The quality inspection standards of sintered mullite mainly include the following aspects:

I. Chemical composition analysis

Main components: The main components of sintered mullite are ALO and SiO₂, and usually the ALO content is between 60% and 75%. According to the binary phase diagram of Al₂O₃-SiO₂ system, the composition of mullite is about 79% ALO and 21% SiO.

Impurity content: Impurities such as Fe₂O₃, TiO₂, KO and Na₂O will affect the properties of mullite. For example, KO and Na₂O can inhibit the formation of mullite and increase the glass phase content. The impurity content of sintered mullite usually requires the following:

Fe₂O₃ ≤ 0.50%

TiO₂ ≤ 0.50%

K₂O ≤ 0.30%

Na₂O ≤ 0.30%

II. Physical performance testing

Bulk density: The bulk density of sintered mullite is usually ≥ 2.80 g/cm. The higher the bulk density, the better the compactness of the material and the stronger the corrosion resistance.

Apparent porosity: Apparent porosity is an important index to measure the compactness of materials, which is usually required to be ≤3.0%. Low porosity is helpful to improve the corrosion resistance and thermal shock stability of materials.

Water absorption: Water absorption should be ≤1.50%, and low water absorption is helpful to improve the stability of materials in wet environment.

III. Fire resistance test

Fire resistance: The fire resistance of sintered mullite is usually ≥1700℃. Refractory degree is a key index to measure the stability of materials in high temperature environment.

Softening temperature under load: Softening temperature under load refers to the temperature at which materials begin to deform under a certain load, which is usually required to be ≥1700℃.

IV. Microstructure analysis

Mullite phase content: Mullite phase content is one of the key indexes to measure the quality of sintered mullite. Usually, the content of mullite phase is required to be ≥55%, and the content of high-purity sintered mullite mullite phase can reach 78%.

Grain size: The smaller the grain size, the higher the compactness and strength of the material. The average particle size (D50) of high-purity mullite raw powder should be ≤ 3 μ m..

V. Testing of mechanical properties

Compressive strength: compressive strength is an important index to measure the mechanical properties of materials in high temperature environment. Generally, universal testing machine is used for testing, and the sample size is φ20mm×20mm.

Thermal shock resistance: Thermal shock resistance refers to the stability of materials when the temperature changes rapidly. Usually, the sample is heated to a certain temperature and then cooled quickly.

VI. Other testing items

PH value: the pH value of sintered mullite is usually between 6.5 and 7.5.

Thermal expansion coefficient: The thermal expansion coefficient is an index to measure the volume change of a material when the temperature changes, and it is usually required to be (4.5 ~ 6.5) × 10/k at room temperature to 1200℃.

Through the above detection standards, the quality and performance of sintered mullite can be comprehensively evaluated to ensure its reliability and stability in high temperature environment.