Fused filament fabrication (FFF), as one of the additive manufacturing technology, provides cost-effective and relatively fast preparation of 3D objects of desired dimensions and design. In this work, a composite filament containing 50 vol. % of sub-micron alumina powder was successfully used for the manufacturing of samples with prismatic design. The influence of the layer thickness (0.1–0.3 mm) on the final bulk density and mechanical properties were investigated. Sintering at 1600 °C for 1 h results in relative densities ranging from 80 to 89 % and the flexural strength reached 200–300 MPa depending on the layer thickness used for the printing. 相似文献
ZnAl2O4 and ZnO nanostructure particles and in situ crystallization of zinc aluminate and zinc oxide coating layers on sintered α-Al2O3 and γ-Al2O3 granules by the microwave-assisted combustion method were investigated. For powders, the effects of solution pH value and for coated samples the influence of support type on the structure, microstructure, and photocatalytic activity of powders were studied. Results showed that variation of synthesis pH value caused to considerable change in agglomeration, specific surface area, obtaining up to 88 and 92% yields for zinc aluminate and zinc oxide nanoparticles, respectively. γ-alumina granules were more appropriate supports than the α-alumina ones because of the better photocatalytic activities and lower extent of the attritions for both zinc aluminate and zinc oxide coating layers. 相似文献
Electro-chemical spark machining (ECSM) is an innovative hybrid machining process, which combines the features of the electro-chemical machining (ECM) and electrodischarge machining (EDM). Unlike ECM and EDM, ECSM is capable of machining electrically non-conducting materials. This paper attempts to develop a thermal model for the calculation of material removal rate (MRR) during ECSM. First, temperature distribution within zone of influence of single spark is obtained with the application of finite element method (FEM). The nodal temperatures are further post processed for estimating MRR. The developed FEM based thermal model is found to be in the range of accuracy with the experimental results. Further the parametric studies are carried out for different parameters like electrolyte concentration, duty factor and energy partition. The increase in MRR is found to increase with increase in electrolyte concentration due to ECSM of soda lime glass workpiece material. Also, the change in the value of MRR for soda lime glass with concentration is found to be more than that of alumina. MRR is found to increase with increase in duty factor and energy partition for both soda lime glass and alumina workpiece material. 相似文献
Dense alumina ceramics doped with 5 wt% 4CuO-TiO2-2Nb2O5 composite sintering aids were obtained at low sintering temperatures of 950∼975 °C. The ceramic sintered at optimal condition shows good microwave dielectric properties (εr = 12.7, Q × f = 7400 GHz), high thermal conductivity (18.4 W/m K) and high bending strength (320 MPa). TEM and EDS analysis revealed that amorphous Cu-Ti-Nb-O interfacial films with nanometer thickness formed at the grain boundaries, which could provide paths of mass transportation for densification. Al3+ ions may be involved in mass transportation through substitution by Ti3+ and Ti4+ ions near the grain boundary during the sintering process. The accumulation of copper ions at the trigeminal grain boundary was observed. The migration and reaction of copper ions in grain boundaries may also play an important role in promoting mass transportation and low-temperature densification of alumina ceramics. 相似文献
Combustion of CO, ethyl acetate and ethanol was studied over CuOx/Al2O3, CuOx–CeO2/Al2O3, CuMn2O4/Al2O3 and Mn2O3/Al2O3 catalysts. It was found that modification of the alumina with ceria before subsequent copper oxide deposition increases the activity for combustion of CO substantially, but the effect of ceria was small on the combustion of ethyl acetate and ethanol. The activity increases with the CuOx loading until crystalline CuO particles are formed, which contribute little to the total active surface. The CuOx–CeO2/Al2O3 catalyst is more active than the CuMn2O4/Al2O3 catalyst for the oxidation of CO but the CuMn2O4/Al2O3 catalyst is more active for the combustion of ethyl acetate and ethanol.
Thermal ageing and water vapour in the feed caused a modest decrease in activity and did not affect the CuOx–CeO2/Al2O3 and CuMn2O4/Al2O3 catalysts differently. In addition, no difference in intermediates formed over the two catalysts was observed.
Characterisation with XRD, FT-Raman and TPR indicates that the copper oxide is present as a copper aluminate surface phase on alumina at low loading. At high loading, bulk CuO crystallites are present as well. Modification of the alumina with ceria before the copper oxide deposition gives well dispersed copper oxide species and bulk CuO crystallites associated to the ceria, in addition to the two copper oxide species on the bare alumina. The distribution of copper species depends on the ceria and copper oxide loading. The alumina supported copper manganese oxide and manganese oxide catalysts consist mainly of crystalline CuMn2O4 and Mn2O3, respectively, on Al2O3. 相似文献
Installation of refractory castables depend not only on flow,but also on how soon the flow is lost because of setting.The loss of flow(flow decay)has always been one of the main problems of refractory castable manufacturers,a problem that has not been too well described in literature.The flow decay has been studied for a castable system based on alumina,pointing out some general trends.The flow decay was found very temperature sensitive,being strongly accelerated by temperature increases.To compensate for excessive flow loss,a retarder like citric acid may be used.Thus flow decay was measured as a function of citric acid(retarder) addition at 35℃. 相似文献
A salt of stearic acid, i.e., magnesium stearate [(C17H35COO)2Mg], can be used as a chemical template for the formation of mesoporous alumina, and is a less expensive reagent than stearic
acid. Mesoporous alumina prepared using this cost-effective surfactant shows similar pore properties with respect to pore
size (3.5 nm) and surface area (above 300 m2Vg) to that prepared using stearic acid. In addition, textural porosity, arising from non-crystalline intraaggregate voids
and spaces, was effectively removed by the addition of magnesium nitrate. The entire transformation from aluminum hydroxide
to active alumina was performed at 550 °C, and the crystallinity of the product was confirmed by powder XRD analysis.27A1 MAS NMR result shows the phase of mesoporous alumina is the γ-alumina form. 相似文献
The catalytic performance of cobalt catalysts supported on γ-Al2O3, TiO2, ZrO2 were studied for bio-ethanol steam reforming (BESR) reaction. The supported catalysts (10 wt%Co) were prepared by impregnation and characterized through Thermogravimetric analysis (TGA), H2 chemisorption, laser Raman Spectroscopy, Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), and temperature-programmed reaction (TPRxn). The metallic cobalt sites were found to correlate with the BESR reaction activity. The reaction and H2 chemisorption showed that ZrO2 supported catalyst showed the best dispersion and best catalytic activity. Over the 10% Co/ZrO2 catalyst, using a H2O:EtOH:inert molar ratio of 10:1:75 and a GHSV = 5000 h−1, 100% ethanol conversion and a yield of 5.5 mol H2/mol EtOH were obtained at 550 °C and atmospheric pressure. 相似文献