Fabrication of porous disk-like Ni/NiO microwave absorber and its excellent broad frequency absorption performance

Article abstract of DOI:10.1016/j.jallcom.2017.09.226

This research reports a novel porous disk-like Ni/NiO binary composite with the diameter of disk ranged in 100–200 nm and the size of the porous distributed in 5–10 nm. The absence of Ni was generated by the partial reduction of NiO. This porous Ni/NiO product owns the matched impedance matching and attenuation electromagnetic wave ability since the moderate complexed permittivity and improved permeability value. In this regard, this composite proves to be desired electromagnetic absorber to treat the increasingly electromagnetic interference issue (EMI). The qualified absorption frequency bandwidth of the optimal Ni/NiO product covers 6.4 GHz (11.2–17.6 GHz) under the coating layer thickness of 1.5 mm. The excellent electromagnetic absorption properties have been discussed in depth. The unique porous structure benefits to the electromagnetic absorption performance which is due to the suppressed eddy current effect.

Full text of DOI:10.1016/j.jallcom.2017.09.226

Accepted Manuscript
Fabrication of porous disk-like Ni/NiO microwave absorber and its excellent broad
frequency absorption performance
Yuhang Guo, Songtao Dong, Suwei Liu, Ye Cheng, Zhenya Zhang, Hongying Wang
PII:
S0925-8388(17)33276-0
10.1016/j.jallcom.2017.09.226
JALCOM 43282
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 22 February 2017
Revised Date: 18 September 2017
Accepted Date: 21 September 2017
Please cite this article as: Y. Guo, S. Dong, S. Liu, Y. Cheng, Z. Zhang, H. Wang, Fabrication of porous
disk-like Ni/NiO microwave absorber and its excellent broad frequency absorption performance, Journal
of Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.09.226.
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ACCEPTED MANUSCRIPT
Fabrication of Porous Disk-like Ni/NiO Microwave Absorber
and Its Excellent Broad Frequency Absorption Performance
a,*
a
b
a
c
Yuhang Guo ,Songtao Dong ,Suwei Liu ,Ye Cheng , Zhenya Zhang , Hongying
d,**
Wang
a
School of Materials Science and Engineering, Jiangsu University of Science and Technology,
Zhenjiang, Jiangsu,212003,China
b
Engineering Training Center, Nantong University, Nantong, Jiangsu,226019,China
c
School of Material Science and Engineering, Jiangsu University, Zhenjiang, 212013, China
d
School of Materials Science and Engineering, Jiamusi University,Jiamusi, Heilongjiang,
1
54007,China
*
Corresponding Author :
Prof Dr. Yuhang Guo
Tel./fax: +86 511 84401188
.
E-mail addresses: guoyuhang@just.edu.cn
*Corresponding Author:
*
Prof Dr. Hongying Wang
Tel./fax: +86 454 8618701.
E-mail addresses: wanghongying_hm@163.com

ACCEPTED MANUSCRIPT
Abstract:
This research reports a novel porous disk-like Ni/NiO binary composite with the diameter of disk
ranged in 100-200 nm and the size of the porous distributed in 5-10 nm. The absence of Ni was
generated by the partial reduction of NiO. This porous Ni/NiO product owns the matched
impedance matching and attenuation electromagnetic wave ability since the moderate complexed
permittivity and improved permeability value. In this regard, this composite proves to be desired
electromagnetic absorber to treat the increasingly electromagnetic interference issue (EMI). The
qualified absorption frequency bandwidth of the optimal Ni/NiO product covers 6.4 GHz
(11.2-17.6 GHz) under the coating layer thickness of 1.5 mm. The excellent electromagnetic
absorption properties have been discussed in depth. The unique porous structure benefits to the
electromagnetic absorption performance which is due to the suppressed eddy current effect.
Key words: porous disk-like, Ni/NiO, electromagnetic interference, qualified absorption
frequency, eddy current effect.
1
: Introduction:
Because of the exposure application of wireless communication, local area networks, radar
detector devices, the problem of electromagnetic interference (EMI) has possess a negative role on
our daily life. [1-2] Therefore, an available method to settle such a problem is to explore a
high-performance electromagnetic absorber to eliminate this electromagnetic interference issue. [3]
As we know, before to attenuate the electromagnetic wave, the electromagnetic absorption layer
can let the indent electromagnetic wave enter in and decrease the interface reflection. In this
regard, a good impedance matching performance is expected to achieve for the absorber. [4-5]
Based on the electromagnetic absorption mechanism, decrease the complex permittivity parameter
or improve the permeability value are the efficient strategy to reach a good impedance matching
behavior. [6] Based on the above consideration, a few ferrites thus have attracted intense interests.
The complex permittivity value of ferrites is ranged in the moderate region. Meanwhile, the
magnetic properties of ferrite will reach an improvement complex permeability value as compared
to nonmagnetic absorber. [7-8] However, ferrites are suffered from the poor attenuation ability and
limited their applications, especially the dielectric loss ability. [9-11] It is widely believed that the
dielectric loss behavior is resulting from the polarization and conductive loss. The high-frequency
(>GHz) polarization form is primary resulting from the interface polarization. [12-13]. Owning to

