How much do you know about weathering of glass

    Glass mildew is an industrial problem in the glass industry. Every spring and summer, due to the weather characteristics of high temperature and high humidity, the mildew of glass enters the peak. Therefore, how to do a good job in the mildew prevention of glass has become the primary task of many glass enterprises.
Reasons for glass mildewing: 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 the research, during the annealing process of soda lime glass, alkali ions will move to the glass surface, making it easy for ion exchange on the glass surface; For example, the glassy SiO2 on the surface can be hydrolyzed.
    Glass mildewing is generally 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 act as sodium carbonate and aggregate on the surface of the glass, forming soluble salts in the facial mask. Because of its strong hygroscopicity, it absorbs water and deliquesces, and finally forms alkali droplets. When the surrounding temperature and humidity change, the concentration of these droplets also changes. If 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 group of white alkali rich ions formed by the migration of sodium ions from the glass body and the reaction with air. The white particle swarm can be observed by scanning electron microscope.
    Moldy glass:
1. White fog and white spot: the slightest mildew on the 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 and are not treated in time, they will form a rainbow. At this time, the mildew only stays on the glass surface and does not corrode into the glass.
3. Sulfur change: the appearance characteristics of glass mildewing are the same as slight mildewing, but the alkaline mildewing components on the glass surface have corroded into the glass, which belongs to serious mildewing.
4. Paper printing: like sulfur change, mildew is on the outside and inside of the glass, which is seriously moldy.
    Identification and inspection methods of mildew:
    Visual appearance method is the most concise and feasible method. Under concentrated strong light, place the sample in reflected light and transmitted light to observe whether there are spots and fog 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 been moldy. If a few spots and mists are observed with the naked eye under concentrated strong light, they are mildly moldy. If under concentrated strong light, many spots and light mists can be observed with the naked eye, which are moderately moldy. If some spots and fogs are observed with the naked eye without concentrated beam irradiation, they are seriously moldy.

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