What are the color-changing silica gels and the cause of discoloration?

Color-changing desiccant: the main component is cobalt chloride, which is very toxic, but at the same time it has a very strong adsorption force for water vapor in the air. What is interesting is that the blue transparent silica gel before moisture absorption gradually reaches saturation with the moisture absorption Degree, it will turn into light red. There are currently three color-changing silica gel desiccants: blue silica gel desiccant, cobalt-free orange silica gel desiccant, and cobalt-free blue desiccant.

Discoloration principle of blue silica gel desiccant: CoCl2 (blue) + 6H2O (light red) = CoCl2·6H2O; anhydrous cobalt dichloride is transparent blue, and becomes light red irregular crystals after absorbing water. When heated, It can be decomposed into cobalt chloride and reused as a silica gel desiccant for packaging. It is widely used in precision instruments, leather, shoes, clothing, food, medicine and household appliances.

Cobalt-free orange silica gel desiccant discoloration principle: methyl violet changes in color due to changes in pH (acid-base), while cobalt-free orange silica gel desiccant uses a pH range of 0.13~0.5 to change from orange The principle of dark green, but the same function, with strong moisture absorption capacity, is also a recycled environmentally friendly desiccant material.

The discoloration principle of the cobalt-free blue silica gel desiccant: Congo red itself is used as an acid-base indicator, the discoloration range is 3.5~5.2, the basic state is red, and the acid state is blue-violet. At present, this kind of desiccant is rarely used. Yellow changes to red.

On the market, quicklime desiccant is mainly used to cross-link polypropylene sodium with stable chemical properties. At 25 degrees Celsius, the relative humidity is 80%, and the adsorption capacity of water vapor can reach 100% of the product’s adsorption performance, which is the water absorption rate of ordinary silica gel desiccant. 10-20 times, due to non-chemical processing composition, environmental protection and cost are more advantages than silica gel desiccant, the content of heavy metals is lower than the international environmental protection standard, the best choice to meet the market demand.