电磁屏蔽材料用银包玻璃微珠核_壳粒子的制备及其性能_英文_

马会娜等：导电颗粒钨对氮化铝陶瓷性能的影响· 301 ·电磁屏蔽材料用银包玻璃微珠核–壳粒子的制备及其性能王一龙1,2，官建国1，邵寒梅1，章桥新1，段君元1，孙斌3(1. 武汉理工大学，材料复合新技术国家重点实验室，武汉 430070；2. 武汉理工大学理学院化学系，武汉 430070；3. 武汉理工大学材料科学与工程学院)摘要：采用自组装化学镀银技术制备了银包玻璃微珠核–壳粒子，并且运用X射线衍射仪、扫描电镜和电子能谱仪等对该核–壳粒子的物相和形貌等进行了表征。

分析了该核–壳粒子的介电性能与结构的关系，并以此为屏蔽填料，研究了电磁屏蔽涂料的相关性能。

结果表明，银粒子在玻璃微珠的表面包覆均匀且致密，该粒子的介电常数较包覆前大幅度提高。

该电磁屏蔽涂料的导电性能随着填料的体积分数(下同)的增加而增加，达到25%时，其表面电阻率为0.0507Ω/cm2。

同时，在电磁波的频率范围为30～1500MHz时，屏蔽效能达40～65dB，并且该材料具有较好力学性能和耐环境性能。

关键词：核–壳粒子；屏蔽涂料；化学镀银；电磁屏蔽；屏蔽效能中图分类号：TQ171.71；TM24 文献标识码：A 文章编号：0454–5648(2007)03–0301–05PREPARATION AND PROPERTIES OF SILVER-COATED GLASS MICROSPHERE CORE–SHELL PARTICLES ON ELECTROMAGNETIC SHIELDING MATERIALSWANG Yilong1,2，GUAN Jianguo1，SHAO Hanmei1，ZHANG Qiaoxin1，DUAN Junyuan1，SUN Bin1(1. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology,Wuhan 430070; 2. Department of Chemistry, School of Sciences, Wuhan University of Technology, Wuhan 430070;3. School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China)Abstract: Silver-coated glass microsphere core–shell particles were prepared by silver (Ag) electroless plating on the self-assembly monolayer technique. The core–shell particles were characterized by X-ray diffraction, scanning electron microscope and energy dis-persive spectrometer. The relationship between the dielectric properties and the microstructure of the core–shell particles was ana-lyzed. The related properties of the electromagnetic shielding coatings based on the core–shell particles were studied. The results show that the Ag shell of composite particles is even and compact. The dielectric constants of the core–shell particles are much bigger than before. The electric properties of the electromagnetic shielding coating increase with the increasing of the volume fraction of the shielding filler. When the volume fraction of the filler reached 25%, the surface resistivity of the shielding coating was 0.0507Ω/cm2. At the same time, shielding effectiveness of the coating varied from 40dB to 65dB when the frequency of electromagnetic wave ranged between 30MHz and 1500MHz. The coating material had good mechanical properties and durability.Key words: core–shell particle; shielding coating; electroless silver plating; electromagnetic shielding; shielding effectivenessAt present, core–shell composite particles with different microstructures have been attracting considerable scien-tific interest both at home and abroad because these par-ticles not only exhibit good properties in their core and shell material, but also possess unique physical and chemical properties. Thus, core–shell composite particles have broad application prospects in the optical, electronic, magnetic, catalytic and biological fields.[1–6] Generally, powder material with high conductivity or magnetocon-ductivity, such as silver (Ag) powder, copper powder or nickel powder, have been used as traditional shielding filler in electromagnetic shielding techniques. Afterwards, some core–shell particles (e.g., Ag-coated nickel compo- site particles and Ag-coated copper composite particles) have been applied in these fields. The common short-coming is prevalently high density and high cost of收稿日期：2007–07–09。

