You know it really is quite ironic that the same water that we use to clean and maintain windows has the power and ability under the right conditions to do such damage to glass surfaces! Here is another totally fascinating example which I am sure you old timers have seen. I am talking about storm windows. Try this next time you do an old house with outer storms. Once clean, run a dry fingertip lightly across the inside and then the outside of the upper storm window. The inside will be very smooth. But not the out. That surface has been literally chewed off by a process called weathering. I am going to get just a little technical here and go to one of my reference books, "Corrosion of Glass" published by Ashlee way back in 1979. My point being we have known about this stuff for a long time. Really nothing new. So you really don't have to take my word for it. I just pretend to be smart. But am actually just connecting the dots here! OK. So the book says on page one of chapter one;...."Stage 1: the initial or primary stage of attack is a process which involves ion exchange between sodium ions from the glass and hydrogen ions from the solution...". This book also states on page one of chapter one;...."Stage 2: the second stage of attack is a process whereby breakdown of the silica structure occurs and total glass dissolution ensues.". The Glass Committee of the IWCA under the leadership of Paul West became aware of this chemistry and how it actually promotes certain chemophysical changes in soda-lime window glass. Several points are of note here but I would like to draw your attention to the fact that hydrogen ions (which come from water) are quite involved in promoting the initial Stage 1 reaction which ultimately leads to Stage 2 which is in fact "total dissolution" or breakdown of the glass surface. In much simply terms water eats glass. How quickly and to what extent depends on various conditions such as relative humidity and temperature. All of this science should convince us and our customers that glass should be sealed with a product. My preference is Nanovations NG1010. You will find more information and video demonstrations of this product elsewhere in this blog. If you have any other questions about it just ask. Here is a picture taken from the above mentioned book demonstrating total dissolution of glass in the furrows of some scratches.
Next up are interleaving systems for the on site storage of window glass at new constructions. The idea is that water or humidity (especially in hot climates) can easily over time cause corrosion of glass plates. This problem is made much worse when we consider that the glass could be placed in storage for as much as six months before installed on the building. So the simple solution is to keep the plates from getting too close together. You see glass naturally loves water. Therefore when moisture condenses between two plates that are very close it doesn't evaporate. Over time the chemical reaction described above takes place. Dissolution occurs. And the window glass is damaged. Here is a link to an online article written by Dr. Paul Duffer on precisely this problem and how to prevent it. http://www.vitroglazings.com/VitroGlazings/media/sitedocuments/TDs/19_TD105F.pdf Dr. Paul has been a tremendous help to the IWCA for many years devoting so much of his time.
Another very interesting condition involves what I call water lines. I have one job in particular where these have formed on the inside over many years. They are difficult to see on cloudy days. Also difficult to see from the inside looking out when they form on the inside. But are very easy to see from the outside looking in when formed on the inside and on a bright sunny day. They result from water running down the window constantly. The water chemically wears a path. Hence each water drop precisely follows the path of the previous drop. Eventually this process creates dark lines. They can be removed by various polishing processes. Such as wet diamond compounds and soft but small polishing pads.
Failed IG Units are a perfect demonstration of a stage two static etch. This type of etch forms on the inside of insulating glass units. It usually takes many months to form. But it is a perfect demonstration of a static etch, not a dynamic etch. Water vapor or moisture collects between the plates as the seal fails. But it cannot easily escape. So it remains there, and heats up very quickly in the hot sun. Which causes the reactions discussed above. Although the reaction byproducts are not removed by dynamic/flowing water. So such salts are not removed. They just stay right there. It is easy to see when this happens. Because initially the condensed moisture is completely clear. Then as the reaction begins you will notice a white cloudiness develop. It will not be even but rather shows up like clouds. Also it starts as a very light cloudiness but becomes more and more opaque.
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Written by Henry Grover Jr.
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3 comments:
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