Viscosity and structure evolution of bearing-BaO slag melt with the low CaO/SiO2 mass ratio of 0.7

The effect of BaO on the viscosity of experimental slag with the CaO/SiO₂ ratio of 0.7 was studied based on the rotating cylinder method, and the structure evolution analysis was performed using Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and ²⁷Al MAS-NMR spectra. The results indicated that the viscosity of molten slag decreased gradually with BaO content rising from 0 wt.% and 5 wt.% due to the dominant effect of free O^2- rather than Ba²⁺. The viscous flow activation energy (Eη) of molten slag was calculated, presenting a similar change trend with that of viscosity. The structure analysis demonstrated that, with the increasing BaO content, the [SiO₄]-tetrahedral structures and Si-O-Al bonds were destroyed due to an increase in the relative fraction of free oxygen (O^2-). For the Al-related structural units, the ²⁷Al magic angles spinning nuclear magnetic resonance (²⁷Al MAS NMR) spectra analysis illustrated that the concentration of [AlO₄] units reduced, whereas that of [AlO₅] and [AlO₆] units increased because of the increase of free oxygen and nonbridged oxygen (O⁰). The results of structure analysis agreed well with the viscosity variations of experimental slag.     

The evolution of the mold flux melt structure during the process of fluorine replacement by B2O3

This study presented the melt structure evolution of mold flux during the substitution of fluorine by B₂O₃, and a computational model for the degree of polymerization (DOP) for borosilicate structure was developed. The results showed that the reduction of fluorine content would promote the replacement of F in [SiF₆]-octahedral unit by the dissociative free oxygen ions (O²⁻), and release F⁻ ions into the melt to compensate the reduction of F⁻ ions. With the 2 mass% addition of B₂O₃, the original Si–O–Si bond would be disrupted, and connect with [BO₃]-trihedral to form boroxol ring structure containing [BO₂O⁻]-trihedral and [BO₃]-trihedral structural units. Then, the Si–O–B bond that [BO₃]-trihedral links [SiO₄]-tetrahedral in boroxol ring was destroyed with the further addition of B₂O₃, and then the [BO₃]-trihedral could link with the dissociative Q¹(Si) and Q⁰(Si) structural units to transform into [BO₄]-tetrahedral and form a borosilicate long chain. Finally, with 6 mass% addition of B₂O₃, the borosilicate chain would combine with simple borate and borosilicate structures, and a complex borosilicate structure containing boroxol ring with certain symmetry was formed ultimately. Besides, the calculated result of DOP suggested that the DOP of the melt structure improved during the process of fluorine replacement by B₂O₃.     

Effect of substituting CaO with BaO on the viscosity and structure of CaO‐BaO‐SiO2‐MgO‐Al2O3 slags

In this study, the effect of CaO and BaO substitution on the viscosity and structure of CaO‐BaO‐SiO₂‐MgO‐Al₂O₃ slags was investigated. The results showed that the viscosity increased with an increase in the BaO substitution concentration, which was correlated to an increase in the degree of polymerization (DOP) of the slag structural units as the activation energy increased from 207.9 to 263.8 kJ/mol for viscous flow. Deconvolution and area integration of the Raman spectrum of the slag revealed that the ratio of Q³/Q² (Qⁱ, i is the number of O⁰ in a [SiO₄]‐tetrahedral unit) increased and NBO/Si (nonbridging oxygen per unit silicon atom) decreased with higher BaO content. It was also observed from the ²⁷Al magic angles pinning nuclear magnetic resonance (²⁷Al MAS‐NMR) spectrum that the relative proportion of Al^IV increased, while that of Al^V decreased because of the decrease in the percentage of nonbridging oxygen (O^?), indicating the polymerization of the slag. O_1s X‐ray photoelectron spectroscopy (XPS) was also carried out to semi‐quantitatively analyze the various types of oxygen anions present in the slag. The XPS results correlated well with the results obtained from the analysis of the Raman and ²⁷Al MAS‐NMR spectra of the slags and its viscous behavior.     

