Electrophoretic co-deposition of Fe2O3 and Mn1,5Co1,5O4: Processing and oxidation performance of Fe-doped Mn-Co coatings for solid oxide cell interconnects

Fe-doped Mn_1,5Co_1,5O₄ coatings on Crofer22APU were processed by an electrophoretic co-deposition method and the corrosion resistance was tested at 750 °C up to 2000 h.The “in-situ” Fe-doping of the manganese cobalt spinel was achieved by electrophoretic co-deposition of Mn_1,5Co_1,5O₄ and Fe₂O₃ powders followed by a two-step reactive sintering treatment. The effects on the coating properties of two different Fe-doping levels (5 and 10 wt.% respectively) and two different temperatures of the reducing treatment (900 and 1000 °C) are discussed. Samples with Fe-doped coatings demonstrated a lower parabolic oxidation rate and thinner oxide scale in comparison with both the undoped Mn_1,5Co_1,5O₄ spinel coating and bare Crofer 22 APU. The best corrosion protection was achieved with the combined effect of Fe-doping and a higher temperature of the reducing step at 1000 °C.     

Facile synthesis of pseudocapacitive Mn3O4 nanoparticles for high-performance supercapacitor

In this work, a facile method to produce the ultrafine (4–14 nm) and mixed valence Mn₃O₄ nanoparticles from low-cost MnSiO₃ (manganese silicate) particles were introduced. The best NaOH concentration in hydrothermal treatment has been determined after a series of experiments. Also, the as-synthesized Mn₃O₄ material with good specific capacitance has been investigated attentively at a high mass loading (∼3 mg cm⁻²). The particles size and the pore size distribution is found to be refined and optimized, respectively. This increased the crystallinity and the capacitive contribution in the energy process. Thereby improving the rate capability and cycling stability, which result in significant improvement of specific capacitance (401 F g⁻¹ at 10 mV s⁻¹). The aqueous asymmetric supercapacitor device AC//Mn₃O₄ with a stable working voltage window up to 2.0 V has been fabricated, and it is found to have an energy density of 40.2 W h kg⁻¹ at 500 W kg⁻¹ power density. This could sustain 5000 cycles galvanostatic charge/discharge with 96.9% retention.     

纳米Fe3O4磁性颗粒表面改性及其在医学和环保领域的应用

纳米Fe₃O₄磁性材料在生物医学、环保、催化及电子信息等领域有巨大的应用潜力,但单独的纳米Fe₃O₄颗粒存在一些弊端,难以直接使用,在生物医药领域尤其如此。对Fe₃O₄磁性纳米粒子进行表面改性,可以改善其结构与性能,因此,备受科学界关注。对近年来Fe₃O₄磁性纳米颗粒的表面改性方法及其在生物医学、环境工程两大领域中的应用做了综述,并对今后发展趋势做了初步的展望。     

Comparison of corrosion behavior of Ti3SiC2 and Ti3AlC2 in NaCl solutions with Ti

Corrosion behavior of self-sintered, ternary-layered titanium silicon carbide (Ti₃SiC₂) and titanium aluminum carbide (Ti₃AlC₂) fabricated by an in-situ solid-liquid reaction/hot pressing process was investigated by potentiodynamic polarization, potentiostatic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution. Commercially pure titanium (Ti) was selected for comparison through XRD, XPS, SEM and EDS examinations for elucidating both the passivation behavior and corrosion mechanism of the alloys. Both Ti₃SiC₂ and Ti₃AlC₂ exhibited significantly superior passivation characteristics compared to Ti; Ti₃SiC₂ also showed better corrosion resistance. The silicon/aluminum site is prone to attack, and the difference in the diffusion rate between the A-site atoms and titanium decreases the passivation ability of the MAX phase. CP titanium exhibited a lower passivation current density and did not undergo breakdown in the test potential region while two MAX phases are destroyed. Nevertheless, the corrosion resistances of Ti₃SiC₂ and Ti₃AlC₂ are comparable to that of CP titanium.     

