Effect of CaO-doped in NiMn2O4–LaMnO3 composite ceramics on microstructure and electrical properties

The composite ceramics (NiMn₂O₄)_0.50(La_1?x Ca _x MnO₃)_0.50 (0?≤?x?≤?0.3) consisting of spinel-structured NiMn₂O₄ and perovskite-structured CaO-doped LaMnO₃ were prepared by classical solid state reaction. The X-ray diffraction (XRD) patterns have shown that the major phases presented in the sintered samples are NiMn₂O₄ compounds with a spinel structure, La_1?x Ca _x MnO₃ with a perovskite structure. The Scanning Electron Microscope (SEM) pictures have exhibited that the grain size of the composite ceramics decreases from ca. 6.5 to 2.0?μm as the mole fraction of CaO increases from 0 to 0.3. The ρ _25?°C and B _25/50 constants of the composite samples are in the range of 0.234–8.61?Ω?cm and 2,600–2,962?K, respectively. In particular, CaO-doped leads to a decrease in the resistance drift of the (NiMn₂O₄)_0.50(La_1?x Ca _x MnO₃)_0.50 composite NTC (negative temperature coefficient) ceramics after aging test. This indicates that the CaO-doped (NiMn₂O₄)_0.50(La_1?x Ca _x MnO₃)_0.50 NTC ceramics display high electrical stability in comparison with the Ca-free (NiMn₂O₄)_0.50(LaMnO₃)_0.50 ceramics. The X-ray photoelectron spectroscopy (XPS) analysis verifies that the valence states of the manganese ions have a highly mixed state of Mn²⁺, Mn³⁺ and Mn⁴⁺ at B site. And the electrical conduction of the composite ceramics can be elaborated by the ions migration mechanism.     

Effects of ZrO2 and Y2O3 dissolved in zyttrite on the densification and theα/β phase transformation of Si3N4 in Si3N4-ZrO2 composite

In Si₃N₄-ZrO₂ composite, the effects of zirconia and Y₂O₃ dissolved in zyttrite on the densification and the/ phase transformation of Si₃N₄ were studied using hot-pressing of Si₃N₄ with the addition of pure, 3, 6, and 8 mol% Y₂O₃-doped zirconia. Reaction couples between Si₃N₄ and ZrO₂ of zyttrite were made to observe the reaction phenomena. The addition of pure zirconia was not effective to obtain full density of the Si₃N₄-ZrO₂ composite. However, Y₂O₃ diffused from the added zyttrite promoted densification; the density of Si₃N₄ with 5 vol% pure ZrO₂ composite was 71% theoretical, and nearly full density (>97%) could be obtained in Si₃N₄ with 5 vol% 6, 8 mol% Y₂O₃-doped ZrO₂ composite. On the basis of observations of the Si₃N₄-pure ZrO₂ reaction couple, the reaction between Si₃N₄ and ZrO₂ resulted in the formation of Si₂N₂O phase, and the/ phase transformation of Si₃N₄ occurred via this Si₂N₂O phase. From the XRD analysis of the reaction layer between Si₃N₄ and zyttrite, it is suggested that the reaction products, Y₂Si₂O₇ and Y₂Si₃N₄O₃ phases, play an important role in the densification of Si₃N₄-zyttrite composite.     

Selection of eutectic systems in Al2O3–Y2O3 ceramics

There are two eutectic reactions in the Al₂O₃-rich portion of the Al₂O₃–Y₂O₃ pseudo-binary system; one is the equilibrium Al₂O₃–YAG eutectic reaction at 1826°C, and the other is the metastable Al₂O₃–YAP eutectic reaction at 1702°C. Selection of the Al₂O₃–YAG and the Al₂O₃–YAP eutectics was examined in terms of cooling rate, nucleation temperature and maximum melt temperature. When the melt was cooled from 2100°C at any cooling rate, it always nucleated below the Al₂O₃–YAP eutectic temperature, therefore the Al₂O₃–YAP eutectic was selected. The Al₂O₃–YAG eutectic was selected when the melt was cooled from 1900°C at a cooling rate of less than 1 K s⁻¹. The selection of the two eutectic systems was determined by the nucleation temperature, although the maximum holding temperature of the melt and the cooling rate significantly affected the nucleation temperature. The structure of the melt, such as coordination of oxygen and chemical order when being heated to 2100°C may affect the nucleation behavior.     

