AMP_04_May_June_2021_Digital_Edition

A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 2 1 6 FEEDBACK Stretching an elastic band caus- es it to become thinner, a physical be- havior that applies to most materials. However, the opposite behavior is also The first two entries below are recent posts on the member discus- sion board, ASM Connect. To join in the discussions or start a new thread, log on to www.connect.asm international.org . COPPER CONUNDRUM I browsed through the article, “EPA Says Copper Surfaces Help Fight COVID-10” by Harold Michels ( AM&P April) and while it says that alloys with as little as 60% Cu were tested, the EPA certificate linked (EPA Reg. No. 82012-1) only refers RESEARCH TRACKS/FEEDBACK We welcome all comments and suggestions. Send letters to joanne.miller@asminternational.org. possible: So-called auxetic materials expand in the direction orthogonal to the strain. Likewise, they shrink when they are compressed and are character- ized by a negative Poisson’s ratio. Prob- ably the best known and oldest appli- cation of unusual Poisson’s ratios is the bottle cork, which has a Poisson’s ratio of zero. This has the effect that the cork can be put into the thinner neck of the bottle. Due to their special properties, auxetic materials enable new designs for a variety of products with adjustable properties, including applications in medical technology or for use in protec- tive equipment such as bicycle helmets. Thomas Heine, professor of the- oretical chemistry at TU Dresden, Ger- many, and his team recently discovered a previously unknown phenomenon. Based on borophene, an atomical- ly thin configuration of boron, a stable EXPANDING USE OF AUXETIC MATERIALS Whether strained or compressed, a newly discovered material always expands. Courtesy of Thomas Heine et al. form was found by adding palladium, yielding the chemical composition PdB 4 . Computational modeling shows that this material behaves like an aux- etic material under strain, but expands like an ordinary material under com- pression. Whether it is strained or com- pressed, the material always expands. “In addition to thorough characteriza- tion in terms of stability, and the me- chanical and electronic properties of the material, we identified the origin of this half-auxetic character and believe that this mechanism can be used as a design concept for new half-auxetic ma- terials,” says Heine. “These novel mate- rials could lead to innovative applica- tions in nanotechnology, for example in sensing or magneto-optics. A trans- fer to macroscopic materials is equally conceivable .” www.tu-dresden.de. to alloys with >96.2% Cu. So I pulled up the online ASM Desk Edition, 2nd Ed., and it shows that alloys meeting this should be coppers C10100-10576, and high-copper alloys C16200-C19600 for wrought, and coppers C80100-C81100, and high-copper alloys C81300-C82800 for castings. (The latter group is techni- cally “>94% Cu.” So all might not quali- fy under that particular EPA certificate.) Paul Tibbals AUTHOR RESPONSE You are correct, but this regis- tration is a pioneering event in the COVID-19 era. The initial submission to the EPA, which resulted in the regis- tration alloys, only covered alloys with >96.2% Cu. I am no longer involved in the EPA submission process since I am retired. I do recall that the EPA generally limits the composition ranges and number of alloys that can be sub- mitted at one time. However, sub- sequent submissions will no doubt work their way down to alloys of low- er copper content. This pattern was followed in the initial registration of antimicrobial copper against specific infection-causing bacteria, in which I was heavily involved. Harold Michels HONORING HISTORY Greetings, Patricia, with ap- preciation for your article on histor- ical metals in South America ( AM&P April). I enjoyed reading it and noting the mention of the alpha-brass and leaded brass cones. Ronald W. Armstrong