CN102564932A - Method for determining magnesium or magnesium alloy corrosion rate and special experimental device - Google Patents

Abstract

The invention discloses a method for determining a magnesium or magnesium alloy corrosion rate and a special experimental device, which have the characteristics of high sensitivity and capabilities of obtaining an average corrosion rate, monitoring an instantaneous corrosion rate simultaneously, converting a hydrogen gas release rate into the instantaneous corrosion rate through collecting and determining the hydrogen gas release rate in a magnesium alloy corrosion process, and obtaining more information about the corrosion process. A hopper is inversely covered on a container with a corrosive medium; a magnesium metal or magnesium alloy specimen is hung inside the hopper; a burette is further inversely covered on the tail end of the hopper; the burette mouth is lower than the liquid level of the corrosive medium; a vacuumization operation is carried out inside the burette, and the solution in the burette is sucked to the highest scale of the burette; the burette is sealed; hydrogen gas, generated through the corrosion of the magnesium metal or magnesium alloy specimen, enters into the space above the liquid level of the burette in a bubble form through the hopper; an amount of the hydrogen gas generated on a unit surface area in unit corrosion time is read through the descending scale change of the liquid level; and the instantaneous corrosion rate or the average corrosion rate of magnesium metal or magnesium alloy on a certain moment is calculated.

Description

A method and special experimental device for measuring the corrosion rate of magnesium or magnesium alloy

technical field

The invention relates to a method and a special experimental device for measuring the corrosion rate of magnesium or magnesium alloys, which can conveniently calculate the corrosion rate of magnesium and magnesium alloys by collecting and measuring the amount and rate of hydrogen released during the corrosion process, and is suitable for magnesium and magnesium alloys. Corrosion Behavior of Magnesium Alloys.

Background technique

Magnesium is one of the lightest metals with a density of only 1.7g/cm ³ . Magnesium alloys have high specific stiffness and specific strength, so under the current international background of energy saving and consumption reduction, they are more and more used in automobile transportation, electronics, and aerospace industries. In addition, magnesium reserves are very abundant on the earth, the content in the earth's crust can account for about 2.7%, and the content in seawater is about 0.13%. China is one of the countries with the most abundant magnesium resources in the world, so the development of my country's magnesium industry has great potential and prospects. However, the chemical activity of magnesium determines that the corrosion resistance of magnesium is very poor. In various application environments, the application effect or life of magnesium alloys may be affected due to corrosion problems, and the application cost of magnesium alloys will be greatly increased. It is said that the corrosion problem is one of the key problems restricting the application of magnesium in various fields. Therefore, studying the corrosion resistance of magnesium alloys is a hot topic for material scientists today.

Corrosion rate is an important index to measure the corrosion resistance of materials. The corrosion rate of magnesium alloys is the main basis for evaluating the corrosion resistance of magnesium alloys, and it is also an indispensable data in the application design of magnesium alloys. Therefore, it is of great significance to measure the corrosion rate of magnesium alloys.

The weight loss method is currently the most commonly used method for determining the corrosion rate of magnesium alloys, that is, the magnesium alloy sample is soaked in the corrosive medium for a certain period of time, then taken out, and then the surface corrosion products are removed to measure the weight loss of the sample. Convert the sample weight loss rate ΔW (mg/cm ² /day) into the annual average corrosion rate P _W (mm/year):

P _W ＝2.10ΔW (1)

The weight loss method is generally considered to be the most basic and reliable corrosion rate evaluation method. Often used as a standard to measure the reliability of other measurement methods. However, the weightlessness method has the following disadvantages:

(1) The weight loss method can only measure the average corrosion rate during the entire immersion time, but cannot monitor the instantaneous and real-time corrosion rate during the immersion process, which is inconvenient to understand the corrosion process of magnesium alloys. For example, if one wants to understand the change of the corrosion rate of a magnesium alloy with the soaking time, multiple samples can only be soaked for different times. The influence of individual differences will affect the reliability of the experimental results.

(2) Due to the limitation of the change in weight caused by corrosion, the sensitivity is low when measuring a small amount of corrosion.

(3) Since the corrosion products need to be removed by the weight loss method, part of the uncorroded magnesium metal will inevitably be removed in the process of removing the corrosion products, thus affecting the reliability of the calculation of the corrosion rate.

Contents of the invention

The present invention aims to overcome the deficiencies in the prior art, and provides a method for measuring the corrosion rate of magnesium or magnesium alloys, which can not only obtain the average corrosion rate, but also monitor the instantaneous corrosion rate, and collect and measure the corrosion rate of magnesium alloys. The hydrogen release rate in the process is converted into an instantaneous corrosion rate, and more useful information in the corrosion process can be obtained, and the sensitivity is high.

Another object of the present invention is to provide a dedicated experimental device for determining the corrosion rate of magnesium or magnesium alloys.