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the weakly conductive loss and polarization ability, thus ferrites are hard to present the good
performance on the electromagnetic absorption properties. Based on above consideration, design
of metal/metal oxide binary composites has been proved to be an efficient strategy to strong the
polarization intensity with the below advantages. [14]. On the one hand, the absence of metal in
metal/metal oxide benefits to the conductive loss intensity since the improved conductive value.
On the other hand, the interface between metal and metal oxide is enable to boost the polarization
intensity. As a result, the dielectric loss can be boosted."[15] Zn/ZnO product was prepared by the
reduction strategy and the RLmin value was -23.0 dB. [16] Zhao et.al. used the hydrothermal
method to prepare Ni/SnO absorber and the minimum reflection loss value was up to be -37.6 dB.
2
[17] Recent findings revealed that these types of metal/metal oxides are suffered from the eddy
current.[18] According to the electromagnetic absorption theory, the eddy current effect happens at
magnetic absorber and prevents the electromagnetic wave enter into the absorption layer which
should be suppressed.[19] Design of porous metal/metal oxide composite is able to suppress this
unwanted eddy current effect, according to Ji’s review.[20] For example, the porous 3-dimentional
flower-like Co/CoO composite was synthesized by Lv et.al and the optimal reflection loss value
was up to -50.0 dB.[21] The electromagnetic absorption properties of porous cube-like Fe/SiO2
also have been researched by Yang et.al and the optimal absorption value was approximately -50
dB.[22]
In this research, the electromagnetic absorption properties of porous disk-like Ni/NiO was
investigated. NiO was obtained at the initial stage and subsequently followed reduction process,
the Ni was generated and resulted in the Ni/NiO binary composite. This product presented the
novel electromagnetic absorption properties.
2
2
: Experimental Section:
.1 Fabrication of porous disk-like NiO sample.
Porous disk-like NiO was synthesized by a simple hydrothermal method. In a typical process, 500
mg anhydrous nickel chloride (NiCl ) was dissolved in 50 ml of distilled water with ultrasonic
2
treatment for 30 min. Then, ammonia solution was dropwise into the solution and the control the
PH value to 10. Afterward, the transparent solution was added into the autoclave (100 mL) for
o
hydrothermal reaction at 160 C for 10 h. The obtained precipitate was collected and then washed
o
3
-5 times. Finally, the precipitate was dried at 80 C for 24 h. Porous disk-like NiO (denote as S1)