Selection of eutectic systems in AI2O3–Y2O3 ceramics

There are two eutectic reactions in the Al₂0₃–rich portion of the AI₂O₃-Y₂O₃ pseudo–binary system; one is the equilibrium A1₂0₃–YAG eutectic reaction at 1826%C, and the other is the metastable A1₂0₃–YAP eutectic reaction at 1702%C. Selection of the A1₂0₃–YAG and the A1₂0₃–YAP eutectics was examined in terms of cooling rate, nucleation temperature and maximum melt temperature. When the melt was cooled from 2100%C at any cooling rate, it always nucleated below the Al₂0₃–YAP eutectic temperature, therefore the Al₂0₃–YAP eutectic was selected. The Al₂0₃–YAG eutectic was selected when the melt was cooled from 1900%C at a cooling rate of less than 1 K s^-1. The selection of the two eutectic systems was determined by the nucleation temperature, although the maximum holding temperature of the melt and the cooling rate significantly affected the nucleation temperature. The structure of the melt, such as coordination of oxygen and chemical order when being heated to 2100%C may affect the nucleation behavior.     

Preparation and characterization of α-Fe2O3–CeO2 composite

In our previous study we attempted to see the effect of cerium doping (Ce/Fe ratio 0.015 to 0.074) on goethite matrix and conversion of doped goethite to hematite. In the present communication, nano-structured α-Fe₂O₃–CeO₂ composite with Fe/Ce weight ratio as 1.1 has been synthesized by calcination of goethite-cerium hydroxide precursor prepared by co-precipitation method. It was observed that co-precipitation of cerium along with iron in hydroxide medium resulted in hindering the formation of crystalline order as the precursor formed showed poorly crystallized goethite and almost no crystallinity in Ce(OH)₄. Calcination of the precursor at 400 °C showed the formation of hematite together with a broad peak corresponding to cerium oxide whereas at 800 °C, two distinct phases of α-Fe₂O₃ and CeO₂ were observed. The Mössbauer spectra showed the presence of a paramagnetic component both for the precursor as well as for the sample calcined at 400 °C but on raising the calcination temperature to 800 °C, the paramagnetic component disappeared and the spectrum corresponding to pure α-Fe₂O₃ phase was observed. The microstructure of the product obtained by calcining at 800 °C showed rod like structure (30 to 50 nm width and 300 to 500 nm length) of α-Fe₂O₃ having equi-dimensional CeO₂ particles on and around the surface. Besides the rods, equi-dimensional particles and agglomerates corresponding to CeO₂ were also observed. The results show that co-precipitation followed by calcinations gives nanorods hematite with CeO₂ particles bonded to its surface.     

In situ formation of Al2O3–ZrO2–Y2O3 composite ceramic coating by plasma electrolytic oxidation on ZAlSi12Cu3Ni2 alloy

In situ formation of Al₂O₃–ZrO₂–Y₂O₃ composite ceramic coating on ZAlSi12Cu3Ni2 aluminum alloy was successfully prepared by plasma electrolytic oxidation (PEO) technology in a zirconate electrolytic solution. The morphologies, phase components, the thermal diffusion coefficient and thermal conductivity of the composite coatings were investigated by scanning electron microscope, energy dispersive spectroscopy, X-ray diffraction and laser pulse tester. The results indicate that the composite coatings are relatively dense and uniform in thickness, and predominantly composed of Al₂O₃, c-Y0.15Zr0·85O1·93Vo0·07(Vo-oxygen vacancies), monoclinic ZrO₂ (m-ZrO₂) and littleY₂O₃. The composite coatings exhibit a gradient distribution in phase component from the surface to the inner part. With the increase of the applied voltage, the micropores, the discharges products, thickness and the ZrO₂ content of the composite coatings increase. With the oxidation time increasing, the surface of coating generates oxide ceramic particles around the holes and accumulates repeatedly. The content of zirconium is the higher on the surface and interface. The content of Al is less and it shows that the ceramic coating contains mainly the zirconium oxide. This is attributed to the presence of micropores and microcracks, plus the extremely fine grain size and the presence of an amorphous phase. When considered in conjunction with the possible thickness range, it’s clear that this PEO coatings offer considerable promise as thermal barriers.     

