The galvanoluminescence spectra of barrier oxide films on aluminum formed in organic electrolytes

In this paper, for the first time we have presented the results of the galvanoluminescence (GL) spectra measurement obtained from barrier oxide films during aluminum anodization in various barrier film forming organic electrolytes (aqueous solution of citric acid, tartaric acid, malic acid, succinic acid and ammonium tartarate). Galvanoluminescence spectral measurements were performed utilizing spectrograph system based on the Intensified Charge Coupled Device (ICCD) camera, intended for time-resolved detection of GL phenomena dynamics. The spectra were recorded for different values of electrolyte temperature and anodization current density. We have showed that there are strong GL bands in the visible region and the shape of the spectra as well as peak intensity of the GL bands depend on the anodization voltage. The results cleraly indicate the existance of more then one type of GL centra or GL mechanisms in barrier films formed in organic electrolytes.     

Effect of aluminum annealing on the galvanoluminescence properties of anodic oxide films formed in organic electrolytes

The galvanoluminescence (GL) properties of anodic oxide films formed in organic electrolytes were investigated at different aluminum annealing temperatures. The results of the spectral measurements showed two different types of GL sources: carboxylate ions incorporated in oxide films during the anodization and the molecules AlH, AlO, Al₂, AlH₂, also formed during anodization process and already recognized in the case of inorganic electrolytes. The latter was related to gamma alumina crystalline regions formed by annealing of the aluminum samples at temperatures above 500 °C.     

Interaction of NO and NO2 on 12-tungstophosphoric acid

On exposure of the solid 12-tungstophosphoric acid (H₃PW₁₂O₄₀· nH₂O (HPW)) to NO₂ at 150°C NO₂ is sorbed, while HNO₃ is produced. NO₂ is found to penetrate into the bulk structure whose reaction occurs with the water hydrogen-bonded to the protons to produce HNO₃. The NO₂ retained on the catalyst is stoichiometrically equivalent to the total number of protons on and in the solid. This, together with infrared spectra, suggests that NO₂ is associating (1/1) with the protons, producing a nitronium salt of the solid acid. Although insignificant quantities of NO are taken up by HPW, after exposure to NO₂, approximately stoichiometric quantities of NO are sorbed and the infrared spectra show the presence of N₂O₃.     

Structure and reactivity of silica-supported 12-tungstophosphoric acid

The structure and reactivity of silica-supported 12-tungstophosphoric acid (HPW) with 10–60 wt.% loading prepared by the impregnation method are studied by using chemical analysis, X-ray diffraction (XRD), FT-IR, FT-Raman, TG, ³¹P MAS NMR, surface area measurement and microreactor tests. It is found that most of HPW in samples is well dispersed on the support, and may mainly exist as small crystalline particles with an average size around 24.3–27.6 nm, calculated by XRD results. Based on various characterization techniques, it may be concluded that silica-supported HPW still keeps its Keggin structure. The effect of different loading on the reactivity of silica-supported HPW without promoter or promoted by Pt/Al₂O₃ is studied by using isomerization of n-hexane as a probe reaction, and the reactivity is found to be strongly loading related.     

磷钨酸/多壁碳纳米管催化合成乙酸正丁酯

利用多壁碳纳米管(MWCNTs)为载体,用浸渍法制备了负载磷钨酸(H3PW12O40,简写为HPW)的复合材料磷钨酸/多壁碳纳米管(HPW/MWCNTs)。磷钨酸/多壁碳纳米管具有很高的催化活性,在磷钨酸负载量为30%,醇酸物质的量比为1.4∶1,催化剂用量为反应物总质量的1.3%,反应温度为117℃,反应时间为3h的条件下,酯化率可达96.08%。     

The growth kinetics and properties of potentiodynamically formed thin oxide films on aluminium in citric acid solutions

