Volcanic Ash and Aviation
May 23, 2022
The most famous
volcanic eruption, that of
Mount Vesuvius in 79 AD, is known to most through the
remains of the
Ancient Roman city of
Pompeii. Pompeii, now a
UNESCO World Heritage Site, was
buried under about five
meterss (15
feet) of
volcanic ash and
pumice that
preserved the city as it was through the two
millennia to the present day. The Vesuvius eruption caused the
death of
Pliny the Elder (AD 23/24-79),
author of the
Naturalis Historia (Natural History), probably through a
heart attack, while on a
naval rescue mission of its
inhabitants.
There are many examples of how volcanic eruptions have modified
human history. The
island of
Santorini, known in
antiquity as Thera, was nearly destroyed by a violent volcanic eruption at about 1650
BC. This eruption, thought to be among the most powerful in
civilized times, may have been the source of the
Atlantis myth, a myth that started with an
account by
Plato in his
Timaeus.
Plato described the demise of Atlantis at about 9,600 BC, about seven
millennia before his time. Atlantis sank into the
ocean in a single day and night, an event consistent with a volcanic eruption. Plato also described a resultant
tsunami, and
evidence of this is found in the
geologic record. I wrote about the Atlantis myth in an
earlier article (Science and the Atlantis Myth, May 18, 2012).
A Landsat image of Santorini (Thera), taken on November 21, 2000.
Santorini is the largest island in this image, and the smaller islands are Nea Kameni, Palea Kameni, Therasia and Aspronisi.
(NASA image via Wikimedia Commons. Click for larger image.)
There was an extreme
weather event
starting around the years 535-536 that's been shown to have a volcanic origin.[1-3]
Europe, the
Middle East, and parts of
Asia were blanketed by a
mysterious fog for 18 months, and
tree ring studies, a traditional
climate-tracking method, revealed that the years around 540 were unusually cold.[2-3]
Summer temperatures in 536 were 1.5°C to 2.5°C lower, and this was the start of the coldest
decade in the past 2300 years.[8-9]
Ice core analysis showed that the 536 eruption was followed by two others, in 540 and 547.[8] I wrote about this volcanic influence on weather in an
earlier article (The Year 536, March 18, 2019)
Closer to our present time was the
1883 eruption of
Krakatoa in which 70% of the Krakatoa island and its surrounding
archipelago were destroyed. This volcanic eruption was heard 3,110
kilometers (1,930
miles) away in
Perth, Western Australia. More than 35,000 deaths were a consequence of the eruption and the resultant tsunamis. The eruption injected large amounts of
sulfur dioxide (SO2) into the
stratosphere, and this was
dispersed globally and converted to
sulfuric acid aerosols that blocked incoming
solar radiation to cause a
volcanic winter. In 1884, the
average Northern Hemisphere summer temperatures fell by 0.4 °C (0.72 °F).
The "afterglow" of the 1883 Krakatoa eruption, as published by the Royal Society of Great Britain Krakatoa Committee. (Illustration from "The eruption of Krakatoa, and subsequent phenomena," 1888, George James Symonds, Ed., Item 71-1250 from the Houghton Library, Harvard University, via Wikimedia Commons.)
Less than half a
century ago, the
continental United States experienced the
Mount St. Helens eruption of May 18, 1980, an event with the thermal equivalent of 24
megatons of TNT, about 1,600 times that of the
Hiroshima atomic bomb. It was reported that 57 people were killed and the
economic cost in
today's money was about $3.5 billion. The eruption released more than half a billion
tons of volcanic ash having a
composition listed in the following table. The atmospheric fine ash caused problems for
internal combustion engines, other
mechanical equipment, and
aircraft engines.
Atmospheric
volcanic ash is a problem for
aircraft gas turbine engines.
Sea salt aerosols are a problem, also. Volcanic ash is a
hard,
abrasive material that causes
erosion of
turbine engine blades; and, the ash has low
melting point components that
melt in a
turbine engine combustion chamber. These molten oxides stick to turbine blades,
fuel nozzles, and other engine components.
Turbine blades have
holes for
cooling by
airflow, and these very small holes are easily plugged by such material. This causes blade temperature to exceed a
safe operating point. Turbine blades are usually
coated with
thermal barrier (TBC) and
environmental barrier (EBC) layers, and these coatings are compromised by the molten volcanic ash.
