NMR SPECTROSCOPY

CROSS REFERENCE TO RELATED APPLICATIONS

[001] This application claims priority to U.S. Provisional Patent Application No.

62/568,072, filed October 4, 2017, the entire content of which is hereby incorporated by reference.

BACKGROUND

[002] Nuclear Magnetic Resonance (NMR) is based on the fact that when a population of magnetic nuclei is placed in an external magnetic field, the nuclei become aligned in a predictable and finite number of orientations. It is a nondestructive evaluation technique useful for characterizing organic matrix composites and other polymer based materials. NMR depends on the interaction between the nuclear magnetic moment and a magnetic field and thus it is sensitive to localized field variations caused by molecular motions, changes in molecular or crystal structure, and chemical composition differences.

[003] A common application of NMR to material science involves measurement of the hydrogen nucleus (proton) NMR signal. The proton NMR signal is very strong and easily measured. Much of the physical and chemical information available through the use of NMR is associated with the relaxation characteristics of the nuclear magnetic moments, which can be measured using pulsed NMR techniques. The energy exchange between nuclear moments and the surrounding lattice is characterized by the spin-lattice relaxation time, Ti, while the energy exchange among nuclear magnetic moments is described by the spin-spin relaxation time, T ₂ . These relaxation times are very sensitive to molecular motions and structural changes and can be used to provide both qualitative and quantitative information on the dynamic environment in which the nuclei are located. Proton NMR has been used to characterize water absorption, molecular diffusion, environmental degradation, aging, degree of cure, and modulus variations.

[004] NMR Relaxation technique is widely used as a diagnostic method in biology, medical, material science, engineering aspects. Researches also use proton NMR to study metal- hydrogen (e.g. n-Pd-Ho.7) nanoparticles. However, no one has use this technique in calibrating reactors involving hydrogen gas.

[005] In- situ system calibration is a critical and relatively unexplored field in reactions involving hydrogen gas and metal lattice interactions. For example, it is difficult to monitor the hydrogen/deuterium loading status in metal lattices (e.g., the amount of hydrogen absorbed in Pd metal). Traditionally, people monitor the system resistance, the hydrogen gas pressure/volume to determine the loading ratio. These methods are susceptible of side reactions, change of outer conditions etc. and have limited accuracy. Also, it remains challenging to probe chemical environment, the interactions between metal lattice and hydrogen/deuterium atoms. These factors are important to understand and monitor for any operating hydrogen reactors.

SUMMARY OF THE INVENTION

[006] This disclosure describes a design of a micro NMR device, and the method of monitoring its signals including free induction decay (FID), and relaxation time (Ti or T ₂ ), to achieve in-situ system calibration in hydrogen gas reactions with solids materials. Specifically, this disclosure describes an in-situ system calibration method using NMR technique by monitoring the hydrogen relaxation time, free induction decay (FID), Ti and/or T ₂ in nuclear magnetic resonance. Ti and T ₂ are extremely sensitive to dynamics of the molecular mobility in the hydrogen environment. So the free hydrogen and lattice hydrogen have different relaxation time. Therefore, this technique can efficiently and accurately monitor the interactions between hydrogen and metal lattices, and recognize the ideal loading status. With predetermined calibration parameters, we can obtain in- situ system calibration and diagnosis for reactors. One of ordinary skill in the art will appreciate that references to hydrogen throughout the

specification may refer to all stable isotopes of hydrogen including protium, deuterium, and/or tritium.

[007] In one embodiment of the present invention, an NMR system for measuring hydrogen loading status in a hydrogen reactor may include a reaction chamber having an interior reaction area. The system may further include a helical coil disposed around the interior reaction area. The helical coil may be capable of generating an RF pulse and detecting free induction decay (FID) signals. The system may further include a magnet disposed around the helical coil. The magnet may create a uniform magnetic field substantially perpendicular to the RF pulse generated by the helical coil.

