Designing low-carbon MgO–Al2O3–La2O3–C refractories with balanced performance for ladle furnaces

In order to achieve high-quality and stable production of special steel, the performance of low-carbon MgO-C refractories needs to be further optimized. For this purpose, low-carbon MgO–Al₂O₃–La₂O₃–C refractories with enhanced thermal shock resistance and slag resistance were designed and successfully prepared by introducing Al₂O₃ as a reinforcer and La₂O₃ as a modifier. The results showed that the refractory samples with additives show better overall performance than those without additives. When 10 wt% of Al₂O₃ and La₂O₃ were added, the oxidation resistance, thermal shock resistance and slag resistance of the refractory samples coked at 1400 °C are increased by 13.57%, 17.75% and 43.09%, respectively. The analysis found that this can be mainly attributed to the formation of MgAl₂O₄, Mg₂SiO₄, and 2CaO·4La₂O₃·6SiO₂ and the consequent volume expansion effect and intergranular phase enhancement effect. Therefore, a low-cost and enforceable reinforcement strategy for low-carbon MgO-C refractories is proposed, which is expected to be applied in steelmaking.     

Ag2O–Al2O3–ZrO2 Trimetallic Nanocatalyst for High Performance Photodegradation of Nicosulfuron Herbicide

Topics in Catalysis - In the present study, Ag2O–Al2O3–ZrO2 based trimetallic oxide nanocatalyst was designed using simple microwave assisted reduction method. It was characterized...     

Dy3+ doped LiCl–CaO–Bi2O3–B2O3 glasses for WLED applications

Dy³⁺ doped calcium bismuth borate glasses were synthesized in the composition range of xLiCl-(30 − x)CaO-20Bi₂O₃-50B₂O₃ + 1 mol% Dy₂O₃ (x = 0, 2, 5, 7, 10 and 15 mol%, LC0, LC2, LC5, LC7, LC10 and LC15 respectively) using conventional melt-quench technique. Broad XRD profiles confirmed non-crystalline nature of synthesized compositions. The compositional dependencies of structural changes (using FTIR spectra), thermal behavior (using DSC thermographs) and optical band gap (using UV–Vis–NIR spectra) were discussed. Photoluminescence (PL) excitation spectra recorded at 577 nm yielded six different excitation peaks belonging to Dy³⁺ ions. The PL emission spectra recorded at 451 nm were analyzed to extract different light emission parameters viz. Y/B ratio, color coordinates, correlated color temperature (CCT) following CIE 1931 chromaticity diagram. The emission colors were found to lie in white light region and lies very close to standard white light emission. The CCT of sample LC10 (5335 K) is closest to CCT of standard white light (5615 K) which depicted the optimized concentration of LiCl for application of these glasses in WLED application.     

Porous ZnO@C core–shell nanocomposites as high performance electrode materials for rechargeable lithium-ion batteries

A novel porous spherical ZnO@carbon (C) nanocomposite based on zeolitic imidazolate frameworks (ZIFs-8)-directed method was prepared for lithium-ion batteries (LIBs). In this strategy, spherical ZnO nanoparticles were firstly prepared, then 2-methylimidazolate and Zn²⁺ were added alternately under ultrasound to fabricate ZnO@ZIF-8. Finally, the novel porous spherical ZnO@C nanocomposites were obtained via pyrolyzing the corresponding ZnO@ZIF-8. The novel porous spherical ZnO@C nanocomposites were characterized with different analysis techniques such as scanning electron microscopy, transmission electron microscopy and X-ray powder diffraction. The resulted spherical ZnO@C nanocomposites exhibited a high reversible capacity of 932 mA h g^?1 at 0.1 A g^?1 after 100 cycles, which is much higher than that of the pure ZnO nanoparticles. The porous structure, high specific surface area and good electrical conductivity eventually contribute to the good performance of the resulted ZnO@C nanocomposites for LIBs should be ascribed to the proous structure and high BET surface area derived from ZIFs, as well as the good electrical conductivity of the amourphous carbon derived from ZIFs.     

