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  • Title: [Determination of silanol group content on the surface of fumed silica by chemical reaction-headspace gas chromatography].
    Author: Bai Y, Duan X, Wang D, Hu G, Wu C, Zhang M, Liu W.
    Journal: Se Pu; 2021 Jul 08; 39(7):715-720. PubMed ID: 34227369.
    Abstract:
    Fumed silica is prepared by flame pyrolysis, where silicon halide is combusted in an oxygen-hydrogen flame, resulting in finely dispersed and thermally stable silicon dioxide. Because of its unique physical and chemical properties, including high porosity, large pore volumes, large specific area, and high chemical activity, fumed silica is widely used in rubbers, plastics, adhesives, paints, and printing inks for reinforcement, as well as in thixotropy, anti-setting, and anti-sagging applications. These functional properties of fumed silica are related to the silanol group on its surface. However, there is no accurate and convenient test method to determine the silanol group content on the surface of fumed silica. This work explores a novel method to determine the silanol group content on the surface of fumed silica by chemical reaction-headspace gas chromatography (HS-GC). Theoretically, by this method, the silanol group can rapidly react with the Grignard reagent and generate methane, the amount of which can be determined accurately by GC analysis. GC analysis was conducted using a headspace flask as a closed reactor to transform the silanol group into a volatile component through a chemical reaction, so as to realize the accurate determination of silica hydroxyl. The amount of methane produced in the reaction was directly proportional to the content of silanol groups on the surface of fumed silica. Therefore, the silanol group content was calculated using the chemical reaction equation. Before the experiment, fumed silica was dried for 2 h in an oven at 105 ℃ to remove adsorbed moisture. The dried fumed silica sample was then reacted with the Grignard reagent dispersed in toluene in an airtight reaction bottle. Toluene was used as a dispersion agent to promote contact and reaction between the fumed silica sample and Grignard reagent. The methane produced by the reaction was injected into a gas chromatograph for separation and further detected using a flame ionization detector (FID). Methane was quantified from the peak areas of the GC signals using the external standard method, and the silanol content in the sample was obtained. Simultaneously, factors influencing the outcome of the method, such as the dosage of the Grignard reagent and reaction time with it, were optimized by a comparison test. Accordingly, 2.0 mL of 0.3 mol/L Grignard reagent and a reaction time of 15 min were found to be optimal for testing. The test results showed that there was good linear correlation between the content of the silanol group and the GC signals, with a correlation coefficient of 0.9990. The limit of detection was 0.30 mg/g, and the limit of quantification was 1.00 mg/g. The relative standard deviation of reproducibility was less than 3%. Based on an interlaboratory test conducted by four laboratories on five samples with different silanol group contents, the repeatability limit (r) was less than 2.5%, and the reproducibility limit (R) was less than 6.5%. Compared with the traditional chemical method, the method involving HS-GC presents distinct advantages in terms of lower reagent consumption, high sensitivity, good stability, and reliability. It is suitable for the rapid detection of the silanol group content on the surface of fumed silica, and can aid in the quality control of fumed silica during its production and application. This method has important theoretical and practical significance for developing accurate methods to determine silica hydroxyl in the silicon industry for standards and the optimization of industrial technology. This study serves as a foundation to standardize and promote the rapid development of silicon material-related industries. 建立了一种基于化学反应-顶空气相色谱测定气相二氧化硅表面硅羟基含量的新方法。实验取气相二氧化硅放入顶空瓶中于105 ℃烘箱中加热2 h去除水分,将甲苯稀释的格氏试剂注入密闭的顶空瓶中,格氏试剂与气相二氧化硅表面硅羟基快速反应产生甲烷(CH4),甲烷量与气相二氧化硅表面硅羟基含量成正比。经过气相色谱-氢火焰离子化检测器测定甲烷,通过外标法定量,根据化学反应方程式计算出样品中羟基含量。同时对反应溶液用量与反应时间等条件进行优化,确定2.0 mL反应溶液,反应15 min为最优的前处理条件。结果表明,硅羟基含量与气相色谱信号值之间存在良好的线性相关性,相关系数为0.9990,相对标准偏差小于3%,本方法的检出限为0.30 mg/g,定量限为1.00 mg/g,开展了4家实验室对5个不同比表面积的样品测试,数据结果的重复性限(r)小于2.5%,再现性限(R)小于6.5%。该方法结合自动化技术,顶空反应操作简单,样品量和试剂用量少,准确性高,重复性好,优于酸碱滴定法,适用于快速检测气相二氧化硅表面硅羟基的含量,解决了硅羟基利用传统方法难以准确测定的难题。该方法的建立对我国二氧化硅产业硅羟基检测标准的制定和产业技术优化,均具有重要的理论和现实意义。
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