Porosity and Pore Size Distribution Measurement of Cement/Carbon Nanofiber Composites by ~1H Low Field Nuclear Magnetic Resonance

The dispersion effect of carbon nanofibers （CNFs） in aqueous solution and the mechanical properties, porosity, pore size distribution and microstructure of CNFs reinforced cement-based composites were investigated in this paper. To achieve effective dispersion of CNFs, a method utilizing ultrasonic processing and a commercially surfactant were employed. CNFs were incorporated to cementitious materials with the addition of 0.1 wt% and 0.2 wt% of cement with a water/cement ratio of 0.35. The mechanical properties of CNFs/ cement composites were analyzed, the porosity and pore size distribution were characterized by ^1H low field nuclear magnetic resonance （NMR）, and the microstructure was observed by scanning electron microscopy （SEM）. The results indicate that the optimum concentration ratio of MC to CNFs is 2：1 for dispersing in aqueous solution. Moreover, in the field of mechanical properties, CNFs can improve the flexural strength and compressive strength. The increased mechanical properties and the decreased porosity of the matrices correspond to the increasing CNFs content and CNFs act as bridges and networks across cracks and voids.

Utilization of nuclear magnetic resonance (NMR) in the determination of water status on rice seeds

The relation between seed viability and waterstatus in seed was studied.The experimentwas carried out at Zhongshan University.Seeds of hybrid rice Shanyou 63 were collectedfrom Guangdong Academy of Agriculture Sci-ences in 1993 and then stored for one year inopen air or with silica gel.Before and afterstorage,the relative content of free water andbound water in seeds were measured with

Application of nuclear magnetic resonance technology to carbon capture,utilization and storage:A review

Carbon capture,utilization and storage (CCUS) is considered as a very important technology for mitigating global climate change.Carbon dioxide (CO2) injected into an underground reservoir will induce changes in its physical properties and the migration of CO2 will be affected by many factors.Accurately understanding these changes and migration characteristics of CO2 is crucial for selecting a CCUS project site,estimating storage capacity and ensuring storage security.In this paper,the basic principles of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) technologies are briefly introduced in the context of laboratory experiments related to CCUS.The types of NMR apparatus,experimental samples and testing approaches applied worldwide are discussed and analyzed.Then two typical NMR core analysis systems used in CCUS field and a self-developed high-pressure,low-field NMR rock core flooding experimental system are compared.Finally,a summary of the current deficiencies related to NMR applied to CCUS field is given and future research plans are proposed.

Relaxation study of cement based grouting material using nuclear magnetic resonance

Aiming at actual condition of poor effect of hole sealing for the reason of poor cement paste fluidity in the process of coal mine gas drainage,by adding a water reducing agent,cement paste for hole sealing was produced.The changes of initial distribution,weighted average values and total relaxation signal intensity of transverse relaxation time(T 2) of water in pure cement paste and water reducing agent added cement paste were studied with low field proton nuclear magnetic resonance(NMR).The results show that there are four peaks in T2 distribution curves of cement paste:the first peak is related to the bound water in flocculation,the second and the third peaks are related to the water in flocculation,water reducing agent makes it extending towards the long relaxation time,increasing its liquidity,and the fourth peak is related to the free water.By using weighted average values of T2 and total relaxation signal intensity,hydration process of cement pastes could be roughly divided into four stages:the initial period,reaction period,accelerated period and steady period.By analyzing the periods,it makes sure that the grouting process should be completed in the reaction period in the site,and the drainage process should be started in the steady period.The results have great guiding significance to the hole sealing and methane drainage.

Investigation of reinforcement of the modified carbon black from wasted tires by nuclear magnetic resonance

Pyrolysis has the potential of transforming waste into recyclable products. Pyrolytic carbon black (PCB) is one of the most important products from the pyrolysis of used tires. Techniques for surface modifications of PCB have been developed. One of the most significant applications for modified PCB is to reinforce the rubber matrix to obtain high added values. The transverse relaxation and the chain dynamics of vulcanized rubber networks with PCB and modified PCB were studied and compared with those of the commercial carbon blacks using selective 1H transverse relaxation (T2) experiments and dipolar correlation effect (DCE) experiments on the stimulated echo. Demineralization and coupling agent modification not only intensified the interactions between the modified PCB and the neighboring polyisoprene chains, but also increased the chemical cross-link density of the vulcanized rubber with modified PCB. The mechanical testing of the rubbers with different kinds of carbon blacks showed that the maximum strain of the rubber with modified PCB was improved greatly. The mechanical testing results confirmed the conclusion obtained by nuclear magnetic resonance (NMR). PCB modified by the demineralization and NDZ-105 titanate coupling agent could be used to replace the commercial semi-reinforcing carbon black.

