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Journal of Applied Physics & Nanotechnology

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Research Article

The Negative Temperature Coefficient for the Nitrogen Oxidation Chain Reaction and its Effect on Super Luminescence Initiated by Electrical Discharge

Fedotov VG, Fedotova EY

Correspondence Address :

Fedotov VG
Semenov Institute of Chemical Physics Kinetics and Catalysis
Kosygina Street 4, Moscow, 119991, Russia
Email: Vgfedotov47@inbox.ru

Received on: January 29, 2018, Accepted on: February 20, 2018, Published on: February 26, 2018

Citation: Fedotov VG, Fedotova EYa (2018). The Negative Temperature Coefficient for the Nitrogen Oxidation Chain Reaction and its Effect on Super Luminescence Initiated by Electrical Discharge

Copyright: 2018 Fedotov VG, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract
Adiabatic expansion of the active medium of Electronic Energy Explosion in the Air enhances the nitrogen oxidation chain reaction velocity and super luminescence intensity of NO (B 2П) molecules. This observation is explained by Negative Temperature Coefficient of the nitrogen oxidation chain reaction (as usual, the term NTC means that reaction velocity and photon emission increase as the temperature decreases) after detailed energy balance analysis of the investigated reaction.
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Introduction

Electronic Energy Explosion (EEE) in Air is connected with nitrogen oxidation branched chain reaction [1]. Тhe term EEE was used in [1] because of observation of avalanche-like growth of excited molecules and free charges concentrations in our system. It is well known that NO formation from nitrogen and oxygen is an endothermic process [2].



The needed energy for NO formation is given by electric discharge. Further NO transformations proceed with energy release [3].



If the reaction would finish at this stage the whole process together with initiating discharge would lead to release of approximately 7 kcal/mole. But the expected continuation of the reaction connected with equilibrium establishing between dimers and monomers of NO2 concentrations needs energy. The decay of dimer to two NO2 molecules proceeds with energy consumption:



Thus the entire energy balance is negative (it needs about 6 kcal/mole). The energy needed for the reaction (4) is to be got from gaseous mixture. In this case the gas temperature will diminish. From cooling of air to 100 degrees it is possible to obtain only (5/2)*2[cаl/ (mole*Kelvin)]*100(Kelvin) = 500 cаl/mole. It follows from this that the equilibrium establishing dimers monomers will happen at some temperature lower than the initial T, and the percentage of monomers will be small. At low temperature a rise of luminescence intensity can be expected resulting from the contribution of N2O3 molecules [4,5].



NTC should be expected for the rate of nitrogen oxidation chain reaction, as it follows from results of [6,7]: it was shown in [6] that chain branching in this reaction can be described by the equation:



Where k is the rate constant for the recombination process O + NO + M => NO2* + M.
NTC was observed for this rate constant in [7].

In accordance with mentioned above data we have found that super luminescence from EEE initiated by electrical discharge near the ferrite surface can be observed only at lower (relative to room temperature) temperatures. The super luminescence was not observed at 25o C. The cooling of electrodes to 0o C at the temperature 25o C of surrounding air resulted in arising bright blue super luminescence analogical to radiation described in [8]. This result indicates on the existence of some "super luminescence limit" of a nitrogen oxidation branched chain reaction (There is no continued change in the super luminescence intensity, but abrupt appearance or disappearance of super luminescence with temperature variation). NTC of an endothermic reaction can result in avalanche-like cooling and avalanche-like growth of reaction velocity in active medium.

Is it possible to use the described above properties of nitrogen oxidation reaction for enhancing its velocity and thus for enhancing the excited molecules concentration? If EEE would be performed in a long reactor open at one end, the active medium would have a possibility to expand adiabatically through the open end. During such expansion the product L*n will remain constant (n - is concentration of excited molecules, L is the length of the part of reactor occupied by active medium of EEE). For this reason the value of optical amplification coefficient would remain constant too.
But lowering the temperature resulting from adiabatic expansion of the reacting gas will cause the enhancement of the chemical reaction rate and of super luminescence intensity. The aim of the present work was the experimental investigation of possibility to enhance the optical amplification coefficient of the EEE active medium by using its adiabatic expansion.

Methods

Longitudinal and transverse cross-sections of the reactor are shown on the figure 1. The reactor is made of organic glass. A part (70 mm long) of one outer angle is removed and the ferrite core of a TV fly-back transformer is positioned at this place. Two steel electrodes are in contact with ferrite core from inside of reactor. The minimal dimension of the discharge gap between the electrodes makes 5 mm. Electrodes are connected to the capacitors battery (two electrolytic capacitors with capasity1000 μF, charged to 220 V on each of them). The circuit of electrical connections is shown on figure 2.

For the experiments with adiabatic expansion of the EEE active medium two additional elements were fitted to the open end of the reactor. These additional elements ("box" and "nozzle") are shown on the figure 3.

