BG-42 Rust-O-Rama!

fulloflead

fulloflead

Joined
May 3, 2002
Messages
6,192
The other night I ate my dinner dinner with a fork and my TiNi-coated BG-42 Sog Autoclip because TV was good and I was too lazy to get up and go get a knife from the kitchen. Then I left it there to let the caked-on food dry into a sticky goo as I reclined in a chinese-food and reality-TV induced semi-coma.

Later when I went to stick my dishes in the dishwasher I looked at the Autoclip there stuck to the plate with super-glue-like Mu Shu Chicken sauce and wondered. "Hmmm.... I THINK BG-42 is only borderline stainless but it DOES have that Titanium Nitrade coating on it..." Since I've become a bit of a knife snob lately (buying customs and Sebenzas and all that), and my level of curiosity being what it is, I didn't hesitate much longer. (I've been known to do worse to satisfy curiosity. ;) )

After a 45-minute bath with a nugget of dishwasher detergent and a crowd of other utilitarian stainless riff-raff my Autoclip was allowed to slowly air-dry in the dishwasher over the next 24 hours or so.

Guess what! It rusted! Oh, boy, did it rusted! ;) Right through the TiNi like it wasn't even there. It's the kind of rust that's like oozing, growing leprosy that stains the dishrack and gets on other things.

Curiosity cured.

If you ever get the hankering to test the corrosion-resistance of a particular steel or blade coating, I'd say a night dancing in the 'ole dishwater disco would do the trick. :D
 
I am not surprised, Cliff Stamp took one of those SOG knives to the 'wood shed' a while back, and since then, I will never own a SOG.
 
Before you lose track of the specifics, let me ask a few questions: Did you use the temperature boost wash cycle? Did you use the heated dry cycle? What brand of dishwasher detergent did you use? Was your knife in contact with any other metal items?

Some things to know. Metals like stainless steel, titanium and aluminum are protected from corrosion by a thin nonelectrically conductive oxide film. If you remove the film they can corrode. High temperature washing with cheap dishwasher detergent is likely to remove the oxide film and set up the knife for corrosion. Corrosion will also be accelerated if you have a hot, wet, environment with dissimilar metals in contact with each other. This causes a galvanic reaction where the metals act as different poles of a battery. For example if you have aluminum in contact with stainless in salt water you will tend to get corrosion. The TiNi coating itself might incourage corrosion of stainless steel under the right wet conditions (particularly if the solution is electrically conductive). If there are aluminum items in the same dishwasher you might have aluminum ions in the wash solution to attack the stainless. Your test case may have been more challenging than you expected. The blade might have done better without the TiNi coating.
 
Jeff Clark said:
Before you lose track of the specifics, let me ask a few questions: Did you use the temperature boost wash cycle? Did you use the heated dry cycle? What brand of dishwasher detergent did you use? Was your knife in contact with any other metal items?
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Temp Boost?: No. Hot, but no boost.

Heated dry?: No. Which probably added to the rust-inducing environment by allowing it to sit in a hot, humid box for a while and then drying VERY slowly.

Detergent?: Um... Cascade maybe? It's the little rectangle nugget with a little round ball of Rinse Agent embeded in it. (Definately not the cheap stuff.)

Other metal?: Yes, lots. Other silverware and cooking utensils - all stainless steel. There MAY have been an aluminum baking sheet or something in there too not in direct contact.

Jeff Clark said:
Some things to know. Metals like stainless steel, titanium and aluminum are protected from corrosion by a thin nonelectrically conductive oxide film. If you remove the film they can corrode. High temperature washing with cheap dishwasher detergent is likely to remove the oxide film and set up the knife for corrosion.
Click to expand...

I'll buy that. I have stainless kitchenware that is actually starting to get dots of rust after YEARS of use and washings. From my experience, detergents with citrus additives can be ESPECIALLY harmful to kitchen cutlery. (It's a REAL bad idea - and bad knife Karma - to put nice kitchen cutlery in the dishwasher ANYWAY.


Jeff Clark said:
Corrosion will also be accelerated if you have a hot, wet, environment with dissimilar metals in contact with each other. This causes a galvanic reaction where the metals act as different poles of a battery. For example if you have aluminum in contact with stainless in salt water you will tend to get corrosion. The TiNi coating itself might incourage corrosion of stainless steel under the right wet conditions (particularly if the solution is electrically conductive). If there are aluminum items in the same dishwasher you might have aluminum ions in the wash solution to attack the stainless.
Click to expand...

