Na2O Al2O3 SiO2 Research Articles

Novel nanostructured transparent Na2O–Al2O3–SiO2 carnegieite-based glass ceramics with high crystallinity

Developing next-generation cover glasses with high crystallinity and transmittance, such as transparent nanocrystalline Na2O–Al2O3–SiO2 (NAS) glass, has proved highly challenging. Herein, we propose a novel nanostructured transparent NAS glass–ceramic with high crystallinity (65 %) and transmittance (91 %) owing to the involved separation of crystallization peaks and the diffusion barrier properties of ZrO2. Compared with untreated glass, this glass-ceramic shows a considerable increase in hardness (from 5.18 to 7.15 GPa, i.e. >38 %). With the increased crystallinity, no substantial reduction in transmission is detected and the crystal type and size can be effectively controlled by the limitation of ZrO2. Hence, the findings project a novel method for creating high crystallinity and transmittance, providing new directions for transparent NAS glass–ceramic.

Correlation of rare earth coordination and spectral properties in Er3+ doped Na2O–Al2O3–SiO2 glasses with different Al2O3 concentrations by molecular dynamics simulations

The molecular structure of Er2O3 doped Na2O–Al2O3–SiO2 glasses with varying Na2O/Al2O3 ratios is explored via molecular dynamics (MD) simulations using the so-called inherent structure sampling method, which allows the calculation of a large number of local structures of low concentration, as needed to determine the surrounding of low concentration dopants. General structural parameters, including radial distribution functions, coordination numbers and interatomic distances of all network forming and network modifying ions are reported. However, in this work, special attention is devoted to the effect of Al2O3 concentration on the local surrounding of the doped Er3+ ions. It is shown that the Er atoms coordinate 5–6 oxygen ions in their first coordination sphere in the investigated glasses. The Er–O coordination number increases monotonically with increasing Al2O3 concentration and decreasing Na2O/Al2O3 ratio. It is found that the Er atoms are preferably connected to non-bridging oxygen atoms (NBO) in all glasses, even in the peraluminous composition. Additionally, the MD simulation results are compared to the glasses spectral properties that were already investigated in detail by Tanabe and Hanada. The increasing Er-NBO coordination number derived by MD simulations could be correlated with the increased peak splitting of the Er3+ absorption peaks reported by Tanabe and Hanada. Furthermore, a correlation between the Judd-Ofelt parameters published by Tanabe and Hanada and the Er3+ coordination in the glass structure is discussed. It is shown that the Er–O coordination increases with increasing Ω2 parameter as the Al2O3 concentration increases in the glass composition. A correlation of the average overall Er–O coordination number with the symmetry of the local Er site is proposed.

Gamma attenuation characteristics of silicon-rich glasses in Na2O–SiO2–Al2O3– CaO–ZnO system for radiation applications

This study focuses on the investigation of the gamma attenuation properties of a 15Na2O–50SiO2–10Al2O3-(25-x)CaO-xZnO-1CeO2-1Yb2O3 (x = 0, 5, and 10 mol%) glassy system using Geant4 Monte Carlo and theoretical approaches. Geant4, a Monte Carlo simulation package, is employed to accurately model the interaction of photons with the glassy system involved. Additionally, theoretical calculations are utilized to obtain the attenuation parameters based on the elemental composition and density of the glass system by the helping of computer software. Such evaluated key attenuation parameters includes attenuation coefficients, energy deposition profiles, and transmission factors for different radiation sources and energies. Various configurations of the glass system, incorporating different compositions and thicknesses, are analyzed to optimize the shielding effectiveness. The results revealed that the replacement of CaO by ZnO in the composition of the present silicate glassy system lead to increase in the density and this impacts clearly on attenuation ability to be high. For example, the μ/ρ values, at 15 keV, are 15.649, 18.286, and 20.831 cm2/g for the samples SiNaAl/CZ1, SiNaAl/CZ2, and SiNaAl/CZ3, respectively as ZnO increases from 0 to 10 mol%. The glass system under examination shows promising potential for radiation shielding applications in nuclear and medical settings. This research contributes to the development of efficient radiation shielding materials, facilitating the design of enhanced safety measures in nuclear and medical industries.

