Silica, as an important inorganic material, is widely used in industries such as rubber, plastics, and coatings. With technological advancements, characterization techniques for silica have continuously developed, and analytical methods such as BET and XRD have become key tools for quality control. The following section analyzes in detail the current status of silica characterization techniques and the application of various analytical techniques from multiple perspectives.

Overview of Silica Characterization Techniques
Silica (precipitated hydrated silica) is a white, powdery amorphous silicate material, mainly composed of SiO₂. Its structure consists of randomly arranged tetrahedral units with silicon atoms at the center and oxygen atoms at the vertices. During particle aggregation, abundant capillary channels are formed, giving the material a large specific surface area and a well-developed porous structure.

The development of characterization techniques for precipitated silica has gone through the following important stages:
Early stage: Primarily relied on simple physical property tests (such as sieve residue, color, etc.) and chemical analyses (such as SiO₂ content determination).

Mid-term development: Introduced modern analytical techniques such as specific surface area determination (BET method) and X-ray diffraction (XRD).

Current stage: A comprehensive characterization system has been formed, including multiple techniques such as BET, XRD, FTIR, and SEM.

Application of BET Analysis in precipitated silica quality control
The BET (Bruno-Emmett-Teller) method is a technique for determining the specific surface area and pore size distribution of materials through gas adsorption, and it plays an important role in the quality control of precipitated silica.

BET Analysis Principles and Standards
According to GB/T 10722-2014 "Carbon Black - Determination of Total Surface Area and External Surface Area - Nitrogen Adsorption Method" and GB/T 19587-2017 "Determination of Specific Surface Area of Solid Substances by Gas Adsorption BET Method", the specific surface area of precipitated silica should be determined using the nitrogen adsorption method. This method calculates the specific surface area and pore size distribution by measuring the amount of nitrogen adsorbed on the sample surface.

Pretreatment Condition Selection: Sample pretreatment is a crucial step in BET analysis, aiming to thoroughly remove adsorbed impurity molecules (such as moisture and gases) from the sample surface and pores. Silica contains various types of hydroxyl groups (isolated free hydroxyl, associated hydroxyl, and twinned hydroxyl), which determine the surface properties of the material; therefore, vacuum degassing is essential.

Quality Control Applications:
**Specific Surface Area Control:** The specific surface area of conventional silica is typically between 100 and 400 m²/g. The BET method can accurately determine this key parameter.
**Pore Size Distribution Analysis:** Silica's pore size distribution is predominantly mesopores of 2–50 nm. The BET method can accurately characterize this characteristic.
**Production Process Monitoring:** Changes in specific surface area and pore size distribution allow for real-time monitoring of the stability of the silica production process.