Corrosion of magnesia–chrome brick in molten MgO–Al2O3–SiO2–CaO–FetO slag

The corrosion of magnesia–chrome (MgO–Cr₂O₃) brick in molten MgO–Al₂O₃–SiO₂–CaO–Fe_tO slag has been characterized using a dynamic rotary slag corrosion testing for various test cycles at 1650 °C. The open porosity decreases from 15.3 to 4.0% for three cycles, then it gradually increases from 4.0 to 4.8% when the test is extended to nine cycles, in which the permeating depth of the slag maintains at about 20 mm. The XRD pattern of the permeated layer shows the presence of the MgO, MgCr₂O₄ and CaMgSiO₄ phases. In the interior of the permeating layer cracks are formed and corrosion starts at the pores and cracks of MgO and decreases gradually. However, at 20–40 mm beneath the permeated layer edge, different shapes of MgO particles are found.     

Preparation and optical properties of sol–gel derived Er-doped Al2O3–Ta2O5 films

Thin films of the system xAl₂O₃–(100 − x)Ta₂O₅–1Er₂O₃ were prepared by a sol–gel method and a dip-coating technique. The influences of the composition and the crystallization of the films on Er³⁺ optical properties were investigated. Results of X-ray diffraction indicated that the crystallization temperature of Ta₂O₅ increased from 800 to 1000 °C with increased values of x. In crystallized films, the intensities of the visible fluorescence and upconversion fluorescence tend to decrease with an increase in x values, due to the high phonon energy of Al₂O₃; the strongest fluorescence is observed in a crystallized film for x = 4 heat treated at 1000 °C. In amorphous films obtained by heat treatment at relatively low temperatures the Er³⁺ fluorescence could not be observed because strong fluorescence from organic residues remaining in the films thoroughly covered the Er³⁺ fluorescence. On the other hand, the Er³⁺ upconversion fluorescence in the amorphous films was observed to be stronger than that in the crystallized films. The strongest upconversion fluorescence is observed in an amorphous film for x = 75 heat treated at 800 °C.     

Synthesis and characterization of Zn/Al2O3 nanocomposite by mechanical alloying

In this study, fabrication and characterization of zinc-based metal matrix nanocomposite reinforced by Al₂O₃ particles was investigated. Aluminum and zinc oxide powder mixture was milled in a planetary ball mill in order to produce Zn/Al₂O₃ nanocomposite. The structural evaluation milled and annealed powders studied by X-ray diffraction, SEM observation and hardness measurement. The zinc crystallite size estimated with broadening of XRD peaks by Williamson-Hall formula. The zinc oxide was found to react with Al through a rapid self-sustaining combustion reaction process. As a result a zinc matrix composite reinforced by Al₂O₃ particulate was formed. The microhardness value of produced nanocomposite powder was about 350 HV which was 10–15 times higher than the microhardness of pure zinc (20–30 HV).     

Synthesis and mechanical properties of niobium aluminide-based composites

Niobium aluminide-based composites reinforced with in situ and externally added Al₂O₃ and TiC particulates were fabricated by hot-pressed sintering at 1400 °C. In particular, Nb₂Al–Al₂O₃–TiC in situ composites were successfully obtained from the raw powder mixtures of Nb60Al40 (in at.%)–TiO₂20C8 (in wt.%) by means of this process. The influences of ceramic particulates on the microstructures, flexural strength and fracture toughness were examined. The experimental results indicate that the presence of ceramic particulates yielded a remarkable improvement in both the strength and fracture toughness in comparison with previous results for monolithic niobium aluminide compounds.     

