Study On The Conservation Of Sandstone Artefacts With SiON Surface Protection Materials

Due to natural influences,human factors and other reasons,sandstone relics in the open air have been damaged to varying degrees.Therefore,effective measures should be taken as soon as possible to protect these cultural treasures.Today,many stone protection materials have been developed,such as acrylics（B72）,polydimethylsiloxanes（PDMS）,and epoxy resins（EP）.However,the differences in physical and chemical properties between these organic materials and inorganic stone are so great that it is difficult to meet the current protection requirements.As a result,many new materials have emerged for research.Inorganic SiON materials can form stable Si-O-Sibonds with sandstone and are very compatible,which can have a long-term sealing and curing effect on sandstone artefacts.The aim of this paper is to evaluate the protective and durable performance of SiON as a protective material for sandstone and to select SiON materials that are breathable,water-repellent,UV ageing resistant,and weather-resistant.（1）Performance study of SiON coatings prepared from low-temperature cured perhydropolysilazane（PHPS）.An orthogonal test was designed to investigate the effects of catalyst 1-dimethylamino-2-propanol（DMAPO）concentration,curing temperature,curing time,and humidity on the curing of PHPS.The optimum combination for the preparation of the SiON coating by FTIR semi-quantitative analysis was 1.5%DMAPO,a curing temperature of80°C,a curing time of 6 h and a humidity of 40%.To investigate the effects of different materials on sandstone protection,SiON,B72,PDMS,and EP were used as sealing materials,and protective materials were applied to the sandstone surface using the lifting method.The results show that:the colour difference value of sandstoneΔEab*=1.36 after the application of colourless and transparent SiON protective material,with stable colour difference performance;the cohesion of water molecules on the hydrophilic pore wall in the SiON coating is low,and the water and gas transport parameterΔVP of the SiON-treated sandstone is-11.7%,ensuring the balance of water and gas transport inside and outside the rock;Excellent barrier properties of SiON-protected sandstone,preventing the accumulation of crystals of soluble salts within the sandstone,and a small rate of mass change during weathering tests compared to B72,PDMS,and EP-treated stones,with significantly enhanced weathering resistance.The SiON-treated sandstone has high acid resistance,and the simulated acid rain test ensures that the substrate is not eroded by acid.（2）Performance study of hydrophobic SiON-SiO₂ coatings.To improve the stain resistance and water repellency of the SiON coating,the surface modification of the SiO₂ nanoparticles was carried out using the modifier vinyltrimethoxysilane,the silane coupling agent G-570 and stearic acid,and finally,the SiON-SiO₂ coating was prepared by mixing the treated SiO₂ with PHPS solution.The results show that:a high concentration of nano-SiO₂ applied to sandstone will cause the surface to turn white,and 1.5%nano-SiO₂ added to SiON coating will not cause visible appearance changes;a large number of nanoparticles are loaded on the sandstone surface,and the rough micro-nanostructure is beneficial to improving the hydrophobicity of the sandstone.The surface capillary water absorption coefficient of the hydrophobic treated sandstone is at least 59%lower than that of the blank sample;the nearly spherical droplet shape reduces the contact between the pollutants and the sandstone and avoids the deposition of pollutants in the surface pores,and the stain resistance test shows that the stain resistance level is less than I;The hydrophobic treatment of the sandstone was not easily wetted by water,resulting in the deposition of large amounts of soluble salts on the exterior of the sandstone and the occurrence of laminar spalling with a maximum decrease in weathering resistance of 23.9%compared to blank specimens.（3）Performance study of hydrophobic TX-100/SiON-SiO₂ coatings.To avoid salt crystallisation exacerbating the weathering of the sandstone,a versatile two-layer coating was prepared on the sandstone surface,the bottom layer consisting of different concentrations（0.1-0.5 mmol/L）of Trilatone X-100（TX-100）and the top layer consisting of a SiON-SiO₂ coating.The results show that:the wettability of the sandstone surface is influenced by the wettability of the top layer of SiON-SiO₂ coating,and that the static contact angle of the sandstone specimens treated with the double layer is as high as 110°,and the capillary absorption coefficient is reduced by at least 50%;the compatibility of TX-100with sandstone is good,reducing the difference between hydrophobic and hydrophilic interfaces and increasing the weathering resistance of treated specimens by more than 42.8%compared to blank specimens.The coatings prepared with low concentrations（0.1-0.3 mmol/L）of TX-100 ensure a stable colour difference in the sandstone during UV ageing,while coatings prepared with high concentrations（0.4-0.5 mmol/L）of TX-100 do not bond well with the sandstone and have a colour difference value ofΔEab*>3 after UV ageing,resulting in a colour change change visible to the naked eye.Taken together,the TX-100/SiON-SiO₂ coating prepared with TX-100 at a concentration of 0.3 mmol/L maintains the good colour stability and permeability of the sandstone,improves water repellency,UV ageing resistance,and weathering resistance of the sandstone,and minimises the weathering rate of the outdoor sandstone.