The growth kinetics and properties of potentiodynamically formed thin oxide films on Al were investigated in 0.05 M citric acid solutions of different pH (5, 6 and 7) by means of potentiodynamic polarization and a.c. electrochemical impedance spectroscopy (EIS) measurements. Al showed passive behaviour within the pH range that was examined. The potentiodynamic growth of the oxide film on Al takes place due to ionic conductivity under the influence of the high electric field. Characteristic kinetic oxide film growth parameters such as the high-field growth exponential law constants (A and B), ionic conductivity through the oxide film, field strength and half barrier width have been calculated. Impedance measurements were used to determine the parameters related to the characteristic sizes and properties of oxide film. The capacitive response of the impedance spectrum was related to the thickness and dielectric properties of the barrier oxide film. The oxide film resistance values were very high, indicating that the oxide films formed under potentiodynamic conditions are highly uniform in thickness and very resistant. The anodic behaviour of Al in the citric solutions under potentiodynamic conditions were characterized by the rapid growth of the oxide film which diminished the influence of relaxation processes on the growth kinetics and structural characteristics of the aluminium/anodic oxide film/electrolyte system.     

Formation of Ti-Si composite oxide films on Mg-Al-Zn alloy by electrophoretic deposition and anodization

TiO₂ or SiO₂ nanoparticles dispersed in an acetone solvent containing iodine were deposited on Mg-Al-Zn alloy by electrophoretic deposition (EPD). Subsequently, the composite oxide films were formed on the substrate by anodization in KOH-Na₂SiO₃ aqueous solutions containing TiO₂ or SiO₂ nanoparticles. The films formed by EPD were improved binding with the substrate by anodization under high voltages with sparking, and then the anodic films consisted of Si-Mg or Ti-Si-Mg composite oxides. The film thicknesses of TiO₂ and SiO₂ on the alloy increased with anodization time. In polarization tests, the films anodized under high voltages with sparking in the alkaline solutions had high corrosion resistance. Thus, the composite oxide films formed in the present method were successful in providing corrosion resistance to Mg alloy.     

The sorption and reduction of nitrogen oxides by 12-tungstophosphoric acid and its ammonium salt

Nitrogen dioxide is removed from the gas phase by 12-tungstophosphoric (HPW), 12-tungstosilicic and 12-molybdophosphoric acids, with the two solid acids containing tungsten sorbing significantly larger quantities of NO₂ than that containing molybdenum, indicating the dependence on acidic strength. NO₂ interacts with the water contained on and in HPW to form HNO₃ which desorbs. On depletion of the water additional NO₂ remains held on HPW as

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In contrast the ammonium salt of HPW reduces NO₂ to N₂ , NO and N₂O at an optimal temperature of 175°C for the reduction to N₂. The interaction process occurs between NO₂ and the reductant NH₃ while it is bound as

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on the solid. Thus NH₃ is not lost to the gas phase during the reduction process, and ammonia slip is effectively eliminated. The ammonium salt can be regenerated by exposure of HPW to gaseous NH₃ or by precipitation from aqueous solution.     

Influence of the morphology and microstructure on the photocatalytic properties of titanium oxide films obtained by sparking anodization in H3PO4

The aim of this paper is to investigate changes in morphology and microstructure of TiO₂ films, prepared by sparking anodization of Ti in a H₃PO₄ solution, by applying different formation charges. We show that although films obtained by this technique are rarely used in photocatalytic applications, the morphological and microstructural changes during sparking anodization produce TiO₂ films that can be used as photocatalysts. In contrast to qualitative analysis commonly found in the literature, we used quantitative methods of analysis to quantify average pore diameter and pore density from the morphology and structural parameters from X-ray diffraction (XRD) patterns using the Rietveld refinement. The results indicated that changes in both the morphology and crystalline structure have a strong influence on the photoactivity of the films. From this investigation, we concluded that, for films prepared in early stages of anodization, the morphology had the biggest influence on photoactivity, and after applying 72C of charge, crystalline properties dominated the photocatalytic characteristics of the films.     

