Papers by Author: Jian Feng Chen

Abstract: Sintering behavior of pure and Nb-doped barium titanate powders prepared by high-gravity reactive precipitation (HGRP) process was investigated. A thermal dilatometer was employed to monitor the sintering shrinkage continuously during sintering. TEM and SEM were used to characterize the microstructures of the samples. The experimental results confirmed that Nb-doped BaTiO3 ceramics sintered at 1220°C for 2 h reached a larger densification of 97.0% relative density compared with 94.6% of pure BaTiO3 ceramics sintered at 1265°C for 2 h, and Nb-doped BaTiO3 ceramics had a smaller grain size (1.2μm) than that of pure BaTiO3 ceramics (2μm).

Abstract: In this work, a sub-micron grained sized (<500nm) ceramic (> 92% of theoretical) has been obtained using nano-sized BaTiO3 powders synthesized through a high-gravity reactive precipitation (HGRP) process. Permittivity of the prepared ceramic is greater than 2500. Also, low change ratio of temperature in the range of −55°C~ 125°C
i.e.< ±15% renders the ceramic to meet the EIA X7R characteristics. In the ceramic compositions, Dy2O3, BaCO3, CaCO3, MnCO3 and MgO were used as dopants. After being mixed and dry-pressed, the above mentioned compositions in reducing atmosphere (N2 and 5% H2) were sintered at 1210°C−1290°C for 2h, respectively. Experimental results show that HGRP BaTiO3 powders have good dielectric properties. The dielectric properties as well as the microstructure of the ceramic are both sensitive to the change of sintering temperature.

Abstract: Precursors of calcium strontium zirconate (Ca0.8Sr0.2ZrO3) were synthesized by oxalate coprecipitation method. TG-DTA was used to characterize the thermal decomposition behaviors of the precursors. The XRD results revealed that the powders crystallized as cubic Ca0.8Sr0.2ZrO3 with increasing heating temperature up to 1000°C. Calcium strontium zirconate ceramics were obtained under conventional sintering conditions by using the as-prepared Ca0.8Sr0.2ZrO3 powders. The SEM micrographs of the ceramics sintered at 1450oC exhibited narrow grain-size distribution with the average grain size around 0.7 4m. The dielectric properties showed that, dielectric constant of the Ca0.8Sr0.2ZrO3 was about 24.0 and dielectric loss was 0.002 at the frequency of 1GHz and the room temperature.

Abstract: The nano-CaCO3/Acrylonitrile-Butadiene-Styrene (ABS) composites were prepared by melting-blend with the single-screw extruder. The mechanical properties of the nanocomposites and the dispersion of nano-CaCO3 were investigated by means of transmission electron microscopy (TEM) and mechanical tests. The micro structure of the fracture section of the nanocomposites was analyzed by means of scanning electron microscopy (SEM). The results show that not only the impact property but also the rigidity property and the bending modulus of the system have been increased evidently by added modificated nano-CaCO3. However, the tensile strength of the nano-composites has a little decreased by added the modificated nano- CaCO3. The modificated nano-CaCO3 has been dispersed well in the matrix in the nanometer scale. The micro structure of the fracture section of the nanocomposites proved that when the composites have been impacted, the modificated nano-CaCO3 particles have taken an action of initiating and terminating crazing (silver streak), which can absorb more impact energy than the pure ABS resin. Compared with the pure ABS resin material, the notched impact strength of the nano-CaCO3/ABS composites added 2 percent hundred resin (PHR) modificated nano-CaCO3 reach 36.77 kJ/m2, which have been increased up to 44%. At the same time, the rigidity of the nanocomposites has also been enhanced by 23.5% which is increased from 28.16N to 34.87 N.

