Sound Absorption Characteristics and Structure Optimization of Porous Metal Fibrous Materials

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1 Rre Metl Mterils n Engineering Volume 44, Issue 11, Novemer 2015 Online English eition of the Chinese lnguge journl Cite this rtile s: Rre Metl Mterils n Engineering, 2015, 44(11): ARTICLE Soun Asorption Chrteristis n Struture Optimiztion of Porous Metl Firous Mterils Ao Qingo, Wng Jinzhong, Tng Huiping, Zhi Ho, M Jun, Bo Tengfei Stte Key Lortory of Porous Metl Mterils, Northwest Institute for Nonferrous Metl Reserh, Xi n , Chin Astrt: Porous stinless steel firous felt mterils with thikness of only 1 to 3 mm were use s the reserh ojet for the soun sorption mteril in eletroni omponents with nrrow spe. The struture of the mterils ws optimize y hnging preprtion proessing n struture prmeters. The results inite tht the soun sorption performne of the felt is high when the sintering temperture is low n no runoes re forme. Furthermore, the felt with exellent soun sorption performne n e prepre y justing the mth etween the men pore size n the firous imeter for ifferent frequenies. Bse on the results of the struture optimiztion, the following fining n e rwn: in the frequeny rnge of 50~6400 Hz, the felts me from Φ12 μm fire, sintere t 850 C, with men pore sizes of 10, 30 n 40 μm, exhiit goo soun sorption performne. Key wors: porous metl firous felt mterils; men pore sizes; firous imeter; struture optimiztion Environmentl noise hs gret influene on the preision of eletroni omponents. Therefore, omplite hrwre n softwre re neessry to just the signl, whih inrese the mss n the ost, n erese the reliility of the system [1-3]. Aousti shiele enlosure is the most effetive metho to reue the influene of environment noise. But, very nrrow spe oul e use in eletroni omponents, so thin soun insultion mterils re require to ontrol the noise, espeilly low frequeny noise. The omposite struture with soun soring mterils n lmin plte is n effetive wy to improve the preision of eletroni omponents. The sintering of stinless steel firous felt mterils is novel proess omining struture evelope with new mnufturing tehnology n mterils proessing. It eomes the fous of stuy in soun soring mteril fiels ue to its exellent soun soring performne [4-9], ut there re few relevnt reports out the sintere stinless steel firous mterils use in soun insultion of preision eletroni omponents. Some previous rguments on the soun sorption hrteristis of porous stinless steel firous mterils were minly fouse on the porosity, the vity n the thikness ( 10 mm) [10-13], ut there re only few reports out the men pore sizes n fire imeters use for prouing 1~3 mm thikness felts. In the present pper, we investigte the porous stinless steel firous felts with only 1~3 mm thikness whih re use to ontrol noise for the eletroni omponents with nrrow spe. In ition, effets of preprtion, men pore sizes n firous imeter on soun sorption performne were lso isusse. As result, soun sorption strutures were reeive with the est soun sorption performne. 1 Experiment The fires for the present experiment were stinless steel fires with 8, 12, 20 n 28 μm in imeter, whih were use to prepre porous felt smples. The preprtion metho ws reporte in Ref. [10-13]. The men pore size n e lulte oring to the empiril formul s follows [14] : =6.15D 3.35 (1) where, is the men pore size; D is the firous imeter; ε is the porosity. Reeive te: Novemer 15, 2014 Fountion item: Ntionl Bsi Reserh Progrm of Chin (2011CB610302); Ntionl Nture Siene Fountion of Chin ( , , ); Ntionl Siene & Tehnology Support Pln of Chin (2012BAC02B05) Corresponing uthor: Tng Huiping, Ph. D., Professor, Stte Key Lortory of Porous Metl Mterils, Northwest Institute for Nonferrous Metl Reserh, Xi n , P. R. Chin, Tel: , E-mil: hptng@-nin.om Copyright 2015, Northwest Institute for Nonferrous Metl Reserh. Pulishe y Elsevier BV. All rights reserve. 2646

