Baokun Xu

Microwave absorptive behavior of ZnCo-substituted W-type Ba hexaferrite nanocrystalline composite material

ZnCo-substituted W-type barium hexagonal ferrite of the order of nanoscale is synthesized and investigated as microwave absorber. Based on a two-layer structure with the thickness of only 1 mm, a big reflection loss over broadband is obtained. The microwave absorptive mechanisms of nanocrystalline composite material are also discussed.

Humidity sensors based on composite material of nano-BaTiO3 and polymer RMX

Abstract The composite material made of nanocrystal BaTiO3 and polymer material quaternary acrylic resin (RMX) can be used to make humidity sensors. The infrared (IR) and X-ray photoelectron spectroscope (XPS) spectra of the material were analyzed and compared with those of nanocrystal BaTiO3. An equivalent circuit was given by analyzing the complex impedance plots of the composite material sensor. The electrical properties of the sensor were investigated, including resistance versus relative humidity, humidity hysteresis, response–recover time and long-term stability. The results indicated that the humidity sensing properties of the composite material is better than those of nanocrystal BaTiO3.

Surface state studies of TiO2 nanoparticles and photocatalytic degradation of methyl orange in aqueous TiO2 dispersions

Abstract Nanocrystalline TiO2 is prepared using a stearic acid gel method. Their surface state is analyzed by means of X-ray photoelectron spectroscopy (XPS). The photocatalytic degradation of methyl orange in TiO2 suspension is investigated. The relationships between surface state and photocatalytic activity are discussed.

A high performance ethanol sensor based on field-effect transistor using a LaFeO3 nano-crystalline thin-film as a gate electrode

Abstract The LaFeO3 nano-crystalline thin-film of perovskite-type composite-oxides is obtained by using a sol–gel coating technique, and the photo-etching technique is employed to etch and pattern the film. Combining this thin-film technology with the NMOS integrated circuit technology, we have developed an ethanol-sensitive field-effect transistor by using a LaFeO3 nano-crystalline thin-film as a gate electrode of an ordinary n-channel MOSFET. The sensor has excellent selectivity, good sensitivity to ethanol, and a good stability. In order to improve the recovery transient of the sensor, the LaFeO3 doped with strontium ions has been investigated.

Synthesis of monocrystalline composite oxides La1−xSrxFe1−yCoyO3 with the perovskite structure using polyethylene glycol-gel method

Precursors to La1−xSrxFe1−yCoyO3 have been prepared glycol as a protecting agent of colloidal particle via the sol-gel process. After the solid phase reaction at 500–600°C for 2 h, nanocrystalline composite oxides La1−xSrxFe1−yCoyO3 (x = 0.0, 0.1, 0.2, 0.4; y = 0.1, 0.2, 0.5, 0.6, 1.0) were obtained. The effects of various conditions of the synthesis processes on the products containing the various components and the preparation processes of nanocrystalline composite oxides by the direct heat decomposition method are reported. The results indicate that the solid phase reaction can be completed at a lower temperature and with a shorter reaction time and that it has a direct relationship to the distribution of the various components in the precursors.

Improvement of nanocrystalline BaTiO3 humidity sensing properties

Abstract Two methods were used to improve the properties of nanocrystalline BaTiO3 humidity sensors: doping a certain amount of impurities into BaTiO3, and mixing some polymer humidity sensing materials with BaTiO3 to fabricate humidity sensors of composite materials.

Property analysis and humidity sensitivity of the composite material of BaTiO3 and RMX

Nanocrystal BaTiO3 and polymer (R)nM+X− are mixed to make a composite material. IR and XPS spectra of the composite material were analyzed and compared with those of BaTiO3. The humidity sensor made of the composite material shows better humidity sensing properties than the BaTiO3 sensor such as higher sensitivity and smaller humidity hysteresis.

