SiO2-TiO2复合气凝胶制备研究

采用同步溶胶凝胶方法,制备了TiO2分布均匀的SiO2-TiO2复合气凝胶.研究了SiO2溶胶预反应时间、不同催化剂和螯合剂对复合溶胶凝胶过程的影响,并用BET、SEM和XRD等测试方法对其结构进行了表征;复合SiO2-TiO2气凝胶具有典型的气凝胶特征,其比表面积为483.35m2/g,密度在0.1～0.12g/cm3范围内.     

由多聚硅氧烷制备二氧化硅气凝胶

SiO2 气凝胶是一种新型轻质纳米多孔材料。本工作以多聚硅氧烷 (E -4 0 )为硅源 ,用溶胶 -凝胶法制备出了SiO2气凝胶。研究了催化剂、温度、水等因素对其溶胶 -凝胶过程的影响 ;讨论了F离子以及水对E -4 0水解 -缩聚反应的作用机理 ;并用孔径分布测定仪、TEM等方法对其微结构进行了研究。结果表明 :由E -4 0为硅源制备的SiO2 气凝胶骨架颗粒为十几nm ;孔径分布较广 ,其峰值在 3 0nm附近 ,此外 ,还存在几nm的微孔。     

SiO2/TiO2复合气凝胶的孔道结构研究

为了在常压干燥下制备高比表面积且具有多级孔道结构的SiO2/TiO2复合气凝胶,以正硅酸乙酯、钛酸丁酯为原料,利用低聚体聚合将分相平行引入到溶胶凝胶过程中,获得SiO2/TiO2醇凝胶,并通过溶剂替换技术实现气凝胶的常压干燥制备.不同硅钛比气凝胶的内部结构研究表明:合成的气凝胶是由纳米SiO2和TiO2颗粒分散复合而成的介孔块体,其中Ti—O—Ti、Si—O—Si和Ti—O—Si键相互交织.气凝胶的结构变化是分相与溶胶凝胶过程相互竞争的结果.Si含量能显著改善气凝胶的结构,当n(Ti)∶n(Si)为3∶1时,比表面积高达712.2 m2/g,平均孔径为3.36 nm;当n(Ti)∶n(Si)为1.5∶1时,复合气凝胶具有明显双连续孔道,比表面积高,同时孔状结构清晰.     

间苯二酚－甲醛有机气凝胶的结构控制研究

以间苯二酚（Ｒｅｓｏｒｃｉｎｏｌ）－甲醛（Ｆｏｒｍａｌｄｅｈｙｄｅ）为原料，用溶胶－凝胶法和超临界干燥工艺制备了纳米多孔ＲＦ有机气凝胶。系统研究了原料配比、催化剂的使用、反应温度及溶剂用量等因素对ＲＦ气凝胶凝结时间和结构的影响，可以实现对该材料的结构进行纳米尺寸上的控制，从而为该材料的应用开发奠定了基础。     

SiO2/M纳米复合材料的结构及催化性能

采用溶胶-凝胶法和超临界干燥法制备了SiO2/M(Cu,Co)纳米复合材料,对其结构、形貌进行了TEM和比表面分析,并研究了SiO2/M纳米复合材料的催化性能.结果表明,制得的SiO2/M纳米复合材料保留了SiO2气凝胶的纳米网络和高比表面积,金属组份Cu与Co均匀地分散在纳米级SiO2气凝胶骨架中,对CO的氧化反应以及CO-NO反应均表现出高的催化活性.     

二氧化硅气凝胶合成新工艺

以Ｅ－４０（多聚硅氧烷）为硅源,以ＨＦ为催化剂,用溶胶－凝胶法制备出了ＳｉＯ２气凝胶法时研究了催化剂、溶剂、水等制备因素对其溶胶－凝胶过程的影响,用孔径分布测定仪、透射电镜（ＴＥＭ）、比表面测试（ＢＥＴ）等方法对其微结构进行了研究。研究结果表明,ＨＦ的加入大大加束字溶胶－凝胶反应速度;ＢＥＴ以及ＴＥＭ测试结果表明所制备的ＳｉＯ２气凝胶具有大的比表面积和纳米多孔结构（骨架颗粒约为１０纳米,孔洞尺政变     

