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以硫酸铝为原料,用沉淀法制取纳米氧化铝,研究了其相变过程。用XRD、SEM、AFM及IR等手段对不同温度下煅烧所得的产品进行了表征。结果表明,该方法制备的氧化铝粉体呈球形、团聚程度轻、粒度分布较均匀、γ相和δ相平均粒径20-30nm、α相平均粒径53nm,其物相变化次序为:非晶态Al2O3→γ-Al2O3→δ-A12O3→α-Al2O3。 相似文献
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用烧结法生产喷涂氧化铝。实验采用水冷非转移式等离子喷枪 ,工作气体为N2 、H2 ,其纯度 99.9%。稳定相α-Al2 O3经等离子射流熔融、淬冷后 ,转变为亚稳相γ -Al2 O3及球化低钠氧化铝 ,经试验确定 ,Al2 O3的相变历程如下 :α -Al2 O3等离子射流 熔体 淬冷 γ -Al2 O380 0℃ ε -Al2 O3110 0℃ α -Al2 O3 相似文献
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Xuelian Du 《Materials Research Bulletin》2009,44(3):660-665
Bayerite [α-Al(OH)3] was ground for 2 h and its structure change was characterized. Soft grinding reduces the grain size of bayerite, causes a lattice distortion in bayerite, and accelerates the phase transition from bayerite to the stable phases. With addition of α-Al2O3 seeds, calcining the ground bayerite at 300 °C leads to the onset of the α-Al2O3 formation. The onset temperature and the completion temperature of the transformation to α-Al2O3 in the ground bayerite are about 800 and 150 °C lower than the onset temperature and the completion temperature of the transformation to α-Al2O3 in the unground bayerite, respectively. The thermal decomposition of the ground bayerite undergoes the α-Al(OH)3 → γ-AlOOH → γ-Al2O3 → α-Al2O3 path without the formation of the θ-Al2O3 transition phase. The effect of soft grinding on the structure of bayerite and the final thermal decomposition product of bayerite will be discussed. 相似文献
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以440℃预烧后的AlOOH或无定形Al2O3为原料,乙醇为分散剂,采用机械球磨和常压焙烧法制备α-Al2O3粉体,探讨矿化剂AlF3及机械球磨对α-Al2O3性能的影响,利用扫描电镜、X射线衍射、X射线圆盘式离心粒度分析仪等手段对α-Al2O3粉体分散性、颗粒形貌和物相进行表征。结果表明,焙烧后得到纯α-Al2O3相粉体,且随着AlF3用量的增加,α-Al2O3粉体的分散性变差,α-Al2O3的形貌由多维向二维转化,从而形成片状α-Al2O3;由于机械力化学及F-的作用,球磨4 h出现六方片状α-Al2O3,且随着球磨时间的延长,六方片状α-Al2O3数量增多,粒径增大。 相似文献
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在碳酸铝铵法制备氧化铝工艺的基础上,通过加入晶体生长促进剂及改变热分解工艺等方法,有效控制了α-Al2O3颗粒的大小和形貌。结果表明:促进剂对α-Al2O3的相变过程影响很大,加入促进剂后使其相转变温度降低了200℃,至1000℃时已完全转变为α-Al2O3相;升温方式对α-A2lO3颗粒的形貌影响很大,将含促进剂的样品直接入高温炉煅烧时,倾向于形成六角片状颗粒;而先低温后高温煅烧时则会形成圆饼状颗粒。通过控制升温过程,可以控制得到粒径较小的圆饼状α-Al2O3颗粒,且分散性良好。 相似文献
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The ZrO2-CeO2-AI2O3 system has been assessed with the CALPHAD (Calculation of Phase Diagrams) technique using the PARROT procedure. The experimental information on the ZrO2-AI2O3, AI2O3-CeO2 systems as well as the isothermal sections of the ternary system at 1673 K and 1873 K is well reproduced. According to the assessed isothermal section at 1723 K, no alumina dissolves into the tetragonal zirconia phase. Specimens with different alumina content are fabricated from commercial 12 mol pct CeO2-stabilized ZrO2 powder (12Ce-ZrO2). The thermodynamic properties are consistent with the observed microstructure, which present a combination of tetragonal phase and alumina grains. 相似文献
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Gravani S Polychronopoulou K Stolojan V Cui Q Gibson PN Hinder SJ Gu Z Doumanidis CC Baker MA Rebholz C 《Nanotechnology》2010,21(46):465606
