纳米级硼酸钙的制备

以硼砂和氯化钙为原料，采用超临界流体干燥技术(Supercritical Fluid Drying简称SCFD)制备纳米级硼酸钙。其过程主要包括制备水溶液中的胶体，经过过滤，用正丁醇、石油醚的混合溶液置换胶体中的水，然后进行超临界干燥。考察了制备沉淀过程中的反应物浓度和干燥条件对硼酸钙粒径大小的影响。采用SCFD技术可制备出大孔、高比表面积、低密度气凝胶超细粉。采用吸附法对其物性进行表征测定。该方法制备的纳米级硼酸钙超细粉体，表观密度可达到0．13g／mL，比表面积可达到388．8m^2／g。     

超临界流体干燥法制备莫来石超细粉

ＳｏｌＧｅｌ法是制备超细粉的一种有效方法,但胶体在干燥脱去溶剂过程中,由于表面张力的存在,常使凝胶发生收缩,孔结构塌陷,粒子凝聚,妨碍超细粒子的生成。超临界流体干燥法（简称ＳＣＦＤ）是在超临界流体条件下驱除凝胶中的液相,从而有效地消除引起胶体粒子聚集的表面张力,保持湿凝胶原有结构,得到小粒径,大孔容,高比表面超细粒子。为此我们采用ＳｏｌＧｅｌ法制备前驱体铝硅酸凝胶,利用超临界流体干燥技术,在１１５０℃合成了高比表面积的莫来石超细粉。采用ＣＯ２为超临界干燥介质,以化学纯正硅酸乙酯（ＴＥＯＳ）、…     

CuO(CoO,MnO)/SiO_2纳米复合气凝胶催化剂载体的制备及其在合成碳酸二苯酯中的应用

以正硅酸乙酯为硅源,以乙酸铜、乙酸钴和乙酸锰的水溶液为前驱体,采用溶胶–凝胶法和CO2超临界干燥工艺制备了CuO(CoO,MnO)/SiO2纳米复合气凝胶。采用场发射扫描电镜、透射电镜和电子散射能谱分析等对纳米复合气凝胶的微观结构和组成进行了表征。采用Brunauer–Emmett–Teller法测定了纳米复合气凝胶的比表面积、孔径及孔径分布。以纳米复合气凝胶为载体制备了负载型催化剂,用于催化合成碳酸二苯酯(diphenyl carbonate,DPC),并用气相色谱仪对反应液进行了分析。结果表明:纳米复合气凝胶的粒径为20～100nm,孔径为2～8nm,平均孔径为3.16nm,比表面积为664.4m2/g;过渡金属的摩尔含量为13.77%;催化合成DPC的质量收率达27.14%。     

Al2O3/SiO2气凝胶纳米粉的制备与表征

本文以正硅酸乙酯(TEOS)和硝酸铝Al(NO3)3·9H2O为原料,采用溶胶-凝胶(Sol-Gel)法和CO2超临界流体干燥(SCFD)技术制备了双元氧化物Al2O3/SiO气凝胶纳米粉,并利用物理吸附(BET)、透射电镜(TEM)和红外光谱(IR)技术测试分析了Al2O3/SiO2气凝胶的结构性能.该法制得的气凝胶纳米粉,粒径在5～15 nm,比表面高,热稳定性好.     

Sol-Gel-SCFD法合成莫来石超细粉的结构性能表征

采用溶胶（Ｓｏｌ）－凝胶（Ｇｅｌ）－超临界流体干燥（ＳＣＦＤ）法合成了莫来石超细粉,并对其结构性能进行了现代测试分析表征,结果表明,ＣＯ２低温超临界流体干燥能有效地防止凝胶干燥过程中粒子间硬团聚现象的发生,该法制备的莫来石超细粉成分准确,平均粒径小于２００ｎｍ,比表面积大于３８ｍ＾２／ｇ,具有很高的烧结活性。     

