水热处理异丙醇铝及其煅烧产物的显微结构

以异丙醇铝为原料,经水热处理获得菱形片状薄水铝石。利用X射线衍射、Fourier变换红外光谱和透射电子显微镜研究了水热温度及煅烧温度对产物相结构及微观形貌的影响。结果表明,随水热处理温度的提高,产物由结晶性能较差的拟薄水铝石向结晶性良好的薄水铝石相转变,表明水热处理提高了产物晶体结构的对称性,使其非对称伸缩受到限制,而对称性伸缩得到增强。未经水热处理的产物呈褶皱的纳米薄片交联在一起的无规则团聚结构,经水热处理的产物逐渐向规则的菱形片状形貌转变,随水热处理温度升高,片状产物的厚度增大。水热处理影响煅烧产物的热稳定,随水热处理温度提高,α-Al2O3出现的温度提高,表明煅烧过程中中间相的热稳定性得到提高,同时α-Al2O3出现是在θ-Al2O3相晶格中发生层错产生的。     

拟薄水铝石脱水产物γ-Al2O3在较低温度下的再水合过程研究

研究了γ-Al₂O₃经过较低温度的水热处理后的晶型变化情况。XRD、SEM和FT-IR表征结果表明，影响γ-Al₂O₃再水合产物晶型的主要因素是水热温度。100 ℃以下水热处理的产物是湃铝石，100～110 ℃水合产物是湃铝石和薄水铝石的混合物，110 ℃以上水热处理的产物是薄水铝石，且不经过湃铝石的中间阶段。随着水合温度升高，薄水铝石的结晶度增大。在保证充分润湿的前提下，水合产物的结晶度和晶粒度与水铝质量比无关。     

二步法低温制备六铝酸钙/镁铝尖晶石复相陶瓷

以白云石和工业Al(OH)3为原料,采用水热合成和低温煅烧二步法工艺制备六铝酸钙-镁铝尖晶复相陶瓷,探索了水热处理温度对前驱体性能及六铝酸钙/镁铝尖晶石复相陶瓷物相组成和形貌的影响。结果表明:200℃水热处理后的前驱体中,板状三水铝石转变为多孔薄片状薄水铝石;前驱体高温分解后可为复相陶瓷的生成提供高活性原料和六铝酸钙片状形貌的生长空间;二步法工艺可使烧成温度降低100℃以上。白云石添加量为13%时,配料经200℃水热、1 400℃煅烧3 h即可制备出主晶相为六铝酸钙和镁铝尖晶的复相陶瓷,六铝酸钙形貌发育完整,呈交叉片状存在。复相陶瓷的体积密度为1.56 g/cm3,气孔率为61.5%,孔径分布在0.2~1.1μm之间。未水热处理配料于1 500℃保温3 h,制备出六铝酸钙/镁铝尖晶石复相陶瓷,六铝酸钙和镁铝尖晶石晶体衍射峰强度较弱,六铝酸钙片状形貌发育不完整。     

氢氧化铝制备α-Al2O3微观结构分析

为研究氢氧化铝制备α-Al₂O₃过程中的相转变和微观结构的变化,以氢氧化铝为原料,研究了不同煅烧温度（500、800、900、1 100、1 200、1 300℃）下氢氧化铝的相变过程和显微结构的变化。结果表明：1)在500℃时,一部分三水铝石脱除结晶水转化为一水软铝石;500～800℃时,三水铝石和一水软铝石继续脱除结晶水转化为氧化铝过渡相。2)在800～1 200℃时,氧化铝过渡相之间进行相转变;1 300℃时,过渡相全部转化为α-Al₂O₃。3)煅烧温度为800℃时生成的γ-Al₂O₃和η-Al₂O₃比表面积最大,活性最高,为催化剂载体和提高电池循环寿命提供了新途径。     

采用引入晶种的水热合成法制备α-Al2O3纳米粉

采用水热合成法制备a-Al2O3微粉时,水热处理温度需要在大于 450℃下才能进行,这在工艺上难以实现,但引入与a-Al2O3具有等结构的晶种,可以增加成核密度,提高成核速率,降低成核的活化能,从而降低相变温度,使水热处理温度降低到200℃以下,并使粉末的煅烧温度降到930℃实验结果表明,采用添加4%(in ms)a-Al2O3晶种的水热合成法制备的a-Al2O3为粒度分布均匀、颗粒近似球形的纳米级(68 Bnm)的粉末.     

