Nuclear Magnetic Resonance T2 Research Articles

Assessment of structural changes of human teeth by low-field nuclear magnetic resonance (NMR)

A technique of low-field pulsed proton nuclear magnetic resonance (NMR) spin relaxation is described for assessment of age-related structural changes (dentin and pulp) of human teeth in vitro. The technique involves spin–spin relaxation measurement and inversion spin–spin spectral analysis methods. The spin–spin relaxation decay curve is converted into a T2 distribution spectrum by a sum of single exponential decays. The NMR spectra from the extracted dentin-portion-only and dental pulp-cells-only were compared with the whole extracted teeth spectra, for the dentin and pulp peak assignments. While dentin and pulp are highly significant parameters in determining tooth quality, variations in these parameters with age can be used as an effective tool for estimating tooth quality. Here we propose an NMR calibration method—the ratio of the amount of dentin to the amount of pulp obtained from NMR T2 distribution spectra can be used for measuring the age-related structural changes in teeth while eliminating any variations in size of teeth. Eight teeth (third molars) extracted from humans, aged among 17–67 years old, were tested in this study. It is found that the intensity ratio of dentin to pulp sensitively changes from 0.48 to 3.2 approaching a linear growth with age. This indicates that age-related structural changes in human teeth can be detected using the low-field NMR technique.

Magnetic resonance studies of hydration kinetics and microstructural evolution in plaster pastes

This paper details a comparison of the evolution in the microstructure of the α and β forms of gypsum plaster that occur during hydration. The comparison has been performed using a combination of rapid Nuclear Magnetic Resonance (NMR) relaxation measurements and Scanning Electron Microscopy images, acquired as a function of hydration time. The α plaster hydrates to an interconnected network of uniform gypsum crystals providing a homogeneous structure, whereas the β plaster exhibits growth of crystals with irregular shape leading to a more open pore network and a heterogeneous product. An additional NMR T 2 relaxation time component is observed in the β plaster compared to the α plaster, suggesting the presence of large pores in the β plaster. This conclusion is confirmed by pore volume distributions determined from X-ray micro-computerised tomography (μ-CT) images of the set plasters. To the best of our knowledge, this is the first study of both forms of plaster utilising this combination of experimental techniques. The hydration kinetics have also been compared using one-dimensional NMR profiles, from which effective rate constants are determined. Consistent with previous results, the hydration reactions of the α and β forms of plaster are seen to occur at very different rates: the α plaster has a short initiation period and a slow hydration reaction. In contrast, the β plaster has a long initiation period, although the hydration reaction proceeds more rapidly thereafter. This work demonstrates the applicability of several NMR techniques to monitor, in situ, the hydration kinetics and microstructural evolution in plaster pastes, which will be crucial to the further understanding of mechanical properties (e.g. moisture transport) in these systems.

Improved Interpretation of Nuclear Magnetic Resonance T1 and T2 Distributions for Permeability Prediction: Simulation of Diffusion Coupling for a Fractal Cluster of Pores

NMR relaxometry is a powerful tool for inferring porosity and permeability data. In practice, measured magnetization decay curves are inverted for relaxation time distributions. Subsequently, one presumes a linear relationship between the pore radius distribution and the T1 and T2 distribution, for longitudinal and transverse magnetization, respectively. The fundamental equations used are based on a pore model, in which pores are assumed to be isolated from each other with respect to the NMR process and have smooth walls. The present study is based on a geometrical pore space model with connected pores and structured pore walls. The physical processes of surface relaxation, irreversible dephasing of magnetic spins and diffusive proton exchange between pores, are described by a system of differential equations. The solution yields a set of exponential functions representing the relaxation time distribution. We describe the difference between the distributions obtained for diffusion coupling and for isolated pores. With diffusion coupling on, the spectral width of the T1 distribution is strongly reduced, which indicates that the influence of large and small radii according to the T1-pore radius relationship is mixed to some extent. For a fractal pore space structure, where large pores are surrounded by adjacent minor pores, the T1 distribution does not resolve these substructures. Nevertheless, permeability values calculated from the logarithmic mean relaxation time T1,LM are quite the same for diffusion coupling and for isolated pores. The T2 distribution for diffusion coupling is little constricted and gives a better resolution of the pore wall structures than the corresponding T1 distribution. The permeability values from T2 distributions agree with the values from longitudinal magnetization, provided that we use a corrected relaxation time T2,corr, accounting for the dependence of the surface relaxivity ρ2 on pore radius. The study shows that radius distributions calculated from a T1 and from a T2 distribution differ from one another and both present an altered image of the true pore radius distribution. In practice, this has no serious influence on estimating permeability of medium- to high-permeability sandstones with the currently applied methods. The presented methodology of calculating the NMR response of pore space models with diffusion coupling may facilitate understanding porosity-permeability relationships of different rock types such as carbonate rocks with micro-porosity.

