Densities Of Melts Research Articles

Densities of Au-X (X = Cu, Ni and Pd) binary melts and thermodynamic correlations

Our group has previously investigated the correlations between the excess volumes, thermodynamic functions and phase diagrams of binary alloy melts, and the present study focused on binary Au-X (X = Cu, Pd and Ni) alloy melts. The Au-Cu and Au-Pd systems have intermetallic compounds with order–disorder transitions. The densities of these alloy melts were determined with small uncertainties using a combination of an electromagnetic levitation technique and a static magnetic field. The densities of these melts varied linearly with temperature, including those temperatures within the supercooled range. These results are discussed herein within a thermodynamic framework based on the correlation between excess volume (VE) and excess Gibbs energy (GE). The data obtained in this work confirmed that binary alloy systems having an order–disorder transition, such as the Au-Cu and Au-Pd systems, belonged to the group defined by VE ≥ 0 and GE < 0. The effect of composition on VE was examined with regard to cluster formation in the liquids. The Au-Ni system was shown to possess a miscibility gap in the solid solution and the corresponding melts had positive VE and positive GE values.

Sound velocity and compressibility of melts along the hedenbergite (CaFeSi2O6)-diopside (CaMgSi2O6) join at high pressure: Implications for stability and seismic signature of Fe-rich melts in the mantle

Iron-rich silicate melts play an important role in the magmatic history of the Earth and the Moon. However, their elastic properties at high pressures, especially the sound velocities, are poorly understood. Here we determined the ultrasonic sound velocities of two silicate melts along the hedenbergite (Hd, CaFeSi2O6) – diopside (Di, CaMgSi2O6) join at high pressure and temperature conditions up to 6 GPa and 2329 K, using the high-pressure ultrasonic technique combined with synchrotron radiation in a multi-anvil apparatus. Our results show that Fe can significantly reduce the sound velocity while increasing the density of silicate melts. Comparing the melts of Di, Hd, and a mixture of 50 mol% hedenbergite + 50 mol% diopside (Hd50Di50), we find that although densities of the Hd-Di melts can be well-described by a linear mixing law empirically at high pressures, sound velocities do not vary with composition linearly. Assuming that the low-velocity regions in Earth's upper mantle are mainly due to the presence of partial melt, we applied our results to study the gravitational stability and seismic signature of Fe-rich silicate melts in the mantle, combined with melt geometry and compaction models. For the low-velocity zone (LVZ) in mantle asthenosphere, although the degree of seismic velocity reduction can be explained by the presence of a small amount of partial melt distributed in film/band geometry along grain boundaries, silicate melts formed in this depth range are too light to be gravitationally stable, but may be completely entrained in the convecting mantle due to the small melt fraction and low melt-matrix separation velocity. For the low-velocity layer (LVL) above the mantle transition zone, the presence of Fe-rich melts (with FeO>∼10 wt%) distributed in textural equilibrium with the ambient mantle is a plausible explanation.

Density and Molar Volume of Molten GdCl3–NaCl and GdCl3–KCl Binary Mixtures

The densities of the salt melts of the GdCl3–NaCl and GdCl3–KCl systems are determined by the dilatometric method over the entire concentration range and in a wide temperature range. The molar volumes of the systems and their deviations from additivity are calculated. All electrolyte composition dependences are nonlinear. The results can be used in the manufacture of gadolinium and its compounds and for the refinement of the structures of the molten salt systems under study.

A petrologic study on the effect of mantle overturn: Implications for evolution of the lunar interior