高铝粉煤灰脱硅液与煤矸石制备13X分子筛的工艺研究

以13X分子筛的低成本制备与煤基固废协同利用为目标,利用煤矸石与高铝粉煤灰碱法提铝过程中副产的脱硅液为原料,通过水热反应制备了13X分子筛,实现了两种固废资源的协同利用.考察了水热反应体系水钠比、硅铝比、晶化温度、搅拌速率等因素对合成产物晶型和比表面积的影响规律.通过X射线衍射、红外光谱和扫描电镜等方法对产物结构和形貌的演化过程进行了表征分析.结果表明,在优化工艺为n(SiO2/Al2O3)=3.0,n(Na2O/SiO2)=1.9,n(H2O/Na2O)=60,室温下老化24 h,100 r·min-1下于95 ℃水热晶化8 h制备的13X分子筛比表面积为681.7 m2·g-1,相对结晶度94.59%.通过对水热反应过程分析,13X分子筛合成过程前期主要为煤矸石与脱硅液反应形成无定型凝胶,后期为凝胶相溶解和分子筛晶体的生长.     

薄水铝石粒度对煅烧形成α-Al2O3粉体的影响

研究了薄水铝石粒度对其煅烧形成α-Al2O3粉体的影响.先用水热法制备出均匀分散的纳米、亚微米及几个微米的薄水铝石前驱体,用x射线衍射仪和电子显微镜分析了薄水铝石在不同温度煅烧所得产物的相结构及形貌.结果表明,粒度30～100 nm的薄水铝石在1200℃煅烧1 h转变为α-Al2O3,为蠕虫状的烧结颗粒;粒度0.4～0.6 μm的薄水铝石在1 250℃煅烧1 h可转变为α-Al2O3,颗粒尺寸变化不大,仍在0.4～0.6 μm范围内;粒度1 μm左右的薄水铝石在1350℃下煅烧2 h尚不能完全转变为α相,并已出现明显烧结.因此,以水热法制备的亚微米级薄水铝石晶体作为前驱体,经直接煅烧可以制备出分散性较好的亚微米级α-Al2O3粉体.     

拜尔法三水铝石受热相变的形貌特征

研究了拜尔-三水铝石煅烧成α-Al2O3的相变过程和显微结构演变.用扫描电镜和x射线衍射(X-ray diffraction,XRD)研究了三水铝石及其热处理过程中的相组成和结晶形貌.拜尔一三水铝石原料为<200ttm的球形多晶粒团聚体颗粒,由六方柱状三水铝石和少量勃姆石组成.经200～1200 ℃处理,热处理中每间隔100℃保温3h,热处理后球形团聚体颗粒轮廓只有少许变化,晶粒保持了原三水铝石形貌.XRD分析表明:经200℃处理3h后,三水铝石大部分分解为勃姆石;至400℃,三水铝石全部分解,勃姆石绝大部分分解,开始生成γ-Al2O3;900℃时,开始生成θ-Al2O3和κ-Al2O3相,为γ-Al2O3,θ-Al2O3和κ-Al2O3三相共存;热处理至1 000℃,开始出现洳A1203,形成四相共存结构;至1 200℃,所有过渡相均已转变为α-Al2O3.     

引入晶种对水热合成α-Al2O3微粉的影响

以一水软铝石为前驱物．加入矿化剂和晶种，在水热每件下，可以制出纳米级的氧化铝微粉。通常水热处理温度要求很高。这在工艺上很难实现。引入与α-Al2O3具有等结构的晶种，降低了成核的活化能，可使水热处理温度下降到400℃，同时也缩短了保温时间。试验证明，添加5wt％的α-Al2O3晶种可以水热合成粒度分布均匀、颗粒近似板状的α-Al2O3微粉．晶种的种类和晶种的添加量等对水热过程有很大的影响。     

煅烧温度与保温时间对合成莫来石材料结构与性能的影响

本研究是利用铝型材厂污泥与叶腊石合成莫来石材料.主要探讨煅烧温度和保温时间对莫来石合成料中形成的晶相、微观形貌及其含量的影响;从中确定较佳的煅烧温度和保温时间.采用XRD法和SEM法表征各试样形成的晶相和显微结构;用Rietveld Quantification 法确定各试样中各晶相的含量.实验结果表明不同煅烧温度和保温时间各试样形成的主晶相都是莫来石固溶体(Al4.59Si1.41O9.7),确定较佳煅烧反应温度为1600 ℃,较佳煅烧保温时间为3 h,对应的莫来石固溶体含量为96.4wt%.     