γ-Al(2)O(3) is a well known catalyst support. The addition of Ce to γ-Al(2)O(3) is known to beneficially retard the phase transformation of γ-Al(2)O(3) to α-Al(2)O(3) and stabilize the γ-pore structure. In this work, Ce-doped γ-Al(2)O(3) nanowires have been prepared by a novel method employing an anodic aluminium oxide (AAO) template in a 0.01 M cerium nitrate solution, assisted by urea hydrolysis. Calcination at 500?°C for 6 h resulted in the crystallization of the Ce-doped AlOOH gel to form Ce-doped γ-Al(2)O(3) nanowires. Ce(3+) ions within the nanowires were present at a concentration of < 1 at.%. On the template surface, a nanocrystalline CeO(2) thin film was deposited with a cubic fluorite structure and a crystallite size of 6-7 nm. Characterization of the nanowires and thin films was performed using scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction. The nanowire formation mechanism and urea hydrolysis kinetics are discussed in terms of the pH evolution during the reaction. The Ce-doped γ-Al(2)O(3) nanowires are likely to find useful applications in catalysis and this novel method can be exploited further for doping alumina nanowires with other rare earth elements. 相似文献
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以氯化铝、碳酸钠为原料,采用直接沉淀法,并于500~1,200℃煅烧,制备纳米Al2O3粉体。然后用TiO2、BaO对纳米Al2O3粉体掺杂,控制其物相转变过程。通过X射线衍射仪、差式扫描量热仪和透射电子显微镜分析纯净和掺杂后的纳米Al2O3的物相转变过程。结果表明,直接沉淀法所得水合Al2O3,经500℃煅烧后可转变为纳米活性Al2O3,粒径约为10 nm;纯净和掺杂Al2O3样品经1,200℃煅烧2 h后均为纳米粉体,其粒径为40~50 nm;在较高温度下,掺杂氧化钡对Al2O3的物相转变具有强烈抑制作用,粉体直至1,200℃仍未转变为结晶良好的α-Al2O3物相;而氧化钛则对其物相转变有显著促进作用,在1,000℃时粉体的主要物相即为α-Al2O3,1,100℃之后粉体已完全转变为α-Al2O3。 相似文献
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在勃姆石AlOOH溶胶中引入一定量的H2BO3溶液,经不同温度的热处理,制成不同硼掺杂含量的无支撑的γ-A12O3催化膜。用XRD、BET分别对膜的晶相和膜的微孔结构,包括比表面积、孔径和孔容进行了研究,结果发现:随着硼含量的增加,在低温下,膜的比表面积和孔容都不断增加,而对孔径的影响不大;经1200℃处理后,未掺杂硼的膜的比表面积,孔径和孔容分别为5.4m2/g,49nm和0.063cm3/g,而经掺杂16%摩尔硼的膜的比表面积,孔径和孔容分别为35m2/g,13nm和0.225cm3/g,这说明硼的掺杂对γ-A12O3膜的热稳定性有很好的改善作用。 相似文献
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研究了CeO2/γ-Al2O3单分子层复合微粉的制备机理.研究结果说明,CeO2可以在γ-Al2O3表面形成单层分散相,可以通过浸渍、焙烧的方法制备CeO2/γ-Al2O3单分子层复合微粉;CeO2起始物的种类对其单层分散阈值(最大单层分散容量)有影响,以硝酸亚铈为起始物的CeO2/γ-Al2O3复合微粉的CeO2单层分散阈值为0.042gCeO2/g(γ-Al2O3),而以醋酸亚铈为起始物的CeO2单层分散阈值则为0.10gCeO2/g(γ-Al2O3). 相似文献
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Microstructures and phase composition of the ceramic coatings formed on pure aluminum by heteropolar pulsed current ceramic synthesizing system for different periods were investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). Results show that the amount of the discharge channels in the ceramic coating sminish while the aperture largen in the micro-arc oxidation process, and the surface of the ceramic coatingmelted and solidified in the process.XRD studies of ceramic coatings deposited for different time show that these coatings consist mainly of α-Al2 O3, γ-Al2 O3 , θ-Al2 O3 and a little amorphous phase, and phase composition of compact and porous ceramic coatings don' t have much difference but have a little change of the content of α-Al2 O3 and amorphous phase. 相似文献
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采用预置粉末式激光熔覆法在钛合金(Ti-6Al-4V)表面开展了Al_2O_3-13%(质量分数)TiO_2涂层的研究。利用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射分析仪(XRD)和显微硬度计研究了激光熔覆熔池的特征和涂层的显微结构,分析了涂层的成分分布、相组成和显微硬度分布情况。预置粉末激光熔覆制备的Al_2O_3-13%(质量分数)TiO_2涂层界面结合良好,涂层组织均匀,没有明显的裂纹和气孔。激光熔覆涂层表现出明显流线型特征,熔覆层截面分为热影响区、扩散结合区和涂层区。涂层由Ti、AlTi_3、α-Al_2O_3和γ-Al_2O_3等相组成。涂层的显微硬度达到1000~1300HV_(0.3),比基体硬度360~390HV_(0.3)高2倍。 相似文献