Meng Guangyao

Sol-gel synthesis of yttria stabilized zirconia membranes through controlled hydrolysis of zirconium alkoxide

Abstract Yttria stabilized zirconia (YSZ) polymeric sols were synthesized by controlled hydrolysis and condensation of zirconium tetra- n -propoxide. Yttrium nitrate was added before hydrolysis as the source of yttria. Acetylacetone was used as chelating ligand to modify the reaction rate of zirconium alkoxide. The dependence of YSZ sol formation as well as gelation time was investigated experimentally on the contents of acetylacetone, n -propanol (solvent) and water for hydrolysis. With a stable sol, YSZ membranes were prepared on porous α-alumina supports by a dip-coating process. The membranes were characterized by scanning electron microscopy and gas permeability testing. Unsupported YSZ membranes were also prepared with the same sol, and were investigated with isothermal nitrogen adsorption/desorption porosimetry and X-ray diffraction. The results show that YSZ membranes with nanosize pores were successfully prepared by the sol–gel technique with the polymeric sols.

PREPARATION AND GAS SENSITIVITY PROPERTIES OF ZNFE2O4 SEMICONDUCTORS

Abstract This paper reports the preparation and gas-sensing properties of ZnFe 2 O 4 . Raw powders of ZnFe 2 O 4 were obtained by chemical coprecipitation. Effects of the calcining temperature on the phase constituents and microstructure are characterized by TG-DTA and XRD. The conductance-temperature, gas-sensing properties of ZnFe 2 O 4 were investigated. The results demonstrated that ZnFe 2 O 4 can be used as a new type of gas-sensing material which has a high sensitivity and good selectivity to C 2 H 5 OH.

Effects of CdO dopant on the gas sensitivity properties of ZnFe2O4 semiconductors

Abstract This paper reports the preparation and gas sensitivity properties of Zn 1− x Cd x Fe 2 O 4 to C 2 H 2 OH. Raw powders of Zn 1− x Cd x Fe 2 O 4 were obtained by a chemical co-precipitation and solid-state reaction method. The effects of the calcining temperature on the phase constituents are characterized by X-ray diffraction (XRD). We investigated the influence of CdO on the conductance–temperature correlation, and gas sensing properties of ZnFe 2 O 4 . The results demonstrated that CdO could improve the sensitivity, selectivity and response time of ZnFe 2 O 4 .

Boehmite sol properties and preparation of two-layer alumina membrane by a sol-gel process

A two layer ultrafiltration alumina membrane was prepared by a sol-gel process using boehmite sol as precursor. The sol was prepared by hydrolysation of aluminium tri-sec-butoxide. Sol properties, such as viscosity as a function of concentration and acidity, were investigated by using capillary viscometry, transmission electron microscopy and laser scattering photometry etc. The viscosity increased with an increase in concentration and a decrease in pH, while the particle shape and size of the sol were mainly determined by pH. The membrane prepared by a dipping procedure was characterized by both scanning electron microscopy and transmission electron microscopy. The results showed that the membrane thickness and surface morphology were affected by the dipping time, the viscosity and the temperature.

Preparation of asymmetric Ni/ceramic composite membrane by electroless plating

Abstract Although a lot of work has been done on electroless nickel coating, work on preparing asymmetric nickel membranes on porous ceramic supports is rarely reported. In this work, microfiltration nickel membranes are prepared on porous alumina supports with electroless plating. A new approach technique, sol–gel process is used to activate the alumina supports. The coated membranes were investigated by means of scanning electron microscopy and gas permeation test. Membrane thickness and amount of nickel increase with plating time. Membrane pore size decreases greatly as electroless coating is processed for 15 min. After 15-min coating the pore size decreases slightly. For a 90-min electroless plated membrane, the thickness reaches 4.5 μm and the mean pore radius is 0.13 μm with a narrow distribution.

The catalytic effect of SmInO3 on the gas-sensing properties of CdIn2O4

Abstract The catalytic effect of SmInO 3 , on the conduction and gas-sensing properties of CdIn 2 O 4 was investigated. The results demonstrated that SmInO 3 increases the electrical impedance and improves the sensitivity and selectivity of CdIn 2 O 4 materials to ethanol gas though SmInO 3 based sensors exhibit no sensitivity to reducing gases. The XPS analysis shows that the increase in sensitivity is not related to the increase in the amount of adsorbed oxygen O − (ad) on the material surface. We attribute the sensitivity improvement to the easy adsorption of reducing gas on the surface of SmInO 3 and CdIn 2 O 4 composite and the interfaces between the CdIn 2 O 4 grains and the SmInO 3 grains. The sensors based on CdIn 2 O 4 and SmInO 3 , (molar ratio 3:2) have a high sensitivity and selectivity to ethanol gas and are promising for practical use.

