Abstract：Carbon-based/carbonyl iron composite microwave absorption materials have become a hot topic in recent years because of the combination of their respective advantages and unique physical and chemical characteristic and good absorbing properties. In this paper, the most recent and important research advances in carbon-based/carbonyl iron composite microwave absorption materials were reviewed. Firstly, the recent research of property improving of carbonyl iron itself was introduced. Then, the research achievements of carbon-based/carbonyl iron composite microwave absorption materials were summarized in six major categories, graphene/carbonyl iron microwave absorption materials, carbon nanotubes/carbonyl iron microwave absorption materials, carbon fibre/carbonyl iron microwave absorption materials, carbon black/carbonyl iron microwave absorption materials, graphite/carbonyl iron microwave absorption materials and the other composites were reviewed in detail. Finally, the performance control and lightweight of carbon-based/carbonyl iron composite microwave absorption materials were pointed out, and its development prospect in broadband stealth was prospected.
葛超群, 汪刘应, 刘顾. 碳基/羰基铁复合吸波材料的研究进展[J]. 材料工程, 2019, 47(12): 43-54.
GE Chao-qun, WANG Liu-ying, LIU Gu. Research progress in carbon-based/carbonyl iron composite microwave absorption materials. Journal of Materials Engineering, 2019, 47(12): 43-54.
[1] KONG L B,LI Z W,LIU L,et al. Recent progress in some composite materials and structures for specific electromagnetic applications[J]. International Materials Reviews,2013,58(4):203-259.
[2] ZHU M,DIAO G. Review on the progress in synthesis and application of magnetic carbon nanocomposites[J]. Nanoscale,2011,3(7):2748-2767.
[3] 刘渊,刘祥萱,王煊军. 铁氧体基核壳结构复合吸波材料研究进展[J]. 材料工程,2014(7):98-106. LIU Y,LIU X X,WANG X J. Research progress in ferrite based core-shell structured composite microwave absorb materials[J]. Journal of Materials Engineering,2014(7):98-106.
[4] PATON K R,WINDLE A H. Efficient microwave energy absorption by carbon nanotubes[J]. Carbon,2008,46(14):1935-1941.
[5] XU Y,YUAN L,ZHANG D. Enhancement mechanism of the additional absorbent on the absorption of the absorbing composite using a type-based mixing rule[J]. Journal of Physics D:Applied Physics,2016,49(15):155001.
[6] CAO M, HAN C, WANG X, et al. Graphene nanohybrids:excellent electromagnetic properties for the absorbing and shielding of electromagnetic waves[J]. Journal of Materials Che-mistry C,2018,6(17):4586-4602.
[7] WEN F,ZHANG F,LIU Z. Investigation on microwave absorption properties for multiwalled carbon nanotubes/Fe/Co/Ni nanopowders as lightweight absorbers[J]. The Journal of Physical Chemistry C,2011,115(29):14025-14030.
[8] WANG X,ZHANG B,ZHANG W,et al. Super-light Cu@Ni nanowires/graphene oxide composites for significantly enhanced microwave absorption performance[J]. Scientific Reports,2017,7(1):1584.
[9] WANG X,MA T,SHU J,et al. Confinedly tailoring Fe3O4 clusters-NG to tune electromagnetic parameters and microwave absorption with broadened bandwidth[J]. Chemical Engineering Journal,2018,332:321-330.
[10] LU M,CAO M,CHEN Y,et al. Multiscale assembly of grape-like ferroferric oxide and carbon nanotubes:a smart absorber prototype varying temperature to tune intensities[J]. ACS Applied Materials & Interfaces,2015,7(34):19408-19415.
[11] MOVASSAGH-ALANAGH F,BORDBAR K A, SALIMK-HANI H. Improvement in magnetic and microwave absorption properties of nano-Fe3O4@CFs composites using a modified multi-step EPD process[J]. Applied Surface Science,2017,420:726-739.
[12] FENG J,HOU Y,WANG Y,et al. Synthesis of hierarchical ZnFe2O4@SiO2@RGO core-shell microspheres for enhanced electromagnetic wave absorption[J]. ACS Applied Materials & Interfaces,2017,9(16):14103-14111.
