Detergent cause Surface Pitting Effect?
The detergent may cause surface pitting and this is not an extraordinary effect. Perhaps it is a real fact that happening in many metal surface cleaning. By the way, the pitting is a corrosion effect that appears in a microstructure manner.
An agressive detergent will causing pitting effect on a metal surface.
From field application, we are always very cautious on detergent selection because we know that improper detergent selection may cause adverse effects to the clean substances. In this article, we are going to discuss the corrosion pitting caused by improper detergent selection
The Surface Pitting Effect
Many surfactants or detergents are selected base on their cleaning ability. Unfortunately, some of the negative impacts have been overlooked. The most common negative impact is the detergent is causing a surface pitting effect. This is because the pit appears in micro size and sporadic distribution on the substrate surface.
Pitting is a localized corrosion spot that causes by the working metal substance and the cleaning detergent. The surface pit has been neglected because the pit on the metal surface is so small and unable to detect under normal eye inspection. Unfortunately, the pit may cause catastrophic effects as it may lead to crevice corrosion.
Similar as pitting, the etching effect also a chemistry process that involve chemical to corrode the metal surface. Normally the traditional way of etching involves copper or zinc metal together with an acid solution. For instance, the PCB engineer is using chemicals to etch a printed circuit board to get the circuit he wants. This is the type of controllable etching process. In a contradictory manner, the pitting effect is more on an uncontrollable and unwanted corrosion process. The pit appears because of the detergent react on the metal surface.
How to Inspect for Pitting?
Pitting is a detrimental surface change within a small area. The light may reflect and scatter in different directions and show as a white reflection spot.
Under a bright light setup and proper orientation, we could recognize a white spot (scatter light) with a naked-eyes inspection. In most cases, this white spot could be the reflection of the pitting. However, particle on the substrate surface may appear similar white spot and this cause false examination. The user could verify the white sponge under the microscope.
Pitting normally come in a very smaller size, the pit surface need to be inspected under at least 100x – 200X magnification in order to recognize the existence. For a demanding user, they may use AFM (Atomic Force Microscopy) in order to plot the 3D image for the corrosion pit.
Under the microscope, the pit shows as a dark spot with a clear-cut edge. In most cases, the pitting forms a round shape. With the help of a modern surface profiler, we could easily identify the size of the pitting.
Select Appropriate Detergent
In detergent formulation, most of the detergent either formulate at an acidic or alkaline base solution. This is because most of the surfactants perform better cleanability at this range of pH. Unfortunately, at both extreme types of pH detergent solution may cause a pitting effect to the cleaned substrate surface.
From our field experience, the pit occurrence is due to inappropriate detergent selection. The field engineer over-emphasized on surface cleaning effect but neglected the pitting occurence. This is because the field engineer selects the detergent solution from the product catalog but without looking at the entire cleaning process.
In general, the field engineer has to obtain good material science knowledge so that they know the effect between the detergent and the substrate alloy. Moreover, a knowledgeable detergent supplier should able to advise the appropriate detergent to use. The detergent supplier could even re-formulate the cleaning detergent to optimize the cleaning process to obtain the best solution.
In case you are experiencing a surface pit in your process, good chances the chemical or the detergent is causing the pitting effect. Feel free to discuss your situation with DST, and we are always here to work with you to overcome this situation.