Preparation method of high purity mullite material

Source: | Author:ChangXing Refractory | Published time: 1561 days ago | 902 Views | Share:

1 Sol-Gel method (sol-gel method)

Sol-Gel method (sol-gel method) takes metal alkoxide or inorganic substance as the precursor of material preparation. Firstly, raw materials are uniformly mixed, then hydrolysis and condensation chemical reactions are carried out to form a stable and transparent sol system solution in the solution. Finally, after the sol is aged and slowly polymerized among colloidal particles, a multi-dimensional network structure gel is formed, and the multi-dimensional network structure is filled with a non-flowing solvent, and finally a gel is formed. Then, the gel is dried to remove organic substances, and inorganic functional materials can be prepared.

Synthesized mullite ceramic functional materials with aluminum powder, TEOS and HCl as raw materials by Sol-Gel method. They studied the relationship between sintering density, microwave dielectric properties, sintering aid MgO and testing frequency of mullite ceramic materials. The results show that the sintering conditions have great influence on the density and dielectric constant of mullite ceramic materials, and the hot pressing temperature has the greatest influence on the density and complex dielectric constant of mullite ceramic materials. With the addition of MgO, the real part and imaginary part of the complex dielectric constant of mullite ceramic materials are also increased, and the complex dielectric constant has no obvious dispersion effect. Studied the preparation of xerogel ultrafine powder by using TEOS and Al (NO3) 3 9H2O as raw materials, using the Sol-Gel method, replacing the solvent with alcohol gel, and using CO2 supercritical fluid to extract and dry the alcohol gel at low temperature. After being heated at 1150℃ for 2 hours, it is easy to prepare high-purity mullite ultrafine powder. The particle size of mullite powder is 5~15nm, its specific surface is as high as 376m2/g, and the particles are evenly distributed, showing short needle shape or short column shape.
Zhang Xintao used aluminum nitrate and tetraethoxysilane as raw materials to prepare mullite powder functional materials by Sol-Gel method. After heat treatment at 1300℃ for 2 hours, the prepared powder mullite materials showed excellent properties, such as low dielectric properties. The relative dielectric loss and dielectric constant increased with the increase of mullite content, and the dielectric loss decreased with the increase of sintering temperature.

2 hydrothermal crystallization method

Hydrothermal crystallization method is usually in a closed special reactor container, such as autoclave and other special equipment, using water solution as the medium of hydrothermal reaction, heating the reaction generator, creating a high-pressure and high-temperature reaction environment, so that substances which are difficult to dissolve or insoluble under general conditions are dissolved, and highly dispersed nano-crystal nuclei are formed by recrystallization. This method is called hydrothermal crystallization method. Synthesized composite nanocrystalline materials with mullite as the main crystalline phase by hydrothermal crystallization method using natural minerals. Researchers have heated the composite nanocrystals at 500℃~1005℃, and found that the composite nanocrystals have very good chemical and thermal stability. The results of TPR test show that the composite material has structural effect on the carrier, and it consumes different hydrogen with the different crystal surface structure.

3 hydrolytic precipitation method

Hydrolysis precipitation method refers to adding precipitant to clear solution to obtain precipitate, then calcining the precipitate at high temperature to decompose it, and finally obtaining powder material. Hydrolysis precipitation method is divided into coprecipitation method and single-phase precipitation method. Co-precipitation method is to add precipitant into solution to form precipitation; The latter firstly dissolves the precipitant in the solution, then changes the pH value of the solution through the decomposition of the precipitant, and finally forms a precipitate. Researcher Zhang Zhijie used Al13 and activated silicic acid as refractory raw materials, and firstly synthesized mullite precursor by hydrolysis precipitation method. The precursor was heat treated at less than 900℃ for about 1 hour, forming mullite crystal phase. The temperature of mullite synthesized by hydrolysis precipitation method is lower, which reduces the preparation difficulty and has the advantage of low temperature synthesis.

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