水热制备TiO2纳米管及其光催化性能

本文利用TiO₂粉体在高浓度NaOH溶液中水热反应制备TiO₂纳米管,采用X射线衍射(XRD)、扫描电镜(SEM),透射电镜(TEM),紫外可见分光光度计(UV-Vis)考察了NaOH浓度、水热反应温度、水热反应时间等因素对TiO₂纳米管结构和性能的影响。结果表明：当NaOH浓度为10mol/L,水热反应温度为160℃,水热反应时间20h时,所制备的TiO₂纳米管显示出较高的光催化活性,经紫外光照30min后,对甲基橙(MO)的降解率可达75.48%。     

Photocatalytic performance of nano-photocatalyst from TiO2 and Fe2O3 by mechanochemical synthesis

Nano-particles of homogeneous solid solution between TiO₂ and Fe₂O₃ (up to 10 mol%) have been prepared by mechanochemical milling of TiO₂ and yellow Fe₂O₃/red Fe₂O₃/precipitated Fe (OH)₃ using a planetary ball mill. Such novel solid solution cannot be prepared by conventional co-precipitation technique. A preliminary investigation of photocatalytic activity of mixed oxide (TiO₂/Fe₂O₃) on photo-oxidation of different organic dyes like Rhodamine B (RB), Methyl orange (MO), Thymol blue (TB) and Bromocresol green (BG) under visible light (300-W Xe lamp; λ > 420 nm) showed that TiO₂ having 5 mol% of Fe₂O₃ (YFT1) is 3-5 times higher photoactive than that of P25 TiO₂. The XRD result did not show the peaks assigned to the Fe components (for example Fe₂O₃, Fe₃O₄, FeO₃, and Fe metal) on the external surface of the anatase structure in the Fe₂O₃/TiO₂ attained through mechanochemical treatment. This meant that Fe components were well incorporated into the TiO₂ anatase structure. The average crystallite size and particle size of YFT1 were found to be 12 nm and 30 ± 5 nm respectively measured from XRD and TEM conforming to nanodimensions. Together with the Fe component, they absorbed wavelength of above 387 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe₂O₃/TiO₂ particle attained through mechanochemical method. This meant that Fe components were well inserted into the framework of the TiO₂ anatase structure. EPR and magnetic susceptibility show that Fe³⁺ is in low spin state corresponding to μ_B = 1.8 BM. The temperature variation of μ_B shows that Fe³⁺ is well separated from each other and does not have any antiferromagnetic or ferromagnetic interaction. The evidence of Fe³⁺ in TiO₂/Fe₂O₃ alloy is also proved by a new method that is redox titration which is again support by the XPS spectrum.     

Fe2O3-CaO-TiO2 体系下铁酸钙的合成过程及TiO2 和CaTiO3 的影响

为了确定高钛型钒钛磁铁矿烧结过程中铁酸钙的生成是受TiO₂还是TiO₂和CaO形成的CaTiO₃影响,首先利用Fe₂O₃和CaO的纯试剂合成了铁酸钙,并研究了TiO₂和CaTiO₃对钛铁酸钙 （FCT） 形成的影响。在Factsage 7.0软件进行热力学计算的基础上,通过在空气气氛下进行烧结,获得了在1023~1423 K温度范围内、不同烧结时间的不同样品。通过X射线衍射和扫描电镜-能谱分析等表征手段,对烧结样品的物相转变和微观结构变化进行了表征。发现FCT的形成过程主要分为2个阶段：前一阶段为1023~1223 K温度范围内Fe₂O₃与CaO之间的反应,合成产物为Ca₂Fe₂O₅,反应方程式为“Fe₂O₃(s)+ 2CaO(s)= Ca₂Fe₂O₅(s)”;后一阶段为1223~1423 K温度范围内Ca₂Fe₂O₅和Fe₂O₃的反应,主要产物为CaFe₂O₄,反应为“Ca₂Fe₂O₅(s)+ Fe₂O₃(s)= 2CaFe₂O₄(s)”,该阶段尤其是温度为1423 K时,反应速率显著加快,随温度的升高CaTiO₃显著增加。然而,Ti元素在铁酸钙中的固溶很难实现,TiO₂与铁酸钙之间的反应不是形成FCT的有效途径。随着保温时间的延长,CaTiO₃和FCT相界中Fe元素含量增加。FCT主要是通过Fe组分在CaTiO₃中固溶形成的,主要反应是“Fe₂O₃+CaTiO₃(s)=FCT(s)”。     

