Main indicators of pseudo boehmite

Pseudoboehmite has a unique structure and therefore exhibits unique physicochemical properties, which differ from other alumina hydrates in the following aspects.

1. Specific surface area and pore volume

The water content in the layered structure of pseudo boehmite can reach up to 30%, resulting in the formation of many internal pores and surface areas during its dehydration process. The following table lists the changes in specific surface area of pseudo boehmite with different crystallinity.

It can be seen that with the increase of crystallinity, the specific surface area of pseudo boehmite significantly decreases. The main reason is that the crystallinity increases, the layer structure water decreases, and the internal pores and specific surface area decrease after dehydration. Moreover, when pseudo boehmite is dried at 120 ℃ and 150 ℃, there is a significant difference in specific surface area. When dried at high temperature, the specific surface area decreases. Therefore, by adjusting the surface properties of pseudo boehmite grains and improving dehydration conditions, significant changes can be made to the pore volume and structure of pseudo boehmite.

2. Thermal stability

Pseudo boehmite has high thermal stability, and its DTA (differential thermal analysis) curve exhibits endothermic peaks between 400-450 ℃. However, the DTA curve of general gibbsite exhibits endothermic peaks around 200 ℃. After dehydration, the specific surface area of pseudo boehmite further increases, which is about 100mL/g larger than that of catalysts made of gibbsite.

3. Gel solubility

Pseudoboehmite is widely used in the catalyst industry, and more importantly, it has another characteristic - gel solubility. Pseudo boehmite has good adhesive solubility, and the adhesive solubility of carbonization products is generally greater than 95%, while the adhesive solubility of SB (pseudo boehmite) powder produced by alcohol aluminum method can reach 98%.

When a small amount of nitric acid is added to the pseudo boehmite dispersion, the following reaction occurs:

The generated Al3+ionizes in water and coordinates with OH to form a colloidal core. The colloidal core selectively adsorbs the positively charged H+, while the negatively charged NO3- dissociates around the colloidal core due to attraction and diffusion, forming a double electron layer structure. Only a small amount of HNO3 is enough to make all the gelled filter cakes gelatinize and become a very fluid sol.