The principle of determining specific surface area using the gas adsorption method relies on the interaction between gas molecules and solid surfaces. At a given pressure, gas molecules (adsorbates) are reversibly adsorbed onto the surface of the sample (adsorbent) at ultra-low temperatures. This adsorption reaches an equilibrium, and the amount of gas adsorbed corresponds to the surface area, pore volume, and pore size distribution of the material. By measuring this equilibrium, these properties can be calculated using theoretical models.
Nitrogen and liquid nitrogen are commonly used as adsorbents due to their availability and good adsorption characteristics. However, for microporous materials like molecular sieves or activated carbon, and for samples with low surface area such as natural ores or organic materials, nitrogen may not provide accurate results. In such cases, other gases like argon, carbon dioxide, or helium may be more suitable.
Argon is particularly effective for micropore analysis because it can be stably adsorbed at 87K (liquid argon temperature) or 77K (liquid nitrogen temperature). It offers several advantages: first, argon is a non-polar, spherical molecule, which reduces unwanted interactions with pore walls, leading to more accurate pore size distribution. Second, argon allows adsorption at higher P/P0 values compared to nitrogen, improving measurement accuracy. Third, using argon at 87K helps reduce equilibration time, increasing testing efficiency.
However, argon is only suitable for microporous materials, as capillary condensation disappears when pore sizes exceed 12 nm. For activated carbon samples with many micropores, carbon dioxide is often preferred. It is adsorbed at 273K (freezing point), offering faster diffusion and better saturation capacity. Although the vapor pressure of COâ‚‚ is high (3485.3 kPa), making it unsuitable for larger pores unless high-pressure equipment is used, it remains ideal for microporous activated carbon testing.
For materials with small surface areas, such as metal powders or certain natural ores, helium is often used. It provides excellent adsorption characteristics and is well-suited for low-surface-area samples.
Bethed Instrument Technology (Beijing) Co., Ltd. has been a pioneer in the development of nitrogen adsorption-based specific surface area instruments. As a high-tech enterprise recognized by Beijing Zhongguancun Science and Technology Park, the company holds ten technical patents and leads the industry in innovation. Since 2012, it has received support from the Ministry of Science and Technology through the SME Technology Innovation Fund, enabling continuous R&D improvements and the launch of advanced instruments.
With over a decade of experience, Bethed has served hundreds of clients, including universities, research institutions, and leading companies. The company is ISO9001-certified and maintains a comprehensive sales, training, and service system. Its professional team ensures high-quality equipment and top-tier customer support.
The R&D team at Bethed focuses on cutting-edge designs, integrating modular assembly, high vacuum systems, and stable performance. Their products match or exceed imported high-end equipment in performance. With a strong after-sales network, including 24-hour phone support and 48-hour on-site service in major cities like Beijing, Shanghai, and Guangzhou, the company guarantees reliable operation of its instruments.
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