Composites of V2O3–ordered mesoporous carbon as anode materials for lithium-ion batteries

The composites of V₂O₃–ordered mesoporous carbon (V₂O₃–OMC) were synthesized and used as anode materials for Li-ion intercalation. These materials exhibited large reversible capacity, high rate performance and excellent cycling stability. For instance, a reversible capacity of V₂O₃–OMC composites was 536 mA h g⁻¹ after 180 cycles at a current density of 0.1 A g⁻¹. The high electrochemical performance of the V₂O₃–OMC composites is attributed to the anchoring of nanoparticles on mesoporous carbon for improving the electrochemical active of V₂O₃ particles for energy storage applications in high performance lithium-ion batteries.     

Evaluation of substrates for zinc negative electrode in acid PbO_2–Zn single flow batteries

An investigation was performed on the suitability of carbon materials, metallic lead and its alloys as substrates for zinc negative electrode in acid Pb O2–Zn single flow batteries. The zinc deposition process was carried out in the medium of 1 mol·L-1H2SO4 at room temperature. No maximum current appears on the potentiostatic current transients for the zinc deposition on lead and its alloys. With increasing overpotential, the progressive nucleation turns to be a 3D-instantaneous nucleation process for the resin-graphite composite. Hydrogen evolution on the graphite composite is effectively suppressed with the doping of a polymer resin. The hydrogen evolution reaction on the lead is relatively weak, while on the lead alloys, it becomes serious to a certain degree. Although the exchange current density of zinc deposition and dissolution process on the graphite composite is relatively low,the zinc corrosion is weakened to a great extent. With the increase of deposition time, zinc deposits are more compact. The cyclings of zinc galvanostatic charge–discharge on the graphite composite provide more than90% of coulombic and 80% of energy efficiencies, and exhibit superior cycling stability during the first 10 cycles.     

Thermal shock resistance of Cr2O3–Al2O3–ZrO2 bricks with the microstructure of Cr2O3 aggregates coated by ZrO2

Zirconia-coated Cr₂O₃ aggregates synthesized by mixing ZrO₂ powders and Cr₂O₃ aggregates with a phenolic resin binder followed by thermosetting treatment were employed as modified Cr₂O₃ aggregates to obtain Cr₂O₃–Al₂O₃–ZrO₂ bricks (high-chromia bricks). The elastic modulus (E) and cold modulus of rupture (CMOR) of these high-chromia bricks before and after thermal shock cycles were systematically investigated, and the residual ratios of CMOR and E were calculated. The thermal shock resistance of the high-chromia bricks was significantly improved by the factor of modification of Cr₂O₃ aggregates. The mechanism of the improved thermal shock resistance of these high-chromia bricks was studied via microstructure analysis, and the crack propagation behavior was analyzed by scanning electron microscopy (SEM). The fracture work (γ_WOF), thermal shock damage factor (R′′′′), and thermal stress crack stability parameter (R_st) were measured and calculated using the wedge splitting test (WST). The results indicate that the porous ZrO₂ coating layer wrapped the Cr₂O₃ aggregates, forming modified Cr₂O₃ aggregates that can increase crack deflection, free path of crack propagation, and fracture work, thus improving the thermal shock resistance of high-chromia bricks. The thermal shock resistance of the fabricated high-chromia bricks was highly correlated with the thickness of the ZrO₂ coating layer surrounding the Cr₂O₃ aggregates. The variation trend of R_st is well consistent with the experimental results, which is suitable to evaluate the thermal shock resistance of high-chromia bricks.     

Characterization of sol–gel coated 316L stainless steel for biomedical applications

Silica based organic–inorganic hybrid coatings were deposited on 316L stainless steel by sol–gel technique. The hybrid sols were prepared by hydrolysis and condensation of 3-methacryloxypropyltrimethoxysilane (TMSM) and tetraethylorthosilicate (TEOS) at different molar ratios. Electrochemical experiments were performed to evaluate the corrosion resistance properties of the coatings. Structural characterization of the coatings was performed using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Contact angle measurement and cell morphology assay were performed to investigate the hydrophilicity and in vitro cytotoxicity of the coatings, respectively. The results indicate formation of a crack-free and highly adherent film acting as a protective barrier against the physiological medium. Corrosion resistance of hybrid coatings was influenced by the molar ratios of TMSM:TEOS. The best corrosion protection was obtained at TMSM:TEOS molar ratio of 1:1. Sol–gel coatings enhanced the hydrophilicity of 316L steel surfaces. Also, these coatings showed non-toxicity for L929 cells.     

