KR20100024833A - Palladium(pd) coating electrolyte solution for hydrogen delayed fracture quality evaluation of high strength steel, method for pd coating using the same and plating bath - Google Patents

Abstract

PURPOSE: A palladium coating electrolyte solution for hydrogen delayed fracture quality evaluation of a steel material, and a method and a plating bath for palladium coating using the same are provided to achieve excellent hydrogen release prevention characteristic compared to cadmium coating, secure data stably and reduce the risk of safety accidents. CONSTITUTION: A palladium coating electrolyte solution comprises potassium hydroxide(KOH) aqueous solution and/or sodium hydroxide(NaOH) aqueous solution, and palladium chloride(PdCl2). The concentration of PdCl2 is 0.008~0.015M. The concentration of KOH aqueous solution is 2~15M. The concentration of NaOH aqueous solution is 6~10M.

Description

Palladium (Pd) coating electrolyte for evaluating hydrogen delayed fracture properties of steel, Palladium (Pd) coating method and coating bath using the same FOR Pd COATING USING THE SAME AND PLATING BATH}

The present invention proposes an electrolytic solution for palladium (Pd) coating proposed to replace a cadmium (Cd) coating, which is essentially required to form a coating film for suppressing the release of charged hydrogen during a hydrogen delayed fracture test of steel materials. It relates to the palladium (Pd) coating method used and the plating bath used in the coating.

With the recent increase in size and complexity of structures, research and development efforts are underway with the aim of increasing the strength. The most widely used high-strength bolts are manufactured through the process of drawing, cold heading and rolling for forming and quenching and tempering to impart mechanical properties. Tissues undergoing this process show higher strength than other tissues, but when tempering, carbides preferentially precipitate at the austenite grain boundary preceding the trap site of hydrogen, and these carbides act as a trap site for hydrogen. Therefore, it is known to be susceptible to delayed fracture because the accumulation of diffusible hydrogen occurs at the previous austenite grain boundary and acts as a breaking point along with the decrease in strength.

Therefore, in order to impart the hydrogen delayed destruction mechanism and resistance, the hydrogen absorption evaluation through simulation experiment is used as the most important evaluation index of high strength bolts. In general, when using a Thermal Desorption Spectroscopy (TDS) which can measure the amount of diffuse and non-diffusible hydrogen at elevated temperatures, the hydrogen is charged for hydrogen analysis and then the charged hydrogen is released. Cadmium (Cd) must be coated by electrochemical method. However, in the case of cadmium, the poisoning by cadmium oxide vapor or cadmium compounds generated during dissolution to remove cadmium violates the basic laws of environmental policy (0.005 mg / L of water and human health standards), In addition, the coating has disadvantages such as lack of reproducibility of cadmium aqueous solution and a uniform coating layer.

On the other hand, when the electric arc spray method or the plasma method is applied to the non-electrochemical method, it is impossible to form an accurate hydrogen inhibiting film because the coating price is not increased and the coating is required in a short time required for the experiment.

Looking at the prior art in connection with the above-mentioned technical field in the experimental method for the hydrogen delayed fracture characteristic analysis,

Korean Patent Application No. 2007-0112654 relates to a method for measuring the trap activation energy of metallic hydrogen using the release rate of hydrogen according to the rate of temperature rise. As a technique for calculating the energy, cadmium coating is essential for specimen analysis, but there is no mention of how to improve it.

In addition, Korean Patent Publication Nos. 2005-0032270 and 2006-0017408 disclose palladium (Pd) coating methods, but most of them are limited to chemical or physical coatings for the selective permeation of nano metal catalysts or fuel cells. However, no technology has been applied to cadmium-substituted electrochemical coatings for hydrogen delayed fracture characterization.

In addition, in the case of cadmium coating, cadmium accumulates without filtration in the human body and is very addictive enough to cause death through osteomalacia and systemic weakness, which is controlled internationally under very strict regulations on usage. And it is very difficult to build reliability data.

The present invention is an electrolytic solution for palladium (Pd) coating used to replace the palladium (Pd) coating harmless to the human body, instead of the cadmium (Cd) coating used to block hydrogen emissions when analyzing the hydrogen delayed fracture characteristics of steel, It is to provide a coating method and a plating bath used in the coating.

