1、文章编号:摇 1007鄄8827(2017)02鄄0138鄄06Ni(NO3)2催化酚醛树脂的炭化结构特性及其力学性能马天飞1,摇 吴小贤2,摇 李红霞1,摇 刘国齐1,摇杨文刚1(1. 中钢集团洛阳耐火材料研究院 先进耐火材料国家重点实验室,河南 洛阳 471039;2. 浙江省地质矿产研究所,浙江 杭州 310007)摘摇 要:摇 在酚醛树脂中添加Ni(NO3)2,逐步固化、高温炭化后,用 X 射线衍射、扫描电镜和透射电镜观察表征树脂高温炭化显微结构,并测试树脂炭的抗折强度、弹性模量和断裂能来分析其力学性能。 显微结构观察表明:添加质量分数 5% 的Ni(NO3)2会在酚醛树脂炭化结构中生
2、成体积分数约 2%的纳米炭纤维,纳米炭纤维交错排布;由于酚醛树脂热解产生的含碳小分子气体成分复杂,在树脂玻璃炭出现了炭纳米纤维与碳纳米管接替生长的现象。 力学性能测试结果表明:树脂玻璃炭中原位生成的纳米炭纤维与树脂炭基体有一定的结合强度,能提高树脂玻璃炭的抗折强度、弹性模量;可显著提高树脂炭的断裂能,增强其抗拉强度和断裂韧性。关键词:摇 酚醛树脂; Ni(NO3)2; 炭化结构; 力学性能中图分类号: 摇 TB333文献标识码: 摇 A基金项目: 国家自然科学基金(51372231).通讯作者: 李红霞,教授. E鄄mail: lihongx lirrc. com第一作者: 马天飞,硕士,工程
3、师. E鄄mail: heshui0a126. comMicrostructures and mechanical properties of pyrocarbonsproduced from phenolic resin with added Ni(NO3)2MA Tian鄄fei1,摇 WU Xiao鄄xian2,摇 LI Hong鄄xia1,摇 LIU Guo鄄qi1,摇 YANG Wen鄄gang1(1. State Key Laboratory of Advanced Refractories, Sinosteel Luoyang Institute of Refractories
4、Research, Luoyang471039, China;2. Zhe Jiang Institute of Geology and Mineral Resource, Hangzhou310007, China)Abstract: 摇 A refractory containing graphite is commonly used in the metallurgical industry in locations subject to severe thermalshock because of the high thermal conductivity and good therm
5、al shock resistance of graphite. However, a refractory that uses phe鄄nolic resin as the carbon precursor is brittle, and to improve its strength and toughness, Ni(NO3)2is added to the resin to catalyzethe in鄄situ formation of carbon nanofibers/ nanotubes. The microstructure and mechanical properties
6、 of the Ni(NO3)2鄄modified phe鄄nolic resin carbons were characterized by XRD, SEM, TEM and mechanical tests. Results indicate that carbon nanofibers/ nanotubes(2% by volume) were formed within the pyrocarbons as a result of the nickel catalyst and these are interconnected to form a net鄄work structure
7、. The nanocarbon fibers/ tubes significantly improve the bend strength, elastic modulus, tensile strength and fracturetoughness of the pyrocarbons and their fracture energies are increased accordingly.Keywords:摇 Phenolic resin; Ni(NO3)2; Carbonized structure; Mechanical propertiesReceived date: 2017
8、鄄01鄄05;摇 Revised date: 2017鄄03鄄07Foundation item: National Natural Science Foundation of China (51372231).Corresponding author: LI Hong鄄xia, Professor. E鄄mail: lihongx lirrc. comAuthor introduction: MA Tian鄄fei, Engineer. E鄄mail: heshui0a126. comEnglish edition available online ScienceDirect (http:蛐
9、蛐www. sciencedirect. com蛐science蛐journal蛐18725805).DOI: 10. 1016/ S1872鄄5805(17)60111鄄21摇 IntroductionRefractorycontaininggraphitewascommonlyused in metallurgical process and thermal shock harshplace (such as ladle pouring protective sleeve, slide,the tundish control flow stopper, Sen) owing to itsh
10、igh thermal conductivity and good thermal shock re鄄sistance. Because the graphite is easily dissolved inthe molten steel, dissolved graphite will produce morepores in refractory products and parts of slag line,slag easily infiltrated inside the refractory erosion,thereby reducing the service life of
11、 the refractory ma鄄terial.A method to improve service life of refractorycontaining graphite is to reduce graphite content,摇第 32 卷摇 第 2 期2017 年 4 月新摇 型摇 炭摇 材摇 料NEW CARBON MATERIALSVol. 32摇 No. 2Apr. 2017摇thereby reducing the slag erosion channel. But a less鄄er graphite content will debase thermal sho
12、ck resist鄄ance of refractory material.Refractory containinggraphite usually use phenolic resin as a binder, whichforms resin carbon鄄based refractories after high tem鄄perature firing. The resin carbon is fragile, so if itsfragility can be improved, the content of graphite canbe possibly reduced to im
13、prove the service life of therefractory.Fiber is often used to strengthen and toughen ce鄄ramic material and resin material, the cohesion be鄄tween reinforcement material and matrix is key to re鄄alize the strengthening and toughening effect. Manystudies found that fiber was pulled out of matrix whenfi
