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高温高表面氧化铝新材料的制备化学研究——La、Ba共添加对氧化铝热稳定性的影响 总被引:9,自引:0,他引:9
本文用镧、钢共同添加并使用溶胶-凝胶法制得改性氧化铝,详细研究了在保持La含量为5.2 wt%时,Ba添加量的改变对氧化铝热稳定性的影响,实验结果表明镧,钡元素的共添加能大大增加氧化铝的热稳定性,从而使氧化铝在高温下保持高比表面积,体相中同时添加5.2wt%La和2wt?以及5.2wt%La和7wt?能使氧化铝保持较好的热稳定性,样品经1100℃煅烧20h后,比表面分别达100.8m^2.g^-1和92.3m^2.g^-1.通过对添加物与氧化铝保持高温高表面能力的内在联系的探讨,得出Ba、La元素的添加提高氧化铝热稳定性的原因主要表现在两方面,一是抑制氧化铝的微孔烧结速度,二是阻止了氧化铝向α相的转变。 相似文献
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高温高表面氧化铝新材料的制备化学研究——La、Ba共添加对氧化铝热稳定性的影响 总被引:1,自引:0,他引:1
本文用镧、钡共同添加并使用溶胶-凝胶法制得改性氧化铝。详细研究了在保持 La含量为 5.2wt%时, Ba添加量的改变对氧化铝热稳定性的影响。实验结果表明镧、钡元素的共添加能大大增加氧化铝的热稳定性,从而使氧化铝在高温下保持高比表面积。体相中同时添加 5.2wt% La和 2wt% Ba以及 5.2wt% La和 7wt% Ba能使氧化铝保持较好的热稳定性,样品经 1100℃煅烧 20h后,比表面分别达 100.8m2· g-1和 92.3m2· g-1。通过对添加物与氧化铝保持高温高表面能力的内在联系的探讨,得出 Ba、 La元素的添加提高氧化铝热稳定性的原因主要表现在两方面:一是抑制氧化铝的微孔烧结速度;二是阻止了氧化铝向α相的转变。 相似文献
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堇青石蜂窝陶瓷载体涂层热稳定性及改性机制研究 总被引:3,自引:0,他引:3
利用XPS,PLS,XRD,BET,TEM等现代分析手段,研究了本实验中制备的经镧和钡修饰的改性氧化铝涂层的热稳定性和改性机理,认为介稳态的γ相向介稳态的δ相和θ相转变和氧化铝颗粒的长大是改性涂层高温烧结的原因,镧和钡的加入可有效地抑制介稳态的氧化铝向热力学上稳定的α-Al2O3的转变,一定程度上提高了氧化铝的高温热稳定性.通过考察La3 与Ba2 在改性氧化铝涂层中的分布规律,提出掺杂离子进入氧化铝晶格缺陷的改性机理,并探讨了不同类型的缺陷的大小和浓度随温度的变化规律. 相似文献
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以铂为活性组分,氧化铝颗粒、单晶硅片及单晶硅片支撑的氧化铝薄膜为载体,制备了甲醇室温催化燃烧催化剂,研究了载体种类、载体性质、制备方法及铂负载量对催化剂活性的影响.结果表明,所制备的催化剂均可使甲醇在室温下燃烧;作为甲醇燃烧催化剂的载体,氧化铝优于单晶硅,薄膜状氧化铝优于颗粒状氧化铝.当载体种类和性质均相同时,化学分散... 相似文献
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氧化铝基表层镁铝尖晶石的研究Ⅰ.表层镁铝尖晶石的相结构、孔结构、表面酸性及负载钯的化学状态 总被引:10,自引:0,他引:10
对<1000℃焙烧的的r-AL2O3载镁体系进行了相表征,发现在基质氧化铝上形成了表层镁铝尖晶石 ,具有“原晶石结构”的r-Al2O3则在<1000℃保持物相不变。进一步研究玻了这种氧化铝基表层镁铝晶石的孔结构,表面酸性以及负载钯的分散与化学状态,结果表明:氧化铝基表层晶石的孔结构和表面酸性由构成的氧化铝基决定,并随温度变化;表层尖晶石仅可稳定氧化铝基的物相,与其孔性质和酸性无关;负载在氧化铝基表 相似文献
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丙烯是一种重要的化工原料,目前工业上主要来自石脑油、轻质油以及其他石油副产物的蒸汽裂解和催化裂解.这些过程能耗巨大,碳排放严重.丙烷直接脱氢制丙烯原料利用率高,副产物少,是一条更加经济环保的丙烯生产路线.Cr_2O_3-Al_2O_3催化剂因其出色的性能和低廉的价格已在工业中应用,但氧化铝表面酸位点易催化副反应及积碳的形成,从而造成催化剂失活.因此,调控载体氧化铝结构具有重要的意义.氧化铝的结构性质取决于合成条件以及焙烧过程表面羟基和水分的逐步脱除.我们课题组通过水热法合成了一系列表面粗糙的棒状氧化铝和富含五配位铝离子的片状氧化铝,以这些氧化铝为载体制备的负载型贵金属催化剂在催化反应中表现出优异的活性和稳定性.本文在前期工作基础上研究了不同焙烧温度对棒状氧化铝表面结构的影响,采用X射线衍射(XRD)、氮吸附、电镜(SEM/TEM)、氨气程序升温脱附(NH3-TPD)和紫外-可见光谱(UV-Vis)等手段表征了氧化铝结构,并探究了其对负载氧化铬催化剂上丙烷脱氢反应的影响.XRD结果表明,低温焙烧所得主要为γ相氧化铝,提高焙烧温度至900oC时出现δ相氧化铝.氧化铝氮气吸附-脱附表现出IV型等温线,随焙烧温度升高,介孔结构保持,但比表面积和孔体积呈减小趋势.电镜观察显示氧化铝为棒状结构,表面粗糙.NH_3-TPD结果表明自制氧化铝酸量低于商业氧化铝,且随焙烧温度升高酸量下降.以上结果表明焙烧温度在氧化铝性质调控过程中起重要作用.以不同焙烧温度下制得的氧化铝等体积浸渍氧化铬制得氧化铬催化剂.丙烷脱氢反应结果表明,催化剂表现出优异的稳定性和再生性能.氮吸附等温线表明新鲜催化剂为介孔结构,这有利于反应物接触活性位点,并提供抗积碳阻塞能力.对比氧化铝负载氧化铬前后的电镜照片可知,催化剂表面粗糙度降低,说明活性组分均匀分散于氧化铝粗糙表面;反应前后催化剂形貌保持不变,催化剂在反应中表现出优异的结构稳定性.UV-Vis和H_2-TPR结果表明,自制氧化铝和参比氧化铝表面的铬物种以相似配位状态存在,但铬物种在自制氧化铝表面更难还原,表现出更强的金属与载体相互作用.NH_3-TPD结果表明,自制催化剂表面酸量(64μmol NH_3 g~(–1))远低于参比催化剂(140μmol NH_3 g~(–1)).热重分析证实反应后自制催化剂积碳量明显低于参比催化剂.自制棒状氧化铝作为载体制备的氧化铬低酸催化剂可抑制积碳形成,提高丙烯选择性,在丙烷脱氢反应中表现出优异的活性和抗积碳能力. 相似文献
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D.R. Glasson 《Thermochimica Acta》1984,82(1):201-210