[008] In another embodiment of the present invention, a method for measuring hydrogen loading status in a hydrogen reactor may include disposing a helical coil around an interior reaction area of a reaction chamber. The helical coil may be capable of generating an RF pulse and detecting free induction decay (FID) signals. The method may further include disposing a magnet around the helical coil. The magnet may create a uniform magnetic field substantially perpendicular to the RF pulse generated by the helical coil. The method may further include generating calibration data by: emptying the interior reaction area of the reaction chamber, generating an RF pulse from the coil during all reaction stages of the hydrogen reactor, collecting the calibration FID signals generated as a result of the RF pulse during all stages of the hydrogen reactor, calculating a calibration spin-lattice relaxation time (T from the FID signals through exponential fitting, calculating a calibration spin-spin relaxation time (T ₂ ) from the FID signals through exponential fitting, and recording the calibration FID signals, calibration Ti, and calibration T ₂ as a function of time. The method may further include generating reaction data by: placing reactants into the interior reaction area of the reaction chamber, generating an RF pulse from the coil during all reaction stages of the hydrogen reactor, collecting the reaction FID signals generated as a result of the RF pulse during all reaction stages of the hydrogen reactor, calculating a reaction spin-lattice relaxation time (TO from the FID signals through exponential fitting, calculating a reaction spin-spin relaxation time (T ₂ ) from the FID signals through exponential fitting, and recording the reaction FID signals, reaction Ti, and reaction T ₂ as a function of time. The method may further include calculating the hydrogen loading status at a given time by comparing the reaction Ti/reaction T ₂ ratio at a given time to the calibration Ti/calibration T ₂ ratio at the given time.

[009] In another embodiment of the present invention, a signal amplifier may be coupled to the helical coil.

[0010] In another embodiment of the present invention, an analog digital converter is coupled to the amplifier.

[0011] In another embodiment of the present invention, the reactants comprise a metal lattice and at least one of hydrogen or deuterium.

[0012] In another embodiment of the present invention, the coil is disposed outside the reaction chamber. [0013] In another embodiment of the present invention, the reaction chamber is comprised of a non-conductive material.

[0014] In another embodiment of the present invention, the reaction chamber is at least one of ceramic or quartz.

[0015] In another embodiment of the present invention, all reaction stages of the hydrogen reactor comprise the initial stage, operation stage, and the termination stage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1A is a diagram of an NMR system for measuring hydrogen loading status in a hydrogen reactor according to an embodiment of the present invention.

[0017] FIG. IB is a diagram of an NMR system for measuring hydrogen loading status in a hydrogen reactor according to an embodiment of the present invention.

[0018] FIG. 2A is a detailed diagram of an NMR system for measuring hydrogen loading status in a hydrogen reactor according to an embodiment of the present invention.

[0019] FIG. 2B is a cross-section diagram of an NMR system for measuring hydrogen loading status in a hydrogen reactor according to an embodiment of the present invention.

[0020] FIG. 3A is a representation of NMR raw spectra according to an embodiment of the present invention.

[0021] FIG. 3B is a representation of FID signals, plotted as induced voltage versus signal relaxation time, and its exponential fitting, according to an embodiment of the present invention. [0022] FIG. 4 is a representation of NMR spectra from the Fourier transform of the FID signals, plotted as intensity versus frequency, according to an embodiment of the present invention.

[0023] FIG. 5 is a representation of the relationship between FID relaxation time and the hydrogen loading status according to an embodiment of the present invention.

[0024] FIG. 6 is a representation of the relationship between T ₂ and the hydrogen loading status according to an embodiment of the present invention.

[0025] FIG. 7 is a representation of the relationship between Ti and the hydrogen loading status according to an embodiment of the present invention.

[0026] FIG. 8 is a representation of the relationship between Ti/T ₂ ratio and the hydrogen loading status.

DETAILED DESCRIPTION

[0027] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. One skilled in the art will recognize that the embodiments of the invention may be practiced without these specific details or with an equivalent arrangement. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention.

[0028] The presently disclosed subject matter is presented with sufficient details to provide an understanding of one or more particular embodiments of broader inventive subject matters. The descriptions expound upon and exemplify particular features of those particular embodiments without limiting the inventive subject matters to the explicitly described embodiments and features. Considerations in view of these descriptions will likely give rise to additional and similar embodiments and features without departing from the scope of the presently disclosed subject matter.