Application of low field NMR T2 measurements to clathrate hydrates

Low field (2 MHz) Nuclear Magnetic Resonance (NMR) proton spin–spin relaxation time ( T 2) distribution measurements were employed to investigate tetrahydrofuran (THF)—deuterium oxide (D 2O) clathrate hydrate formation and dissociation processes. In particular, T 2 distributions were obtained at the point of hydrate phase transition as a function of the co-existing solid/liquid ratios. Because T 2 of the target molecules reflect the structural arrangements of the molecules surrounding them, T 2 changes of THF in D 2O during hydrate formation and dissociation should yield insights into the hydrate mechanisms on a molecular level. This work demonstrated that such T 2 measurements could easily distinguish THF in the solid hydrate phase from THF in the coexisting liquid phase. To our knowledge, this is the first time that T 2 of guest molecules in hydrate cages has been measured using this low frequency NMR T 2 distribution technique. At this low frequency, results also proved that the technique can accurately capture the percentages of THF molecules residing in the solid and liquid phases and quantify the hydrate conversion progress. Therefore, an extension of this technique can be applied to measure hydrate kinetics. It was found that T 2 of THF in the liquid phase changed as hydrate formation/dissociation progressed, implying that the presence of solid hydrate influenced the coexisting fluid structure. The rotational activation measured from the proton response of THF in the hydrate phase was 31 KJ/mole, which agreed with values reported in the literature.

Cation Exchange at the Mineral−Water Interface: H3O+/K+ Competition at the Surface of Nano-Muscovite

This article describes a (39)K nuclear magnetic resonance (NMR) spectroscopic study of K+ displacement at the muscovite/water interface as a function of aqueous phase pH. (39)K NMR spectra and T 2 relaxation data for nanocrystalline muscovite wet with a solid/solution weight ratio of 1 at pH 1, 3, and 5.5 show substantial liquid-like K+ only at pH 1. At pH 3 and 5.5, all K+ appears to be associated with muscovite as inner- or outer-sphere complexes, indicating that H(3)O+ does not displace basal surface K+ beyond the (39)K detection limit under these conditions. In our pH 1 mixture, only approximately 1/3 of the initial basal surface K+ population is located more than 3-4 A from the surface. (29)Si and (27)Al MAS NMR spectra and SEM images show no evidence of dissolution during the (39)K experiments, consistent with the liquid-like (39)K fraction originating from displaced basal surface K+. Assuming no muscovite dissolution or interlayer exchange, the K+/H(3)O+ ratio relevant to the solution/surface exchange equilibrium is controlled by the total amount of K+ on the surface and H(3)O+ in solution (K+(surf)/H(3)O+(aq)). These parameters, in turn, depend on the basal surface area, solution pH, and the solid/solution ratio. The results here are consistent with significant displacement of surface K+ only under conditions where the initial K+(surf)/H(3)O+(aq). ratio is less than approximately 1. Computational molecular models of the muscovite/water interface should account for both K+ and H(3)O+ in the near-surface region.

