KH-570硅烷偶联剂表面改性微硅粉分散性研究

采用KH-570硅烷偶联剂在酸性条件下对微硅粉(SF)表面进行了改性,通过控制改性时间和改性剂用量确定了最佳工艺参数,并对改性前后的微硅粉进行了表征,同时测定接枝改性样品表面的羟基数和吸油值,分析其改性效果.结果表明:改性后的微硅粉(KH570-SF)吸油值明显降低,表面羟基数急剧减少,KH-570硅烷偶联剂分子成功的以化学键的形式接枝在微硅粉表面,微硅粉团聚现象减少,分散性得到改善,同时对硅烷偶联剂改性微硅粉机理进行了探讨,结合热重和红外光谱分析表明,KH-570硅烷偶联剂主要通过与微硅粉颗粒表面的-OH形成氢键缔合而吸附到微硅粉颗粒表面上.     

纳米钛白粉改性丙烯酸聚氨酯涂料的制备及其紫外线耐候性能

利用γ-甲基丙烯酰氧基丙基三甲氧基硅烷(KH-570硅烷)实现了对金红石型纳米TiO2的表面处理,对表面处理前后纳米TiO2粉体的形貌及粒度分布状况进行了表征.将处理后的钛白粉加入到航空油罐所用的丙烯酸聚氨酯涂料中进行改性,研究了改性涂料的紫外线耐候性能.研究表明,表面处理可使钛白粉粉体的分散性能得到显著改善.经纳米TiO2改性后,丙烯酸聚氨酯涂料的紫外线耐候性能均得到了不同程度地提高.在涂料中添加5wt;的纳米TiO2并配合使用0.5wt;的纳米SiO2进行改性时,涂膜的紫外线耐候性能较好.     

乳液聚合法制备纳米SiO2/PMMA复合粒子及其表征

利用可聚合乳化剂在纳米SiO2表面进行乳液聚合,成功制备出了具有核壳结构的纳米SiO2/PMMA复合粒子,并通过FTIR、TEM、XPS和TGA分析了其粒子形态和包覆效果.结果表明:偶联剂MPTMS已成功接到了改性后的纳米siO2的表面,其谱图呈现了PMMA和纳米SiO2的复合结构而没改变原来纳米SiO2结构.复合粒子的粒径约50～100 nm,形态具有外层较浅内层较深的核壳结构.XPS分析表明,SiO2被PMMA包覆后,其表面的Si含量降为1.29;,用甲苯对纳米SiO2/PMMA复合粒子抽提后,Si含量增加到3.50;.基于索氏抽提实验和TGA分析,PMMA与SiO2比(fp)、PMMA对SiO2接枝率(fr)和PMMA的有效接枝率(fe)分别为95.8;、63.4;和67.1;.     

溶胶-凝胶法制备CaCO3/SiO2复合粒子

采用复分解法制得纺锤形CaCO3,以正硅酸乙酯(TEOS)为硅源,通过溶胶-凝胶法对其进行SiO2包覆改性,制备出CaCO3/SiO2复合粒子.通过改变反应温度、氨水用量和TEOS用量,探究了包覆改性的最佳工艺条件.利用扫描电子显微镜(SEM)、X射线衍射(XRD)、透射电子显微镜(TEM)、傅里叶红外光谱(FTIR)和X射线光电子能谱(XPS)对样品的形貌、结构、物相、化学组成和包覆性质进行了分析和表征.结果表明:当温度为45℃,氨水用量为10 mL,TEOS用量为3 mL时,制备的复合粒子耐酸性最好.SiO2包覆不会改变CaCO3形貌与结构.在包覆界面处,SiO2通过形成Ca-O-Si化学键包覆于CaCO3表面.     

静电纺丝法制备超疏水/超亲油SiO2微纳米纤维膜

采用静电纺丝法制备SiO2微纳米纤维膜,经六甲基硅氮烷(HMDS)改性后获得疏水/亲油特性,用FTIR、SEM、接触角等手段表征纤维膜的成分、微观形貌和对水及正十二烷的润湿性能等,研究了制备工艺对纤维膜物性参数以及润湿性能的影响,并测试了改性后纤维膜的高温稳定性和耐腐蚀性能.结果表明:SiO2微纳米纤维膜具有较多的孔隙和较高的比表面积,经HMDS改性后其表面粗糙结构结合疏水亲油的-Si(CH3)3基团使得纤维膜获得超疏水/超亲油特性,其水接触角为153.7°、水滚动接触角为8.2°、油接触角为0°;超疏水/超亲油SiO2微纳米纤维膜的最高耐受温度为450℃,最大拉伸强力为(40.7 ±9.4)×10-2N,且具有较好的耐腐蚀性能.     

