Mas Subramanian didn’t expect to find a brilliant blue pigment when he was looking for new semiconductors. But the Milton Harris Chair Professor of Materials Science in the Oregon State University Department of Chemistry was shocked in 2009 when he saw a graduate student take a powder with a vibrant blue hue out of a laboratory furnace.
The student was worried. He thought it was a mistake.
“We were trying to find a material with novel magnetic properties for electronics applications, but it didn’t work. I didn’t think it would have a special color. I expected it to be brown or black,” says Subramanian, who grew up in Madras (now called Chennai), India, and received his Ph.D. at the Indian Institute of Technology. “But when I saw what he had, I knew this was something unusual.”
The new blue is stable and relatively non-toxic. Produced at temperatures in excess of 2,200 degrees Fahrenheit, it reflects infrared energy and may thus help to cool buildings and reduce air conditioning costs. And it can be “tuned,” says Subramanian, to produce a range of shades from sky blue to nearly black.
Since publishing the discovery in the Journal of the American Chemical Society, Subramanian has worked with artists (such as Portland-based Rebecca Shapiro), paint manufacturers, energy conservation companies and the German chemical firm Merck KGaA, which makes pigments for coatings (automobiles, aircraft), plastics, inks and cosmetics. Even the U.S. Navy has expressed interest since ships painted with the heat-reflecting pigment may be less visible to detection through infrared imaging.
Merck, one of the world’s oldest chemical and pharmaceutical companies, combines colorants with particles of mica, silica or alumina to give them a vibrant sheen. The firm has even developed a line that changes hues as the viewer’s perspective shifts. Although the company supplies pigments to some of the world’s largest manufacturing companies, it continues to look for colorants that work better in complex mixtures and have environmental benefits.
The promise of Subramanian’s discovery has prompted Merck to fund an ongoing research program in his lab. The company’s customers are always looking for ways to create new color effects and to reduce the use of heavy metals, says Gerhard Pfaff, senior director of research and development for Merck.
“New pigments should improve application properties, for example, in the paint industry. This means, besides special color effects, a better adaptation of the pigment surface to the binder systems,” says Pfaff in an email. “Only a very few university groups in the world are working in this field. The development of new colorant systems based on a fundamental understanding of inorganic materials and their structure is an intelligent way to create innovative new pigments.”
The new OSU blue stems from an unusual crystal arrangement known to chemists as “trigonal-bipyramidal coordination.” Even though chemists have known for decades that such structures exist, no one had proposed that they would provide the basis for new vibrant colors. By introducing manganese ions into the crystal, Subramanian’s team intended to make new materials with effective magnetic properties for use in computer hard drives. Instead, they created a material with surprising light-absorption properties that result in shades of blue. Subramanian has added zinc and titanium to produce a range of purples. He and his team have substituted iron for manganese to produce a new orange pigment, and they are exploring the use of copper and titanium to make green. Other elements produce yellows and browns.
Chemical theory did not predict that such a structure would generate intense colors, says Subramanian. His lab still focuses on semiconductors, and although his students produce papers on new materials with novel magnetic and electrical properties, pigment chemistry competes with electronic material research for their attention.
“We are making new pigments based on a mineral called hibonite, which is normally found in meteorites,” Subramanian says. “They are blue sometimes, and we are now producing them in our laboratory furnace using cheap raw materials.”
The search for dazzling blues has occupied artists and explorers for millennia. Neolithic artisans fashioned beads from lapis lazuli (a silicate mineral mixed with flecks of iron pyrite, aka fool’s gold) mined in what is now Afghanistan. Marco Polo marveled at quarries of the valuable mineral, and Italian Renaissance painters had access to it through trade routes managed by Venice.
Lapis lazuli became the basis for a high-value pigment known as ultramarine. Until the discovery of Prussian blue (ferrocyanide) in the early 1700s, ultramarine was the blue of choice and used to evoke a sacred quality in religious art. However, ultramarine costs about 10 times more than Prussian blue, and artists gradually shifted to the less expensive color.
Today, pigments are still woven with economics. “The price of paint is not the big deal. Durability is the problem,” says Subramanian. Pigments made from organic materials tend to fade in sunlight and require costly repainting. Moreover, some blue pigments, such as Prussian blue, have toxic properties.
The search continues for pigments that are durable, nontoxic, energy efficient and tunable to a variety of shades. Subramanian has produced blues, greens, yellows and oranges, but he would love to find a good red. “Reds that have good color use mercury and cadmium,” he says. “They are not environmentally desirable.”