Nuclear magnetic resonance and acoustic investigations of the melting - freezing phase transition of gallium in a porous glass

Abstract

The melting-freezing phase transition of gallium in a porous glass was studied by NMR and acoustical techniques. A depression of the freezing and melting phase transition temperatures and a pronounced hysteresis in the melting-freezing processes were found. An intricate 71 Ga NMR lineshape for liquid gallium was observed with a temperature coefficient of the Knight shift more than twice that measured for the bulk melt. The results are discussed on the basis of the Gibbs-Thompson equation and by means of a geometric freezing model.

Nuclear magnetic resonance cryoporometry

“…The freezing and melting of gallium (Borisov et al, 1997 (Strange and Webber, 1997). (Borisov et al, 1998) in porous glass has been studied by 71 Ga and 199 Hg NMR respectively .…”

“…The gallium appeared to exhibit a freezing point depression determined by the confining pore size, whereas the melting phase transition was considerably narrower and did not appear to reflect the pore size distribution. The NMR Knight shift of the confined metal suggested it had entered an unusual liquid state (Borisov et al, 1997) and the crystal appeared to have several possible structural phases . On some occasions the freezing of the gallium and the mercury was seen to be an irreversible process.…”

Solidification and melting of mercury in a porous glass as studied by NMR and acoustic techniques

“…10-12, and references therein͒, phase transitions in liquid crystals ͑Refs. 13-16, and references therein͒, the ferroelectric phase transition, 17 solid-solid phase transitions, 8,18,19 the glass phase transition, 20 the gasliquid phase transition, 21 and the melting-freezing transitions 3,19,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] have been intensively studied. It was found that the interplay of short-range and long-range couplings greatly influences the phase transitions in confined geometries.…”

“…[29][30][31][32][33]38 For gallium in porous glasses and in an opal-like matrix it was found using NMR and acoustic techniques that freezing occurred sharply when the distribution of pore sizes was narrow and was broadened when the distribution of pore sizes was wide, while melting was broadened for any pore size distribution. [29][30][31][32] Both melting and freezing occurred well below the bulk gallium melting point. For indium in a Vycor glass a lowering of temperatures of specific heat peaks associated with melting and freezing was observed 38 and heterogeneous nucleation was suggested.…”

Nanostructured Coatings of Inner Surfaces in Microporous Matrixes

“…The melting and freezing within porous glasses have been observed for materials such as water, organic liquids [5,6], metals with low melting point [7][8][9][10][11], helium [12], oxygen and some other simple liquids [13][14][15]. The ferroelectric phase transition within porous glass has been observed for NaNO 2 and K 2 HPO 4 [16,17].…”