Phase diagram calculations of ZrO2-based ceramics with an emphasis on the reduction/oxidation equilibria of cerium ions in the ZrO2-YO1.5-CeO2-CeO1.5 system

Phase diagram calculations that were made previously for the ZrO₂-MO _m/2 (m = 2, 3, 4) systems and for the ZrO₂-YO_1.5-MO _m/2 (M = transition metals) systems have been extended to the ZrO₂-YO_1.5-CeO₂(-CeO_1.5) system to make an attempt to explain (1) thermogravimetric (TG) results as a function of oxygen potential, (2) electronic conductivity as a function of oxygen potential, and (3) a miscibility gap observed in air. The interaction parameters for the CeO₂-CeO_1.5-YO_1.5 system were obtained from the reported oxygen nonstoichiometry in CeO_2−x and rate earth doped ceria, (Ce,RE)O_2−δ . The interaction parameters for the ZrO₂-CeO₂ subsystem were obtained so as to reproduce the observed miscibility gap at 1273 K. Those thermodynamic properties can reproduce consistently the experimental behaviors of the electronic conductivity and the TG results in the (Zr_1−x Ce _x )_0.8Y_0.2O_1.9 solid solutions; these indicate the enhancement of reduction of CeO₂.     

Thermal and mechanical properties of ZrO2-CeO2 plasma-sprayed coatings

The thermal and mechanical properties of ZrC₂-C_{eO 2}plasma-sprayed coatings were evaluated to examine their potential as a thermal barrier coating. ZrO₂-CeO₂ solid-solution powders containing up to 70 mol % CeO₂ are successfully plasma sprayed, but cerium content decreases during spraying due to the vaporization of cerium oxide. Hardness is greatest at 30 mol% CeO₂. With increased CeO₂ content, the thermal conductivity decreases to 0.5 W/m K and the thermal expansion coefficient increases to 12.5 x 10_-6 /K. Increased torch input power causes both the relative density and the hardness to increase monotonically, while the thermal conductivity and the thermal expansion coefficient are not significantly affected. When heated above 1300 K, the coating shrinks considerably due to sintering and its thermal conductivity increases abruptly.     

Investigation on Oxygen Chemical Diffusion Properties of Perovskite Oxides (La1?x Pr x )0.6Sr0.4Co0.8Fe0.2O3?δ

Perovskite oxide samples of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (x = 0.2, 0.4, 0.6, 0.8) are obtained by solid-state reaction method. The oxygen chemical diffusion properties of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ are determined by electrical conductivity relaxation technique. The results show that the conductivity of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ increases with the increase of oxygen partial pressure. The (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ samples have a high oxygen chemical diffusion coefficient, which decreases linearly with a decrease in temperature and an increase in Pr content. The oxygen chemical diffusion coefficient D _chem remains fairly constant at high PO₂. The oxygen chemical diffusion coefficient is the highest for (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ with x = 0.2, and attains a value of 9.41 × 10⁻⁵ cm² s⁻¹ at 600 °C. This shows the material’s promise as a cathode material for intermediate temperature solid oxide fuel cells.     

Effects of Sc doping on electrical conductivity of BaZrO<Subscript>3</Subscript> protonic conductors

BaZr1-xScxO3-0.5x (x=0.07,0.10,0.13,0.16) powders were prepared by solid-state reaction method,and ZnO was used as sintering aid.Samples with different amount of ZnO additive were sintered at 1450 ℃ for 6 h in air.Single cubic perovskite phase proton conductors were obtained.Conductivity was measured by electrochemical workstation.It was shown that Sc doping could increase conductivity through enhancing the carrier concentration in the material,but excessive Sc content might decrease the carrier concentration because of its charge compensation.ZnO had an influence on carrier concentration and mobility and affected the electrical conductivity.2 mol％ ZnO and 13 mol％ ScO1.5 doped sample showed the highest DC conductivity of 3.6 × 10-3 S·cm-1 tested at 800 ℃ in wet hydrogen atmosphere.     

