How to test the quality of heavy water (D2O)?

For posts specifically relating to fusor design, construction, and operation.
Post Reply
Harald_Consul
Posts: 23
Joined: Sat Oct 20, 2018 10:01 am
Real name: Harald Consul

How to test the quality of heavy water (D2O)?

Post by Harald_Consul » Mon Oct 22, 2018 1:00 pm

Hello!

Qualitity testing the origin material is always an issue. Especially in heavy water, there a different qualities offered (80%, 90%, 95%, 98%, ...).

How can I roughly estimate the quality of heavy water, or even that there is any D2O in the water I get delivered?

Roberto Ferrari
Posts: 329
Joined: Tue Mar 02, 2004 5:21 pm
Real name: Roberto Ferrari
Location: Argentina
Contact:

Re: How to test the quality of heavy water (D2O)?

Post by Roberto Ferrari » Mon Oct 22, 2018 1:47 pm

Harald
You answer your question.
Different qualities offered have their own spec.
Having doubts of your provider, change it or test it.
Typically % of heavy water is evaluated by IR spectrometry.
See this plot.
The-typical-IR-spectra-of-water-with-varying-content-of-deuterium.png
May be by density measurements also.

Harald_Consul
Posts: 23
Joined: Sat Oct 20, 2018 10:01 am
Real name: Harald Consul

Re: How to test the quality of heavy water (D2O)?

Post by Harald_Consul » Mon Oct 22, 2018 3:37 pm

So, if I've understood you right, for a rough test I would weight e.g. 10ml of heavy water in a volume measuring cylinder on a high precision weighting scale. Just one question to that. D2O is how much heavier than H20, exactly?

If I am fortunate to posess an infrared spectrometer, I will use this one for a more precise test, instead.

Roberto Ferrari
Posts: 329
Joined: Tue Mar 02, 2004 5:21 pm
Real name: Roberto Ferrari
Location: Argentina
Contact:

Re: How to test the quality of heavy water (D2O)?

Post by Roberto Ferrari » Mon Oct 22, 2018 4:04 pm

googled: 10% heavier.
For precise density measurements use a picnometer.

User avatar
Rich Feldman
Posts: 998
Joined: Mon Dec 21, 2009 11:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

Re: How to test the quality of heavy water (D2O)?

Post by Rich Feldman » Mon Oct 22, 2018 4:51 pm

Roberto, thank you for posting the infrared spectrum plot. A thing I hadn't seen before. Anybody know if gaseous D2, H2, HD mixtures can easily be assayed by absorbtion or emission spectra?

Here's a warning for conventional density measurements, even with a picnometer.
They say D2O is very hygroscopic -- it readily picks up moisture when exposed to air, changing the isotope ratio.
I think there's a continuous traffic of water molecules passing between the liquid and vapor phases. The net evaporation rate may be small, but it's the difference between two larger numbers.

I've been thinking about ways to precisely measure the speed of sound in small samples of gas. The compressibility difference is negligible; what matters is the ratio between compressibility and gas density.
.
heavy-water-500x365.jpg
ref: http://www.dancingwithwater.com/deuteri ... hat-is-it/, who probably pirated the image.
Richard Feldman

Roberto Ferrari
Posts: 329
Joined: Tue Mar 02, 2004 5:21 pm
Real name: Roberto Ferrari
Location: Argentina
Contact:

Re: How to test the quality of heavy water (D2O)?

Post by Roberto Ferrari » Mon Oct 22, 2018 5:13 pm

Hi Rich

Thanks for the warning. I had forgotten the hygroscopic property of D2O.

There is a US thesis from the 60's about chromatographic separation of H2, HD and D2 with packed column and low temperature.

User avatar
Rich Feldman
Posts: 998
Joined: Mon Dec 21, 2009 11:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

Re: How to test the quality of heavy water (D2O)?

Post by Rich Feldman » Tue Oct 23, 2018 12:39 am

Oh what fun, infrared spectra of water! Here's an animated gif
v1.gif
from http://www1.lsbu.ac.uk/water/water_vibr ... ctrum.html, which lists wavenumbers for 12 isotopically different kinds of water.
Here's another reference: https://analusis.edpsciences.org/articl ... heinze.pdf
.
The resonances of free molecules (water vapor) change significantly in the liquid. Internet just taught me about Attenuated Total Reflectance, which allows measurement at frequencies (wave numbers) where the transmission is almost zero after just a dozen wavelengths.

It would be great if somebody here can quantify the amount of H in almost pure D2O, using home made equipment.

This is a good opportunity to bring up the promiscuity of hydrogen atoms in water. We all know that pH = 7.0 comes from the fraction of water molecules that are naturally ionized at 20 °C, at any given instant. Continuous ionization and recombination pay no respect to the original partnering of the atoms.

One section of the reference above begins with "HDO (50 mole % H2O plus 50 mole % D2O; ≈ 50% HDO, ≈ 25% H2O, ≈ 25% D2O)"
That is to say: if you mix equal mole quantities of pure H2O and pure D2O, in equilibrium half of the molecules will be the HDO species.
In natural water with a H/D ratio of 6000, 1/3000 of the molecules are HDO and less than 1 in a million is D2O.
How 'bout commercial heavy water, let's say 99% grade? At any instant, 2% of the molecules are HDO, so that's what we need to measure.
Is the equilibrium concentration of H2O 1% of 1%, or 2% of 2% ? Not a rhetorical question, this is a call for a chemist!
Richard Feldman

Harald_Consul
Posts: 23
Joined: Sat Oct 20, 2018 10:01 am
Real name: Harald Consul

Re: How to test the quality of heavy water (D2O)?

Post by Harald_Consul » Tue Oct 23, 2018 9:49 am

Roberto Ferrari wrote:
Mon Oct 22, 2018 4:04 pm
googled: 10% heavier.
To be precise 1.107 g mL−1 (density of D2O) / 0,9982067 g·cm−3 (density of H2O), both at 20°C.
Roberto Ferrari wrote:
Mon Oct 22, 2018 4:04 pm
For precise density measurements use a picnometer.
Thanks for the tip. Picnometer at Ebay about 20 EUR (10 ml Size).

Post Reply