Methods of phosphate bonding of oxide ceramics are summarised. Applications of vacuum balance techniques are described to study the sintering of lime, magnesia, alumina and kaolin in the presence of phosphoric acid and sodium polymetaphosphate additives. Changes in surface area, crystallite and aggregate sizes during sintering have been determined by gravimetric B.E.T. nitrogen gas sorption techniques, supported by X-ray diffractometry, optical and electronmicroscopy.Phosphoric acid has comparatively little influence on lime and magnesia sintering. There is no enhancement of sintering and even slight activation at temperatures between 800–1000 °C, when chemical reactions with the additive are completed. In contrast, sodium polymetaphosphate additive enhances sintering of lime and magnesia at temperatures between 500–1000 °C. When kaolin is calcined with sodium polymetaphosphate, the activated alumina in the intermediate metakaolinite readily forms aluminium phosphate to accelerate sintering. 相似文献
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Zicheng Li Aiju Zhang Zhihong Li Yumei Zhu Liangjun Liu Huiqiang Xiang 《Journal of Sol-Gel Science and Technology》2011,57(1):24-30
The effect of ball milling process, co-doped seed and two step sintering technique on the properties of sol–gel derived alumina
abrasive sintered at low temperature was investigated. The results showed that ball milling time with 10 h can be effective
in enhancing the activity of the precursor and the microstructural uniformity of sintered alumina abrasive. A small amount
of Al2O3–(NH4)3AlF6 co-doped seed addition had potential synergistic effects for reducing α-Al2O3 phase transformation temperature and improving the mechanical property of alumina abrasive. A remarkable suppression of grain
growth was achieved by controlling sintering temperature with two-step sintering method. Therefore, by using ball milling
process, co-doping α-Al2O3–(NH4)3AlF6 seed and two-step sintering technique, the sol–gel derived uniform nanocrystalline alumina abrasive is easily achieved at
low temperature. Nanocrystalline alumina abrasive prepared at these conditions exhibited excellent mechanical properties and
wear resistance compared to fused corundum abrasive and those sol–gel derived corundum abrasive with conventional sintering
methods. 相似文献
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A. Sedaghat E. Taheri-Nassaj G. D. Soraru T. Ebadzadeh 《Journal of Sol-Gel Science and Technology》2011,58(3):689-697
This paper compares the microstructure development of two alumina–15 vol% mullite composites during the sintering. The nanopowders
of alumina–mullite composite were synthesized by the sol–gel method using aluminum chloride hexahydrate and two different
silicon sources (colloidal silica in route 1 and tetraethyl orthosilicate in route 2). The alumina–mullite composites were
prepared by pressing and sintering of the nanopowders. Although the intergranular mullites were observed in both routes, there
were mullite particles in route 2 formed inside the alumina grains (intragranular mullite). Formation of the intragranular
mullite is attributed to the drop in silica solubility, which occurs during the transition from metastable alumina to stable
