Sc2O3 Content Research Articles

Nanocrystalline Cubic Phase Scandium-Stabilized Zirconia Thin Films.

The cubic zirconia (ZrO2) is attractive for a broad range of applications. However, at room temperature, the cubic phase needs to be stabilized. The most studied stabilization method is the addition of the oxides of trivalent metals, such as Sc2O3. Another method is the stabilization of the cubic phase in nanostructures-nanopowders or nanocrystallites of pure zirconia. We studied the relationship between the size factor and the dopant concentration range for the formation and stabilization of the cubic phase in scandium-stabilized zirconia (ScSZ) films. The thin films of (ZrO2)1-x(Sc2O3)x, with x from 0 to 0.2, were deposited on room-temperature substrates by reactive direct current magnetron co-sputtering. The crystal structure of films with an average crystallite size of 85 Å was cubic at Sc2O3 content from 6.5 to 17.5 mol%, which is much broader than the range of 8-12 mol.% of the conventional deposition methods. The sputtering of ScSZ films on hot substrates resulted in a doubling of crystallite size and a decrease in the cubic phase range to 7.4-11 mol% of Sc2O3 content. This confirmed that the size of crystallites is one of the determining factors for expanding the concentration range for forming and stabilizing the cubic phase of ScSZ films.

New insights on scandium separation from scandium concentrate with titanium dioxide wastewater.

In this study, a scandium concentrate with Sc2O3 content of 66.24g/t was obtained from V-Ti magnetite tailings by physical concentration, and the main Sc-bearing minerals were augite and hornblende. A novel process of roasting and leaching was proposed to extract scandium from scandium concentrate with titanium dioxide wastewater. Scandium concentrate was pretreated by roasting, and titanium dioxide wastewater was used to directly leach scandium from the roasted ore. The effects of roasting and leaching parameters such as roasting temperature, roasting time, roasting agents, leaching temperature, leaching time, liquid-to-solid ratio, and leaching agents on scandium separation were thoroughly researched in the experimental procedure. The results show that a scandium leaching efficiency of 85.89% was obtained, and the scandium content of leaching residue decreased to 9.31g/t under the optimal conditions: a roasting temperature of 1123K, a roasting time of 120min, a leaching temperature of 343K, a leaching time of 120min, and a m (titanium dioxide wastewater)∶m (roasted ore)∶m (ammonium fluoride) ratio of 8∶1∶0.09. The main findings of the scandium separation mechanism show that Sc-bearing minerals can effectively decompose and release scandium element after roasting, and created favorable conditions for scandium leaching with titanium dioxide wastewater to achieve the purpose of scandium recovery.

The corrosion behavior of Sc2O3-Y2O3 co-doped ZrO2 influenced by Sc2O3 content in CMAS at 1300 °C

The effect of Sc2O3 content on the corrosion behaviors of xSc2O3-3.5Y2O3 co-doped ZrO2 (ScYSZ, x = 4.5, 5.5 and 6.5 mol.%) in calcium-magnesium-alumino-silicate (CMAS) at 1300 °C was investigated in this paper. It is shown that the ScYSZ ceramic exhibits better resistance to molten CMAS attack when doping with more Sc2O3. The CMAS penetration depth in the ScYSZ ceramic decreases with increasing Sc2O3. It is about 18 µm of CMAS penetrated depth in the 6.5Sc3.5YSZ after corrosion for 4 h at 1300 °C, including an 11 µm and 7 µm for the reaction-reprecipitation and grain-boundary infiltration layers, respectively. High thermochemical stability and weak reactivity of the ScYSZ to the glassy CMAS melt are beneficial to enhance the high temperature corrosion resistance, attributing to the low solubility in molten CMAS and the weak affinity to Ca2+ for small ionic radius Sc3+. The mechanism of enhancing the resistance to CMAS is discussed.

Processing of alumina grinding media using scandia as a sintering aid

AbstractWear resistance is one of the essential properties of grinding media. Good wear resistance is the quality guarantee of preparing high‐purity ultrafine powder. This paper mainly studied the influence rule and enhanced mechanism of Sc2O3 on the wear resistance of Al2O3 ceramics. The relationship between Sc2O3 content and sintering properties, wear resistance, and microstructure of ceramics was studied. According to research findings, Sc2O3 could promote the densification of ceramics, improve the morphology of grain boundaries, enhance the binding force of grains, and increase the mechanical property of alumina grain.

