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The peculiarities of ir laser induced oxidations of metals
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THE PECULIARITIES
Ninai L., Hevesi
I., Bunkin
Department of Experimental *General Physics Institute
OF IR LASER
F.V.,*
INDUCED OXIDATIONS
Luk'yanchuk
OF METALS
B.S.*
Physics JATE, Szeged (Hungary) Dc?m t. 9. of AS USSR, Moscow (USSR) Vavilov st. 38.
Among modern industrial lasers, CO -lasers have the highest mean continuous wave (cw) power, therefore they could be considere ii as the most promising radiation source for technological processes. However the coupling coefficient of metals - frequently used targets - at the wavelength of CO lasers is relatively small 111. If the target surface is in contact with a chemically act Pve gas (as well as air) the reaction products can be produced and the surface absorptivity (coupling) could be sufficiently increased, e.g. in the air enviroment the oxides are formed (with good absorptivity characteristics at CO2 laser wavelength) on the surface of targets 12-61. In this case the chemically active media experience a purely thermal effect of laser radiation. Such processes are often referred to as laser thermochemistry or nonresonance laser chemistry. The features of thermochemical processes, e.g. oxidizing metal heating, taking place under the influence of laser radiation could be connected with combination of the following factors: a/ non-isothermality of processes; b/ the dependence of the chemical reaction rate constants on the temperature is strongly Arrhenius-type; c/ there is a feedback between the "chemical" and the "thermal" degrees of freedom because of the changing of absorption characteristics d/ because of the faster variation of the temperature in comparison with chemical relaxation ones there is a possibility for establishment of macroscopic inequilibrium in a system. In this paper we present the results concerning the laser light induced oxidation of some metals - firstly vanadium - in air enviroment. The surface of targets was illuminated at right angle, by W-CO laser irradiation. The temperature (T) and its derivative (dT/dt) were recorded with t e helo of a Chromel-Alumel thermocouole alloved into the back surface of the object and by a loop oscillograph in order to compute the 'time as well as temperature dependence of the coupling coefficient. The results of experiments performed on the vanadium plates show:
2
1. At the initial stage of heating the value of absorptivity A is equal to A = 0.08 obtained for pure vanadium at h = 10.6 urn. However at the subsequent s eages, the increase of thickness x of the oxide layer is in direct proportion to the increase of absorptivity of the sample 14,61. 2. The oxidat-Ion stages of the samples were found to differ due to different irradiation times and powers. Besides metallic vanadium different oxides: VO,, V203, V204 and V205 were identified 161. 3. Microscopic investigations showed the existence far from the zone of direct laser action ordinary scaly crystals of V 0 whereas in the zone of laser action a developed surface made30f ubula 6 5' 205 crystals, the total surface area increased by a factor 21 10 -10 i times. This offers promise for use in chemical engineering. 4. It was found a new phenomenon called "plasmachemical resonance" which is related to the decrease in absorptivity A in the temperature range cllOO-1200°C. 5. Many autowave and stochastic processes were observed such as: a) rotatior of heat field: a luminous spot could be seen circulating around the irradiated area of the sample with a constant period b) decay ard autowave processing of the temperature field during irradiation. Auto-wave processes are typical of many distributed nonlinear media. The examination - theoretical and experimental - of these processes now are in progress in many laboratories.
212
L. NANAI et
al.
References: Konov V.I.
Int. Conf. and School "Lasers and Applications", Bucharest, 1982. pp. 665-718
:: Luk'yanchuk B.S. 3rd Conference CIRP, Ziirich,1984. pp. 119-125
3. Bobyrev V.A., Bunkin F.V., Kirichenko N.A., Luk'yanchuk B.S., Simakhin A.V. Sov. Journ. QE 10, 611 (1983) 4. BunEn F.V., Kirichenko N.A., Luk'yanchuk B.S., Simakhin A.V., Shafeev G.A., Na'naiL., Hevesi I. Acta Phys. Hungarica 54(1-2), 111 (1984) Bunkin F.V., Kirichenko N.A., LX'yanchuk B.S. Izv. An. SSSR ser. fiz. 45, 1018 (1981) :: Ursu I., Nanu L., Dinescu M., Hening A., Mihailescu I.N., Nistor L.C., TZodorescu V.S., Szil E., Kovics J., Hevesi I., Na'naiL. Appl. Phys. A. 35, 103-108 (1984)
THE PECULIARITIES
Ninai L., Hevesi
I., Bunkin
Department of Experimental *General Physics Institute
OF IR LASER
F.V.,*
INDUCED OXIDATIONS
Luk'yanchuk
OF METALS
B.S.*
Physics JATE, Szeged (Hungary) Dc?m t. 9. of AS USSR, Moscow (USSR) Vavilov st. 38.