乙烯基三甲氧基硅烷对二氧化硅的超疏水改性研究

采用乙烯基三甲氧基硅烷(VTMO)为改性剂,以氨水为pH调节剂制备改性二氧化硅(SiO2)超疏水材料.通过CA、FTIR和SEM对材料接触角、组成和形貌进行表征.考察了VTMO与SiO2的比例、反应时间、干燥时间对改性二氧化硅超疏水材料接触角和形貌的影响.结果表明,VTMO可在较短时间内改性二氧化硅制备出超疏水二氧化硅粉体,VTMO与SiO2比例对改性SiO2粉体的水接触角和微观二重结构有明显影响,而反应时间和干燥时间的影响较小.     

HNTs/SiO2复合气凝胶制备及其性能研究

采用正硅酸乙酯(TEOS)为硅原,以硅烷改性的埃洛石纳米管(HNTs)为增强相,利用CO2超临界干燥技术制备具有优良力学和隔热性能的HNTs/SiO2复合气凝胶.利用傅立叶红外光谱、扫描电镜、比表面积与孔径分析仪、万能试验机和导热率测量仪等手段对HNTs改性后的表面状态、HNTs/SiO2复合气凝胶的微观形貌、孔结构、力学和导热性能进行了测试分析.结果表明:改性后的HNTs均匀分散到二氧化硅气凝胶基体中,并与SiO2纳米颗粒实现良好的结合,HNTs/SiO2复合气凝胶呈三维网络结构,当HNTs含量为15wt;时,平均孔径为10.47 nm;随着HNTs含量的增加,复合气凝胶的力学性能不断增强,同时其导热系数也不断增大,当HNTs含量为15wt;时,HNTs/SiO2复合气凝胶的抗压强度为0.85 MPa,导热系数为0.024 W/mK.     

沉积温度对热蒸发法制备SiO2一维纳米材料的影响

利用热蒸发法在N型硅片表面成功制备出大面积SiO2纳米线和SiO2纳米棒结构.采用X射线粉末衍射(XRD),扫描电子显微镜(SEM),X射线能量色散谱(EDX),拉曼光谱(RS)和光致发光(PL)对合成的产物进行了表征.结果表明,用此方法生长的SiO2纳米材料,其结构和形貌与生长参数关系密切,随着沉积温度降低纳米线长度变短,最后呈现出棒状结构.此外,还研究了SiO2纳米结构独特的光学性质.该研究对改善光电子半导体器件的性能应用具有重要意义.     

硫化锌纳米晶的合成及性能表征

采用水热法以油酸和十二烷基硫酸钠(简记为SDS)作为复合型表面活性剂制备ZnS纳米晶,并对制备的ZnS纳米晶进行了表征.通过正交实验考察了油酸用量、SDS用量、反应温度、反应时间及pH值对ZnS发光性能的影响,确定了最佳工艺条件.结果表明,制备的ZnS为闪锌矿结构,单分散,粒径尺寸为6 nm,ZnS纳米晶表面的亲水性得到了有效的改善.所以,复合型表面活性剂的使用既可以提高ZnS纳米晶的发光性能又起到表面改性的作用.     

