Papers by Author: Li Hua Dong

Abstract: Ti3Al inter-metallic compounds were successfully prepared via high energy ball milling and the subsequently heat treatment. Near full dense (TiB2, TiCx)/B4C matrix composites were fabricated by the addition of Ti3Al. The maximum values of hardness, flexural strength and fracture toughness are HRA 94.1, 580.34MPa and 8.07MPa•m1/2 respectively for 20wt% Ti3Al content. Furthermore, the microstructures of the composites were analyzed by XRD, SEM and energy spectrum methods.

Abstract: Fluorene and its derivatives which have an aromatic biphenyl structure with wide energy gap in the backbone and high luminescent efficiency have been drawn much attention to materials chemists and device physicists. In this research, 9,9-Bis(methoxycarbonylethy)fluorene and fluorene-containing polyester were prepared and their chemical structure and properties were initially studied. Furthermore, It is found that this fluorene-containing polyester might be a promising candidate for electroluminescent materials due to its excellent luminescent properties, solubility, film-forming property and thermal stability.

Abstract: “Underwater super-hydrophobic” surface applied in the corrosion protection was prepared by melting myristic acid (CH3(CH2)12COOH) adsorbed onto the anodized aluminum. The static contact angle for seawater on the surface was measured to be 154°. The surface structure and composition were then characterized by means of scanning electron microscopy (SEM) with energy dispersive X-ray spectrum (EDX) and atomic force microscope (AFM). The electrochemical measurements showed that the super-hydrophobic surface significantly improved the corrosion resistance of aluminum in sterile seawater.

Abstract: Molecular simulations of the interfacial properties of (1) a composite with an epoxy(EP) matrix and a carbon nanotube(CNT)/carbon fiber(CF) multi-scale reinforcement and (2) a traditional CF/EP composite were performed employing Materials Studio 4.0 software. Results indicate that the interfacial atom concentration of material 1 is higher that that of material 2 by interfacial molecular structure analysis, and there are many benzene rings in both material 1 and material 2 which are parallel to the crystal layers of CF. The contact layer thickness of material 1 and material 2 is 0.25 and 0.10 nm, respectively. The concentration distribution calculation of EP molecules in the interface shows that the most concentrated part of EP in material 2 appears in the carry-forward area of the contact layer, while it is more close to the contact layer in material 1.

Abstract: Hollow carbon spheres containing Fe3N nanocrystals (Fe3N/HCSs) are synthesized by ferrocene and ammonium chloride in high pressure argon at 500 °C. The structure, morphology and properties of the products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TG) and vibrating sample magnetometry (VSM). The hollow carbon spheres have diameters of 1-10 µm and shell thickness of hundreds of nanometers. The dimensions of the acicular Fe3N nanocrystals have diameters of ca. 100 nm and lengths of 600-800 nm. The weight percent of Fe3N nanocrystals in Fe3N/HCSs is about 37.8%. The saturation magnetization value of the hollow carbon spheres containing Fe3N nanocrystals is 10.61 emu/g.

Abstract: Near full dense B4C ceramic matrix composites were fabricated from Ti-Al-B4C system by combining high energy milling with hot pressing sintering. The effect of different content of Ti-Al on the mechanical properties and microstructure of the as-prepared composites was investigated. A TiAl/B4C composite, whose typical bending strength and fracture toughness are 437.3 MPa and 4.85 MPa•m1/2, respectively, was made. The sintering mechanism and reinforcement mechanism were discussed with the assistant of X-Ray diffraction and electron microscopy.

Abstract: An thin reagent containing optochemical film sensor for detecting and measuring free chlorine in water is described. The film sensor has been manufactured by immobilisation indicator of 3,5-dimethyl-4-hydroxybenzaldazine in a permeable transparent polymeric membrane. A linear calibration for free available chlorine can be obtained in the range between 0.05 and 3ppm. The limit of quantitation is 0.3 ppm, and the accuracy exceeds 7%. It takes about 150s to measure the relatively low occupational exposure concentration of 0.1ppm. The interference of combined chlorine has been studied. The sensor has no response to combined chlorine. And the stability of the sensors and the effect of external parameters like relative humidity (RH), temperature on the sensor response have been investigated. The sensor response is affected by varying the temperature; however, humidity in the range between 0 and 90% RH does not affect sensor response. The 3,5-dimethyl-4-hydroxybenzaldazine remained stable inside the polymeric film and no chemical reaction, crystallization or leaching occurred during 6 months of observation. Proper choice of indicator dye and polymeric material and successful application of kinetic evaluation method for the exposure experiments determine the desired features of the sensor. Introduction

Abstract: Piezoelectric Pb(Sb1/2Nb1/2)O3-Pb(Mn1/3Nb2/3)O3-PbZrO3-PbTiO3 (PSN-PMN-PZT) quaternary ceramics with the various contents of Pb(Mn1/3Nb2/3)O3 from 4 to 10mol% were prepared. The phase structure of the system was delineated by X-ray diffraction analysis. The surface morphology was examined by SEM. The piezoelectric and dielectric properties were also measured. X-ray diffraction patterns showed that the PSN-PMN-PZT piezoelectric ceramics was composed of tetragonal phase with perovskite-type structure. Study on the influence of Pb(Mn1/3Nb2/3)O3 additives on dielectric and piezoelectric properties indicated that the PSN-PMN-PZT quaternary system exhibited a high mechanical quality factor and well-situated piezoelectric properties. The optimized results of d33 =332pC/N, d31= -105pC/N, Kp=0.58, K31=0.34 and Qm=1658 can be obtained at 6 mol% Pb(Mn1/3Nb2/3)O3. The obtained electrical properties make this composition a good candidate for underwater acoustic devices.

Abstract: Theoretical study on the geometric structures and magnetic properties of small (FeAl)n (n=1-4) clusters has been carried out at the BPW91 level. In all the (FeAl)n clusters, the iron atoms are brought together, yielding a maximum of Fe-Fe bonds, and the aluminum atoms are located around a Fe core with a maximum of Fe-Al bonds which is different the bulk ordered FeAl alloy dominated by the Fe-Al bonds. As opposed to the bulk FeAl with non-magnetic, the small nano-clusters are highly magnetic moment dominated by Fe-Fe clustering.

Abstract: Ba0.7Sr0.3TiO3 (BST) thin films have been prepared on copper foils via sol-gel method in almost inert atmosphere containing different level of oxygen which was achieved by flowing high purified argon with the varied rate from 0.3 L/min to 2.0 L/min. X-ray diffraction pattern of the BST thin film exhibits dominant perovskite phase. SEM images reveal good crystallization and much dense structure of the thin film. The BST thin film annealed at almost inert atmosphere by flowing the high purified argon at the rate of 0.5 L/min, exhibits highest dielectric constants which are 1549.65 and 1350.86 at the frequency of 10 kHz and 1 MHz, respectively. Additionally, the film also shows optimized ferroelectric behavior and low leakage current density. The mechanism of the annealing atmosphere on properties of BST thin films was investigated.