铝阳极氧化法制备Al2O3纳米线

采用二次铝阳极氧化法在草酸体系中制备多孔铝阳极氧化膜,用逆电剥离技术将氧化膜从铝基体上剥离：经超声清洗后,放入磷酸溶液中去除阻挡层,使纳米孔贯通。再将膜放入c=1mol／L的NaOH溶液和w=6％的铬酸、w=1．8％的磷酸混合溶液中进行溶解,可获得Al2O3纳米线。纳米线长度为40μm,与模板厚度一致,直径为10～20nm.通孔前后铝阳极氧化膜的形貌由SEM进行表征,纳米线的形貌由SEM和TEM表征．此外,本文还结合模板在溶解过程中的实验现象,对Al2O3纳米线的形成机理进行了初步分析。     

Electronic properties of thermally formed thin iron oxide films

The oxide layer, present between an organic coating and the substrate, guarantees adhesion of the coating and plays a determinating role in the delamination rate of the organic coating. The purpose of this study is to compare the resistive and semiconducting properties of thermal oxides formed on steel in two different atmospheres at 250 °C: an oxygen rich atmosphere, air, and an oxygen deficient atmosphere, N₂. In N₂, a magnetite layer grows while in air a duplex oxide film forms composed by an inner magnetite layer and a thin outer hematite scale. The heat treatment for different amounts of time at high temperature was used as method to sample the thickness variation and change in electronic and semiconducting properties of the thermal oxide layers. Firstly, linear voltammetric measurements were performed to have a first insight in the electrochemical behavior of the thermal oxides in a borate buffer solution. Electrochemical impedance spectroscopy in the same buffer combined with the Mott-Schottky analysis were used to determine the semiconducting properties of the thermal oxides. By spectroscopic ellipsometry (SE) and atomic force microscopy (AFM), respectively, the thickness and roughness of the oxide layers were determined supporting the physical interpretation of the voltammetric and EIS data. These measurements clearly showed that oxide layers with different constitution, oxide resistance, flatband potential and doping concentration can be grown by changing the atmosphere.     

Adsorption and reduction of CO2 on 12-tungstophosphoric and 12-molybdophosphoric acids in the absence of added reductants

12-tungstophosphoric and 12-molybdophosphoric acids are capable of sorbing and reducing CO₂ without the presence of added reductants. The adsorbed CO₂ (physisorbed as CO₂) desorbs from the acids and salts at low temperatures (50–200°C). Carbon dioxide also desorbs only from the acids at high temperatures (500–600°C), suggesting the direct or indirect involvement of the protons in the process and the importance of the Keggin unit as well. Raman and DRIFTS results show that the species responsible for the evolution of CO₂ (at high temperatures) are carbonaceous in nature. Carbon deposits extract the anionic oxygen atoms from the Keggin units during the high-temperature desorption process. The extraction of anionic oxygen atoms by carbon is confirmed using labeled carbon dioxide. The spectroscopic data imply that carbon exists on the surface as such but, additionally, as either carbon or CO₂ bound to the terminal oxygen atoms of the Keggin anion. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solid-state NMR and FT-IR investigation of 12-tungstophosphoric acid on TiO2

The chemical and dynamic nature of the tungstophosphoric acid (TPA) species adsorbed on pressed, extruded, and powdered TiO₂ support was studied by ³¹P and ¹H solid-state NMR spectroscopy and diffuse reflectance FT-IR. From ³¹P NMR and FT-IR results the TPA appeared to be present in at least five forms on the titania surface: a bulk salt phase, two weakly bound intact Keggin species, a range of partially fragmented clusters such as the 11-“defect” Keggin ion, and a range of species formed by high or complete fragmentation of the Keggin ion. The relative amount of these species varied depending on the form of the support. Adsorption was incomplete on extruded titania resulting in bulk salt formation. There was almost complete adsorption on pressed titania pellets, yielding predominantly fragmented Keggin units, along with a small amount of bulk salt. However, complete adsorption (and fragmentation) without bulk salt formation was attained by impregnation of powdered TiO₂. The acidic nature of the catalysts and the degree of TPA dispersion were investigated by solid-state ¹H high-speed MAS-NMR. Pure TPA salt yielded resonances at about 6.5 ppm. The catalysts yielded acidic proton resonances at about 7–8 and 10–11.5 ppm. The broad resonance observed at 7–8 ppm is due to a dispersion of acidic sites on the surface. The intensity of the acidic resonance at around 11 ppm increased with adsorption effectiveness and could, therefore, be related to the formation of hydroxonium ions upon fragmentation of adsorbed Keggin ions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Photocatalytic properties of visible-light enabling layered titanium oxide/tin indium oxide films

