Dependence of the current-voltage characteristics of a non-transferred DC cascaded plasma torch used for nanoparticle synthesis, on the plasma current and the plasma argon gas flow rate are reported in this paper. The...Dependence of the current-voltage characteristics of a non-transferred DC cascaded plasma torch used for nanoparticle synthesis, on the plasma current and the plasma argon gas flow rate are reported in this paper. The potential structure inside the torch and its dependence on the plasma current and gas flow rate are also investigated. The arc voltage is seen to exhibit negative characteristic for a current below 150 A and positive characteristic above that current value. The voltage drop near the electrodes is found to decrease with the increase in plasma current. 25~ of the total voltage is dropped near the cathode at a plasma current of 50 A and a argon plasma gas flow rate of 10 liter per minute （LPM）, and it decreases to 12% with the current increasing to 300 A, and to 17% with a gas flow rate of 25 LPM. The variation in the torch efficiency with the gas flow rate and plasma current is also reported. The efficiency of the torch is found to be between 36% and 48%. In addition, the plasma gas temperature at various positions of the reactor and for different currents and voltages are measured by calorimetric estimation with a heat balance technique.展开更多
Silicon carbides are basilic ceramics with proper bandgaps （2.4-3.3 eV） and unique optical properties. SiC@C monocrystal nanocapsules with different morphologies, sizes, and crystal types were synthesized via the fa...Silicon carbides are basilic ceramics with proper bandgaps （2.4-3.3 eV） and unique optical properties. SiC@C monocrystal nanocapsules with different morphologies, sizes, and crystal types were synthesized via the fast and facile direct current （DC） arc discharge plasma method. The influence of Ar atmosphere on the formation of nanocrystal SiC polytypes was investigated by optical emission spectroscopy （OES） diagnoses on the arc discharge plasma. Boltzmann＇s plot was used to estimate the temperatures of plasma containing different Ar concentrations as 10,582 K （in 2 × 10^4 Pa of Ar partial pressure） and 14,523 K （in 4 × 10^4 Pa of Ar partial pressure）. It was found that higher energy state of plasma favors the ionization of carbon atoms and promotes the formation of α-SiC, while β-SiC is generally coexistent. Heat-treatment in air was applied to remove the carbon species in as-prepared SiC nanopowders. Thus, the intrinsic characters of SiC polytypes reappeared in the ultraviolet-visible （UV-vis） light absorbance. It was experimentally revealed that the direct bandgap of SiC is 5.72 eV, the indirect bandgap of β-SiC （3C） is 3.13 eV, and the indirect bandgap of α-SiC （6H） is 3.32 eV; visible quantum confinement effect is predicted for these polytypic SiC nanocrystals.展开更多
文摘Dependence of the current-voltage characteristics of a non-transferred DC cascaded plasma torch used for nanoparticle synthesis, on the plasma current and the plasma argon gas flow rate are reported in this paper. The potential structure inside the torch and its dependence on the plasma current and gas flow rate are also investigated. The arc voltage is seen to exhibit negative characteristic for a current below 150 A and positive characteristic above that current value. The voltage drop near the electrodes is found to decrease with the increase in plasma current. 25~ of the total voltage is dropped near the cathode at a plasma current of 50 A and a argon plasma gas flow rate of 10 liter per minute （LPM）, and it decreases to 12% with the current increasing to 300 A, and to 17% with a gas flow rate of 25 LPM. The variation in the torch efficiency with the gas flow rate and plasma current is also reported. The efficiency of the torch is found to be between 36% and 48%. In addition, the plasma gas temperature at various positions of the reactor and for different currents and voltages are measured by calorimetric estimation with a heat balance technique.
基金This work was financially supported by the National Natural Science Foundations of China （Nos. 51331006 and 51271044）.
文摘Silicon carbides are basilic ceramics with proper bandgaps （2.4-3.3 eV） and unique optical properties. SiC@C monocrystal nanocapsules with different morphologies, sizes, and crystal types were synthesized via the fast and facile direct current （DC） arc discharge plasma method. The influence of Ar atmosphere on the formation of nanocrystal SiC polytypes was investigated by optical emission spectroscopy （OES） diagnoses on the arc discharge plasma. Boltzmann＇s plot was used to estimate the temperatures of plasma containing different Ar concentrations as 10,582 K （in 2 × 10^4 Pa of Ar partial pressure） and 14,523 K （in 4 × 10^4 Pa of Ar partial pressure）. It was found that higher energy state of plasma favors the ionization of carbon atoms and promotes the formation of α-SiC, while β-SiC is generally coexistent. Heat-treatment in air was applied to remove the carbon species in as-prepared SiC nanopowders. Thus, the intrinsic characters of SiC polytypes reappeared in the ultraviolet-visible （UV-vis） light absorbance. It was experimentally revealed that the direct bandgap of SiC is 5.72 eV, the indirect bandgap of β-SiC （3C） is 3.13 eV, and the indirect bandgap of α-SiC （6H） is 3.32 eV; visible quantum confinement effect is predicted for these polytypic SiC nanocrystals.
