纳米氧化铝制备中若干反应过程的研究

本文报道纳米氧化铝材料研制中若干关键步骤的反应过程的考察结果.(1)铝酸钠溶液与碳酸氢钠溶液混合后,产生无定形氢氧化铝沉淀.在碳酸氢钠未大量过剩条件下,氢氧化铝沉淀前有一个反应诱导期.在此期间溶液的紫外吸收光谱已有显著变化.在260nm附近紫外吸收增强;和Ba2[Al2(OH)10]等含六配位铝原子的晶体的紫外光谱对比,讨论了铝酸钠溶液分解的机理;(2)实验表明:和丝钠铝石相比,在上述反应条件下无定形氢氧化铝不是平衡固相而是亚稳相;(3)实验表明:无定形氢氧化铝在拍散和凝胶形成过程中晶化,形成拟薄水铝石.     

以离子液体为铝源和模板合成氧化铝纳米纤维

以咪唑类氯铝酸盐离子液体(x Al Cl_3-[C_(10)mim]Cl)为模板和铝源,采用溶胶-凝胶法合成了氧化铝纳米纤维.考察了氯铝酸盐离子液体中Al Cl_3的摩尔分数以及焙烧温度对纤维状氧化铝合成的影响,通过X射线衍射仪(XRD)、场发射透射电子显微镜(TEM)和物理吸附仪对样品进行了表征.研究结果表明,氯铝酸盐离子液体可以同时作为模板剂和铝源合成具有一定形貌的氧化铝.当Al Cl_3的摩尔分数x(Al Cl_3)=0.5时,可以合成出纳米纤维状氧化铝,纳米纤维直径约为2 nm,长度约为200 nm,比表面积为238.38 m~2/g,孔容为0.54 cm~3/g,平均孔径为8.43 nm.合成的氧化铝具有高的热稳定性,在900℃下焙烧依然能够很好地保持其形貌结构和γ晶型.此外,提出了氢键共π-π键堆积机理来解释超细纤维氧化铝的合成过程.     

氧化铝柱层状磷酸锡的制备和表征

采用分步交换法制备铝Keggin离子柱层状磷酸锡。产物经500℃焙烧处理,得到层间距为1．35nm的氧化铝柱层状材料(比母体α-SnP的层间距高出0．57nm),而且Al13^7 柱化程度大大优于直接法合成的产物。比较了不同柱化方法的柱化效果,以有机胺水解Alcl3制备的含铝Keggin离子柱化剂的柱化效果明显好于无机碱水解体系.XRD,IR,TG-DTA等分析结果证实有机胺在铝Keggin离子柱化过程中起重要作用。     

高温高表面氧化铝新材料的制备化学研究——镧和表面活性剂对氧化铝性质的影响

在汽车尾气催化净化、催化燃烧等高温严酷环境中,催化剂载体由于烧结等原因,其比表面剧烈减少,引起活性组分聚集,从而使催化剂活性明显下降^[1,2]。氧化铝是一种常用载体,但经高温煅烧后容易烧结并向α相转变,导致比表面减少。目前许多文献报道了稀土元素、碱土金属以及硅元素对氧化铝的改性作用^[3-5],这些元素的添加可在一定程度上提高氧化铝的热稳定性,但表面活性剂在这一方面的应用未见报道。本文采用溶胶－凝胶法制备了镧改性的氧化铝,通过添加不同比例表面活性剂[聚乙烯醇（PVA）]研究了镧和聚乙烯醇对氧化铝孔性质及热稳定性的影响。     

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

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。     

以多孔钛片为载体的氧化铝膜的制备和表征

γ-alumine membranes supported by porous titanium plate were prepared by sol-gel techniqe with alumina isopropoxide. The factors, which influenced membrane per formance, in the membrane preparing process were investigated. A dynamic flow-weighted active pore size distribution apparatus for inorganic membrane were set-up on the basis of Kelvine equation. The results showed that for composite porous membrane the active pore size distribution is about 6-8nm, the most probable pore size is about 7nm and nitrogen permeability is 7.1×10-6mol﹒m-2﹒Pa-1﹒s-2.     