Chemical Vapour Deposition of Scandia-Stabilised Zirconia Layers on Tubular Substrates at Low Temperatures.

The paper presents results of investigation on synthesis of non-porous ZrO2-Sc2O2 layers on tubular substrates by MOCVD (metalorganic chemical vapor deposition) method using Sc(tmhd)3 (Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)scandium(III), 99%) and Zr(tmhd)4 (Tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium)(IV), 99.9+%) as basic reactants. The molar content of Sc(tmhd)3 in the gas mixture was as follows: 14, 28%. The synthesis temperature was in the range of 600–700 °C. The value of extended Grx/Rex2 expression (Gr-Grashof number, Re-Reynolds number and x-the distance from the gas inflow point) was less than 0.01. The layers were deposited under reduced pressure or close to atmospheric pressure. The layers obtained were tested using scanning electron microscope (SEM) with an energy dispersive X-ray spectroscope (EDS) microanalyzer, X-ray diffractometer and UV-Vis spectrophotometer. The layers deposited were non-porous, amorphous or nanocrystalline with controlled chemical composition. The layers synthesized at 700 °C were nanocrystalline. ZrO2-Sc2O3 layers with 14 mol.% Sc2O3 content had a rhombohedral structure.

The Role of Scandium Substitution in Babingtonite Group Minerals

Sc-rich babingtonite from Heftetjern, Norway and Baveno, Italy were examined using electron microprobe analysis and X-ray single-crystal refinement in order to re-examine the behavior of Sc3+ and analyze its effect on the crystal structure of babingtonite. The Sc2O3 content is 13.78 wt.% in the Heftetjern specimen, and 8.44 wt.% in the Baveno one. In contrast, the latter has higher Fe content (11.13 wt.% as FeO) rather than the former one (8.63 wt.% as FeO). Characteristically, both specimens contain sodium. Although the oxidation state of octahedral cations in babingtonites is in general Me2+:Me3+ = 1:1, trivalent cations in the Heftetjern specimen attain 1.14 apfu. This excess of trivalent cations must be counterbalanced by monovalent Na substituted for Ca. The unit-cell parameters are a = 7.5272(1), b = 11.7175(1), c = 6.7613(1) Å, α = 91.710(1), β = 93.637(1), γ = 104.522(1)°, and V = 575.49(2) Å3 for the Heftetjern specimen, and a = 7.5199(2), b = 11.7145(3), c = 6.7408(2) Å, α = 91.756(2), β = 93.786(2), γ = 104.549(2)°, and V = 573.83(3) Å3 for the Baveno one. The structural formulae are A1Ca1.00A2(Ca0.879Na0.121)M1(Sc3+0.42Fe2+0.37Mn2+0.21)M2(Sc3+0.68Fe2+0.27Mg0.03Fe3+0.02)Si5O14(OH) for Heftetjern, and A1Ca1.00A2(Ca0.819Na0.181)M1(Sc3+0.43Mn2+0.36Fe2+0.21)M2(Fe3+0.36Fe2+0.30Sc3+0.26Sn4+0.05Al0.03)Si5O14(OH) for Baveno. Due to Sc3+ substitution, the <M2–O> distance, 2.09–2.11 Å, is longer than that of Sc-free babingtonite, 2.03–2.05 Å. The M2O6 expansion leads to the lengthened O4–O10 edge shared between the M1O6 and M2O6 octahedra, and causes the stronger angular distortion of M2O6. This can be explained by the increase of the O4–M1–O10 angle and decrease of the O4–M1–O8 angle with lengthening of the O4–O10 edge.

