Glass container "alkali precipitation" and prevention

In the process of production and operation of glass container (bottle and jar) enterprises, there will be weak and prosperous time for the sales of products. Beer bottles fall in winter and liquor bottles fall in summer as our customers' demand falls. However, glass container manufacturers cannot stop production due to the continuity of glass production and the particularity of the glass melting process, so there will be some stocks of products. During the product inventory period, due to the glass container itself and the conditions of the products , the inventory glass containers will be "foggy and moldy". cause great economic losses. This kind of glass container is foggy and moldy, also known as "alkali precipitation". The "fog" of glass containers are problems during storage and transportation. The glass container will lose its luster, transparency and show white fog and white spots when "alkali precipitation" happens.

Analysis of the Causes of the Formation of "Alkali Precipitation" in Glass

        Glass "alkali precipitation" is a chemical reaction caused by the long storage time of the glass container or the wet weather when the product is stored. During the storage of glass containers, the surface of the glass container is adsorbed due to water or moisture in the air. Soluble silicates in the surface of glass containers are hydrolyzed and destroyed. The first is that sodium silicate and potassium silicate are hydrolyzed and destroyed. Caustic soda (NaOH) is formed and SiO2 is separated. The separated SiO2 forms a silica gel, which forms a protective film on the surface of the glass container, which prevents further erosion. As the storage time of the glass container increases, the caustic soda (NaOH) attached to the surface of the glass container formed by hydrolysis reacts with CO2 in the air to form sodium carbonate (Na2CO3), which accumulates on the surface of the glass container and forms a film on the surface.    Due to the strong hygroscopicity of sodium carbonate, it absorbs moisture and deliquesces, and finally forms small droplets of lye. When the surrounding temperature and humidity change, the concentration of these droplets also changes. Sodium carbonate concentrate will gradually form fine crystals on the surface of glass containers, resulting in fog spots. This kind of fog spot on the surface of glass container is also called "alkali precipitation". In the early stage, simple cleaning can remove the Na2CO3 crystals on the surface. At this stage, the body of the glass container has not been eroded.

        If the concentrated lye droplets are in contact with the glass container for a long time, the gelatinous silicon oxide film may be partially dissolved therein, and the surface of the glass container may undergo severe erosion and form spots. This is a white alkali-rich ion group formed by the migration of sodium ions from the glass body and the reaction with air. At the same time, with the reaction process of sodium ions and water vapor (hydrated protons) in the glass container, the NaOH and Na2CO3 on the surface of the glass container will gradually increase, and the pH value of the surface will become more alkaline. When the silicon-oxygen bond in the glass is damaged, sodium ions and calcium ions are precipitated. In this case, the surface of the glass container begins to become rough and white spots appear, and the glass container is difficult to clean.

Glass "alkali precipitation" prevention

        "Alkali precipitation" is a common problem in the soda lime silica glass industry, which is caused by the structure of the glass itself. According to the above analysis of the causes of the formation of "alkali precipitation" in glass containers, the main means of "alkali precipitation" in glass containers should be moisture-proof, and at the same time Appropriate adjustments should be made to improve the chemical stability of the glass and enhance the hydrolytic resistance of the glass.

1.    Strengthen the rain-proof and moisture-proof measures for stock glass containers , add dehumidifiers in the stock warehouse, reduce humidity, avoid temperature increase, and cut off the conditions for "alkali precipitation" of glass from the external environment

2.    Change the packaging method. When the product comes out of the production line, only stacking and packaging are carried out. After the glass container is cooled down, plastic bundling is carried out.

3.    Properly adjust the glass compositions to improve the hydrolytic resistance of the glass. Borosilicate glass is more hydrolytic resistant and also heat resistant which is a better packaging material.