Tie-lines and mixing properties of solid solutions in the system CaO-SrO-PbO-O at 1100 K

Phase relations in the system CaO-SrO-PbO-O₂ at 1100 K have been determined by equilibrating samples with different compositions in air, oxygen, or evacuated ampoules for 7 days and characterizing quenched specimens by optical and scanning electron microscopy, energy-dispersive analysis of x-rays (EDX), and x-ray diffraction (XRD). There is a solid-state miscibility gap in the pseudo-binary system CaO-SrO, and continuous solid solubility between Ca₂PbO₄ and Sr₂PbO₄ at 1100 K. Substitution of Ca for Sr occurs only to a limited extent (∼2 mol.%) in SrPbO₃. The calcium-rich solid solutions (Ca_1−y Sr _y )₂PbO₄ characterized by y≤0.255 are in equilibrium with PbO in air; compositions with y≥0.255 coexist with (Ca_1−z Sr _z )PbO₃. There is a three-phase region involving the two monoxide solid solutions (Ca_1−x Sr _x )O on either side of the miscibility gap with x=0.24 and 0.71 and (Ca_1−y Sr _y )₂PbO₄ with y=0.96. Accurately determined are the locations of tie-lines between the solid solutions. Attainment of equilibrium was checked by the conventional tie-line rotation technique. The excess Gibbs energy of mixing of the solid solution with orthorhombic structure is obtained by an analysis of tie-line data; for the mixing of one mole of Ca and Sr represented by (Ca_1−y Sr _y )Pb_0.5O₂, ΔG ^E =y(1−y) [15,840−2950 y] J/mol. The thermodynamic properties suggest the onset of immiscibility in this solid solution below 884 (±5) K. The miscibility gap is asymmetric with a critical composition at y=0.43 (±0.02). Inside the triangle (Ca_1−y Sr _y )Pb_0.5O₂−(Ca_1−z Sr _z )PbO₃−PbO, a small liquid-phase region is present close to the PbO corner, surrounded by three two-phase fields. Each corner of the approximately triangular liquid-phase region is associated with a three-phase field.     

Tie-lines and mixing properties of solid solutions in the system CaO-SrO-PbO-O at 1100 K

Phase relations in the system CaO-SrO-PbO-O₂ at 1100 K have been determined by equilibrating samples with different compositions in air, oxygen, or evacuated ampoules for 7 days and characterizing quenched specimens by optical and scanning electron microscopy, energy-dispersive analysis of x-rays (EDX), and x-ray diffraction (XRD). There is a solid-state miscibility gap in the pseudo-binary system CaO-SrO, and continuous solid solubility between Ca₂PbO₄ and Sr₂PbO₄ at 1100 K. Substitution of Ca for Sr occurs only to a limited extent (∼2 mol.%) in SrPbO₃. The calcium-rich solid solutions (Ca_1−y Sr _y )₂PbO₄ characterized by y≤0.255 are in equilibrium with PbO in air; compositions with y≥0.255 coexist with (Ca_1−z Sr _z )PbO₃. There is a three-phase region involving the two monoxide solid solutions (Ca_1−x Sr _x )O on either side of the miscibility gap with x=0.24 and 0.71 and (Ca_1−y Sr _y )₂PbO₄ with y=0.96. Accurately determined are the locations of tie-lines between the solid solutions. Attainment of equilibrium was checked by the conventional tie-line rotation technique. The excess Gibbs energy of mixing of the solid solution with orthorhombic structure is obtained by an analysis of tie-line data; for the mixing of one mole of Ca and Sr represented by (Ca_1−y Sr _y )Pb_0.5O₂, ΔG ^E =y(1−y) [15,840−2950 y] J/mol. The thermodynamic properties suggest the onset of immiscibility in this solid solution below 884 (±5) K. The miscibility gap is asymmetric with a critical composition at y=0.43 (±0.02). Inside the triangle (Ca_1−y Sr _y )Pb_0.5O₂−(Ca_1−z Sr _z )PbO₃−PbO, a small liquid-phase region is present close to the PbO corner, surrounded by three two-phase fields. Each corner of the approximately triangular liquid-phase region is associated with a three-phase field.     

