Materials Letters 205 (2017) 261–263
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Electromagnetic interference shielding effectiveness of titanium carbide sheets Xinli Liu a,⇑, Jisi Wu b, Jun He c, Lei Zhang b,⇑ a
School of Materials Science and Engineering, Central South University, Changsha 410083, China State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China c School of Physics and Electronics, Central South University, Changsha 410083, China b
a r t i c l e
i n f o
Article history: Received 27 May 2017 Received in revised form 20 June 2017 Accepted 21 June 2017 Available online 22 June 2017 Keywords: MXene Ti3C2 Electromagnetic interference shielding Absorption
a b s t r a c t Ti3C2 sheets with typical lamellar structure have been successfully obtained by etching Ti3AlC2 powders in HF. The electromagnetic interference shielding effectiveness (EMI SE) of the Ti3C2/paraffin composites with different Ti3C2 contents were measured in the frequency of 2.0–18.0 GHz. Results show that EMI SE increases with the filled content of Ti3C2, and the total shielding effectiveness reaches up to a maximum of 39.1 decibels (dB) for the Ti3C2/paraffin composites with 60 wt% Ti3C2 and a thickness of 2.0 mm. The Ti3C2/paraffin composites are both absorptive and reflective to electromagnetic radiation, and the main shielding effectiveness is resulting from absorption. Our findings suggest these kinds of 2D transition metal carbides (MXene) will be good candidates for fabricating EMI SE composites with high performance and light weight. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction The rapid development of electronic devices generates severe EMI and radiation, which has detrimental effects on the equipment performance as well as the surrounding environment for human health [1,2]. Many kinds of materials have been developed to combat EMI interference. Recently, great efforts have been made for the development of novel high performance EMI shielding materials with light, low cost, good corrosion resistance and processability. Among them, the polymer composites with conductive fillers can meet the requirements. The EMI SE of the polymer composites mainly depends on the intrinsic property and the content of the conductive fillers [2,3]. Carbon-based fillers [4–6] have been investigated extensively in the past few years, but no breakthrough has been reported thus far . Therefore, new EMI SE material is strongly needed for the requirements of smarter electronic devices. MXenes are a family of two-dimensional transition metal carbides and/or nitrides prepared by selective exfoliation the A layers from the MAX phases [7,8] (where M is transition metal; A is an A-group element, mostly IIIA and VIA; X is C or N element). MXenes were first reported by Naguib , and have attracted much interest due to their unique structure and good electronic conductivity, and already shown promising performance in the
area of energy storage , catalysis , sensor , electromagnetic materials [1,13] etc. Recently, Shahzad et al.  studied the EMI SE of a 45 mm thick Ti3C2Tx film, and found the Ti3C2Tx film exhibit EMI SE of 92 dB in the frequency of 8.2–12.4 GHz. Qing et al.  investigated the electromagnetic properties of Ti3C2 sheets in the frequency of 12.4–18.0 GHz, and showed the Ti3C2 nanosheets have high relative complex permittivity and microwave absorption property. These results illustrate Ti3C2 has high EMI SE. However, the EMI SE data varies with many uncontrolled factors such as the thickness of the shielding samples, the content of conductive fillers, the frequency at which the EMI shielding performance was carried out, the polymer matrix type, the fabrication method and processing conditions . Therefore, the EMI shielding properties of Ti3C2Tx sheets in broad band and act as fillers should be studied, which is important to the practical application of the materials. In this study, Ti3C2 sheets obtained by etching Ti3AlC2 powders were loaded into paraffin matrix to form composites. The EMI SE of the composites with different ratio of Ti3C2 filler were studied. The results indicate that Ti3C2-based composites have highperformance EMI SE.
2. Materials and methods ⇑ Corresponding authors. E-mail addresses: [email protected]
(X. Liu), [email protected]
(L. Zhang). http://dx.doi.org/10.1016/j.matlet.2017.06.101 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
Ti3AlC2 powders were prepared using commercially pure TiH2, Al and C powders as the starting materials. The mole ratio of Ti
X. Liu et al. / Materials Letters 205 (2017) 261–263
to Al to C is being 3:1.2:2. Excessive Al addition can ensure the purity of Ti3AlC2 . The powders were gently ball-mixed for 12 h using a powder rotator mixer, and then sintered in a vacuum furnace. The compacts were initially sintered at 600 °C for 60 min to remove H from TiH2. Then, the compact discs were held at 1350 °C for 3 h. The samples were milled and passed through 400 mesh sieve. The as-prepared Ti3AlC2 powders were immersed in 40% HF for 24 h at room temperature. The corrosion products were filtered and washed several times with deionized water until the pH = 7, and then dried in a vacuum oven at 80 °C for 12 h. The morphology of Ti3C2 was observed by field-emission scanning microscopy (SEM: Quanta FEG250, FEI, Hillsboro, USA). The phase composition of the samples before and after etching were analyzed by X-ray diffraction (XRD: Dmax 2500VB, Rigaku, Tokyo, Japan) using a Cu Ka source. The structure of Ti3C2 was investigated by transmission electron microscopy (TEM, JEOL-2100F, Tokyo, Japan) operating at 200 kV. The S parameters (S11, S12, S21 and S22) were obtained according to the ASTM-1999 standard by using an enlarged coaxial transmission line sample holder in the frequency range from 2.0 to 18.0 GHz using a vector Network Analyzer (AV3629). The Ti3C2 sheets with different contents were added into paraffin which was completely melted. Then the uniform mixed composites were poured into a metal mold and pressed into the required shape with outer and inner diameter of 7.0 mm and 3.0 mm. All samples are 2.0 mm thick.
