仿壁虎碳納米管陣列制備及黏附性能研究
發(fā)布時間：2018-11-21 14:43
【摘要】：碳納米管陣列(VACNTs)以其優(yōu)異的力學、電學、熱學性能以及對極端環(huán)境的適應性,成為仿壁虎干黏附極具潛力的材料,在爬壁機器人領域體現(xiàn)出重要的應用價值。本文針對目前VACNTs可控制備存在的問題,設計了具有不同緩沖層和催化劑厚度的生長基底,并調節(jié)了化學氣相沉積工藝過程中的氫氣預處理時間,氫氣濃度,沉積時間和反應壓力等,以探究這些因素對制備的VACNTs的形貌結構、缺陷程度、純度質量及黏附性能的影響,為實現(xiàn)其可控制備建立方法和理解上的基礎。本文的主要成果和結論如下:1.支撐層和催化劑層的厚度對VACNTs的生長狀況有顯著的影響。Fe層的厚度直接決定形成的催化劑Fe顆粒的分布狀況,進一步影響以此為模板生長的VACNTs的形貌結構。多孔結構的Al_2O_3使還原后的Fe進入其空隙分散成均勻分布的顆粒,過厚的Al_2O_3層增大了Fe顆粒的擴散損耗。而比Al_2O_3層更加致密的SiO_2層有效阻斷了Fe顆粒的擴散損耗。2.通過調節(jié)預處理階段和沉積階段的氫氣濃度,可以控制VACNTs的生長速率實現(xiàn)快速生長。AFM觀察表明,預處理階段適宜濃度的氫氣將催化劑Fe膜還原到具有催化活性的金屬狀態(tài)并形成均勻分布的Fe顆粒。實驗中以SiO_2/Al_2O_3/Fe=300nm/15nm/1nm的生長基底,在25%的氫氣濃度下制備的VACNTs高度達到949μm,生長速率為23.72μm/min。拉曼光譜表明,該條件下生長的VACNTs呈現(xiàn)較高的石墨化結晶程度,具有相對最佳的純度和質量。3.本文提出了反應氣氛中氫氣濃度對VACNTs黏附性能的影響機理:當氫氣比例過低(0%~5%)時,VACNTs生長高度較低,不足以適應目標表面形成大面積的線接觸。而當氫氣比例過高(25%~35%)時,多余的氫氣改變了催化劑的晶相,從具有催化活性的FeC_3轉變?yōu)轶w心立方(BCC)Fe,使生長的VACNTs缺陷程度更高而石墨化結晶程度較差。實驗中以SiO_2/Al_2O_3/Fe=300nm/20nm/2nm的生長基底,在15%的氫氣濃度下制備的VACNTs在黏附測試中表現(xiàn)出優(yōu)良的黏附性能,宏觀切向黏附力達到32N/cm2,是壁虎腳掌的3.2倍。
[Abstract]:Because of its excellent mechanical, electrical, thermal properties and adaptability to extreme environments, carbon nanotube array (VACNTs) has become a potential material for dry adhesion of Gecko, and has shown great application value in the field of wall-climbing robot. Aiming at the existing problems of controllable preparation of VACNTs, the growth substrate with different buffer layer and catalyst thickness was designed, and the pretreatment time and concentration of hydrogen in the process of chemical vapor deposition were adjusted. The deposition time and reaction pressure were used to investigate the influence of these factors on the morphology, defect degree, purity quality and adhesion property of the prepared VACNTs. The main results and conclusions are as follows: 1. The thickness of the supporting layer and the catalyst layer has a significant effect on the growth of VACNTs. The thickness of the Fe layer directly determines the distribution of the formed catalyst Fe particles, and further influences the morphology and structure of the VACNTs grown on the template. Al_2O_3 with porous structure makes the reduced Fe into its pore space to disperse into uniformly distributed particles, and the excessive thickness of Al_2O_3 layer increases the diffusion loss of Fe particles. SiO_2 layer, which is denser than Al_2O_3 layer, effectively blocks the diffusion loss of Fe particles. 2. The growth rate of VACNTs can be controlled by adjusting the concentration of hydrogen in pretreatment stage and deposition stage. The Fe membrane of the catalyst was reduced to a metal state with catalytic activity by hydrogen at a suitable concentration in the pretreatment stage and a uniform distribution of Fe particles was formed. In the experiment, the growth rate of SiO_2/Al_2O_3/Fe=300nm/15nm/1nm was 23.72 渭 m / min and the height of VACNTs was 949 渭 m at 25% hydrogen concentration. The Raman spectra show that the VACNTs grown under this condition has a relatively high degree of graphitization and crystallization, and has the best purity and quality of 3. 3%. The mechanism of the effect of hydrogen concentration in the reaction atmosphere on the adhesion properties of VACNTs is presented. When the hydrogen ratio is too low (0%), the growth height of VACNTs is low, which is not enough to adapt to the formation of large area linear contact on the target surface. When the hydrogen ratio is too high (25%), the excess hydrogen changes the crystalline phase of the catalyst, from the catalytic activity of FeC_3 to the bulk centered cubic (BCC) Fe,), resulting in higher degree of defect of VACNTs growth and less degree of graphitization crystallization. In the experiment, the VACNTs prepared on the growth substrate of SiO_2/Al_2O_3/Fe=300nm/20nm/2nm with 15% hydrogen concentration showed excellent adhesion performance in the adhesion test. The macroscopic tangential adhesion force reached 32N / cm ~ 2. 3.2 times the gecko's soles.
