Difference between a Porosimeter and a Porometer
In the field of pore structure analysis, two commonly used techniques are mercury intrusion porosimetry and capillary flow porometry. While both methods provide valuable information about pore characteristics, they differ in their approach and the pore size range they are primarily focused on. This technical article aims to compare and highlight the distinctions between these two techniques.
Porometers
A porometer is an instrument primarily used to measure the pore size distribution in porous materials. It works based on the principle of capillary flow porometry, a technique where a wetting liquid is displaced by a flow of liquid (usually gas) from the material's pores, which allows us to establish the pore size and its distribution. By systematically increasing the pressure of the gas, the wetting liquid is pushed out from large to smaller pores, and these displacements are carefully recorded to calculate pore sizes. Porometers are particularly useful in industries such as non-woven, membranes, textiles, and paper where pore size, distribution, and characteristics significantly influence the performance of the materials. The Porometers are especially utilized for application where the filtration or separation efficiency determines the key characteristics of a material.
Porosimeters
Porosimeters are tools that quantify the porosity of a material — the measurement of void spaces within a material. Mercury porosimetry is based on the principle of mercury intrusion into a sample under controlled pressure. The Laplace-Washburn equation is used to calculate the size of pores intruded by mercury. By measuring the volume of mercury intruded at various pressures, the pore size distribution can be determined as well as the pore volume and the porosity of the sample. Porosimeters have wide-ranging applications across geology, construction, and materials science. For instance, in construction, concrete's porosity directly impacts its durability, strength, and resistance to freeze-thaw cycles. Hence, porosimeters are used to evaluate these critical parameters and maintain the integrity of the construction material.
Comparison and Distinctions:
Both porometers and porosimeters are techniques used to measure the pore size and pore size distribution of porous materials. However, there are often misconceptions about the differences, proper use, and data obtained from each method. The characteristics of each device can be summarized as follows:
Porometer:
-Selectively measures the necks (narrowest parts) of individual pores.
-Provides data related to sample permeability and liquid permeability.
-Non-through pores are not included in the data.
Porosimeter:
-Measures the volume of pores.
-Includes data on both through and non-through pores.
-Can calculate sample void fraction, specific surface area, and tortuosity.
The main point is that while a porosimeter measures pores volumetrically, regardless of whether they are through or non-through, and obtains volumetric data of the pores, a porometer only measures the necks of the pores that traverse through the sample from top to bottom. In other words, if a single pore with an hourglass shape is measured with both a porometer and a porosimeter, the porometer will provide data only for the narrowest point of the pore, while the porosimeter will provide data for all pore sizes along the pore, including from the entrance to the narrowest point. Now, the question arises as to why a porometer, which provides data only for the necks of each through pore, is necessary when a porosimeter can provide data for all pore sizes, including both through and non-through pores. This is because in porous materials that require separation functions like filters, the performance of the filter and the permeability of gas/liquid flowing through depend significantly on the neck size of the pores traversing through the sample. On the other hand, when data is obtained using a porosimeter for such samples with these functions, the data will include the sizes of non-through pores that do not contribute to the sample's filtering performance, as well as the sizes of surface openings. This would result in data acquisition that does not correlate well with the quality of the sample.
As mentioned earlier, due to the measurement principle of porometers, which only measure the necks of each pore, they do not provide data related to sample volume or void rate. Additionally, because the pores being measured need to traverse through the sample from the primary side to the secondary side, porometers are not suitable for measuring particles or other irregular shaped samples. Therefore, the use of a porosimeter is necessary for measuring catalysts or powdered molded products where not only pore size distribution but also void rate data is required. One example of the differentiation in the use of these two devices is the evaluation of separator films for lithium-ion batteries. Many customers who evaluate separator films for batteries possess both porometers and porosimeters. This is because they use porometers to evaluate the neck size of the separator, which directly affects the battery's charge-discharge performance, and use porosimeters to evaluate factors such as electrolyte retention performance. Unfortunately, one device cannot fully substitute for the data obtained from the other device, hence the need for both instruments.
Conclusion:
While both porometers and porosimeters play a crucial role in understanding porous materials, they are fundamentally different. Porometers primarily focus on analyzing the pore size and distribution, while porosimeters are used to measure porosity. Choosing the right tool requires an understanding of the material's characteristics and the specific requirements of the measurement. By clearly defining the need for either pore size/distribution or porosity information, one can effectively employ these instruments to their maximum potential. Both instruments ultimately contribute to the better understanding, performance, and application of a vast range of materials across numerous industries, highlighting their indispensability in materials science and industry.