# Liquid in a vacuum

## Main Question or Discussion Point

Is it possible for a liquid to exist in a high quality vacuum? For example, a few Torr.

If so what are the methods for doing this?

## Answers and Replies

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I should start reading what I write... :yuck:
The surface tension doesn't get bigger as the radius of the droplet gets smaller. The pressure difference between inside and outside of the droplet (or the bubble) gets bigger, and that's due to surface tension (which, in turn, depends on T and on the presence of solutes in the liquid).

But how would you get such droplets into the vacuum? You would have to start with 100% liquid, with no dissolved gases. Otherwise you would corrupt the vacuum. Its almost like a paradoxical situation.

If a liquid phase is too much, then is it possible to get the solution in there without any dissolved gases? Also taking the above into account.

But how would you get such droplets into the vacuum?
Well, maybe by using something like car engine fuel-injectors? They create very tiny droplets.
Why don't we go another way round... what do you really need to accomplish?
If you need a nice flat liquid surface then I don't really know any method for obtaining that.

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Remember that phases are defined by their pressure and temperatures. Phase equilibrium is achieved when the chemical potential of the two phases are equal --- or equivalently when the Gibbs free energy is at a minimum. High vacuum generally means that the system can lower the Gibbs energy by boiling. Thus as a rule it's not possible to hold a liquid at high vacuum. However, if you are willing to look past a strict equilibrium state, and look at metastable situations, then things like lack of nucleation sites, etc. can lengthen the lifetime of the metastable state. In essence, lower pressure is equivalent to higher temperature, so you are trying to achieve a superheated liquid state --- perhaps you can find literature on that easier?

Well I suppose I'm asking how to get a pure liquid solution with no gases but that of the evaporated liquid.

Say that you put a glass of some substace in the liquid state in a chamber and then create vacuum in that chamber. The liquid will start to evaporate and thus you will have both liquid and gas phase of the same substance in the chamber.
The evaporation will go on until an equilibrium is attained, where the pressure of the gas phase in the chamber equals the so-called "vapor pressure". The vapor pressure is a function of temperature, so if you need to have low vapor pressure you need to keep the chamber at low temperature.

http://en.wikipedia.org/wiki/Vapor_pressure
and here:
http://en.wikipedia.org/wiki/Vapor-liquid_equilibrium

You can find the numerical values for water here:
http://en.wikipedia.org/wiki/Vapor_Pressure_of_Water_at_Various_Temperatures

Hope that's what you were looking for.

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Gas pressure ~1 Torr is not the high quality vacuum :)
It's quite bad vacuum.
As to the question - it depends on the type of liquid and temperature. For example, mercury can exist as a liquid at the room temperature and pressure ~10^-2 torr.

water's boild point is in connection with the atmosphere pressure and temperature. I often pump air from a equipment to get a vacuum of good quality. I have to heat the equipment to evaporate the water.

quite an interesting topic.. the variables are of course heat viscosity and also volatility of the fluid, volume and level of vacuum.....

it depends on the vaour pressure of the liquid being pumped within the vacuum..
ie a pot of water can be pumped toa level of 100 mbar beore it will boill and evaporate

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imagine the possibilities if you could! you would have highly sterile liquids, resulting in indefinite shelf lives for liquid products without the need for dangerous preservatives. I metallurgy, you could work without the interference of oxidizing gases.

the pharmaceutical companies already do vacuum stoppering and shelf life product extension with vacuum storage and , there are a global network of metallury oxide free welding..commonly known as electron beam welding and vacuum brazing ovens and heat treatment in vacuum

I believe the system you are looking for is one which uses a room temperature ionic liquid. These materials have been a hot topic in the literature lately since they have almost no vapor pressure and can be used in vacuums. For example in the paper in Nature (2007) v.447 p.949, they placed an ionic liquid in a vacuum and evaporated metal onto it to make a high quality mirror. Check out the wikipedia article on ionic liquids, there's a great review reference from PCCP at the bottom.

The liquids that are (were) used in vacuum diffusion pumps (DPs) have very low vapor pressure. See
http://www.vacuumoil.com/dc704.htm
Mercury was also used in DPs because its vapor pressure is 1.2 ~μmHg.at room temp.
Bob S