Analytical Characterization of Nd 2 Fe 14 B sintered magnet
Mehenni Mohamed
Laboratory of science and engineering USTHB BP32 El Alia, Bab Ezzouar. Algiers. Algeria.
Lounis Azzeddine
Laboratory of science and engineering USTHB BP32 El Alia, Bab Ezzouar. Algiers. Algeria.
.
Abstract—The remarkable properties (magnetism and corrosion resistance) of the Nd-Fe-B sintered magnet are associated with the presence of other metal elements that Neodymium-Iron-Boron like Cu, Mn, Al, V, Ni and others. With an aim of having information on the components in the Nd-Fe-B matrix and on the distribution of these elements, in this work, the NAA has highlighted the presence of several metallic elements.
Using a mass ratio equal to an activity ratio we can calculate the proportions of detected Elements. The results are: iron with 51.30%, neodymium with 25.41% and other elements like nickel with 1.25%. The rest from the matrix, 22.04%, represents the proportions of B and the other elements traces. In this work we are interested in neutron activation analysis (NAA) in the only reason is to identify the metallic Elements in trace (ppm).
Keywords—NdFeB Sintered magnets, NdFeB characterization, NAA.
I. INTRODUCTION
Magnetic materials of many different types continue to play a critical role in the generation, distribution and utilization of energy. They are both an underpinning technology in existing
equipment and infrastructure, and a
key enabling technology for emerging future applications, for example, the move towards increased generation from renewable, the more efficient use of energy in domestic and industrial settings and in the emerging market for all-electric and hybrid electric vehicles. The breadth of applications for magnetic materials and the scale they cover are very substantial, from devices with dimensions of a few microns at ratings of µW through to single machines of many meters in length with ratings of 1 GW [1].
Magnetic materials exhibit a wide spectrum of magnetic properties which are often tailored to meet the demands of particular applications. They can be classified very broadly into soft or hard magnetic materials, although this rather sweeping categorization inevitably has its limitations for classes of material which sit near the boundary. There are many intricate aspects of behavior and performance which distinguish hard magnetic materials from their soft magnetic counterparts. This distinction is related to several factors, one
of the most important is the presence of trace elements in the matrix of this type of magnet, which leads us to make an approach to understanding the link between the existence of these trace elements and the remarkable properties of these rare earth magnets. The neutron activation analysis is choosing the most effective for this purpose. The results of neutron activation are presented in the form of γ radiation intensity spectra as a function of energy. The methodology adopted in this work is to identify all the elements present in the sample.
This step is very important because it allows us to identify the short period of elements, ie, elements that have a very short half-life. These elements rapidly reaching capacity and therefore they require very short irradiation time. The elements of long time slowly reaching saturation they require higher fluence neutron irradiation [2-3].
II. EXPERIMENTALPROCEDURES Sample preparation
Samples should be prepared before starting the analysis for easy and fast handling. Recovery of NdFeB magnets from hard disk followed by embrittlement liquid nitrogen. This method is linked firstly to the thermo-mechanical shock due to the temperature drop, and secondly to the presence of a high concentration of nitrogen atoms in the cavities and defects (feature of this process) [4-5].
A.Neutron Activation Analysis (NAA)
The neutron activation analysis is a method of making a radioactive sample by irradiating a neutron field and later identified her with the energy emitted by the isotopes and their corresponding half life. This technique allows to determine the concentrations of elements without component materials provided impose conditions on the physical or chemical form.
III. RESULTS AND DISCUSSION
We presented the results of neutron activation as intensity spectra of γ radiation as a function of energy. The
Gedioura Bouzide
Reactor Division. Nuclear Research Centre. Draria.
Algiers. Algeria.
methodology adopted in this work is to identify all the elements present in the sample. This step is very important because it allows us to identify short and long period elements.
The short-period elements become saturated quickly and therefore they require very short irradiation time. The long- period elements slowly reach saturation. They require higher fluence neutron irradiation. The qualitative analysis of elements is performed by short periods γ spectrometry.
Induced activity in the sample is due to radioisotope production. When N1stable atoms of a material are irradiated by a neutron flux φ(n/cm2/s) for a time dt, the number of radioactive atoms N1formed is given by the (equation 1). At the same time begin the disappearance decay of radioisotopes formed. The system of evolution equations is obtained by producing the balance production – disappearance (equation
2). dN1/ dt = σ1.φ.N1 (1)
dN2/dt = σ1.φ.N1– σ2.φ.N2– λ2N2 (2) Where:
σ
i(cm²) the capture cross section of the radioisotope i
N1
et
N2(at/cm
3): density numbers respectively of the isotopes X
1and X
2
λ
i(s
-1): constant of radioactive decay of the radioisotope i
( n/cm²/s): neutron flux
t
(s): neutron irradiation time
With the following conditions at t=0, N1(0)=
N
10and N2(0)=0, the solution of the system of equations (1) and (2) is written:e
tN t
N
1( )
10 1. (3) MAN m
. .
10
(4)
Where: m: mass of the sample
N: Avogadro's number
MA
: atomic mass,
: isotopic enrichment
) ) (
( . ) .
(
. . ( . )2 1 2
10
2 t 1 N e 1 t e 2 2 t
N
(5)
The activityA2(t)is written:
A2(t) = λ2.N2(t) (6) Askingλ*.= λ2.N2 +σ2.φequation (6) is written:
) . (
. ) .
( 1.. *
1
* 0 1 1
2 2 ti ti
i N e e
t
A
(7)
This relation is valid in most cases. However when it comes to a long irradiation for the elements with a large cross sections of absorption (high neutron flux), then take into account the consumption of target (burn-up).