乙醇超临界干燥制备二氧化锰超细粉体

以MnCl2和NaOH为原料,利用超临界流体干燥技术(SCFD)制备了MnO2超细粉 体,采用X-射线衍射、粒度分析和扫描电镜确定了粒子的形貌和粒径,结果表明,采用超临界流 体干燥技术可以制备出颗粒细、大小均匀的纳米粒子。     

厘米级SiO2气凝胶球体的制备及表征

以正硅酸乙酯(TEOS)为硅源,采用酸碱两步催化溶胶-凝胶法和CO2超临界干燥技术成功制备出完整的厘米级SiO2气凝胶球体.当配比条件为TEOS∶ EtOH∶ H2O=1∶10∶4时制备的SiO2气凝胶球体具有典型的纳米多孔网络结构.采用扫描电镜(SEM)、透射电镜(TEM)、傅里叶变换红外光谱仪(FT-IR)、孔径分布及比表面积测试仪(BET)、纳压痕技术对SiO2气凝胶球体的表面形貌、内部结构、化学成分、比表面积、孔径分布及力学性能进行研究分析.研究表明:低温有利于制备出完整的厘米级SiO2气凝胶球体.随着凝胶温度的增加,SiO2气凝胶球体样品的收缩率逐渐增加,而孔隙率和比表面积逐渐减小.当凝胶温度为-5℃时,厘米级SiO2气凝胶球体样品的平均孔径为24.8 nm,孔体积为4.9 m3/g,比表面积高达1004.38 m2/g,密度为0.104g/cm3,收缩率约为16.2％,孔隙率约为95.3％,弹性模量和硬度最大分别为8.79 MPa与5.24 MPa.     

纳米锑掺杂氧化锡制备中超临界CO_2干燥的工艺优化及动力学

纳米锑掺杂氧化锡(ATO)具有优越的光电性能,在制备过程中前驱体干燥处理至关重要。为掌握ATO前驱体的超临界CO2干燥工艺特性,研究了超临界干燥的时间、温度、压力和CO2流量等工艺参数对纳米ATO粒径、比表面积等的影响,进一步探讨了超临界CO2流量对干燥动力学的影响规律,并拟合了干燥曲线方程。结果表明:温度35~40℃、压力10~14 MPa、CO2流量1.2~1.8 L·h-1、干燥5~6 h,最终能够获得平均粒径20~30 nm、高比表面积的纳米ATO材料;流量对干燥速率有明显影响,醇分比0.4为干燥速率由恒速转为降速的临界点,醇凝胶干燥动力学方程能够很好地描述ATO醇凝胶干燥工艺过程。研究结果可为湿法制备纳米材料的湿凝胶干燥工业化生产和控制提供参考。     

撞击流-沉淀法制取超细白炭黑中试研究

介绍了以工业级硫酸和工业级水玻璃为原料,利用撞击流反应-沉淀法制取超细白炭黑的中试试验。其反应过程在无旋立式循环撞击流反应器中进行。反应后物料经过陈化、过滤、洗涤,最后通过再浆进行喷雾干燥制得了超细白炭黑。用激光颗粒分析仪和比表面积-孔隙分析仪测定粒径及比表面积,结果表明:产品的平均粒径为2—3μm、比表面积高达822 m2/g,进一步证明了无旋立式循环撞击流反应器性能优越,操作稳定可靠,有利于制备超细粉体材料。     

改进两步法制备高透光率SiO2气凝胶的研究

以正硅酸甲酯为硅源,采用溶剂甲醇和N,N-二甲基甲酰胺,通过酸碱两步催化溶胶-凝胶法,结合CO2超临界干燥技术制备出高透光率SiO2气凝胶.利用扫描电镜、比表面积和空隙分析仪、紫外-可见分光光度计对该气凝胶的结构和光学性能进行了研究.结果表明,用N,N-二甲基甲酰胺为溶剂获得的气凝胶具有好的三维纳米多孔结构,平均孔径15.16 nm,比表面积922.1 m2/g;0.4 cm厚的样品在波长800 nm处的透光率高达92.4％.由于该气凝胶具有较高的透过率,因此在太阳能集热器方面具有极高的应用价值.     

