Research On Phosphating Steel Surface

Phosphating steel is one of the important measures to protect steel.After phosphating,phosphate will be formed on the steel surface.This phosphate can isolate the steel matrix from the outside world,protect the steel itself,and prolong the service life of the steel itself.In this paper,the application of auxiliary film-forming agent A,B and C in phosphating solution was studied by traditional chemical phosphating method,the auxiliary film-forming agent C was extracted from the phosphate ore containing rare-earths,the treatment method of phosphating residue after steel phosphating was studied.Firstly,phosphoric acid,nitric acid,zinc oxide,auxiliary film-forming agent A and auxiliary film-forming agent B were used to synthesize phosphating solution,which was diluted for a certain number of times.The specific application process of phosphating solution was studied,and the phosphating film on the surface of steel under the optimum technological conditions was characterized.The results showed that the optimum technological conditions for phosphating solution were as follows:free acidity is 17.8mg/g,total acidity is 93.0mg/g,phosphating temperature is 60℃,phosphating time is 5min.The phosphating film was grey black,compact and uniform.The element composition of the phosphating film was C,P,O,Fe and Zn,and its content is 2.39%,10.83%,31.78,20.66%and 34.34%,respectively.The phosphating film also has certain hydrophobicity and acid(alkali)resistance.Secondly,this paper uses concentrated nitric acid to decompose Zhijin’s phosphate rock containing rare-earths,and then uses mixed salt filtered,concentrated and crystallized as auxiliary film-forming agent C to prepare phosphating solution with phosphoric acid,nitric acid and zinc oxide,the effect of auxiliary film forming agent C on Phosphating of iron and steel was studied.The results show that the addition of auxiliary film-forming agent C which can only change the total acidity of phosphating solution,but it has little effect on the free acidity of phosphating solution.When the addition of auxiliary film-forming agent C is 1.50g,the steel exhibits better corrosion resistance.The element composition of phosphating film is C,P,O,Fe,Zn,Na,and its content is 7.25%,9.82%,33.01%,16.83%,31.35%,1.74%respectively,The unit film quality of phosphating film is ranged from 6.30 g/m~2 to 7.42 g/m~2.The results show that the rare earth-bearing phosphorite from Zhijin which can improve the corrosion resistance of steel to a certain extent.Finally,the phosphating residue of steel is treated with potassium hydroxide solution to prepare potassium dihydrogen phosphate.The purity of the product potassium dihydrogen phosphate is very high,and the recovery rate of P is as high as96%.The by-product elements consist of O,P,K,Fe,Zn and Si,and its contents is34.35%,1.31%,11.88%,46.61%,4.65%and 1.21%respectively.It can be used in the production of trace element compound fertilizer.