Low-field Proton Nuclear Magnetic Resonance Research Articles

Study of the spent catalysts as internal curing agents on the hydration kinetics and microstructure development of ultra-high performance concrete (UHPC)

In this study, the effect of 5–30 % (by mass) of spent catalyst (SC) on the characteristics of ultra-high-performance concrete (UHPC) is investigated, including mechanical properties, volumetric stability, hydration kinetics, and microstructural development. Specifically, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and low-field proton nuclear magnetic resonance spectroscopy (1H NMR) are employed to clarify the microstructures, while thermogravimetric analysis (TG), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS) are carried out to understand the phase variation. The results obtained show that the samples containing SC and additional water exhibit good mechanical properties, such as a 1.0 %-2.9 % higher compressive strength of UHPC with SC (5–15 %) and additional water compared to SC1 at 60 days. Additionally, SC can also improve the volumetric stability of UHPC. Moreover, the Ca/Si ratio of the hydration products decreases and the Al/Ca ratio increases with the enhancement of SC and additional water content. Furthermore, the water release effect of SC promotes the hydration of cement and pozzolanic reactions, leading to the generation of more hydration products and optimization of the pore structure and interfacial transition zone (ITZ) of UHPC in this study.

Effects of pure carbonation on pore structure and water permeability of white cement mortars

The effects of carbonation on cement-based materials have drawn much attention because of its profound influences on durability performance of concrete structures. Most accelerated carbonation in lab is conducted at RH 50%–70%, which also dries out cement-based materials. The introduced drying action changes pore structure significantly, making the effects of carbonation obscure. To clarify the effects of pure carbonation, water permeability and related micro-structural characteristics are measured on mature mortars, which have been carbonated at water-saturated state. It is found that after carbonation, the porosity of mortars decreases slightly, with finer overall pore structure and lower characteristic pore size. The water permeability also decreases by roughly 40% on average. Based on the pore size distribution curves obtained through the low-field proton nuclear magnetic resonance technique, water permeability is predicted by the Katz-Thompson and Kozeny-Carman theories with satisfactory accuracy. The decrease of water permeability after carbonation agrees well with the reduced characteristic pore length, which quantitatively verifies the observed refinement of nanoscale pore structure due to pure carbonation.

Screening Metal-Organic Frameworks for Separation of Binary Solvent Mixtures by Compact NMR Relaxometry.

Metal–organic frameworks (MOFs) have great potential as an efficient alternative to current separation and purification procedures of a large variety of solvent mixtures—a critical process in many applications. Due to the huge number of existing MOFs, it is of key importance to identify high-throughput analytical tools, which can be used for their screening and performance ranking. In this context, the present work introduces a simple, fast, and inexpensive approach by compact low-field proton nuclear magnetic resonance (NMR) relaxometry to investigate the efficiency of MOF materials for the separation of a binary solvent mixture. The mass proportions of two solvents within a particular solvent mixture can be quantified before and after separation with the help of a priori established correlation curves relating the effective transverse relaxation times T2eff and the mass proportions of the two solvents. The new method is applied to test the separation efficiency of powdered UiO-66(Zr) for various solvent mixtures, including linear and cyclic alkanes and benzene derivate, under static conditions at room temperature. Its reliability is demonstrated by comparison with results from 1H liquid-state NMR spectroscopy.

Urine NMR-based TB metabolic fingerprinting for the diagnosis of TB in children

Tuberculosis (TB) is a major cause of morbidity and mortality in children, and early diagnosis and treatment are crucial to reduce long-term morbidity and mortality. In this study, we explore whether urine nuclear magnetic resonance (NMR)-based metabolomics could be used to identify differences in the metabolic response of children with different diagnostic certainty of TB. We included 62 children with signs and symptoms of TB and 55 apparently healthy children. Six of the children with presumptive TB had bacteriologically confirmed TB, 52 children with unconfirmed TB, and 4 children with unlikely TB. Urine metabolic fingerprints were identified using high- and low-field proton NMR platforms and assessed with pattern recognition techniques such as principal components analysis and partial least squares discriminant analysis. We observed differences in the metabolic fingerprint of children with bacteriologically confirmed and unconfirmed TB compared to children with unlikely TB (p = 0.041 and p = 0.013, respectively). Moreover, children with unconfirmed TB with X-rays compatible with TB showed differences in the metabolic fingerprint compared to children with non-pathological X-rays (p = 0.009). Differences in the metabolic fingerprint in children with different diagnostic certainty of TB could contribute to a more accurate characterisation of TB in the paediatric population. The use of metabolomics could be useful to improve the prediction of TB progression and diagnosis in children.

