NMR MAS rotor with external support for increased load capacity

Abstract

An NMR MAS rotor (10) comprises an inner sleeve (10i) which is surrounded by at least one outer sleeve (10a) of a different material, wherein the maximum diameter dmax of the NMR MAS rotor perpendicular to a rotor axis (a) is less than 5 mm, and wherein the NMR MAS rotor is constructed in such a way that, during the NMR measurement, it can be rotated at a rotational frequency fMAS of at least 20 kHz while tilted by a MAS angle relative to the direction of the NMR magnetic field, the NMR MAS rotor being characterized in that the materials of the inner and outer sleeve(s) and the respective consistencies thereof are selected in such a way that the NMR MAS rotor can be used to carry out solid-state NMR measurements such that the inner sleeve and the outer sleeve remain integrally, force-lockingly or form-lockingly connected to each other, and in that the material combinations of the inner and the outer sleeve(s) have the following ratio of the quotients Sinnen and Saußen of their associated density Dinnen or Daußen and their associated mechanical yield point Rinnen or Raußen: Sinnen / Saußen ≥ 2, with Sinnen = Dinnen / Rinnen and Saußen = Daußen / Raußen. This allows a considerable increase in the rotational speed for the same body geometry and the same material, without taking into account the driving gas and without special measures for sealing liquid samples. The rotor can be loaded with larger amounts of pulverulent sample material without having to worry about the NMR MAS rotor being destroyed.

Description

[0001] NMR MAS rotor with external support for increased load capacity

[0002] The invention relates to an NMR-MAS rotor for receiving sample substance for carrying out NMR measurements in a homogeneous region of an NMR magnetic field, wherein the NMR-MAS rotor comprises an inner sleeve which is surrounded by at least one outer sleeve which has a different material from the inner sleeve, wherein the maximum diameter dmax of the NMR-MAS rotor transverse to a rotor axis is less than 5 mm, and wherein the NMR-MAS rotor is mechanically constructed and designed such that it can be rotated inclined against the direction of the NMR magnetic field by a MAS angle during the NMR measurement with a rotation frequency fMAs of at least 20 kHz.

[0003] An NMR MAS rotor with these features for the analysis of liquid NMR samples is known per se from US Pat. No. 6,054,857 A (= reference [1]). Background of the invention

[0004] The present invention generally relates to the field of magnetic resonance. Nuclear magnetic resonance (NMR) spectroscopy is a commercially widely used, highly efficient method of instrumental analysis for characterizing the chemical composition of substances or for determining the structure of substances in samples. Radiofrequency pulses are radiated into a sample placed in a strong, static magnetic field, which causes the nuclear spins in the sample to align, and the electromagnetic response of the sample is measured. The information is then acquired integrally over a specific area of ​​the sample, the so-called active volume, and evaluated to determine the chemical composition.

[0005] The sample substance, typically in solid or liquid form, is filled into a substantially cylindrical sample tube. For measurement, it is placed in the measuring area of ​​an NMR probe head of an NMR apparatus. There, the sample substance is exposed to a strong, static magnetic field with a flux density Bo that is homogeneous in the z-direction, causing the nuclear spins in the sample substance to align. High-frequency electromagnetic pulses are then radiated into the sample. This, in turn, generates high-frequency electromagnetic fields, which are detected in the NMR apparatus. Information about the properties of the sample can be obtained from the detected RF fields. In particular, the position and intensity of NMR lines can be used to determine the chemical composition and chemical bonding conditions in the sample.

[0006] This is demonstrated, for example, in DE 10 2020 204 379 B3 « EP 3 889 630 B1 « US 11 073 579 B1 « JP 7079770 (= reference [2]), which specifically describes the design of a magnetically compensated NMR rotor. In solid-state NMR spectroscopy, it is also known to rotate an NMR sample at a high frequency (typically several kHz) at the so-called "magic angle" of arcta / 2 « 54.74° relative to the static magnetic field during spectroscopic measurements ("MAS" = magic angle spinning). For this purpose, the sample is loaded into a MAS rotor. MAS rotors are typically cylindrical tubes open at one end and sealed with a cap. The cap is equipped with vane elements, particularly paddle wheels. The MAS rotor is mounted in a MAS stator, and the MAS rotor is driven by gas pressure via the vane elements to rotate.The combination of the MAS rotor and MAS stator is called the MAS turbine.

[0007] This is set out, for example, in EP 3 301 467 B1 « US 10,459,044 B2 « JP 6517896 B2 « CN 107870309 B (= reference [3]), where specifically an improved temperature control of an NMR-MAS rotor is described.

[0008] Specific state of the art

[0009] A general trend in MAS technology is toward operating MAS rotors at ever-increasing rotation frequencies. The literature consistently cites the speed of sound of the drive gas as a limiting factor. The effectiveness of nitrogen as a drive gas diminishes even before the speed of sound is reached. Other gases (e.g., helium) exhibit advantageous properties for use in MAS systems for solid-state NMR with MAS rotors that require particularly fast rotation due to their higher speed of sound and / or different viscosity.

[0010] For example, US Pat. No. 5,508,615 A ​​(=reference [4]) describes a "supersonic sample spinner," i.e., an NMR MAS rotor designed to rotate in the supersonic range. According to reference [4], this can be operated either purely with helium (i.e., supported and driven) or with a helium / nitrogen mixture to reduce bearing heating caused by the rapid rotation of the NMR MAS rotor. Up to 5% helium in nitrogen should therefore be possible without causing significant problems with voltage flashover between the MAS rotor and MAS stator during operation.