Measuring Porosity and Permeability From Drill Cuttings

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 111286, "Advances in Measuring Porosity and Permeability From Drill Cuttings," by R. Lenormand, SPE, IFP, and O. Fonta, Geopetrol, prepared for the 2007 SPE/EAGE Reservoir Characterization and Simulation Conference, Abu Dhabi, UAE, 28-31 October. The paper has not been peer reviewed. Drill cuttings can provide quick and useful information for reservoir characterization, especially when cores are not available. Several petrophysical properties can be determined from cuttings: porosity, permeability, and transverse-relaxation-time (T2) nuclear-magnetic-resonance (NMR) distributions (related directly to the pore-size distribution). Results are presented for porosity and permeability measurements on cuttings with diameters of approximately 0.5 mm and for a field test. Introduction Early determination of rock petrophysical properties is needed during the reservoir-characterization process because it affects estimates of reserves (porosity and saturation) and of well deliverability (permeability). Generally, well logs provide a good estimate of porosity and saturations along the wellbore, but permeability is more difficult to obtain. Cuttings are used routinely by mud loggers to build the "master log" of the geological description of the drilled formation. Hydrocarbon indices are determined from cuttings to identify the reservoir levels. Although rock-cutting material comes directly from the reservoir, few applications of porosity and permeability characterization are reported in the literature. The full-length paper details the methods used for porosity and permeability determinations from cuttings and presents results from tests on crushed cores. The main result is accurate determination of porosities for 0.5-mm-diameter cuttings for permeability of less than 1 md. The porosities and T2 NMR data measured on real cuttings from a well in the Paris basin are presented and compared to log results. Porosity Measurement on Cuttings The methods for measuring porosity on cuttings are the same as those for cores when the cutting size is larger than 3 mm. For smaller cuttings (most cases), the best results are obtained by use of a centrifuge or a porous plate to remove the interstitial liquid with a controlled capillary pressure. Porosities were measured to within 1 to 2 p.u., even for flat cuttings with diameters of approximately 1 mm and thickness of 0.5 mm collected during the field case. Improved Methods. To improve measurement accuracy for cutting sizes down to 0.5 mm, most of the existing methods were tested. A porous-plate method provided the most consistent results and is detailed in the full-length paper. The saturated cuttings are placed in a tube set on its end on the porous plate. Vacuum is applied through the plate to remove interstitial liquid and partially desaturate the plate. Then, the porous plate pulls the remaining interstitial liquid with a controlled capillary pressure. When the excess water is removed, the cuttings no longer stick together and move freely like dry samples.

Proton NMR relaxation as a probe for setting cement pastes

We report a 20-MHz proton nuclear magnetic resonance T1 relaxation study of cement paste hydration in the early stages of setting, using different centimeter-sized samples of cements of various origins and different water-to-cement ratios. In every sample, during the first few minutes of hydration, it is found that inverse Laplace processing of inversion-recovery measurements systematically exhibits at least two T1 values: a long one, around 100 ms, whose value correlates well with water content and which may be attributed to bulk water surrounding cement grains; and a short one, around 2 ms, which is quite insensitive to water-to-cement ratio and which may be attributed to water embedded in floculated cement grains before setting occurs. The time evolution of the longest T1 value for several hours is also shown to exhibit a characteristic five-stage behavior that is well correlated with known stages of the hydration process: initial reaction, induction period, acceleration period, deceleration period and slow hydration reaction. These results are compared with calorimetric measurements and electrical conductivity literature.

