Krzysztof Turek | AGH University of Science and Technology (original) (raw)

Papers by Krzysztof Turek

Research paper thumbnail of A magnetic resonance imager for the international space station

A complete understanding of the pathophysiological changes that occur during long-duration spacef... more A complete understanding of the pathophysiological changes that occur during long-duration spaceflight, and of the countermeasures needed to ameliorate their effects, remains elusive. A primary reason for that lack of basic knowledge is the very limited amount of in-flight physiological data available. The ability to image astronauts frequently with a magnetic resonance imager (MRI), during their mission, would provide a wealth of information, especially of the musculoskeletal system, that could be used to solve the problem of keeping them fit and healthy on long spaceflights. MRI would provide important information about bone and muscle mass and, in addition, it would provide information about bone and muscle strength and muscle metabolic efficiency using imaging protocols that have been developed for the study of athletes and patients with osteoporosis on Earth. It is now possible to build a whole-body "Compact MRI" that can fit within the mass and space envelope of an International Space Station (ISS) International Standard Payload Rack (ISPR) using technology that has recently been developed and is currently undergoing development. The new technology is composed of two critical pieces: 1. an RF image encoding system ("TRASE" RF system) and 2. a lightweight Halbach magnet that additionally produces no magnetic field external to the magnet. The TRASE RF system eliminates the need for heavy, power-consuming, magnetic gradient field coils. Elimination of the magnetic gradients leads to an MRI design that is simple from the hardware point of view and will therefore be robust and reliable. With modest funding, the ISS MRI could be functional in approximately 5 years. Beyond the ISS, the Compact MRI will provide the basis for the development of MRI for solar system-wide medical care. On Earth, the development of the Compact MRI promises to have a significant impact on worldwide healthcare delivery by making portable MRI available to populations that otherwise could not afford MRI or who would otherwise have to wait in long queues for an MRI exam. On the Moon, Mars, Phobos, Deimos and the many other destinations of interest to our descendants, derivatives of the Compact MRI would provide both medical diagnostic capability and a tool for basic research on physiological adaptation to the hypogravity of those distant worlds.

Research paper thumbnail of Attempt to measure the magnetocrystalline anisotropy of the Y-Co system by FMR

Physica B+C, 1985

ABSTRACT

Research paper thumbnail of Micro-imaging of implanted scaffolds using combined MRI and micro-CT

Computerized medical imaging and graphics : the official journal of the Computerized Medical Imaging Society, 2014

Thanks to the advanced studies in biomaterial engineering a panoply of polymers can be used to ma... more Thanks to the advanced studies in biomaterial engineering a panoply of polymers can be used to manufacture porous scaffolds for bone tissue regeneration. Suitability of the scaffold for its purpose is determined by factors like size of the pores, its orientation and shape, as well as biocompatibility of the material. Even though a variety of analysis methods is available for in vitro studies, investigating the process of bone reconstruction on implanted scaffold meets with difficulties. Polylactide porous sponges imbued in hydroxyapatite were implanted into long bones of white New Zealand rabbits for 3 months. The bones obtained from the animals were subjected to MRI and μCT imaging. The obtained images were subsequently fused together. Combined MRI and μCT resulted in high resolution diagnostic images which allow for: implant positioning, inflammation divulgement, rating degree of implant resorption, observation of newly formed trabeculae, texture analysis and other quantitative me...

Research paper thumbnail of On-line error analysis for X-BEM for nonlinear magnetostatics

Research paper thumbnail of Compact MRI for Astronaut Physiological Research and Medical Diagnosis

AIAA SPACE 2012 Conference & Exposition, 2012

The change and deterioration of an astronaut's physiology during long-term space flight remains a... more The change and deterioration of an astronaut's physiology during long-term space flight remains a significant concern. A magnetic resonance imager (MRI), that is available during space flight, would be a valuable tool that can be used to understand more fully the altered physiological processes, and to find ways of ameliorating those changes. The first application of an MRI in space would be to study the physiology of mass and strength change in bone and muscle. Such studies could be done on the International Space Station (ISS) with a new generation of Compact MRIs. Other applications include monitoring the formation of renal stones, monitoring the effects of radiation on the nervous and musculoskeletal systems, imaging body-wide fluid shifts, and imaging changes in cardiovascular morphology and function. Beyond basic research, an MRI in space, on the Moon or Mars would have the same clinical diagnostic utility as MRIs on Earth.

