【作者】 张乐；

【导师】 慈立杰；

【作者基本信息】 山东大学 ， 材料加工工程， 2018， 硕士

【摘要】 石墨烯(graphene)是一种具有优良力学及热学性能的碳纳米材料,将其代替陶瓷增强相(碳化硅、氧化铝等)加入到铝基体中,微量添加即可获得显著增强的力学性能,同时也可能提高基体的热学性能。相对于陶瓷添加相,石墨烯的密度极低,能够进一步减小复合材料的密度。更重要的,石墨烯可以解决陶瓷相硬、脆的本征属性导致的铝合金难以加工的问题。基于当前对石墨烯铝基复合材料研究的实际情况,本文选择了先使用原位还原法来使石墨烯包覆于铝粉体颗粒的表面,再通过粉末冶金工艺成型,烧结得到的复合材料块体力学与热学性能均优于纯铝块体。论文中对使用的氧化石墨烯(GO)溶液浓度进行了调整,发现在0.2 mg/ml时溶液的分散性与稳定性均比较好。pH为4.0的弱酸条件可以除去铝粉表面的薄氧化层,又不会对铝粉产生严重腐蚀。氧化层的去除使铝与GO水溶液充分接触,确保原位还原反应顺利进行,使还原后的还原氧化石墨烯(rGO)层片紧密包覆在铝粉体表面。在干燥工艺中发现,干燥前使用无水乙醇对反应后的复合粉体进行洗涤,可以有效抑制铝粉体在长达8小时的干燥过程中发生水解反应,生成副产物氢氧化铝,影响复合块体的纯度及最终的材料性能。论文选取未洗涤直接干燥的粉体做了对比实验,微米级铝粉的高表面能导致水解反应进行剧烈,表面生成大量氢氧化铝使粉体发生明显增重。经参数优化,复合材料块体烧结温度为600℃,保温时长为5小时,烧结过程中氩气作为保护气氛。最终得到了纯铝以及rGO质量分数分别为0.1%,0.2%,和0.3%的尺寸为φ40×5 mm的饼状复合材料块体。论文对包覆粉体以及复合材料块体进行了形貌与结构表征。扫描电镜(SEM)与透射电镜(TEM)下可观察到rGO紧密地包覆于铝颗粒表面,并可观察到还原后石墨烯有明显的晶格结构;拉曼(Raman)光谱分析可以看到GO经包覆过程后ID/IG值由0.84变为1.13,结构发生了明显还原;X射线衍射仪(XRD)的分析结果表明,该法烧结制备出的复合材料块体中未生成明显的氧化物与碳化物;阿基米德排无水乙醇法测得块体密度分别为1.132g/cm3,1.128 g/cm3,1.125 g/cm3和1.132 g/cm3,这表明在该范围内,提高石墨烯的加入量,复合材料的密度逐渐减小。论文对复合材料块体的力学、热学性能进行了测试。实验发现,纯铝以及rGO添加量分别为0.1%,0.2%,和0.3%的块体材料压缩强度分别为207 MPa,232 MPa,249 MPa和 260 MPa;显微硬度分别为43.1±2.5 HV,49.2±2.5HV,50.7±1.2HV和52.2±1.9 HV;20℃ 下的导热系数分别为 143 W/(m*K),154 W/(m*K),159 W/(m*K)和 165 W/(m*K);20℃ 下的比热容分别为 0.905 J/(g*K),0.921 J/(g*K),0.928 J/(g*K)和 0.987 J/(g*K);针对纯铝和rGO质量分数为0.3%的复合块体的DSC测试结果也证明了在熔点温度之下后者的比热容始终高于前者。除铝粉体外,论文还选取了铜和钛粉体进行原位还原包覆法的辅助验证,辅助实验证明了该法的适用性。需要注意的是,在铜的包覆实验中,要在GO水溶液中加入乙醇以改善铜粉与溶液的润湿性,使铜粉得以与溶液充分接触发生反应;在钛的包覆实验中,要先用氢氟酸与硝酸的混合酸液对钛粉进行酸洗去除表面氧化层,再进行包覆反应。鉴于酸液使用上的不安全性,对钛粉这类氧化层较难除去的金属粉,本实验还探索了利用电荷吸附的原理将GO包覆于粉体表面的方法,也收到了较好的效果。更多还原

