固体核磁共振技术及其在氟聚合物研究中的应用

固体核磁共振作为一种重要的现代分析研究手段，在许多研究领域都有广泛的用途。通过对常用的固体核磁共振技术的介绍结合其在聚四氟乙烯、聚偏氟乙烯、四氟乙烯-六氟丙烯共聚物分析研究中的应用，说明固体核磁共振技术是研究常见氟聚合物结构和分子运动的重要方法。     

核磁共振技术及其应用进展

核磁共振技术是有机物结构测定的有力手段,不破坏样品,是一种无损检测技术.从连续波核磁共振波谱发展为脉冲傅立叶变换波谱,从传统一维谱到多维谱,技术不断发展,应用领域也越广泛.核磁共振技术在有机分子结构测定中扮演了非常重要的角色,核磁共振谱与紫外光谱、红外光谱和质谱一起被有机化学家们称为"四大名谱".     

核磁共振氢谱法在食用油研究中的应用

主要综述了核磁共振氢谱技术在油脂指标的测定、油脂产地区分、油脂掺伪以及油脂氧化过程产物的鉴定等方面的应用,为进一步开发核磁共振技术在油脂上的应用提供一些参考。     

核磁共振技术及其在农药残留分析中的应用

简述核磁共振技术(NMR)的发展史、基本原理.分别介绍了近年来NMR技术在含磷、含氟农药残留分析、农药杂质及其残留毒性、农药代谢物及其残留毒性、农药降解历程研究中的应用.展望了核磁共振技术在农药残留检测中的应用前景.     

Nuclear Magnetic Resonance Studies of Silicon Carbide Polytypes

The ²⁹Si MAS NMR spectra of the 2H, 4H, 6H, and 3C polytypes of silicon carbide are presented. An attempt is made to correlate differences in the chemical shifts with local atomic environment. The results of the analysis of the spectra of pure polytypes are used as a basic for the interpretation of the spectra of mixed polytypes and a discussion of the crystallinity and impurity levels of different samples. Carbon-13 chemical shifts obtained from spectra of the same polytypes are also tabulated.     

核磁共振技术在化学物质定量分析中的应用

文章首先介绍了核磁共振技术定量分析原理,然后从内标法、外标法、相对含量法三个方面简述了核磁共振技术在化学物质定量分析中的应用现状,并且对核磁共振技术在定量分析上的优势做了分析,最后,对其应用前景做了总结和展望。     

Detection of Drying-Induced Microcracking in Cementitious Materials with Space-Resolved 1H Nuclear Magnetic Resonance Relaxometry

Nuclear magnetic resonance (NMR) relaxation time mapping in partially dried mortar is presented. Relaxation times in concrete are typically multi-exponential, and exhibit highly effective relaxation mechanisms ( T _1L∼ 3 ms, Δν_1/2∼ 2500 Hz). One-dimensional mapping of the spin–lattice relaxation time is used to study relative changes in the water-occupied surface-to-volume ratio, as a function of mixture conditions, initial hydration period, and drying time. These results provide evidence for a penetrating microcracking phenomenon, due to local drying-induced tensile stresses. This conclusion was further supported by a relaxation time study of samples which were preconditioned so as to be at equilibrium with various relative humidities.     

核磁共振在线分析技术在催化装置油品分析中的应用

我国大陆第一套Invensys的核磁共振 (NMR)在线分析系统 2 0 0 2 0 5应用于独山子石化公司炼油厂8× 10 5t/a馏分油催化裂化装置 ,可实时提供多物流多种性质的分析参数 ,经过一年半的安装调试运行 ,分析结果满足工艺操作和控制的要求。     

右旋樟脑磺酸的合成工艺优化及NMR结构确证

以天然樟脑为原料,在乙酐/硫酸体系中制备右旋樟脑磺酸,优化合成和结晶工艺,使收率提高到85%,生产周期缩短到20小时,不用甲苯等毒性试剂,无须重结晶,并通过1H NMR和13C NMR检测获得樟脑磺酸核磁共振图谱。     

Silicon-29 Magic Angle Spinning Nuclear Magnetic Resonance Study of Calcium Silicate Hydrates

The reaction products formed in a series of fully "equilibrated," roomtemperature-hydrated, fumed colloidal silica plus lime water mixtures were examined using ²⁹Si magic angle spinning nuclear magnetic resonance. The data suggest that two structurally distinct calcium silicate hydrate (C-S-H) phases exist in the system CaO–SiO₂–H₂O. The more silica-rich C-S-H (Ca/Si = 0.65 to 1.0) consists predominantly of long chains of silica tetrahedra (Q² middle units) similar to those found in 1.4-nm tobermorite. The studied more lime-rich C-S-H (Ca / Si = 1.1 to 1.3) consists of a mixture of dimer (Q¹) and shorter chains (Q¹ end units and Q² middle units) similar to that reported for synthetic jennite. No monomer units (Q⁰) were detected.     

