Composition Of Bath And Properties Of Chrome-plated Plate With Impurity Ions Impact Study

Chrome plate with low cost,strong adhesion,non-toxic,etc,in areas such as food cans office supplies auto parts are widely used due to the plating chromium liquid composition concentration and additive category is different,difference obvious solution properties,its obvious effects on the properties of chrome plate.In addition,introduced the production process of impurity ions will also affect the solution itself are plated with deep plating ability,then the quality of the chrome plate surface finishes.Therefore,in the study of chromium plating solution and chromium liquid impurity ion effect on the properties of chrome plated surface has the important theoretical and practical significance.This paper uses cyclic voltammograms timing ampere law,the ammonium fluoride fluosilicate chromium electrodeposit nucleation type fluorine sodium silicate system,combined with the coating porosity test method of scanning electron microscopy(sem)analysis method,electrochemical detection studies three kinds of chromium plating solution system board surface density and the corrosion resistance of the difference,to explore the different composition of plating solution concentration on the properties of chrome plate coating effect.The effect of impurity ions of the coating was discussed by analyzing the co-precipitation coupling of iron,aluminum and titanium ions under different conditions when they exist separately and simultaneously.The following conclusions were reached:(1)The cyclic volts of the three bath systems(ammonium fluoride system,fluorosilicic acid system and sodium fluorosilicic acid system),which were composed of different components,all showed "resistive current loop" near the corresponding reduction peak potential,and the higher the concentration of chromium anhydride,the higher the step potential.The three kinds of plating systems were 3d nucleation,while 2d nucleation in chrome oxide,and with the decrease of CrO3 concentration,the deposition of chromium changed from 3d nucleation to 2d nucleation.The nucleation transformation of ammonium fluoride system occurred in the concentration range of 85～100 g/L CrO3.The nucleation transformation of fluorosilicic acid system occurred in the concentration range of 35～45 g/L CrO3.The nucleation transformation of sodium fluorosilicate system occurs in the concentration range of 3 5～50 g/L CrO3.(2)When the concentration of CrO3 is 150 g/L and the concentration of NH4F is 3.5 g/L,the pH is 1.09,which is three-dimensional instantaneous nucleation.The coating on the surface of chromium-plated plate has high chromium content,low porosity and good corrosion resistance.The high conductivity of ammonium fluoride solution is beneficial to the generation of chromium oxide.Compared with the ammonium fluoride system,the pH of fluosilicic acid system plating solution is lower,the pH range of chromium metal plating solution is 0.86～0.91,the chromium plating plate surface coating chromium content is high,lower pH is conducive to the formation of chromium oxide.When CrO3150 g/L,H2SiF6 2 g/L,the coating has good corrosion resistance.For sodium fluorosilicate system bath,the pH range of metallic chromium bath is 0.92～1.02.When CrO3 is 180 g/L and Na2SiF6 is 4.8 g/L,the corrosion resistance of the coating is better.(3)The pH of bath is the key factor that affects the ion capacity.With the increase of pH,the gibbs free energy for the precipitation of ions gradually decreases,and the capacity of the bath to hold impurities is greatly reduced.Under the condition of electroplating,it is easier to make Fe3+,Al3+ and Ti3+ generate corresponding precipitation.Current density is an important factor for the precipitation of ions.With the increase of current density,the pH of the bath containing Fe3+,Al3+ and Ti3+gradually decreases,and the gibbs free energy of the precipitation reaction generated by each ion increases,which has an inhibitory effect on the precipitation generated by its own crystallization.(4)In chromium anhydride solution,the gibbs free energy of precipitation reaction produced by single ion is larger.In a single ion bath,the addition of other ions will reduce the gibbs free energy of the precipitation reaction generated by the ions of the total components of the bath and reduce the receptivity of the solution to the ions.Under the coupling effect of ion co-precipitation in the bath containing iron,aluminum and titanium ions,aluminum hydroxide and titanium hydroxide enter the crystal of iron hydroxide in the form of impurities,and multi-component impurity ions are more likely to precipitate in the solution.The presence of impurity iron ion and aluminum ion in the plating solution will cause the increase of the porosity of chrome-plated plate,and with the increase of impurity concentration,the porosity value of chrome-plated plate will also increase.