Microstructure evolution and mechanical properties of a vacuum-brazed Al2O3/Ti joint with Mo-coating on Al2O3 and Ti surfaces

Au-foil was used to braze Al₂O₃ and Ti to obtain a joint with biocompatibility. Mo-coatings of thicknesses 2 or 4?μm were deposited on the surfaces of Al2O3 and Ti by magnetron sputtering before the brazing experiments. The microstructure evolution and mechanical property of the Al₂O₃/Ti joint were systematically investigated. Due to the (i) different wettabilities of Ti and Mo and (ii) thermal expansion mismatch between dissimilar components, defects were observed in the Al₂O₃Mo/Au/Ti joint when only Al₂O₃ was metallised by a Mo-coating. However, the Al₂O₃Mo/Au/MoTi joints were nearly defect free when both Al₂O₃ and Ti were coated with Mo films. The typical microstructure of an Al₂O₃Mo/Au/MoTi joint was characterised by Al₂O₃/Mo-rich phase + Au-rich phase/TiAl intermetallic compound/Au-rich phase + TiAu₂ intermetallic compound+(Ti, Mo) solid solution/Ti. The distribution of the (Ti, Mo) solid solution, width of the reaction layer, and quantity of the TiAl intermetallic compound varied with brazing temperature and holding time. The thickness of Mo-coating only affected the width of the reaction layer. Compared to those of the holding time and Mo-coating thickness, the influence of the brazing temperature on the microstructure and shear strength of joints was the most noticeable. The mechanical properties of the Al₂O₃/braze interface and seam were key factors for determining the shear strength of the Al₂O₃Mo/Au/MoTi specimens. The maximum shear strength was 208?MPa for the Al₂O₃Mo/Au/MoTi couple obtained at 1100?°C for 5?min with a Mo-coating thickness of 2?μm.     

Effect of reactivity of silicon and magnesium on the preparation of SiCMgAl2O4 composites for immobilizing graphite

SiCMgAl₂O₄ ceramic has a novel application for immobilizing radioactive graphite. The interface reaction between silicon and magnesium offers a significant challenge in the synthesis of SiCMgAl₂O₄ composites. In this paper, the effects of silicon source, magnesium source, sintering temperature and holding time on the interface reactivity were investigated by characterizing the phase compositions, microstructures, and hardness. The results show that the reactivity of silicon and magnesium varies with silicon sources and magnesium sources which also have a great effect on the microstructure of SiCMgAl₂O₄ composites. Either excessive sintering temperature or excessive holding time makes SiCMgAl₂O₄ composites decomposed into different phases, leading to a decreased hardness value. It is found that silicon as silicon source can contribute to the formation of SiC nanowires, which is in line with VS growth mechanism of SiC. The interface reactivity of element Si and Mg, which is positively correlated with high temperature and long holding time, has a negative effect on the phase compositions and performance of SiCMgAl₂O₄ ceramic by pressureless sintering.     

Microstructure and oxidation behaviors at 800°C and 1250°C of MoSi2/ReSi2/NbSi2 compound coating prepared by electrodeposition and then pack cementation

MoRe duplex film has been electrodeposited from aqueous solution innovatively and then applied to fabricate protective silicide coating for the NbTiSi based alloy successively. The XRD, SEM and EDS results indicated the formation of MoSi₂/ReSi₂/NbSi₂ compound coating after halide reactivated pack cementation (HAPC) treatment. Pesting oxidation of MoSi₂ layer was suppressed and the NbTiSi based alloy was effectively protected at 800?°C with a mass gain of 0.48?mg?cm^?2 after oxidation for 100?h. At 1250?°C, continuous mass gain was observed with a mass gain of 2.6?mg?cm^?2 after exposure of 10?h. The synergistic combination of MoSi₂ and NbSi₂ layer enabled admirable protection of the substrate, in which MoSi₂ layer worked as the major anti-oxidation coating and the NbSi₂ layer could be a reservoir for Si. The contrast experiments indicate that ReSi₂ layer could improve the integrity and adherence of MoSi₂ layer, reduce the outward diffusion of alloying elements and oxidation of NbSi₂ layer, and then improve oxidation resistance of the compound coating ultimately.     

