| Button battery is widely used in micro-electronics industry. In the alkaline zinc-manganese button battery, the battery may expand and bring the safety problems due to the hydrogen evolution reaction between anode zinc powder or the zinc oil and the impurities, which can produce large amounts of gas. To solve this problem, the traditional method is to add a certain amount of metal mercury which can react with the copper coating in the anode lid to produce amalgam and lower hydrogen evolution corrosion, so as to restrain the production of hydrogen. However, the mercury is greatly badly to body and environment and mercury-free battery is an inevitable trend in the development of the battery. Tin is friendly to the environment and it can improve the hydrogen evolution reaction over-potential and reduce the hydrogen evolution. In the development of mercury-free batteries, the tin coating is always electroplated on the copper of the anode lid, which can hold the contract of anode zinc powder with copper so as to lower hydrogen evolution corrosion and decrease the expansion of the battery. Now the existing battery producers always take the technology that make the anode lid stamping forming after electroplating tin on the strip substrate, while there are many problems during stamping forming such as being scratched easily, many cracks and expose copper and so on, leading to the expansion of battery for the conventional tin coating strip, which hinders the development and wide use of the mercury-free batteries, so it is very important to solve the problem of the densification and hardness of the tin coating for the industrialization of mercury-free button batteries. To settle the matter, in this thesis, the tin coating of different grain size were prepared by pulse electroplating on the copper substrate with different technological conditions such as pulse parameters. Many measurement method, XRD, SEM, EDS were used to analysis the micro-structure and the corrosion resistant property after tensile deformation of the samples. The details are followed.1. On the foundation of thorough study on the conventional tin electroplating technology, the technology formula were improved, and the pulse electroplating method is used to prepare tin coating with 4μm thickness when pulse parameters such as the pulse duty, frequency, ratio of double direction pulse current of pros and cons were changed respectively.2. The effects of the three pulse parameters, the pulse duty, frequency, ratio of double direction pulse current of pros and cons, on the micro-structure were studied on the basis of characterization of the surface morphology and phase. The results showed, first, the grain size of the tin coating and the porosity increased with the increase of the pulse duty, and the texture of the tin coating transformed from Sn(101) to Sn(211). Second, the grain size of the tin coating and the porosity decreased with the increase of the frequency, and the texture of the tin coating transformed from Sn(211) to Sn(101). Third, the grain size of the tin coating increased gradually with the decrease of ratio of double direction pulse current of pros and cons, and the texture of the tin coating transformed from Sn(101) to Sn(211).3. The hardness of the tin coatings prepared in different pulse conditions are tested, and the relations between the hardness of the tin coatings and the pulse conditions were studied. The corrosion resistant properties after tensile deformation of the samples were estimated by the electrochemical workstation. The relations between the pulse conditions and the hardness, the change of the cracks and the corrosion resistant properties after tensile deformation were observed, and the results were showed as follows. First, the hardness of the tin coatings decreased, the surface cracks reduced gradually, and the corrosion resistant properties were improved with the increase of the pulse duty. Second, the hardness of the tin coatings increased notably, the surface cracks extended gradually, and the corrosion resistant properties were diminished with the increase of the ratio of double direction pulse current of pros and cons. |
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