Surface area analyzers determine the characteristics of a solid, including how it burns, corrodes or reacts with other materials. Analysis is based on the interaction of the atoms on the surface of the solid material. As these atoms are not completely bound on all sides by other atoms in the solid, they are more reactive and, therefore, more likely to attract nearby gases or liquids, which form a monolayer on the solid’s surface.

The first step in surface area analysis is to remove any adsorbed contaminants on a sample surface by applying a combination of heat, vacuum or flowing gas. While under vacuum in a chamber, the sample is cooled. It is then exposed to a gas adsorptive, usually nitrogen, in increments at constant temperature. After each dose of adsorptive, the chamber pressure is allowed to equilibrate, and the quantity of gas adsorbed into a monolayer on the sample surface is calculated by measuring the chamber pressure. The surface area is calculated with additional pressure measurements upon further exposure to the gas.

If the sample is exposed to gas beyond the amount needed to produce a surface monolayer, the sample’s pore structure can be evaluated. With the adsorptive gas condensing first in the pores with the smallest dimensions, the pressure is increased until saturation is reached. The pressure is then reduced incrementally, evaporating the condensed gas from the system. The resulting sorption and desorption data can provide information on the size, volume, area and shape of the sample’s pores. Most instruments measure both surface area and porosity.

A key application area for these instruments is pharmaceuticals. Differences in surface area and porosity can influence the performance of a drug, including its shelf life, dissolution rate and bioavailability. The results of surface area analysis therefore affect the purification, processing and even packaging of a pharmaceutical product. The technology can also be used to evaluate activated carbon, a high-porosity material used for purification and other purposes. The quality of catalysts, which are active at their surfaces, can also be analyzed. Other industrial applications include the assessment of chemicals, cement, polymers and cosmetics.

The largest supplier of surface area analyzers is Micromeritics, which recently introduced the ASAP 2020 Plus, featuring several options for gas sorption techniques. Beckman Coulter (Danaher) offers the SA 3100, which uses helium and features continuous saturation pressure management. Quantachrome’s products for surface area and porosity analysis include the Autosorb series, the new QUADRASORB evo for high analytical throughput and the high-speed NOVA series. Other significant suppliers of the technology include HORIBA, Microtrac and Thermo Fisher Scientific.

The total market for surface area analyzers was a little less than $50 million in 2014. Although driven by the pharmaceutical industry, the current growth rate remains modest.

Surface Area Analyzers at a Glance:

Leading Suppliers

• Micromeritics

• Beckman Coulter

(Danaher)

• Quantachrome

Largest Markets

• Chemicals

• Pharmaceuticals

• Cement

Instrument Cost

• $18,000–$100,000