Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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How volatile is H2O?
How volatile is Dihydrogen Oxide? As it truly does not evaporate readily at normal temperatures and pressures such as benzene ⇦ this on Amazon affil link] and toluene. Is it a volatile because it evaporates over some time period? Is it a "real" volatile with any consequence? Do I need to account for it other then to ensure that materials are dry prior to use?
James Montenegro- Union Dale , Pennsylvania, USA
2003
Please try to post your actual situation, James. Sorry, but I have no idea what you are talking about :-)
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Do a quick test - try jumping into a lake, get out and see how fast you dry off. Do this at different air temperatures and let us know the result of your experiments.
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
Ted, it is somebody playing games with the site or somebody playing games with the person. Answer- it is water- look in any chemistry handbook and you will find all that you need to know.
James Watts- Navarre, Florida
Thanks, Jim. I don't know if this is a student trying to get someone else to write his homework essay for them, a prof pranking them, or if the inquirer needs to do a serious report on the weight of something before, during, or after processing compared to its dry weight for some environmental report or production report. We do remind posters to please post their own actual situation, rather than casting the question in abstract terms.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. It appears that I did not make myself clear. It is a given that I am addressing Water by the title (I used the compound name as it searches better on the web). What I am trying to get a handle on is how you compensate during a process when you are preparing the material to accept powder coating or base adhesives. Water is not like other volatile material as it does not stay driven off (unless the treatment areas are controlled). What I don't know is how much of a volatile it is. The only method I found to determine this I am unable to accomplish. I am also unable to locate a table that defines volatile levels of material, compounds, elements and such. I am hoping by understanding water's evaporation that I can use materials less volatile to compensate as the water should be driven off before the material I am trying to coat. This is important as I need to know the resin to weight ratio without the volatile of the resin of which water is not one but is present due to atmosphere
James Montenegro [returning]- Union Dale, Pennsylvania, USA
A. If I understand your question correctly, are you trying to evaluate how dry your material or surface is prior to however you are processing it?
Water volatility is difficult to predict unless you have an environment controlled for temperature, humidity, and atmospheric pressure. Also take into consideration the surface physics of the material on which the water is on, water as a thin film will evaporate faster than droplets, etc. Air motion also affects evaporation rates. Contaminants in the water will also affect volatility. Porosity of the surface of your material will affect water retention ("sponge" affect). Regardless, it would be difficult to predict dryness at any point in time.
Evaporation rate would relate to the vapor pressure of water under the atmospheric conditions at your process. The vapor pressure at 20 °C is 17.5 mm Hg, from this and some thermodynamics, you could possibly calculate an evaporation rate.... Regardless, you may test water content on the surface by trying a Karl Fisher (KF) titration after letting your material sit in the potassium fluoride
⇦ this on
Amazon [affil links]
reagent for a while. Sample preparation and timeliness of getting the sample into the solution before evaporation would be critical. Other surface techniques such as EDS or ESCA (expensive) are other alternatives for bound moisture, these techniques would pick up the oxygen molecules. The KF method would most likely be the best, but am I going in the right direction with what you are looking for?
- Litchfield, Minnesota, USA
Gene, yes your are in the right direction. I think I can get it from here. Thanks for the info. Lastly are there any tables that show the basic volatile information for materials?
Have a good day.
- Union Dale, Pennsylvania
A. Hi again,
I'm not sure that this is of any help to you, but for other readers with somewhat related questions about water evaporation rates, cooling tower sizing, etc., there are tables of historical "wet bulb temperatures" for the different months available for different geographical areas -- which is important, of course, because evaporation rate depends upon temperature and humidity, and "wet bulb temperature" gives you the asymptote that you are approaching.
Luck & Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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