Controllable formation of Er–Yb codoped Al2O3 films by the non-aqueous sol–gel method

1 mol%Er³⁺–10 mol%Yb³⁺ codoped Al₂O₃ thin films have been prepared on thermally oxidized SiO₂/Si(110) substrates by a dip-coating process in the non-aqueous sol–gel method from the hydrolysis of aluminum isopropoxide [Al(OC₃H₇)₃] under isopropanol environment. Addition of N,N-dimethylformamide (DMF) as a drying control chemical additive (DCCA) into the sol suppresses formation of the cracks in the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films when the rare-earth ion is doped with a high doping concentration. Homogeneous, smooth and crack-free Er³⁺–Yb³⁺ codoped Al₂O₃ thin films form at the conditions by a molar ratio of 1:1 for DMF:Al(OC₃H₇)₃. A strong photoluminescence spectrum with a broadband extending from 1.400 to 1.700 µm centered at 1.533 µm is obtained for the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films, which is unrelated to the addition of DMF. Controllable formation of the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films may be explained by the fact that the DMF assisted the deprotonation process of Al–OH at the surfaces of gel particles, resulting in enhancement of the degree of polymerization of sols and improvement of the mechanical properties of gel thin films.     

Synthesis of MoSi2–Al2O3 nanocomposite by mechanical alloying

MoSi₂–Al₂O₃ nanocomposite was synthesized by mechanical alloying (MA) of MoO₃, SiO₂ and Al powder mixture. The structural evolution of the powders was studied by X-ray diffraction (XRD). Both β-MoSi₂ and -MoSi₂ were obtained after 3 h of milling. The spontaneous formation of β-MoSi₂ during milling proceeded by a mechanically induced self propagating reaction (MSR), analogous to that of the self propagating high temperature synthesis (SHS). After 70 h of milling the β-phase transformed to -phase. The crystallite size of -MoSi₂ and Al₂O₃ after milling for 100 h was 12 and 17 nm, respectively. Residual Mo and Si in the 3 and 70 h milled samples formed β-MoSi₂ and Mo₅Si₃ during heating at 1000 °C, respectively.     

Improvements in mechanical properties of TiB2 ceramics tool materials by the dispersion of Al2O3 particles

TiB₂–Al₂O₃ composites with Ni–Mo as sintering aid have been fabricated by a hot-press technique at a lower temperature of 1530 °C for 1 h, and the mechanical properties and microstructure were investigated. The microstructure consists of dispersed Al₂O₃ particles in a fine-grained TiB₂ matrix. The addition of Al₂O₃ increases the fracture toughness up to 6.02 MPa m^1/2 at an amount of 40 vol.% Al₂O₃ and the flexural strength up to 913.86 MPa at an amount of 10 vol.% Al₂O₃. The improved flexural strength of the composites is a result of higher density than that of monolithic TiB₂. The increase of fracture toughness is a result of crack bridging by the metal grains on the boundaries, and crack deflection by weak grain boundaries due to the bad wetting characters between Ni–Mo and Al₂O₃.     

Processing, microstructure and properties of C40 Mo(Si,Al)2/Al2O3 composites

The C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composites were prepared by spark plasma sintering (SPS) of mechanically alloyed (MA) powders. The Mo(Si_0.75Al_0.25)₂/0–20 vol.% Al₂O₃ materials, showing micron and submicron composite structure, possess a hardness of 13.9–14.6 GPa but a poor toughness of 1.78–1.80 MPa m^1/2. The addition of 30 vol.% Al₂O₃ leads to the formation of the micron C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composite with an intergranular distribution of Al₂O₃, that results in a drop of the hardness to 10.2 GPa and an improvement of the toughness to 3.67 MPa m^1/2. The transition of the cleavage facets to the intergranular fracture with the addition of Al₂O₃ is assumed as the main toughening mechanism.     

Highly stable persistent spectral hole burning in Eu ions doped oxy-fluoride glasses of 30CaF2–10Al2O3–60B2O3

High temperature persistent spectral hole burning up to room temperature has been observed in Eu³⁺ ions doped oxy-fluoride glasses with a composition of 30CaF₂–10Al₂O₃–60B₂O₃ (mol%) melted in a reducing atmosphere. The hole stability was studied through light-induced hole refilling and temperature cycling experiments. The burned holes survive thermal cycling to 300 K due to a high barrier height of 0.69 eV in the sample.     

