DE2710556A1 - METHOD OF MEASURING THE DYNAMIC POTENTIAL ON THE SURFACE OF AN ELECTRODE OF A CHEMICAL BATH - Google Patents

Description

PATENT LAWYERS

* 3

D-1 BERLIN-DAHLEM 33 · PODBIELSKIALLEE 08 DB MUNICH 99 ■ WI DE NM AYERSTR ASSE

BrIo Robert BERLIN: DIPL.-ΙΝβ. R. MÜLLER-BORNER

MUNICH: DIPL.-IN3. HANS-HEINRICH WEV DIPL.-ΙΝβ. EKKEHARO KORNER

Berlin, March 8, 1977

Method for measuring the dynamic potential on the surface of an electrode in a chemical bath

(Schwel ", No. 2.691 / 76 of March 9, 1976)

Rare description Claims Sheet drawing

27 I06 - kr

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The invention relates to a method for measuring the dynamic potential that prevails on the surface of an electrode of an electrochemical bath, as well as a Device for carrying out the method and an application of the method.

The polarization of an electrode that is immersed in an electrochemical, in particular galvanoplastic, bath is the difference between the dynamic potential - the electromotive force between the electrode and the bath when a current flows - and the static potential - the electromotive force between the electrode and the electrolyte Power when no electricity is flowing.

The following definitions are chosen:

pol s polarization of the electrode, ns * static potential (without current flow) and nd - dynamic potential (with current flow).

The following applies:

pol = ns - nd

In the steady state, i.e. when equilibrium has been established after the bath has been put into operation, the three variables depend on various factors, such as the Example of the composition of the electrode and that of the electrolyte as well as the current density on the surface the electrode. In the case of stable operating conditions, the relationship applies in particular

pol - f (d),

in which d is the current density on the surface of the electrode under consideration.

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It is based on the foregoing that the value of the polarization on the surface of the cathode of an electroplating bath in operation depends on the current density at the cathode, which is determined by the parts treated in this bath. Knowledge of the current density is now extremely useful and necessary for the plater in order to create a correct transition. Finally, the bathrooms are designed in a particular current density range which does not exceed but shall not be less than well. Moreover, - and this is especially important in the Plattieruny with precious metals - the thickness of the plating depends on the performance of the cathode of the bath, the operating time and the current density is applied to the parts to be machined, from.

Knowing the relationship between the dynamic potential and the current density, which occurs at the surface of an electrode in a galvanoplastic bath prevails, linked, can equally well for the knowledge of the state of the Bades can be useful if the other parameters that influence it are also known.

The measurement of the static potential π does not pose a major problem, since it can be effected with the aid of reference electrodes. It is different with the dynamic potential if the measurement is to be carried out industrially and not in the laboratory: It was found that when the treatment current flows on the electrodes, an ion imbalance of very small thickness is established, which influences the said polarization, which is determined by means of an in at a very small distance from the electrode attached probe was determined, so that the measurement could not be affected by the ohmic voltage drop in the bath. This method, which can be used in laboratories, can not be applied to industrial

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vanoplastische facilities are transferred in which the treated parts are generally moved in the bath and do not allow the dynamic polarization to be measured, which are carried out with probes that touch them as it were.

The invention is based on the object of a method for measuring the dynamic potential in an electrochemical Specify bath and means for its implementation, which are industrially applicable.

This object is achieved according to the invention in that the passage of current through the bath is interrupted and immediately after this interruption the electromotive Force between the electrode and a probe immersed in the bath is measured.

An apparatus for carrying out the invention The method is characterized in that means for interrupting the flow through the bath are provided as well a probe immersed in the bath, which makes it possible immediately after the interruption while the current is still is interrupted to measure the electromotive force between itself and the electrode and a storage means , which allows the measured value obtained for direct evaluation or later use to hold on.

The invention also has an application of the above-mentioned method, in which the measurement result is used to regulate the current density on the surface of the electrode to determine the condition of the bath, wherein the current is maintained at a predetermined value.

The invention is based on the fact that the polarization

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tion of one of the two electrodes of an electrochemical bath in the immediate vicinity of the electrode, corresponds to the accumulation or reduction of the electrochemical reaction products arising as a result of the current flow. If the current flow is interrupted abruptly, the system needs some time to regain its equilibrium. The electrode-electrolyte surface behaves like a battery, in which the electromotive force is an exact image of the polarization. Now this electromotive force can be between the electrode and one at any point in the bath - and can no longer be measured in the immediate vicinity of one or the other electrode - placed probe. In addition, the measured value is no longer affected by the ohmic voltage drop in the bathroom or the cables of the arrangement, since the current is zero.

