Mas Subramanian, a distinguished professor of chemistry and the Milton Harris Chair of Materials Science at Oregon State University (OSU) (Corvallis, Oregon, USA), is leading an effort to design stable, durable, and non-toxic pigments in a variety of vivid hues. To do this, Subramanian and his team analyzed the structure of pigments based on hibonite, a mineral found in meteorites.
In 2009, Subramanian and graduate student Andrew E. Smith accidentally discovered an inorganic blue pigment known as YinMn Blue. The discovery of this inorganic blue pigment—the first discovery of its kind since the synthesis of cobalt blue in 1802—was made during a research project exploring the electronic properties of manganese oxides. Subramanian instructed Smith to heat black manganese oxide, yttrium and indium to 2,000 °F (1093.3 °C) resulting in a compound with a striking blue hue.
Subramanian recognized the implications of this discovery. He subsequently filed a patent on the invention and OSU reached an exclusive licensing agreement with The Shepherd Color Company (Cincinnati, Ohio, USA) to produce YinMn Blue on a commercial scale. Admitting that “most pigments are discovered by chance,” Subramanian was hardly content to rest on his laurels.
“We got lucky the first time with YInMn blue, and now we have come up with some design principles,” says Subramanian.
While cobalt blue is still widely used in commercial applications, its production relies heavily on the use of the toxic material cobalt ion (Co2+). However, Subramanian and his team have discovered that hibonite-based pigments are more thermally stable than cobalt blue and remain unaltered structurally and optically when exposed to strong acid and alkali. Moreover, an oxide containing Ca, Al and Ti, along with Co or Ni, can crystallize into a structure similar to hibonite that’s able to produce vivid blue colors, the researchers claim.
As opposed to most blue pigments, which are unstable, fade easily, and are made of toxic materials, Subramanian’s team has developed a stable pigment by synthesizing it at a high temperature. The new pigment can be “tuned” by adjusting the amounts of Co2+, Ni2+, and Ti4+ placed in the hibonite structure’s “chromophore” environments, which are the parts of a molecule that determine color.
“This part of the crystal structure of hibonite, like YInMn blue, allows for vivid blue colors with a reddish hue,” Subramanian says. “The hibonite blue exhibits better energy-saving, heat-reflecting properties than traditional cobalt blue due to the presence of titanium and less cobalt content.”
Source: Oregon State University, www.today.oregonstate.edu.