Improved H2-generation performance of Pt/CdS photocatalyst by a dual-function TiO2 mediator for effective electron transfer and hole blocking

Surface modification with noble metal cocatalysts was proved to be a useful route for boosting photocatalytic efficiency of various photocatalysts. Nevertheless, considering the random dispersion of metallic cocatalysts on the photocatalyst surface, the noble metal-loaded photocatalyst generally shows a limited enhancement of its activity because the noble metals can also work as the recombination sites of photoinduced charges. In this paper, TiO₂ as a dual-function mediator (for effective electron transport and hole block) is successfully introduced into the interface of Pt and CdS to form PtTiO₂/CdS photocatalyst, with an aim of suppressing the high recombination rate of electron-hole pairs on the Pt active sites. Under visible light, all the prepared PtTiO₂/CdS displayed distinctly enhanced photocatalytic hydrogen-generation performance and the PtTiO₂/CdS(8%) attains the highest photocatalytic H₂-production rate (294.2?μmol/h), a value significantly higher than that of Pt/CdS about 3.2 time. A dual-function TiO₂-mediated mechanism was put forward to account for the superior hydrogen production of PtTiO₂/CdS photocatalyst, namely, the TiO₂ layer in the PtTiO₂/CdS not only works as electron-transport layers to effectively transfer photogenerated electrons to promote the H₂-production reaction on Pt cocatalysts, but also acts as hole-block layer to prevent the possible recombination of photogenerated charges on the Pt active sites, resulting in a distinct improvement of final H₂-generation activity.     

Effects of Bi2O3 and Li2OB2O3Bi2O3SiO2 glass on electromagnetic properties of NiCuZn/BaTiO3 composite material at low sintering temperature

Bi₂O₃ and Li₂OB₂O₃Bi₂O₃SiO₂ (LBBS) glass were introduced into Ni_0.15Cu_0.24Zn_0.61Fe₂O₄BaTiO₃ ((NCZF-BTO) composite materials as sintering aids and sintered at 920?°C. Effects of Bi₂O₃ and LBBS glass on phases, microstructures, magnetic and dielectric properties of these composites were comparatively studied. In contrast to undoped composites, the addition of Bi₂O₃ or LBBS glass to samples enhances performance. Hence, when Bi₂O₃ content reached 1.5?wt%, saturation magnetization (4πM_s) increased from 3825.4 to 4912.5 Gs, static permeability (μ₀) increased from 53.2 to 197, and dielectric constant (ε′) increased from 18.3 to 23.4. When LBBS glass content reached 1.5?wt%, 4πM_s increased to 4145.6 Gs, μ₀ increased to 79.3, ε′ increased to 25.4. However, both coercivity (H_c) and dielectric loss (tan?δ) were reduced. In short, Bi₂O₃ promoted magnetic properties, whereas LBBS glass promotes dielectric properties more effectively.     

Microstructure and shear strength of ZrB2SiC/Ti6Al4V joint by TiCuZrNi with Cu foam

In this paper, brazing behaviors between ZrB₂SiC and Ti6Al4V by Cu foam interlayer were studied. The microstructure, formation mechanism, mechanical property and fracture surface of the joints were systematically studied. The results showed that the phases in the joints were α+β-Ti, TiCu, Ti₂Cu, Cu(s, s), TiC, TiB₂ and Ti₃SiC₂. An optimum shear strength reached up to 435??MPa?at a brazing temperature of 910?°C and holding time of 20?min. Such a shear strength was 90?MPa higher than the one without the Cu foam. The obtained high shear strength of joint was discussed from microstructure and residual stress. With the increase of brazing time, Cu(s,s) gradually disappeared and the content of Ti₂Cu intermetallic compound increased, which was harmful for the joint. Furthermore, the residual stress of joint with Cu foam was calculated to be 324?MPa, lower than the one without Cu foam interlayer.     

