applications of nanotubes.pptx

applications of nanotubes

1. applications of carbon nanotubes 1.8.2020 Field Emission and Shielding Computers Fuel Cells Chemical Sensors Mechanical Reinforcement

2. Field Emission and Shielding When a small electric field is applied parallel to the axis of a nanotube, electrons are emitted at a very high rate from the ends of the tube. This is called field emission. This effect can easily be observed by applying a small voltage between two parallel metal electrodes, and spreading a composite paste of nanotubes on one electrode. A sufficient number of tubes will be perpendicular to the electrode so that electron emission can be observed. One application of this effect is the development of flat panel displays. Television and computer monitors use a controlled electron gun to impinge electrons on the phosphors of the screen, which then emit light of the appropriate colors. A thin film of nanotubes is placed over control electronics with a phosphor-coated glass plate on top.

3. A Japanese company is using this electron emission effect to make vacuum tube lamps that are as bright as conventional light bulbs, and longer-lived and more efficient. Other researchers are using the effect to develop a way to generate microwaves. The high electrical conductivity of carbon nanotubes means that they will be poor transmitters of electromagnetic energy. A plastic composite of carbon nanotubes could provide lightweight shielding material for electromagnetic radiation. This is a matter of much concern to the military, which is developing a highly digitized battlefield for command, control, and communication. The computers and electronic devices that are a part of this system need to be protected from weapons that emit electromagnetic pulses.

4. Computers I nsulating layer(SiO 2 ) Gate(Silicon Substrate) carbon nanotube Drain source(Gold)

5. FUEL CELLS Carbon nanotubes have applications in battery technology. Lithium , which is a charge carrier in some batteries, can be stored inside nanotubes. It is estimated that one lithium atom can be stored for every six carbons of the tube. Storing hydrogen in nanotubes is another possible application, one that is related to the development of fuel cells as sources of electrical energy for future automobiles. A fuel cell consists of two electrodes separated by a special electrolyte that allows hydrogen ions, but not electrons , to pass through it . Hydrogen is sent to the anode, where it is ionized.

6. CNT Negative electrode Positive electrode 6M KOH electrolye , H 2 O Charger

7. CHEMICAL SENSORS A field-effect transistor similar to the one shown in Fig. 5.21 made of the chiral semiconducting carbon nanotubes has been demonstrated to be a sensitive detector of various gases. The transistor was placed in a 500ml flask having electrical feed throughs and inlet and outlet valves to allow gases to flow over the carbon nanotubes of the FET. Two to 200 parts per million of NO2 flowing at a rate of 700 ml/min for 10min caused a threefold increase in the conductance of the carbon nanotubes.

8. Wave number Intensity

9. shows the current-voltage relationship before and after exposure to NO2. These data were taken for a gate voltage of 4 V. The effect occurs because when NO2 bonds to the carbon nanotube, charge is transferred from the nanotube to the NO2, increasing the hole concentration in the carbon nanotube and enhancing the conductance .

10. Mechanical Reinforcement The use of long carbon fibers such as polyacrylonitrile (PAN) is an established technology to increase the strength of plastic composites. PAN has a tensile strength in the order of 7 Gpa and can have diameters of 1-10 pm. The use of this fiber for reinforcement requires developing methods to have the fibers preferentially oriented and uniformly dispersed in the material. The fiber must be able to survive the processing conditions. Important parameters in determining how effective a fiber is in increasing the strength of a composite are the tensile strength of the fiber and the 1ength:diameter ratio, as well as the ability of the fiber to bind to the matrix .

11. Because of their high tensile strength and large length : diameter ratios, carbon nanotubes should be excellent materials for composite reinforcement. Some preliminary work has been done in this area. Work at General Motors Research and Development Center has shown that adding to polypropylene 11.5% by weight of nested carbon nanotubes having an 0.2 pm diameter approximately doubled the tensile strength of the polypropylene.

12. A study at the University of Tokyo showed that incorporation of 5% by volume of nanotubes in aluminum increased the tensile strength by a factor of 2 compared to pure aluminum subjected to the same processing . The composites were prepared by hot pressing and hot extrusion. Aluminum powder and carbon nanotubes were mixed and heated to over 800 K in a vacuum, and then compressed with steel dies. After this the melt was extruded into rods . This work is very important in that it demonstrates that the carbon nanotubes can be put into aluminum, and are chemically stable through the necessary processing. The researchers believe a substantial increase in the tensile strength can be achieved by producing a more homogenous and an aligned distribution of nanotubes in the material. Theoretical estimates suggest that with optimum fabrication a 10% volume fraction of nanotubes should increase the tensile strength by a factor of 6.

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