A stray-field imaging,CRAMPS and MQMAS study of the drying process of precasting materials used in a steel-making converter

Optimization of the drying process conditions in a steel-making converter in a steel works is very difficult since the process is off-line and time-consuming. However, it is important to optimize drying process conditions (temperature, surface active agents, etc.), as steam explosion can readily occur with insufficient drying time. To help understanding, we have demonstrated that we can monitor the drying of real refractory mortar with stray-field imaging. We chose, this method because of the possibility of detecting shortT ₂ components. This paper shows the effect of varying water content in different materials on the drying rate. In particular, we find that the free-water loss rate is relatively independent of water content. However the bound-water loss rate is more affected. Also, solid-state nuclear magnetic resonance (NMR) (¹H-CRAMPS and²⁷Al M(3 and 5)QMAS) studies are performed to clarify the change of chemical structure by drying treatment. It is clear that imaging and solid-state NMR give useful information to optimize drying conditions. With this data, we can adjust and optimize the drying process and time in steel works.     

Solid-state NMR as an analytical tool: quantitative aspects

Analytical methods based on solid-state NMR are becoming increasingly popular. However, these flourishing activities bring up the issue of how accurately NMR can assess an analyte proportion in a solid sample. The use of a chemical intensity reference for this purpose is a natural but often unsuitable choice, due to sample stability or preciousness. We propose here a protocol to perform quantitative measurements in solid-state NMR, by calibration of the circuit response through a low-power pulse injected during the acquisition (the so-called ERETIC method). Although this method has been in use for some time in liquid-phase and in vivo NMR, we point out here some peculiarities and useful applications typical of solids. Namely, the temperature dependence of the signal intensity imposes care in the application to MAS experiments.     

Solid-state nuclear magnetic resonance investigations of the nature, property, and activity of acid sites on solid catalysts

Further progress in the field of heterogeneous catalysis depends on our knowledge of the nature and behavior of surface sites on solid catalysts and of the mechanisms of chemical reactions catalyzed by these materials. In the past decades, solid-state NMR spectroscopy has been developed to an important tool for routine characterization of solid catalysts. The present work gives a review on experimental approaches and applications of solid-state NMR spectroscopy for investigating Brønsted and Lewis sites on solid acids. Studies focusing on the generation of surface sites via post-synthesis modification routes of microporous and mesoporous materials support the development of new and the improvement of existing catalyst systems. High-temperature and flow techniques of in situ solid-state NMR spectroscopy allow a deeper insight into the mechanisms of heterogeneously catalyzed reactions and open the way for studying the activity of acidic surface sites. They help to clarify the activation of reactants on Brønsted and Lewis acid sites and improve our understanding of mechanisms affecting the selectivity of acid-catalyzed reactions.     

A review of oxygen-17 solid-state NMR of organic materials--towards biological applications

¹⁷O solid state NMR of organic materials is developing rapidly. This article provides a snapshot of the current state of development of this field. The NMR techniques and enrichment protocols that are driving this progress are outlined. The ¹⁷O parameters derived from solid-state NMR experiments are summarized and the structural sensitivity of the approach to effects such as hydrogen bonding highlighted. The prospects and challenges for ¹⁷O solid-state NMR of biomolecules are discussed.     

固体核磁共振技术在锂/钠离子电池碳负极中的应用及研究进展

碳负极材料作为锂/钠离子电池的传统负极材料一直获得广泛的推广和应用，但其仍存在充电时间长、库伦效率低等问题，研究碳负极材料充放电机理是解决这些问题的关键.固体核磁共振（NMR）技术是一种研究固体材料中目标原子所处化学环境以及材料内部结构变化的有效手段.通过测定锂/钠离子电池中⁶Li、⁷Li和²³Na高速魔角旋转（MAS）条件下的固体NMR谱图，能够清晰获得锂/钠离子电池碳负极脱/嵌过程中的结构变化，以及碳原子与Li/Na的配位情况，从而为碳负极材料的设计及其电化学性能的提升提供充分的理论依据.本文综述了近年来固体NMR技术在锂/钠离子电池碳负极材料研究中的应用以及相关研究进展.     

