Moisture-vapor Permeability of Sealers & the "Sealed-in Corrosion" Risk
封护剂的透湿性机理与"闷锈"风险
标签：透湿性, 闷锈, 水汽透过率, 封护机理, 缓蚀
封护膜并非绝对隔水：有机涂层均允许水汽以分子态透入（以透湿率 WVPR 计），氟碳约 20–40 g/m²·d、微晶蜡小于 10、丙烯酸 40–80。透入水汽在膜下积聚，若基面残留氯离子或可溶盐，便形成"闷锈"——外观完好但膜下点蚀鼓包，掀开即溃。机理决定工艺三原则：①封护前必须除盐清洗（终洗水电导率低于 50 μS/cm）；②先涂 BTA 类缓蚀剂形成化学钝化底层，再靠封护膜物理阻隔，构成双防线；③膜厚并非越厚越好，超 80 μm 厚膜附着力应力大、易整片剥落，反而让水汽沿剥离界面侧向扩展。
Seal films never fully block water: all organic coatings transmit vapor as molecules (WVPR) — fluorocarbons ~20–40 g/m²·d, microcrystalline wax under 10, acrylics 40–80. Trapped vapor under the film, meeting residual chlorides or soluble salts, drives "sealed-in corrosion": intact-looking surfaces with blistering pitting beneath. Three process rules follow. First, desalinate before sealing (final rinse conductivity under 50 μS/cm). Second, lay a chemical passive layer first — BTA-type inhibitor — then the physical barrier film, as a two-line defense. Third, thicker is not safer: films past 80 μm build adhesion stress and peel in sheets, letting vapor spread laterally along the debond.