Influence of B2O3 additives on microstructure and electrical properties of ZnO-Bi2O3-Sb2O3-based varistors

B₂O₃-doped ZnO-Bi₂O₃-Sb₂O₃-based varistors were fabricated by conventional ceramic technique. The microstructure and electrical properties were investigated by SEM, XRD and electrical measurements. With the addition of B₂O₃, the liquid-assisted sintering based on Bi₂O₃ was improved, and the Bi₂O₃-B₂O₃ glass and Zn₃(BO₃)₂ phase were formed on the grain boundaries. The doping of B₂O₃ markedly improved the varistor performance of the ZnO-Bi₂O₃-Sb₂O₃-based varistors. The nonlinear coefficient of the sample with 3.5 mol% B₂O₃ sintered at 1100 °C reached 56 and the leakage current was only 0.3 μA.     

Microstructure and electrical properties of Lu2O3-doped ZnO-Bi2O3-based varistor ceramics

Lu2O3-doped ZnO-Bi2O3-based varistor ceramics samples were prepared by a conventional mixed oxide route and sintered at temperatures in the range of 900-1 000°C,and the microstructures of the varistor ceramics samples were characterized by X-ray diffractometry(XRD)and scanning electron microscopy(SEM);at the same time,the electrical properties and V-I characteristics of the varistor ceramics samples were investigated by a DC parameter instrument for varistors.The results show that the ZnO-Bi2O3-based varistor ceramics with 0.3%Lu2O3(molar fraction)sintered at 950°C exhibit comparatively ideal comprehensive electrical properties.The XRD analysis of the samples shows the presence of ZnO,Bi-rich,spinel Zn7Sb2O12 and Lu2O3-based phases.     

Effects of adding yttrium nitrate on the mechanical properties of hot-pressed AlN ceramics

Aluminum nitride (AlN) ceramics were prepared by hot-pressing with Y(NO₃)₃·6H₂O as sintering additive. The mechanical properties including flexural strength, Vickers’ hardness, and fracture toughness were studied. The relative density and mechanical property of the monolithic AlN were improved by adding Y(NO₃)₃·6H₂O, which decreased the porosity. At 2 wt% Y₂O₃, the AlN ceramic exhibited the highest strength of 383 MPa, the highest hardness of 15.39 GPa, and the highest fracture toughness of 3.1 MPa m^1/2. However, doping with more additive, the strength, hardness, and toughness of AlN ceramics decreased because of the weak interfacial bonding between AlN matrix and the yttrium aluminates phase.     

Self-healing mechanism of a protective film prepared on a Ce(NO3)3-pretreated zinc electrode by modification with Zn(NO3)2 and Na3PO4

Self-healing mechanism of a protective film against corrosion of zinc at scratches in an aerated 0.5 M NaCl solution was investigated by polarization measurements, X-ray photoelectron spectroscopy (XPS) and electron-probe microanalysis (EPMA). The film was prepared on a zinc electrode by treatment in a Ce(NO₃)₃ solution and addition of aqueous solutions containing 9.98 or 19.9 μg/cm² of Zn(NO₃)₂ · 6H₂O and 55.2 μg/cm² of Na₃PO₄ · 12H₂O. After the coated electrode was scratched with a knife-edge crosswise and immersed in the NaCl solution for many hours, polarization measurements, observation of pit formation at the scratches, XPS and EPMA were carried out. This film was remarkably protective and self-healing against zinc corrosion on the scratched electrode. The cathodic and anodic processes of zinc corrosion were markedly suppressed by coverage of the surface except for scratches with a thin Ce₂O₃ layer containing a small amount of Ce⁴⁺ and the surface of scratches with a layer composed of Zn₃(PO₄)₂ · 4H₂O, Zn(OH)₂ and ZnO mostly.     

Sintering process as relevant parameter for Bi2O3 vaporization from ZnO-Bi2O3-based varistor ceramics

The relationship between sintering process and vaporization of the Bi₂O₃ in ZnO-Bi₂O₃-based varistor ceramics was investigated. The phase and microstructure evolution during the sintering process were examined. The results show that the higher the sintering temperature or the longer the sintering time is, the more the Bi₂O₃ is volatilized. The heating rate has little effects on the Bi₂O₃ volatilized in ZnO-Bi₂O₃-based varistor ceramics. This is in accordance with the relative X-ray diffraction peak area ratio analysis. The results also show that the sintering temperature has the greatest impact on the vaporization of the Bi₂O₃, then followed by sintering time, and the effect of the heating rate is the minimum.     

