水热处理和尿素改性对三水铝石微观结构的影响

以尿素为改性剂,用水热处理方法对三水铝石进行了改性处理。结果表明,尿素的加入量和水热处理时间对产物微观结构有显著的影响,当尿素与三水铝石的摩尔比小于6∶1时,水热处理24 h的产物为片状薄水铝石;当摩尔比超过8∶1时,产物为板条组装的球形碱式碳酸铝铵.纯相碱式碳酸铝铵的形成与水热处理的时间有关,随处理时间的延长,氢氧化铝经历了由三水铝石到薄水铝石与碱式碳酸铝铵混相结构再到纯相碱式碳酸铝铵的演变过程,期间发生由块体到片状再到片组装块体的微观形貌变化,最后演变为板条组装球形结构。     

醇盐水解-水热法制备高结晶度纳米氢氧化铝

以异丙醇铝为主要原料,采用醇盐水解结合水热处理的合成方法,制备出了高纯度、高结晶度、易分散的勃姆石型纳米氢氧化铝材料.实验结果表明,醇铝水解后生成拟薄水铝石,然后在水热条件下转变为勃姆石;升高水解温度和水热温度,延长水热时间有利于提高勃姆石型氢氧化铝的结晶度.     

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.     

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.     

水热合成三维花状薄水铝石微观结构

在水溶液体系中,利用十六烷基三甲基溴化铵（CTAB）作为模板剂,水热合成了由纳米薄片自组装成的三维花状薄水铝石微观结构,采用XRD、SEM和TEM对其物相结构和形貌进行了分析,研究表明,该花状微观结构是由厚度50mm左右的纳米薄片自组装而成,形貌规则统一,分散均匀,平均直径为1．5μm,在其形成过程中,模板剂CTAB起到关键性的作用,并推断了纳米薄片自组装花状微观结构的形成机理。经过500℃焙烧得到的γ-Al2O3保持了该花状微观结构。     

碳分法制备氢氧化铝过程的研究

以偏铝酸钠溶液和二氧化碳气体为原料,成功地制备了不同晶型的氢氧化铝纳米粉末.叙述了实验过程中工艺条件对产品粒度、形貌和晶型等方面的影响.采用TEM、SEM、XRD分析表征了产品的形貌、粒度和晶型,结果表明,产品分别为片状三水氢氧化铝、纤维状的-水拟薄水铝石和无定形的三水氢氧化铝.     

钛酸盐一维纳米材料向TiO2纳米材料的水热转化研究

采用强碱性水热处理法分别控制第一次水热反应为160℃和200℃,制备出一维纳米管和纳米棒2种形貌的产物,将其作为第二次水热反应的前驱体,考察了第二次水热体系中pH值和温度对TiO2纳米材料的晶相组成及其微观形貌的影响;采用XRD、TEM以及HRTEM对样品进行了分析.结果表明,当以纳米管为前驱体时,除在pH=0的体系中得到了以金红石相为主的单晶纳米棒外,在pH值为2、4和7的条件下均得到了单晶纯锐钛矿相TiO2纳米颗粒.当以纳米棒为前驱体时,在pH=0的体系中得到了金红石相与板钛矿相共存的纳米棒和纳米颗粒混合产物;在pH值为2、4和7的条件下均得到了纯锐钛矿相TiO2纳米棒;当二次水热温度低于180℃时,前驱体没有转化完全,所得产物为前驱体与锐钛矿相TiO2共存的纳米棒;当水热温度为180℃和210℃时,产物为纯锐钛矿相纳米棒.     

水热辅助溶胶-凝胶法制备分等级拟薄水铝石/PVA复合薄膜及其Cr(Ⅵ)吸附性能

在调节偏铝酸钠溶液pH制备氢氧化铝溶胶的基础上,以聚乙烯醇(PVA)为成膜剂,结合水浴、水热和焙烧等过程,制得了拟薄水铝石/PVA复合薄膜,采用扫描电镜对产物的微结构和形貌进行表征,并对比研究了PVA和水热处理对产物Cr(Ⅵ)静态吸附性能的影响。研究表明:添加PVA可以有效地促进拟薄水铝石溶胶成膜,而不添加PVA只能得到粉体样品;加入PVA后水热辅助溶胶-凝胶法制备的分级拟薄水铝石/PVA复合薄膜对Cr(Ⅵ)具有优异的吸附性能,Cr(Ⅵ)初始浓度为20mg/L时在4h左右即达到吸附平衡,平衡吸附率达82.3%,循环2次后的平衡吸附率分别为76.4%和73.9%。相比之下,加入PVA后直接水浴加热处理得到分级拟薄水铝石/PVA复合薄膜的吸附性能较差,需要8h才能达到吸附平衡,平衡吸附率为74.7%;不加PVA时拟薄水铝石粉体在8h时对Cr(Ⅵ)溶液的吸附率仅为40.3%。     

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.     