[13] ZHANG K,GAO X,ZHANG Q,et al. Preparation and microwave absorption properties of asphalt carbon coated reduced graphene oxide/magnetic CoFe2O4 hollow particles modified multi-wall carbon nanotube composites[J]. Journal of Alloys and Compounds,2017,723:912-921.
[14] ZHANG Y,WANG X,CAO M. Confinedly implanted NiFe2O4-rGO:cluster tailoring and highly tunable electromagnetic properties for selective-frequency microwave absorption[J]. Nano Research,2018,11(3):1426-1436.
[15] MA J,WANG X,CAO W,et al. A facile fabrication and highly tunable microwave absorption of 3D flower-like Co3O4-rGO hybrid-architectures[J]. Chemical Engineering Journal,2018,339:487-498.
[16] MA?ECKI P,KOLMAN K,PIG?OWSKI J,et al. Sol-gel method as a way of carbonyl iron powder surface modification for interaction improvement[J]. Journal of Solid State Chemistry,2015,226:224-230.
[17] REN X,CHENG Y. Electromagnetic and microwave absorbing properties of carbonyl iron/BaTiO3 composite absorber for matched load of isolator[J]. Journal of Magnetism and Magnetic Materials,2015,393:293-296.
[18] 刘彦峰,李磊削,王韫宇,等. 原子层沉积氧化铝包覆羰基铁粉的抗腐蚀性及吸波性能[J]. 无机材料学报,2017,32(7):751-757. LIU Y F,LI L X,WANG Y Y,et al. Corrosion resistance and wave absorbing property of carbonyl iron powder coating with alumina by atomic layer deposition[J]. Journal of Inorganic Materials,2017,32(7):751-757.
[19] 景红霞,李巧玲,叶云,等. 羰基铁/钛酸钡复合材料的制备及吸波性能[J]. 材料工程,2015,43(7):38-42. JING H X,LI Q L,YE Y,et al. Preparation and microwave absorbing properties of Fe(CO)5/BaTiO3 composites[J]. Journal of Materials Engineering,2015,43(7):38-42.
[20] QING Y,ZHOU W,LUO F,et al. Microwave-absorbing and mechanical properties of carbonyl-iron/epoxy-silicone resin coatings[J]. Journal of Magnetism and Magnetic Materials,2009,321(1):25-28.
[21] WEN F,ZUO W,YI H,et al. Microwave-absorbing properties of shape-optimized carbonyl iron particles with maximum microwave permeability[J]. Physica B:Condensed Matter,2009,404(20):3567-3570.
[22] LONG C,XU B C,HAN C Z,et al. Flaky core-shell particles of iron@iron oxides for broadband microwave absorbers in S and C bands[J]. Journal of Alloys and Compounds, 2017,709:735-741.
[23] YIN C,FAN J,BAI L,et al. Microwave absorption and antioxidation properties of flaky carbonyl iron passivated with carbon dioxide[J]. Journal of Magnetism and Magnetic Materials,2013,340:65-69.
[24] ZHOU Y,ZHOU W,LI R,et al. Enhanced antioxidation and electromagnetic properties of Co-coated flaky carbonyl iron particles prepared by electroless plating[J]. Journal of Alloys and Compounds,2015,637:10-15.
[25] KANG Y,HUANG Y,YANG R,et al. Synthesis and properties of core-shell structured Fe(CO)5/SiO2 composites[J]. Journal of Magnetism and Magnetic Materials,2016,399:149-154.
[26] WANG H,ZHU D,ZHOU W,et al. Electromagnetic property of SiO2-coated carbonyl iron/polyimide composites as heat resistant microwave absorbing materials[J]. Journal of Magnetism and Magnetic Materials,2015,375:111-116.
[27] LI J,FENG W J,WANG J S,et al. Impact of silica-coating on the microwave absorption properties of carbonyl iron powder[J]. Journal of Magnetism and Magnetic Materials,2015,393:82-87.
[28] ZHANG W,BIE S,CHEN H,et al. Electromagnetic and microwave absorption properties of carbonyl iron/MnO2 com-posite[J]. Journal of Magnetism and Magnetic Materials,2014,358/359:1-4.
[29] 郭飞,杜红亮,屈绍波,等. 海胆状氧化锌/羰基铁粉核壳结构复合粒子的抗氧化及吸波性能[J]. 无机化学学报, 2015,31(4):755-760. GUO F,DU H L,QU S B,et al. Oxidation resistance and microwave absorption property of core shell urchin-like ZnO/carbonyl iron powder composite particles[J]. Chinese Journal of Inorganic Chemistry,2015,31(4):755-760.