Synthesis of CeO2/TiO2 nanoparticles by laser ablation of Ti target in cerium (III) nitrate hexahydrate (Ce(NO3)3·6H2O) aqueous solution

A new synthesis process, laser ablation in an aqueous solution of target material, was applied to synthesize nanostructured CeO₂/TiO₂ catalyst particles. Reactivity within the laser plume (plasma) can be used to synthesize CeO₂ from an aqueous solution, 2 M cerium (III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O) aqueous solution, and to fabricate TiO₂ from Ti target. CeO₂/TiO₂ nanoparticles were successfully synthesized by the laser ablation of Ti target in 2 M cerium (III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O) aqueous solution. Laser ablation of Ti in a liquid environment and chemical reactions of the solution within a plasma plume are discussed.     

One-pot facile synthesis and optical properties of porous La2O2CO3 hollow microspheres

Lanthanum oxycarbonate (La₂O₂CO₃) hollow microspheres with novel porous architectures were successfully fabricated by a simple one-pot hydrothermal treatment of an aqueous solution containing glucose, La(NO₃)₃·6H₂O, and subsequent calcination. The as-prepared La₂O₂CO₃ porous hollow spheres are composed of nanoparticles with a mean particle size of 15 nm. Carbon microspheres act as not only templates but also carbon sources for the formation of La₂O₂CO₃ hollow spheres. Interestingly, the as-prepared La₂O₂CO₃ hollow spheres show a green emission band under UV excitation, which may be used as fluorescent biological labels.     

Fabrication of V3O7·H2O@C core-shell nanostructured composites and the effect of V3O7·H2O and V3O7·H2O@C on decomposition of ammonium perchlorate

V₃O₇·H₂O@C core-shell materials have been synthesized using V₃O₇·H₂O nanobelts as the cores and glucose as the source of carbon via an environmental hydrothermal method. The as-obtained V₃O₇·H₂O@C core-shell materials were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), elemental analysis (EA), Fourier transform infrared spectroscopy (FT-IR) and Raman spectrum. The influences of the reaction temperature, concentration of glucose and reaction time on the morphologies of the samples were respectively discussed in detail. The possible formation mechanism of V₃O₇·H₂O@C was proposed according to our experimental results. Furthermore, the effect of V₃O₇·H₂O and V₃O₇·H₂O@C on the thermal decomposition of ammonium perchlorate (AP) were investigated by thermal gravimetric analyzer (TG) and differential thermal analysis (DTA). The thermal decomposition temperatures of AP in the presence of V₃O₇·H₂O and V₃O₇·H₂O@C were reduced by 70 and 89 °C, respectively, which indicates that V₃O₇·H₂O@C core-shell composites have higher activity than V₃O₇·H₂O.     

The effects of Bi(Mg2/3Nb1/3)O3 on piezoelectric and ferroelectric properties of K0.5Na0.5NbO3 lead-free piezoelectric ceramics

To improve the temperature stability of piezoelectric properties of Na_0.5K_0.5NbO₃ (KNN)-based ceramics, Bi(Mg_2/3Nb_1/3)O₃ (BMN) was used to modify Na_0.5K_0.5NbO₃ (KNN)-based ceramics by a conventional sintering technique. Piezoelectric and ferroelectric properties of 0.99K_0.5Na_0.5NbO₃-0.01Bi(Mg_2/3Nb_1/3)O₃ ceramics were studied. It is found that 0.01BMN-0.99KNN ceramics exhibits stable piezoelectric properties as the temperature changes due to the composition fluctuation on B sites (d₃₃ ≈ 130 pC/N, dielectric loss tg θ ≤ 5% in the range 25-300 °C). These results indicate that these materials are promising lead-free piezoelectric ceramic candidates for practical applications.     