The present invention provides an electrolytic solution for palladium coating comprising at least one of potassium hydroxide (KOH) solution and sodium hydroxide (NaOH) solution and palladium chloride (PdCl ₂ ).

In addition, the present invention comprises the steps of preparing a plating bath for a palladium coating electrolyte solution containing at least one of potassium hydroxide (KOH) solution and sodium hydroxide (NaOH) solution and palladium chloride (PdCl ₂ );

Installing a specimen for delayed destruction as a cathode of the plating bath, and installing platinum or palladium metal as an anode; And

Forming a palladium coating layer on the specimen by connecting an anode and a cathode immersed in the plating bath containing the electrolytic solution for palladium coating to an anode and a cathode of a power source, respectively, and flowing a current;

It provides a palladium coating method comprising a.

In addition, the present invention provides a plating bath, characterized in that the material of the plating bath used in the coating method is a Teflon material.

As described above, the present invention is not only harmless to the human body by coating palladium (Pd) instead of the cadmium (Cd) coating which is essential for the hydrogen delayed fracture characteristics experiment, as well as the hydrogen release inhibitory properties compared to the cadmium coating It is more effective and secures data, and has a great effect on reducing safety accidents.

In order to overcome the above-mentioned problems, the present inventors have studied in depth a method of coating palladium (Pd) instead of the conventional cadmium (Cd) coating. Hereinafter, the palladium coating electrolyte solution applied in the present invention, a palladium coating method using the same, and a plating bath used for coating will be described in detail.

First, the electrolytic solution for palladium (Pd) coating will be described in detail.

In the hydrogen delayed fracture test, palladium is plated on the specimen to act as a shield for hydrogen release, contributing to the increase in reliability of the hydrogen delayed fracture test, and easy analysis through the formation of a uniform thickness coating film. When removing the coating film, the pores can be completely removed.

In the coating electrolyte of the present invention, palladium (Pd) is added in the form of palladium chloride (PdCl ₂ ). When palladium is added to a conventional electrolyte solution, since the addition effect is insignificant, it is preferable to add it in the form of palladium chloride (PdCl ₂ ).

In addition, if the addition amount is too small, fine holes are formed in the palladium coating film, if too much is added, the coating layer is formed too thick in the delayed fracture specimens, it is not easy to remove the coating layer. Therefore, the addition amount of palladium chloride (PdCl ₂ ) is preferably set to 0.008 to 0.015 M (molar concentration), more preferably 0.009 to 0.013 M.

According to the present invention, the electrolyte to which palladium chloride (PdCl ₂ ) is added is not particularly limited. As an example of the electrolyte solution to which palladium chloride (PdCl ₂ ) is added, it is preferable to use an aqueous solution of potassium hydroxide (KOH), an aqueous solution of sodium hydroxide (NaOH) or a mixture thereof.

The concentration of the potassium hydroxide (KOH) solution is more preferably 2 to 15M, the concentration of the sodium hydroxide (NaOH) solution is 6 to 10M.

Hereinafter, a coating method using the palladium coating electrolyte solution will be described in detail.

First, a palladium coating electrolyte is prepared in a plating bath, and then a delayed fracture specimen is installed as a cathode, and platinum or palladium metal is installed as an anode.

A positive electrode and a negative electrode immersed in the plating bath containing the palladium-coated electrolyte solution are connected to an anode and a cathode of an external power source, respectively, to flow a current.

In the present invention, the mechanism of forming the palladium coating layer is plated on the surface of the delayed fracture specimen by reacting with electrons generated in the cathode by moving in the direction of the delayed fracture specimen as the palladium chloride (PdCl ₂ ) of the electrolyte is changed to palladium ions by the current will be.

It is preferable that the thickness of the palladium coating layer by this invention is 14-25 micrometers. If the thickness of the coating layer is too thin, the flammability of hydrogen delayed fracture is not stable and too thick. When the coating layer is removed for the experiment after hydrogen filling, it is difficult to remove by the ion bonding layer of Pd ions, and the flammability is not guaranteed.

Plating bath applied to the palladium coating method is preferably made of Teflon material. This is to suppress the electrical conduction of the plating bath in the electrochemical plating.

Hereinafter, embodiments of the present invention will be described in detail.

