Study on the double-layrs structure of electnodeposits on the marine steel structures catbodicay probed in seawater

近年来，利用海洋空间进行人类某些活动的趋势日益明显。这一趋势使得各种结构物有必要在海水中建造。因此，这些海洋结构物的维护变得重要，特别是因为海洋环境在维护结构物方面比陆地环境严重得多。维护含铁海洋结构物的一种方法是伴随着钙质沉积物的阴极保护(CP)。此前，我们揭示了沉积在海洋构造上的钙质薄膜由Mg(OH)2和CaCO3两层组成，两者之间有明显的边界。这项研究的目的是提出一种简单的方法来分别分析双层结构，即富镁层和富钙层，并检验该方法的有效性。由于钙质沉积物在伴随沉积物的海洋构造物的阴极保护中起着主要作用，因此了解钙质沉积物的结构是非常重要的。该方法的基础是假定沉积物中的孔隙水应根据水亲性的不同在各层之间分配。从这一假设出发，推导出与矿床中双层有关的各种结构因素。为了验证双层结构分析理论模型的有效性，通过改变阴极周围海水的水动力状态或在恒定的阴极电流密度和温度下稀释海水，制备了不同钙镁比的钙质沉积膜。上述模型在这些矿床中的应用证明了该模型分析双层结构的有效性。

Recently, there is an increasing trend of utilizing oceanic space for some activities of human being. This trend makes various kinds of structures be necessary to be constructed in seawater. In accordance with this, the maintenance of these marine structures has become important, particularly because oceanic environments are far more severe in maintaining structures than terrestrial ones. A method of maintaining ferrous marine structures is a cathodic protection (CP) accompanied with calcareous deposits. Previously, we revealed that the calcareous film deposited on a marine structure is composed of double layers of Mg(OH)_2 and CaCO_3 with a clear boundary between the two. The objective of this study is to propose a simple method of analyzing the respective structures of the double layers, i.e., Mg-and Ca-rich layers, separately, and to examine the validity of the method. Needless to say, it is very important to know the structure of calcareous deposits, because the calcareous deposits play a main part in the cathodic protection of a marine structure accompanied with a deposit.In this study, a new method was proposed of analyzing the double layrs structures of calcareous deposit films formed on the surface of steel cathodically polarized in seawater. The method was based on the assumption that pore-water in the deposits should be distributed between the layrs according to the difference of their water-affinities. From the assumption, various structural factors concerning the double layers in the deposits were derived. In order to examine the validity of the theoretical model for analyzing the double layers structures, calcareous deposit films with various Ca/Mg compositions was prepared through either varying hydrodynamic state of seawater around the cathode or diluting seawater under a constant cathodic current density and temperature. The application of the above model to these deposits proved the validity of the model to analyze the double layrs structures.