A simple and an effective method for the fabrication of densified glass-ceramics of low temperature co-fired ceramics

This study reports a new, simple and effective pre-calcined method for fabrication BaO–TiO₂–B₂O₃–SiO₂ low temperature co-fired ceramics (LTCC) at a sintering temperature below 900 °C, and with dielectric losses (tan δ) lower than 2 × 10⁻³. The research results have shown that the addition of 2–5 wt% Al₂O₃ could easily eliminate the porosity of the glass-ceramics because of the excellent wetting behavior between alumina and the BaO–B₂O₃–SiO₂ glass liquid phase in the low temperature co-fired ceramic system.     

Synthesis of in situ Al–TiB2 composites using stir cast route

When elemental Ti and B powders were added to molten Al at above 1000°C, fine in situ TiB₂ particulates were formed through Al–Ti–B exothermic reaction. By optimising the nucleation of TiB₂, the tensile and yield strengths of a synthesised Al–15V_f%TiB_s composite were twice that of matrix material. Modification of Al-matrix with 4.5 wt%Cu tripled the tensile and yield strengths at peak-aged condition. Owing to the co-presence of brittle Al₃Ti flakes with TiB₂ particles in the composites synthesised by the Al–Ti–B system, ductility was reduced to 68% and 84% in composites with Al- and Al–Cu matrices, respectively. When the (Ti + B) mixture was incorporated with 3 wt%C, TiB₂ and TiC reinforcing phases were simultaneously produced in the composite with Al–Cu matrix. Such an approach reduced Al₃Ti compound in the composite considerably. Although the presence of Cu in the composite was found to promote the formation of Al₃Ti, its effect on the fluidity caused the melt recovery to increase from 33% to 52%.     

Low-temperature ionic conductivity of the solid solution in the system ZrO2–Y2O3–Yb2O3

Compositional dependence of ionic conductivity in the system ZrO₂–Y₂O₃–Yb₂O₃ was investigated in the temperature range 573–873 K using the complex impedance technique. It was shown that the conductivity decreases with increasing concentration of Yb₂O₃ in the system ZrO₂–Y₂O₃–Yb₂O₃. Analyzing the experimental data according to the classic Arrhenius equation showed that such an experimental phenomenon can be attributed to the tighter association between Yb³⁺ and oxygen vacancy, compared with that between Y³⁺ and oxygen vacancy, which hinders the migration of oxygen vacancy in the materials.     

Effect of Al2O3 particles on mechanical properties of directionally solidified intermetallic Ti–46Al–2W–0.5Si alloy

The effect of Al₂O₃ particles on microhardness and room-temperature compression properties of directionally solidified (DS) intermetallic Ti–46Al–2W–0.5Si (at.%) alloy was studied. The ingots with various volume fractions of Al₂O₃ particles and mean ₂–₂ interlamellar spacings were prepared by directional solidification at constant growth rates ranging from 2.78×10⁻⁶ to 1.18×10⁻⁴ ms⁻¹ in alumina moulds. The ingots with constant volume fraction of Al₂O₃ particles and various mean interlamellar spacings were prepared by directional solidification at a growth rate of 1.18×10⁻⁴ ms⁻¹ and subsequent solution annealing followed by cooling at constant rates varying between 0.078 and 1.889 K s⁻¹. The mean ₂–₂ interlamellar spacing λ for both DS and heat-treated (HT) ingots decreased with increasing cooling rate according to the relationship λ∝ ^−0.46. In DS ingots, microhardness, ultimate compression strength, yield strength and plastic deformation to fracture increased with increasing cooling rate. In HT ingots, microhardness and yield strength increased and ultimate compression strength and plastic deformation to fracture decreased with increasing cooling rate. The yield stress increased with decreasing interlamellar spacing and increasing volume fraction of Al₂O₃ particles. A linear relationship between the Vickers microhardness and yield stress was found for both DS and HT ingots. A simple model including the effect of interlamellar spacing and increasing volume fraction of Al₂O₃ particles was proposed for the prediction of the yield stress.     

