Small knife rust resistance experiment

[HawkeyX]

Based on kareem's post http://forum.multitool.org/index.php/topic,27022.0.html I thought I would put a few spare blades to the rust resistance test. I didnt want to sacrifice full SAK's as I know that the alloy liners do not fair as well as the stainless and do corrode. As we know 'Stainless steel does not stain, corrode, or rust as easily as ordinary steel, but it is not stain-proof'. Obviously also there are different grades of stainless.

So, I started with two small blades (different ages if we were to go into variables) both wiped over with acetone to remove any wax/oil.

One jar of sea water and one of fresh/tap water. The tongue test suggested it was fairly salty, but not as salty as earlier this year.

In they go, brave blades of science.

now we wait...(forever?)

[Gareth]

This'll be interesting.   As I said in the other thread I'd expect to see some rust around the nail nick first. 

[jzmtl]

Correct me if I'm wrong, but in order to rust, you need oxygen, which is lacking when submerged. Perhaps pour out some of the liquid and lean the blade against side of bottle so some is exposed, at surface of water you have all the ingredient for rust.

[edcgear]

There is Oxygen enough in water to start process... Don't forget water is H2O! And its that atom of oxygen that provides rusting process in water...

"When iron is in contact with water and oxygen, or other strong oxidants and/or acids, it rusts. If salt is present as, for example, in salt water, it tends to rust more quickly, as a result of the electro-chemical reactions. Iron metal is relatively unaffected by pure water or by dry oxygen. As with other metals, like aluminium, a tightly adhering oxide coating, a passivation layer, protects the bulk iron from further oxidation. Thus, the conversion of the passivating iron oxide layer to rust results from the combined action of two agents, usually oxygen and water. Other degrading solutions are sulfur dioxide in water and carbon dioxide in water. Under these corrosive conditions, iron hydroxide species are formed. Unlike iron oxides, the hydroxides do not adhere to the bulk metal. As they form and flake off from the surface, fresh iron is exposed, and the corrosion process continues until all of the iron is either consumed or all of the oxygen, water, carbon dioxide, or sulfur dioxide in the system are removed or consumed."

http://en.wikipedia.org/wiki/Rust

[jzmtl]

Yes, but in my experience rust forms quickest when air is available.

[HawkeyX]

I considered taking it in/out of the liquid (and still could), but normal steel still tends to rust fairly quickly when totally submerged, as said, there is air.
Theres no hard & fast rules here so i'll leave it as is for a while and then look at trying different things if my little blades seem invincible.
I dont expect to see anything for a while either way.

[HawkeyX]

So...third day in, lets check back with the blades.
Looking a little murky in the salt water container

Fresh blade looks as clean as new

Salt blade is suffering already!

So this is with fully submerged blades, I shook the containers once about 36 hours ago to aerate the water a little more.
So far, this tells us to always rinse off when you have been in the ocean (nothing new there)...and that seawater will hurt your SAK
Will post back again later in the week...

[jatrias]

 

[Reinier]

More rust than I expected!

Oh, how does Vegemite taste?

[AimlessWanderer]

More rust than I expected!

Oh, how does Vegemite taste?

A bit like marmite ... but not as good 

Yes, but in my experience rust forms quickest when air is available.

Yup!! Steel hulled boats suffer the worst corrosion at the waterline where the water laps

Interesting results so far 

[Gareth]

More rust than I expected!

Oh, how does Vegemite taste?

A bit like marmite ... but not as good 

Yes, but in my experience rust forms quickest when air is available.

Yup!! Steel hulled boats suffer the worst corrosion at the waterline where the water laps

Interesting results so far 

LOL, beat me to it.

Don't some steel boats use a zinc plate as sacrificial material to stop the hull and prop from corroding?  I'm casting my memory back a long way with this one so I could be wrong.

[AimlessWanderer]

More rust than I expected!

Oh, how does Vegemite taste?

A bit like marmite ... but not as good 

Yes, but in my experience rust forms quickest when air is available.

Yup!! Steel hulled boats suffer the worst corrosion at the waterline where the water laps

Interesting results so far 

LOL, beat me to it.

Don't some steel boats use a zinc plate as sacrificial material to stop the hull and prop from corroding?  I'm casting my memory back a long way with this one so I could be wrong.