The effects of temperature and composition on the thermal conductivities of [(ZrO2)1−x(CeO2)x]0.92(Y2O3)0.08 (0 ? x ? 1) solid solutions

The thermal conductivities of [(ZrO₂)_1−x(CeO₂)_x]_0.92(Y₂O₃)_0.08 (0 ? x ? 1) solid solutions are studied in this paper. The incorporation of ZrO₂ and CeO₂ in the solid solution decreases the thermal conductivity compared with their end members (YSZ and YDC). The thermal conductivities of the solid solutions show clearly different temperature dependences in the ZrO₂-rich (0 ? x ? 0.5) region and in the CeO₂-rich region (0.5 ? x ? 1). The composition and the temperature dependence of the thermal conductivities are discussed based on established phonon scattering theories. We have concluded that the composition dependence of the thermal conductivity of this system is mainly controlled by the mass difference between Zr⁴⁺ and Ce⁴⁺, while the thermal conductivity-temperature relationship is dominated by the randomness of the defect distribution.     

Amorphization of ZrO2 + CeO2 Powders Through Mechanical Milling for the Use of Kinetic Spray

The coating formation in a kinetic spray process mainly depends on the impact of inflight particles at a high velocity. The plastic deformation at the impact interface would disrupt the native oxide scale on the particle and the substrate to generate the intimate contact of the atomic structures. Accordingly, it poses a challenge in producing ceramic coating during kinetic spray because of the lack of plasticity of ceramic powders at room temperature. In this study, we proposed to prepare ZrO₂ ceramic coatings using partially amorphized powder with nanometer size in the kinetic spray process. To prepare the powder for the use of the kinetic spray, the amorphization and grain refinement of ZrO₂ powder in mechanical ball milling were studied. The results showed that the amorphization and grain refinement were improved because of the formation of solid solution when the CeO₂ agent was added. Subsequently, a nearly spherical powder was achieved via spray drying using the milled powders. The plasticity of the milled powders was tested in the kinetic spray process using Nitrogen as process gas. A dense ZrO₂-CeO₂ coating with a thickness of 50 μm was formed, whereas spraying milled ZrO₂ powder can only lead to an inhomogeneous dispersion of the destructible particles on the surface of the substrate.     

Opportunities for TBCs in the ZrO2-YO1.5-TaO2.5 system

An examination of the ZrO₂-YO_1.5-TaO_2.5 system reveals several promising attributes for use in thermal barrier coating applications. The rather unique presence of a stable, non-transformable tetragonal region in this ternary oxide system allows for phase stability to high temperatures (1500 °C). Selected compositions with high levels of yttria and tantala have also shown superior resistance to vanadate corrosion than the commercially utilized 7YSZ. In addition, Y + Ta stabilized zirconia compositions within the non-transformable tetragonal phase field exhibit toughness values comparable or somewhat higher than those of 7YSZ, which bodes well for their durability as TBCs. These promising attributes are discussed in this paper in the context of recent experimental work.     

To Journal of Phase Equilibria and Diffusion Phase Relationship of the BaO-ZrO<Subscript>2</Subscript>-YO<Subscript>1.5</Subscript> System at 1500 and 1600 °C

Phase relationship of a BaO-ZrO₂-YO_1.5 system at 1500 and 1600 °C was examined in order to determine whether a phase separation at the composition of 15% yttrium-doped barium zirconate exists. According to a pseudoternary phase diagram of the BaO-ZrO₂-YO_1.5 system established by this work, the solubility of yttria into cubic barium zirconate at 1600 °C is 0.25 in a mole fraction of yttria (X_\textYO1.5 ) (X_{{{\text{YO}}_{1.5} }} ) . Thus, we confirmed that there is no phase separation at the composition of 15% yttrium-doped barium zirconate at 1600 °C. On the other hand, at 1500 °C, there might be a phase separation at the composition of 15% yttrium-doped barium zirconate into yttrium-doped barium zirconate where quite small amount of yttrium is doped and a new phase whose composition is close to reported BZ(II) phase.     