alumina. Compared to route 1, the relative density and the average grain size were increased and accelerated by route 2. The
two-stage sintering is not useful for the mullite decomposition. 相似文献
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L.R.B. Santos S.H. Pulcinelli C.V. Santilli 《Journal of Sol-Gel Science and Technology》1997,8(1-3):477-481
In this work, the effect of the substrate microstructure on the formation of SnO2 membranes and of the sintering conditions on their porosity have been analysed. Samples have been prepared by colloidal suspensions
cast on alumina or kaolin substrates. Supported membranes have been characterized by Hg porosimetry, MEV, XRD and N2 adsorption-desorption isotherms. The results show that the narrower pore size distribution of alumina substrate allowed to
prepare membranes more homogeneous and free of cracks than that supported on kaolin. The crystallite and pore sizes of the
membranes could be controlled by adjusting the temperature of sintering, allowing materials with adequate microstructure with
application for ultrafiltration process. 相似文献
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Song-Taek Oh Sang-Min Kim Man-Suk Yoon Hyo-Kyung Lee Gwon-Koo Yeo Ho-In Lee 《Reaction Kinetics and Catalysis Letters》2007,90(2):339-345
Two kinds of vehicle-aged diesel oxidation catalysts were analyzed. The phase transition of alumina as a support and Pt sintering
after a long-time operation caused serious deactivation of the catalysts. 相似文献
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Rou-Jane Liu Peter A Crozier C Michael Smith Dennis A Hucul John Blackson Ghaleb Salaita 《Microscopy and microanalysis》2004,10(1):77-85
Sintering of a palladium catalyst supported on alumina (Al2O3) in an oxidizing environment was studied by in situ transmission electron microscopy (TEM). In the case of a fresh catalyst, sintering of Pd particles on an alumina surface in a 500 mTorr steam environment happened via traditional ripening or migration and coalescence mechanisms and was not significant unless heating above 500 degrees C. After the catalyst was used for the hydrogenation of alkynes, TEM coupled with convergent beam electron diffraction and electron energy loss spectroscopy analysis revealed that most of the Pd particles were lifted from the alumina surface by hydrocarbon buildup. This dramatically different morphology totally changed the sintering mechanism of Pd particles during the regeneration process. Catalytic gasification of hydrocarbon around these particles in an oxidizing environment allowed the Pd particles to move around and coalesce with each other at temperatures as low as 350 degrees C. For catalysts heating under 500 mTorr steam at 350 degrees C, steam stripped hydrocarbon catalytically at the beginning, but the reaction stopped after 4 h. Heating in air resulted in both catalytic and noncatalytic stripping of hydrocarbon. 相似文献
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Laura Montanaro Paola Palmero Mariangela Lombardi Claude Esnouf Jérôme Chevalier Sandrine Cardinal 《Journal of Thermal Analysis and Calorimetry》2013,112(1):437-445