Impact of Short Chain Branching on Conformations of Metallocene LLDPE Melts: NMR, Light Scattering and MD Simulation Study

AbstractSummary: The influence of short chain branching on molecular conformations of melts and solutions of metallocene linear Low‐density polyethylene (m‐LLDPE) was studied by nuclear magnetic resonance (NMR) spectroscopy, light scattering, and Molecular Dynamics (MD) simulation techniques. Both T2 relaxation measurements by NMR and MD simulations suggest the loss of molecular order in m‐LLDPE at temperatures >135°C. Similar trends were observed for the radius of gyration as measured by light scattering and calculated from MD simulations vs. branch content (BC) and type. At high BC (>40 branches/1000 C) m‐LLDPE tends towards self assembly. Neither the branch type nor the BC has significant effect on the intermolecular orientation correlation function. This might be attributed to the fact that the high temperature of the melt results in loss of order in the chains. This lack of order is independent of BC or type. This result is in agreement with the results of the dihedral distribution analysis. Also, it is in agreement with our NMR T2 measurements. The radial distribution functions are nearly identical indicating no effect of branch type at low branch density on the correlation between branches and backbone segments. However, increasing the BC to 80 branches/1000C resulted in a change in the correlation between the branches and backbone segments.

Curing‐induced water mobility and distribution within intra‐ and extra‐myofibrillar spaces of three pork qualities

SummaryThis study introduces the use of nuclear magnetic resonance (NMR) relaxometry in the elucidation of the curing‐induced water mobility and distribution within pork. Fresh meat samples of three different meat qualities [normal; pale, soft and exudative (PSE); dark, firm and dry (DFD)] were cured by using different curing conditions (0.9–9% NaCl and 6% NaCl + 10 mm Na4P2O7). Distributed NMR T2 relaxation data revealed the presence of three distinct water populations (T2b, T21, T22), with the T21 population being most influenced by the curing conditions, which was reflected by strong correlations between the salt‐induced swelling and the mean relaxation time of the T21 population. Consequently, the T21 population reflects the myofibrillar swelling, and is an excellent indicator of myofibrillar geometry upon curing. Both the NMR data and the salt‐induced swelling capacity were highly dependent on fresh meat quality. Independent of brine composition, the DFD meat had a significantly higher swelling capacity than the two other meat qualities. A higher response to NaCl concentration on the swelling capacity was observed for PSE and normal meat than for DFD meat, which suggests interactions between the pH of the meat and NaCl‐induced swelling.

Petrophysical Measurements From Drill Cuttings: An Added Value for the Reservoir Characterization Process

Summary Permeability and porosity are necessary for reservoir characterization, and cuttings can provide quick information using dedicated measurement techniques. In this paper, we present the first applications of these techniques on real reservoir characterization cases and the comparisons with logs and core data. The method of permeability measurement from cuttings is based on a pressure pulse applied to a cell filled initially with cuttings saturated with viscous fluid in the presence of trapped gas. The permeability is derived from the transient response of the oil invasion into the cuttings by using a numerical approximation of a mathematical model. The porosity of dry drill cuttings is measured using the routine helium technique. These methods were tested and validated by using various samples of crushed rock of known permeability and porosity. Both measurement techniques are fast, require light conditioning, are applicable over a large range of permeability, and need only 1 mL of sieved rock to be carried out. In this paper, we present a field application of an integrated drill cuttings measurement program [permeability, porosity, nuclear magnetic resonance (NMR) T2 distribution] on a carbonate reservoir. Various drilling conditions [including water-based mud (WBM) and oil-based mud (OBM)] and lithologies have been investigated to develop the different techniques that are presented in the paper. The question of whether measurements on cuttings are representative of the native reservoir is of primary importance and was checked by comparing the consistency of the porosity measurements obtained from cuttings with other data (cores or logs). The overall results demonstrate the added value of k and ϕ measurements from cuttings in addition to the data that are commonly collected.

Noninvasive characterization of gonad maturation and determination of the sex of Pacific oysters by MRI

The aim of this study was to test the ability of magnetic resonance imaging (MRI) technique to characterize gonad development and to determine the sex of live Pacific oysters through their shells. A preliminary nuclear magnetic resonance (NMR) relaxometry study was conducted to characterize T1 and T2 NMR relaxation parameters for the main oyster organs. This showed that T1-weighted MRI sequences were most appropriate to optimize contrasts between tissues in images. The results showed that gray levels of gonads in images acquired with gradient-echo sequence were variably affected by T2* weighting effect. However, the ovaries systematically gave a hypersignal in spin-echo T1-weighted images, and stack histograms of female oysters showed a peak well separated from that of male oysters. An automated method is proposed to quantify the development of oysters and their gonad maturation and to identify their sex.

