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[en] In order to improve the tribological properties of titanium substrate, self-assembly technique was used to prepare a graphene-silane coating: RGO-APTES coating on titanium substrate. The γ-aminopropyltriethoxysilane (APTES) was used to prepare a self-assembled APTES coating as a function of adhesive interlayer, aiming to improve the assembly efficient for graphene coating. The influence of that interlayer on the assembly and tribological properties of graphene coatings on titanium substrate was investigated. Morphology, thickness, chemical characteristic and tribological tests were utilized to investigate the assembly process and tribological properties of coatings. The results show that: (1) the pH values of APTES aqueous solution plays an important role in the molecule orientation of the APTES interlayer, and thus the properties of graphene coating is influenced. When pH is approximately 8.5, the molecule orientation of the interlayer is consistent, so that it has improved adsorption effect on graphene sheets and the graphene coating is uniformly distributed and well-covered; (2) the thickness influences the tribological properties of graphene-APTES coating -- single layered APTES interlayer provides a stronger interlayer strength. The obtained RGO-APTES2 samples have novel friction reducing and wear resisting properties, and can be applied on the surface of titanium substrate as lubricating coating. (paper)
[en] Lanthanum-based thin films deposited on the phosphonate 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM) were prepared on the hydroxylated glass substrate by a self-assembling process from specially formulated solution. Chemical compositions of the films and chemical state of the elements were detected by X-ray photoelectron spectrometry (XPS). The thickness of the films was determined with an ellipsometer, while the morphologies of the original and worn surfaces of the samples were analyzed by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The tribological properties of the films sliding against GCr15 steel ball were evaluated on a UMT-2MT reciprocating friction and wear tester. As the results, the target film was obtained and reaction may have taken place between the film and the glass substrate. The tribological results show that lanthanum-based thin films are superior in reducing friction and resisting wear compared with APTES-SAM and phosphorylated APTES-SAM. SEM observation of the morphologies of worn surfaces indicates that the wear of APTES-SAM and the phosphorylated APTES-SAM is characteristic of brittle fracture and severe abrasion. Differently, slight abrasion and micro-crack dominate the wear of lanthanum-based thin films. The superior friction reduction and wear resistance of lanthanum-based thin films are attributed to the enhanced load-carrying capacity of the inorganic lanthanum particles in the lanthanum-based thin films as well as good adhesion of the films to the substrate
[en] Highlights: • CNT-containing film was self-assembled on silicon substrates. • CNTs are strongly bonded with the substrates by chemical combination between La and oxygen-containing functional groups. • CNT-containing film has excellent friction reduction, load-carrying capacity and anti-wear ability. - Abstract: Carbon nanotubes (CNTs) were functionalized with Lanthanum (La) modifier and appropriate acid-treatment methods. CNT-containing film was deposited on silicon substrates via a self-assembly process. The formation and microstructure of La treated CNTs and CNT-containing film were characterized by high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS) and water contact angle (WCA). Its tribological properties were evaluated with a UMT-2MT reciprocating friction tester. The results show that CNTs were adsorbed on silicon substrates by means of chemically bonding between La and oxygen-containing functional groups. The friction coefficient of the silicon substrates is reduced from 0.87 to 0.12 after the deposition of CNT-containing film on its surface. CNT-containing film shows excellent antiwear, friction reducing ability and load-carrying capacity due to excellent mechanical and self-lubrication properties of CNTs.
[en] Highlights: • β-NaYF_4:Yb,Er upconversion (UC) film was synthesized on silicon substrate. • Tribological test was used to qualitatively evaluate the adhesion of the UC film. • The UC film was combined with Si substrate by covalent chemical bonds. • The method used in this work can be applicable for other UC films. - Abstract: In this work, β-NaYF_4:Yb,Er upconversion (UC) film was successfully prepared on silicon (Si) substrate via self-assemble method for the first time. The chemical composition and surface morphology of the UC film were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA), X-ray power diffraction (XRD), and scanning electron microscopy (SEM) measurements. To investigate the effects of KH-560 primer film and chemical reactions on the UC luminescence properties of β-NaYF_4:Yb,Er UC film, decay profiles of the 540 nm and 655 nm radiations were measured. Furthermore, tribological test was applied to qualitatively evaluate the adhesion of the UC film. The results indicate that the UC film has been successfully prepared on Si substrate by covalent chemical bonds. This work provides a facile way to synthesize β-NaYF_4:Yb,Er UC film with robust adhesion to the substrate, which can be applicable for other UC films.
