超低密度SiO2气凝胶的制备及成型研究

 以正硅酸乙酯(TEOS)为硅源，采用酸碱二步催化溶胶-凝胶法，结合超临界干燥技术制备了超低密度SiO₂气凝胶,最低密度为3.4 mg/cm³；进一步结合成型工艺，在解决了模具设计和脱模技术后制备了具有不同密度的柱状和微型套筒样品，密度10～50 mg/cm³。研究了水、催化剂、稀释剂对二步溶胶-凝胶过程的影响，获得了制备低密度SiO₂气凝胶的最佳条件。利用扫描电镜、孔径分布及比表面积测试仪等对SiO₂气凝胶微结构进行了研究。结果表明，获得的超低密度SiO₂气凝胶具有较好的纳米网络，平均孔径18.9 nm，还具有高比表面积898 9 m²/g。     

种子法制备金掺杂二氧化硅气凝胶

 采用羟胺种子法合成了金掺杂二氧化硅气凝胶。采用紫外 可见光分光光度计研究了还原过程中体系的变化情况。使用透射电镜（TEM）研究了气凝胶的微观结构，气凝胶的比表面积和孔径分布由BET-BJH方法测试。结果表明通过种子法可以制备金掺杂质量分数0.01%~1.00%，密度25～50 mg／cm³，比表面积达800 m²/g以上的SiO₂气凝胶样品。     

密度渐变多层碳气凝胶靶型的制备

 以间苯二酚-甲醛为原料,结合自制活动式微模具成型工艺制备不同厚度和密度的碳气凝胶薄片,采用密度为10 mg·cm^-3的SiO₂溶胶为“粘合剂”,获得单元薄片厚度在100～580 μm,密度在50～400 mg·cm^-3范围内变化的5层密度渐变碳气凝胶靶型。重点研究了该特殊靶型内部C/SiO₂气凝胶层间界面情况。采用场发射扫描电镜（FESEM）,X射线相衬成像仪等对靶型整体结构及碳气凝胶单元薄片表面和内部微观结构进行了表征。结果表明：胶粘层SiO₂气凝胶厚度约为15 μm,厚度一致,远小于碳气凝胶层厚度且与碳气凝胶薄片的胶粘程度较好,界面平整,靶结构均匀。     

块状Ta2O5-TiO2复合气凝胶的制备与表征

 以乙醇钽、钛酸丁酯为原料,以乙醇为溶剂,通过溶胶-凝胶法及超临界干燥成功制备了Ta₂O₅-TiO₂复合气凝胶。用场发射扫描电镜（SEM）、透射电镜（TEM）、扫描电镜模式下的电子能谱仪（EDS）以及比表面积吸附仪（BET）对其进行表征。结果表明:该气凝胶是由粒径在nm量级的Ti和Ta的羟基氧化物胶体颗粒堆积而成的低密度、高比表积的多孔网络结构材料,孔径分布主要集中在5~15 nm,比表面积为492.9 m²/g,密度为90 mg/cm³左右。     

基于TaCl5的Ta2O2气凝胶制备工艺

 主要介绍了以TaCl₅为前驱体,低分子醇类为溶剂,分别采用环氧丙烷和环氧氯丙烷作为凝胶促进剂制备Ta₂O₂湿凝胶,湿凝胶经过CO₂超临界干燥而获得白色Ta₂O₂气凝胶。透射电镜图谱表明气凝胶是由粒度为10～20 nm的颗粒堆积而成。N₂等温吸附-脱附分析表明,气凝胶的比表面积为800～900 m²/g。     

高折射率光学薄膜的化学法制备研究

 报道了一种以ZrOC₁₂·8H₂O为源,溶胶-凝胶法制备高激光负载高折射率薄膜的新方法。薄膜采用旋转镀膜法制备,对薄膜的结构、光学特性及激光损伤阈值进行了测量,有机粘接剂对薄膜折射率及机械强度的影响也作了探讨。以该薄膜与SiO₂溶胶凝胶膜交替涂覆制成的多层高反膜,剩余透过率仅0.98%,激光损伤阈值达16J/cm²（3ns）。     

水含量对溶胶-凝胶SiO2增透膜结构和性能的影响

利用正硅酸乙脂(TEOS)的碱催化,溶胶-凝胶法制备多孔SiO₂增透膜.较详细地研究了工艺参量H₂O/TEOS摩尔比对薄膜结构和性能的影响.结果表明,随H₂O/TEOS摩尔比的增大,薄膜厚度、折射率和致密度减小;而薄膜透射率增大.     