Abstract Lunar mantle overturn caused by gravitational instability of the Fe-Ti rich KREEP layer (formed as the last 5% of a crystallizing magma ocean, and emplaced between the overlying anorthitic crust and the underlying lunar mantle) is a process that would introduce Fe-Ti enriched bodies deep inside the lunar interior. These chemical heterogeneities in the lunar mantle may be the source of the very Fe-Ti enriched near-primary Apollo basalts. Also, the Fe-Ti and KREEP enriched layer deep inside the Moon may be responsible for the 5–30% partial melt seismically detected close to the core-mantle boundary (CMB). This is assuming that the partial melt is neutrally buoyant at P-T conditions of the CMB. Here, we experimentally investigate the phase equilibria of the overturned Fe-Ti rich layer mixed with the mantle, at P-T conditions deep inside the lunar interior, focusing on the partial melt compositions formed. Our aim is to test (a) whether potential partial melt compositions formed near the CMB are neutrally buoyant with respect to the surrounding mantle, hence, stable; (b) if the partial melts formed within the lunar interior are positively buoyant and ascend, whether they can reproduce chemical characteristics of Apollo basalts. The densities calculated for the Fe-Ti rich partial melts from this study, using the physical parameters from previous studies, range from lower to higher values compared to that of the lunar mantle. This provides a basis for future investigations to experimentally constrain better the densities of these partial melts. Depending on the buoyancy of the partial melts, the following two scenarios are likely to happen. Firstly, if the partial melts are neutrally buoyant at the CMB, 5–30% partial melt would constrain the CMB temperatures between 1330(±1) and 1470(±19) °C. This can be used by future studies to derive the selenotherm better. Secondly, if the partial melts are positively buoyant, they should ascend and react with the mantle along their path. Upon reaching shallow depths below the crust, they may likely assimilate any Fe-Ti rich layer that was left over from the gravitational overturn, as well as undergo olivine fractionation upon pooling in a shallow magma chamber. We modeled assimilation-fractional crystallization of the partial melts using the Gibb’s-free minimization algorithm alphaMELTS. Our results show that reactive ascent of Fe-Ti rich partial melts through the lunar mantle and subsequent olivine fractionation in a shallow magma chamber is a promising way to evolve the melt compositions to converge with the lunar basalts better. Shallow level assimilation of Fe-Ti rich lithology post reactive-ascent through the mantle is also feasible, but only for low degrees of assimilation.

DensityX: A program for calculating the densities of magmatic liquids up to 1,627 °C and 30 kbar

Here we present a standalone program, DensityX, to calculate the densities of hydrous silicate melts (1000s of samples in a single model run) given pressures, temperatures, and major oxide compositions in wt.% in the 10-component system SiO2-TiO2-Al2O3-Fe2O3-FeO-MgO-CaO-Na2O-K2O-H2O. We use DensityX to analyze over 3,000 melt inclusions over a wide compositional range to visualize the distribution of natural silicate liquid densities in the Earth’s crust. The program is open-source, written in Python, and can be accessed and run via an online interface through a web browser at https://densityx.herokuapp.com or by downloading and running the code from a github repository. A companion Excel spreadsheet can also be used to run density calculations identical to those in the Python script but only for one sample at a time. In another example application, we demonstrate how DensityX can be used to constrain density-driven convective cycling in the phonolitic lava lake of Erebus volcano, Antarctica.

A Brillouin scattering study of hydrous basaltic glasses: the effect of H2O on their elastic behavior and implications for the densities of basaltic melts

Hydrous basalt glasses with water contents of 0–6.82% were synthesized using a multi-anvil press at 1.0–2.0 GPa and 1200–1400 °C. The starting materials were natural Mesozoic basalts from the eastern North China Craton (NCC). Their sound velocities and elastic properties were measured by Brillouin scattering spectroscopy. The longitudinal (VP) and shear (VS) wave velocities decreased with increasing water content. Increasing the synthesis pressure resulted in the glass becoming denser, and finally led to an increase in VP. As the degree of depolymerization increased, the VP, VS, and shear and bulk moduli of the hydrous basalt glasses decreased, whereas the adiabatic compressibility increased. The partial molar volumes of water (\(\nu\)) under ambient conditions were independent of composition, having values of 11.6 ± 0.8, 10.9 ± 0.6 and 11.5 ± 0.5 cm3/mol for the FX (Feixian), FW (Fuxin), and SHT (Sihetun) basalt glasses, respectively. However, the \({{V}_{{{\text{H}}_{\text{2}}}\text{O}}}\) values measured at elevated temperatures and pressures are increasing with increasing temperature or decreasing pressure. The contrasting densities of these hydrous basalt melts with those previously reported for mid-ocean ridge basalt and preliminary reference Earth model data indicate that hydrous basalt melts may not maintain gravitational stability at the base of the upper mantle.