Spatial Quantification of Mn2+and Mn3+Concentrations in the Mn-Catalyzed 1,4-Cyclohexanedione/Acid/Bromate Reaction Using Magnetic Resonance Imaging

This paper presents a magnetic resonance imaging (MRI) method for quantifying the spatial concentrations of the paramagnetic species Mn2+ and Mn3+, during pattern formation, in the manganese-catalyzed 1,4-cyclohexanedione-acid-bromate reaction. The relaxivity of each species was measured, which enabled their concentration to be calculated from nuclear magnetic resonance T2 relaxation times. Images were acquired using the fast spin-echo imaging method RARE. By determining the relation, in these experiments, between signal intensity and T2 relaxation time, it was possible to produce T2 maps from the images. These T2 maps were then used to produce concentration maps for the oxidized (Mn3+) and reduced (Mn2+) states of the catalyst.

The characterization of human cortical bone microdamage by nuclear magnetic resonance

A nuclear magnetic resonance (NMR) spin–spin (T2) relaxation technique has been described for detecting post-damage microstructural changes in human cortical bone tissue. The technique is applied to quantify apparent changes in bone porosity resulting from cyclic loading induced microdamage in cortical bone. Overall bone porosity is determined using the calibrated NMR fluid volume from the proton relaxation data divided by the overall bone volume. The NMR porosities obtained from cortical bone specimens pre- and post-damage are compared with the currently available but destructive histomorphometrically determined porosity. The advantages of using NMR T2 relaxation techniques for bone microdamage are illustrated. The T2 relaxation data can be inverted to T2 relaxation distribution. The inversion T2 relaxation distribution can then be transformed to a pore-size distribution with the longer relaxation times corresponding to larger pores if the surface relaxivity constant is known. It is shown that by using NMR 2 MHz or 27 MHz proton resonance, similar surface relaxivity constants are obtained. It is also demonstrated that the NMR T2 relaxation data are sensitive to changes resulting from the creation of microdamage in cortical bone, which can be interpreted as an effective increase in bone porosity. These results indicate that the detection of cortical bone microdamage is possible by this technique.

Study of Vuggy Carbonates Using NMR and X-Ray CT Scanning

Summary Most existing nuclear magnetic resonance (NMR) permeability correlations for carbonates assume that vugs do not contribute to permeability. The objective of this work is to improve permeability estimation from NMR responses for carbonates by including vug connectivity. Six carbonate samples from a west Texas field were studied. NMR T2 measurement, mercury porosimetry, thin-section imaging [using optical microscopy and a scanning electron microscope (SEM)], computerized tomography (CT) scanning, and electrical measurements were conducted. The permeability of the samples studied is controlled by the channels that connect vugs. Capillary pressure and NMR T2 measurements show multimodal pore-throat and pore-body-size distributions. A modified Chang model, which includes the tortuosity factor, is proposed and proven to yield a better permeability prediction than the original Chang model. It is also shown that for the samples studied, the tortuosity can be estimated from NMR T2 distribution, hence allowing permeability prediction from the NMR T2 distribution alone.

A Comparative Nuclear Magnetic Resonance and Rheological Study on Mash and Spent Grain Suspensions, Worts, and Carbohydrate Solutions

Nuclear magnetic resonance (NMR) was used to determine the T2 NMR relaxation times of mash and spent grain suspensions, worts, and carbohydrate solutions. T2 characterizes the molecular mobility of fluids. The T2 values, furthermore, correlate with both the zero-shear-rate viscosity and the viscosity at high shear rates that have been determined with a rotational rheometer. Thus, NMR provides the possibility to determine characteristic viscosities of materials during the brewing process by means of T2 experiments. The viscosities of the mash and the wort are important process parameters, since they are used 1) as a process and quality control of the brewing and filtering/lautering processes, and 2) for the determination of the wort density as a measure of the dissolving process of carbohydrates in spent grain. This NMR application, which has comparatively short measuring times, is especially interesting for use with dispersal systems in which the use of conventional rheometric techniques may cause great errors. The only prerequisite for measuring viscosities using NMR is a previous calibration.