Comparison of the electrochemical behavior of CeO2–SnO2 and CeO2–TiO2 electrodes produced by the Pechini method

CeO₂–SnO₂ and CeO₂–TiO₂ thin films were prepared by the Pechini method and their characteristics were compared, using a fractional factorial design to quantify the effect of five preparation variables. It was observed that CeO₂–SnO₂ electrodes show a greater electrochemical response than the CeO₂–TiO₂ films. The best intercalation charge densities were 18.11 and 9.91 mC/cm² for CeO₂–SnO₂ and CeO₂–TiO₂, respectively. Both films were optically inactive with transparencies, in most cases, higher than 90%.     

Frequency dependent electrical conductivity and dielectric relaxation behavior in amorphous (90V2O5–10Bi2O3) oxide semiconductors doped with SrTiO3

We report on the experimental results of frequency dependent a.c. conductivity and dielectric constant of SrTiO₃ doped 90V₂O₅–10Bi₂O₃ semiconducting oxide glasses for wide ranges of frequency (500–10⁴ Hz) and temperature (80–400 K). These glasses show very large dielectric constants (10²–10⁴) compared with that of the pure base glass (≈10²) without SrTiO₃ and exhibit Debye-type dielectric relaxation behavior. The increase in dielectric constant is considered to be due to the formation of microcrystals of SrTiO₃ and TiO₂ in the glass matrix. These glasses are n-type semiconductors as observed from the measurements of the thermoelectric power. Unlike many vanadate glasses, Long's overlapping large polaron tunnelling (OLPT) model is found to be most appropriate for fitting the experimental conductivity data, while for the undoped V₂O₅–Bi₂O₃ glasses, correlated barrier hopping conduction mechanism is valid. This is due to the change of glass network structure caused by doping base glass with SrTiO₃. The power law behavior (σ_ac=A(ω^s) with s<1) is, however, followed by both the doped and undoped glassy systems. The model parameters calculated are reasonable and consistent with the change of concentrations (x).     

Influence of Mn doping on microstructure and DC-accelerated aging behaviors of ZnO–V2O5-based varistors

The microstructure, electrical properties, dielectric characteristics, and DC-accelerated aging behavior of the ZnO–V₂O₅–MnO₂ system sintered were investigated for MnO₂ content of 0.0–2.0 mol% by sintering at 900 °C. For all samples, the microstructure of the ZnO–V₂O₅–MnO₂ system consisted of mainly ZnO grain and secondary phase Zn₃(VO₄)₂. The incorporation of MnO₂ to the ZnO–V₂O₅ system was found to restrict the abnormal grain growth of ZnO. The nonlinear properties and stability against DC-accelerated aging stress improved with the increase of MnO₂ content. The ZnO–V₂O₅–MnO₂ system added with MnO₂ content of 2.0 mol% exhibited not only a high nonlinearity, in which the nonlinear coefficient is 27.2 and the leakage current density is 0.17 mA/cm², but also a good stability, in which %ΔE_1 mA = −0.6%, %Δ = −26.1%, and %Δtan δ = +22% for DC-accelerated aging stress of 0.85E_1 mA/85 °C/24 h.     