Tailoring electromagnetic wave absorption using in-situ precipitation of BaTiO3–BaFe12O19 glass ceramic

Utilizing a BaO–TiO2–B2O3–Na2O–SiO2–Al2O3–Fe2O3 multicomponent glass system, this study achieves in-situ precipitation of BaTiO3 and BaFe12O19 within a glass matrix. This method enables precise control over crystal content and electromagnetic properties. An optimal composition ratio of BaTiO3 to BaFe12O19 at 3:2 demonstrates exceptional impedance matching and remarkable electromagnetic attenuation. At 3.7 GHz, the glass ceramic exhibits a minimal reflection loss of −44.5 dB, while maintaining an effective absorption bandwidth of 3.93 GHz with a 2 mm thickness. This research underscores the promising potential of magnetoelectric glass ceramics as advanced materials for achieving high-performance electromagnetic wave absorption.

Hydrogen Permeability of Tectosilicate Glasses for Tank Barrier Liners

The permeation of hydrogen gas was studied in meta-aluminous (tectosilicate) glass powders of Li2O×Al2O3×SiO2 (LAS), Na2O×Al2O3×SiO2 (NAS) and MgO×Al2O3×SiO2 (MAS) systems by pressure loading and vacuum extraction in the temperatures range 210–310 °C. With this method, both the solubility S and the diffusivity D were determined, while the permeability was given by the product SD. For all glasses, S was found to decrease with temperature, while D increased. Since the activation energy of diffusion of H2 molecules exceeded that of dissolution, permeation increased slightly with temperature. When extrapolated to standard conditions (25 °C), the permeability of tectosilicate glasses was found to be only 10-22–10-24 mol H2 (m s Pa)-1, which is 8–10 magnitudes lower than most polymers. Thin glass liners of these compositions are expected to be the most effective barrier for tanks of pressurised hydrogen.

Study on Slagging Characteristics of Co-Combustion of Meager Coal and Spent Cathode Carbon Block

The harmless disposal of spent cathode carbon blocks (SCCBs) has become an urgent issue in the primary aluminum industry, and the disposal of SCCBs by co-combustion in pulverized coal boilers is expected to be the most effective treatment method. A muffle furnace at 815 °C was used in this study to perform a co-combustion experiment of meager coal and SCCBs. The ash fusion characteristics (AFTs), microscopic morphology, and minerals composition of co-combustion ash were characterized. The interaction mechanism of different mineral components and the change in AFTs and viscosity-temperature characteristics were investigated using FactSage software. Results show that the change in the ash deformation temperature (DT) is correlated linearly with the SCCB addition ratio, whereas other characteristic temperatures exhibit a nonlinear relationship. The contents of SiO2, Al2O3, and Na2O collectively determine the DT in the ash, and the influence degree from high to low is in the order of SiO2, Na2O, and Al2O3. The phase diagram of Na2O–Al2O3–SiO2 is used to accurately predict the changing trend of the melting point of co-combustion ash. The ratio changes between refractory and fusible minerals in the ash, as well as the degree of low-temperature eutectic reaction between sodium- and calcium-containing minerals, are the main factors affecting the melting point of ash. When the blending amount of SCCBs is 5%, mostly complete combustion is achieved, and slagging does not occur easily. The optimal blending ratio of SCCBs is obtained using the co-combustion method from the aspect of AFTs and viscosity-temperature characteristics. This work lays a theoretical foundation for industrial application.