Cu2O/MWCNTs的制备、机理及气敏性研究

以Cu(Ac)2和多壁碳纳米管(MWCNTs)为原料,乙二醇(EG)作溶剂和还原剂制备了Cu2O/MWCNTs纳米复合材料。通过傅里叶红外光谱(FT-IR)、X射线粉末衍射(XRD)和透射电镜(TEM)对材料进行了表征,探讨了Cu2O以纳米粒子负载于MWCNTs表面的形成机理,并测试了复合材料对NOx的气敏性。结果表明Cu2O纳米粒子能够以键合作用负载在MWCNTs表面,Cu2O以纳米粒子形式有效负载是MWCNTs表面的化学吸附中心和Cu2+使用量的综合作用结果;Cu2O的负载有效增强了MWCNTs对NOx的气敏范围和灵敏度。     

Medium-range ordering in glass structures as a background of photosensitivity in silica fibers

Using picosecond stimulated Raman scattering (SRS) in silica-based fibers as a spectroscopic tool, some correlations between medium-range ordering and photosensitivity in silica glasses were experimentally established. Apart from the fundamental Raman-active vibrations attributed to the silica tetrahedra and dopant groups and their overtones, the intense Raman combination bands were observed. Based on the overtone band sequences, the vibrational anharmonicity constants were calculated and analyzed, including the ones corresponding to the 570 cm⁻¹ band. This band is forbidden in Raman scattering in silica crude selection rules are used. However, the transition is activated owing to the tetrahedron distortions by outer shells of the first and second peripheral atoms in a silica network. It is the intensity of the 570 cm⁻¹ Stokes band that grows enormously in the SRS spectra of germanium-doped silica fibers as a result of photoinduced changes in the glass structure resulting in second harmonic generation (SHG). The experimental data are interpreted using a modern glass theory. Practical applications of picosecond SRS spectroscopy for glass microstructural studies are discussed.     

Synthesis and characterization of high nickel-containing mesoporous silica via a modified direct synthesis method

A method by modifying tetraethyl orthosilicate (TEOS) with nickel species has been developed for the synthesis of mesoporous silica with high nickel content (up to 14.7 wt% of Ni). Using the method, nickel-containing mesoporous materials were obtained with high BET surface area and pore volume. The materials were characterized by means of X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, N₂ adsorption, Fourier transform infrared. Nickel species were incorporated into the silica frameworks. Formation of nickel phyllosilicates was also confirmed. After activation, mesostructures are still intact. Small nickel clusters embedded in the silica walls were found.     

Structural relaxation in sputter-deposited silica glass

We investigated structural relaxation below the glass transition temperature in sputter-deposited silica glass. Structural relaxation was obtained from annealing behavior of the IR reflection structural band position. Results were compared with that of bulk silica glass. Results showed the following. (1) The structural relaxation time is 10⁶ times shorter than that of bulk silica glass. (2) The activation energy is close to that of bulk silica glass. (3) Once the structural relaxation reaches a steady state, the structure of silica glass film resembles that of bulk silica glass.     

The influence of titania content on structure and properties of spherical mixed silica/titania particles

Spherical mixed silica/titania particles are prepared from silica/titania sol by an ultrasonic vibrator. The titania content of the samples varies from pure silica to a titania mole fraction of 0.31. Narrow size distributions with most frequent particle diameter of about 1 μm are obtained. Specific surface area and pore volume, mean pore radius as well as the meso pore size distribution are influenced by titania content. The spheres are composed of both silica and titania homogeneous distributed as it is indicated by scanning electron microscopy. X-ray diffraction studies show that the particles must be considered amorphous. Structural modifications of the framework are detected. Samples with varying refractive index may be prepared.     

Rheological behavior of alkali-activated metakaolin during geopolymerization

The dynamic rheological behavior of geopolymers, inorganic materials synthesized by activation of an aluminosilicate source by an alkaline solution, is described. The pastes studied were mixtures of an activation solution (alkali + silica) and metakaolin. The influence of the activation solution (NaOH vs. KOH), the silica (Aerosil vs. Tixosil), and the temperature on the evolution of the elastic modulus (G′) and viscous modulus (G′) over time were studied in the linear viscoelastic range. The results show that the nature of the silica has little influence on the viscous and elastic moduli when the geopolymer is activated by KOH, and that the setting time is faster with sodium hydroxide and at higher temperatures regardless of the geopolymer. In addition, during geopolymerization the stepwise variation of the modulus values indicates that the formation of the 3D network occurs in several steps. Moreover, geopolymers activated by potassium hydroxide exhibit slower kinetics but the interactions between constituents are stronger, as the loss tangent (tanδ = G″/G′) is lower. Finally, the maximum loss tangent, tanδ, was also used as a criterion to determine the temperature dependence of the geopolymers synthesized. This criterion is a precursor of the transition to the glassy state. The activation energies could thus be determined for the geopolymers synthesized with potassium hydroxide or sodium hydroxide.     