[0011] However, when aiming for higher rotation speeds, the NMR MAS rotor itself can (and usually will) be a weak point, as it can often be destroyed due to the centrifugal forces and the resulting shear forces at excessively high frequencies. Due to the centrifugal forces acting on it, the maximum rotational speed of a rotating body is limited by its material properties and the resulting forces.

[0012] WO 2021 / 097382 A1 (=reference [5]) relates to a laser micromachining process for machining microstructures in diamond. This process is intended to produce MAS rotors with high tensile and flexural strength to achieve higher rotation frequencies. The machining process cuts the diamond through laser-induced graphitization of the diamond and subsequent oxidation of the newly formed graphite to remove it. The presented process is therefore intended to produce NMR MAS rotors exclusively from diamond. There is no indication here of a possible use of composite materials.

[0013] WO 2014 / 026020 A1 (=reference [6]) describes reusable MAS NMR rotors made of ceramic with high mechanical strength. They contain a sample chamber in which high pressures of at least 10 atm and a high temperature of at least 250°C can be maintained during operation. For example, a rotor cylinder is provided into which a rotor cylinder insert (sleeve) made of a machinable ceramic such as MACOR® is inserted. Preferably, the rotor cylinder insert is positively secured with a thin layer of a high-temperature adhesive.

[0014] However, reference [6] does not contain any information on the physical quantities of elastic modulus or tensile strength of the material used, nor on their ratios in the rotor cylinder and rotor cylinder insert.

[0015] Reference [1], already cited at the beginning, describes the provision of specially sealed NMR-MAS rotors for liquid or semi-solid sample materials, which remain sealed even at speeds up to 18 kHz to prevent leakage of the liquid NMR sample. A cylindrical NMR sample cell is manufactured from a soft plastic material with a defined elastic modulus Y (0.8 GPa < Y < 4 GPa), tensile strength, and density, as well as a precise outer diameter, so that the sample cell fits into a ceramic NMR-MAS rotor. This results in an NMR-MAS sealing cell for use within a standard ceramic rotor sleeve to enable effective external locking. Reference

[0001] discloses various ratios of elastic modulus, tensile strength, and density of the inner sample cell and the outer rotor sleeve.However, reference

[0001] does not address the reinforcement of the NMR-MAS rotor as a whole to achieve higher rotational strength, which would not be feasible even with a material having the elastic modulus Y defined therein.

[0016] With the high-frequency NMR MAS rotors known to date, the amount of sample that can be loaded into the rotor for measurement is also severely limited. This is because the sample material exerts an additional, not insignificant force on the rotor wall during rotation. However, an insufficient amount of material leads to low signal strength in NMR spectroscopic investigations, especially with relatively small rotor diameters (< 1 mm). In summary, the following can be stated:

[0017] A significant increase in the rotational speed of known NMR-MAS rotors with the same body geometry is currently only possible by adapting the material properties or by using a different material.

[0018] On the other hand, such an increase in rotational speed while maintaining the same material is currently only possible by adapting the body geometry of the NMR MAS rotor. This is usually attempted by reducing the geometry.

[0019] Disadvantages:

[0020] • Increasingly complex manufacturing and complicated handling of geometries

[0021] • Increase in the NMR measurement time (required for the same signal quality) due to lower filling volume of the NMR-MAS rotor

[0022] • Reduction in measurement quality and results due to the use of materials other than those proven previously

[0023] Object of the invention

[0024] In contrast, the present invention is based on the object of achieving a very significant increase in the rotational speed of a rotor using conventional MAS stators, as are common for an NMR apparatus with the features defined above, with the same body geometry and the same material and without taking the drive gas into account and without special measures for sealing liquid samples.

[0025] In addition, an NMR-MAS rotor is to be provided which is not only characterized by high load capacity at very high rotation frequencies, but can also be loaded with larger quantities of sample material, especially in powder form, without having to fear that the NMR-MAS rotor will be destroyed during operation.

[0026] Brief description of the invention

[0027] This complex problem is solved with the present invention in a surprisingly simple and effective manner by means of an NMR-MAS rotor with the generic features described at the outset, in that the materials of the inner sleeve and of the at least one outer sleeve and their respective consistencies are selected such that solid-state NMR measurements can be carried out on a solid or powdery sample substance using the NMR-MAS rotor, the inner sleeve and the at least one outer sleeve remaining connected to one another in a materially bonded, force-locked or form-locked manner; and in that the material combinations of the inner sleeve and the at least one outer sleeve have the following ratio of the quotient S in and S out of their respective densities D inside and D outside and their respective mechanical yield strength R inside and R outside: S in and S out - 2 with S inside - D inside / R inside and R outside - D outside / R outside.

[0028] The basic idea of ​​the present invention is to significantly strengthen the wall of the NMR MAS rotor by cleverly using combinations of different materials with suitable different densities and mechanical yield strengths that follow a very specific rule.

[0029] Possible - and generally practically always to be feared - material failure at significantly increased rotation frequencies in solid-state NMR measurement mode is reliably avoided - in a surprisingly simple manner and with relatively easily available means - by reinforcing the rotor with a very special coating, winding, or additional outer sleeve(s) produced according to the teaching of the invention.

[0030] Simulations have shown that these novel composite rotors designed according to the invention have a significantly higher tensile strength than all conventional NMR-MAS rotors.

[0031] The present invention provides an NMR MAS rotor comprising at least two concentrically arranged (usually cylindrical) "shells" made of different materials with different physical properties. These shells—inner shell and outer shell—are preferably nested within one another in a materially bonded (coated or glued) or force-fit (tensioned, e.g., by shrinkage). A positive fit is also possible, for example, in a winding or in nested, untensioned shells.

