Relationship between Surface Roughness and Corrosion

Surface roughness of the metal surface is a major influence on general corrosion. The roughness of the surface also influences boundary layer on the metal’s surface which affects the various chemical performance of that surface. The results of some experiments reveal that there is rise in the rate of corrosion with the growing roughness on the surface. To evaluate corrosion rate the finishing of the surface needs to be considered. There are various factors which can have an effect on the electrochemical reactions. These factors are temperature, impurities, oxidizing agents, velocity, and the variety of electrolyte.

Illustrations of Surface Roughness and Corrosion
Illustration No.1
In one analysis varied surface roughness are formed on the surface of a metal by Silicone Carbide grinding papers. After which comparisons were drawn for the behavior of corrosion. Various tests like the ‘Profilometry test’, ‘Laser Ablation Method’ and ‘Electrochemical Impedance Spectroscopy’ (EIS) are performed on each sample. And then all the outcomes are balanced with each other. Calculations are made on the values of rate of corrosion and comparisons are done according to the cause of roughness. Images taken at various point of time during such analysis are also considered for comparisons. A variety of mechanisms were made out for samples formed through various processes. This helped in understanding the causes of corrosion and find out the best possible ways to eradicate it. A metal can resist corrosion with due effectiveness if the rate of roughness is lesser.   

Illustration No.2
In another analysis, the consequence of surface roughness was studied. The property of corrosion upon the thermally oxidized commercially pure Titanium was the matter of study. It was detected that the values of surface roughness got higher following the thermal oxidation. After the oxidation process some single rutile phase got casted on the surface. Surface roughness had no result on the preferred development course of the rutile phase, which was taken into notice. For the crude or raw commercially pure Titanium (CP-Ti) the coefficients achieved were unbalanced and had higher friction. But the same didn’t happen in case of the oxidized samplings. Same outcomes were also detected for the corrosion activities. The potentiality of corrosion swings to larger value when the value of surface roughness lessens.    

The Roughness of a Surface enhances Corrosion
To determine the properties of corrosion, of the various substances, the essential factors are composition of substance, manufacturing geometry and the roughness of substance. An important part, for the metals to get corroded, is done by the roughness of the surface. If the surface roughness of certain metals and alloys are increased the common rate of corrosion and the exposure to pitting also increases. Copper, Stainless steel is such metals and Titanium-based alloys, Aluminum alloys and Magnesium alloys are the examples of alloy. Normally, the common and restricted corrosion activity of alloys relies on the passivation characters. To draw a connection of roughness of surface with the common tendency of corrosion and pitting it is essential to recognize the passivation character of alloys. Passivation is a process by which any metal or other substance is made nonreactive through alteration of the surface layer.

To look into different features of the roughness in the surface of metal, with regard to the corrosion rate, numerous studies have so far been done. It finally shows that by and large the rate of corrosion on rough surface is more in comparison to the smoother surface. The rate of corrosion in rough surfaces is enhanced by the increase of surface area which engages in circulation of electro-chemical reaction. The corrosion environment of a metal’s roughened surface has bigger section of surface contact. Consequently, if surface roughness rises, it strengthens the process of corrosion by intensifying the surface contact for corrosion, of the metal or alloy.

Corrosion Resistance of Different Surface Roughness Finishes
Any metals resistance towards corrosion increases if the surface roughness decreases and it happens so when metals have the capacity to structure a passive coating. But, many metals don’t possess the capacity to form a passive coating and in such situation a reverse movement is detected. Sometimes when the surface roughness is higher the pitting possibility is lower. A report on corrosion says if the surface is smoother, like that of stainless steel, it is less competent of spreading metastable pits compared to the roughened surface. It is so for the reason that the location of pitting on surface that are smoother, are usually very much open.

Another report puts forward that the confined absorption of a solution was influenced by the roughness of the metal’s surface. Thus, it changed the flow of dynamic ions in the process of corrosion. The report further mentions that the resistance of corrosion is strongly correlated on how the gaps and cracks on the surface are spread. The important affect of the cracks for resisting corrosion is linked to the deepness of the cracks and gaps. And as such it affects the flow of ions (active) when corrosion occurs.  

How to Estimate Surface Roughness?
There are several ways to estimate how surface roughness can relate to the impact of corrosion in metals. Two important ways are EIS or Electrochemical Impedance Spectroscopy and Potantiodynamic Polarization. One of the most proper manners for conducting a complete examination of various mechanisms of electrochemical reactions and other kinetics is the EIS method. The EIS diagrams make available facts and figures on the basic steps that occur during an electrochemical reaction as well as on the kinetics. It also helps to study thoroughly the function of in-between substance soaked in upon the surface of metal. This method also allows discovering the various methods of reaction and the characteristics of passive films.

The Summary
There are many interactive reasons that administer the behavior of corrosion. The data collected from experiments and from field might always differ. And it differs because of the surface conditions. The rough surface of metal influences the electro-chemical or the mechano-chemical activity. Various circumstances uphold diverse interaction during micro-electrical activity which impacts the rate of corrosion. 

Therefore, the consequence of rough surface is a significant aspect which is all the time taken into consideration to identify the rate of corrosion.