The effect of Al content on the wettability between liquid iron and MgOAl2O3 binary substrate

In the present study, the wettability between liquid iron with two different Al contents and MgOAl₂O₃ binary substrates was studied in reducing atmosphere. The contact angles between liquid iron with 18?ppm Al and MgO, MgO·Al₂O₃, Al₂O₃ were 133.5°, 113.7°, 126.9° respectively. With the variation of the substrate composition, the contact angles for the intermediate binary phases of the three components (MgO, MgO·Al₂O₃, Al₂O₃) obeyed the Cassie theory. In the experiment using iron with 370?ppm Al, all the contact angles were higher than that using low Al-containing iron. The surface of the iron drop was covered with an oxide layer, which mainly consisted of many small particles. With the variation of the substrate gradually from MgO to Al₂O₃, the composition of the oxide layer changed from MgO·Al₂O₃ to CaOAl₂O₃. The formation of the oxide layer prevented the spreading of liquid iron, leading to the increase of the contact angle.     

An extensive investigation on gamma-ray and neutron attenuation parameters of cobalt oxide and nickel oxide substituted bioactive glasses

This study aimed to investigate the gamma-ray and neutron attenuation parameters of cobalt oxide and nickel oxide substituted ten bioactive glasses. The mass attenuation coefficient ($\text{μ}/\text{ρ}$) for the selected bioactive glasses was calculated using MCNPX code in photon energy range (0.02?MeV - 20?MeV) and the results were compared with the output of WinXcom software. Other vital gamma-ray attenuation parameters such as half value layer (HVL), tenth value layer (TVL), mean free path (MFP), effective atomic number (Z_eff), and effective electron density (N_el) for the selected bioactive glasses were also calculated for each approach. Gamma-ray and neutron transmission factors as well as neutron effective removal cross-sections of each bioactive glass (ΣR) were also taken into consideration to underline the distinctive parameters. Additionally, exposure buildup factor (EBF) values were found with G-P fitting approach depending on the energy and penetration depths. The results points that, the lowest HVL, TVL and MFP values and the highest neutron effective removal cross-sections (Σ_R) values are the characteristics of NiO4C and CoO-4. The results indicate that the density of the material affects the photon and neutron interaction parameters. While NiO4C has the lowest TF values for both gamma and neutron radiation, the highest Σ_R values are collected from NiO4C glass material. The gamma and neutron transmission factors (TF) of the studied bioactive glasses support the aforementioned results. The lowest Z_eff values were generated for 45S5C and 45S5 ordinary glasses, while CoO-4 and NiO4C doped glasses are having the highest values of Z_eff. EBF values of the glasses were also calculated in the energy range 0.015–15?MeV up to 40 mfp. The smallest EBF values were measured for CoO-4 and NiO4C glasses. It can be concluded that NiO4C bioactive glass outperformed compared to other studied samples and is a promising bioactive glass for gamma-ray and neutron attenuation.     

Evidence for non-thermal microwave effect in processing of tailing-based glass-ceramics

Tailing-based glass-ceramics were crystallized via conventional and microwave heating at 720 °C for 30 min and 820 °C without holding and compared in order to obtain evidence for a non-thermal microwave effect. The comparative analytical results showed that the microstructural uniformity was greatly enhanced and the crystallization activation energy was significantly reduced by microwave processing compared to conventional heating, suggesting accelerated grain growth during crystallization. Microwave radiation affected the crystal orientation and induced corresponding changes in the SiO bond lengths and SiOSi angles, thus enhancing the formation of the diopside crystal structure. In addition, the samples under microwave processing exhibited superior physicochemical performance, including greater relative density, bending strength, microhardness, and resistance to acids and alkali, compared to conventionally processed samples. All these results provided positive evidence supporting the existence of a genuine microwave non-thermal effect, allowing deepened understanding for fine control over microwave-assisted metallurgy.     

