[redwraith94]

I am trying to figure this out for ultra secure erasure purposes (and mostly because I am a geek) I have not been able to figure out what the platters are made of, or their curie point. So anyone with info please post.

[Celeron_Phreak]

Hard disk drive platters are made of aluminum. There have been rumers of some brands using glass for their platters though, but I haven't seen any true confirmations of this.

As for the curie point....

I was watching a history of data storage confrence lecture and they used to use 24 inch steel platters with a magnetic iron oxide(?) which was poured onto the rotating platter from a dixie cup (no, I'm not joking here). Keep in mind that this was at the begining of data storage!

[Snugglebear]

http://www.storagereview.com/guide20...ediaMedia.html

The platter doesn't store the data; most of it is aluminum alloy or glass substrate, with a thin film of pixie dust on top. I'm not sure what the curie point is since there's a wide variety of substances in use. However, I can guarantee that with a couple dozen passes with dban, a stressful day, and a hammer, your worries about data leakage will be put to rest.

[redwraith94]

LOL thanks for that, I should have said 'media layer' then. The curie point is just where the magnetic material is no longer magnetic. ie it loses all information, without the possibility of recovery. I can not figure out what the actual 'substrate' that stores the information is made out of for hdd's today. I figure that ea manufacturer uses the same substance, but idk what it is. Thnx for the linkies too.

[JigPu]

I did a quick google, but didn't come up with much in the way of curie points. Materials were a bit easier to find though.

Hitachi shows on one of their pages that they use CoPtCrB as their ferromagnetic material.

A japanese company that does sputtering has a list of recording films used here (it's a PDF, and in japanese I think I found an english HTML version though here).

JigPu

[redwraith94]

Ah holy wow, thanks jigpu. I actually took some japanese in cowwege so far, not enough to translate that pdf though lol.

I tried google b4, but never had ne luck finding materials, I have been looking on and off for quite a while, and I will post again the temps for all to see...after I look them up.

[L337 M33P]

Less than the typical reaction operating temperature of thermite

[redwraith94]

I will make a table of all of the materials listed in that pdf, and their curie temperature (So that a hard drive would have to be heated to at least this temperature to completely , albeit geekily erase it

FeCo (Iron Cobalt) >1230 degrees Celsius (>2246 deg F)
25% Co 75% Pt Tc = 227 deg C, 441 deg F
10% Co 90% Pt Tc = -33 deg C, -28 deg F
http://lucy.mrs.org/meetings/spring9...ractBookL.html
64% Co 14% Pt 22% Cr Tc = 400 deg C, 752 deg F
61% Co 14% Pt 25% Cr Tc = 160 deg C, 320 deg F
http://www.priorartdatabase.com/IPCOM/000111895/

I will add on to this list as time allows, with the eventual hopes of finding a maximum temperature guarunteed to erase any hard drive.

Apparently, when a material is made into a thin film (in a hard drive, for instance) the curie temperature of the material decreases. It seems to be a fairly severe decrease. This website quotes a value of 225 Kelvin for a thin film of Fe (Iron) which is -48 degrees Celsius (-54 deg F), much colder than a freezer. The accepted curie point for Iron is 1043 deg Celsius. This is for a chunk large enough to be visible. From what I can tell the 'bulk curie temperature' is much higher than the curie temperature of the same material when made into a thin film. Films for hard disk drive substrates are on the order of Microns (millionths of a meter).

http://www.physicstoday.org/pt/vol-54/iss-5/p31.html

I found a document on the U.S. patents website, arguing about the refusal of a patent being granted that stated the CoPtCrB alloy had a curie temperature near 80 deg C (The curie temperature varies with the amount of each individual element), this seems too low to be accurate, but I am not sure right now.

[Snugglebear]

You do realize that aluminum melts well below that, right? Just a wee bit of overkill to continue heating platters after the substrate turns to sludge.

[JigPu]

Not if they're using ceramic or glass substrate

But then again, it'd still be a bit difficult to recover data even with one of those substrates with the aluminum housing molten on it

JigPu

[Snugglebear]

Originally Posted by JigPu

Not if they're using ceramic or glass substrate

But then again, it'd still be a bit difficult to recover data even with one of those substrates with the aluminum housing molten on it

JigPu

Hammers and/or gravity work well on non-Al platters and are, to an extent, have a superior fun/$ ratio. Not that melting things isn't fun, it just tends to take a lot longer and run you more out of pocket.

