A method for displaying the metallographic structure of platinum

Abstract

The present invention relates to the field of metal material microstructure analysis, and in particular to a method for displaying the metallographic structure of platinum, comprising the following steps: taking a cubic platinum sample, selecting one of the surfaces as a metallographic observation surface to inlay and fix the platinum sample, so that the metallographic observation surface of the platinum sample is closely attached to the bottom of the inlay mold; taking out the inlaid platinum sample from the inlay mold, and grinding the metallographic observation surface of the platinum sample, and then polishing until there are no obvious scratches and contamination points on the metallographic observation surface; the polished platinum sample is used as a positive electrode, and a graphite rod is used as a negative electrode, and is placed in a corrosion solution composed of water, concentrated hydrochloric acid, and hydrogen peroxide, and a direct current is used for corrosion for 2min to 10min to obtain a sample displaying the metallographic structure of platinum. The present invention is simple to operate, highly efficient, and has low requirements on operators, and the test results have good repeatability and high reliability, and are very suitable for the preparation of platinum metallographic phases in general laboratories. Since no aqua regia and potassium cyanide are used, harm to the human body and pollution to the environment are also avoided.

Description

Technical Field

[0001] The invention relates to the field of metal material microstructure analysis, and in particular to a method for displaying the metallographic structure of platinum. Background Art

[0002] The microstructure of metal materials determines the performance of the metal materials. By observing the microstructure of metal materials, we can analyze the relationship between the microstructure of metal materials and their processing technology, judge the quality of metal materials, adjust the heat treatment process, and optimize product performance. Therefore, whether the metallographic structure of platinum can be clearly prepared becomes the basis for studying platinum.

[0003] Platinum metal has the advantages of high melting point, strong corrosion resistance and good thermoelectric properties, and is often used as a high-temperature temperature measurement material. Due to the strong corrosion resistance of platinum metal, usually only the use of aqua regia with a higher temperature can accelerate the corrosion of platinum metal, so the metallographic corrosion of platinum metal is a difficult point in the metallographic preparation process.

[0004] "Metallographic Sample Preparation and Display Technology" (Han Dewei, Zhang Jianxin. Metallographic Sample Preparation and Display Technology [M]. Central South University Press, 2014.05.01) records two chemical etching methods in the prior art as follows:

[0005] ① Use aqua regia to metallographically corrode platinum. It is difficult to ensure that the metallographic structure of the corrosion is clear and reliable during the corrosion process. Aqua regia will volatilize corrosive gases at room temperature. The volatilization speed is significantly accelerated at high temperature. The volatile gases are harmful to the human body. When using it, you need to wear a mask and equip it with exhaust ventilation devices;

[0006] ② Potassium cyanide is used to perform metallographic corrosion on platinum. However, potassium cyanide is highly toxic and poses a great hazard to operators, so it is generally not considered for use.

[0007] In addition, "Metallographic Specimen Preparation and Display Technology" also records the use of alternating current for electrochemical corrosion, but the AC power supply requires the configuration of a transformer and a voltage regulator, which are large equipment, take a long time to corrode, and have high requirements for operators.

[0008] Therefore, there is currently no method that can quickly, stably and simply corrode metal platinum. Although "Metallographic Specimen Preparation and Display Technology" gives a rough introduction to existing metallographic corrosion methods for platinum, it does not involve the specific content of metallographic corrosion of platinum. Technical personnel in this field cannot implement it according to the above method.

[0009] Patent CN107478481A discloses a method for observing the metallographic structure of platinum-rhodium alloys. A polished platinum-rhodium alloy sample is placed in a mixed solution container containing concentrated nitric acid, concentrated hydrochloric acid, sodium chloride and water. The corrosion solution is heated to 110°C in a fume hood, and the platinum-rhodium alloy sample needs to be taken out for observation every 30 seconds. Although this method can be used in the process of metal corrosion of metal platinum, its disadvantages are also very prominent: 1) Concentrated nitric acid and concentrated hydrochloric acid heated to 110°C volatilize severely, producing a large amount of toxic and polluting gases; 2) The solution concentration is constantly changing during the corrosion process, and it is not easy to control the corrosion rate; 3) Special corrosion containers are required, which is not suitable for promotion in laboratories.