Abstract: Nanocomposites of nanosized-CaCO3/polypropylene-ethylene copolymer (PPE) and nanosized CaCO3/ PPE/ styrene-butadiene-styrene (SBS) were prepared by using two-roll mill and single screw extruder. The average particle size of nanosized CaCO3 was determined to be about 30 nm. By adding nanosized CaCO3 into PPE matrix, the toughness of the matrix improves significantly. At nanosized CaCO3 content of 12 phr (parts per hundred PPE resin by weight), the impact strength of CaCO3/PPE at room temperature reaches 61.6 KJ/m2, which is 3.02 times that of unfilled PPE matrix. In addition, the synergistic toughening effect of nanosized CaCO3 and SBS particles on PPE matrix was investigated.

Abstract: The sensitivity of CuO dispersed on fluorite-type oxide, namely CeO2 was studied in this work. Mixed oxide sample of nanostructured CuxCe1-xO2-y of various composition were generated by step chemical precipitation method. Distinct copper species were identified as a function of copper content by X-ray photoelectron spectroscopy, X-ray powder diffraction, the special surface areas, transmission electron microscopy, scanning electron microscopy analysis, and sensing properties to CO. It was found that only small amounts of copper are sufficient to promote the sensitivity of CeO2 by several orders of magnitude, which excessive amounts of copper (Cu/(Cu+Ce)>0.12) are detrimental to the sensing properties of nanocompositions. The possible causes for this behavior are also discussed.

Abstract: The dielectric properties and sintering activity of nano-BaTiO3 powders synthesized by HGRP method were investigated. The starting BaTiO3 powders were calcined at different temperatures from 700 to 900°C to improve their crystallinity and the mean particle size of BaTiO3 powders obtained increased from 40nm to 80nm. After being formed by conventional dry pressing the green bodies were sintered at 1100°C and 1200°C for 2hr in air. The effects of both calcinating and sintering temperatures on the sinterability, dielectric property and microstructure of BaTiO3 ceramics were discussed. The experimental results showed that the BaTiO3 powders have high sintering activity and the highest dielectric constant of this material at room temperature may reach 2880.

Abstract: This paper aims at a simple preparation method of nanocrystalline copper powders through copper sulfate reduction by potassium borohydride in aqueous solution. The product powders obtained in various conditions were investigated by X-ray powder diffraction, transmission electron microscope and particle size distribution analyzer. The parameters that influence the preparation process of copper crystalline were researched, such as the effect of complexing agent, the molar ratio of copper sulfate to potassium borohydride and the quantity of protective polymer. Finally, the preferable reaction conditions were determined, and well-dispersed nanocrystalline copper powders with average diameter of 28.4nm were obtained.

Abstract: To prepare stable electrophoretic ink (E Ink) contains titanium dioxide particles, oil soluble red, dispersant and tetrachloroethylene (TCE), the modification of organic and inorganic material onto the particle surface was investigated. Modified particles were characterized by measurement of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) to confirm the composites and structures. The electrophoretic properties of sample in TCE were investigated by static sedimentation experiment and electrophoresis instrument. The type of inorganic and organic materials used for the surface modification influence dispersibility and charge property of particles. On the whole, organic modified particles especially modified by anionic surfactant show better properties. The process conditions were investigated in detail using SDBS as the modifier. The dispersibility and charge property have significantly improved in optimized modifying condition that the proportion of surfactant is 15%, pH is 6 and reaction time is 1 hour which means SDBS modified TiO2 is suitable for electrophoretic particles.

Abstract: Submicrosized porous hollow silica spheres with a diameter of 350 nm and a shell thickness of approximately 10 nm were synthesized by a hydrothermal method using PMMA hollow particles as template. Through the hydrolysis of TEOS, a continuous and uniform coating of SiO2 was deposited over the surface of PMMA cores to form the core-shell structures. After calcining to remove the template, a pure hollow silica structure with holes in the shells was obtained. The as-prepared hollow products were characterized with TEM, SEM, EDS, BET and FT-IR. Its large surface area and hollow morphology will make this new material a promising agent for the applications of catalysts, controlled drug delivery and etc.