Differences btn DI and Distilled water 1

I am looking for some answers to a question about water. Namely, chemistry of distilled and DI water. Some say there are no real differences, but I know from experience that DI is very corrosive when in contact with Fe and Cu pipes. I need to know the why's to this difference or where I can find the answers.

Thanks

 

[dprice]

Distilled water is that water which is produced by distillation (boiling and re-condensation). <br>
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When you boil water salts are carried over to the condenser. This results in impurities in the water. These fractionation rates are species dependent and equipment dependent so the composition of distilled water can vary quite alot. <br>
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DI water is normally produced by pumping accross a membrane with small holes. The holes are small enough that ions (dissolved salts) cannot penetrate. Thus only water migrates through. <br>
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The reason iron pipes and DI water is not compatible is the iron leaches out into the water from the pipes. The water in this state has a high affinity for some ions.<br>
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So unless I have detailed knowledge of the process producing the distilled water I cannot give you a constituency. If it is bottled you might be able to ask the supplier for a breakdown. Often times they monitor the chemistry to indicate when the equipment requires maintenance.<br>
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Hope this helps.

 

[greg87]

DI (deionized) water is a general term, and the degree of deionization can vary depending on the method used to produce it and the production system design. (Water produced by distillation will be deionized.) The degree to which water is deionized is measured by its conductivity, or the inverse, resistivity. The purest water would be at 18 megohm-cm, but 1 meg water could still be called &quot;deionized&quot;.
Deionized water could still contain bacteria and organic material; which would be other measures of purity.
As far as materials go, you would not want to use iron or copper for any deionized water; it will want to dissolve metal ions. PVC or Polyproplene are good materials. 316L stainless also; but the highest resitivity water can be a problem with it as well.

 

[IRstuff]

Distilled water is condensed water from boiling, which means that volatiles with similar boiling points are carried along, unless fractional distillation is employed, where you try to condense at a specific point and exclude the other products.

Deionized water, in the semiconductor industry, involves using gross filtration, reverse osmosis and deionization beds to physically purify the water. This is generally followed by UV and other biocidals and more filtration.

The reverse osmosis is a diffusion under pressure through a semi-permeable membrane. The clean side is pressurized to overcome the osmosis that would normally occur from the dirty side.

The deionization beds use resin beads that are bonded to specific ionic species that can bind to ions in the water. The water flows through the beads and the ions are trapped on the beads.

TTFN

 

[Galgo]

As Greg87 and IRstuff point out, DI and Distilled are very different.

Distilled is a simple boiling/vapor condensation process which does not remove similar boiling point volatiles nor does it eliminate dissolved oxygen and CO2. Both of which are &quot;terminal&quot; when it comes to a high purity situation.

Water purity is best identified using resistivity or conductivity ( they are exact inverses ).

The most pure condition available with current technology is 0.055 microSiemens or about 18 MegOhm water. Essentially, water without ions.

However, the although the purity of water remains unchanged, its conductivity is dramatically affected by temperature.

Take 18 MegOhm water at 0C. It will become 5 Megohm water at 50C. Without any contamination whatsoever.
Add 20 ppm of NaCl and it will become 1 Megohm water.

Temperature and contamination are the concerns.

Materials of construction and elimination of ambient gas contamination by Oxygen and CO2 are other concerns.

DI water &quot;wants&quot; ions because it has none. The driving force is tremendous.

Distilled water has a resistivity of 100K ohm to 1 Megohm.

DI water is 5 to 10 times that value.

The point here is produce what you need and use it fairly quickly. If DI water stays around it will become contaminated. Sure, DI resin beds can keep it deionized, but if your piping system is metallic and/or there is oxygen present, then you will fail to keep it DI.

Good luck.