氢氧化铝活化对水热法制备勃姆石的影响

采用氢氧化铝粉体为原料,活化后通过水热法制备勃姆石。研究了氢氧化铝活化对勃姆石颗粒尺寸的影响,并讨论了相关机理。研究结果表明：未活化氢氧化铝水热反应所得产物颗粒粒径为2μm,经过加热（160～220℃）活化的氢氧化铝,水热反应所得产物的颗粒粒径在0.3～2μm变化。对活化氢氧化铝和水热反应中间产物进行表征,由结构分析推测作用机制：氢氧化铝加热活化过程中生成少量勃姆石,这些勃姆石在氢氧化铝水热反应转化为勃姆石（AlOOH）的过程中成为晶种,活化温度升高和活化时间延长,勃姆石晶种数量增加,氢氧化铝水热反应所得产物的颗粒粒径减小,并且加快了水热反应速率。该工作有望提供一种氢氧化铝水热法制备勃姆石的新途径和相关基础理论。     

Synthesis of morphology-controlled mesoporous transition aluminas derived from the decomposition of alumina hydrates

Aluminum hydroxides were synthesized through the acidification of sodium aluminate solution using single organic diester or diacid as pH adjustor and aluminum chelating agent. The obtained alumina hydrates are investigated by XRD, SEM, IR and TG. Bayerite firstly formed at room temperature, and its morphology greatly varied with the pH adjustors used, which probably attributes to different kinetics of the acidification. The bayerite can evolve to gibbsite and boehmite after the hydrothermal treatment at 100 °C and 145 °C, respectively, where these alumina hydrates show diverse morphologies. After the calcination, these alumina hydrates of bayerite, gibbsite and boehmite could pseudomorphically transform to the corresponding η-, χ- and γ-aluminas, respectively, exhibiting different structural and textural properties. Interestingly, the transition aluminas derived from the aluminum tri-hydroxides, bayerite and gibbsite, both display locally organized mesopores, while no such meso-structure can be observed in γ-alumina obtained from the aluminum mono-hydroxide, boehmite. The changes of bayerite during calcination are investigated detailed. The dehydration of non-porous bayerite accompanied with the formation of meso-structured transition aluminas, where the meso-structure becomes more and more clearly defined and pore size expands with the calcination temperature increasing.     

Phase Transformation and Morphology Evolution Characteristics of Hydrothermally Prepared Boehmite Particles

Under hydrothermal condition, benefiting from dehydration and in situ nucleation processes, well-crystallized 3-dimensional (3D) boehmite nanoparticles with an average diameter of around 400 nm was directly converted from gibbsite phase in aluminum oxyhydroxide powder without adding any kinds of other assistants. Through investigation the influences of different factors, it is concluded that, hydrothermal treating temperature, time and initial slurry pH play an important role in obtaining well-crystallized boehmite particles. Besides XRD and FE-SEM, TG/DTA, FT-IR and Raman spectra were also employed to follow and confirm the formation of boehmite, which is useful for optimizing the synthesis condition. Moreover, after the hydrothermal treatment under the optimum condition, because as-prepared 3D boehmite nanoparticles have abundant surface oxygen anionic vacancies (F and F⁺-centers), thus endowing it optical band gap around 5.41 eV. This technique is significant and useful for developing a new opportunity for large scale production of well-crystallized boehmite powder with high purity from aluminum oxyhydroxide powder.     

Effect of temperature on the rates of dissolution of gibbsite and boehmite

The effect of temperature on the rate of dissolution of gibbsite and boehmite in caustic soda solutions was studied in the temperature range 25-100°C. The results fitted the Arrhenius rate equation and the activation energy was found to be 30.6 ± 0.9 k. cal/g-mole for the gibbsite reaction and 29.4 ± 1.3 k. cal/g-mole for the boehmite reaction. While the effect of temperature on the boehmite dissolution has not been reported before, the value of the activation energy for gibbsite was higher than previously reported values. Reasons for these differences are given and a consistent value of the activation energy was obtained which agreed both with experimental data for different gibbsite samples and with modified forms of the previously published data.     

甲醇溶析铝酸钠制备氢氧化铝

以甲醇水溶液分解铝酸钠晶体,采用溶析法制备了超细氢氧化铝. 考察了30℃下氧化铝、氧化钠溶解度随甲醇质量分数的变化规律,研究了甲醇质量分数和反应温度对水合铝酸钠晶体分解工艺的影响,用XRD, IR, SEM及粒度分析、纯度分析等手段对制备的氢氧化铝产品进行了表征. 结果表明,随着溶剂中甲醇质量分数的增加,氧化铝和氧化钠溶解度均下降,但氧化铝下降幅度更大;铝酸钠溶液分子比(氧化钠/氧化铝摩尔比)先增加后减小,到甲醇质量分数为0.8左右时达到最大值. 30℃下水合铝酸钠晶体与甲醇质量分数为0.5~0.8的甲醇-水混合溶剂反应1~3 h,铝酸钠分解率可达到80%~90%,温度升高,分解率略有下降. 甲醇溶析得到的氢氧化铝30℃下为拜耳石型,温度升高逐渐变为三水铝石型,红外光谱完整. 产品形貌规则,为高纯薄片状超细氢氧化铝,平均厚度100 nm,平均粒径1.05 mm.     