Influence of Al2O3/SiO2 ratio in multicomponent LNAS glasses and glass-ceramics on the crystallization behavior, microstructure and mechanical performance

Transparent glass-ceramics containing eucryptite and nepheline crystalline phases were prepared from alkali (Li, Na) aluminosilicate glasses with various mole substitutions of Al2O3 for SiO2. The relationships between glass network structure and crystallization behavior of Li2O–Na2O–Al2O3–SiO2 (LNAS) glasses were investigated. It was found that the crystallization of the eucryptite and nepheline in LNAS glasses significantly depended on the concentration of Al2O3. LNAS glasses with the addition of Al2O3 from 16 to 18 mol% exhibited increasing Q4 (mAl) structural units confirmed by NMR and Raman spectroscopy, which promoted the formation of eucryptite and nepheline crystalline phases. With the Al2O3 content increasing to 19–20 mol%, the formation of highly disordered (Li, Na)3PO4 phase which can serve as nucleation sites was inhibited and the crystallization mechanism of glass became surface crystallization. Glass-ceramics containing 18 mol% Al2O3 showed high transparency ∼84% at 550 nm. Moreover, the microhardness, elastic modulus and fracture toughness are 8.56 GPa, 95.7 GPa and 0.78 MPa m1/2 respectively. The transparent glass-ceramics with good mechanical properties show high potential in the applications of protective cover of displays.

Comparative study of the isothermal solid-state reaction systems of kaolinite–Na2CO3 and kaolinite–quartz–Na2CO3 for coal gangue activation

A clear understanding of the solid-state reaction of kaolinite (Kln), quartz (Qtz), and sodium carbonate (Na2CO3) is of great significance for the process optimization of coal gangue calcined with Na2CO3. In this work, a comparative study of the isothermal solid-state reaction systems of Kln–Na2CO3 and Kln–Qtz–Na2CO3 was performed by means of X-ray diffraction (XRD), scanning electron microscope, and energy dispersion spectroscopy (SEM-EDS). The results showed that the calcined products both for these reaction systems mainly contain different kinds of sodium aluminum silicates (e.g., NaAlSiO4, Na1.55Al1.55Si0.45O4, and Na1.95Al1.95Si0.05O4) and various kinds of sodium silicates (e.g., Na2Si3O7, Na2SiO3, and Na6Si2O7). The mass percentage of Na2CO3 played a key role in the phase transformation, determining the Na/Al/Si molar ratio of the formed sodium aluminum silicates. Compared with the reaction system of Kln–Na2CO3, the existence of Qtz inhibited the formation of sodium aluminum silicates in the reaction system of Kln–Qtz–Na2CO3. It should be noted that the formed phases both for these reaction systems were slightly different from that of the thermodynamical calculated results of Na2O–SiO2–Al2O3 using FactSage™ software. According to both the experimental and calculated results, a reasonable batching area for coal gangue activation was proposed that the addition of Na2CO3 should be in the range of 20–50% of the total mass of Kln, Qtz, and Na2CO3.

Thermodynamics of Impurities Removal From Si–Fe Alloy by CaO–Al2O3–SiO2–Na2O Slag Refining

Thermodynamics of Impurities Removal From Si–Fe Alloy by CaO–Al2O3–SiO2–Na2O Slag Refining

Utilization of recycled fine powder as an activator in fly ash based geopolymer mortar

The paper discusses the potential of recycled fine powder as an activator in fly ash based geopolymer mortar. In current study, the recycled fine powder was used as partial substitute of fly ash at different replacement levels i.e., 10%, 20%, 30%, 40% and 50%. The sodium hydroxide and sodium silicate solutions were used as an alkaline solution for geopolymer mortar. The alkali/binder ratio of 0.45, sodium hydroxide of 12 molarity, sodium silicate / sodium hydroxide ratio of 2 and water/solid ratio of 0.35 kept constant for all geopolymer mortar mixes. The fresh properties of geopolymer mortar were evaluated in terms of slump flow and setting time. Further, the compressive strength and durability properties were assessed in terms of water absorption, porosity and dry shrinkage for all geopolymer mortar mixes at both ambient and heat curing. The observed results show that up to 30% substitution of recycled fine powder enhances the strength and durability properties of geopolymer mortar mixes. The recycled fine powder shows prominent results for compressive strength at early stage of ambient curing. The microstructure analysis validates the presence of calcium content in recycled fine powder provides additional Na2O–Al2O3–SiO2–H2O / CaO–Al2O3–SiO2–H2O gel with geopolymer matrix and densify the microstructure to enhance all properties of geopolymer mortar.

