Researchers Find Way To Minimize Evolution Of A Toxic Gas

Dr. Claudia Nassaralla and Dr. Richard Heckel, professors of metallurgical and materials engineering, spent four years studying the process that controls the development of phosphine gas in ferrosilicon.

"Ferrosilicon alloys are important materials for the steel industry because they are used as de-oxidants and alloying additions in the production of steels used in the manufacturing of transformers and electric motors" says Nassaralla. But when ferrosilicon alloys are exposed to water and water vapor during transportation to steel mills and prior to the steelmaking process, they evolve phosphine gas which smells like garlic and rotten fish and is toxic. Phosphine has been blamed for several accidents in the early 1900's, and at that time many people died from exposure to it. The most recent accident with fatalities was reported in 1997 in Japan. It occurred in a Chinese cargo ship transporting an inferior quality ferrosilicon.

The process that controls phosphine gas evolution in ferrosilicon is directly related to the presence of specific impurity phases in the alloys, Nassaralla says. The MTU team found a relationship between the evolution of phosphine gas and the presence of reactive phosphide forming elements in ferrosilicon---- especially aluminum, calcium, magnesium and phosphorus. They discovered that suppressing the formation of the reactive phosphide phases in ferrosilicon alloys can reduce the evolution of phosphine gas.

The MTU study has shown that "a chemically inactive phosphide phase can be formed by adding the appropriate alloying elements to the ferrosilicon alloy," Nassaralla explains. The MTU research team found that phosphine gas evolution can be dramatically reduced when sufficient amounts (10 percent or more) of magnesium are added.

Nassaralla believes that this technique "could have a significant economic impact for the producers and consumers of ferrosilicon alloys, as well as improve the safety of its handling and transportation."

The project is being funded by a grant from the Norwegian Ferroalloy Producers Research Organization.