Review of nuclear magnetic resonance studies on iron-based superconductors

The newly discovered iron-based superconductors have triggered renewed enormous research interest in the condensed matter physics community. Nuclear magnetic resonance （NMR） is a low-energy local probe for studying strongly correlated electrons, and particularly important for high-Tc superconductors. In this paper, we review NMR studies on the structural transition, antiferromagnetic order, spin fluctuations, and superconducting properties of several iron-based high-Tc superconductors, including LaFeAsOl_xFx, LaFeAsOl_x, BaFe2As2, Bal_xKxFe2As2, Cao.23Nao.67Fe2As2, BaFe2（Asl_xPx）2, Ba（Fel_xRux）2As2, Ba（Fel_xCox）2As2, Lil＋xFeAs, LiFel_xCoxAs, NaFeAs, NaFel_xCoxAs, KyFe2_xSe2, and （T1,Rb）yFe2_xSe2.

Three dimensional structure prediction and proton nuclear magnetic resonance analysis of toxic pesticides in human blood plasma

The purpose of this study was to investigate the nuclear magnetic resonance （NMR） assignments of hydrolyzed products extracted from human blood plasma. The correlations between chemical, functional and structural prop- erties of highly toxic pesticides were investigated using the PreADME analysis. We observed that toxic pesticides possessed higher molecular weight and, more hydrogen bond donors and acceptors when compared with less toxic pesticides. The occurrence of functional groups and structural properties was analyzed using ~H-NMR. The ~H- NMR spectra of the phosphomethoxy class of pesticides were characterized by methyl resonances at 3.7-3.9 ppm （8） with the coupling constants of 11-16 Hz （Je-cns）. In phosphoethoxy pesticides, the methyl resonance was about 1.4 ppm （8） with the coupling constant of 10 Hz （Je-cH2） and the methylene resonances was 4.2-4.4 ppm （8） with the coupling constant of 0.8 Hz （Jp-cH3）, respectively. Our study shows that the values of four parameters such as chemical shift, coupling constant, integration and relaxation time correlated with the concentration of toxic pesticides, and can be used to characterise the proton groups in the molecular structures of toxic pesticides.

Nuclear magnetic resonance measurement station in SECUF using hybrid superconducting magnets

Nuclear magnetic resonance （NMR） is one of the most powerful tools to explore new quantum states of condensed matter induced by high magnetic fields at a microscopic level. High magnetic field enhances the intensity of the NMR signal, and more importantly, can induce novel phenomena. In this article, examples are given on the field-induced charge density wave （CDW） in high-To superconductors and on the studies of quantum spin liquids. We provide a brief introduction to the high magnetic field NMR platform, the station 4 of the Synergetic Extreme Condition User Facility （SECUF）, being built at Huairou, Beijing.

Characterization of Average Molecular Structure of Heavy Oil Fractions by ~1H Nuclear Magnetic Resonance and X-ray Diffraction

The chemical structure of heavy oil fractions obtained by liquid-solid adsorption chromatography was character-ized by 1 H nuclear magnetic resonance and X-ray diffraction.The molecular weight and molecular formula of asphaltene molecules were estimated by combining 1 H nuclear magnetic resonance and X-ray diffraction analyses,and were also ob-tained from vapor pressure osmometry and elemental analysis.Heteroatoms,such as S,N,and O atoms,were considered in the construction of average molecular structure of heavy oils.Two important structural parameters were proposed,including the number of alkyl chain substituents to aromatic rings and the number of total rings with heteroatoms.Ultimately,the av-erage molecular structures of polycyclic aromatics,heavy resins and asphaltene molecules were constructed.The number of α-,β-,γ-,and aromatic hydrogen atoms of the constructed average molecular structures fits well with the number of hydro-gen atoms derived from the experimental spectral data.

