The carbon nanotube is one of the most recent innovations in the material structure science domain. A carbon nanotube, an allotrope of carbon, takes the form of a tube made up of carbon atoms. These nanotubes boast incredible durability while remaining lightweight.
Their remarkable mechanical, electrical, and thermal attributes have made carbon nanotubes a focal point in nanomaterial research. Multiwall CNTs contain multiple concentric cylindrical layers of carbon atoms, while single-wall variants consist of just one such layer . These properties have made CNTs an ideal structural material for space travel.
Sometimes referred to as “buckytubes,” CNTs are essentially two-dimensional graphite that has been folded or rolled into cylindrical structures. These tubes are hollow inside and typically possess a diameter ranging from 1 to 3 nanometers.
Need of Carbon Nanotubes in Space Travel
Space travel relies on the balance between weight and thrust—higher thrust and lighter weight are key. The Apollo 8 rocket, which journeyed to the moon, weighed 49,735 kg, crafted from an aluminum alloy with a honeycomb structure. If the same craft were constructed using CNTs, its weight would be approximately one-fifth of the weight of an aluminum alloy rocket due to the lower density of CNTs (1.57 g/cc compared to aluminum alloy’s 2.83 g/cc).
Comparing CNTs to compound steel highlights their impressive properties. The tensile strength of Multi-walled CNTs (MWCNT) measures around 60 GPa, a staggering 60 times higher than that of steel. Even when considering a relatively weaker type of CNT, these properties make a compelling case for integrating carbon nanotubes into space travel endeavors.
The invention of Carbon Nanotubes
In 1991, Iijima’s discovery of carbon nanotubes (CNTs) sparked the emergence of a new field in materials science—Nanoscience. Substantial investments, totaling hundreds of millions of dollars, have been dedicated to unraveling the mysteries of these innovative materials. The investment has proven immensely valuable as these functional nanoscale materials exhibit an array of unique, astonishing, and previously unseen properties.
Remarkably, these materials have led to the identification of a new state of matter: water confined within a carbon nanotube. This state behaves unlike gas, liquid, or solid, marking a groundbreaking discovery in the realm of material science.
1:- Structure of CNTs
Composed entirely of carbon, a pure Single-Walled Carbon Nanotube (SWCNT) resembles a tubular shell rolled from a graphene sheet. These sheets are seamless cylinders formed from a honeycomb lattice, representing a single atomic layer of crystalline graphite. On the other hand, Multi-Walled Carbon Nanotubes (MWCNTs) are stacks of graphene sheets rolled into concentric cylinders. Each nanotube, a single molecule comprised of millions of atoms, can extend tens of micrometers in length with diameters as small as 0.7 nm.
SWCNTs typically feature just 10 atoms around their circumference, with a tube thickness of only one atomic layer. These nanotubes possess a notably high length-to-diameter ratio (aspect ratio) of about 1000, rendering them nearly one-dimensional structures. MWCNTs, larger in size, consist of multiple single-walled tubes nested within one another.
Specifically, MWCNTs are designated for nanostructures with an outer diameter below 15 nm. Beyond this diameter, these structures are referred to as carbon nanofibers. It’s crucial to differentiate CNTs from carbon fibers, which aren’t single molecules but rather strands composed of layered graphite sheets.
2:- Properties of CNTs
The exceptional strength of carbon-carbon bonds grants carbon nanotubes unparalleled mechanical properties, combining superb mechanical, thermal, and electronic attributes in a way no prior material has achieved. These nanotubes can have remarkably low densities, as light as 1.3 g/cm³ (one-sixth that of stainless steel). Their Young’s moduli, a measure of stiffness, surpass all carbon fibers, boasting values exceeding 1 TPa, roughly 5 times higher than steel.
Yet, it’s their incredible strength that truly distinguishes them. Carbon nanotubes stand as humanity’s strongest known materials. The highest recorded tensile strength reaches up to 63 GPa, approximately 50 times greater than steel. Even the least robust types exhibit strengths in the several GPa range. Furthermore, CNTs demonstrate admirable chemical and environmental stability and possess high thermal conductivity (around 3000 W/m/K, akin to diamond).
