SU911299A1 - Method of oxygen diffusion coefficient in metals and oxides - Google Patents

Description

(54) METHOD FOR DETERMINING THE ACID DIFFUSION RATE IN METALS AND OXIDES

one

This invention relates to the metrology of diffusion oxygen transfer processes in metals and nonstoichiometric compounds and can be used to determine the chemical diffusion coefficient of oxygen in metals and in such compounds as

TiOj, Nb2Os, CeOjfx. A method is known for determining the diffusion coefficient of oxygen using a device including a solid electrolyte galvanic cell (TTL) with oxygen ionic conductivity by passing DC current through the cell and measuring the change in cell emf over time (1 ..

The disadvantage of this method is that it is influenced by the charging of double electric layers and electronic currents of the cell, which leads to an increase in the measurement accuracy and, moreover, it gives an average value of the diffusion coefficient when the composition of specimens changes.

The closest technical solution to the invention is a method for determining

the diffusion coefficient of oxygen in metals and oxides using a solid electrolyte galvanic cell, which implies that a voltage is applied to the cell electrodes, the ion current passing through the cell is measured over time, and the diffusion coefficient 2 is calculated using the data obtained.

The diffusion coefficient of oxygen is determined from the Cottrell equation

ten

, -. 2ffik), (,

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where, the e-ion current flowing through

cell;

F is the Farad constant; B is the coefficient of chemical diffusion of oxygen;

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COL, initial and final concentration of oxygen in the sample under study: t - time; S is the plateau (the electrolyte – sample interface is a sample; X is the first root of the Bessel function, zero order. In equation (I), the oxygen concentration Co, determined by the magnitude of the applied voltage to the sample electrolyte surface, must be constant over time current measurement. However, in a known method, a constant voltage applied to a galvanic cell is maintained, according to the equation i-EI (2.) 4-F where and is the applied voltage; E is the current; R is the ohmic resistance litas; potential l of oxygen n GU Oa. of the reference electrode and the sample under study at the electrolyte interface surface — the sample will increase the applied sample-electrolyte-voltage-voltage interface, which at the end of the measurements, the current is almost zero, make up a value equal to the product Jp R, and this, in turn, will lead to a change in the oxygen concentration of the sample – electrolyte interface, which can cause a significant increase in the measurement error of the diffusion coefficient of oxygen. Moreover, since the concentration kis loroda on the free surface of the sample is not controlled or maintained at the initial level, it also leads to an increase potreshnostn. The purpose of the invention is to improve the accuracy of determining the oxygen diffusion coefficient in metals and oxides. The goal is achieved by the fact that in the method of determining the diffusion coefficient of oxygen in metaslachs and oxides with a solid electrolyte galvanic cell mud, consisting in that a voltage is applied to the electrodes of the cell, the ion current passing through the cell is measured in time and calculated from the received - according to the diffusion coefficient, the magnitude of the voltage is reduced inversely proportional to the square root of the time interval elapsed since the moment the voltage was applied. The drawing shows a device implementing the method. Test sample 1 is placed on the flat bottom of a solid electrolyte tube 2, the inner space of which is filled with a uniform metal-metal oxide mixture, which serves as the reference electrode 3. In the center of the tube is a potentiometric outlet 4. On the free noBepixHoosity of the sample, there is a platinum ring-shaped layer 5, equipped with a potentiometric outlet 6, and a conical solid electrolyte body 7, having an outlet 8. The assembly is located inside an oxygen ceramic Koro pump made of solid solid electrolyte tube 9 containing dosing 10 and measuring 11 electrodes are sealed, evacuated and heated to a predetermined temperature lying in the range from 900 to 1800 K. The method is carried out as follows. A voltage of 60-100 mV is applied to the electrodes of the solid electrolyte cell, the ion current passing through the cell is measured in time, and as the current decreases, the voltage decreases inversely proportional to the square root from the time interval that the voltage passed. Due to the fact that the tube material at the measurement temperature has pure ionic conductivity, the current flowing through the cell carries oxygen ions and reduces or increases the oxygen concentration on the sample interface - electrolyte in accordance with the applied voltage. The diffusion coefficient of oxygen in the sample under study is determined by the nature of the change in the ion current. PRI im p Measure the change in ion current over time for the sample at. Analyzing Eq. (1), it is easy to see that by constructing the dependence of the current on I / V-b, it is possible to determine the value of the diff-oxygen ratio at the known remaining values. A value of 5 was obtained equal to (2.7 + 0.3) S for the ratio, 0001. Thus, the method makes it possible to measure the oxygen diffusion coefficient in metals and oxides using the simple Cottrell equation, for which it is necessary to maintain stable values of oxygen concentration with high accuracy by applying the described operations. The advantages of the method are that it can be used to determine the diffusion coefficient of oxygen in the range of values from III up to

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in the temperature range from 900 to 1800 ° K with an accuracy of 8-10%. The obtained values are necessary for calculating the kinematic characteristics of various technological processes in nuclear power engineering.

Claims (2)

1.R. Z. Pastore L. and R.A. Rapp  .from electrochemical measurement, 245 (1969), p- 1711-1720. 2.R. C. Steel and Riccardi in Metallurgical Chemistry Measuring Chemicals, diffusion coeffisient in non-stehiometrical  oxides using solid state electrochemical technics. 0. Kuba schevsd, London, 1972, p. 123 (prototype) ..