2 Asorption Coeffiient In the present investigtion the men pore size ws fixe vlue. Aoring to the empiril formul, n e lulte y the firous imeter, for exmple, when the men pore size ws fixe t 10 μm, n the firous imeter ws 8 μm, the porosity n e lulte to e 62%. Mirostrutures of the smples were stuie using snning eletron mirosopy (SEM). Aoustis performne ws mesure y stning wve pipe metho. The test of oustis performne ws performe y oule mirophone impene mesurement tue of B&K Compny in Denmrk. The soun sorption performne of the smples ws etete. The frequeny istne etween two points ws 2 Hz n the etetion rnges ws from 50 Hz to 6400 Hz. 2 Results n Disussion 2.1 Effet of sintering temperture on soun sorption oeffiient Sintering is key proess to ffet the mirostrutures of porous metl firous mterils. For the metl fier, its sintering proess is ifferent from tht of metl power euse of serious ypss phenomenon etween fiers t loose stte, so the rel ontt proility ereses resulting in ifferent sintering. To solve this prolem, the effets of firous imeter, sintering temperture n other prmeters on the forming of sintere runoes were etete first. The sintering tempertures of forming runoes for stinless steel fires with ifferent imeters re shown in Tle 1. Mirostruture of porous stinless steel firous felts sintere re shown in Fig.1 n the effet of sintere runoes etween fiers (Φ 12 μm) on soun sorption oeffiient is shown s shown in Fig.2. In the present se e.g. Φ=12 μm, =10 μm, the porosity of the felt n e lulte from Eq. 1. Due to the ft tht porous stinless steel firous felts oul not e shpe uner temperture t 750 C, the lowest sintering temperture ws hosen to e 850 C. It n e seen from Fig.2 tht the soun sorption oeffiient is the highest when the sintering temperture is 850 C euse it will e enefiil to use the fier virtion frition y soni upon inter-fiers loose ontt [15], n the soun sorption oeffiient is enhne y 14.3% in the frequeny rnge etween 50 n 3000 Hz. 2.2 Effet of men pore size on soun sorption oeffiient The SEM imges of the porous stinless steel firous felts prepre using Φ12 μm fires with ifferent men pore sizes re shown in Fig.3. It n e seen tht t the sme firous imeter, the igger the men pore size is, the fewer the mount of the fiers re, so the mount of interonnete pores elines. Tle 1 Sintering tempertures of forming runoes of porous stinless steel felts with ifferent imeters Dimeter, Φ/µm Sintering temperture/ C Fig.1 Comprison of runoes stte etween fiers (Φ12 μm) t Fig.2 ifferent sintering tempertures: () 850 C, () 1050 C, () 1150 C, n () 1250 C Effet of sintere runoes on soun sorption oeffiient (fire imeter =12 μm) 12 m-850 C 12 m-1050 C 12 m-1150 C 12 m-1250 C The effets of the men pore sizes on the soun sorption performne re shown in Fig.4, where the thikness is 3mm n the firous imeters re Φ20 μm, Φ12 μm, n Φ8 μm. It is ovious from Fig.4 n 4 tht for the firous imeters of Φ20 μm n Φ12 μm, the effets of the men pore size on the soun sorption oeffiient re lmost ientil. In the low frequeny rnge of 2000 Hz, the smller the men pore size is, the etter the ousti performne is. But, the rule is just reverse in frequeny rnge 2000 Hz. The min resons my e s follows: the flow resistne of the porous felts is iretly ontrolle y the men pore size. The smller the men pore size is, the esier the soun wve is reflete, so it is very hr to let the soun wve enter the mteril. Consequently, the soun sorption performne of the felt is the est t the frequeny of 6400 Hz with the men pore size of 40 μm. The lower the frequenies of soun wve re, the longer the wvelength is, the more ovious the iffrtion phenomenon is, n so the soun sorption 2647

