Study On The Construction And Application Performance Of Functional Surface Layer On The Aluminum Powder

Aluminum metal powder is one of the most popular and applied metal powders in the market due to its excellent performance,low cost,and simple manufacturing process.There are two main types of aluminum powder according to their shape and manufacturing process:flake aluminum powder and spherical aluminum powder.However,aluminum atoms are active and easily react with acid and alkali,making them easily corroded in the application process.Therefore,it is necessary to modify the surface of flake aluminum powder to prevent it from corrosion.In addition,the problem of the single color of flake aluminum powder also limits its application.Enriching the color of aluminum pigments has been a significant research direction.The typical coloring methods are complicated and have poor coloring effects.MOFs with bright colors and excellent adsorption can effectively solve the problem.In addition,flake aluminum powder is susceptible to corrosion,which causes many difficulties in practical applications.The modifications of flake aluminum powder are corrosion inhibitor and film coating methods,which have many drawbacks.The combination of MOF and polymer film constructs a functional composite layer on the aluminum powder,which combines the advantages of the corrosion inhibitor and film coating methods and enables the intelligent corrosion protection of flake aluminum powder.Spherical aluminum powder has the advantages of high energy density,large specific surface area,low cost,and simple process,which makes it widely used as a metal fuel in solid propellants.Generally,spherical aluminum powder and oxidizer are physically doped in the solid propellant without sufficient contact in the combustion process,which will reduce the energy release of solid propellant,slow down the energy release rate,increase the ignition temperature,and cause many adverse effects on subsequent applications.The composite spherical aluminum powder with a core-shell structure can solve the above problems.The composite aluminum powder has a larger contact surface area and shorter diffusion distance,which can increase the energy release,improve the problem of insufficient combustion and easy agglomeration,and significantly increase the combustion rate.In this paper,we have mainly studied the surface modification of metallic aluminum powder.On the one hand,we combined MOF and coating film to construct a functional surface layer on the flake aluminum powder,which prepared smart aluminum pigments with self-healing ability and bright colors;on the other hand,we grew oxidant（CuO）in situ on the surface of spherical aluminum powder and prepared composite spherical aluminum powder with a core-shell structure and high performance.The main parts of the paper include the following:（1）Preparation of colored aluminum pigments with self-healing properties and strong alkali resistance.First,the SiO₂ layer was formed on the surface of the aluminum pigment by sol-gel method.Subsequently,the aluminum pigments were modified with polyvinylpyrrolidone（PVP）to make the surface electronegative.Then the copper-based metal-organic backbone（Cu-MOF）was prepared by in situ electrostatic self-assembly method as a carrier for the adsorption of corrosion inhibitor（BTA）and to impart the aluminum pigments with bright colors.Trimethylolpropane trimethacrylate（TMPTMA）as the crosslinking agent and trifluoroethyl methacrylate（TFEMA）as the monomer formed a fluoropolymer layer on the MOF layer by in situ polymerization.The fluoropolymer layer enhanced the compatibility of the aluminum powder with the resin and improved the long-lasting chemical stability of the aluminum powder.Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,X-ray energy spectroscopy（EDS）,thermogravimetric analysis（TGA）,scanning electron microscopy（SEM）,and X-ray photoelectron spectroscopy（XPS）were used to characterize the flake aluminum powders with functional composite layer.Ultraviolet-visible spectroscopy（UV-vis）tests were used to evaluate the release behavior of BTA from CuMOF.Electrochemical impedance spectroscopy（EIS）and alkaline resistance tests were used to characterize the anti-corrosion behavior of the modified aluminum powders.The results showed that the impedance of Al@CuMOF-BTA@PTFEMA can be up to 7.23x10⁵Ω·cm²,which proved its excellent and long-lasting chemical stability.（2）Preparation of aqueous-colored aluminum pigments with pH responsiveness and self-healing properties.First,the aluminum pigments were modified with silane coupling agents containing amino groups to provide attachment sites for the growth of ZIF.Subsequently,the zinc-based metal-organic backbone（ZIF-7）was prepared on the aluminum pigment using an in situ self-assembly method.Due to the excellent adsorption and loading ability of ZIF-7,the blue Al@ZIF-7 was prepared by the inorganic color lake method.In addition,the ZIF layer exhibited good binding ability with SiO₂.The introduction of the SiO₂ layer improved the compatibility of aluminum pigments with waterborne coatings,and it endowed the functional composite layer with passive corrosion inhibition ability,which improved the chemical stability of aluminum pigments.The modified flake aluminum powders were characterized by Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,X-ray energy spectroscopy（EDS）,thermogravimetric analysis（TGA）,scanning electron microscopy（SEM）and X-ray photoelectron spectroscopy（XPS）.Electrochemical impedance spectroscopy（EIS）and acid resistance tests were performed to characterize the corrosion resistance of the modified aluminum powder.The aluminum powders with the multifunctional composite layer（Al@ZIF-B@SiO₂）were stable at pH=1.The highest impedance of Al@ZIF-B@SiO₂ reached4.35×10⁵Ω·cm² after pH response.The results indicated that Al pigments with multifunctional composite layers have sensitive pH responsiveness and durable chemical stability.（3）In order to further meet the demand for high-performance metal fuels in solid propellants,we first modified the spherical aluminum powder with 3-aminopropyltriethoxysilane to provide attachment sites for the growth of CuO.Subsequently,the oxidant（CuO）was grown on the spherical aluminum powder by in situ growth method,which successfully prepared a high-performance composite aluminum powder with the core-shell structure.The surface morphology of the spherical aluminum powder with the core-shell structure was analyzed by scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The composite spherical aluminum powders were characterized by Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and X-ray photoelectron spectroscopy（XPS）.The results showed the successful construction of CuO on the surface of spherical aluminum powders.The exothermic behavior of the spherical aluminum powder with the core-shell structure was characterized by simultaneous thermal analysis.It can be concluded that the composite aluminum powder with a core-shell structure can significantly improve the property of solid propellants.