Controlled Rate Thermal Analysis of Hydrated Borates

Quasi-isothermal-isobaric analysis was applied as a main method for investigation of thermal decomposition of borates. The structural mechanism of the dehydration and dehydroxylation of selected borates is considered. It has been found that they consist of two independent stages: formation of gaseous water molecules localized into the structural framework and their release. The internal pressure of gaseous water molecules is the factor influencing the course of these processes. The strengths of the chemical bonds of the components and the freedom of their displacement also determine thermal stability of hydrated borates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modification of the Kaolinite Hydroxyl Surfaces through the Application of Pressure and Temperature, Part III

Kaolinite hydroxyl surfaces have been modified by the combined application of heat and pressure in the presence of water at 120 degrees C and 2 bars and at 220 degrees C and 20 bars. X-ray diffraction shows that some of the layers are expanded. It is hypothesized that this expansion occurs at the edges of the crystals due to the intercalation of water. The X-ray diffraction data is supported by diffuse reflectance infrared spectroscopy, with additional hydroxyl stretching bands observed around 3550 and 3590 cm-1. These bands are attributed to adsorbed water and to edge-intercalated water. Additional bands are observed in the hydroxyl deformation region around 895 and 877 cm-1. The position of these bands depends on the defect structure of the kaolinite and the conditions under which the kaolinite was thermally treated. Additional water bending vibrations were observed at 1651 and 1623 cm-1 for the thermally treated high-defect kaolinite and at 1682 and 1610 cm-1 for the low-defect kaolinite. The bands at 1651 and 1682 cm-1 are attributed to the bending modes of water coordinated to the kaolinite surface. The role of water in the edge intercalation of water in the high- and low-defect kaolinites is apparently different. Copyright 1999 Academic Press.     

控制结晶-微波碳热还原法制备高密度LiFePO4/C

应用控制结晶法从溶液相制备球形FePO4.xH2O,再高温烧结得到FePO4前驱体,最后用微波碳热还原法合成高密度L iFePO4/C.由XRD和SEM表征该材料的结构、形貌,并测试其电化学性能.     

Controlled Rate Thermal Analysis of kaolinite dehydroxylation: effect of water vapour pressure on the mechanism

The present kinetic study is focused on one aspect of kaolinite dehydroxylation, namely the influence of water vapour pressure in the 10⁻³ to 5 hPa range and in the presence of crystalline defects. The experimental problem of keeping, throughout the dehydroxylation, the pressure gradients negligible around and within the sample is solved by means of Controlled Rate Evolved Gas Detection (CR-EGD). The dehydroxylation rate selected is as low as 0.014 h⁻¹ (which corresponds to a duration of 70 h for the whole experiment). Moreover, more than 20 independent measurements of the apparent Arrhenius energy of activation are carried out all along the dehydroxylation, with help of the rate–jump method, and therefore, without any assumption about the rate law of the determining step. In these conditions, the apparent Arrhenius energy of activation measured during the dehydroxylation of a poorly crystallised kaolinite is shown to be constant in the range 0.02<<0.84 (under 10⁻³ hPa) and in the range 0.18<<0.80 (under 5 hPa), indicating that the rate law obeys the Arrhenius law in this range of extent of reaction. The corresponding activation energies obtained are (233±15) kJ/mol under 10⁻³ hPa and only (188±10) kJ/mol under 5 hPa. Although this decrease is in contradiction with previously published results, it can be interpreted by considering that, under 10⁻³ hPa, diffusion is the limiting step whereas, under 5 hPa, the part of water desorption probably becomes predominant.     

Workshop on Sample Controlled Thermal Analysis

Journal of Thermal Analysis and Calorimetry -     

硅烷热分解制备硅原子簇

当前，半导体硅原子簇的物理与化学性能已成为人们广泛研究的热点[1]．尽管近几年来硅原子簇研究取得很大进展，但对于大于10个原子的硅原子簇的实验及理论研究尚很少见[2]．目前，均采用在超高真空系统中，利用脉冲激光蒸发硅棒获得硅原子簇，然后进行分析．检测及化学反应研究，还不能离开真空系统．为此，发展一种能够制备可观量的、在大气中稳定的原子簇的方法很有必要．我们利用硅烷热分解的化学方法，制备硅原子簇工艺，如图1所示．采用MO丝加热，以Ar气稀释SM。气体，为防止气管喷嘴在反应中被产物堵塞，使用了Cap2保护，控制温度…     

