Glass container “alkali separation “ and prevention
The sales of glass containers (bottles and jars) will have off-season and peak season, so there will be some product overstock. During the product inventory period, due to the glass container itself and the condition of the product stock, the glass products in stock will be “foggy” and “moldy”, causing great economic loss. The foggy and moldy of glass containers also called ” alkali separation “. Glass containers will lose luster, lose transparency, with white fog, white spot and other phenomena after being foggy and moldy.
1. Analysis on the reason of glass “alkali separation”
Glass “alkali separation” is a chemical reaction caused by too long storage time of glass container products or wet weather when the products are stored.
During storage of glass containers(bottles and jars), water or moisture in the air is adsorbed on the surface of the glass containers. The soluble silicate in the surface layer of the glass container is hydrolyzed and destroyed. Firstly, sodium silicate and potassium silicate are hydrolyzed and destroyed. The caustic soda (NaOH) is formed and SiO2 is separated. The separated SiO2 forms a silicon-oxygen gel that forms a protective film on the surface of the glass container, which prevents further erosion. With the increase of the storage time of the glass container, caustic soda (NaOH) formed by hydrolysis on the surface of the glass container reacts with CO2 in the air to form sodium carbonate (Na2CO3), which accumulates on the surface of the glass container and forms.
Due to the strong hygroscopicity of sodium carbonate, it absorbs water and deliquesces, finally forming lye droplets. With the ambient temperature and humidity change, the concentration of these droplets changes accordingly. As the ambient temperature and humidity change, so does the concentration of these droplets. The sodium carbonate concentrate will gradually form fine crystals on the surface of the glass container, producing fog spots. The fog marks on the surface of such glass containers are also called “alkali separation”. In the early stage, Na2CO3 crystals can be removed from the surface by simple cleaning, at this stage, the glass container body has not been eroded.
If the concentrated lye droplets come into contact with the glass container for a long time, the gelatinous silicon-oxygen film may be partially dissolved in it, causing severe local erosion on the surface of the glass container and formation of spots. This is the migration of sodium ions from the glass body and the reaction with the air to create a white base rich ion group. At the same time, with the reaction process of sodium ion and water vapor (hydrating proton) in the glass container, Na OH and Na2CO3 on the surface of the glass container will gradually increase, and the PH value of the surface will become more alkaline. Sodium and calcium ions precipitate when the silicon-oxygen bond in the glass is damaged. In this case, the surface of the glass container starts to become rough and white spots appear, making it difficult to clean.
2.The prevention of glass “alkali separation ”
Alkali separation is a common problem in sodium calcium silicate glass industry, which is caused by the structure of glass itself. According to the above analysis on the formation reason of “alkali separation” of glass container, moisture-proof should be taken as the main methods for “alkali separation” of glass container, and appropriate adjustment should be made in improving the chemical stability of glass and enhancing the water resistance of glass.
In the production process of glass container (bottle), the traditional melting method is used to prepare glass liquid, and soda is selected as flux, resulting in the glass container (bottle) products are easy to produce “alkali separation” under certain conditions. In particular, stock products must be stored in a well-ventilated warehouse.
For the prevention of alkali separation of glass containers, moisture-proof products should be taken as the main method, and the composition of glass should be properly adjusted to improve the chemical stability of glass containers and enhance the water resistance of glass containers.
Post time: Jun-10-2020