However, the generated electromotive force disappears very quickly, for example at a rate of 0.6 mV / μs in a gold cyanide bath. The reason for it lies in the recombination of the ions in the vicinity of the electrode, more generally in the re-adjustment the equilibrium of the substances involved in the reaction. The measurement can therefore be brief and defined Period of time carried out after the interruption of the power and the data obtained can be stored in a memory for later processing.

Preferred developments of the invention are specified in the subclaims. An advantageous embodiment is shown in the drawing and is described in more detail below.

The single figure shows a block diagram of a device for electroplating, which is equipped with the means according to the invention for measuring the dynamic potential.

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is prepared.

The device comprises a galvanoplastic vessel 1, which contains an electrolyte 2 in which two electrodes are immersed, i.e. an anode 3 and a cathode 4, which in practice is formed by the parts to be plated.

The electroplating current comes from a stabilized rectifier 5 (the possibility of setting the Values for the voltage u and the current i are indicated by arrows) via an LC filter 6 and two lines 7 and 8 to the two electrodes 3 and 4. A voltmeter 9 is connected to the two lines 8 and 9 and an ammeter 10 is in parallel with a shunt resistor 11 inserted in the line 8 electronically controlled breaker 12 is also switched into line 8. That breaker can also be switched on in line 7.

The device comprises a probe 13 made of noble metal, which is immersed in the electrolyte 2 and with a Preamplifier 14 is provided, which is preferably built into the probe and whose dynamic potential the cathode related signals via a line 15 to the stabilized rectifier 5 for control of the same be directed.

In order to enable the measurements following the interruptions in the bath current, the electronically controlled interrupter 12 is controlled to generate these interruptions at a fixed frequency by means of a device which contains an oscillator 16, a Schmitt trigger 17 and a logic circuit 18 which connected to the electronically controlled breaker 12 via a line 19 iat. The logic circuit 18 is

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In addition, controlled by three timers T., T- and T ₃ , which are labeled 20, 21 and 22 and are primarily used to determine the delay that lies between the power interruption and the start of the measurement and is the same for each measurement. On the other hand, they also determine the duration of the reading in, which is also constant for all measurements and, thirdly, the delay in switching the current on again after the reading in, which is necessary to prevent parasitic effects that occur when the current is switched on again prematurely could.

The logic circuit not only controls the continuous interruptions of the current via the interrupter 12, but also the periodic reading. For this purpose, it is connected via a line 23 to an electronic interrupter 24 which is arranged in the line which connects the preamplifier 14 of the probe 13 to the rectifier 5. An amplifier 25 is arranged between the preamplifier 14 of the probe and the electronic breaker 24. A capacitor 29, which is connected to the output of the interrupter 24, is charged to a voltage value proportional to the voltage between the cathode 4 and the probe 13 during the reading-in period. The capacitor retains its charge even after the end of reading and thus conserves the value of the measurement mentioned as a memory. An amplifier 31 with a large input impedance is the voltage value, which is held by the capacitor 29, on the line 15 without causing a detectable voltage reduction of the capacitor. A millivoltmeter 30 is connected to lines 15 and 28 and allows the measured potential to be read off directly. It should be noted that the measured potential contains a constant that depends on the probe 13

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forming metal depends, and is of no importance, since the electrochemical potential of the metal in question is known. The course of reading in on line 23 is at 26 in relation to the course of power cut-off, denoted by 27, which is transmitted over the line 19 is shown.

It should be noted that the amplifier 25, the electronic breaker 24, the capacitor 29 and the amplifier 31 represent a circuit known by the English designation "sample and hold" is.

With regard to certain applications of the method, the stabilized rectifier 5 is provided via lines 28 and 32 are supplied with the voltage at the terminals of the shunt resistor 11. The comparison between this tension and the set value i gives an error signal which causes the stabilized rectifier 5 to operate as a current regulator.

A rapid shutdown circuit 33, which is connected to the shunt resistor 11 via the lines 28 and 32, causes a disconnection of the main current controlled by the breaker 12 via the intermediary of the logic circuit 18 and the line 19 to protect the device in the event of a short circuit.

