Galvanising small objects

Does the Zn-Fe intermetallic produce the same cathodic protection that zinc does?[/QUOTE]

Based on it not rusting, yes.

I've been using it for 15 months, obviously in seawater, its either in the sea or in our anchor locker all the time and there is no sign of rust. On that basis it works. I have not been especially looking after it - we wash with seawater on retrieval, the anchor locker can be warm (today its 27 degrees outside :) ) but the anchor locker drains very well.

The proof is in its longevity, rather than the immediate result. I ran a whole series of abrasion tests, on the seabed, and the claims that the Armorgalv coating is more abrasion resistant than HDG stand up - but to ensure longevity you need a decent thickness - which I put at 100 microns (vs the US Navy/Army at 70-80 microns). My coating is 100/110 microns over a 75 metre length (and I had some connectors coated at the same time) so I achieved what I thought was adequate. Some chain coated previously with much thinner coating thickness, maybe 20 micron, was a major disappointment.

Based on my success someone else is looking at making 8mm x 100m (+15m for a second rode with nylon) of HT, probably G100 (it seems a better option than my G80) it will be stronger, by about 10% than Maggi's G70, 20% cheaper and should last longer. Initial tests suggest it is possible, in the fullness of time, to recoat without any loss of strength.

Jonathan
 
JD,

Just for you:

http://armorgalv.com/uploads/downloads/9.pdf

And to save you searching:

quote

In 1993, after many years of research, Dr. Shtikan - an Israeli scientist and principal of Distek
Ltd, developed the Distek Thermal Diffusion process which forms the basis for the ArmorGalv®
technology. The ArmorGalv® process is based on a proprietary alloy of zinc, which sublimates
at a relatively low temperature, far below the melting point of zinc, and causes the zinc vapor to
react with the steel on the molecular level. This nano-scale reaction, creates layers of
intermetallic zinc/iron alloy similar to that of Sherardizing but richer in iron content. Unlike
Sherardizing, the ArmorGalv® process is completely environment-friendly, simple to apply and
is cost effective. It is also much more user-friendly and controllable and offers superior
performance to that of Sherardizing.

end quote


Jonathan
 
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Neeves said:
"In 1993, after many years of research, Dr. Shtikan - an Israeli scientist and principal of Distek
Ltd, developed the Distek Thermal Diffusion process which forms the basis for the ArmorGalv®
technology. The ArmorGalv® process is based on a proprietary alloy of zinc, which sublimates
at a relatively low temperature, far below the melting point of zinc, and causes the zinc vapor to
react with the steel on the molecular level. This nano-scale reaction, creates layers of
intermetallic zinc/iron alloy similar to that of Sherardizing but richer in iron content. Unlike
Sherardizing, the ArmorGalv® process is completely environment-friendly, simple to apply and
is cost effective. It is also much more user-friendly and controllable and offers superior
performance to that of Sherardizing."
Click to expand...

Thanks. There is so much wrong with this that it's hard to know where to start. Is it the proprietary alloy which is sublimating or is it zinc from it? How do they get zinc vapour to exist at low temperatures and way above triple point pressure? At the level of what molecules, and why do they think this is preferable to the atomic-scale processes of hot dip galvanising or Sherardising? The only molecules in zinc and steel are the iron carbide in the steel, there isn't much of that and it's needed. Intermetallics have, by definition, defined stoichiometry so you can't make them "richer in iron content", though what they may mean is that they change the proportions of zeta, delta and gamma phase intermetallics - the top layer of galvanising is normally zeta phase which is zinc-rich and vulnerable to damage.

If that paragraph was written by scientists they should be ashamed of themselves; if it was written by marketers they will already be beyond shame.

My best guess from all the waffle flying around is that they have replaced the zinc dust + inert filler of Sherardising with a zinc alloy (alloy with what, though?) which supplies lower concentrations of zinc at the interface, allowing deeper diffusion before the zeta phase layer gets too thick.

Of course if it works, who cares about the process, but one should in general take care not to be too entranced by grandiose claims with hand-waving explanations, whether about anchors, chain or anti-corrosion coatings. See also; hi-fi.
 
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OK, now I have done a little more digging and I have found three patents which looks relevant:

plus https://www.google.com/patents/US7241350 (Rosenthul) which gives some useful context

It seems that in Sherardising the inert filler is there to stop the zinc powder melting and coalescing, as the process temperature has to be near the melting point of zinc for effective diffusion. None of the Shtikan patents make any mention of sublimation or vapour-phase zinc. On the contrary, all three make clear that this is a powder thermal diffusion process. The claim for the first patent I list is

A powder mixture comprising a base metal powder suitable for use in thermal diffusion coating process in which an article to be coated is embedded into said powder mixture and is thermally treated therein so as to cause diffusion of atoms of said base metal within said article, characterized in that said powder mixture comprises 0.1-5 mas.% of an additive consisting of at least one oxide of a metal chosen from the group consisting of iron, titanium, chromium, cobalt, nickel, molybdenum, said additive having particle size not more than 5 micron and being preferably less than 1 micron.
Click to expand...

This section of the European patent is maybe worth pondering too:

It should be pointed out that improvement of corrosion resistance and coloration effect does not take place on account of the coating thickness.
Click to expand...
 