亚临界干燥制备疏水SiO2气凝胶

以E－40（多聚硅氧烷）为硅源,三甲基氯硅烷的异丁醇溶液为干燥介质,用溶胶凝胶法,在亚临界条件下制备出疏水的SiO2气凝胶,通过SEM,孔径分布,比表面积,接触角以及红外光谱的测试对其物性进行了研究,结果表明,所制备的SiO2气凝胶具有典型的纳米网络结构,比表面大具具有疏水性能,亚临界干燥使得制备压力从6．4MPa降低到2．3MPa,降低了制备成本和风险,同时疏水性能提高了SiO2气凝胶环境适应性,从而十分有利于气凝胶的商业应用。     

SiO2—TiO2—ZrO2系涂层的制备及其特性

用溶胶－凝胶法（sol-gel method）在不锈钢表面制备了SiO2-TiO2-ZrO2系无机氧化膜（STZ）。用DTA／TG、IR、XRD和SEM等手段研究了涂层制备时由凝胶向玻璃态的转变以及涂层薄膜的显微结构特点，考察了涂层对基体的保护效果。试验结果表明，在溶胶至凝胶最终转变为无机氧化物的过程中形成了无机网络，Si^4 和Zr^4 充当了网络骨架的形成离子。涂层为无定型玻璃态，其间混有石英、锐钛矿或金红石等微晶。     

水玻璃制备纳米孔SiO2气凝胶块体材料的研究

以廉价水玻璃为硅源,经溶胶-凝胶工艺和超临界干燥技术制备了SiO2气凝胶块体,并研究了制备条件对其成胶时间的影响.结果表明,成胶时间随稀释剂用量(水或无水乙醇)的减少和温度的升高而缩短,但随NH3·H2O添加量的增加先缩短后延长,并且以无水乙醇为稀释剂时较以水为稀释剂时短.典型样品的扫描电镜(SEM)表明纳米尺寸球形骨架颗粒构成了连续网状纳米多孔结构,并且由N2吸附测试得知所有孔径均＜61nm,平均为6.3nm,比表面积为297.7m2/g.     

HF催化快速制备SiO2气凝胶

ＳｉＯ２气凝胶晃一种新型轻质纳米多孔泡沫材料,本文以正硅酸乙酯（ＴＥＯＳ）为原料,以乙醇为溶剂,以ＨＦ为催化溶胶－凝胶法快速制备出了ＳｉＯ２气凝胶。ＨＦ的加入大大加速了溶胶－凝胶反应速度,使凝胶时间减少至几分钟甚至更短;同时使凝胶温度降低至室温。ＢＥＴ及ＴＥＭ测试结果表明所制备的ＳｉＯ２气凝胶具有大比表面积（６７３．８ｍ＾２ｇ＾－１）、纳米多孔结构（骨架颗粒为几纳米,孔洞尺寸为５～３０ｎｍ）。     

VLE data for CO2-CF2Cl2, N2-CO2, N2-CF2Cl2 and N2-CO2-CF2Cl

Knowledge about vapour-liquid (VLE) is required as a basis of reliable calculations for separation processes. Correlations available for the prediction of T, p, x, y data are less accurate for mixtures at high pressures and mixtures containing supercritical components. The results of VLE experiments are reported and compared with data calculated with equations of state.     

Preparation of ZrO2-CeO2 and HfO2-CeO2 nanopowders

We prepared weakly agglomerated powders of ZrO₂-CeO₂ and HfO₂-CeO₂ solid solutions 5–8 nm in particle size, consisting of monoclinic and tetragonal phases. After heat treatment at 1200°C, the crystallite size was 30 and 14 nm, respectively. We also examined the effect of precipitate freeze drying on the crystallization of hafnia-based solid solutions containing up to 20 mol % CeO₂.     

Thermal diffusion in binary mixtures H2-CCl2F2 and H2-CHClF2

Thermal diffusion coefficients were measured in two gaseous mixtures, in which one component was close to the critical temperature, in the pressure range (19.6–127.4)·10⁴ N/m² and at a freon concentration of 0.25–0.8.     

Radial GRIN glasses in Li2O-Na2O-Al2O3-TiO2-SiO2 systems

A series of GRIN glass rods have been developed in Li2O-Na2O-Al2O3-TiO2-SiO2 systems. Negative radial refractive index profiles were generated by exchanging Na+ for Li+ ions in these glass rods. It has been observed that TiO2 plays a vital role in increase in the profile depth and maximum change in the refractive index because of its ambivalent nature. Change in the refractive index can be further increased by increasing the concentration of exchanging cation in the base glass.     