Moreover, their electronic properties are equally extraordinary. With high electrical conductivity comparable to copper, carbon nanotubes exhibit a distinctive feature: they can be either metallic or semiconducting. The rolling action disrupts the planar symmetry, establishing a distinct direction concerning the hexagonal lattice and axial direction. Depending on this relationship, nanotubes can behave electrically as metals or semiconductors. Semiconducting nanotubes showcase bandgaps inversely related to their diameter, varying from approximately 1.8 eV for smaller tubes to 0.18 eV for the widest stable SWCNT.
Uses of CNTs
CNTs have various applications in both industrial, space, and biomedical applications. Let’s discuss more about this in the points below.
1:- CNTs industrial uses
As technology matures and costs decrease, CNTs are poised to replace the traditional bulky cathode ray tube (CRT) screens. Their high toughness allows them to be integrated into high-strength composites alongside other materials, significantly enhancing their utility. This positions carbon nanotubes as a material of immense economic value, warranting extensive research efforts.
Moreover, the dual nature of carbon nanotubes—exhibiting both conductor and semiconductor properties—adds to their versatility. In electronic circuits, the semiconductor attribute of CNTs enables their application as field emission transistor (FET) gate electrodes. When voltage is applied, these FET gate electrodes demonstrate electric conductivity approximately 100 times greater than silicon semiconductors. Additionally, they offer operational frequencies about 1000 times higher than current Complementary Metal-Oxide Semiconductor (CMOS) technology. This remarkable combination of properties positions CNTs as a transformative element in advancing electronic applications.
2:- Carbon nanotubes used in space industry
The electrical conductivity of CNTs serves practical purposes in antenna design, elevating performance levels by a staggering twenty times compared to conventional antennas. Additionally, CNTs’ conductivity plays a pivotal role in providing exceptional electromagnetic radiation shielding.
Their significance extends to advancements in battery technology where CNTs, when utilized as electrode materials, contribute to augmenting energy density while effectively managing high temperatures.
3:- Uses of carbon nanotubes in the Military
CNTs, surpassing Kevlar in tensile strength, offer a groundbreaking avenue for protective clothing. Their exceptional resilience positions them as ideal materials for crafting highly durable and robust protective gear. Integrating CNTs into such clothing enhances its ability to withstand and mitigate various threats, setting new standards in protective wear for unparalleled safety and defense.
Mega Project based on Carbon Nanotubes
The concept of a space elevator has been pondered since the space age’s inception—a system comprising a carrier cable and climber cabin for Earth-space transport. Until the discovery of CNTs, this notion remained a distant fantasy. Prior materials couldn’t support such a lengthy and durable structure. However, CNTs, with their remarkable tensile strength and low density, reignited hope for the space elevator’s realization.
Using CNTs as cable material addresses the primary hurdle in its construction. Yet, challenges persist. Presently produced CNTs fall short of their envisioned strength due to structural flaws, necessitating high-quality CNTs for progress. Other obstacles include micrometeorite impacts, radiation damage, spacecraft collisions, natural frequency impact on the cable, deployment logistics, risks of damage, and malfunctioning climbers. Scientists strive to surmount these challenges, recognizing that overcoming engineering hurdles is intrinsic to innovation. The journey to construct a space elevator may be daunting, but engineering thrives on solving complex problems.
CNTs, a recent marvel in material science, revolutionized industry, space exploration, and defense. With unmatched tensile strength and exceptional properties—mechanical, electrical, and thermal—CNTs hold promise for space elevators, electronics, and protective wear. These nanotubes address challenges in aerospace, screen technology, and battery enhancement. They pave the way for innovative applications in antennas, electromagnetic shielding, and high-performance batteries. Despite hurdles in realizing space elevators and ensuring flawless CNT production, scientists persist in conquering these obstacles. The impact of carbon nanotubes spans industries, fostering innovation, fortifying defense, and propelling exploration into new frontiers.
Source: Carbon Nanotube