Binbin Li

Dopant position of Co atom in Zn1−xCoxO nanoparticles studied by extended X-ray absorption fine structure

Zn1−xCoxO nanoparticles were prepared by sol–gel method. The microstructure and dopant position were studied by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS). The XRD patterns did not show any signal of impurity in the Zn1−xCoxO nanoparticles with Co concentration from xxa0=xa00.01 to 0.08. Neither did the HRTEM image for the highest concentration sample with xxa0=xa00.08. The nanoparticles have also been investigated by the EXAFS measurements at Co k-edge. The radical distribution functions, the fitting result of bond length and coordination numbers, indicated there was an impurity in the highest Co concentration sample with xxa0=xa00.08. Although most of the Co atoms were substituted for Zn sites in ZnO with xxa0=xa00.08, a few of Co atoms formed a microstructure similar to Co3O4, which was not found in the XRD and HRTEM. The room temperature ferromagnetic behaviour was found for xxa0=xa00.01 sample by superconducting quantum interference device .

Sound insulation of multi-layer glass-fiber felts: Role of morphology

Glass-fiber felts have emerged as a popular material for noise reduction. This paper investigates the effect of various morphologies (micro-layer, macro-layer and air-layer) of glass-fiber felts on sound insulation. The sound transmission loss is measured by a Brüel & Kjár (B&K) impedance tube. The results show that the sound insulation of glass-fiber felts can be improved by increasing the number of macro-layers. The comparison between the macro- and micro-layer of glass-fiber felts on sound insulation is systematically carried out. Notably, the sound transmission loss of glass-fiber felts with similar areal density and thickness favors macro-layer structures over micro-layer structures. A simple model is established to explain this phenomenon. In addition, the sound transmission loss exhibits period fluctuations due to the presence of the air-layer between glass-fiber felts, which can be theoretically explained by the resonance effect. It is found that sound transmission loss can be improved by increasing the number of air-layers.

Effect of cross-sectional morphology and composite structure of glass fiber felts on their corresponding acoustic properties

This paper presents the effect of cross-sectional morphologies and composite structures of glass fiber felts on their corresponding acoustic properties. Glass fiber felts with random and layered cross-sectional structure are produced by centrifugal-spinneret-blow system. Acoustic properties are determined by a B&K impedance tube. The results show that sound transmission loss (STL) of glass fiber felts with layered cross-sectional structure exhibit greater than that with random cross-sectional structure. However, there is a little difference between the absorption coefficient values for random and layered cross-section. It means that glass fiber felts with layered cross-section are better to improve the sound insulation. With the increase of thickness, STLs of glass fiber felts with the same areal density do not increase monotonically due to the changing of porosity and characteristic impedances. Different glass fiber felts with layered cross-sectional structure are combined to form a variety of composite structures. It finds that assembly order of glass fiber felts have an effect on the total sound insulation. The large mismatch between the acoustic impedances causes multiple reflections leading to the best STL.

Mechanical properties and mechanical behavior of (SiO2)f/SiO2 composites with 3D six-directional braided quartz fiber preform

Abstract (SiO2)f/SiO2 composites reinforced with three-dimensional (3D) six-directional preform were fabricated by the silicasol-infiltration-sintering method. The nominal fiber volume fraction was 47%. To characterize the mechanical properties of the composites, mechanical testing was carried out under various loading conditions, including tensile, flexural, and shear loading. The composite exhibited highly nonlinear stress-strain behavior under all the three types of loading. The results indicated that the 3D six-directional braided (SiO2)f/SiO2 composites exhibited superior flexural properties and good shear resistant as compared with other types of preform (2.5D and 3D four-directional)-reinforced (SiO2)f/SiO2 composites. 3D six-directional braided (SiO2)f/SiO2 composite exhibited graceful failure behavior under loading. The addition of 5th and 6th yarns resulted in controlled fracture and hence these 3D six-directional braided composites could possibly be suitable for thermal structure components.

Effect of Service Time of Centrifugal Pan on Glass Wool

In this article, the effect of service time of centrifugal pan on glass wool has been studied in centrifugal-spinneret-blow (CSB) process. Glass wool was sampled every 24 h and examined by scanning electron microscopy (SEM) and vertical optical microscopy (VOM). The relationship between mean fiber diameter and service time is fitted by exponential growth function. We nominate the service life (τ) of centrifugal pan, where the mean fiber diameter (dτ) of service time is e times as large as that of initial time (d0). The service life (τ) was determined to be 273 h, where the mean fiber diameter was determined to be 10 µm. The centrifugal pan was made of Ni-Cr alloy. It was corroded by hot glass fluid with centrifugal force. With increased service time, corrosion accumulated, and the pore diameter was enlarged, which caused the mean fiber diameter to increase with the service time.