Research paper thumbnail of The influence of the local Co anisotropy on ferromagnetic resonance in YCo3 and Y2Co17

Journal of Magnetism and Magnetic Materials, 1986

It is shown that the difference in the results of the macroscopic anisotropy field measurements i... more It is shown that the difference in the results of the macroscopic anisotropy field measurements in YCo3 and Y2Co17 and these obtained by FMR technique can be explained by the local Co anisotropy. In spite of the ferromagnetic ordering of the magnetic moments in these compounds the magnetic resonance in the microwave region cannot be treated as the classical ferromagnetic one. The simplified resonant condition is effected by the anisotropy in other ways than that for an ordinary ferromagnetic material with one magnetic sublattice.

Research paper thumbnail of Magnetic fibers

Journal of Magnetism and Magnetic Materials, 1990

Thin, flexible magnetic fibers are spun from a mixture of a fiber forming polymer and a powder of... more Thin, flexible magnetic fibers are spun from a mixture of a fiber forming polymer and a powder of soft or hard magnetic materials. In the paper some magnetic and mechanical properties of such fibers as well as their possible applications are presented.

Research paper thumbnail of Search for new magnetic materials based on uranium and iron

Journal of Magnetism and Magnetic Materials, 1990

ABSTRACT Magnetic and Mössbauer effect studies have been reported for new UFe10Si2, UCo10Si2 and ... more ABSTRACT Magnetic and Mössbauer effect studies have been reported for new UFe10Si2, UCo10Si2 and UFe10Mo2 compounds crystallizing with tetragonal structure of the ThMn12-type. The magnetization measurements have been performed for the magnetic field preoriented sample of UFe10Si2 and bulk sample of UCo10Si2, in high fields up to 140 kOe. The 57Fe Mössbauer spectra for UFe10Si2 and UFe10Mo2 have been recorded below the corresponding Curie temperatures.

Research paper thumbnail of Compensation of the temperature coefficient of the magnetic flux produced by a NdFeB magnet in the air gap of a magnetic circuit

Journal of Magnetism and Magnetic Materials, 1996

The effect of flux shunting on the temperature coefficient c~ of flux q~ in the air gap of a magn... more The effect of flux shunting on the temperature coefficient c~ of flux q~ in the air gap of a magnetic circuit of a Nd-Fe-B magnet is studied by a current balance in the temperature range from 20 to 70°C, 20°C above the typical elevated temperature working regime of measuring instruments.

Research paper thumbnail of Electron spin resonance and magnetocrystalline anisotropy in YCo3

Journal of Magnetism and Magnetic Materials, 1987

... Electron spin resonance in YC03 O=Orad U "j O=21r118rad O=51r118rad =71CI18rad O=ifl2rad... more ... Electron spin resonance in YC03 O=Orad U "j O=21r118rad O=51r118rad =71CI18rad O=ifl2rad 0 4 8 12 16 Hlx105A M1 Fig. 3. The FMR spectra of YC03 at 35 GHz and at room temperature versus the angle B between the do field and the alligment axis of the sample. ...

