Synthesis and properties of CaZrO<Subscript>3</Subscript> films on YSZ electrolyte surface

CaZrO₃ films are studied that were obtained on ceramic supports of solid electrolyte of ZrO₂ + 9 mol % Y₂O₃ (YSZ, yttria stabilized zirconia) from alcohol solutions of zirconium oxychloride and calcium nitrate using the method of dipping with the following drying and annealing. The thickness and morphology of films depend on the concentration of the film-forming solution. Vickers microhardness of the CaZrO₃ films was determined. The impedance spectroscopy method was used to study conductivity of films at the temperature of 400–600°C by comparison of impedance spectra of clean supports and supports with a film coating.     

Specific heat capacity and Debye temperature of zirconia and its solid solution

Specific heat C_P of zirconia and yttria stabilized zirconia doped or not with erbia and ceria was measured from 128 to 823 K and of yttria stabilized zirconia doped with erbia and plutonia from 443 to 1573 K. The new determined data were modelled using Debye theory. Data for the tetravalent oxide and for the studied solid solutions show that the extended Dulong and Petit law in Neumann-Kopp rule is verified for zirconia and the quaternary compounds. The Debye temperature of zirconia (590 K) and its yttria, erbia and ceria doped solid solutions (575-625 K) derived from these C_P measurements between 150 and 823 K is discussed and compared with that reported for other tetravalent metal oxides.     

Reduction kinetics of NiO–YSZ composite for application in solid oxide fuel cell

A porous nickel–8 mol% yttria stabilized zirconia (Ni–8YSZ) composite, used as anode for solid oxide fuel cell, was obtained by reduction of NiO–8YSZ cermet. The first goal was the evaluation of the temperature effect of powder processing by thermogravimetry. In addition, the influence of porosity in the reduction kinetic of the sample sintered at 1450 °C was evaluated. The final porosity produced in NiO–8YSZ composite by pore former was 30.4 and 37.9 vol.%, respectively, for 10 and 15 mass% of corn starch. The sample with 15 mass% of corn starch promotes a reduction rate almost twice higher than sample with 10 mass% of corn starch. The porosity introduced by the reduction of NiO was 23 vol.%.     

Phase transformation and crystalline growth of 4 mol% yttria partially stabilized zirconia

The phase transformation and crystalline growth of 4 mol% yttria partially stabilized zirconia (4Y-PSZ) precursor powders have been investigated using the coprecipitation route, using zirconium oxide chloride octahydrate (ZrOCl₂·8H₂O) and yttrium nitrate (Y(NO₃)₃·6H₂O) as the initial materials. Differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED), and high resolution TEM (HRTEM) were utilized to characterize the behavior of phase transformation and crystalline growth of the 4Y-PSZ precursor powders after calcined. Tetragonal ZrO₂ crystallization occurred at about 718.2 K. The activation energy of tetragonal ZrO₂ crystallization was 227.0 ± 17.4 kJ/mol, obtained by a non-isothermal method. The growth morphology parameter (n) and growth mechanism index were close to 2.0, showing that tetragonal ZrO₂ had a plate-like morphology. The crystalline size of tetragonal ZrO₂ increased from 7.9 to 27.6 nm when the calcination temperature was increased from 973 to 1,273 K. The activation energies of tetragonal ZrO₂ growth were 14.97 ± 0.33 and 84.46 ± 6.65 kJ/mol when precursor powders after calcined from 723–973 and 973–1,273 K, respectively.     

Fabrication of high Li:water molar ratio electrolytes for lithium-ion batteries

Hydrous electrolytes with high electrochemical potentials were obtained by hydrating water molecules into solutes to form high Li:water molar ratio electrolytes(HMRE).Solid polyethylene glycol(PEG) were e mployed to enha nce the molar ratio of Li+to water in the electrolytes while reducing the consumption of Li-salt.The obtained mole ratio of Li~+ to wa ter molecules in the hydrous electrolytes was greater than 1:1;however,the mass fraction of Li-salt was reduced to 61%(approximately 5.5 mol/kg,based on water and PEG).Compared with that of water-in-salt electrolytes,the mass fraction of Li-salt could be remarkably reduced by adding solid PEG.The electrochemical stability of the electrolytes improved considerably because of the strong hydration of Li~+ by the water molecules.A beneficial passivation effect,arising from the decomposition of the electrolyte,at a wide potential window was observed.     

