Synthesis and tribological properties of NbSe3 nanofibers and NbSe2 microsheets

NbSe₃ nanofibers and NbSe₂ sheets were prepared by solid state reaction. The as‐prepared products are characterized by powder X‐ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that the obtained NbSe₃ nanofibers have a diameter in the range of 100–300 nm and length about 10 μm, while the NbSe₂ sheets have a hexagon structure. The tribological properties of the as‐prepared NbSe_x powders as additives in HVI500 base oil were investigated on UMT‐2 multispecimen tribo‐tester. The wear scars were measured by VEECO WYKO NT1100 non‐contact optical profile testing instrument. It is found that the addition of both NbSe_x nanofibers/sheets improves the tribological properties of base oil. Furthermore, NbSe₂ sheets exhibit better friction reduction and wear resistance properties than NbSe₃ nanofibers in HVI500 base oil. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and magnetism of manganese‐doped ZnO powder samples

The magnetic and structural properties of manganese‐doped ZnO powder samples prepared by a solid state method are reported. Magnetization measurements indicate ferromagnetic behavior, with hysteresis observed in the M vs. H behavior at 300 K. Coercive fields were <100 Oe at 300 K. Temperature‐dependent magnetization measurements showed evidence for ordering temperatures of >300 K. However, the results show that ferromagnetism originates from the doped matrix rather than any type of magnetic cluster and the ferromagnetism is due to the defects and/or oxygen vacancies confined to the surface of the grains. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tribological properties of WSe2 nanorods as additives

This work demonstrats a convenient and effective approach to synthesize WSe₂ nanorods at only 600 °C in argon atmosphere after ball milling. The friction and wear properties of WSe₂ nanorods as additives in two kinds of base oil, GyT130 oil and 60N oil were systematically investigated. Compared to base oil, the friction coefficient of the base oil containing WSe₂ nanorods was obviously reduced and the wear behaviour was improved. The nanorods in the 60N base oil showed better tribological properties than that in the GYT130 oil. The friction‐and‐wear mechanism of the WSe₂ nanorods as lubrication additive was discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,characterization, and tribological properties of two‐dimensional Ti3C2

We report on the preparation of two‐dimensional (2D) Ti₃C₂ and its friction and wear properties. Laminated Ti₃AlC₂ was synthesized by pressureless sintering using Ti, Al, and graphite, followed by HF exfoliation and sonication treatment to form 2D‐layered Ti₃C₂, which exhibited individual layer or stack of several layers. Analysis of microstructure and composition was used to confirm the successful exfoliation of laminated Ti₃AlC₂. The tribological behaviors of the as‐prepared 2D Ti₃C₂ as a lubrication additive in base oil were investigated. Results indicate that 2D‐layered Ti₃C₂ can greatly enhance the friction‐reducing and anti‐friction properties of base oil, especially with 1.0 wt% Ti₃C₂. This novel 2D‐layered Ti₃C₂ would be a good candidate for lubricating materials to meet emerging needs in practical applications.     

Synthesis and tribological properties of copper matrix solid self‐lubricant composites reinforced with NbSe2 nanoparticles

Copper matrix solid self‐lubricant composites were prepared by powder metallurgy route using copper powders and NbSe₂ nanofiber or sheet. The tribological properties of the as‐prepared materials were estimated by a ball‐on‐disc on UMT‐2 multi‐function friction and wear tester under dry conditions in a normal laboratory atmosphere (55‐70% relative humidity, 15‐25 °C). The NbSe₂ nanofiber or sheet was very effective in improving the tribological properties of the composites. It is found that the composites with 15 wt.% NbSe₂ nanofibers showed a very low coefficient of friction of 0.1487. Furthermore, the value levels of electrical resistivity for the composites with different contents of NbSe₂ nanofiber reached to 10^‐6 Ω.cm. When the NbSe₂ content was high enough, a continuous supply of NbSe₂ nanofiber to the tribo‐surface is an important precondition and the benefit of its anti‐friction properties for the copper matrix composites. This behavior is related that little NbSe₂ is reacted with the Cu‐base in the sintering process, although there needs enough NbSe₂ nanofibers as solid lubricants; too much NbSe₂ nanofibers will decrease the intensity of the composites, reducing the wear resistance. So adding the appropriate contents of NbSe₂ nanofiber to the composites play an important role in anti‐friction and wear resistance. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and tribological properties of laminated Ti3SiC2 crystals