Preparation of NiW/TiNY2O3 composite ceramic coating for metallic parts protection by direct current deposition

A novel NiW/TiNY₂O₃ composite ceramic coating has been synthesized by direct current deposition for metallic parts protection. The structural, morphology, hardness and anti-corrosion properties of the NiW/TiNY₂O₃ coating have been evaluated by SEM, EDS, TEM, XRD and EIS methods. Results indicated that the samples have uniform and compact nodular structure without defects. It demonstrated that the TiN and Y₂O₃ nanoparticles had been uniformly distributed in the composites. The incorporation of TiN and Y₂O₃ in NiW matrix could improve the hardness and anti-corrosion properties. The crystallite size was in the diameter of 13–16 nm. The electrochemical results illustrated that 6-8 Adm⁻² and 30 min were beneficial to the improvement of anti-corrosion behaviors of the produced composite coating. After immersed 168 h in 3.5 wt% NaCl aqueous solution, the coating prepared at 30 min and 2 A dm⁻² owns better anti-corrosion properties. The embedded TiN and Y₂O₃ nanoparticles in NiW matrix could decrease the electrochemical activity and enhance the protective properties.     

Structure,bond characteristics and microwave dielectric properties of new A0.75Ti0.75Ta1.5O6 (ANi,Co, Zn and Mg) ceramics based on complex chemical bond theory

Tri-rutile structured A_0.75Ti_0.75Ta_1.5O₆ (ANi, Co, Mg, Zn) ceramics were synthesized using traditional solid reaction method. The crystal structures were studied by X-ray diffraction in conjunction with Rietveld refinement analysis. Based on the complex chemical bond theory and crystallographic data, some principle chemical bond characteristics such as bond ionicity, lattice energy, bond energy and coefficient of thermal expansion of complex A_0.75Ti_0.75Ta_1.5O₆ ceramics were obtained through quantitative calculation. The calculated results provided useful information to clarify the correlations between chemical bond characteristics and microwave dielectric properties of A_0.75Ti_0.75Ta_1.5O₆ ceramics. The dielectric constant was closely associated with the ionicity of TaO bond, and the Q × f values were correlated with the lattice energy of TaO bond. The τ_f values were affected by the bond energy of TaO bond and the coefficient of thermal expansion of AO bond.     

A family of functional oxides of titanosilicates: A2TiSi2O8 (A= Ba,Sr) with temperature insensitive ultrahigh breakdown strength

Discovering new materials with high breakdown strength is of great significance for scientific research and industrial applications. Here, we combine experiments and density functional theory (DFT) calculations to report a systematic study of two titanosilicates - A₂TiSi₂O₈ (A = Br, Sr) as a family of functional materials with wide band gaps, ultrahigh breakdown strength, and high thermal stability. The A₂TiSi₂O₈ materials possess ultrahigh electric breakdown (E_b >200 kVmm⁻¹, at 200 ℃), and good temperature stability (the variation of capacitance 3 %, from −100 to 200 ℃). DFT results show that electrons are likely localized in the SiO and TiO polyhedrons. The electron difference density map and density of states (DOS) results elucidate the wide band gaps in titanosilicate family due to the strong SiO and TiO bonds, indicating that the semiconductive behaviors are similar. The temperature-dependent structural evolution (from −100 to 500 ℃) is investigated via in-situ Raman spectroscopy.     

Structure characteristics and microwave dielectric properties of novel Re2Ce6O15 (ReY,Sm, Nd,La) ceramics

Based on the cubic fluorite structure, novel ceramic series with Re₂Ce₆O₁₅ (ReY, Sm, Nd, La) formula had been designed and prepared successfully using solid-state reaction method. The new Re₂Ce₆O₁₅ (ReY, Sm, Nd, La) ceramics all presented a single phase indexed as CeO₂-type structure, belonged to Fm-3m space. The formation mechanism and lattice constant of the crystal structure had been investigated using Rietveld structural refine method. The microstructure of the Re₂Ce₆O₁₅ (ReY, Sm, Nd, La) ceramics had been evaluated by pores, grain size and its distribution. The dielectric constant had been corrected for the exclusion of pores and depended on the ionic polarizability. The quality factors of the Re₂Ce₆O₁₅ (ReY, Sm, Nd, La) ceramics had been investigated by packing fraction related to the phonon vibration. The temperature coefficient of resonance frequency had been analyzed using the bond valence theory. The Re₂Ce₆O₁₅ (ReY, Sm, Nd, La) ceramics exhibited excellent microwave dielectric properties with medium dielectric constant, high quality factors and stable resonant frequency temperature coefficient.     