14、ber material differed from matrix material. This roleof the reinforced fiber cannot effectively be real鄄ized1鄄6when fiber material is same with matrix mate鄄rial (such as C/ C composites), where reinforcing fi鄄ber and the matrix can be firmly combined. Homoge鄄neous dispersion of fiber in the matrix i
15、s one of thekey technologies in the preparation of reinforced com鄄posites. If fiber is unevenly distributed in glass ma鄄trix, there will be no鄄glass areas and no鄄fiber area.Internal defects and weak strength parts determine theoverall strength of the material, the uneven dispersionin reinforced mate
16、rial will weaken its enhancementeffect7. Recent studies show that carbon nanotube/carbon fiber are formed at high temperature carboniza鄄tion with Fe, Co, Ni catalytic materials added in phe鄄nolic resin8鄄10, but changes of the mechanical prop鄄erties of resin carbon have not been reported. In thispape
17、r, high temperature catalytic pyrolysis of phenolicresin by adding Ni(NO3)2to form carbon fiber in鄄si鄄tu to reinforce the resin carbon was investigated byobserving the characteristics of the material micro鄄structure and testing its mechanical properties. Thestrengthening and toughening mechanism by
18、the in鄄si鄄tu carbon fiber was proposed.2摇 Experimental2. 1摇 PreparationPF鄄5405 resin was used, which was made inShandong Shengquan group. The viscosity of phenol鄄ic resin is 7. 5鄄8. 5 Pa S (20 益), solid content is 80依3 wt% and free phenol content is less than 12 wt%;Nickel nitrate Ni(NO3)26H2O is an
19、alytical grade,made in Tianjin Municipality Kemiou Chemical Rea鄄gent Co. , Ltd.Nickel nitrate with contents of 1, 2 and 5 wt%of the resin was dispersed separately in the resin by ahigh speed dispersion machine, and poured into thesample mould. The sample was cured at 60 益 for24 h, then heated to 120
20、 益 for 24 h. Under the pro鄄tection of N2, the sample was carbonized at 1 100 益for 3 h at a heating rate of 1 益 / min and naturallycooled to room temperature. As a comparison, thepure phenolic resin was cured and carbonized in ac鄄cordance with this procedure and conditions.2. 2 摇Microstructural chara
21、cterization and me鄄chanical property testCrystalline phases of samples were identified byX鄄ray diffraction (The Holland Philips X Pert ProMPD, Cu ray source target, characteristic spectralline wavelength K琢10. 154 056 nm). The microstruc鄄ture was analyzed by scanning electron microscopy(SEM, Zeiss E
22、VO鄄18, Germany), energy鄄dispersivespectroscopy (EDS, X鄄Max50, Oxford instrument,Oxford, UK) and transmission electron microscopy( Zeiss LIBRA鄄200FE, Germany).Microstructuralparameters were determined through an image analysison SEM micrographs of polished surfaces ( ImagePro鄄plus 4. 5. 1, Media Cybe
23、rnetics, Silver Springs,MD).Rupture strength was tested by a three鄄point ben鄄ding test. Elastic modulus was measured by a pulseexcitation method.Fracture energy was measuredusing a wedge splitting test.3摇 Results and discussion3. 1摇 Crystalline PhasesX鄄ray diffraction patterns of samples from pureph
24、enolic resin and Ni(NO3)2added ones are shownin Fig. 1. As shown in Fig. 1, clear peak cannot befound in the diffraction pattern of the carbonized sam鄄ple from pure phenolic resin, indicating that the crys鄄talline phase is amorphous. But (002) characteristicgraphite diffraction peaks can be found in
25、 the diffrac鄄tion patterns of the carbonized samples added withNi(NO3)2. Under high temperature, Ni(NO3)2isdecompose and reduced to Ni. Many researches11鄄13about glass carbon from phenolic resin indicate thatphenolic resin decompose into free carbon atoms withsp2and sp3hybridization, sp2carbon atoms
