Study On Corrosion Behaviour Of Metal/Polymer Composite And Diffusion Dynamics Of Metal Ion

Being safe, effective, economic, reversible and simple, intrauterine device (IUD) is one of the most popular contraceptive methods that are used all around the world. IUD can be divided into two categories, namely, the inert and the active one. Owing to its weak effect of contraceptive, the inert IUD has been replaced gradually with the active one. The active IUD covers copper-containing IUD (Cu-IUD) and drug slow-release IUD. Recently, Cu-IUD has been widely investigated and employed due to great contraceptive effect of copper.The copper/low-density polyethylene (Cu/LDPE) composite is one kind of new IUD, because it has the many kinds of merits to become the hot spot of the present IUD research. To optimize the properties of these composite systems, it is necessary to study their corrosion behaviour in the uterine solution thoroughly. Currently on the corrosion research of the metal/polymer composite, high resistivity and dispersing type composite are less.By testing the volume resistivity and the dielectric constant of the composite, the resistivity of the microcomposite have of a sudden decreased region and the percolation threshold of the microcomposite probably is 50% copper quality percentage. Around the percolation threshold, the volume resistivity of the microcomposite does not change along with the copper content change. There are not obvious mutation region for the volume resistivity of the nanocomposite, its volume resistivity gradually reduces along with the copper content increase. The dielectric constant of two composites all are rise along with the copper content increase. The dielectric constant of the microcomposite has a leap in the vicinity of the percolation threshold.The corrosion behaviour of the microcomposite immersion in the simulated uterine solution is depended on the copper content. Corrosion in stable, the corrosion rate of the microcomposite with high copper content much high than the microcomposite with low copper content. The surface of the microcomposite appears obvious passivation phenomenon and schistose sediment when the copper content of the microcomposite was exceeding the percolation threshold. The corrosion rate of the nanocomposite was fluctuations in early immersion. Compared with bulk copper, the composite have more stable the corrosion rate, less burst release of Cu²⁺ and hardly passivation. Immersion after period time, the surface of the bulk copper is covered the massive sediment. Corresponding, the surface of the composite, especially the nanocomposite, is cleaner.The bulk copper and two kinds composite have similar corrosion mechanism in the course of corrosion in the simulated uterine solution, all is some two steps of oxidizing reaction. The intermediate products of them are mainly Cu2O. For the microcomposite, the copper content have some effect to its corrosion mechanism. When the copper content is lower than the percolation threshold, the microcomposite only has a step of reduction reaction; but when the copper content is higher than the percolation threshold, the microcomposite has two steps of reduction reaction. The copper content has not affected to the corrosion mechanism of the nanocomposite immersion in the simulated uterine solution.The copper transformation ratio of two composites is higher than the bulk copper, and the transformation ratio of the nanocomposite is close to 100%. The copper content has greater impact to the transformation ratio of the microcomposite, especially the transformation ratio reduces obviously while the copper contents exceed the percolation threshold. And the copper content is not significantly affected to the transformation ratio of the nanocomposite. Is soaking the initial period, the transformation ratio of the bulk and the microcomposite all has an obvious rise process. The nanocomposite throughout to maintain the very high the transformation ratio when immersion in the simulated uterine solution.The weight and capacitance of the composite all are along with the immersion time of the rising trend, and all tends to stable finally. Be immersed initial stage, the diffusion characteristics of the solution in the composite according to the Fickâ…¡. The diffusion coefficient of Cu²⁺ in the surface layer of the bulk is far high than the composite, and the diffusion coefficient of Cu²⁺ in the composite about 10-9cm2s-1. When corrosion of the composite reaches stable, Cu²⁺ generated within composite disperses through solution path to penetrate to simulated uterine solution outside the composite. The corrosion behaviour of the bulk and the composite all can be explained by the similar electrical equivalent circuits, and it was controlled by both the processes of the pervasion of Cu²⁺ and the transfer of the charge.Compared with the bulk copper, the Cu/LDPE composite have high copper transformation ratio, clean surface, single product and hardly passivation quality when immersion in the simulated uterine solution. We can conclude that the Cu/LDPE composite, especially the nanocomposite, is favorable to as the novel material of IUD. Further, the electrochemical method in this study is proved to be useful to characterize the corrosion behaviour of high resistivity and dispersing type metal/polymer composite.