Segmental dynamics in a blend of alkanes: Nuclear magnetic resonance experiments and molecular dynamics simulation

The segmental dynamics of a model miscible blend, C24H50 and C6D14, were investigated as a function of temperature and composition. The segmental dynamics of the C24H50 component were measured with C13 nuclear magnetic resonance T1 and nuclear Overhauser effect measurements, while H2 T1 measurements were utilized for the C6D14 component. Use of low molecular weight alkanes provides a monodisperse system in both components and allows differentiation of dynamics near the chain ends. From these measurements, correlation times can be calculated for the C–H and C–D bond reorientation as a function of component, position along the chain backbone, temperature, and composition. At 337 K, the segmental dynamics of both molecules change by a factor of 2 to 4 across the composition range, with the central C–H vectors of tetracosane showing a stronger composition dependence than other C–H or C–D vectors. Molecular simulations in the canonical and isobaric–isothermal ensembles were conducted with a united-atom force field that is known to reproduce the thermodynamic properties of pure alkanes and their mixtures with good accuracy. With a minor change to the torsion parameters, the correlation times for pure tetracosane are in good agreement with experiment. For pure hexane and its mixtures with tetracosane, the simulated dynamics are faster than experiment.

Study of Odd−Even Effect of Flexible Spacer Length on the Chain Dynamics of Main-Chain Thermotropic Liquid-Crystalline Polymers Using High-Resolution Solid-State 13C Nuclear Magnetic Resonance Spectroscopy

The odd−even effect of flexible spacer length on the molecular dynamics of poly[(phenylsulfonyl)-p-phenylenealkylenebis(4-oxybenzoate)]s (PSHQn) having varying lengths (n) of methylene groups of flexible spacers and bulky pendent side groups was investigated using high-resolution solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. The temperature dependences of 13C NMR spectra and spin−lattice relaxation time (T1) were measured for PSHQn over the temperature range of 293−520 K. Line broadening of α-CH2 and rigid core carbons, due to the interference between proton decoupling and local polymer chain motion about the preferred direction of alignment accompanying the fluctuation of the rigid core, was observed in the nematic phase. The local polymer chain motion in the nematic phase was found to vary over a frequency range of 104−106 Hz. The activation energy (77−104 kJ/mol) of this motion was found to increase with decreasing number of methylene groups and exhibits odd−even fluctuations. The motions of the local polymer chains in the nematic phase were also observed via the 1H line width in two-dimensional wideline separation (WISE) NMR spectra. It was found that the 13C NMR T1 of flexible spacer carbon was dominated by the fast trans−gauche exchange. The frequency of the trans−gauche exchange was found to occur above 108 Hz in the nematic mesophase, since T1 increased with increasing temperature. The activation energy (6.5−9.8 kJ/mol) of the trans−gauche exchange estimated from T1 was found to increase with decreasing number of methylene groups and exhibits odd−even fluctuations. The odd−even fluctuations of the activation energy of local polymer chain motion and trans−gauche exchange are indicative of the differences in molecular packing between PSHQn having odd-numbered n and PSHQn having even-numbered n.