Synthesis of yttrium aluminum garnet (YAG) powder by homogeneous precipitation combined with supercritical carbon dioxide or ethanol fluid drying

YAG precursors were synthesized by the urea method in aqueous solution using supercritical carbon dioxide and ethanol fluid drying technique, respectively. The composition of the precursors, the phase formation process and the properties of the calcined powders were investigated by means of XRD, IR, TG/DSC, BET, TEM and SEM. Compared with the classically prepared powders at room temperature in air, the amorphous precursor dried by supercritical CO₂ fluid was loosely agglomerated and directly converted to pure YAG at about 900 °C. The resultant YAG powders showed good dispersity with an average crystallite size about 20 nm and specific surface area of 52 m² g⁻¹. However, the precursor dried by supercritical ethanol fluid was crystalline. Extensive phase segregation occurred during the drying process and resulted in the formation of separate phases such as monoclinic Y(OH)₃ and pseudoboehmite. YAM and YAP phases appeared in the calcination process and phase pure were not detected until 1200 °C.     

Supercritical Fluid Drying of Aqueous 2-Propanol Suspension

Abstract

To prepare fine powders of oxides, supercritical fluid drying was applied. As the case of point, Y–Ba–Cu complex oxide was taken up. A suspension of Y–Ba–Cu complex oxide was synthesized by simultaneous hydrolyzation of 2-propanol solution of yttrium triisopropoxide–barium diisopropoxide–copper diisopropoxide. The supercritical fluid drying by carbon dioxide was confirmed to dry the suspensions, expecting no aggregation of particles throughout the drying procedure. First of all, solubilities of 2-propanol, water, and aqueous 2-propanol solution in high pressure carbon dioxide were measured. Judging from the observed solubilities, temperatures, and pressures in drying conditions were determined. The drying rates were measured and the dried powders were characterized by DTA, TGA, and SEM. The results of these experiments suggested that the supercritical fluid drying process is useful for drying of the suspensions of superconducting compound prepared by hydrolyzation of alkoxides.     

超临界流体干燥法制备纳米掺锑氧化锡粉体

以SnCl4.5H2O和SbCl3乙醇溶液为原料制备前驱体掺锑氢氧化锡胶体沉淀,采用乙醇超临界流体干燥法干燥前驱体;用TG-DTA、XRD、TEM、BET等方法对粉体的结构、物相、形貌进行表征。结果表明,采用乙醇超临界流体干燥法可得到高比表面积的掺锑氧化锡纳米粉体。     

DRYING OF Y-Ba-Cu-O COMPLEX OXIDE SUSPENSION BY SUPERCRITICAL CARBON DIOXIDE

Fine and homogeneous powders of Y-Ba-Cu complex oxides are necessary to improve the quality of YBCO bulk high temperature superconductors. The powders which contain BaCO₃ must be sintered for producing YBCO super-conductors at temperature above 850 °C. Therefore, complex oxide is desired. In order to prepare fine complex oxides powders, suspension was synthesized by simultaneous hydrolization of 2-propanol solution of metal isopropoxides. However, the suspension was not dried by a hot air drying method, because aggregation occurs due to cohesion of particle along with evaporation. Also, the suspension could not be freeze-dried, because the freezing point of 2-propanol is -88.5°C. So, supercritical fluid drying method using supercritical carbon dioxide was applied. The results from these experiments suggest that this method is useful for drying of the suspension prepared by the alkoxide route.     

Alumina/silica aerogel with zinc chloride alkylation catalyst: Influence of supercritical drying conditions and aerogel structure on alkylation catalytic activity

Alumina/silica aerogel with zinc chloride alkylation catalyst, was obtained using one step sol–gel synthesis and subsequent drying with the supercritical carbon dioxide. The high density supercritical carbon dioxide drying conditions resulted in zinc chloride removal from the catalyst surface, surface area and pore volume increase and catalytic activity decrease. The low density supercritical carbon dioxide drying conditions, pore size distribution centred around 6 nm pore radius and high degree of mixed Al–O–Si bonds in the alumina/silica aerogel network, were found to increase the catalytic activity of the obtained aerogel catalysts.     

