最近，在一篇由英国航空研究所（ATI）和曼切斯特大学国家石墨烯研究院（NGI）联合发表的论文中，研究人员指出，石墨烯的应用有可能给航空航天领域带来颠覆性的变革。

2004年，曼切斯特大学的两名科学家在用胶带清理一块石墨晶体时，发现他们在胶带上分离出了一层碳原子。石墨烯由此诞生。至此以后，石墨烯因其惊人的特性引发了科研界的密切关注。石墨烯的强度是钢的200倍，不仅具备优异的柔韧性，还是绝佳的导电体。

曼切斯特大学的科研人员表示，这种二维材料有望帮助改善飞行器的性能、降低造价、提高能效。如果在当前的飞行器制造材料中添加只有一个原子厚度的石墨烯，那么飞行器的安全性将显著增强，其它性能也将明显改善。如此一来，还能实现机身轻量化和节能环保的目标。

该篇论文发表于ATI的《INSIGHT》期刊，前言由理查德·布兰森爵士亲自撰写。文中写道，“石墨烯有望解决航空航天领域中一些由来已久的挑战，继而引发行业革命，成为未来航空航天技术发展的关键动力。我们需要大力开展石墨烯相关科研技术项目，加深国内对石墨烯优点的认识，为我国航空业的发展做出实质性贡献。”

石墨烯研发的最新进展

石墨烯近来的迅猛发展让这一材料成为了关注焦点。

二月，日本东北大学和名古屋大学的科研人员成功研制出两种新型三层石墨烯。这两种新材料均由三层石墨烯组成，但堆垛方式和导电性不同。这一成果将推动光电转换光伏电池等新型电子设备的研发。

石墨烯的碳原子呈六角形蜂巢晶格状分布，有两种常见的双层堆垛方式：一是AA堆垛，即上下两层紧密重合；二是AB堆垛，即上下两层之间存在一个碳原子的距离。这两种堆垛方式目前已成功实现。如果加上外电场，AB堆垛双层石墨烯便会成为半导体。

相较之下，三层堆垛很难实现。日本科研人员用两种特殊方法加热碳化硅，终于成功制备出了两个三层石墨烯样品。

科研人员将碳化硅在加压氩气和高真空中分别加热到1510℃和1300℃，再喷上氢气。氢气中的氢键破裂，形成单层氢原子，最后结合形成三层石墨烯。

在加压氩气中加热的碳化硅呈ABA堆垛，即上下两层重合，中间层错开。而在真空下加热的碳化硅则呈ABC堆垛，即每层稍微错开。

研究人员在检测两个石墨烯样本的物理性质时，发现两者的导电性是不同的。

ABA堆垛的样品和单层石墨烯相似，都是极佳的导电体。而ABC堆垛的性质更接近于AB堆垛双层，具有半导体特性。

本月，新加坡国立大学的一个科研小组又发明了新的石墨烯制备方法，所用的溶剂量是现行方法的1/50，为大规模、可持续合成打开了大门。

传统的石墨烯制备方法是利用剪力剥离石墨，再将其置于大量溶剂中，（比例为一千克石墨烯兑近一吨有机溶剂），这就产生了生态可持续性问题。如果减少溶剂，石墨烯层又会重新吸附到石墨上。

新的制备法是在高碱性环境下剥离预处理后的石墨。石墨烯在碱性环境下会发生絮凝，无需增加溶剂就能使石墨烯层聚集形成石墨烯浆料，接着把浆料分离成更常用的单层石墨烯即可。

新制备法通过引进静电工艺，成功防止了石墨烯片层的重新吸附。此外，石墨烯浆料是一种具有海绵状结构的超轻材料，也可直接用作3D打印的导电气凝胶。

前进的道路

曼切斯特大学Graphene@Manchester公司CEO James Baker在评论这篇发表于《INSIGHT》的论文时表示，“航空航天领域的重要进步历来都是和新材料的应用有关。铝材和碳纤维让飞机更快、更环保、成本更低、功能更强大。现在，石墨烯和相关的二维材料将引发下一场变革。”

“在现有的飞机制造材料中加入石墨烯，将改善飞机的许多关键性能。多功能石墨烯的应用和产学研合作的加深将为下一代航空技术的加速发展提供契机。”

与此同时，中国和英国也已在石墨烯研发领域建立了深层合作关系。中国目前是最大的石墨烯制造国，英国则是全球石墨烯研发中心。中英两国的航空业目前都处在关键发展时期，英国政府力图振兴历史悠久的航空业，而中国正在崛起成为全球商业中心和技术高地。

石墨烯颠覆航空航天行业，或将指日可待？

Recent innovations in Japan, Singapore as University of Manchester launches graphene aerospace strategy

In a recent joint paper by the Aerospace Technology Institute (ATI) and the National Graphene Institute (NGI) at the University of Manchester, researchers outlined the disruptive impact potential of graphene applications in aerospace.