Water loss and status in sponge cake: Impact of Eucheuma as a flour replacement.

The impact of Eucheuma on water loss and status in sponge cakes was measured and analyzed in this study. Eucheuma was used to replace 0%, 10%, and 20% of wheat flour to make sponge cakes, coded as the control, EP10, and EP20, respectively. The initial water content of batters showed no significant differences (around 57.0%, dry basis), whereas the final EP10 and EP20 products had higher water content. Three stages were found during baking in control sample and these three stages were fitted by linear, linear, and exponential models with root mean squared error (RMSE) of 0.016, 0.018, and 0.133, respectively. Eucheuma addition decreased the water loss rate and changed the water loss stages, which were fitted by linear, linear, and linear models in EP20 sample (RMSE = 0.027, 0.047, and 0.108, respectively). The crust formation and crumb structure analysis showed that the formation of cracks and the disappearance of pore structures hindered the water evaporation. The low-field proton nuclear magnetic resonance and magnetic resonance imaging results showed that the water status in the final EP20 products was not as tightly as that in the control samples. A proposed schematic diagram was developed based on the qualitative analysis of the transfer mechanisms to explain the total effect of Eucheuma on the water loss rate and status. These results aid our understanding of the water loss process of sponge cakes and promote the potential application of Eucheuma in bakery products. PRACTICAL APPLICATION: Eucheuma as a flour replacement can improve the contents of dietary fiber and minerals like potassium of sponge cake. The impact of Eucheuma on water loss and status in sponge cake was measured and analyzed in this study. The results can promote the potential application of Eucheuma in bakery products and predict the quality attributes of baking products.

Calibration Transfer of Partial Least Squares Regression Models between Desktop Nuclear Magnetic Resonance Spectrometers.

Low-field proton nuclear magnetic resonance (LF-1H NMR) devices based on permanent magnets are a promising analytical tool to be extensively applied to the process analytical chemistry scenario. To enhance its analytical applicability in samples where the spectral resolution is compromised, multivariate regression methods are required. However, building a robust calibration model, such as partial least squares (PLS) regression, is a laborious task because (1) the number of measurements required during the calibration process is large and (2) the procedure must be repeated when the instrument is changed or after a certain period due to the long-term stability of the instrument. Thus, the present work describes the application of calibration transfer methodologies (direct standardization (DS), piece-wise direct standardization (PDS), and double-window piece-wise direct standardization (DWPDS)) on LF-1H NMR to exempt the necessity of a recalibration procedure when moving from the original spectrometer to a second one with the same, lower, or higher magnetic field. These calibration transfer methodologies were tested with PLS models built on a 60 MHz (for the proton Larmor frequency) spectrometer to predict the specific gravity (SG), distillation temperature (T50%), and final boiling point (FBP) of commercial gasoline. The results showed that the DWPDS method applying only 2 to 7 transference samples enables the transference of all PLS models built on the primary instrument (60 MHz) to other (43, 60, and 80 MHz) different instruments, reaching the same RMSEP values as the primary instrument: 1.2 kg/m3 for SG, 5.1 °C for FBP, and 1.1 °C for T50%.

Online monitoring of transesterification reaction by medium-resolution benchtop 1H NMR and NIR spectroscopy

Despite the fact that there are many works treating new analytical approaches to monitor the transesterification reaction to produce biodiesel, only a few of them are able to quantify the minority, but important compounds, such as monoglyceride (MG) and diglyceride (DG), directly in the reaction medium for online quantification. Overcoming the lack of analytical applications in the biodiesel production, the present work proposes a new utilization of low-field proton nuclear magnetic resonance (LF-1H NMR) and near-infrared (NIR), applying Partial Least Squares (PLS) regression models, for the online monitoring of fatty acid methyl esters, triglycerides, diglycerides and monoglycerides. The compounds presented acceptable errors of prediction employing developed PLS models for the range of concentration, usually presented during the whole reaction time, except for the 1,2-diglyceride (1,2-DG).

