在自然环境(海水、淡水、土壤)中采用保护器或直流电源保护金属结构物时,在金属表面上常常会形成一层主要由氢氧化镁和碳酸钙等(有时有硅酸盐)组成的白色覆盖膜。这层覆盖膜具有相当好的防蚀作用。国外许多作者对于它的形成动力学和保护作用,稳固性,化学组成和结构,以及如何评价它的保护作用等方面进行了研究。据报导,由于膜的存在可以大大地減小保护电流,仅需原来的十分之一;或者 In the natural environment (seawater, fresh water, soil) protector or DC power to protect the metal structure, the metal surface is often formed by a layer mainly composed of magnesium hydroxide and calcium carbonate, etc. (sometimes silicate) White cover film. This layer of cover film has a very good anti-corrosion effect. Many foreign authors have conducted research on its dynamics of formation and protection, its stability, its chemical composition and structure, and its evaluation of its protection. It has been reported that the protective current can be greatly reduced due to the presence of the membrane, only one tenth of the original; or