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 Post subject: Does anyone know what color has the magnetic coat?
PostPosted: November 7th, 2018, 17:24 
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I am referring to the magnetic layer of a current high-density hard disk. Those of before I think they had coppery color.

I have not found a single photo on the internet. Only from the top layer of chrome. The protective layer

Thank you.


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 Post subject: Re: Does anyone know what color has the magnetic coat?
PostPosted: November 7th, 2018, 19:37 
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the color you see is the color of magnetic layer
the protective layer is transparent

the reason why older drives had coppery color is because they used iron oxide-based magnetic layers
newer drives use magnetic alloys that could include Iron, Cobalt, Platinum

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 Post subject: Re: Does anyone know what color has the magnetic coat?
PostPosted: November 8th, 2018, 5:24 
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Thank you very much, I did not know that the protective layer was transparent.
Do you know if there is any layer that has copper / brown?

We made an experiemento: We dipped the plates of a hard drive of 2tb 48 hours and let it dry 2-3 days. After that time we hit the top of the plate and made holes with a drill. We wanted to see the different layers. One was copper / dark brown. Would it have corroded? Or is there a layer of that color?


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 Post subject: Re: Does anyone know what color has the magnetic coat?
PostPosted: November 8th, 2018, 9:52 
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There are several layers on modern hdd platter and there are many different combinations of materials used, so I simply don't know the answer but I can try to describe you what layers could have made of.

the platter itself is aluminum or glass (on 2.5" drives)
on top of it is a thin layer of Ruthenium
on top of it is so-called Soft Underlayer made of FeCo alloy but it is usually not one layer but several, sometimes separated either by Ruthenium or by other materials
on top of it is a thin layer of Ruthenium
then come recording layers that could be made of CoCrPt alloys, layers are separated by Ruthenium
on top of it could be thin magnetic cap layer or grain-boundary segregation layer, it's needed for better orientation of magnetic grains in the recording layers
on top of it is protecting Carbon layer
and finally on top of is lubricant layer

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 Post subject: Re: Does anyone know what color has the magnetic coat?
PostPosted: November 8th, 2018, 10:54 
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Very interesting, thank you.

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 Post subject: Re: Does anyone know what color has the magnetic coat?
PostPosted: November 8th, 2018, 11:16 
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If I would have to guess I would think that brown color comes from oxidized soft underlayer but water was not the reason
It is very unlikely that water would penetrate protective coating in 48 hours
More likely the layer oxidized when exposed to air (which could have happened on the factory too)

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 Post subject: Re: Does anyone know what color has the magnetic coat?
PostPosted: November 8th, 2018, 11:40 
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Doomer wrote:
There are several layers on modern hdd platter and there are many different combinations of materials used, so I simply don't know the answer but I can try to describe you what layers could have made of.

the platter itself is aluminum or glass (on 2.5" drives)
on top of it is a thin layer of Ruthenium
on top of it is so-called Soft Underlayer made of FeCo alloy but it is usually not one layer but several, sometimes separated either by Ruthenium or by other materials
on top of it is a thin layer of Ruthenium
then come recording layers that could be made of CoCrPt alloys, layers are separated by Ruthenium
on top of it could be thin magnetic cap layer or grain-boundary segregation layer, it's needed for better orientation of magnetic grains in the recording layers
on top of it is protecting Carbon layer
and finally on top of is lubricant layer


Wow . that's very interesting , thanks for explaining

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 Post subject: Re: Does anyone know what color has the magnetic coat?
PostPosted: November 8th, 2018, 12:39 
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Does anyone know how long a magnetic layer would last without corroding if the protective carbon layer is cracked and comes in contact with air / moisture?

On the GillWare website it says the following:

" The substrate is made up of very thin layers of Ruthenium, cobalt-nickel-iron alloys, and cobalt-chromium-platinum alloys. The substrate actually corrodes very readily. Platters are delicate, and only a small amount of corrosion can cause data loss "

But it does not clarify if it takes a few days or years.


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 Post subject: Re: Does anyone know what color has the magnetic coat?
PostPosted: November 8th, 2018, 15:43 
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http://patentimages.storage.googleapis.com/pdfs/US8883249.pdf


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