The principle of determining specific surface area using gas adsorption is based on the interaction between gas molecules and solid surfaces. At ultra-low temperatures, under a given pressure, the sample (adsorbent) undergoes reversible physical adsorption of gas molecules (adsorbate), reaching an equilibrium state. By measuring this equilibrium adsorption amount, the specific surface area, pore volume, and pore size distribution can be determined through theoretical models.
Nitrogen and liquid nitrogen are commonly used as adsorbents due to their availability and good adsorption properties, making them ideal for surface area measurements. However, for microporous materials such as molecular sieves or activated carbon, nitrogen may not be the best choice. In such cases, gases like argon, carbon dioxide, or helium are preferred, especially when dealing with samples that have small pores or limited surface area, such as natural ores or organic materials.
Argon is particularly effective for micropore analysis because it is a non-polar, spherical molecule, which leads to more accurate pore size distribution results compared to nitrogen. Additionally, argon allows adsorption at higher P/P0 values, improving measurement accuracy. It also enables adsorption at 87K, which increases the efficiency of the test by reducing the time required to reach equilibrium.
However, argon has limitations: capillary condensation disappears in pores larger than 12 nm, so it’s only suitable for micropore testing. For activated carbon samples rich in micropores, carbon dioxide is often used at its freezing point (273K), offering faster diffusion and higher adsorption capacity. While CO₂ provides better performance in terms of saturation, its high vapor pressure limits its use to microporous ranges unless a high-pressure system is employed.
For materials with low surface area, such as metal powders or certain natural ores, helium is a suitable alternative. Its small molecular size and high diffusivity make it ideal for such applications.
Bethed Instrument Technology (Beijing) Co., Ltd. is a leading company in the development and production of nitrogen adsorption surface area instruments. As a high-tech enterprise recognized by Beijing Zhongguancun Science and Technology Park, it holds ten technical patents and is known for its advanced R&D capabilities. Since 2012, the company has been supported by the Ministry of Science and Technology as a technology-based SME, allowing it to develop next-generation instruments and continuously improve its product quality.
With a strong reputation among universities, research institutions, and industry leaders, Bethed has maintained a leading position in the market for years. The company has achieved ISO9001 certification and offers comprehensive sales, training, and service support. A dedicated team ensures that customers receive top-quality equipment and reliable after-sales service.
Its professional R&D team has developed cutting-edge designs, including integrated valve systems, modular assembly, and high-vacuum stability, ensuring performance that rivals imported high-end equipment. With 24-hour phone support and on-site service within 48 hours, and service centers in Beijing, Shanghai, and Guangzhou, Bethed guarantees the smooth operation of its customers' equipment.
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