Where liq­uid ends, and solid be­gins

DEMM Engineering & Manufacturing - - NEWS -

For the first time, sci­en­tists have mapped the struc­ture of a metal­lic glass on the atomic scale, bring­ing them closer to un­der­stand­ing where the liq­uid ends and the solid be­gins in glassy ma­te­ri­als.

A study led by Monash Univer­sity re­searchers and pub­lished in Phys­i­cal Re­view Letters has used a newly de­vel­oped tech­nique on one of the world’s high­est-res­o­lu­tion elec­tron mi­cro­scopes to un­der­stand the struc­ture of a zir­co­nium (Zr)-based metal­lic glass.

The find­ings could help ex­plain the mys­tery of why glasses, or dis­or­dered solids, form.

At the liq­uid-glass tran­si­tion, the melt doesn’t be­come solid at a dis­tinct point, but be­comes grad­u­ally more vis­cous un­til it is rigid.

When crys­talline solids such as graphite, salt and di­a­monds form, they be­come abruptly rigid as the atoms form a reg­u­lar, pe­ri­odic ar­range­ment. Glass never de­vel­ops into an or­dered atomic ar­range­ment, but seems to re­tain the dis­or­dered struc­ture of the liq­uid, de­spite its so­lid­ity.

This dis­or­dered struc­ture gives glasses unique prop­er­ties. Metal­lic glasses have a higher strength-to-weight ra­tio than alu­minium and ti­ta­nium al­loys, and are ex­tremely promis­ing struc­tural ma­te­ri­als with ap­pli­ca­tions as bio­ma­te­ri­als and mi­cro­elec­trome­chan­i­cal sys­tems.

Led by Dr Amelia Liu from Monash Univer­sity’s School of Physics and the Monash Cen­tre for Elec­tron Mi­croscopy, the re­searchers found that the struc­ture of this Zr-based glass was not ran­dom, but com­posed in large part by ef­fi­ciently ar­ranged 13-atom icoso­he­dral clus­ters.

Icosa­he­dra have 20 faces, 12 ver­tices and 12 axes of five­fold sym­me­try, which means they can­not be packed into an or­dered three di­men­sional, crys­talline struc­ture.

“It has long been the­o­rised that icosa­he­dra were a key atomic mo­tif in the struc­ture of metal­lic glasses and could, in fact, un­der­lie glass for­ma­tion. We have pro­vided the first ex­per­i­men­tal con­fir­ma­tion of this,” Dr Liu said.

“Our find­ings also point the way to­wards un­der­stand­ing the glass tran­si­tion from liq­uid to solid – a grand chal­lenge in mod­ern condensed mat­ter physics.”

Us­ing a new elec­tron scat­ter­ing tech­nique, sci­en­tists were able to an­a­lyse the dif­frac­tion pat­terns from nano-scale vol­umes in glass, and were able to iden­tify sym­me­tries in in­di­vid­ual atomic clus­ters in the Zr-glass. Pre­vi­ous tech­niques had not pro­vided suf­fi­cient de­tail to do this.

Dr Liu said that the new tech­nique can be used to un­der­stand the struc­ture of other glasses and help progress the study of dis­or­dered ma­te­ri­als.

Newspapers in English

Newspapers from New Zealand

© PressReader. All rights reserved.