The development of graphene dates back to 2004, when two University of Manchester scientists realized they had isolated a single layer of carbon atoms on a piece of scotch tape used to clean a graphite crystal. Since then, graphene has captured the imagination of researchers due to its fascinating properties. It is 200 times stronger than steel, very flexible, and is an excellent conductor of electricity.

According to the Manchester researchers, the two-dimensional material has the potential to positively impact aircraft performance, cost, and fuel efficiency. By incorporating atomically-thin graphene into existing materials used to build aircraft, the safety and performance properties of aircraft could be significantly improved. This in turn, could lead to reduced material weight and positive impact on the fuel efficiency of the aircraft and, as result, the environment.

In an exclusive introduction to the paper (published in ATI’s INSIGHT series), Sir Richard Branson said, “The potential for graphene to solve enduring challenges within the aerospace sector presents real opportunities for the material to become disruptive, and a key enabler in future aircraft technology. We need to accelerate the opportunity for the UK to realize the benefits from graphene by creating a portfolio of graphene-related research and technology projects which if undertaken would lead to real impact in our aerospace industry.”
Recent graphene development

This focus on graphene comes during a period of marked development of the material.

In February, Tohoku University and Nagoya University researchers discovered a way to form two new tri-layer graphene materials. Each of the novel material—both made of three layers of graphene—is layered differently and has unique electrical properties. The work has implications for the development of novel electronic devices, such as photovoltaic cells that convert light into electrical energy.

Graphene's carbon atoms are arranged into hexagons, forming a honeycomb-like lattice. The deliberate bi-layering graphene—either with the centers of the carbon hexagons layered immediately above one another, “AA-stacking,” or the displaced layering with a hexagon center above a carbon atom of the second layer “AB-stacking”—has been achieved successfully in the past. Furthermore, if an external electric field is applied, AB-stacking of two layers of graphene leads to the formation of a material with semiconducting properties.

However, the deliberate stacking three layers of graphene has proven difficult. The Japanese researchers developed a way to fabricate the two tri-layer graphene samples by heating silicon carbide using two distinct methods.

In one experiment, the silicon carbide was heated to 1,510°C under pressurized argon. In another, it was heated to 1,300°C in a high vacuum. Both materials were then sprayed with hydrogen gas in which the bonds were broken to form single hydrogen atoms, forming the tri-layer graphene.

The silicon carbide heated under pressurized argon formed into ABA-stacked graphene, with matching top and bottom hexagon layers sandwiching a displaced middle layer. The silicon carbide heated in a vacuum developed into ABC-stacked graphene, in which each layer was slightly displaced in front of the one below it.

When the researchers examined the physical properties of each material, they found that electrons behaved differently between the two types of graphene samples.

The ABA graphene was an excellent electrical conductor, similar to mono-layer grapheme. However, the ABC graphene, behaved more like AB graphene in that it had semi-conducting properties.

Just this month, a research team from the National University of Singapore developed a new graphene production method requiring 50 times less solvent than current methods, potentially opening the door for larger-scale, sustainable synthesis.

The conventional method for graphene production makes use of shearing forces to lift layers from graphite. These are then dispersed in large volumes of solvent (approximately one ton of organic solvent to one kilogram of graphene), which presents an issue of ecological sustainability. Often, when reducing solvent volume graphene layers reattach to the graphite.

The new method was discovered by exfoliating pre-treated graphite under higher than normal alkaline conditions, which triggers flocculation, prompting the graphene layers to cluster together into a slurry without the need to increase solvent content. The graphene slurry can then be separated into more commonly used monolayers.

The method prevents reattachment to the graphite via a newly introduced electrostatic process. The slurry can also be used directly to 3D-print conductive graphene aerogels, an ultra-lightweight sponge-like material.
The path forward

In a comment published concerning the INSIGHT paper, James Baker, CEO of Graphene@Manchester at the University of Manchester concluded, “Major generational improvements in the aerospace sector have been associated with embracing new materials. Aluminum and carbon fiber have seen planes become faster, greener, cheaper with more functionality. Now graphene and related two-dimensional materials can mark the next step-change.

“By incorporating graphene into the existing materials used to manufacture planes, performance properties could be improved across number of key areas. By utilizing the multi-functional properties of graphene and through collaboration between industry and academia, there are significant opportunities which can accelerate the next-generation of aerospace technologies.”

Furthermore, there is currently heavy cooperation regarding graphene development between Chinese researchers (China is a top producer of graphite) and UK researchers (at epicenter of graphene development). Both countries are in the midst of aerospace development, with the UK working to restore a waning industry full of aviation heritage and China becoming a burgeoning commercial hub and early adopter of new technologies.

How long before the aerospace industry sees the disruptive impact?

Author: William Kucinski
Source: SAE Aerospace Engineering Magazine