Effect of Y2O3 on the corrosion resistance of two-step sintered Al5Y3O12-MgAl2O4 sidewalls in the aluminum electrolyte

Magnesium–aluminum spinel (MAS) precursor powder was synthesized through a microwave hydrothermal method. The synergistic effects of sintering process and sintering aids on the densification, hardness and corrosion resistance of MAS were revealed. X-ray diffraction analysis (XRD), Archimedes’ drainage method, fully automatic micro-Vickers hardness test and scanning electron microscopy (SEM) were performed to analyze the phase composition, bulk density, hardness microstructure and corrosion depth of the samples, respectively. Results revealed that the best two-step sintering condition is 1650 °C/3 min/1550 °C/20 h. The MAS products obtained under the best condition have clear grain boundaries, uniform particle size distribution, and few pores. When the amount of Y₂O₃ added is 4 wt.%, Y₂O₃ and Al₂O₃ form the second-phase solid solution Al₅Y₃O₁₂, which activates the crystal lattice and benefits the sintering densification of MAS. Under these conditions, the relative density of the MAS composite ceramics prepared is relatively large (95.94 %), the grain size is relatively uniform, the hardness is relatively large (1264 HV), and the corrosion depth is relatively small (94.58 μm).     

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.     

Preparation,characterization and application of Al2O3 nanoparticles for the protection of boiler steel tubes from high temperature corrosion

In this study, α-Al₂O₃ nanoparticles were prepared using a simple sol-gel method. Synthesized nanoparticles with NiCrAlY alloy were used as coating layer for high temperature corrosion control of boiler tubes in absence and presence of fuel ash. Thermal plasma technique was used for coating process. Corrosion rates of austenitic stainless steel tubes were evaluated via weight loss technique as a function of temperature. Prepared α-Al₂O₃ nanoparticles and surface morphology of austenitic stainless steel tubes were characterized by XRD, SEM and EDS analyses. The results show that the corrosion rate increases with increasing temperatures, in absence and presence of coating. Maximum coating efficiency was 82 and 88% in absence and presence of fuel ash respectively.     

Red tetrazolium as an effective inhibitor for the corrosion of cold rolled steel in 7.0 mol·L− 1 H2SO4 solution

The corrosion inhibition of cold rolled steel (CRS) in 7.0 mol·L^-1 H₂SO₄ solution by red tetrazolium (RTZ) was carefully investigated using both experimental procedures and theoretical techniques. The results show that RTZ acts as an effective inhibitor for the corrosion of CRS in 7.0 mol·L^-1 H₂SO₄, and the maximum inhibition efficiency is higher than 95% with a RTZ concentration of 2.0 mmol·L^-1. The adsorption of RTZ on CRS surface follows Langmuir isotherm. RTZ effectively retards both cathodic and anodic reactions, and acts as a mixed-type inhibitor. EIS exhibits two capacitive loops, and their resistances increase drastically in the presence of RTZ. SEM and AFM confirm that the addition of RTZ could significantly retard the corrosion of CRS surface. A series of characterizations like FTIR, RS, XRD and XPS reveal that the corrosion CRS surface is composed of the corrosion products of iron sulfates, iron oxides and iron hydroxide, as well as inhibitor. Theoretical results of quantum chemical calculation and molecular dynamics (MD) indicate that the adsorption center of RTZ⁺ (organic cationic part of RTZ) mainly relies on its tetrazole ring, and the adsorption of RTZ⁺ on Fe (001) surface is in a nearly flat orientation mode.     

