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排序方式: 共有165条查询结果,搜索用时 0 毫秒
1.
Sittichai Natesakhawat Xueqin Wang Lingzhi Zhang Umit S. Ozkan 《Journal of molecular catalysis. A, Chemical》2006,260(1-2):82-94
Chromium-free iron-based catalysts were prepared and studied in regard to their performance in the high-temperature water-gas shift reaction (HTS). The effects of various catalyst preparation variables (i.e., Fe/promoter ratio, pH of precipitation medium, calcination and reduction temperatures) and preparation methods were investigated. Aluminum is a potential chromium replacement in HTS catalysts. Further improvement in WGS activity of Fe–Al catalysts can be achieved by the addition of small amounts of copper or cobalt. Catalysts were characterized using BET surface area measurements, temperature-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). As a textural promoter, aluminum and chromium prevent the sintering of iron oxides and stabilize magnetite phase by retarding its further reduction to FeO and metallic Fe. The promotional effect of Cu is found to be strongly dependent on the preparation method. 相似文献
2.
《中国化学快报》2021,32(10):3221-3225
Electrochemical heterogeneous catalytic ozonation (E-catazone) is a promising and advanced oxidation technology that uses a titanium dioxide nanoflower (TiO2-NF)-coated porous Ti gas diffuser as an anode material. Our previous study has highlighted that the importance of the TiO2-NF coating layer in enhancing OH production and rapidly degrading O3-resistant drugs. It is well known that the properties of TiO2-NF are closely related to its sintering temperature. However, to date, related research has not been conducted in E-catazone systems. Thus, this study evaluated the effect of the sintering temperature on the degradation of the O3-resistant drug para-chlorobenzoic acid (p-CBA) using both experimental and kinetic modeling and revealed its influence mechanism. The results indicated that the TiO2-NF sintering temperature could influence p-CBA degradation and OH production. TiO2-NF prepared at 450 °C showcased the highest p-CBA removal efficiency (98.5% in 5 min) at a rate of 0.82 min−1, and an OH exposure of 8.41 × 10−10 mol L−1 s. Kinetic modeling results and interface characterization data revealed that the sintering temperature could alter the TiO2 crystallized phase and the content of surface-adsorbed oxygen, thus affecting the two key limiting reactions in the E-catazone process. That is, ≡TiO2 surface reacted with H2O to form TiO2-(OH)2, which then heterogeneously catalyzed O3 to form OH. Consequently, E-catazone with a TiO2-NF anode prepared at 450 °C generated the highest surface reaction rate (5.00 × 10−1 s−1 and 4.00 × 10-3 L mol-1 s−1, respectively), owing to its higher anatase content and adsorbed oxygen. Thus, a rapid O3-TiO2 reaction was achieved, resulting in an enhanced OH formation and a highly effective p-CBA degradation. Overall, this study provides novel baseline data to improve the application of E-catazone technology. 相似文献
3.
Duncan?P.?FaggEmail author Vladislav?V.?Kharton Jorge?R.?Frade 《Journal of Solid State Electrochemistry》2004,8(9):618-625
Small (2 mol%) cobalt oxide additions to ceria-gadolinia (CGO) materials considerably improve sinterability, making it possible to obtain ceramics with 95–99% density and sub-micrometre grain sizes at 1,170–1,370 K. The addition of Co causes a significant shift of the electrolytic domain to lower pO2. This modification to the minor electronic conductivity of the electrolyte material has influence on the cathodic oxygen reduction reaction. The impedance technique is shown to provide information not only about polarisation resistance, but also about the active electrode area from analysis of the current constriction resistance. It is demonstrated that this current constriction resistance can be related to the minor electronic contributions to total conductivity in these materials. A simple imbedded grid approach gives control of the contact area allowing the properties of the electrolyte materials to be studied. A much lower polarisation resistance for the Co-containing CGO electrolyte is observed, which can be clearly attributed to an increased three-phase reaction area in the Co-containing material, as a consequence of elevated p-type conductivity. 相似文献
4.
