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First of all, Class A desiccant, i.e. 3A molecular sieve, according to the static water adsorption capacity of 16.5% (RH11.3%, 25 ℃) in JC/T2072-2011, this material is characterized by large deep adsorption capacity under low humidity conditions, and its deep effective adsorption capacity has successfully defeated all inert desiccant materials. Defeated inert desiccant materials include silica gel, activated alumina, aluminosilicate, pure clay desiccant, etc. These desiccants do not have the characteristics of good selectivity, large effective adsorption capacity, and physical and chemical stability of 3A molecular sieve under low humidity conditions, which has formed a consensus in the industry. 3A molecular sieve is recognized as the best desiccant choice for insulating glass in the world.

The second is Class B desiccant, which is defined in the original standard as a spherical drying material with attapulgite as the main material. However, according to the situation of market sampling inspection, in recent years, there have been many manufacturers who have exploited the shortcomings of the desiccant standard to adulterate and falsify it. These manufacturers mainly focus on the requirements of no component identification and physical and chemical properties in the standard, and add one or several substances with other desiccant properties to the attapulgite. If the method specified in the standard is used, the results are in conformity with the requirements. We take samples from the market and test the content of some elements and CaCl2 in the samples according to X-ray fluorescence analysis and T/SDG 002-2020 Test Method for Detection of Dopants (Calcium Chloride, Calcium Oxide) in Desiccants for Insulating Glass.

The content of some elements in desiccant samples in Table 1 is obtained by X-ray fluorescence spectrometer. From Table 1, it can be seen that the highest content of the three samples is Si and Ca, followed by Al and Cl. In the standard, type B desiccant is a kind of hydrous magnesium-rich aluminosilicate mineral with layered chain structure, and the ideal molecular formula is (Mg, Al, Fe) 5Si8O20 (OH) 2 (OH2) 4 ・ 4H2O. According to the composition of the sample and the composition of attapulgite, there is a large deviation.

According to the standard preparation requirements: attapulgite is the main material, and generally speaking, attapulgite should be the main active ingredient. But in fact, although attapulgite has a certain drying effect, its deep drying ability in low humidity environment is weak, and the drying ability of attapulgite is much lower than that of silica gel and activated alumina, and even greater than that of 3A molecular sieve. In the standard technical indicators, when the temperature is 25 ℃± 2 ℃ and the relative humidity is 11.3%, the static water adsorption capacity of 3A molecular sieve should reach 16.5% of its own gravity; The requirement for class B desiccant is that class B desiccant should reach 11% of its own weight under the same conditions. Although this value is lower than 3A molecular sieve, if it is pure attapulgite desiccant, it is almost impossible to reach this adsorption capacity. It can not be found from the relevant literature and practice. However, according to the calcium chloride content in the desiccant samples in Table 2, it can be judged that the three samples are all doped with 9% to 11% calcium chloride. As a common desiccant, calcium chloride doped with it has become the main ingredient of Class B desiccant.