Atomic Force Microscopy Analysis of Statistical Roughness of GaAs Surfaces Originated by Thermal Oxidation

We have determined the important statistical quantities of the rough boundary between a GaAs single crystal and its oxide film formed by thermal oxidation. Thermal oxidation of the GaAs surfaces was performed at the temperature of 500°C. Using mathematical procedures developed for treating AFM data consisting of a family of the values of the heights of the irregularities of this roughness the values of the important statistical quantities of roughness were determined for 11 samples of the GaAs surfaces created by dissolution of the thermal oxide films originated during thermal oxidation of the smooth GaAs samples (the times of oxidation of these 11 samples were within interval of 20min–8 hours). From the AFM analysis of the roughness of GaAs surfaces it was found that the roughnening of these surfaces was the most pronounced for shorter oxidation times, i.e. for times smaller than about 2 hours.     

Covalent Surface Modification of Oxide Surfaces

The modification of surfaces by the deposition of a robust overlayer provides an excellent handle with which to tune the properties of a bulk substrate to those of interest. Such control over the surface properties becomes increasingly important with the continuing efforts at down‐sizing the active components in optoelectronic devices, and the corresponding increase in the surface area/volume ratio. Relevant properties to tune include the degree to which a surface is wetted by water or oil. Analogously, for biosensing applications there is an increasing interest in so‐called “romantic surfaces”: surfaces that repel all biological entities, apart from one, to which it binds strongly. Such systems require both long lasting and highly specific tuning of the surface properties. This Review presents one approach to obtain robust surface modifications of the surface of oxides, namely the covalent attachment of monolayers.     

基于不锈钢模板热压微模塑构建聚乙烯超疏水表面

采用含FeCl3的蚀刻液对不锈钢表面进行刻蚀,再以此蚀刻面为模板热压低密度聚乙烯(LDPE),冷却剥离得到LDPE微模塑表面。研究结果表明:静、动态接触角均超过150°,滚动角约5°,LDPE表面呈"花菜状"结构,即大"包"上密集分布着微米及亚微米级的小突起。本工艺可望结合工业上生产塑料薄膜的流延技术,实现聚合物超疏水表面的规模化生产。     

Aqueous Amino Silane Modification of E-glass Surfaces

The majority of work available in the literature examines the effect of epoxy silane, gamma-aminopropyltrimethoxy silane, and methacrylate silane on E-glass surfaces. As alternatives to the most commonly used silanes, we investigated two novel silanes: gamma-ureidopropyltriethoxy silane and Nbeta(aminoethyl) gamma-aminotrimethoxy silane and additionally an amino-functional polysiloxane. The ureido silane-treated E-glass fibers demonstrated a zeta potential similar to that of the untreated E-glass fibers, which was independent of deposition solution pH over the pH range investigated. A moderately hydrophobic E-glass surface, which was silane concentration dependent, was noted as being due to condensed Si-O-Si bonds at the surface. The diamino silane demonstrated an extremely basic surface at the higher silane concentrations investigated. These outer surface layers were modified by changing the pH and the concentration of the deposition solution. The polysiloxane produced an increase in the hydrophobicity of the E-glass fiber, especially when deposited from extremely basic solutions. At the higher solution concentrations investigated, the silanes and the siloxane was initially deposited in patches and an outer surface or "skin" was formed over these patches, giving the appearance of fully coated fibers. Copyright 2001 Academic Press.     