Nucleating role of P2O5 in nepheline‐based transparent glass‐ceramics

AbstractThe nepheline‐based transparent glass‐ceramics are promising candidates for cover glass applications in electronic displays owing to their superior mechanical properties (than glasses) and ability to be chemically strengthened. However, our poor understanding about the kinetic and thermodynamic drivers controlling their crystallization processes usually results in their opacification and development of large internal stresses. The present work focuses on the development of nepheline‐based nanocrystalline transparent glass‐ceramic designed in the Na2O–Al2O3–SiO2 ternary system nucleated with P2O5. The temporal evolution of the phosphate and nepheline nanocrystal formation has been followed using X‐ray diffraction, scanning/transmission electron microscopy, and energy‐dispersive spectroscopy. The incorporation of P2O5 in the glass structure leads to the phase separation resulting in the crystallization of nanocrystalline Na3PO4 as an intermediate phase; thus, acting as a nucleating site for volume crystallization of nepheline. The optimization of nucleation and growth profile in the designed composition results in the formation of a transparent glass‐ceramic with high optical transmittance (91.5 ± 0.1%).

Study on recycled Er-incorporated waste CRT glasses for photon and neutron shielding

The present study is extremely associated with the evaluation of cathode ray tube (CRT) waste which is a growing hazardous waste management and disposal issue. The Er-added recycled glasses derived from CRT have been successfully fabricated as a component for Na2O–Al2O3–SiO2–K2O–CaO–SrO–BaO–PbO–Fe2O3–TiO2–Er2O3 glass systems. The waste cathode ray tube panel glass (WPG) series were obtained by inserting the Er2O3 in substitution for CRT in the amounts of 0, 1, 3 and 5 mol%. The synthesized WPG series were then subjected to numerous characterization analysis. One can firmly report that the insertion ratio from 0 to 5 mol% in Er2O3 increased the glass density from 2.9216 to 2.9763 g/cm3. Further, there exists no crystalline formation with the addition of Er2O3, instead, an amorphous nature in all WPG series emerges. Microstructural images captured by the SEM technique also confirm the non-crystallinity of the fabricated samples. Energy dispersive spectroscopy (EDS) in SEM, besides, paved the way for revealing the elemental mapping of the WPG series. From the perspective of radiation shielding competencies, nuclear shielding features have been evaluated in terms of μm and related attenuation parameters at several photon energies of 276.4–1332.5 keV by utilizing narrow beam transmission methods. The experimental data have been also confirmed to those of theoretical results by WinXCom software. The HVL results revealed superior photon radiation shielding performances for recycled WPG glasses in comparison to various concretes. In addition, exposure buildup factor (EBF) values estimated utilizing the G-P fitting approach would be useful to design or develop the synthesized glass systems for shielding applications. Furthermore, the macroscopic effective removal cross-sections for fast neutron (ΣR) have been estimated. In conclusion, the findings clearly demonstrated that Er-incorporated CRT glasses can effectively be implemented in radiation shielding applications instead of Pb having toxic effects.