Research paper thumbnail of Magnetic field homogeneity perturbations in finite Halbach dipole magnets

Journal of Magnetic Resonance, 2014

Halbach hollow cylinder dipole magnets of a low or relatively low aspect ratio attract considerab... more Halbach hollow cylinder dipole magnets of a low or relatively low aspect ratio attract considerable attention due to their applications, among others, in compact NMR and MRI systems for investigating small objects. However, a complete mathematical framework for the analysis of magnetic fields in these magnets has been developed only for their infinitely long precursors. In such a case the analysis is reduced to two-dimensions (2D). The paper details the analysis of the 3D magnetic field in the Halbach dipole cylinders of a finite length. The analysis is based on three equations in which the components of the magnetic flux density Bx, By and Bz are expanded to infinite power series of the radial coordinate r. The zeroth term in the series corresponds to a homogeneous magnetic field Bc, which is perturbed by the higher order terms due to a finite magnet length. This set of equations is supplemented with an equation for the field profile B(z) along the magnet axis, presented for the first time. It is demonstrated that the geometrical factors in the coefficients of particular powers of r, defined by intricate integrals are the coefficients of the Taylor expansion of the homogeneity profile (B(z)-Bc)/Bc. As a consequence, the components of B can be easily calculated with an arbitrary accuracy. In order to describe perturbations of the field due to segmentation, two additional equations are borrowed from the 2D theory. It is shown that the 2D approach to the perturbations generated by the segmentation can be applied to the 3D Halbach structures unless r is not too close to the inner radius of the cylinder ri. The mathematical framework presented in the paper was verified with great precision by computations of B by a highly accurate integration of the magnetostatic Coulomb law and utilized to analyze the inhomogeneity of the magnetic field in the magnet with the accuracy better than 1 ppm.

Research paper thumbnail of The influence of decrepitation on the diffusion kinetics of hydrogen in Nd–Fe–B

Journal of Alloys and Compounds, 2000

The decrepitation process and related changes in the sample temperature are analysed to explain t... more The decrepitation process and related changes in the sample temperature are analysed to explain the experimentally observed weight gain curve of a Nd-Fe-B sample due to hydrogen uptake. It is shown that the expansion of the specific surface resulting from decrepitation of the sample is the most important parameter controlling the hydrogen diffusion process. As it follows from the presented analysis of the experimental weight gain curve and the theoretical one for a bulk sample, decrepitation accelerates the diffusion rate by five orders of magnitude. A one-dimensional model of decrepitation is presented to discuss in detail hydrogen diffusion into an Nd-Fe-B alloy. On the basis of this simple model the experimental weight gain curve and the particle size distribution of the decrepitation output are reproduced with a reasonable accuracy.

Research paper thumbnail of The influence of the kinetics of the hydrogenation of Nd–Fe–B alloys on hydrogen distribution in the alloy phases

Journal of Alloys and Compounds, 2000

We present results of experiments on hydrogenation of Nd Fe B controlled by two parameters: the a... more We present results of experiments on hydrogenation of Nd Fe B controlled by two parameters: the amount of hydrogen and the 16 75.8 8.2 rate of feeding the sample with hydrogen at low pressures. By proper combination of these parameters four different schemes for the hydrogenation process were generated: selective hydrogenation of the Nd-rich phase, (2) hydrogenation of the Nd-rich phase followed by diffusion of hydrogen into the Nd Fe B phase, (3) simultaneous partial hydrogenation of both phases, (4) simultaneous complete 2 14 hydrogenation of both phases. For the first two cases the results of measurements of equilibrium pressure versus hydrogen concentration at room temperature are presented in the form of a p-c diagram with three phase regions: (1) Nd1NdH 1Nd Fe B, (2) y 2 14

Research paper thumbnail of Corrigendum to ‘The influence of the kinetics of the hydrogenation of Nd–Fe–B alloys on hydrogen distribution in the alloy phases’

Journal of Alloys and Compounds, 2001

Research paper thumbnail of The intermediate stages of the corrosion of Nd–Fe–B powders in ambient air