Simulation-Based Sensitivity Analysis of Regularization Parameters for Robust Reconstruction of Complex Material’s T1 − T21H LF-NMR Energy Relaxation Signals

We recently showed, in a simulation study using two artificial signals, that our PDCO (Primal Dual interior method for Convex Objectives) reconstruction algorithm can be efficiently used for the reconstruction of low-field proton nuclear magnetic resonance (1H LF-NMR) relaxation signals into T1 (spin–lattice) vs. T2 (spin–spin) time 2D graphs of a material’s composition. In the present study, for highly complex materials, we demonstrate the PDCO’s reconstruction efficacy for a much wider range of simulated signals with higher complexity and different signal-to-noise ratios (SNR) taken from actual reconstructed 1H LF-NMR spectroscopy signals of oleic acid and cattle manure. The optimal regularization parameters of the PDCO’s reconstructing algorithm were identified for this large range of simulated LF-NMR signals and noise values. These simulated compact graphical and numerical representations demonstrated 1H LF-NMR relaxation signals of complex materials can be accurately reconstructed into T1 − T2 time graphs of a material’s chemical and morphology. The present study further confirmed that an optimal single set of regulatory parameters for the data reconstruction algorithms could be used for different materials or different batches of the same material.

Assessment of nutrient remobilization through structural changes of palisade and spongy parenchyma in oilseed rape leaves during senescence.

Differential palisade and spongy parenchyma structural changes in oilseed rape leaf were demonstrated. These dismantling processes were linked to early senescence events and associated to remobilization processes. During leaf senescence, an ordered cell dismantling process allows efficient nutrient remobilization. However, in Brassica napus plants, an important amount of nitrogen (N) in fallen leaves is associated with low N remobilization efficiency (NRE). The leaf is a complex organ mainly constituted of palisade and spongy parenchyma characterized by different structures and functions concerning water relations and carbon fixation. The aim of the present study was to demonstrate a specific structural evolution of these parenchyma throughout natural senescence in B. napus, probably linked to differential nutrient remobilization processes. The study was performed on 340 leaves from 32 plants during an 8-week development period under controlled growing conditions. Water distribution and status at the cellular level were investigated by low-field proton nuclear magnetic resonance (NMR), while light and electron microscopy were used to observe cell and plast structure. Physiological parameters were determined on all leaves studied and used as indicators of leaf development and remobilization progress. The results revealed a process of hydration and cell enlargement of leaf tissues associated with senescence. Wide variations were observed in the palisade parenchyma while spongy cells changed only very slightly. The major new functional information revealed was the link between the early senescence events and specific tissue dismantling processes.

Innovative Nondestructive Measurements of Water Activity and the Content of Salts in Low-Salt Hake Minces

Impedance spectroscopy (IS), low-field proton nuclear magnetic resonance (LF (1)H NMR), chloride titration, ion chromatography, and an ion selective electrode were used to investigate the physicochemical parameters and measure sodium and potassium contents in low-salt brines and fish. Salt solutions (0-3 w/w, %) and model products of minced hake with added NaCl (0.5-3.0 w/w, %), or a mixture of NaCl and KCl (50/50 w/w, %), were analyzed. Good correlation was observed between the sodium content determined by using the ion selective electrode method and ion chromatography (R(2) = 0.97). In both salt solutions and fish minces, the impedance spectroscopy measurements could detect the difference in salt contents in mince with salt contents down to 0.5%. The NMR transversal relaxation time T2 measurements clearly distinguished samples with 0, 0.5, and 1.0-3.0% salt, based on principal component analysis (PCA). Therefore, LF (1)H NMR seems to be a suitable technique for studies of low-salt products.

Proton NMR spin-diffusion studies of PS-PB block copolymers at low field: two- vs three-phase model and recalibration of spin-diffusion coefficients

Low-field proton nuclear magnetic resonance (NMR) methods were used to assess the phase fractions, domain thicknesses, T1 relaxation properties and spin diffusion (SD) coefficients D of different phases in nanophase-separated polystyrene-polybutadiene block copolymers. At low field, SD experiments are challenged by rather short longitudinal relaxation times (T1), requiring careful consideration of the interplay of T1 relaxation and SD effects. Building on earlier work, we used a numerical fitting procedure for a separate as well as combined analysis of phase-resolved rigid- and mobile-phase filtered SD, as well as saturation recovery curves taken on a well-defined lamellar sample. We demonstrate the advantages in using three-component model, distinguishing a rigid and a mobile, as well as an interphase that can be resolved by fits to the refocused free-induction decay. We further use domain sizes from small-angle X-ray scattering as a gauge and find that SD coefficients from literature calibrations are overestimated. Under static low-field conditions, D for the rigid polystyrene phase is found to be 0.38±0.06 nm2 ms−1, and we propose a rescaling of a literature calibration correlating D for the mobile phase with its T2 relaxation time.