二氧化碳加氢直接合成二甲醚催化剂的研究 Ⅰ. 沉淀剂对催化剂结构和性能的影响

使用不同沉淀剂制备了CuO-ZnO-Al2O3/HZSM-5复合型催化剂，考察了其对CO2直接加氢的催化性能，并采用H2-TPR、XRD、BET、CO2-TPD、H2-TPD等表征方法对催化剂物化性质进行了表征。研究结果表明，沉淀剂对催化剂的反应性能、晶相结构、还原难易程度、以及对CO2、H2的吸附性能等均有显著影响。催化剂上存在两种吸附位，催化剂的活性、选择性与其吸附性能密切相关。研究结果可以较好地解释CO2直接转化为甲醇和二甲醚的反应机理。     

炭包覆氧化铝负载镍催化剂的制备和表征及其催化加氢性能

以炭包覆A12O3(CCA)为载体,采用等体积浸渍法制备了17%Ni/CCA催化剂,采用热重-差示量热扫描、扫描电镜、X射线光电子能谱、N2物理吸附、H2程序升温还原和X射线衍射等手段对样品进行了表征,并用于粗1,4-丁二醇加氢反应中.结果表明,炭的引入显著改变了Al2O3的表面性质、负载Ni的存在形态以及金属.载体间...     

基于阳极氧化铝的简易气体酸碱性检测器的制备和性能研究

利用工业上应用广泛的铝阳极氧化电解实验及其着色工艺,阐述该实验原理及着色机理,用食用色素对阳极氧化后的铝片着色,得到色彩丰富的铝片,并制备出一种可以检验气体酸碱性的简易气体酸碱性检测器。该实验可以用于拓展课堂的实验教学,简便易行、原料易得、成本低、趣味性强。     

钕的氢氧化物和氧化物纳米线的制备及表征

以金属钕为起始原料，采用简单的碱性溶液下水热法制备出氢氧化钕纳米线。所得到的水热产物采用X-射线衍射、扫描电镜和透射电镜等进行了结构与形态表征。研究发现，水热处理的温度、碱液浓度和碱的种类等对水热产物的形貌、长径比和结晶状态有较大影响，提高水热温度和增加碱液浓度有利于氢氧化钕纳米线的生长。在相同水热反应温度(180 ℃)、水热时间(45 h)和碱浓度下，5 mol·L^-1 NaOH溶液体系制备的氢氧化钕纳米线具有较高纯度和较长的长径比，其直径为20～40 nm，长度为2～10 μm。该氢氧化钕纳米线在空气气氛下500 ℃烧结后形成具有体心立方结构的C型Nd₂O₃，该Nd₂O₃仍具有一维纳米线形貌。升高焙烧温度时产物的形貌和相结构都发生了明显变化。     

Ammonium hydroxide detoxification of spruce acid hydrolysates

When dilute-acid hydrolysates from spruce are fermented to produce ethanol, detoxification is required to make the hydrolysates fermentable at reasonable rates. Treatment with alkali, usually by overliming, is one of the most efficient approaches. Several nutrients, such as ammonium and phosphate, are added to the hydrolysates prior to fermentation. We investigated the use of NH₄OH for simultaneous detoxification and addition of nitrogen source. Treatment with NH₄OH compared favorably with Ca(OH)₂, Mg(OH)₂, Ba(OH)₂, and NaOH to improve fermentability using Saccharomyces cerevisiae. Analysis of monosaccharides, furan aldehydes, phenols, and aliphatic acids was performed after the different treatments. The NH₄OH treatments, performed at pH 10.0, resulted in a substantial decrease in the concentrations of furfural and hydroxymethylfurfural. Under the conditions studied, NH₄OH treatments gave better results than Ca(OH)₂ treatments. The addition of an extra nitrogen source in the form of NH₄Cl at pH 5.5 did not result in any improvement in fermentability that was comparable to NH₄OH treatments at alkaline conditions. The addition of CaCl₂ or NH₄Cl at pH 5.5 after treatment with NH₄OH or Ca(OH)₂ resulted in poorer fermentability, and the negative effects were attributed to salt stress. The results strongly suggest that the highly positive effects of NH₄OH treatments are owing to chemical conversions rather than stimulation of the yeast cells by ammonium ions during the fermentation.     

微胶囊化超细红磷的制备及其安定性研究

研究了用硝酸铝溶胶凝胶法制备微胶囊化超细红磷的工艺，通过着火点测试研究了包覆材料和包覆工艺以及影响包覆效果的因素，发现以5%氢氧化铝溶胶凝胶制备微胶囊化红磷在150 ℃左右真空干燥得到的样品安定性较好，XPS表明有95.3%的红磷被包覆，透射电镜显示形成一层均匀的包覆层，超细红磷的安定性得到了较大的提高。     

Pre-Eutectic Densification of Calcium Carbonate Doped with Lithium Carbonate

Pressureless sintering of CaCO₃ was carried out, with Li₂CO₃ (from 0.5 to 8 wt%) as an additive, under different pressures of CO₂. Densification occurs between 600 and 700°C. Sintering above the eutectic temperature (T>662°C) leads to the decomposition of calcium carbonate and the materials become expanded. At 620° under 1 kPa of CO₂, a relative density of 96% is reached. Li₂CO₃ enhances the densification process and grain growth of calcium carbonate. CO₂ pressure slows down densification and grain growth kinetics. These results are explained by the influence of carbonate and calcium ion vacancies on the sintering mechanisms. This revised version was published online in August 2006 with corrections to the Cover Date.     

