Three ISU scientists are facing a dilemma – what to do after having discovered the second-hardest known substance?

In fall 1999, Bruce Cook, associate scientist for Ames Lab, Alan Russell, associate professor of materials science and engineering, and Joel Harringa, assistant scientist for Ames Lab, added silicon to an aluminum-magnesium-boron compound.

They found that the silicon caused the compound to harden, and they have been working to find out more about the substance and how it can be applied to industrial applications.

“We’re looking at developing methods of producing large quantities of the material, the properties of cutting, preparing additional materials for testing and optimizing the composition,” Cook said.

The aluminum-magnesium-boron compound first was discovered in the 1970s, but there was limited research done until Cook and Russell started examining its electrical conductivity in the early 1990s.

“We were looking at replacing the aluminum with silicon to see how it changed the electrical properties of the substance and discovered that it changed the hardness instead,” Cook said. “As the ratios of the elements of the substance change, so do the properties of the material.”

They are looking at producing large quantities for the cutting ability of the compound, which is about as hard as cubic boron nitride, but only laboratory-scale amounts have been produced so far, Russell said.

“At the time, no one is buying it or using it because we’re making it in very small qualities,” he said, adding that the biggest amount produced is about the size of a shirt button.

Once it is being made in industrial-size amounts, however, there are many possibilities for use of the compound, Russell said.

“The substance could be used for cutting, machining, sawing and possibly spraying it on steel to make it more wear-resistant,” he said. “Anything from mining operations to surgical instruments.”

The scientists specifically have been looking at what is added to the compound and how it changes the properties.

“We don’t know all the details,” Cook said. “We believe it has something to do with changing the electronic structure – the distribution of the electrons. It’s still an open question. We are working with the physics department to answer it. It will take awhile.”

Besides being the second-hardest bulk substance next to diamonds, the aluminum-magnesium-boron-silicon compound also may be significantly cheaper.

Diamonds, the hardest known substance, are estimated at about $2,000 per pound, Cook said, while the new compound is estimated at about $700 per pound.

The savings could be significant for the industry, he said.

“We’ve been researching the use of less-expensive starting materials, and the results so far have been encouraging,” Cook said. “If we are successful in this area, the cost could drop to as low as $70 per pound.”