Corrosin resistant material in high chloride, high graphite enviroment

[copshaw]

Hi,

I'm trying to develop a material that will be stable in a aquous mixture of 10% graphite and 40% wt. chloride salt. It should have a low dissolved oxygen content due to being sealed. As you can imagine, quite corrosive! - plastics not an option.

Where's the best place to start?

Nickle showed signs of nickle chloride after just a day so are nickle alloys a lost cause?

Cheers

 

[cloa]

What sort of temperatures and pressures/stresses?
Is the chloride salt just sodium chloride or some combination of non-oxidising cationic salts i.e.
If temperatures/stresses aren't high, why do you think plastics are out?
Graphite is nasty as its extreme electropotential is almost certain to generate galvanic corrosion unless you use a noble metal.

 

[copshaw]

quick reply!

plastics are out as they are not compatable with the rest of the system, otherwise would be ideal!

temp <100 degrees, atmospheric pressure and no stress, although the system will be agitated.

yes just NaCl.

tantalum/silicon carbide coating overkill? bit costly...

thanks

 

[cloa]

You might consider Silver- its a lot closer in potential- with the labour costs it would be close to your other option. Any reason environment modification is out- corrosion inhibitors or oxygen scavengers- seal environment means you don't need much.

 

[cloa]

How big is this structure? Any reason not to use a ceramic?

 

[copshaw]

Would need too do a lot of reading up on corrosion inhibitors as I've never used them before, do they not just slow corrosion down slightly anyway?

I think salt water on its own would corrodes silver.

about 10 litre inner volume, streached cubiod shaped.

 

[TVP]

copshaw,

I concur with cloa, some type of ceramic should be considered, due to low stresses/pressure. Depending on the desired durability/life of the system, you may want to consider a Ni-Cr-Mo alloy like C-276 or titanium (ASTM Grade 7, CP + 0.15Pd)?

 

[EdStainless]

Many ceramics actually have a glassy boundary phase that will not like hot salt water.

Have you looked at a Cr alloy such as 33?
At Ti with Ru or Pd (one of the very low %) would be a good option as well.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[moltenmetal]

Glasses shouldn't mind hot salt water unless I'm missing something- EdStainless should elaborate as I sense I'm learning something here! Certainly glassy ceramics and glasses find very successful service in chloride-containing, VERY hot, acidic services. Hot alkaline water, salty or not, would be a problem due to the dissolution of silica. In neutral closed media, I'd imagine you'd get to equilibrium with your silicate ions pretty quickly and corrosion would stop.

We don't know your geometry or anything else about your process, but if it really is "no stress, atmospheric pressure" and nothing else is important, but plastics are out, glass sounds good- unless EdStainless proves me wrong. Or make it out of graphite!

The graphite and the resulting galvanic cell is the problem for the metals. But your conditions aren't all that severe really. Hastelloy C, titanium (as others have noted, added Pd gives some crevice corrosion resistance) would probably do.

Tantalum would too, but would be at risk of embrittlement. Beware- not all tantalum coatings are usefully protective. Have a look at

http://www.tantaline.com

- but the sizes they can do are limited and the price can be steep.

 

[EdStainless]

The thought of using graphite is a good one.

I have seen alumina, zirconia, and reaction bonded SiC come apart in hot water due to attack of grain boundary phases.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[davefitz]

what exactly are you building with this unknown material?

A new,low cost material that has very low permiability and good chloride resistance is geopolymer concrete, with many varieties to choose from. Ductility is improved by addition of fibres.

 

[cloa]

I was thinking it was medical- that's why he excluded polymers as poor hygiene.

 

[unclesyd]

Depending on what your configuration and form needed you may want to look at InnerArmor from Sub-One Technology.

http://www.sub-one.com/breakthrough.html