Electrochemical Al2O3–ZrO2 composite coatings on non-oxide ceramic substrates

Aqueous solutions of xAl(NO3)3+(1–x)ZrO(NO3)2 were used for electrodeposition of ceramic Al2O3–ZrO2 composite on TiC, TiB2 and SiC sunstrates. The weight of the deposit was studied versus the duration of deposition, the current density and the temperature of the bath for Al-rich (x=0.9), Zr-rich (x=0.4) and eutectic (x=0.75) electrolyte compositions. Optimal current densities and durations of deposition were determined to obtain maxima weights of deposits. Amorphous deposits with thicknesses up to 10 m were formed. The microstructure and microchemical composition of the as-deposited and sintered deposits were characterized. Increase in the temperature of the bath inhibited microcracking due to shrinkage during drying. Coated TiC substrates exhibited enhanced oxidation resistance in air at 1100°C.     

Effects of Y2O3 and La2O3 addition on the crystallization of Li2O·Al2O3·4SiO2 glass-ceramic

Effects of adding Y₂O₃ and La₂O₃ on the crystallization of -quartz solid solution (ss) and the subsequent -quartz ss to -spodumene transformation of Li₂O·Al₂O₃·4SiO₂ glass-ceramic were investigated. Adding 4 mol% YO_3/2 or 8 mol % LaO_3/2 effectively improved the control of the crystallization process of the glass. Y₂O₃ did not effectively induce bulk crystallization of -quartz ss, but can reduce the rate of surface crystallization. La₂O₃ completely suppressed the surface crystallization and promoted a uniform, bulk crystallization of -quartz ss. For both the Y₂O₃- and La₂O₃-doped glasses, the kinetics for glass crystallization to -quartz ss was delayed as the doping level increased. Except for the 8 mol % LaO_3/2-doped glass in which no -spodumene was formed, the kinetics for the -quartz ss to -spodumene transformation for the doped glasses was enhanced compared with that for the undoped glass. For the 4 and 8 mol % YO_3/2-doped compositions, the relative amount of -spodumene to -quartz revealed an anomalous decrease trend with heating temperature in a particular temperature range. This can be explained by the surface crystallization characteristic, which induced an overlap of crystallization and -quartz ss to -spodumene transformation. Glass doped with 8 mol % LaO_3/2 exhibited an Avrami exponent of about 2.4 and an activation energy for crystal growth of -quartz ss of about 418 kJ mol^–1.     

BaWO4–BaCuO2–Y2Cu2O5–“1010” Section of the Y2O3–BaO–WO3–CuO System

The phase region of cubic perovskite-like solid solutions (a = 8.28–8.40 Å) in the Y₂O₃–BaO–WO₃–CuO system is outlined, and the phase compatibility diagram of the BaWO₄–BaCuO₂–Y₂Cu₂O₅–1010 (1010 = Y₂WO₆ + Y₂W₃O₁₂) is constructed.     

Effect of surface roughness on fatigue performance of additive manufactured Ti–6Al–4V

Additive manufacturing is increasingly considered for production of high quality, metallic, aerospace parts. Despite the high potential of this manufacturing process to reduce weight and lead time, the fundamental understanding of additive manufactured Ti–6Al–4V material is still at an early stage, especially in the area of fatigue and damage tolerance. This paper covers the effects of inherent surface roughness on the fatigue life. In the as built condition, metallic parts have a poor surface texture, which is generally removed in fatigue critical areas. It is shown that the fatigue properties of Ti–6Al–4V samples, produced by direct metal laser sintering and electron beam melting, are dominated by surface roughness effects. A simple model based on an equivalent initial flaw size is formulated.     