Effect of BaO substitution for CaO on the structural and thermal properties of SiO2–B2O3–Al2O3–CaO–Na2O–P2O5 bioactive glass system used for implant coating applications

The present study replaced 3.30 and 9.00 mol.% BaO for CaO in a SiO₂–B₂O₃–Al₂O₃–CaO–Na₂O–P₂O₅ bioactive glass system used for implant coating applications. Variations of the glass structure, thermal properties, cytotoxicity, and radiopacity of glasses were studied. As demonstrated by the results, upon adding barium oxide to the glass structure, the weight density increased significantly, while a slight decrease in oxygen density was determined. Introducing barium oxide into glass composition did not cause any considerable change in the spectra of FTIR and Raman. It was demonstrated that the amount of bridging oxygen in the glass structure remained quite unaffected. The hot stage microscopy evaluations revealed further shrinkage of barium-containing frits due to lower viscosity and hence, higher viscous flow of these glasses. By substituting barium oxide for calcium oxide and increasing its concentration, the glass transition temperature (T_g) and the dilatometric softening temperature (T_d) decreased, while the thermal expansion coefficient increased. Moreover, upon substituting 9 mol.% barium oxide for calcium oxide, a 30 °C reduction in maximum sintering temperature (T_ms) of the glass was obtained, whereas the shrinkage rate was increased 1.7 times. It was indicated that the sintering process of barium-incorporated glasses would easily proceed without any phase crystallization. The barium-incorporated glasses exhibited more radiopacity. Additionally, no cytotoxic effect was caused by the substitution, and the Ba-containing glasses could be used for biomedical applications and implant coating as well.     

Enhanced performance of low-carbon MgO–C refractories with nano-sized ZrO2–Al2O3 composite powder

Low-carbon MgO–C refractories are facing great challenges with severe thermal shock and slag corrosion in service. Here, a new approach, based on the incorporation of nano-sized ZrO₂–Al₂O₃ composite powder, is proposed to enhance the thermal shock resistance and slag resistance of such refractories in this work. The results showed that addition of ZrO₂–Al₂O₃ composite powder was helpful for improving their comprehensive performances. Particularly, the thermal shock resistance of the specimen containing 0.5 wt% composite powder was enhanced significantly which was related to the transformation toughening of zirconia and in-situ formation of more spinel phases in the matrix; also, the slag resistance of the corresponding specimen was significantly improved, which was attributed to the optimization of pore structure and formation of much thicker MgO dense layer.     

Gas sensing performance of hydrothermally grown CeO2–ZnO composites

The sensors based on cerium oxide–zinc oxide (CeO₂–ZnO) composites were fabricated by using thick-film screen printing of hydrothermally grown powders. The structural, morphological investigations were carried out by using XRD, FESEM and TEM and these studies revealed that the synthesized products were grown in high-density and possessed well-crystallinity. Furthermore, the gas responses were evaluated towards the ethanol, acetone, liquid petroleum gas (LPG) and ammonia gases. The 2 wt% CeO₂–ZnO composite exhibited excellent response of 94% at 325 °C and better selectivity towards ethanol with low response and recovery time as compared to pure ZnO and can stand as reliable sensor element for ethanol sensor related applications.     

Ultrathin Ti3C2Tx nanosheets modified separators for lithium–sulphur batteries

Currently, among the various emerging energy storage systems, the lithium–sulphur (Li-S) battery is expected to be one of the next-generation lithium secondary batteries with high efficiency. However, the practical application of Li-S batteries still faces many obstacles. To solve the shuttle effect of lithium polysulphides, ultrathin Ti₃C₂T_x nanosheets were prepared through the in-situ acid etching method and applied to separator modification to suppress the shuttle effect of lithium polysulphides. Ultrathin Ti₃C₂T_x nanosheets with enlarged interlayer spacing accelerated the migration of Li⁺. The abundant termination groups on the surface of Ti₃C₂T_x played the role of the lithium polysulphide capture centre. When the mass loading of separator modification materials was set as 0.025 mg cm⁻², the as-prepared battery exhibited a reversible specific capacity as high as 780 mAh g⁻¹ after 200 cycles at 0.2 C, and the single-cycle capacity decay rate was only 0.09%.     

