What Does Porous Surface Mean?
Porous surfaces refer to surfaces that contain pores. A porous surface allows the passing through of water, liquid or vapor. Objects containing porous surfaces have empty spaces or pores that allow external matter—like water, air and particles—to penetrate into the object. Paper, untreated wood, cardboard, sponge and fabric are some examples of porous surfaces.
The estimation of surface porosity is evident in many fields, such as:
- Engineering and soil mechanics
A porous surface helps moisture to penetrate matter, which can cause different types of corrosion, e.g. corrosion under insulation. A coating with pores and pinhole defects creates ways for corrosive fluids or aggressive chemicals to attack the substrate material and leads to structure failure.
A porous surface may also be known as a porous substrate.
Corrosionpedia Explains Porous Surface
Porous surfaces come in two types: macroporous and microporous surfaces. The pore sizes of microporous surfaces are comparable to the size of molecules. Water management, gas separation, oil recovery and the removal of organic and metal contaminants from process streams all use microporous surfaces. Macroporous surfaces have large pores that allow the smooth movement of water and air.
In plating, the base metal is exposed through pores. The degree of porosity depends on plating thickness, application method, base metal roughness and base metal cleanliness. Porosity decreases with the increase of plating thickness. Rough metal surfaces, and dirt or oxide on the surface of the base metal lead to the appearance of pores. Pore corrosion results when the base metal is exposed to a corrosive environment through these pores. This may cause base metal corrosion or the corrosion product may creep across the surface. This corrosion can be minimized by using thicker coatings. PM stainless steels have weak corrosion resistance due to porosity, and this leads to crevice corrosion. This corrosion resistance is improved when a greater percentage of the porosity is sealed.
Surface porosity can be reduced by using a chemical vapor deposition (CVD) process. In this process, a coating is crystallized, atom by atom from the gas phase. Since atoms have high surface mobility, they are attracted to holes or pores. So, the surface defects are filled as the coating grows. The CVD process manufactures a highly dense and impervious coating layer that protects the substrate from the attack of corrosion and aggressive chemicals.