Preparation and luminescence characterization of new carbonate (Y2(CO3)3·nH2O:Eu) phosphors via the hydrothermal route

A new Eu³⁺-activated Y₂(CO₃)₃·nH₂O phosphor was successfully prepared via the hydrothermal process using urea as a reaction agent. Y₂(CO₃)₃·nH₂O:Eu³⁺ phosphors displayed an intense red emission at 615 nm due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions under 254 nm excitation. The intensity of this emission was significantly increased with a rise in the hydrothermal temperatures. The study of photoluminescence properties demonstrated that Y³⁺ ions were replaced by Eu³⁺ ions in the host lattice at the 9-coordination sites. With an increase in heating temperatures, the morphology of Y₂(CO₃)₃·nH₂O:Eu³⁺ powders changed from a spherical to a rod-like shape. Calcination at elevated temperatures resulted in thermal decomposition of Y₂(CO₃)₃·nH₂O:Eu³⁺ to form Y₂O₃:Eu³⁺. The formed Y₂O₃:Eu³⁺ powder exhibited a rod-like morphology with an intense red emission.     

Hydrothermal synthesis of Cu3(OH)2V2O7·nH2O nanoparticles and its application in lithium ion battery

Well crystallized copper vanadium oxide hydroxide hydrate (Cu₃(OH)₂V₂O₇·nH₂O) nanoparticles have been successfully synthesized by a simple hydrothermal method. The morphology and structure of the as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The composition of Cu₃(OH)₂V₂O₇·nH₂O was studied by thermal analysis (TG, DTA), which indicates that there are two molecules of water in a Cu₃(OH)₂V₂O₇·nH₂O molecular formula. Electrochemical properties of Cu₃(OH)₂V₂O₇·2H₂O nanoparticles as positive electrode of lithium ion battery were studied by conventional charge/discharge tests at different current density, showing steady initial discharge platforms near 1.7 V. The first discharge capacity of Cu₃(OH)₂V₂O₇·2H₂O electrode arrives at 868 and 845 mAh g⁻¹ at current density of 0.01 and 0.02 mA cm⁻², respectively.     

The ternary system: H2O–Fe(NO3)3–Co(NO3)2 isotherms −15 and −25 °C

The binary system H₂O–Fe(NO₃)₃ has been investigated at temperature ranging between –25 and 47 °C.The solid–liquid equilibria of the ternary system H₂O–Fe(NO₃)₃–Co(NO₃)₂ were studied at −15 and −25 °C by using a synthetic method based on conductivity measurements which allows all the characteristic points of the isotherms to be determined, and the stable solid phases which appear are respectively: ice, Fe(NO₃)₃·9H₂O, Fe(NO₃)₃·6H₂O, Co(NO₃)₂·9H₂O, Co(NO₃)₂·6H₂O and Co(NO₃)₂·3H₂O.     

Analysis of the electrochemical reaction behavior of alloy AZ91 by EIS technique in H3PO4/KOH buffered K2SO4 solutions

The EIS technique was used to analyze the electrochemical reaction behavior of Alloy AZ91 in H₃PO₄/KOH buffered K₂SO₄ solution at pH 7. The corrosion resistance of Alloy AZ91 was directly related with the stability of Al₂O₃ · xH₂O rich part of the composite oxide/hydroxide layer on the alloy surface. The break down of the oxide layer was estimated to occur mainly on the matrix solid solution phase in Alloy AZ91. The mf capacitive loop arose from the relaxation of mass transport in the solid oxide phase in the presence of Al₂O₃ · xH₂O rich part and from Mg⁺ ion concentration within the broken area in the absence of Al₂O₃ · xH₂O rich part in the composite oxide structure on the alloy surface. The lf inductive loop had tendency of disappear when the dissolution rate of the alloy decreased as a result of the formation of the protective oxide layer.     

Effect of SnO2 doping on microstructural and electrical properties of ZnO-Pr6O11 based varistor ceramics

ZnO-Pr₆O₁₁ based varistor ceramics doped with 0-2.0 mol% SnO₂ were fabricated by sintering samples at 1300 °C for 2 h with conventional ceramic processing method. X-ray diffraction analysis indicated that the doped SnO₂ reacted with praseodymium oxides during sintering, generating Pr₂Sn₂O₇ phase. Through scanning electron microscopy, it was found that the doping of SnO₂ played a role against the growth of ZnO grains. Capacitance-voltage analysis revealed that the doped SnO₂ acted as a donor in the varistor. The measured electric-field/current-density characteristics of the samples showed that the varistor voltage increased with the increase of SnO₂ doping content, when the SnO₂ content was no more than 1.0 mol%; with the SnO₂ content up to no more than 0.5 mol%, the doping of SnO₂ could increase the nonlinear coefficient; but, when the SnO₂ doping content was further increased, the nonlinear coefficient and varistor voltage of the samples decreased, and the leakage current increased.     