3. Results and discussion The XRD patterns of Ti3AlC2 powders before and after HF treatment are shown in Fig. 1. It can be seen there is a distinct difference between the two patterns. After etching, the peaks for Ti3AlC2 are disappeared, and the peaks indexed to Ti3C2 shift to lower angles as compared with the peaks of Ti3AlC2, indicating the Al atoms present in the Ti3AlC2 crystal have been selectively etched. The different magnification SEM images of the prepared Ti3C2 sheets are shown in Fig. 2(a) and its inset, confirming the Ti3AlC2 powders have been successfully etched into a flake structure. The sheets are quite thin and transparent to electrons as illustrated in the TEM image (Fig. 2(b)). The corresponding SEAD pattern present in the inset of Fig. 2(b) clearly reveals Ti3C2 has the same hexagonal crystalline structure as the precursor of Ti3AlC2. The EMI shielding effectiveness of the Ti3C2/paraffin was measured through the S parameters obtained from a vector Network Analyzer. The reflection (R) and transmission (T) coefficients were calculated to be
R ¼ jS11 j2 ¼ jS22 j2
T ¼ jS12 j2 ¼ jS21 j2
The total EMI SE is the sum of the contributions from reflection (SER), absorption (SEA) and multiple internal reflections (SEM). At higher EMI SE values, the SEM is generally neglected. So the total SE can be written as [1,3]:
SET ¼ SER þ SEA
SER and SEA can be expressed in terms of reflection and effective absorption considering the power of the incident electromagnetic waves inside the shielding material as [3,16]:
SER ¼ 10 log
! 1 1 ¼ 10log 1R 1 jS11 j2
! 1R 1 jS11 j2 ¼ 10log T jS21 j2
SEA ¼ 10 log
Fig. 1. XRD patterns of Ti3AlC2 and as prepared Ti3C2.
Fig. 3(a) shows the SE total of the Ti3C2/paraffin composites with different contents of Ti3C2 as the function of frequency. It can be seen that, as the Ti3C2 content increases, the total EMI SE (SEtotal) increases to a maximum of 39.1 dB for theTi3C2/paraffin composites with 60 wt% Ti3C2, which is much higher than the
Fig. 2. (a) Different magnification SEM images of Ti3C2; (b) TEM image and inset is the corresponding SAED pattern.
X. Liu et al. / Materials Letters 205 (2017) 261–263
Fig. 3. (a) EMI SE of the composites with different Ti3C2 contents (5–60 wt%) in frequency range of 2.0–18.0 GHz at a thickness of 2.0 mm; (b) Comparison of SEtotal, SEA and SER of Ti3C2/paraffin composites with Ti3C2 content of 60 wt%.
required for commercially applicable in EMI shielding devices around 20 dB . The shielding efficiency of the material is calculated according to the following equation :
Shielding efficiency ð%Þ ¼ 100
The shielding efficiency calculated according to Eq. (6) is nearly 99.99%. The contribution of absorption and reflection for the composite with 60 wt% Ti3C2 content is present in Fig. 3(b), and it can be clearly seen that the contribution of absorption to the EMI SE is much higher than that of reflection. For the composites with 60 wt% Ti3C2, SEtotal, SEA and SER are 39.1, 29.3 and 9.8 dB, respectively at the frequency of 2.0 GHz. At the frequency of 18.0 GHz, the SEtotal, SEA and SER are 37.9, 33.6 and 4.3 dB, respectively. The absorption loss contributes to almost 75% of the total EMI SE whether in high frequency or low frequency. These results illustrate Ti3C2/paraffin composites are both absorptive and reflective to electromagnetic radiation in the frequency of 2.0–18.0 GHz, and the main SE resulting from absorption. The EMI SE for Ti3C2 is based on the two-dimensional structure which has excellent electrical conductivity and large surface area. The EM waves are immediately reflected when the EM waves strike the surface of a MXene flake because of abundant free electrons at the surface of the highly conductive MXene . In addition, the incident wave propagated and reflected between the flakes until completely absorbed in the structure. These results indicate that composites with Ti3C2 fillers have a perfect EM SE. Thus, a large family of MXenes obtained by etching the A element from MAX phases are promising EMI shielding materials with tailored composition and functional groups , which will be significant for its application in aerospace and electronic devices. 4. Conclusions Ti3C2 sheets with a typical lamellar structure have been successfully obtained by the treatment of Ti3AlC2 powders in HF.
The EMI SE of the Ti3C2/paraffin composites increases with the filled content of Ti3C2.The SEtotal increases to a maximum of 39.1 dB for the 60 wt% Ti3C2/paraffin composites in the frequency of 2.0–18.0 GHz with a thickness of 2.0 mm. The Ti3C2/paraffin composites are both absorptive and reflective to electromagnetic radiation, and the main SE resulting from absorption. Therefore, the large family of MXenes obtained by etching of A element from MAX phases are promising EMI shielding materials, can be good candidates for application in the electronic devices. Acknowledgments This research was supported by the National Nature Science Foundation of China (Nos. 51674304, 51604305), China Postdoctoral Science Foundation (2016M592445). References                
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