Laminated Ti₃SiC₂ crystals are prepared of Ti, Si, C and Al powders by the method of hot isostatic pressing with NaCl additive in argon at 1350 °C. The laminated morphology of Ti₃SiC₂ is presented through the SEM and TEM observations. The results of high resolution transmission electron microscope (HRTEM) and selected area electron diffraction (SAED) patterns combined, it can be seen that the layers are of Ti₃SiC₂ crystals. The growth mechanism of Ti₃SiC₂ crystals, controlled by two‐dimensional nucleation, is also explained. The tribological properties of Ti₃SiC₂ crystals as additives in HVI500 base oil are investigated by a UMT‐2 ball‐on‐plate friction and wear tester. The study shows that under determinate conditions, the friction coefficient of the base oil containing Ti₃SiC₂ crystals is lower than that of pure base oil, and it decreases with the increase of mass percent of Ti₃SiC₂ nanolayers when its proportion is lower than 5wt. %. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of MoSe2/Reduced graphene oxide composites with improved tribological properties for oil‐based additives

In this work, we developed a facile and effective hydrothermal method synthesis of MoSe₂ nanoflowers on reduced graphene oxide (RGO) sheets. The as‐prepared MoSe₂/reduced graphene oxide (MoSe₂/RGO) composites are characterized by X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that MoSe₂ nanoflowers were successfully deposited on RGO nanosheets to form a well interconnected hybrid structure. The tribological properties of MoSe₂/RGO composites as lubricating oil additive were investigated by a UMT‐2 ball‐on‐plate friction and wear tester. By the addition of MoSe₂/RGO composites in paraffin oil, the antiwear ability was improved and the friction coefficient was decreased. The based oil with MoSe₂/RGO composites showed better tribological properties than the oil with MoSe₂ and pure oil. The good friction and wear properties of MoSe₂/RGO composites as additives were attributed to the formation of a thin physical tribofilm on the substrate.     

Multi‐factors on photocatalytic properties of Y‐doped Bi2WO6 crystallites prepared by microwave‐hydrothermal method

Different contents of Y‐doped Bi₂WO₆ crystallites were synthesized by a microwave‐hydrothermal method. The photocatalytic properties with different contents of Y‐doped Bi₂WO₆ crystallites were studied. The Y‐doped Bi₂WO₆ crystallites were also characterized by XRD, EDX, SEM and UV‐vis DRS and the multi‐factors on photocatalytic properties of Y‐Doped Bi₂WO₆ crystallites were discussed. The results indicate that Y³⁺ replacing Bi³⁺ enters into the Bi₂WO₆ lattice, producing a degree of Bi₂WO₆ lattice distortion. It also has an impact on the crystallinity of Bi₂WO₆ and the band gap is from 2.49 eV to 2.71 eV. The photocatalytic results show that when the content of Y doping becomes 10%, the degradation rate of rhodamine B is above 90% after 40 min irradiation, which shows that doping the proper rare earth ions is conducive to the photocatalytic properties of Bi₂WO₆ crystallites.     

硒化钨花状纳米晶的可控合成及电催化产氢性能研究

采用胶体化学法,以氧化钨(W18O49)为钨源制备出花状硒化钨纳米晶.采用透射电子显微镜(TEM)、高分辨透射电镜(HRTEM)和X射线衍射(XRD)手段对硒化钨纳米晶进行表征.本文对硒化钨花状纳米晶体的可控合成进行了初步探索,同时对烧结后的硒化钨纳米晶进行了电催化产氢测试.结果表明,硒化钨花状纳米晶具有良好的电催化性能.     