Effects of scandium oxide on domain structure, dielectric and ferroelectric properties of barium zirconate titanate ceramics

The Sc2O3 doped Ba(Zr0.1Ti0.9)O3 ferroelectric ceramics were fabricated by the conventional solid state reaction method. The influences of Sc2O3 on their microstructure, especially domain structure, dielectric and ferroelectric properties were investigated by X-ray diffractometer, scanning electron microscope, LCR measurement system and ferroelectric tester. The Sc2O3 doped Ba(Zr0.1Ti0.9)O3 ceramics are tetragonal perovskites with no impurity phases. The average grain size of Ba(Zr0.1Ti0.9)O3 ceramics decreases from ~40 µm to ~5 µm as the Sc2O3 content increases. Both the 90° ferroelectric domains and the 180° ones exist in the 0.2 mol% Sc2O3 doped Ba(Zr0.1Ti0.9)O3 ceramics with an average grain size of ~26 µm. The ferroelectric -paraelectric phase transition temperature and the dielectric permittivity maximum of Ba(Zr0.1Ti0.9)O3 ceramics decrease with increasing Sc2O3 doping content, while the temperature stability of relative dielectric constant is improved effectively after Sc2O3 modification in BZT ceramics. The remnant polarization and the coercive field of BZT ceramics decrease in Sc2O3 highly doped BZT ceramics as the Sc2O3 content increases.

Extraction of Sc from Sc-Bearing V–Ti Magnetite Tailings

In this study, a magnetic separation–shaking table gravity separation process was used to treat Sc-bearing V–Ti magnetite tailings, and the Sc2O3 content in the Sc concentrate was enhanced from 0.0039 to 0.0061%. The majority of the Sc in the Sc concentrate originates from augite, hornblende, and aluminosilicate. Magnesium chloride and the Sc concentrate were placed in a roasting furnace for chloridizing roasting, causing the partial chlorination of Sc to ScCl3. Sc was extracted from the roasted ore using hydrochloric acid leaching. Sc extraction indices demonstrated 95.12% Sc2O3 leaching efficiency and 0.0011% Sc2O3 content in the acid leaching residue, clearly indicating the extraction of Sc. No noticeable peak of Sc was observed in the spectrum of the acid leaching residue. Most of the Sc in the roasted ores was dissolved as Sc3+, and it entered the liquid phase. The main minerals in the acid leaching residue were Mg2SiO4, CaTiO3, and Fe2SiO4.

Effect of Sc2O3 addition on the phase composition and electron emission performance of Co-precipitated aluminates for impregnated cathodes

Herein, a series of 6BaO·1CaO·2Al2O3 + x wt% Sc2O3 (x = 1, 3, 5, 7, 9) impregnants were synthesized by a liquid-phase co-precipitation method and subsequent sintering at 1200 °C. The as-synthesized emissive materials were impregnated into porous tungsten matrices at 1700 °C, and their phase composition and electron emission performance were investigated. The X-ray diffraction analysis of the sintered and melted impregnated products revealed that they comprised multi-phase structures consisting of (Ba,Ca)3Al2O6, Ba2ScAlO5, and BaAl2O4 phases. Furthermore, the addition of 3 wt% Sc2O3 to the impregnated test cathodes significantly increased the emission level of the test cathode to 11.4 ± 0.6 A cm−2 at 1100 °CB (i.e., brightness temperature). The relationship between the electron emission properties and phase concentration in the impregnants was analyzed, and the results revealed that the emission performance of the cathodes deteriorated with an increase in the Sc2O3 content, which could be attributed to an increase in the concentration of non-active BaAl2O4 phase in the impregnants.

Morphological and geochemical features of zircon from intrusive rocks of El Sela area, Eastern Desert, Egypt

The intrusive rocks in El Sela area can be arranged from the oldest to the youngest into: two-mica granite and postgranitic dikes which include microgranite, dolerite and bostonite dikes. Zircon is the most abundant accessory mineral. Zircon morphology and geochemical features are good indicators for evolution of rocks. The aim of the work is to determine the morphology, internal structure and chemical composition of zircon to identify the difference of zircon in various intrusive rocks. Results show that morphologically, zircon in the two-mica granite is euhedral coarse- grained with zonation. It is represented by crystals up to 125 µm and corresponds to S10 and P2. Zircon in post-granitic dikes exhibit irregular forms. Geochemically, zircon crystals have higher ZrO2 values in the core whereas HfO2 , UO2 , ThO2 increase at the peripheries of zoned crystals of the two-mica granite. Zircon of two-mica granite contains high HfO2 , UO2 , ThO2 and CaO contents but low Sc2 O3 content. HfO2 is not detected in zircon of microgranite. TiO2 in zircon of two-mica granite and bostonite dikes is under detection limits. REEs are not recorded in zircon of the studied intrusive rocks