The influence of CO2, AlCl3 · 6H2O, MgCl2 · 6H2O, Na2SO4 and NaCl on the atmospheric corrosion of aluminum

The influence of salt deposits on the atmospheric corrosion of high purity Al (99.999%) was studied in the laboratory. Four chloride and sulfate-containing salts, NaCl, Na₂SO₄, AlCl₃ · 6H₂O and MgCl₂ · 6H₂O were investigated. The samples were exposed to purified humid air with careful control of the relative humidity (95%), temperature (22.0 °C), and air flow. The concentration of CO₂ was 350 ppm or <1 ppm and the exposure time was four weeks. Under the experimental conditions all four salts formed aqueous solutions on the metal surface. Mass gain and metal loss results are reported. The corroded surfaces were studied by ESEM, OM, AES and FEG/SEM equipped with EDX. The corrosion products were analyzed by gravimetry, IC and grazing incidence XRD. In the absence of CO₂, the corrosivity of the chloride salts studied increases in the order MgCl₂ · 6H₂O < AlCl₃ · 6H₂O < NaCl. Sodium chloride is very corrosive in this environment because the sodium ion supports the development of high pH in the cathodic areas, resulting in alkaline dissolution of the alumina passive film and rapid general corrosion. The low corrosivity of MgCl₂ · 6H₂O is explained by the inability of Mg²⁺ to support high pH values in the cathodic areas. In the presence of carbon dioxide, the corrosion induced by the salts studied exhibit similar rates. Carbon dioxide strongly inhibits aluminum corrosion in the presence of AlCl₃ · 6H₂O and especially, NaCl, while it is slightly corrosive in the presence of MgCl₂ · 6H₂O. The corrosion effects of CO₂ are explained in terms of its acidic properties and by the precipitation of carbonates. In the absence of CO₂, Na₂SO₄ is less corrosive than NaCl. This is explained by the lower solubility of aluminum hydroxy sulfates in comparison to the chlorides. The average corrosion rate in the presence of CO₂ is the same for both salts. The main difference is that sulfate is less efficient than chloride in causing pitting of aluminum in neutral or acidic media.     

Piezoelectric and dielectric properties of Dy2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ + x wt% Dy₂O₃ with x = 0-0.3 ceramics were synthesized by conventional solid-state processes. The effects of Dy₂O₃ on the microstructure, the piezoelectric and dielectric properties were investigated. X-ray diffraction pattern confirmed that the coexistence of tetragonal and rhombohedral phases in the (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ composition was not changed by adding 0.05-0.3 wt% Dy₂O₃. SEM images indicate that all the ceramics have pore-free microstructures with high density, and that doping of Dy₂O₃ inhibits the grain growth of the ceramics. The addition of Dy₂O₃ shows the double effects on decreasing the piezoelectric and dielectric properties for 0 < x < 0.15 when Dy³⁺ ions substitute B-site Ti⁴⁺ ions, and increasing the properties for 0.15 < x < 0.3 when Dy³⁺ ions enters into A-site of the perovskite structure. The optimum electric properties of piezoelectric constant d₃₃ = 170 pC/N and the dielectric constant ?_r = 1900 (at a frequency of 1 kHz) are obtained at x = 0.3.     

Microwave properties of Ba(Zn1/3Ta2/3)O3 dielectric resonators

Ba(Zn_1/3Ta_2/3)O₃ (BZT) dielectric resonators were prepared by solid-state reaction. The starting materials were BaCO₃, ZnO, and Ta₂O₅ powders with high purity. The double calcined BZT pellets were sintered in air at temperatures of 1575, 1600, 1625, and 1650 °C for 4 h. The X-ray diffraction data allowed the study of the unit cell distortion degree and the presence of the secondary phases. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed with the increase of the sintering temperature. The dielectric constant of BZT resonators measured around 6 GHz was between 26 and 28. High values of Q × f product (120 THz) were obtained for BZT resonators sintered at 1650 °C/4 h. The temperature coefficient of the resonance frequency exhibits positive values less than 6 ppm/°C. The achieved dielectric parameters recommend BZT dielectric resonators for microwave and millimeter wave applications.     