A model of unfrozen water content in rock during freezing and thawing with experimental validation by nuclear magnetic resonance

The unfrozen water content of rock during freezing and thawing has an important influence on its physical and mechanical properties.This study presented a model for calculating the unfrozen water content of rock during freezing and thawing process,considering the influence of unfrozen water film and rock pore structure,which can reflect the hysteresis and super-cooling effects.The pore size distribution cu rves of red sandsto ne and its unfrozen water conte nt under different temperatures during the freezing and thawing process were measured using nuclear magnetic resonance(NMR) to validate the proposed model.Comparison between the experimental and calculated results indicated that the theoretical model accu rately reflected the water content change law of red sandstone during the freezing and thawing process.Furthermore,the influences of Hamaker constant and surface relaxation parameter on the model results were examined.The results showed that the appropriate magnitude order of Hamaker constant for the red sandstone was 10J to 10J;and when the relaxation parameter of the rock surface was within 25-30 μm/ms,the calculated unfrozen water content using the proposed model was consistent with the experimental value.

Nuclear magnetic resonance study of the formation and dissociation process of nature gas hydrate in sandstone

In this work,the authors monitored the formation and dissociation process of methane hydrate in four different rock core samples through nuclear magnetic resonance(NMR)relaxation time(T_(2))and 2D imaging measurement.The result shows that the intensity of T_(2) spectra and magnetic resonance imaging(MRI)signals gradually decreases in the hydrate formation process,and at the same time,the T_(2) spectra move toward the left domain as the growth of hydrate in the pores of the sample accelerates the decay rate.The hydrate grows and dissociates preferentially in the purer sandstone samples with larger pore size and higher porosity.Significantly,for the sample with lower porosity and higher argillaceous content,the intensity of the T_(2) spectra also shows a trend of a great decrease in the hydrate formation process,which means that high-saturation gas hydrate can also be formed in the sample with higher argillaceous content.The changes in MRI of the sample in the process show that the formation and dissociation of methane hydrate can reshape the distribution of water in the pores.

Further discussion of CO_(2) huff-n-puff mechanisms in tight oil reservoirs based on NMR monitored fluids spatial distributions

Due to the poor physical properties of tight reservoirs,CO_(2) huff-n-puff(HNP)is considered a potential enhanced oil recovery(EOR)method after primary depletion.Optimization plays a critical role in the effective implementation of CO_(2) huff-n-puff.But the optimization requires a good understanding of the EOR mechanisms.In this work,the spatial distribution of oil saturation under different experimental conditions was analyzed by the NMR method to further discuss the HNP mechanisms.According to the variation of 1D frequency signal amplitude,we divided the core into the hardly movable area and movable area,the region with the obvious signal decline was defined as the movable area,and the hardly movable area was the region with limited signal decline.Based on that the recovery characteristics of different scenarios were evaluated.Firstly,the necessity of the soaking stage was studied,where three scenarios with different soaking times were carried out.Secondly,the injection pressure was adjusted to investigate the effect of the pressure gradient.The T_(2) spectra show that soaking has significantly improved the production of crude oil in small pores,and higher oil recovery in a single cycle is observed,but it is lower when the elapsed time(total operation time)is the same.31.03% of oil can be recovered after 3 cycles HNP,which increases to 33.8% and 37.06% for the 4 cycles and 6 cycles cases.As the pressure gradient increases,more oil is removed out of the matrix,and the oil in the deep part of the reservoir can be effectively recovered.During the CO_(2) huff-n-puff process,the oil distributions are similar to the solution gas drive,the residual oil is distributed at the close end of the core and the range that the oil can be efficiently recovered is limited.

基于干燥动力学结合LF-NMR分析的不同干燥过程中天麻切片水分变化

为探究天麻(Gastrodia elata Blume)切片干燥过程中水分迁移变化规律,并建立其量化表征方法,本研究采用低场核磁共振(Low-Field Nuclear Magnetic Resonance, LF-NMR)技术分析热风干燥(Hot Air Drying, HAD)和微波干燥(Microwave Drying, MWD)过程中不同热风温度(60、70、80℃)和不同微波功率密度(2、3、4 W/g)条件下的天麻切片,结合干燥特性曲线建立基于LF-NMR参数的天麻切片含水量预测模型。结果表明,MWD速率远大于HAD,在热风温度(60-80℃)和微波功率密度(2-4 W/g)范围内,高温、高功率密度有利于提高干燥速率,缩短干燥时间。Logarithmic模型可以准确描述天麻切片HAD和MWD过程中含水量的变化。经LF-NMR技术分析,在HAD和MWD过程中,天麻切片的横向弛豫时间曲线整体上呈现左移的趋势,各状态水的弛豫峰信号强度不断降低;干燥结束时天麻切片中的自由水完全被脱去,仅存少量的不易流动水和结合水。无论是HAD还是MWD,弛豫峰总面积A_(2)和天麻片的干基含水量相关性均在0.99以上。研究结果可为阐明天麻切片干燥机制和干燥工艺参数的优选提供参考。