Visible-light enabling titanium oxide/tin indium oxide (TiO₂/ITO) thin films deposited on unheated glass slides with prolonged deposition duration were investigated in this study. Structural properties characterized by X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM) showed typical polycrystalline structure with primary anatase phase along with elongated pyramid-like grains lying on the film surface and densely packed columnar structure from cross-sectional profile. The XRD preferential peak of (2 1 1) and the Raman peak intensity at 640 cm⁻¹ dramatically increased without noticeable broadening and shift as the deposition time was prolonged beyond 2 h. This implies that more perfectly crystalline structure, less internal stress, and comparatively larger grains were obtained by this technique. The Ti2p_3/2 and O1s XPS peaks shifted toward higher binding energy suggest that the local chemical state was influenced by the prolonged deposition duration in the film, which resulted in red shift of absorption threshold into visible-light region. Under ultra-violet (UV) and visible-light illumination, the visible-light enabling film exhibited the best photocatalytic activity on MB degradation with the rate-constant of about 0.231 h⁻¹. Hydrophilic conversion rate was estimated to be 8.14 × 10⁻³ deg⁻¹ min⁻¹ and long-term UV-induced hydrophilicity of 10° in the dark storage up to 72 h was observed. In addition to its inherent characteristics of the layered TiO₂/ITO structure on hole/electron separation, all these could be attributed to more perfectly formed crystalline structure, densely packed columnar crystals and the surface roughness along with its enlarged surface area.     

Electrochemical properties of boron-carbon-nitride films formed by magnetron sputtering

The electrochemical behavior of B_1.0C_2.4N_1.0 thin film was investigated in acidic, neutral and alkaline solutions. The anodic polarization curve of the film in 1 M NaOH showed the anodic dissolution of the film. The curve of the film in 1 M HCl showed no anodic dissolution. The cathodic polarization curve in 1 M NaCl showed shift to a negative potential side, but the anodic polarization curve was the same as that of Pt. The anodic dissolution in 1 M NaOH depended on potentials, that is, no anodic dissolution was recognized in a potential range of −0.2 to 0.1 V but the dissolution rate increased with increasing potential in a range of 0.1-0.6 V. The anodic current density of the film is directly proportional to the dissolution rate at potentials higher than 0.1 V. The dissolution rate of the film was increased with increasing solution pH.     

Esterification of palmitic acid on the ammonium salt of 12-tungstophosphoric acid: The influence of partial proton exchange on the activity of the catalyst

Esterification of palmitic acid was studied on the ammonium salt of 12-tungstophosphoric acid (TPA). The influence of ammonium content of the acid was investigated by preparing partially and fully proton exchanged catalysts. The catalysts were characterised by XRD and FT-IR for their structure and ammonium content, respectively. Potentiometric titration method was employed for the quantification of their acidity. The partially exchanged catalyst, possessing stronger acidic sites, was found to be more active than its fully exchanged analogue.     

Heterogenization of 12-tungstophosphoric acid on stabilized zeolite Y

Topics in Catalysis - 12-tungstophosphoric acid (PW12) has been supported on dealuminated zeolite Y, containing a secondary pore system with the predominant pore radii of 15 Å. The interaction...     

聚乙二醇改性壳聚糖薄膜结构与性质的研究

将壳聚糖与聚乙二醇进行共混,利用溶剂挥发成膜法制备了壳聚糖/聚乙二醇二元共混薄膜。通过红外光谱、偏光显微镜、AFM等研究了共混膜的表面形貌、微结构及力学性能。结果表明:聚乙二醇可明显改善壳聚糖薄膜的脆性,当w(PEO)≤20%时,共混物各组分间有较好的相容性。偏光显微镜照片显示共混膜中聚乙二醇颗粒结晶结构随着聚乙二醇量的增加变得更为完整。     

铝合金阳极氧化废酸的再生

介绍了铝合金阳极氧化的工艺流程及其污染物的来源.采用离子膜分离技术处理阳极氧化废酸,研究了废酸的初始质量浓度和流量对硫酸回收率和铝离子去除率的影响.当废酸中硫酸的初始质量浓度为160 g/L、废酸流量为1.5 m3/h时,硫酸回收率可达到90.62％,铝去除率达到96.78％,回收所得硫酸可用于配制阳极氧化溶液.