Density measurements of gasified coal and synthesized slag melts for next-generation IGCC

The densities of re-melted coal slag melts were measured in air using Archimedean double-bob method in the temperature range from 1350 to 1600°C. The main components of gasified coal slags are SiO2, Al2O3, CaO, MgO, FeO and Fe2O3. Slags consisting of the main components with systematic composition variations were synthesized and evaluated for comparison. The experimental results of chelate titration analysis revealed that the percentages of Fe3+ in coal and synthesized slag samples were 47–56% and 68–80% of total Fe, respectively. The density decreased linearly with increasing temperature for all melt samples. The density of gasified and synthesized coal slag melts was found to decrease with increasing Al2O3 and SiO2 contents and to increase with increasing Fe2O3 and FeO contents. The molar volume and the coefficient of volume expansion, which were calculated from measured density values, increased monotonically with increasing Al2O3 content for CaOAl2O3SiO2 (CAS) synthesized samples with 40mol% SiO2. The molar volume for CaOFeOFe2O3SiO2 (CFS) synthesized samples with 60mol% SiO2 increased with Fe2O3 addition and exhibited discontinuous change at ∼7.5mol% Fe2O3. The coefficient of volume expansion in the same CFS series decreased with increasing Fe2O3 content showing a minimum value at ∼7mol% Fe2O3 and increased in higher Fe2O3 content. A composition parameter calculated from chemical composition was proposed to predict the density of coal slag melts. The relationship between measured density and the composition parameter was analyzed.

Density and seismic velocity of hydrous melts under crustal and upper mantle conditions

We present a new model for calculating the density of hydrous silicate melts as a function of P, T, H2O concentration, and melt composition. We optimize VPr,Tr, ∂V/∂T, ∂V/∂P, ∂V2/∂T∂P, and K′ of H2O end-member components in hydrous silicate melts, as well as K′ of anhydrous silicate melts, using previously reported experimental results. The parameter set for H2O end-member component in silicate melt optimized in this study is internally consistent with the parameter values for the properties of anhydrous silicate melt reported by Lange and Carmichael (1987, 1990). The model calculation developed in this study reproduces the experimentally determined densities of various hydrous melts, and can be used to calculate the relationships between pressures, temperatures, and H2O concentrations of various hydrous melts from ultramafic to felsic compositions at pressures of 0–4.29 GPa. Using the new parameter set, we investigate the effects of H2O content on the seismic velocity of hydrous melts, as well as seismic velocities in partially molten regions of subduction zones. The results show that water content in silicate melt plays a key role in determining seismic velocity structure, and therefore must be taken into account when interpreting seismic tomography.

Melt-phase behavior of collapsed PMMA/PVC chains revealed by multiscale simulations.

Single- and double-chain models of three stereoregular polymers, iso- and syndiotactic poly(methyl methacrylate) and isotactic poly(vinyl chloride), were extensively simulated using systematic coarse-grained (CG) potentials. It was found that, in vacuum, all of these long chains collapse in a two-stage process from their fully extended configurations into coils, and the two chains in each double-chain model ultimately become intertwined. Strong intermolecular interactions were found to occur between two chains of the same polymer ("like pairs"), which helps to explain the high densities of single-component melts. However, the intermolecular interactions between two chains of different polymers ("unlike pairs") were stronger than those in like pairs. The enthalpy of mixing for unlike pairs-obtained from their intermolecular interaction energies-was negative, indicating that the two binary blends considered here are homogeneous systems. Moreover, a more negative enthalpy of mixing is suggested to correlate with better miscibility. These results agree well with corresponding experimental and simulated results, once again validating the accuracy of CG potentials when they are used to explore structural and energetic properties. The local structure captured by the isolated long chains dictates the ability to elucidate melt-phase behavior. A scheme involving the preparation of bulk models with initially collapsed chains was proposed; such CG models could be widely used to rapidly screen pairs of polymers for specific applications.

Thermal analysis and volume properties of the systems (LiF–CaF2)eut.–LnF3 (Ln = Sm, Gd, and Nd) up to 1273 K

Systems (LiF–CaF2)eut.–LnF3 (Ln = Sm, Gd, and Nd) were investigated by means of thermal analysis and density measurements. Temperatures of primary crystallisation were measured and solidified samples were analysed by XRD as well as by SEM images and EDX mapping of the solidified samples. Densities of individual melts were measured by hydrostatic weighting (Archimedean method). Consequently, molar volumes were calculated. Unusual behaviour was observed in all three cases, when molar volumes decrease with initial LnF3 additions up to 1 mol % of LnF3. Further LnF3 additions result in molar volumes increase. In the case of GdF3 system, anomalous molar volume behaviour was observed: over 1 mol % of GdF3 molar volume is higher at lower temperatures. Partial molar volumes of LnF3 components were analysed by both simple linear or polynomial regression and multicomponent polynomial regression using least square parameters minimisation procedure. With increasing temperature, partial molar volumes of LnF3 decrease even to negative values.