ASSURE-NMR-HSQC实验检测保健食品中西地那非类物质

本研究通过使用灵敏度增强的带梯度形状脉冲进行异核单量子相干(HSQC)实验检测保健食品中违法添加的西地那非类物质。待测样品以甲醇溶解超声辅助提取,减压浓缩后以氘代DMSO溶解上机测试;利用Assure-NMR软件将得到的未知样品异核单量子相干(Heteronculear Single Quantum Coherence)谱图与已知西地那非类物质谱图进行模拟匹配。本方法检出限可以达到200μg·kg-1,能快速有效的对保健食品中西地那非类物质的违法添加侦察识别。该方法简便快捷,可以为食品安全监管部门提供一种新颖便捷的那非类物质监管稽查参考办法。

二维核磁共振评价页岩流体饱和度实验仿真

二维核磁共振(2D NMR)T_(1)-T_(2)测量在页岩油勘探中具有重要优势,但其数据处理与解释过程复杂,涉及抽象的理论知识。设计了一套基于Matlab图形用户界面的2D NMR T_(1)-T_(2)谱储层流体识别与饱和度评价实验仿真。仿真系统包括地层T_(1)-T_(2)谱模型构建、回波数据正演、回波数据反演以及流体识别与饱和度评价模块。通过输入不同参数,模拟得到页岩地层的T_(1)-T_(2)谱模型、回波数据、T_(1)-T_(2)谱反演结果以及页岩储层流体识别与饱和度评价结果。实验以直观、实用的方式向学生展示了基于2D NMR T_(1)-T_(2)谱的页岩储层流体识别与饱和度评价过程,增强学生对NMR数据处理与解释方法的理解,提高NMR教学效果。

基于低场核磁共振技术进行黄酒发酵进程监测及品牌的分析

该文对不同发酵阶段的黄酒样品进行低场核磁共振(low-field nuclear magnetic resonance,LF-NMR)检测,比较了陈酿时间、酒精度和品牌对黄酒低场核磁弛豫特性的影响,最后对9个品牌黄酒的LF-NMR弛豫信息进行了主成分分析。结果表明,发酵后样品的单组分弛豫时间(T_(2W))显著缩短,而陈酿后黄酒的T_(2W)又相对延长。多组分弛豫图谱(T_(2))表明,对照组和浸米样品均只有1个峰。发酵后样品的T_(2)图谱均出现2个峰。从第一次发酵到煎酒期间,T_(21)和T_(22)不断缩短,而陈酿期间T_(21)和T_(22)相对延长。同一品牌及陈酿时间的黄酒,酒精度越大,体系的T_(2W),T_(21)和T_(22)越短;同一品牌及酒精度下,陈酿时间仅对T_(21)有一定影响。不同品牌黄酒因酿造工艺的区别而使弛豫分布有一定特点。主成分分析表明,不同酒精度、陈酿时间、品牌及种类的黄酒的弛豫特性的PCA分布及间距不同。说明应用LF-NMR技术可实现对不同工艺生产的黄酒的快速辨别。

震动载荷多次作用下烟煤孔裂隙结构演化特征试验研究

煤层开采过程中频繁采掘扰动或远场顶板周期性破断会产生多次的震动载荷,震动载荷对于煤样微观孔裂隙结构和宏观力学行为具有重要影响。为探索震动载荷下煤样孔裂隙结构演化特征,选取烟煤煤样,利用霍普金森压杆(SHPB)试验系统开展了多次震动载荷冲击煤样试验,借助低场核磁共振分析仪测试了每次冲击后煤样T_(2)谱,并通过核磁共振成像(MRI)分析了煤样孔裂隙分布及其损伤演化特征。结果表明,随着震动载荷作用次数增加,煤样峰值应力与动态弹性模量均呈现线性下降趋势,震动载荷冲击效应使得煤样承载和抵抗变形能力显著弱化,因此有必要对煤样孔裂隙演化特征展开深入分析。从T_(2)谱和MRI信息得出,震动载荷初次作用下煤样总体孔隙体积大幅增加,其中吸附孔体积增高达5.0倍,随着震动载荷持续作用,煤样微裂隙开始连通汇聚形成宏观裂纹,使得渗流孔之间连通性大幅提高,煤样总体孔隙率达到峰值,较煤样原始孔隙率提高约6倍。在煤样受震动载荷损伤、破坏的整个过程中,渗流孔的连通性逐渐提高与改善,其分形维数呈线性下降趋势。通过核磁共振成像揭示了震动载荷对煤样孔裂隙作用机制,结果表明煤样中部区域孔隙最先发育并逐步形成微裂隙,在后续震动波反射、拉伸作用下,损伤破坏区域向两侧逐渐演变直至贯通试样。