Mechanical properties of the SiCf/SiC composites reinforced with KD-I and KD-II fibers fabricated assisted by a microwave heating method

SiC_f/SiC composites using KD-I and KD-II SiC fibers braided preforms as the reinforcements were fabricated by applying the polymer impregnation and pyrolysis (PIP) technique with a microwave heating assistance. The microwave heating temperature was 1100 °C, 1200 °C, 1300 °C, and 1400 °C, respectively. Microstructures, flexure properties, and fracture behaviors of the composites were investigated. The KDIISiC_f/SiC composites exhibited higher flexure properties and improved non-brittle fracture characteristics than those of the KD-ISiC_f/SiC composites. The differences in the flexural properties, fracture behaviors and microstructures between the KD-I and KDIISiC_f/SiC composites were discussed based on the tensile properties of the SiC filaments and the interfacial bonding statues in the composites.     

Effect of nano-AlN addition on thermal diffusivity and mechanical strength of porous AL2O3 ceramic composites

In a properly made porous abrasive composite, the vitrified bond should ideally cover the grains and form a continuous network of bridges, and thus part of the heat energy from the grinding process is also transferred to the vitrified bond. Until recently, most studies on the design of composite properties have focused mainly on improving their mechanical strength and wear resistance, but increasingly the very important aspect of their thermal properties is noticed. The vitrified Al₂O₃ composites were made from Al₂O₃ grains, vitrified bond of Na₂OK₂OAl₂OB₂O₃SiO₂ and AlN nanopowder. The increase in porosity in the tested composites is the effect of the AlN decomposition reaction. Crystalline phases were identified in both composites - α-Al₂O₃ and NaAl₁₁O₁₇, but with a different percentage share in individual composites. In composites doped with AlN nanopowder, the proportion of NaAl₁₁O₁₇ crystalline phase decreases, due to its high susceptibility to reduction by Al, obtained from the AlN decomposition reaction. The product of the redox reaction is also Na⁺ ions, which may participate in the formation of the glass phase and thus increasing the fraction of the residual glass phase. As a result of the partial reduction of NaAl₁₁O₁₇ phase, an increase in α-Al₂O₃ content is observed. A higher proportion of α-Al₂O₃ phase with high thermal conductivity can be a factor that increases the rate of heat removal from the work zone.     

A comparative process simulation study of CaCu looping involving post-combustion CO2 capture

This work presents a simulation study of several CaCu looping variants with CO₂ capture, aiming at both parameter optimization and exergy analysis of these CaCu looping systems. Three kinds of CaCu looping are considered: 1) carbonation–calcination/reduction–oxidation; 2) carbonation–oxidation–calcination/reduction and 3) carbonation/oxidation–calcination/reduction. A conventional Ca looping is also simulated for comparison. The influences of the calcination temperature on the mole fractions of CO₂ and CaO at the calciner outlet, the CaCO₃ flow rate on the carbonator performance and the Cu/Ca ratio on the calciner performance are analyzed. The second kind of CaCu looping has the highest carbonation conversion. At 1 × 10⁵ Pa and 820 °C, complete decomposition of CaCO₃ can be achieved in three CaCu looping systems, while the operation condition of 1 × 10⁵ Pa, 840 °C is required for the conventional Ca looping system. Furthermore, the Cu/Ca molar ratio of 5.13–5.19 is required for the CaCu looping. Exergy analyses show that the maximum exergy destruction occurs in the calciner for the four modes and the second CaCu looping system (i.e., carbonation–oxidation–calcination/reduction) performs the highest exergy efficiency, up to 65.04%, which is about 30% higher than that of the conventional Ca looping.     

