Jian Er Zhou

Effect of Al2O3 Addition on Microstructure, Thermal Expansion and Mechanical Properties of Ta2O5 Ceramics

The Ta2O5-based ceramics were prepared by dry pressing/sintering technique using Ta2O5 and Al2O3 as the starting materials. The present work investigated the effect of alumina (Al2O3) additions on the composition, microstructure, thermal expansion coefficient (TEC) and bending strength of Ta2O5 ceramics. The thermal expansion of the samples was measured by the dilatometry method. It was found that Al2O3 additions can effectively inhibit the β to α phase transformation in Ta2O5 ceramics. Orthorhombic AlTaO4 as the minor phase formed when 2.5 and 7.0 wt% Al2O3 was added. The addition of Al2O3 results in obvious change of TEC and an increase of bending strength. This work demonstrated that the addition of Al2O3 is an effective way to modify the TEC and mechanical strength of Ta2O5 ceramics.

Effects of Pore Former on Properties of Alumina Porous Ceramic for Application in Micro-Filtration Membrane Supports

Due to its excellent chemical stability, high temperature resistance and mechanical properties, alumina porous ceramic was the first choice of the production of microfiltration membrane support body material. In this paper, alumina porous ceramic was prepared by alumina as main materials and adding proper amount of adhesives and sintering additives. Effects of the kinds and addition of pore formers, such as starch, graphite and carbon-black, on properties of alumina porous ceramic was studied. The porosity of the fired samples was evaluated by Archimedes law. The fired samples were characterized by scanning electron microscopy (SEM), compressive strength and mercury porosimeter measurements. Alumina porous ceramic composition was prepared by mixing 100% alumina with different particle size and 8 % graphite pore former. The sample was pressured at 10 MPa and fired at 1650 °C for 2 h, and endowed with 6-8 μm of the average pore diameter, 37.65 % of the porosity and 40.33 MPa of the compressive strength, respectively. The influence law of the kinds and addition of graphite pore former on the performance of alumina porous ceramic was studied for application in micro-filtration mmembrane supports.

Preparation of SiC Porous Ceramic for Application in Filter Plate Supports

In order to improve the efficiency of solid-liquid separation, dewatering and filtration, as well as to reduce the loss of concentrate and production costs, silicon carbide porous ceramic filter plate with high porosity and high bending strength was prepared by using the particles close packing method adding proper amount of adhesives and sintering additives at 1450 oC. The porosity of the fired samples was evaluated by Archimedes law. The morphology and properties of the samples were characterized. Effects of SiC grains gradation, pore formers content, molding pressure and soaking time on the bending strength and porosity of ceramic filter plate was studied. SiC porous ceramic composition was prepared by mixing 90wt% and 10wt% SiC powders with D50 of 200.7 μm and 312.6 μm, respectively, 4% walnut powder as pore former and 5% Kaolin clay as binder. The sample was pressured at 8 MPa and fired at 1450 oC for 30 min, and endowed with 6-8 μm of the average pore diameter, 41% of the porosity and 11 MPa of the bending strength, respectively, which is especially not easy to plug hole. The obtained results can be applied in ceramic filter core parts for heavy metal concentration.

Particle Size and Chroma Control of CoAl2O4 Pigment

To meet the requirement of ceramic pigment for ink jet printing, CoAl2O4 pigment was prepared by nitrate-glycine method. The effect of nitrate/glycine ratio, calcination temperature and organic sacrificial agent on the particle size and chroma of the blue pigment were considered. The results show that the particle size of the pigment increases with the increase of glycine in the ratio and the decrease of the calcination temperature. However, the increase of the calcination temperature results in the broadening of the particle size distribution of the pigment. The addition of the organic sacrificial agent contributes to decrease the particle size of the pigment, which is about 2.0 μm. The chroma of the pigment is L*=47.62、a*=9.49、b*=-51.41. The blue pigment can be used in ink jet printing.

Preparation and Characterization of Nb2O5-Al2O3 System Ceramics with Different Al2O3 Additions

The Nb2O5-Al2O3 binary system ceramics were prepared by high temperature solid state reaction sintering, using Nb2O5 and Al2O3 micro powder as the raw materials. The samples were characterized by XRD, SEM, thermodilatometric analysis and mechanical strength measurement. The influences of Al2O3 content on the phase composition, microstructure, thermal expansion properties and bending strength were investigated. Results show the samples shows obvious changes in phase composition and microstructure with the addition of Al2O3 from 2.5% to 15%. The pure Nb2O5 ceramic is composed of monoclinic phase Nb2O5, while different monoclinic aluminum niobates were formed with different Al2O3 additions. Obvious microcracking can be observed for the samples without and with 2.5% and 7.5% Al2O3 additions. The addition of Al2O3 leads to significant increase of bending strength, and all the samples keep relatively low thermal expansion coefficient (TEC). The Nb2O5-Al2O3 binary system ceramics with ultra low TEC (0.55~0.86×10-6°C-1) and improved bending strength (50.4~70.6MPa) could be obtained with the addition of 7.5~15% Al2O3 when sintered at 1390°C for 2h.