[redwraith94]

Originally Posted by Snugglebear

You do realize that aluminum melts well below that, right? Just a wee bit of overkill to continue heating platters after the substrate turns to sludge.

Lol, yeah I know that. Preliminary research indicates that the majority of substrates are made from a Platinum-Chromium alloy. I only posted that alloy so far, because, in all honesty, I am having a very difficult time finding curie points for any of these alloys, so far it is the only one I could find. I have also been somewhat lazy.

Originally Posted by Snugglebear

Hammers and/or gravity work well on non-Al platters and are, to an extent, have a superior fun/$ ratio. Not that melting things isn't fun, it just tends to take a lot longer and run you more out of pocket.

While I must agree with you about the fun ratio, I am looking into this in the hopes that people who need a completely secure erasure method will find it via google, once it is complete. As for finding these ellusive curie points, I still don't know where to look, the almighty google has failed me

Redwraith94

[redwraith94]

Primary layer

64% Co 14% Pt 22% Cr Tc = 400 deg C, 752 deg F
61% Co 14% Pt 25% Cr Tc = 160 deg C, 320 deg F
http://www.priorartdatabase.com/IPCOM/000111895/

Both the paper (above), and this one (below) state that the magnetic properties of the CoPtCr alloy is nearly independent of the % platinum:

http://www.slac.stanford.edu/cgi-wra...c-pub-9991.pdf

According to my research so far, most drives seem to be made out of a:

Co Pt Cr alloy (Cobalt Platinum Chromium) ^^^^^^

FeCo (Iron Cobalt) >1230 degrees Celsius (>2246 deg F)
25% Co 75% Pt Tc = 227 deg C, 441 deg F
10% Co 90% Pt Tc = -33 deg C, -28 deg F
http://lucy.mrs.org/meetings/spring9...ractBookL.html

Sublayer

(Iron Platinum alloy) FePt Tc = 417 deg C, 782 deg F (Thin Film Value)
http://www.fujitsu.com/downloads/MAG...rpt%20curie%22
(Magnetite) Fe3O4 Tc = 587 deg C, 1089 deg F (Bulk Value)

Another resource (5 values listed, bulk curie points only):
http://depts.washington.edu/chemcrs/...ent_Pres_2.pdf

I will be adding to, and modifying this table, as time allows.

Updated list of possible media layers:
CoCr, CoPt, CoCrPt, CoCrTa, CoTaCrPt, FePt, TbFe, TbFeCo, and GdFeCo
(From a "Matsu****a Electric Industrial Co. Ltd" patent application filed in Nov 2002)

[redwraith94]

After talking at length with an associate of one of my professors. I have decided that I have to find a way to test individual hard drives, instead of trying to find these elusive numbers.

Originally Posted by Dr. Fischer

But this is too big a challenge: even if there are good bulk Curie
point values for this alloy, there is no good data for its thin film form (and in principle, there can not be). The reason for this is that the physical properties of thin films depend strongly on an infinitely long list of
extraneous factors, such as the method of preparation, thickness, morphology surface and bulk), substrate conditions, and measurement conditions.

I briefly touch upon this problem on our website (look under www.ivactech.com > Services > Coatings -the red colored couple of paragraphs on the bottom. If this is really important, you can estimate the Curie point under your specific conditions.

How do you deposit (all specs, including background pressure and other contamination sources are important)? What is your substrate? How do you deposit? Why Curie point is of importance and what measurable parameters does it effect? It is possible that your substrate will be destroyed before reaching the Curie temperature.

I am not sure how to determine the curie points accurately, I understand the theory, but actually building a machine for this would be very taxing, if I could do it at all. If anyone knows engineers in the hard drive industry, then I am sure that they have these numbers on file some where, for each individual line of drives. Other than that I need to find a machine that could test curie points, and then get a bunch of old drives. This is a continuing project, that I hope will be solved one day, if anyone thinks they can help, please send me a pm, or post back here.

Redwraith94

[soulfly1448]

I've never even thought to do that before.