[0032] The following applies

[0033] • E-modulus outer sleeve >>> E-modulus inner sleeve

[0034] • Tensile strength outer sleeve >>> Tensile strength inner sleeve

[0035] • The higher the elastic modulus of the coating, the higher the rotation speed

[0036] • The higher the tensile strength of the outer sleeve, the higher the rotation speed

[0037] • The expansion or deformation must be within the elastic range of the material and the coating (=yield strength R P o,2).

[0038] This novel principle is applicable to many NMR MAS rotors, especially those intended for use at very high speeds, where centrifugal and shear forces play a particularly significant role. However, it is also conceivable to use the inventive principle to manufacture NMR MAS rotors using comparatively inexpensive materials (such as polymers), which, with a stabilizing outer shell, can achieve higher rotation speeds without bursting. This could potentially replace the well-known, expensive sapphire rotors as consumables for high-throughput experiments.

[0039] Precisely because of the present invention, previously unimagined possibilities for solid-state NMR are now opening up.

[0040] Preferred embodiments of the invention

[0041] In a particularly preferred embodiment of the NMR-MAS rotor according to the invention, the maximum diameter dmax of the NMR-MAS rotor across the axis is: 0.4mm — dmax — 4mm.

[0042] This allows higher rotation frequencies or a larger filling volume to be achieved with the same rotor diameter compared to the state of the art.

[0043] In practice, embodiments of the NMR-MAS rotor according to the invention have proven successful in which the materials of the inner sleeve and also of the at least one outer sleeve are selected such that the NMR-MAS rotor can be rotated non-destructively at a rotation frequency fMAs > 20 kHz inclined by the MAS angle.

[0044] One class of advantageous embodiments of the invention is characterized by the fact that the inner sleeve and the at least one outer sleeve are nested, preferably concentrically, within each other. This has a particularly positive effect on the achievable service life of the NMR MAS rotor according to the invention, which is significantly longer at the same rotation frequency than that of a conventional NMR rotor without an outer sleeve.

[0045] In preferred developments of this class of embodiments, the inner sleeve is shrunk, glued or welded into the at least one outer sleeve.

[0046] This allows high rotation frequencies and filling volumes to be achieved while maintaining a long rotor service life.

[0047] Embodiments of the invention in which the inner sleeve and the at least one outer sleeve are each constructed in the shape of a hollow cylinder, in particular a circular cylinder, are also advantageous with regard to the achievable rotation frequency, the filling volume, the service life of the rotor and its manufacturability.

[0048] Cylindrical rotors are also particularly easy to manufacture.

[0049] Alternatively, for special applications, the inner sleeve and at least one outer sleeve can each be constructed in the shape of a hollow sphere.

[0050] This alternative also enables a higher rotation frequency or higher filling volume at the same diameter, longer service life at the same rotation frequency compared to a standard NMR rotor without an outer sleeve, and simplifies the production of the inner sleeve due to the inventive distribution of tasks between the inner and outer sleeve.

[0051] A further class of preferred embodiments of the NMR-MAS rotor according to the invention is characterized in that the at least one outer sleeve is constructed as a coating or wrapping of the inner sleeve.

[0052] This allows the overall weight of the NMR MAS rotor to be kept low.

[0053] Advantageous further developments of this class of embodiments are characterized in that the materials of the NMR-MAS rotor with different properties are at least partially applied in several layers.

[0054] In this way, a particularly high level of variability is achieved for optimization in individual special applications.

[0055] In further advantageous embodiments of the NMR MAS rotor according to the invention, the materials of the inner sleeve and of the at least one outer sleeve and their respective consistency are selected such that the NMR MAS rotor can be rotated non-destructively at a rotation frequency fMAs between 60 kHz and 300 kHz, in particular between 100 kHz and 160 kHz, inclined by the MAS angle, wherein the inner sleeve and the at least one outer sleeve remain connected to one another in a materially bonded, force-locked or form-locked manner.

[0056] Particular advantages here also include a) an improvement in the NMR measurement properties due to the material of the outer sleeve; for example, this effect can occur with graphene (superconductor properties), b) the integration of a coil geometry on the outer layer of the outer sleeve (e.g., by laser processing).

[0057] Alternatively or additionally, in further preferred embodiments of the invention, the materials of the inner sleeve and the at least one outer sleeve and their respective consistency and mechanical structure can be selected such that the modulus of elasticity E inside of the inner sleeve is smaller than the modulus of elasticity E outside of the at least one outer sleeve. Embodiments in which the materials of the inner sleeve and the at least one outer sleeve and their respective consistency and mechanical structure are selected such that the modulus of elasticity E inside of the inner sleeve and the modulus of elasticity E outside of the at least one outer sleeve are each greater than 200 GPa, where: E outside > One.

[0058] This allows particularly high speeds to be achieved during operation of the NMR MAS rotor.

[0059] Also preferred are embodiments of the NMR-MAS rotor according to the invention which are characterized in that the materials of the inner sleeve and of the at least one outer sleeve and their respective consistency and mechanical structure are selected such that the tensile strength of the inner sleeve is smaller than the tensile strength of the outer sleeve.

[0060] This material combination further improves the resistance to failure.

[0061] In further preferred embodiments, the materials of the inner sleeve and of the at least one outer sleeve and their respective consistency and mechanical structure are selected such that the tensile strength Rinnen of the inner sleeve and the tensile strength Raußen of the at least one outer sleeve is each greater than 500MPa, where: Raußen > Rinnen.

[0062] Such high tensile strength is particularly advantageous at very high speeds of the NMR MAS rotor during operation.