Optical and magnetic properties of Nd‐doped ZnO nanoparticles

Nd‐doped ZnO nanoparticles with different concentration were synthesized by sol‐gel method. The structures, magnetic and optical properties of as‐synthesized nanorods were investigated. X‐ray diffraction (XRD) and x‐ray photoelectron spectroscopy (XPS) results demonstrated that Nd ions were incorporated into ZnO lattice; but Zn_1‐xNd_xO nanoparticles with Nd concentration of x = 0.05 showed Nd₂O₃ phase, so the saturation concentration of Nd in Zn_1‐xNd_xO is less than 5 at%. Vibrating sample magnetometer (VSM) measurements indicated that Nd doped ZnO possessed dilute ferromagnetis behaviour at room temperature. Photoluminescence spectroscopy (PL) showed that Nd ions doping induced a red slight shift and decrease in UV emission with increase of Nd concentration.     

Heterodoped nanoflakes: synthesis and characterization of sulfur‐doped NbSe2 nanoflakes

Doping of NbSe₂ with heteroatoms is an effective way to tailor its properties. Here, solid phase synthesis process has been utilized for growing uniform and excellent crystalline nano‐NbSe₂ by sulfur dopant during the growing process. The sulfur‐doped mechanism of nano‐NbS_2xSe_2(1‐x)(x = 0.03∼0.2) has been investigated: the sulfur atoms not only replace the Se position but also intercalate in layer gap by one‐step reaction. In the structure of NbSe₂, the sulfur atoms replace the positions of Se atoms and then are located in the empty octahedral positions of van der waals gap between the NbSe₂ layers with the increase of sulfur content. The lubrication properties of the as‐prepared NbSe₂ and sulfur‐doped NbSe₂ powders as additives in HVI1500 base oil were discussed. The lubrication properties of base oil was improved by both NbSe₂ and sulfur‐doped NbSe₂. Furthermore, the lubrication properties of sulfur‐doped (0.1at%) NbSe₂ are better than those of pure NbSe₂ in HVI1500 base oil, which could be attributed to their thin laminated structure and the sulfur dopant.     

Structure and optical properties of Mg‐doped ZnO nanoparticles by polyacrylamide method

Mg‐doped ZnO (Mg_xZn_1‐xO) nanoparticles with precise stoichiometry are synthesized through polyacrylamide polymer method. Calcination of the polymer precursor at 650 °C gives particles of the homogeneous solid solution of the (Mg_xZn_1‐xO) system in the composition range (x < 0.15). ZnO doping with Mg causes shrinkage of lattice parameter c. The synthesized Mg_xZn_1‐xO nanoparticles are typically with the diameter of 70–85 nm. Blue shift of band gap with the Mg‐content is demonstrated, and photoluminescence (PL) from ZnO has been found to be tunable in a wide range from green to blue through Mg doping. The blue‐related PL therefore appeared to be caused by energetic shifts of the valence band and/or the conduction band of ZnO. Mg_xZn_1‐xO nanoparticles synthesized by polyacrylamide‐gel method after modified by polyethylene glycol surfactant have a remarkable improvement of stability in the ethanol solvent, indicating that these MZO nanoparticles could be considered as the candidate for the application of solution–processed technologies for optoelectronics at ambient temperature conditions.     

