Sunday, September 27, 2009

Tsinghua Researchers Reveal Keys to Carbon Nanotube Mass Production Method

There are also reports forecasting that industrial application of carbon nanotubes will remain unpractical until its price falls below $2/pound, i.e. 0.4 cent/g, and it needs a production rate of 10,000,000 pound per year or about 12.5 tons per day to bring the price down to this level. Prices are currently about $200-$250 per pound for industrial grade multiwall carbon nanotubes and much higher for other grades. Novel process and reactor technology are the keys to the mass production of carbon nanotubes and reducing the price.

Tsinghua University (CN) researchers reveal in U.S. Patent 7,563,427 a method for the continuous production of carbon nanotubes in large quantities in a nano-agglomerate fluidized bed. The process is comprised of the following steps: loading transition metal compounds on a support, obtaining supported nanosized metal catalysts by reducing, dissociating, or catalytically decomposing a carbon-source gas, and growing carbon nanotubes on the catalyst support by chemical vapor deposition of carbon atoms. The carbon nanotubes are 4 to 100 nanometers (nm) in diameter and 0.5 to 1000 microns in length. The apparatus is simple and easy to operate, has a high reaction rate, and it can be used to produce carbon nanotubes with a high degree of crystallization, high purity, and high yield, according to inventors Fei Wei, Yao Wang, Guohua Luo, Hao Yu, Zhifei Li, Weizhong Qian, Zhanwen Wang and Yong Jin. The carbon nanotubes are free of amorphous carbon deposits.

The apparatus comprises a main reactor (1), a catalyst activation reactor (6), a gas distributor (2), a gas-solid separator (7) and a product degassing section (9), wherein the catalyst activation reactor (6) is connected to the main reactor (1), the gas distributor (2) is placed in the bottom of the main reactor (1), the gas-solid separator (7) is arranged at the top of the main reactor (1), the main reactor (1) is provided with heat exchange tubes (3) and a gas feeder at its bottom, and the product degassing section (9) is connected to the main reactor (1) though a product outlet (5). By properly adjusting the reaction rate, operating conditions and fluidized-bed structure, the reactor bed is kept in an agglomerate fluidization state and so continuously mass produces carbon nanotubes with a high degree of crystallization, high purity, and high yield.

In 2008, a new kind of flexible, stretchable, and transparent loudspeaker made with carbon nanotube (CNT) film was invented by a team led by Professor Fan Shoufan and Associate Professor Jiang Kaili from Tsinghua’s Department of Physics. The CNT film loudspeaker possesses all the functions of a voice-coil loudspeaker as well as the merits of being magnet-free and without moving components. The nano-thick CNT films are flexible, stretchable, and transparent and can be tailored to any shape and size to fit various rigid or flexible insulating surfaces such as walls, roofs, windows, flagpoles or even clothes. Several CNT films can also be configured into a large-size loudspeaker.

Photo by Professor Jiang Kaili

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