Preparation And Characterization Of Multifunctional Aluminum Pigments

As a kind of promising metallic pigment,the flaky aluminum pigment has been widely used in chemical coatings,automotive paints and printing inks because of its excellent metallic luster and flop effect.And aluminum pigment with low emissivity is the most reported infrared stealth pigment in recent years.However,the traditional solvent aluminum pigment has many disadvantages,such as single color,significant environmental pollution and so on which has been unable to satisfy people's growing aesthetic consciousness and regulations of relevant environmental protection laws and is developing towards colored and waterborne aluminum pigment.The key to preparing waterborne aluminum pigments is to improve their corrosion resistance,And the high reflection of visible light of aluminum pigments limits its stealth in the visible light.Therefore,the metal oxide coated on the surface of aluminum pigment improved the anti-corrosion resistance and reduced reflectivity of aluminum pigment,prepared the multi-band stealth color waterborne aluminum pigment has become the primary direction of research.Therefore,we prepared the aluminum pigments was encapsulated with iron oxide and tin oxide?Al@Fe₂O₃ and Al@SnO₂?,which using H₂O₂ as anchoring agent,FeCl₂·4H₂O and SnCl₄ as precursors respectively.The main contents were as follows:?1?In acidic conditions and the system temperature at 45?,H₂O₂ can oxidation aluminum forming diaspore as an anchor point.The structure of aluminum hydroxide transitions from diaspore to boehmite with the increase of coating medium pH;?2?The preparation of Al@Fe₂O₃:In weak acid conditions,iron oxide encapsulated aluminum pigment was prepared using FeCl₂·4H₂O as precursor and isopropanol/H₂O as the medium.The influence of the medium pH and the n(Fe²⁺):n(Fe³⁺)on the phases of coating and the encapsulation effect was investigated through XRD,optical microscopy and anti-corrosion resistance test,and the oxidation-transformation mechanism of Fe²⁺induced by Fe³⁺is also discussed.The results showed that high pH and excess Fe³⁺resulted in the rate of supplying iron oxide crystal too fast,which lead the agglomeration of iron oxide particles and disadvantaged the anchoring on the surface of the aluminum pigment.Moderately increasing medium pH and the amount of Fe³⁺added to the precursor can form the amorphous iron oxide that can induce the oxidation and transformation of Fe²⁺and accelerate the supply rate of iron oxide seed,which is beneficial to the formation of amorphous iron oxide on the aluminum pigment.The iron oxide can deposit on the aluminum surface to form a dense coating layer at pH of encapsulated media above 4.70,the proportion of ferrous and ferric iron were 12:1 in isopropyl/water medium.The products of Al@Fe₂O₃ aluminum pigments with best anti-corrosion resistance,low gloss and khaki and can be used as stealth pigment.?3?The preparation of Al@SnO₂:The waterborne aluminum pigments of Al@SnO₂ that used aluminum as the core,SnO₂ as shell and Al?OH?₃ or Sn?OH?₂ as the bridge was prepared by using SnCl₄/isopropyl as the precursor in isopropyl/H₂O at weak acidity media.The effect of preparation conditions on the anchoring effect and photocatalytic activity of SnO₂ were discussed through optical microscopy,X-ray diffraction,anti-corrosion resistance and photocatalytic degradation efficiency test.The rate of supplying tin oxide crystal was fast,which were inferior to SnO₂ that anchoring on the surface of aluminum and the improvement anti-corrosion resistance when the encapsulation pH and M_SnO2/S_All were too high.SnO₂anchoring on the surface of aluminum used Sn?OH?₂ as the bridge when the encapsulation media pH was low,which disadvantage to the improvement of photocatalytic activity.SnO₂coating on the surface of aluminum was incomplete when M_SnO2/S_All was low,which lead the poor anti-corrosion resistance.SnO₂ can be anchored on the surface of aluminum by the bridge of Al?OH?₃ and formed a dense coating layer and Al?III?doping SnO₂ between SnO₂shell and aluminum core when controlling the encapsulation medium pH=5.0-5.8 and(M_SnO2/S_Al)=?0.07-0.10?g·m^-2,which prepared the khaki Al@SnO₂ with excellent anti-corrosion resistance,low gloss and photocatalytic activity can be used for multi-band stealth.At the same time,Al@SnO₂ can be recovered and used as waterborne aluminum pigment after degradation.SnO₂ supported on glass powder was prepared and synthesized to study the effect of Al?OH?₃ on the photocatalytic activity of SnO₂;?4?The preparation of SnO₂ photocatalyst supported on glass powder:The previous work that using SiO₂ encapsulated aluminum pigment,and then prepared Al@SiO₂@Fe₂O₃used SiO₂ as a bridge,but fewer reports that are using Al?OH?₃ as a bridge was reported.The photocatalyst of GP@SnO₂ that used glass powder?GP?as the core,SnO₂ as shell and Al?OH?₃ as the bridge were prepared by using SnCl₄/isopropyl as the precursor in isopropyl/H₂O at weak acidity media.The influence of medium pH,n[Al?OH?₃]/n?SnCl₄?and m?SnO₂?:m?GP?on the photocatalytic activity of GP@SnO₂ were investigated through photocatalytic degradation test,PL and UV-Vis.The results showed that n[Al?OH?₃]/n?SnCl₄?directly affects the amount of Al?III?doping SnO₂.When the medium pH is high,the supply rate of SnO₂ seeds was fast and resulted in the self-polymerization of SnO₂;When the content of m?SnO₂?:m?GP?was high,the anchoring surface of SnO₂ is small,which were disadvantage to SnO₂ seeds anchored on the surface of glass powder.When m?SnO₂?:m?GP?is low,the SnO₂ coating on GP surface was thin and sparse,which lead the decreasing of the load effect.When the medium pH=5.8-6.0,m?SnO₂?:m?GP?=0.17,the SnO₂ seed crystals crystallized on the surface of GP and formed appropriate amount Al?III?doped SnO₂ between the SnO₂ shell and the GP core,which increases the concentration of oxygen vacancies on the surface of SnO₂,promotes the separation of photogenerated electrons and holes,and is advantage to the improvement of the photocatalytic activity of SnO₂.Therefore,multi-functional aluminum pigments with excellent corrosion resistance and optical properties were successfully synthesized using Fe₂O₃ and SnO₂ as coating layers respectively,which provided a theoretical foundation for large-scale industrialization in the future.