Min Qu

Effects of hydrogen atoms on surface conductivity of diamond film

To investigate the effects of surface chemisorbed hydrogen atoms and hydrogen atoms in the subsurface region of diamond on surface conductivity, models of hydrogen atoms chemisorbed on diamond with (100) orientation and various concentrations of hydrogen atoms in the subsurface layer of the diamond were built. By using the first-principles method based on density functional theory, the equilibrium geometries and densities of states of the models were studied. The results showed that the surface chemisorbed hydrogen alone could not induce high surface conductivity. In addition, isolated hydrogen atoms in the subsurface layer of the diamond prefer to exist at the bond centre site of the C-C bond. However, such a structure would induce deep localized states, which could not improve the surface conductivity. When the hydrogen concentration increases, the C-H-C-H structure and C-3Hbc-C structure in the subsurface region are more stable than other configurations. The former is not beneficial to the increase of ...

Electrochemical Behaviors of Chlorophenol Aqueous Solutions at Boron- Doped Diamond Electrode

The electrochemical behaviors of different chlorophenols at boron-doped diamond thin film electrode were investigated. Four chlorophenols, the 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6- TCP) and pentachlorophenol (PCP), with various number of chlorine atoms in the benzene rings, were studied by using cyclic voltammetry at different scan rates over the potential range of -1 V to 2.5 V (vs MSE). The results indicated that the reactions of the 2-CP, 2,4-DCP and 2,4,6-TCP at the diamond electrode are irreversible and controlled by diffusion, and the irreversible trend increases with the decrease of the chlorine atom number in the benzene ring. However, the activity of the boron-doped diamond film electrode does not depend on the number of the chlorine atom. Different from the three chlorophenols, fouling of the electrode occurs in PCP solutions. The possible electro-oxidation mechanisms are discussed for different chlorophenols.

Voltammetric and impedance behaviours of surface-treated nano-crystalline diamond film electrodes

The electrochemical performances of hydrogen- and oxygen-terminated nano-crystalline diamond film electrodes were investigated by cyclic voltammetry and AC impedance spectroscopy. In addition, the surface morphologies, phase structures, and chemical states of the two diamond films were analysed by scanning probe microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. The results indicated that the potential window is narrower for the hydrogen-terminated nano-crystalline diamond film than for the oxygen-terminated one. The diamond film resistance and capacitance of oxygen-terminated diamond film are much larger than those of the hydrogen-terminated diamond film, and the polarization resistances and double-layer capacitance corresponding to oxygen-terminated diamond film are both one order of magnitude larger than those corresponding to the hydrogen-terminated diamond film. The electrochemical behaviours of the two diamond film electrodes are discussed.

Tribological Behavior of Ion Implanted AISI 440C Stainless Steel under Oil Lubricated Condition

The tribological behaviors of nitrogen and titanium ion implanted AISI 440C stainless steel were studied by using an oscillating ball-on-disk tribometer under oil lubricated condition. The results showed that the ion implantations would significantly decrease the friction coefficient of the samples. To interpret the effect mechanism of the ion implantation on tribological performance, the surface morphology and oil wettability of the ion implanted samples were investigated by using a three-dimensional white interferometer and a contact angle analyzer, respectively. In addition, the surface structures and components of the samples were analyzed by using XRD and XPS techniques. The results indicated that the low friction coefficients of the ion implanted samples can be attributed to the new phases formed on the sample surfaces. For nitrogen ion implanted sample, the metal nitrides, supersaturated interstitial N and some C-O-N compounds appear on the sample surface. For titanium ion implanted sample, apart from TiO2 and TiC phases form at the AISI 440C steel surface. Those components increase the surface energy of the AISI 440C steel and are in favor of the formation of the thin oil film.

Effect of Interval Aging Mode on IMC Growth between Low Ag Content Sn-0.3Ag-0.7Cu-0.5Bi-Ni and Cu Substrate

To simulate the application environment of a number of electronic products, the growth of Sn-0.3Ag-0.7Cu-0.5Bi-Ni/Cu solder joints with low content of Ag was investigated during aging in an interval mode. It shows that the intermetallic compound (IMC) (Cu,Ni)6Sn5 layer becomes thicker with increasing aging time. The growth of IMC (Cu,Ni)6Sn5 layer during aging follows the diffusion control mechanism. Furthermore, it is demonstrated that there is no IMC Cu3Sn layer appear whatever increasing the aging time. It is explained the phenomenon is mainly attribute to the interval aging mode. According to kinetics, the activation energy is not high enough to overcome the energy obstacle due to the interval aging mode and finally the Cu3Sn phase doesn’t form. Hence, the reliability of solder joints is improved. Keywords-Sn-0.3Ag-0.7Cu-0.5Bi-Ni solder; intermetallic compound; interval aging; thickness

Studies on the Influence of Ti on Mechanical Properties in A356 Alloy

The effect of different contents of Ti on mechanical properties in A356 alloy was researched in this study. The results reveal that the variation is not following the law that the more the content of Ti is, the better the tensile strength and hardness would be in the range of 0% to 7.5% Ti. However, the mechanical properties undergo improving first as the content of Ti is less than 0.3% and then reducing with the addition of Ti. Based on the different contents of Ti, the tensile fracture surfaces are studied to verify the effect of different contents of Ti, It is concluded that the variations of tensile fracture surfaces are in accordance with those of mechanical properties.

Effect of Ti Content on Microstructure and Hardness of A356 Alloy

In order to refine the microstructure of A356 alloy, the effect of different contents of Ti on A356 alloy was analyzed with scanning electron microscopy (SEM). Experimental results show that it is not following the law of the more the content of Ti is, the finer the microstructure in the range of 0% to 7.5% Ti. However, the microstructure undergoes a first refining as the content of Ti is less than 0.3% and then coarsening with the increasing of Ti. Further, the mechanism of grain refiner is explained from three aspects. Finally, the hardness of A356 alloy is studied to verify the effect of different contents of Ti. The results confirm that the variety of hardness is in accordance with that of microstructure.

Cold Fusion Experimental Research on Repairing Shaft of Automatic Transmission

The cold fusion at room temperature is used to repair the shaft of automatic transmission. In the experiment, the low-carbon steel, the high-carbon steel and 65Mn steel were selected as restorative materials. The microstructures of shaft repaired with different materials were observed by the scanning electric microscope (SEM) after the shafts were repaired. The results show that the microstructure of shaft which was repaired by the high-carbon steel and 65Mn steel is martensite that has high hardness and better wear resistance. The interface of the matrix and filled material is metallurgic combine. The cold fusion can improve the surface properties of the matrix when the suitable material is selected as restorative material.

Microstructure Evolution of Directionally Solidified Al-Cu Alloys

The microstructure evolution of Al-Cu alloys with different compositions is investigated in directional solidification. Two distinctly different microstructure evolution mechanisms are obtained in Al-0.85%Cu and Al-4%Cu systems, respectively. In Al-0.85%Cu alloy, it shows a peculiar phenomenon, the microstructure evolution is always cells and no dendrites are obtained. In other words, the cells undergo several transitions as the pulling velocity increasing from 15μm/s to 300μm/s, they follow the sequences: mixed microstructure of pox and banded cells →mixed microstructure of polygonal and banded cells →banded cells →elongated cells. Particularly, it is studied what caused the dendrites not appear in Al-0.85%Cu system. Finally, it comes to the conclusion that there are two aspects which lead to the phenomenon: a dilute alloy composition and a relatively higher temperature gradient.