硅酸薄荷酯的合成研究

以硅酸乙酯和薄荷醇为原料,在碱性催化剂作用下合成了硅酸薄荷二酯;以四氯化硅和薄荷醇为原料,三乙胺为缚酸剂合成了硅酸薄荷三酯。用1HNMR和GC-MS对合成的产物进行了结构表征。     

原硅酸乙酯的水解缩聚

综述了原硅酸乙酯的水解缩聚反应机理和所形成聚合物之结构。     

Mechanical Properties of Polycrystalline Lithium Orthosilicate

Room-temperature mechanical properties and high-temperature creep deformation of lithium orthosilicate (Li₄SiO₄) were studied. Elastic constants, flexural strength, and fracture toughness were determined for specimens with densities between 68% and 98% of theoretical. Critical quenching temperature and thermal-shock resistance parameters for 90% dense specimens were also measured. High-temperature creep deformation was investigated by a constant-strain-rate test in an argon atmosphere at temperatures between 750° and 1025°C and strain rates ranging from about 10⁻⁶ to 10⁻³ s⁻¹. At 950°C and above, the stress exponent, n , was determined to be 3.6, with a creep activation energy of 715 kJ/mol. Selected results obtained for Li₄SiO₄ are compared with results obtained for other Li-containing ceramics that are under consideration as candidates for fusion reactor breeder blankets.     

Crystallization Kinetics of Lithium Orthosilicate Glasses

The formation of crystalline Li₄SiO₄ and Li₂SiO₃ from lithium orthosilicate glasses has been studied by means of in situ high-temperature X-ray diffraction. The first phase that crystallizes from the glass could not be identified, but was followed by the transformation to crystalline orthosilicate and metasilicate. Orthosilicate formation was tracked at temperatures between 600° and 650°C, whereas at higher temperatures, the formation of a small amount of crystalline metasilicate occurs. The kinetics of the initial phase of both crystallization processes are described by the Avrami–Erofeev equation, resulting in activation energies of 90 kJ/mol for the formation of the unidentified phase, and 68 kJ/mol for the formation of Li₄SiO₄. The rate constant for the crystallization of the unidentified phase is 0.014 s⁻¹ at 510°C, equaling that of the orthosilicate formation at 630°C. After isothermal heat treatment for 100–800 s, depending on temperature, 80%–95% of the sample is crystallized and further crystallization is controlled by diffusion in both cases.     

正硅酸乙酯溶胶-凝胶行为的超声波原位监测研究

利用超声波原位监测的方法,研究了酸催化条件下正硅酸乙酯的溶胶-凝胶行为,得到信号特征值随反应的变化曲线,结合红外和电镜图谱,对结果进行了分析。研究表明,低温利于水解,高温利于缩合,80℃的反应温度相对适合;相同温度下,当H2O/TEOS=8∶1时,正硅酸乙酯水解-缩合的过程最短。由此考察了超声波监测信号特征值变化与正硅酸乙酯溶胶-凝胶反应过程的联系,可获得过程中粒子形成、粒径变化、反应程度以及凝胶生成等信息,提供了一种材料制备过程中实时在线的监测和研究手段。     

毛细管气相色谱法测定正硅酸乙酯

以HP-5毛细管柱为色谱柱,醋酸戊酯为内标物,采用氢火焰离子化检测器(FID),定量测定正硅酸乙酯含量。峰面积与浓度呈良好的线性关系,r=0.9999,精密度良好,回收率99.1%～101.2%。     

Study of Tetraethyl Orthosilicate Hydrolysis by in Situ Generation of Water

The effect of acetic acid on acid-catalyzed tetraethyl orthosilicate (TEOS) hydrolysis has been followed with ¹H NMR. The changes in [CH₂] and [CH₃] of TEOS, [OH] of ethanol, and the formation of ethyl acetate are observed during the sequential addition of acetic acid. Mixed S_Nl and S_N2 reaction mechanisms are proposed to explain the TEOS hydrolytic behavior by the esterification process.     

Orthosilicate Analyses: A Measure of Hydration in Pastes of Alite and Portland Cement

The proportion of monomeric silicate in a hydrated paste can be used to estimate the degree of hydration of alite or portland cement. The monomer was estimated by gel permeation chromatography of the trimethylsilylated pastes.     