[0063] In practice, embodiments of the invention have also proven successful in which the inner sleeve is made of zirconium oxide and the at least one outer sleeve is made of, preferably layered, graphene or diamond. The present invention also provides a method for designing and manufacturing an NMR-MAS rotor which comprises an inner sleeve surrounded by at least one outer sleeve which has a different material than the inner sleeve, comprising the following method steps: i. Specification of the requirements for the rotation frequency fMAs; ii. Selection of the material of the inner sleeve with a defined tensile stress; iii. Calculation of the outer diameter of the inner sleeve and the length, as well as the wall thickness, with at least 20% certainty against breakage and provision of the inner sleeve; iv. Selection of the material of the outer sleeve depending on the material of the inner sleeve with a defined tensile stress; v.Calculation of the new rotation frequency fMAS2 from the combination with the outer sleeve as a support sleeve, with at least 20% safety against fracture; vi. Iterative recalculation of the inner sleeve from step iii. until fMAS2 = fMAS; vii. Application of the outer sleeve material to the outside of the inner sleeve, optionally by coating, insertion, or winding.

[0064] This is a particularly practical process, allowing for flexible combinations of materials to create rotors with a wide range of properties, from extremely solid and break-resistant rotors at high rotation frequencies to inexpensive yet powerful rotors. The actual available filling volume for the NMR sample is already determined from step ii.

[0065] When calculating the geometry of the inner sleeve of the inventive NMR-MAS rotor in step iii, the speed of sound of nitrogen at 20°C is typically assumed. Generally speaking, the geometry is determined or simulated as a function of the speed of sound of the drive gas, and also as a function of the sleeve material to be used. The specific wall thickness and rotor length then result from this simulation. The wall thickness must be kept as small as possible, in particular < 1 mm - again, this depends on the selected sleeve material. The rotor length is calculated using simulations using the finite element method (FEM) against vibration failure, as a function of the desired target rotation frequency fMAS.

[0066] The choice of material for the outer sleeve in step iv ultimately results in a limited selection for the optimal manufacturing and application process to be used in practice.

[0067] The iterative recalculation of the inner sleeve in step vi. normally always results in an increase in the filling volume at the required rotation frequency fMAS.

[0068] The result will therefore be a larger fill volume. This is, of course, equivalent to an increase in the rotation frequency fMAS, because depending on the optimization approach used—i.e., adjusting either the fill volume or the rotation frequency—the coating according to the invention always results in an improvement in the other parameter.

[0069] Particularly preferred is a variant of the method according to the invention which is characterized in that the material combinations of the inner sleeve and the outer sleeve have the following ratio of the quotient S inside or S outside of their respective density D inside or D outside and their respective mechanical yield strength R inside or R outside: S inside / S outside - 2 with S inside - D inside / R inside and S outside - D outside / R outside.

[0070] Further advantages of the invention will become apparent from the description and the drawings. Likewise, the above-mentioned and further-described features can be used individually or in combination in any desired manner. The embodiments shown and described are not intended to be exhaustive, but rather are exemplary in nature for describing the invention.

[0071] Detailed description of the invention and drawing

[0072] The invention is illustrated in the drawing and is explained in more detail using exemplary embodiments.

[0073] They show:

[0074] Fig. 1a is a roughly schematic representation of an embodiment of the NMR-MAS rotor according to the invention in a spatial view obliquely from above;

[0075] Fig. 1b is a schematic vertical sectional view of the embodiment of Fig. 1a;

[0076] Fig. 2 shows a schematic principle diagram for the centrifugal force management with an externally coated embodiment of the NMR-MAS rotor according to the invention with

[0077] 1. spatial oblique view of the NMR-MAS rotor,

[0078] 2. schematic half horizontal section of the coated rotor perpendicular to the rotor axis, 3. horizontal overall section with indicated centrifugal forces in the rotating operating state;

[0079] Fig. 3a is a schematic spatial oblique view of an embodiment with a wrapping as an outer sleeve;

[0080] Fig. 3b shows an embodiment as in Fig. 1a with a cylindrical outer sleeve arranged concentrically around the inner sleeve;

[0081] Fig. 4 shows a schematic horizontal section perpendicular to the rotor axis through a spherical embodiment of the NMR-MAS rotor according to the invention with rotor caps on both sides of the sample volume and turbine grooves;

[0082] Fig. 5 a graph of the tensile stress acting on the rotor (N / mm 2 ) as a function of the rotation frequency fMAs (Hz) for an aluminum rotor without an outer sleeve according to the state of the art (solid line) and for an NMR-MAS rotor according to the invention with an inner sleeve made of aluminum and an outer sleeve made of steel (dashed line);

[0083] Fig. 6 a graph of the tensile stress acting on the rotor (N / mm 2) as a function of the rotation frequency fMAs (Hz) for a zirconium oxide rotor without an outer sleeve according to the state of the art (solid line) and for an NMR-MAS rotor according to the invention with an inner sleeve made of zirconium oxide and an outer coating made of graphene (dashed line); and

[0084] Fig. 7 Simulation calculations for the safety against failure as a function of the rotation frequency for various NMR-MAS rotors according to the invention and rotors according to the state of the art.

[0085] The present invention relates to an NMR-MAS rotor 10; 20; 30; 40 for receiving sample substance for carrying out NMR measurements in a homogeneous region of an NMR magnetic field, wherein the NMR-MAS rotor 10; 20; 30; 40 comprises an inner sleeve 10i; 20i; 30i; 40i which is surrounded by at least one outer sleeve 10a; 20a; 30a; 40a which has a different material than the inner sleeve 10i; 20i; 30i; 40i, wherein the maximum diameter dmax of the NMR-MAS rotor 10; 20; 30; 40 transverse to a rotor axis a is less than 5mm, and wherein the NMR-MAS rotor 10; 20; 30; 40 is mechanically constructed and designed in such a way that it can be rotated by an MAS angle inclined against the direction of the NMR magnetic field during the NMR measurement with a rotation frequency fMAs of at least 20 kHz.

