Cerium‐based thermal conversion treatments on silicon carbide reinforced 2009 aluminum alloy composites

The conversion coatings on SiC_p/2009 aluminum (Al) composites and 2009 Al alloy were obtained by immersing the samples into the cerium (Ce)‐based solutions with varying the chemical concentration (CeCl₃·7H₂O, NaCl), solution pH/temperature, immersing time, and drying temperature. The corrosion inhibition mechanism and kinetics were studied by using the electrochemical techniques and surface analyses. Potentiodynamic polarization tests showed that coatings improved corrosion resistance as compared to untreated samples and environmental factors played important role in the formation of conversion layer. Scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), and X‐ray photoelectron spectroscopy (XPS) analysis revealed that relatively high inhibition efficiency for composite with 25 vol% SiC_p was due to the existence of rather high surface area of cathodic intermetallics/SiC_p, which support to deposit Ce oxides/hydroxides on the entire surface.     

High temperature crystallographic and low temperature magnetic phase transitions in Fe doped Sr2RuMnO6

Fe doped Sr₂RuMnO₆ (SRMO) double perovskites (Sr₂RuMn_1-xFe_xO₆, x = 0, 0.1, 0.2 and 0.3) were prepared by solid-state route. Both x-ray diffraction and Raman spectroscopy were performed to investigate the crystal structure of the synthesized double perovskites. Rietveld refinement of the x-ray diffraction patterns confirmed a phase transition from tetragonal to cubic space group as a function of doping concentration of iron. Raman spectroscopy at room temperature and group theory analysis revealed the phonon modes associated with the space group of the samples. The temperature dependent Raman spectroscopy showed an anharmonic behaviour of the phonon modes of the Fe doped SRMO samples. The temperature evolution of the phononic modes in the range of 300 K–620 K is predominantly influenced by the lattice degrees of freedom. The presence of several oxidation states Mn (2⁺, 3⁺ and 4⁺) and Fe (3⁺ and 4⁺) was confirmed by an X-ray photoemission spectroscopy analysis of the highest doped sample (x = 0.3). The magnetic properties measurements showed that the samples were completely paramagnetic at room temperature. The samples exhibit antiferromagnetism at very low temperatures and we conclude that they exhibit ferrimagnetic ground state in the mid temperature region.     

Effect of small addition of Mn on the passivation of Zn in 0.1 M NaOH solution

The passivation of pure Zn (99.995 wt%) and Zn–0.4Mn (0.4 wt% Mn) alloy in a deaerated 0.1 M NaOH solution (pH 12.9) was investigated by electrochemical measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The potentiodynamic polarization and electrochemical impedance measurements show that addition of 0.4 wt% Mn can decrease the passive current density of Zn in the passive region. XPS surface analysis indicates that there is approximately 1.0–2.0 at% Mn²⁺ being incorporated into the passive film on Zn–0.4Mn alloy with Mn content being higher in the outer layers. Mott–Schottky analysis shows that the incorporated Mn can decrease concentration of defects in the film. AFM observations disclose that Mn can decrease the grain size of the film. The mechanism by which Mn additions improve the passivity of Zn is that the incorporated Mn can inhibit ions transportation in the film and inhibit its growth. Meanwhile, Mn can also promote the nucleation of Zn oxides and decrease film porosity.     

Demonstration of enhanced the photocatalytic effect with PtSe2 and TiO2 treated large area graphene obtained by CVD method

Here, we report our method on enhancing the photocatalytic effect with PtSe₂ and TiO₂ treated large area graphene (LAG). The LAG was growth on copper foil at a low temperature (500 °C) under atmospheric pressure by chemical vapor deposition (CVD) method. A facile, fast ultrasonic method was then used to successfully synthesize PtSe₂-LAG/TiO₂ nanocomposites. The composites that were obtained were characterized using X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), Raman spectroscopic analysis, and X-ray photoelectron spectroscopy (XPS). UV–vis diffuse reflectance spectra (DRS) analyses were also performed, and the catalytic behavior was investigated by the decomposition of methylene blue (MB).The as-prepared LAG with a Raman D band was obtained, and graphene layers can be clearly seen in High-Resolution Transmission Electron Microscopy (HRTEM) images. The degradation performance of the MB solution was determined via UV–vis spectrophotometry. This improved photocatalytic activity is a result of the positive synergetic effect between PtSe₂ and LAG in the heterogeneous photocatalyst. In this study, the LAG behaves as an electron transfer agent, contributor, collector, and source of active adsorption sites. The optical properties were also observed to be affected by the different weight ratios of the LAG in the composites by observing their respective band gaps from diffuse reflectance spectra.     