酸化对高阶煤不同层理方向增透效果影响研究

为了研究酸化对寺河矿高阶煤垂直、平行两个层理方向的增透效果,开展了多组分酸煤粉和煤柱溶蚀试验,优选出了合适的酸液体系,分析了两个层理方向煤柱不同酸化时长下的溶蚀效果,并进行了两个层理方向煤柱的煤岩三轴吸附-解吸-渗流试验和低场核磁共振试验,对比了酸化前后的渗透率、孔隙度、孔径分布变化。结果表明:(1)寺河矿酸化选用质量分数2%HCl+2%CH3COOH+5%HF的酸液配比溶蚀效果最优;(2)酸化使垂直层理方向煤柱的孔隙率增幅更大,而平行层理方向煤柱达到最大增幅用时更短;(3)酸化后两个层理方向煤柱的渗透率、孔隙度均提升,垂直层理方向煤柱孔隙度增幅更大,渗透率增幅则小于平行层理方向煤柱,且二者的渗透率增幅都在滑脱效应拐点处最小;(4)酸化使两个层理方向煤柱的瓦斯吸附孔占比下降,其中平行层理方向煤柱降比更大,且酸化前后中大孔占比也都更高;确定了寺河矿酸化后以煤样平行层理方向作为钻孔瓦斯抽采方向能更好地提高瓦斯抽采率。

核磁共振测井在古龙页岩油评价中的应用

古龙页岩油储层黏土含量高,孔隙结构较为复杂,微米-纳米孔喉及微裂缝发育,利用常规方法评价储层孔隙结构及物性、含油性具有较大难度。针对以上难题,在岩石物理实验基础上,提出了核磁共振变T_(2)谱截止值有效孔隙度计算方法和考虑小孔隙含油的二维核磁共振含油饱和度计算模型,并通过核磁共振区间孔隙度分析,厘清了古龙页岩储层孔隙结构。利用该方法计算的有效孔隙度平均相对误差为7.3%,含油饱和度平均绝对误差为4.0%,这不仅提高了计算储量关键参数的解释精度,还为后续开发提供了技术保障。该技术流程和方法对于类似页岩油的有效孔隙度和含油饱和度的评价同样具有指导意义,有助于推动页岩油等非常规油气资源的开发利用。

CO_(2)-C_(2)H_(6)吞吐提高致密油藏采收率实验研究

注CO_(2)已经成为致密油藏提高采收率的重要手段之一,相较于纯CO_(2),部分烃类气体对原油的降黏及混相能力更强。为此,通过高温高压PVT实验研究了CO_(2)及复合气体(CO_(2)-C_(2)H_(6))-原油的饱和压力及黏度的变化特征,并利用高温高压岩心吞吐实验揭示了不同气体介质、吞吐压力及吞吐轮次下原油动用程度。研究结果表明:复合气体中C_(2)H_(6)增强了气液两相混相能力,提高了CO_(2)降黏及溶解能力,原油流动性显著增加。复合气体中随着C_(2)H_(6)摩尔分数的增加,原油饱和压力由14.24 MPa增至18.02 MPa,提高了26.54%;原油黏度由23.68 mPa·s降至8.76 mPa·s。不同吞吐压力下复合气体(CO_(2)-C_(2)H_(6))的采收率提高效果均强于纯CO_(2)的,且吞吐压力在最小混相压力附近采收率提高程度高于其他吞吐压力。复合气体(CO_(2)-C_(2)H_(6))对孔隙半径为0.0001~0.001和0.01~1μm孔隙中的原油动用程度强于纯CO_(2)的。