LiTi2（PO4）3表面包覆LiNi0.05Mn1.95O4及其性质

采用湿化学法在LiNi0.05Mn1.95O4表面包覆锂离子导体LiTi2(PO4)3。采用X射线衍射、扫描电子显微镜、恒电流充放电、电位阶跃、交流阻抗技术对合成产物进行物相、形貌和电化学分析。结果表明:LiTi2(PO4)3包覆LiNi0.05Mn1.95O4与未包覆LiNi0.05Mn1.95O4具有相似的X射线衍射结果,LiNi0.05Mn1.95O4包覆LiTi2(PO4)3前后的锂离子扩散系数变化不大,但包覆LiTi2(PO4)3后的LiNi0.05Mn1.95O4颗粒边界和轮廓变得模糊。LiTi2(PO4)3包覆LiNi0.05Mn1.95O4的比容量略低于未包覆LiNi0.05Mn1.95O4,且随着LiTi2(PO4)3包覆量的增加而减小,但包覆LiTi2(PO4)3后的LiNi0.05Mn1.95O4循环性能得到了大幅提高。     

Surface bound nanostructures of ternary r-GO / Mn3O4/V2O5 system for room temperature selectivity of hydrogen gas

Room temperature detection of highly sensitive Hydrogen (H₂) gas sensing material preparation was taken as a major objective in this present work. Herein, a novel one pot hydrothermal method is proposed for the synthesis of ternary r-GO decorated Manganese oxide (Mn₃O₄) and Vanadium pentoxide (V₂O₅) nanocomposite. The significant electrical conductivity of r-GO plays an important role here to enhance the sensing property. Tunable band bending features of metal oxides over the r-GO surface makes the composite works at room temperature with high selectivity of H₂. The optical, structural and morphological characteristics were analyzed by UV–Visible spectroscopy (UV–Vis), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray Photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), and High Resolution-Transmission Electron Microscope (HR-TEM). The sensing results reveals that the present nanocomposite is selectively sensitive towards H₂ with sensitivity value of (175%) at room temperature with response time (82 s) and recovery time (92 s). To investigate the low detection limit gas concentration was varied in the range from 20 ppm to 50 ppm. The synergetic sensing performance and stability of this nanocomposite could be due to the formation of metal oxides with perspicuous nanostructures as heterojunction decorated over the r-GO stack layer.     

Monolayer and bilayer conducting polymer coatings for corrosion protection of steel in 1 M H2SO4 solution

In this study, monolayer polypyrrole (PPY), polyaniline (PANI), and bilayer PPY/PANI, PANI/PPY coatings were deposited onto steel electrodes by electropolymerization in 0.1 M monomer and 0.3 M oxalic acid solution. Such corrosion parameters of these electrodes, as corrosion potentials, anodic Tafel constants and corrosion current densities were determined by means of current–potential curves as a function of time in 1 M H₂SO₄ solution. These findings were compared to the corrosion parameters of a bare steel electrode in the same acid solution. The monolayer and bilayer polymer coatings were characterized by the Fourier transform infrared (FTIR) spectroscopy and SEM. Bilayer coatings displayed better corrosion inhibition efficiencies than monolayer coatings. Furthermore, the PPY/PANI coatings offered superior corrosion protection than the PANI/PPY coatings.     

Intensification of levofloxacin sono-degradation in a US/H2O2 system with Fe3O4 magnetic nanoparticles

Fe3O4 magnetic nanoparticles (MNPs) were synthesised, characterised, and used as a peroxidase mimetic to ac-celerate levofloxacin sono-degradation in an ultrasound (US)/H2O2 system. The Fe3O4 MNPs were in nanometre scale with an average diameter of approximately 12 to 18 nm. The introduction of Fe3O4 MNPs increased levofloxacin sono-degradation in the US/H2O2 system. Experimental parameters, such as Fe3O4 MNP dose, initial solution pH, and H2O2 concentration, were investigated by a one-factor-at-a-time approach. The results showed that Fe3O4 MNPs enhanced levofloxacin removal in the pH range from 4.0 to 9.0. Levofloxacin removal ratio in-creased with Fe3O4 MNP dose up to 1.0 g·L?1 and with H2O2 concentration until reaching the maximum. More-over, three main intermediate compounds were identified by HPLC with electrospray ionisation tandem mass spectrometry, and a possible degradation pathway was proposed. This study suggests that combination of H2O2, Fe3O4 MNPs and US is a good way to improve the degradation efficiency of antibiotics.     

