Glass media hard drives

From: Dwight Elvey <elvey_at_hal.com>
Date: Mon Dec 11 16:43:54 2000

THETechnoid_at_home.com wrote:
> If glass is a slow moving liquid as demonstrated by 50 year old running
> window glass, how do drive makers expect thier media not to 'dish out'
> from the centrifugal force exerted on them?

Hi
 There is no evidence that 50 year old glass runs.
This was an erroneous conclusion from looking at old
stained glass. This old glass was not made like float
glass of today and almost always had some wedge. The
glass was placed in the came with the fat end down
to help in shedding water.
 There are both lenses and mirrors made over 100 years
ago that are holding an optical shape that would be
impossible to keep with even the slightest running or
slipping ( less then 2X10^-9 inches ). I don't find it
conceivable that adding another 200 years could make a
change on the order of tenths of an inch, as in the case
of the stained glass. Many of the finest refractor lenses
made and still in use were made in the last 50 to 100 years ago.
These could not be useful at all with the suggested
running stated.
 This is an argument the comes up every now and again
that just doesn't make sense. The only thing that 50 year
old glass does is what is called surface chemical tempering.
This is why it is hard to cut old glass. This is caused
by chemicals diffusing in the glass surface ( a method often used
to temper glass for special purposes to day ).
 While it is true that glass is still semi liquid, like the
rings of Saturn that are made of ice and will sublime over
time, the rate of sagging of glass at normal temperature is
no relevant on human time scales.
Dwight
Received on Mon Dec 11 2000 - 16:43:54 GMT

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