How Can You Remove Dissolved Oxygen from Water Without Chemicals?

[Fabricator123]

Hello, I am working with an artist to build enclosures that would hold magnetite sculptures in water filled test tubes... and they are rusting. One of the specifications I was given is it has to be chemical free water, so that rules out oxygen scavengers. Seeing as it is the dissolved oxygen I believe that is causing the rusting, I was looking for a 'relatively' easy process I can do myself to remove the dissolved oxygen. I know there are a lot of problems with this idea, but first I would like to tackle the dissolved oxygen. Many thanks.

 

[ISamson]

Welcome to PF!
Is the water deionized in your project?

 

[Borek]

Standard procedure for removing oxygen call for purging it with an inert gas (like argon or nitrogen). Note that it has to be sealed after that.

Chemical free water in this context means mostly water that has no dissolved ions that speed up charge transfer. If you have an oxygen free water dissolved ions should not matter (no oxygen -> no oxidation). So in the sealed container presence of the oxygen scavenger should not facilitate rusting - yes, there are ions, but there is no process they can speed up.

Distilled (DI, RO) water will definitely slow down the rusting, but whole things still has to be sealed so that no oxygen can enter the solution.

 

[Lord Jestocost]

One of the specifications I was given is it has to be chemical free water, so that rules out oxygen scavengers. Seeing as it is the dissolved oxygen I believe that is causing the rusting, I was looking for a 'relatively' easy process I can do myself to remove the dissolved oxygen.

Have a look at "The rusting process of water" (http://www.docbrown.info/page03/Reactivitya.htm). Put the sculptures into boiled, distilled water in a sealed enclosure, with a layer of oil, too. The boiling drives off dissolved air and the oil provides an extra barrier.

 

[alchemyst]

Removal of oxygen will stop rust forming ie iron 3 oxide. However corrosion to the iron2 stage is possible and will generate hydrogen, but very slowly. The oxidation of iron in central heating systems in the absence of oxygen produces hydrogen, which is vented away normally. Are you creating a system that could overpressureise over time?

 

[alchemyst]

Oops sorry, misread magnatite not iron, you should be OK

 

[Fabricator123]

Welcome to PF!
Is the water deionized in your project?

Yes, I have tried deionized and distilled water.

 

[Fabricator123]

Have a look at "The rusting process of water" (http://www.docbrown.info/page03/Reactivitya.htm). Put the sculptures into boiled, distilled water in a sealed enclosure, with a layer of oil, too. The boiling drives off dissolved air and the oil provides an extra barrier.

I have tried this and still a browning of the scuplture is occurring, I have also added Polyvinyl Alcohol to create a barrier, but still I get a slight browning.

 

[Fabricator123]

Removal of oxygen will stop rust forming ie iron 3 oxide. However corrosion to the iron2 stage is possible and will generate hydrogen, but very slowly. The oxidation of iron in central heating systems in the absence of oxygen produces hydrogen, which is vented away normally. Are you creating a system that could overpressureise over time?

I was leaving an air bubble at the top to help with heating and expanding, but no way to release pressure. The sculptures are quite small, so I am not sure how much hydrogen would be released.

 

[Fabricator123]

Standard procedure for removing oxygen call for purging it with an inert gas (like argon or nitrogen). Note that it has to be sealed after that.

Chemical free water in this context means mostly water that has no dissolved ions that speed up charge transfer. If you have an oxygen free water dissolved ions should not matter (no oxygen -> no oxidation). So in the sealed container presence of the oxygen scavenger should not facilitate rusting - yes, there are ions, but there is no process they can speed up.

Distilled (DI, RO) water will definitely slow down the rusting, but whole things still has to be sealed so that no oxygen can enter the solution.

The test tubes have a cap are and tightly sealed. Would degassing water with a vacuum chamber have the same effect of removing dissolved oxygen as purging it would?

 

[Borek]

The test tubes have a cap are and tightly sealed. Would degassing water with a vacuum chamber have the same effect of removing dissolved oxygen as purging it would?

In general probably yes, but I have no idea how fast it will be. Purging with an inert gas - for small volumes, like 50-100 mL - does the trick in about 15 minutes. Or at least that was the standard procedure we followed during experiments.

 

[Lord Jestocost]

I have tried this and still a browning of the scuplture is occurring, I have also added Polyvinyl Alcohol to create a barrier, but still I get a slight browning.

What about cathodic protection or sacrificial protection (see under "Rust prevention" at http://www.docbrown.info/page03/Reactivitya.htm) with a small piece of zinc connected to the sculpture?