Silicon carbide in nitric acid. 1

[enmax]

I realise that this is not a question about metals but perhaps someone out there can point me in the right direction. I've been scouring the web and numerous books for quantitaive data on the chemical resistance of silicon carbide in nitric acid. Occasionally I can find a general comment giving a vague suggestion about silicon carbide being inert or chemically resistant but no actual data. I'm interested in two situations: 1. 5M nitric acid at 50 deg C 2. 12M nitric acid with intermittent exposure. I suspect that sintered carbide would be a better bet than reaction bonded silicon carbide (because of the presence of free silicon). The application is as a bearing in some pumps my company is trying to source.
Any pointers would be appreciated.

 

[IRstuff]

Perhaps, the converse is appropriate to search for, i.e., when nitric is actually used in conjunction with silicon carbide:

http://www.patentstorm.us/patents/6419757/claims.html

http://ieeexplore.ieee.org/Xplore/l...453970.pdf?arnumber=1453970&authDecision=-203

However, HF/nitric can do things to the surface, and is used to remove free carbon from the surface:

http://www.ceramtec.com/co/cz-en/materials/00106,0001,0000,5105.php

TTFN

FAQ731-376

 

[unclesyd]

We run SiC in mechanical seals in 65% HNO3 and the same with organics. I haven't heard of any problems.
Here is on bit of literature for Hexaloy. Normally if a material will handle hot concentrated HNO3 anything less is that much better, not like sulphuric.

http://www.hexoloy.com/data-sheets/fluid-handling-components/pdf/B-1002.pdf

 

[tomwalz]

I'd talk to the Sic supplier.

See exactly what they mean by SiC. Pure SiC and SiC with a binder (no matter how minimal) may be two different things. We see this with "binderless" WC.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[EdStainless]

Yes, you would need sintered SiC and not reaction bonded. The latter has a binder phase in it.
You can also contact CoorTek

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

 

[enmax]

Thanks for all your advice. The Hexoloy site was a good lead and confirmed that sintered SiC was superior to reaction bonded SiC. The test time for the Hexoloy SiC was only 300hours so I was a little cautious about the data ( I shouldn't really grumble - most chemical resistance tables/corrosion tables don't report the time of exposure). Unclesyd's practical experience would also suggest that SiC would be OK. My supplier could not actually support the use of SiC in nitric acid but, after taking into account other factors, offered to supply PTFE components instead without impairment to the function of the bearings so I went for that.
Once again - thanks for your interest.