Journal of Wuhan University of Technology-Mater. Sci. Ed.

Diamond-like carbon (DLC) films have recently been pursued as the protection of MEMS against their friction and wear. Plasma enhanced chemical vapor deposition (PECVD) technique is very attractive to prepare DLC coating for MEMS. This paper describes the preparation of DLC films using twinned electron cyclotron resonance (ECR) microwave PECVD process. Raman spectra confirmed the DLC characteristics of the films. Fourier-transform infrared (FT-IR) characterization indicates the carbon is bonded in the form sp3 and sp2 with hydrogen participating in bonding. The surface roughness of the films is as low as approximately 0.093 nm measured with an atomic force microscope. A CERT microtribometer system is employed to obtain information about the scratch resistance, friction properties, and sliding wear resistance of the films. The results show the deposited DLC films have low friction and good scratch/ wear resistance properties.

Magnesium alloy Mg-3%Al-1%Zn (AZ31) billets prepared from equal channel angular pressing (ECAP) were utilized in low-cycle fatigue tests in order to investigate their fatigue life. Fully reversed strain-controlled tension-compression fatigue tests were conducted at the frequency of 1 Hz in ambient air. The microstructures were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The hysteresis loops of the ECAP processed and conventionally extruded samples display obviously different shapes in the total strain amplitude range from 0.2% to 0.6%. Accordingly, the low cycle fatigue lives of ECAP processed samples are found to be longer than those of extruded samples, which can be attributed to the different in the hysteresis energy incorporating tensile strain energy.

Re-swelling capacity is a key factor influencing the self-sealing efficiency of superabsorbent polymers (SAPs) in concrete. In this paper, a new parameter (re-swelling ratio, η), the volume ratio of the crack which was filled with the expansive SAPs and the dry SAPs, was given to quantify the re-swelling capacity of a single SAPs particle. An innovative immersion test was used to study the η value of SAPs in the hardened cement paste with an artificial crack. Moreover, the influence of the crack width and particle size on the sealing efficiency of SAPs in the cracked paste was investigated by a water permeability test. The results showed that the mass ratios of the expansive SAPs in an artificial crack were less than those in a free state. The η value of SAPs in the hardened paste with an artificial crack increased with the increase of the crack width due to the restricting effects of the crack. The expansive SAPs in the cracked paste could totally seal or partly seal the crack within the original void. Moreover, the sealing efficiency of SAPs slightly increased with the rise of the crack width (0.25 to 0.5 mm) and the reduction of the particle size. This research demonstrates that the crack width in concrete and the particle size of SAPs are the key factors influencing the re-swelling behavior of SAPs which should be taken into consideration when designing the self-sealing concrete containing SAPs.

Onion-like carbon (OLC) was fabricated by annealing nanodiamond at 1000 °C for 2 hours in low vacuum (1 Pa). The OLC was characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and differential scanning calorimetry (DSC). The experimental results show that the OLC exhibits similarity to the original nanodiamond particles in shape. The size of the OLC is found to be approximately 5 nm. The transformation mechanism of the OLC from nanodiamond was discussed also.

An approach named “pore structure collapsed replication route” has been developed to prepare mesoporous WC materials with a high surface area (105 m2/g) and crystallized framework at a temperature as low as 700 °C. The XRD, TEM, EDS, and BET characterizations were conducted to analyze the effects of the synthesis parameters and the template types on the structure of mesoporous WC. The compaction on the templates is the key to form mesoporous structure of WC while the templates help to control the size of crystalline. At a content of 7 wt% for the precursor of WC, the mesoporous WC could be formed with well ordered structure.

The crystallization behavior and transparent property of MgO-Al2O3-SiO2 (MAS) glasses with TiO2 and TiO2+ZrO2 as nucleating agents were discussed by differential thermal analysis, X-ray diffraction, field emission-environment scanning electron microscope, energy dispersive spectrum and UV-VIS-NIR scanning spectrophotometer. It was found that the glass crystallized at 950 °C with ZrO2 less than 3% could obtain transparent glass ceramic, which presented purple to colorless. With the nucleating agent additives (5% TiO2+3% ZrO2), the colorless transparent glass-ceramics with spinel as the main crystal phase could be prepared, and the transmittance reached about 80%. As the crystallized temperature increase to 1 000 °C, besides spinel(MgAl2O4), sapphirine (Mg3.5Al9Si1.5O20) and ZrTiO4 precipitated from matrix glass, and the transmitance of glass-ceramic decreased.

The effect of relative humidity on the corrosion-resisting property of fluorocarbon coating was investigated by water vapor transmission technique and electrochemical impedance spectroscopy technique. Measurements were carried out on samples, which were tested in an accelerated corrosion environment for the same time (300, 500, 800 and 1000 h). The experimental results were obtained as follows: (i) The water absorption, coating resistance and corrosion rate of metal under the coating changed with relative humidity and aging time, the results obtained by EIS are good consistent with those by water vapor transmission technique; (ii) when the subject investigated presented two time constant, the goodness of fit by EEC R(C(R(CR))) was inferior to that by EEC R(C(R(QR))), but the error of parameters acquired from the former was smaller, by which we could analyze the experiment result quantitatively. With the appearance of diffusion layer on the metal, the difference of metal capacitance was aggravated, the error of parameters acquired from EEC R(C(R(C(RW)))) was bigger than that from EEC R(C(R(Q(RW)))).

The nanosized Ca3Co2O6 powder was synthesized via sol-gel process. The phase composition was characterized by means of X-ray diffraction. Polycrystalline samples of Ca3Co2O6 were prepared by a sintering procedure of nanosized power. The seebeck coefficient and electrical conductivity of the samples were measured from 450K up to 750K. The results show that the Seebeck coefficient increases with the increasing temperature. The electronic structures were calculated using the self-consistent full-potential linearized augmented plane-wave (LAPW) method within the density functional theory. The relationship between thermoelectric property and electronic structures was discussed.