Glass Surface Corrosion


Sep 15, 2016

New glass is bright and sparkling, easy to see through and easy to clean and keep clean. Contrary to popular belief, the surface of the glass is not completely smooth. It has what glass manufacturers call ‘lattice’ or ‘honeycomb’ patterns. Under a microscope glass reveals a rougher surface made of peaks and potholes. Organic and inorganic contaminants fill these potholes and react chemically with the glass, firmly bonding to its surface. As a result, glass easily becomes stained and discoloured, difficult to see through and difficult to clean and keep clean. The surface of the glass also possesses hydrophilic properties and is over time subjected to a corrosion process that will make its surface rougher and therefore its damage greater, in some cases irreversibly.

Glass is much more resistant to corrosion than most materials, so much so that it is easy to think of it as corrosion-proof. Glass windows after several years’ exposure to the elements remain clear and apparently unaffected.

This has great implications on the property owner and any other users of glass, increased costs and efforts in maintenance, renovation or replacement, and in all cases a reduction in the expected performance.

Just as metal rusts, glass is subjected to a corrosion process caused by reactions between the glass surface and gases in the atmosphere. It is commonly associated with moisture or vapor attack through condensation, or reaction with an alkaline solution.

Glass is hydrophilic, meaning it attracts and holds moisture. All glass has a molecular layer of moisture on the surface. When this layer increases because of humidity or rainfall, it can obscure visibility and create a risk to comfort or safety. But most of all, it participates greatly to the destruction of the surface of the glass.

CORROSION BY WATER

Corrosion by water is similar to acid corrosion in that alkali is removed from the glass surface. Water corrosion acts at a much slower rate.

There are two distinct stages to the corrosion process, occurring together or separately. The first stage is aqueous corrosion, caused by moisture. It is referred to as ion exchange or alkali extraction (leaching). An ion exchange occurs between sodium ions from the glass and hydrogen ions from the corrosion solution. The remaining components of the glass are not altered, but the effective surface area in contact with the solution is increased. This increase in surface area leads to extraction or leaching of the alkali ions from the glass, leaving a silica-rich layer on the surface. As silica (SiO2) concentration in the glass goes down, surface area increases through dissolution of the glass surface. The pH of the solution in contact with the glass will greatly affect the corrosion process. A rapid pH increase will cause a rapid breakdown of the glass surface.

UNPROTECTED GLASS

During the World Trade Centre terrorist attack, numerous deaths and injuries resulted from the shards of glass, which flew up to 1/2 a mile away from the collapsed structure. An explosion or violent weather can catapult razor sharp glass up to 150 miles per hour. More than 50% of the injuries sustained were the result of flying glass from the blast. Neighbouring property damage to the interior of buildings was also costly, as shattered and fallen glass left dozens of buildings vulnerable to looters and water damage.

There are also safety issues. Because industrial factories, chemical refineries and food processing plants store and transport materials, workers, as well as emergency personnel who arrive on the scene are in danger of flying glass from accidental explosions. In addition, preventing the glass from breaking and feeding oxygen to a fire decreases the risk of fire damage.

Ordinary, unprotected glass is not hygienic. An alternative to using potentially hazardous chemical disinfectants is frequent and intensive washing with water and detergents. However, this approach is high-maintenance, labour-intensive and, if the use of detergents and water consumption is not controlled, cannot be considered as either green or hygienic.

It is difficult – sometimes impossible – to clean, keep clean and disinfect ordinary glass. Even when new, glass is microscopically rough with countless places for bacteria to hide and multiply. With exposure to alkalinity from industrial cleaning products and moisture, both liquid and vapour, the surface of unprotected glass becomes corroded and even rougher. Also, unprotected glass chemically reacts with contaminants, such as hard water deposits, which bond firmly to glass – making it even more difficult to clean, keep clean and disinfect.

ADVANCES IN GLASS PROTECTION

Glass usage in the country has been growing dramatically over the past decade. We all like our houses and buildings to open up to the environment and be flooded with natural light. Architects and decorators are innovatively using glass for a variety of applications from skylights to partitions, balustrades to staircases, and many-many more that make our surroundings look more spacious and beautiful. In this past, this has led to a tradeoff with safety, security, energy efficiency, and noise insulation.

Glass is more than functional-it is architectural. It gives the illusion of more space, increases natural lighting, and lends character to interior spaces. Architectural glass goes beyond architecture to become art, using textures, patterns, colours, and technique to define and highlight individual tastes. Glass can incorporate rice paper for a softer look, be mouth-blown for a more authentic, vintage feel, or be rolled for a three-dimensional look. It can be practical, like sleek, contemporary frosted glass that leaves no fingerprints behind. Glass can be patterned, laminated, frosted or acid-etched, offering varying degrees of translucency for privacy and design.

Glass can transform space with colour, light, and pattern. Used in doors as insets or panels, art glass allows light to penetrate interior spaces while capturing the eye with colours, patterns, and laminates that make an architectural statement.

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