修改稿收到日期：2007–12–13。

基金项目：国家“863”计划(2006AA03Z461)；国防基础科研(A1420080185)资助项目。

第一作者：王一龙(1974—)，男，博士研究生，讲师。

通讯作者：官建国(1969—)，男，教授，博士研究生导师。

Received date:2007–07–09. Approved date: 2007–12–13.First author: WANG Yilong (1974–), male, postgraduate student for doctor degree, lecturer.E-mail: wangyilong@Correspondent author: GUAN Jianguo (1969–), male, professor.E-mail: guanjg@第36卷第3期2008年3月硅酸盐学报JOURNAL OF THE CHINESE CERAMIC SOCIETYVol. 36，No. 3March，2008硅酸盐学报· 302 ·2008年shielding materials based on these shielding fillers. Fillers with high density will lead to sedimentation when the materials are being painted with electromagnetic shiel- ding coating, which increases the surface resistivity of the electromagnetic shielding coating. Compared with the former fillers, Ag-coated glass microspheres with hollow structures show better promise for application in shielding materials. Although their preparation has been reported in many articles, these studies mostly involved the traditional electroless plating technique. This method involves several processing steps, including roughening, sensitization and activation, making it time-consuming and complicated.[7–8] In addition, research about the electric and electromagnetic properties of Ag-coated glass microsphere core–shell par-ticles is seldom discussed in the literature.In this study, self-assembly technique of chemical plating was firstly used to prepare core–shell particles with even and compact Ag shells. The electromagnetic shielding coating based on core–shell particles has good electric properties, shielding effectiveness, mechanical properties and durability, which indicated that the Ag-coated glass microsphere core–shell particles should have extensive application prospects in the electromag-netic compatibility (EMC) field.1 Experiment1.1 Materials and reagentsThe glass microspheres (1250mesh, 10µm) were purchased from Shanghai Green Sub-Nanoscale Material Co., Ltd. 3–mercaptopropyltrimethoxysilane (MPTS) was purchased from Wuhan University Organosilicon New Material Co., Ltd. and was vacuum distilled before usage. Silver nitrate (AgNO3), glucose (C12H12O6), tar-taric acid, ammonia water (NH3·H2O), sodium hydroxide (NaOH), alcohol (C2H5OH) and polyvinyl pyrrolidone (PVP) were all analytical-reagent grade. The epoxy resin adhesive was made in our laboratory.1.2 Preparation of samplesFirst, the surfaces of glass microspheres were func-tionalized by usage of 3–mercaptopropyltrimethoxy- silane[9] and some improvements were done in this step. The electroless plating solution was prepared according to the literature [10].2000mL reduction solution was added in the reactor, and then some PVP and 200g of functionalized glass microspheres were added. The above mixtures were stirred for 30min. The Ag[(NH3)2]+ solution with the same volume was dropped into the reactor with stirring for 4 h. The products were filtrated and washed by deionized water with 10.0MΩ electrical resistivity. Then the Ag-coated glass microsphere core–shell particles were dried in an incubator at 120℃ for 2h.The Ag-coated glass microsphere core–shell particles with different volume fractions were mixed into the epoxy resin adhesive, and the coating samples were processed at 100℃ for 10h. [11]1.3 Characterization of core–shell particles andproperties of the coating samplesX-ray diffraction (XRD) with Cu Kα radiation was used for phase analysis. The surface morphology and structure of particles were determined using a field emis-sion scanning electron microscope (FESEM) with an energy dispersive spectrometer (EDS). The complex permittivity of 2–18GHz was determined with a coaxial cell on a Hewlett–Packard 8510C Vector Network Ana-lyzer. The glass microsphere and core–shell particles were processed as well-dispersed mixtures, respectively. For example, the mixtures containing 30% (in volume, the same below) glass microsphere sample and 70% solid paraffin as an adhesive resulted in the coaxial cylindrical samples with the following characteristics: outer diameter of 7.00mm, inner diameter of 3.02mm and thickness of about 3.5mm. For core–shell particles, samples were produced as well-dispersed mixtures at the same volume percent using solid paraffin.The electric properties of electromagnetic shielding coating materials were measured according to the method described in General Specification for Military Electromag-netic Shielding Coating (GJB 2604–96). The shielding ef-fectiveness of the coating was measured according to ASTM–ES–7. The mechanical properties of the coating were determined by Determination of Adhesive Force of Film (GB1720–79), Determination of Film Hardness by Pencil Test (GB/T 6739–96), Determination of Impact Re-sistance of Film (GB/T 1732–93) and Determination of Abrasive Resistance of Film (GB/T 1768–79). The dura-bility of the shielding coating was analyzed by Environ-mental Test Method for Military Equipments Damp Heat Test (GJB 150.9–86) and Environmental Test Method for Military Equipments Salt Fog Test (GJB 360.2–87).2 Results and discussion2.1 Characterization of the Ag-coated glass mic-rosphere core–shell particles2.1.1 XRD analysis Figure 1 shows the XRD pat-terns of the functionalized glass spheres (curve 1 in Fig. 1). According to the figure, the wide peaks from 20°to 25°at 2θ corresponded to the characteristics of the XRD peak of the amorphous glass microspheres, and no other pat-tern of diffraction peaks existed.