| Metal corrosion causes great economic loss and damage to industry and society. With the progress of industry and technology, anti-corrosion holds more and more important position in the national economy. Due to the unique physical, chemical and mechanical characteristics of Ni-P deposits, such as the anticorrosive property, wear resistance, paramagnetic characteristic, high hardness and the electro-catalytic activity of hydrogen evolution, the Ni-P deposits had been used widely in various fields. But the particles of the Ni-P deposits were unregulated. So it was hard to avoid the pinholes in the deposits especially in brine mediums. Pit corrosion was the main reason why the electroless Ni-P deposits were limited to be used widely. So how to effectively enhance the corrosion resistance of the electroless Ni-P deposits was the urgent affair.This article initially researched the process of single / double nickel-phosphorus electroless deposit(s) on common industry iron mat slices. Through the test it was found that,in 3.5wt% NaCl solution, the corrosion potential of the double Ni-P electroless deposits was higher more than 100mV than the single electroless deposit, the polarization resistance was significantly larger, and the charge transfer resistance and the passivation film resistance also became larger. And in the test on the plates plunging in the sea water completely,the time of the appearance of pitting was longer 1～5h than the latter. Experiment results showed that the double electroless deposits enhanced the corrosion resistance better than the single electroless deposit.Electroless deposits have porosity inevitably. When the thickness of electroless deposits isn't high, or the disfigurements aren't eliminated just by increasing the thickness of electroless deposits, the surface of electroless deposits needs to be sealing-treated. Silicone was used for sealing-treatment to electroless deposits in this article. Because the sealing agent could penetrate into the pinholes of the deposit and had good crosslink with the deposit, the number of the pinholes on the corroded deposit decreased after sealing-treatment, thus corrosion resistance is increased. Through experiments it was found that after sealing-treatment, the corrosion potential improved significantly, the time of the appearance of pitting in the corrosive environment was extend significantly, the polarization resistance was significantly larger, and the charge transfer resistance and surface film resistance also became larger. Experiment results showed that the corrosion resistance could be enhanced through the sealing-treatment. At the same time, temperature made a great impact on sealing effect. Electrochemical experiments and the test on the plates plunging in the sea water completely showed that sealing-treatment could improve corrosion resistance of deposits at different temperature and up to the best effect at 50℃.If the improvement of corrosion resistance of electroless deposits is far from ideal after first sealing-treatment, or the disfigurements aren't eliminated after first sealing-treatment, electroless deposits need to be second sealing-treated. In this article, acrylic resin was used for second sealing-treatment to double electroless Ni-P deposits after first sealing-treatment by silicone. Acrylic ester polymers have good characters such as good filming character and adhesive ability and so on, so it has the function of sealing the pores again and can improve corrosion resistance of deposits. Through experiments it was found that after second sealing-treatment the time of the appearance of pitting in the corrosive environment extended significantly, the polarization resistance was significantly larger, and the charge transfer resistance, surface film resistance and hole resistance in impedance spectra also became larger. The impact of second sealing-treatment on corrosion resistance was explained through the results, and it showed that second sealing-treatment could improve corrosion resistance of deposits. At the same time, quality proportion of second sealing-treatment liquid made a great impact on second sealing effect. Experiment results showed that second sealing-treatment could improve corrosion resistance of deposits at different quality proportion and up to the best effect at acrylic resin:xylene=3:7. |