The drying and sintering processes of SiO2–ZrO2 alkoxide-derived gels have been studied by means of DSC technique. In the drying process, most part of water and alcohols are removed from the gels. For the SiO2 gel such elimination occurs at the end of the drying process, however for the ZrO2 gel this elimination occurs during the whole drying time. An intermediate behavior is observed for the binary system SiO2–ZrO2 gels. In the sintering process, the DSC technique allows to determine the elimination of water and alcohols retained within the structure (open or close pores) and the well-known hydroxyl condensation of silica gel between 700° and 800°C is also observed. The ZrO2 gel shows the final hydroxyl condensation at the heating temperature of 600°C. For the binary SiO2–ZrO2 gels, the hydroxyl condensation has been associated to the activation energy needed for the dissociation of silica hydroxyls. This energy decreases with the ZrO2 concentration in the gel resulting in a sintering treatment of 500°C leading to the entire hydroxyl condensation for the gel with 75% ZrO2–25% SiO2.
By studying the temperature of the DSC peaks, it is possible to know the temperature at which most part of water and alcohols are leaving the gel, and these results can be used in order to select the corresponding drying or sintering schedules for obtaining a well-fabricated material. 相似文献
5.
Densification of boron carbide during sintering may be improved by a two-stage process, namely heating to 2000°C under vacuum and sintering at 2190°C under argon. This sintering regime allows achieving a relative density of the ceramic bodies fabricated from a fine powder higher than 95%. The nitrogen treatment of the boron carbide phase at 1900°C leads to the formation of the BN phase and precipitation of graphite. Vacuum treatment of these samples at 2000°C leads to decomposition of the boron nitride phase. The liberated free boron may again react with graphite to form in situ boron carbide particles. The experimental investigations of the sintering behavior of the boron carbide phase under various atmospheres supported the thermodynamic predictions regarding the phase transformation. No evidence, however, was found for enhanced sintering under a nitrogen atmosphere. 相似文献
6.
Anatoliy Nechepurenko 《Journal of solid state chemistry》2004,177(2):616-618
The investigation of sintering conditions for magnesiothermic amorphous boron (MgmBn) powder is presented. The results of chemical and X-ray analyses of magnesiothermic boron (MgmBn) indicate that it consists of amorphous boron MgB12 and a lesser amount of β-rhombohedral boron. The MgmBn-sintering process is determined by the conditions of amorphous boron transformation into β-boron (crystallization), such as the process of decomposition of MgB12 followed by formation of the “new” centers of active elementary boron. As a result of the experimental investigations of this process the following three stages—thermal decompositions, crystallization and MgmBn sintering—were combined into one sintering process with the sintered bodies as a result of it. 相似文献
7.
Electromagnetic processing was used to study the effects of electro-magneto forming on the dimensional control and thermal stability of sintered powder metal (PM) parts. The investigation was carried out on sinter-hardened, low chromium-molybdenum bainitic steel. The results show an increase in the microhardness of about 14% for the electromagnetic processed parts compared to the as-sintered parts. This was attributed to the 2% increase in the density, 17% and 29% reduction in the volume fraction of porosity and width of the bainitic lath, respectively, due to the electromagnetic processing. Dimensional characterization was carried out using a vertically aligned push-rod dilatometer. After four thermal cycles of heating and cooling, at a controlled rate of 5 °C/min to 1000 °C, the electromagnetic processed parts exhibited reduced dimensional change of about 44% lower than for the as-sintered parts. This is significantly important for applications that demand high dimensional tolerance and performance, especially at elevated temperatures. 相似文献
8.