[12] The typical XRD pattern for Ag-coated glass microsphere core–shell parti-cles is illustrated in Fig.1 (see curve 2). The XRD analy-sis revealed four main characteristic peaks for the (111), (2 0 0), (2 2 0), and (3 1 1) planes of the intact face-centered cubic (fcc) Ag at 2θ=38.2°, 44.4°, 64.6°, and 77.6°, and indicated the formation of pure Ag of high crystallinity in the shell of the as-synthesized composite particles.2.1.2 FESEM analysis Figure 2 shows the FESEM王一龙 等：电磁屏蔽材料用银包玻璃微珠核–壳粒子的制备及其性能· 303 ·第36卷第3期Fig.1 XRD patterns of glass microspheres and Ag-coatedglass microspheres core-shell particlesFig.2 FESEM photographs of glass microspheres andas-synthesized core-shell particlesphotographs of glass microspheres (see Fig.2(a)) and core–shell particles (see Fig.2(b)–2(c)). The SEM image in Fig.1a shows that the glass microspheres consisted of well-dispersed microspheres with smooth surfaces. By electroless Ag plating on the self-assembly monolayer technique, the Ag nanoparticles were constantly reduced on the glass microspheres and finally formed even and compact Ag shells. No Ag nanoparticle was free, and Ag nanoparticles did not agglomerate. This indicated that the composite particles had perfect core–shell structures. 2.1.3 EDS analysis Figure 3 shows the EDS spectra of the glass microspheres and core–shell particles. Figure 3(a) indicates that the glass microsphere samples con-tained Si, Al, O, K, and Na. Figure 3(b) shows the presence of Ag in addition to these elements. These results revealed further that the shells of the as-synthesized composite particles contained Ag element.Fig.3 EDS analysis of glass microspheres and as-synthesizedcore–shell particles2.2 Dielectric properties of the Ag-coated glassmicrosphere core–shell particlesThe profile of the electromagnetic wave frequencies for the real and image parts of the dielectric constants of glass microsphere and Ag-coated glass microsphere core–shell particles are shown in Fig.4. According to Fig.4(a), the real part of the dielectric constants for glass microsphere was between 3.25 and 3.50 with the frequency of electromag-netic wave ranging from 2 GHz to 18 GHz. At the same time, the image part did not exceed 0.3. However, the real and image parts of the dielectric constants for Ag-coated glass microsphere core–shell particles were much bigger than those of glass microsphere. This indicated that the Ag硅酸盐学报· 304 ·2008年Fig.4 Real and image parts of of dielectric constants glass microspheres and as-synthesized core–shell particles shell of the special structure for composite particles pos-sibly contributed to the above results. In addition, ε' and ε'' for composite particles decreased sharply with the in-crease of the frequency of the electromagnetic wave.2.3 Electric properties of the electromagneticshielding coatingThe electromagnetic shielding coatings were processed by mixing various quantities of shielding filler (Ag- coated glass spheres core–shell particles) into epoxy resin adhesive. After the coating samples were processed at 100℃ for 10h, the electric property of the shielding coatings was studied.Table 1 shows the relationship between the volume fraction of Ag-coated glass microsphere core–shell parti-cles in electromagnetic shielding coating and the surface resistivity of the coating. As far as the Ag-coated glass microsphere core–shell particles are concerned, the core of the glass microsphere is insulated by powder, and the Ag shell is a good conductive material. Therefore, the electric properties of fillers depend on the core–shell structure of the composite particles; that is, whether or not the Ag shell is even and compact for each composite particle. The con-ductive pathway theory can explain the electrical conduc-tivity of the coating. If the coating materials have goodTable 1 Relationship between the volume fraction of Ag- coated glass microsphere core-shell particles and sur-face resistivity of electromagnetic shielding coatingSampleNo.V olume fraction offiller/ %V olume fraction of epoxyresin adhesive/ %Surface resistivity/(Ω·cm–2)1 18 82 7.6642 20 80 1.2473 22.5 77.5 0.1814 25 75 0.05075 27 73 0.04636 30 70 0.0442 electric properties, a high volume fraction of filler will be required to establish a sufficient three- dimensional con-ductive pathway.