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o
was obtained by annealed in a tube furnace at 400 C for 5 h in air.
2
.2 Preparation of Ni/NiO composite:
"The Ni/NiO composite was prepared by another hydrothermal method. Typically, 100 mg of
disk-like NiO and a certain volume of ammonia were dissolved in 30 mL distilled water and
stirring 30 min. The PH value should be ranged in the region of 12~14.Then, hydrazine hydrate
was added into the above solution as the reduce agent to transfer the NiO into metal. After 5 mins,
o
the mixture solution was transferred into a 100 mL autoclave and heated at 150 C for 20 h. The
samples obtained with 5, 10,15 mL of hydrazine hydrate were denoted as S2 S3 and S4,
respectively."
2
.3 Characterization
The power X-ray diffraction (XRD) patterns spectral were obtained by a Bruker D8 X-ray
diffraction using Cu Kα radiation (λ=0.154178 nm). The magnetic properties of coercive force
and magnetization were examined by a vibrating sample magnetometer (VSM, Lakeshore,
Model 7400 series) at 298 K. The XPS spectrum was obtained with a PHI 5000 VersaProbe
systems which an Al Kα X-ray source operating at 150 W. The magnetization hysteresis curves of
the samples were conducted by a vibration sample magnetization (VSM, Lakeshore, Model 7400
series). The electromagnetic parameters of these products were measured using the coaxial-line
method utilizing an Agilent Network Analyzer N5230 and the tested frequency was in the range of
2
-18 GHz. The sample was prepared by homogenously mixing the paraffin wax with 50 wt% of
the sample and then compressing into toroidal-shaped samples with 7.0 mm in outer diameter and
.04 mm in inner diameter. In this way, the electromagnetic parameters (includes ε', ε'', ꢀ', ꢀ'')
3
could be obtained. The reflection loss curves could be drawn by inputting the electromagnetic
parameters into the below formulas (1) and (2): [23-26]
1
/2
1/2
Z =Z (ꢀ /ε ) tanh[j(2πfd(ꢀ ε ) /c)]
(1)
(2)
in
o
r
r
r r
RL(dB)=20log|(Z -Z )/(Z +Z )|
in
o
in
o
Where Z is the input impedance of the absorber, f is the frequency of electromagnetic wave, d is
in
the coating thickness of the absorber while c is the velocity of electromagnetic wave in free space.
ε (ε =ε'-jε'') and µ (µ =µ'-jµ'') are the complex permittivity and permeability of the absorber.
r
r
r
r
3
: Results and Discussion:
Figure 1a shows the XRD patterns of the as prepared composite under addition of 10 mL

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o
hydrazine hydrate. The diffraction peaks at 37.2, 43.2, and 62.8 can be assigned, respectively to
(101), (012) (110) crystal planes of the NiO (JSPDF card no: 44-1159). Whereas, the sharply
o
diffraction peaks at 44.5, and 51.8 can be indexed to the (111) and (200) crystal planes of metal
Ni (JSPDF card no: 04-0850). There are no any other impurities peaks could be observed. In
Figure 1b, the porous disk-like shaped structure could be observed in the TEM images. The size of
each disk ranges in 80-100 nm. Magnify the image, the diameters of these porous are distributed
in the range of 5-10 nm, as seen in the Figure 1c. The HR-TEM images reveals that there are two
types of lattice fringes, with the lattice spacing d values of 0.241 and 0.202 nm, which are ascribed
to the (111) plane of NiO and (111) plane of metal Ni, respectively.
The atomic ratios of Ni/NiO are easily controlled by tuning the volume of hydrazine hydrate.
Without addition of the reduction agent, the obtained product is NiO (denoted as S1), as seen in
the Figure 2a. If more the hydrazine hydrate (V=20 mL) was added, the initial porous NiO was
totally converted into metal Ni (S4), as proved by the XRD patterns (Figure 2a). If the volume of
reduction agent is fixed at 5 and 10 mL, the phase compositions of obtained samples are Ni and
NiO. The TEM images of S1, S2 and S4 were showed in Figure S1(Support information). Actually,
all of these products show disk-like structure. The size of porous is larger with more volumes of
hydrazine hydrate.
In this research, the Ni/NiO products reduced by 5 and 10 mL are denoted as S2 and S3,
respectively. To analyze the atomic ratios of Ni/NiO, X-ray photoelectron (XPS) technique as an
efficient way to analysis the composite and valance state, as presented in Figure 2 b-c. [27-30]
By fitting the Ni 3/2p peak, the metal Ni and NiO characterized peaks can be obtained with the
binding energy value of 852.0, 854.2 eV, respectively. [31] The surface area ratios of Ni and NiO
peaks are estimated to be 1:4 and 2:1 for S2 and S3, suggesting their atomic ratios. It is widely
believed that the larger magnetization value will lead to the bigger magnetic loss and improvement
impedance matching behavior, since the enhancement of complex permeability value. [32] The
magnetization values were obtained on a vibrating sample magnetometer. In Figure 3, the
magnetization values are 0, 14.2, 32.8, 48.2 emu/g for the S1, S2, S3 and S4 products
3
.2: The Electromagnetic Absorption Properties:
The electromagnetic absorption properties of these products are shown in Figure 4. To evaluate the
electromagnetic absorption property of one absorber, the qualified frequency bandwidth (also