Synthesis and characterization of non-transformable tetragonal YSZ nanopowder by means of Pechini method for thermal barrier coatings (TBCs) applications

A simple soft chemical method of synthesizing tetragonal yttria stabilized zirconia nanopowders is described here. Zirconium oxy-chloride octahydrate and yttrium nitrate hexahydrate were taken as a source of zirconium, citric acid was taken as a chelating agent, and ethylene glycol was used as a polysterification agent. The synthesized powders were characterized by X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry, transmission electron microscopy, field emission scanning electron microscope, Fourier transform infrared spectroscopy and Raman spectroscopy. Furthermore, precise cell parameters were calculated in order to exactly determine non-transformable tetragonal crystal structure, which was the best zirconia phase for thermal barrier coatings applications. In this process, tetragonal yttria stabilized zirconia nanopowders could be prepared at a temperature of 1,000 °C and the process was simple and cost-effective.     

Co-doping effect on the properties of scandia stabilized ZrO2

The influence of low concentrations (1 mol %) of few co-dopants (Y₂O₃, La₂O₃, CeO₂, Gd₂O₃, Er₂O₃, ZnO) on the structure and characteristic of 10 mol % scandia stabilized zirconia was studied. Sintering kinetics and thermal expansion coefficients of synthesized solid eletrolytes were determined. It was found that co-doping increased the conductivity of electrolytes at temperature below 550°C. However, at high temperatures, the introduction of co-dopants decreased the conductivity; moreover, this reduction was more severe the more the ionic radii of Zr⁴⁺ and co-dopant differ.     

Research on the electrochemistry of oxygen ion conductors in the former Soviet Union. I. ZrO2-based ceramic materials

Developments of solid electrolytes and mixed conductors based on stabilized zirconia in the former Soviet Union are reviewed. Primary attention is given to experimental data on high-conducting electrolytes, mixed conductors obtained by doping zirconia with transition metal oxides, oxygen exchange and oxygen permeation processes, as well as properties of metal electrodes in contact with the stabilized zirconia. Received: 26 March 1998 / Accepted: 4 June 1998     

PALS study on the defect structure of yttria-stabilized zirconia

Powders of stabilized ZrO₂–8 mol% Y₂O₃ (YSZ) have been obtained by mechanical milling in zirconia vials. The samples were characterized by X-ray diffraction (XRD). Positron annihilation lifetime (PALS) measurements were performed to investigate the lattice defects originated by the incorporation of yttria and those mechanically induced. The XRD results indicate the formation of tetragonal YSZ solid solution. PALS results indicate that positron trapping occurs at different kinds of defects such as vacancy-like defects, grain boundary and associated defects.     

Influence of yttria addition on the phase transformations of zirconia from zircon ore by carbothermal reduction process

Zircon ore carbothermal reduction with yttria addition has been carried out. The influences of heating temperature and yttria addition on the phase transformations of zirconia from zircon ore by carbothermal reduction have been investigated in detail. The phase transformations of zirconia from zircon ore by carbothermal reduction were monitored by X-ray diffraction. The microstructure and micro-area chemical analysis of the products were characterized by scanning electron microscopy and energy dispersive spectrometer. The chemical states of Zr 3d, Y 3d and O 1s presented in the products of zircon carbothermal reduction with 10 wt% yttria addition were investigated by X-ray photoelectron spectroscopy. The results showed that the optimized heating temperature of zircon carbothermal reduction with no addition was 1600 °C, and the main phase of the products consists of m-ZrO₂, c-ZrO₂, ZrC and β-SiC. Yttria addition could be introduced into zirconia lattice and caused it to form Y₂O₃ stabilized zirconia. Zirconia in the products would be turned into partially stabilized zirconia with yttria addition from 1 wt% to 5 wt% while it would exist in the form of fully stabilized zirconia with over 8 wt% yttria addition.     

生物质气为燃料的燃料电池理论电动势计算

The electromotive force (e.m.f.) of solid oxide fuel cells using biomass produced gas (BPG) as the fuels is calculated at 700-1,200 K using an in-house computer program, based on thermodynamic equilibrium analysis. Tour program also predicts the concentration of oxygen in the fuel chamber as well as the concentration of equilibrium species such as H2, CO, CO2 and CH4. Compared with using hydrogen as a fuel, the e.m.f.for cells using BPG as the fuels is relative low and strongly influenced by carbon deposition. To remove carbon deposition, the optimum amount of H2O to add is determined at various operating temperatures.Further the e.m.f, for cells based on yttria stabilized zirconia and doped ceria as electrolytes are compared.The study reveals that when using BPG as fuel, the depression of e.m.f, for a SOFC using doped ceria as electrolyte is relatively small when compared with that using Yttria stabilized zirconia.     