Analysis of the Thermokinetics Under Dynamic Conditions by Relative Rate of Thermal Decomposition

A novel parameter of the relative rate of thermal decomposition has been defined on the basis of an analysis of equation relating the logarithm of the conversion degree on the temperature. The dependence of this parameter on temperature in the dynamic conditions has been analyzed and discussed. The dependence of the relative rate of thermal decomposition is a linear relationship involving two coefficients. These coefficients can be related to the enthalpy and activation energy. The parameter developed has been used for the analysis of a series of consecutive reactions of thermal decomposition of calcium oxalate monohydrate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Constant Rate Thermal Analysis (CRTA) as a Tool for the Synthesis of Materials with Controlled Texture and Structure

Some examples of the use of the CRTA method for the synthesis of materials with controlled texture and structure are given. BaTiO₃ has been obtained from the thermal decomposition of Barium Titanyl Oxalate (BTO) and Barium Titanyl Citrate (BTC) by controlling the reaction temperature in such a way that the partial pressure of the gases generated in the reaction was maintained constant at a value close to 10^-2 mbar. It has been shown that this method allows getting BaTiO₃ with crystal sizes considerably lower than those obtained by decomposing the same precursors by conventional methods. This small crystal sizes lead to the stabilisation of the metastable cubic phase with regards to the tetragonal phase. It has been also shown that the control of the CO generated in the carbothermal reduction of silica allows tailoring the phase composition of the silicon nitride obtained as final product. This revised version was published online in August 2006 with corrections to the Cover Date.     

A procedure for determining the concentration of Hydroxyl Groups on Silica Surfaces

By determining the concentration of D₂O in D₂O/H₂O liquid mixtures, it has been possible to develop a method to obtain the concentration of hydroxyl groups on the surface of silica gel. The results of 4.4 ± 0.2 –OH groups per 100 Ų of surface are in good agreement with the findings of other workers.     

Optical Properties of CdS Nanobelts and Nanosaws Synthesized by Thermal Evaporation Method

By a simple one-step H2-assisted thermal evaporation method, high quality CdS nanos-tructures have been successfully fabricated on Au coated Si substrates in large scale. The as-synthesized CdS nanostructures consisted of sword-like nanobelts and toothed nanosaws with a single-crystal hexagonal wurtzite structure. The deposition temperature played an important role in determining the size and morphology of the CdS nanostructures. A combi-nation of vapor-liquid-solid and vapor-solid growth mechanisms were proposed to interpret the formation of CdS nanostructures. Photoluminescence measurement indicated that the nanobelts and nanosaws have a prominent green emission at about 512 nm, which is the band-to-band emission of CdS. The waveguide characteristics of both types of CdS nanos-tructures were observed and discussed.     

醇热解法合成超顺磁性氧化铁纳米粒子及其性能

以甲氧基聚乙二醇同时作为溶剂、还原剂及修饰剂,在高温下分解乙酰丙酮铁,制备了纳米Fe3O4粒子,采用透射电子显微镜和X射线衍射分析表征材料的形貌和相组成,傅里叶变换红外光谱仪表征材料的表面修饰物,超导量子干涉仪测试合成的纳米粒子的磁性能,纳米粒度与zeta电势分析仪测试磁性纳米粒子在水中的zeta电势。 结果表明,纳米Fe3O4粒子的大小为（10.1±1.6） nm,粒度均一,单分散性好,在300 K下具有超顺磁性,饱和磁化强度为45 A·m2/kg。 红外结果表明,-COO-共价结合在粒子表面。 zeta电势为-25 mV。 其在水中的稳定性与以三甘醇为反应介质、高温分解法制备的纳米Fe3O4粒子作比较,表现出长时间（60 d以上）的良好分散性。 静电作用及空间位阻效应是其高稳定分散性的原因。     

功能聚合物表面的制备及其化学修饰

介绍了一个综合化学实验--功能聚合物表面的制备和化学修饰,及其教学思路。通过相分离法制备功能聚合物表面,探究不同溶剂组分对聚合物表面功能的影响,同时通过点击化学的方法对亲水表面进行修饰制备疏水表面,用静滴法测量表面接触角大小,并借助扫描电子显微镜对修饰前后的功能聚合物进行表征。结果显示,随着溶剂配方中1-癸醇的减少和环己醇的增加,亲水表面的接触角增大,疏水表面接触角减小,修饰过后的亲水表面表现出良好的疏水性能。该综合实验整合了大学化学基础知识、化学学术前沿以及实验基本技能,有利于培养学生的创新思维,提高综合能力。     

Organic Surface Modification of TEOS Based Silica Aerogels Synthesized by Co-Precursor and Derivatization Methods