Effects of Process Parameters on the Particle Size Distribution of Graphene Oxide Aqueous Dispersion

During graphene oxide separation process, the effects of the process parameters such as centrifugal separation time and ultrasonic treatment time on the particle size distribution of graphene oxide aqueous dispersion were studied. The results show graphene oxide has the narrower particle size distribution and the smaller nominal effective particle size with increasing the centrifugal separation time from 20 min to 160 min. And there is a critical time in the ultrasonic treatment to obtain the narrower particle size distribution and smaller nominal effective particle size of graphene oxide. Graphene oxide has the narrower particle size distribution and the smaller nominal effective particle size when the ultrasonic treatment time is 4 h.

Preparation of Carboxymethyl Cellulose Sodium/PEI Nanofiltration Membrane

Carboxymethyl cellulose (CMC) sodium with negatively charged character was used as functional layer of polyetherimide (PEI) ultrafiltration membrane. The preparation parameter such as CMC concentration, cross-linking agent concentration and curing temperature are studied in detail. When the composite membrane was prepared under optimized conditions and tested at 0.4 MPa and 20 °C, the flux of the composite NF membrane was about 3 L/m2h and the MgCl2 rejection of it was about 87%. The composite membrane showed classical negatively charged membrane character which had higher rejection to high valent anion.

Investigation of Cobalt-Free Cathode Material Ba0.5Sr0.5Fe0.8Cu0.2O3−δ for Micro-Tubular SOFC with Asymmetric Structure Anode

A cobalt-free perovskite oxide Ba0.5Sr0.5Fe0.8Cu0.2O3−δ (BSFCu) is applied as the cathode material for intermediate temperature micro-tubular solid oxide fuel cells (SOFCs) with asymmetric structure anode. The NiO-YSZ hollow fiber anode as support was prepared by the phase inversion technique. The as-prepared fiber anode shows a special asymmetric structure consisting of porous sponge-like structure in the middle and finger-like porous structure on the inner and outer side. Dense thin YSZ electrolyte membrane and SDC transition layer were deposited on the NiO-YSZ hollow fiber anode by a vacuum-assisted dip-coating and co-sintering technique. Laboratory-sized micro-tubular single cells of NiO-YSZ/YSZ+SDC/BSFCu-SDC were tested at 650-750°C with humidified H2 as the fuel and static ambient air as the oxidant. The peak power densities of 437.2, 326.5 and 214.4 mWcm-2 can be obtained at 750, 700 and 650°C, respectively. The experimental results indicate that the cobalt-free perovskite oxide BSFCu is a promising cathode material candidate for the developed intermediate temperature micro-tubular SOFC with asymmetric hollow fiber anode.

Preparation of CaTiO3 Thin Film by Sol-Gel Dipping Coating

Smooth and dense films of CaTiO3 were prepared on the glass substrate by a sol-gel dip coating method. Characterization of the product was carried out by different techniques such as powder X-ray diffraction (XRD), scanning electron microscope (SEM) and UV–vis optical spectroscopy. The results showed that pH and water contents had a great influence on morphology of CaTiO3 film. When water content is 0.128 mol at PH=1.56, CaTiO3 film presents an absorption in the UV region and the band gap is estimated to 3.35 ev. The results show the large potential of this material in electronic structure.

Micro-Tubular Solid Oxide Fuel Cell with Graded Anode and Cobalt-Free SrFe0.9Sb0.1O 3−δ Perovskite Cathode

Micro-tubular solid oxide fuel cell (SOFC) has been fabricated with NiO-YSZ hollow fiber as anode support and SrFe0.9Sb0.1O 3−δ-Sm0.2Ce0.8O1.9 (SFSb-SDC) composite cathode. The NiO-YSZ hollow fiber anode was prepared by the immersion-induced phase inversion technique and shows a special asymmetrical structure with long and large finger-like porous structure near the lumen side of the hollow fiber. A thin and dense electrolyte membrane (about 12μm) was deposited on the anode by a vacuum-assisted dip-coating process. The performance of the as-prepared micro-tubular SOFC was tested at 600-800°C with humidified H2 as fuel and ambient air as the oxidant. The peak power densities of 462.8, 336.6 and 201.4 mWcm-2 can be obtained at 800, 700 and 600°C, respectively. The experimental results indicate that the cobalt-free SFSb was a promising cathode material and the prepared YSZ-based micro-tubular SOFC has potential applications as power sources for portable devices.