Why Does Glass Corrode and What Can We Do About it?

Technical Articles3

By Satya Prakash Rath, 3P Nanopac Pvt. Ltd.

Glass in any of its forms, shapes or applications will corrode on coming in contact with hard water. The effects of weather and corrosion on glass, even on a new car windshield, shower door, window or facade, can be readily seen upon close examination after only a few months of exposure — and after a few years, the problems can be viewed from a distance.

Usually, the process begins with “water spots” or staining. By the time one can see these symptoms, corrosion has already done preliminary damage to the molecular structure of the glass. By the time one sees iridescence (a rainbow-like effect), there has been substantial glass deterioration. Eventually, glass may appear foggy or cloudy. An attempt at washing these symptoms away with soap and water will lead to frustration and wastage of time, energy and soap. An attempt to scrape them off with a razor blade will result in scratched (but still foggy) windows, shower doors and facades. Can anything be done about it? Yes. The best thing to do is to prevent the corrosion in the first place by protecting the glass surface with a Diamon-Fusion® coating during or soon after installation at site. If one chooses not to do that and glass becomes corroded, up to a point, the glass be can be professionally restored and sealed. But, while this process will make the glass appear normal, it does not reverse the damage already done, and beyond a certain stage (stage II glass corrosion), attempts to restore the glass will simply fail and the only recourse will be to replace the glass. Corrosion as a chemical phenomenon is complex and only recently has yielded itself to scientific inquiry. The short answer is by exposure to hard water – i.e. repeated cycles of wetting and drying of water on glass. This can be by rainfall, showers, water runoff, cycles of condensation, or even just humidity. Add contaminants, such as pollutants, soap, dust or hard water (especially anything alkaline) and the process can be sped up dramatically. Examine the illustrations below for a simplified explanation:

Step 1: Water drops form on the surface of the glass. The source of the moisture may be precipitation, water spray, shower or sprinkler, building runoff, condensation or humidity or just wiping cloth. The water had dissolved contaminants like alkaline salts from ground water, from pollution or absorption from other materials in its path (masonry, metal window frames, silicone window sealants, etc.).

Step 2. Immediately, soda and other chemicals begin to leach out of the glass and into the water drop, forming a soda solution on the glass surface. Usually, this is a fairly slow process to begin with because the pH has not reached a critical level. The exception is when the water drop is high in alkalinity (like high TDS ground water found in most cities in India) initially from pollution, hard water, or contaminants the process occurs extremely rapidly.

Step 3. As the water evaporates, the soda solution condenses and the pH level rises. When the pH level of this droplet reaches about 9, the rate of corrosion accelerates rapidly. Microscopic channels form beneath the surface of the glass, whereby molecules in the water drop and the glass can exchange and bond. Over time, as more soda leaches out of the glass, the remaining silica network becomes honeycombed and highly porous, eventually destroying the structural integrity of the glass.

Step 4. When the water drop has evaporated (repeatedly), it leaves behind a deposit of soda (and other chemicals) firmly bonded to the glass surface. This is the most noticeable visual effect of glass corrosion — a “foggy” or “cloudy” appearance. One may also notice in areas where acid rain is a problem that glass will have streaks caused by the acidic rain partially dissolving the soda deposits as it runs down the surface of the glass. These deposits and streaks resist normal cleaning methods, and if cleared (using specially formulated acidic agents) they will quickly return in the exact locations since the corrosion channels are already established. That is why it is critical to seal the glass from contact with water and not just “clean” off the appearance of fogginess. It is obvious from above that cleaning glass with either hard or soft water will aggravate this problem; cleaning your glass with “purified water” will simply allow the water to absorb more soda and other chemicals from within the glass structure. If it were possible to keep glass clean and dry at all times (or even just squeegee off the water immediately after wetting), glass would stay in clear condition for a long time. If one cannot keep glass in a temperature-controlled environment and continually squeegee off the glass so that water never dries on the surface when it gets wet, one will eventually have to deal with glass corrosion. Alternately, glass surfaces can be sealed with Diamon-Fusion®, which lets the nano-chemical-treatment process form an invisible barrier between glass and water. Should we wait till glass is corroded to apply Diamon- Fusion®? No, that is not the wisest thing to do. It is because while sealing glass with Diamon-Fusion® will stop the corrosion process, it cannot repair the damage already done, nothing can. So, don’t delay – Diamon- Fusion® glass today! Users will gain many other benefits as well, including hydrophobic (water beads up and sheds quickly, improving visibility), oleophobic (resists petroleum-based film from exhaust from attaching to the glass), glare reduction (improves night vision), scratch and impact resistant (up to 10 times stronger than untreated glass) and makes removing graffiti, smudges, finger prints much easier.

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