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called as effective absorption frequency region) referring to the region of RLmin value less than -10
dB should be as broader as possible. At the same time, a good electromagnetic absorption property
should be obtained within a small absorption layer thickness (d). [33] To see the Figure 4a, all the
RLmin values calculated at 1.5-3.0 mm are smaller than -5.0 dB for S1, indicating the poor
electromagnetic absorption properties. As for S2 product, the effective absorption bandwidth at
1
.5 mm reached 2.2 GHz (15.8~18 GHz). When the absorption layer thickness more than 2.0 mm,
the absorption frequency bandwidth is smaller than 2.0 GHz. The qualified absorption frequency
bandwidth at 1.5 mm improves to 6.4 GHz (11.2~17.6 GHz) for S3. Even so, the qualified
absorption bandwidth of S3 still are larger than 4.0 GHz at 2.0 and 2.5 mm. While for S4, the
minimum reflection loss values are all bigger than -10 dB and thus have no qualified absorption
region.
To better understanding the difference in the electromagnetic absorption properties, the
electromagnetic parameters have been given in the Figure 5-6. It is widely believed that the
electromagnetic parameters influence both the impedance matching and attenuation (including
dielectric and magnetic loss ability) ability. By this way, the final electromagnetic absorption
properties can be achieved and thus indirectly decides the final electromagnetic absorption
properties. [34] Figure 5 lists the permittivity parameters (ε'/ε'') of S1-S4 products. The
electromagnetic absorption theory reveals that the real part permittivity value (ε') refers to the
storage electrical ability while the imaginary part of permittivity value (ε'') means the dielectric
loss ability which composed by the polarization and conductive loss behavior (ε''). [35] In Figure
5
a, the ε' value of S1 is ~3.2 at whole frequency region and the ε'' value is almost approximately 0.
In Figure 5b, due to the presence of Ni, the value of S2 improves to 8.4-8.0. Meanwhile, the ε''
value improved to 1.9-3.3 which probably attributes to the stronger conductive loss ability. At
higher frequency region (12-18 GHz), two obvious peaks can be seen. These two peaks may relate
to the interface polarization effect at the Ni and NiO interface. [36-37] As for S3, the ε'' value also
further increases to 12.2-12.0. Similar two peaks also can be found at S3 (seen Figure 5c). After
the NiO totally be reduced to Ni, both the ε' and ε'' values present the sharply increase,
representing the strongest conductive ability. Besides, the two peaks disappeared which probably
due to disappeared Ni and NiO interface, as shown in Figure 5d.
The permeability parameters have been given in Figure 6. Similarly, the real part of permeability

