emanuel wrote: ↑
Tue Nov 26, 2019 12:07 pm
I'm glad to be of help Lance and Stefan.
Chumango wrote: ↑
Tue Nov 26, 2019 9:28 am
It is better to have no coating than to have a coating with imperfections, at least in terms of structural failure. A good paint layer will protect carbon steel, but a paint layer with pinhole imperfections can actually lead to premature failure of the substrate (for example a chemical tank with coated steel walls, pinholes in the paint can lead to rapid wall perforation at the pinholes). The imperfections set up a very unfavorable area effect for galvanic corrosion. The inert areas that receive electrons are large (cathode), while the active areas that supply the electrons are small (anode - and corrosion occurs at the anode). The result can be accelerated corrosion of the small anode areas. For a coated knife blade this is limited somewhat by the need for a conductive path for the electrons, which could be provided by a combination of moisture and salt.
If you take the DLC by itself only, yes, you are correct. But thanks to surface tension, oil will infiltrate and bond to do sides of those "pinholes", cracks or any other microscopic imperfections, sealing them (of course, not forever, the oil can be displaced with other materials, react chemically with the material being cut or simply evaporate). Also, the analogy with a hole isn't exactly correct, you need to understand that at a microscopic level that layer of DLC is actually surprisingly thick in regard to its molecular constituents, and no imperfection goes straight down towards the metal, but instead its more like a 3D labyrinth of small cracks and cavities, explaining why oil is so effective at transforming a flawed coating into something that can withstand substantially more corrosive exposure than just an oiled satin blade, without the annoying friction from paint or other rubbery coatings.
Thanks, Emanuel. I have long wondered about this question. Not owning any DLC coated blades I always wondered about this. Vivi’s very positive experience with DLC over S30V combined with other users seeing massive rust growing up through their DLC coatings had caused me to conclude that this is not some simple binary thing like 1095 vs H-1 rust resistance.
The tip about DLC plus oil is excellent and if I ever get a DLC’d knife I will oil it ASAP! A rigid sponge, yeah.
Part of why I don’t own any DLC is because I like to modify my users by polishing or regrinding the blades to be more what I want. A coating would be ruined by this, and only increase the difficulty of the mod.
Edited to add the following:
I suggest treating the rusted blade in Evapo-Rust, which will chelate our all the iron oxide. Rinse really well in distilled water, then rinse again with alcohol or acetone to pull out all the remaining water. Once dry, oil the blade, wiping off the excess surface oil. Should be like new, only better due to the retained oil. If the porosity is extremely fine it might be good to oil with a mixture of mineral oil and mineral spirits. The solvent thins the oil so it can penetrate better, then evaporates, leaving the oil behind.