[30] WU X,LUO H,WAN Y. Preparation of SnO2-coated carbonyl iron flaky composites with enhanced microwave absorption properties[J]. Materials Letters,2013,92:139-142.
[31] TANG J,MA L,HUO Q,et al. The influence of PVP on the synthesis and electromagnetic properties of PANI/PVP/CIP composites[J]. Polymer Composites,2015,36(10):1799-1806.
[32] TANG J,MA L,TIAN N,et al. Synthesis and electromagnetic properties of PANI/PVP/CIP core-shell composites[J]. Materials Science and Engineering:B,2014,186:26-32.
[33] 汪晓芹,徐金鑫,黄大庆,等. 羰基铁粉@聚苯胺防腐吸波粉体的制备与性能[J]. 材料工程,2014(11):90-96. WANG X Q,XU J X,HUANG D Q,et al. Synthesis and properties of CIP@PANI composite powders for anticorrosion and microwave-absorbing application[J]. Journal of Materials Engineering,2014(11):90-96.
[34] SUI M,LÜ X,XIE A,et al. The synthesis of three-dimensional (3D) polydopamine-functioned carbonyl iron powder@polyp-yrrole (CIP@PPy) aerogel composites for excellent microwave absorption[J]. Synthetic Metals,2015,210:156-164.
[35] SONG Z,DENG L,XIE J,et al. Synthesis, dielectric, and microwave absorption properties of flake carbonyl iron particles coated with nanostructure polymer[J]. Surface and Interface Analysis,2014,46(2):77-82.
[36] KHANI O,SHOUSHTARI M Z,ACKLAND K,et al. The structural, magnetic and microwave properties of spherical and flake shaped carbonyl iron particles as thin multilayer microwave absorbers[J]. Journal of Magnetism and Magnetic Materials,2017,428:28-35.
[37] XU Y,YUAN L,WANG X,et al. Two-step milling on the carbonyl iron particles and optimizing on the composite absorption[J]. Journal of Alloys and Compounds,2016,676:251-259.
[38] QIAO L,HAN R,WANG T,et al. Greatly enhanced microwave absorbing properties of planar anisotropy carbonyl-iron particle composites[J]. Journal of Magnetism and Magnetic Materials,2015,375:100-105.
[39] ABSHINOVA M A,LI Z W. Effect of milling time on dynamic permeability values of reduced carbonyl iron filled composites[J]. Journal of Magnetism and Magnetic Materials,2014,369:147-154.
[40] WANG W,GUO J,LONG C,et al. Flaky carbonyl iron particles with both small grain size and low internal strain for broadband microwave absorption[J]. Journal of Alloys and Compounds,2015,637:106-111.
[41] 童国秀,官建国,樊希安,等. 气流诱导多晶铁纤维的可控制备及生长机理[J]. 无机化学学报,2008,24(2):270-274. TONG G X,GUAN J G,FAN X A,et al. Controllable preparation and growth mechanism of polycrystalline iron fibers induced by carrier gas flow[J]. Chinese Journal of Inorganic Chemistry,2008,24(2):270-274.
[42] 童国秀,官建国,樊希安,等. 热解温度对多晶铁纤维的静磁和微波电磁性能的影响[J]. 金属学报,2008,44(7):867-870. TONG G X,GUAN J G,FAN X A,et al. Influences of pyrolysis temperature on static magnetic and microwave electro-magnetic properties of polycrystalline iron fibers[J]. Acta Metallurgica Sinica,2008,44(7):867-870.
[43] 李小莉,杨东方. 纳米晶铁纤维的制备及其电磁参数的测量[J]. 太原理工大学学报,2012,43(1):42-46. LI X L, YANG D F. Preparation of nanocrystalline iron of their electromagnetic fibers and measurement parameters[J]. Journal of Taiyuan University of Technology,2012,43(1):42-46.
[44] 贺君,胡照文,邓联文,等. 多晶铁纤维表面原位氧化及其微波吸收性能[J]. 矿冶工程,2016,36(3):98-101. HE J,HU Z W, DENG L W, et al. In-situ surface oxidation and microwave absorbing properties of polycrystalline iron fibers[J]. Mining and Metallurgical Engineering,2016,36(3):98-101.
