B. F. Borisov

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

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.

Phase transitions for gallium microparticles in a porous glass

Abstract Studies of sound velocity and absorption supplemented with studies of heat capacity were carried out for the first time in the melting-freezing phase transition temperature range for Ga microparticles in a porous glass. The pronounced asymmetry of temperature behavior in cooling-heating processes was obtained, which was interpreted as the first order phase transition at cooling and the smeared phase transition at heating.

Acoustic studies of melting and freezing for mercury embedded into vycor glass

Acoustic technique was used to study the melting and freezing phase transitions of mercury embedded into Vycor glass. Both freezing and melting were found to be smeared and shifted noticeably to low temperatures compared to the melting point of bulk mercury, the offset of melting occurred at 223 K. The liquid skin model which was developed to treat melting in isolated metallic particles was used to explain the partly reversible character of melting for confined mercury and the difference between results obtained for longitudinal and transverse waves. The temperature dependence of the liquid skin thickness was calculated. Freezing was suggested to be driven by nucleation processes. It was shown that for confined mercury there is no unambiguous correspondence between pore sizes and temperatures of melting.

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

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 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.

Solidification and melting of gallium and mercury in porous glasses as studied by NMR and acoustic techniques

Abstract The melting and freezing phase transitions of mercury and gallium in porous glasses were studied. A depression of the phase transition temperatures, a pronounced hysteresis between melting and freezing, and the melting and freezing broadening were found. The measurements on confined mercury showed that melting could be treated within the frameworks of the model of a liquid layer on solid cores, while freezing is probably driven by nucleation. The Knight shift and line shape studies revealed peculiarities in the structure of liquid confined gallium. No correlation was obtained between the melting reduction and pore sizes for the glasses filled with gallium that was treated as a result of various confined solid modifications formed within pores.

Acoustic study of melting and freezing of mercury nanoparticles in porous glasses

The processes of melting and freezing of small mercury particles embedded in porous glasses with nanometric pore sizes are studied by an ultrasonic method for various values of the pore filling factor. The filling factor is found to have a threshold, below which the acoustic anomalies accompanying phase transitions change their character. The critical radius of mercury nanoparticles that corresponds to the zero melting temperature is estimated.

Acoustical studies of phase transitions in some lithium-containing ferroelastics

Abstract Results of acoustical property studies in lithium-containing crystals LiKSO4, LiCsSO4 and K4LiH3(SO4)4 in wide temperature ranges including structural phase transitions are reported.

Acoustic studies of melting and crystallization of nanostructured decane

Acoustic studies of melting and crystallization of decane loaded in porous glasses (Vycor and laboratory-produced glass) have been performed. Measurements of the temperature dependences of the ultrasound velocity have revealed a decrease in the melting and crystallization temperatures of decane as compared to the melting point of bulk decane and a diffuseness of these phase transitions. The results obtained are compared with the predictions of the models describing melting of individual small particles. The specific features revealed in the acoustic properties of nanocomposites based on decane-loaded porous glasses are discussed.

Acoustic Studies of Low-Temperature Phase Transitions in LiKSO4 Crystals

Acoustic studies of low-temperature phase transitions in LiKSO4 crystals were performed in the range 165 to 290 K. Anomalies in velocity and attenuation were found around 204 and 185 K under cooling and around 195 and 260 K under warming. A dip in the velocity of the yx shear wave was observed at the III-IV phase transition. The results are treated in the framework of the Landau theory and fluctuation models.

The effect of melting and crystallization of indium within pores on properties of photonic crystals at different pore fillings

Acoustic properties of synthetic opal filled with indium at different factors of pore filling is investigated using the pulse-interference technique in the frequency range from 4 to 8 MHz and in the temperature range of 300–480 K. A shift to lower temperatures and widening of the indium melting region in nanopores depending on the factor of pore filling is observed. It is shown that melting and crystallization of indium in pores during heating and cooling are accompanied with variations in velocity and absorption of longitudinal ultrasonic waves, respectively, under conditions that the filling factor exceeds the threshold value.