Correct, zinc or magnesium dependent upon whether salt water or fresh water ... and you have to get the right kind for it to work. Just to bore you a little more  these protect the boats superstructure too, not just the vessel at/beneath the water. I've also been told they work on wooden boats ... they stop the nails rusting (but I'm not sure how true that is-electrical current doesn't flow well through wood )

Some of the older style Sheffield knives had a cast zinc pommel, and sometimes wondered if these would work as a sacrificial anode, but boats tend to have anodes at both ends of the boat (both poles of the magnetic field) so ... maybe on a draw knife ... 

I'm not too well up on the science aspects of it (there's probably folks wetting themselves at my daftness already  ) but I have sometimes wondered why sacrificial anodes of sorts haven't reared up more in the knife and tool arena

[jzmtl]

I'm not too well up on the science aspects of it (there's probably folks wetting themselves at my daftness already  ) but I have sometimes wondered why sacrificial anodes of sorts haven't reared up more in the knife and tool arena

Without water you don't have a complete electric path for the sacrificial anode to work. There are some people selling similar stuff for cars as well, but I've seen no proof it actually works.

[AimlessWanderer]

I'm not too well up on the science aspects of it (there's probably folks wetting themselves at my daftness already  ) but I have sometimes wondered why sacrificial anodes of sorts haven't reared up more in the knife and tool arena

Without water you don't have a complete electric path for the sacrificial anode to work. There are some people selling similar stuff for cars as well, but I've seen no proof it actually works.

But without water (even just humidity) you wouldn't get corrosion in the first place 
So ... if the knife/tool was capable of conducting electricity ... and the right anode was used ...
(Not trying to correct you - just get my head round it)

[alelser]

Wow. That's a real eye opener! Never expected that kind of rust to show so quickly, especially totally submerged without exposure to air. Wonder though if those spots are where air was trapped as surface bubbles or something.

[HawkeyX]

Yes, when I had a close look before taking the photo I do believe the spots are where air bubbles were. Also worth noting that the plain tap water blade also had air bubbles on it. I will post up more say in the weekend.

On the vegemite question, without wanting this topic to go off topic, yes, a little like marmite, but being vegemite is Australian and marmite is New Zealand (slightly different ingredients to UK marmite), I'd have to say marmite is better (Im sure Aussies will understand my Kiwi logic here)...maybe that is why I am sacrificing these containers 

[nsa-x-file]

Thanks for the info. Very interesting reading. 

[Cyclone82]

More rust than I expected!

Oh, how does Vegemite taste?

Vegemite is good. I have it for breakfast everyday.

[jzmtl]

So.... Which is more corrosive, sea water or vegemite? 

[Reinier]

Excellent question

[Mr. Whippy]

I would guess sea water, since (from what I've heard) vegemite sucks the oxygen out of everything around it.

[HawkeyX]

So about a week in things were looking ugly for sea water blade:


However fresh water blade is happy as larry just sitting in fresh water shining:

I decided to change out the mucky salt water for some 'fresh' salt water and to suspend the blades partially out next. As in the salt water photo, you can see a lot of the rust substance is like a fine growth coming off the blade. Once I wiped this off I was left with the three main rust spots. I gave this a fairly strong rub with a hard material cloth and almost returned the blade to its former glory!

and then suspended the blades half in/out of the water.

Will revisit again in a half weekish...

[Cyclone82]

After you think you have completed the test, can you take the blade in fresh water and try it in the salt water so we can see if it starts to rust in the same amount of time as the first one you had in salt water.

[HawkeyX]

Good idea and will do. Will probably look at the current configuration for say a week and then do that.

[Cyclone82]

I just want to see if another blade will rust as quick in the same way so we have a little bit more to go by than just the one blade in salt water.

[Zag]

On the first picture, one blade seems more scratched than the other. Could this be a factor? 

[HawkeyX]

I agree more than one needs to be tried.
Also with the scratches it could be a factor, however the rush spots were in different areas...?
A the moment I cant even see the scratches!?

Edit: Now I look, the blade with the scratches is the fresh water blade. the salt water one was the better of the two.

[HawkeyX]

So a week on, no surprises, the salt blade has rusted more. What is interesting to point out based on earlier discussions is that it has rusted much more in the totally submerged areas than the point which was at the water/air level:


What is great to see is that after two weeks now, the fresh water blade is as good as if I had just left it out of the water. Noting also it is the more scratched blade.

So for the next week, I have again placed 'fresh' salt water in, kept the rusting blade as it was and dropped the fresh water blade in the bottom.We should see rust forming on it by next week in theory...

[Gareth]

Loving the experiment Hawkeye.

[knyha]

Loving the experiment Hawkeye.

Me too! It spared me one Rally that I wanted to proove in some simmilar way.