For items with a large full resonance, consideration should account the fraction of the neutron spectrum located beyond
the thermal field. The term σ1φ will be replaced by (σ1φ+I0.φepi)
Where:
φepi
is the epi-thermal neutron flux and I
0, the resonance integral (in barns).
The sample activity at the end of irradiation (at time t = ti) and after a time decreasetdis given by equation (8).
td i d
i t A t e
t
A2
( , )
2( )
2 (8) The cumulative activity of the sample after a timetccount is:dt e t t A t t t
A (i, d, c) tc (i, d) 2tc
0 2
2
(9)
d c
i t t
c t d
i t t N e e e
t
A( , , ) . . (1 2 )(1 2 ) 2
2 10 2 1
(10)
Determining the individual half-life of each radioelement is made by following the decrease of this one at constant time intervals. Table 1 provides the nuclear reactions used for sample analysis. The presence of specific radioisotopes is demonstrated in the γ spectra (Fig.1-4).
Figure.1:Gamma spectrum of Nd-Fe-B matrix in [500, 1200] (KeV)
Figure.2:Gamma spectrum of Nd-Fe-B matrix in [1200, 1900] (KeV).
Figure.3 :Gamma spectrum of Nd-Fe-B matrix in [500, 1000] (KeV).
Figure.4 :Gamma spectrum of Nd-Fe-B matrix in [1000, 1400] (KeV).
Table1. Nuclear reactions for sample analysis
Element Target
isotopes Nuclear
reactions product ε
(%) λ (s-1) γ peak (KeV) Nd 146Nd 146Nd (n, γ)
147Nd 147Nd 17.2 7.30E-
07 531
Fe 58Fe 58Fe (n, γ)
59Fe 59Fe 0.28 1.68E-
07 1099
Co 59Co
59Co (n, γ)
60Co
61Ni (n, p)
60Co
60Co 100 3.79E-
09 1173
Al 28Al 28Al (n, γ)
29Al 29Al 100 4.68E-
03 1780
V 51V 51V (n, γ)
52V 52V 99.7
5 2.8E-
03 1435
Cu 63Cu 63Cu (n, γ)
64Cu 64Cu 69.1
5 1.36E-
05 511
For the four energy intervals we can clearly infer the existence of elements that accompany Fe and Nd, these are: Al28, V52, Mn56, Cu66, Ge66, Ag108, Cs 136, Bk246, Tb160, Bk246.
Note also the presence of rare earth elements such as Dy160 and its isotope Dy165. The elements of long period require very large irradiation time and do not appear on these spectra.
The time counting of the vanadium element is taken as the reference time. The time decay of the respective elements will be determined from time decay vanadium which is given in table 2.
Table2. Reference time of the elements analyzed by NAA
The energy measured by the neutron activation technique is confirmed by tables and energy isotopes. Tables 3 and 4 show the ratios of the Nd-Fe-B matrix obtained by neutron activation analysis, where all the elements short and long periods present appeared.
Table3. Elements present in the Nd-Fe-B matrix after 2Min of a decay time
Probable
radioisotope Energy
measured Probable
radioisotope Energy measured
Ti-51 242 Lu-177m 54.07
Ni-65 55 Sm-153 69.67
In-116m 92 Eu-155 86.54
Ni-65 39 Cd-109 88.03
Cu-64 274 Nd-147 91.11
Ti-51 14 Np-239 99.55
Ni-65 24 Ta-182 100.11
In-116m 818.70 Sm-153 103.18
Mg-27 843.76 Gd-153 103.18
Mn-56 846.77 Np-239 103.76
Ni-65 852.70 Eu-155 105.31
Ti-51 928.63 Lu-177m 105.36
Ni-65 952.99 Np-239 106.12
Cu-64 1346.55 Np-239 117
V-52 1434 Se-75 121.12
Al-28 1778 Eu-154 123.07
Mn-56 1810.67 Ba-131 123.84
Element Decay time (s)
Vanadium 0
Cooper/Manganese 9035
Neodymium 18585
Iron 91534
Nickel 100219
Nd-Fe-B Matrix 169477
Cobalt 176891
IV.CONCLUSION
We showed that the neutron activation analysis method provides qualitative information on all metallic elements present in the Nd-Fe-B matrix. This technique is very fast and easy to implement, it helped to highlight the presence of several metal elements (Fe, Nd, V, Ni, Al, Mn, Cu, rare earth ultra trace that accompanies neodymium as Dy, Pr). The results are: at 51.30% iron, 25.41% neodymium and other elements such as nickel, 1.25% of the matrix. The rest of the matrix, 22.04%, representing the proportions of B and other trace elements.
The remarkable properties of NdFeB magnets are associated with the presence of trace elements such as Dy, Pr, Ti, Al, V, Co, Mn and Mg.
Acknowledgment
This work was supported in part bythe laboratory of science and material engineering. In part by the reactor division of
nuclear research center of draria.
References
[1] I. R. HARRIS, G. W. JEWELL , Rare-earth magnets: properties, processing and applications, University of Birmingham and University of Sheffi eld, Woodhead Publishing Limited, pp 600. 2012, UK.
[2] A. KANDROM, “Fragilisation par le froid“, Air Liquide Canada, Gas Association, 2006, CANADA.
[3] H. LARIBOU, “Mécanismes d’endommagement et de traitement des surfaces métalliques par un jet d’azote à basse température“, thèse de doctorat, Université Paul Verlaine-Metz, Octobre 2011.
[4] A. HUSTONE, “the use of cryogenic fluids“,TIS/GS, Edms 335812, 1998.
[5] G.H. Yan, R.J. Chen, Y. Ding, S. Guo, A. Don Lee, R. Yan, J. Phys.:
Conf. Ser. 266 (2011) 012052.
