Qunji Xue

Characterization of hydrogenated diamond-like carbon films electrochemically deposited on a silicon substrate

Diamond-like carbon (DLC) films were deposited on a Si substrate by electrolysis in a methanol solution at ambient pressure and low temperature. The morphology and microstructure of the resulting DLC films were analysed using atomic force microscopy, Raman spectroscopy, Fourier transformation infrared spectrometry, x-ray photoelectron spectroscopy (XPS), and x-ray excited Auger electron spectroscopy (XAES). The surface energy and mechanical properties of the DLC films were examined, and the growth mechanism of the DLC films in liquid phase electro-deposition is discussed as well. The results of the study show that the hydrogenated diamond-like carbon films are smooth and compact. The percentage of sp3 carbon in the DLC films is determined as 55?60%, based on the corresponding XPS and first-derivative XAES spectra of graphite, diamond, and the tested films. The DLC films show low surface free energy, good mechanical properties, excellent friction?reduction and wear-resistance. It is suggested that methanol dissociates to generate the active species of and C2H4 at high voltage applied to the electrode, followed by the generation of the alkyl chain [?CH2?CH2?]n whose C?C and C?H bond lengths and C?C?C and H?C?H bond angles are close to that of diamond. Subsequently, a diamond-like structure was formed by the ordered dehydrogenation of a short-chain [?CH2?CH2?]n in the electrolysis process.

A simple and 'green' synthesis of polymer-based silver colloids and their antibacterial properties.

Stable silver colloids were prepared using polyethylene glycol (PEG) as an environment friendly reduction agent and stabilizer, and with H2O as solvent. The Ag colloids were characterized by UV/VIS spectroscopy, transmission electron microscopy (TEM), and atom force microscopy (AFM). TEM and AFM of the sample showed uniform and monodispersive particle distribution in the colloids. The particle size is found to be less than 10 nm. The antibacterial activity of the Ag colloids was also studied. The results showed that the sample had high antibacterial activity toward Gram-positive and Gram-negative bacteria, and fungi.

Tribological behavior of gradient modified layer on 2024 aluminum alloy modified by plasma-based ion implantation

The N-pre-implanted 2024 aluminum alloy was implanted with Ti and N, or implanted with Ti, and then with Ti and N by plasma-based ion implantation (PBII) to form two gradient layers, respectively. The composition depth profiles of the gradient layers were characterized by X-ray photoelectron spectroscopy. A series of ball-on-disk wear experiments have been carried out in ambient air, to investigate the tribological behavior of the gradient layer against steel ball under dry and un-lubricated conditions, employing various applied loads and a constant sliding speed. The results revealed that tribological properties of the gradient layers were improved markedly in contrast with those of the unmodified sample, and strongly dependent on their composition depth profiles. The gradient layer implanted with Ti, and then with Ti and N was much thicker and contains higher N, thus it corresponded to higher hardness which slowly decrease from surface to substrate and the optimal tribological properties including higher load carrying capacity. As load was increasing, the tribological properties decreased, and the adhesive degree increased since the gradient layer became thinner rapidly. Of course, more proper gradient layers will be obtained as the qualified candidates in some particular engineering applications by optimizing PBII parameters.

The structure and tribological properties of gradient layers prepared by plasma-based ion implantation on 2024 Al alloy

Using plasma-based ion implantation, two types of gradient layers have been prepared on 2024 Al alloy. One is prepared by N-implantation then C-deposition, the other adds an interlayer composed of a Ti layer and a Ti–N layer between N-implantation and C-deposition. C-deposition is carried out at various implanting voltages or C2H2/H2 ratios. The composition depth profiles of these layers were characterized by x-ray photoelectron spectroscopy. The structure, morphologies and microstructure of the C layers were studied using Raman spectroscopy, atomic force microscope and transmission electron microscope, respectively. The surface hardness was measured with a Knoop tester and a mechanical property microprobe. The dry ball-on-disc wear tests were performed in ambient air. The gradient layer without interlayer is composed of an N-implanted layer rich in AlN and a diamond-like carbon (DLC) layer (film), and the two layers are connected with a C–Al transition layer containing Al4C3. The Ti layer rich in α -Ti and the N-implanted layer are connected by a Ti–Al transition layer containing TiAl3, while the Ti–N layer rich in TiN and the DLC film are connected by a C–Ti transition layer containing TiC, TiCN, etc. Thus, the gradient layer with interlayers has optimized the gradient structure. DLC films are compact and amorphous, contain high sp3/sp2 ratios and depend on the implanting voltage and the C2H2/H2 ratio. Similarly, these gradient layers exhibit significant improvement in morphologies, surface hardness and tribological properties; the interlayer, the implanting voltage and the C2H2/H2 ratio all have prominent effects on these properties.

Preparation of SnO2 Nanocrystals by Microwave Irradiation and Their Catalytic Activity

Microwave irradiation technique was applied to the preparation of SnO2 nanocrystals by hydrolyzing tin(IV) chloride. The crystallization time was shortened drastically to 11 min from several hours for typical hydrothermal synthesis. The synthesized products were characterized by XRD, TEM, and TG‐DTA. The size of crystals changed from 3 to 24 nm when power and time of microwave irradiation, as well as the difference in calcination temperatures were varied, indicating a possibility for controlling the crystal size. The use of polyvinyl alcohol (PVA) as a protective agent effectively prevented the synthesized particles from agglomeration and favored formation of spherical particles. The catalytic activity of the SnO2 nanocrystals for the esterification of acetic acid with ethanol was also studied.