Are you making this up? :confused: ;) :D

Jeff Clark said:
Your test case may have been more challenging than you expected. The blade might have done better without the TiNi coating.
Click to expand...

Perhaps. I can try it again. Want me to take the TiNi off and send it back to the detergent disco?
 
Jeff Clark made some good points about the dissimilar metals in a salt water environment. Check the ingredients of your Cascade - the principle active ingredient is probably sodium silicate, which in addition to being a salt, is HIGHLY corrosive.

This is an excerpt from the Material Safety Data Sheet of sodium silicate:

Toxicology

Harmful by ingestion. Corrosive - may cause burns through skin or eye contact. Very destructive of mucous membranes.

It won't harm most silverware due to its high chromium, low carbon content, but vise-versa, it'll rust the hell out of BG-42 et al.
 
I agree on everything except the galvanic element between Ti and steel. The coating is TiN, which is not elemental Ti and should act completely different (You would have to look up the position of the redox pair of TiN with respect to a standard hydrogen electrode). Besides, since the coating is in direct contact with the blade, so the galvanic element should persist regardless whether the blade is wet or not.

Nice test though, I wish I would have thought of that when I had the Spyderco Pacific for a test. I wonder how well H-1 would have faired.
 
Congrats you made a home based salt chamber. The heat, humidity. and detergent combined certanly was a prime atmosphere for rust to form. I used to work for a sainless steel sink manufacturer in their product development and testing lab. You know what is a great product to induce rust on even a stainless steel sink? Ivory dish soap! Yep believe it or not it contains something that would eat the heck out of the sinks if left in the right environment.

Sorry to hear about the knife hopefully treatment with some oil etc will put the rust in check.
 
Jeff Clark said:
PS. Looking at this chart, elemental titanium should corrode stainless steel.
Click to expand...

That's a claim Mission Knives made for years. A few years back there was a fad of putting titanium blades on folders, and the folders usually had stainless steel hardware (screws, liners & liner lock, etc.). Many of these knives were sold for dive use, but Mission claimed that the battery effect between the sea water, titanium, stainless fittings would corrode the fittings at an advanced rate.

Mission's folder, of course, was all titanium, including screws, etc.
 
The TiN could have reacted with the salt in the detergent and creating another salt? (excuse my elementary chem)
 
Warbird_Scimitar said:
Jeff Clark made some good points about the dissimilar metals in a salt water environment. Check the ingredients of your Cascade - the principle active ingredient is probably sodium silicate, which in addition to being a salt, is HIGHLY corrosive.

This is an excerpt from the Material Safety Data Sheet of sodium silicate:

Toxicology

Harmful by ingestion. Corrosive - may cause burns through skin or eye contact. Very destructive of mucous membranes.

It won't harm most silverware due to its high chromium, low carbon content, but vise-versa, it'll rust the hell out of BG-42 et al.
Click to expand...

I think we have the cascading answer :grumpy: Keep that stuff away from your blades!!
 
from the web

Titanium nitride is used as a hard material for abrasive resistant surfaces as well as for the lining of crucibles and for the coating of graphites. It is stable against liquid metals such as aluminium, copper and iron.

if it's stable against liquid metals it's very unlikely the coating had anything to do with the rust
 
It's likely that the Titanium Nitride is somewhat porous. It might protect against rust in a typical environment, but perhaps, as the other forumites have pointed out, the combination of heat, humidity and presence of corrosive salts might have led to the rust.

Slightly off-topic:
Interesting points regarding galvanic corrosion. I do question, however, how much of the titanium used in folder fittings will remain in elemental form. I believe that the somewhat reactive metal titanium gains its "inert" properties by forming a layer of titanium dioxide on its surface, sort of like aluminum.

That makes me wonder how durable this oxide layer is, especially when it occurs at points of contact. I'm thinking stuff like aluminum backspacers with stainless screws, or titanium liners with phosphor bronze washers. I think that I've seen the latter case, where the washers seem to have some "nastiness" on them that can be polished away. Has anybody seen galvanic corrosion on aluminum backspacers?
 
HoB. It was not an accident that I included the qualifier "elemental" in my explanation. I know that the redox pair TiN won't be the same as pure Ti. The thing that was suggestive to me was just how far down the galvanic table titanium is located. As a light metal I intuitively expected it to occur higher in the table like magnesium or aluminum. If there is any disassociation of the TiN the Ti ions would probably like to replace Fe in the stainless. In contrast Mg or Al would be attacked by Fe ions.