The free sintering of ceramic powders into fully dense nanostructured materials is still a challenging process, even more complex when nanostructured transition alumina is used as starting powder. In this paper, biphasic (Alumina–YAG) and triphasic (Alumina–YAG–ZrO2) composite powders were produced by doping the same nanocrystalline transition alumina with inorganic precursors of the second-phases, which were subsequently yielded under controlled thermal treatments. The added dopants significantly increased both the θ- to α-phase transformation and the sintering temperatures, making even more difficult the retention of the starting nanometric grain size into the final dense materials. Thermal analyses (such as TG–DTA and dilatometry) are here used to support most of the ceramic processing steps involved in a successful elaboration of the desired ultra-fine structures. In fact, the thermal pre-treatments of the doped powders were set up on the ground of the DTA–TG curves whereas the dilatometric analyses were exploited to design optimised sintering cycles, through which the green bodies were successfully consolidated into fully dense materials, characterised by highly homogeneous and tailored micro/nanostructures. 相似文献
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溶胶-凝胶法制备钯催化剂的织构与性能 总被引:1,自引:0,他引:1
采用溶胶-凝胶法制备了Pd/Al2O3催化剂,用LLS(激光光散射)、XRD和BET等技术考察了溶液pH值对所成胶体粒子流体力学半径、相应催化剂产品孔径分布及热稳定性的影响.研究发现,由pH=4.1的胶体制备的催化剂具有良好的热稳定性和CO、C3H6的氧化活性.氧化镧添加剂可抑制Al2O3载体在高温下由γ相向α相的转化,同时也促进了催化剂上Pd粒子的生长. La2O3可提高新鲜Pd催化剂的氧化活性,但对老化后催化剂活性的提高无促进作用. 相似文献
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V. S. Rimkevich A. A. Pushkin Yu. N. Malovitskii L. P. Dem’yanova I. V. Girenko 《Russian Journal of Applied Chemistry》2009,82(1):6-11
Integrated processing of non-bauxite ores using ammonium hydrogen difluoride was studied. The kinetics of sintering of the raw material, sublimation of ammonium hexafluorosilicate, and formation of aluminum fluoride and alumina were described. The rate constants and activation energies of the reactions were determined. 相似文献
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Gelcasting is a new method for forming advanced ceramics based on obtaining intermediary gels promoted by polimerization “in situ” within the ceramic slurry. Gelcast composites of an ALCOA A-1000 alumina and the copolymer obtained using acrylamide and N,N′-metylene-bisacrylamide as monomers were characterized by thermogravimetry. Polymer distribution was determined by thermogravimetric analysis of small size specimens that were taken from different parts of the alumina composites formed in different shapes. Derivative thermogravimetry was used to identify the resulting polymerization stage within the gelcast body, as well as to study the influence of mold materials and operating conditions. All the composites show an even distribution of the polymer in the bulk, which enables machining in the green state and obtaining high density alumina bodies after sintering. 相似文献