[0086] The present invention is distinguished from conventional NMR-MAS rotors according to the prior art in that the materials of the inner sleeve 10i; 20i; 30i; 40i and of the at least one outer sleeve 10a; 20a; 30a; 40a and their respective consistencies are selected such that solid-state NMR measurements can be carried out on a solid or powdery sample substance using the NMR-MAS rotor 10; 20; 30; 40, wherein the inner sleeve 10i; 20i; 30i; 40i and the at least one outer sleeve 10a; 20a; 30a; 40a remain connected to one another in a materially bonded, force-locked or form-locked manner; and that the material combinations of the inner sleeve 10i; 20i; 30i; 40i and the at least one outer sleeve 10a; 20a; 30a; 40a the following ratio of the quotient Sinnen or Saußen of their respective density Dinnen or Daußen and their respective mechanical yield strength Rinnen or.Have outside: S inside - D inside / R inside and S outside - D outside / R outside Such an inventive NMR-MAS rotor 10 with an inner sleeve 10i, an outer sleeve 10a and a rotor axis a, around which the rotor rotates in NMR measuring mode with a rotation frequency fMAs, which is indicated by the curved arrow, is shown schematically in Fig. 1a.

[0087] Fig. 1b shows the NMR-MAS rotor 10 of Fig. 1a in a schematic vertical section through a cutting plane containing the rotor axis a, using the example of an inner sleeve 10i, which is concentrically nested and surrounded by an outer sleeve 10a.

[0088] In embodiments of the invention not specifically shown in the drawing, several outer sleeves arranged in a nested manner can also enclose the inner sleeve.

[0089] The inner sleeve 10i; 20i; 30i; 40i can be shrunk, glued or welded into the at least one outer sleeve(s) 10a; 20a; 30a; 40a.

[0090] It is advantageous if the density of the actual rotor body (i.e. the inner sleeve 10i in the case of the NMR-MAS rotor 10 according to the invention) is limited so that as little force as possible acts on the outer shell during rotation.

[0091] By using an outer sleeve 10a with a higher modulus of elasticity or greater tensile strength according to the invention, the expansion of the inner rotor in the direction of the centrifugal force is limited and a composite rotor is obtained which can be operated safely at high speeds and with a high load.

[0092] A crucial factor is the ratio of density and tensile strength or yield strength S=D / R of the two materials for the body and the outer shell, namely:

[0093] Simulations have shown that density and yield strength are key parameters related to the rotors' resistance to fracture during rotation. In particular, it has been shown that the S of the inner sleeve material must be at least twice as large as the S of the outer sleeve material.

[0094] The wall thicknesses are determined by the individual design of the rotors for their specific application. However, the rule of thumb is: the thinner, the better.

[0095] As a rule, the maximum diameter dmax of the NMR-MAS rotor 10; 20; 30; 40 transverse to the rotor axis a is: 0.4 mm — dmax — 4 mm.

[0096] The materials of the inner sleeve 10i; 20i; 30i; 40i and also of the at least one outer sleeve 10a; 20a; 30a; 40a are selected such that the NMR MAS rotor 10; 20; 30; 40 can be rotated non-destructively at a rotation frequency TMAS > 21 kHz, inclined by the MAS angle.

[0097] Figure 11 illustrates the basic operating principle for centrifugal force management using the example of an NMR-MAS rotor 20 designed and constructed according to the invention, with a solid inner sleeve 20i and an outer sleeve 20a in the form of a coating attached to its outer circumference. Several successive coatings can also be present, in particular with different properties and materials, although this is not specifically shown in the drawing. 1 . The spatial oblique view of the NMR-MAS rotor on the left side of the figure is intended to indicate the high-frequency rotation around the rotor axis a during NMR measurement operation.

[0098] 2. In the horizontal half-section perpendicular to the rotor axis in the center of Fig. 2, the coated NMR MAS rotor can be seen rotating around the rotor axis. Arrows pointing radially outward in the body of the inner sleeve indicate the radial expansion caused by the centrifugal force due to rotation. The direction of tensile stress in the coating forming the outer sleeve is illustrated by a double arrow.

[0099] 3. The horizontal section on the right side of the image, with double arrows pointing radially outward, indicates the respective local expansion direction due to the centrifugal forces represented by hollow arrows during the rotating operating state of the NMR MAS rotor 20. The rotor expands in the direction of the centrifugal force. The coating supports the rotor and thus slows its radial expansion in the direction of the centrifugal force.

[0100] The centrifugal forces occurring during rotation cause the rotor's body geometry to expand orthogonally to the axis of rotation. The maximum elastic expansion of the body geometry is limited by the material properties of the composite rotor (Young's modulus, tensile stress, density). In the illustrated embodiment, the outer coating serves as a support to reduce the tensile stress. In order for the body geometry to expand further, it must also displace or stretch the outer coating. The resulting increased force, in turn, causes an increase in the centrifugal force or rotational speed. Figures 3a and 3b schematically show two further embodiments of the invention, each with a hollow cylindrical, in particular circular cylindrical, rotor.

[0101] In Fig. 3a, the inner sleeve 30i of the NMR-M AS rotor 30 is wrapped several times with a thin thread / wire / tape to reduce tensile stress. This wrapping can be applied directly to the inner sleeve 30i, as shown in the drawing, thus forming an outer covering 30a. Ideally, the wrapping is regular, so that each turn is at the same distance to avoid imbalance. In order for the rotor to expand further radially during rotation due to centrifugal force, the inner sleeve 30i must also displace the thread / wire / tape, or expand it radially outward. The resulting increased force, in turn, increases the counterforce acting against the centrifugal force, which slows the radial expansion and enables a higher rotational speed without the risk of breakage.

