Nuclear magnetic resonance, resistance and acoustic studies of the melting-freezing phase transition of gallium in Vycor glass

Abstract

The melting-freezing phase transition of gallium confined within Vycor glass was studied by NMR, resistance and acoustic techniques. A single although broadened 71Ga NMR line corresponding to melted gallium was observed in contrast to lineshapes found until now for liquid gallium in porous matrices. A difference between results obtained using the three methods was explained by formation of various confined solid gallium modifications. A depression of the freezing and melting phase transition temperatures and a pronounced hysteresis in the melting-freezing processes were found and are discussed. Heterogeneous nucleation was suggested to explain the dependence of crystallization on temperatures of pre-warming. Irreversible melting was observed for the second gallium modification.

Imaging droplet freezing using MRI

“…They have been used to study the solidiÿcation of gallium-containing vycor glasses (Borisov et al, 1999), the eutectic behaviour of benzidine with p-nitrophenol (Rai, 1994), the freezing of ower bud tissues (Price et al, 1997) and characterise the pore structure and di usivity of salt water ice (Menzel et al, 2000). Hills and Remigereau (1997a) and Hills et al (1997b) used MRI to monitor the freezing of apples and potatoes, using the acquired data to verify several theoretical models.…”

Spin-Lattice Relaxation Enhancement in Liquid Gallium Confined within Nanoporous Matrices

“…It was obtained that nuclear spin-lattice relaxation occurs via coupling of nuclear magnetic moments with conduction electrons and of nuclear quadrupole moments with dynamic gradients of electric fields produced by atomic motion; the main contribution to relaxation is magnetic. Since atomic mobility in bulk liquid gallium is fast enough, the total relaxation is described by a single exponential (the extreme narrowing limit) with the field-independent relaxation times of about 710 ms for 69 Ga and 530 ms for 71 Ga [20] at room temperature.The freezing transition for gallium within nanopores is lowered compared to that in bulk [17,18] and confined gallium still remains liquid at room temperature. Thus, spin-lattice relaxation for liquid gallium embedded into a porous glass with the pore size of 8 nm and within an artificial opal consisted of close-packed silica spheres with a diameter of 250 nm was measured by us at ambient conditions.…”

“…The freezing transition for gallium within nanopores is lowered compared to that in bulk [17,18] and confined gallium still remains liquid at room temperature. Thus, spin-lattice relaxation for liquid gallium embedded into a porous glass with the pore size of 8 nm and within an artificial opal consisted of close-packed silica spheres with a diameter of 250 nm was measured by us at ambient conditions.…”

“…Nevertheless, in spite of numerous studies of liquids within porous matrices, no studies were carried out to reveal peculiarities in spin relaxation and dynamics of confined metallic melts. Meanwhile, recent measurements on some low-melting-point metals as gallium, indium, and mercury inserted into porous glasses and artificial opals showed that confinement affects many of their properties, in particular, the melting and freezing processes, structure of solid phases, and the superconducting phase transition (see [15][16][17][18][19] and references therein). In the present Letter we report results of first studies of nuclear spinlattice relaxation in liquid gallium confined within random and quasiregular pore networks of a porous glass and artificial opal.…”

“…Thus, spin-lattice relaxation for liquid gallium embedded into a porous glass with the pore size of 8 nm and within an artificial opal consisted of close-packed silica spheres with a diameter of 250 nm was measured by us at ambient conditions. The sample preparation was described elsewhere [17]. The inversion recovery procedure was used for both gallium isotopes in magnetic fields of 7, 11, and 14 T in the case of the porous glass and in magnetic fields of 7 and 11 T in the case of the opal.…”