DRYING OF Y-Ba-Cu-O COMPLEX OXIDE SUSPENSION BY SUPERCRITICAL CARBON DIOXIDE

Abstract

Fine and homogeneous powders of Y-Ba-Cu complex oxides are necessary to improve the quality of YBCO bulk high temperature superconductors. The powders which contain BaCO₃ must be sintered for producing YBCO super-conductors at temperature above 850 °C. Therefore, complex oxide is desired. In order to prepare fine complex oxides powders, suspension was synthesized by simultaneous hydrolization of 2-propanol solution of metal isopropoxides. However, the suspension was not dried by a hot air drying method, because aggregation occurs due to cohesion of particle along with evaporation. Also, the suspension could not be freeze-dried, because the freezing point of 2-propanol is ?88.5°C. So, supercritical fluid drying method using supercritical carbon dioxide was applied. The results from these experiments suggest that this method is useful for drying of the suspension prepared by the alkoxide route.     

Drying processes for preparation of titania aerogel using supercritical carbon dioxide

Supercritical carbon dioxide drying was performed for the preparation of titania aerogels from sol–gel routes. The conditions of supercritical carbon dioxide drying were 313–323 K and 7.8–15.5 MPa. The solvents in titania wet gels obtained from the sol–gel routes were replaced by acetone. The titania aerogels obtained from supercritical carbon dioxide drying form needle-like structures. In supercritical carbon dioxide drying, the extraction rates of acetone from the wet gels were measured by using an on-line Fourier transform infrared spectroscope. It was found that the titania aerogels with lower cohesion were induced from the formations of homogenous phase for carbon dioxide + acetone system and the lower extraction rates of acetone. Furthermore, titania films were prepared by the depositions of the titania aerogels on ITO-coated PET substrates. The needle-like aerogels with lower cohesion derive the titania film with high surface area.     

超临界流体干燥技术在纳米粉体制备中的应用

由于纳米粒子的表面效应，用传统的干燥方法干燥纳米粉体时极可能产生团聚结构。超临界流体干燥技术是制备具有高比表面积、孔体积、较低密度和低热导率的块状气凝胶和纳米粉体的重要途径之一。介绍了超临界流体的性质、超临界流体干燥技术的研究进展、超临界流体干燥的工艺与设备及过程的影响因素，阐述了超临界流体干燥技术在纳米材料制备中的应用，并指出了超临界流体干燥过程的控制技术及注意点，为进一步加强超临界流体干燥技术的理论研究和拓展超临界流体干燥技术的应用领域奠定了基础。     

The influence of starting materials on the structure of ultrafine carbon powders

The primary ultrafine carbon powders were prepared by sol–gel supercritical fluid drying method using different starting materials. After heat-treatment at 1100 and 2600°C, respectively, the ultrafine carbon powders were obtained. The properties of primary ultrafine carbon powders and their annealed products were characterized by TEM, XRD, Raman spectra and nitrogen adsorption. The results reveal that starting materials have influence on the structure of ultrafine carbon powders.     

Characterization of High-Surface-Area Zirconia Aerogel Synthesized from Combined Alcohothermal and Supercritical Fluid Drying Techniques

Thermally stable tetragonal zirconia aerogel with a high surface area can be obtained by a novel alcohothermal route, followed by the supercritical fluid drying technique. In addition, a cheaper inorganic salt was used as raw material instead of the expensive and harmful zirconium alkoxides. The zirconia aerogel samples were characterized using X-ray diffraction, thermal analysis, N₂ adsorption measurements, diffuse reflectance infrared Fourier transform spectroscopy, and transmission electron microscopies. The results show that the resulting zirconia aerogel was composed primarily of narrowly distributed nanoparticles with loose aggregation. It is shown that the thermally stable zirconia aerogel has a high specific surface area and a well-developed textural mesoporosity with narrow pore size distribution, which is highly attractive for potential applications in heterogeneous catalysis.