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 and tribological properties of Mo‐doped WSe2 Nanolamellars

The Mo‐doped WSe₂ nanolamellars have been successfully prepared via solid‐state thermal (750 °C) reaction between micro‐sized W, Mo with Se powders under inert atmosphere in a closed reactor and characterized by X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the morphologies of the as‐prepared products changed from microplates to nanolamellars to aggregations composed of nanoparticles with the doping of Mo powders. And the sizes of crystallites evidently reduced while the contents of dopant increased within a certain limit (1 wt.%–7 wt.%). The tribological properties of the as‐prepared products as additives in HVI750 base oil were investigated by UMT‐2 multispecimen tribotester. The friction coefficient of the base oil containing Mo‐doped WSe₂ nanolamellars was lower and more stable than that of WSe₂ nanolamellars. A combination of rolling friction, sliding friction, and stable tribofilm on the rubbing surface could further explain the good friction and wear properties of Mo‐WSe₂ nanoparticles as additives than that of WSe₂.     

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.     

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 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)     

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.     

Facile synthesis of ultrathin NbTe2 nanosheets for enhanced tribological properties as a lubricant additive

Graphite‐like bulk NbTe₂ powders were prepared by a facile solid phase synthesis process and ultrathin NbTe₂ nanosheets were obtained by using wet ball milling induced delamination. The X‐ray diffraction analysis illustrated that the reduction of particle size was mainly along the stacking direction of the basal planes without great influence on the short range order of NbTe₂ crystals. Scanning electron microscopy, transmission electron microscopy, and atomic force microscope observations revealed that the longitudinal dimension of NbTe₂ samples changed into the nanoscale from the larger micron level after mechanical exfoliation. The exfoliated NbTe₂ nanosheets had better long‐term dispersion stability in paraffin oil than bulk NbTe₂. The tribological properties were determined on an UMT‐2 ball‐on‐disk friction and wear tester. The results indicated that the paraffin oil with NbTe₂ nanosheets exhibited better lubricating behaviors with the lower friction coefficient and wear rate in comparison with the bulk NbTe₂. It was demonstrated that NbTe₂ nanosheets could easily enter into a point of friction contact, and form an available tribofilm to prevent the direct contact between counterparts during the friction process. Furthermore, this work shows the potential applications of ultrathin NbTe₂ nanosheets in the field of tribology.     

Synthesis of zinc oxide crystals with different shapes from zincate aqueous solutions stabilized with triethanolamine

ZnO crystals were synthesized from basic aqueous solutions including zincate ions stabilized with triethanolamine (N(C₂H₄OH)₃, teaH₃) by heating at 60°C. The influence of the basicity of the solutions on the morphology of the ZnO crystals was examined. The aqueous solutions were prepared using ZnSO₄·7H₂O, N(CH₃)₄OH (TMAOH), and teaH₃ as a zinc source, a base, and a stabilizer, respectively, at a zinc concentration of 0.2 M at a teaH₃ / Zn molar ratio of 4. Clear solutions were obtained at a molar ratio of TMAOH / Zn ≥ 3.0. When the clear solutions, in which glass or polyester substrates were placed, were heated at 60°C, agglomerates of ZnO crystals were deposited on the substrates in the TMAOH / Zn range from 3.0 to 3.6. With increasing the TMAOH / Zn ratio, the shape of the resulting ZnO crystals changed from a short asymmetric column with a hexagonal flat edge and a rounded one, through a rocket‐like shape formed by intergrowth, to a hexagonal rod. Although no films of ZnO were formed, ZnO crystals with different shapes were synthesized. When the glass substrates pre‐coated with a ZnO thin film by a sol‐gel method were used, highly oriented, dense ZnO films were formed. The films consisted of rod‐like crystals aligned normal to the substrate surface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Direct melt crystal growth of isotactic polybutene‐1 trigonal phase