纳米四氧化三铁模拟酶催化光度法 测定食品中痕量双氧水

纳米四氧化三铁具有过氧化物模拟酶功能,在pH=1.42的HCl-NaAc介质中,催化双氧水产生羟基自由基迅速氧化甲基橙使其褪色,基于此建立了一种过氧化氢-甲基橙-纳米四氧化三铁模拟酶催化反应体系测定痕量双氧水的新方法。讨论了缓冲溶液、纳米四氧化三铁用量、反应温度及反应时间的影响,确立了最佳反应条件。在优化的条件下,该方法的线性范围为1.17 ~35.2 μmol/L,检出限为0.6 μmol/L。该法用于食品中痕量双氧水的测定,取得满意的结果。     

Promotional effect for SCR of NO with CO over MnOx-doped Fe3O4 nanoparticles derived from metal-organic frameworks

MnO_x-Fe₃O₄ nanomaterials were fabricated by using the innovative scheme of pyrolyzing manganese-doped iron-based metal organic framework in inert atmosphere and exhibited extraordinary performance of NO reduction by CO (CO-SCR). Multi-technology characterizations were conducted to ascertain the properties of fabricated materials (e.g., TGA, XRD, SEM, FT-IR, XPS, BET, H₂-TPR and O₂-TPD). Moreover, the interaction between reactants and catalysts was ascertained by in situ FT-IR. Experimental results demonstrated that Mn was an ideal promoter for iron oxides, resulting in decrease of crystallite size, improve reducibility property, enhance the mobility and the amount of lattice O^2- species, as well as strength the adsorption ability of active NO and CO to form multiple species (e.g., nitrate and carbonate). The unprecedented enhancement of CO-SCR activity over Mn-Fe nanomaterials follows the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction pathway.     

宽pH条件下Mn3O4/ACF复合阴极类电芬顿体系降解亚甲基蓝

用电化学方法将Mn₃O₄负载于活性炭纤维（activated carbon fiber,ACF）表面制备了Mn₃O₄/ACF复合阴极,与铂丝阳极构成了异相类电芬顿体系对模型污染物亚甲基蓝（MB）进行降解,考察了该体系在不同pH条件下对MB去除率,并对体系中的活性氧物种进行了检测,初步探讨了降解机理。实验结果表明,在pH 3.0、pH 5.0和pH 7.0时亚甲基蓝脱色率分别达到97.3%、99.9%、99.8%,pH5.0时TOC去除率达到88.6%,pH 7.0和pH 3.0时也分别达到了80.4%和73.4%,拓宽了电芬顿反应的适宜pH范围。体系中活性氧物种的检测结果表明,氧在阴极电还原产生H₂O₂,并与Mn₃O₄反应生成羟基自由基·OH,同时,氧的一电子还原产物超氧自由基O₂·^-也对阴极表面污染物的脱色有重要贡献。     

改性Fe3O4纳米粒子的定性及对功能菌固定化与脱氮特性

为解决水体富营养化所导致的恶臭现象, 用SiO₂和壳聚糖(CS)对Fe₃O₄纳米粒子进行改性, 再运用纳米粒子与微胶囊吸附-包埋的方法固定化功能性菌株, 进而对该体系的脱氮特性进行了研究。通过扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、热重分析(TGA)及振动样品磁强计(VSM)等手段对材料的形貌、结构、磁学性能等进行表征。研究结果表明, SiO₂与CS在Fe₃O₄微球表面形成的包覆层具有产物结晶度高、形态规则、磁性能优良等特点。磁性微球在20min时对菌株的吸附率达85.00%, 吸附的活菌数达(2.1～2.2)×10⁶cfu/mL。在对水体脱氮的研究中, 游离态菌株对氨氮和硝氮的去除率分别为54.13%和59.17%, 固定化菌株对氨氮和硝氮的去除率分别达到72.26%和74.56%。实验结果表明, 改性Fe₃O₄磁性微球对菌株吸附能力强, 微胶囊结构使固定化菌株比游离态菌株具有更强的脱氮性能, 且能延长Fe₃O₄磁性微球的生命周期。     

