Study On Preparation And Modification Of Calcium Carbonate For Sandstone Protection

Stone cultural relics are the cultural heritage of all ethnic groups in the world.The progress of human industrial civilization has exacerbated the deterioration of the natural environment,making the stone cultural relics exposed outdoors extremely vulnerable to be eroded.Traditional organic protective materials cannot provide effective protection due to poor compatibility,poor aging resistance,and difficulty in removal.How to use modern material science and technology to effectively protect and restore stone cultural relics has become an important research topic at present.Calcium carbonate certainly has potential advantage of the application to the protection of stone cultural relics due to its advantages of low price,simple preparation,environmental friendliness,and good compatibility with stone materials.In this paper,based on calcium carbonate materials of different crystal forms,calcium carbonate-based fatty acids and calcium carbonate-based fatty acids-titanium dioxide protective coatings were prepared.The work content and conclusions are as follows:（1）Controllable synthesis and properties of different crystalline calcium carbonates.Selecting different types of surfactants,the action time of surfactants,the titration rate of sodium carbonate and the concentration of surfactants as experimental factors,an L₉（3⁴）orthogonal experiment was designed to prepare two crystal forms of calcium carbonate aragonite and vaterite.The prepared vaterite calcium carbonate had small size（46 nm）and good permeability.The water absorption rate of the sandstone sample treated with vaterite calcium carbonate was 1.6%,and the weather resistance cycle was 20 times.Compared with the blank sandstone sample,the weather resistance was increased by 4times,which effectively improved the ability of the sandstone to resist salt damage.（2）Preparation and properties of calcium carbonate-based fatty acid coatings.In order to improve the anti-corrosion and fouling resistance of outdoor sandstone buildings,a calcium carbonate-based fatty acid modified coating with calcium carbonate as the base material and fatty acid as the hydrophobic modified material was synthesized by liquid-phase reaction.XRD and FTIR test results showed that the addition of fatty acid did not change the crystal form of vaterite calcium carbonate.Among them,the average grain size of octadecanoic acid-modified vaterite calcium carbonate was larger（31 nm）,the surface roughness of sandstone varies greatly,the hydrophobic angle can reach 119°,the stain resistance grade is 5,and the water absorption rate is only 1.0%.Compared with the sandstone samples treated with the unmodified coating,the fouling resistance of the sandstone surface is effectively improved.（3）Preparation and properties of calcium carbonate based fatty acid-TiO₂ composite modified coatings.In order to relieve the dry and wet expansion stress of the hydrophobic coating and the hydrophilic sandstone surface,titanium dioxide was used as a buffer layer to disperse the hydrophobic-hydrophilic stress difference on the surface of the stone,and a calcium carbonate-based fatty acid-titanium dioxide composite modified coating was prepared on the surface of the sandstone sample by a two-step method.Titanium dioxide coatings had excellent acid and corrosion resistance,the acid resistance of the composite modified coating was 0.1%,the sandstone samples were hardly corroded by acid.The number of weathering cycles was 25,five times that of the untreated sandstone samples,further improving the ability of sandstone to resist salt damage.In this paper,two crystal forms of aragonite and vaterite are prepared for the weathering protection of sandstone,which provides a new development direction for calcium carbonate in the field of stone protection.The calcium carbonate-based fatty acid-titanium dioxide composite modified coating has the best protection performance and can minimize the weathering rate of outdoor sandstone buildings.