Determining crystallization kinetic parameters of Li2O–Al2O3–SiO2 glass from derivative differential thermal analysis curves

The kinetic parameters such as crystallization activation energy, E, and the frequency factor, ν, of Li₂O–Al₂O₃–SiO₂ glass were determined by a new non-isothermal method. The method is described by the equation

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, where β is the heating rate and T_f is the inflection-point temperature of differential thermal analysis (DTA). The value of T_f is determined as the maximum peak temperature on derivative differential thermal analysis (DDTA) curves. Values of E and ν of Li₂O–Al₂O₃–SiO₂ glass were also determined by two existing non-isothermal methods, namely the Kissinger plot and the Ozawa plot, and compared with those determined by isothermal method. Values of E and ν determined by the proposed equation were 332 kJ/mol and 1.4×10¹³ s⁻¹, respectively. They are excellent agreement with the isothermal analysis results, 336 kJ/mol and 1.8×10¹³ s⁻¹, respectively. In contrast, both the Kissinger equation and the Ozawa equation give much higher values of E and ν.     

Modeling and optimizing of factors affecting erosion–corrosion of AA6063–(TiC/Al2O3) hybrid composites by experimental design method

In this article, modeling and optimizing of factors affecting erosion–corrosion wear of aluminum alloy A6063 reinforced with (Al₂O₃/TiC) particles have been determined by experimental design method. The erosion–corrosion wear characteristics and mechanism of AA6063–(TiC/Al₂O₃) with experimental parameters namely; type and concentration of corrosive media in the slurry, erosion speed and time have been investigated. Two models for reinforced and unreinforced alloys were applied to describe the influences of these factors on the erosion behavior of alloys. The erosion–corrosion mechanisms of the AA6063–(TiC/Al₂O₃) were dominated by particles erosion wear in alkaline slurry, and by the interaction of particle erosion wear and medium corrosion in acidic slurry. The results of experimental work are coinciding with that of calculated ones confirming the successful modelization.     

RuO2–TiO2 mixed oxides prepared from the hydrolysis of the metal alkoxides

The hydrolysis of ruthenium alkoxide/titanium tetraethoxide mixtures to gels and powders containing 30–40 mol% Ru was investigated. Basic or neutral conditions led to powders consisting of 2–10 nm diameter crystalline RuO₂ nanoparticles embedded in a matrix of crystalline (anatase) and amorphous TiO₂. Acid hydrolysis conditions gave gels containing smaller, amorphous RuO₂ nanoparticles (1–3 nm). In all samples the RuO₂ nanoparticles tended to clump into aggregates up to 0.5 μm across. Acid or neutral hydrolysis of ruthenium ethoxide gave samples which displayed lower surface Ru:Ti ratios as measured by XPS compared to the bulk (XRF), and also contained more low-valent Ru (as measured by XRF), probably due to incomplete hydrolysis of the precursors. These samples also contained more Ru metal after calcination (XRD). Calcination (450 °C) was accompanied by Ru-promoted combustion of organic material and led to crystalline (anatase) TiO₂ and Ti_xRu_1−xO₂ solid solution (rutile phase).     

Enhanced ferroelectric properties of multilayer SrBi2Ta2O9/SrBi2Nb2O9 thin films for NVRAM applications

Ferroelectric SrBi₂Ta₂O₉/SrBi₂Nb₂O₉ (SBT/SBN) multilayer thin films with various stacking periodicity were deposited on Pt/TiO₂/SiO₂/Si substrate by pulsed laser deposition technique. The X-ray diffraction patterns indicated that the perovskite phase was fully formed with polycrystalline structure in all the films. The Raman spectra showed the frequency of the O–Ta–O stretching mode for multilayer and single layer SrBi₂(Ta_0.5Nb_0.5)₂O₉ (SBNT) samples was 827–829 cm⁻¹, which was in between the stretching mode frequency in SBT (813 cm⁻¹) and SBN (834 cm⁻¹) thin films. The dielectric constant was increased from 300 (SBT) to 373 at 100 kHz in the double layer SBT/SBN sample with thickness of each layer being 200 nm. The remanent polarization (2P_r) for this film was obtained 41.7 μC/cm², which is much higher, compared to pure SBT film (19.2 μC/cm²). The coercive field of this double layer film (67 kV/cm) was found to be lower than SBN film (98 kV/cm).