Current industrial acid based CNT purification processes suffer from low purification yields and low efficiency. Purification yields of less than 50% are common. The harsh oxidizing acids used in current CNT purification methods also result in significant CNT sidewall defects which can result in decreased performance in many applications. Strength and electrical conductivity can be increased by attaining higher CNT purity.
In recent industrial practice, metallic catalyst amounts less than 4% have rarely been achieved. Significant amorphous carbon is often also left behind by these liquid phase methods of purification.
Neutron Star Nano Technology (NSN) has developed a unique gas phase method of purification which allows purification yields of greater than 90%. Metallic catalyst residue amounts of less than 0.1% have also been achieved with our method of purification along with little or no amorphous carbon.
The high yield and extremely high purity of the CNT product resulting from our purification process both minimizes cost and maximizes CNT performance in many applications.
Theory indicates that impurity amounts of less than 0.1% with minimal sidewall defects may be necessary to realize the extremely high performance potential of CNTs. Our method of purification can achieve these goals and may therefore be necessary to advance CNT applications to the next level.
Metal Infiltrated Carbon Nano Tubes
Carbon nano tubes display an array of electrical properties ranging from highly metallic to highly semi conducting depending on the diameter and chirality of the tubes.
In practice it would be advantageous to be able to access an even wider array of CNT properties for varied applications. One way to do this is to utilize metal infiltrated carbon nano tubes. Metal infiltration provides a method to increase the range of CNT properties independent of chirality.
Filling CNTs with desired metals can alter CNT capacitance as well as electrical resistance properties. Thereby optimizing their suitability for various applications. The utility of this process has just begun to be explored.
NSN’s process can also be used to both fill and coat CNTs with metal nano particles. One lucrative possible application of these filled and coated materials is as catalysts. In tests both Platinum and Rhodium filled single walled carbon nano tubes have proven to be more effective catalyst than the respective metal nano particles alone.
NSN has experience in infiltrating single, double and multi-wall CNTs with various metals, including Titanium, Iron, Platinum, Palladium and Silver. In principle nearly any desired metal can be infiltrated into CNTs by this process.
Carbon Nano Tube Membrane
NSN has developed a process to turn carbon nano tube powders into a flexible, paper like membrane material. These CNT membrane materials are ideal for use as electrodes. They are highly resistant to chemical and electrolytic oxidation and can be used as high performance electrodes in and per capacitors, fuel cells and batteries.
The potential also exists to make CNT membrane materials using metal nano particle filled and or coated CNTs. These hybrid membrane materials could be used as high performance catalysts and super capacitor electrodes with higher intrinsic capacitance than CNTs containing no added metal.
Devices made using these CNT membrane materials would be flexible and this would therefore be an advantage which has been highly sought in many applications such as fuel cells which could fit on the surface of a laptop computer.