Journal of Alloys and Compounds, 2001

Nd-Fe-B alloys powdered by hydrogenation and mechanical grinding were oxidised at room temperatur... more Nd-Fe-B alloys powdered by hydrogenation and mechanical grinding were oxidised at room temperature in ambient air. Changes in the X-ray spectra of the powder at the subsequent stages of the oxidation are explained by the progressive absorption of water molecules from ambient air to form structurally imperfect Nd(OH) and the subsequent improvement of the hydroxide structure. The structural 3 imperfectness of Nd(OH) results in a very low intensity of the hydroxide spectra even at advanced stages of oxidation. This means either 3 that the hydroxide is composed of very fine grains and / or that its structure is amorphous. We observed the similar improvement of the structure with time for hydroxides produced by oxidation of the hydrogenated Nd-Fe-B and NdH . It is well established that the x oxidation proceeds much slower in the virgin Nd-Fe-B powder than in the hydrogenated one. We present evidence that the rate of the oxidation process can be controlled by the amount of hydrogen absorbed by the alloy. We also show that the oxidation curves of the partially hydrogenated samples can be decomposed into the oxidation curves of fully hydrogenated and not hydrogenated samples.

Research paper thumbnail of Local Co anisotropy in Y-Co compounds

IEEE Transactions on Magnetics, 1984

Research paper thumbnail of The kinetics of oxidation of Nd-Fe-B powders

IEEE Transactions on Magnetics, 1993

ABSTRACT The kinetics of oxidation of 2.5 μm Nd-Fe-B powder are studied at temperatures 20, 80, 1... more ABSTRACT The kinetics of oxidation of 2.5 μm Nd-Fe-B powder are studied at temperatures 20, 80, 100 and 115 °C. The powdered alloy compromises 62.5 wt.% Fe, 35 wt.% Nd and 1.3 wt.% B. The percentage of weight gain is measured and compared with X-ray spectra recorded after various periods of oxidation. Two stages of oxidation, with powder-like and exponential weight gain reaching a plateau, are distinguished at all temperatures. The effect of changes in phase composition on ferromagnetic properties due to oxidation are examined by a magnetic balance. On the basis of reported measurements, it is concluded that two processes contribute to oxidation of Nd-Fe-B in air, i.e., relatively quick, total oxidation of intergranular Nd and oxidation of Nd2 Fe14B (Φ) which stops at 12% level. The recognition of three products of the oxidation at X-ray spectra, Nd2O3, NdFeO3 and Fe3O4 , makes it possible to deduce a final phase composition

Research paper thumbnail of A magnetic resonance imager for the international space station

A complete understanding of the pathophysiological changes that occur during long-duration spacef... more A complete understanding of the pathophysiological changes that occur during long-duration spaceflight, and of the countermeasures needed to ameliorate their effects, remains elusive. A primary reason for that lack of basic knowledge is the very limited amount of in-flight physiological data available. The ability to image astronauts frequently with a magnetic resonance imager (MRI), during their mission, would provide a wealth of information, especially of the musculoskeletal system, that could be used to solve the problem of keeping them fit and healthy on long spaceflights. MRI would provide important information about bone and muscle mass and, in addition, it would provide information about bone and muscle strength and muscle metabolic efficiency using imaging protocols that have been developed for the study of athletes and patients with osteoporosis on Earth. It is now possible to build a whole-body "Compact MRI" that can fit within the mass and space envelope of an International Space Station (ISS) International Standard Payload Rack (ISPR) using technology that has recently been developed and is currently undergoing development. The new technology is composed of two critical pieces: 1. an RF image encoding system ("TRASE" RF system) and 2. a lightweight Halbach magnet that additionally produces no magnetic field external to the magnet. The TRASE RF system eliminates the need for heavy, power-consuming, magnetic gradient field coils. Elimination of the magnetic gradients leads to an MRI design that is simple from the hardware point of view and will therefore be robust and reliable. With modest funding, the ISS MRI could be functional in approximately 5 years. Beyond the ISS, the Compact MRI will provide the basis for the development of MRI for solar system-wide medical care. On Earth, the development of the Compact MRI promises to have a significant impact on worldwide healthcare delivery by making portable MRI available to populations that otherwise could not afford MRI or who would otherwise have to wait in long queues for an MRI exam. On the Moon, Mars, Phobos, Deimos and the many other destinations of interest to our descendants, derivatives of the Compact MRI would provide both medical diagnostic capability and a tool for basic research on physiological adaptation to the hypogravity of those distant worlds.