Structural characteristics of melt-grown (ZrO2)0.99-x(Sc2O3)x(Yb2O3)0.01 solid solution crystals and their effect on ionic conductivity

(ZrO2)0.99-x(Sc2O3)x(Yb2O3)0.01 solid solutions crystals (x = 0.08–0.10) have been grown by directional crystallization of the melt in a cold crucible. Single-phase optically transparent single crystals were obtained only for the (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 composition. The phase composition, local structure and transport properties of the crystals have been studied using X-ray diffraction, Raman, optical and impedance spectroscopy. The dependence of the lattice parameters and the phase composition of (ZrO2)0.99-x(Sc2O3)x(Yb2O3)0.01 solid solutions on Sc2O3 content has been discussed. The (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 single-phase cubic single crystals had the maximum conductivity throughout the entire temperature range. It is shown that the high-temperature conductivity of the (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 single-phase cubic single crystals is close to the conductivity of the (ZrO2)0.90(Sc2O3)0.10 crystals. The results of studying the local structure of crystals by optical spectroscopy are presented.

Recovering Scandium from Scandium Rough Concentrate Using Roasting-Hydrolysis-Leaching Process

In this study, a roasting-hydrolysis-acid leaching process is used to extract scandium from the scandium rough concentrate. The scandium rough concentrate containing Sc2O3 of 76.98 g/t was obtained by magnetic separation, gravity separation, and electric separation from Sc-bearing Vi-Ti magnetite tailings in the Panxi area of China. The majority of scandium in scandium rough concentrate mainly occurs in diopside, titanopyroxene, montmorillonite, chlorite, talc, aluminosilicate minerals, and isomorphism. Sodium salt and scandium coarse concentrate are added into the roasting furnace for roasting, which makes the fusion reaction of silicon, aluminum and sodium salt to produce soluble salts such as sodium silicate and sodium metaaluminate. Scandium is further recovered from the hydrolysis residue by acid leaching. Test results show scandium leaching recovery of 95.12% and the acid leaching residue with Sc2O3 content of 8.12 g/t are obtained, while the extraction of scandium is obvious. There is no obvious peak value of Scandium spectrum in hydrochloric acid leach residue. Most of scandium in hydrolytic residue is dissolved into Sc3+ and enters into the liquid phase. The main minerals in leach residue are perovskite, ferric silicate, and olivine.

Phase compositions, structures and properties of scandia-stabilized zirconia solid solution crystals co-doped with yttria or ytterbia and grown by directional melt crystallization

The effect of co-doping an impurity on the transport parameters and cubic phase stabilization of ZrO2–Sc2O3-based solid solutions has been compared for Y2O3 and Yb2O3 dopants. Solid solution crystals of (ZrO2)1-x-y(Sc2O3)x(Yb2O3)y and (ZrO2)1-x-y(Sc2O3)x(Y2O3)y (x = 0.08–0.10, y = 0.01, 0.02) were grown by directional melt crystallization in a cold crucible. Co-doping of the (ZrO2)1-x(Sc2O3)x crystals (x = 0.08–0.10) with 2 mol% Y2O3 or Yb2O3 for all experimental compositions produced transparent homogeneous single crystals of the t” phase or the cubic phase. For co-doping of the scandia-stabilized zirconia crystals with 1 mol% Y2O3 or Yb2O3, the stabilization of the high-temperature phases depended on the Sc2O3 content in the solid solutions. For co-doping of the solid solutions with 1 mol% Y2O3 or Yb2O3, the conductivity of the crystals increased with the Sc2O3 concentration. For co-doping of the crystals with 2 mol% Y2O3 or Yb2O3, the conductivity decreased with the Sc2O3 concentration. At scandia concentrations of 9–10 mol%, the high-temperature conductivity of the crystals co-doped with ytterbia were higher compared to those with yttria co-doping. The (ZrO2)0.9(Sc2O3)0.09(Yb2O3)0.01 crystals had the highest conductivity over the entire experimental temperature range.