The present invention realizes through following technical scheme:

A method for measuring the corrosion rate of magnesium or magnesium alloys is characterized in that it comprises the steps of: placing the funnel upside down in a container containing a corrosive medium, suspending a magnesium metal or magnesium alloy sample inside the funnel, and placing the funnel at the end of the funnel Then buckle a burette, the burette mouth is lower than the liquid level of the corrosive medium; vacuumize the inside of the burette and suck the solution to the highest mark of the burette, then seal the burette, and the hydrogen gas generated by the corrosion of the magnesium metal or magnesium alloy sample will be in the form of bubbles The form enters the space above the liquid level of the burette from the funnel, causing the liquid level in the burette to drop, and the unit surface area of the sample and the amount of hydrogen generated per unit corrosion time V _H are obtained through the scale change of the liquid level drop, and the calculation of magnesium metal or magnesium The instantaneous corrosion rate P _H of the alloy = 2.279 V _H or the average corrosion rate P _AH = 2.279 V _TH where: V _TH is the average hydrogen evolution rate.

A special experimental device used in the above method for measuring the corrosion rate of magnesium or magnesium alloy, characterized in that it is composed of a burette, a funnel and a corrosion liquid container, the corrosion liquid container has a funnel upside down, and the tail end of the funnel is reversed There is a burette, the sample is placed in an inverted funnel, and the mouth of the burette is lower than the liquid level of the corrosion solution in the beaker.

The present invention has following technical effect:

(1) The method of the present invention can not only obtain the average corrosion rate of magnesium metal or magnesium alloy within a period of corrosion immersion, but also can monitor the instantaneous corrosion rate, and can measure the relationship between the continuous corrosion amount and time on a sample The curve can obtain more useful information in the corrosion process.

(2) The method of the present invention obtains the corrosion rate by collecting and measuring the hydrogen release rate in the magnesium metal or magnesium alloy corrosion process, because the magnesium metal of the same amount of corrosion releases hydrogen in a relatively large volume, and the change in weight is relatively much smaller , Therefore, to measure the same tiny amount of corrosion, gas measuring is more sensitive than weighing.

(3) The method of the present invention will not be affected by the removal of corrosion products by collecting and measuring the release of hydrogen, and the calculation results are more reliable.

(4) The experimental device used in the method of the present invention has a simple structure, can collect all the hydrogen generated by the magnesium corrosion reaction without omission, and is easy to use.

Description of drawings

Fig. 1 is the schematic diagram that the present invention is used for measuring the special experimental device of magnesium or magnesium alloy corrosion rate;

Fig. 2 is a graph showing the relationship between the corrosion rate of magnesium metal and the corrosion time measured by the method of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is the schematic diagram that the present invention is used for measuring the special experimental device of magnesium or magnesium alloy corrosion rate, is made up of burette 1, funnel 2 and corrosion liquid container 4, and funnel 2 is arranged upside down in described corrosion liquid container 4, and the tail of described funnel There is a burette 1 reversed at the end, and the sample 3 is placed in an inverted funnel, and the mouth of the burette is lower than the liquid level of the corrosive solution in the corrosive liquid container to achieve liquid sealing. Beakers can be used for corrosive liquid containers.

The method for measuring the corrosion rate of magnesium or magnesium alloy of the present invention comprises the following steps: the funnel 2 is buckled upside down in the beaker that fills corrosive medium, magnesium metal or magnesium alloy sample 3 is suspended in funnel 2 inside with fishing line, funnel 2 At the end, buckle a burette 1 upside down. The mouth of the burette is lower than the liquid level of the corrosive solution in the beaker. According to the different corrosion properties of the sample, the burette can choose different volumes, such as 50ml or 100ml. Use an aspirator to evacuate the inside of the burette, and suck the solution to the highest mark of the burette, after that, seal the burette. The hydrogen gas produced by the corrosion of the magnesium metal or magnesium alloy sample enters the space above the liquid level of the burette from the funnel in the form of bubbles, and the hydrogen will replace part of the solution in the burette and cause the liquid level in the burette to drop. The amount of collected hydrogen can be directly reflected by the scale change through the drop of the liquid level in the burette. During the experiment, by recording the corrosion immersion time and the volume of hydrogen collected, the hydrogen release rate can be fitted to reflect the change of the corrosion rate of the magnesium sample with the corrosion immersion time, that is, the instantaneous rate during the magnesium corrosion process can be obtained. After the experiment, the total amount of hydrogen released per unit surface area of the sample can also be converted to obtain the average corrosion rate P _AH =2.279 _VH during the entire immersion period, where: V _TH is the average hydrogen evolution rate.