Influence of B2O3 on viscosity and structure of the CaO–Al2O3-waste electrolyte (WE) based melt

The fluorides contained waste electrolyte (WE) from the electrolytic aluminum industry can be used as a substitution of fluorite (CaF₂) in the newly designed mold flux. In this study, the influence of B₂O₃ on viscosity and structure of CaO–Al₂O₃-WE based melt was investigated. Results show that the viscosity of mold flux melt decreases with both increasing temperature and B₂O₃ content. The apparent activation energy (E_a) also reduces from 78.96 ± 1.75 to 55.26 ± 2.79 kJ/mol with the addition of B₂O₃ from 0 to 7 wt%. The analyses of fourier transform infrared (FTIR) and Raman spectroscopies suggest that the lower symmetry of the original aluminate and silicate structure due to the insertion of [BO₄]-tetrahedral and [BO₃]-triangular, and the formation of more non-bridging oxygen (O⁻) and 2D structural units in the network with the addition of B₂O₃, deceases the viscosity and E_a of the CaO–Al₂O₃-WE Based Melt.     

Effect of the Al2O3/SiO2 mass ratio on the crystallization behavior of CaO-SiO2-MgO-Al2O3 slags using confocal laser scanning microscopy

The crystallization behavior of a CaO-SiO₂-MgO-Al₂O₃ slag system with varying Al₂O₃/SiO₂ mass ratios from 0.03 to 1.10 has been investigated using a confocal laser scanning microscopy (CLSM). The resulting continuous cooling transformation (CCT) and time-temperature-transformation (TTT) curves showed that the initial crystallization temperature increased and the incubation time for crystallization slightly decreased with increasing Al₂O₃/SiO₂ ratio. The crystal growth rate first increased and then decreased with decreasing isothermal temperature. X-ray diffraction (XRD) analysis suggested that Ca₂MgSi₂O₇ or Ca₃MgSi₂O₈ precipitated as the primary phase at lower Al₂O₃/SiO₂ ratios, while the Ca₂Al₂SiO₇ phase was preferred at higher Al₂O₃/SiO₂ ratios. The observed crystalline phases correlated well with the expected thermodynamic predictions from FactSage. In addition, structural analysis using ²⁷Al magic angle spinning nuclear magnetic resonance (²⁷Al MAS-NMR) microscopy of the as-quenched slags indicated the presence of a higher ratio of tetrahedral [AlO₄]^5-structural units with increasing Al₂O₃/SiO₂ ratio, which enhanced the polymerization of tetrahedral [AlO₄]^5- and [SiO₄]^4- structural units to form Ca₂Al₂SiO₇.     

Crystal structure evolution and luminescence property of Ce3+-doped Y2O3-Al2O3-Sc2O3 ternary ceramics

Ce³⁺-doped Y₂O₃-Al₂O₃-Sc₂O₃ ternary ceramics with varying Sc₂O₃ were prepared via solid-state-reactive method. Their constitutions, crystal structures, microstructures and luminescence properties were thoroughly investigated by powder X-ray diffraction, ⁴⁵Sc and ²⁷Al solid-state nuclear magnetic resonance (NMR), scanning electron microscope (SEM) as well as photoluminescence (PL) characterizations. Single-phased YSAG transparent ceramics with garnet structure and homogeneous microstructures can be obtained. The NMR results suggest that partial [AlO₆] octahedrons are converted into [AlO₄] tetrahedrons with increased Sc³⁺. Partial Sc³⁺ occupies the remaining octahedral sites, the other Sc³⁺ occupies the dodecahedral sites. The luminescence spectra of the as-prepared ceramics show broadened emission bands with excessive Sc³⁺ incorporation. More significantly, the solubility of Ce³⁺ in garnet ceramics extensively increases due to the incorporation of Sc³⁺, leading to a considerable red-shift and broadening of emission spectra with little luminescence decline, indicating that the new ceramic phosphors are promising for white-light illumination with improved color rendering index.     

