The distance from the coil to the mirror is about 60 cm (2 feet) in our chamber. Our pressure gauge, which I don't necessarily believe, indicates that we get down to about 7 x 10^ -5 to 1 x 10^4 torr, depending on the day and how much time we have to pump things down.? I use an ordinary reinforced automobile radiator hose at one point in our setup. I wonder if things would be better if I used something else.
? Guy Brandenburg, Washington, DC? ============================
From: Vladimir Chutko
To: VacuumX@...
Sent: Sun, June 19, 2011 9:58:00 PM
Subject: Re: [VacuumX] Re: "Cheap" vacuum
?
Molecules free mean path about 1 meter and more is when pressure in
the chamber is below about 2x10-4 torr. Actually for Al evaporation
than pressure is less, than better. The best is below 2x10^-5 torr.
I produce a good Al mirrors with Cr underlayer starting evaporate Cr
at pressure about 8X10-6 - 10^-5 torr. After Cr evaporation pressure
drops down to (2-3)x10^-6 torr, and I start evaporate Al.
On 6/19/2011 6:29 PM, Guy Brandenburg wrote:
Sorry, Vladimir, as Simon points out, I was joking.?
The weird spelling was supposed to be a clue to that. I
should have added a smiley face for the benefit of those who
aren't familiar with American slang, etc.
I think I get it down so that the mean distance between
collisions of air and aluminum molecules is on the order of a
meter. That is, if the OTHER vacuum gauge is right.
Obviously, I mostly ignore the one that says "zero".
Anyway, it has a linear, rather than a logarithmic scale.
?
Guy Brandenburg, Washington, DC?
============================
From:
Simon Quellen Field
To:
VacuumX@...
Sent: Sun,
June 19, 2011 9:23:48 PM
Subject:
Re: [VacuumX] Re: "Cheap" vacuum
?
He was joking.
;-)
Carrying your analysis a little farther, however,
what is the vapor pressure of the walls
of your vacuum chamber at room temperature?
But we're clearly getting pedantic here, which is why
I put a smiling face on my
original comment.
-----
Get a free science project every week! ""
On Sun, Jun 19, 2011 at 5:36
PM, Vladimir Chutko <chutko@...>
wrote:
?
If you even passed through indicated 10
torr, 10^-1 torr, 10^-3 torr, 10^-6 torr,
10^-9 torr, 10^-11 torr, 10^-14 torr, and
then your meter indicates ZERO - it means
that you have reached edge of your meter
sensitivity, no more. You can't say that
you have no one air molecule or atom
there. Connect mass-spectrometer with very
high sensitivity and try to see what are
in your chamber. If you see nothing, it
means that your mass-spectrometer also has
not enough sensitivity. It is actually
very easy to calculate how many gas
molecules you need to provide pressure
10-14 torr, for instance. It should be
about 10^6 molecules in
or something like that, as far as I
remember constants...
Regards,
Vladimir
On 6/19/2011 5:11 PM, Guy Brandenburg
wrote:
Watchoo mean, Simon? I got a
dial right THAR on my vacuum pump
and it says plain as day that Ah
get down to a pressure of ZERO.
And that means there ain't a
single molecule or atom of air in
that thar vacyoom chamber. Beleeve
yoo mee. Yessiree bob.
?
Guy Brandenburg, Washington, DC?
============================
From:
Simon Quellen Field
To: VacuumX@...
Sent:
Sun, June 19, 2011 7:13:14 PM
Subject:
Re: [VacuumX] Re: "Cheap"
vacuum
?
Nothing gets to zero.
;-)
Mine is getting to 70 microns
(0.07 millimeters of mercury,
0.001 kiloPascals, 0.01
millibars).
Sounds like you might
have a leak.
-----
Get a free science
project every week! ""
On
Sun, Jun 19, 2011 at
11:02 AM, brian whatcott
<betwys1@...>
wrote:
?
On
6/19/2011
10:38 AM,
Simon Quellen
Field wrote:
?
""
[Note to
others on the
list -- this
is a great
price on a
nice pump.]
I bought the
next step up
(theoretically)
- a 2 stage
for? about
$130.
Trouble is -
when I
obtained a
vacuum gauge,
it gets
nowhere near
zero!
Brian W
|