Prediction of thermodynamic behavior of copolymers using equation of state and artificial neural network

A simplified procedure with minimum input information for predicting of the densities of copolymer melts is presented. This new correlation has been applied to the Tao-Mason (TM) equation of state to predict the volumetric behavior of copolymer melts including poly(ethylene-co-propylene) (PEP), poly(ethylene-co-vinyl acetate) (PEVA), poly(ethylene-co-metacrylic acid) (PEMA), poly(ethylene-co-acrylic acid) (PEAA), poly(ethylene-co-vinyl alcohol) (PEVOH), poly(styrene-co-acrylonitrile) (PSAN), and poly(acrylonitrile-co-butadiene) (PANB). Also another model such as an artificial neural network (ANN) based on backpropagation training with 13 neurons was used. The obtained results by TM and ANN models had good agreement with the experimental data with absolute average deviations of 1.34 and 0.49 %, respectively.

High-temperature heat capacity and density of simulated high-level waste glass

The heat capacities of two simulated high-level waste borosilicate glasses and glass melts have been determined from differential scanning calorimetry and drop-calorimetry measurements between 345K and 1673K. The densities of the glass melts have been measured by double-bob Archimedean method between 1273K and 1573K. The volume expansivity between glass transition temperature and 1573K has been determined by combining the measured densities and density of supercooled melts below 1273K reported previously. Both of the heat capacity and the volume expansivity of the simulated high-level waste glass melts are characterized by a large increase at the glass transition temperature and the rapid decrease with increasing temperature. The configurational contributions to the heat capacity and the volume expansivity at the glass transition temperature are 35% and 88%, respectively. The significant change of the heat capacity is probably attributed to temperature dependence of chemical mixing of boron, aluminum and silicon in the tetrahedral sites, while the change of the volume expansivity is caused by temperature-induced coordination change of boron.

The fate of magmas in planetesimals and the retention of primitive chondritic crusts

High abundances of short-lived radiogenic isotopes in the early solar system led to interior melting and differentiation on many of the first planetesimals. Petrologic, isotopic, and paleomagnetic evidence suggests that some differentiated planetesimals retained primitive chondritic material. The preservation of a cold chondritic lid depends on whether deep melts are able to ascend and breach the chondritic crust. We evaluate the likelihood of melt ascent on a range of chondritic parent bodies. We find that, due to the efficient ascent of free volatiles in the gas and supercritical fluid phases at temperatures still below the solidus for silicates and metals, mobile silicate melts on planetesimals were likely volatile-depleted. By calculating the densities of such melts, we show that silicate melts likely breached crusts of enstatite chondrite compositions but did not ascend in the CV and CM parent bodies. Ordinary chondrite melts represent an intermediate case. These predictions are consistent with paleomagnetic results from CV and CM chondrites as well as spectral observations of large E-type asteroids.

Densities and Apparent Molar Volumes of Atmospherically Important Electrolyte Solutions. 1. The Solutes H2SO4, HNO3, HCl, Na2SO4, NaNO3, NaCl, (NH4)2SO4, NH4NO3, and NH4Cl from 0 to 50 °C, Including Extrapolations to Very Low Temperature and to the Pure Liquid State, and NaHSO4, NaOH, and NH3 at 25 °C

Calculations of the size and density of atmospheric aerosols are complicated by the fact that they can exist at concentrations highly supersaturated with respect to dissolved salts and supercooled with respect to ice. Densities and apparent molar volumes of solutes in aqueous solutions containing the solutes H(2)SO(4), HNO(3), HCl, Na(2)SO(4), NaNO(3), NaCl, (NH(4))(2)SO(4), NH(4)NO(3), and NH(4)Cl have been critically evaluated and represented using fitted equations from 0 to 50 °C or greater and from infinite dilution to concentrations saturated or supersaturated with respect to the dissolved salts. Using extrapolated densities of high-temperature solutions and melts, the relationship between density and concentration is extended to the hypothetical pure liquid solutes. Above a given reference concentration of a few mol kg(-1), it is observed that density increases almost linearly with decreasing temperature, and comparisons with available data below 0 °C suggest that the fitted equations for density can be extrapolated to very low temperatures. As concentration is decreased below the reference concentration, the variation of density with temperature tends to that of water (which decreases as temperature is reduced below 3.98 °C). In this region below the reference concentration, and below 0 °C, densities are calculated using extrapolated apparent molar volumes which are constrained to agree at the reference concentrations with an equation for the directly fitted density. Calculated volume properties agree well with available data at low temperatures, for both concentrated and dilute solutions. Comparisons are made with literature data for temperatures of maximum density. Apparent molar volumes at infinite dilution are consistent, on a single ion basis, to better than ±0.1 cm(3) mol(-1) from 0 to 50 °C. Volume properties of aqueous NaHSO(4), NaOH, and NH(3) have also been evaluated, at 25 °C only. In part 2 of this work (ref 1 ) an ion interaction (Pitzer) model has been used to calculate apparent molar volumes of H(2)SO(4) in 0-3 mol kg(-1) aqueous solutions of the pure acid and to represent directly the effect of the HSO(4)(-) ↔ H(+) + SO(4)(2-) reaction. The results are incorporated into the treatment of aqueous H(2)SO(4) density described here. Densities and apparent molar volumes from -20 to 50 °C, and from 0 to 100 wt % of solute, are tabulated for the electrolytes listed in the title and have also been incorporated into the extended aerosol inorganics model (E-AIM, http://www.aim.env.uea.ac.uk/aim/aim.php) together with densities of the solid salts and hydrates.