[0102] Such designs are also suitable for larger rotors with diameters starting at 3 mm. They are also advantageous due to the lower weight of the winding, which is not continuous compared to the sleeve.

[0103] Fig. 3b shows a comparison of the embodiment according to Fig. 1a. Here, the outer shell of the NMR-MAS rotor 10 is formed by the sleeve 10a. This outer sleeve serves as a support to reduce tensile stress. For the body geometry to expand further, it must also displace or stretch the outer sleeve. The resulting increased force, in turn, increases the counterforce to the centrifugal force and enables a higher rotational speed. The outer sleeve can be joined to the rotor as follows:

[0104] • A slight fit

[0105] • By negative preload of the rotor via the sleeve (press fit)

[0106] While the NMR-MAS rotors 10; 20; 30 in the embodiments of Figures 1 to 3 are each cylindrical, in particular designed as hollow circular cylinders, Figure 4 shows, in a schematic horizontal section perpendicular to the rotor axis, a spherical embodiment of the NMR-MAS rotor 40 designed according to the invention with rotor caps 41 that seal the sample volume 42 on both sides. Turbine grooves 43 are also shown here, which set the NMR-MAS rotor 40 in rotation when blown with drive gas.

[0107] The following are examples of different materials, where E = Young’s modulus

[0108] R = Yield strength = Rpo,2 D = Density

[0109] The following materials are suitable for the production of the inner sleeve

[0110] 10i 20i 30i 40i including the corresponding geometries:

[0111] The following materials are used to manufacture / apply the outer shell 10a; 20a; 30a; 40a: Further examples

[0112] Possible coating: Graphene - 2D structure

[0113] • Graphene modulus of elasticity: approx. 1,020 GPa

[0114] (Steel: 210 GPa)

[0115] (Titanium: 105 GPa)

[0116] (Diamond: 1,050 GPa)

[0117] • Graphene tensile strength: 125 GPa

[0118] (Steel: 1.1 GPa)

[0119] (Titanium: 1.2 GPa)

[0120] (Diamond: 0.75 GPa)

[0121] The materials differ from those used in the prior art in terms of their modulus of elasticity and tensile strength. Furthermore, the invention stipulates a limitation on the density of the material for the inner cylinder component.

[0122] Examples of simulations:

[0123] The simplified assumption is made that the inner sleeve rests against the outer sleeve. This causes the additional mass to act on the outer sleeve.

[0124] The tensile stress in the inner sleeve is neglected. Only the mass, or density, is considered. The assumed rotor diameter is 4 mm in each case.

[0125] Material pair aluminum steel:

[0126] The graph in Fig. 5 shows the tensile stress acting on the rotor (measured in N / mm 2 ) as a function of the rotation frequency TMAS (measured in Hz) for an aluminum rotor without outer sleeve according to the state of the art (solid line) and an NMR-MAS rotor according to the invention with inner sleeve made of aluminum and outer sleeve made of steel (dashed line).

[0127] For the aluminum / steel material pair, it is evident that the tensile stress is significantly increased compared to pure aluminum. The limiting speed at which the elastic character of the material ends and the material undergoes irreversible plastic deformation is 4000 Hz for aluminum and 5000 Hz for the composite rotor with a steel shell (values ​​not shown in the graph above). This represents a significant increase in speed. The inner / outer ratio here is only 2.15. Zirconium oxide graphene material pair:

[0128] The graph in Fig. 6 shows the tensile stress acting on the rotor (measured in N / mm 2 ) as a function of the rotation frequency TMAS (measured in Hz) for a zirconium oxide rotor without an outer sleeve according to the state of the art (solid line) and for an NMR MAS rotor according to the invention with an inner sleeve made of zirconium oxide and an outer coating made of graphene (dashed line).

[0129] In this example, zirconium oxide was chosen as a common material for MAS rotors. To strengthen these rotors, they were combined with graphene in the simulation, resulting in a center-to-center ratio of 145.97.

[0130] In this example, a significant increase in tensile stress can also be seen compared to the pure zirconia rotor. However, the calculated increase in the limiting speed from 10 kHz for the zirconia rotor to 61.5 kHz for the composite rotor is significant, which represents a significant increase in speed. These results are not specifically highlighted in the graph. Examples: Simulation of various standard and composite rotors using the von Mises deformation hypothesis, taking all stresses into account:

[0131] Finally, Fig. L7 shows simulation calculations for the safety against failure (i.e., breakage of the rotor) as a function of the rotation frequency for various NMR-MAS rotors according to the invention as well as for rotors according to the state of the art.

[0132] The x-axis represents the speed of a 3.2 mm rotor, while the y-axis represents the "safety against failure." This is defined as the ratio of load to the material's resilience. In the simplest case of a conventional rotor, we compare the resilience of zirconium oxide or diamond with the load that occurs on the inner surface of an empty rotor during rotation. Since the equivalent stress relevant to failure results from the centrifugal force, which depends on the square of the speed, the resulting stress is not a straight line, but rather a power function.

[0133] For a composite rotor, the shell and core must be considered separately in the simulation. The two parts of the rotor experience different loads. In the presented concepts, the shell, due to its greater stiffness, absorbs the tensile stresses that the selected materials can better withstand, resulting in a high degree of safety against failure within the shell. Limiting the expansion of the core relieves its load and results in only minimal tensile stresses developing on the inner wall of the core. However, limiting the expansion of the core leads to significant compressive stresses on the outer wall of the core.