Characterization of Polyphasic Silicon Carbide Using Surface-Enhanced Raman and Nuclear Magnetic Resonance Spectroscopy

The present report explores the use of cross-polarization (CP) and single-pulse magic angle spinning nuclear magnetic resonance (MAS-NMR) as well as normal and surfaceenhanced Raman spectroscopy (SERS), in concert, for characterizing highly crystalline polymorphic silicon carbide ceramics. The combined use of these techniques provides a wealth of information regarding bulk, near-surface, and surface speciation. Both Raman and SERS are promising techniques for fracture surface characterization of these systems. The application of CPMAS-NMR and SERS to the study of ceramics is reported for the first time in this investigation.     

早期地聚合反应过程的~1H低场核磁共振

在地聚合物体系中,浆体的组成及微观结构对于其硬化后的性能有着重要的影响。利用1H低场核磁共振仪对比研究了纯偏高岭土基(MK-100)及掺高钙粉煤灰(MK-85)的地聚合物的早期反应过程,探测了不同结合状态的水分子的质子信号,获得了水的纵向弛豫时间(T1)和横向弛豫时间(T2)。研究表明:1H低场核磁共振法适宜于研究地聚合物的早期反应过程,根据浆体纵向弛豫时间T1的加权平均值,可以将早期地聚合反应过程划分为加速期、减速期和稳定期3个阶段;高钙粉煤灰的加入使地聚合物浆体加速期缩短,减速期延长。早期地聚合反应过程中水的横向弛豫时间T2可以很好地表征毛细水或凝胶水的变化趋势。高钙粉煤灰的加入会延缓毛细水向凝胶水的转变过程。     

PC—120小型脉冲核磁共振分析仪测定喷气燃料氢含量

本文研究了采用ＰＣ－１２０小型脉冲核磁共振分析仪测定喷气燃料中氢含量的方法，试验结果表明本方法具有较好的准确度和精度度，测定快速，简便。     

Internal Structure of Porous Silica: A Model System for Characterization by Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) relaxation methods have been used to investigate the internal structure of porous silica gelled from colloidal silica and potassium silicate mixtures. These materials possess a narrow pore size distribution with average pore diameter ranging from 470 to 2400 Å (47 to 240 nm) as determined from mercury intrusion porosimetry. NMR relaxation measurements were performed on deionized water impregnated into the pore space. These results determine the distribution of local surface-to-volume ratios and show that all of the silica samples are very uniform on a length scale greater than 5 μ. NMR relaxation measurements performed on silica samples partially filled with water provide a precise confirmation of the theoretical model upon which the NMR pore structure analysis is based. Measurements of the relaxation strength at the water—silica interface were found to depend systematically on the initial composition of the material. The self-diffusion coefficient of water, saturated in the pore space, is reduced by 14% from its bulk value.     

基于低场核磁共振技术水泥砂浆反复高温热损伤的研究

为了研究水泥砂浆反复经历高温及局部水冷作用后的损伤演化特征,将水泥砂浆试件中部进行钻孔,将试件加热到400 ℃并且向孔洞注水冷却至室温,重复操作。采用低场核磁共振技术、数字声波仪器、数码显微镜分别研究了水泥砂浆试件在高温及局部水冷作用下的损伤行为。结果表明,随着高温及局部冷却次数增多,试件小孔孔径及数量不断增大,而大孔孔径则减小,试件在经过第一次处理后其性能劣化最明显,且局部注水冷却使得孔洞周围的损伤大于其他部位。同时,随着高温及局部冷却次数增多,概率密度峰值所对应的灰度值增大并向右移动。另外,高温弱化了胶凝材料与砂粒的胶结能力,反复高温处理使得水泥浆与砂粒之间的胶结能力进一步削弱,试件的波速减小,但孔洞中注水冷却产生的温度应力使得胶凝材料与砂粒的胶结能力急剧下降,温度骤降产生的温度应力对胶凝材料与砂粒间的胶结能力的影响远大于反复高温处理。     