[0029] The NMR diagnostic system adopts the conventional NMR configuration, includes a coil closely surrounding the reactor, and a magnet creating a uniform magnetic field perpendicular to the applied radio frequency (RF) pulse. The embodiments described below use exothermic reactors as examples. Those exothermic reactors use metal hydride as reactants and the hydrogen loading ratio achieved by the metal hydride is an important indication of the reactor's efficacy. An in-situ hydrogen loading measurement device using NMR techniques becomes a useful calibration tool of the exothermic reactors.

[0030] Referring now to FIGS. 1A-2B, an NMR system 1 for measuring hydrogen loading status according to an embodiment of the present invention is shown. The system 1 may comprise a reaction chamber 10 having an interior reaction area 11. The system 1 may further comprise a helical coil 12 disposed around the interior reaction area 11, wherein the helical coil 12 is capable of generating an RF pulse and detecting free induction decay (FID) signals. The system 1 may further comprise a magnet 13 around the helical coil 12, wherein the magnet 13 creates a uniform magnetic field Bi substantially perpendicular to the RF pulse generated by the helical coil 12.

[0031] FIG. 1A depicts an embodiment in which the helical coil 12 is disposed outside the reaction chamber 10. In such embodiments, the reaction chamber 10 may be comprised of non-conductive material, preferably material that is non-conductive as to electricity, heat, and sound. Highly conductive metal can produce inductive current under alternating electromagnetic field, and disturb NMR signals, so if helical coil 12 is disposed outside the reaction chamber 10, the reaction chamber 10 cannot be made of metal. Ceramic and quartz are preferable choices for reaction chamber 10 materials in such embodiments.

[0032] FIG. IB depicts an embodiment in which the helical coil 12 is disposed inside the reaction chamber 10. In such embodiments, the helical coil 12 is disposed inside the reaction chamber 10, but surrounds the reactants inside the reaction chamber 10. If the helical coil 12 is inside of the reaction chamber 10, there is no restriction in reaction chamber materials. The reaction chamber surface may also be made of the permanent magnet itself, with the helical coil 12 attached to the inside of the magnet 12. Also, the device is not suitable to test bulk metal piece (metal rod etc.), but can be used to analysis metal thin films, metal nanoparticles, metal oxides, metal hydrides, gases, solutions etc.

[0033] The helical coil 12 is a RF pulse generator as well as a signal detector. The RF pulse is usually in MHz range, and the relationship between a nucleus' frequency v and magnetic field strength of the permanent magnet 13 is given by Equation 1. The RF pulses used here are 21 and 53 MHz for H-Pd system.

[0034] v = Hz

2π

[0035] Equation 1

[0036] In this equation, Hz is the RF frequency, γ is the gyromagnetic ratio ( 26.7522128 x 10 7 rad T - ^" 1 s - ^" 1 for proton), and Bi is the magnetic field strength of the magnet 13 expressed in Tesla.

[0037] Under the magnetic field Bi, the applied RF pulse excites the hydrogen nuclei, and then relax during the signal acquisition time, giving an NMR signal due to an oscillating voltage induced by the precession of the nuclear spin in the X-Y plane. This results in the observed exponentially decaying sine wave, as shown in FIGS. 3A-3B. This decaying sine wave is termed free induction decay (FID). The induced current may then goes through the current amplifier 14 and an analog digital converter 15, and become digital current signals (NMR signal) being detected.

[0038] The direction of the magnet 13 does not have to be perfectly perpendicular to the

RF pulse, however, the device is optimized when the magnetic field B ₁ and RF pulse are perpendicular. The magnet 13 can be permanent magnet or magnetic coil, as long as there are sufficient uniform magnetic field inside the magnet 13 that can cover the helical coil 12. Magnet 13 is depicted in FIGS. 1 and 2 as partially covering the reaction chamber 10 for illustrative purposes only. The system 1 may partially or entirely cover the reaction chamber 10

[0039] Referring now to FIG. 2B the system 1, shaped like a donut with the reaction chamber 10 sitting in the middle, should have smooth inner surface and may be attached and detached to the reaction chamber 10 easily.

