Glass disease
As the glass corrosion, rust glass, glass fire or glass Glaspest disease the structural change and associated weathering of the surface of glass is referred to by a variety of chemical and physical influences.
Description
From glass corrosion affected glasses show in the case of transparent objects haziness, which is caused by microscopic thin roughening of the surface. Glasses that were decades or centuries in the ground, show a typical dirty rainbow colored surface.
Explanation
The glass corrosion begins with the dissolution of oxides of various elements, such as the sodium, potassium, calcium, barium, or boron, the physical properties change to the affected area of the material. It forms a gel layer, which further reacts with ions of the substance into an acting veil stick coating. This impairs the transparency of the surface, leading to microscopic cracks.
Influence of glass composition
The corrosion can be reduced by the addition of certain oxides in glass manufacture. Commonly used are alumina, zirconia, moderate concentrations of boron trioxide (see borosilicate glass) or high concentrations of silica. Excessive Boroxidgehalte reduce the resistance to corrosion. Special phosphate or borosilicate glasses corrode very strong due to phase separation phenomena in the glass, which is used technically in the Vycor process.
Influence of the applied substance
In acidic medium, an exchange of cations from the glass surface against native of oxonium ions protons takes place. If the resulting salts washed away (water excess), is formed on the glass, a gel layer that slows down further corrosion. In the case of water deficiency caused salts that deposit on the glass. In neutral medium, the same exchange of cations with hydrogen ions takes place, however, the leached cations lead to an alkalinization of the environment. In an alkaline medium, constituents of the glass network (SiO - ) are replaced with OH groups, whereby the glass network is reduced. In the case of water deficiency, this process accelerated. The transport and storage of glasses should therefore be done in a slightly acidic environment.
A low pH and low salt content of the liquid and high temperature accelerate the corrosion by the acidic milieu in easily. To soften the water in the dishwasher or acid rain of glass windows provides a higher dissolution of minerals from the surface. Accordingly, various standardized methods for quantifying the glass corrosion, including tests to determine the chemical resistance of glass exist with respect to water (DIN 12111 and ISO 719 with division into hydrolytic classes ), acids (DIN 12116 ), bases (DIN 52322 and ISO 695 ), and the weather.
Examples
- The Würzburg Fraunhofer Institute for Silicate Research conducted in 1993 by a literature study on corrosion mechanisms of historic stained glass windows. The researchers discovered that the window glasses because of high levels of potassium and calcium have low chemical resistance against environmental influences from the 11th to the 16th century. A silica content below 66 % thus causes a higher weathering. To protect against further destruction of monuments of glass a corrosion protection system was developed based on organically modified silicates, the so-called ORMOCER.
- In 2001, the Association of German glassblower eV reported on the destruction of an existing glass pipe in a chemical plant. This caused the slow corrosion of the glass material by passing therethrough along with hydrochloric acid contained in the solution is abrasive glass particles the destruction of the line.
Others
The manufacturers of dishwashing detergents use the terms glass rust and corrosion of glass like to describe supposedly new improved materials in their products. The glass corrosion in the dishwasher in fact depends primarily on the quality of the glass material used. Further damage caused often by purely mechanical effects, such as rubbing the glasses or contact with parts of the dishwasher.
Similar phenomena
- Glass Mushroom - A fungus on glass, which can be removed.