Dielectric relaxation behaviors of pure and Pr6O11-doped CaCu3Ti4O12 ceramics in high temperature range

Pure and Pr₆O₁₁-doped CaCu₃Ti₄O₁₂ (CCTO) ceramics were prepared by conventional solid-state reaction method. The compositions and structures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of Pr-ion concentration on dielectric properties of CCTO were measured in the ranges of 60 Hz-3 MHz and 290-490 K. The third phase of Ca₂CuO₃ was observed from the XRD of CCTO ceramics. From SEM, the grain size was decreased obviously with high valence Pr-ion (mixing valence of Pr³⁺ and Pr⁴⁺) substituting Ca²⁺. The room temperature dielectric constant of Pr-doped CCTO ceramics, sintered at 1323 K, was an order of magnitude lower than the pure CCTO ceramics due to the grain size decreasing and Schottky potential increasing. The dielectric spectra of Pr-doped CCTO were flatter than that of pure CCTO. The loss tangent of Pr-doped CCTO ceramics was less than 0.20 in 2 × 10²-10⁵ Hz region below 440 K. The complex impedance spectra of pure and Pr-doped CCTOs were fitted by ZView. From low to high frequency, three semicircles were observed corresponding to three different conducting regions: electrode interface, grain boundary and grain. By fitting the resistors R and capacitors C, the activation energies of grain boundary and electrode contact were calculated. All doped CCTOs showed higher activation energies of grain boundary and electrode than those of pure CCTO ceramics, which were concordant with the decreasing of dielectric constant after Pr₆O₁₁ doping.     

A self-healing protective film prepared on zinc by treatment in a Ce(NO3)3 solution and modification with Ce(NO3)3

A self-healing protective film was prepared on a zinc electrode by treatment in 1 × 10⁻³ M Ce(NO₃)₃ at 30 °C for 30 min to form a thin layer of hydrated Ce₂O₃ and by modification with 114 μg/cm² of Ce(NO₃)₃ · 6H₂O. The film was dried at 30 °C under a dry atmosphere. After the electrode surface was scratched with a knife-edge crosswise and immersed in an aerated 0.5 M NaCl solution at 30 °C for many hours, polarization measurement of the electrode was carried out in the NaCl solution. The protective efficiency of the film was markedly high, 97.7% at the immersion time, t_i=24 h. Neither pit-like anodic dissolution feature nor pit was observed within the scratches at t_i=72 h. X-ray photoelectron spectroscopy and electron-probe microanalysis revealed that Ce³⁺ migrating into the scratches from the film was adsorbed on the hydrated or hydroxylated zinc surface to form a new layer of hydrated Ce₂O₃ within the scratches, resulting in the self-healing activity of the film for preventing zinc corrosion at the scratched surface.     

Effect of addition of Ba(W0.5Cu0.5)O3 in Pb(Mg1/3Nb2/3)O3-Pb(Zn1/3Nb2/3)O3-Pb(Zr0.52Ti0.48)O3 ceramics on the sintering temperature, electrical properties and phase transition

In this work, we report on the Pb(Mg_1/3Nb_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃-Pb(Zr_0.52Ti_0.48)O₃ (PMN-PZN-PZT) ceramics with Ba(W_0.5Cu_0.5)O₃ as the sintering aid that was manufactured in order to develop the low-temperature sintering materials for piezoelectric device applications. The phase transition, microstructure, dielectric, piezoelectric properties, and the temperature stability of the ceramics were investigated. The results showed that the addition of Ba(W_0.5Cu_0.5)O₃ significantly improved the sintering temperature of PMN-PZN-PZT ceramics and could lower the sintering temperature from 1005 to 920 °C. Besides, the obtained Ba(W_0.5Cu_0.5)O₃-doped ceramics sintered at 920 °C have optimized electrical properties, which are listed as follows: (K_p = 0.63, Q_m = 1415 and d₃₃ = 351 pC/N), and high depolarization temperature above 320 °C. These results indicated that this material was a promising candidate for high-power multilayer piezoelectric device applications.