[0040] Referring now to FIG. 9, according to another embodiment of the present invention, a method for measuring hydrogen loading status in a hydrogen reactor using NMR spectroscopy is provided. The method may comprise disposing a helical coil around an interior reaction area of a reaction chamber 900, wherein the helical coil is capable of generating an RF pulse and detecting free induction decay (FID) signals. The method may further comprise disposing a magnet around the helical coil 901, wherein the magnet creates a uniform magnetic field substantially perpendicular to the RF pulse generated by the helical coil. The method may further comprise generating calibration data 902 by: emptying the interior reaction area of the reaction chamber, generating an RF pulse from the coil during all reaction stages of the hydrogen reactor, collecting the calibration FID signals generated as a result of the RF pulse during all reaction stages of the hydrogen reactor, calculating a calibration spin-lattice relaxation time (T from the FID signals through exponential fitting, calculating a calibration spin-spin relaxation time (T ₂ ) from the FID signals through exponential fitting, and recording the calibration FID signals, calibration Ti, and calibration T ₂ as a function of time 903.

[0041] The method may further comprise generating reaction data 904 by: placing reactants into the interior reaction area of the reaction chamber, generating an RF pulse from the coil during all reaction stages of the hydrogen reactor, collecting the reaction FID signals generated as a result of the RF pulse during all reaction stages of the hydrogen reactor, calculating a reaction spin-lattice relaxation time (TO from the FID signals through exponential fitting, calculating a reaction spin-spin relaxation time (T ₂ ) from the FID signals through exponential fitting, and recording the reaction FID signals, reaction Ti, and reaction T ₂ as a function of time 905. The method may further comprise calculating the hydrogen loading status 906 at a given time by comparing the reaction Ti/reaction T ₂ ratio at a given time to the calibration Ti/calibrationT ₂ ration at a given time.

[0042] Based on the chemical environment of hydrogen (free hydrogen atoms or photons, in the lattice), concentration and the distance between each hydrogen nuclei, each stage

(initializing, triggering, and operating) has its own characterization FID, Ti and T ₂ signals. A calibration database will be generated by collecting data for the initial system before any activation, fully operating systems, and deactivated systems. The NMR measurement will be performed during the entire process, and Ti and T ₂ would be derived from the FID signals that collected by the coil and received by the amplifier and ADC. The data acquisition starts before any activation of the system, and kept collecting data during the activation process, normal operation, until the reactor has been shut down and achieve stable status.

[0043] During the calibration, the applied voltage intensity and frequency in the coil will be tuned and accurately monitored by the ADC at the beginning of each step (before activation, during activation, after activation, and termination) and kept constant.

[0044] During the calibration, a calibration plot will be generated with four parameters

(FID intensity, duration, derived Ti and T ₂ ) vs reaction time, with the key event labeled

(initialize, activation, reacting and termination).

[0045] During the calibration, the signals of an empty reactor (container) will be collected under the same parameters, and be used as a background signal. The calibration methodology is described in the procedures in further detail below. Once the calibration database is established, the device can be applied to the in-situ system to calculate the progress of the reaction by performing NMR technique and monitoring FID, Ti and T ₂ during each stage of the reaction.

[0046] PROCEDURES

[0047] Generate a Calibration Database

[0048] There are three reaction stages in an entire process: initial stage (before any reaction starts), operation stage (including the initial activation and operation stages), and the termination (including reactor shutting down and returning to the original stable status). The calibration process will be performed over the entire process with an empty reaction chamber and be used as background or calibration data.

[0049] Under a constant magnetic field, an RF pulse is produced by the helical coil. The

FID signal from the induced current in the coil is recorded after passing through the current amplifier and the analogue digital converter.

[0050] The data is collected over all three reaction stages: initial stage, operation stage, and termination stage.

[0051] The data may be recorded as a calibration plot over all three stages. The parameter (the current and RF pulse frequency in the helical coil) can be adjusted to achieve the best signal intensity at the beginning of each stages according to methods known in the art.

[0052] Data Processing

[0053] FID signals: under the magnetic field and the RF pulse perpendicular to it, the induced current is sent to an amplifier and analogue digital converter, and its intensity and decay time is recorded and analyzed. The signal intensity and decay time is related to the hydrogen chemical environment and concentration.

[0054] Ti and T ₂ is obtained by a conventional NMR technique by performing exponential fitting of RF pulse frequency versus magnetization intensity data. Conventionally, Ti is measured by applying a pulsed current with a sine wave shape, but the present invention uses a pulsed current with a square wave shape. [0055] Reaction Measurements

[0056] During the actual reaction, a current pulse identical to the current pulse applied in the calibration procedure is applied. The raw spectra of the FID signal is recorded and Ti and T ₂ are derived through exponential fitting, by comparing and diagnose the system, as shown in FIGS. 3A-4. A significant decrease in FID relaxation time, as well as Ti and T ₂ — compared to the corresponding calibration values— is expected when hydrogen is loaded into the lattice, as depicted in FIGS. 5-7.

