Negative Magnetoresistance in Activated Carbon Fibers Heat-Treated Above 2000°C

1993 ◽  
Vol 328 ◽  
Author(s):  
A. W. P. Fung ◽  
Z. H. Wang ◽  
M. S. Dresselhaus ◽  
G. Dresselhaus ◽  
M. Endo
Keyword(s):  
Activated Carbon ◽  
Carbon Fibers ◽  
Room Temperature ◽  
Weak Localization ◽  
Quantum Mechanical ◽  
Activated Carbon Fibers ◽  
Two Dimensional ◽  
Measurement Temperature ◽  
Heat Treated ◽  
Different Temperatures

ABSTRACTActivated carbon fibers (ACFs) were heat-treated at temperatures above 2000°C to study both the effect of heat treatment on the order development in ACFs and the effect of granularity on the transport properties of granular materials in general. The electrical conductivity σ(T) and Magnetoresistance (MR) were measured as a function of temperature for ACFs Made of two different precursors and heat-treated at different temperatures. While the field dependence of the observed negative MR could be fit to the two-dimensional weak localization (2D WL) theory at each measurement temperature, σ(T) showed only a weak temperature dependence, inconsistent with the ln (T) dependence predicted by the same theory. Even More interesting is the observation of a negative MR, which is a quantum-Mechanical phenomenon, near room temperature. It is thought that the grain boundaries might be responsible for such deviations from the standard 2D WL theory.

scholarly journals Photoconductivity of activated carbon fibers

1991 ◽  
Vol 6 (5) ◽  
pp. 1040-1047 ◽  
Author(s):  
K. Kuriyama ◽  
M.S. Dresselhaus
Keyword(s):  
Activated Carbon ◽  
Surface Area ◽  
Carbon Fibers ◽  
Low Temperatures ◽  
Room Temperature ◽  
High Surface ◽  
Localized States ◽  
Activated Carbon Fibers ◽  
Disordered Carbon ◽  
Increasing Temperature

The conductivity and photoconductivity are measured on a high-surface-area disordered carbon material, i.e., activated carbon fibers, to investigate their electronic properties. This material is a highly disordered carbon derived from a phenolic precursor, having a huge specific surface area of 1000–2000 m2/g. Our preliminary thermopower measurements show that the dominant carriers are holes at room temperature. The x-ray diffraction pattern reveals that the microstructure is amorphous-like with Lc ≃ 10 Å. The intrinsic electrical conductivity, on the order of 20 S/cm at room temperature, increases by a factor of several with increasing temperature in the range 30–290 K. In contrast, the photoconductivity in vacuum decreases with increasing temperature. The magnitude of the photoconductive signal was reduced by a factor of ten when the sample was exposed to air. The recombination kinetics changes from a monomolecular process at room temperature to a bimolecular process at low temperatures, indicative of an increase in the photocarrier density at low temperatures. The high density of localized states, which limits the motion of carriers and results in a slow recombination process, is responsible for the observed photoconductivity.

scholarly journals Structural characterization of heat-treated activated carbon fibers

1992 ◽  
Vol 7 (7) ◽  
pp. 1788-1794 ◽  
Author(s):  
A.M. Rao ◽  
A.W.P. Fung ◽  
M.S. Dresselhaus ◽  
M. Endo
Keyword(s):  
Heat Treatment ◽  
Activated Carbon ◽  
Raman Scattering ◽  
Carbon Fibers ◽  
Insulator Transition ◽  
Activated Carbon Fibers ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Sequence Of Events ◽  
Heat Treated

Raman scattering, x-ray diffraction, and BET measurements are used to study the effect of heat treatment on the microstructure of activated carbon fibers (ACFs) and to correlate the structural changes with the metal-insulator transition observed in the electronic transport properties of heat-treated ACFs. A sequence of events is identified, starting with desorption, followed by micropore collapse plus the stacking of basic structural units in the c-direction, and ending up with in-plane crystallization. The graphitization process closely resembles that depicted by Oberlin's model, except that the final material at high-temperature heat treatment remains turbostratic. Because the metal-insulator transition was observed to occur at heat-treatment temperature THT ≃ 1200 °C, which is well below the THT value (2000 °C) for in-plane crystallization, we conclude that this electronic transition is not due to in-plane ordering but rather to the collapse of the micropore structure in the ACFs. Raman scattering also provides strong evidence for the presence of local two-dimensional graphene structures, which is the basis for the transport phenomena observed in heat-treated ACFs.

scholarly journals Activated carbon fibers loaded with MnO2 for removing NO at room temperature

