Cross polarization, magic-angle spinning C nuclear magnetic resonance spectroscopy of soil humic fractions

Cross polarization, magic-angle spinning ¹³C nuclear magnetic resonance spectroscopy was used to characterize humic fractions isolated from different soils. The acid fractions are more aromatic than the humin fractions, probably due to the higher polyssaccharide content of humins. However, fulvic acid fractions are more aromatic than the corresponding humic acid and humin fractions. These results can be interpreted in terms of the isolation procedure, because the high affinity of Polyclar AT for phenols results in higher aromaticities as compared with other isolation methods (e.g. charcoal).     

Nuclear magnetic resonance spectroscopy of soils and related materials. Relaxation of 13C nuclei in cross polarization nuclear magnetic resonance experiments

Relaxation of ¹³C nuclei in a peat, a soil, and three soil fractions have been investigated in order to improve structural resolution and to investigate quantification of various carbon types. Rotating frame spin lattice relaxation times (T_1?'s) and transverse relaxation times (T₂′'s) are similar to those observed for coals. T₂′'s of carbons in different magnetic environments differ sufficiently that spectra can be obtained containing only nonprotonated carbon and methyl substituents if a 40 μsec delay without decoupling is inserted into the pulse programme before data acquisition (dipolar dephasing). Provided quantitative data is obtained in simple cross polarization experiments and allowance is made for loss in signal intensity of nonprotonated carbon during dipolar dephasing, then the fraction of aromatic carbon which is protonated in the samples can be determined.     

Cross polarization magic-angle spinning 13C NMR spectra of oil shales

Cross plarization magic-angle spinning ¹³C NMR spectra have been obtained on oil shales representing a variety of geologic ages, origins, depositional environments, and source locations. The spectra show variations in the aliphatic and aromatic carbon distributions of the oil shales and reveal correlations between aliphatic carbon contents and potential shale oil yields. Hints of additional fine structure are present in the spectra of some samples, and examples are given of the spectral resolution that may be obtainable on other solid samples of geochemical interest.     

Investigation of seawater and terrestrial humic substances with carbon-13 and proton nuclear magnetic resonance

Seawater and terrestrial fulvic acids have been investigated with carbon-13 and proton nuclear magnetic resonance and by i.r. spectroscopy. The structural differences observed seem to result mainly from the low abundance of aromatic precursors (i.e. lignin) in seawater as compared to the terrestrial environment.     

Chemical structural studies of natural lignin by dipolar dephasing solid-state 13C nuclear magnetic resonance

Two natural lignins, one from a gymnosperm wood the other from angiosperm wood, were examined by conventional solid-state and dipolar dephasing ¹³C nuclear magnetic resonance (NMR) techniques. The results obtained from both techniques show that the structure of natural lignins is consistent with models of softwood and hardwood lignin. The dipolar dephasing NMR data provide a measure of the degree of substitution on aromatic rings which is consistent with the models.     

Comparison of oil shales and kerogen concentrates by 13C nuclear magnetic resonance

Six oil shales and their kerogen concentrates have been studied using ¹³C CP/MAS NMR techniques to study the distribution of organic carbon species. It is found that if the aromatic and aliphatic regions are divided at about 80 or 100 ppm, the apparent aromaticities of a raw shale and its kerogen concentrate are in good agreement. The presence of oxygen-substituted carbons in the raw shales and their depletion in the kerogen concentrates are observed and discussed.     

Analysis of fluid inclusions using nuclear magnetic resonance

Nuclear magnetic resonance (NMR) spectra from ²³Na and ³⁵C1 in fluid inclusions in samples of quartz and beryl show the potential of NMR as a powerful analytical technique for the study of fluid inclusions.     

