How to identify moldy glass?

Glass mildew is a difficult problem in the glass industry. In spring and summer every year, due to the high temperature and high humidity weather characteristics, glass mildew has entered the peak period. Therefore, how to do a good job in glass anti mildew work has become the primary task of many glass enterprises.

1、 Causes of glass mildew

The glass used in daily life is mostly made of quartz sand (SiO2), soda ash (Na2CO3), limestone (CaCO3) and feldspar. Among them, SiO2 (about 72%), Na2O (about 15%) and Cao (about 9%) are called soda lime glass, which is widely used because of its low cost.

According to research, alkali ions will move to the glass surface during the annealing process of soda lime glass, which makes it easy to carry out ion exchange on the glass surface; for example, the glass state SiO2 on the surface can be hydrolyzed.

Therefore, when soda lime glass is stored in a humid environment, water or moisture will be absorbed from the surface of the glass and gradually diffuse into the glass. When the soluble sodium silicate (Na2SiO3) in the surface layer is hydrolyzed, it will contact again H2CO3 (H2O) and carbon dioxide (CO2) form H2CO3, which produces less acidic than silicic acid (H4SiO4). If the saturated orthosilicate (H4SiO4) solution is placed for a long time, there will be amorphous silicon dioxide (SiO2) precipitated, and the color is milky white, with colloidal particles, precipitates or gels.

2、 Glass mildew can be divided into five stages

1. Initially, water or moisture is adsorbed on the glass surface.

2. Then, water or moisture diffuses into the glass.

3. The soluble silicate in the surface layer is hydrolyzed and destroyed. First, sodium silicate and potassium silicate are hydrolyzed and destroyed. Caustic soda (NaOH) was formed and SiO2 was separated.

4. The separated SiO2 generates silica gel and forms protective film on the surface of glass, which prevents further erosion.

5, the caustic soda formed by hydrolysis and carbon dioxide in the air react to form sodium carbonate and aggregate on the surface of the glass, forming soluble salts in the surface film. Because of its strong hygroscopicity, it absorbs water and deliquesces, and finally forms alkali droplets. When the ambient temperature and humidity change, the concentration of these droplets also changes. If the concentrated alkali droplets and glass are in contact for a long time, the gel silica film can be dissolved in part, resulting in serious local corrosion and formation of spots on the glass surface. This is a white alkali rich ion group formed by sodium ions migrating from the glass body and reacting with air. The white particles could be observed by SEM.

3、 Mould phenomenon of glass

1. White fog, white spot: the mildest mildew on glass surface due to storage time, air humidity or glass quality problems.

2. Rainbow: when white fog and white spots appear for a long time without timely treatment, they will form a rainbow. At this time, the mildew still stays on the glass surface and does not corrode into the glass.

3. Sulfur change: the appearance of moldy glass is the same as that of mildly moldy glass, but the basic moldy components on the glass surface have corroded into the glass, which is seriously moldy.

4. Paper printing: the same as sulfur change, moldy on the outside and inside of glass, is seriously moldy.

4、 Identification and inspection methods of mildew

The visual appearance method is the most simple and feasible method. Under the concentrated strong light, the sample is placed in the reflected and transmitted light to observe whether there are spots and fogs on the glass surface. These spots and mists cannot be wiped off with cloth or water. The glass with the above phenomenon indicates that the sample has moldy. If a few spots and mist are observed by naked eyes under concentrated strong light, it is mildly moldy. If in the concentrated strong light, the naked eye can observe a lot of spots and mist, which is moderate mildew. If some spots and fogs are observed by naked eyes without concentrated beam irradiation, they are seriously moldy.