Posted by Gordon England on November 05, 2003 at 02:45:05:
In Reply to: Re: Material Suitability posted by John on November 01, 2003 at 00:32:56:
: : : Hi Gordan,
: : : I've trialed a WcNi coating operating in 10% Sodium Hypochlorate 40 C. The ground finish has become very rough with a black powder residue when you wipe a cloth over it. There has been no loss in Ø. I'm a bit baffeled as an earler trial has gone extremly well. Any ideas?? One thought was that the Nickle was breaking down but i cant find any info on nickel suitability with AvCl2. Any info or sites to visit would be greatfully appreciated.
: : : P.s. congratulations on a good forum
: : Hi John
: : Sodium Hypochlorate or more correctly named sodium hypochlorite (chemist out there please correct me if I'm wrong!)is the main constituent of bleach.
: : The nickel will probably be attacked, although I think the WC will be resistant. Unfortunately, most metals are attacked. Well sealed ceramic, titanium or Hastelloy C based coatings should give better corrosion protection. Have you tried WC/10Co/4Cr? though I suspect it will be no better than WC/Ni.
: : Info from a MSDS:
: : Corrosivity to Metals:
: : Sodium hypochlorite solutions (20%) are corrosive to brass (aluminium, naval and silicon) bronze, carbon steel, cast iron, Hastelloy, Inconel, nickel, stainless steels (types 304/347, 316 and 400 series) and silicon copper. Concentrated sodium hypochlorite is corrosive to most metals, including aluminium, copper, brass, bronze, carbon steel, Hastelloy, Inconel, lead, Monel, nickel and stainless steel type 400 series. Sodium hypochlorite solutions are not corrosive to tantalum, titanium and zirconium. Dilute solutions are not corrosive to Hastelloy C/C-276 (10%), Incolloy (5%) and high silicon iron.
: : This link may be worth viewing:
: : http://126.96.36.199/search?q=cache:VxSi62GSA6wJ:www.odysseymanufacturing.com/bleach_information.doc+metals+resistant+to+sodium+hypochlorite&hl=en&ie=UTF-8
: : Hope this helps
: : Regards gordon
: Tht info was very ineresting. If I spray a bond coat of titanium with a top coat of chrome oxide for abrasion resistance can you forsee any problems. I've heard reports from the states that this combination of coating is difficult to spray. Any thoughts?
Titanium + chromium oxide sounds good, but can't comment from practical experience of this combination. I know titanium can be an awkward material to spray due to it's reactivity and absorption of oxygen, nitrogen and hydrogen. Plasma spraying (APS) normally requires the use of an argon shroud to reduce oxidation and embrittlement. HVOF may be a better alternative?
Titanium sprayed without shrouding does appear to bond extremely well to most substrates, although I'm not sure about the actual coating strength or the bond to chromium oxide.
I think this would a be good R&D or "suck it and see" project. Failing that I would try HVOF Hastalloy C (or possibly diamalloy 4006 or Inconel 625)as a base coat. I certainly would not go as far as guaranteeing these coatings to your customer though!
John, I would be very interested in any feed back you get from this project.
Its late and after a few beers I hope this makes sense.
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