The close association of the coating and the steel would not likely provide protection. There is a galvanic component of rusting even on a simple bar of steel. Regional differences in the alloy distribution and crystal lattices produce galvanic effects. Put the steel in a conductive/ionic salt water solution (or better yet dilute bleach) and just watch the galvanic corrosion. Regional differences between the TiN coating and the underlying steel will tend to do the same. Mostly this would happen at the exposed edge, but if the coating is scratched or pitted the effect will occur in the middle of the blade.

DEA, There are a lot of differences between reactions with liquid metals and ionic solutions. You still tend to get electrons crossing between the materials, but you don't have a flow of ions to complete the return circuit. You do make an interesting point. I can think of examples of non aqueous redox reactions that are pretty spectacular. For example when you apply sufficient heat to a mixture of powdered aluminum and powdered rust (ferric oxide) the aluminum replaces the iron in the oxide (it forms aluminum oxide) and the iron is reduced to elemental iron. The fun part is that this releases tremendous heat and the iron comes out molten. This is the Goldschmidt, thermite, reaction. It is noteworthy that you don't get a reaction like that when you put molten aluminum in contact with TiN. I suspect that you might need an even higher temperature to get the TiN to break down.
 
actually my point was that if it can take molten metals without being adversely affected, it should be inert enough not to induce rust in a blade
sorta like the way teflon works

you're in the chemical line, jeff? sure sounds that way :)
 
Jeff Clark said:
Making things up is no challenge. The real test is if you can get your concept broadly published on the net and in textbooks printed before you are born. I have that power.
Click to expand...

LOL! :D


Who knew this would turn into such a fascinating thread? Some day this thread will be a link that people will paste into FUTURE threads on the subject where people go, "Read this..." - it'll become a reference thread like has happened with some previous sharpening, steel discussions, etc. on this forum.

I once did a test where I took a bead-blasted ATS34 blade, divided it into sections and coated each with a different rust-preventative product and then submerged it in a glass of salt water for a long period of time and recorded the results. That generated a lot of interest. Maybe we're onto something fun like that. I've got some stainless steel wool and "RustRidder" at home. I should go get some Ivory dish soap and various dishwasher detergents. Somebody send me some different knife steels and a few other metals. I'll turn my dishwasher into a chemestry lab (and see if I can't lose my rental deposit :D ).

Jeez. My girlfriend is going to hate me for this. (Or maybe she'll love me. The dishes will get done. ;) )
 
DEA, My interest in chemicals goes back to trying to make fireworks, firearms, and explosives as a kid. Did you know that you can melt a steel rural mailbox with aluminum filings and rust? Hypothetically you can make a lot of rust by taking ultra-fine steel wool, boiling it in a detergent solution to remove oil and wax, then leaving it soaking in a paper cup filled with water and a couple drops of bleach.

I got my degree in physics and spent some time working on producing submillimeter wavelength telescopes. The frame structure needed to be extremely rigid so we devised a sort of hexagonal space lattice structure. The joints were pinned together using stainless steel bushing which passed through holes in carbon steel tubing and aluminum junction flanges. One of my tasks was to put together a test structure, soak it in a corrosion-enhancing environment, and measure changes in the stress-strain curve of the assembly. I did a lot of chemistry on the project since I developed surface etching procedures to improve epoxy and paint adhesion and a process to tune the dish surface by chemical milling.

In more recent years I spent time engineering electronics for naval systems where you need to worry about corrosion, galvanic and thermocouple effects. I've also spent some time teaching an after school hands-on science class. Chemistry can be impressive stuff. You can do a lot of things with root killer (copper sulfate) that approach the effects of sulfuric acid. If I couldn't blow things up in class I could at least melt them or dissolve them.
 
That thermite is great stuff, but not for the uninitiated. It releases a LOT of heat (3000 degrees C when using iron oxide as the oxidizer). It has been used for welding large sheets of steel together, just put the powder in the joint and ignite. The aluminum oxide goes off as a gas, leaving white molten iron behind. Of course, when I made it years ago I was not satisfied to use plain old iron oxide, so I used a real oxidizer, with good results.

Titanium is a very highly reactive metal, but it readily forms a tenacious oxide layer. That's why titanium is so corrosion resistant in many chemical applications. The caveat is that oxygen must be present. In a reducing environment, the oxide layer is readily dissolved, and corrosion rates can be very high. This is for Ti metal, I don't know how TiN acts.

If the TiN coating is porous, it could have led to a very bad area effect. If the TiN is more noble than the BG-42, and it has a few pores, then the cathode area (overall coating) would be a lot more than the anode area (area of pores), leading to high localized corrosion at the TiN imperfections. The galvanic effect highly accelerated by the area effect.
 
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