Effects of La2O3 on the viscosity of copper smelting slag and corrosion resistance of magnesia refractory bricks

The rotating method is carried out to investigate the effects of La₂O₃ content (0–4 wt%) on the viscosity of copper smelting slag at high temperatures, the apparent activation energy is evaluated according to the Arrhenius equation and the structural characterization of this quenched slag is characterized by Raman spectroscopy. Meanwhile, the corrosion resistance of copper smelting slag with different content of La₂O₃ on magnesia refractory bricks is researched by employing a static crucible method. The experimental results show that the viscosity of copper smelting slag decreased with the La₂O₃ ratio increases from 0 to 3 wt% in a certain temperature range, which is because La₂O₃ simplifies the structural units of [SiO₄] tetrahedral groups. However, the melt viscosity increases after add 4 wt% La₂O₃, the reason is that more La₂O₃ addition improves the structural compactness of [SiO₄] tetrahedral groups in the molten slag due to the strong accumulation effect of La³⁺. Observation of the corroded samples found that the corroded magnesia refractory brick has a lower penetration index when the copper smelting slag with the content of 4 wt% La₂O₃. Therefore, the copper smelting slag containing 4 wt% La₂O₃ has a higher viscosity, and thus impeded the penetration behavior of copper smelting slag on magnesia refractory bricks.     

Effect of fluorine and CaO/Al2O3 mass ratio on the viscosity and structure of CaO–Al2O3-based mold fluxes

The effect of CaO/Al₂O₃ mass ratio (C/A) and fluorine content on the viscosity and structure of CaO–Al₂O₃-based mold fluxes has been researched in this paper. The viscosity results indicated that increasing fluorine only slightly decreases the viscosity of the slag melt, and higher C/A is also observed to decrease the viscosity of molten slag when the C/A changes from 1.3 to 1.7. Structural analysis of the as-quenched fluxes using the Raman spectroscopy showed that the amounts of Al–O⁰ and Si–O–Al structural units all decrease with higher fluorine content and C/A, indicating that a depolymerization of the molten structure is occurring. The results of ²⁷Al and ¹⁹F magic angle spinning nuclear magnetic resonance showed that fluorine tends to participate in the network structure and coordinate with Al³⁺ ions to form complex ionic clusters. The results suggested that the role of fluorine in the CaO–Al₂O₃-based slag system is different from the traditional slag system in which fluorine only acts as a diluent, thus reducing the effect of fluorine on lowering the viscosity. In addition, the coordination environment of Al³⁺ ions can be simplified by higher C/A through promoting the generation of [AlO₄]⁻ tetrahedral structures. Besides, the free O²⁻ ions provided by excess CaO would break the Al–O⁰ bonds and further depolymerize the network structure, thereby decrease the viscosity.     

Structure and viscosity of CaO–Al2O3–B2O3–BaO slags with varying mass ratio of BaO to CaO

The structure of CaO–Al₂O₃–B₂O₃–BaO glassy slags with varying mass ratio of BaO to CaO has been investigated by Raman spectroscopy, ¹¹B and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy and atomic pair distribution function (PDF). ¹¹B MAS-NMR spectra reveal the dominant coordination of boron as trigonal. Both simulations on ¹¹B MAS-NMR spectra and Raman spectroscopy indicate the presence of orthoborate as the primary borate group with a few borate groups with one bridging oxygen and minor four-coordinated boron sites. ²⁷Al MAS-NMR and PDF show the Al coordination as tetrahedral. Raman spectral study shows that the transverse vibration of Al^IV–O–Al^IV and Al^IV–O–B^III, stretching vibration of aluminate structural units and vibration of orthoborate and pyroborate structural groups. A broader distribution of Al–O bond lengths in PDF also supports the enhanced network connectivity. Viscosity measurements show the increase in viscosity of molten slags with increasing mass ratio of BaO to CaO, which further attributes to the enhanced degree of polymerization of the aluminate network.     

Rheological behavior of the CaO-Al2O3-based mold fluxes with different Na2O contents

The CaO-Al₂O₃-based mold flux is expected during the casting of aluminum containing advanced high strength steels. In this study, the rheological behavior of the CaO-Al₂O₃-based mold fluxes with different Na₂O contents was investigated. The results show that the viscosity in the range of 1423–1573 K reduced sharply when the Na₂O content increased from 0 wt % to 10 wt %, but the tendency slowed down with further increasing Na₂O from 10 wt % to 15 wt %. The activation energy for viscous flow also decreased from 237.76 ± 4.88 kJ/mol to 180.37 ± 7.10 kJ/mol with increasing Na₂O. The structure analyses show that the melt networks were mainly constructed by [SiO₄]^4--tetrahedral, [AlO₄]⁵-tetrahedral and Si-O-Al structural units. These networks were depolymerized with the addition of Na₂O since the charge compensation effect from Na⁺ was relativity weaker comparing with the network breaking effect from O²⁻. In addition, the break temperature of the mold fluxes also decreased from 1406 K to 1198 K due to the more precipitation of low melting point Ca₂Al₂SiO₇, rather than MgAl₂O₄ in the mold flux, during the cooling cycle.     