The experimental results on the organic modification of tetraethoxysilane (TEOS) based silica aerogels synthesized by co-precursor and derivatization methods are reported and discussed. In order to obtain silica aerogels with better physicochemical properties in terms of higher hydrophobicity, optical transmission and thermal stability, eight organosilane compounds (hydrophobic reagents) of the type R _n SiX_4–n have been used. The molar ratio of tetraethoxysilane (TEOS), ethanol (EtOH), water (0.001 M oxalic acid catalyst) was kept constant at 1:5:7 respectively. The organically modified silica aerogels were produced by two different methods: (i) Co-precursor method and (ii) Derivatization method. In the former method, the molar ratio of hydrophobic reagent (HR) to TEOS was varied from 0.1 to 0.6. In the later method, derivatization of the wet gels was carried out using 20% hydrophobic reagent in methanol. The merits and demerits of both these methods have been presented. The organic surface modification of the aerogels was confirmed by the Fourier Transform Infrared (FTIR) spectroscopic studies and the contact angle measurements. In the co-precursor method, with the increase in hydrophobic reagent/TEOS molar ratio, the hydrophobicity increases ( = 136°) and the optical transmission decreases (5%), whereas in the derivatization method the optical transmission is very high (T 85%) but the hydrophobicity is low ( = 120°). The thermal stability of the hydrophobic aerogels (the temperature up to which the hydrophobicity is retained) was studied in the temperature range of 25–800°C. The aerogels based on the co-precursor method retained the hydrophobicity up to a temperature as high as 520°C and on the other hand, the derivatized aerogels are hydrophobic only up to a temperature of 285°C. For the first time, TEOS based hydrophobic silica aerogels have been obtained with negligible volume shrinkage using the trimethylethoxysilane (TMES) co-precursor. The aerogels were characterized by Fourier transform infrared spectroscopy (FTIR), optical transmittance, Scanning Electron Microscope (SEM), thermogravimetric (TG) and differential thermal (DT) analyses and the contact angle measurements.     

Thermal Behavior Analysis of Two Synthesized Flavor Precursors of N‐alkylpyrrole Derivatives

To expand the library of pyrrole‐containing flavor precursors, two new flavor precursors—methyl N‐benzyl‐2‐methyl‐5‐formylpyrrole‐3‐carboxylate (NBMF) and methyl N‐butyl‐2‐methyl‐5‐formylpyrrole‐3‐carboxylate (NUMF)—were synthesized by cyclization, oxidation, and alkylation reactions. Thermogravimetry (TG), differential scanning calorimeter, and pyrolysis–gas chromatography/mass spectrometry were utilized to analyze the thermal degradation behavior and thermal degradation products of NBMF and NUMF. The TG‐DTG curve indicated that the maximum mass loss rates of NBMF and NUMF appear at 310 and 268°C, respectively. The largest peaks of NBMF and NUMF showed by the differential scanning calorimeter curve were 315 and 274°C, respectively. Pyrolysis–gas chromatography/mass spectrometry detected small molecule fragrance compounds appeared during thermal degradation, such as 2‐methylpyrrole, 1‐methylpyrrole‐2‐carboxylic acid methyl ester, limonene, and methyl formate. Finally, the thermal degradation mechanism of NBMF and NUMF was discussed, which provided a theoretical basis for their application in tobacco flavoring additives.     

氧原子和羟基在Ni低指数表面的吸附动力学研究

应用5-参数Morse势方法模拟了O－Ni表面相互作用势,考察了氧原子在镍三个低指数表面的吸附特性.同时构造了羟基与Ni（100）、Ni（110）和Ni（111）表面相互作用的推广LEPS势,获得了羟基在表面的吸附位、吸附几何、结合能及本征振动等数据.理论结果表明,羟基垂直吸附于镍表面的高对称位是稳定的,垂直吸附于Ni（100）表面4-重洞位的吸附能为96.98 kJ•mol－1,垂直吸附于Ni（111）表面3-重洞位的吸附能为96.00 kJ•mol－1,在Ni（110）表面存在两种吸附态：垂直吸附于长桥位的吸附能为99.38 kJ•mol－1,倾斜14°吸附于赝势三重位吸附能为96.98 kJ•mol－1.理论结果与实验结果符合得较好.