[13–15] Here, the electric properties of the electromagnetic shielding coating increased with the in-crease of the volume fraction of the shielding filler. When the volume fraction reached 25%, the surface resistivity of the shielding coating was 0.0507Ω/cm2 (as shown in Ta-ble 1). When the volume fraction of the shielding filler progressively increased, the surface resistivity of the coating did not improve obviously. However, the volume fraction of the filler was too high, which resulted in the poor mechanical properties of material. This is disadvanta-geous to its application in EMC.2.4 Shielding effectiveness of the electromagneticshielding coatingCompared to coating material with excessive volume fraction for fillers, inadequate fillers will lead to inferior electric properties of the coating. According to Schelku- noff’s theory, shielding material with perfect electric properties will have perfect electromagnetic shielding properties. The perfect electric properties contribute to strong reflection and absorbance losses in the shielding effectiveness of electromagnetic shielding material. Ac-cording to the results (listed in chapter 2.3), the shielding effectiveness of the coatings was studied when the vo- lume fraction of the filler was 25%. The shielding effec-tiveness (SE) of coatings with the frequency of electro-magnetic wave ranging from 30MHz to 1500MHz using ASTM–ES–7 coaxial transmission line method is shown in Fig.5. In Fig.5, the SE varied from 40dB to 50dB with the frequency of electromagnetic wave ranging from 30 MHz to 244MHz. The SE was 50dB to 61dB with the frequency ranging from 244MHz to 633MHz, and the SE was between 60 and 65 in the last frequency range. Therefore, the electromagnetic shielding coating had good electromagnetic shielding properties when the Ag-coated glass microsphere core–shell particles synthe-sized in this study were used as electromagnetic shielding filler. However, the mechanical properties and durability of the shielding coating should be investigated, to con-firm whether these coating materials will have extensive application in the electromagnetic compatibility field.王一龙等：电磁屏蔽材料用银包玻璃微珠核–壳粒子的制备及其性能· 305 ·第36卷第3期Fig5 Shielding effectiveness of electromagnetic shielding coatings with the frequency of electromagnetic waveranging from 30MHz to 1500MHz2.5 Mechanical properties and durability of theelectromagnetic shielding coatingAccording to the national standard determination (listed in chapter 1.3), the mechanical properties of the coating were determined when the volume fraction of the filler was 25% for the coating samples. Its adhesive force was not less than the first level and its hardness was 6 H. After the coating samples were impacted, no cracking or peeling occurred. The samples’ impact resistance was at least 50cm·Kg. The loss mass of the coating samples was 0.00171g/cm2 for determination of abrasive resistance.To assess the material’s durability, relevant tests, in-cluding damp heat and salt fog tests, were carried out ac-cording to GJB 150.9–86 and GJB 360.2–87. After these tests, there was no cracking, bubbling or peeling on the coating samples, its surface resistivity still remained 0.0588Ω/cm2. For the electromagnetic shielding properties of the coating samples, there was no obvious decrease with the same frequency range of electromagnetic wave. Specifi-cally, the SE did not change for the frequency of electro-magnetic wave varying from 30MHz to 244MHz, but decreased for another frequency range (244–1500MHz), and the ∆SE was only about 3dB to 4dB. From the results, it could be concluded that the shielding materials based on Ag-coated glass microsphere core–shell particles described in this paper have good application prospects on the field of electromagnetic compatibility.3 ConclusionsThe Ag-coated glass microsphere core–shell particles with even and compact Ag shells were firstly prepared by electroless Ag plating on the self-assembly monolayer technique. The Ag nanoparticles in the shells of the core–shell particles were the intact face-centered cubic structure. The dielectric constants of the core–shell parti-cles were much higher than before. The electric proper-ties of the electromagnetic shielding coating increased with the increase of the quantity of the shielding filler. When the volume fraction of the filler reached 25%, the surface resistivity of the shielding coating was 0.0507Ω/cm2 and the shielding effectiveness of it was between 40dB and 65 dB with the frequency of electromagnetic wave ranging from 30MHz to 1500MHz. The coating had good mechanical properties and durability. These results indicated that the Ag-coated glass microsphere core–shell particles should have extensive application prospects in the electromagnetic compatibility field. Reference:[1] GUAN Jianguo, DENG Huiyong, WANG Wei, et al. Preparation ofwell-defined core–shell nanocomposite particles based on colloidal templates [J]. Prog Chem (in Chinese), 2004,16(3): 321–334.[2] KOBAYASHI Y, KATAKAMI H, MINE E, et al. Silica coating ofsilver nanoparticles using a modified Stöber method [J]. J Colloid In-terf Sci, 2005, 283: 392–396.[3] CHEN Z M, CHEN X, ZHENG L L, et al. A simple and controlledmethod of preparing uniform Ag midnanoparticles on Tollens-soaked silica spheres [J]. 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