Crystallization behavior of transparent Na2O-Al2O3-SiO2 glass-ceramic containing rare-earth oxides

Transparent nepheline glass-ceramics were prepared from Na2O-Al2O3-SiO2 (NAS) glasses with TiO2, ZrO2 and P2O5 as multiple nucleation agents. Effects of Eu2O3 and Nd2O3 on the crystallization behavior on the NAS glasses were discussed. As the calculation results of crystallization kinetics, the NAS glass without rare-earth oxides is surface crystallization mechanism with the Avrami parameter n ~ 1.4. With the addition of Eu2O3 and Nd2O3, the crystallization activation energy decreased and the Avrami parameter n increased to 2.40 and 2.44, respectively. The mechanism of crystallization tend to be bulk crystallization and two dimensional crystal growth. In all the studies NAS glasses without and with RE oxides, ZrO2, low- carnegieite and nepheline crystals successively precipitated with the increasing of heating temperatures from 650 to 780 °C for 5 h. The glass with 0.4 mol% Nd2O3 containing nepheline as main crystalline phase kept the visible transparency ~65% upon the heat treatment 750 °C for 5 h. While, the glass without RE oxides is opaque, and the transmittance of glass with 0.4 mol% Eu2O3 significantly decrease to 21%. It is suggested that Nd2O3 is more effective to promote crystallization and form ultra-fine microstructure of NAS glass-ceramics than Eu2O3.

Improved the Comprehensive Properties of Low‐Temperature Co‐Fired Ceramic Composites Based on ZnO–B2O3–Na2O–Al2O3–SiO2 Glass by Introducing AlN Nano particles

ZnO–B2O3–Na2O–Al2O3–SiO2 (ZBNAS) glass/Al2O3/AlN biphasic ceramics are prepared by a standard tape casting process and solid phase sintering. The low‐temperature co‐fired ceramic (LTCC) tapes are sintered at 850 °C for 2 h under a nitrogen atmosphere. The new phase of ZnAl2O4 is formed by the reaction between glass phase and ceramic fillers during the sintering process. The addition of AlN improves the comprehensive properties of the ZBNAS glass/Al2O3 composites. The samples with 30 wt% AlN exhibit a thermal conductivity of 5.48 W m−1 K−1, a low dielectric constant of 2.99 and a dielectric loss of 0.029 at 18 GHz, and a coefficient of thermal expansion (CTE) of 6.98 × 10−6 °C−1. The obtained composite ceramic with good comprehensive performance may be the promising candidates for high‐power devices.

Impact of pressure on structure and properties of hot‐compressed Na2O–Al2O3–SiO2 glass by molecular dynamics simulations

AbstractWe conduct systematic studies to investigate the impact of pressure on structure and properties of Na2O–Al2O3–SiO2 glass system using molecular dynamics simulations. Glass compositions range from peralkaline, to charge‐balancing, to peraluminous. Hot‐compression operation is applied to as‐prepared glasses with pressure up to 4 GPa. Several key learnings are obtained from the study: (a) Density and elastic moduli increase with increasing Al/Na ratio (RAl/Na) and pressure, which are mainly driven by average internetwork bond angle reduction and void size reduction upon compression. (b) Population of three bonded oxygen (TBO) show some presence in the peralkaline composition space, while gain significantly in the peraluminous regime. Pressure essentially encourages conversion of bridging oxygen to nonbridging and three bonded oxygens. Local nearest neighbor environment of TBO is predominately Al atoms rather than Si atoms regardless of RAl/Na and applied pressure. (c) Analysis of first sharp diffraction peak (FSDP) from neutron scattering suggests that medium‐range structure is compacted and small size rings are noticeably distorted over the hot‐compression process. (d) Ring size distribution analysis shows that pressure has a more pronounced effect on altering medium‐range structure for peralkaline glasses as compared to peraluminous glasses.