[45] YIN C,CAO Y,FAN J,et al. Synthesis of hollow carbonyl iron microspheres via pitting corrosion method and their microwave absorption properties[J]. Applied Surface Science,2013,270:432-438.
[46] 杨芾藜,侯兴哲,郑可,等. 羰基铁粉形貌对吸波性能的影响[J]. 重庆大学学报,2017,40(10):53-59. YANG F L,HOU X Z,ZHENG K,et al. Effect of carbonyl iron powder morphology on the absorption properties of microwave[J]. Journal of Chongqing University,2017,40(10):53-59.
[47] LI J,HUANG H,ZHOU Y,et al. Research progress of graphene-based microwave absorbing materials in the last decade[J]. Journal of Materials Research,2017,32(7):1213-1230.
[48] 黄琪惠,张豹山,唐东明,等. 石墨烯-Fe@Fe3O4纳米复合材料的制备及其电磁性能研究[J]. 无机化学学报,2012,28(10):2077-2082. HUANG Q H,ZHANG B S,TANG D M,et al. Synthesis and characteristics of graphene-Fe@Fe3O4 nano-composites materials[J]. Chinese Journal of Inorganic Chemistry,2012,28(10):2077-2082.
[49] XU Y,LUO J,YAO W,et al. Preparation of reduced graphene oxide/flake carbonyl iron powders/polyaniline composites and their enhanced microwave absorption properties[J]. Journal of Alloys and Compounds,2015,636:310-316.
[50] WENG X,LV X,LI B,et al. One-pot preparation of reduced graphene oxide/carbonyl iron/polyvinyl pyrrolidone ternary nanocomposite and its synergistic microwave absorbing properties[J]. Materials Letters,2017,188:280-283.
[51] WENG X,LI B,ZHANG Y,et al. Synthesis of flake shaped carbonyl iron/reduced graphene oxide/polyvinyl pyrrolidone ternary nanocomposites and their microwave absorbing properties[J]. Journal of Alloys and Compounds,2017,695:508-519.
[52] CHEN C,LIANG W,NIEN Y,et al. Microwave absorbing properties of flake-shaped carbonyl iron/reduced graphene oxide/epoxy composites[J]. Materials Research Bulletin,2017,96:81-85.
[53] ZHU Z,SUN X,XUE H,et al. Graphene-carbonyl iron cross-linked composites with excellent electromagnetic wave absorption properties[J]. Journal of Materials Chemistry C,2014,2(32):6582-6591.
[54] 王洁萱. 石墨烯复合吸波剂的制备及电磁防护性能研究[D]. 北京:北京理工大学,2015. WANG J X. Research on synthesis of graphene composites and their electromagnetic shielding performance[D]. Beijing:Beijing Institute of Technology,2015.
[55] 李国显. 石墨烯/磁性纳米复合材料的制备及吸波性能[D]. 南京:南京航空航天大学,2012. LI G X. Properties of graphene/magnetic-particle nanocomposite materials[D]. Nanjing:Nanjing University of Aeronautics & Astronautics,2012.
[56] QING Y,MIN D,ZHOU Y,et al. Graphene nanosheet and flake carbonyl iron particle-filled epoxy-silicone composites as thin-thickness and wide-bandwidth microwave absorber[J]. Carbon, 2015,86:98-107.
[57] 刘顾,汪刘应,程建良,等. 碳纳米管吸波材料研究进展[J]. 材料工程,2015,43(1):104-112. LIU G,WANG L Y,CHENG J L,et al. Progress in research on carbon nanotubes microwave absorbers[J]. Journal of Materials Engineering,2015,43(1):104-112.
[58] LIU Y,LIU X,WANG X. Preparation of multi-walled carbon nanotube-Fe composites and their application as light weight and broadband electromagnetic wave absorbers[J]. Chinese Physics B,2014,23(11):117705.
[59] LIU T,ZHOU L,ZHENG D,et al. Absorption property of C@CIPs composites by the mechanical milling process[J]. Applied Physics A,2017,123(9):565.
[60] XU Y,ZHANG D,CAI J,et al. Effects of multi-walled carbon nanotubes on the electromagnetic absorbing characteristics of composites filled with carbonyl iron particles[J]. Journal of Materials Science & Technology,2012,28(1):34-40.