Research paper thumbnail of Attempt to measure the magnetocrystalline anisotropy of the Y-Co system by FMR

Physica B+C, 1985

ABSTRACT

Research paper thumbnail of Micro-imaging of implanted scaffolds using combined MRI and micro-CT

Computerized medical imaging and graphics : the official journal of the Computerized Medical Imaging Society, 2014

Thanks to the advanced studies in biomaterial engineering a panoply of polymers can be used to ma... more Thanks to the advanced studies in biomaterial engineering a panoply of polymers can be used to manufacture porous scaffolds for bone tissue regeneration. Suitability of the scaffold for its purpose is determined by factors like size of the pores, its orientation and shape, as well as biocompatibility of the material. Even though a variety of analysis methods is available for in vitro studies, investigating the process of bone reconstruction on implanted scaffold meets with difficulties. Polylactide porous sponges imbued in hydroxyapatite were implanted into long bones of white New Zealand rabbits for 3 months. The bones obtained from the animals were subjected to MRI and μCT imaging. The obtained images were subsequently fused together. Combined MRI and μCT resulted in high resolution diagnostic images which allow for: implant positioning, inflammation divulgement, rating degree of implant resorption, observation of newly formed trabeculae, texture analysis and other quantitative me...

Research paper thumbnail of On-line error analysis for X-BEM for nonlinear magnetostatics

Research paper thumbnail of Compact MRI for Astronaut Physiological Research and Medical Diagnosis

AIAA SPACE 2012 Conference & Exposition, 2012

The change and deterioration of an astronaut's physiology during long-term space flight remains a... more The change and deterioration of an astronaut's physiology during long-term space flight remains a significant concern. A magnetic resonance imager (MRI), that is available during space flight, would be a valuable tool that can be used to understand more fully the altered physiological processes, and to find ways of ameliorating those changes. The first application of an MRI in space would be to study the physiology of mass and strength change in bone and muscle. Such studies could be done on the International Space Station (ISS) with a new generation of Compact MRIs. Other applications include monitoring the formation of renal stones, monitoring the effects of radiation on the nervous and musculoskeletal systems, imaging body-wide fluid shifts, and imaging changes in cardiovascular morphology and function. Beyond basic research, an MRI in space, on the Moon or Mars would have the same clinical diagnostic utility as MRIs on Earth.

Research paper thumbnail of The influence of the local Co anisotropy on ferromagnetic resonance in YCo3 and Y2Co17

Journal of Magnetism and Magnetic Materials, 1986

It is shown that the difference in the results of the macroscopic anisotropy field measurements i... more It is shown that the difference in the results of the macroscopic anisotropy field measurements in YCo3 and Y2Co17 and these obtained by FMR technique can be explained by the local Co anisotropy. In spite of the ferromagnetic ordering of the magnetic moments in these compounds the magnetic resonance in the microwave region cannot be treated as the classical ferromagnetic one. The simplified resonant condition is effected by the anisotropy in other ways than that for an ordinary ferromagnetic material with one magnetic sublattice.

Research paper thumbnail of Magnetic fibers

Journal of Magnetism and Magnetic Materials, 1990

Thin, flexible magnetic fibers are spun from a mixture of a fiber forming polymer and a powder of... more Thin, flexible magnetic fibers are spun from a mixture of a fiber forming polymer and a powder of soft or hard magnetic materials. In the paper some magnetic and mechanical properties of such fibers as well as their possible applications are presented.

Research paper thumbnail of Search for new magnetic materials based on uranium and iron

Journal of Magnetism and Magnetic Materials, 1990

ABSTRACT Magnetic and Mössbauer effect studies have been reported for new UFe10Si2, UCo10Si2 and ... more ABSTRACT Magnetic and Mössbauer effect studies have been reported for new UFe10Si2, UCo10Si2 and UFe10Mo2 compounds crystallizing with tetragonal structure of the ThMn12-type. The magnetization measurements have been performed for the magnetic field preoriented sample of UFe10Si2 and bulk sample of UCo10Si2, in high fields up to 140 kOe. The 57Fe Mössbauer spectra for UFe10Si2 and UFe10Mo2 have been recorded below the corresponding Curie temperatures.