Mg2+掺杂Zn2SiO4:Mn2+的溶胶-凝胶法合成及真空紫外发光特性研究

采用溶胶-凝胶法（sol-gel method）于不同气氛条件下成功合成了Zn_1.92-xMg_xSiO₄:0.08Mn²⁺（0≤x≤0.12）系列粉末样品.利用X射线衍射(XRD)、光致发光(PL)谱等分析手段对Zn_1.92-xMg_xSiO₄:0.08Mn²⁺系列     

对苯二酚-甲醛碳气凝胶的制备

 溶胶-凝胶法制备了高HC比（10~40，对苯二酚与催化剂(Na₂CO_{3/sub>)的物质的量之比）的对苯二酚-甲醛有机气凝胶，并经高温碳化处理得到其碳气凝胶。借助有机气凝胶的红外光谱研究了其化学结构，说明其网孔结构形成的可能性；研究了有机气凝胶的扫描电镜图像、比表面积及孔径分布等，并得到碳化前后的一些对比数据：有机气凝胶颗粒大小30~50 nm，碳化后约为10 nm，比表面积从341.77 m²/g增大到452.75 m²/g，密度从0.170 8 g/cm^{3/sup>增大到0.335 6 g/cm3/sup>。}}     

高密度间苯二酚-甲醛碳气凝胶ICF靶的制备与吸附性能研究

 以间苯二酚和甲醛为前驱体，通过改进传统制备技术解决了高密度间苯二酚-甲醛(CRF)碳气凝胶制备过程中的龟裂问题，制备出了符合ICF实验需要的高密度CRF碳气凝胶材料。分别对CRF碳气凝胶的元素组成和物相组成进行了鉴定，采用自动吸附仪考察了CRF碳气凝胶对N₂和H₂的吸附性能。结果表明：该碳气凝胶是一种由C元素组成的类似石墨结构的非晶固态材料，结构均匀性好，具有良好的机械加工性能，比表面积达676 m²·g^-1，平均孔径为7.16 nm；氢吸附质量分数达2.28%，相应体积密度为17.83 kg·m^-3。     

疏水介孔SiO2的制备与性能表征

以廉价的工业级正硅酸乙酯为原料,经过酸碱两步催化制备二氧化硅凝胶,以三甲基氯硅烷/六甲基二硅氧烷混合液对凝胶进行直接表面改性,常压干燥下得到高比表面积疏水性二氧化硅气凝胶.用SEM、IR、N2吸脱附、TG-DTA、接触角的测定等分析方法对二氧化硅化学成分、结构形貌、比表面积、热稳定性和疏水性能进行了研究.结果表明,经改...     

Visible,near-infrared and infrared optical properties of silica aerogels

Silica aerogel is an excellent thermal insulation material with a low thermal conductivity and a high porosity and has attracted great concern in applications. This paper was to experimentally investigate the optical properties of optically thick silica aerogel in the visible, near-infrared and infrared spectrum region. The fiber-loaded silica aerogel sample was prepared through sol–gel technique and supercritical drying process. Silica fibers were added into the aerogel during the preparation procedure to strength the skeleton of aerogel. As a comparison with the fiber-load silica aerogel, a silica fiber composite sample with the same chemical component and different physical structure was also prepared. A simplified two-flux model neglecting the boundary effect was used to describe the radiation propagation characteristics inside the samples. The spectral normal-hemispherical reflectances, transmittances, and normal emittances of silica aerogel and silica fiber samples were measured and compared in the wavelengths of 0.38–15 μm. Then the spectral optical constants of samples were determined using the experimental data. The spectral absorption and scattering coefficients of silica aerogel were within (0.01 cm⁻¹, 31.0 cm⁻¹) and (1.4 cm⁻¹, 25.8 cm⁻¹). The results showed that the spectrum region where the scattering coefficient is low usually corresponds to a high absorption coefficient. In addition, the total radiation properties of samples were predicted at high temperatures. The analysis of optical properties of silica aerogel is necessary to provide valuable data in applications.     