Influence of electropulsing treatment on crystallization and structure of calcium silicate-based melt

Electropulsing treatment (EPT) is a promising technology for controlling the phase transition during the solidification of melts owing to its electric and thermal effects. In this study, the influence of EPT on the crystallization and melt structure of a calcium silicate-based mold flux was investigated. The results showed that the morphology of crystals that precipitated in the mold flux changed from elongated columnar to block shape, and the equivalent grain diameter of the crystals increased with increasing voltage from 0 to 20 V. The mass fraction of Ca₄Si₂O₇F₂ precipitated in the mold flux decreased with increasing impulse voltage, whereas that of Ca₂Mg_0.75Al_0.5Si_1.75O₇ increased. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses suggest that the network structure of both silicate and aluminate was simplified by electropulsing because the simpler structural units of Q₀, Q₁, [AlO₆]⁹⁺, etc., increased with increasing impulse voltage, whereas the complex structural units of Q₂, Q₃, and [AlO₄]⁵⁺ decreased. The extra electric field force is the repulsion force between two oppositely charged ions, which was the root of the network structure simplification and crystallization promotion. The results obtained in this study provide an innovative method for locally controlling the crystallization behavior of mold flux in a mold.     

Effect of CaF2, B2O3 and the CaO/SiO2 mass ratio on the viscosity and structure of B2O3-containing calcium-silicate-based melts

The relationship between the viscosity and structure of B₂O₃-containing calcium-silicate-based mold fluxes and the effects of fluidizers including CaF₂, CaO, and B₂O₃ on the viscosity and their correlation with the structural aspects were studied using a rheometer with Fourier transformation infrared and Raman spectroscopy. The viscosity decreased with increasing CaF₂ addition up to 28 wt% at a fixed CaO/SiO₂ ratio of 0.3, which was related to depolymerization. Furthermore, CaF₂ addition also affected the apparent activation energy for viscous flow, which decreased with increasing CaF₂ content to 105.1 from 151.1 kJ/mol. At higher C/S ratios, the viscosity decreased in the presence of greater Ca²⁺ and O²⁻ supplied from CaO, which subsequently increased the activation energy to 149.7 from 122.0 kJ/mol. With regard to the B₂O₃-melt, polymerization of the network structure was observed by comparing the B₂O₃-free to 4.4 wt% B₂O₃ content. However, the viscosity was relatively constant with increasing B₂O₃ addition. However, the viscosity decreased due to greater simplification of the network structure above 4.4 wt% B₂O₃. The break temperature decreased with greater B₂O₃ addition as the crystallization was inhibited. Furthermore, the apparent activation energy decreased as depolymerization of the network structures occurred above 4.4 wt% B₂O₃.     

Effect of Na2O on the High‐Temperature Thermal Conductivity and Structure of Na2O–B2O3 Melts

The effect of Na₂O and temperature on the thermal conductivity of the Na₂O–B₂O₃ binary system has been measured using the hot‐wire method to examine the relationship between the thermal conductivity and structure in high‐temperature melts. The thermal conductivity of the binary melt is measured from 1173 to 1473 K in the fully liquid state. The thermal conductivity slightly increases with Na₂O content up to 20 wt%. Above 20 wt% Na₂O, the thermal conductivity decreases with increasing Na₂O. The network structure of molten glass was analyzed using Fourier transform infrared (FTIR), Raman spectroscopy, and XPS. The FTIR analysis shows that 3‐D complex borate structures, such as tri‐, tetra‐, and pentaborate are made by [BO₄] tetrahedral units interconnected with 2‐D structure boroxol rings in the low Na₂O region. Above 20 wt% Na₂O content, nonbridged oxygen in [BO₂O^?] units and diborate groups increase with increase in Na₂O. The same tendency is shown by the Raman spectroscopy and XPS analyses. The Raman analysis shows that boroxol rings disappeared with large [BO₄] groups, such as tri‐, tetra‐, and pentaborate structures, which increase at low Na₂O content. Isolated diborate groups and nonbridged oxygen in [BO₂O^?] units increase at high Na₂O content. It can be inferred that single structure units, such as isolated diborate groups, interfere with conduction. The XPS analysis results show that free oxygen produced by the interconnection of Na₂O in the borate structure does not cause significant changes to O^2? in the low Na₂O region, but increases the O^o and decreases the O^?. Above 20 wt% Na₂O, O^? slightly increases and O^o shows a decreasing trend.     

