Preparation Of ?-Al₂O₃ Nano-Dispersion And Its Application In Transparent Wear-resistant Coatings

Friction and wear can be seen everywhere in production and life,causing a large amount of waste of resources.Wear-resistant coatings are widely used to alleviate friction and wear problems due to their simple usage and low cost.In particular,the transparent wear-resistant coating can protect the substrate while preserving the original appearance of the substrate,which can be widely used in the surface protection of materials such as resin lenses,sanitary ware,and floors.When some nanomaterial with wear resistance is added to the polymer matrix as a wear resistance enhancer,it will greatly increase its wear resistance.Nano ?-Al2O3 is an ideal wear-resistant enhancer due to its excellent properties such as high hardness,wear resistance,corrosion resistance,high temperature resistance,oxidation resistance,and low price.However,nano Al2O3 has large specific surface area and high surface energy,and it is easy to agglomerate in transparent coatings,thereby reducing the transparency of the coating and limiting its application potential.Therefore,how to achieve uniform dispersion of small and uniform Al2O3 particles in the transparent coating is one of the important scientific problems that need to be solved urgently for its large-scale application.In this thesis,nano-?-Al2O3 is firstly prepared by traditional hydrothermal process and high-gravity method,and the surface modification of alumina nanoparticles is carried out by ball milling modification to prepare a stable dispersion of isopropyl alcohol phase ?-Al2O3 nano-dispersion.Then,the prepared Al2O3 is mixed with polymer matrix to prepare wear-resistant coating.The influence of preparation process conditions on the morphology and dispersion of ?-Al2O3 is discussed.The following are the main research contents and results.The precursor was prepared by traditional hydrothermal method,and y-Al2O3 nano-dispersion was prepared by calcination dehydration and wet modification.The effects of preparation and modification process on the structure and dispersion of nano Al2O3 were studied.The better preparation process conditions are as follows:the pH value is adjusted to about 9 during the precipitation process;the hydrothermal temperature is 140?;the hydrothermal time is 6 h;the calcination temperature is 500?;the modifying agent is in an amount of 20 wt%;the ball diameter is 0.1 mm;the milling rotation speed is 400 rpm;the ratio of grinding media to material is 15:1.The average particle diameter of the prepared ?-Al2O3 particles is about 20 nm,which can be stably dispersed in isopropanol to ?-Al2O3 nano-dispersion.The precursor was also prepared by high-gravity method,and the ?-Al2O3 nano-dispersion with better dispersibility was prepared by calcination and ball mill modification.The better preparation process conditions are as follows:the aluminum salt concentration is 0.8 mol/L;NH3/A13+ mole ratio is 5.0;the rotating speed of RPB is 2000 rpm;the reaction time is 5 min;the modifying agent in an amount of 20 wt%;the milling time is 10 h.?-Al2O3 nanoparticles with an average particle size of about 20 nm and a narrow particle size distribution were successfully prepared,which have well dispersion stability in isopropanol.Compared with the traditional hydrothermal method,the ?-Al2O3 particles prepared by the high-gravity method have a narrow particle size distribution and better dispersion in isopropanol.The results of the DLS shows that the particle size distribution of ?-Al2O3 in isopropanol is 40?180 nm,and the average dispersed particle size is 78 nm.In contrast,the particle size distribution of particles prepared by traditional hydrothermal method is 30-300 nm,and the average dispersed particle size is 96 nm.Nano ?-Al2O3 is added to the coating containing polyurethane acrylate(PUA)resin,and the nanocomposite wear-resistant coating has been prepared by ultraviolet curing method.The influence of the amount of ?-Al2O3 and the thickness of the coating on the transparency and wear resistance of the composite coating has been explored.When the addition amount of ?-Al2O3 is 10 phr and the coating thickness is about 40 ?m,the visible light transmittance of the nanocomposite wear-resistant coating is 90.8%,and the visible light transmittance decreases by 4.2%after rubbing the coating surface for 3000 times.In contrast,the visible light transmittance of the coating prepared by adding the traditional hydrothermal method of ?-Al2O3 decreased by 6.3%.In addition,the performance of Al2O3/PUA nanocomposite coatings has been compared with those of imported and domestic nano Al2O3 coatings.The results show that the transparency and wear resistance of the nanocomposite coating is significantly better than the coatings with domestic products,and slightly better than the imported products.After rubbing,the visible light transmittance of the domestic ?-Al2O3/PUA composite coating decreases obviously by more than 10%.