Preparing of nanostructured Al2O3–TiO2–ZrO2 composite powders and plasma spraying nanostructured composite coating

Nanostructured Al₂O₃–TiO₂–ZrO₂ composite powders for plasma spraying were prepared by spray drying granulation technology. The effects of processing parameters on the microstructure and properties of composite powders were investigated. The results show that with increasing the slurry solid content, the particle size of powders increases, and the bulk density of powders increases, and the flowability of powders increases firstly and then decreases. With increasing the binder content, the particle size of powders increases, and the bulk density of powders increases, and the flowability of powders increases firstly and then decreases. With increasing the spray drying temperature, the particle size of powders increases, and the bulk density and flowability of powders increases firstly and then decreases. The most appropriate spray drying parameters are the slurry solid content of 40 wt.%, the binder content of 2.0 wt.% and the spray drying temperature of 250 °C. The nanostructured composite coating was successfully prepared by using the as-prepared nanostructured Al₂O₃–TiO₂–ZrO₂ composite powders as feedstocks. The nanostructured coating possessed higher hardness and toughness compared with the conventional microstructured one, which was attributed to the use of the nanostructured composite powders feedstocks.     

Li2O–ZnO–Co3O4–TiO2 composite thin-film electrocatalyst for efficient water oxidation catalysis

Thin films of different Li₂O–ZnO–Co₃O₄–TiO₂ (LZCT) compositions were prepared and employed as electrocatalysts (i.e., anodes) to perform water oxidation reaction (WOR). The electrocatalytic activities of these thin films were compared with those exhibited by the sodium salt of cobalt phosphate (Na₂CoP₂O₇) (CP) thin-film electrocatalyst, which is a well-known water oxidation catalyst (WOC). These results suggest that the 10Li₂O–10ZnO–40Co₃O₄–40TiO₂ composition exhibits a better catalytic activity in terms of higher faradaic efficiency (>98%), lower over potentials (<400?mV), higher reaction stability (up to 30 continuous cyclic voltammetry (CV) cycles), and the rate of O₂ and H₂ gas evolution in terms of current density (about 1?mA/cm²) in comparison with those exhibited by CP thin-film electrocatalyst. Furthermore, these LZCT thin films exhibited very high specific surface area values and due to the unique microstructure of ZnCo₂O₄ phase evolved out of these LZCT compositions at a calcination temperature of 550°C for 30?min it has been found to be responsible for the higher specific surface area values measured for these thin-film compositions.     

Relationship between microstructural evolution and electric properties of B2O3–CaCu3Ti4O12 composite ceramics

Calcium copper titanate (CaCu₃Ti₄O₁₂, CCTO) powder was mixed with boric oxide (B₂O₃) glassy phase up to 8% by weight to prepare the composite ceramics. The effects of B₂O₃ incorporation on the microstructures, electric and dielectric properties of CCTO ceramics have been systematically investigated. Adding B₂O₃ results in both the decrease of the CCTO grain size. These microstructural changes conjointly affect the dielectric constant. In addition, further B₂O₃ increase leads to its aggregation at grain boundaries. Meanwhile, the B₂O₃ addition reduces the nonlinear coefficient and influences the breakdown electric field.     

New negative temperature coefficient thermistor ceramics in (Y2O3 + CeO2)–LaCr0.5Mn0.5O3 composite system

A new series of composite, negative temperature coefficient (NTC) ceramics based on the (aY₂O₃ + bCeO₂)?0.4LaCr_0.5Mn_0.5O₃ (a + b = 0.6) were carefully prepared and related electrical properties were investigated. All the NTC thermistors showed a linear relationship between the natural logarithm of the resistance and the reciprocal of the absolute temperature, indicative of NTC characteristics. The obtained B _25/85 constants were in range of 2,100–2,700 K. The magnitude order of the resistivity at 25 °C was of 10³–10⁹ Ωcm and activation energies varied from 0.185 to 0.231 eV. The aging coefficient of the NTC thermistors with CeO₂ was less than 2 % for the time period of 900 h, suggesting that NTC thermistors with CeO₂ possessed a better electrical stability in comparison with CeO₂-free thermistors.     