Fabrication of La1−xSrxFe1−yCoyO3 sensitive ceramics, nanocrystalline thin films and the manufacture of the NCTF-OSFET gas sensing device

Abstract LaFeO 3 , La 1− x Sr x FeO 3 ( x = 0.1, 0.2 and 0.4) and LaFe 1− y Co y O 3 ( y = 0.1, 0.2, 0.3, 0.4, 0.6 and 1.0) nanocrystalline thin films were fabricated on monocrystalline silicon wafers by a new sol-gel method with microtechnology. The XRD and SEM studies of the samples showed that the doping of the Sr 2+ and Co 3+ ions in LaFeO 3 , substituting for La 3+ and Fe 3+ ions, respectively, has different effects on the solid state reaction and the average grain size of the thin films obtained. We have tried to manufacture a new type NCTF-OSFET gas sensing device for the first time, in which the aluminum gate was replaced by LaFeO 3 nanocrystalline thin films (NCTF) combined with the planar technique of integrated circuits, and the results are satisfactory. This device not only has an excellent selectivity to ethanol, but also has a good sensivitity.

The effect of pressure on the specific surface area and density of nanocrystalline ceramic powders

Abstract Nanocrystalline LaFeO3, LaCoO3, La1-xSrxFeO3 and La1-xSrxFe1-yCoyO3 powders were compacted at room temperature, under pressures of 0.0, 0.5, 1.0 and 1.5 GPa, respectively. The specimens were examined by rotating anode X-ray diffractometry and their specific surface areas and densities measured. Results show that deformation, fracture and phase transition can occur to different extents in the nanocrystalline materials subjected to different compaction pressures. The characteristics of the interfaces, which are changed under the contact stresses between adjacent crystalline grains, are related to the compaction pressure and the types of interaction forces between interfacial atoms, which may be between those of van der Waals bonds and covalent bonds. The specific surface area and the density of the nanocrystalline materials change with increasing compaction pressure.

A polymer sensitive to humidity and its electrical properties analysis

A humidity sensor is a device which can covert the ambient moisture variation into an electrical signal (resistance or capacitance) variation, so it can be easily installed in electronic equipment to detect or control the ambient humidity. The humidity sensors based on polymers can be classified as resistive-type and capacitivetype. Because it has a simple fabrication technique and small hysteresis, is easily decorated and does not need heat cleaning, the former type is more interesting. But for all humidity sensors based on polymers, a problem still remains that they cannot be used in high humidity or at a place where dew (condensation water) may occur. Otherwise, the sensitive film will gradually change due to a very slow irreversible reaction with water vapor in atmosphere. The investigation for the problem is focused on improving water-resistive properties of the material. The main methods to solve the problem are interpenetrated polymer network (INP), graft polymerization and modification of substrate and/or surface [1, 2]. In general, the molecular structure of polymers sensitive to moisture has either hydrophilic group or hydrophobic group. We made hydrophilic monomer graft polymerized with hydrophobic monomer and obtained copolymer. The ratio of the two monomers in the reaction is an important parameter to effect the characteristics of the humidity sensor. The humidity sensor based on the polymer is water-resistive, even when put in water atmosphere for 48 min, its characteristic has no change. We utilize the hydrophilic monomer graft polymerization reaction with hydrophobic monomer. The hydrophilic monomer is hydroxyethylate methylacrylate trimethyl ammonium chloride (Qb), the hydrophobic monomer is butyl methylacrylate (Bu). Fig. 1 gives the structures of the two monomers. From many experiments, we found the proportion of two monomers, reaction path and reaction time is important to material properties. The best result shows that Bu : Qb= 7 : 3 is a suitable ratio. The reaction path is better, when Qb is dipped into the reaction container after Bu has been heated for a period of time under 351 K (absolute temperature). The infrared spectrograph (IR) gives main absorption peaks as shown in Fig. 2. The N–C bond vibration peaks appear at 3087.48 cm−1 and 952.06 cm−1. We believe polymerization really took place because homo-copolymer of Bu and Bu itself are both dissolvable in water, and the special peaks still exist after the material obtained dissolves in water. The substrate is a ceramic plate with gold interdigital electrodes made by screen-printing. The ceramic plate scale is 10 mm× 5 mm, electrode dimension is 4 mm× 4 mm, and the wire width and span of electrode are both 0.5 mm, as shown in Fig. 3. The spin-coating technique is employed to fabricate the sensitive film. In order to improve water-resistive properties of the sensor further, another polymer (cellulose) film is coated on the surface of the sensing film. We called the film “protecting film”, which can allow water molecules to