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。     

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.     

Preparation of Nanocrystalline Alumina under Hydrothermal Conditions

Thermodynamic analysis of phase equilibria in the Al₂O₃-H₂O system at temperatures from 120 to 380°C and pressures from 1 to 70 MPa is carried out, and the dehydration of aluminum hydroxide under hydrothermal conditions is studied experimentally. The results indicate that -AlOOH (boehmite), which commonly appears in experimental phase diagrams, is a nonequilibrium phase in these temperature and pressure ranges. The dehydration rate and mechanism are shown to strongly depend on the crystallinity of the parent aluminum hydroxide and the pressure in the hydrothermal system.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 540–547.Original Russian Text Copyright © 2005 by Almyasheva, Korytkova, Maslov, Gusarov.     

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.     

Synthesis of high-purity α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> from boehmite obtained by hydrothermal oxidation of aluminum

We demonstrate the possibility of obtaining high-purity aluminum oxide by successive processes of hydrothermal oxidation of aluminum and vacuum heat treatment of the solid oxidation product (boehmite). The results of studies of changes in the structural properties and chemical purity of alumina samples obtained in the different modes of vacuum heat treatment of boehmite are presented. Experiments have shown the ability to produce alumina with a purity of 99.997% (the total content of all impurities is approximately 30 ppm) of aluminum with a purity of 99.8%. It was shown that the chemical purity of the final product depends on not only the temperature and time of heat treatment but also a number of other parameters of the process.     

Formation characteristics of an aluminum hydroxide fiber by a hydrolysis of aluminum nano powder

Formation of aluminum hydroxide by a hydrolytic reaction of nano aluminum powder synthesized by a pulsed wire evaporation (PWE) method has been studied. The type and morphology of the hydroxides were investigated with various initial pH and temperatures. The nano fibrous boehmite (AlOOH) was formed predominantly over 40°C of the hydrolytic temperature, while the bayerite (Al(OH)₃) was formed predominantly below 30°C with a faceted crystalline structure. As a result, the boehmite showed a much larger specific surface area (SSA) than that of bayerite. The highest SSA of the boehmite was found about 409 m²/g.     

水热法合成氢氧化钇纳米管

以Y₂O₃为原料,在密闭反应器中采用水热法合成氢氧化钇纳米管. 分别采用X射线粉末衍射(XRD)、扫描电镜（SEM）、能谱（EDS）和热重－差热分析（TG-DTA）方法对所合成的氢氧化钇纳米管进行了物相、形貌、成分表征和热稳定性分析. 对影响氢氧化钇纳米管形成的反应条件如水热温度和水热时间进行了研究,采用透射电镜（TEM）分析了产物各个生长阶段的形貌,推测了氢氧化钇纳米管的形成机理. 研究表明：水热法制备氢氧化钇纳米管材料的最佳合成条件是乙醇和水作为溶剂,pH值为11~12、反应温度为220℃、反应时间为24h;氢氧化钇纳米管的形成过程可以分为两个阶段：第一阶段为钇前驱体的产生,第二阶段为钇前驱体转变为氢氧化钇纳米管.     

The reaction conditions influence on hydrothermal synthesis of boehmite nanorods

Synthesis of boehmite (γ-AlOOH) nanorods were performed by using aluminum nitrate and sodium hydroxide as starting materials in conditions of controlled pH value of reaction mixture, temperature and holding time. X-ray diffraction, transmission electron microscope, high resolution transmission electron microscope, selected area electron diffraction and N₂ adsorption-desorption analysis were used to characterize morphology and structure feathers of the obtained products. The results show that γ-AlOOH nanorods with diameter of 10–30 nm, length of 200–300 nm, aspect ratio of 5–15, regular shape and clear surface were synthesized at 200–220°C for 24 h under pH = 5. The effect of reaction conditions on the morphology of 1D boehmite nanomaterials was discussed.     

W掺杂二氧化钒的水热晶化机理及其相变性能

以硫酸氧钒为钒源,采用沉淀-胶溶法制备VO_2溶胶。然后向溶胶中加入偏钒酸铵,利用溶胶水热晶化制备出W掺杂二氧化钒(W-VO_2,M相)粉体。通过XRD,FESEM和DSC对合成产物的物相组成、形貌和相变性能进行研究。结果表明:在280℃条件下水热处理4~48h,VO_2溶胶经过水热晶化生成长约1~2μm、直径约100~200nm棒状W-VO_2(B)晶体,伴随着B相向M相晶型转变,W-VO_2(B)逐渐消溶,而W-VO_2(M)逐渐长大,形貌由棒状转变为片状或雪花状;W-VO_2(M)相变温度随着W掺杂量增加而降低,当名义掺杂量为6.0%(原子分数)时,相变温度降低到28℃。根据水热晶化和形貌演变过程,提出了W-VO_2(M)可能的"形核-生长-转化-熟化"形成机理。