In industries from textiles to automobiles and from pharmaceuticals to semiconductors, accurately measuring empty spaces--technically speaking, porosity--is a substantial matter, important to efforts to ensure high product quality and low scrap rates.
This is because tiny pores--usually smaller than 50 nanometers in diameter--come in many varieties, creating complex internal and external surface features that strongly influence the performance of catalysts, filters, brake pads, pigments, ceramic components, time-release capsules and many other engineered products.
A new Recommended Practice Guide from the National Institute of Standards and Technology (NIST) provides useful advice and instruction on how to analyze the size, distribution and total volume of tiny pores. The 79-page manual, Porosity and Specific Surface Area Measurement for Solid Materials, was jointly produced by scientists from NIST and Germany's Federal Institute for Materials Research and Testing (BAM).
The two government research organizations are collaborating to produce certified reference materials. These reference materials are carefully characterized samples that serve as benchmarks for evaluating the accuracy of instruments used to measure the chemical composition or certain physical properties of materials. For example, NIST and BAM offer samples of alumina beads (NIST Standard Reference Material 1917) with certified values for pore volume, mean pore diameter, and most common pore diameter.
Industry uses a variety of methods to measure the surface area and pore characteristics of powders and other materials characterized by large surface-to-volume ratios. Differences among the methods complicate efforts to compare and interpret measurement results. Also, strengths and limitations of the various techniques are important for manufacturers to know when designing materials with pore sizes and distributions optimized for specific applications and products. The new guide details the "practical issues that need to be considered when conducting a measurement or analysis" by one or more of the commonly used porosimetry techniques.