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排序方式: 共有1713条查询结果,搜索用时 31 毫秒
41.
Changmook Kim Younghun Kim Pil Kim Jongheop Yi 《Korean Journal of Chemical Engineering》2003,20(6):1142-1144
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
42.
The generation of oxygen gas within an amorphous anodic alumina film is reported. The film was formed by anodizing aluminum, which was first electropolished and then chemically polished in CrO3-H3PO4 solution, in sodium tungstate electrolyte. The procedure results in incorporation of mobile Cr3+ species, from the chemical polishing film, and mobile W6+ species, from the electrolyte, into the amorphous structure. The tungsten species are present in the outer 27% of the film thickness, while Cr6+ species occupy a thin layer within the tungsten-containing region. Above the Cr3+ containing layer, a band develops that contains oxygen bubbles of a few nanometres size. The oxygen is generated by oxidation of O2− ions of the alumina. A mechanism of oxygen generation within the alumina is proposed based on the electronic band structure of the oxide, modified by the Cr3+ and W6+ species, and on the ionic transport processes during oxide growth. 相似文献
43.
CHENZhiqiang BjomMyhre BjornSandberg 《中国耐火材料》2003,12(4):16-19
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
44.
本文介绍了用一种再结晶技术制造高炖、超细Al_2O_3粉体的新方法。 将硫酸铝铵溶液(AA)滴入碳酸氢铵溶液(AHC),经过反应合成一种新的含铝化合物,碳酸氢铝铵(AACH),然后在高温下煅烧,生成超细Al_2O_3粉体。另外还采用了X射线,红外光谱,DTA,以及TEM等手段,研究了反应温度、浓度、PH值和老化条件等对生成物AACH和Al_2O_3的影响。 相似文献
45.
Christine Baatz Nadine Thielecke Ulf Prüße 《Applied catalysis. B, Environmental》2007,70(1-4):653-660
In this work, two deposition–precipitation methods for the preparation of gold catalysts for glucose oxidation were investigated. Thus far, gold colloids immobilized on carbon have been used for catalytic glucose oxidation, but the long-term stability of these systems was not sufficient. To improve the long-term stability we used the deposition–precipitation methods using NaOH (DP NaOH) or urea (DP urea) as precipitation agents as they were described by Haruta and Dekkers, respectively, using alumina as a support material. With these methods, it was possible to prepare highly active and selective catalysts which showed an excellent long-term stability. DP urea was found to be the preferred method, because in contrast to DP NaOH, no losses of gold occurred during the preparation, and it was possible to adjust various gold contents up to 10 wt% Au. 相似文献
46.
喷雾热解法制备高纯超细氧化铝粉 总被引:3,自引:0,他引:3
本文以高纯硫酸铝铵为原料,用喷雾热解法制得纯度大于99.9%、细度为10 ̄20nm的高纯超细α-Al2O3粉。探讨喷雾热解工艺条件对粉体性能的影响。 相似文献
47.
采用微波加热法在堇青石蜂窝陶瓷基体表面涂覆多孔Al2O3涂层,研究了制备条件对堇青石蜂窝陶瓷表面Al2O3涂层中Al2O3的质量分数的影响。通过BET、SEM对涂层结构及形貌进行了表征,结果表明,采用微波加热法制备的Al2O3涂层均匀、稳定,具有较大的比表面积、孔容和较高的Al2O3质量分数。 相似文献
48.
A closed form solution has been obtained for laser drilling of silicon nitride (Si3N4) and alumina ceramics (Al2O3). The drilling of workpiece is performed by using a TEM00 10 ns pulse Nd:YAG laser. It is assumed that the phase transition from solid to vapor occurs without melting. Considering the absorption of plasma plume formed on the surface of the ceramics, the one-dimensional thermal model is developed in order to describe the drilling process. The governing equation of heat-diffusion is solved analytically using a Laplace transformation method. Erosion depth per laser pulse obtained from the closed form solution agrees with the available experimental data. 相似文献
49.
T.J. Nijdam 《Surface & coatings technology》2006,201(7):3894-3900
A combined pre-annealing and pre-oxidation treatment was developed for the processing of partially yttria stabilized (PYSZ) thermal barrier coatings (TBC) on top of NiCoCrAlY bond coatings (BC). To develop this pre-treatment, the influence of the oxygen potential during pre-annealing and pre-oxidation on the life span and failure mechanisms of the entire high temperature coating system upon thermal cycling was investigated. The results of this study showed that the service life of the coating system depended strongly on the composition and microstructure of the thermally grown oxide (TGO) after pre-oxidation. The longer life spans were obtained if the TGO thickened very slowly during thermal cycling due to a large α-Al2O3 grain size. Such a slow-growing TGO corresponded with a pre-treatment for which θ-Al2O3 was formed during pre-oxidation and for which the yttrium was located within a high density of pegs along the TGO/BC interface after pre-oxidation. If the yttrium was present on top of the TGO after pre-oxidation, a thick mixed alumina-zirconia layer formed upon thermal cycling. This mixed oxide layer contributed significantly to the total oxide layer thickness, resulting in short life spans. The formation of NiAl2O4 spinel in between the TBC and the α-Al2O3 should be avoided, since this can lead to premature failure along the spinel/α-Al2O3 interface. 相似文献
50.
Finite element prediction of material removal rate due to electro-chemical spark machining 总被引:1,自引:1,他引:1
K.L. Bhondwe Vinod Yadava G. Kathiresan 《International Journal of Machine Tools and Manufacture》2006,46(14):1699-1706
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