High-pressure melting relations in Fe–C–S systems: Implications for formation, evolution, and structure of metallic cores in planetary bodies

We present new high-pressure temperature experiments on melting phase relations of Fe–C–S systems with applications to metallic core formation in planetary interiors. Experiments were performed on Fe–5 wt% C–5 wt% S and Fe–5 wt% C–15 wt% S at 2–6 GPa and 1050–2000 °C in MgO capsules and on Fe–13 wt% S, Fe–5 wt% S, and Fe–1.4 wt% S at 2 GPa and 1600 °C in graphite capsules. Our experiments show that: (a) At a given P– T, the solubility of carbon in iron-rich metallic melt decreases modestly with increasing sulfur content and at sufficiently high concentration, the interaction between carbon and sulfur can cause formation of two immiscible melts, one rich in Fe-carbide and the other rich in Fe-sulfide. (b) The mutual solubility of carbon and sulfur increases with increasing pressure and no super-liquidus immiscibility in Fe-rich compositions is likely expected at pressures greater than 5–6 GPa even for bulk compositions that are volatile-rich. (c) The liquidus temperature in the Fe–C–S ternary is significantly different compared to the binary liquidus in the Fe–C and Fe–S systems. At 6 GPa, the liquidus of Fe–5 wt% C–5 wt% S is 150–200 °C lower than the Fe–5 wt% S. (d) For Fe–C–S bulk compositions with modest concentration of carbon, the sole liquidus phase is iron carbide, Fe 3C at 2 GPa and Fe 7C 3 at 6 GPa and metallic iron crystallizes only with further cooling as sulfur is concentrated in the late crystallizing liquid. Our results suggest that for carbon and sulfur-rich core compositions, immiscibility induced core stratification can be expected for planets with core pressure less than ∼6 GPa. Thus planetary bodies in the outer solar system such as Ganymede, Europa, and Io with present day core–mantle boundary (CMB) pressures of ∼8, ∼5, and 7 GPa, respectively, if sufficiently volatile-rich, may either have a stratified core or may have experienced core stratification owing to liquid immiscibility at some stage of their accretion. A similar argument can be made for terrestrial planetary bodies such as Mercury and Earth’s Moon, but no such stratification is predicted for cores of terrestrial planets such as Earth, Venus, and Mars with the present day core pressure in the order ⩾136 GPa, ⩾100 GPa, and ⩾23 GPa. (e) Owing to different expected densities of Fe-rich (and carbon-bearing) and sulfur-rich metallic melts, their settling velocities are likely different; thus core formation in terrestrial planets may involve rain of more than one metallic melt through silicate magma ocean. (f) For small planetary bodies that have core pressures <6 GPa and have a molten core or outer core, settling of denser carbide-rich liquid or flotation of lighter, sulfide-rich melt may contribute to an early, short-lived geodynamo.

The density of volatile bearing melts in the Earth's deep mantle: The role of chemical composition

Density of silicate melts in the Earth's deep interior is important to understand the material circulations in the mantle. We study the role of chemical composition on melt density based on the ideal-mixing model and the third-order Birch–Murnaghan equation of state (EOS). Using this EOS, the role of composition can be understood through its effect on three EOS parameters: room-pressure density, room-pressure bulk modulus, and the pressure derivative of bulk modulus at room pressure. The dependences of these parameters on compositional variables such as Mg# (molar MgO/(MgO + FeO) × 100) of the melt, SiO 2 content in the dry part of the melt, and H 2O content in the melt are estimated from available experimental data in the literature using the ideal-mixing model. Results show that H 2O content and Mg# of the melt are the most important factors that control the melt density at high pressure. Calculated densities of silicate melts are compared to the density of the ambient upper mantle from the PREM model near 410 km depth where dehydration-induced melting may occur. The relative density between the melt and the surrounding solid minerals is sensitive to the water content, Mg# and temperature at the conditions of melting. For an Mg# that is consistent with the pyrolite model, the conditions for density crossovers are marginally satisfied for a system when water (hydrogen) is the only volatile component to promote melting.

