热浸锌铝合金镀层表面纳米晶腐蚀产物共沉积机理

Co-precipitation of nano-crystalline corrosion products on hot dip Zn-Al alloy coating

采用XRD和TEM对热浸锌铝合金镀层在动态充气海水全浸试验时所形成的白色腐蚀产物进行了研究。结果表明 :腐蚀产物主要由典型的纳米级Zn4 CO3(OH) 6·H2 O ,Zn5(OH) 8Cl2 和Zn6Al2 CO3(OH) 16·4H2 O微晶组成 ,而这种纳米晶的形成与由吸附引起的Zn2 +和Al3+离子的共沉积有关 ;镀层表面腐蚀后首先生成Al(OH) 3凝胶 ,当凝胶吸附的锌离子超过异相形核的临界过饱和度时 ,发生锌、铝氢氧化物的共沉淀 ,生成双氢氧化物。由于晶体长大速度较慢不能与沉淀形核同步进行 。

The white corrosion products on hot dip Zn Al alloy coating exposed to seawater in dynamic aerated immersion were investigated by means of XRD and TEM. The results show that the corrosion products are typical nanometer microcrystals, containing mainly Zn 4CO 3(OH)6·H 2O, Zn 5(OH) 8Cl 2 and Zn 6Al 2CO 3(OH) 16 ·4H 2O, and that the formation of the nano crystalline corrosion products probably is related with the co precipitation of Zn 2+ and Al 3+ caused by adsorption. Zn Al alloy coating seawater attack, Al(OH) 3 gel is first produced on the coating surface. Zn and Al hydroxides co precipitate and form double hydroxide when the concentration of adsorbed Zn 2+ ions by the newly produced gel exceeded the critical supersaturation of the interphase nucleation. However, because the growth of the crystals is too low to keep in step with the nucleation, a layer of nano crystalline corrosion products are produced on the surface of the coating finally. [