Synthesis of superconducting sphere‐like Mo2C nanoparticles in an autoclave

Sphere‐like Mo₂C nanoparticles have been synthesized through the reaction of sodium molybdate, anhydrous ethanol and sodium azide at 450 °C for 10 h in a sealed stainless steel autoclave. X‐ray powder diffraction results indicated that the final product was Mo₂C. Transmission electron microscopy (TEM) and scanning elctron microscopy (SEM) were employed to characterize the as‐prepared sample. The sample was mostly composed of sphere‐like particles, which has a superconducting transition temperature of 9.5 K, and its calculated surface area is 30.859 m²/g. The experimental parameters such as reaction temperature and reactants were studied to investigate the reaction mechanism. It was found that sodium azide and reaction temperature played key roles in the formation of sphere‐like Mo₂C nanoparticles. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and magnetic studies of Mn‐doped ZnO

The bulk samples of Mn‐doped ZnO were synthesized with the nominal compositions Zn_1‐xMn_xO (x = 0.02, 0.05, 0.10, 0.15) by the solid‐state reaction and sol‐gel methods. In both the methods the samples were finally sintered at ∼700 °C in air. The X‐ray diffraction (XRD) studies of the samples synthesized by the solid‐state reaction method exhibit the presence of wurtzite (hexagonal) crystal structure similar to the parent compound (ZnO) in all the samples, suggesting that doped Mn ions sit at the regular Zn sites. However, same studies spread over the samples with Mn content ≥5% and synthesized by the sol‐gel method reveal the occurrence of some secondary phase in addition to the majority wurtzite phase. The magnetic measurements by vibrating sample magnetometer (VSM) clearly indicate ferromagnetic interaction at room temperature in all the samples. The Curie temperatures (T_c) and magnetization vary with concentration of Mn ions in the samples. However, the samples synthesized by sol‐gel method were found to have lower Tc values and also lower magnetization as compared to the corresponding samples synthesized by solid‐state reaction method. It could possibly be due to the presence of antiferromagnetic islands and smaller crystallite sizes in the samples prepared by sol‐gel method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and tribological properties of hexagonal titanium silicon carbide crystals

Hexagonal titanium silicon carbide (Ti₃SiC₂) crystals were prepared by vacuum sintering of Ti, Si, and C powders at 1300 °C. The microstructure and grain deformations of Ti₃SiC₂ were examined by scanning electron microscopy and transmission electron microscopy. The tribological properties of hexagonal Ti₃SiC₂ crystals as lubrication additive in HVI500 base oil were investigated by a UMT‐2 ball‐on‐plate friction and wear tester. The Ti₃SiC₂ additives exhibited good friction reduction. Under determinate conditions, the friction coefficient of base oil containing Ti₃SiC₂ crystals is lower than that of pure base oil. The base oil with 3.0 wt.% hexagonal Ti₃SiC₂ crystals presented good anti‐wear capability. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of Co‐doped CeO2 nanorods modified glassy carbon electrode for electrochemical detection of nitrobenzene

CeO₂ nanoparticles (CNPs), Co‐doped CeO₂ nanoparticles (CCNPs) and Co‐doped CeO₂ nanorods (CCNRs) were synthesized by simple co‐precipitation method and explored their sensing behaviour towards nitrobenzene. XRD and TEM analysis confirmed the presence of cubic fluorite structure of the CNPs, CCNPs and CCNRs. EDX analysis confirmed the presence of Cobalt in CeO₂ nanorods. The electrochemical sensing of nitrobenzene was carried out using CCNRs‐modified glassy carbon (GC) electrodes by means of cyclic voltammetric (CV) technique. The peak current (I_p) was found to be linearly co‐related to nitrobenzene (NB) concentration (R² = 0.9665). A substantial enhancement in cathodic peak current (C1), and sensitivity (∼738.8 nA/μM) was observed for the CCNRs‐modified GC electrode than those of CNPs and CCNPs‐modified electrodes.     