Synthesis and electrochemical performance of α-Fe2O3@carbon aerogel composite as an anode material for Li-ion batteries

A α-Fe₂O₃@carbon aerogel (CA) composite material has been successfully synthesized via a simple hydrothermal method in water solution. The microstructure, morphologies, α-Fe₂O₃ loading content in α-Fe₂O₃@CA, porous nanostructure and electrochemical properties of these materials are investigated by X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, N₂ adsorption-desorption isotherms, constant current charge/discharge tests and cyclic voltammetry tests. The results show that α-Fe₂O₃ is uniformly dispersed on CA with a rugby-like morphology, and the α-Fe₂O₃ active material loading content in α-Fe₂O₃@CA composite is up to 95.72%. The α-Fe₂O₃@CA revealed a high reversible capacity of 581.9 mAh g⁻¹ and stable cyclic retention at 50th cycle. The improvement of reversible capacity and cyclic performance of the α-Fe₂O₃@CA composite is attributed to the unique structure of CA, with high electronic conductivity and three-dimensional porous structures among the interconnected α-Fe₂O₃@CA composite, which could not only effectively load the α-Fe₂O₃ active material, but also could prevent the aggregation of α-Fe₂O₃ nanoparticles and facilitate the transport of electrons and shorten the distance for Li⁺ diffusion. The encouraging experimental results suggest that the novel α-Fe₂O₃@CA composite have great potential for use as an anode material for lithium rechargeable cells.     

Nonlinear dielectric effect of Fe2O3-doped PMS–PZT piezoelectric ceramics for high-power applications

Piezoelectric ceramics of Pb_0.98Sr_0.02(Mn_1/3Sb_2/3)_0.05Zr_0.48Ti_0.47O₃ with 0.25 wt% CeO₂, 0.50 wt% Yb₂O₃, and x wt% Fe₂O₃ (x = 0.02, 0.05, 0.1, 0.15, and 0.2) additives were synthesized using a conventional solid-state reaction. Their piezoelectric properties and, in particular their nonlinear dielectric behaviors were systematically investigated. Iron was mainly present in the form of Fe³⁺ based on X-ray photoelectron spectroscopy; a small amount of the iron was reduced to Fe²⁺. Iron occupied the B-site of the perovskite structure, as shown in the refinement results. The samples displayed both “soft” and “hard” properties because Fe³⁺ can be incorporated at the Mn²⁺, Zr⁴⁺, Ti⁴⁺, and Sb⁵⁺ sites. The domain wall motion was found to be related not only to the type of deficiency but also to the grain size and grain boundary effects based on the nonlinear dielectric behaviors under alternating electric fields. The optimal overall properties of d₃₃ = 360 pC/N, tan δ = 0.295%, Q_m = 1500, k_p = 0.61, ε_r = 1055, α_ε = 4.574*10⁻⁴ m/V, and tan δ = 2.76% (under 500 V/mm) were obtained for samples sintered at 1150 °C(x=0.15).     

Improvement of gold electrode conductivity after cofiring with CaO–B2O3–SiO2 green tapes for LTCC application

The cofiring process of Au paste containing various amount of glass additive with different properties and CaO–B₂O₃–SiO₂ (CBS) green tapes was investigated. The initial shrinkage temperature of Au paste was strongly associated with the softening point and the content of glass additive. The swell of sample and its mechanism during cofiring process was reported. The sheet resistivity of Au electrode was greatly depended on the content of CBS glass additive. When the content of CBS glass additive with the softening point of 704 °C was 3 wt %, the Au electrode exhibited the highest conductivity with the sheet resistivity of 2.4 mΩ/sq. The results obtained in this paper revealed the relationship between the glass additive and cofiring defects of Au electrode in the metal/ceramic multilayer structure, which gave an avenue to manufacture Low temperature co-fired ceramics (LTCC) modules with good quality.     

