 |
Business | Industries | Finance | Tax |
| Index: > A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
|
|||||
| First Prev [ 1 2 3 ] Next Last |
One application for nanotubes that is currently being researched is high tensile strength fibers. Two methods are currently being tested for the manufacture of such fibers. A French team has developed a liquid spun system that involves pulling a fiber of nanotubes from a bath which yields a product that is approximately 60% nanotubes. The other method, which is simpler but produces weaker fibers uses traditional melt-drawn polymer fiber techniques with nanotubes mixed in the polymer. After drawing, the fibers can have the polymer burned out of them to make them purely nanotube or they can be left as they are.
Scientists working at the University of Texas at Dallas produced the current toughest material known in mid- 2003 by spinning fibers of single wall carbon nanotubes with polyvinyl alcohol. Beating the previous contender, spider silk, by a factor of four, the fibers require 600J/g to break. In comparison, the bullet-resistant fiber Kevlar is 27-33J/g.
In 2004 Alan Windle's group of scientists at the Cambridge-MIT Institute developed a way to make carbon nanotube fibre continuously at the speed of several centimetres per second just as nanotubes are produced. One thread of carbon nanotubes was more than 100 metres long. The resulting fibres are electrically conductive and as strong as ordinary textile threads. [3] [4]
High purity (80%) nanotubes with metallic properties can be extracted with electrophoretic techniques. [5]
In April of 2001, IBM announced it had developed a technique for automatically developing pure semiconductor surfaces from nanotubes.
On September 19, 2003, NEC Corporation, Japan, announced stable fabrication technology of carbon nanotube transistors.
In June 2004 scientists from China's Tsinghua University and Louisiana State University demonstrated the use of nanotubes in incandescent lamps, replacing a tungsten filament in a lightbulb with a carbon nanotube one.
Nanomechanical computer storage devices using nanotubes are currently in the prototype stages. Both high speed non-volatile memory which can be used to replace nearly all solid state memory in computers today, and high density storage that may replace hard drives, are being developed. Major limiting factors in the development of nanotubes include their cost and difficulties in orienting the nanotubes, which tend to tangle because of their length.
As of 2003, nanotubes cost upwards from 20 euro per gram to 1000 euro per gram, depending on purity, composition (single-wall, double-wall, multi-wall) and other characteristics.
Carbon nanotubes have many properties--from their unique dimensions to an unusual current conduction mechanism--that make them ideal components of electrical circuits, and it is exciting to envision, or even to implement, novel transistors, MEMS devices, interconnect s, and other circuit elements.
The major hurdles that must be jumped for carbon nanotubes to find prominent places in circuits relate to fabrication difficulties. The carbon nanotube production processes are very different from the traditional IC fabrication process. The IC fabrication process is somewhat like sculpture--films are deposited onto a wafer and pattern-etched away. Carbon nanotubes are fundamentally different from films; they are like atomic-level spaghetti (and every bit as sticky).
Today, there is no reliable way to arrange carbon nanotubes into a circuit. Researchers sometimes resort to manipulating nanotubes one-by-one with the tip of an atomic force microscope in a painstaking, time-consuming process. Perhaps the best hope is that carbon nanotubes can be grown through a chemical vapor deposition process from patterned catalyst material on a wafer. Though such a CVD process has been shown to allow a circuit designer to locate one end of a nanotube, there is no obvious way to control where the other end goes as the nanotube grows out of the catalyst. Another way for the self assembly of the carbon nanotube transistors consist in using chemical or biological techniques to place the nanotubes from solution to determinate place on a substrate.
Even if nanotubes could be precisely positioned, there remains the problem that, to this date, engineers have been unable to control the types of nanotubes--metallic, semiconducting, single-walled, multi-walled--produced. This is a problem that chemical engineers must solve if nanotubes are to find a place in commercial circuits.
| Politics | Business | Finance |
 |
 |
 |
|