Surface modification of LiMn2O4 cathode with LaCoO3 by a molten salt method for lithium ion batteries

Spinel LiMn₂O₄ is a promising cathode due to its advantages of low-cost, nontoxicity and thermal stability. However, the dissolution of manganese and the phase transformation induce the rapid capacity fade. Surface coating is an effective method to improve its electrochemical performance. In this work, spinel LiMn₂O₄ modified with perovskite LaCoO₃ was prepared using a novel molten salt method. The resulted samples were characterized by X-ray diffraction (XRD), transmission/scanning electron microscopy (TEM/SEM), Fourier transformation infrared (FT-IR), Raman, and X-ray photoelectronic spectroscopy. The content of Mn³⁺ increased with the LaCoO₃ coating accompanied by the increased concentration of oxygen vacancy. LiMn₂O₄ modified with 2% LaCoO₃ shows a higher capacity and cycling stability than others at 0.2 C, while the cathode with 4% LaCoO₃ shows the best rate performance at a larger current at 2 and 5 C. This enhanced performance can be attributed to improved interfacial conductivity between the cathode and electrolyte and the protective effects of coating.     

Hot corrosion behaviors of SrZrO3 ceramic co-doped with Y2O3 and Yb2O3 in molten Na2SO4, V2O5, and Na2SO4 + V2O5 salts mixture

The hot corrosion behaviors of Sr(Y_0.05Yb_0.05Zr_0.9)O_2.95 (SYYZ) ceramic were investigated in Na₂SO₄, V₂O₅, and Na₂SO₄ + V₂O₅ salts mixture, respectively. Na₂SO₄ did not react with SYYZ ceramic at 900, 950 and 1000 °C. m-ZrO₂, YVO₄ and YbVO₄ were the main corrosion products on the SYYZ ceramic surface in V₂O₅ at 800 and 900 °C, whereas Sr₃V₂O₈ and t-ZrO₂ appeared at 1000 °C. In Na₂SO₄ + V₂O₅ salts mixture, the corrosion products were Sr₃V₂O₈ and t-ZrO₂ at 800 and 900 °C on the SYYZ ceramic surface, however, a new phase of SrZrO₃ developed at 1000 °C. The phase transformation and chemical interaction are the primary corrosion mechanisms for degradation of SYYZ ceramic.     

Surface tuning of halloysite nanotubes with Fe3O4 and 3-D MnO2 nanoflakes for highly selective and sensitive acetone gas sensing

Nanosized M-HNTs-MnO₂ (Magnetic halloysite nanotubes-manganese dioxide) nanocomposite was synthesized by the reduction-precipitation method followed by the hydrothermal process. The existence of MnO₂ nanoflakes on M-HNTs represents 3-D nanostructures without stacking of nanotubes and agglomeration. The sensor-based on M-HNTs-MnO₂ nanocomposites exhibits higher sensor response (R_air/R_gas = 35.6) to 100 ppm of acetone gas at operating temperature (150 °C), with a short response-recovery time (3 s/7 s). The M-HNTs-MnO₂ nanocomposite sensor shows excellent potential to act as a low cost, low-temperature sensor for acetone gas, with high acetone selectivity under high humidity conditions and with the interference of other gases. The high surface to volume ratio, three-dimensional nanostructure, and strong interactions between M-HNTs and MnO₂ nanoflakes are accountable for the improvement of acetone sensing performance. Based on the high acetone selectivity, high stability and fast dynamic response, the M-HNTs and MnO₂ sensor is an extremely appropriate candidate for a low-cost acetone sensor, and the projected approach offers a way to develop gas sensors that can be function at low temperatures for a wide variety of applications.