Effects of M2O3–Y2O3 (M = Sc and Al) additives on electrical conductivity of hot-pressed SiC ceramics

Highly densified silicon carbide ceramics were fabricated by hot-pressing β-SiC powders with Sc2O3–Y2O3 and Al2O3–Y2O3 additives. The Sc2O3 and Al2O3 contents of the additives were varied while maintaining a constant Y2O3 content. For the same Y2O3 content (0.849 wt%), the electrical conductivity (σ) of the ceramics decreased to 2.3 × 102, 4.5 × 101, and 5.3 Ω-1 cm−1 with an increase in the Sc2O3 content to 0.259, 0.519, and 1.038 wt%, respectively. Similarly in the case of Al doping, the σ of the ceramics decreased to 1.2, 7.9 × 10−1, and 1.2 × 10−1 Ω−1 cm−1 with an increase in the Al2O3 content to 0.219, 0.437, and 0.874 wt%, respectively, at a fixed Y2O3 content of 0.967 wt%. This decrease in σ can be primarily attributed to the increase in the concentration of the deep acceptors generated by Sc or Al doping in the SiC lattice. The ScSi and AlSi acceptors compensated the NC donors, leading to a decrease in the carrier density of the ceramics. The lower σ of the Al-doped specimens than that of the Sc-doped ones can be attributed to their lower carrier mobility.

Effect of scandia content on the hot corrosion behavior of Sc2O3 and Y2O3 co-doped ZrO2 in Na2SO4 + V2O5 molten salts at 1000 °C

The effect of Sc2O3 content on the hot corrosion behavior of x mol.% Sc2O3-1.5 mol.% Y2O3 co-doped ZrO2 ceramics (ScYSZ) in Na2SO4 + V2O5 (50/50 wt.%) molten salts at 1000 °C was investigated. The experiments revealed that the hot corrosion resistance and phase stability of the ScYSZ ceramics increase with the Sc2O3 content as results of the enhanced strength of rare earth-oxygen bond and the increased prohibition effect on the vanadate penetration due to the small ionic radius of Sc3+ and the weak reactivity of Sc2O3 with vanadates. The hot corrosion mechanism was also discussed.

Sintering of translucent and single-phase nanostructured scandia-stabilized zirconia

Fully-dense and single-phase nanostructured scandia-stabilized zirconia specimens were produced by high-pressure spark plasma sintering technique. Nanocrystalline powders were prepared by the coprecipitation method. Green pellets were sintered at temperatures varying from 700 to 900 °C and pressures from 1.4 to 2 GPa, resulting in dense microstructures with single-phase fluorite-type cubic structure within a wide range of Sc2O3 content (6–15 mol%). The average grain size of sintered specimens ranged from 8 to 20 nm. Transmittance spectra confirm translucence in sintered specimens, which is consistent with full density. The results reported here reveal that the polymorphism challenge in the zirconia-scandia system can be successfully suppressed by this consolidation technique, which allows for controlling the grain size of bulk specimens.

Tuning Selectivity of Maleic Anhydride Hydrogenation Reaction over Ni/Sc-Doped ZrO2 Catalysts

A series of Sc-doped ZrO2 supports, with Sc2O3 content in the range of 0 to 7.5% (mol/mol), were prepared using the hydrothermal method. Ni/Sc-doped ZrO2 catalysts with nickel loading of 10% (w/w) were prepared using impregnation method, and characterized with the use of XRD, Raman, H2 temperature-programmed reduction (H2-TPR), H2 temperature-programmed desorption (H2-TPD), XPS, and in situ FT-IR techniques. The catalytic performances of Ni/Sc-doped ZrO2 catalysts in maleic anhydride hydrogenation were tested. The results showed that the introduction of Sc3+ into ZrO2 support could effectively manipulate the distribution of maleic anhydride hydrogenation products. γ-butyrolactone was the major hydrogenation product over Sc-free Ni/ZrO2 catalyst with selectivity as high as 65.8% at 210 °C and 5 MPa of H2 pressure. The Ni/Sc-doped ZrO2 catalyst, with 7.5 mol% of Sc2O3 content, selectively catalyzed maleic anhydride hydrogenation to succinic anhydride, the selectivity towards succinic anhydride was up to 97.6% under the same reaction condition. The results of the catalysts’ structure–activity relationships revealed that there was an interdependence between the surface structure of ZrO2-based support and the C=O hydrogenation performance of the ZrO2-based supported nickel catalysts. By controlling the Sc2O3 content, the surface structure of ZrO2-based support could be regulated effectively. The different surface structure of ZrO2-based supports, resulted in the different degree of interaction between the nickel species and ZrO2-based supports; furthermore, the different interaction led to the different surface oxygen vacancies electron properties of ZrO2-based supported nickel catalysts and the C=O hydrogenation activity of the catalyst. This result provides new insight into the effect of ZrO2 support on the selective hydrogenation activity of ZrO2-supported metal catalysts and contributes to the design of selective hydrogenation catalysts for other unsaturated carbonyl compounds.