Zr‐doped CeO2 Hollow slightly‐truncated nano‐octahedrons: One‐pot synthesis,characterization and their application in catalysis of CO oxidation

Zirconium‐doped ceria hollow slightly‐truncated nano‐octahedrons (HTNOs) (Ce_1‐xZr_xO₂) were synthesized by a one‐pot, facile hydrothermal method. The morphology and crystalline structure were characterized with powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and the high resolution transmission electron microscopy (HRTEM). The composition and chemical valence on the surface of the as‐prepared Ce_1‐xZr_xO₂ powders were detected by X‐ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS). The surface area and pore size distribution of as‐obtained Zr‐doped ceria HTNOs were measured by N₂ adsorption‐desorption measurement. Mechanisms for the growth of Zr‐doped ceria HTNOs are proposed as both oriented attachment and Ostwald ripening process and the formation of the hollow structure is strongly dependent on the addition of Zr⁴⁺ ions. Furthermore, the as‐obtained Zr‐doped ceria HTNOs revealed superior catalytic activity and thermal stability toward CO oxidation compared to pure ceria. It may provide a new path for the fabrication of inorganic hollow structures on introducing alien metal ions.     

Synthesis of Fe‐doped chrysotile and characterization of the resulting chrysotile fibers

This study describes the formation of Fe‐doped chrysotile fibers with partial and total substitution of Mg by Fe. Syntheses were carried out with various starting mixtures (oxides, pure synthetic forsterite) in an externally heated pressure vessel in controlled hydrothermal conditions: temperature, 270 – 400 °C; pressure, 0.5 – 2 kbar; duration of treatment 160 – 480 hours. Pure synthetic forsterite was prepared by the flux growth technique. The starting material and run products were characterized by X‐ray powder diffraction (XRPD), scanning and transmission electron microscopies combined with energy‐dispersive spectrometry (SEM‐EDS and TEM‐EDS), differential scanning calorimetry (DSC) and thermogravimetry (TG). Variations observed in abundance and size of Fe‐doped chrysotile fibers were attributed to different experimental conditions for their synthesis. However, morphological shape turned out to depend on the starting mixtures used. Since natural samples are often difficult to obtain in a sufficiently pure state, these synthetic and well‐characterized Fe‐doped chrysotile fibers can be used for better understanding of the mechanisms involved in asbestos toxicity, as well as of the role of Fe in diseases induced by asbestos phases. These synthetic Fe‐doped chrysotile fibers, together with non‐toxicity testing, may also have potential for exploitation in industrial fields. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Flux growth and characterization of Ti‐ and Ni‐doped forsterite single crystals

Forsterite monocrystals doped with Ti and Ni were grown by the flux growth technique. A suitable mixture of flux (MoO₃, V₂O₅, Li₂CO₃) and nutrient was slowly cooled down to 750 °C from 1250 °C or 1350 °C. The crystals were then characterized by powder and single‐crystal X‐ray diffraction, scanning electron microscopy and differential scanning calorimetry (DSC). Variations observed in crystal size were attributed by both the varying experimental conditions in which they had been obtained, and to the amount of Ni substituted for Mg in the structure. High abundances of doped forsterite required a cooling rate of 1.8 K h^‐1. These synthetic, well‐characterized Ti and Ni doped forsterite crystals may have potential for exploitation in industrial fields. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of Zn‐doped talc in hydrothermal atmosphere

Zn‐doped talc were synthesized under hydrothermal conditions at constant reaction time and pressure of 160 hours and 2 kbar respectively, at three different temperatures (300, 500 and 650 °C) with pH‐values of 5 and 7. The starting materials and run products were characterized by X‐ray powder diffraction (XRPD), scanning electron microscopy with annexed energy‐dispersive spectrometry (SEM‐EDS), differential scanning calorimetry thermogravimetric analysis (DSC‐TG) and Fourier transform infrared (FT‐IR). The results showed that the temperature, pH‐value of the reaction mixture and amount of zinc in the starting mixture affected the growth of the Zn‐doped talc. When synthesized at low temperature talc presents low crystallinity, flawed morphology but higher content in zinc in its lattice. A thermal treatment at, or above 500 °C allowed a significant flaw reduction in talc morphology, a higher crystallinity and a lower content in dopant. When large amounts of Zn were present in the starting mixtures, Zn‐doped talc grew small in size and poorly shaped. The effect of Zn doping on some chemical/physical characteristics of the synthesized talc was also discussed.