The unusual “trigonal bipyramidal” crystalline structure seen here is being used by researchers at Oregon State University to create a range of new pigments with properties of safety and stability that should have important applications in the paint and pigment industries. Image: Oregon State University |
Chemists at Oregon
State University
have discovered that the same crystal structure they identified two years ago
to create what may be the world’s best blue pigment can also be used with
different elements to create other colors, with significant potential in the
paint and pigment industries.
First on the list is a brilliant orange pigment.
But the broader potential for these pigments, researchers
say, is the ability to tweak essentially the same chemical structure in
slightly different ways to create a whole range of new colors in pigments that
may be safer to produce, more durable and more environmentally benign than many
of those that now exist.
Among the possibilities, they say, are yellow and green.
“The basic crystal structure we’re using for these pigments
was known before, but no one had ever considered using it for any commercial purpose,
including pigments,” says Mas Subramanian, the Milton Harris Professor of
Materials Science in the OSU Department of Chemistry.
“All of these colors should share the same characteristics
of being extremely stable, durable, and resistant to heat and acid,” he says. “And they are based on the same crystal structure, so minor adjustments to the
technology will produce very different colors and very high quality pigments.”
OSU has already applied for a patent on this technology,
samples are now being tested by private industry, and the latest findings were
published in Inorganic Chemistry.
This invention evolved from what was essentially an
accidental discovery in 2009 in an OSU lab, where Subramanian was exploring
some manganese oxides for interesting electronic properties. At one stage of the
process, when a sample had been heated to almost 2,000 Fahrenheit, the compound
turned a vivid blue.
It was found that this chemistry had interesting properties
that affects the absorption of light and consequently its color. So Subramanian
and his research team, including OSU professor emeritus Art Sleight, quickly
shifted their electronics research into what may become a revolution in the
paint and pigment industry. Future applications may range from inkjet printers
to automobiles or even ordinary house paint.
The work created, at first, a beautiful blue pigment, which
had properties that had eluded humans for thousands of years, dating back to
the Han dynasty in China,
ancient Egyptians, and Mayan culture. Most previous blue pigments had various
problems with toxicity, durability and vulnerability to heat or acid. Some are
carcinogenic, others emit cyanide.
Expanding that research, the scientists further studied this
unusual “trigonal-bypyramidal coordination” of crystalline structure, atoms
that are combined in a certain five-part coordinated network. The initial blue
color in the pigment came from the manganese used in the compound. The
scientists have now discovered that the same structure will produce other
colors simply by substituting different elements.
“The new orange pigment is based on iron, and we might use
copper and titanium for a green pigment,” Subramanian says. “Yellow and deep
brown should be possible, and we should be able to make a new red pigment. A
lot of red pigments are now made with cadmium and mercury, which can be toxic.”
“These should all be very attractive for commercial use,” he
says.