【學位授予單位】：南京航空航天大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ127.11;TB383.1
本文編號：2347278
[Abstract]:Because of its excellent mechanical, electrical, thermal properties and adaptability to extreme environments, carbon nanotube array (VACNTs) has become a potential material for dry adhesion of Gecko, and has shown great application value in the field of wall-climbing robot. Aiming at the existing problems of controllable preparation of VACNTs, the growth substrate with different buffer layer and catalyst thickness was designed, and the pretreatment time and concentration of hydrogen in the process of chemical vapor deposition were adjusted. The deposition time and reaction pressure were used to investigate the influence of these factors on the morphology, defect degree, purity quality and adhesion property of the prepared VACNTs. The main results and conclusions are as follows: 1. The thickness of the supporting layer and the catalyst layer has a significant effect on the growth of VACNTs. The thickness of the Fe layer directly determines the distribution of the formed catalyst Fe particles, and further influences the morphology and structure of the VACNTs grown on the template. Al_2O_3 with porous structure makes the reduced Fe into its pore space to disperse into uniformly distributed particles, and the excessive thickness of Al_2O_3 layer increases the diffusion loss of Fe particles. SiO_2 layer, which is denser than Al_2O_3 layer, effectively blocks the diffusion loss of Fe particles. 2. The growth rate of VACNTs can be controlled by adjusting the concentration of hydrogen in pretreatment stage and deposition stage. The Fe membrane of the catalyst was reduced to a metal state with catalytic activity by hydrogen at a suitable concentration in the pretreatment stage and a uniform distribution of Fe particles was formed. In the experiment, the growth rate of SiO_2/Al_2O_3/Fe=300nm/15nm/1nm was 23.72 渭 m / min and the height of VACNTs was 949 渭 m at 25% hydrogen concentration. The Raman spectra show that the VACNTs grown under this condition has a relatively high degree of graphitization and crystallization, and has the best purity and quality of 3. 3%. The mechanism of the effect of hydrogen concentration in the reaction atmosphere on the adhesion properties of VACNTs is presented. When the hydrogen ratio is too low (0%), the growth height of VACNTs is low, which is not enough to adapt to the formation of large area linear contact on the target surface. When the hydrogen ratio is too high (25%), the excess hydrogen changes the crystalline phase of the catalyst, from the catalytic activity of FeC_3 to the bulk centered cubic (BCC) Fe,), resulting in higher degree of defect of VACNTs growth and less degree of graphitization crystallization. In the experiment, the VACNTs prepared on the growth substrate of SiO_2/Al_2O_3/Fe=300nm/20nm/2nm with 15% hydrogen concentration showed excellent adhesion performance in the adhesion test. The macroscopic tangential adhesion force reached 32N / cm ~ 2. 3.2 times the gecko's soles.
【學位授予單位】：南京航空航天大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ127.11;TB383.1
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