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I too (like JD) think that the physics of this situation suggest no vapour phase occurs, and that some marketing speak has introduces a bit of pseudo-science. They're not alone, I've had to correct some marketing gobbledegook in our company to get closer to the real science that happens.
On the question of relative corrosion protection of HDG versus fully alloyed coating: There's no measurable difference i protection of life expectancy. In HDG as a result of steel chemistry (Si, P mainly), it's not uncommon for a steel article to get fully alloy coated, with no "pure" zinc at the surface. It's also quite normal to have one end of a longer article fully alloy coated and the other end part alloy with pure zinc on surface, at the other end (result of immersion time being longer for the lower end as suspended, and that as a result of poor fabricator provision for vent and drainage holes in hollow items), and no discernable difference after decades of exposure. My guess thouhg, is that alloy doesn't last quite as long, but the difference is small.
 
Having a debate about an actual process about which we know nothing makes a good forum topic but does not seem particularly useful, given our complete absence of information.

Most people agree that galvanised coating life is a function of thickness and the thicker the coat the longer it will last. However having too thick an HDG coating and its adherance to the substrate suffers - so there is a limit. We also know that some HDG coatings are 'good' and some are 'not so good' based on forum member reports of performance - different suppliers have a different reputation - suggesting control is not very good - or they are not coating to engender longevity of their chain.

The same will be true of Amorgalv or Sheradizing - if its a thin coating life expectancy in some environments will be poor. Geoff might care to comment for HDG but for Armorgalv you can specify coating thickness and get that thickness, in my experience, to within 10 microns. Whether that degree of accuracy can be maintained over years - its about quality control. There are specifications for HDG coating thickness, but not specifically for anchor chain, and the application of a thickness designed for engineering components (say beams) is totally irrelevant for an item that will spend much of its time dragged over the seabed or sitting in a damp fusty anchor locker.

If you are prepared to pay both Sheradizing and Armorgalv (and there is another process called Greenkote) will coat to whatever thickness specified, its easy to measure - so the processes can be refined to cater for the specific environment within which they will be used. On the assumption you have taken the trouble to check what is possible and how it performs.

However some main advantages for 'thermal diffussion', ignore how it works, are:

you can coat tiny, the smallest I have had coated are 30mm x 2mm pins, items with an accurate coating thickness. Hammer gun nails are a common product.

You can coat intricate shapes and hollows and voids - as long as there is at least one opening, again with an accurately defined coating.

You can coat HT items, the highest I've had coated are 1000 MPa, with a strength loss of 15%, which cannot be achieved with HDG. Armorgalv claim 1000MPa with a strength loss of only 5% - but processing times might be inordinately long (the US military might be prepared to pay the costs but whether its economically feasible for anyone else - I don't know).

The big issue is that for single one off items, as Geoff says, the cost of producing the invoice is more than the cost of the galvanising and, as an example, another, UK, company I work with now have minimum invoice charges of Stg200!

HDG and Thermal Diffusion can compete directly, say coating a G30 chain. But at the extremes they can compliment each other. Steel engineering beams are too big for the ovens I have seen and HDG last decades for many engineering products. For HT items and intricate or small components, say nails, Thermal Diffusion appears to be a better process. The US military are changing to Thermal Diffusion coated anchor and tie down chain - because they say it has a longer life. My tests would agree - but testing is one thing, actual real life might be different. But speculation on TD coated chain life is just, well - speculation.

I'll be reporting back in 5 years.

Jonathan
 
Neeves said:
Having a debate about an actual process about which we know nothing makes a good forum topic but does not seem particularly useful, given our complete absence of information. n
Click to expand...

The same, with all due respect, goes for evangelically promoting processes and materials about which one clearly knows very little. I look forward to hearing how your investment works out in practice.
 
Hardly promoting - simply recording. It had the desired effect - you checked it out (as did others). There are options of which you were unaware. The fact, currently, you don't like or approve of the options does not matter, other people have different ideas to yours. Maybe if you knew more about the process, to the detail you think is necessary - you would approve. If you investigated and found chain might last twice as long and cost less - I would hope your idea might change - in the meantime maybe you can keep an open mind.

2 new convertors came on stream in America last year, anchor chain is one of the bigger product lines, tie down chains are another. HT chains are of emerging interest - a lot of people are putting money in a process you seem to reject. Greenkote seem to be making waves. Valmont one of America's bigger galvanisers have apparently, the information is anecdotal - and I'm suspicious of authenticity, stopped galvanising (HDG) chain. Valmont do still gal chain here in Oz. For a smoke stack industry - change is happening.

Jonathan
 
Neeves said:
Hardly promoting - simply recording. It had the desired effect - you checked it out (as did others). There are options of which you were unaware. The fact, currently, you don't like or approve of the options does not matter ...
Click to expand...

What makes you think that I "don't like or approve of the options"? I've had lots of small bits of my DS sherardised during its restoration. If these new thermal diffusion processes work even better, great. All I am pointing out is that much of what you write about the processes makes little or no sense. Since materials engineering clearly isn't your thing, it would probably be more sensible to stick to the effects and not worry too much about the processes.
 
JD, no-one knows about the process (let alone you) - I repeated what the owners of the license said. I fail to understand why this upsets you. If you have a grouse please take it up with Distekna. If everyone who repeated what manufacturers said enjoyed your personal criticism - no-one would want to post.

My post has allowed you to show your undoubted and deep expertise and to belittle my knowledge, the latter has been gained from the licence makers website. Nothing quite like encouragement.

When you do find out about the process, maybe you can enlighten us all.

But I'm interested - you have had items Sherardized, care to elaborate, why, what - and if is was conducted at Bodycote - was it Sheradized or Armorgalv. I have never heard of anyone using/having 'sheradized items on a yacht - so it is interesting.

Jonathan
 
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