Thermodynamic and rheological properties of rhyolite and andesite melts

The heat capacities of a rhyolite and an andesite glass and liquid have been investigated from relative-enthalpy measurements made between 400 and 1800 K. For the glass phases, the experimental data agree with empirical models of calculation of the heat capacity. For the liquid phases, the agreement is less good owing to strong interactions between alkali metals and aluminum, which are not currently accounted for by empirical heat capacity models. The viscosity of both liquids has been measured from the glass transition to 1800 K. The temperature dependence of the viscosity is quantitatively related to the configurational heat capacity (determined calorimetrically) through the configurational entropy theory of relaxation processes. For both rhyolite and andesite melts, the heat capacity and viscosity do not differ markedly from those obtained by additive modeling from components with mineral compositions

Glass, an ubiquitous material

Glasses play a fundamental role in our daily lives at the economic, cultural, societal, energy and geological levels. Geological glasses testify to igneous activity of the Earth and represent an important material for tools and ornamental objects from the Paleolithic to the present day. Glasses are also used to manufacture technical materials, such as containers (dishes, glasses, jars, bottles ...), screens (television, computer, smartphone ...), fibers with multiple applications (reinforcement, information, transport, energy, health ...), to ensure the storage of domestic or nuclear waste and, more recently, biomaterials (dental or bone implants ...). Thus, silica-based glasses are at the heart of the history of the Earth and humanity. The variation in composition of natural and industrial glasses is vast but its structure is generally based on a tetrahedral frame of $\mathrm{SiO}_{4}$ units, the backbone of more than 90% of the glasses that surround us in our daily lives. Around this silica frame, other chemical elements are well constrained to form to form a single unit structure for use as network modifying elements, charge compensator, dyes, volatiles, and other substances. This article is a short introduction on glass

Glass, an ubiquitous material

Glasses play a fundamental role in our daily lives at the economic, cultural, societal, energy and geological levels. Geological glasses testify to igneous activity of the Earth and represent an important material for tools and ornamental objects from the Paleolithic to the present day. Glasses are also used to manufacture technical materials, such as containers (dishes, glasses, jars, bottles ...), screens (television, computer, smartphone ...), fibers with multiple applications (reinforcement, information, transport, energy, health ...), to ensure the storage of domestic or nuclear waste and, more recently, biomaterials (dental or bone implants ...). Thus, silica-based glasses are at the heart of the history of the Earth and humanity. The variation in composition of natural and industrial glasses is vast but its structure is generally based on a tetrahedral frame of $\mathrm{SiO}_{4}$ units, the backbone of more than 90% of the glasses that surround us in our daily lives. Around this silica frame, other chemical elements are well constrained to form to form a single unit structure for use as network modifying elements, charge compensator, dyes, volatiles, and other substances. This article is a short introduction on glass

Deformation of silica glass studied by molecular dynamics: Structural origin of the anisotropy and non-Newtonian behavior

International audienceA novel aspect of the medium-range structure of silica drawn into fibers is studied. The network of silica glass structure is composed of corner-shared SiO 4 tetrahedra, and it can be seen as a structure of interconnected rings (Si-O) n of various size, denoted nMR (n-Membered Ring). Molecular Dynamics simulations show that small-sized silica rings get a preferential orientation during the drawing, either during the high-temperature stage for 3MR, or during the cooling for 4MR and 5MR, and they persist in this state in the fiber at ambient temperature. This leads to a structural anisotropy, more specifically a " transverse isotropy " , because of different longitudinal and transversal physical properties. This anisotropic structural rearrangement during the drawing process induces a non-Newtonian behavior of the modeled glass melt, with strain-rate dependent properties. Highlights: Anisotropy in silica glass comes from the orientation that small silica rings acquire during the deformation. The model is in agreement with experiments (non-Newtonian behavior of the melt, anisotropic elasticity of the fiber). The anisotropy in silica fiber is a " transverse isotropy "

Thermodynamic and rheological properties of rhyolite and andesite melts

The heat capacities of a rhyolite and an andesite glass and liquid have been investigated from relative-enthalpy measurements made between 400 and 1800 K. For the glass phases, the experimental data agree with empirical models of calculation of the heat capacity. For the liquid phases, the agreement is less good owing to strong interactions between alkali metals and aluminum, which are not currently accounted for by empirical heat capacity models. The viscosity of both liquids has been measured from the glass transition to 1800 K. The temperature dependence of the viscosity is quantitatively related to the configurational heat capacity (determined calorimetrically) through the configurational entropy theory of relaxation processes. For both rhyolite and andesite melts, the heat capacity and viscosity do not differ markedly from those obtained by additive modeling from components with mineral compositions

Structural characterization of SiO2-Na2O-CaO-B2O3-MoO3 glasses

5 pagesNuclear spent fuel reprocessing generates high level radioactive waste with high Mo concentration that are currently immobilized in borosilicate glass matrices containing both alkali and alkaline-earth elements [1]. Because of its high field strength, Mo6+ ion has a limited solubility in silicate and borosilicate glasses and crystallization of alkali or alkaline-earth molybdates can be observed during melt cooling or heat treatment of glasses [2-4]. Glass composition changes can significantly modify the nature and the relative proportions of molybdate crystals that may form during natural cooling of the melt. For instance, in a previous work we showed that CaMoO4 crystallization tendency increased at the expenses of Na2MoO4 when B2O3 concentration increased in a SiO2-Na2O-CaO-MoO3 glass composition [4]. In this study, we present structural results on two series (Mx, By) of quenched glass samples belonging to this system using 29Si, 11B, 23Na MAS NMR and Raman spectroscopies. The effect of MoO3 on the glassy network structure is studied and its structural role is discussed (Mx series). The evolution of the distribution of Na+ ions within the borosilicate network is followed when B2O3 concentration increased (By series) and is discussed according to the evolution of the crystallization tendency of the melt. For all glasses, ESR was used to investigate the nature and the concentration of paramagnetic species

Percolation channels:A universal idea to describe the atomic structure and dynamics of glasses and melts

Understanding the links between chemical composition, nano-structure and the dynamic properties of silicate melts and glasses is fundamental to both Earth and Materials Sciences. Central to this is whether the distribution of mobile metallic ions is random or not. In silicate systems, such as window glass, it is well-established that the short-range structure is not random but metal ions cluster, forming percolation channels through a partly broken network of corner-sharing SiO4 tetrahedra. In alumino-silicate glasses and melts, extensively used in industry and representing most of the Earth magmas, metal ions compensate the electrical charge deficit of AlO4? tetrahedra, but until now clustering has not been confirmed. Here we report how major changes in melt viscosity, together with glass Raman and Nuclear Magnetic Resonance measurements and Molecular Dynamics simulations, demonstrate that metal ions nano-segregate into percolation channels, making this a universal phenomenon of oxide glasses and melts. Furthermore, we can explain how, in both single and mixed alkali compositions, metal ion clustering and percolation radically affect melt mobility, central to understanding industrial and geological processespublishersversionPeer reviewe