JPS6213432B2 - - Google Patents

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. As a component of the phosphating solution, nitrite ions are included as accelerators, and the nitrite ions are supplied to the phosphating solution in the form of soluble nitrites such as sodium nitrite and potassium nitrite. There is. 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. There is.

Methods for measuring the nitrite ion concentration in the phosphate treatment solution include, for example, the oxidation-reduction method and the gas volumetric method using a satsucalometer as a volumetric analysis method, the Kirdahl method as a distillation method, and the n-naphthyl method as a colorimetric method. Analysis methods include the ethylenediamine method and 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 excess sulfamic acid. Gas volumetric method to determine the nitrite ion concentration in the phosphate treatment solution from the gas volume, and volumetric analysis using cerium sulfate using a redox electrode (reaction formula NO ₂ ^- +2Ce ⁴⁺ +H ₂ O→NO ₃ ^- +2Ce ^{3 +}
+2H ⁺ ) is common.

In order to obtain a continuous and uniform phosphate film, it is necessary to increase the frequency of measurement, which is usually about once 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. is difficult. 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, in the case of automatic titration, a titration device with a highly accurate fixed-quantity dispensing mechanism is required, which is not suitable for industrial use.

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

The method for controlling nitrite ion concentration according to the present invention is as follows:
The internal solution is put into a container equipped with a hydrophobic gas permeable membrane at the tip, and the nitrite ions in the phosphate treatment liquid react with hydrogen ions and change _{into N2O3} , which passes through the hydrophobic gas permeable membrane. A nitrite ion selective electrode is used to selectively detect the potential of nitrite ions in the phosphate treatment solution from the potential of hydrogen ions generated by permeation and reaction with water in the internal solution. Continuously measures the nitrite ion concentration in the salt treatment solution,
The present invention is characterized in that nitrite ions are automatically supplied to the phosphate treatment solution so that the nitrite ion concentration becomes a set value within a predetermined range.

The nitrite ion selective electrode used in the present invention is
To explain with the drawing, 1 is a nitrite ion selective electrode, 2 is a PH 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 and change to N ₂ O ₃ .

H ⁺ +O ₂ ^- HONO H ⁺ +HONOH ₂ ONOH ₂ O+NO ⁺ NO ⁺ NO ₂ ^- N ₂ O ₃ When the nitrite ion selective electrode 1 is immersed in the phosphating solution, this N ₂ O ₃ is selective for nitrite ions. The gas permeates through the hydrophobic gas permeable membrane 4 provided at the tip of the sexual electrode 1 and causes a reversible reaction with water in the internal liquid 3.

1/2N ₂ O ₃ +H ₂ OH ⁺ +NO ₂ ^-The amount of N ₂ O ₃ gas that permeates and diffuses through the hydrophobic gas permeable membrane 4 depends on the partial pressure of N ₂ O ₃ in the chemical conversion treatment liquid.
Proportional _{to N2O3} concentration. Since the hydrogen ion concentration of the internal solution 3 is proportional to the nitrite ion concentration 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. The cell 5 includes a cell body 6, which is made of synthetic resin such as vinyl chloride, acrylic, or fluororesin, and has a nitrite ion selective electrode therein for selectively measuring the potential of nitrite ions. 1 and a comparison electrode 7 that provides a comparison potential thereto,
Furthermore, a temperature compensation electrode 8 is installed.

The nitrite ion selective electrode 1 and the comparison electrode 7 are connected to a potential difference detection circuit 12 by lead wires 9 and 10, and the temperature compensation electrode 8 is connected to a lead wire 11.
It is connected to the temperature detection circuit 13 by. 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 a correction circuit 14, where the potential difference is corrected to a potential difference value at a reference temperature. Correction circuit 14
The potential difference value from and the set value by the setting device 15 are compared in the comparator 16, and the difference signal is inputted to the pump drive circuit 17, which is used to supply nitrite ions to the phosphate treatment tank 18 accordingly. A servo pump 19 is driven.

On the other hand, the phosphate treatment solution containing nitrite ions for measuring the nitrite ion concentration, that is, the test solution, is passed 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. It remains in this state all the time during flow and phosphate treatment. The phosphate treatment solution discharged from the outlet B at the top of the cell body returns to the phosphate treatment tank 18 again and is used again as a treatment solution for phosphate treatment.

As described 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 is compared with an appropriate setting value in a predetermined desired range. The servo pump 19 for the nitrite ion replenishment liquid 21 is operated. That is, as shown in FIG. 4, for example, if the potential difference is 222mv
(When the nitrite ion lower limit concentration reaches 0.115 g/), the servo pump 19 is activated and the nitrite ion replenishment liquid 2 is activated.
1 is replenished into the phosphate treatment tank 18, and when it reaches 228mv (nitrite ion upper limit concentration 0.136g/), the servo pump 19 stops and the nitrite ion replenishment liquid 21
supply will stop.

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

[Brief explanation of the drawing]

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, 1
5... Setting device, 16... Comparator, 17... Pump drive circuit, 18... Phosphate treatment tank, 19... Servo pump, 20... Circulation pump, 21... Nitrite ion replenishment liquid.

Claims (1)

[Claims] 1. The internal liquid is put into a container with a hydrophobic gas permeable membrane at the tip, and the nitrite ions in the phosphate treatment liquid react with hydrogen ions and change N ₂ O ₃ through the hydrophobic gas permeable membrane. A nitrite ion-selective electrode is used to selectively detect the potential of nitrite ions in the phosphate treatment solution from the potential of hydrogen ions generated by passing through the water and reacting with water in the internal solution. Continuously measuring the nitrite ion concentration in the salt treatment solution, and automatically supplying nitrite ions 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: