溶剂热处理对氢氧化铝微观形貌分化作用

采用水、异丙醇及二者不同比例混合液为介质,通过140℃下溶剂热处理方法对种分法获得的氢氧化铝粉体进行处理,研究了溶剂类型、热处理时间对产物微观形貌的影响.研究结果表明,当以水为介质时,可以实现三维材料向二维材料的分化,即产物由块体三水铝石分化为片状薄水铝石;当介质中有醇存在时,产物由块体向叶片组合的薄水铝石相花型结构分化.     

多相氢氧化铝向薄水铝石相转变过程的微观结构研究

以铝直接水解法所得氢氧化铝粉为原料,经水热处理获得了纯相的薄水铝石粉体。研究了水热反应温度对产物γ-AlOOH晶体结构及微观形貌的影响,并利用XRD、SEM、TEM、HRTEM、粒度分布和TG-DSC对样品的物相、微观形貌及晶相转变过程进行分析表征。结果表明,水热温度对于制备纯相薄水铝石发挥重要作用,且有利于优化合成条件。随着水热温度的升高,物质结构转变动力也随之增强,可实现由多相氢氧化铝向纯薄水铝石相转变。利用CASTEP软件分别对薄水铝石、拜耳石及诺耳石体系进行几何优化,计算各体系的总能量。证实在同一计算精度下,薄水铝石的总能量最低,说明该体系最稳定。     

自蔓延高温合成锂离子电池正极材料LiCoO2

以四氧化三钴、碳酸锂为原料,尿素为燃料,用自蔓延高温合成法制备层状正极材料LiCoO2,并考察了尿素与钴摩尔比、预制炉温、热处理温度、热处理时间及锂与钴摩尔比等工艺条件对合成产物的结构、微观形貌和电化学性能的影响.结果表明,制备LiCoO2的工艺条件为:锂与钴摩尔比1.05:1.00,尿素与钴摩尔比1:1,预制炉温和热处理800℃、热处理时间2h.所得LiCoO2的放电比容量达155mAh/g,循环10次后容量保持率为95%.     

无模板合成海胆状薄水铝石超结构及其形成机理

在乙醇-水溶液体系中,在无模板剂的情况下,水热合成由纳米棒自组装成的独特海胆状薄水铝石(AlOOH)超结构.采用XRD、SEM、TEM和SAED对其物相结构和形貌进行了分析,讨论了铝盐前驱体、醇水比例和反应温度对产物形貌的影响.研究结果表明:当铝盐前驱体为AlCl3.6H2O,醇水体积比为1:2,反应温度为200℃时,得到形貌规则、分散均匀的三维海胆状薄水铝石超结构,该海胆状超结构是由直径60~80nm的纳米棒自组装而成,海胆球直径为6~10μm,选区电子衍射表明该海胆状薄水铝石的多晶本质.在薄水铝石海胆状超结构的形成过程中,定向附着机制起到关键性作用.     

不同模板剂对氢氧化镧的微观结构及光催化性能的影响

以La(NO3)3·6H2O和KOH为原料,以EDTA、PVP和HMTA等为模板剂,采用微波水热法制备得到纯相La(OH)3,使用X射线衍射分析(XRD)、扫描电子显微镜(SEM)对产物的物相和形貌进行了分析,结果表明,不添加模板剂和添加EDTA、PVP、HMTA为模板剂时,可分别制备得到具有纳米棒状、类球形纳米颗粒、片状、纳米棒组装的片状形貌的纯相La(OH)3。光催化测试结果表明,模板剂可有效调控产物的微观形貌,并进一步提升La(OH)3的光催化性能。其中添加EDTA得到的类球形La(OH)3在21min内对亚甲基蓝的降解率可达99%。     

表面活性剂辅助水热合成异形薄水铝石

为了从廉价的无机铝盐制备高性能的氧化铝前驱物,用表面活性剂调控形貌制得了异形薄水铝石.采用XRD和SEM等表征手段,研究了十二烷基磺酸钠、十二烷基苯磺酸钠、十六烷基三甲基溴化铵、酒石酸钠和聚乙二醇2000共4种表面活性剂对硫酸铝和尿素水热合成薄水铝石晶体结构和形貌的影响,并对其晶体结构和形貌变化的形成机制进行了初步分析.研究表明:表面活性剂均不改变产物的晶型,但可对产物的形貌和粒径进行一定程度的调控,尤其是160℃下加入酒石酸钠时产物的结晶度明显降低,其粒子由数个微米的针状团簇体转变为0.5~3μm的圆饼状粒子;硫酸铝和尿素水热合成薄水铝石时加入适量酒石酸钠可以实现产物形貌的有效调控.     

微乳液法制备六边形薄片状γ-CuI晶体的研究

以粗碘和硫酸铜为原料,水合肼为还原剂,利用微乳液法合成了六边形薄片状γ-CuI晶体.采用XRD和SEM手段研究了微乳液工艺技术条件对合成γ-CuI晶相组成和微观形貌的影响.结果表明,表面活性剂CTAB用量、水含量和反应物浓度对微乳液法制备的γ-CuI晶相组成和晶体形状没有太大影响,但对晶体尺寸具有较大影响.适宜的微乳液制备工艺条件能产生适当的界面膜强度,有效控制碘化压铜晶体尺寸.CTAB-正戊醇-环己烷-水体积比为3∶3∶7∶10,硫酸铜溶液0.1mol/L和碘化铵溶液0.2mol/L,常温下500r/min搅拌2h合成产物为六边形薄片状γ-CuI.     

水热种分法制备低密度薄水铝石及其表征

以硫酸铝和尿素水热沉淀合成的低密度薄水铝石为晶种,采用水热种分过饱和铝酸钠溶液的方法成功地制备了低密度薄水铝石,结合ICP-AES、XRD和SEM等分析和表征手段,着重考察了单相、低密度薄水铝石的析出条件及其对产物晶体结构和形貌的影响.研究表明,100℃下种分48h或187℃下种分3h都可以得到单相、低密度薄水铝石,但种分条件对产物的形貌影响不大.上述低密度薄水铝石的水热种分法合成不仅丰富了传统三水铝石种分过饱和铝酸钠溶液过程的研究,也提供了一种低密度薄水铝石的制备方法.     

拟薄水铝石生产过程中的影响因素分析

本文研究了偏铝酸钠溶液用碳酸化分解法制备拟薄水铝石的规律。解决了使用纯CO_2时吸收过快,气流搅拌不均容易引起局部过量等问题,制备出三水氧化铝杂晶相很少,Na~+含量较低,孔容和比表面积较大,胶溶指数较高的高质量拟薄水铝石。通过实验,本文对用NaAlO_2-CO_2法制备拟薄水铝石的碳酸化分解过程、老化过程、洗涤过程、干燥过程的各种影响因素进行了详细的研究分析,得出了利用NaAlO_2-CO_2法制备拟薄水铝石的工艺参数,为工业生产提供了可靠的理论依据,并成功进行了工业化生产。     

自蔓延-热处理工艺制备层状正极材料LiCoO_2

采用自蔓延-热处理工艺制备层状正极材料LiCoO2,研究热处理温度和热处理时间及Li/Co摩尔比对合成产物中LiCoO2的纯度、晶体结构及微观形貌的影响。利用X射线衍射仪和扫描电镜分析合成产物的相组成及其微观形貌,实验结果表明,制备LiCoO2的最佳工艺条件为n(Li)/n(Co)=1.03∶1、n(NH4NO3)/n(Co)=4∶3、n(C6H12N4)/n(Co)=4∶3、热处理温度800℃、热处理时间1.5h,所得产物中LiCoO2相纯度高达99.25%,且晶体具有较好的层状结构。     

The double hydroxide of Al with Li: mechanism of formation and reversible thermal behavior

All the polymorphic modifications of Al(OH)₃ and the oxide-hydroxide of Al, boehmite, on hydrothermal treatment in Li⁺ containing solutions transform into the layered double hydroxide of Al with Li having the nominal composition [LiAl₂(OH)₆](CO₃)_1/2·1.5H₂O, suggesting that these compounds form via a dissolution-reprecipitation mechanism. The oxide residue obtained by the thermal decomposition of this layered double hydroxide also partially reconstructs the layered double hydroxide on soaking in water lending further evidence to the dissolution-reprecipitation mechanism. Under hydrothermal conditions, in water, the layered double hydroxide undergoes delithiation to yield aluminum hydroxide phases other than gibbsite, suggesting again that delithiation too proceeds by a dissolution-reprecipitation mechanism.     

Structure refinement and thermal stability of gibbsite

The crystal structure of gibbsite (aluminum hydroxide) has been refined by Rietveld powder diffraction analysis, and the thermal stability of the crystal structure of the mineral has been studied in detail by high-temperature X-ray diffraction. The X-ray diffraction data obtained in the temperature range from 25 to 300°C indicate that the crystal structure of gibbsite is stable up to 200–250°C. The unit-cell parameters of gibbsite increase with temperature. Above 200°C, the gibbsite to boehmite (AlO(OH)) phase transformation begins.     

Meso/macroporous γ-Al2O3 fabricated by thermal decomposition of nanorods ammonium aluminium carbonate hydroxide

Through exploring the reaction parameters during the synthesis of the AACH, rod-like ammonium aluminium carbonate hydroxide (AACH) with high crystallinity has been successfully prepared via a facile hydrothermal method. The synthesis parameters like time, the molar ratio of NH₄HCO₃/Al and the properties of starting materials were systematically investigated. The structure was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), IR and transmission electron microscopy (TEM). The experimental results display that the obtained γ-Al₂O₃ materials possess meso/macroporosity and large pore volume, which are mainly attributed to the removal of gas molecules during the decomposition of AACH. Moreover, using the rod-like AACH as precursor, γ-Al₂O₃ nanorods were obtained via a low-temperature thermal decomposition method.     

表面活性剂辅助水热热分解法制备介孔氧化铝纤维

以PEG(Mn=20000)为模板导向剂, 尿素为沉淀剂, 采用水热热分解法制备了纳米介孔结构的氧化铝纤维, 并对其吸附性能进行了研究. 通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、热释重仪(TGA)和N2等温脱附-吸附分析, 考察了介孔氧化铝纤维的相态、结构、形貌、比表面积和介孔特征. 采用选择性催化还原(SCR)烟气脱硝装置对其吸附性能进行了研究. 结果表明：以PEG为模板, 采用简单的水热法就可得到直径(200～300)nm×(8～10)μm的碳酸铝铵纤维; 经900℃煅烧2h得到比表面积为316m²/g、平均孔径为2.5nm的η-Al₂O₃介孔纤维, 形貌基本不发生变化; SCR烟气脱硝测试显示, 相比商品氧化铝粉末, 合成的氧化铝介孔纤维有着更强的吸附性能, 它的脱硝效率较之商品氧化铝粉末约提高了15%.     

pH-dependent formation of AACH fibers with tunable diameters and their in situ transformation to alumina nanocrystals with mesoporous structure

Through a simple hydrothermal and thermal decomposition process of the ammonium aluminum carbonate hydroxide (denoted as AACH) precursors, we prepared mesoporous γ-Al₂O₃ fibers with tunable diameters by manipulating the amount of urea (pH-adjuster) in the reaction mixture (i.e., pH control). The experimental results show that the diameter of the obtained AACH fibers decreased obviously when the pH values of the reaction mixtures changed from 2.5 to 5.0. The as-formed precursors could transform to the morphology-remained cubic γ-Al₂O₃ with a slight shrinkage in diameter of the fibers after an annealing process. N₂ adsorption–desorption experiment indicates that the as-synthesized alumina microfibers and nanofibers have large surface area (176 and 230 m²/g, respectively) and narrow pore-size distributions. Both the γ-Al₂O₃ microfibers and nanofibers are powerful in the removal of Congo red pollutant from waste water.     

Preparation of γ-alumina precursors for metal reinforcement

In the metal matrix composite field, both fine (<0.5 µm) and coarse, crystalline, calcined aluminas with narrow or broad particle size distributions, are being used as reinforcement phase. The effect was studied of the preparation method of fine boehmite (-AlOOH), precursor of the -Al₂O₃, on the product morphology. The material was produced by heating three kinds of hydrothermal precursors at different pH, and for 2 h at 200°C, using constant stirring. Under the conditions investigated (i.e., 0.12 mol/dm³ of Al(OH)₃ and only diluted NaOH and HNO₃ solutions used to adjust the pH of slurry), the pH of hydrothermal slurry influenced the product morphology; in contrast, the three different hydrothermal precursors, namely dry aluminum hydroxide gel, fresh aluminum hydroxide precipitate and gibbsite reagent powders, had only a little effect on the product morphology. The dehydration/transformation mechanism from Al(OH)₃ to -AlOOH is believed to be dissolution/reprecipitation rather than a direct dehydration.     

Nano-porous hydrosodalite fabrication via hydrothermal modification of processed kaolin by boehmite: Aluminum source effect on physico-chemical characteristics of product

The nano-porous hydrosodalite was produced from a poor kaolin containing quartz, as major impurity, via the hydrothermal modification with boehmite and sodium aluminate. The physico-chemical characteristics of products were evaluated by XRD, SEM and BET techniques. The obtained results indicated that the direct reaction between poor metakaolin and sodium hydroxide leads to the zeolite compound formation in which the partially crystallized hydrosodalite and remained quartz were embedded in amorphous phase. Different trends were observed in crystallinity of produced materials with aluminum source content revealed the predominantly crystalline structure for hydrosodalite fabricated via use of sodium aluminate. There is an inverse relationship between the boehmite content and crystallinity whilst the increase in the sodium aluminate content led to production of a well-crystalline hydrosodalite. Although, the dense cabbage-like particle structure was successfully created by hydrothermal reaction between metakaolin and sodium aluminate, NaAlO₂/MK: 0.36, and the nano-porous hydrosodalite can be fabricated at limited content of boehmite, AlOOH/MK: 0.20. Moreover, the hydrothermal reaction in the presence of boehmite causes the generation of nano-porous structure with average pore size of 8.0 nm, accompanied with negligible co-crystallization of cancrinite. This change in porous structure could be useful in engineering applications like water and wastewater treatments.     

Effect of content of Mg(NO3)2 x 6H2O on fabrication of alpha-alumina nanopowders by thermal decomposition of ammonium aluminum carbonate (AACH)

An alpha-Al2O3 and MgAl2O3 spinel phase doped alpha-Al2O3 nanopowders were fabricated by the thermal decomposition and synthetic of ammonium aluminum carbonate hydroxide (AACH). Crystallite size of 5 to 8 nm were fabricated when reaction temperature of AACH was low, 8 degrees C, and the highest [NH4+][AlO(OH)2-][HCO3] ionic concentration of pH 10 from the ammonium hydrogen carbonate (AHC) aqueous solution. The phase transformation of amorphous-s, theta-, alpha-Al2O3, MgAl2O3 spinel phases was examined at each temperature according to the amount of Mg(NO3)2 x 6H2O and AACH. A time-temperature-transformation (TTT) diagram for thermal decomposition in air was determined. Homogeneous, spherical alpha-Al2O3 nanopowders with a particle size of 60 nm were obtained by firing the crystallites, which had been synthesized from AACH at pH 10 and 8 degrees C, at 1050 degrees C for 6 h in air.     

Modifications in the microstructure of alumina porous materials by hydrothermal treatment

Thin films of microporous γ-alumina were prepared by hydrothermal treatment of boehmite which was obtained by a sol-gel process. Films of boehmite hydrothermally treated at different temperatures and times were studied by X-ray diffraction, Nitrogen Adsorption, DTA/TG Thermal Analysis and Scanning Electron Microscopy. The results showed that a well-crystallized boehmite with an anisotropic particle growth mainly in the (002) plane was obtained. The modifications introduced into the boehmite affected the microstructure, such as surface area, pore morphology, pore volume, pore size distribution and thermal stability of the corresponding alumina. Received: 30 March 2000