离子液体改性白炭黑及性能表征

采用离子液体1-烯丙基-3-甲基氯化咪唑(AMI)改性白炭黑(SiO2).通过傅里叶红外光谱(FT-IR),X射线衍射(XRD),X射线光电子能谱(XPS),热失重分析仪(TGA),扫描电镜(SEM),接触角仪,BET比表面积和孔径分析仪,对改性前后白炭黑的微观结构以及性能进行表征.结果表明,经AMI改性后,白炭黑粒子间的相互作用明显减小,团聚倾向减弱,在橡胶复合材料基体中的分散性提高.AMI改性白炭黑疏水性增强,接触角由12.7°增加到80.5°,比表面积由67.84cm2/g增加到124.28cm2/g.改性前后,白炭黑晶型结构变化不大,仍为无定形态.     

Influence of manufacturing variables on surface properties and dynamic adsorption properties of silica gels

The surface properties of silica gel such as surface area, pore volume, and average pore diameter are affected by the manufacturing variables including pH values, gelling and dehydration temperatures. The dynamic adsorption properties of silica gel are also affected by their preparation conditions. The mass transfer zone and the amount of adsorption were discussed using the experimental data of breakthrough curve. The influence of the manufacturing variables on the trends of breakthrough curves is important in most of the adsorbent modification. It was found in this study that the manufacturing variables affected the adsorption performance significantly. Therefore, the relationship between the manufacturing variables and the corresponding adsorbent properties conducted by the dynamic adsorption apparatus was examined in this study. This discussion is rare in most of the studies of preparing silica gels, which are usually focused on the relationship between the manufacturing variables and the surface properties of silica gels only. However, it is not necessary that a silica gel with larger surface area will give a smaller mass transfer zone or mass transfer resistance. The modification of adsorbents should consider not only the improvement of their surface properties but also their adsorption performance.     

Evaluation of activation energy of viscous flow of sol–gel derived phenyl-modified silica glass

The temperature-induced softening behavior in sol–gel derived phenyl-modified low-melting glass (phenyl glass) was investigated in terms of the activation energy for the viscous flow. The temperature dependence of the relative viscous flow was measured from the falling rate of a needle loaded with a constant weight. The activation energy for the viscous flow of phenyl-modified silica glass was found to be irrespective of the time of drying the sample phenyl-modified silica glass, which directly affects the extent of polymerization. Furthermore, the obtained activation energy was in considerably good agreement with that for the viscous flow of potassium alkali glass, and approximately twice larger than that of linear amorphous polymer (polystyrene). This result suggests the common microstructural feature of glassy materials interspaced by additive substances like Na/K or covalently bonded chemical functions such as phenyl groups.     

Fabrication of fluorine-doped silica glasses by the sol-gel method

Fluorine-doped silica glasses are produced by the sol-gel method for optical fiber preforms. In order to dope fluorine into silica glass, fluorinated silicon alkoxide, Si(OC₂H₅)₃F, is titrated into SiO₂ sol solutions. The fluorine content in silica glass depends on: the fluorine concentration in the gel, the specific surface area of SiO₂ particles and the heating rate in the sintering process. Fluorine-doped silica glass with a maximum relative refractive index difference of −0.93% is obtained. Using this technique, optical fibers with a triangular refractive index profile are fabricated with a minimum optical loss of 1.6 dB/km at 1.69 μm wavelength.     

Water concentration profile in silica glasses during surface crystallization

Water concentration profiles in silica glasses during surface crystallization at 1400°C in air were determined by IR spectroscopy with a microscope attachment. Three types of silica glasses with different water contents were examined. Some glass samples initially experienced hydration or dehydration depending upon the original water content. During crystallization, water concentration was highest at the crystal–glass interface and decreased with depth from the interface. Furthermore, water concentration at the interface increased with increasing heat-treatment time for crystallization. The observed water concentration profiles were consistent with the theoretical prediction by Smoluchowski based upon water diffusion modified by water expulsion from the crystal phase. A time-dependent crystal growth rate was also observed for some samples and this behavior appears related to the variation of water content in glasses.