体液无机离子在镁表面的腐蚀机理

Microscale Corrosion Mechanism of Magnesium in Body Fluid with Different Inorganic Ions

为揭示镁在人体中的腐蚀机理,通过分子动力学模拟方法研究计算了体液中无机离子Cl^(-)、SO^(2)-_(4)、HCO^-_(3)和HPO^(2)-_(4)在镁表面的腐蚀,并用实验对模拟的结果进行了验证。研究结果表明:体系加入无机离子后,破坏了水分子的稳定结构,模拟体系的扩散系数明显增大。不同离子溶液与Mg(0001)表面的主要作用力为化学键Mg—O,其会很大程度地破坏镁致密的晶格结构,使镁的表面结构变得疏松有孔。其次,溶液中的Cl^(-)、SO^(2)-_(4)、HCO^(-)_(3)和HPO^(2)-_(4)会通过孔隙进入镁结构内部,通过Mg—Cl、Mg—S、Mg—C和Mg—P间相互作用力拉大Mg—Mg的键长,使得其结构更加疏松,进一步加快其腐蚀进程。加入Cl^(-)、SO^(2)-_(4)、HCO^-_(3)和HPO^(2)-_(4)以后,会生成氧化物MgO_(x)H_(2x),使镁的腐蚀大幅度加快。加入Cl^(-)以后,会生成HCl,加入SO^(2)-_(4)以后,O原子会把Mg原子拉出Mg层,Mg原子会溶入溶液,从而使镁层腐蚀。加入HCO_(3)-以后,会生成H_(3)CO_(4)。HPO^(2)-_(4)的加入,会生成弱酸H_(2)PO_(4)。这些生成物都会对镁的腐蚀产生很大的影响。结果表明:加入无机离子后,模拟体系的氧化反应程度增大,增大了镁的腐蚀程度。生成物中若含有HCl、H_(2)SO_(4),其体系中镁的腐蚀剧烈,程度较深。生成物中若含有OH^-,其也会对镁的腐蚀产生影响,但其生成量很少,影响程度有限。生成物中若含有H_(2)CO_(3)、H _(3)PO_(4)等弱酸,对镁的腐蚀作用相对较小,说明Cl^(-)、SO^(2)-_(4)是引起镁腐蚀的主要原因。

The corrosion mechanism of the inorganic ions Cl-,SO 2-4,HCO-3 and HPO 2-4 in the body fluid on the surface of magnesium was calculated by molecular dynamics simulation method,and the simulation results were verified by experiments.The results show that the diffusion coefficient of the simulated system increases obviously when inorganic ions are added to the system to destroy the stable structure of water molecules.The main force between different ionic solutions and the surface of Mg(0001)is the chemical bond Mg—O,which destroys the dense lattice structure of magnesium to a great extent and makes the surface structure of magnesium become loose and porous.Secondly,the Cl-,SO 2-4,HCO-3 and HPO 2-4 in the solution enter the magnesium structure through the pores,and the interaction between Mg—Cl,Mg—S,Mg—C and Mg—P increases the bond length of Mg—Mg,making the structure more loose and further accelerating the corrosion process.After adding Cl-,SO 2-4,HCO-3 and HPO 2-4,the oxide MgO x H 2 x is formed,which greatly accelerates the corrosion of magnesium.After adding Cl-,HCl is to be generated.After adding SO 2-4,the O atom pulls the Mg atom out of the Mg layer,and the Mg atom is to dissolve into the solution,so that the magnesium layer is corroded.After adding HCO-3,H 3 CO 4 is generated.The addition of HPO 2-4 produces weak acid H 2 PO 4.These products can have a significant impact on the corrosion of magnesium.The results show that the degree of oxidation reaction and corrosion degree of magnesium increased after adding inorganic ions in the simulated system.If the products contain HCl and H 2 SO 4,the corrosion of magnesium in the system is severe and deep,and the influence degree is limited.If OH-is contained in the product,it will also affect the corrosion of magnesium,but the amount of OH-is small and the influence is limited.If the product contains weak acids such as H 2 CO 3 and H 3 PO 4,the corrosion effect on magnesium is relatively small,indicating that Cl-and SO 2-4 are the main causes of magnesium corrosion.