MSGID: 1:317/3 62720175   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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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