13C CP MAS NMR and GIAO-CHF calculations of coumarins

13C cross-polarization magic-angle spinning NMR spectra were recorded for a series of solid coumarins. Ab initio calculations of shielding constants were performed with the use of GIAO-CHF method. The combined CPMAS NMR and theoretical approach was successful in characterizing solid-state conformations of coumarins; a relationship sigma (ppm) = -1.032 xdelta + 205.28 (R(2) = 0.9845) can be used to obtain structural information for coumarins, for which solid-state NMR or crystal structure data are not available.     

Symmetric echo acquisition for absolute-value display in solid-state NMR imaging

A method of solid-state NMR imaging that permits echo Fourier transformation (FT) has been devised using a magic echo train. The echo FT imaging can be implemented simply by modifying the gradient pulse sequence in the previous magic echo imaging (TREV-16TS) so that the one-dimensional k-space trajectory follows the sampling points which are symmetric about the k origin. The implemented ability of echo FT improves the performance of the magic echo imaging: the sensitivity gained by radical2, the phase correction is made unnecessary, and the digital resolution is doubled. One- and two-dimensional imaging experiments have been conducted on some solid samples, confirming the improved performance and revealing a TREV-16TS adjustment parameter that is critical for the successful echo FT imaging.     

Combination of magic-echo and single-point imaging techniques for solid-state MRI

Due to reduced molecular motion the transverse relaxation timeT ₂ in solid materials is typically shorter by a factor of 10³ to 10⁵ in comparison to those in liquids, resulting in a large intrinsic nuclear magnetic resonance line-width that can be well above 20 kHz. Therefore high-resolution solid-state magnetic resonance imaging requires either very strong gradients or special line-narrowing techniques. Single-point imaging (SPI) is a successful pure phase encoding sequence in imaging soft-solid materials; however, when used to study rigid solid materials it still suffers from a very long acquisition time and large gradients. On the other hand, magic echo is a technique that can be used to effectively refocus dipolar interaction, thus achieving a line narrowing. Therefore, the aim of this work is to improve the signal intensity with the combination of the magic echo technique and the SPI sequence. In this paper first applications and a comparison of the SPI sequence with a combination of the magic echo and the SPI sequence to image structures of solid-state materials are presented.     

Subject index to volume 39

Measurements of the normal component of the stray-field at the surface of small permanent magnets were performed with a vibrating pick-up loop magnetometer with high geometrical resolution. They show a structure which reveals deviations from the desired magnetization configuration. A calculation method originally developed for soft magnetic materials was extended to calculations on permanent magnets. The real demagnetization characteristic of the material is introduced into the calculation using two independent susceptibility components. Thus the magnetic surface charges, the stray-field and the magnetization configuration can be calculated.     

Characterization of lipid bilayer formation in aligned nanoporous aluminum oxide nanotube arrays

Aligning lipid bilayers in nanoporous anodized aluminum oxide (AAO) is a new method to help study membrane proteins by electron paramagnetic resonance (EPR) and solid-state nuclear magnetic resonance (NMR) spectroscopic methods. The ability to maintain hydration, sample stability, and compartmentalization over long periods of time, and to easily change solvent composition are major advantages of this new method. To date, 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) has been the only phospholipid used for membrane protein studies with AAO substrates. The different properties of lipids with varying chain lengths require modified sample preparation procedures to achieve well formed bilayers within the lining of the AAO substrates. For the first time, the current study presents a simple methodology to incorporate large quantities of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC), DMPC, and 1,2-dipalmitoyl-3-sn-phosphatidylcholine (DPPC) phospholipids inside AAO substrate nanopores of varying sizes. (2)H and (31)P solid-state NMR were used to confirm the alignment of each lipid and compare the efficiency of alignment. This study is the first step in standardizing the use of AAO substrates as a tool in NMR and EPR and will be useful for future structural studies of membrane proteins. Additionally, the solid-state NMR data suggest possible applications of nanoporous aluminum oxide in future vesicle fusion studies.     