【Abstract】 Compared with ceramic phases(SiC,Al2O3),graphene,with perfect mechanical and thermal properties,can enhance the mechanical and thermal properties of the aluminum matrix with rather low addition.The density of graphene is low,which makes the density of the composites lower.What’s more,the difficulty of machining caused by the hard,brittle ceramic phases can be solved by the use of graphene.Based on the present situation of AI/graphene composite,we first coated graphene onto the surface of aluminum particles by the method of in-situ reduction.Then,the bulk composites were prepared by the powder metallurgy(P/M)technique.The mechanical and thermal properties of bulk composites after sintering are better than that of pure aluminum.The solution was stable when the concentration of graphene oxide was adjusted to 0.2 mg/ml.The weak acid solution with the pH value of 4.0 could remove the thin aluminum oxide layers on the surfaces of A1 powders without severely corroding the powders.The removal of aluminum oxide layers can lead to the sufficient contact between aluminum powders and solution,and in-situ reduction reaction of graphene oxide(GO)will happen on the surface of metallic aluminum.The reduced graphene oxide(rGO)can be attached to the surfaces of aluminum particles closely after in-situ reduction reaction.We found that the hydrolysis reactions occurred during the 8 hours’ drying process.Al(OH)3,as the reaction products,would have bad influence on the properties of composites.In order to avoid this side reaction,the powders after reaction were washed by ethyl alcohol before drying.The composite powders without washing were synthesized as comparison.The spontaneous hydrolysis reaction occurred violently because of the high surface energy of the micro-sized Al particles.The formation of Al(OH)3 on the surface of A1 particles makes the powders heavier.The bulk samples were sintered at 600 ℃ for 5 h in Ar atmosphere after optimization.Pure sample,composite samples(φ40×5 mm)with 0.1 wt.%,0.2 wt.%and 0.3 wt.%graphene additions were prepared.Morphology and structures of graphene coated powders and bulk samples were characterized.SEM and TEM images indicated that graphene was coated onto the surfaces of aluminum particles closely,and the lattice structure of reduced graphene oxide was obvious.Raman spectrum indicates that ID/IG ratio increases from 0.84 to 1.13 after graphene coating,which means that the graphene oxide was reduced in certain degree.No diffraction peaks of oxide or carbide were observed from the XRD pattern.The density of the bulks was measured to be 1.132 g/cm3,1.128 g/cm3,1.125 g/cm3 and 1.132 g/cm3 respectively by the Archimedes principle method,which indicates that the density decreases with the increased addition of graphene.Mechanical and thermal properties of bulk samples were characterized.The compressive strength is 207 MPa,232 MPa,249 MPa and 260 MPa for pure Al,0.1%rGO/Al,0.2%rGO/Al,and 0.3%rGO/Al,respectively.Their Vickers hardness values are 43.1 ±2.5 HV,49.2 ± 2.5 HV,50.7 ± 1.2 HV and 52.2 ± 1.9 HV.Their thermal conductivity are 143 W/(m*K),154 W/(m*K),159 W/(m*K)and1 65 W/(m*K)at 20℃.And the specific heat capacity are 0.905 J/(g*K),0.921 J/(g*K),0.928 J/(g*K),0.987 J/(g*K)at 20 ℃,respectively.The DSC curves indicate that the specific heat capacity of composite with 0.3 wt.%graphene is lager than that of pure A1 before melting.Copper and titanium powders were also used to prove the usability of the method of in-situ reduction reaction method for rGO coating.Ethyl alcohol should be introduced into the graphene oxide solution to improve the wettability between copper powders and solution.What’s more,the oxide layers of titanium particles should be etched away by hydrofluoric acid and nitric acid.In consideration of the risk of using acid,we explored the method of coating graphene oxide layers onto powders by the mechanism of electrostatic self-assembly method,which can be used for metal powders with stubborn oxide layers,such as titanium.The method was turned out to be effective.更多还原