Papers by Keyword: NMR

Abstract: This paper explains and demonstrates the aging performance and structure of bio-asphalt with analytical results from hot stage microscopy, infrared spectroscopic and nuclear magnetic resonance spectra. The experimental results showed that the aging of bio-asphalt is mainly caused by a large amount of coke substance generated during the process, and the addition of BHT can improve the aging resistance of bio-asphalt to some extent. Catalytic hydrogenation facilitate the removal of aldehyde, ketone and carbon-carbon double bond so as to strengthen the aging resistance of bio-asphalt, nuclear magnetic analysis further confirms the results from IR .

Abstract: The difference of movable fluid saturation of tight sandstone gas reservoir is researched, with transverse relaxation time (T₂) distribution derived from nuclear magnetic resonance technique (NMR). This article newly calculate T₂ cutoff value and elaborate the influence of pore structure on the occurrence characteristics of movable fluid. The study had revealed T₂ spectrum distribution includes the following types: (1) wide and flat single peak; (2) left single peak; (3) high left peak with low right peak. Movable fluid saturation is low, with class IV and class V movable fluid mainly. Pore structure control properties and percolation ability of rock reservoir and whether oil could be driven out depends on throat parameters of interconnected pores. Movable fluid saturation is low with bigger pore throat ratio, narrower pore throat distribution and higer pore structure heterogeneity.

Abstract: The tight rock often has low porosity, low permeability and poor pore connectivity, which it is difficult for formation evaluation. Nuclear Magnetic Resonance (NMR) logging is widely used in fluid typing and reservoir parameters determination to provide the information of porosity, permeability and pore size distribution. NMR relaxation mechanisms are characterized by the pore-scale petrophysical models. Monte Carlo algorithm describes the Brownian motion of fluid molecules in pore space. In the paper we setup a 3D digital core of the tight sandstone with X-ray computer tomography (CT) images to model NMR response with Monte Carlo random walk algorithm. We compared T₂ distributions from the numerical calculated pulse echo trains from the measurements. The results show that the simulated NMR response is consisted with the experiment.

Abstract: Nanometer scale Ca-deficient hydroxyapatite (nanoapatite) is a potential candidate as artificial bone substitute materials owing to its similarity to the bone with respect to composition, morphology and osteoclastic degradation or adsorbent materials for blood purification therapy to remove pathogenic substances. The initial biodegradation behaviors, the initial cell-material interaction and the protein adsorption properties of nanoapatite must depend on the microstructure. The purpose of this study is the preparation of nanoapatite particles and their structural characterization by using X-ray diffraction (XRD) and solid-state NMR spectroscopy. The nanoapatite particles were prepared by precipitation processing method, and the effects of magnesium ions on the precipitation of calcium phosphate were examined, because Mg ions are well-known to play a role of inhibition of crystal growth. The addition of Mg ions led to the precipitation of nanometer scale Ca-deficient apatite crystals having 1.33-1.63 of the molar ratio (Mg+Ca)/P. NMR analyses showed that the microstructure of Mg•HAp particles can be explained by a crystalline HAp core covered with a thin amorphous hydrated calcium phosphate layer.

Abstract: The hydration of cement is known to be a complex phenomenon. Although the broad pattern of reactions and microstructural development are known, a number of important questions remain unanswered. How to select the proper techniques is what the research people think of for now. This paper reviewed the domestic and international research progress and presented the advantages and disadvantages of these methods and the application prospects. Nuclear magnetic resonance spectroscopy (NMR), nanoindentation and electron microscopy techniques of cements were expounded in detail. Furthermore, through analyzing the results obtained by different research methods, the paper predicted the development prospect of advanced testing method of cement-based materials.

Abstract: A series of glass compositions with varying equimolar amounts of Na₂O:Al₂O₃ were designed using Appen factors. High purity batch reagents were ball milled for 30 min and transferred to Pt/Rh crucible and melted in an electric furnace (EHF1700, Lenton, UK) at high temperatures then held for 90 min. The molten glass was poured into a graphite mould, annealed at 50°C below the glass transition temperature for 1h and the remaining glass was quenched into water. Glass frits were crushed and ball milled into powders with different particle sizes. Glass powders (PS<125μm) were heat-treated via two-step heat treatment cycles and air quenched. Experimental glasses and glass-ceramics were characterised using X-Ray Diffraction (XRD), Dilatometry, Scanning Electron Microscopy (SEM) and solid state Nuclear Magnetic Resonance (NMR).

Abstract: Aerogels are porous materials with potential applications in fields ranging from thermal insulation, catalyst support, filters, electrical storage, components in optical devices, mechanical damping all the way to drug release. However, careful reliable characterization is the base for both, understanding of fundamental structure - property relationships as well as a directed development of materials and composites for specific applications. The review therefore addressed severe problem upon aerogel characterization that have been identified in the past and presents reliable non-destructive alternatives and novel methods that can be applied for the characterization of aerogels as well as their gel precursors.

Abstract: Nanomaterials are playing a more and more important role in all fields, leading to increasing its release into the environment. Nanomaterials may pose a potential threat to environment and human health. Thus, there is a growing need for adaptable methods and technologies to analyze and characterize the properties of nanoparticle for purpose of understanding and minimizing the potentially unforeseen health or environmental hazards. Nuclear Magnetic Resonance (NMR) method, as a powerful analytical tool which based on the theory of solvent relaxation, breaks through some limitations of conventional methods, making it feasible in analysis and characterization of nanoparticles in aqueous phase. This paper has sketched recent research about specific surface area determination and competitive adsorption between components on the surface of nanoparticles. It also pointed out the pros and cons of NMR and conventional methods. As a result, NMR solvent relaxation will be a promising application in future.

Abstract: In order to quantitatively analyze the contents and distribution of the moveable oil in tight oil reservoir, this research has done experiment on 12 representative cores. The total moveable oil saturation is between 5.17% and 43.30%. And the big throat controls less contents of moveable oil than the small one, throat radius between 0.02μm~0.1μm plays the leading role, and nanometer throat controls most of the pore space of moveable oil. Comparing with permeability higher than 0.1mD, permeability between 0.03mD~0.1mD, permeability between 0.01mD~0.03mD, permeability lower than 0.01mD, the first one has the biggest content of the total moveable oil, and its moveable oil is mainly controlled by throat radius between 0.02μm~1.0μm, while the moveable oil of permeability between 0.01mD~0. 1mD reservoir is mainly controlled by throat radius less than 0.1μm, and the other reservoir is mainly controlled by throat radius between 0.02μm~0.05μm.

Abstract: The electric and magnetic hyperfine interaction parameters (υ_Q, η, H_c) on ^47,49Ti nuclei in lanthanum and yttrium titanates were calculated in the cluster model by the unrestricted Hartree-Fock method. The calculation in the cluster approach describes the experimental data better than that in the frameworks of LDA and LDA+U model and modern crystal-field theory.