Metal Ready, necessary? Options

[swl]

I can't resist wading in here and risking the flames but what the heck. Boy scientist mode engaged.

Let's go back to basic. Rust doesn't cause rust. Iron molecules exposed to oxygen molecules cause rust. Period. Any (well most) rust prevention simply aims at keeping the oxygen away from the iron. How well it does that job depends on how effective it is at getting to the iron and sticking to it. The sales pitch for POR and it's competitors is two fold. One it can penetrate surface rust and find it's way to the underlying metal. Two, the coating is very flexible to prevent cracking yet strong enough to resist abrasion.

Put up your hands if you have ever seen aluminum rust. See all the college boys are going nuts. Aluminum rusts much more easily than iron. Difference is that the size of an molecule of aluminum oxide is exactly the same as the normal aluminum molecule. As a result the aluminum oxide forms a barier to the oxygen trying to get at more aluminum. The 'rust' layer is very very thin so it just looks like there is no rust. With iron however the rust molecule is much larger than the iron molecule. This causes the bubbling, flaking and cracking that we all are so familiar with. This winds up exposing more iron to the oxygen and the rust grows and grows.

I don't know much about phosphate chemistry but by observation the metal ready is transforming the iron oxide into something that is much more powdery and can be easily swept away. It may also be forming a layer like the aluminum does to keep oyxgen away from the iron. Andy has seen this by the protection resulting from just a metal ready application. I would suggest that the protective layer is probably very fragile and you would not want to rely on it alone anywhere that gets any sort of abrasion.

My philosophy. If you are going to buy into someone's chemistry buy in all the way. Unless they are a complete bunch of con artists they have invested a lot of work to come up with the process. Marine clean removes any oil/grease/gunk that would stop the POR from getting to or bonding to the metal. Gross rust has to be removed with a wire brush. Metal ready further reduces the standing rust to give the POR a chance to get to the metal. But again read the instructions - they want you to rinse off the debris. Last step is the POR itself. Like any other paint job it is all about the prep work. Yeah, POR is making a killing off us. But, man, you don't want to ever have to do it again!

Boy scientist mode disengaged.

[SirAndy]

QUOTE (swl @ Jan 26 2006, 05:55 PM)

Let's go back to basic. Rust doesn't cause rust. Iron molecules exposed to oxygen molecules cause rust. Period.

well, actually ....

http://antoine.frostburg.edu/chem/senese/1...ron-rusts.shtml

(IMG:http://www.914world.com/bbs2/html/emoticons/cool_shades.gif) Andy

[swl]

ouch andy - my brain dumped all that complex intermediate stuff after the exam. I just like the bottom line fe2o2 everything before that is jfm. yeah - the reaction only progresses in the presence of water and an electrolite to conduct the electrons. Point for the discussion though is that only involvement of existing rust is to prevent the coating from reaching the iron.

[rjames]

Wow, excellent discussion folks. (IMG:http://www.914world.com/bbs2/html/emoticons/beerchug.gif) I personally think someone should
tip the makers of POR-15 off to this thread so they can provide
free samples for us to experiement with....that stuff aint cheap!

Currently I'm leaning towards their full process....marine clean, metal ready, then POR-15 in black (matches the exterior!)

[sgomes]

I followed this high school chemistry class right up until Steve said that the Iron Oxide is converted into something more powdery to be swept away.

My experience with Navel Jelly (which I believe to be the same kind of converter...I could be wrong here) is that it converts it to this black stuff that I couldn't get off the metal to save my life! It didn't seem to "powdery".

This is a key point. Since POR-15 wants you to use MR underneath, wouldn't this be a bad idea?? Yeah I know they want you to wash it off but who here believes they could wash it well enough to remove it all? My bet is that stuff is attached on there with a vengence and the washing idea is to remove the "unreacted" MR off so that the POR-15 can cling to the metal directly.

Should I go back to high school? (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif)

[SirAndy]

QUOTE (sgomes @ Jan 26 2006, 08:14 PM)

My bet is that stuff is attached on there with a vengence and the washing idea is to remove the "unreacted" MR off so that the POR-15 can cling to the metal directly.

(IMG:http://www.914world.com/bbs2/html/emoticons/agree.gif)

[Katmanken]

Shannon, the hard black stuff is magnetite or converted rust.

Rust is an electrical process. It forms charged cells. The attached picture on the left shows a cross section of a rust cell. The bulge at the top is what we see. Below it is a deep tapering pit of rust. When you sandblast, the sand particles penetrate as deep as they can into the pit but can't reach the narrow bottom......

On the right is an ospho or metal ready treated rust cell. The cell has been wire brushed to knock off the bulge, and then treated. The surface of the remaining rust cell is converted to magnetie, a hard stable form of iron oxide. How deep the treatment is, I can't say. But I do know from sandblasting, you can find rust underneath.

The magnetite is a seal to prevent oxygen from reaching the metal below. The rust cell is still there, still wants to rust but is blocked. The POR or other paint acts as a shield to prevent the treated rust from getting the 2 things it needs- water and oxygen.

[Katmanken]

Ooops, forgot the picture....

[sgomes]

I think I can speak for everyone,

This thread rocks! (IMG:http://www.914world.com/bbs2/html/emoticons/smilie_pokal.gif)