Mixing Rules and Correlations of NMR Relaxation Time With Viscosity, Diffusivity, and Gas/Oil Ratio of Methane/Hydrocarbon Mixtures

Summary Viscosity, diffusivity, relaxation time, and gas/oil ratio are important properties in the characterization of reservoirs by nuclear magnetic resonance (NMR) well logging and in prediction of production performance. For the past few years, NMR well logging has been used to estimate formation properties and hydrocarbon liquid/ vapor characterization. Previous work has shown that pure al-kanes, alkane mixtures, viscosity standards, and stock tank crude oils have NMR relaxation times that vary linearly with viscosity/ temperature and diffusivity on a log-log scale. However, pure methane at some temperatures and pressures does not follow the same trend. Thus, the linear correlation may not be valid for live crude oils that contain a significant amount of methane. Therefore, the study of methane-hydrocarbon mixtures is of interest. An NMR spectrometer equipped with a high-pressure probe was used to study the relationship between NMR T1 relaxation time and viscosity/temperature, diffusivity, and gas/oil ratio of methane-hydrocarbon mixtures. Relaxation time and diffusivity measurements of three mixtures were made: methane-n-hexane, methane-n-decane, and methane-n-hexadecane. It was found that unlike stock tank oil, relaxation times do not depend linearly on viscosity/temperature on a log-log scale. Each of the mixtures forms a different curve. Generalized correlations between viscosity, diffusivity, gas/oil ratio, and NMR relaxation times were developed. First, the relaxation time mixing rule was developed by studying the theory of NMR relaxation mechanism. From the mixing rule, it was found that departure of relaxation times of methane-n-alkane mixtures from linear correlations on a log-log scale can be correlated with the proton fraction of methane, expressed as gas/oil ratio. Thus, correlations between relaxation time, viscosity/temperature, and gas/oil ratio were developed. Correlations between relaxation time, diffusivity, and gas/oil ratio were also developed. There is a linear relation between diffusivity and viscosity/temperature that is independent of composition. From these correlations, viscosity and gas/oil ratio can be estimated from NMR T1 relaxation time and diffusivity.

Nuclear magnetic resonance investigation of Li+-ion dynamics in the perovskitefast-ion conductor Li3xLa2/3-x1/3-2xTiO3

7Li nuclear magnetic resonance relaxation times T1,T1ρ and T2 versus temperature are reported in the150-900 K temperature range for the lithium lanthanum titanateLi3xLa2/3-x□1/3-2xTiO3 perovskite-typefast-ionic conductors. The presence of Li+ ions of two kindswith slightly differing environments is displayed in theseexperiments. These ions exhibit two different motions: a fast onewith a characteristic frequency around 100 MHz at 350 K and a slowone whose frequency is around 60 kHz at 280 K. These two differentLi+ species cannot be differentiated by means of the fastmotion (only one T1 is observed from the experiments), but onlyby means of the slow ones (two T1ρ and two T2 areobserved). These motions are respectively attributed to Li+motion inside the A-cage of the perovskite structure formed by theoxygen ions and to Li+ hops between the cages. T1- andT1ρ-studies also performed on the 6Li nucleus clearlyshow that just dipolar nuclear interaction is responsible forLi+ relaxation. This result is at variance with what has beenpreviously put forward for the relaxation process in thesecompounds.

35Cl NMR relaxation study of cement hydrate suspensions

35Cl nuclear magnetic resonance (NMR) T1 and T2 relaxation study of suspensions of the cement hydrate phases portlandite, C4AC̄H11 (an AFm phase), and jennite provides significant insight into the mechanisms of chloride sorption in Portland cement systems. For these three phases, all observed chloride is in rapid exchange (υex>1.6 kHz) between surface and bulk solution sites and is predominantly in a hydrated, solution-like chemical environment. A two-site exchange model for the T1 relaxation rate data yields sorption densities in excellent quantitative agreement with sorption isotherm measurements for portlandite and C4AC̄H11. For jennite, the NMR results underestimate the sorption isotherm results by about 40%, but the sorption densities are low, and the results are probably in agreement within experimental error. The observed sorption densities are much greater than can be accommodated by bonding directly to atoms on the solid surfaces and the amount predicted to be in the Stern and diffuse layers by a Gouy-Chapman calculation assuming sorption of only isolated chloride ions. The significance of understanding the structural and dynamical properties of solution-state chloride and the roles of ion pairs and clusters in the solution near the solid surface are discussed.