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    Influence of incorrect desiccant on IG unit-Clay with calcium chloride

    Source:Natergy Author:Natergy Release time:2015-07-27

    What will happen if we use clay loaded with calcium chloride as insulating glass desiccant?
    1.    Influence aesthetics:
    1)    Erode aluminum spacer.
    2)    Salt crystallization will leak.
    3)    Erode butyl with rainbow phenomenon and cause IG opaque.
    4)    Desiccants pulverize and leak from aluminum spacers to the glass surface.
    2.    Influence IG’s lifespan:
    Destroy butyl and make IG tightness fail.
    3.   Influence energy-saving effect:
    As the existence of acid gas, low-E film will be seriously corroded.
    4.   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.

    How could that happen?
    Calcium chloride desiccant’s exterior is easy to change after adsorbing water. In IG unit, this desiccant will diffuse to aluminum spacers slowly or to sealant and glass surfaces through aluminum holes.
    The corroding principle to aluminum spacer is as follows: Aluminum is amphoteric metal, it can react with both acid and alkali. Its oxide has also this kind of characteristics. Meantime the micro ions will accelerate the oxidation process. Although catalytic action is very slow for dry gas, the ion concentration in little water will destroy the oxidation film irrevocable.

    2H2O+CaCl2=2H++2OH-+Ca2++2Cl-                                                 (1)
    Oxidation film of aluminum spacer destroyed is in the following way,
    6H++Al2O3=3H2O+2Al3+                                                                       (2)   
    Al3++ 3OH-=Al(OH)3                                                                                (3)
    After Oxidation film is destroyed,
    2 Al+6OH-=2Al(OH)3+6e                                                                        (4)
    6 H++3O2 = 6 OH- -6e                                                                            (5)
    4 Al+6OH-+6H++3O2=4Al(OH)3                                                           (6)
    So, as time goes, the oxide film on aluminum spacer will be totally destroyed and the new dense
    oxide film can not form because of the ions. Then aluminum spacer will be corroded gradually and salt marsh will appear, finally gap and holes will form to cause IG unit invalid.
    This acid 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 judge whether the desiccant is clay loaded with calcium chloride?
    1)  PH value is between 7-9, acerbic and non-irritant.
    2)  There is more precipition after mixing the leaching solution and alkaline solution.
    How to calculate the weight of calcium chloride in desiccant?
    According to some authorized references, water adsorption of calcium chloride desiccant is 35% in the 60% relative humidity. So according to the formula: 6H2O+CaCl2= CaCl2·6H2O, we can calculate the weight of calcium chloride.
    111(molecular weight of CaCl2)/[108(molecular weight of 6H2O )/35%]=35.97%