Investigation on high-temperature resistant sealants for zinc-nickel plating
In the process of hydrogen removal in alkaline zinc-nickel roll plating lines,traditional seal-ing agents are unable to withstand high temperatures,resulting in the hydrogen removal step occurring before the sealing step.Consequently,this leads to complex operations and an inability to fully release production capacity.This article aims to develop a high-temperature resistant alkaline zinc-nickel seal-ing agent,allowing the hydrogen removal heat treatment step to be placed after the passivation sealing step,thereby contributing to the enhancement of the automation level of zinc-nickel plating.By employ-ing an orthogonal experimental approach and combining techniques such as field emission scanning electron microscopy,X-ray photoelectron spectroscopy,Fourier-transform infrared spectroscopy,ther-mogravimetric analysis,Tafel curves,and alternating current impedance,the effects of lithium sili-cate,sodium silicate,sodium tungstate,sodium dihydrogen phosphate dosage,as well as temperature and time on the high-temperature resistance of the sealing layer were investigated.The results indicate that the optimal sealing agent solution contains 100 mL of water,25 mL of lithium silicate solution,5 g of sodium silicate,0.2 g of sodium tungstate,and 0.02 g of sodium dihydrogen phosphate in a total volume of 125 mL.After immersing the specimens in this solution for 10 minutes,followed by removal and drying at 60 ℃,a 3-h hydrogen removal heat treatment at 250 ℃ results in appearance of red rust occurred for more than 2000 hours on specimens under ISO9227 standard,which significantly surpass the 720 h without red rustindustrystandard.