Synthesis and characterization of spherical and rod like nanocrystalline Nd2O3 phosphors

Spherical and rod like nanocrystalline Nd₂O₃ phosphors have been prepared by solution combustion and hydrothermal methods respectively. The Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd₂O₃ has been obtained with calcination at 900 °C for 3 h and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of Nd₂O₃ phosphors show the formation of nanorods in hydrothermal synthesis whereas spherical particles in combustion method. TEM results also confirm the same. Raman studies show major peaks, which are assigned, to F_g and combination of A_g + E_g modes. The PL spectrum shows a series of emission bands at ∼326-373 nm (UV), 421-485 nm (blue), 529-542 nm (green) and 622 nm (red). The UV, blue, green and red emission in the PL spectrum indicates that Nd₂O₃ nanocrystals are promising for high performance materials and white light emitting diodes (LEDs).     

La2O3含量对Al2O3/Cu基复合材料组织与性能的影响

以La₂O₃粉、Al粉、CuO粉为反应物原料、纯铜为基体,采用原位合成技术和近熔点铸造法制备颗粒增强Cu基复合材料,研究La₂O₃对Al-CuO体系制备的Cu基复合材料组织及性能的影响。结果表明：添加La₂O₃可获得纳米Al₂O₃颗粒,且弥散分布于Cu基体中,制备的材料组织更加细小、均匀,其材料的电导率及摩擦磨损性能明显提高。当添加0.6%wtLa₂O₃,复合材料的电导率达到90.2%IACS,磨损量达到最小,相比未添加La₂O₃,其导电率提高10.1%,磨损量减小36.6%。     

In-situ TiB2 and Al2O3 formation by DC plasma spraying

In-situ plasma spraying (IPS) is a promising process to fabricate composite coatings with in-situ formed thermodynamically stable phases. In the present study, mechanically alloyed Al-12Si, B₂O₃ and TiO₂ powder was deposited onto an aluminum substrate using atmospheric plasma spraying (APS). It has been observed that, during the coating process, TiB₂ and Al₂O₃ are in-situ formed through the reaction between starting powders and finely dispersed in hypereutectic Al-Si matrix alloy. Also, obtained results demonstrate that in-situ reaction intensity strongly depends on spray conditions.     

钕的添加对V2O5-MoO3/TiO2平板式脱硝催化剂性能的影响

本研究制备了一系列不同Nd含量的V₂O₅-MoO₃-Nd₂O₃/TiO₂平板式脱硝催化剂。采用XRD、N2-吸附脱附、XPS、H2-TPR、拉曼光谱、NH3-TPD和红外光谱等表征手段对催化剂进行分析。结果表明:适量的Nd2O3(0.25%、0.5%,质量分数)可以增强V₂O₅-MoO₃/TiO₂催化剂的还原性能,增加了催化剂的Oα/(Oα+Oβ)比率,从而提升了催化剂的脱硝活性。然而,过量Nd₂O₃(0.75%、1%)的添加,会导致催化剂酸性性能的显著降低,造成催化剂脱硝性能的下降。此外,过量Nd的添加还会对催化剂的耐磨性能有负面影响。各催化剂中,VMoN d(0.5%)/Ti催化剂显示了最佳的脱硝活性。并且,该催化剂还显示了优良的抗SO₂、H₂O性能。     

Effects of K2O-Li2O doping on surface and catalytic properties of Fe2O3/Cr2O3 system