26、 form im鄄perfect graphite crystal in the micro area, sp3carbonatoms exist in the amorphous form. The XRD diffrac鄄tion patterns did not show strong and sharp peaks, in鄄dicating that the resin carbon has an amorphous glasscarbon structure. But the sharp and narrow diffractionpeaks can be found in this
27、 study for the samples addedwith Ni(NO3)2, which indicates that perfect graphitecrystal is formed with the help of Ni(NO3)2. Weakpeak strength indicates that the amount of perfectgraphite crystal is small.931第 2 期MA Tian鄄fei et al: Microstructures and mechanical properties of pyrocarbons 摇Fig. 1摇 X鄄
28、ray diffraction patterns of phenolic resinbased carbons with and without Ni(NO3)2.摇 摇 In order to get further knowledge about the crys鄄talline structure, crystalline parameters ( includingcorrecteddiffractionangle2兹(002),facespacingd(002), C axis crystal size Lc(002), crystal graphite lay鄄ers Lc(002
29、)/ d(002), graphitization degree) were compu鄄ted as listed in Table 1. From Table 1, along with theamount of Ni(NO3)2added, it is found that 2兹(002)angleincreasesslightlywiththeamountofNi(NO3)2, indicating that d(002)decreases with the a鄄mount of Ni(NO3)2, which are close to the value ofperfect grap
30、hite (0. 335 4 nm). The values of C axiscrystal size Lc(002)and crystalline graphite layersLc(002)/ d(002)indicate that there are 2 to 3 layers ofgraphene stacking in C axis direction. The graphitiza鄄tion degree G increases with the amount of Ni(NO3)2,indicating that the crystal phase approaches the
31、 regularhexagonal graphite sheet.Table 1摇 Crystalline parameters of pyrolysis carbons.No.2兹(002)(毅) d(002)(nm) Lc (002)(nm) Lc (002)/ d(002)g(%)PF鄄鄄鄄鄄鄄1%26.4120. 337170.87212. 5879.532%26.4310. 336940.94012. 7982.095%26.4460. 336750.75132. 0484.303. 2摇 Micro morphology of the carbonized samplesBy th
32、e analysis of the XRD diffraction, theamount of crystal carbon in the phenolic resin carbon鄄ized products increases and the crystal structure alsobecomes more regular with the amount of Ni(NO3)2added. So here, carbonized microstructure of the purephenolic resin carbon and the 5% Ni(NO3)2addedone was
33、 observed and analyzed, and the effect ofNi(NO3)2on microstructure of phenolic resin basedcarbons and its mechanism are discussed.Fig. 2ashows the microstructure of the pure phenolic resinbased carbon, which is a smooth, continuous and uni鄄form, isotropic glass state structure. Fig. 2b showsthe micr
34、ostructure of the phenolic resin based carbonwith 5%Ni(NO3)2. The continuous dark regions de鄄note resin glass carbon, the EDS energy spectrumanalysis (Fig. 2c) shows that highlighted fibers de鄄note carbon fiber and highlighted spots denote Ni par鄄ticles, which are distributed uniformly as a whole,pa
35、rtly aggregative. Small molecular gases containingcarbon released by pyrolysis of phenolic resin are cat鄄alyzed and decomposed into carbon, which dissolveinto metal Ni. Carbon atoms are separated out of met鄄al Ni and form nano fibers when carbon is oversaturat鄄ed in metal Ni.The magnification micros
36、copic image from Fig.2d shows that there are micro pores near Ni particlesproduced by pyrolysis of phenolic resin, some Ni par鄄ticles aggregates. Carbon fibers grow with Ni particlesas the endpoints, whose longest fiber length is42 滋m, diameter is 229 nm and the ratio of length todiameter is 183.The
37、 TEM analysis of fiber morphology is shownin Fig. 3. Under the transmission electron microscopeof a cross section of a carbon nano fiber, black solidline represents hexagonal lamellae of C atom construc鄄ting the nano fiber in microscopic images. It can beseen from the graph, the sample is a linear c
38、arbon fi鄄ber (Fig. 3c), and there are also a lot of coil wind鄄ing of the carbon nano fibers (Fig. 3a). In Fig. 3bof an area magnification observation in Fig. 3a, theorientation layered arrangement of graphite sheet in鄄side of the fiber can be clearly seen, carbon nano fi鄄ber bending is due to the de
