The surface of freshly produced float glass is highly reactive. While the glass is being stored or transported, it may react with humidity that has penetrated the spaces between the layers of glass, which can lead to highly adhesive blotches of corrosion. If the corrosion is distinctive, the glass cannot be processed any further. The level of corrosion depends on the humidity, temperature, conditions of storage and transport and the quality of the glass (composition, hydrolytic class etc). Furthermore, corrosion in the early stages is not recognisable to the eye and only becomes visible when the glass is processed further (eg by low-E coating, silvering or tempering). In the Chemetall development laboratory, corrosion-protected sheets were compared to non-protected sheets as to any reactions following application of a thin film coating (figure 1). In stress tests, the untreated sheets showed signs of flaking much sooner than sheets that were given an initial protective coating. The disturbance in film build-up that was responsible for this can, during further processing into insulation glass, also have a negative effect on the sealant on the glass surface.
Much can be done to protect glass from corrosion but it is not possible to exclude it completely. While corrosion in the initial phases can be removed using suitable polishing agents, visibly corroded glass can no longer be repaired to a reasonable standard. As float glass available on the market can vary, (eg they can possess various hydrolytic qualities, or the year of manufacture may simply be different), polishing, in order to clean the surface of the glass is surely a reasonable step to take prior to further processing of the glass into a higher quality product. It must be pointed out once more that due to initial corrosion, defects on the glass surface will be increased, which may not become visible for some time after the end product has been completed unless silver layers start to flake off, colour defects of low-E glass or adhesion problems with insulating glass occur. Chemetall’s experience shows that corrosion can be reliably held back using tailor-made, anti-corrosive interleavants. However, one must remember that the corrosion protection must be totally washable, leaving no residue, prior to further treatment. The same applies to all other auxiliary agents such as cutting fluids, separating agents or coolants and of course, contamination of the glass surface due to dust, fingerprints, roller prints, gloves etc. This is no longer possible using just water alone; special detergent, used for treating glass is also required. It must also be possible to wash this off completely.
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This article has been published in the GLASS WORLDWIDE - issue sixty one 2015.
Albemarle Corporation, headquartered in Baton Rouge, Louisiana, is a premier specialty chemicals company with leading positions in attractive end markets around the world. With a broad customer reach and diverse end markets, Albemarle develops, manufactures and markets technologically advanced and high value added products, including lithium and lithium compounds, bromine and bromine derivatives, catalysts and surface treatment chemistries used in a wide range of applications including consumer electronics, flame retardants, metal processing, plastics, contemporary and alternative transportation vehicles, refining, pharmaceuticals, agriculture, construction and custom chemistry services. Albemarle is focused on delivering differentiated, performance-based technologies that deliver innovative and sustainable solutions to its customers. Albemarle employs approximately 6,900 people and serves customers in approximately 100 countries. Albemarle regularly posts information to www.albemarle.com, including notification of events, news, financial performance, investor presentations and webcasts, Regulation G reconciliations, SEC filings and other information regarding Albemarle, its businesses and the markets it serves.
Chemetall Surface Treatment, a business unit of Albemarle Corporation, is a leading global supplier of specialty chemicals with a focus on processes for the surface treatment of metals and plastics. To learn more, visit www.chemetall.com.
Matt Juneau, 225-388-7322, Matt.Juneau@albemarle.com
Ashley Mendoza, (225) 388-7137, Ashley.Mendoza@albemarle.com
VP Global Marketing Communications
Phone: +1 908 508 2107
Chemetall US, Inc.
675 Central Avenue
New Providence, NJ 07974
Europe, South America, South Africa
Global Marketing Communications Manager
Phone: +49 69 7165 2308
Trakehner Str. 3
D-60487 Frankfurt a. Main
Global Marketing Communications Manager
Phone: +86 21 581 209 296 105
Shanghai Chemetall Co.
Building 1, 316 Kang Hua Road
Kang Qiao Industrial Zone