Dept. of Chemistry and Biochemistry, Laurentian University, Sudbury, Ontario, Canada P3E 2C6.
J Colloid Interface Sci. 2010 Mar 15;343(2):474-83. doi: 10.1016/j.jcis.2009.11.062. Epub 2009 Dec 4.
Magnesium alloys have a low specific density and a high strength to weight ratio. This makes them sought after light weight construction materials for automotive and aerospace applications. These materials have also recently become of interest for biomedical applications. Unfortunately, the use of magnesium alloys in many applications has been limited due to its high susceptibility to corrosion. One way to improve the corrosion resistance of magnesium alloys is through the deposition of protective coatings. Many of the current pretreatments/coatings available use toxic chemicals such as chromates and hydrofluoric acid. One possible environmentally friendly alternative is organosilane coatings which have been shown to offer significant corrosion protection to both aluminum alloys and steels. Organosilanes are ambifunctional molecules that are capable of covalent bonding to metal hydroxide surfaces. In order for covalent bonding to occur, the organosilane must undergo hydrolysis in the coating bath followed by a condensation reaction with the surface. There are a number of factors that influence the rates of these reactions such as pH and concentration of reactants. These factors can also influence competing reactions in solution such as oligomerization. The rates of hydrolysis and condensation of 3-mercaptopropyltrimethoxy silane in methanol have been analyzed with (1)H NMR and ATR-FTIR. The results indicate that organosilane oligomers begin to form in solution before the molecules are fully hydrolyzed. The organosilane films deposited on magnesium alloy AZ91 at a variety of concentrations and pre-hydrolysis times were characterized with a combination of ATR-FTIR, ellipsometry and SEM/EDS. The results show that both organosilane film thickness and uniformity are affected by the chemistry occurring in the coating bath prior to deposition.
镁合金具有低密度和高比强度的特点。这使得它们成为汽车和航空航天应用中备受追捧的轻质结构材料。这些材料最近也开始引起生物医学应用的关注。不幸的是，由于其高腐蚀性，许多应用中镁合金的使用受到限制。提高镁合金耐腐蚀性的一种方法是通过沉积保护性涂层。许多现有的预处理/涂层使用有毒化学品，如铬酸盐和氢氟酸。一种可能的环保替代品是有机硅烷涂层，它已被证明能为铝合金和钢提供显著的腐蚀保护。有机硅烷是具有双官能团的分子，能够与金属氢氧化物表面形成共价键。为了发生共价键合，有机硅烷必须在涂层浴中水解，然后与表面发生缩合反应。有许多因素会影响这些反应的速率，例如 pH 值和反应物的浓度。这些因素还会影响溶液中的竞争反应，如低聚物化。通过 1H NMR 和 ATR-FTIR 分析了 3-巯丙基三甲氧基硅烷在甲醇中的水解和缩合速率。结果表明，在分子完全水解之前，有机硅烷低聚物开始在溶液中形成。在各种浓度和预水解时间下，将有机硅烷沉积在 AZ91 镁合金上，通过 ATR-FTIR、椭圆偏振术和 SEM/EDS 对其进行了表征。结果表明，有机硅烷膜的厚度和均匀性都受到沉积前涂层浴中发生的化学变化的影响。