使用核磁共振交联密度仪测试不同方法凝固天然橡胶的交联密度和性能的关系

用核磁共振(NMR)法测定不同方法凝固天然橡胶的交联密度,研究其与性能之间的关系。结果表明,硫化胶的交联密度不仅影响其核磁共振的横向弛豫时间(T1),而且影响其纵向弛豫时间(T2)。随着交联密度大,硫化胶的核磁共振弛豫时间缩短。另外,微生物凝固天然橡胶硫化胶的交联密度、正硫化时刻扭矩和拉伸强度均大于酸凝固天然橡胶硫化胶的。     

Structural Changes of Porous Silicon Surface with Thermal Annealing Studied by 29Si Nuclear Magnetic Resonance Spectroscopy and Fourier Transform Infrared Spectroscopy

²9Si nuclear magnetic resonance (NMR) spectra and infrared spectra were measured for as-prepared and annealed porous silicon (PS) samples to characterize the change of PS structure. Annealing changed the infrared spectra remarkably: after 4-h annealing, the signals due to SiH₂ disappeared and the intensity of the signals due to SiH decreased. On the other hand, the ²9Si NMR spectra with magic-angle spinning (MAS) were not much affected by the annealing. The linewidth of spectra without MAS, however, increased with annealing time with the peak location unchanged. Annealing caused hydrogen on the PS surface to be desorbed, especially in the case of SiH₂ species, and (SiH)₂ dimer structure was produced during the annealing.     

Aluminum in Rutile [TiO2]: Characterization by Single-Crystal and Magic-Angle-Spinning Nuclear Magnetic Resonance

Using both single-crystal and magicangle-spinning (MAS) ²⁷Al nuclear magnetic resonance (NMR) spectroscopy, we have characterized the most abundant site for Al dissolved in rutile. The single-crystal spectrum of the dissolved Al indicates that most Al cations are isolated from each other and from paramagnetic defects, and they are in sites with only two orientations in the crystal. Interstitial octahedra, pairs of Al³⁺, and "shear planes" can thus be ruled out as the major Al sites, and substitution of Al in Ti sites is suggested. Spectra collected at temperatures up to 600°C show the onset of structural mobility or cation exchange. MAS NMR gives unique values of the quadrupolar coupling constant and asymmetry patameter of the Al site as 2.8 MHz and 1.0, respectively. Combination of both techniques permits the nature and relative proportions of both dissolved and exsolved Al to be determined, even when the latter dominates.     

13C Nuclear Magnetic Resonance Studies of Phenol-Formaldehyde Resins and Related Model Compounds 2 - Analysis of Sequence Structure in Resins

The paper reports ¹³C nuclear magnetic resonance spectra of novolac resins and the variation of the composition of the reaction mixture during the in situ preparation of resin. It is observed that in the initial stages of the reaction ortho substitution occurs; however the hemiacetal rather than the methylol derivative is observed. These methylol substituted intermediates are highly unstable and a better appreciation of the relative rates of structure formation can be obtained from an analysis of the methylene bridge region, para-para Bridges are the first to appear, the next are the ortho-para and finally the ortho-ortho linkages are observed. Analysis of the relative intensities of ortho and para bridge carbon atoms allows identification of the isomeric composition of the final resin. The proportion of each isomer depends on the catalyst used in synthesis of the resin.     

Solid-Sample 11B Nuclear Magnetic Resonance and X-ray Photoelectron Spectroscopy Study of Boron-Doped β-Silicon Carbide

Solid-sample magic angle spinning (MAS) nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS), in conjunction with scanning electron microscopy (SEM), were used to investigate the fate of boron used as a sintering aid for silicon carbide. The results of the NMR studies indicated that the boron penetrated the silicon carbide grain boundaries during sintering, and was incorporated in a tetrahedral form in the bulk, regardless of the gas used during the process. The NMR spectrum of a sample sintered under nitrogen indicated the formation of a trigonal form of boron as well. XPS identified this trigonal boron as boron nitride; however, no boron was detected by XPS in any form on the fracture surface of the silicon carbide sintered under argon, even though the NMR results confirmed the presence of tetrahedral boron in the bulk sample. The SEM results indicated that the fracture process for these materials was predominantly intergranular. This suggested that the boron in the silicon carbide sintered under argon penetrated the grains and left the grain boundaries depleted of boron.