Results of Experiments

Setting of the switch "Bk" in the "on" position results in 440 V Voltage being applied to the steel electrodes pressed to ferrite core. EEE develops in the discharge gap. At these conditions the radiation of EEE forms rather broad light spot on the white screen remote at 15 cm from the discharge zone (Figure 4).
Attaching of the steel box to the open end of the reactor resulted in abrupt change of the light spot appearance on the screen (Figure 5). The light spot looked then like a rectangular with sharply shaped borders. It means that this light sport was formed by parallel beams. Indeed: in case when some light source radiates in all directions inside a box open at one end, the penumbras are to be observed at the screen. We do not observe any penumbras, thus we conclude about parallel beams. In addition to that the light spot is displaced from the axis of the reactor. Such appearance indicates that the light spot is produced by the stimulated (not spontaneous) emission of radiation. In case of spontaneously radiating light source inside a box open at one end the maximum of illumination on the screen should be observed at the axis of the reactor. The stimulated emission produces maximum at the direction of maximal longitude of active medium. It can be noted that the spontaneous emission of radiation also made some contribution to the even illumination of the screen near the point of intersection between the reactor axis and the screen.
Fitting of the "nozzle" to the open end of the reactor resulted in abrupt narrowing of the light spot (Figure 6). In this case the light source responsible for the observed light spot is located in the enlarging part of the nozzle (out of the reactor). It means that the active medium formed by EEE in air leaved the discharge zone at the beginning, then came through the critical section of the nozzle and only thereafter produced a super luminescence pulse which caused the appearance of the compact light spot on the screen (Figure 6).

Discussion

What can be said about the gaseous medium, which produces super luminescence (Figures 5 and 6)? Initially it was air mixture, then EEE was initiated in it, then it moved from the discharge gap into additional element ("box" or "nozzle") fitted to the reactor. During this transfer its temperature lowered. The time interval between EEE and the transfer of reacting gas in the attached element is 1 millisecond by the order of magnitude. The equal time was needed for the spontaneous inflammation of the EEE products at the conditions of [8]. The spontaneous inflammation in [8] was observed only inside of optical resonator. In present work the loss of active molecules into environment was lower due to application of fitted elements. It could result in spontaneous inflammation in absence of optical resonator.
The great difference between light spots at Figures 5 and 6 can be explained by more intense cooling of gas in the nozzle and therefore the additional rise of reaction velocity and excited molecules concentration. The temperature dependence of the NO-O chemiluminous recombination [7] can explain the observed rising of optical amplification coefficient by two orders of magnitude in assumption that the temperature in case of Figure 6 was about 90 K. Such a great temperature lowering is possible only in an avalanche like cooling process resulting from combination of NTC and endothermic reaction (4).

Conclusions

The conclusion of work [8] about the possibility of spontaneous ignition in products of EEE in air is confirmed. The spontaneous ignition in the EEE active medium is characterized by NTC. The energy balance of entire nitrogen oxidation process is in agreement with proposed mechanism (1) - (4). These facts can be used in experiments with EEE products transfer aimed to initiation of EEE in bigger air volumes to enhance nitrogen oxides yield and laser generation energy.

References
1. Fedotov VG, Fedotova EY. Explosion in atmospheric air initiated by an electric discharge and associated with growth of the concentrations of electronically excited species and free charges. Russian J Phys Chem B. 2015;9(2):223-227.
2. Okabe H. Photochemistry of small molecules. A Wiley-interscience Publication - 1978, John Wiley and Sons New York - Chichester - Brisbane - Toronto. 2007.
3. Gurvich LV, Karachevtsev GV, Kondratyev VN. Energies of chemical bounds rupture, ionization potentials and affinity to the electron. "Nauka", Moscow, 1974.
4. Colomb D, Good RE, Del-Greco FP. NO-O Chemiluminescent reaction in a low-density wind tunnel. J Chem Phys. 1966;44:4349.
5. Gordon EB, Moscvin UL, Sotnichenko SA. Gaseous N2O3 as possible medium for a photo recombination laser. Quantovaya Electronica. 1976;3:2591-5.
6. Fedotov VG, Fedotova EY. Chemical kinetic model of the chain reaction of atmospheric nitrogen oxidation initiated by electric discharge. Russian J Phys Chem B. 2016:10(5):748-752.
7. Golomb D, Brown J H. The temperature dependence of the NO-O chemiluminous recombination. J of Chem Phys. 1975: 63(12):5246-51.
8. Fedotov VG, Fedotova EY. Many-colored laser generation resulting from atmospheric nitrogen oxidation chain reaction initiated by electrical discharge in air. Russian J of Physical Chemistry B. 2017;11(6):928-931.
Tables & Figures


Figure 1:
The outline of the reactor with open end B. 1- walls of the reactor made of organic glass; 2 - ferrite core; 3 - steel electrodes; 4 - glass cover.



Figure 2: The circuit of electrical connections, used for EEE initiation between the electrodes 3. 1 - AC-rectifier with output voltage 440 V; 2- ferrite core; 3 - electrodes; Bk - the switch.



Figure 3: Outline of the additional elements fitted to the open end of the reactor. 1 - "box", 2 - "nozzle".



Figure 4:
The light spot on the screen near the open end of the reactor.



Figure 5: The light spot on the screen in case when additional element "box" is fitted to the open end of the reactor.



Figure 6: The light spot on the screen in case when additional element "nozzle" was fitted to the open end of the reactor.
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