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Influence of incorrect desiccant on IG unit–Calcium oxide

    Source:Natergy Author:Natergy Release time:2015-07-28

What will happen if we use Calcium oxide as IG desiccant?
1.   Influence aesthetics
1)    After adsorbing water, calcium oxide will change into calcium hydroxide to erode aluminum  
spacer.
2)    After adsorbing water, calcium oxide will change into calcium hydroxide to erode butyl and
produce rainbow phenomenon, it will make IG opaque.
3)    Desiccants pulverize and leak from aluminum spacers to glass surface.
2.   Influence IG’s lifespan:
Destroy butyl and make IG tightness fail.
3.   Threaten IG’s safety:
If sealant and aluminum spacers are eroded for a long time, it will probably cause big piece of glass fall down.
4.  It can not adsorb water actually.

         

eroded aluminum spacer                deliquescence                               salting out                                    rainbow

How could that happen?
1. When reacting with water, CaO+H2O→Ca(OH)2. Ca(OH)2 is a kind of strong alkaline base, it can easily react with aluminum and its oxides. So, the calcium oxide desiccant is corrosive to aluminum spacer. Please refer to the chemical reaction in the following formula:

2. Ca(OH)2 is not stable chemical. It not only reacts with CO2 in the air, but also with SiO2 and Al2O3 from the clay. And in the process of reaction, water is released, presenting that lime desiccant has no effective adsorption capacity at all.

When we test the adsorption of the lime desiccant, actually what we test is its carbon dioxide adsorption capacity. In the air, CO2 content is 0.03%, the chemical equation is CaO+CO2=CaCO3. Although the adsorption is high, it is carbon dioxide not water, so its water adsorption is temporary.
3. This alkaline desiccant contact with the sealant throughout the year, which will easily make butyl volatilize and have rainbow phenomenon on the glass surface .It will speed up sealant’s ageing and oxidation to cause IG tightness fail.
How to know whether it contains calcium oxide?
1.    Put desiccant into water, reacts violently and releases too much heat.
2.    Put desiccant into water, test the PH value. The PH value is above 10. Then taste the water with your tongue, there is acerbic and irritant taste in the mixture.
3.    Test delta T value, the calcium oxide desiccant has very high delta T value.
Immerse desiccants with water, if the filtrate is white precipitated with soda solution (Na2CO3), it means the desiccant is loaded with corrosive calcium oxide.