A perspective on sodium-induced agglomeration of Zhundong coal gasification: Experiments and calculations

In order to provide basic knowledge for the gasification utilization of low-rank Zhundong (ZD) coal in the process of circulating fluidized bed (CFB), this study focuses on gasification reactivity and ash related agglomeration of ZD coal mainly induced by sodium transformation. Typical ZD coal was pyrolyzed in a horizontal tube reactor by a rapid pyrolysis method at 900 °C. Isothermal and non-isothermal thermogravimetric analyses were used to study the gasification reactivity of ZD char under CO2 atmosphere. The effect of temperature, ranging from 850 °C to 1050 °C, on isothermal gasification was investigated, and the obtained gasification residues were analyzed to observe microscope morphology and evaluate agglomeration degree. The ternary system relationship of Na2O–SiO2–Al2O3 at each gasification temperature was calculated with FactSage to compare with the experimental results. The results show that: the gasification reactivity of ZD coal char is greatly affected by the gasification temperature. Higher temperature can increase the average specific gasification rate, thus shorten the reaction time that the carbon conversion reaches equilibrium. The gasification reactivity of coal char is proved to be better at higher temperature. The agglomeration characteristics were also affected by the gasification temperature. There is almost no melting and agglomeration phenomenon for 850 °C gasification residue, while a strong tendency to agglomeration is showed in other samples. However, when the mass fraction of local CaO on the surface of large particles is more than 40%, the melting phenomenon can be alleviated. According to the Na2O–SiO2–Al2O3 phase diagram, the positions of ZD coal and ZD char are located near the complete Slag-liq region, indicating that using ZD coal and ZD char at the operation temperature of CFB above 950 °C has strong risk of slagging, and a relatively lower gasification temperature, ∼900 °C, is suitable for ZD coal/char gasification.

Ionic self-diffusion of Na2O–Al2O3–SiO2 glasses from molecular dynamics simulations

The structure of alkali aluminosilicate glasses (NAS) as a function of the molar ratio of Al/Na (RAl/Na) were investigated by using classical molecular dynamics simulations and validated by comparing with the high energy X-ray diffraction experiments. General structural features, including the pair distribution functions, coordination number, Qn distribution, oxygen species and ring size distributions, were analyzed to elucidate the effects of Al content on the structure of the glasses. By inducing effective rings size as a new parameter, the RAl/Na dependence of the alkali ion diffusion ability below the glass transition temperature were analyzed on the basis of medium range structures instead of the calculated diffusion coefficient. The results suggest that the optimum aluminum content for NAS system exists at around RAl/Na = 1.2 not only with a high ionic self-diffusion but also with a good network connectivity, providing a theoretical guidance for the design and optimization of chemically strengthened glasses.

A multi-step chemical ion-exchange process for alkali/alkaline-earth aluminosilicate glasses

The paper describes a multi-step chemical ion exchange method, also known as "Kailly Method", to increase the impact resistance of Na2O–Al2O3–SiO2 based glasses and derivatives. The chemical strengthening methodology comprises of three steps where the first step is a chemical ion-exchange process (labeled as IOX1) in KNO3 melt followed by a second step involving high temperature ion migration (HTIM), and the final step of another chemical ion-exchange (IOX2) step in KNO3 melt. The effect of the proposed strengthening mechanism on the compressive stress layer depth (DOL), diffusion coefficient (D) and surface compressive stress (CS) of a glass with composition 16.11 Na2O-1.47 K2O-2.73 MgO-20.02 Al2O3-59.08 SiO2-0.1 CaO-0.49 SnO2 (wt.%) has been evaluated. The results show that the "Kailly Method" can promote a DOL to 120–150 μm which is 50–80% higher than the conventional one-step ion exchange process. The distribution of compressive stress has been positively correlated with K+ concentration and modulus of elasticity. Further the impact strength of a 0.5 mm thick glass specimen has been demonstrated to be linearly related to the compressive stress and the square root of DOL thus, indicating that the increase of DOL on the glass surface contributes to the improvement of impact resistance.

