtion rate and porosity, and a good air permeation rate after treated by this desipersion.This study combined the Ferroni-Dini method with the nanosized Ca（OH）₂despersion to protect the weathered samples of the Yungang Grottoes for the firsttime. Combined the ion chromatograph with the SEM, the results showed that thecontent of the Cl-and SO₄^2-were effectively reduced to a lower value as much as thefresh stone samples, and the lower porosity abtained with the further conservation ofthe nanosized Ca（OH）₂alchoholic despersion,which demonstrated that this methodcan be used for the desalination and reinforcement treatment of the YungangGrottoes.