预拉伸形变对Mg-Zn-Sr-Zr-Mn合金降解行为的影响

镁合金具有优异的生物相容性和独特降解性,但其在生理环境中的耐蚀性能较差,严重制约了其在临床应用中的发展。使用预拉伸工艺制备Mg-Zn-Sr-Zr-Mn新型镁合金,通过XRD、OM和SEM探究预拉伸形变量与显微组织、腐蚀速率和膜层形貌间的关系。结果表明:随预拉伸形变量的增大(2%、4%、6%),合金晶粒尺寸被逐渐拉长,孪晶数目逐渐增多,析出相离散程度逐渐增大。4%预拉伸合金由于适量孪晶的出现及析出相离散程度的增大,增加了电偶腐蚀形核点位,加速了合金表面均匀氧化产物的快速产生,增大了合金极化电阻阻值;3种预拉伸合金电化学(0.38、0.25、0.74 mm·a^(-1))及失重速率(2.85、1.83、5.88 mm·a^(-1))均呈现先降低后升高的趋势。4%预拉伸合金具有较高的耐蚀性证明适当的预拉伸变形能提高界面析出相的连续性,阻碍腐蚀进程,对合金耐腐蚀性能起到积极作用。而当预拉伸形变量继续增加,产生大量位错,创造氢扩散路径,有利于氢富集,导致合金耐蚀性下降。此外,适当的预拉伸形变通过改变残余应力的重新分布,提高腐蚀均匀性,同时提高膜层致密性与连续性,延缓腐蚀进程。

Efficient degradation of methyl orange via multilayer films of titanium dioxide and silicotungstic acid

We report layer-by-layer （LbL） assembly of TiO2 and H4SiW12O40 （SiW12） multilayer film on silicon wafers and glass slides for photocatalytic degradation of methyl orange （MO）. The photocatalytic efficiency of the obtained multilayer film increases along with the decrease of pH and salt concentration of the incubation solution. The results show that MO can be almost re- moved in pH 2.0 solution without salt addition in the first 60 min incubation when MO concentration is lower than 15 mg/L. Different salts show an apparent inhibitory effect on photocatalytic degradation of MO with the order of ZnC12〉KCI〉 NaC1〉LiCI. The TiO2/SiW12 multilayer film maintains photocatalytic activity even after five degradation cycles. The reaction of MO photodegradation accords with an apparent first-order dynamics.