Probing Asphaltene Aggregation in Native Crude Oils with Low-Field NMR

We show that low-field proton nuclear magnetic resonance (NMR) relaxation and diffusion experiments can be used to study asphaltene aggregation directly in crude oils. Relaxation was found to be multiexponential, reflecting the composition of a complex fluid. Remarkably, the relaxation data for samples with different asphaltene concentrations can be collapsed onto each other by a simple rescaling of the time dimension with a concentration-dependent factor xi, whereas the observed diffusion behavior is unaffected by asphaltene concentration. We interpret this finding in terms of a theoretical model that explains the enhanced relaxation by the transitory entanglement of solvent hydrocarbons within asphaltene clusters and their subsequent slowed motion and diffusion within the cluster. We relate the measured scaling parameters xi to cluster sizes, which we find to be on the order of 2.2-4.4 nm for an effective sphere diameter. These sizes are in agreement with the typical values reported in the literature as well as with the small-angle X-ray scattering (SAXS) experiments performed on our samples.

Using NMR Decay-time Measurements to Monitor and Characterize DNAPL and Moisture in Subsurface Porous Media

Knowing how environmental properties affect dense nonaqueous phase liquid (DNAPL) solvent flow in the subsurface is essential for developing models of flow and transport in the vadose zone necessary for designing remediation and long-term stewardship strategies. For example, one must know if solvents are flowing in water-wetted or solvent-wetted environments, the pore-size distribution of the region containing DNAPLs, and the impact of contaminated plumes and their transport mechanisms in porous media. Our research investigates the capability and limitations of low-field proton nuclear magnetic resonance (NMR) relaxation decay-rate measurements for determining environmental properties affecting DNAPL solvent flow in the subsurface. The measurements that can be performed with the laboratory low-field system can also be performed in situ in the field with the current generation of commercial borehole logging tools. The oil and gas industry uses NMR measurements in deep subsurface, consolidated formations to determine porosity and hydrocarbon content and to estimate formation permeability. These determinations rely on the ability of NMR to distinguish between water and hydrocarbons in the pore space and to obtain the distribution of pore sizes from relaxation decay-rate distributions. In this paper, we will show how NMR measurement techniques can be used to characterize, monitor, and evaluate the dynamics of mixed fluids (water-DNAPL) in unconsolidated near-surface porous environments, and describe the use of proton NMR [Formula: see text] (spin-spin relaxation time) measurements in unconsolidated sandy-soil samples to identify and characterize the presence of DNAPLs in these environments. The potential of NMR decay-rate distributions for characterizing DNAPL fluids in the subsurface and understanding their flow mechanisms has not previously been exploited; however, near-surface unsaturated vadose zone environments do provide unique challenges for using NMR measurements. These challenges are addressed through systematic laboratory experiments and a program of research to extend and adapt current field NMR measurements to near-surface environmental problems.

Characterization of water mobility in dry and wetted roasted coffee using low-field proton nuclear magnetic resonance

Roasted and ground coffee was studied by low-field 1H nuclear magnetic resonance at various water contents and temperatures. The spin–spin relaxation times ( T 2) were measured with single pulse free induction decay (FID) and Carr–Purcell–Meiboom–Gill (CPMG) sequences. Four relaxing components were distinguished: the solid population was observed with FID sequence at T 2s ∼9 μs; the other three populations, measured with the CPMG sequence, corresponded to an apolar phase, the coffee oil, and two polar phases. The two polar populations, observed at T 2m ∼6 ms and ∼27 ms (for coffee with 50% water content at 90 °C) were attributed to water in cell wall polymers and in water filling cells lumen. The T 2 values appeared relatively insensitive to temperature, showing an Arrhenius type evolution with no break due to an important structure change. Furthermore, the intensity of the mobile phase increased as a function of time up to ∼10 min after wetting, providing information about water absorption dynamics in roasted coffee.