Effect of BaOB2O3 composite sintering aid on sinterability and electrical property of BaZr0.85Y0.15O3-δ ceramic

Yttrium-doped barium zirconate (BZY) has been extensively studied as a promising electrolyte material for protonic ceramic fuel cells. However, inferior sinterability is a major barrier in BZY development. In our research, the effect of BaOB₂O₃ composite sintering aid on the sintering behavior and electrical property of BaZr_0.85Y_0.15O_3-δ (BZY15) are examined. BaOB₂O₃ addition reduces the sintering temperature of BZY15 by approximately 200 °C via the liquid-phase sintering mechanism. The corresponding bulk and grain boundary conductivities are prominently improved (<3 wt% BaOB₂O₃ addition), whereas the further addition of sintering aid decreases the grain boundary conductivity. Notably, the scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS) analyses suggest that the enhanced conductivity may be related to the temperature dependence of Ba evaporation.     

Manganese induced ZrSiO4 crystallization from ZrO2SiO2 binary oxide system

The ability of manganese to induce early zircon (ZrSiO₄) crystallization is investigated. An assorted range of manganese additions to the ZrO₂SiO₂ binary system through a Sol-Gel approach is attempted to achieve ZrSiO₄ formation at low temperatures. XRD analysis alongside complementary Rietveld refinement tool has been used to determine the propelling effect of manganese on the low temperature formation of ZrSiO₄. The results revealed the ability of 5?wt% manganese to induce the ZrSiO₄ formation at 900?°C through its occupancy at the ZrO₂ lattice. The lattice substitution of Zr⁴⁺ by the lower sized Mn²⁺ and the concomitant lattice distortion of ZrO₂ have been determined as the prime reason for manganese to enhance the reaction kinetics with amorphous SiO₂ to yield ZrSiO₄. Increments in the manganese content beyond 5?wt% are rejected by the ZrO₂ lattice, making the excess to crystallize as Mn₂O₃. The colour change of ZrSiO₄ is directly influenced by the manganese content in ZrO₂SiO₂ binary system.     

Investigation of affecting parameters on slip casting of yttria-magnesia IR-transparent bodies

Slip casting of MgOY₂O₃ suspensions has been investigated in this research. For this purpose relatively pure commercial raw materials were used. The Taguchi experiment method was used for design of experiments and selection of suitable solvents and dispersants and theirs optimum values. Preparation of suspensions was done in two stages, according to particle size distributions of powders after different milling time and Taguchi results. The best suspensions were selected based on viscosity and solid load of suspensions. Green bodies were slip casted using the optimized suspensions in order to obtain the green bodies with maximum density and a homogeneous structure in term of porosity size distribution. Results showed that using from ethanol as solvent, an optimum dispersant level of 3%wt. TEA +1%wt. DEA with a constant TEA/DEA ratio of 3/1 and mean particle size of 155 nm (milling time of 48 h) was the best choice for preparing of optimum suspensions. The highest relative green density of 65.91% was obtained for a suspension containing 35 vol % of solid particles casted under 3MPa. The dense Y₂O₃MgO submicron composite samples were sintered by SPS technique at 1250?°C under 70MPa for 6?min with a density about 99.5%.     

Analytical solution of the breakthrough curve for rectangular isotherm systems

A general solution including both film and intraparticle diffusion resistances is derived for the breakthrough curve for an adsorption or ion exchange system with irreversible equilibrium. Both fluid and solid resistances are represented by linearized rate expressions but the solution is obtained without recourse to the constant pattern assumption. A numerical solution has also been obtained for intraparticle diffusion with external fluid film resistance. The deviation between the predictions of the two models increases with the magnitude of the intraparticle resistance. Numerical solutions were also obtained for Langmuir and Freundlich isotherms in order to establish the range where the simple rectangular models can be considered as an acceptable approximation.Experimental data for the ion exchange systems of RNaZn(NO₃)₂ and RNaCe(NO₃)₃ and for the adsor