Research paper thumbnail of Compensation of the temperature coefficient of the magnetic flux produced by a NdFeB magnet in the air gap of a magnetic circuit

Journal of Magnetism and Magnetic Materials, 1996

The effect of flux shunting on the temperature coefficient c~ of flux q~ in the air gap of a magn... more The effect of flux shunting on the temperature coefficient c~ of flux q~ in the air gap of a magnetic circuit of a Nd-Fe-B magnet is studied by a current balance in the temperature range from 20 to 70°C, 20°C above the typical elevated temperature working regime of measuring instruments.

Research paper thumbnail of Electron spin resonance and magnetocrystalline anisotropy in YCo3

Journal of Magnetism and Magnetic Materials, 1987

... Electron spin resonance in YC03 O=Orad U "j O=21r118rad O=51r118rad =71CI18rad O=ifl2rad... more ... Electron spin resonance in YC03 O=Orad U "j O=21r118rad O=51r118rad =71CI18rad O=ifl2rad 0 4 8 12 16 Hlx105A M1 Fig. 3. The FMR spectra of YC03 at 35 GHz and at room temperature versus the angle B between the do field and the alligment axis of the sample. ...

Research paper thumbnail of Magnetic field homogeneity perturbations in finite Halbach dipole magnets

Journal of Magnetic Resonance, 2014

Halbach hollow cylinder dipole magnets of a low or relatively low aspect ratio attract considerab... more Halbach hollow cylinder dipole magnets of a low or relatively low aspect ratio attract considerable attention due to their applications, among others, in compact NMR and MRI systems for investigating small objects. However, a complete mathematical framework for the analysis of magnetic fields in these magnets has been developed only for their infinitely long precursors. In such a case the analysis is reduced to two-dimensions (2D). The paper details the analysis of the 3D magnetic field in the Halbach dipole cylinders of a finite length. The analysis is based on three equations in which the components of the magnetic flux density Bx, By and Bz are expanded to infinite power series of the radial coordinate r. The zeroth term in the series corresponds to a homogeneous magnetic field Bc, which is perturbed by the higher order terms due to a finite magnet length. This set of equations is supplemented with an equation for the field profile B(z) along the magnet axis, presented for the first time. It is demonstrated that the geometrical factors in the coefficients of particular powers of r, defined by intricate integrals are the coefficients of the Taylor expansion of the homogeneity profile (B(z)-Bc)/Bc. As a consequence, the components of B can be easily calculated with an arbitrary accuracy. In order to describe perturbations of the field due to segmentation, two additional equations are borrowed from the 2D theory. It is shown that the 2D approach to the perturbations generated by the segmentation can be applied to the 3D Halbach structures unless r is not too close to the inner radius of the cylinder ri. The mathematical framework presented in the paper was verified with great precision by computations of B by a highly accurate integration of the magnetostatic Coulomb law and utilized to analyze the inhomogeneity of the magnetic field in the magnet with the accuracy better than 1 ppm.

Research paper thumbnail of The influence of decrepitation on the diffusion kinetics of hydrogen in Nd–Fe–B

Journal of Alloys and Compounds, 2000

The decrepitation process and related changes in the sample temperature are analysed to explain t... more The decrepitation process and related changes in the sample temperature are analysed to explain the experimentally observed weight gain curve of a Nd-Fe-B sample due to hydrogen uptake. It is shown that the expansion of the specific surface resulting from decrepitation of the sample is the most important parameter controlling the hydrogen diffusion process. As it follows from the presented analysis of the experimental weight gain curve and the theoretical one for a bulk sample, decrepitation accelerates the diffusion rate by five orders of magnitude. A one-dimensional model of decrepitation is presented to discuss in detail hydrogen diffusion into an Nd-Fe-B alloy. On the basis of this simple model the experimental weight gain curve and the particle size distribution of the decrepitation output are reproduced with a reasonable accuracy.