(Example)

Table 1 shows coating electrolytes containing different concentrations of palladium chloride (PdCl ₂ ) in order to form a Pd coating layer of high strength steel, and when current was flowed at each concentration using the plating bath shown in FIG. 1. It shows the result of measuring and comparing the palladium (Pd) coating layer.

PdCl ₂ concentration (M) Repeat count Coating layer thickness (㎛) Thickness error range per number Remarks 0.001 5 1.15 ± 0.15 Comparative example 0.003 5 5.04 ± 0.13 Comparative example 0.006 5 11.2 ± 0.11 Comparative example 0.008 5 14.9 ± 0.03 Inventive Example 0.011 5 19.7 ± 0.03 Inventive Example 0.015 5 24.1 ± 0.03 Inventive Example 0.020 5 30.0 ± 0.08 Comparative example 0.023 5 33.9 ± 0.18 Comparative example

According to Table 1, when the concentration of palladium chloride (PdCl ₂ ) is less than 0.008M, the thickness of the coating layer is too thin, so that fine pores may be formed in the coating layer, and the error range of the thickness per number is increased, thereby preventing reproducibility of the coating. . In addition, when the concentration of palladium chloride (PdCl ₂ ) is greater than 0.015M, the error range of the coating layer thickness is increased, and reproducibility is not guaranteed, and it is difficult to remove the coating layer for the experiment after hydrogen charging.

Figure 2 shows the results of measuring the hydrogen content of the Pd coating and Cd coating with time change after hydrogen charging. Compared to the specimen after cadmium coating, even in the case of the palladium electrochemically coated specimen, the hydrogen content does not decrease or decrease with time, and there is no change in the hydrogen content even in the evaluation of flammability.

1 is a schematic view showing the electrochemical palladium (Pd) coating method of the present invention.

Figure 2 shows the results of measuring the amount of hydrogen over time after the hydrogen filling for cadmium coaching specimens and palladium coated specimens.

Claims (10)

An electrolytic solution for palladium coating for evaluation of hydrogen delayed fracture properties of steel, comprising at least one of potassium hydroxide (KOH) solution and sodium hydroxide (NaOH) solution and palladium chloride (PdCl ₂ ). According to claim 1, The concentration of the palladium chloride (PdCl ₂ ) is a palladium coating electrolyte for the hydrogen delay fracture characteristics evaluation of steel, characterized in that the concentration of 0.008 ~ 0.015 molarity (M). The method of claim 1, wherein the potassium hydroxide (KOH) solution concentration of 2 to 15 molar concentration (M), characterized in that the palladium coating electrolyte for the evaluation of hydrogen delayed fracture characteristics of the steel. The method of claim 1, wherein the concentration of the sodium hydroxide (NaOH) solution is 6 to 10 molarity (M), characterized in that the palladium coating electrolyte for the evaluation of hydrogen delayed fracture characteristics of steel. In the palladium coating method through the electrochemical method, Preparing a palladium coating electrolyte solution containing at least one of potassium hydroxide (KOH) solution and sodium hydroxide (NaOH) solution and palladium chloride (PdCl ₂ ) in a plating bath; Installing a specimen for delayed destruction as a cathode of the plating bath, and installing platinum or palladium metal as an anode; And Forming a palladium coating layer by connecting an anode and a cathode immersed in the plating bath containing the palladium-coated electrolyte solution to an anode and a cathode of a power source, respectively, and flowing a current; Palladium coating method for evaluating the hydrogen delayed fracture characteristics of the steel comprising a. The palladium coating method of claim 5, wherein the palladium coating layer comprises forming a coating layer to have a thickness of 14 to 25 µm. The palladium coating method of claim 5 or 6, wherein the concentration of the palladium chloride (PdCl ₂ ) is 0.008 to 0.015 molarity (M). The method of claim 5 or 6, wherein the concentration of potassium hydroxide (KOH) solution is 2 to 15 molarity (M) palladium coating method for evaluating the hydrogen delayed fracture characteristics of the steel. The method of claim 5 or 6, wherein the concentration of the sodium hydroxide (NaOH) solution is 6-10 molar concentration (M), characterized in that the palladium coating method of the steel material for hydrogen delay fracture characteristics evaluation. Plating bath used for the palladium coating to prevent the release of hydrogen when evaluating the hydrogen delayed fracture properties of high-strength steel is a teflon plating bath, characterized in that the material.

Images