Synthesis and characterization of highly preferred orientation polycrystalline Co-doped ZnO thin films prepared by improved sol–gel method

Highly preferred orientation polycrystalline Zn1−xCoxO (xxa0=xa00, 0.03, 0.06, 0.09) thin films were prepared by improved sol–gel method on quartz glass substrates. The structural, optical and magnetic properties were investigated. The X-ray diffraction patterns show that all the samples have the same structure with one highly oriented c-axis (002) peak. None of the samples showed any signal of impurity phases. The c-axis lattice constant increased linearly with the increase in Co doping content, indicating that the doping of Co ions into the host lattice did not change the wurtzite structure of ZnO. UV–Vis transmittance spectroscopy showed that the average optical transmittance of the films is about 90xa0% in visible wavelength range. The optical band gap (Eg) decreased with increasing Co content. Also, the results of vibration sample magnetization ascertained the ferromagnetic behavior of Co-doped ZnO, having a Curie temperature higher than room temperature.

Characterization of structure and physical properties of centrifugal glass fiber felts and preparation technology

In this paper, glass fiber felts are fabricated by centrifugal-spinneret-blow process. Swing cylinder is designed to obtain a micro-layer structure, and the phase difference of two swing cylinders is π/2u2009+u20092kπ. Tensile strength, flexural rigidity, and thermal conductivity of various glass fiber felts are investigated. The experimental results indicate that the tensile strength of micro-layer glass fiber felts and random glass fiber felts is 0.015u2009MPa and 0.013u2009MPa, respectively. In addition, the tensile strength of glass fiber felts is also improved with the increase of the density and the resin content of glass fiber felts. The micro-layer structure decreases the flexural rigidity of glass fiber felts, and the flexural rigidity of glass fiber felts with micro-layer and random structures is 43.4u2009g.cm and 101.3u2009g.cm, respectively. The mean thermal conductivity of glass fiber felts with micro-layer and random structures is 31.57u2009mW/m·k and 35.69u2009mW/m·k, respectively.

Fabrication of Microchanneled Composites by Novel Selective Polymer Degradation

In this research a new low-cost, highly compatible method is proposed and demonstrated to create microchannels within carbon fiber reinforced polymeric (CFRP) composite laminates that caused a lower mechanical loss due to their presence. In it, microchannels were created within the CFRP composite laminate by selective degradation of the specially selected polymer, whose solid preforms were placed at specific locations within dry fabric layers during composite manufacturing by resin infusion. Interlaminar shear (ILSS) and three-point-bend flexural tests were carried out on CFRP composite laminates with and without microchannels of different diameters to assess their effect on structural strength. The results showed that inclusion of microchannels within the CFRP composite laminates decreased their ILSS and flexural strength, which decreased steadily with the increase in channel diameter. The mechanism for these observed results was found to be the creation of resin-rich areas, microchannels and lessened fiber content by the addition of microchannels. These mechanical testing results were compared with the results of CFRP composite laminates with microchannels, inserted by hollow glass tubes (HGTs), and it was found that the new applied strategy was quite effective in introducing microchannels within CFRP composite laminates with reduced mechanical loss and provided more space for additional functionalities.

Mechanical and electrochemical properties of platinum coating by double glow plasma on titanium alloy substrate

In this paper, a platinum coating was deposited on titanium alloy substrate by a double glow plasma. Phase and microstructure of platinum coating were examined by X-ray diffraction and scanning electron microscopy, respectively. The microhardness of the coating was estimated by nanoindentation instrument. The adhesive force between the coating and the substrate was performed with scratch tester. The electrochemical behavior of the platinum coating in 3.5 wt % sodium chloride solution was investigated by potentiodynamic polarization. The results indicated that an adherent platinum coating could be successfully obtained on titanium alloy substrates. Compared with the titanium alloy substrate, the platinum coating had a relative low corrosion current density and high corrosion potential. It indicated that the platinum coating had a better corrosion resistance than the titanium alloy substrate.

Fracture mechanism of 3D, five-directional braided (SiO2)f/SiO2 composites prepared by silicasol-infiltration-sintering method

Three-dimensional (3D) five-directional braided (SiO2)f/SiO2 composites were prepared by silicasol-infiltration-sintering (SIS) method. The flexural properties and microstructures were studied. The flexural strength and flexural elastic modulus were found to be 73 MPa and 12 GPa, respectively. The results of stress vs deflection curve and SEM examinations revealed that the fracture mechanism of 3D, five-directional braided (SiO2)f/SiO2 composite was a mixture mode of ductile and brittle. The ductile mode was attributed to the weak bonding strength of fiber/matrix at low temperature. The brittle fracture might be caused by the propagation of micro defect or crack, which existed in the as-prepared composites for the ten-cycle process.