JPS6096771A - Controlling method of nitrite ion concentration - Google Patents

Abstract

PURPOSE:To stably form the most excellent phosphate film to the surface of a metal, by automatically and continuously measuring the nitrite ion concn. in the phosphate treating solution on the surface of a metal and automatically replenishing a nitrite ion on the basis of the measured value. CONSTITUTION:A steel plate is immersed in the aqueous phosphate solution in a phosphate treating tank 18 to form a phosphate film to the surface of said steel plate. During this operation, a phosphate treating solution is recirculated to a cell 5 equipped with a nitrite ion selective electrode 1, a comparison electrode 7 and a temp. compensating electrode 8 by a pump 20. The potential difference signal between the electrodes 1, 7 detected by a potential difference detecting circuit 12 and the temp. signal from a temp. detecting circuit 13 are inputted to a correction circuit 14 to correct potential difference to the potential difference value at a reference temp. This value is compared with the set value of a setting device 15 by a comparator 16 and the drive circuit 17 of a nitrite ion replenishing pump 19 is driven by the difference signal and a nitrite ion replenishing solution 21 is automatically replenished into a treating tank 18 so as to keep a proper concn.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling nitrite ion concentration, which measures and controls the nitrite ion concentration in a phosphate treatment solution used in a metal phosphate treatment process.

Conventionally, the phosphate treatment process for metals is carried out in a process consisting of degreasing → water washing → phosphate treatment → water washing → drying, and the phosphate treatment solution is replenished with chemicals according to the consumption of the treatment solution components. The concentration of the processing liquid is always kept constant.

Nitrite ions are contained as accelerators as a component of the phosphate treatment solution, and these nitrite ions are supplied to the phosphate treatment solution in the form of town bath nitrites such as sodium nitrite and potassium nitrite. has been done. In order to produce the best phosphate film on the metal surface, it is desirable to maintain the nitrite ion concentration in the phosphating solution at an optimum level at all times. Therefore, in order to perform this control, it is necessary to constantly measure the nitrite ion concentration in the phosphate treatment solution, replenish nitrite based on the measured value, and maintain the nitrite ion concentration within the desired range. is.

Methods for measuring nitrite ion acidity in a phosphate treatment solution include, for example, the oxidation-reduction method and the gas volumetric method using a satsucalometer as a volumetric analysis method, the kill pool method as a distillation method, and the n-scan method as a colorimetric method. Examples include the 7-tylethylenediamine method and the analytical method using ion chromatography. However, these measurement methods require the addition of reagents, liquid preparation, and complicated analysis operations before measuring the nitrite ion concentration, and require a certain amount of time and troublesome operations. Currently, the industrial method for measuring nitrite ions in phosphate treatment solutions that continuously performs phosphate treatment involves placing the chemical conversion treatment solution in a satsucalometer and adding excessive sulfamic acid. Gas capacitance method to determine the nitrite ion concentration in the phosphate treatment solution from the gas amount and capacitive analysis method using cerium sulfate using a redox electrode (reaction formula NO2+ 2 Ce ” + Ht
O-NOs +2Ce +2H) is common.

In order to obtain a continuous and uniform phosphate film, it is necessary to increase the frequency of measurement, and it is usually necessary to measure at the same rate every 10 minutes. However, the gas capacitance method is an intermittent measurement method that continuously measures changes in the nitrite ion concentration in the phosphate treatment solution, ensuring that nitrite ions are always present in the phosphate treatment solution at a constant level. It is difficult to do so. In the titration method using an oxidizing agent such as cerium sulfate using a redox electrode, the nitrite ion concentration in the chemical conversion treatment solution can be continuously measured and the concentration can be constantly controlled, but it is necessary to adjust the concentration correctly. In addition, if the titration is to be carried out automatically, a titration apparatus having a highly accurate quantitative discharge mechanism is required, which is not suitable for industrial use.

The purpose of the present invention is to compensate for these deficiencies by continuously and automatically measuring the production of nitrite ions in the phosphate treatment solution, and automatically replenishing nitrite ions based on the measured values. An object of the present invention is to provide a method that can always maintain the nitrite ion concentration in a phosphate treatment solution within an appropriate range.

The method for controlling nitrite ion concentration according to the present invention includes continuously measuring the nitrite ion concentration in the phosphate treatment solution using a nitrite ion selective electrode, and controlling the nitrite ion concentration within a predetermined range. The present invention is characterized in that nitrite ions are automatically supplied to the phosphate treatment liquid so as to reach a set value.

The nitrite ion selective electrode used in the present invention will be explained with reference to FIG. 1, where 1 is a nitrite ion selective electrode, 2 is a glass electrode, 3 is an internal liquid, and 4 is a hydrophobic gas permeable membrane.