[61] XU Y,YUAN L,CAI J,et al. Smart absorbing property of com-posites with MWCNTs and carbonyl iron as the filler[J]. Journal of Magnetism and Magnetic Materials,2013,343:239-244.
[62] QING Y,ZHOU W,HUANG S,et al. Evolution of double magnetic resonance behavior and electromagnetic properties of flake carbonyl iron and multi-walled carbon nanotubes filled epoxy-silicone[J]. Journal of Alloys and Compounds,2014,583:471-475.
[63] QING Y,ZHOU W,LUO F,et al. Epoxy-silicone filled with multi-walled carbon nanotubes and carbonyl iron particles as a microwave absorber[J]. Carbon,2010,48(14):4074-4080.
[64] GAO Y,GAO X,LI J,et al. Improved microwave absorbing property provided by the filler's alternating lamellar distribution of carbon nanotube/carbonyl iron/poly (vinyl chloride) composites[J]. Composites Science and Technology,2018,158:175-185.
[65] TONG G,WU W,HUA Q,et al. Enhanced electromagnetic characteristics of carbon nanotubes/carbonyl iron powders complex absorbers in 2-18GHz ranges[J]. Journal of Alloys and Compounds,2011,509(2):451-456.
[66] LI Y,CHEN C,PAN X,et al. Multiband microwave absorption films based on defective multiwalled carbon nanotubes added carbonyl iron/acrylic resin[J]. Physica B:Condensed Matter,2009,404(8/11):1343-1346.
[67] 李斌鹏,王成国,王雯. 碳基吸波材料的研究进展[J]. 材料导报,2012,26(7):9-14. LI B P,WANG C G,WANG W. Progress of electromagnetic wave absorbing materials based on carbon[J]. Materials Review,2012,26(7):9-14.
[68] LIU Y,LIU X,LI R,et al. Design and fabrication of carbon fiber/carbonyl iron core-shell structure composites as high-performance microwave absorbers[J]. RSC Advances,2015,5(12):8713-8720.
[69] 刘渊,刘祥萱,陈鑫,等. 碳纤维表面α-Fe的MOCVD生长制备及吸波性能研究[J]. 无机材料学报,2013,28(12):1328-1332. LIU Y,LIU X X,CHEN X,et al. Preparation by MOCVD and microwave absorbing properties of CF@Fe[J]. Journal of Inorganic Materials,2013,28(12):1328-1332.
[70] ZHANG Z,LIU X,ZHANG H,et al. Electromagnetic and microwave absorption properties of carbon fibers coated with carbonyl iron[J]. Journal of Materials Science:Materials in Electronics,2015,26(9):6518-6525.
[71] SALIMKHANI H,PALMEH P,KHIABANI A B,et al. Electrophoretic deposition of spherical carbonyl iron particles on carbon fibers as a microwave absorbent composite[J]. Surfaces and Interfaces,2016,5:1-7.
[72] YOUH M,WU H,LIN W,et al. A carbonyl iron/carbon fiber material for electromagnetic wave absorption[J]. Journal of Nanoscience and Nanotechnology,2011,11(3):2315-2320.
[73] QING Y C,ZHOU W C,JIA S,et al. Electromagnetic and microwave absorption properties of carbonyl iron and carbon fiber filled epoxy/silicone resin coatings[J]. Applied Physics A,2010,100(4):1177-1181.
[74] MIN D,ZHOU W,QING Y,et al. Highly oriented flake carbonyl iron/carbon fiber composite as thin-thickness and wide-bandwidth microwave absorber[J]. Journal of Alloys and Compounds,2018,744:629-636.
[75] 王振军,李克智,王闯,等. 羰基铁粉-碳纤维水泥基复合材料的吸波性能[J]. 硅酸盐学报,2011,39(1):69-74. WANG Z J,LI K Z,WANG C,et al. Wave-absorbing properties of carbonyl iron powder/carbon fiber reinforced cement-based composites[J]. Journal of the Chinese Ceramic Society,2011,39(1):69-74.
[76] AFGHAHI S S S,MIRZAZADEH A,JAFARIAN M,et al. A new multicomponent material based on carbonyl iron/carbon nanofiber/lanthanum-strontium-manganite as microwave absor-bers in the range of 8-12GHz[J]. Ceramics International,2016,42(8):9697-9702.