Inductively Coupled Plasma Synthesis of CeO<Subscript>2</Subscript>-based Powders from Liquid Solutions for SOFC Electrolytes

Doped cerium oxide (CeO₂) based electrolytes are attractive alternative materials to replace the existing yttria-stabilized zirconia (YSZ) used as electrolyte for SOFC (solid oxide fuel cells). Cerium oxide electrolytes offer a similar performance to YSZ electrolytes at a lower cell operating temperature (~600--800 ^°C), therefore reducing thermal stresses and solid state reactions among the cell components.Doped Ce_1-xMe_xO_2-x/2(Me = Gd, Sm or Y) fine \hbox{powders} were synthesized from nitrate salts dissolved in water using a radio frequency inductively coupled plasma reactor. It was demonstrated that the relative concentrations of Ce and dopants fed in the solutions were retained in the synthesized powders. The products were all nano-crystalline with the basic crystal structure of CeO₂ and the crystal size of the products was essentially independent of the dopant used. The particle size distributions obtained were multimodal and in most cases trimodal. The results obtained differ from a previously reported mechanism of particle synthesis from liquid precursors.     

苏丹红I分子印迹聚合物的制备及其性能评价

以苏丹红I为模板分子,通过沉淀聚合法制备了一种对苏丹红I具有特异性吸附的分子印迹聚合物。通过选择性评价和前沿色谱实验,评价了致孔剂的选择和用量、功能单体和模板分子的物质的量比对分子印迹聚合物识别性能的影响。实验结果表明: 当以甲醇和乙腈的混合液(体积比为30:10)为致孔剂,甲基丙烯酸(MAA)为功能单体,且功能单体和模板分子的物质的量比为8:1时,分子印迹聚合物的印迹因子为2.32,亲和位点总数(Bt)为0.50 μmol/g;将其作为固相萃取柱填料用于辣椒粉样品中痕量苏丹红I的净化和富集,结果表明: 苏丹红I浓度在10～500 μmol/L范围内时,呈现良好的线性关系(r=0.999);检出限为3.3 μmol/L,加标回收率为95.87%～98.41%,相对标准偏差低于3.1%。该方法有望用于辣椒粉样品中苏丹红I添加剂的常规检测。     

Potassium–conducting K<Subscript>1 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GaO<Subscript>2</Subscript> solid electrolytes

Solid electrolytes with potassium-cation conductivity in the K_{1 − 2x} Pb _x GaO₂ system were synthesized and studied. It was found that solid solutions based on potassium monogallate are formed in a wide range of compositions. They contain vacancies in the potassium sublattice that provide for high conductivity of electrolytes. The relationship is considered between electric characteristics of solid electrolytes and the composition and structure of solid solutions. The results are compared to the earlier obtained data for similar solid electrolytes based on potassium monoaluminate and monoferrite.     

High-voltage activation and dynamics of conductivity relaxation in a binary NaHSO<Subscript>4</Subscript>-KHSO<Subscript>4</Subscript> system

The effect of high-voltage pulses on the conductivity of the binary system of protonic solid NaHSO₄-KHSO₄ electrolyte and its melt with the NaHSO₄ content of 25, 50, 75 mol % is studied. The conductivity of both the solid electrolyte and its melt grows at the increase in the electric field intensity and tends to saturation in the melt. The highest relative conductivity increase of molten electrolyte (T = 469 K, 25 mol % NaHSO₄) reaches 296% and that of the solid electrolyte (T = 408 K, equimolar composition) before breakdown phenomena is 78%. The breakdown conductivity increases by several orders of magnitude. The conductivity relaxation processes after high-voltage pulsed discharges are studied. Relaxation times τ for nonequilibrium carriers are calculated that are of the order of 10³ to 10⁴ s. This time is lower for solid electrolytes, as compared to that in the corresponding melts.     

Time‐Resolved High and Low Temperature Phase Transitions of the Nanocrystalline Cubic Phase in the Y2O3‐ZrO2 and Fe2O3‐ZrO2 System

The nanocrystalline cubic Phase of zirconia was found to be thermally stabilized by the addition of 2.56 to 17.65 mol % Y₂O₃ (5.0 to 30.0 mol % Y, 95.0 to 70.0 mol % Zr cation content). The cubic phase of yttria stabilized zirconia was prepared by thermal decomposition of the hydroxides at 400°C for 1 hr. 2.56 mol % Y₂O₃‐ZrO₂ was stable up to 800°C in an argon atmosphere. The samples with 4.17 to 17.65 mol % Y₂O₃ were stable to 1200°C and higher. All samples at temperatures between 1450°C to 1700°C were cubic except the sample with 2.56 mol % Y₂O₃ which was tetragonal. The crystallite sizes observed for the cubic phase ranged from 50 to 150 Å at temperatures below 900°C and varied from 600 to 800 nm between 1450°C and 1700°C. Control of furnace atmosphere is the main factor for obtaining the cubic phase of Y‐SZ at higher temperature. Nanocrystalline cubic Fe‐SZ (Iron Stabilized Zirconia) with crystallite sizes from 70 to 137 Å was also prepared at 400°C. It transformed isothermally at temperatures above 800°C to the tetragonal Fe‐SZ and ultimately to the monoclinic phase at 900°C. The addition of up to 30 mol % Fe(III) thermally stabilized the cubic phase above 800°C in argon. Higher mol % resulted in a separation of Fe₂O₃. The nanocrystalline cubic Fe‐SZ containing a minimum 20 mol % Fe (III) was found to have the greatest thermal stability. The particle size was a primary factor in determining cubic or tetragonal formation. The oxidation state of Fe in zirconia remained Fe³⁺. Fe‐SZ lattice parameters and rate of particle growth were observed to decrease with higher iron content. The thermal stability of Fe‐SZ is comparable with that of Ca‐SZ, Mg‐SZ and Mn‐SZ prepared by this method.     

