Building and Breaking Bonds by Homogenous Nucleation in Glass-Forming Melts Leading to Transitions in Three Liquid States

Abstract

The thermal history of melts leads to three liquid states above the melting temperatures Tm containing clusters—bound colloids with two opposite values of enthalpy +Δεlg × ΔHm and −Δεlg × ΔHm and zero. All colloid bonds disconnect at Tn+ > Tm and give rise in congruent materials, through a first-order transition at TLL = Tn+, forming a homogeneous liquid, containing tiny superatoms, built by short-range order. In non-congruent materials, (Tn+) and (TLL) are separated, Tn+ being the temperature of a second order and TLL the temperature of a first-order phase transition. (Tn+) and (TLL) are predicted from the knowledge of solidus and liquidus temperatures using non-classical homogenous nucleation. The first-order transition at TLL gives rise by cooling to a new liquid state containing colloids. Each colloid is a superatom, melted by homogeneous disintegration of nuclei instead of surface melting, and with a Gibbs free energy equal to that of a liquid droplet containing the same magic atom number. Internal and external bond number of colloids increases at Tn+ or from Tn+ to Tg. These liquid enthalpies reveal the natural presence of colloid–colloid bonding and antibonding in glass-forming melts. The Mpemba effect and its inverse exist in all melts and is due to the presence of these three liquid states.

On Structural Rearrangements Near the Glass Transition Temperature in Amorphous Silica

“…The complete annihilation of configurons occurs by heating above the temperature T n+ > T m toward the homogeneous liquid state. Each configuron has the energy of an antibond, which is equal in size but with an opposite sign to that of a bond that would appear by annealing the homogeneous liquid between T m and T n+ and would disappear by heating above T n+ [ 80 ].…”

“…Kinetically controlled shifts of T g within a relatively narrow temperature interval by the decrease of cooling rate q are thus explained, revealing the logarithmic dependence of T g on q within CPT. The nucleation of bonds also occurs between T m and T n+ and not only below T m [ 36 , 80 ]. Consequently, clusters of bound colloids are built below T n+ , and when the number of new bonds attains the percolation threshold, the crystallization occurs at T m if the liquid is slowly cooled instead of being quenched.…”

Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations

“…At this time, it was already known that crystals covered by a solid thin film or imbedded into a matrix could melt at higher temperatures than T m by homogeneous nucleation in crystal hearts instead of surface melting [ 47 , 48 , 49 , 50 ]. This idea was relaunched in glass-forming melts accompanied by predictions of their melting temperatures T n+ > T m using the non-classical model of homogeneous nucleation [ 1 , 33 , 34 , 51 ] confirmed by experimental observations [ 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ]. These predictions had established that the medium-range order persists in liquids from T g up to T n+ due to residual bonds producing endothermic enthalpy or due to antibonds producing exothermic enthalpy at T n+ where the homogeneous state of liquids appears.…”

“…Glass transition temperatures are observed at a temperature T = T g during heating of quenched melts. Below T g , atomic bonds system produces enthalpy relaxation between the two homogeneous nucleation temperatures T n− of the glassy phase with the highest being T g [ 1 , 2 ]. The glass formation at the lowest T n- occurs in hyperquenched glass-forming melts at the departure of the enthalpy relaxation [ 3 , 4 , 5 , 6 ].…”

“…The reduced temperatures θ 0m and θ 0g are the Vogel–Fulcher–Tammann temperatures of these two liquids and are defined by the coefficients ε ls0 and ε gs0 , depending on the nucleation temperatures in the two liquids equal to [ε ls (θ) − 2]/3 for ∆ε = 0 [ 1 , 36 ]. The reduced glass transition temperature θ g is used to define them [ 37 , 38 , 39 ].…”