利用核磁共振勘测滑坡的水文地质条件

滑坡水文地质条件是最易变、最难确定的,对滑坡的稳定性影响也很大。利用核磁共振(NMR)技术,可以分析确定滑坡各层岩土体的含水量、孔隙度、渗透率、渗透系数等水文地质参数。根据含水量的变化,可以确定滑体的结构特征、滑面位置、地下水的分布,为建立符合实际的滑坡模型及滑坡稳定性分析评价提供依据。介绍了利用NMR技术来查明滑坡水文地质条件的原理和方法及其在赵树岭滑坡工程中的成功应用情况。     

Unfrozen water contents of submarine permafrost determined by nuclear magnetic resonance

Prior work resulted in the development of techniques to measure the unfrozen water contents in frozen soils by nuclear magnetic resonance (NMR). It has been demonstrated that NMR is a promising new method for the determination of phase composition (the measurement of unfrozen water content as a function of temperature) which circumvents many of the limitations inherent in the adiabatic and isothermal calorimetric techniques. The NMR technique makes it possible, in a non-destructive, non-intrusive way, to explore hysteresis by determining both cooling and warming curves. Corrections are made for dissolved paramagnetic impurities which have the effect of increasing the signal intensity at decreasing temperatures. The results demonstrate that NMR techniques can be effectively utilized both at and below the melting point of ice in frozen soils and that accurate melting points (freezing point depressions) can be determined.     

核磁共振在滑坡研究中的应用技术

应用核磁共振找水仪测试成果,分析确定滑坡各层岩土体的含水量、孔隙度、渗透率、渗透系数.根据含水量的变化,确定滑坡结构特征、地下水分布及各层滑动带位置.与钻孔资料的对比分析表明,该技术的分析结果与钻孔数据吻合较好,可为建立符合实际的滑坡模型提供可靠依据.     

固化盐渍土核磁共振微观特征

采用核磁共振技术,对不同配比的水玻璃、石灰+粉煤灰及石灰+粉煤灰+水玻璃的固化盐渍土的微观特征进行检测,结合无侧限抗压强度试验,分析了各固化方案的盐渍土固化效果,讨论了强度成因的微观特征机制。结果表明,不同固化土的孔隙特征有较大差异。石灰+粉煤灰固化盐渍土大孔隙减少;石灰+粉煤灰+水玻璃固化盐渍土孔隙总体积减少,但同时有大孔隙生成;水玻璃固化盐渍土孔隙总体增多,但随水玻璃浓度增大,孔隙体积有所减小。石灰+粉煤灰+水玻璃固化盐渍土抗压强度远大于其他固化方案,但是其孔隙结构并不是最优,说明颗粒间的胶结情况对固化效果的影响远大于孔隙特征。     

31P solid-state nuclear magnetic resonance spectroscopy of aluminum phosphate minerals

This study examines the links between ³¹P solidstate NMR studies of aluminum phosphate minerals and their crystallographic structures. We found that ³¹P isotropic chemical shift values, _iso, carry little information about mineral structures. There seems to be no relation between the chemical shift anisotropy, =₃₃–₁₁ (₃₃>₂₂> ₁₁), and indicies of phosphate-tetrahedra distortion. ³¹P¹H heteronuclear magnetic dipole interactions, on the other hand, carry important information about hydrous phosphate mineral structures, information that should prove to be quite valuable in studies of phosphate adsorbed on mineral surfaces. This interaction can be measured through a variety of qualitative and quantitative experiments. It appears that spin diffusion is so rapid that subtle differences in hydrogen-bonding environments cannot be resolved.     

Analysis of the organic matter of oil shales by nuclear magnetic resonance

¹³C NMR spectroscopy was applied in the investigation of the structure of the organic matter in oil shales. By using Proton Enhanced Nuclear Induction Spectroscopy, a fair resolution of aliphatic and aromatic carbon signals was achieved. This method provided information on the relative ratio of aliphatic and aromatic carbons within a given set of samples (Aleksinac, Kimmeridge, Colorado, Australian torbanite and Estonian kukersite).     