Among modern industrial lasers, CO -lasers have the highest mean continuous wave (cw) power, therefore they could be considere ii as the most promising radiation source for technological processes. However the coupling coefficient of metals - frequently used targets - at the wavelength of CO lasers is relatively small 111. If the target surface is in contact with a chemically act Pve gas (as well as air) the reaction products can be produced and the surface absorptivity (coupling) could be sufficiently increased, e.g. in the air enviroment the oxides are formed (with good absorptivity characteristics at CO2 laser wavelength) on the surface of targets 12-61. In this case the chemically active media experience a purely thermal effect of laser radiation. Such processes are often referred to as laser thermochemistry or nonresonance laser chemistry. The features of thermochemical processes, e.g. oxidizing metal heating, taking place under the influence of laser radiation could be connected with combination of the following factors: a/ non-isothermality of processes; b/ the dependence of the chemical reaction rate constants on the temperature is strongly Arrhenius-type; c/ there is a feedback between the "chemical" and the "thermal" degrees of freedom because of the changing of absorption characteristics d/ because of the faster variation of the temperature in comparison with chemical relaxation ones there is a possibility for establishment of macroscopic inequilibrium in a system. In this paper we present the results concerning the laser light induced oxidation of some metals - firstly vanadium - in air enviroment. The surface of targets was illuminated at right angle, by W-CO laser irradiation. The temperature (T) and its derivative (dT/dt) were recorded with t e helo of a Chromel-Alumel thermocouole alloved into the back surface of the object and by a loop oscillograph in order to compute the 'time as well as temperature dependence of the coupling coefficient. The results of experiments performed on the vanadium plates show:
2
1. At the initial stage of heating the value of absorptivity A is equal to A = 0.08 obtained for pure vanadium at h = 10.6 urn. However at the subsequent s eages, the increase of thickness x of the oxide layer is in direct proportion to the increase of absorptivity of the sample 14,61. 2. The oxidat-Ion stages of the samples were found to differ due to different irradiation times and powers. Besides metallic vanadium different oxides: VO,, V203, V204 and V205 were identified 161. 3. Microscopic investigations showed the existence far from the zone of direct laser action ordinary scaly crystals of V 0 whereas in the zone of laser action a developed surface made30f ubula 6 5' 205 crystals, the total surface area increased by a factor 21 10 -10 i times. This offers promise for use in chemical engineering. 4. It was found a new phenomenon called "plasmachemical resonance" which is related to the decrease in absorptivity A in the temperature range cllOO-1200°C. 5. Many autowave and stochastic processes were observed such as: a) rotatior of heat field: a luminous spot could be seen circulating around the irradiated area of the sample with a constant period b) decay ard autowave processing of the temperature field during irradiation. Auto-wave processes are typical of many distributed nonlinear media. The examination - theoretical and experimental - of these processes now are in progress in many laboratories.
212
L. NANAI et
al.
References: Konov V.I.
Int. Conf. and School "Lasers and Applications", Bucharest, 1982. pp. 665-718
:: Luk'yanchuk B.S. 3rd Conference CIRP, Ziirich,1984. pp. 119-125
3. Bobyrev V.A., Bunkin F.V., Kirichenko N.A., Luk'yanchuk B.S., Simakhin A.V. Sov. Journ. QE 10, 611 (1983) 4. BunEn F.V., Kirichenko N.A., Luk'yanchuk B.S., Simakhin A.V., Shafeev G.A., Na'naiL., Hevesi I. Acta Phys. Hungarica 54(1-2), 111 (1984) Bunkin F.V., Kirichenko N.A., LX'yanchuk B.S. Izv. An. SSSR ser. fiz. 45, 1018 (1981) :: Ursu I., Nanu L., Dinescu M., Hening A., Mihailescu I.N., Nistor L.C., TZodorescu V.S., Szil E., Kovics J., Hevesi I., Na'naiL. Appl. Phys. A. 35, 103-108 (1984)