Stray-Field Imaging of Planar Films Using a Novel Surface Coil

A surface-coil approach to stray-field magnetic resonance imaging (STRAFI), which has certain advantages for the profiling of planar films and layers, is described. Frequency-swept and Fourier-transform versions of the experiment, which are particularly suitable for use with the coil, are reported. As an example application, a latex coating is analyzed during the evaporative drying process, in which a colloidal dispersion is transformed to a continuous polymer film. The ultimate achievable resolution is discussed and contrasted with conventional MR microscopy.     

Solid-state NMR concepts for the investigation of supported transition metal catalysts and nanoparticles

In recent years, solid-state NMR spectroscopy has evolved into an important characterization tool for the study of solid catalysts and chemical processes on their surface. This interest is mainly triggered by the need of environmentally benign organic transformations (“green chemistry”), which has resulted in a large number of new catalytically active hybrid materials, which are organized on the meso- and nanoscale. Typical examples of these catalysts are supported homogeneous transition metal catalysts or transition metal nanoparticles (MNPs). Solid-state NMR spectroscopy is able to characterize both the structures of these materials and the chemical processes on the catalytic surface. This article presents recent trends both on the characterization of immobilized homogeneous transition metal catalysts and on the characterization of surface species on transition metal surfaces.     

High-Resolution Solid-State NMR Spectroscopy of Steroids and Their Derivatives

Abstract: Steroids are an important class of organic compounds containing a vast array of biologically and physiologically essential molecules. Due to their availability, relatively straightforward derivatizability, and endogeneity, they are widely used in pharmacological applications. The investigation of molecular and physicochemical properties of active pharmaceutical ingredients (APIs) in the solid state is important, because these properties are directly related to their pharmacological activity. Several methods are available for this purpose. Solid-state NMR spectroscopy offers a nondestructive and flexible technique, providing both structural and dynamic information. It can be applied to every solid physical state (both crystalline and amorphous) as well as to materials with different compositions. The current article aims at gathering together some of the recent and most important studies in the area of high-resolution solid-state NMR spectroscopy of steroids and their derivatives completed with related theoretical reports not forgetting to outline the future remarks.     

Combining one-dimensional stray-field micro-imaging with mechanical field-cycling NMR: a new spectrometer design

A new spectrometer design combining stray-field micro-imaging with mechanical field-cycling Nuclear Magnetic Resonance (FC-NMR), allowing for one dimensional spatial resolution in the order of 10 μm is described. The field-cycle is implemented by moving the probe in the stray-field of a superconducting gradient magnet. In this way a field range between 10 mT and 6.3 T is covered. The maximum transfer time is less than 5 s. Further, methods to correct for some of the imaging artefacts found in previous studies are implemented. The main objective of this design is a depth- and field-dependent investigation of the defect structure caused by heavy-ion irradiation of ionic crystals.     

Cross polarization, radio frequency field homogeneity, and circuit balancing in high field solid state NMR probes

Homogeneous radio frequency (RF) fields are important for sensitivity and efficiency of magnetization transfer in solid state NMR experiments. If the fields are inhomogeneous the cross polarization (CP) experiment transfers magnetization in only a thin slice of sample rather than throughout the entire volume. Asymmetric patterns have been observed in plots of the CP signal versus RF field mismatch for an 800 MHz solid-state NMR probe where each channel is resonated in a single-ended mode. A simple model of CP shows these patterns can be reproduced if the RF fields for the two nuclei are centered at different places in the coil. Experimental measurements using B1 field imaging, nutation arrays on extremely short NMR samples, and de-tuning experiments involving disks of copper incrementally moved through the coil support this model of spatially offset RF fields. We have found that resonating the high frequency channel in a double-ended or "balanced" mode can alleviate this field offset problem, and have implemented this in a three-channel solid state NMR probe of our own design.     