Exploitation of relaxation in cross-polarization nuclear magnetic resonance spectroscopy of fossil fuels

The judicious choice of dipolar dephasing times or carbon magnetization holding times has been shown to improve resolution in solid state nuclear magnetic resonance (NMR) spectra of complex materials. Signals from protonated and alkylated aromatic carbons are reduced to enhance resolution of aromatic oxygenated groups. Rapidly rotating methyl groups can be resolved from other aliphatic carbon types. These techniques were used to investigate the structure of a brown coal, xylite fractions of a brown coal, a bituminous coal, an oil shale and a solvent-refined coal. The results allow estimates of the fraction of aromatic carbon that is protonated in coal to be made, and demonstrate that methyl groups in coal rotate rapidly at room temperature.     

31P and 27Al solid-state nuclear magnetic resonance study of taranakite

High-resolution ²⁷Al solid-state nuclear magnetic resonance (NMR) spectroscopy indicates that aluminum in taranakite is probably restricted to six-coordinate sites. High-resolution ³¹P solid-state NMR spectroscopy reveals that phosphate groups exist in two environments in taranakite. The rate of ¹H-induced dipolar dephasing of the ³¹P signals in cross-polarization, magic-angle-spinning NMR spectra of taranakite suggests that one or more oxygens of one of two phosphates are directly protonated. The same experiments suggests that the oxygens of the second form of phosphate are not directly protonated but may be hydrogen-bond receptors. The ratio of protonated phosphate to non-protonated phosphate, as measured from ³¹P single-pulse excitation, magic-angle-spinning spectra, is approximately one to three. Current address: Department of Soil Science, 1525 Observatory Drive, University of Wisconsin-Madison, Madison, WI 53706, USA     

Comparison of oil shales and kerogen concentrates by C nuclear magnetic resonance

Six oil shales and their kerogen concentrates have been studied using ¹³C CP/MAS NMR techniques to study the distribution of organic carbon species. It is found that if the aromatic and aliphatic regions are divided at about 80 or 100 ppm, the apparent aromaticities of a raw shale and its kerogen concentrate are in good agreement. The presence of oxygen-substituted carbons in the raw shales and their depletion in the kerogen concentrates are observed and discussed.     

Carbon-13 NMR spectra of macerals separated from individual coals

The density gradient centrifugation technique has recently been applied to the separation of macerals from whole coals. Sufficient quantities have been separated to permit examination of pure exinite, vitrinite and inertinite fractions by combined cross polarization and magic angle sample spinning (CP/MASS) carbon-13 NMR techniques. The similarities and differences observed in the maceral groups of two coals are discussed. Diversity in precursors or in differential chemical maturation or a combination of both of these factors can be used to account for subtle spectral differences in the two coals and macerals studied even though the gross spectral features are very similar for a given maceral type. The data show that CP/MASS is a technique that can address such interesting geochemical questions.     

冻土未冻水含量的低场核磁共振试验研究

采用低场核磁共振技术测试了冻融循环过程中不同土质、不同NaCl离子浓度饱和试样的未冻水含量,结合T2分布曲线从微细观角度分析了冻融过程中未冻水在孔隙赋存分布情况。试验结果表明：冻结过程可分为过冷度段、快速下降段、稳定段3个阶段,而融化过程仅存在稳定段、快速融化段,并不存在与过冷现象对应的过热现象。冻结时大孔隙的水首先冻结,而融化时孔隙水的增加却是从小孔隙开始的,这是由水分热动力学势能的差异导致孔隙水冻结和融化在时间上的有序性。并且分析了冻融循环中土质类型、离子浓度对未冻水含量的影响,以及探讨了冻融过程出现的滞后现象的原因。     

27Al Solid-state nuclear magnetic resonance study of five-coordinate aluminum in augelite and senegalite

This is a report of ²⁷Al magic-angle spinning, nuclear magnetic resonance spectroscopy of 5- and 6-coordinate aluminum in the aluminophosphate minerals augelite and senegalite. We have determined the quadrupolar coupling constants, asymmetry parameters and chemical shifts corrected for quadrupolar-induced shift for both aluminum coordination sites in each mineral. The quadrupolar coupling constants are significantly less in senegalite than in augelite. Structural analysis (viz., longitudinal- and shear-strain of the aluminum coordination polyhedra; coefficient-of-variation for both Al-O bond lengths and senegalite are less distorted than in augelite.