Research paper thumbnail of The influence of the kinetics of the hydrogenation of Nd–Fe–B alloys on hydrogen distribution in the alloy phases

Journal of Alloys and Compounds, 2000

We present results of experiments on hydrogenation of Nd Fe B controlled by two parameters: the a... more We present results of experiments on hydrogenation of Nd Fe B controlled by two parameters: the amount of hydrogen and the 16 75.8 8.2 rate of feeding the sample with hydrogen at low pressures. By proper combination of these parameters four different schemes for the hydrogenation process were generated: selective hydrogenation of the Nd-rich phase, (2) hydrogenation of the Nd-rich phase followed by diffusion of hydrogen into the Nd Fe B phase, (3) simultaneous partial hydrogenation of both phases, (4) simultaneous complete 2 14 hydrogenation of both phases. For the first two cases the results of measurements of equilibrium pressure versus hydrogen concentration at room temperature are presented in the form of a p-c diagram with three phase regions: (1) Nd1NdH 1Nd Fe B, (2) y 2 14

Research paper thumbnail of Corrigendum to ‘The influence of the kinetics of the hydrogenation of Nd–Fe–B alloys on hydrogen distribution in the alloy phases’

Journal of Alloys and Compounds, 2001

Research paper thumbnail of The intermediate stages of the corrosion of Nd–Fe–B powders in ambient air

Journal of Alloys and Compounds, 2001

Nd-Fe-B alloys powdered by hydrogenation and mechanical grinding were oxidised at room temperatur... more Nd-Fe-B alloys powdered by hydrogenation and mechanical grinding were oxidised at room temperature in ambient air. Changes in the X-ray spectra of the powder at the subsequent stages of the oxidation are explained by the progressive absorption of water molecules from ambient air to form structurally imperfect Nd(OH) and the subsequent improvement of the hydroxide structure. The structural 3 imperfectness of Nd(OH) results in a very low intensity of the hydroxide spectra even at advanced stages of oxidation. This means either 3 that the hydroxide is composed of very fine grains and / or that its structure is amorphous. We observed the similar improvement of the structure with time for hydroxides produced by oxidation of the hydrogenated Nd-Fe-B and NdH . It is well established that the x oxidation proceeds much slower in the virgin Nd-Fe-B powder than in the hydrogenated one. We present evidence that the rate of the oxidation process can be controlled by the amount of hydrogen absorbed by the alloy. We also show that the oxidation curves of the partially hydrogenated samples can be decomposed into the oxidation curves of fully hydrogenated and not hydrogenated samples.

Research paper thumbnail of Local Co anisotropy in Y-Co compounds

IEEE Transactions on Magnetics, 1984

Research paper thumbnail of The kinetics of oxidation of Nd-Fe-B powders

IEEE Transactions on Magnetics, 1993

ABSTRACT The kinetics of oxidation of 2.5 μm Nd-Fe-B powder are studied at temperatures 20, 80, 1... more ABSTRACT The kinetics of oxidation of 2.5 μm Nd-Fe-B powder are studied at temperatures 20, 80, 100 and 115 °C. The powdered alloy compromises 62.5 wt.% Fe, 35 wt.% Nd and 1.3 wt.% B. The percentage of weight gain is measured and compared with X-ray spectra recorded after various periods of oxidation. Two stages of oxidation, with powder-like and exponential weight gain reaching a plateau, are distinguished at all temperatures. The effect of changes in phase composition on ferromagnetic properties due to oxidation are examined by a magnetic balance. On the basis of reported measurements, it is concluded that two processes contribute to oxidation of Nd-Fe-B in air, i.e., relatively quick, total oxidation of intergranular Nd and oxidation of Nd2 Fe14B (Φ) which stops at 12% level. The recognition of three products of the oxidation at X-ray spectra, Nd2O3, NdFeO3 and Fe3O4 , makes it possible to deduce a final phase composition