Study On Formulation Development And Properties Of Water-borne High-efficiency Rust Converter

In this paper,three formulations of rust converters were studied.Polyphosphoric acid-tannic acid,phosphoric acid-gallic acid and phosphoric acid-phytic acid were used as the main conversion systems,and they were composed of penetrating agent,corrosion inhibitor,catalyst and other additives.Their characteristics that the rust can be directly covered on the surface of rusted steel without rust removal,and the rust can be transformed into a passive film.The formed conversion film is complete and compact,has the function of physical isolation,good corrosion resistance,good corrosion inhibition effect and adhesion.Qualitative and quantitative screening tests were carried out for the formulations of three kinds of rust converters.The formulation range of water-borne rust converters was determined by orthogonal experiments.The optimum additive types and concentration ratios were determined by single factor experiments.The properties of conversion films formed by water-borne rust converters after construction of rust samples were characterized by metallographic microscope,electrochemical test and EDS analysis,scanning electron microscopy(SEM)characterization,adhesion test and other testing methods were studied.(1)The optimum additive of phosphoric acid-tannic acid type rust converter and its proportion are 45% phosphoric acid,1% tannic acid,1% zinc powder,5%acetic acid,1% urotropine,10% glycerol,5% divalent zinc ion and deionized water.The surface of the conversion film is smooth and compact by metallographic microscopy and SEM image analysis.The main elements in the conversion film are C,O,P,Fe and Zn by EDS test.The results of electrochemical test show that the corrosion current value of the sample coated with rust converter is reduced by about50% compared with that of the untreated sample,which indicates that the anticorrosive ability of the sample is improved,and the adhesion test of the sample coated with the rust converter is 3MPa,indicating that the adhesion of the sampleafter the rust conversion is better.(2)The optimum additives of phosphoric acid-gallic acid type rust converter and their proportion are 30% phosphoric acid,5% gallic acid,10% iron powder,5%glacial acetic acid,1% urotropine,30% glycerol,5% zinc ion and deionized water.Blue-black conversion films were observed by metallographic microscope and SEM images.The elements in the conversion films were analyzed by EDS element composition.The Tafel curve obtained by electrochemical test and its fitting results show that the corrosion current value of the transformed sample is lower than that of the rusty sample and the rusty sample,about 70% lower than that of the rusty sample and the rustless sample,indicating that the anticorrosive effect is good.The adhesion of the transformed sample is 3.5 MPa,which indicates that the transformed film is closely bound to the metal matrix.(3)The optimum additive of phosphoric acid-phytic acid type rust converter and its proportion are 35% phosphoric acid,1% phytic acid,1% zinc powder,5%propionic acid,1% urotropine,10% glycerol,1% zinc ion and deionized water.The metallographic analysis and scanning electron microscopy showed that the converter combined with rust to form a smooth and compact black conversion film.EDS showed that there were more phosphorus and zinc elements in the transformed iron sheet than before.Tafel curve fitting results show that the corrosion current value of transformed iron sheet decreases by about 60%,which indicates that the corrosion protection effect is good.The adhesion test was 3.2 MPa,indicating that the conversion film was closely bound to the metal matrix.