Characterization of a broad range gamma-ray and neutron shielding properties of MgO-Al2O3-SiO2-B2O3 and Na2O-Al2O3-SiO2 glass systems

In this research, the radiation shielding parameters for two glass systems with composition of 20MgO-(20-x)Al2O3-57SiO2-3B2O3-xCr2O3 (x = 0, 0.1, 0.25, 0.5 and 1 mol%) and Na2O-Al2O3 SiO2 glasses were studied. For this purpose, a scintillation detector namely 3 × 3 inch NaI(Tl) has been designed for detection of photons through MCNPX simulation code. Thus, the mass attenuation coefficients (μ/ρ) and some other gamma shielding quantities were calculated. The estimated MCNPX data of all the glasses were compared and approved with those of WinXCOM program. The gamma ray buildup factors for the two glass systems were also determined in a wide energy range of 0.02–15 MeV for penetration depths up to 15 mfp. The results revealed that the mass attenuation coefficients for the glass samples in the first glass system are higher than those in the glasses in the second system and thus the glasses coded as MASBC have more ability in reducing radiation than NAS glasses. Among the selected glasses, C4 has the largest values of μρ and lowest half value layer, and therefore this glass sample has better shielding features than other samples. Besides, 3—1 glass sample has the lowest values; therefore this sample has the least ability to block and reduce the incoming gamma radiation. The results also showed that the effective atomic number (Zeff) of the glasses in the first composition increased with increasing the content of Cr2O3, and Zeff in the second glass system (i.e. NAS) increased with increasing the Al2O3 content. The values of mass removal cross section for neutron (ΣR) vary between 0.09112 and 0.09163 and 0.08415–0.08710 for the first and second glass system respectively. The obtained results from the present investigation can be useful to understanding of influence of Cr2O3 and Al2O3 additive on nuclear radiation shielding properties of tellurite MgO-Al2O3-SiO2-B2O3 and Na2O-Al2O3-SiO2 glasses.

FEATURES OF MELTING IN THE THERMOCHEMICAL PLUME CONDUIT AND HEAT AND MASS TRANSFER DURING CRYSTALLIZATION DIFFERENTIATION OF BASALTIC MELT IN A MUSHROOM-SHAPED PLUME HEAD

The number Ka=N/N1is used to evaluate the thermal power of a plume;Nis the thermal power transferred from the plume base to its conduit, andN1is the thermal power transferred from the plume conduit into the surrounding mantle. At the relative thermal power 1.9<Ka<10, after eruption of the melt from the plume conduit to the surface, melting occurs in the crustal block above the plume roof, resulting in the formation of a mushroom-shaped head of the plume. A thermochemical plume originates at the core-mantle boundary and ascends (melts up) to the surface. Based on laboratory and theoretical modeling data, we present the flow structure of melt in the conduit and the head of the thermochemical plume. The features of melting in the plume conduit are elucidated on the basis of the phase diagram of the CaO-MgO-Al2O3-SiO2model system. The two upper convection cells of the plume conduit relate to the region of basic and ultrabasic compositions. Our study shows that melting in these cells proceeds according to monovariant equilibria of eutectic type L=Cpx+Opx+An+Sp and L=Fo+An+Cpx+Opx. In case of the CaO–MgO–Al2O3–SiO2–Na2O system, crystallization differentiation proceeds as separation of plagioclase crystals. Separation of plagioclase crystals enriched in anorthite component leads to enrichment of the residual melt in silica and alkaline components. Assuming the initial basaltic melt, we calculated the compositional changes in the melt, which are powered by the heat and mass transfer processes in the mushroom-shaped plume head. The calculations were performed in two stages: (1) after settling of refractory minerals; (2) after settling of plagioclase in the melt resulting from the first stage. In the second stage, the melt contains 88.5 % of plagioclase component. The calculations were performed for melt temperatureTmelt=1410 °C and pressureP=2.6 kbar and 6.3 kbar. The calculated weight contents of oxides, the normative compositions for solid phase, and the oxide content and normative composition for the residual melt were tabulated. The SiO2content in the residual melt amounts to 59.6–62.3 % and corresponds to the crustal SiO2content.