The effects of K₂O and Li₂O-doping (0.5, 0.75 and 1.5 mol%) of Fe₂O₃/Cr₂O₃ system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400-600 °C. The formula of the un-doped calcined solid was 0.85Fe₂O₃:0.15Cr₂O₃. The techniques employed were TGA, DTA, XRD, N₂ adsorption at −196 °C and catalytic oxidation of CO oxidation by O₂ at 200-300 °C. The results revealed that DTA curves of pure mixed solids consisted of one endothermic peak and two exothermic peaks. Pure and doped mixed solids calcined at 400 °C are amorphous in nature and turned to α-Fe₂O₃ upon heating at 500 and 600 °C. K₂O and Li₂O doping conducted at 500 or 600 °C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline α- and γ-Fe₂O₃ together with K₂FeO₄ and LiFe₅O₈ phases. However, the heavily Li₂O-doped sample consisted only of LiFe₅O₈ phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K₂O and Li₂O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K₂O and Li₂O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 °C, attained 30.8% and 26.5% for K₂O and Li₂O doping, respectively. The doping process did not modify the activation energy of the catalyzed reaction but rather increased the concentration of the active sites without changing their energetic nature.     

Modification of Parylene film-coated glass with TiO2 nanoparticles and its photocatalytic properties

A titania film was deposited on Parylene-coated glass by a one-step, ultrasound-assisted procedure. The TiO₂ nanoparticles formed during the sonochemical hydrolysis of Ti(i-OPr)₄ were thrown to the surface and strongly attached to the Parylene substrate. By using different solvents (water, ethanol or their mixture) and reagent concentrations, the thickness, uniformity and crystallinity of the deposited layer were regulated. PVP was used to stabilize the highly homogeneous distribution of TiO₂ nanocrystals on the Parylene surface. The morphology and structure of the coated films were characterized by physical and chemical methods such as: X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), and optical spectroscopy. The photocatalytic activity of the titania-modified Parylene film in the photo discoloration of methylene blue was demonstrated. The experimental results revealed a correlation between the uniformity of the nanostructured anatase titania film and its photocatalytic properties.     

Residual stress measurement of an EB-PVD Y2O3-ZrO2 thermal barrier coating by micro-Raman spectroscopy

Residual stress distribution in an EB-PVD 4 mol% Y₂O₃-ZrO₂ thermal barrier coating (TBC) layer coated on a superalloy substrate has been measured by micro-Raman spectroscopy. Piezo-spectroscopic coefficient was independently calibrated on a freestanding TBC layer. The coefficient for uniaxial stress is Π_uni = 5.43 cm^− 1GPa^− 1. The stress measurement through the TBC thickness shows compressive stress distribution from small to an almost large constant value. Such a distribution agrees with theoretical consideration since the small stress correctly reflects the free edge effect and the large constant stress is closely related to TBC bulk stresses.     

Effect of Bi2O3 on structure and wetting studies of Bi2O3-ZnO-B2O3 glasses

Glasses with different Bi₂O₃ contents (37-42 mol%) have been prepared by conventional melt quench technique. The IR and Raman studies indicate that these glasses are made up of [BiO₆], [BiO₃], [BO₃] and [BO₄] basic structural units. The vibrations of [BiO₃] and [BO₃] become stronger as the content of Bi₂O₃ increases, which makes glass structure loosened. Viscosity of the glasses was measured by using a Rheotronic III paralleled plate rheometry, which shows that the viscosity of glass samples decreased when the content of Bi₂O₃ increased at the same temperature (400-460 °C). The temperature range which suits for glasses sealing was calculated by using the approximation of Arrhenian behaviour. The wetting performance of Bi₂O₃-ZnO-B₂O₃ glasses was described by using high-temperature microscope, which also proves that the structure of investigated Bi₂O₃-ZnO-B₂O₃ glasses become loosened due to the increasing of the content of Bi₂O₃.     