3 Asorption Coeffiient 2648 Fig.3 SEM morphologies of firous porous mterils with ifferent men pore sizes: () 10 μm, () 20 μm, () 30 μm, n () 40 μm performne is the est in the frequeny rnge from 50 to 2000 Hz with the men pore size of 10 μm. Furthermore, it n e seen from Fig.4 tht when the firous imeter is Φ8 μm n the men pore size is 20 μm, the soun sorption oeffiient is the est t testing frequeny ( 2000 Hz). But the felt with the smller pore size (10 μm) hs the highest soun sorption performne t low frequeny ( 2000 Hz). 2.3 Effet of firous imeter on soun sorption oeffiient The SEM imges of porous stinless steel firous felts with ifferent firous imeters t the men pore size of 20 μm re shown in Fig.5. It n e seen tht the mount of the fiers per volume ereses n the length of the pore hnnel shortens with the firous imeter inresing, while the soun wve reflete rops. The effets of firous imeters on soun sorption oeffiients re shown in Fig.6, where the felt thikness is 3 mm n the men pore sizes for Fig.6, 6, 6 n 6 re 10, 20, 30 n 40 μm, respetively. In the frequeny rnge from 50 Hz to 1000 Hz, when the men pore size is 10 μm, the smller the firous imeter is, the higher the soun sorption oeffiient is (Fig.6). The ousti performne of the felt trens to e stle stte when the firous imeter is Φ8 μm, while the soun sorption oeffiient is the lowest. For the firous imeter of Φ12 μm, the soun sorption oeffiient is the highest when the frequeny rnge is from 1800 Hz to 6400 Hz. On the whole,the ousti performne of the felt me y the fires with Φ12 μm is optiml. The primry reson is tht the firous imeter n the mount of pores re orreltive, i.e. the less the firous imeter is, the more the mount of pores is. In ition, t the pproprite men pore size, the more the mount of pores is, the higher the soun sorption oeffiient is. But the less the firous imeter is, the lrger the surfe re is, so the esier the soun wve is reflete. At the sme men pore size of 10 μm with the firous imeter of Φ8 μm, the soun wve is reflete seriously leing to the soun sorption oeffiient eresing. Beuse t the sme men pore size, the less the firous imeter is, the more the numer of the fiers re, the more seriously the reflete phenomen is. Compre with Fig.6, 6, 6 n 6, the rules re sme silly. The soun sorption performne of the felt for the firous imeter of Φ8 μm is very poor (exept Fig.6), while tht of Φ12 μm is the est. On the one hn, the felt me y the fires with Φ12 μm hs more open pores thn tht with Φ 8 μm. On the other hn, the soun wve reflete for the former is less thn tht for the ltter. It lso n e seen from Fig.6 tht the felt me y the fires with Φ 8 μm, hs exellent soun sorption performne in the frequeny rnge from 3500 Hz to 6400 Hz, while the soun sorption performne is very poor in the frequeny rnge from 50 Hz to 3500 Hz. In summry, for the preprtion of the stinless steel felts with the sme thikness (3 mm) ut ifferent men pore sizes (10, 30 n 40 μm) the est fire imeter selete is 12 μm euse the felts prepre y it exhiit very goo soun sorption performne in the frequeny rnge from 50~6400 Hz. Fig.4 Effets of men pore sizes on soun sorption oeffiient (the thikness is 3 mm): () Φ20 μm, () Φ12 μm, n () Φ8 μm

4 Asorption Coeffiient Asorption Coeffiient 2649 Fig.5 SEM morphologies of porous firous mterils with ifferent imeters t 20 μm men pore size: () Φ8 μm, () Φ12 μm, n () Φ 20 μm Fig.6 Effets of firous imeters on sorption oeffiients (the thikness is 3 mm) with ifferent the men pore sizes: () 10 μm, () 20 μm, () 30 μm, n () 40 μm 3 Conlusions 1) The soun sorption oeffiient of the porous felt n inrese y 14.3% when it is prepre t lower sintering temperture of 850 C. 2) For the monolyer porous felt in the lower frequeny rnge from 50~3500 Hz, the less the men pore sizes is, the etter the soun sorption performne. 3) The effet of the firous imeter on the soun sorption performne is very omplex. The soun sorption performne of the felt me y the fire with of Φ12 μm is etter, when the men pore sizes re 10, 30 n 40 μm. Referenes 1 Zuo Hu, Che Zuho, Zhng Wei. Computer Engineering & Siene[J], 2005, 27(4): Xie Shilin, Zhu Chnghun, Zhou Tong et l. Chinese Qurterly of Mehnis[J], 2009, 30(1): 109 (in Chinese) 3 Luo Gng. Experiment Siene n Tehnology[J], 2010, 8(3): 20 4 Li Hito, Zhu Xi, Shi Yong. Journl of Mterils Siene & Engineering[J], 2004, 22(6): Dun Cuiyun, Cui Gung, Liu Peisheng. Metlli Funtionl Mterils[J], 2011, 18(1): 60 6 Ru Gihong, Wng Xinheng. Mehnil Engineer[J], 2006, 6: 17 (in Chinese) 7 Tng Huiping, Zhu Jilei, Ge Yun. Rre Metl Mterils n Engineering[J], 2007, 36(12): 2220 (in Chinese) 8 Mrkki A E, Clyne T W. Stiffness[J], 2003, 51: Xin Fengxin, Lu Tinjin, Chen Chngqing. At Austi[J], 2008, 33(4): Ao Qingo, Tng Huiping, Zhu Jilei. Piezoeletris & Aoustooptis[J], 2010, 32(5): 849 (in Chinese) 11 Ao Qingo, Tng Huiping, Zhu Jilei. Rre Metl Mterils n Engineering[J], 2009, 38(10): 1765 (in Chinese)

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