作为渗透检测中的润湿现象有三种方式：即粘湿、浸湿和铺展。若渗透液在固体受检试件表面上的接触角θ≤180°，则可发生粘湿；若接触角θ≤90°，则可发生浸湿；若接触角θ≈0°，则可发生铺展。凡能铺展者，必能浸湿，更能沾湿。渗透检测要求铺展。接触角θ的大小是由在气、液、固三种界面张力的大小所决定的。从接触角θ数值大小可看出液体对固体润湿的程度。这些讨论有助于对渗透检测中实际问题的认识。

There are three methods as wetting phenomena in penetrant testing: adhesion wetting, immersion wetting, spreading. The adhesion wetting will occur on the condition that the contact angle θ on the surface of the specimen is less than or equal to 180°. If θ is less than or equal to 90°, immersion wetting will happen. Spreading occurs when θ≈0°. The requirement of spreading is the highest; immersion wetting is in the middle; the adhesion wetting comes to the last. Penetrant testing needs spreading. The contact angle θ is determined by the interfacial tension of gas, liquid and solid. The degree of wetting can be known by the value of θ. These discussions will help to understand the practical problem of the Penetrant testing.