利用新的单中心Ziegler-Natta(Z-N)催化剂,通过干预分子链的生长与聚集行为,可获得低缠结的超高分子量聚乙烯(UHMWPE)初生树脂.本研究利用这类低缠结UHMWPE,通过设置不同的烧结温度(Ts)来改变熔体缠结状态,并探讨了链缠结程度对烧结制品结构与性能的影响.实验结果表明TS=220℃下,UHMWPE样品发生显著的复缠,造成高缠结度;而Ts=170℃下,初始低缠结状态能够得以充分保留,从而获得了缠结度具有明显差别的不同样品.示差扫描量热法(DSC)测试表明,在Ts=170℃下,低缠结度有利于在随后等温及冷却结晶过程中生成高熔点(最高达141℃)晶体与高的结晶度(最高达65%).力学测试表明低缠结度制品的综合力学性能显著提升,其中屈服强度提高72%,拉伸断裂强度提升139%,弹性模量提升162%以及断裂伸长率提升36%,实现了同时增强增韧.这就提供了一种从调节链缠结温度实现UHMWPE烧结制品高性能化的新思路. 相似文献
9.
钢渣是冶金工业中产生的主要固体废弃物,其产量约为每年粗钢产量的15%~20%。由于技术的局限,导致我国钢渣利用率较低,仅为年钢渣产量的10%,同时加之管理制度的不健全,导致钢渣大量露天堆放,对土地资源、地下水源,以及空气质量形成严重影响。固体废弃物再利用是资源可持续发展的重要途径之一,钢渣的主要化学成分为CaO, SiO2, Al2O3, MgO, Fe2O3, MnO, f-CaO等。面对上述问题,利用冶金固体废弃物与活性炭开发一种价格低廉且性能优越的活性炭混合钢渣复合材料,既是冶金固体废弃物的高附加值利用与资源可持续发展的重要途径之一,也是大幅降低改性活性炭生产成本与提高经济效益的重要途径之一。该研究创新性以活性炭与钢渣为研究对象,利用钢渣中含有的金属氧化物对活性炭进行改性处理制备用于烧结烟气脱硫脱硝的活性炭混合钢渣复合材料,通过搭建实验反应装置对活性炭混合钢渣复合材料的脱硫脱硝性能进行测试。利用X射线荧光光谱仪(XRF)对钢渣的化学成分进行测试与分析,比表面积及孔径测定仪(BET)对活性炭混合钢渣复合材料的孔结构进行测试与分析,傅里叶变换红外光谱仪(FTIR)对钢渣的结构组成进行测试与分析,扫描电子显微镜(SEM)对活性炭混合钢渣复合材料的微观结构进行测试与分析,以揭示活性炭与钢渣制备活性炭混合钢渣复合材料的机理,以及活性炭混合钢渣复合材料对烧结烟气脱硫脱硝的机理。结果表明:当钢渣为电炉热泼渣、钢渣与活性炭质量比为2∶4、钢渣与活性炭细度为400目时,活性炭混合钢渣复合材料具有良好的脱硫脱硝性能与合理的经济性,即脱硫效率为100%、脱硝效率为58%。活性炭混合钢渣复合材料具有的多孔结构对SO2和NO进行有作用,钢渣中Fe2O3与MnO2促使活性炭官能团进行催化还原反应提高脱硫脱硝性能,其中吸附作用是主导与前提,催化还原反应是辅助与协同。以期为高附加值的钢渣利用提供新途径,实现钢铁企业以废治废、以废增效的目的。 相似文献
10.
Nanosized cobalt ferrite spinel particles have been prepared by using mechanically alloyed nanoparticles. The effects of various preparation parameters on the crystallite size of cobalt ferrite which includes milling time; ball-to powder weight ratio (BPR) and sintering temperature, were studied using X-ray diffractometer (XRD). Scherrer's equation was used to study the crystallite size evolution of the as-prepared materials. The results of the as-milled sample revealed that both milling time and BPR plays a role in determining the crystallite size of the milled powder. However, where sintering is involved, the sintering temperature results in grain growth, and thus plays a dominant role in determining the final crystallite size of the samples sintered at higher temperature (above 900 °C). From the vibrating-sample magnetometer (VSM) measurement it was observed that the coercivity of the as-milled samples without sintering is almost negligible, which is a type characteristic of superparamagnetic material. However, for the sintered samples, the saturation increases while coercivity decreases with increases sintering temperature. 相似文献