固体核磁共振研究固体酸催化剂酸性进展

酸性直接与固体酸催化剂的活性相关,因此研究固体酸催化剂的酸性受到了科研工作者的广泛关注. 固体核磁共振技术已经成为研究固体酸催化剂酸性的一种强有力的工具. 该文介绍了固体核磁共振的特点和各种常用技术,着重综述了固体核磁共振研究固体酸催化剂酸性的进展.     

Indirectly detected through-bond chemical shift correlation NMR spectroscopy in solids under fast MAS: studies of organic-inorganic hybrid materials

Indirectly detected, through-bond NMR correlation spectra between (13)C and (1)H nuclei are reported for the first time in solid state. The capabilities of the new method are demonstrated using naturally abundant organic-inorganic mesoporous hybrid materials. The time performance is significantly better, almost by a factor of 10, than in the corresponding (13)C detected experiment. The proposed scheme represents a new analytical tool for studying other solid-state systems and the basis for the development of more advanced 2D and 3D correlation methods.     

核磁共振技术在物质表面性质表征领域的新应用

核磁共振(nuclear magnetic resonance)技术具有快速、精确、分辨率高等优点,并已不断成熟成为土壤分析、物质结构鉴定、食品分析和医学成像等领域重要的研究分析手段。本文通过介绍利用NMR技术研究液相环境中高分子聚合物在颗粒表面(主要为SiO₂颗粒)的吸附、解吸及扩散等行为和利用NMR技术研究受污染土壤中水的摄取过程及土壤润湿性两大方面,综述了NMR技术在物质表面性质表征领域的重要应用,展现了NMR技术在高分子材料和环境领域中独特的重要作用。重点介绍基于NMR技术的Acorn比表面分析仪能够直接测定液相环境中物质的弛豫时间,反映物质的表面性质和结构特征,为解释污染物环境行为提供数据支持从而在环境领域发挥重要作用,展现出Acorn比表面分析仪相比于传统BET法在测量环境和测量时间等方面的优越性,尤其是Acorn比表面分析仪可以反映液相环境中物质的表面性质和结构特征的重要特性,解决了传统BET法无法直接获得液相环境中物质的比表面积信息的难题,是液相环境中NMR技术在物质表面性质表征领域的新突破。对Acorn比表面分析仪在制药、化妆品材料和电子产品等方面的应用进行了分析,并在土壤有机质、药物和天然产物检测等方面对NMR技术的应用进行了展望。     

一种高效的星载高速固态存储器坏块管理算法

随着卫星技术的发展和功能的多样化,星载固态存储器需要存储的数据量越来越大,存储速率越来越高,在轨寿命越来越长。基于NAND Flash的星载固态存储器的并行存储方案得到广泛应用。但是由于NAND Flash存在初始坏块,且Flash芯片中坏块分布离散性较大。当固态存储器存储速率较高,并行存储的Flash芯片数增多,坏块经叠加映射后,使固态存储器有效容量损失较大。针对高速固态存储器的坏块问题,提出了一种高效的坏块管理算法,通过对坏块进行地址映射和替换,使固态存储器初始有效容量与装机容量的比值在高速并行存储的情况下仍能保持在97%左右,提高了Flash芯片存储容量的利用率,延长了大容量星载高速固态存储器的使用寿命。     

Applications of Nuclear Magnetic Resonance Imaging in Particle Technology

During the past decade, the application of Nuclear Magnetic Resonance (NMR) imaging techniques to problems of relevance to the process industries has been identified. In the context of particle technology, NMR imaging, in addition to the more routinely used techniques of Pulsed Gradient Spin Echo (PGSE) NMR and NMR spectroscopy, offer new methods of characterising pore structure, adsorption and diffusion processes within particles and packed beds of particles, as well as enabling time-resolved in-situ study of processes such as twophase flow, aggregation, polymerisation, crystallisation and phase separation phenomena. This paper reviews recent work in these areas, and also highlights the new insights NMR imaging can give us regarding the characterisation of porous materials, and the influence of the structure of the pore space on the transport processes occuring within a given porous solid.