The morphology, crystalline structure and crystal growth kinetics of melt‐crystallized thin isotactic polybutene‐1 films have been studied with transmission electron microscopy, electron diffraction and optical microscopy. It is demonstrated that a bypass of tetragonal phase crystallization and direct melt crystal growth of the trigonal phase can be achieved via self‐seeding at atmospheric pressure using solution‐grown trigonal crystals as nuclei. Electron microscopy and optical microscopy observations show that melt‐crystallized isotactic polybutene‐1 single crystals of the trigonal phase have rounded or hexagonal morphologies around 75°C. The growth rate of trigonal crystals in the melt has been obtained by in‐situ optical microscopy. The growth rate of trigonal crystals in the melt is 1/100 and 1/1000 that of tetragonal crystals in the melt around 70 and 90°C, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and properties of α‐Fe2O3 nanorods

We report synthesis of α‐Fe₂O₃ (hematite) nanorods by reverse micelles method using cetyltrimethyl ammonium bromide (CTAB) as surfactant and calcined at 300 °C. The calcined α‐Fe₂O₃ nanorods were characterized by X‐ray diffraction (XRD), high‐resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The result showed that the α‐Fe₂O₃ nanorods were hexagonal structure. The nanorods have diameter of 30‐50 nm and length of 120‐150 nm. The weak ferromagnetic behavior was observed with saturation magnetization = 0.6 emu/g, coercive force = 25 Oe and remanant magnetization = 0.03 emu/g. (© 2010 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 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)     

Microstructure and phase transformation of Ti3AC2 (A = Al,Si) in hydrofluoric acid solution

In this paper, Ti₃AC₂ (A = Al, Si) were prepared by pressureless argon shielding synthesis technique. The microstructure and phase transformation of as‐prepared Ti₃AC₂ (A = Al, Si) in hydrothermal hydrofluoric acid (HF) solution were investigated systematically. Results showed that the obtained Ti₃AlC₂ and Ti₃SiC₂ were closely aligned layered structure. In hydrothermal HF solution, Al or Si element was preferentially etched from the layered structure, inducing obvious transformation of microstructure and phase composition. For Ti₃AlC₂, Al atoms diffused out of the structure and reacted with HF to form AlF₃•H₂O, which induced the rearrangement of the Ti and C atoms, and finally resulted in the formation of TiC_x cubic phase. With the hydrothermal temperature and reaction time increasing, the TiC_x phase gradually disappeared and the grain size of AlF₃•H₂O gradually increased. When Ti₃SiC₂ was immersed in hydrothermal HF solution, the main products were TiC and SiC. Interestingly, with the hydrothermal treatment temperature and reaction time increasing, TiC gradually disappeared, while SiC nearly kept unchanged. This can be explained that SiC was covalently bonded carbide, while TiC was metallically bonded, having relatively weak bond energy and consequently being unstable in hydrothermal HF solution.     

Crystallisation and performance characteristics of high‐temperature annealed electroless Ni‐W‐P coatings

Electroless deposition of Ni–P based alloys is a well‐known commercial process that has numerous applications because of their excellent anticorrosive and wear properties. However, for some special occasions, like the components for gas making furnaces in chemical fertiliser industry, the coatings must be reinforced to withstand short‐term high temperatures between 600 °C and 700 °C as well as light erosive wear. Therefore, co‐deposition of high melting point metallic element, W, has been considered as a preferred choice. In the present study, two Ni–W–P alloy coatings were deposited on mild steel panels from different alkaline baths. The microstructures of the annealed coatings were characterised by quantitative XRD, XPS and SEM/EDS analysis techniques and their microhardness, friction and wear behaviour, corrosion mechanism as well as microstrain and residual stress are discussed in comparison with the as‐plated state. The results indicate that the hardness mainly depends on the volume fraction and crystallite size of Ni₃P phase; the uniform corrosion in sulfuric acid solution is closely related to the ratio of I_Ni/I_Ni3P as well as grain size. The wear mechanism of the high‐temperature annealed coating is dominated by abrasive wear, but the wear in the early stages started from mild adhesive wear caused by adhesion between the friction couples. Electroless deposited Ni‐W‐P alloys with high phosphorus present relatively good properties, including hardness, wear and corrosion resistance when 700 °C is applied for annealing process.     