An instrument for determining the densities of liquid metals and alloys

An instrument for determining the densities of liquid-metal melts with the pyknometry technique is described. The performed tests of the instrument that involved measurements of the temperature dependence of the liquid-bismuth density have shown that the device allows obtainment of reliable and highly accurate (measurement accuracy of ∼0.06%) data on the density under the conditions of a high vacuum or an atmosphere of various gases.

Temperature dependence of densities of Sb and Bi melts

The densities of Sb and Bi melts were investigated by an improved Archimedean method. The results show that the density of the Sb melt decreases linearly with increasing temperature, but the density of the Bi melt firstly increases and then decreases as the temperature increases. There is a maximum density value of 10.002 g/cm3 at 310°C, about 39°C above the melting point. The temperature dependence of the Sb melt is well fitted with the expression ρ=6.8590−5.8105×10−4 T, and that of the Bi melt is fitted with ρ=10.3312−1.18×10−3 T. The results were discussed from a microstructure viewpoint.

A partial molar volume for La 2O 3 in silicate melts

The densities of several La-bearing silicate melts distributed along binary joins have been measured using the double-bob Archimedean method. The results show that the addition of La 2O 3 leads to an increase in the melt density. From these density data, the partial molar volume of La 2O 3 in silicate melts has been determined. Distinct values for partial molar volume of La 2O 3 have been obtained (i.e., 44.01 and 37.04 cm 3/mol at 1273 K for the La 2O 3–Na 2O–SiO 2 and La 2O 3–CaO–MgO–Al 2O 3–SiO 2 systems, respectively) indicating a compositional dependence of the partial molar volume of La 2O 3. Nevertheless, a single value for the partial molar volume of La 2O 3 (i.e., 43.47 cm 3/mol at 1273 K) suffices to describe the molar volume of melts within errors in the entire multi-component system La 2O 3–Na 2O–CaO–MgO–Al 2O 3–SiO 2 and for La 2O 3 concentrations not greater than 7 mol%. In addition, this work points out that the molar volumes behave ideally within the composition range investigated (i.e., linear variation of the molar volume along the binary joins). Distinct values for the partial molar volume of La 2O 3 obtained in this study and their differences with the molar volumes of molten La 2O 3 given in the literature raise the possibility however that this ideality is not maintained within the entire system.

High-temperature density of lanthanide-bearing Na-silicate melts: Partial molar volumes for Ce2O3, Pr2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, and Yb2O3

This work presents the first systematic determination of the partial molar volumes of lanthanide sesquioxides in silicate melts. For this purpose, the densities of various lanthanide-bearing Na-silicate melts distributed along various binary joins, where the end-members are Na-disilicate and one of the lanthanide sesquioxides (i.e., Ce 2 O 3 , Pr 2 O 3 , Nd 2 O 3 , Sm 2 O 3 , Eu 2 O 3 , Gd 2 O 3 , Tb 2 O 3 , Dy 2 O 3 , Ho 2 O 3 , Er 2 O 3 , Tm 2 O 3 , and Yb 2 O 3 ), have been measured using the double-bob Archimedean method. The present results show that the addition of any lanthanide to Na-disilicate leads to an increase in the melt density and that the melt density increases with increasing atomic number of the lanthanide. From the present density data set, the molar volumes of these melts have been calculated and the partial molar volumes of each lanthanide sesquioxide in these melts have been determined using a linear regression through each binary join (i.e., Na-disilicate-lanthanide sesquioxide). This study indicates an ideal behavior with respect to the molar volume (i.e., a linear variation of the molar volume along each binary join) for Na-silicate melts containing up to 6 mol% of lanthanide oxide. Comparison between the partial molar volumes of lanthanide sesquioxides obtained in this study and the molar volumes of molten lanthanide sesquioxides given in the literature raises the possibility, however, that this ideality is not maintained along the entire Na-disilicate-lanthanide sesquioxide binary joins. Excess volumes of mixing appear to be required to describe the combined volumetric data set.