Manufacture of Inexpensive Carbon Nanotubes

碳纳米管（CNT）具有优异的机械、热和电子性能，但制造成本仍然非常昂贵。碳纳米管的生产量目前以每年约15%的速度增长，但与炭黑相比，目前生产的碳纳米管的数量微不足道（0.01%），炭黑是当今许多应用中常用的材料，如汽车轮胎。由于目前的CNT生长工艺不具有成本效益，因此尽管CNT具有更高的性能，但其并不用于许多应用中。本研究项目调查和开发新的合成可扩展工艺的基础科学和技术，通过利用最小化所需的种子化学品（催化剂）的量来制造超长CNT。目前使用的炭黑中超过90%用于橡胶增强，主要用于汽车轮胎，其中碳在滚动阻力/湿牵引力之间提供优选的折衷以改善汽油里程。如果在轮胎中使用碳纳米管代替炭黑，可以增加3-5%的油耗，这反过来可以减少美国约1%的温室气体排放，为美国提供显着的社会和经济效益。该项目由土木、机械和制造创新部门和刺激竞争力研究的既定计划（EPSCoR）共同资助，研究了在商业规模化的过程中，在剥离的层状矿物片材上生长~1 mm长的碳纳米管的机制。预期的产率比目前实现的高10-100倍，并且将消除将催化剂/载体与纳米管分离的需要。关键的科学和技术挑战包括用于改进催化剂在窄层状催化剂层内的分散的模型以及所需的反应-扩散条件，使得反应物和共进料的水可以到达所有活性位点并延长催化剂寿命。反应物浓度梯度的理解和控制是至关重要的，因为它影响纳米管的长度和均匀性。长的纳米管不适合于涉及将管与聚合物复合的应用，因此将管研磨以产生类似于当今商业上使用的长度（平均长度1-10微米）。将确定长度减少和球磨参数之间的关系，特别是单次碰撞的冲击能量和累积冲击能量，以允许将该方法按比例放大到商业研磨装置。还将生产平均长度为10-50微米的管，以更好地探索更长的管在配混操作中的性能。将管混合在一种热塑性塑料（聚碳酸酯）和一种轮胎配方中，以确定纳米管性能。三种不同直径的碳纳米管将被研磨成相同的纵横比，以确定纵横比是否对填充聚合物的性能很重要。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Carbon nanotubes (CNTs) exhibit exceptional mechanical, thermal, and electronic properties but are still very expensive to manufacture. The production volume of CNTs is currently growing at ~15%/year but the amount of CNTs produced today is miniscule (0.01%) compared to carbon black, a material commonly used today in many applications such as automotive tires. Because the current CNT growth processes are not cost effective, CNTs are not used in many applications despite their higher performance. This research project investigates and develops the underlying science and technology of new synthetic scalable processes to make ultralong CNTs by taking advantage of minimizing the amount of seed chemical (catalyst) required. Over 90% of carbon black in use today is for rubber reinforcement, mostly in automobile tires where the carbon provides a preferred trade-off between the rolling resistance/wet traction for improved gas mileage. Increased gas mileage of 3-5% could be achieved if CNTs were used instead of carbon black in tires, which in turn could reduce US greenhouse gas emissions by ~1%, providing significant societal and economic benefits for the US. This project is jointly funded by the Division of Civil, Mechanical and Manufacturing Innovation and the Established Program to Stimulate Competitive Research (EPSCoR).The mechanism underlying the growth of ~1 mm long carbon nanotubes on exfoliated laminar mineral sheets, in a commercially scalable process, is investigated. The expected yield is 10-100 times higher than currently achieved and would eliminate the need to separate the catalyst/support from the nanotubes. Critical scientific and technical challenges include models for the improved catalyst dispersion within narrow lamellar catalyst layers and the reaction – diffusion conditions required so that the reactants and co-fed water can reach all active sites and extend catalyst lifetimes. The understanding and control of reactant concentration gradients is critical as it impacts the nanotube length and uniformity. Long nanotubes are unsuitable for applications that involve compounding tubes with a polymer and hence the tubes will be milled to produce lengths similar to what is commercially used today (average lengths 1-10 microns). The relationship between length reduction and ball milling parameters, specifically impact energy of a single collision and cumulative impact energy, will be determined to allow scaling up of this process to commercial milling devices. Average lengths of 10-50 microns will also be produced to better explore how longer tubes perform in compounding operations. Tubes will be mixed in one thermoplastic (polycarbonate) and one tire formulation to determine nanotube performance. CNTs of three different diameters will be milled to the same aspect ratio to determine if aspect ratio is important in filled polymer properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.