Oxidation kinetics of iron alloy drops in oxidizing slags
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een d r o p s of F e - C , F e - C - P and F e - C - S alloys of various compositions and synthetic oxidizing s l a g s of constant basicity and v a r i e d d e g r e e s of oxidation.
EXPERIMENTALPROCEDURE Apparatus The crucible assembly used in the study is shown in Fig. 1. The experiments were performed in a vert i c a l resistance furnace with t h r e e molybdenum windings powered independently to improve the constant temperature zone. At 1550°C, 150 m m of the furnace tube were within +5°C. An automatic temperature regulation based on the adjustment of the resistance of the heating elements was used. The thermocouple for temperature readings was set against the bottom of the alumina crucible containing the s l a g . The m e t a l was initially contained in a s m a l l alumina crucible held just above the surface of the s l a g . The drop was dispensed by tilting the s m a l l crucible by the rupture, by Joule's effect, of a thin platinum wire holding it in the upright position, thus establishing time zero of the reaction. The experiments were performed under an atmosphere of purified nitrogen.
Measurement of Reaction Rates Two methods were used to determine the reaction rates. The f i r s t method consists in water quenching the crucible containing the m e t a l and the slag a f t e r v a r i ous t i m e s of contact, and in obtaining the advancement of the reactions from the chemical analysis of b o t h phases. It was used to study the kinetics of oxidation of iron, phosphorus and, in some c a s e s , carbon. However, the precision on the reaction time is relatively poor, especially for short times, and we did not succeed in quenching the crucible for contacts of less than 10 seconds. The second method, used only t o follow decarburization, consists in measuring continuously the flowrate of gas evolved: the instantaneous rate of decarburization is thus obtained at any time, including the f i r s t instants of reaction. A carbon balance VOLUME 8B, SEPTEMBER 1977-409
the content calculated by mass balance from the flowrate measured n e v e r exceeds 5 pct. Operating Procedure
Fig. 1--Experimental set-up. (a) Laboratory tube, (b) heating element, (c) furnace insulation, (d) alumina crucible containing the slag, (e) alumina crucible containing the metal, {f) platinum fuse for dispensing the metal, and (g) thermocouple.
can then be applied t o calculate the change, with reaction t i m e , in the carbon content of the metal, the kinetics of iron oxidation having previously been determined by the first method. The flow-rate of gas evolved is obtained from the continuous recording, by m e a n s of a differential pressure sensor, of the pressure drop in a capillary tube through which the g a s e s leaving the reaction tube are channeled. Calibration curves, determined for the appropriate g a s e ous mixtures ( i . e . Ns, and CO and COs formed by the reaction), allow the calculation of the instantaneous flow-rate. It has been verified that within the domain of flow-rates relevant to this study, variations of the r
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