[0134] Since ceramics can tolerate compressive stresses significantly better than tensile loads, the safety against failure of the core also increases. The figure shows the lowest safety value, regardless of whether it occurs in the shell or the core. A process with the following steps is suitable for the design and manufacture of an NMR-MAS rotor 10; 20; 30; 40 according to the invention: i. Specification of the requirements for the rotation frequency fi iAs.

[0135] This determines the rotor diameter, limited by the material properties. The goal is always to rotate as quickly as possible with a large volume in the sample. ii. Selection of the material for the inner sleeve 10i; 20i; 30i; 40i with a defined tensile stress.

[0136] This results in the base rotation speed for the inner sleeve. iii. Calculate the outer diameter of the inner sleeve 10i; 20i; 30i; 40i and the length, as well as the wall thickness, with at least 20% safety against breakage and provide the inner sleeve 10i; 20i; 30i; 40i. iv. Select the material of the outer sleeve 10a; 20a; 30a; 40a depending on the material of the inner sleeve 10i; 20i; 30i; 40i with a defined tensile stress.

[0137] The material combination results in a limiting speed, which is higher as desired, i.e. the base rotational speed (according to ii.) of the inner sleeve. v. Calculation of the new rotational frequency fMAS2 from the combination with the outer sleeve 10a; 20a; 30a; 40a as a support sleeve, with at least 20% safety against breakage. vi. Iterative recalculation of the inner sleeve 10i; 20i; 30i; 40i from step iii. until fMAS2 = f1VIAS. vii. Application of the material of the outer sleeve 10a; 20a; 30a; 40a to the outside of the inner sleeve 10i; 20i; 30i; 40i either by coating, by insertion, or by winding.

[0138] The following flow chart is intended to graphically illustrate the method according to the invention: A further developed variant of this method according to the invention is characterized in that the material combinations of the inner sleeve 10i; 20i; 30i; 40i and the outer sleeve 10a; 20a; 30a; 40a have the following ratio of the quotient S inn or S outn of their respective density D inside or D outside and their respective mechanical yield strength R inn or R out:

[0139] Senses / Outside — 2 with S inside — Inside / Outside and Sausage — Outside / Outside.

[0140] Here again, the desired higher limit speed for the base rotation speed of the inner sleeve 10i; 20i; 30i; 40i results from the material combination.

[0141] Special advantages of the invention:

[0142] - Easy to implement in production

[0143] - High potential for the NMR product platform:

[0144] Potential for covering the entire NMR speed spectrum Significant reduction of measurement time (reduced from weeks to hours) Improved measurement results (more filling volume and speeds)

[0145] List of reference symbols:

[0146] 10; 20; 30; 40 NMR-MAS rotor

[0147] 10a; 20a; 30a; 40a outer sleeve(s) 10i; 20i; 30i; 40i inner sleeve

[0148] 41 sample volumes

[0149] 42 Rotor cap

[0150] 43 Turbine groove a Rotor axis Reference list:

[0151] Publications considered for the assessment of patentability: [1] US 6, 054, 857 A

[0152] [2] DE 10 2020204 379 B3 « EP 3 889630 B1 « US 11 073 579 B1 «

[0153] JP 7079770 B

[0154] [3] EP 3 301 467 B1 « US 10,459,044 B2 « JP 6517896 B2 « CN 107870309 B

[0155] [4] US 5,508,615 A ​​[5] WO 2021 / 097382 A1

[0156] [6] WO 2014 / 026020 A1

Claims

Patent claims 1 . NMR-MAS rotor (10; 20; 30; 40) for receiving sample substance for carrying out NMR measurements in a homogeneous region of an NMR magnetic field, wherein the NMR-MAS rotor (10; 20; 30; 40) comprises an inner sleeve (10i; 20i; 30i; 40i) surrounded by at least one outer sleeve (10a; 20a; 30a; 40a) which has a different material from the inner sleeve (10i; 20i; 30i; 40i), wherein the maximum diameter dmax of the NMR-MAS rotor (10; 20; 30; 40) transverse to a rotor axis (a) is less than 5 mm, and wherein the NMR-MAS rotor (10; 20; 30; 40) is mechanically constructed and designed such that it during the NMR measurement, it can be rotated at a rotation frequency fMAs of at least 20 kHz by an MAS angle inclined against the direction of the NMR magnetic field, characterized in that the materials of the inner sleeve (10i; 20i; 30i; 40i) and of the at least one outer sleeve (10a; 20a; 30a;40a) and their respective consistencies are selected such that solid-state NMR measurements can be carried out on a solid or powdered sample substance using the NMR-MAS rotor (10; 20; 30; 40), wherein the inner sleeve (10i; 20i; 30i; 40i) and the at least one outer sleeve (10a; 20a; 30a; 40a) remain connected to one another in a materially bonded, force-locked or form-locked manner; and that the material combinations of the inner sleeve (10i; 20i; 30i; 40i) and the at least one outer sleeve (10a; 20a; 30a; 40a) have the following ratio of the quotient S in and S out of their respective densities D inside and D outside and their respective mechanical yield strength R inside and R outside: S in / S outside - 2 with S inside - D inside / R inside and S out - D outside / R outside.; 2. NMR-MAS rotor according to claim 1, characterized in that the maximum diameter dmax of the NMR-MAS rotor (10; 20; 30; 40) transverse to the rotor axis (a) is: 0.4mm — dmax < 4mm.