The device shown enables automatic control of the current density for the parts to be treated:

The bath 2 is supplied with a current and a voltage by the rectifier 5, which is stabilized via the filter 6 are. The breaker 12 periodically interrupts the current at intervals at set times, which are determined by the oscillator 16. if

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- • τ

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the corresponding point in time is reached, after a delay predetermined by the timer 20, the in the voltage measured by the timer 21 between the cathode 4 and the probe 13 im Memory of the capacitor 29 held. The measurement is now stored and after a safety delay which is set by the timer 22 to To avoid disruptive effects that can occur when the power is switched on again, the power starts again to flow. The recorded polarization value is entered directly via the line 15 into the control circuit of the rectifier 5, the main current in the way sets that the polarization assumes and maintains the predetermined value.

The result of this procedure is that the current density at the cathode is independent of its surface. It is kept exactly constant if the frequency of the measurements is sufficiently high so that the regulation is practically continuous. For this purpose, the interruption frequency of the current is, for example, essentially of the order of magnitude of 1 kHz, the duration of the interruptions being in the order of magnitude of 10 to 50 μβ .

This facility can also be used to check the quality of the bathroom:

An electrode with a known surface is used. The control loop of the rectifier 5 is no longer controlled by the recorded value of the polarization, but via an internal bridge of the rectifier that it allows you to work at a voltage or a current that is constant and controllable. Under change of the current and plotting the corresponding recorded polarization values can be the aforementioned curve pol «f (d). Investigating this

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The curve and its comparison with curves recorded with known standard solutions provide information about the condition of the bathroom and its possible deviations from a standard that can be maintained. These Measurements can be carried out just as well for the cathode as they are for the anode.

It should be noted, however, that with the present method for measuring the dynamic potential, certain conditions must be met in order to obtain good results:

The arrangement of the electrodes in the vessel should be such that the current density can also be adjusted over their entire surface. Noticeable differences in current density, and consequently polarization, between Different points of the same electrode can create a parasitic electric field in the bathroom at the moment of the Generate shutdown of the electricity. It is therefore pointed out that this requirement of the distribution of the Current density over the surface of the electrodes must also be fulfilled for the entire electroforming bath, so that the thickness of the covering can be adjusted.

The contact between the electrodes of the same polarity that occurs between the treated parts must be of be of good quality so that the entire active surface has the same potential. This condition must at all are generally observed.

The automatic regulation of the current density can be done very precisely when viewed Bad the function pol = f (d) exhibits good behavior, that is, the curve representing this function has a steep slope. So it must be the polarization in Depending on the current density, they change sufficiently so that this change can be exploited can.

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It should also be pointed out that instead of interrupting the current, the cathode is also used that of the anode can be interrupted. In the case of the presence of several anodes, the current can be separated be interrupted at each anode, which has the advantage that one or the other can be switched off, so that in this way the surrounding electric fields occurring during the interruption are suppressed or can be reduced, which occur when the electrodes are polarized differently as a result of a poor distribution of the electric field in the bathroom while the current is flowing.

The method described above and the associated devices can be applied to all electrochemical Applications are transferred in which polarization phenomena on electrodes immersed in a bath occur (electrolytic paving, electroforming, electropolishing, electrical deburring, electrolytic Xtzen, analyzes etc.).

Claims ;

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Claims (1)

Claims Method for measuring the dynamic potential that appears on the surface of an electrode of an electrochemical Bath prevails, characterized in that the passage of current through the bath (2) is interrupted and immediately after this interruption the electromotive force between the electrode (3 or 4) and one immersed in the bath (2) Probe (13) is measured. Method according to Claim 1, characterized in that interruptions and subsequent Reconnection of the current through the bath (2) can be effected at a constant frequency and that during each interruption at the same times, calculated from the beginning of the interruption, and for the same Period a measurement of the electromotive force is carried out. Method according to claim 2, characterized in that the repetitive Measurements of the electromotive force obtained information can be used to determine the current that the bath (2) is exposed to control in such a way that the electromotive force and, consequently, that at one too current density applied to the treated part remains constant within narrow limits. 4. Apparatus for performing the method according to claim 1, characterized in that Means (12) for interrupting the flow through the bath 709840/0709 ORIGINAL INSPECTED (2) are provided as well as a probe (13) immersed in the bath, which makes it possible, immediately after the interruption, while the current is still broken, the electromotive force between itself and the electrode (3 or 4) to measure, and a storage means (29), which makes it possible to record the measured value obtained for direct evaluation or later use. 5. Apparatus according to claim 4, characterized in that the means (12) for interruption of the flow through the bath (2) are provided in such a way that they are successive at a fixed frequency Generate interruptions. 6. Application of the method according to claim 1, characterized in that the measurement result for regulation the current density at the surface of the electrode is used to determine the state of the bath, whereby the current is kept at a predetermined value. 27 Io6 - hon 709840/0709