三甲基硅烷化改性二氧化硅气凝胶

 采用六甲基二硅氮烷对二氧化硅凝胶进行疏水处理,得到了疏水性的二氧化硅气凝胶。用红外光谱和热分析表征处理前后二氧化硅气凝胶的性质,用测量显微镜跟踪处理前后气凝胶柱在空气中直径变化。结果表明,处理后气凝胶的表面羟基明显减少,在空气中的吸潮性大大降低,圆柱体在空气中的径向收缩率从30%降至3%。     

浸渍过程对纳米纤维素/二氧化硅复合气凝胶结构与性能研究

纳米纤维素(CNF)气凝胶兼具传统气凝胶的优异特性和自身优良的生物相容性和可降解性,在很多领域应用前景广阔。然而纤维素自身的超亲水性严重限制了其更广泛的应用,为改善纤维素气凝胶的亲水性能,提高其综合应用性能,采用简单浸渍法在纤维素气凝胶基体中引入二氧化硅(SiO₂)颗粒制备纳米纤维素/二氧化硅复合气凝胶,利用傅里叶红外光谱仪(FTIR)分析纤维素气凝胶和复合气凝胶的化学结构;用扫描电镜(SEM)观察气凝胶的微观结构;测定气凝胶的物理、力学性能和接触角。结果表明,复合气凝胶在3 340 cm-1处-OH吸收峰较纤维素气凝胶均有所减弱,表明SiO₂的引入促使Si-OH形成,也降低了气凝胶的亲水性,同时有Si-CH₃和Si-O-Si吸收振动峰出现,表明三甲基氯硅烷(TMCS)的改性作用以及纤维素与SiO₂颗粒之间形成稳定化学键连接。浸渍时间影响硅含量,进而影响气凝胶的密度、比表面积和孔隙率。当浸渍时间为10 min时制备的复合气凝胶性能较好,其微观结构分布均匀,具有疏水性能,接触角可达152°,同时气凝胶仍具有较好的力学性能和较低密度,其压缩模量和压缩性能分别为5.91和1.38 MPa,密度为0.1 g·cm-3。     

Effect of different trimethyl silylating agents on the hydrophobic and physical properties of silica aerogels

An essential feature of the ambient pressure dried aerogel manufacturing process is the end-capping of the reactive silanol groups in the silica wet gel. In this report, we have presented the effect of two different trimethyl silylating agents viz. trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) on the hydrophobic and physical properties of ambient pressure dried silica aerogels. The hydrogels were prepared by sol-gel processing of sodium silicate precursor (Na₂SiO₃) in the presence of acetic acid catalyst followed by vapour passing treatment and different solvent exchanging steps. The silylating agent in hexane was used for end-capping of the silanols present on the silica surface of the gel. To study silylation behavior silylating agent/Na₂SiO₃ molar ratio was varied from 2.4 to 5.6. The aerogels have been characterized by density, % of volume shrinkage, porosity, % of optical transmission, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermo-gravimetric and Differential Thermal Analysis (TG-DTA) and contact angle measurements.     

Some comments on superfluid 3He placed in globally deformed aerogel

New experimental results focused on the behavior of the superfluid A-like phase placed in globally deformed aerogel environment are considered. We compare experimental data collected by using optically attested axially stretched silica aerogel, on the one hand, and “nematically ordered” aerogel consisting of nearly parallel Al₂O₃ · H₂O polymer strands, on the other. In the case of axially stretched silica aerogel the point of view was adopted according to which the orbital anisotropy axis l? is long-ranged. The experiments were carried out by pulsed NMR techniques in keeping the direction of an externally applied magnetic field normal to aerogel stretching axis. We have generalized the dipole-locked configuration for arbitrary angle of inclination of the magnetic field with respect to aerogel stretching axis. The experimental data collected in using “nematically ordered” aerogel cannot be reconciled with above-mentioned results.     

High finesse microfiber knot resonators made from double-ended tapered fibers

We fabricated optical microfiber knot resonators from thin tapered fibers (diameter down to 1 μm) linked to untapered fiber at both ends. We demonstrated a finesse of about 100, over twice as high as previously reported for microfiber resonators. Low-loss encapsulation of microfiber knot resonators in hydrophobic silica aerogel was also investigated.     

Oxidation activity of Au nanoparticles on aerogel supports

We have prepared titania aerogel and titania-coated silica aerogel incorporating thiol-capped Au nanoparticles. Both composite materials showed high CO oxidation activity after they were calcined at 673 K. Compositional and morphological changes driven by calcination were evaluated with thermogravimetry and X-ray diffractometry. From the results, it was suggested that the nanoparticles transformed from a faulted to a near-regular FCC structure presumably in concert with the formation of firm contacts between the nanoparticles and the gel substrates. While the diameters of the Au particles in the titania aerogel considerably increased upon calcination, those in the titania-coated silica aerogel were almost unchanged. As a consequence, the latter composite aerogel showed higher activity for oxidation of CO.