3. NMR-MAS rotor according to one of the preceding claims, characterized in that the materials of the inner sleeve (10i; 20i; 30i; 40i) and also of the at least one outer sleeve (10a; 20a; 30a; 40a) are selected such that the NMR-MAS rotor (10; 20; 30; 40) can be rotated non-destructively at a rotation frequency TMAS > 20kHz inclined by the MAS angle.

4. NMR-MAS rotor according to one of the preceding claims, characterized in that the inner sleeve (10i; 20i; 30i; 40i) and the at least one outer sleeve (10a; 20a; 30a; 40a) are nested, preferably concentrically, inside each other.

5. NMR-MAS rotor according to one of claims 1 to 4, characterized in that the inner sleeve (10i; 20i; 30i) and the at least one outer sleeve (10a; 20a; 30a) are each constructed in the shape of a hollow cylinder, in particular a circular cylinder.

6. NMR-MAS rotor according to one of claims 1 to 4, characterized in that the inner sleeve (40i) and the at least one outer sleeve (40a) are each constructed in the shape of a hollow sphere.

7. NMR-MAS rotor according to one of the preceding claims, characterized in that the at least one outer sleeve (10a; 20a; 30a; 40a) is constructed as a coating or wrapping of the inner sleeve (10i; 20i; 30i; 40i).

8. NMR-MAS rotor according to one of the preceding claims, characterized in that the materials of the inner sleeve (10i; 20i; 30i; 40i) and of the at least one outer sleeve (10a; 20a; 30a; 40a) and their respective consistency are selected such that the NMR-MAS rotor (10; 20; 30; 40) with a rotation frequency fMAs between 60kHz and 300kHz, in particular between 100 kHz and 160 kHz, can be rotated non-destructively at an angle inclined by the MAS angle, wherein the inner sleeve (10i; 20i; 30i; 40i) and the at least one outer sleeve (10a; 20a; 30a; 40a) remain connected to one another in a materially bonded, force-locked or form-locked manner.

9. NMR-MAS rotor according to one of the preceding claims, characterized in that the materials of the inner sleeve (10i; 20i; 30i; 40i) and of the at least one outer sleeve (10a; 20a; 30a; 40a) and their respective consistency and mechanical structure are selected such that the elastic modulus E inside of the inner sleeve (10i; 20i; 30i; 40i) is smaller than the elastic modulus E outside of the at least one outer sleeve (10a; 20a; 30a; 40a).

10. NMR-MAS rotor according to one of the preceding claims, characterized in that the materials of the inner sleeve (10i; 20i; 30i; 40i) and of the at least one outer sleeve (10a; 20a; 30a; 40a) and their respective consistency and mechanical structure are selected such that the elastic modulus E inside of the inner sleeve (10i; 20i; 30i; 40i) and the elastic modulus E outside of the at least one outer sleeve (10a; 20a; 30a; 40a) is each greater than 200GPa.

11. NMR-MAS rotor according to one of the preceding claims, characterized in that the materials of the inner sleeve (10i; 20i; 30i; 40i) and of the at least one outer sleeve (10a; 20a; 30a; 40a) and their respective consistency and mechanical structure are selected such that the tensile strength Rinnen of the inner sleeve (10i; 20i; 30i; 40i) is smaller than the tensile strength Ruß of the at least one outer sleeve (10a; 20a; 30a; 40a).

12. NMR-MAS rotor according to one of the preceding claims, characterized in that the materials of the inner sleeve (10i; 20i; 30i; 40i) and of the at least one outer sleeve (10a; 20a; 30a; 40a) and their respective consistency and mechanical structure are selected such that the tensile strength of the inner sleeve (10i; 20i; 30i; 40i) and the Tensile strength of the at least one outer sleeve (10a; 20a; 30a; 40a) is greater than 500MPa.

13. NMR-MAS rotor according to one of the preceding claims, characterized in that the inner sleeve (10i; 20i; 30i; 40i) is made of zirconium oxide and the at least one outer sleeve (10a; 20a; 30a; 40a) is made of, preferably layered, graphene or diamond.

14. A method for designing and manufacturing an NMR MAS rotor (10; 20; 30; 40) comprising an inner sleeve (10i; 20i; 30i; 40i) surrounded by at least one outer sleeve (10a; 20a; 30a; 40a) made of a different material than the inner sleeve (10i; 20i; 30i; 40i), comprising the following method steps: i. specifying the requirements for the rotation frequency fMAs; ii. selecting the material of the inner sleeve (10i; 20i; 30i; 40i) with a defined tensile stress; iii. calculating the outer diameter of the inner sleeve and the length, as well as the wall thickness, with at least 20% safety against breakage and providing the inner sleeve (10i; 20i; 30i; 40i); iv. Selection of the material of the outer sleeve (10a; 20a; 30a; 40a) depending on the material of the inner sleeve (10i; 20i; 30i; 40i) with a defined tensile stress; v.Calculation of the new rotation frequency fMAS2 from the combination with the outer sleeve as a support sleeve, with at least 20% safety against fracture; vi. Iterative recalculation of the inner sleeve (10i; 20i; 30i; 40i) from step iii. until fMAS2 = fMAs; vii. Application of the material of the outer sleeve (10a; 20a; 30a; 40a) to the outside of the inner sleeve (10i; 20i; 30i; 40i) optionally by coating, by insertion, or by winding.

15. The method according to claim 14, characterized in that the material combinations of the inner sleeve (10i; 20i; 30i; 40i) and the outer sleeve (10a; 20a; 30a; 40a) have the following ratio of the quotient S inn or S outn of their respective density D inn or D outn and their respective mechanical yield strength R inn or R outn: Senses / Outside — 2 with S inside — Inside / Outside and Sausage — Outside / Outside.

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