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(ꢀ') value means the storage magnetic ability and the imaginary part of permeability refers to the
magnetic loss ability. [38] For nonmagnetic material, the ꢀ' value is ~1.0 and the ꢀ'' value is
almost 0, liking carbon materials. [39-41] As seen the Figure 6b, the ꢀ' value of S2 is larger than
1
.0 (1.23-1.15). For S3, the ꢀ' value is further increases to 1.31-1.18 and ꢀ'' value in the region of
.5-0.1 (seen Figure 6c). In Figure 6d, the ꢀ' value of S4 is 1.4-1.2 and ꢀ'' value is nearly 0.25.
0
One conclusion can be made that the improvement of Ni atomic ratio will lead to the stronger
magnetic loss ability.
Generally, the attenuation constant α represents the integral attenuation ability including magnetic
and dielectric loss ability which can be expressed by the below equation: [42]
2
π
f
2
2
α
=
×
(
µ
′
ε
′ −
µ
′
ε
′
)
+
(
µ
′′
ε
′ −
µ
′
ε
′
)
+
(
µ
′
ε
′′ +
µ
′′
ε
′
)
c
(3)
It could be observed from Figure 7 that S4 presents the largest attenuation value among these
samples which is due to the contribution of conductive and magnetic loss ability. S1 owns the
lowest attenuation constant value α value. This is primary reason why S1 shows the poorest
electromagnetic absorption properties. However, S4 was suffered from the poor impedance
matching ability which is due to the larger ε value (ε =ε'-jε''). S3 with the optimal absorption
r
r
properties can be attributed to the matched impedance matching and attenuation ability.
The porous structure also benefits to the electromagnetic absorption properties since the
suppressed eddy current. As we know, eddy current effect generally happens at the magnetic
material. [43] Although eddy current loss is one of the magnetic form, the generated circle current
will prevent the incident electromagnetic wave enter into the absorption. For example, the
microwave absorption properties of flaky carbonyl iron were no more than -10 dB. [44] The
optimal reflection loss value of spherical-shape Ni is also bigger than -10 dB. [45] The poor
electromagnetic absorption properties of these magnetic materials all attributed to the current eddy
effect. Design porous structure has been considered to be an efficient route to prevent the
fabrication of circle eddy, according to current literature. [46] To best of our knowledge, the eddy
current effect could be expressed in the below equation: [47]
-
2 -1
2
C =ꢀ''(ꢀ') f =2πꢀ d δ
o
0
Where δ is the electric conductive. If the eddy current effect happens at the magnetic material
the C will be a constant at tested frequency. If not, it means the current effected did not
o

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happened on this material. As seen in Figure 8 a-d, the C values of the four samples are
o
changeable at 2-18 GHz.
4
: Conclusion:
The Ni/NiO binary composite with porous disk-like structure has been introduced in this research.
Firstly, porous disk-like NiO was prepared by a simple hydrothermal process and followed by
another hydrothermal reduction route, partial NiO can be converted into metal Ni and resulted in
magnetic Ni/NiO porous disk-like structure. This binary composite presented the moderate
impedance matching and attenuation ability if applied as electromagnetic absorber to treat the
electromagnetic interference issue. The calculated electromagnetic absorption results revealed that
the qualified absorption frequency of this optimal Ni/NiO composite was up to 6.4 GHz (11.2-17.6
GHz) which was much better than single component of NiO or Ni. The excellent electromagnetic
properties were proposed in this research which were attributed to the probable conductive loss. At
the same time, the interface between Ni and NiO also benefited to the attenuation of
electromagnetic wave.
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Figure 1.
Figure 2.

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Figure 3.

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Figure 4.

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Figure 5.

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Figure 6.
Figure 7.

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Figure 8.
Captions:
Figure 1: (a): The XRD patterns of the Ni/NiO porous disk-like composite; (b-c): The
low-resolution TEM images of the Ni/NiO composites; (d): The High Resolution TEM
(HRTEM) image of the Ni/NiO composite;
Figure 2: The XRD patterns of the samples prepared with 0 and 15 mL hydrazine hydrate; (b):
The XPS spectrum of Ni/NiO sample obtained with 5 mL hydrazine hydrate; (c): XPS spectrum
of Ni/NiO sample obtained with 10 mL hydrazine hydrate;
Figure 3: The magnetization values of the four samples. (S1-S4);
Figure 4: The reflection loss images of the samples prepared with various of hydrazine hydrate; (a)
S1 (0 mL); S2(5 mL); (c) S3(10 mL); (d) S4 (15 mL);
Figure 5: The real/imaginary part permittivity values of the samples prepared of the S1-S4
samples: (a) S1; S2; (c) S3; (d) S4;
Figure 6: The real/imaginary part permeability values of the samples prepared of the S1-S4

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samples: (a) S1; S2; (c) S3; (d) S4;
Figure 7: The attenuation constant of the S1-S4 samples;
Figure 8: The Co-f curves of the four samples; (a) S1; S2; (c) S3; (d) S4;

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Highlights:
1
) The porous disk-like structure is able to suppress the unwanted eddy current effect.
) The partial reduction of NiO benefits to the impedance matching and attenuation
electromagnetic ability;
2
3
) The electromagnetic absorption performance was tunable by adjusting the reduction degree.
) The optimal qualified absorption frequency bandwidth could up to 6.2 GHz while the
thickness was only 1.5 mm.
4