Effect of Li2O on the crystallization behavior of CaO-Al2O3-SiO2-Li2O-Ce2O3 mold slags

The effect of Li₂O on the crystallization properties of CaO-Al₂O₃-SiO₂-Li₂O-Ce₂O₃ slags was investigated. With increasing the Li₂O content, LiAlO₂ and CaCeAlO₄ were the main crystalline phases. LiAlO₂ formed for the charge compensating of Li⁺ ions to [AlO₄^5?]-tetrahedrons, and CaCeAlO₄ formed as a result of the charge balance of Ce³⁺ ions, Ca²⁺ ions, and [AlO₆^9?]-octahedrons. Increasing the content of Li₂O to 10%, the crystallization temperature was the highest, and the incubation time was the shortest. The crystallization ability was strong due to the three factors of strengthening the interaction between ions and ion groups, decreasing the polymerization degree, and increasing the melting temperature. Further increasing the content of Li₂O, the crystallization performance was obviously suppressed, because the melting temperature and the force between the cations and the anion groups decreased.     

Performance and transition mechanism from acidity to basicity of amphoteric oxides (Al2O3 and B2O3) in SiO2–CaO–Al2O3–B2O3 system: A molecular dynamics study

Amphoteric oxides (Al₂O₃ and B₂O₃) represent opposite effects on the structure and properties of silicate melts in different conditions, while the understanding about the transition from acidity to basicity is far from complete. Molecular dynamics simulation was adopted in the present study to investigate the performance and acidity-basicity transformation of Al₂O₃ and B₂O₃ in the SiO₂–CaO–Al₂O₃–B₂O₃ system. The results showed that, different from Ca²⁺ ions, excessive Al³⁺ or B³⁺ ions tend to destroy the bridge oxygen structures, showing the function of basic oxide. This is similar to the behavior of Ca²⁺ ions and other basicity ions. It was found that, on the one hand, B³⁺ ions tend to form [BO₃]^3- planar triangular structures with the increase of B³⁺ ions contents, on the other hand, B³⁺ ions could reduce the stability of Si–O bonds. Therefore, B³⁺ ions could make the system structure less stable, which is the reason why the B₂O₃ is a kind of active agent. In addition, because of the significant differences in lattice energy and atomic structure between Al₂O₃ and B₂O₃, the effects of Al₂O₃ and B₂O₃ on the thermodynamic properties of silicate melts are quite different.     

Thermal history driven molecular structure transitions in alumino‐borosilicate glass

The glass network structure governs various thermos‐physical properties such as viscosity, thermal, and electrical conductivities, and crystallization kinetics. We investigated the effect of temperature on structural changes in a Na₂O‐CaO‐Al₂O₃‐SiO₂‐B₂O₃ glass system using ²⁷Al MAS NMR spectroscopy. Around the glass transition temperature, most of aluminate structures exist as AlO₄, acting as a glass former. When the temperature is above the melt crystallization temperature, the AlO₄ structure is drastically decreased and glass structures are mainly composed of AlO₅ and AlO₆, acting as glass modifiers. Thermodynamic assessment based on Gibbs energy minimization was used to confirm the dependency of aluminate structure's amphoteric characteristic on temperature by calculating the site fraction of aluminate molecular structures at different temperatures. Temperature‐induced aluminate structural variation can also influence silicate and borate structural changes, which have been confirmed by the ²⁹Si and ¹¹B NMR spectra.     