[0057] By comparing the ratio of Ti/T ₂ in the reaction to the Ti/T ₂ ratio in the calibration, the hydrogen loading status in the lattice can be obtained, as shown in FIG. 8. In addition, the Ti relaxation rate (Ri) of hydrogen in the nanocrystalline particles is significantly greater than hydrogen in coarse-grained systems. For example, at 155 K the measured Ri for PdHo _.7 (at 21 MHz) is 33 s ^"1 , as compared with 4.6 s ^"1 for hydrogen in the coarse-grained system. Accordingly, this method may also be used to measure particle size by analyzing Ti/Ri ratios during the operation stage.

[0058] The above description and drawings are illustrative and are not to be construed as limiting the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. Numerous specific details are described to provide a thorough understanding of the disclosure. However, in certain instances, well-known or conventional details are not described in order to avoid obscuring the description.

[0059] Reference in this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments.

[0060] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling of connection between the elements can be physical, logical, or any combination thereof. Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0061] The teachings of the disclosure provided herein can be applied to other systems, not necessarily the system described above. The elements and acts of the various embodiments described above can be combined to provide further embodiments. [0062] These and other changes can be made to the disclosure in light of the above

Detailed Description. While the above description describes certain embodiments of the disclosure, and describes the best mode contemplated, no matter how detailed the above appears in text, the teachings can be practiced in many ways. Details of the system may vary

considerably in its implementation details, while still being encompassed by the subject matter disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the disclosure should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the disclosure with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the disclosure to the specific embodiments disclosed in the

specification, unless the above Detailed Description section explicitly defines such terms.

Accordingly, the actual scope of the disclosure encompasses not only the disclosed

embodiments, but also all equivalent ways of practicing or implementing the disclosure under the claims.

[0063] The terms used in this specification generally have their ordinary meanings in the art, within the context of the disclosure, and in the specific context where each term is used. Certain terms that are used to describe the disclosure are discussed above, or elsewhere in the specification, to provide additional guidance to the practitioner regarding the description of the disclosure. For convenience, certain terms may be highlighted, for example using capitalization, italics and/or quotation marks. The use of highlighting has no influence on the scope and meaning of a term; the scope and meaning of a term is the same, in the same context, whether or not it is highlighted. It will be appreciated that same element can be described in more than one way. [0064] Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and is not intended to further limit the scope and meaning of the disclosure or of any exemplified term. Likewise, the disclosure is not limited to various embodiments given in this specification.

[0065] Without intent to further limit the scope of the disclosure, examples of instruments, apparatus, methods and their related results according to the embodiments of the present disclosure are given below. Note that titles or subtitles may be used in the examples for convenience of a reader, which in no way should limit the scope of the disclosure. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. In the case of conflict, the present document, including definitions will control.

[0066] Some portions of this description describe the embodiments of the invention in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, computationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. Furthermore, it has also proven convenient at times, to refer to these arrangements of operations as modules, without loss of generality. The described operations and their associated modules may be embodied in software, firmware, hardware, or any combinations thereof.

[0067] Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

[0068] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the presently disclosed subject matter pertains. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the presently disclosed subject matter, representative methods, devices, and materials are now described.

[0069] Following long-standing patent law convention, the terms "a", "an", and "the" refer to "one or more" when used in the subject specification, including the claims. Thus, for example reference to "an additive" can include a plurality of such additives, and so forth.

[0070] Unless otherwise indicated, all numbers expressing quantities of components, conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the instant specification and attached claims are

approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter. [0071] As used herein, the term "about", when referring to a value or to an amount of mass, weight, time, volume, concentration, and/or percentage can encompass variations of, in some embodiments +/-20%, in some embodiments, +/-10%, in some embodiments +/- 5%, in some embodiments +/-1%, in some embodiments +/-0.5%, and in some embodiments, +/-0.1%, from the specified amount, as such variations are appropriate in the disclosed products and methods.