Nitrite ions react with hydrogen ions in the phosphate treatment solution through the following route, resulting in N, 0. Changes to

H1NOt':'KONO H+HONOi H2No: H20+No +NO+
NCh = Nt Os When the nitrite ion selective electrode 1 is immersed in a phosphate treatment solution, Neon passes through the hydrophobic gas permeable membrane 4 provided at the tip of the nitrite ion selective electrode 1 and enters the interior. liquid 3
Causes a reversible reaction with the water inside.

”/!NtOa + H, Od H” + NO.

The amount of NtOs gas that permeated and diffused through the hydrophobic gas permeable membrane 4 was N20. It depends on the partial pressure of and is proportional to the N, O, concentration in the chemical conversion treatment solution. Since the hydrogen ion concentration of the internal solution 3 is proportional to the production of nitrite ions in the phosphate treatment solution, the electrode potential is detected from this to measure the nitrite ion concentration in the phosphate treatment solution.

To explain how this nitrite ion selective electrode 1 is applied to a phosphate treatment solution, Fig. 2 shows a cell 5 for continuously measuring the nitrite ion concentration contained in a phosphate treatment solution. FIG. 3 is an explanatory diagram of an operation for automatically and continuously replenishing nitrite ions. Cell 5 is cell body 6
The cell body 6 is made of synthetic resin such as vinyl chloride, acrylic, fluororesin, etc., and therein is a nitrite ion selective electrode 1 for selectively measuring the potential of nitrite ions.
A comparison electrode 7 that provides a comparison potential thereto, and a temperature compensation electrode 8 are also installed.

Nitrite ion selective electrode 1 and comparison electrode 7 are connected to lead wire 9
, 10 to a potential difference detection circuit 12, and the temperature compensation electrode 8 is connected to a temperature detection circuit 13 by a lead wire 11. The potential difference signal between the electrodes 1-7 detected by the potential difference detection circuit 12 and the temperature signal from the temperature detection circuit 13 are input to the correction circuit 14, and the potential difference is corrected to the potential difference value at the reference temperature. Correction circuit 14
The potential difference value from the comparator 1 and the set value by the setting device 15 are
6 and the difference signal is sent to the pump drive circuit 17.
The servo pump 19 for replenishing the phosphate treatment tank 18 with nitrite ions is driven accordingly.

On the other hand, a phosphate treatment solution containing nitrite ions for measuring nitrite ion concentration, that is, a test solution flows from the lower inlet A of the cell body 6 to the upper outlet B of the cell body on the opposite side by the circulation pump 20. This state is always present during phosphate treatment. The phosphate treatment solution discharged from the outlet B at the top of the cell body is returned to the phosphate treatment tank 18 and used again as a treatment solution for phosphate treatment.

As mentioned above, the nitrite ion concentration in the phosphate treatment solution is detected by the potential difference between the nitrite ion selective electrode 1 and the reference electrode 7, and compared with a predetermined appropriate setting value in a desired range. The servo pump 19 for the nitrate ion replenishment liquid 21 is operated. That is, as shown in FIG. 4, for example, if the potential difference is 222 m? (Nitrite ion lower limit concentration 0.115
t/1), the servo pump 19 operates and the nitrite ion replenishing solution 21 is replenished into the phosphate treatment tank 18.
28m? (Nitrite ion upper limit concentration 0.136 f/1
), the servo pump 19 stops and the supply of the nitrite ion replenishing liquid 21 stops.

As described above, by carrying out the present invention, the nitrite ion concentration in the phosphate treatment solution can be continuously and automatically measured,
Nitrite ions are automatically replenished based on the measured values, and the nitrite ion concentration in the phosphate treatment solution can always be maintained within an appropriate range.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the nitrite ion selective electrode, Figure 2 is an explanatory diagram of the cell, Figure 3 is an explanatory diagram of the operation for automatically and continuously replenishing nitrite ions, and Figure 4 is an explanatory diagram of the nitrite ion selective electrode. It is a graph showing the relationship between the potential difference detected by the selective electrode, that is, the nitrite ion concentration, and time. 1. Nitrite ion selective electrode, 5. Cell, 7.
... Comparison electrode, 8 ... Temperature compensation electrode, 12 ... Potential difference detection circuit, 13 ... Temperature detection circuit, 14 ... Correction circuit, 15 ... Setting device, 16 ... Comparator, 17...
・Pump drive circuit, 18... Phosphate treatment tank, 19・
...Servo pump, 20...Circulation pump, 21...
Nitrite ion replenishment solution. Agent Masayoshi Okabe Figure 1 Figure 2 Figure 3 Figure 4 Haruma

Claims (1)

[Claims] The nitrite ion concentration in the phosphate treatment solution is continuously measured using a nitrite ion selective electrode, and the nitrite ion is added to the phosphate treatment solution so that the nitrite ion concentration becomes a set value within a predetermined range. A method for controlling nitrite ion concentration, characterized in that the concentration of nitrite ions is automatically supplied to a salt treatment solution.