Microstructure characterization and photocatalytic activity of mesoporous TiO2 films with ultrafine anatase nanocrystallites

A series of mesoporous TiO₂ films on borosilicate glass with ultrafine anatase nanocrystallites were successfully synthesized using a non-acidic sol gel preparation route, which involves the use of nonionic surfactant Tween 20 as template through a self assembly pathway. The microstructure of these TiO₂ films was characterized by XRD, SEM, HR-TEM, UV-Vis spectroscopy, and N₂ adsorption-desorption isotherm analysis. Their photocatalytic activities were investigated by using creatinine as a model organic contaminate in water. It was found that all mesoporous TiO₂ films prepared with Tween 20 exhibited a partially ordered mesoporous structure. The photocatalytic activity of the TiO₂ films could be remarkably improved by increasing Tween 20 loading in the sol at the range of 50% (v/v), which yielded large amount of catalyst (anatase) on the glass support and enhanced specific surface area. The optimum Tween 20 loading was 50% (v/v) in the sol, above which good adhesion between TiO₂ films and borosilicate glass could not be maintained. The final TiO₂ film (Tween 20: final sol = 50%,v/v) exhibits high BET surface area (∼ 120 m²/g) and pore volume (0.1554 cm³/g), ultrafine anatase nanocrystallinity (7 nm), uniform and crack free surface morphology, and improved photocatalytic activity.     

Synthesis and characterization of Al2O3-Ce0.5Zr0.5O2 powders prepared by chemical coprecipitation method

Al₂O₃-Ce_0.5Zr_0.5O₂ catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al³⁺ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce_0.5Zr_0.5O₂ powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al₂O₃ formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m²/g) was larger than that of ACZ-M (62.1 m²/g) and Ce_0.5Zr_0.5O₂ (17.1 m²/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al₂O₃, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al₂O₃. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce_0.5Zr_0.5O₂ powders.     

Laser-induced enhancement of the surface hardness of nanoparticulate TiO2 self-cleaning layer

We here report that the abrasion resistance of nanoparticulate TiO₂ self-cleaning layers can be highly enhanced without a considerable loss of photocatalytic capability. TiO₂ coating layers solution-deposited onto the glass substrate were irradiated by a pulsed ultraviolet (UV) laser at 355 nm, which modified the surface morphologies via laser-induced local melting of TiO₂ nanoparticles. The surface hardness, measured by pencil scratch test, improved with increasing laser power (P). While an unmodified TiO₂ layer revealed a hardness of 6B, it increased to 2H after the surface was irradiated at P = 0.3 W. Almost all of the stearic acid deposited on an unmodified sample disappeared after UV exposure for 12 h. The photocatalytic decomposition was slowed down on laser-irradiated TiO₂ surfaces and this is attributed to the reduction of specific surface areas as a result of the morphological modifications. However, a TiO₂ layer hardened to 2H still exhibited fairly good photocatalytic activity, decomposing more than 75% of the stearic acid after exposure for the same duration.     

Effects of protecting layer [Li,La]TiO3 on electrochemical properties of LiMn2O4 for lithium batteries

A sample of LiMn₂O₄ spinel oxide was surface-modified with lithium lanthanum titanate ([Li,La]TiO₃), which was developed as a lithium ionic conductor, by means of hydrothermal processing and subsequent heat treatment at 400 °C. The surface coating layers were analyzed by morphology observation using a transmission electron microscopy. Energy-dispersive spectrometry and X-ray photoelectron spectroscopy were used for element investigation. The surface modification effects on rate capability during cycling and capacity retention for the LiMn₂O₄ spinel oxide were confirmed. Then Mn dissolution during storage at elevated temperatures of the pristine, coated sample was characterized. The Mn dissolution characterization was based on the idea that Mn dissolution is one of the most significant reasons for capacity loss for LiMn₂O₄ spinel oxide, and this phenomenon is especially severe at elevated temperatures. Our experimental results indicate that the surface-modified sample shows much a better initial capacity and rate capability compared with the pristine sample. The [Li,La]TiO₃ coating effectively enhances the structural stability of LiMn₂O₄ at elevated temperatures, most likely because the [Li,La]TiO₃-modifying layers play a definitive role in suppressing Mn dissolution in the electrolyte during storage.     