Catalytic behavior of V2O5 in rechargeable Li–O2 batteries

The possibility of using vanadium pentoxide (V₂O₅) as a catalyst in rechargeable lithium–oxygen (Li–O₂) batteries was studied. A V₂O₅-carbon composite was cast onto Ni foam to form a cathode. Electrochemical cells designed based on the flat cell manufactured by Hohsen Corporation were fabricated. The initial discharge capacity was 715 mA?h?g^?1, and the maximum discharge capacity reached 2,260 mA?h?g^?1 during the twelfth cycle. The cell had high capacity retention during cycling (1.24?% during cycles 2–8). V₂O₅ acted as a catalyst as well as an active material, improving the specific capacity and capacity retention of the non-aqueous Li–O₂ cell more effectively than do other materials.     

Effect of partial substitution of alumina–chromium slag for Al2O3 on microstructures and properties of Al2O3–SiC–C trough castables

Alumina–chromium slag (ACS), a cheap and abundant refractory raw material comprising aluminum–chromium oxides and β-Al₂O₃, is a byproduct of ferrochrome smelting. For this reason, we investigated the relationships between composition and mechanical properties, abrasion resistance, oxidation resistance, and resistance to iron slag erosion for Al₂O₃–SiC–C trough castables in which ACS was substituted for alumina. Due to the presence of β-Al₂O₃ in ACS, the aluminum-chromium slag reacted with SiO₂ to form a low-melting phase of albite and promoted the formation of mullite, which filled the pores at high temperatures and reduced the porosity, thereby promoting densification and strengthening of the sample. The cold mechanical properties of the sample and the normal temperature wear resistance were enhanced, but the high-temperature mechanical properties and the resistance to iron slag corrosion of the sample were impaired. According to the results of the anti-oxidation experiment, the presence of β-Al₂O₃ in the ACS reduced the porosity and made the sample more dense, which remarkably improved oxidation resistance of the sample. For industrial production requirements, ACS substitution should not exceed 48?wt% due to of thermomechanical properties and anti-slag corrosion performance in Al₂O₃–SiC–C trough castables.     

Preparation and electrochemical properties of SiO2–non-graphitizable carbon composites as negative electrode materials for Li-ion batteries

SiO₂–non-graphitizable carbon composites were prepared by pyrolysis of a mixture of ethyl cellulose and nano-sized SiO₂. The composite electrode showed high reversibility in insertion and/or extraction reactions of Li ions at potentials below 1 V with little hysteresis after the 2nd cycle, whereas a large irreversible capacity was observed in the 1st cycle. This reversible capacity increased with increasing SiO₂ content above 5 wt%. Li ion transfer at the interface between a composite electrode and an electrolyte was studied by ac impedance spectroscopy. In the Nyquist plots, a semi-circle that was assigned to charge-transfer resistance (R _ct) because of Li ion transfer across the interface between the composite electrode and electrolyte appeared at potentials below 1 V. The values of R _ct decreased with increasing SiO₂ content. These results indicate that both a decrease in R _ct and an increase in reversible capacity can be achieved by use of SiO₂–non-graphitizable carbon composite electrodes; this would lead to Li-ion batteries with higher power and energy density.     

Joining of Cf/SiC composites and Si3N4 ceramic with Y2O3–Al2O3–SiO2 glass filler for high-temperature applications

C_f/SiC composites and Si₃N₄ ceramics are candidate materials for applications in thermal protection system. This paper investigated the joining of C_f/SiC and Si₃N₄ using Y₂O₃–Al₂O₃–SiO₂ glass. The reliability of joints was evaluated by thermal shock tests. In this present work, the typical joint structure was C_f/SiC-glass-Si₃N₄. The results demonstrate that Direct bonding has been identified as the interfacial bonding mechanism at the SiC/glass and glass/Si₃N₄ interfaces. The maximum shear strength of the C_f/SiC–Si₃N₄ joint was ~34 MPa, which delivered an effective method to achieve strong, reliable bonding between the dissimilar materials. In addition, after thermal shock for 10 cycles, the residual strength remained ~13 MPa. Bubbles instead of microcracks formed in the glass filler, which was the main factor causing the degradation of the joint performance. It is suggested that improving the high temperature resistance of joining materials is the key to realize the application of this joint structure.