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4hv.org :: Forums :: General Science and Electronics
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Spark Discharge Anodizing, PEO, MAO, Keronite. Resources and Questions inside.

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Storken
Wed Apr 23 2014, 04:19PM Print
Storken Registered Member #1960 Joined: Thu Feb 05 2009, 11:57PM
Location:
Posts: 48
Plasma Electrolytic Oxide (PEO), Microarc (MAO), Keronite and Spark Discharge Anodizing all are names of the same process.

First, some videos to spark your interest.





Sites with info:
Cambridge PEO resource page.
Keronite titanium PP-slides. Nice introduction to the process. Explains how the ceramic is formed.
Keronite homepage. Applications etc. "Advertizing"-vibe. Does not go in-depth, "Contact us and we'll do it".
Lighter Bikes, one of the Keronite application ads.
Wikipedia: Plasma Electolytic Oxide. Good introduction.
Plasma Electrolytic Oxidation of Valve Metals. A good overview of some of the techniques used.

I would like to read more about this technology, I'm looking for a suitable book now. I want to use this technology to prepare (electically isolate) heatsinks for power transistors.

I will build a full-bridge power supply (bipolar capable) and a simple spectrum analyzer. The latter one to quantify the temperature of the sparks - a vital process parameter.

Any hints and tips, other experiences or similar, are warmly welcome :)
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Sulaiman
Wed Apr 23 2014, 05:25PM
Sulaiman Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
nice videos
I doubt that a book will help compared to internet resources.

Often the most useful resources are manufacturers data, instructions, application notes etc.
as they want their customers to succed.

If I understand correctly,
a porous layer will be formed which would not guarantee electrical isolation if moisture is present
so use as insulation for heatsinks may not be reliable
especially if the protective layer is scratched during installation.

If you watch the second video,
even after the protective layer has formed small nebulous discharges can still be seen
which implies to me that the protective layer is not ideal.
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Proud Mary
Wed Apr 23 2014, 07:33PM
Proud Mary Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Google variations around these three searches "self-organized porous alumina nanoholes array" "anodic porous alumina" "alumina nanoholes"

You can even put a carbon nanotube inside an alumina nanohole if you know how.
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Ash Small
Wed Apr 23 2014, 07:52PM
Ash Small Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
There are also the old 'wet chemistry' anodizing methods as well, some of which can build up quite thick layers of oxide. These are generally porous as well, allowing them to hold a 'dye'. I just mention this as there 'may' be alternatives to 'plasma processing' that might achieve similar results.
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Storken
Thu Apr 24 2014, 07:21AM
Storken Registered Member #1960 Joined: Thu Feb 05 2009, 11:57PM
Location:
Posts: 48
@Sulaiman
I continued the search for good internet resources, found one more.

Applications for PEO, by naain
More on PEO technology, by naain

Still, process parameters are not discussed wrt heatsinks. Same as Keronite. They know how to protect and profit from their immaterial findings.

As the surface is very hard (from 1000 HV to 2000 HV), I don't think scratching is a problem during installation. Post installation ohmic test will quickly tell if the insulation is good or not. I've dabbed some with anodizing, some heatsinks are perfect with GOhms of resistance, others come in at low kOhms.

@Ash. The main pro with this method is the lack of sulfuric acid. It corrodes everything around it. But yes, hard anodizing are absolutely suitable for heatsink insulation.
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Ash Small
Thu Apr 24 2014, 07:42AM
Ash Small Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Storken wrote ...

@Ash. The main pro with this method is the lack of sulfuric acid. It corrodes everything around it. But yes, hard anodizing are absolutely suitable for heatsink insulation.

It's a while since I looked into this myself, that's why I've not posted any details, but I do remember that there are loads of different 'recipes', some just use sodium bicarbonate, if I remember correctly (although this doesn't give 'hard' anodizing). I imagine there will be some 'hard anodizing' recipes that don't use sulphuric, although I'm not certain, I'd have to refresh my memory.

EDIT: just looked on Wikipedia, and it says anodizing with borate or tartrate produces a non-porous coating:

"Borate and tartrate baths

Anodizing can also be performed in borate or tartrate baths in which aluminium oxide is insoluble. In these processes, the coating growth stops when the part is fully covered, and the thickness is linearly related to the voltage applied. These coatings are free of pores, relative to the sulfuric and chromic acid processes. This type of coating is widely used to make electrolytic capacitors, because the thin aluminium films (typically less than 0.5 μm) would risk being pierced by acidic processes."


Link2

If it's used for capacitors it 'may' be suitable for your application, although it doesn't say how hard it is, but thickness is voltage dependant.

I'm currently reading through this:
]taleb_kaled_h_x.pdf[/file]
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Conundrum
Thu Apr 24 2014, 05:39PM
Conundrum Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Interesting, thanks for sharing!

-A
Conundrum Drive page:- Link2
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Patrick
Thu Apr 24 2014, 07:26PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Is any of this easier and cheaper than using the normal stick'em thermal pads. Or mica?
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Ash Small
Thu Apr 24 2014, 07:56PM
Ash Small Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...

Is any of this easier and cheaper than using the normal stick'em thermal pads. Or mica?

I'm guessing the idea is that it should conduct more heat than thermal pads, but I'm only guessing here. Whether or not it works out any cheaper would probably depend on quantity, but I'm only guessing again. The process I've linked to and which is described in the pdf I posted doesn't look that difficult, although preparation and cleanliness, as with most electrochemical processes is vital.

I'm interested enough to try this myself, pharmaceutical grade boric acid and borax are easy enough to get hold of.

I've not looked to deeply into what's involved in the plasma process that Storken posted, though.
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Patrick
Thu Apr 24 2014, 09:15PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
im going out on a limb here, but going to say that spark/plasma forming l must be more difficult than electrolytic deposition (like capacitor plates, as others mentioned.) and more difficult to quality control.

just my opinion, but the aqueous-electrolytic method looks easier and more reliable. and youll still get to choose the shape of the deposition area.







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