What are hard disk platters made of?

The reason I'm asking is, I have 3 portable hard drives that no long work. I took them outside, wore a dusk mask, and gloves, and used a hammer to destroy the platters. There was a weird smell to it, but because I was outside it didn't last long.

Do they spray something on the platter before putting it in the enclosure? Is it toxic to breathe in? Should I be worried?

2 Answers

Straight from Wikipedia. You may want to Google these chemicals/metals to get a better understanding of their toxicity.

Platters are typically made using an aluminium or glass and ceramic substrate. In disk manufacturing, a thin coating is deposited on both sides of the substrate, mostly by a vacuum deposition process called magnetron sputtering. The coating has a complex layered structure consisting of various metallic (mostly non-magnetic) alloys as underlayers, optimized for the control of the crystallographic orientation and the grain size of the actual magnetic media layer on top of them, i.e. the film storing the bits of information. On top of it a protective carbon-based overcoat is deposited in the same sputtering process. In post-processing a nanometer thin polymeric lubricant layer gets deposited on top of the sputtered structure by dipping the disk into a solvent solution, after which the disk is buffed by various processes to eliminate small defects and verified by a special sensor on a flying head for absence of any remaining impurities or other defects (where the size of the bit given above roughly sets the scale for what constitutes a significant defect size).

For many years the material of choice was aluminum, although that has been changing as ceramics improve and drop in cost. There are four requirements for choice of material for platter substrate:

• Not magnetic. As the way drives work is by manipulating magnetic fields, you want the coating to be magnetic, not the substrate.
• Strong. Spinning at over 3000 rpm at the slow end, centrifugal fractures or deformation would be 'a bad thing'.
• Smooth. As the distance between the head and the platter is small, and both the platter coating and the head are delicate you don't want them to unexpectedly meet. This would present some real challenges if you were trying to make the platters of say cottonwood.
• Cheap. Although there are some advanced alloys that would be suitable, they are cost prohibitive when the other guys are using recycled popcans.