Trimethylation of the R5 Silica-Precipitating Peptide Increases Silica Particle Size by Redirecting Orthosilicate Binding

The unmodified R5 peptide from silaffin in the diatom Cylindrotheca fusiformis rapidly precipitates silica particles from neutral aqueous solutions of orthosilicic acid. A range of post-translational modifications found in R5 contribute toward tailoring silica morphologies in a species-specific manner. We investigated the specific effect of R5 lysine side-chain trimethylation, which adds permanent positive charges, on silica particle formation. Our studies revealed that a doubly trimethylated R5K3,4me3 peptide has reduced maximum activity yet, surprisingly, generates larger silica particles. Molecular dynamics simulations of R5K3,4me3 binding by the precursor orthosilicate anion revealed that orthosilicate preferentially associates with unmodified lysine side-chain amines and the peptide N terminus. Thus, larger silica particles arise from reduced orthosilicate association with trimethylated lysine side chains and their redirection to the N terminus of the R5 peptide.     

Optical Properties and Radiation Resistance of Zinc Orthosilicate Obtained by the Hydrothermal–Microwave Method

A hydrothermal–microwave method for the synthesis of zinc orthosilicate is developed. A crystalline phase of zinc orthosilicate, willemite, is synthesized at low temperature and its optical characteristics are determined. The dependence of the diffuse reflection coefficient on the irradiation at low temperatures (90 K) and pressures of 10^–5–10^–6 Pa is studied. The results of gravimetric, X-ray phase, and thermographic studies shows that the microwave synthesis of zinc orthosilicate from water-soluble salts of the initial components accelerates at lower temperatures of willemite formation. The microwave treatment of the initial zinc orthosilicate provides the production of nanodispersed willemite powder at lower temperatures and shorter expositions.     

分光光度法测定钙制剂中微量钙

通过吸光强度值可定量地确定元素离子的浓度值,因此选择合适的显色剂成为方法的关键.利用钙指示剂与钙的显色反应,确定最佳操作条件以后,指示剂在水相中与钙络合,无需萃取,便可准确快速测定;对于微量钙的测定,分光光度法显示出较高的灵敏度,具有稳定性好,准确度高,试剂和仪器廉价,操作简便快速等优点.     

纤维素酶的多型性

纤维素酶是一类具有多组分的复杂酶系。其多型性体现在酶系组分、酶蛋白的结构形式、理化性质以及催化机理等方面。造成纤维素酶多型性的原因包括结构基因的不同和翻译后加工的差异。另外,酶分子的表观多型性也是原因之一。文章主要对纤维素酶多型性的表现形式和可能的原因进行了分析。     

间规聚苯乙烯的多晶现象

概述了间规聚苯乙烯多晶的成因及分析方法。     

Polymorphism of synthetic glycerides

Summary Transition point data are reported for a series of unsymmetrical mono?leyl — disaturated triglycerides and a series of unsymmetrical monosaturated-dioleins. The results of thermometric measurements on a series of saturated 2-monoglycerides are also reported. This paper was presented at the Chicago meeting of the American Oil Chemists’ Society, October 25–27. Contribution No. 551 from the Department of Chemistry, University of Pittsburgh. The authors are indebted to the Buhl Foundation for a grant in support of this investigation.     

Polymorphism of cocoa butter

Largely by x-ray diffraction six crystalline states, I–VI, in order of increasing melting point, have been identified for cocoa butter. Of these states II, IV, V and VI are pure and identifiable with previously (or presently) identified polymorphs of 2-oleoylpalmitoyl stearin (POS), namelyα-2,β′-2,β-3 (“V”) andβ-3 (“VI”); V and VI representing distinct but very closely related crystalline structures. State I is a definite but fleeting and not readily characterized subα state and may be a phase mixture, as state III may be also. Melting points, heats of fusion and dilatometric data are reported for all states to the extent that their stability permits. The normal state of cocoa butter in chocolate is apparently V, certainlyβ-3. While it is true that “bloom” has not been observed for pure V nor observed to exist in the absence of VI, it is premature to say that VI is specifically the phase of chocolate “bloom”.     

电石渣制备纳米碳酸钙的初步研究

分别采用XRD和DTA/TG等手段,分析了电石渣的矿物组成和热行为。对电石渣代替石灰石制备纳米碳酸钙的技术进行了实验研究。结果表明,电石渣的主要成份是氢氧化钙。对电石渣采用水洗、过筛、干燥、煅烧等方式预处理后,可以代替石灰石用于制备纳米碳酸钙。经XD和TEM分析,所制得的纳米碳酸钙为球状方解石型,平均粒径为60nm。