Effect of Na diffusion from glass substrate on the microstructural and photocatalytic properties of post-annealed TiO2 films synthesised by reactive sputtering

Amorphous columnar TiO₂ films were synthesised by reactive sputtering on cold soda–lime glass substrates (TiO₂/glass films). The films were subsequently heated in order to crystallise the photoactive anatase phase. The surface chemical composition assessment demonstrates the occurrence of metallic Na, the amount of which increases with the annealing temperature. The evolution of the structural, microstructural and photocatalytic properties of the films with the annealing temperature was investigated and compared to that of TiO₂ films deposited in same conditions, but on glass pre-coated with a SiN_x diffusion barrier (TiO₂/SiN_x/glass films). Once crystallised, both series of TiO₂ films exhibit [001] preferential orientation corresponding to the columnar growth. Grain coalescence associated to a modification of the grain shape is only observed in TiO₂/glass films for annealing temperatures higher than 450 °C, whereas neither microstructural nor structural change is observed in TiO₂/SiN_x/glass films. The Na-contaminated TiO₂ films exhibit different photocatalytic behaviour with the annealing temperature compared to the Na-free TiO₂ films. A discussion is finally based on these differences.     

Subsolidus phase relations in the ZnO-WO3-Bi2O3 system

The subsolidus phase relations of the ternary system ZnO-WO₃-Bi₂O₃ were investigated by means of X-ray diffraction (XRD). Six binary compounds and seven 3-phase regions were determined, and no ternary compounds were found in this ternary system. The phase diagram of pseudobinary system ZnO-Bi₂WO₆ was also constructed through XRD and differential thermal analysis (DTA) methods, which forms eutectic system with eutectic temperature about 945 °C, the corresponding eutectic component is 35 mol% ZnO and 65 mol% Bi₂WO₆.     

Preparation of nanometric CeO2–ZrO2–Nd2O3 solid solution and its catalytic performances

A kind of nanometric CeO₂–ZrO₂–Nd₂O₃ (CZN) solid solution for a carrier in the automotive three-way catalysts was synthesized by a coprecipitation method and characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption (BET), scanning electron microscopy (SEM) and oxygen storage capacity (OSC). For the purpose of comparison, an unincorporated CeO₂–ZrO₂ (CZ) was also synthesized. The XRD measurements disclose the prepared CeO₂–ZrO₂–Nd₂O₃ have a face-centered cubic fluorite structure and nanoparticle sizes. According to the results of XPS, Nd³⁺ ions can enter the CZ lattice and form a homogenous solid solution. Oxygen storage capacity measurements reveal that CeO₂–ZrO₂–Nd₂O₃ display high oxygen mobility at a low temperature. The results of the activity tests show that the catalyst exhibits good three-way catalytic activity and fairly wide range of air-to-fuel ratios.     

Scratching of Al2O3 under pre-stressing

Pre-stressing scratching tests have been preformed on polished surfaces of Al₂O₃ ceramic under a Rockwell diamond indenter which moved with uniform speed and constant normal load to investigate how the pre-stress contributes to the material removal mechanism. With the measurement of acoustic emission signals as well as indenter tangential forces, surface damages and cross-section of grooves of Al₂O₃ ceramic were evaluated under the action of different values of pre-stress. It was found that the scratched groove width was increased with the increasing of pre-stress when same normal loads were applied. The existence of pre-stress tends to restrain the crack propagation along the direction of pre-stress, and obvious plastic deformation at the bottom of scratched groove has been observed. Moreover, the fluctuation of tangential force was obviously enhanced, and the magnitude of tangential force in the test of pre-stress was higher than that of without pre-stress. The acoustic emission signals showed that fewer damages were produced in the process of scratching with an appropriate pre-stress. However, the continuing increase of pre-stress would aggravate the machining process.     

Thermal conductivity and thermal cycle life of La2O3 and HfO2 doped ZrO2-Y2O3 coatings produced by EB-PVD

The effects of La₂O₃ and HfO₂ addition on thermal conductivity and thermal cycle life of EB-PVD YSZ coatings were investigated. La₂O₃ and HfO₂ were selected as additives, because they significantly suppress the sintering of YSZ. The developed coating showed low thermal conductivity as well as high resistance to sintering. Burner rig tests confirmed that the developed coating have a superior thermal insulating effect and have a longer life than that of a coating with conventional composition.