Effect of the Gas Phase on the Current Magnitude in a Contactless Reduction Cell
Abstract Generated abstract
This study examines emission currents in a contactless reduction cell as a possible indicator of surface processes during reactions between separated solid reactants, using graphite and iron oxide as model materials. A quartz cell with fixed sample spacing and electrometer measurement was used to determine whether the recorded current passes through the heated gas space, how electrode reactions affect it, and how cell components influence the signal. The experiments showed that current flows through the gas phase, varies with pressure and gas medium, and is strongly affected by quartz parts, requiring constant cell geometry. Oxidizing, reducing, and neutral atmospheres produced distinct current magnitudes and polarities, supporting the method while indicating that further work is needed to increase the useful signal.
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INFLUENCE OF THE GAS PHASE ON THE CURRENT MAGNITUDE IN A CONTACTLESS REDUCTION CELL
V. S. Arkhipov, N. F. Tolkacheva
(Presented by the scientific-methodological seminar of the organic departments of the Faculty of Chemical Technology)
At present, the opinion is generally accepted that the interaction between a metal oxide and solid carbon in various kinds of fuel-ore mixtures proceeds mainly through the gas phase. However, specific reactions of solid-phase reduction by no means always fit into this scheme, which testifies to their complexity. Existing methods for studying solid-phase reactions allow one to judge the mechanism of their occurrence only indirectly, since such important stages of solid-phase reactions as mass transfer and surface phenomena remain outside the scope of investigation. These deficiencies can be overcome by using the method of separate arrangement of the reactants, or contactless reduction. For continuous monitoring of the transformation of reactants during the interaction process, it appears promising to use such a characteristic of the surface state as the electron work function, which directly reflects the most subtle surface phenomena of a solid. Emission currents arising between the reactants at the reaction temperature, which can be recorded fairly well, may serve as a signal adequate to the work function. In order to study the currents arising, a quartz cell was constructed that made it possible to rigidly set samples of graphite and iron oxide at a definite distance from one another.
To measure the current arising, the ionization section of a VIT-2 vacuum gauge was used; it is an electrometer with an input resistance of \(10^8\) ohms.
The purpose of the investigations carried out was:
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To demonstrate that the current flows precisely in the heated gas space of the chamber, and not through parallel circuits via the parts of the cell.
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To investigate the influence of chemical reactions at each electrode on the magnitude of the current.
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To investigate the influence of the cell parts on the magnitude of the current.
The flow of current in the gas space of the chamber was demonstrated both by direct measurements of the conductivity of the measuring circuit and indirectly—by the increase in current during evacuation from atmospheric pressure to \(0.1\) mm Hg.
The current arising at a temperature of \(650\text{--}900^\circ\mathrm{C}\) varies at atmospheric pressure within the range \(10^{-10}\text{--}10^{-8}\) A. The placement of the reactants in the absence of reaction between them does not introduce noticeable changes into the recorded current. At the same time, the quartz parts of the cell significantly...
significantly affect the magnitude of the current, which proves the necessity of keeping their position in the chamber constant.
Tests in various gas media made it possible to determine the influence of the reactions at each electrode on the magnitude of the current. In the cell, it is intended subsequently to carry out studies of the process of reducing iron oxide with solid carbon, with each reactant, being oxidized or reduced during the reaction, making its own contribution to the recorded current. Oxidation and reduction reactions were reproduced by creating the corresponding medium in the chamber—air and hydrogen. For comparison, tests were conducted in the neutral medium of helium.
Oxidation of graphite in an air medium is accompanied by an increase in the current of positive polarity.
In the reducing medium of hydrogen the current values are small. In the presence of iron oxide the polarity becomes negative.
In a neutral medium the current has positive polarity, and its magnitude does not depend on the presence of one reactant or another.
Thus, the tests carried out confirm the correctness of the initial premises underlying the method. At the same time, further work is needed to increase the magnitude of the useful signal in the recorded current.