[77] DUAN Y P,WANG L,LIU Z,et al. Microwave properties of double layer absorber reinforced with carbon fibre powders[J]. Plastics, Rubber and Composites,2013,42(2):82-87.
[78] LIU L,DUAN Y,MA L,et al. Microwave absorption properties of a wave-absorbing coating employing carbonyl-iron powder and carbon black[J]. Applied Surface Science,2010,257(3):842-846.
[79] QING Y,ZHOU W,JIA S,et al. Dielectric properties of carbon black and carbonyl iron filled epoxy-silicone resin coating[J]. Journal of Materials Science,2010,45(7):1885-1888.
[80] SHEN X,XIE S,GUO J,et al. Microwave absorbing properties of ternary linear low-density polyethylene/carbonyl iron powder/carbon black composites[J]. Journal of Applied Polymer Science,2009,114(6):3434-3439.
[81] LI X,ZHANG Y,CHEN J,et al. Composite coatings reinforced with carbonyl iron nanoparticles:preparation and microwave absorbing properties[J]. Materials Technology,2014,29(1):57-64.
[82] PINHO M S, Da COSTA L R,SILVA M R D,et al. Microwave absorption of carbon black and carbonyl iron composites with polychloroprene[J]. Materials Technology,2013,21(1):27-31.
[83] MIN D,ZHOU W,QING Y,et al. Enhanced microwave absorption properties of oriented carbonyl iron/carbon black composite induced by shear force[J]. Journal of Electronic Materials,2017,46(8):4903-4911.
[84] WANG M,DUAN Y,LIU S,et al. Absorption properties of carbonyl-iron/carbon black double-layer microwave absorbers[J]. Journal of Magnetism and Magnetic Materials,2009,321(20):3442-3446.
[85] CHEN L,DUAN Y,LIU L,et al. Influence of SiO2 fillers on microwave absorption properties of carbonyl iron/carbon black double-layer coatings[J]. Materials & Design,2011,32(2):570-574.
[86] 陈雪刚,叶瑛,程继鹏. 电磁波吸收材料的研究进展[J]. 无机材料学报,2011,26(5):449-457. CHEN X G,YE Y,CHENG J P. Recent progress in electro-magnetic wave absorbers[J]. Journal of Inorganic Materials,2011,26(5):449-457.
[87] WOO S,YOO C,KIM H,et al. Development of CIP/graphite composite additives for electromagnetic wave absorption applications[J]. Electronic Materials Letters,2017,13(5):398-405.
[88] XU Y,YAN Z,ZHANG D. Microwave absorbing property of a hybrid absorbent with carbonyl irons coating on the graphite[J]. Applied Surface Science,2015,356:1032-1038.
[89] TAN Y,TANG J,DENG A,et al. Magnetic properties and microwave absorption properties of chlorosulfonated polye-thylene matrices containing graphite and carbonyl-iron powder[J]. Journal of Magnetism and Magnetic Materials,2013,326:41-44.
[90] XU Y,ZHANG D,CAI J,et al. Microwave absorbing property of silicone rubber composites with added carbonyl iron particles and graphite platelet[J]. Journal of Magnetism and Magnetic Materials,2013,327:82-86.
[91] DENG J L,FENG B. Carbonyl iron/graphite double-layer structural absorbing composite[J]. Advanced Materials Research,2012,557/559:390-393.
[92] LI B P,WANG C G,WANG W,et al. Electromagnetic wave absorption properties of composites with micro-sized magnetic particles dispersed in amorphous carbon[J]. Journal of Magnetism and Magnetic Materials,2014,365:40-44.
[93] 李斌鹏,王成国,王雯,等. 无定形炭/磁性粒子复合吸波材料的制备和电磁性能研究[J]. 功能材料,2012,43(14):1941-1944. LI B P,WANG C G,WANG W,et al. Electromagnetic wave absorption properties of amorphous carbon/magnetic particle composites[J]. Functional Materials,2012,43(14):1941-1944.
[94] WU H,WANG L,WANG Y,et al. Enhanced microwave absorbing properties of carbonyl iron-doped Ag/ordered mesoporous carbon nanocomposites[J]. Materials Science and Engineering:B,2012,177(6):476-482.
2019, Vol. 47 
