Washington: A new research led by an Indian-origin scientist has discovered that a new class of ceramic coatings could offer jet engines special protection against volcanic ash damage in the future.
For their study, the researchers at the Ohio State University tested two coatings that were originally developed to keep airborne sand from damaging jet engines, and found that the coatings also resist damage caused by ash deposits.
Like sand, ash is made mostly of silica. When the Icelandic volcano Eyjafjallajokull erupted in April 2010, it billowed clouds of silicate ash.
"Ash poses a threat very similar to sand, but ash composition varies widely depending on the type of volcano," said Nitin Padture, College of Engineering Distinguished Professor at the University, who led the study.
"After what happened in Iceland, we wanted to see how ash interacted with our new thermal barrier coating, and whether the underlying damage mechanisms were any different," he said.
Doctoral students Julie Drexler and Andrew Gledhill took samples of the ceramic coatings on pieces of metal, and coated them with ash from the Eyjafjallajokull eruption. Then they heated the samples in a furnace to simulate the high temperatures created in a jet engine.
They experimented with a typical jet engine coating and two sand-resistant coatings. One was Padture`s formula, containing zirconia and alumina, and the other was a commercially available new formula based on gadolinium zirconate.
The ash badly damaged the typical coating, while coatings made of Padture`s formula and the gadolinium zirconate formula retained their overall structure.
Looking at cross-sections of the samples, the researchers saw why: molten ash had penetrated through the pores of the typical ceramic coating all the way to its base. But in the other two, the molten ash barely penetrated.
On the sand-resistant coatings, the ash filled the pores only near the surface.
Chemical analysis revealed that the ash reacted with the alumina in the first coating to produce a thin layer of the mineral anorthite below the surface, while on the gadolinium zirconate it produced a layer of the mineral apatite.
"The chemical reaction arrests the penetration of the ash into the coatings. The unaffected pores allow the coating to expand and contract," explained Gledhill.
However, large amounts of ash can temporarily jam a jet engine and cause it to stall. These coatings would not be useful in those extreme circumstances, Padture explained.
The study was published online in the early view edition of the journal Advanced Materials.