Preparation of new sunscreen materials Ce1-xZnxO2-x via solid-state reaction at room temperature and study on their properties

Superfine cerium-zinc oxides Ce1-xZnxO2-x with x = 0, 0.1, 0.3, 0.5, and 1.0 were obtained by grinding Ce(SO4)2·4H2O, ZnSO4·7H2O and NH4HCO3 under the condition of surfactant PEG-400 being present at room temperature, washing the mixture with water to remove soluble inorganic salts, drying at 80°C, and calcining.The precursor and its calcined samples were characterized using thermogravimetry and differential thermal analyses(TG/DTA), UV-vis absorption spectroscopy, X-ray powder diffraction(XRD), and scanning electron microscopy(SEM).The results showed that superfine Ce1-xZnxO2-x behaved as an excellent UV-shielding material.The ZnO-doped CeO2 can facilitate the formation of crystalline state CeO2.The catalytic ability of products used in air oxidation of castor oil was investigated.The results showed that the catalytic abilities of products decreased with increasing zinc amount.     

Thermophysical properties of Sm2（Zr（1-x）Cex）2O7 ceramics

Sm₂(Zr_1−x Ce _x )₂O₇ (x = 0.1, 0.2, and 0.3) ceramics were prepared by solid reaction method at 1600°C for 10 h using Sm₂O₃, ZrO₂, and CeO₂ as starting reactants. The phase compositions, microstructures, thermal expansion coefficients, and partial thermal conductivities of these materials were investigated. X-ray diffraction (XRD) results reveal that Sm₂(Zr_0.9Ce_0.1)₂O₇ with pyrochlore structure and Sm₂(Zr_1−x Ce _x )₂O₇ (x = 0.2 and 0.3) with fluorite structure were synthesized, and scanning electrical microscopy (SEM) images show that the microstructures of these products are very dense. The linear thermal expansion coefficients increase with increasing temperature in the temperature range from ambient to 1200°C, and the thermal expansion coefficients increase with increasing content of doped CeO₂. The thermal conductivities of Sm₂(Zr_0.8Ce_0.2)₂O₇ and Sm₂(Zr_0.7Ce_0.3)₂O₇ decrease gradually with an increase in temperature. These results show that the synthesized ceramic materials can be explored as novel prospective candidate materials for use in new thermal barrier coating systems in the future.     

Preparation of nanometric CeO2–ZrO2–Nd2O3 solid solution and its catalytic performances

A kind of nanometric CeO₂–ZrO₂–Nd₂O₃ (CZN) solid solution for a carrier in the automotive three-way catalysts was synthesized by a coprecipitation method and characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption (BET), scanning electron microscopy (SEM) and oxygen storage capacity (OSC). For the purpose of comparison, an unincorporated CeO₂–ZrO₂ (CZ) was also synthesized. The XRD measurements disclose the prepared CeO₂–ZrO₂–Nd₂O₃ have a face-centered cubic fluorite structure and nanoparticle sizes. According to the results of XPS, Nd³⁺ ions can enter the CZ lattice and form a homogenous solid solution. Oxygen storage capacity measurements reveal that CeO₂–ZrO₂–Nd₂O₃ display high oxygen mobility at a low temperature. The results of the activity tests show that the catalyst exhibits good three-way catalytic activity and fairly wide range of air-to-fuel ratios.     

Experimental determination of interfacial energy for solid Zn solution in the Sn-Zn eutectic system

The grain boundary groove shapes for Zn solid solution in equilibrium with Sn-Zn eutectic liquid were observed with a radial heat flow apparatus. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient, the solid-liquid and the grain boundary energy for the Zn solid solution in equilibrium with Sn-Zn eutectic liquid were determined to be (2.32 ± 0.13)×10⁻⁸ Km, (120.87 ± 13.29)×10⁻³ J.m⁻² and (194.76 ± 23.37)×10⁻³ J.m⁻², respectively. The termal conductivity of the eutectic Sn-9 wt% Zn solid solution, κ _S , was obtained as 74.74 W/Km by using a radial heat flow apparatus. The thermal conductivity ratio of the eutectic liquid to the eutectic solid, R = κ _L /κ _S was found to be 0.58 with a Bridgman-type directional growth apparatus. Thus, the value of the thermal conductivity of eutectic Sn-9 wt% Zn liquid solution, κ _L , was obtained as 43.82 W/Km.     

