In many fields such as materials science, geological engineering, petroleum extraction, and biomedicine, the performance of materials often depends not only on their chemical composition, but also on their internal microstructure. And porosity - the percentage of the internal pore volume of the material to the total volume - is the core parameter that describes this microstructure. It is like a key that unlocks many secrets about the strength, permeability, adsorption, and thermal insulation properties of materials. Porosity analysis is the "perspective eye" that provides insight into the internal world of materials, providing us with scientific basis for understanding and optimizing material properties.
Pores are not always defects in materials, and in many cases, they are even crucial for materials to achieve specific functions. In petroleum geology, the porosity of rocks directly determines their oil storage capacity and is a core indicator for evaluating the abundance of oil and gas reservoirs. In the field of catalysts, the large specific surface area of porous materials (provided by pores) is the site for efficient catalytic reactions. In building insulation materials, a closed pore network is the key to blocking heat conduction and achieving insulation. In biomedical materials such as artificial bone, appropriate pore structure is beneficial for cell growth and tissue regeneration. Therefore, accurate determination of porosity, understanding of pore size distribution, morphology, and connectivity are of crucial guiding significance for the design, preparation, and application of materials.
Porosity analysisMultiple mature technologies have been developed to meet the measurement needs of different materials and scales.
Gas adsorption method (BET): This is the "gold standard" for measuring micropores and mesopores (diameter<50 nanometers). By allowing gas molecules (such as nitrogen) to undergo single-layer or even multi-layer adsorption on the surface of materials at low temperatures (usually liquid nitrogen temperature), the specific surface area and pore size distribution of the material can be calculated based on the relationship between adsorption capacity and pressure. This method is crucial for the characterization of porous materials such as activated carbon and molecular sieves.
Mercury injection method: This method utilizes the characteristic of mercury not wetting most solid surfaces to inject mercury into the pores of the material under external pressure. Based on the relationship between the volume of mercury injected and pressure (Washburn equation), the pore size distribution can be calculated, which is particularly suitable for measuring large pores (diameter>50 nanometers) and total porosity. However, due to the use of toxic mercury, extra caution is required during operation.
Gas expansion method (helium specific gravity meter method): By utilizing the characteristics of helium molecules being extremely small and able to penetrate almost all connected pores, the skeleton volume of the material can be accurately obtained by measuring the volume of helium gas displaced from the sample, and then the total porosity including open and closed pores can be calculated. This method has high accuracy and is widely used for porosity determination of dense materials such as rocks, ceramics, and metals.
Microscopic imaging method: With the help of scanning electron microscopy (SEM), focused ion beam (FIB), or micro/nano CT scanning techniques, the two-dimensional or three-dimensional morphology of pores can be directly observed, and the size, shape, and spatial distribution of pores can be analyzed intuitively. This method provides visual information of pore structure and is a powerful supplement to other measurement methods.
The application of porosity analysis runs through the entire process of material research and engineering practice. In the petroleum industry, it is the foundation for reserve calculation and extraction plan design; In the field of new energy, it is the key to optimizing battery electrode materials and improving energy storage efficiency; In the environmental protection industry, it is the basis for evaluating the performance of adsorbents and designing efficient water treatment materials; In advanced manufacturing, it guides the preparation of lightweight, high-strength porous metals and ceramics. Through porosity analysis, researchers can "see" and quantify the internal structure of materials, thereby adjusting process parameters in a targeted manner and achieving precise control of material properties.