Effect of acidic pretreatment on the chemistry and distribution of lignin in aspen wood and wheat straw substrates

In this work, aspen and wheat straw substrates were pretreated using aqueous dilute acid (DA) and chemimechanical (CM) pretreatment, and the impact of these pretreatments on biomass lignin was investigated. Here DA pretreatment refers to the acidic treatment of biomass powders and CM pretreatment refers to the acidic treatments of chips or stalks followed by disc refining. The resulting substrates were observed using advanced microscopy techniques to determine changes in lignin distribution throughout the fiber cell wall due to the acid treatments. Following acid treatment, lignin within the cell wall was divided into spherical or elongated bundles. The surface of DA and CM pretreated substrates were shown to differ, with CM pretreated aspen exhibited a more cellulose-rich surface. X-ray Photoelectron Spectroscopy data indicated reduced surface lignin on CM pretreated aspen and increased surface lignin on CM pretreated wheat straw. Fourier transform infrared spectroscopy (FT-IR) spectra illustrated changes in bands related to hemicellulose lignin, and surface hydroxyl content suggesting possible differences in lignin chemistry. It was hypothesized that differences in lignin distribution based on biomass type and pretreatment method were due to interactions between the chemical treatment and the mechanical size reductions steps. Particle size prior to chemical treatment could impact the movement of lignin onto sample surface, and chemical treatment prior to size reduction could impact the fracture plane during the downsizing process. It is expected that both these effects could impact lignin distribution within the sample and on the sample surface.     

炼焦煤中有机硫对微波的响应规律

在固定腔微波反应器中,分别使用不同频率的微波对3种炼焦煤开展脱硫试验,采用XPS分析方法解析微波辐照前后煤中有机硫赋存形态及相对含量的变化,利用Materials Studio模拟平台计算煤中不同有机含硫结构化学键特性在微波作用后的变化,探寻微波作用下煤中有机硫的变化和响应机理。研究表明,山西高硫炼焦煤中有机含硫组分包括硫醇(醚)、噻吩和(亚)砜,840 MHz和915 MHz频率微波辐照后,硫醇(醚)相对含量下降,噻吩相对含量升高,2 450 MH频率微波辐照后,有机含硫组分相对含量变化不明显。模拟计算显示,在外加电场作用下,煤中C—S键长增大、键级减小,有机含硫分子偶极矩增大。说明频率为840 MHz和915 MHz的微波辐照能改变煤中有机硫的化学结构参数,进而影响煤中有机硫的脱除。     

硫化铵钝化锑化镓表面的化学与电学性质研究

本文利用X射线光电子能谱（XPS）,飞行时间二次离子质谱（TOF-SIMS）和电流-电压特性（I-V）对不同硫化铵溶液（(NH4)2S）钝化后的锑化镓（GaSb）表面化学性质进行了研究。通过对比,发现中性(NH4)2S S溶液对GaSb表面的钝化能力要优于纯(NH4)2S溶液和碱性(NH4)2S S溶液。碱性(NH4)2S S溶液在有效去除GaSb表面氧化物的同时形成硫化物产物以改善器件性能。TOF-SIMS测试结果从另一方面证实纯(NH4)2S溶液钝化也会形成硫化物产物,但该产物在纯(NH4)2S溶液中是可溶的,以至于很难稳定地存在。3D光学轮廓仪测试结果显示中性(NH4)2S S溶液钝化的GaSb表面具有最低的粗糙度。I-V测试结果表明中性(NH4)2S S溶液钝化能显著提高GaSb基肖特基二极管的电学性能。综上所述,中性(NH4)2S S溶液的钝化效果在改进GaSb表面性质方面具有最优的结果。     

喷雾干燥-煅烧制备钨钴氧化物粉末的反应机理

以偏钨酸铵(AMT)、醋酸钴Co(CH3COO)2·4H2O、有机碳为原料,通过喷雾干燥得到前驱体粉末,然后在氮气氛下煅烧制备钨钴氧化物复合粉末;并对AMT、醋酸钴及前驱体粉末进行TG-DSC-DTA分析,用XPS对钨钴氧化物粉末进行价态分析,以X射线衍射对钨钴氧化物粉末进行物相分析,用SEM对粉末进行形貌分析。结果表明:煅烧温度550℃、氮气流量6.5 m3/h、煅烧时间20 min制备的钨钴氧化物粉末粒度为10~125μm,平均粒度为50μm,产物为裂解碳、WO3、Co3O4。此温度可避免AMT分解生成的WO3在水蒸气作用下生成钨水化物WO2(OH)2;避免WO2(OH)2在H2作用下还原成W粉;及避免W粉沉积在早先被还原的W核上使W粉颗粒长大。     

不同气氛下电火花沉积钛合金涂层的组织性能

分别在氮气、氩气和空气3种气氛下,在45钢上电火花沉积制备TC4钛合金涂层。利用OM、SEM、EDS、XRD、XPS等对钛合金沉积层的微观形貌、组织结构进行分析;利用纳米力学探针仪测试对比沉积层的力学性能;采用CETR摩擦磨损仪测试涂层的耐磨性。结果表明:氮气下电火花沉积生成含TiN及少量TiO和TiO2的陶瓷增强层。氮气中制取的涂层微裂纹较明显,但几无坑蚀和微孔,表面形貌优于氩气和空气下的沉积层。纳米硬度高达15.18GPa,无需增加沉积层厚度,即可获得较高硬度和抗变形能力。其摩擦因数为0.41,磨损量为2.2mg,均远低于45钢,也低于空气和氩气下制备的普通的钛合金涂层,并且改善了钛合金涂层的粘着磨损。