Interface proximity effects on ionic conductivity in nanoscale oxide-ion conducting yttria stabilized zirconia: an atomistic simulation study

We present an atomistic simulation study on the size dependence of dopant distribution and the influence of nanoscale film thickness on carrier transport properties of the model oxide-ion conductor yttria stabilized zirconia (YSZ). Simulated amorphization and recrystallization approach was utilized to generate YSZ films with varying thicknesses (3-9 nm) on insulating MgO substrates. The atomic trajectories generated in the molecular dynamics simulations are used to study the structural evolution of the YSZ thin films and correlate the resulting microstructure with ionic transport properties at the nanoscale. The interfacial conductivity increases by 2 orders of magnitude as the YSZ film size decreases from 9 to 3 nm owing to a decrease in activation energy barrier from 0.54 to 0.35 eV in the 1200-2000 K temperature range. Analysis of dopant distribution indicates surface enrichment, the extent of which depends on the film thickness. The mechanisms of oxygen conductivity for the various film thicknesses at the nanoscale are discussed in detail and comparisons with experimental and other modeling studies are presented where possible. The study offers insights into mesoscopic ion conduction mechanisms in low-dimensional solid oxide electrolytes.     

Investigations of nanocrystalline ceramics and powders by TEM, AFM and plasticity measurements

Nanocrystalline zirconia powders prepared by laser evaporation were analyzed by electron microscopy and X-ray diffraction. A very high volume fraction of tetragonal particles was found, although the majority of particles is significantly larger than the equilibrium size of the tetragonal → monoclinic transformation. Nanopowder of yttria stabilized (2.4 mol% Y₂O₃) zirconia was used to prepare nanocrystalline ceramics by pressureless sintering at T = 1400?°C. At T ≥ 1200?°C the samples show superplastic behavior with an activation energy of 585 kJ mol^–1 and a stress exponent of about 1.8.     

Yttria stabilized zirconia solid electrolyte surface modification with ZrO<Subscript>2</Subscript>, Y<Subscript>2</Subscript>O<Subscript>3</Subscript>, and ZrO<Subscript>2</Subscript> + 9 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> films

The surface of ceramic electrolyte ZrO₂ + 9 mol % Y₂O₃, hereinafter referred to as YSZ (abbreviated yttria stabilized zirconia), was modified with 0.1 to 0.2 μm oxide films of ZrO₂, Y₂O₃, and YSZ (same composition as substrate) by dip coating in alcohol solutions of the relevant salts and further annealing. The results of scanning electronic microscopy and X-ray diffraction evidence epitaxial film growth. By means of impedance spectroscopy at the temperatures of 500 to 600°C, the effect of YZS electrolyte surface modification with ZrO₂, Y₂O₃, and YSZ films to the polarization resistance of silver electrode was studied.     

Fabrication and surface characterization of NH4PAA-stabilized HAZ suspensions

Fine composite powders of yttria (3 mol%) stabilized zirconia (Z, 10 wt%) and hydroxyapatite (HA), denoted as HAZ, were prepared by the co-precipitation method. The resulting powders were characterized by XRF, TEM, EDS, XRD, FTIR, TG-DTA, and BET surface area techniques. AES and FTIR were employed to determine the surface properties of the HAZ suspensions in the presence of NH4PAA as a dispersant, which confirmed that the surfaces of both HA and Z were affected by the adsorbed polymers. The mechanism of NH4PAA adsorption on the particles was discussed. Zeta potential measurements showed that the addition of NH4PAA resulted in a dramatic increase in the absolute value of zeta potential. NH4PAA considerably enhanced the stability of the HAZ suspension via electrosteric barrier mechanisms. TEM micrographs confirmed that particles were well dispersed in the suspension. The adsorption density of the dispersant was found to decrease with an increase in pH value.