Calcium-Magnesium-Alumina-Silicate (CMAS, (Ca,Mg)2Al2SiO7) is typically used as a
simulant material for volcanic ash when testing turbine engine components.
Basic components of a gas turbine engine. Federal Aviation Administration diagram, via Wikimedia Commons. Click for larger image.)
The
US Navy, which is expected to fly aircraft under all conditions, has a special interest in
particulate corrosion of turbine engine components by such materials as
sand.
Researchers from the
Naval Postgraduate School (Monterey, California) and the
University of California-San Diego (La Jolla, California) has recently
published research on a novel
idea to prevent such corrosion. The idea is that
ultra-high temperature ceramics (UHTCs) might be sand-
phobic; that is, molten sand won't stick to them.[4-5] I'm reminded of work I did
decades ago on using
single crystals of
yttrium aluminum garnet (YAG, Y
3Al
5O
12, melting point, 1940 °C) as turbine blades.[6]
Sand,
dust, and other particulates have been a problem for aircraft for decades. Initially, the research focus was on erosion, and engine coatings solved that problem. Now, with turbine engines operating at higher temperatures for increased
power and
fuel efficiency, particulates are melting when ingested into engines to cause a variety of problems.[5]
filters reduce sand intake, but they're not 100%
effective, and the smallest particles are the ones that pass through filters and are the quickest to melt. Research has focused on ways to quickly resolidify these through
counter-reactions.[5]
A United States Marine Corps MV-22B Osprey landing in a dust cloud at Babadag, Romania.
Such clouds of potentially dangerous particulates have the potential to damage turbine engines through particulate ingestion. (US Navy image. Click for larger image.)
The research team investigated the
resistance of the ultra-high temperature ceramic borides,
zirconium diboride (ZrB2) and
hafnium diboride (HfB2), to CMAS attack at 1000 °C, 1300 °C and 1600 °C for time up to 100 hours in
air.[4] They found that these borides first
oxidize before
reacting with CMAS to form
zirconium orthosilicate (ZrSiO4) and
hafnium(IV) silicate (HfSiO4). The oxidation peaks at 1300 °C, and at 1600 °C, the reaction with CMAS to form HfSiO
4 is greatly suppressed[4] ZrB
2 was found to exhibit only oxidation, no reaction with CMAS, and no formation of ZrSiO
4 or any other CMAS induced reaction product.[4] This finding could lead to thermal and environmental barrier coatings that prevent CMAS reaction.[4]
Says
Andy Nieto, Naval Postgraduate School
Assistant Professor of
Mechanical and Aerospace Engineering,
"We were the first to even experiment at these higher temperatures for any material for these applications... It was completely unexpected that as you would go higher in temperature, you would actually get some degree of chemical inertness from these ultra-high temperature ceramics where they were not interacting with the molten sand. It opens up a possible path forward in how we are designing these engines."[5]
Their study, the first to look at the potential of utilizing ultra-high temperature ceramics in aircraft turbines, was funded by the
Strategic Engineering and Research Development Program, a joint effort by the
United States Department of Defense, the
United States Environmental Protection Agency, and the
United States Department of Energy.[5]
References:
- Ann Gibbons, "Eruption made 536 'the worst year to be alive'," Science, vol. 362, no. 6416 (November 16, 2018), pp. 733-734, DOI: 10.1126/science.362.6416.733.
- Ann Gibbons, "Why 536 was 'the worst year to be alive'," Science (November 15, 2018), doi:10.1126/science.aaw0632.
- Ultra-Precise Ice Core Sampling and the Explosive Cause of the Dark Ages – Mayewski & Kurbatov, University of Maine Climate Change News, December 18, 2018.
- Andy Nieto, Erick Samayoa. Troy Ansell, and Jian Luo, "Unusual temperature-dependent reactivity of ultra-high temperature ceramic (UHTC) borides with calcia-magnesia-alumina-silicate (CMAS)," Materialia, vol. 20 (December, 2021), Article no. 101265, https://doi.org/10.1016/j.mtla.2021.101265.
- Rebecca Hoag, "NPS Research Seeks to Advance Aircraft Turbine Resilience to Particulates," Naval Postgraduate School Press Release, March 24, 2022
- Devlin M. Gualtieri, Robert C. Morris, Dave Narasimhan, and Philip J. Whalen, "Single Crystal Oxide Turbine Blades," U.S. Pat. No. 5,573,862 (November 12, 1996).
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