2014 ◽  
Vol 256 ◽  
pp. 101-106 ◽  
Author(s):  
Mingxi Wang ◽  
Henian Liu ◽  
Zheng-Hong Huang ◽  
Feiyu Kang
Keyword(s):  
Activated Carbon ◽  
Carbon Fibers ◽  
Room Temperature ◽  
Activated Carbon Fibers

ESR study of activated carbon fibers: preliminary results

1993 ◽  
Vol 8 (9) ◽  
pp. 2282-2287 ◽  
Author(s):  
S.L. di Vittorio ◽  
A. Nakayama ◽  
T. Enoki ◽  
M.S. Dresselhaus ◽  
M. Endo ◽  
...  
Keyword(s):  
Activated Carbon ◽  
Specific Surface ◽  
Carbon Fibers ◽  
Room Temperature ◽  
Broad Peak ◽  
Activated Carbon Fibers ◽  
Temperature Peak ◽  
Dangling Bond ◽  
Surface Areas ◽  
Spin Resonance

We have carried out Electron Spin Resonance (ESR) measurements on activated carbon fibers (ACF) with specific surface areas (SSA) of 3000 and 2000 m2/g. The ESR spectrum of ACF fibers in air is extremely broad (500 to 1000 Gauss), and the spin susceptibility decreases rapidly with decreasing specific surface area. Also measured was the ESR signal of the desorbed fibers in vacuum. As a result of desorption, the broad peak decreases slightly in intensity, and a narrow (≍65 Gauss at room temperature) peak appears. We report results on the temperature dependence of both peaks. The narrow peak is interpreted as due to spins associated with dangling bonds, whereas we attribute the broad peak to the conduction carrier spins which is broadened by the boundary scattering process (T1 contribution) and the dipolar broadening process (T2 contribution) associated with the dangling bond spins.

Adsorption of SO2 onto oxidized and heat-treated activated carbon fibers (ACFs)

Carbon ◽  
1997 ◽  
Vol 35 (3) ◽  
pp. 411-417 ◽  
Author(s):  
M.A. Daley ◽  
C.L. Mangun ◽  
J.A. DeBarrb ◽  
S. Riha ◽  
A.A. Lizzio ◽  
...  
Keyword(s):  
Activated Carbon ◽  
Carbon Fibers ◽  
Activated Carbon Fibers ◽  
Heat Treated

Oxidation of Activated Carbon Fibers:  Effect on Pore Size, Surface Chemistry, and Adsorption Properties

1999 ◽  
Vol 11 (12) ◽  
pp. 3476-3483 ◽  
Author(s):  
Christian L. Mangun ◽  
Kelly R. Benak ◽  
Michael A. Daley ◽  
James Economy
Keyword(s):  
Activated Carbon ◽  
Surface Chemistry ◽  
Pore Size ◽  
Carbon Fibers ◽  
Adsorption Properties ◽  
Activated Carbon Fibers

Visualized observation of pores in activated carbon fibers by HRTEM and combined image processor

1998 ◽  
Vol 5 (3-4) ◽  
pp. 261-266 ◽  
Author(s):  
M. Endo ◽  
T. Furuta ◽  
F. Minoura ◽  
C. Kim ◽  
K. Oshida ◽  
...  
Keyword(s):  
Activated Carbon ◽  
Carbon Fibers ◽  
Activated Carbon Fibers ◽  
Image Processor

Preparation and Characterization of Activated Carbon Fibers from Jute Fibers by Phosphoric Acid Activation

2012 ◽  
Vol 184-185 ◽  
pp. 1110-1113 ◽  
Author(s):  
Li Fen He ◽  
Qi Xia Liu ◽  
Tao Ji ◽  
Qiang Gao
Keyword(s):  
Activated Carbon ◽  
Carbon Fiber ◽  
Phosphoric Acid ◽  
Carbon Fibers ◽  
Activated Carbon Fibers ◽  
Optimum Conditions ◽  
Activation Time ◽  
Activation Temperature ◽  
Jute Fibers ◽  
Activating Agent

Various jute-based activated carbon fibers were prepared by using jute fibers as raw materials and phosphoric acid as activating agent. The effects of three main factors such as concentration of activating agent, activation temperature and activation time on the yield and adsorptive properties of active carbon fibers were investigated via orthogonal experiments. The surface physical morphology of jute-based activated carbon fiber was also observed by using Scanning Electron Microscope. Results showed that the optimum conditions were phosphoric acid concentration of 4 mol/L, activation temperature of 600 °C and activation time of 1h. The yield, iodine number and amount of methylene blue adsorption of the active carbon fiber prepared under optimum conditions were 37.99 %, 1208.87 mg/g and 374.65 mg/g, respectively.

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