Study On Fly Ash-based Superhydrophobic Coating

The superhydrophobic coatings have self-cleaning properties,which provide great convenience in all aspects of modern life.So the superhydrophobic coatings become the heated topic in recent years.Aiming at the problems of complex preparation method,high cost and to unfavorable large-scale use of superhydrophobic coatings.In this paper,the silane modified fly ash-based superhydrophobic coatings were prepared by spraying with superfine fly ash(carbon dioxide/calcium hydroxide/ carbide slag)and silane coupling agent as main raw materials.The influence of different formulations on the hydrophobic effect of coatings was studied and the optimum formulation was obtained.It is applied to foam concrete and casting moulds.The main research contents of this paper are as follows:(1)Using superfine fly ash,silane coupling agent and ethanol as raw materials,fly ash particles were added to the ethanol solution in which the silane coupling agent is dissolved,and then the silane modified fly ash-based superhydrophobic coatings was obtained after ultrasonic treatment for 20 minutes.silane coupling agents with different hydrophobic functional groups on the surface of fly ash,its additions and fly ash additions on the hydrophobic effect of the coatings were studied,the silane coupling agent with the best hydrophobic effect and its additions and fly ash additions were selected.The results showed that the surface energy of heptafluorodecyl triethoxysilane is the lowest among the five silane coupling agents,including aminopropyltriethoxysilane,methacryloxypropyltrimethoxysilane,trimethyl chlorosilane,phenyltriethoxysilane and heptafluorodecyltriethoxysilane.The optimum addition amount of heptafluorodecyltriethoxysilane was 2% in 50 m L ethanol,5 g in superfine fly ash in coatings.The contact angle was 154.34 degrees,which meets the requirement of superhydrophobicity.The microstructure,surface functional groups and roughness of superhydrophobic coatings were analyzed by means of FTIR,SEM-EDS and AFM,and the superhydrophobic principle of coatings was explored.The results of IR,SEM-EDS and AFM test showed that fluosilane was successfully grafted onto the surface of fly ash.The gap between the coated fly ash particles and the tiny protrusions on the surface of the fly ash particles form a micro-nano roughness structure,making the coating superhydrophobic.The surface mean square roughness was 237 nm.The percentage of water contact area on the surface of the coating was calculated by Cassie theory fs=18.87%,and the area percentage of air cushion was 81.13%,which further indicated that the coating surface formed micro-and nano-structures similar to lotus leaf.(2)Fly ash,calcium hydroxide/carbide slag were mixed into water,then carbonized with carbon dioxide to prepare fly ash particles.Then ethanol solution of fluorosilane was added to prepare superhydrophobic coatings.The influence of the degree of carbonization(different carbonization time)of a certain amount of fly ash and calcium hydroxide mixture on the hydrophobic properties of the coatings was investigated.The results showed that the optimum carbonization time of fly ash(10 g)and calcium hydroxide(10 g)mixture was 10 minutes to prepare fly ash particles.Then coating with the contact angle of 156.4 degrees was prepared by adding 5 g to 50 m L ethanol solution with 0.1% fluorosilane.In addition,the degree of carbonized particles was not determined by carbonization time,then the calcium hydroxide is inspected.The effect of carbonization products on the hydrophobicity of the coatings after carbonization of the mixture(calcium carbide slag)with different proportion of fly ash was completed.The contact angle of water of the coatings was greater than 150 degrees when the optimum addition of calcium hydroxide/calcium carbide slag was 5%.Under the condition of meeting the hydrophobic requirements,the degree of carbonization was better determined and the carbide slag was treated.Compared with the fluorosilane modified fly ash based superhydrophobic coating,the addition of fluorosilane in the carbonized fly ash based superhydrophobic coating decreased from 2% to 0.1%,which greatly reducing the cost.The results of SEM and AFM analysis showed that the surface of fly ash particles after carbonization distributes calcium carbonate particles,forming large protuberances.The surface roughness of fly ash increases obviously,and the coating satisfied Cassie theory.(3)On the surface of the foam concrete block,the fly-ash waterproof coating was applied as the base coating.After spraying the super hydrophobic coating as the surface coating,the composite coating obviously reduces the water absorption ratio and had good waterproof characteristics.The polyester epoxy composite coating was sprayed on the surface of the concrete placement,and then the super hydrophobic coating is coated on the surface,dried and solidified at high temperature.The demoulding coating was prepared,and the demoulding test was carried out.There was no obvious change in the surface of the coating after and ten demoulding,and it was still had superhydrophobic effect.The fly ash based superhydrophobic coating prepared in this paper has the advantages of excellent hydrophobic performance,simple preparation method and low cost,so it is potentied to scale up.