Electrical properties of dense and nanocrystalline Sm3+-doped Ce1?xSmxO2?δ (0.05 ≤ x ≤ 0.3) electrolytes for IT-SOFCs

Sm³⁺-doped Ce_1−xSm_xO_2−δ (0.05 ≤ x ≤ 0.3) nano-sized powders for solid electrolytes were synthesized by a solution combustion method, using aspartic acid as a combustion fuel. The calcined Ce_1−xSm_xO_2−δ powders were a ceria-based single phase with a cubic fluorite structure. The nano-sized Ce_1−xSmxO_2−δ powders provided a high density, ultra-fine grain size, and high electrical conductivity even at a low sintering temperature of 1400 °C. The grain size and relative density of the Ce_1−xSm_xO_2−δ pellets ranged from 329 nm to 496 nm and from 91.9 % to 99.2 %, respectively. The grain size and density of the Ce_1−xSm_xO_2−δ pellets decreased with an increase of Sm³⁺ content. The electrical conductivity of the Ce_1−xSmxO_2−δ increased with an increase of Sm³⁺ content up to x = 0.25 and then decreased with higher Sm³⁺ content. The maximal electrical conductivity (0.105 Scm⁻¹) was obtained with Ce_0.75Sm_0.25O_2−δ at 800 °C.     

Microstructure, Mechanical Properties, and Pyroconductivity of NiFe2O4 Composite Reinforced with ZrO2 Fibers

NiO-Fe₂O₃-ZrO_2f composites were fabricated by a two-step sintering process. No phase transformation for ZrO_2f was observed. The as-prepared NiO-Fe₂O₃-ZrO_2f ceramic showed excellent mechanical properties because of the introduction of ZrO₂ fiber. The values for both the bending strength and fracture strength of 3 wt.% ZrO_2f-reinforced NiFe₂O₄ samples reached the maximum values of ~89.0 MPa and ~4.67 MPa m^1/2, respectively, The toughness mechanism is mainly attributed to fibers’ fracture, crack deflection, fibers’ pull-out, and fibers’ debonding. The conductivity of ZrO_2f-reinforced NiFe₂O₄ is dependent on temperature and ZrO_2f content. When the electrolytic temperature is up to 950 °C, the conductivity value of the sample reinforced with 4 wt.% ZrO₂ fibers is 0.63 S/cm, which has been improved by 37.8% compared with the conductivity value of 0.45 S/cm for the un-doped samples. The main conductive mechanisms of ZrO₂ fiber in the matrix are the one based on the substitution of Zr⁴⁺ ions to produce quasi-free electrons, and the other based on oxygen ionic conducting mechanism.     

The effect of high-temperature annealing on LaFe_(11.5)Si_(1.5) and the magneto-caloric properties of La_(1-x)Ce_xFe_(11.5)Si_(1.5) compounds

The powder X-ray diffraction patterns of LaFe11.5Si1.5 compounds annealed at different high temperatures from 1323 K (5 h) to 1623 K (2 h) show that a large amount of 1:13 phase begins to form in LaFe11.5Si1.5 compound annealed at 1423 K (5 h). In the temperature range from 1423 to 1523 K, α-Fe and LaFeSi phases rapidly decrease to form 1:13 phase. LaFeSi phase is rarely observed, and the most amount of 1:13 phase is obtained in the compound annealed at 1523 K (5 h). With the annealing temperature increasin...     

Effect of lattice defects on thermal conductivity of Ti-doped,Y2O3-stabilized ZrO2

The evolution of lattice structure and thermal conductivity has been studied systematically for a range of Ti-doped, Y₂O₃-stabilized ZrO₂ (YSZ) solid solutions. The mechanism of reducing the thermal conductivity by Ti doping has been determined. Ti⁴⁺ mainly substitutes for Zr⁴⁺ below a critical composition factor (x ? 0.08), above which the interstitial Ti⁴⁺ need to be considered separately. The effect of lattice defects caused by mass and radius differences between Ti⁴⁺ and Zr⁴⁺ ions on the phonon scattering coefficient was discussed quantitatively. And the reduction of oxygen vacancy by interstitial Ti⁴⁺ ions which increases the thermal conductivity at high Ti doping content was also determined. Concerning the integrated phase stability and thermo-mechanical properties, Ti-doped YSZ is believed to be a promising candidate for thermal barrier coatings at higher temperature.