The principle of determining specific surface area using the gas adsorption method relies on the adsorption behavior of gases on solid surfaces. At a given pressure, gas molecules (adsorbates) are reversibly adsorbed onto the surface of the sample (adsorbent) at ultra-low temperatures. This process reaches an equilibrium, where a certain amount of gas is adsorbed depending on the pressure. By measuring this equilibrium adsorption amount, the specific surface area, pore volume, and pore size distribution of the sample can be calculated using theoretical models.
High-purity nitrogen and liquid nitrogen are commonly used as adsorbents due to their availability and good reversible adsorption properties. They are widely applied for surface area measurements. However, for microporous samples like molecular sieves or activated carbon, or for materials with low surface area such as natural ores and organic compounds, nitrogen may not provide accurate results. In these cases, alternative gases like argon, carbon dioxide, or helium are preferred.
Argon is particularly suitable for micropore analysis because it can stably adsorb on material surfaces at 87K (liquid argon) or 77K (liquid nitrogen). It is widely used in testing molecular sieve samples. The advantages include:
1. Argon is a non-polar, spherical molecule, which leads to more accurate micropore distribution compared to nitrogen, which has a quadrupole moment and may cause characteristic adsorption that complicates pore size identification.
2. For a given pore width, nitrogen requires a lower P/P0 ratio than argon, so using argon allows adsorption at higher P/P0 values, improving measurement accuracy.
3. Argon adsorption at 87K increases the cold bath temperature, reducing equilibration time and enhancing testing efficiency.
However, argon adsorption is limited to pores smaller than 12 nm, as capillary condensation disappears beyond this size. For activated carbon samples rich in micropores, carbon dioxide is often used as the adsorbate at its freezing point (273K), which significantly increases the diffusion rate. This makes it ideal for measuring saturated adsorption capacity. However, the high vapor pressure of COâ‚‚ at its freezing point (3485.3 kPa) limits its use to microporous ranges unless high-pressure equipment is employed.
For materials with low surface area, such as metal powders, organic materials, or certain natural ores, helium is a suitable choice due to its small molecular size and high diffusivity.
Bethed Instrument Technology (Beijing) Co., Ltd. is one of the pioneers in the development and production of nitrogen adsorption-specific surface area instruments. As a high-tech enterprise recognized by Beijing Zhongguancun Science and Technology Park, the company holds ten technical patents and is the leader in patented technology within the industry. With strong R&D capabilities, many of its patents are designed to enhance the accuracy and stability of its instruments.
In 2012, the company was selected by the Ministry of Science and Technology as a technology-based SME innovation fund recipient, allowing significant investment in research and development. This led to the launch of a new generation of instruments, propelling the company into a new stage of growth.
With hundreds of satisfied clients, including universities, research institutions, and well-known companies, Bethed has maintained a leading position in instrument sales for years. The company achieved ISO9001 certification in 2009, establishing a comprehensive sales, training, and service system. A dedicated team ensures top-quality equipment and first-class support for customers.
The company's professional R&D team has been working for over a year, incorporating international frontier design concepts, integrated valve and pipeline systems, full modular assembly, and high vacuum stability. Their instruments offer performance comparable to imported high-end equipment.
A robust after-sales service system provides 24-hour phone consultation, 48-hour on-site service, and local service centers in Beijing, Shanghai, and Guangzhou, ensuring the smooth operation of customer equipment.
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