SCHOTT solutions no. 1/2014 > Nanoporous Glass
Photo: SCHOTT/H.-J. Schulz
By developing CoralPor® 1000 and CoralPor® 2000, researchers at SCHOTT have introduced a porous glass product that has applications in a variety of sectors.
Thomas H. Loewe
They are inconspicuous but very important: in labs around the world, reference electrodes detect single particles among trillions. As such, they are inevitably part of almost all electrochemical measurements. Tiny porous plugs are often used to separate the reference fluid inside the reference electrodes from the sample. For this, SCHOTT now offers CoralPor® 1000, a nanoporous glass solution that improves measurements and is even suitable for applications far beyond the laboratory.
Seen under a scanning electron microscope, CoralPor® resembles the tender structure of name-giving coral skeletons. At high magnification, countless pores and channels are revealed. The interconnected coral-like structure is created during a special production process, in which borosilicate glass is melted, rapidly quenched and then phase separated. This process triggers separation of the individual components in the glass, resulting in a sodium borate phase and a silicate phase. At the end of the process, special chemicals are used to dissolve the sodium borate phase, which yields an interconnected microstructure with open porosity. The innovative glass is currently available in two product variants: CoralPor® 1000 is typically employed in applications such as reference electrode junctions, desiccants, coatings, or as components in devices for the medical, aerospace, defense, and oil and gas industries. CoralPor® 2000 exhibits larger pore sizes (40 – 300 nm) and is best suited for use in separations or as a synthesis substrate. Both CoralPor® products were developed under the leadership of Dr. William James, Supervisor of Materials Development at SCHOTT North America. ”Our goal was simple: to produce a porous glass that offered high chemical and mechanical stability,” says James.
The nanoporous glass CoralPor® (image top right) has a broad spectrum of applications, e. g. in the area of electrochemistry, chromatography (left) and for heat-resistant coatings on spacecrafts (right). Photo left: Novasep, Photo right: Thinkstock
One example that clearly demonstrates CoralPor® 1000’s extreme stability: “CoralPor® can even be utilized as a key element for heat-resistant coatings on spacecraft,” says Ed Hart, Senior Manager of Market Development and Innovation at SCHOTT North America. Since the material consists of 95-97 percent silica, it also has a low thermal expansion coefficient. This renders the glass extremely robust for thermal protection applications and ensures that it expands minimally – a major advantage at high temperatures, which makes CoralPor® 1000 a ”universally” applicable material in the truest sense of the word. But Hart also emphasizes another main advantage: ”CoralPor® 1000 has lots of tiny pores on the order of 4 nanometers. This makes the product ideal for reference electrodes and other lab applications.” In fact, lab applications were the actual inspiration for developing CoralPor® 1000.
For many years, nanoporous glass was manufactured by one supplier. But the recent discontinuation of the product caused major concern in the scientific community. Between 2012 and 2013 alone, more than 70 publications in various scientific journals explicitly reported using reference electrodes with glass plugs sold under the now discontinued brand. ”We were quite worried,” says Philippe Buhlmann, Professor of Chemistry and Chemical Physics at the University of Minnesota. ”But now, many members of the community are relieved to see that SCHOTT is stepping in with its CoralPor® product line,” Buhlmann adds. CoralPor® has also gained trust among users of chromatography applications – a chemical separation method used in the purification of biotechnology products. For this process, researchers require the separation media to withstand up to pH 14 to survive the cleaning process between chromatography cycles. ”Up to now, conventional chromatography glass-based media could only remain chemically stable in a range of pH 2 to pH 8,” says James. The specific surface area of CoralPor® delivers an advantage by maximizing the amount of target molecules separated per cycle.
”The great thing about CoralPor® is that we can adapt so much to the customer’s specific demands,” says Hart. SCHOTT researchers can tailor CoralPor® to a wide range of geometries, surface areas and pore sizes. This flexibility also shows that CoralPor® has a broad spectrum of possible applications remaining to be explored: ”One direction we’re interested in is to further increase the surface area of CoralPor® in turn increasing the material’s capability as an absorbent material and synthesis substrate,” says James. Heat-resistant coatings for turbines and engines are another possibility. All this shows: the experts at SCHOTT won’t be running out of ideas any time soon. <