预碳化辅助双氧水沉淀高碱铝酸钠溶液强化薄水铝石合成工艺(英文)

Hydrogen peroxide (H2O2) precipitation from sodium aluminate (SA) solution at close-ambient temperature is an efficient method to synthesize boehmite and its derived alumina with high surface area, but the precipitation yield of Al2O3 is usually below 50% in highly alkaline SA solutions. Here the synthesis of boehmite is enhanced through a precarbonization-assisted H2O2 route in highly alkaline SA solutions. It is found that the crystal structure of the precipitation product is evidently influenced by the precipitation conditions. As the precipitation temperature increases from 273 to 325 K, a small amount of gibbsite by-product is formed. As the aging temperature increases from 301 to 333 K, the crystallinity of boehmite decreases and part of the boehmite dissolves due to an increase in the pH value. Based on the above results, a precarbonization-assisted H2O2 route is proposed to obtain pure boehmite with more complete recovery of Al2O3 from highly alkaline SA solutions. The route includes a controllable precarbonization step of SA solutions with a molar ratio of Na2O to Al2O3 higher than 2︰1, followed by the H2O2-precipitated step with a molar ratio of H2O2 to Al2O3 less than 7︰1. Because of its facile operation conditions, no extraneous impurity, time saving and a possible recycle of the filtrate, the route has great potential to be an alternative method for preparation of boehmite and its derived alumina.     

Studies on the Gibbsite to Boehmite Transition

Abstract

The transition of gibbsite to boehmite is of interest with regard to high level waste processing associated with the Hanford and Savannah River sites. Both materials have been observed in core samples. From the temperature histories of the waste, it is possible that some fraction of gibbsite has been converted to boehmite. This paper describes thermal gravimetric analysis studies of products resulting from controlled temperature measurements of pure gibbsite in NaOH. Results indicate that the gibbsite to boehmite transformation can take place at temperatures as low as 100°C. This information, along with available data on waste inventories and temperature histories, may be used to estimate the fractions of gibbsite and of boehmite in a given waste tank. Site engineers can then tailor the sludge leaching process for a particular tank to account for the delayed dissolution of boehmite, allowing separation of the aluminum and processing as a low activity waste.     

4A沸石合成工艺研究与产物表征

利用正交优选实验研究了硅铝比、钠硅比、水钠比、反应温度和反应时间等5个因素对水热合成4A沸石的影响,在此基础上还研究了超声波辅助水热合成4A沸石,利用XRD、场发射扫描电子显微镜(FESEM)和钙离子交换能力对4A沸石进行了表征。正交优选实验结果表明:硅铝比是影响4A沸石钙离子交换能力的主要因素,其次是钠硅比和反应时间,水钠比和反应温度的影响最小;水热合成4A沸石的最佳工艺为以硅铝物质的量比为1.5、钠硅物质的量比为2.05、水钠物质的量比为150配制硅铝酸钠凝胶,于130℃下晶化5 h。通过水热合成及超声波辅助水热合成的4A沸石的对比表明:一定时间的超声波辅助水热合成更容易得到较高性能的4A沸石。     

绿茶水热还原制备微纳米金属铜

以绿茶茶水兼为溶剂和还原剂,采用水热法直接还原制备出不同形貌的微纳米金属Cu粉,同时研究了pH、茶水浓度（茶粉与水的质量比）、水热温度以及TiOSO₄对微纳米Cu的相纯度和颗粒形貌的影响。研究结果表明:在pH=3～12、m(茶)∶m(H₂O)=1∶100,反应温度为200℃的条件下,均可得到聚集态的球状金属Cu;降低茶水的浓度或反应温度,产物中存在Cu和Cu₂O两相,且随着茶水浓度或反应温度的降低,产物中Cu₂O的相对含量均逐渐升高;另外,在一次水热合成获得的单相Cu₂O中加入0.1gTiOSO₄并经过200℃、24h二次水热处理后,制备出长度为10～40μm、直径为0.4～0.9μm的一维棒状金属Cu。     

The effect of concentration on the rates of dissolution of gibbsite and boehmite

The effect of caustic soda concentration on the rate of dissolution of gibbsite and boehmite was studied. The activity of sodium hydroxide rather than cencentration was found to be the best parameter for kinetically describing the effect of concentration on dissolution rate. For the gibbsite reaction, a first order dependence on sodium hydroxide activity was observed whilst the boehmite dissolution exhibited a dependence on the term (a_NaOH. a_H2O) which was first order above 210 g/1 Na₂O and half order below that concentration.