SiC crystal growth from transition metal silicide fluxes

SiC crystal growth in transition metal silicide melts was investigated by using spontaneous infiltration and solution methods. In the infiltration experiments, SiC powder preforms were infiltrated with Fe_xSi_y (Fe₃Si, Fe₅Si₃ and FeSi) and CoSi melts. The dissolution and precipitation of SiC led to SiC crystals growth in the infiltrated Fe₅Si₃ and CoSi melts, SiC particles coalescing in FeSi and free carbon precipitation in Fe₃Si. In the solution experiments, carbon from the graphite crucible dissolved in and reacted with FeSi₂ and Ti_2.3Si_7.7 to form SiC crystals. Scanning electron microscopy (SEM), X‐ray diffraction (XRD) and Raman scattering spectrometer were employed to investigate SiC crystals growth. Based on the investigation, the effect of solution content on the SiC crystal growth, the growth mechanisms in both methods and prototypes of the SiC crystals are also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the crystallochemical origin of the disordered form of Ba7(EuII)F12Cl2 and the structural changes induced at high temperature

The crystal structure of the disordered modification of Ba₇F₁₂Cl₂ has been carefully re‐examined on several new crystals prepared under different conditions of synthesis. All single crystal structure refinements reveal a residual electron density of ∼3 e^–/ų in the 0,0,0 position which is explained by the introduction of a small amount of sodium ions in the crystal. The title compound transforms from a disordered to an ordered modification at ∼800 °C. New structural data show a change in space group from P6₃/m to P6. During this process, a slight chemical change and the formation of nano‐channels in the crystals is observed by electron microscopy. These changes were further studied by electron microprobe analysis, by spectroscopic methods and thermal analysis. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of epitaxial Ti3GeC2 thin films on 4H-SiC(0001)

Epitaxial Ti₃GeC₂ thin films were deposited on 4° off-cut 4H-SiC(0001) using magnetron sputtering from high purity Ti, C, and Ge targets. Scanning electron microscopy and helium ion microscopy show that the Ti₃GeC₂ films grow by lateral step-flow with {112?0} faceting on the SiC surface. Using elastic recoil detection analysis, atomic force microscopy, and X-Ray diffraction the films were found to be substoichiometric in Ge with the presence of small Ge particles at the surface of the film.     

Surfactant directed synthesis of mesoporous alumina and α‐alumina single crystal

Mesoporous Al₂O₃ were positively synthesized via treatment of the freshly precipitated amorphous alumina gel using aluminium sulphate as aluminium source, and sodium dodecyl sulphate (SDS) as structure‐directing agent (SDAs). The microstructures, morphologies and textural properties of the as‐prepared materials were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM) and thermo gravimetric analysis (TG‐DTA). The calcined product at 600 °C was highly porous in nature having a BET surface area of 42 m²/g. These porous Al₂O₃ exhibits excellent adsorption performance for Congo red and the corresponding decolourisation efficiencies reached 99% in just 15 min at 27 °C. The subsequent calcined product at 1200 °C is the alpha alumina single crystal hexagonal platelets with rhombohedral crystallization.     

Flux growth of straw‐like rutile monocrystals

Millimetric straw‐like rutile monocrystals were grown by the flux growth technique. A suitable mixture of flux (MoO₃, V₂O₅, Li₂CO₃) and amorphous TiO₂ gel was slowly cooled down to 750°C from 1250°C or 1350°C. The best yields of straw‐like rutile were obtained with a nutrient/flux ratio and a cooling rate in the range 0.015‐0.006 and 1.8‐1.9 K h^‐1, respectively. The hollowed crystals were characterized by powder and single‐crystal X‐ray diffraction, scanning electron microscopy, microthermometry, and µ‐Raman spectroscopy. As for skeletal crystal, the formation of axial canals in rutile is attributed to a lack of nutrient due to the viscosity of the melt and the high growth rate along [001]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Contribution to the tin‐rich region of the Sn‐Zn‐Ti system

The tin‐rich region of the system Sn‐Zn‐Ti system has been studied by diffusion couples, differential scanning calorimetry and electron microprobe analyses. Ternary eutectic reaction occurs at 193.7°C near to the binary tin‐zinc eutectic point and titanium content less than 0.9 at.% Ti. Three ternary compounds with approximate formulae: Ti₈Sn₅Zn₂ to Ti₅Sn₃Zn, TiSn₄Zn₅ and Ti₂Sn₄Zn₃ have been observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)