Surface Modification Of Metal Aluminum Powder And Its Application

Metal aluminum powder is one of the most widely used metal powders in recent years due to its excellent properties such as abundant raw materials,low cost,and wide application.The most widely used are mainly divided into flake aluminum powder and spherical aluminum powder.Flake aluminum powder has been widely useful for applications in the field of coatings owing to its unique "flip-flap effeec" characteristics and excellent metallic gloss.However,the flake aluminum powder is easily corroded in the air due to the active property,the large specific surface area and exposed aluminum atoms with large quantity and high activity.The surface modification should be carried out before the use of flake aluminum powder.A large amount of literature on the modification of flake aluminum powder to improve the acid and alkali resistance has been reported.Among them,coating modification has been widely studied by scientists for its excellent coating effect and simple operation process.However,the coated flake aluminum prepared by these studies still cannot meet the requirements of alkali resistance under the strong acid and alkali.Because the fluoropolymer has excellent acid and alkali resistance,if the fluoropolymer can be coated on the surface of the flake aluminum powder,it will greatly improve the acid and alkali resistance of the flake aluminum powder.However,no report on the the flake aluminum powder modification via fluoropolymer is found in the literature so far.Because of spherical aluminum powder properties of large specific surface area,low oxygen consumption and high enthalpy of combustion,there are many researches on improving the performance of solid propellant by using spherical aluminum powder at home and abroad.Highly active spherical aluminum powder has complete combustion,high combustion efficiency,and excellent ignition performance.As a metal combustion agent,it can significantly increase the impulse and combustion rate of the solid propellant,enhance the combustion stability of the propellant,and significantly increase the specific impulse of the propellant.Therefore,spherical aluminum powder has broad application prospects in the field of solid propellants.However,due to the existence of the alumina layer on the surface of the spherical aluminum powder,spherical aluminum powder is prone to insufficient combustion during the combustion process.If the aluminum powder particles are not affected by the surface alumina layer,it can be burned quickly ignite and can rupture aluminum particles during combustion,which will minimize the loss of spherical aluminum powder and make it burn more completely.However,at this stage,there are no reports about removing the aluminum oxide film on the surface of the spherical aluminum powder to improve its combustion performance.In this paper,the preparation and application of modified metal aluminum powder are mainly studied.On the one hand,fluorine-containing acrylates with excellent acid and alkali resistance are used as monomers to prepare fluoropolymer single-layer coated aluminum powder and fluoropolymer/silica double-layer coated flake aluminum powder respectively.The coated flake aluminum powder significantly improves the alkali resistance.On the other hand,using hydrofluoric acid as the fluorinating agent,the aluminum oxide film on the surface of the spherical aluminum powder was successfully removed by fluorination under the condition that the active aluminum content of the spherical aluminum powder did not decrease significantly.The main research contents of the thesis include the following parts:(1)This section uses trifluoroethyl methacrylate(TFEMA)as the monomer,trimethylolpropane trimethacrylate(TMPTMA)as the crosslinking agent,and azobisisobutyronitrile(AIBN)as the initiator,an in-situ polymerization method was used to coat the surface of the flake aluminum powder with a uniform and dense fluoropolymer film.The fluoropolymer-coated aluminum powder was successfully prepared.Scanning electron microscope(SEM)and energy dispersive spectroscopy(EDS)proved the stable existence of fluoropolymer film.The existence of this layer of fluoropolymer film can effectively block the erosion of flake aluminum powder by external corrosion factors.The thermogravimetric analysis(TGA)and hydrogen evolution experiments have proved the excellent thermal stability and chemical resistance of fluoropolymer-coated flake aluminum powder.Finally,the prepared fluoropolymer-coated aluminum powder was mixed with acrylic resin to make a coating and sprayed on a tinplate.The results showed excellent alkali resistance and proved the excellent practical application of this technology.(2)In order to further improve the acid and alkali resistance of flaky aluminum powder,this section combines the sol-gel method with the in-situ polymerization method.First,a solgel method was used with tetraethyl orthosilicate(TEOS)as a precursor and ethylenediamine as a catalyst,to coat a layer of silica on the surface of aluminum powder;Then,using trifluoroethyl methacrylate(TFEMA)as the fluorine-containing monomer and trimethylolpropane trimethacrylate(TMPTMA)as the crosslinking agent,a layer of fluorinecontaining polymer film was in-situ polymerized on the surface of silica monolayer coated flake aluminum powder by intermolecular force.Fluoropolymer / silica double-layer coated flake aluminum powder was obtained.Scanning electron microscope(SEM)and X-ray photoelectron spectroscopy(XPS)proved the successful preparation of the double-layered coating on the surface of the aluminum powder.Then,the alkali resistance and practical application of the double-layer coated aluminum powder were tested by hydrogen evolution experiment and spray plate experiment.The results show that the alkali resistance of flake aluminum powder has been greatly improved after the fluoropolymer film and silica double-layer coating modification.The fluoropolymer/silica double-layer coating type flake aluminum powder was placed in 5% strong alkaline sodium hydroxide solution for more than 24 hours without any gas evolution.This is an excellent alkaline resistance which has never been achieved in the field of coating modification of flake aluminum powder so far.(3)In order to improve the combustion performance of the spherical aluminum powder and further improve the specific impulse of solid propellants,hydrofluoric acid(HF)is used as the fluorinating agent in this section,and the aluminum oxide layer on the surface of the spherical aluminum powder is fluorinated and removed by a solvothermal method in a polytetrafluoroethylene-lined reactor to further enhance the combustion of the spherical aluminum powder performance.Scanning electron microscope(SEM)and redox titration methods were used to investigate the effects of preparation conditions such as reaction temperature,reaction time,and addition amount of HF on the surface morphology and active aluminum content of spherical aluminum powder.The results indicate that the active aluminum content of the spherical aluminum powder will gradually decrease with the extension of the reaction time,the increase of the reaction temperature,and the increase of the amount of hydrofluoric acid.The active aluminum content is particularly affected by the amount of hydrofluoric acid,while the effect of reaction time on the active aluminum content is less.The results show that the reaction conditions such as reaction time,reaction temperature and the amount of hydrofluoric acid can be adjusted to adjust the morphology and active aluminum content of spherical aluminum powder as required,so as to obtain the fluorinated spherical aluminum powder applied in different fields.