Effect of lactic acid on nucleation morphology and surface roughness of electroless Ni–P deposition in nanoscale

The present work aims to study effect of lactic acid concentration as complexing agent on surface roughness and nucleation morphology of electroless N?CP deposition. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used to study nucleation morphology and surface roughness of deposition. Deposition process started at some initial priority growing centres independently distributed on the substrate. We found that the morphology and surface roughness of deposition strongly depends on the complexing agent concentration. Morphology of initial deposited centres with no concentration of lactic acid was in coniform structure. By increasing the complexing agent concentration, the structure of initial growing centres changed from coniform to nodular shape and the surface roughness of depositions decreased.     

Phase relations in the systems ZrO2Y2O3Nd2O3 and ZrO2Y2O3CeO2

The phase relations of ZrO₂Y₂O₃Nd₂O₃ and ZrO₂Y₂O₃CeO₂ systems have been studied at 1100–1600°C. The single region of the fluorite phase was intensively examined using the relation between lattice parameter and composition. In the ZrO₂Y₂O₃Nd₂O₃ system, 37 mol% Nd₂O₃ is soluble in Y₂O₃-stabilized zirconia (fluorite phase) at 1100°C and 42 mol% Nd₂O₃ at 1600°C. In the ZrO₂Y₂O₃CeO₂ system, 40 mol% CeO₂ dissolves into the stabilized zirconia at 1600°C.     

Surface crystallization and second-order optical non-linearity in Gd2O3–Bi2O3–B2O3 glasses

Some ternary Gd₂O₃–Bi₂O₃–B₂O₃ glasses are prepared, and crystallization behavior and second harmonic intensity are examined to develop new non-linear optical crystallized glasses. The glasses with Gd₂O₃ contents of 8–14 mol% have large densities of over 6 g/cm³ and large refractive indices of ～ 1.9. Transparent surface crystallized glasses consisting of two kinds of crystalline phases with different morphologies, i.e. plate shape and needle shape crystals, are fabricated by heat-treatment at temperatures between glass transition and crystallization temperatures. From second harmonic generation microscope observations, micro-Raman scattering spectra and XRD analyses, plate shape crystals are determined to be non-linear optical Gd_xBi_1KxBO₃ and needle shape crystals are Bi₃B₅O₁₂ having no second-order optical non-linearity. Since crystallized glasses consisting of Gd_xBi_1KxBO₃ crystals exhibit relatively strong SHGs, they have a high potential for application to light control devices.     

Surface crystallization and second-order optical non-linearity in Gd2O3–Bi2O3–B2O3 glasses

Some ternary Gd₂O₃–Bi₂O₃–B₂O₃ glasses are prepared, and crystallization behavior and second harmonic intensity are examined to develop new non-linear optical crystallized glasses. The glasses with Gd₂O₃ contents of 8–14 mol% have large densities of over 6 g/cm³ and large refractive indices of ∼1.9. Transparent surface crystallized glasses consisting of two kinds of crystalline phases with different morphologies, i.e. plate shape and needle shape crystals, are fabricated by heat-treatment at temperatures between glass transition and crystallization temperatures. From second harmonic generation microscope observations, micro-Raman scattering spectra and XRD analyses, plate shape crystals are determined to be non-linear optical Gd_xBi_1−xBO₃ and needle shape crystals are Bi₃B₅O₁₂ having no second-order optical non-linearity. Since crystallized glasses consisting of Gd_xBi_1−xBO₃ crystals exhibit relatively strong SHGs, they have a high potential for application to light control devices.