39、position and the migrationof carbon atoms caused by uneven extrusion, bendingparts is pentagon or heptagon C atomic sheet, linesegment is hexagonal C atomic sheet. One end is asolid structure, and the other end is a hollow struc鄄ture, which can be found in Fig. 3c, this illustratesthat carbon nano f
40、ibers and carbon nanotubes grow al鄄ternately in phenolic resin carbonized products withNi(NO3)2.Whether gaseous carbon deposed intocarbon nanotubes or nano fibers depends on theamount of gases containing hydrogen bond in thegrowth environment15. A large amount of gases con鄄taining hydrogen bond are
41、produced in the early stageof pyrolysis of phenolic resin, strong hydrogen bondscan stabilize impending carbon bonds which exist inthe graphite hexagonal structure boundary, so as toform a solid fiber filaments with layered heaps. Withthe pyrolysis of phenolic resin, the released gases con鄄taining h
42、ydrogen bond is reduced, carbon bond sus鄄pended in the edge of graphite hexagonal structure be鄄comes unstable, which tends to change into the strainenergy, forming a closed tubular structure, therebyeliminating the suspended unstable carbon bond.041摇新摇 型摇 炭摇 材摇 料第 32 卷Fig. 2摇 SEM images of pyrolysis
43、 carbons with and without Ni(NO3)2.(a) Pure phenolic resin; (b) Adding 5% Ni(NO3)2; (c) EDS anlysis; (d) Magnification image of Fig. 2b.Fig. 3摇 TEM images of pyrolysis carbon with Ni(NO3)2.3. 3摇 Mechanical properties of pyrolysis carbonThepurephenolicresincarbonandtheNi(NO3)2added ones were cut into
44、 25 伊 25 伊150 mm3. The flexural strength and elastic moduluswere tested and the testing data are shown in Table 2and Table 3. The variation trend are shown in Fig. 4and Fig. 5 using averaged data. Because samples arecured at low temperature for a long time and heated ata slow rate, the carbonized sa
45、mple has little largepores as shown in Fig. 2 and the discreteness of me鄄chanical testing data is small as shown in Table 2 andTable 3. As shown in Fig. 4 and Fig. 5, the flexuralstrength and elastic modulus of the carbonized samplesincrease with the amount of Ni(NO3)2added. When5% Ni(NO3)2was added
46、, the flexural strength ofthe carbonized samples increase by 13. 8% comparedwith that of the pure phenolic resin based one as listedin Table 2. Through area estimation in microstructureimage, carbon nano fiber volume accounts for about2%, so a small amount of carbon nano fibers genera鄄ted in鄄situ ca
47、n effectively improve the bending resist鄄ance of the pyrolysis carbons.The fracture energy of phenolic resin carbonsamples is shown in Table 4 and Fig. 6, and the frac鄄ture energy testing results are shown in Fig. 7. Underwedge splitting force, tensile stress exists in samplesand transmits between p
48、yrolysis carbon and carbonnano fibers produced with added Ni(NO3)2. When5% Ni(NO3)2is added, fracture energy of the car鄄bonized samples increases by 65% compared with the141第 2 期MA Tian鄄fei et al: Microstructures and mechanical properties of pyrocarbons 摇pure phenolic resin carbon, indicating that t
49、he addi鄄tion of Ni(NO3)2effectively improves the fracture re鄄sistance of the pyrolysis carbon.Table 2摇 Flexural strength of samples.Ni(NO3)2content (wt%)Testingstrength (MPa)Averagestrength (MPa)Averagedeviation (MPa)032.5832.2430.6433.1531.820. 79132.4035.2833.9333.611. 11234.2536.0735.1634.750. 88
50、537.4036.2536.270. 75Table 3摇 Elastic modulus of samples.Ni(NO3)2content (wt%)Testingmodulus (MPa)Averagemodulus (MPa)Averagedeviation (MPa)0260. 21275. 64254. 20291. 57263.358. 191276. 38273. 46294. 26280.477. 402301. 24282. 15306. 34292.556. 935326. 38313. 54315.427. 30Fig. 4摇 Flexural strength of