The method of the present invention measures the principle of magnesium corrosion as follows:

The overall reaction formula of known magnesium corrosion is:

Mg+2H ₂ O＝Mg ²⁺ +2(OH) ^- +H ₂ (2)

That is, every time a magnesium atom is dissolved, a hydrogen molecule will be produced. Therefore, by measuring the volume of hydrogen precipitated during the corrosion process, the amount of corroded magnesium metal should be known, and the instantaneous rate of magnesium metal corrosion can be known from the speed of hydrogen gas precipitation. speed. That is, the precipitation of 1 mol of hydrogen gas (equivalent to 22.4 liters under standard conditions) corresponds to almost 22.3 g of magnesium alloy, that is to say, the precipitation of hydrogen gas per milliliter is equivalent to the corrosion and dissolution of 1 mg of magnesium, so the weight loss rate ΔW (mg/Gm ² /day) and the hydrogen evolution rate V _H (ml/Gm ² /day) have the following relationship:

ΔW＝1.085V _H (3)

It can be seen that by collecting and measuring the hydrogen release rate during the corrosion process of magnesium alloys, the weight loss rate of magnesium metal can be obtained, and then the instantaneous rate of magnesium corrosion _PH can be obtained. Substituting formula (3) into formula (1), we get:

P _H =2.279V _H (4)

When the collected hydrogen exceeds the volume of the burette, the solution can be sucked up to the highest scale of the burette again by using the aspirator, and the measurement can be continued. For magnesium samples with different corrosion resistance, burettes of different thickness can also be selected to increase the sensitivity of the read data, that is, thick burettes can be used for fast corrosion rates, and thin burettes can be selected for slow corrosion rates.

Example 1

Put the funnel upside down in a container filled with 3.5% NaCl solution, hang the cast high-purity magnesium inside the funnel with a fishing line, and turn upside down a burette at the end of the funnel, the mouth of the burette is lower than the liquid level of the corrosive solution in the beaker. Vacuum the inside of the burette with an aspirator, and suck the solution to the highest mark of the burette. The hydrogen gas generated by the corrosion of the sample enters the space above the liquid level of the burette from the funnel in the form of bubbles, and the hydrogen will replace the burette in the burette. Part of the solution causes the liquid level in the burette to drop.

The corrosion immersion time and released hydrogen volume recorded during the experiment are shown in Table 1. The surface area of the sample is 3.73cm ² , and the total corrosion immersion time is 14 days, which can be obtained by converting the total amount of hydrogen released per unit surface area of the sample (21.7965ml/cm ² ) in Table 1 (336.8/24=14 days) The average corrosion rate P _AH =2.279V _TH =3.54mm/year. In addition, the relationship between corrosion rate and immersion time can also be monitored, as shown in Figure 2. It can be seen from the figure that the corrosion rate of the high-purity magnesium sample changes significantly with the length of corrosion immersion. In the initial stage of immersion (as shown in Figure 2, stage I), the corrosion rate is very slow. When the immersion time exceeds 24 hours, the corrosion rate accelerates sharply. (Stage II in Figure 2), after the immersion time was further extended to 170 hours, the corrosion rate slowed down again (Stage III in Figure 2). It can be seen that some information in the corrosion process of magnesium metal can be monitored by using this method, which is helpful for the study of the corrosion mechanism of magnesium metal. After the experiment, the average corrosion rate of the sample during this period can still be obtained by the weight loss method. The weight loss rate of the sample is known by weighing

ΔW=1.723 (mg/cm ² /day), calculated from the formula (1), it can be seen that P _W is 3.62mm/year, which is very consistent with the result of the hydrogen evolution of the present invention, thus also confirming the method of the present invention for the determination of magnesium metal Corrosion rate reliability.

Table 1

In order to verify the reliability of the method of the present invention to measure the corrosion rate of magnesium metal, we utilize the method of the present invention to test a series of different magnesium metal samples (pure magnesium Mg, AZ91D and ZE41), will utilize the total amount of hydrogen evolution to calculate The average corrosion rate P _H is compared with the average corrosion rate P _W obtained by the weight loss method, as shown in Table 2. It can be seen that the average corrosion rates obtained by the two methods agree very well, thus verifying that the method for measuring the corrosion rate of magnesium alloys of the present invention has high reliability.

Table 2

magnesium metal P _w (mm/year) P _H (mm/year) P _w /P _H Pure Mg 0.96 1.0 96% AZ91D 6.5 7.1 92% ZE41 13.1 14 94%

Claims (2)

1. a method of measuring magnesium or magnesium alloy corrosion rate is characterized in that, comprises the steps:

The funnel back-off in the container that fills corrosive medium, is hung on funnel inside with magnesium metal or magnesium alloy sample, and the funnel tail end is back-off one buret again, and the titration mouth of pipe is lower than the liquid level of corrosive medium; Buret inside is vacuumized and solution is drawn to the highest scale place of buret; Afterwards buret is sealed; The hydrogen that magnesium metal or magnesium alloy sample corrosion produce enters into the space on the buret meniscus with bubble form by funnel; Cause the liquid level in the buret to descend, the scale that descends through liquid level changes the amount V that draws sample per surface area and unit etching time generation hydrogen _H, calculate the instantaneous corrosion rate P of magnesium metal or magnesium alloy then _H=2.279V _HOr average corrosion rate P _AH=2.279V _TH, in the formula: V _THBe the average precipitation rate of hydrogen.

2. the employed special-purpose experimental provision of method of described mensuration magnesium of claim 1 or magnesium alloy corrosion rate; It is characterized in that; Be made up of buret, funnel and corrosive liquid container, being inverted in the said corrosive liquid container has funnel, and said funnel tail end back-off has buret; Sample is placed in the inverted funnel, and the titration mouth of pipe is lower than the liquid level of etchant solution in the beaker.

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