Seashell-inspired shield protects materials in hostile environments
Environmentally friendly coating outperforms conventional materials

Date:
May 3, 2022
Source:
DOE/Sandia National Laboratories
Summary:
An ecological protective coating, stronger yet less expensive than
potentially dangerous beryllium shielding, is baked of alternating
layers of sugar and silica. The simple result, which mimics the
structure of a seashell, should lower costs for pulsed power
machines and space satellites.



FULL STORY ==========================================================================
Word of an extraordinarily inexpensive material, lightweight enough to
protect satellites against debris in the cold of outer space, cohesive
enough to strengthen the walls of pressurized vessels experiencing average conditions on Earth and yet heat-resistant enough at 1,500 degrees Celsius
or 2,732 degrees Fahrenheit to shield instruments against flying debris,
raises the question: what single material could do all this? The answer,
found at Sandia National Laboratories, is sweet as sugar.


========================================================================== That's because it is, in fact, sugar -- very thin layers of confectioners' sugar from the grocers, burnt to a state called carbon black, interspersed between only slightly thicker layers of silica, which is the most common material on Earth, and baked. The result resembles a fine layer cake,
or more precisely, the organic and inorganic layering of a seashell,
each layer helping the next to contain and mitigate shock.

"A material that can survive a variety of insults -- mechanical, shock
and X- ray -- can be used to withstand harsh environmental conditions,"
said Sandia researcher Guangping Xu, who led development of the new
coating. "That material has not been readily available. We believe our
layered nanocomposite, mimicking the structure of a seashell, is that
answer." Most significantly, Xu said, "The self-assembled coating is
not only lightweight and mechanically strong, but also thermally stable
enough to protect instruments in experimental fusion machines against
their own generated debris where temperatures may be about 1,500 C. This
was the initial focus of the work." "And that may be only the beginning,"
said consultant Rick Spielman, senior scientist and physics professor
at the Laboratory for Laser Energetics at the University of Rochester,
credited with leading the initial design of Sandia's Z machine, one
of the destinations for which the new material is intended. "There are
probably a hundred uses we haven't thought of." He envisions possible
electrode applications delaying, rather than blocking, surface electron emissions. Aiding the nuclear survivability mission The coating, which
can be layered on a variety of substrates without environmental problems,
was the subject of a Sandia patent application in June 2021, an invited
talk at a pulsed power conference in December 2021 and again in a recent technical article in MRS Advances, of which Xu is lead author.



==========================================================================
The work was done in anticipation of the increased shielding that will
be needed to protect test objects, diagnostics and drivers inside the
more powerful pulsed power machines of the future. Sandia's pulsed-power
Z machine - - currently the most powerful producer of X-rays on Earth --
and its successors will certainly require still greater debris protection against forces that could compare to numerous sticks of dynamite exploding
at close range. Chad McCoy loads sample coatings at Sandia's Z machine Physicist Chad McCoy at Sandia National Laboratories' Z machine loads
sample coatings into holders. When Z fires, researchers will observe how
well particular coatings protect objects stacked behind them. (Photo by
Bret Latter) Click the thumbnail for a high-resolution image.

"The new shielding should favorably impact our nuclear survivability
mission," said paper author and Sandia physicist Chad McCoy. "Z is
the brightest X-ray source in the world, but the amount of X-rays is
only a couple percent of the total energy released. The rest is shock
and debris. When we try to understand how matter -- such as metals and
polymers -- interacts with X-rays, we want to know if debris is damaging
our samples, has changed its microstructure. Right now, we're at the
limit where we can protect sample materials from unwanted insults,
but more powerful testing machines will require better shielding,
and this new technology may enable appropriate protection." Other,
less specialized uses remain possibilities.

The inexpensive, environmentally friendly shield is light enough to ride
into space as a protective layer on satellites because comparatively
little material is needed to achieve the same resilience as heavier but
less effective shielding currently in use to protect against collisions
with space junk.

"Satellites in space get hit constantly by debris moving at a few
kilometers per second, the same velocity as debris from Z," McCoy
said. "With this coating, we can make the debris shield thinner,
decreasing weight." Thicker shield coatings are durable enough to
strengthen the walls of pressurized vessels when added ounces are not
an issue. Dramatic cost reduction anticipated


========================================================================== According to Guangping, the material cost to fabricate a 2-inch diameter coating of the new protective material, 45 millionths of a meter and
microns thick, is only 25 cents. In contrast, a beryllium wafer --
the closest match to the thermal and mechanical properties of the new
coating, and in use at Sandia's Z machine and other fusion locations as protective shields -- costs $700 at recent market prices for a 1-inch
square, 23-micron-thick wafer, which is 3,800 times more expensive than
the new film of same area and thickness.

Both coatings can survive temperatures well above 1,000 C, but a further consideration is that the new coating is environmentally friendly. Only
ethanol is added to facilitate the coating process. Beryllium creates
toxic conditions, and its environs must be cleansed of the hazard after
its use. How testing proceeded The principle of alternating organic
and inorganic layers, a major factor in seashell longevity, is key to strengthening the Sandia coating. The organic sugar layers burnt to carbon black act like a caulk, said Sandia manager and paper author Hongyou
Fan. They also stop cracks from spreading through the inorganic silica structure and provide layers of cushioning to increase its mechanical
strength, as was reported 20 years ago in an earlier Sandia attempt to
mimic the seashell mode.

Greg Frye-Mason, Sandia campaign manager for the Assured Survivability
and Agility with Pulsed Power, or ASAP, Laboratory Directed Research
and Development mission campaign funding the research, initially had
his doubts about the carbon insertion.

"I thought that the organic layers would limit applicability since most
degrade by 400 to 500 C," he said.

But when the carbon-black concept demonstrated robustness to well over
1,000 C, the positive result overcame the largest risk Frye-Mason saw
as facing the project.

Seashell-like coatings initially tested at Sandia varied between a few
to 13 layers. These alternating materials were pressed against each other
after being heated in pairs, so their surfaces crosslinked. Tests showed
that such interwoven nanocomposite layers of silica with the burnt sugar,
known as carbon black after pyrolysis, are 80% stronger than silica itself
and thermally stable to an estimated 1,650 C. Later sintering efforts
showed that layers, self- assembled through a spin-coating process,
could be batch-baked and their individual surfaces still crosslinked satisfactorily, removing the tediousness of baking each layer. The more efficient process achieved very nearly the same mechanical strength.

Research into the coating was funded by ASAP to develop methods to
protect diagnostics and test samples on Z and on next-generation pulsed
power machines from flying debris.

"This coating qualifies," Frye-Mason said.


========================================================================== Story Source: Materials provided by
DOE/Sandia_National_Laboratories. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Guangping Xu, Hongyou Fan, Chad A. McCoy, Melissa M. Mills,
Jens Schwarz.

Bioinspired synthesis of thermally stable and mechanically strong
nanocomposite coatings. MRS Advances, 2022; DOI: 10.1557/s43580-022-
00245-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/05/220503201658.htm

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