Role of Drying Techniques on the Development of Porosity in Silica Gels

Silica gel has been prepared by the hydrolysis of TEOS under three different pH conditions. These gels have been subjected to drying in an air oven, under humidity, and also by exposure to microwaves, followed by further calcination at 500°C under slow heating schedule (3°C/min). Silica samples thus obtained are characterised by B.E.T. specific surface area and pore volume data. The thermal decomposition behaviour of the precursor gels are also reported. The adsorption isotherms of these samples indicate different behaviour related to the method of synthesis. Increase in pH of hydrolysis of the TEOS from 3 to 8 results in increase in specific surface area in tune with the earlier reports. However more significant observation is the variation in pore size distribution as evidenced from adsorption isotherms related to method of drying. Silica gels prepared at pH 3 show Type I behaviour irrespective of the method of drying. However gel prepared at pH 6 shows Type II behaviour when dried under microwave with specific surface area as high as 635 m₂/g and pore volume 0.9733 cc/g. The precursor gels prepared at still higher pH exhibit Type IV behaviour when subjected to microwave drying. The pH conditions of synthesis of precursor gels along with drying techniques appear to affect not only the surface areas and porosities but also the resultant adsorption isotherms, in sol-gel silica.     

Designing Double Pore Structure in Alkoxy-Derived Silica Incorporated with Nonionic Surfactant

The principle of designing double-pore structure in alkoxy-derived silica is described with the experimental system containing polyoxyethylene nonylphenylether. The formation of macropores is consistently explained in terms of the concurrence of a phase separation and a sol-gel transition in the polymerizing silica-surfactant-solvent system. The composition-morphology relationship exhibited a substantial variation depending on the length of oxyethylene units in the surfactant molecule. The mesopore volume obtained after basic solvent exchange and a heat-treatment suggested that the surfactant with shorter oxyethylene chain tends to be incorporated more in the gel phase to give higher mesopore volume. The small-angle X-ray scattering measurement of the gelling and aging system supported this hypothesis indicating micelle formation in the system containing a surfactant with shorter oxyethylene chain.     

聚酰胺/硅胶吸附剂在茶多酚提取中的应用

介绍了用聚酰胺／硅胶吸附剂提取茶叶中茶多酚,提取率达12％,茶多酚纯度达85％～90％。     

高纯稀土氧化物中的非稀土杂质的测定流动注射微柱预富集ICP-AES法

利用自合成的碳硅凝胶为吸附材料,以铜试剂［二乙基二硫代氨基甲酸钠（ＮａＤＤＴＣ）］为柱前衍生化试剂。在优化的实验条件下,于ｐＨ４．６的缓冲介质中在线预富集Ａｌ（Ⅲ）,Ｃｒ（Ⅵ）,Ｃｕ（Ⅱ）,Ｆｅ（Ⅲ）,Ｐｂ（Ⅱ）,Ｖ（Ⅴ）和Ｚｎ（Ⅱ）．采用停流技术洗脱,富集倍数可达８．１～１２．６倍,检出限为ｎｇ／ｍＬ级。对高纯氧化铕（Ｅｕ２Ｏ３）中的非稀土杂质进行测定,可避免大量稀土基体对测定的干扰。     

超低密度二氧化硅气凝胶制备新方法

以多聚硅氧烷（ Ｅ４０）为硅源,用溶胶凝胶一步法制备了 Ｘ 光激光靶及惯性约束聚变冷冻靶用超低密度 Ｓｉ Ｏ２ 气凝胶。研究了催化剂、溶剂等对其溶胶凝胶过程的影响。制备出的气凝胶密度为５ ｋｇ·ｍ － ３。用 Ｓ Ｅ Ｍ 、 Ｂ Ｅ Ｔ 等方法对其微结构进行了研究。     

超微细气相法白炭黑的表面改性

气相法白炭黑是重要的高科技超微细无机新材料之一。然而, 呈亲水性的表面硅醇基结构使其在某些疏水领域的应用受到限制。为进一步改善其性能和拓宽其应用领域, 人们对其表面结构和性质进行了大量卓有成效的改性研究。本文综述了近几年来气相法白炭黑表面活性的研究成果和工业化技术     

Thermal treatment of the precipitated solid material (PSM) from the waste black liquor (WBL)

Preciptated solid materials (PSM) from waste black liquor (WBL), at pH 8·5–9·0, produced from cooking of rice straw in paper mill factories were thermally treated. The cooking process led to decrease in organic material and partial substitution in silica structure. During this cooking process, three probable stages of mass loss comprise removal of moisture, volatile release, and combustion. The chemical analysis depicts the cooking effect on leaching either the high percentage elements (Ca, Na, and K) or some metallic cations (Mn, Cd, Zn and Cu) in the parent rice straw. Silica hydrate, amorphous silica and crystalline silica were obtained at <600°C, 600–700°C and at>800°C, respectively. The infrared spectra show gradual removal of the hydrocarbon bond (C–H), molecular H₂O, and sianol group (Si-OH) with temperature. TG, DTA, XRD and SEM were used in this study.     

石英微粉表面结构对硬硅钙石中空二次粒子形貌的影响

利用TEM、SED和EDS方法,检测石英微粉表面非晶态层的厚度,估算出非晶态二氧化硅所占的体积和质量百分含量,并着重研究石英微粉表面非结晶层对水热反应合成硬硅钙石中空二次粒子球形貌的影响．通过XRD和XEM方法鉴别反应料浆的晶相组成和形貌．结果表明：石英微粉表面存在少量非晶态二氧化硅时,未影响硬硅钙石中空二次粒子球的合成;而非晶态二氧化硅的含量较高时,会阻碍硬硅钙石中空二次粒子球的合成,最终形成硬硅钙石晶体和托贝莫来石晶体的堆积体．     

纳米微孔SiO2薄膜的Sol—Gel制备及气孔率控制

本文报道了纳米微孔ＳｉＯ２薄膜的溶胶－凝胶（ｓｏｌ－ｇｅｌ）制备工艺,利用椭圆偏振光测试仪（Ｅｌｌｉｐｓｏｍｅｔｅｒ）直接测量了薄膜的厚度、折射率、从而得到了ＳｉＯ２薄膜的气孔率及气孔大小分布。研究了合成工艺条件及浓Ｈ２ＳＯ４表面修饰对ＳｉＯ２薄膜气孔率及稳定性的影响。     

微波辐照对硅酸溶胶胶凝过程的影响

采取沉淀法结合微波照射对硅酸溶胶进行胶凝实验,发现在相同的条件下利用微波照射可使硅酸溶胶的凝聚速度大大加快。通过物理参数的对比测定,得到了在微波辐照下凝聚所产生的硅胶粒子具有更大的表面积和更强的吸附能力。