Effects of Sc2O3 and MgO additions on the dielectric properties of BaTiO3-based X8R materials

In the present study, dielectric formulations compatible with the base-metal electrode process, using a host material (BaTiO3 + 0.05 mol% MnCO3 + 1.37 mol% BaSiO3) with 0.3–0.6 mol% Sc2O3 and 0–2.0 mol% MgO, were examined. The addition of Sc2O3 and MgO led to the formation of a grain core-shell structure and therefore gave rise to temperature-stable dielectric properties, while the TEM and EDS results revealed the chemical inhomogeneity of the Sc3+ ions across the grains. The Sc2O3 content played an important role in the reducing the dielectric constant (K), improving the electrical resistivity, and flattening the TCC curve of the ceramics by inhibiting grain growth. Meanwhile, the existence of MgO was proven to enhance the densification, affect the room-temperature electrical resistivity, reduce the tanδ value, and improve the TCC value at - 55 °C. The optimum formulation derived in the present study involved adding 0.45 mol% Sc2O3 and 1.0 mol% MgO to the host material. This yielded the following dielectric properties: K = 1,744, tanδ = 0.58%, TCC = - 3.9% (- 55 °C) and - 8.5% (150 °C), and electrical resistivity = 2.8 × 1012 Ω cm (25 °C) and 1.7 × 1011 Ω cm (150 °C). These dielectric properties satisfied the requirements of the EIA-X8R specification, thus validating the material's potential for application to commercial capacitors.

Structure and Transport Properties of Zirconia-Based Solid Solution Crystals Co-Doped with Scandium and Cerium Oxides

The crystals of (ZrO2)1–x(Sc2O3) x (СeO2)0.01 solid solutions (x = 0.08–0.10) were obtained by directional crystallization. The crystals of the grown composites were semitransparent, opalescent, and without cracks and had varying microstructure in the bulk. In the range of compositions under study, it was impossible to obtain optically homogeneous, fully transparent crystals. The crystals grown at a growth rate of 10 mm/h had a nonuniform distribution of ceria along the length of the ingot. The introduction of ceria in an amount of 1 mol % increased the conductivity of the crystals, but the increase in the specific electric conductivity depended on the Sc2O3 content and the phase composition of the crystals. The highest conductivity was inherent in the (ZrO2)0.89(Sc2O3)0.10(CeO2)0.01 crystals.

Enhancement of Dielectric Breakdown Strength and Energy Conversion Efficiency of Niobate Glass-Ceramics by Sc2O3 Doping

Niobate glass-ceramics K2O-SrO-Nb2O5-B2O3-Al2O3-SiO2 (KSN-BAS) doped with different amounts of Sc2O3 have been prepared through a melt quenching/controlled crystallization method, and the influence of the Sc2O3 content on their phase composition, microstructure, dielectric performance, and charge–discharge properties investigated. X-ray powder diffraction results showed that the peak positions of the KSr2Nb5O15 phase shifted to higher angle and the glass-ceramic microstructures were significantly improved by Sc2O3 addition. Based on these results, 0.5 mol.% Sc2O3 doping was found to achieve remarkable enhancement in energy storage density, which reached 9.63 ± 0.39 J/cm3 at dielectric breakdown strength of 1450.38 ± 29.01 kV/cm with high conversion efficiency of ∼ 92.1%. For pulsed power applications, discharge speed of 17 ns and power density of 0.48 MW/cm3 were obtained in the glass-ceramic with 0.5 mol.% Sc2O3. These results could provide a new design strategy for high-performance dielectric capacitors.