Comparison of the Electronic Structures of La2CuO4, Sr2CuO2Cl2, and Sr2CuO2F2

First-principles cluster calculations are reported of the local electronic structure of the three compounds: La₂CuO₄, Sr₂CuO₂Cl₂, and Sr₂CuO₂F₂. The copper ${\text{3d}}_{x^2 - y^2 } $ and the planar oxygen 2p _σ atomic orbitals exhibit a similar degree of covalency. The out-of-plane orbitals, however, are quite different with the ${\text{3}}d_{3z^2 - r^2 } $ atomic orbital lowered significantly in energy for chlorine and fluorine apical positions.     

Thermoelectric power of single-phase samples of Tl2CaBa2Cu2O y and Ba2CaSr2Cu2O y

Single-phase 2122 samples of thallium and bismuth superconductors were made by the precursor matrix method. The thermopower of these samples was measured in the temperature range 250 K-T _c . The thermopower was positive and decreased linearly with increasing temperature aboveT _c (onset). The exponential enhancement of thermopower seen in the undoped and doped YBCO was not observed in these samples. The linear variation of thermopower can be explained on the basis of either a two-band model or a narrow band model.     

Si_2N_2O-Al_2O_3-La_2O_3和Si_2N_2O-Al_2O_3-CaO系统的亚固相关系

本文给出了 Si_2N_2O-Al_2O_3-La_2O_3和 Si_2N_2O-Al_2O_3-CaO 系统的亚固相图。实验结果表明:在 Si_2N_2O-Al_2O_3-CaO 系统中有一个未知结构的新化合物 CaO·Si_2N_2O,在3CaO·Si_2N_2O 和3CaO·Al_2O_3两化合物之间形成连续立方固溶体。而 Si_2N_2O-Al_2O_3-La_2O_3系统中则没有发现新化合物。在两个系统的富 Si_2N_2O区,过量的 Si_2N_2O 与 La_2O_3和 CaO 分别反应形成 Si_3N_4与 La_(10)[SiO_4]_(?)N_2(H-相)(和 CaSiO_3。所研究的这两个三元系统中,分别形成了如下几个四元相容性区。在 Si_2N_2O-Al_2O_3-La_2O_3系统内有:H-Si_3N_4-La_2O_3·Si_2N_2O-La_2O_3·Al_2O_3;H-Si_3N_4-La_2O_3·Al_2O_3-La_2O_3·11 Al_2O_3;H-Si_3N_4-La_2O_3·11 Al_2O_3-Al_2O_3;H-Si_3N_4-Al_2O_3-O′s.s;H-Si_3N_4-O′s.s-Si_2N_2O在 Si_2N_2O-Al_2O_3-CaO 系统内有:Si_3N_4-CaSiO_3-CaO·Si_2N_2O-3CaO·Al_2O_3;Si_3N_3-CaSiO_3-3CaO·Al_2O_3-2CaO·Al_2O_3·SiO_(?);Si_(?)N_(?)-CaSiO_3-2CaO·Al_2O_3·SiO_2-Al_2O_3;Si_3N_4-CaSiO_3-Al_2O_(?)-O′s.s;Si_3N_4-CaSiO_3-O′s.s-Si_(?)N_(?)O     

Elastic and Electronic Properties of Superconducting CaPd 2 As 2 and SrPd 2 As 2 vs. Non-superconducting BaPd 2 As 2

The first-principles calculations were performed to predict the elastic and electronic properties of the superconducting ThCr₂Si₂-type phases CaPd₂As₂ and SrPd₂As₂ in comparison with the non-superconducting CeMg₂Si₂-type phase BaPd₂As₂. Besides, the same properties were compared for CeMg₂Si₂- and ThCr₂Si₂-type polymorphs of BaPd₂As₂. We found that all these phases are mechanically stable and belong to soft materials with low hardness. The near-Fermi region is formed by the valence states of the blocks [Pd₂As₂] with decisive contributions of Pd 4d states. The values of N(E _F) increase in the sequence: CaPd₂As₂ < SrPd₂As₂ < BaPd₂As₂, i.e. in the reverse sequence relative to the transition temperatures T _C. Thus, the change in T _C cannot be explained by the electronic factor, i.e. by the simple correlation T _C～N(E _F). Most likely the decrease in T _C in the sequence CaPd₂As₂ → SrPd₂As₂ and the absence of a superconducting transition in BaPd₂As₂ are related to the structural factors and the peculiarities of the electron–phonon coupling mechanism.