[en] This paper reports the wear behaviors of TiNi alloy processed by equal channel angular extrusion (ECAE) under dry sliding condition against GCr15 steel ring in ambient environment and at varying load and sliding distance. Worn surfaces of the deformed and annealed TiNi alloy are examined with a scanning electron microscope. It is found that the wear mass loss of the deformed and annealed TiNi alloy is one order of magnitude, which is lower than that of as-received TiNi alloy. The wear mass loss of the deformed and annealed TiNi alloy increases with the applied load and sliding distance. The wear mechanism of the deformed and annealed TiNi alloy is dominated by micro-ploughing and delamination. These results demonstrate that fine-grained structures, fabricated by ECAE, improve the wear resistance. In addition, the phase transformation temperature lag also contributes to improve the wear resistance
[en] Highlights: • β-NaYF_4 crystals with predictable size and morphology were synthesized. • The effects of pH value on controlled growth of β-NaYF_4 crystals was clarified. • The slenderness ratio linearly decreases with the increase of NaNO_3/RE"3"+ ratio. • The luminescence intensities can be modulated by pH value and NaNO_3/RE"3"+ ratio. • The emission colors can be tuned by pH value and NaNO_3/RE"3"+ ratio. - Abstract: Using a facile hydrothermal method, hexagonal β-NaYF_4:Yb"3"+ 20 mol%, Er"3"+ 1 mol% crystals with predictable size and morphology were synthesized and the upconversion (UC) luminescence properties were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectra were used to characterize the samples. The results indicated that the size and morphology of the crystals can be precisely controlled by tuning the pH values of the initial reaction solution and the molar ratio of NaNO_3 to RE"3"+ (RE = Y + Yb + Er), and the mechanism was proposed. The UC luminescence properties of β-NaYF_4:Yb"3"+/Er"3"+ crystals were found to strongly depend on the crystal morphologies and sizes. The peak area ratio of green to red (R/G) increased from 0.29 to 1.03 with pH values increasing from 3 to 10, and increased from 1.03 to 1.26 with the increase of molar ratio of NaNO_3 to RE"3"+ from 0 to 90. The emission colors were tuned from pure green to orange yellow. This study provides a facile way to synthesize β-NaYF_4:Yb"3"+/Er"3"+ crystals with predictable morphology and size, and tunable luminescence properties, which can be applicable for other rare earth fluoride compounds
[en] β-NaYF_4:Yb"3"+/Er"3"+ microcrystals codoped with Cr"3"+ ions were prepared for the first time via a facile hydrothermal method. The influence of doping concentration of Cr"3"+ ions on growth and upconversion (UC) luminescence properties of β-NaYF_4:Yb"3"+/Er"3"+ microcrystals were investigated in detail. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra and photoluminescence (PL) spectra were used for characterization. The results demonstrated that the morphology and size of β-NaYF_4:Yb"3"+/Er"3"+ microcrystals were influenced by doping concentration of Cr"3"+ ions, the possible mechanism was proposed. The UC intensity of β-NaYF_4:Yb"3"+/Er"3"+ microcrystals was significantly enhanced by doping of Cr"3"+ ions. In contrast to β-NaYF_4:Yb"3"+/Er"3"+ microcrystals without doping of Cr"3"+ ions, the green and red emission intensities of the microcrystals codoped with 15 mol% Cr"3"+ ions were enhanced by 16 and 7 times, respectively. The enhancement of the UC intensities should be ascribed to the distortion of local symmetry around Er"3"+ ions, the UC mechanism was discussed. This work will be helpful for improving the UC intensity of other lanthanide-doped UC nano- and micro-crystals. - Highlights: • β-NaYF_4:Yb"3"+/Er"3"+ crystals codoped with Cr"3"+ ions were synthesized. • The effects of Cr"3"+ ions on growth of β-NaYF_4 crystals were clarified. • The green and red UC intensities were enhanced by 16 and 7 times, respectively. • The UC mechanism of β-NaYF_4 crystals codoped with Cr"3"+ ions was proposed
[en] Silane coupling regent (3-mercaptopropyl trimethoxysilane (MPTS)) is prepared on a single-crystal silicon substrate to form two-dimensional self-assembled monolayer (SAM). The terminal thiol groups (-SH) in the film is oxidized to sulfonic acid groups (-SO3H) in situ to enhance the chemisorption property of the film. Lanthanum-based thin films are deposited on the oxidized MPTS-SAM by means of chemisorption with the -SO3H group. The surface energy, chemical composition, phase transformation and surface morphology of the films are analyzed using contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy. The results show that MPTS is a self-assembled layer on the substrate and that the terminal -SH groups of the self-assembled MPTS films are closer to the air/silane interface than the silicon atoms. The study also shows that the treatment of SAM with 30% nitric acid (HNO3) at 80 deg. C in sufficient duration can completely transform the terminal groups in the top-most layer into desirable sulfonate groups. Then the substrates coated with the sulfonated MPTS-SAM were immersed in the RE solution to form lanthanum-based thin films. The experimental results indicate that the lanthanum-based thin films are adsorbed on oxidized MPTS-SAM and that the lanthanum element with different states of oxidation exists in the thin films that are deposited on the surface of self-assembly monolayers. Also, shape analyses of the La3+ XPS peaks reveal that the rare-earth film can react with the substrate by chemical bonding and that some lanthanum molecules are adsorbed on the MPTS-SAM. The above results show that it is the -SO3H group that has good chemisorption trend
[en] Carbon fibers (CF) were surface treated with air-oxidation and rare earths (RE), respectively. The friction and wear properties of polytetrafluoroethylene (PTFE) composites filled with differently surface treated carbon fibers, sliding against GCr15 steel under dry sliding condition, were investigated on a block-on-ring M-2000 tribometer. Experimental results revealed that RE treatment largely reduced the friction and wear of CF reinforced PTFE (CF/PTFE) composites. The RE treated composite exhibited the lowest friction and wear under dry sliding. Scanning electron microscopy (SEM) investigation of worn surfaces and transfer films of CF/PTFE composites showed that RE treated CF/PTFE composites had the smoothest worn surface under given load and sliding speed, and a continuous and uniform transfer film formed on the counterface. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RE treatment, and more carboxyl groups were introduced onto CF surfaces after RE treatment. The increase in the amount of oxygen-containing groups increased the interfacial adhesion between CF and PTFE matrix, and accordingly increased the tribological properties of the composite