General Route to Synthesize Monodisperse Oxide (Hydroxide) Nanoparticles

Mono-dispersed oxide and hydroxide nanoparticles have been synthesized through the solvothermal process in alcohol-water mixtures. The products were characterized by powder x-ray diffraction (XRD) and scanning electron microscopy (SEM). Plate-like nanoparticles are obtained for Bi₂O_2.33, Fe₂O₃, and Cd(OH)₂, and spherical nanoparticles are obtained for SnO₂. The growth mechanism for the mono-dispersed nanoparticles has been preliminarily discussed.     

反应器内流场分布对球形氢氧化镍生长结晶的影响

在相同停留时间、不同搅拌桨线速度条件下,利用化学沉淀法制备球形氢氧化镍样品并运用SEM技术考察制得样品的形貌。研究表明:在相同的停留时间和化学条件下,随着搅拌桨线速度的提高样品的微观形貌由无定型状晶体变为大颗粒类球状晶体再变为较规则的球状晶体。利用PIV物理模拟技术模拟反应器内流场分布情况并结合XRD表征结果分析得出:在相同的停留时间和化学条件下,反应器内流场分布越均匀、速度矢量越大氢氧化镍晶体的生长越完整,结晶性、球形度和相对结晶度越高,并从流场分布的角度描述了球形氢氧化镍生长结晶的过程。     

矿化剂对水热法改性氢氧化镁晶体的影响

近几年来,氢氧化镁作为一种无机阻燃剂由于其具有制备条件相对温和,生产工艺简单且产品与自然环境友好等特点,在研究及生产活动方面备受关注且得到了长足的发展[1～4].目前采用氢氧化钠法进行反应一水热制备高分散阻燃级氢氧化镁的工艺路线已经比较成熟[5～8].然而,不利的是,氢氧化钠偏高的价格导致了产品的制造成本较高.而采用石灰法制备氢氧化镁阻燃剂具有价格低廉的特点,引起了人们的关注.     

Chromium(III) Hydroxide Solubility in the Aqueous K+-H+-OH?-CO2-HCO 3? -CO 32? -H2O System: A?Thermodynamic Model

Chromium(III)-carbonate reactions are expected to be important in managing high-level radioactive wastes. Extensive studies on the solubility of amorphous Cr(III) hydroxide solid in a wide range of pH (3–13) at two different fixed partial pressures of CO₂(g) (0.003 or 0.03 atm.), and as functions of K₂CO₃ concentrations (0.01 to 5.8 mol⋅kg⁻¹) in the presence of 0.01 mol⋅dm⁻³ KOH and KHCO₃ concentrations (0.001 to 0.826 mol⋅kg⁻¹) at room temperature (22±2 °C) were carried out to obtain reliable thermodynamic data for important Cr(III)-carbonate reactions. A combination of techniques (XRD, XANES, EXAFS, UV-Vis-NIR spectroscopy, thermodynamic analyses of solubility data, and quantum mechanical calculations) was used to characterize the solid and aqueous species. The Pitzer ion-interaction approach was used to interpret the solubility data. Only two aqueous species [Cr(OH)(CO₃)₂²⁻ and Cr(OH)₄CO₃³⁻] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO₂(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support the existence of these species. The log ₁₀ K° values of reactions involving these species [{Cr(OH)₃(am) + 2CO₂(g)⇌Cr(OH)(CO₃)₂²⁻+2H⁺} and {Cr(OH)₃(am) + OH⁻+CO₃²⁻ ⇌Cr(OH)₄CO₃³⁻}] were found to be −(19.07±0.41) and −(4.19±0.19), respectively. No other data on any Cr(III)-carbonato complexes are available for comparisons.     

Microwave-Assisted Synthesis of Dimethyl Carbonate

Microwave assisted synthesis of dimethyl carbonate directly from CO₂ and methanol can be completed in a relative short time, at lower temperature and fewer by-products compared with conventional heating mode. This revised version was published online in June 2006 with corrections to the Cover Date.