Microstructure evolution and cooperative reinforcement mechanisms of Al2O3/Al2O3 joints brazed by low-melting borosilicate glass

The Al₂O₃/SiO₂–B₂O₃–Al₂O₃–Na₂O glass/Al₂O₃ joints reinforced cooperatively by glass matrix and in-situ Al₄B₂O₉ whiskers were obtained via a low-melting borosilicate glass braze. The composition of glass seam transformed from SiO₂–B₂O₃–Na₂O to SiO₂–B₂O₃–Al₂O₃–Na₂O due to continuous diffusion and dissolution of Al₂O₃. An appropriate amount of [AlO₄] units introduced into the glass braze played a vital role in strengthening the glass network structure resulting to considerably improved mechanical strength of the glass seam. Meanwhile, plenty of in-situ Al₄B₂O₉ whiskers growing from the Al₂O₃/glass braze interface to the center of glass seam in various directions generated. Three-dimensional crisscross structures were fabricated at the Al₂O₃/glass braze interface domains, where were enhanced by crack-bridging and pull-out effect of the whiskers. Generally, ascribed to the cooperative reinforcement of the glass matrix in the seam and in-situ Al₄B₂O₉ whiskers at Al₂O₃/glass braze interface domains through reactions of Al₂O₃ and borosilicate glass braze, strength of the as-brazed joints was promoted prominently. The shear strength of the joints reached a maximum of 61 MPa brazed at 1050 °C for 60 min.     

Understanding the structure,thermal, and optical properties in Al2O3-incorporated La2O3-TiO2-Nb2O5 glasses

Glasses in the 30La₂O₃-40TiO₂-30Nb₂O₅ system are known to have excellent optical properties such as refractive indices over 2.25 and wide transmittance within the visible to mid-infrared (MIR) region. However, titanoniobate glasses also tend to crystallize easily, significantly limiting their applications in optical glasses due to processing challenges. Therefore, the 30La₂O₃-40TiO₂-(30−x) Nb₂O₅-xAl₂O₃ (LTNA) glass system was successfully synthesized using a aerodynamic containerless technique, which improves glass thermal stability and expands the glass-forming region. The effects of Al₂O₃ on the structure, thermal, and optical properties of base composition glasses were investigated by XRD, DSC, NMR, Raman spectroscopy, and optical measurements. DSC results indicated that as the content of Al₂O₃ increased, the thermal stability of the glasses and glass-forming ability increased, as the 30La₂O₃-40TiO₂-25Nb₂O₅-5Al₂O₃ (Nb-Al-5) glass obtained the highest ΔT value (103.5°C). Structural analysis indicates that the proportion of [AlO₄] units increases gradually and participates in the glass network structure to increase connectivity, promoting more oxygen to become bridging oxygen and form [AlO₄] tetrahedral linkages to [TiO₅] and [NbO₆] groups. The refractive index values of amorphous glasses remained above 2.1 upon Al₂O₃ substitution, and a transmittance exceeding 65% in the visible and mid-infrared range. The crystallization activation energies of 30La₂O₃-40TiO₂-30Nb₂O₅ (Nb-Al-0) and Nb-Al-5 glasses were calculated to be 611.7 and 561.4 kJ/mol, and the Avrami parameters are 5.28 and 4.96, respectively. These results are useful to design new optical glass with good thermal stability, high refractive index and low wavelength dispersion for optical applications such as lenses, endoscopes, mini size lasers, and optical couplers.     

Influence of Al2O3 on the electrical conductivity and structure of calcium-silicate-based melts

Electrical conductivity and structure of the CaO-SiO₂-based mold flux melts with various Al₂O₃ contents were investigated. The results show that the electrical conductivity increases with the addition of Al₂O₃ from 2 wt% to 4 wt%, but decreases with the further increase of Al₂O₃ from 4 wt% to 8 wt%. Correspondingly, the apparent activation energy reduces firstly from 55.12 ± 1.20 kJ mol to 41.09± 0.38 kJ mol, and then increases from 41.09 ± 0.38 kJ mol to 98.99 ± 1.42 kJ mol. The structure analyses suggest that complex structural units, such as Si-O-Al, Al-O⁰, Si-O-Si and Q³(Si), reduce first, but increase with the further addition of Al₂O₃. Conversely, these simple structural units, such as Al-O^-, Q⁰(Si), Q¹(Si) and Q²(Si) vary in the opposite way with the change of Al₂O₃ content. From the variations of electrical conductivity, activation energy and structural units, it can be found that when Al₂O₃ works as network breaker to simplify the melt structure, the energy barrier for transportation of conducting ions/ionic reduce, which results in the increase of electrical conductivity; while when Al₂O₃ becomes into network former, the conductivity increases, correspondingly.