Study on SnO2-Fe2O3 gas-sensing system by a.c. impedance technique

Abstract A.c. complex impedance measurement has been used in a mixed system of tin oxide and iron oxide in an attempt to obtain more information about the gas-sensitive mechanism of semiconducting metallic oxide gas sensors. The impedance spectra in air, liquid petroleum gas (LPG) and acetylene have been obtained for the thick-film elements at different temperatures. A simple equivalent circuit, which contains the contributions from grain bulks and grain boundaries, is proposed to account for the spectra. The results show that both the grain bulks and grain boundaries of tin oxide (doped with a small amount of antimony oxide) are responsible for the reducing-gas sensitivities. For the iron oxide sample, the grain-boundary resistance is dominant in the total resistance and its change in various atmospheres is the main origin of the sensitivity to reducing gases. For the mixed system, the role of grain boundaries is also found to be more important than that of grain bulks. Some structural analyses and direct-current (d.c.) measurement have also been performed. This preliminary study indicates that a.c. complex impedance measurement might be a powerful tool in studying chemical sensors.

New solid state fuel cells - green power source for 21st century

The exhaustion of the major fossil energy sources on earth in near future and the serious environmental pollution from the fuel combustion processes in the presently applied technologies are the most important problems of modern society. The sustainable development of mankind requests strongly to develop “green” power devices characterized by high fuel energy conversion efficiency, less pollution to the environment and convenience to use.Fuel cells have been commonly accepted to be a kind of clean, safe and convenient power source with high energy efficiency and are on the verge of revolutionizing the electric power industry by offering better ways to produce electricity and to deliver it to the consumers.Among all the advanced fuel cells being developed, which one might be the better choice for ideal green power generators in the 21st century? The answer is solid state fuel cells, particularly the solid oxide fuel cells(SOFCs) but not in the present stage of development. The new generation of SOFCs will certainly be based on all the results and experiences achieved so far in the fuel cell field and a lot of R & D work has to be performed furthermore.This paper attempts to present the current status of the R & D work on fuel cells, especially SOFCs, new concepts and trends, problems and possible measures which may initiate further discussion.The present article includes the following sub-topics:The best electric power plants for the 21st CenturyR & D on SOFCs: current status, problems and new trendsIntermediate temperature SOFCs - what do we need to do?Fabrication techniques - soft chemistry routesWhat to do for coming up with “green” power plants?

A fully solid-state SOx (x = 2,3) gas sensor utilizing Ag-ß″-alumina as solid electrolyte

Abstract A galvanic-cell-type SO x ( x = 2,3) gas sensor with Ag-s″-Al 2 O 3 solid electrolyte, porous Pt as working electrode and Ag as reference electrode has been constructed and tested. The electromotive force (e.m.f.) responses are in good agreement with theoretical values for SO x concentrations from 10 to 10 4 ppm in the temperature range 550–750 °C. The experimental results show that CO 2 and NO 2 did not disturb the measurement of SO x .

Preparation and characterization of SrFeCo0.5O3.25+δ by gelcasting

Abstract SrFeCo 0.5 O 3.25+δ powders have been successfully synthesized from SrCO 3 , 2CoCO 3 ·3Co(OH) 2 ·xH 2 O and Fe 2 O 3 based on using the principle of gelcasting. Thermal decomposition of the gelcasting powder was analyzed by differential thermal analysis and thermogravimetry. The crystal structure of the sintered body was investigated by X-ray diffraction. It was found that SrFeCo 0.5 O 3.25+δ samples formed by sintering the gelcasting powder over 1000°C consist mainly of the perovskite phase SrFe 1-x Co x O 3-δ . Electrical conductivity was measured by a DC four-probe technique and oxygen permeation flux was measured by applying oxygen partial pressure difference to a 1.4 mm thick pellet. Both the electrical conductivity and oxygen permeation flux of the gelcasting samples were much higher than that of samples prepared by a traditional solid state reaction method. Though further work should be performed on the higher transfer velocity of electron and oxygen ion, experimental data shows that the gelcasting process is a promising technique for the preparation of mixed conducting SrFeCo 0.5 O 3.25+δ .