[0010] In summary, how to safely, quickly, stably and simply use metal corrosion methods to prepare the metallographic structure of metal platinum and improve scientific research efficiency is a problem that needs to be solved urgently. Summary of the invention

[0011] The purpose of the present invention is to provide a method for displaying the metallographic structure of platinum in view of the corresponding deficiencies of the prior art. The method adopts a platinum sample as a positive electrode and a graphite rod as a negative electrode, and puts a corrosive solution composed of water, concentrated hydrochloric acid and hydrogen peroxide into the solution and passes direct current for electrochemical corrosion. The method has the advantages of simple operation, high efficiency and low requirements for operators, and the test results have good repeatability and high reliability. The method is very suitable for the preparation of platinum metallographic structure in general laboratories. Since aqua regia and potassium cyanide are not used, harm to human body and pollution to the environment are also avoided.

[0012] The objective of the present invention is achieved by adopting the following scheme:

[0013] A method for displaying the metallographic structure of platinum comprises the following steps:

[0014] 1) Inlay:

[0015] Mounting and fixing the platinum sample so that the observation surface of the platinum sample is in close contact with the bottom of the mounting mold;

[0016] 2) Grinding and polishing:

[0017] Grind the observation surface of the platinum sample and then polish it until there are no obvious scratches or contamination spots on the observation surface;

[0018] 3) Corrosion of platinum specimens:

[0019] The polished platinum sample is used as the positive electrode and the graphite rod is used as the negative electrode. They are placed in a corrosion solution composed of water, concentrated hydrochloric acid and hydrogen peroxide and are electrically corroded for 2 minutes to 10 minutes to obtain a sample showing the metallographic structure of platinum.

[0020] Preferably, the grinding in step 2) is performed by a grinder at a rotation speed of 250 r / min to 600 r / min, and 400#, 800#, and 1000# metallographic sandpapers are used in sequence, and the grinding direction forms 90° with the scratch direction during grinding.

[0021] Preferably, in step 2), polishing is performed using a polishing machine with a rotation speed of 250 r / min to 1000 r / min.

[0022] Preferably, in step 2), water is used as a polishing agent, the polishing paste is a diamond grinding paste, the polishing direction forms a 90° angle with the direction of the old scratches, and the polishing surface is cleaned with anhydrous ethanol until there are no obvious scratches and contamination points on the observation surface.

[0023] Preferably, the mass concentration of concentrated hydrochloric acid in the etching solution in step 3) is 36% to 38%, and the mass concentration of hydrogen peroxide is 30%.

[0024] Preferably, in step 3), the volume ratio of water: concentrated hydrochloric acid: hydrogen peroxide is 2-9:10-14:1-4.

[0025] Preferably, in step 3), a direct current power supply is used for electrical corrosion.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The etching solution of the present invention is made by mixing water, concentrated hydrochloric acid and hydrogen peroxide, and does not use aqua regia and potassium cyanide, thereby avoiding harm to the human body and pollution to the environment. The hydrochloric acid in the etching solution provides a large amount of chloride ions and an acidic environment. Chloride ions can form complex ions with metal cations, reducing the enrichment of platinum ions on the surface of the platinum sample; hydrogen peroxide is called a "green oxidant", and the oxidation product is water green and pollution-free. In addition, under the oxidation action of hydrogen peroxide, chloride ions can form complex ions with metal ions. Hydrogen peroxide reduces the electrode potential of the metal to a certain extent, helps dissolve the metal, and improves the corrosion efficiency.

[0028] 2. The present invention adopts an electrolytic corrosion method to prepare the metallographic structure of platinum, the purpose of which is to provide an external current to force the metal to lose electrons and show the metallographic structure. The corrosion process only needs to adjust the current and voltage to control the corrosion rate, making the corrosion process stable and reliable.

[0029] 3. The present invention adopts electrochemical corrosion method to carry out metallographic corrosion on platinum samples, which has the advantages of obvious effect, fast speed, stable corrosion process, simple method, simple power supply equipment, safe power supply voltage, low technical requirements for operators, high repeatability, etc. It is easy to promote and is suitable for the preparation of platinum metallographic phase in general laboratories. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1The metallographic structure diagram of platinum in the embodiment of the present invention;

[0031] Figure 2 This is the metallographic structure of platinum after conventional chemical etching. DETAILED DESCRIPTION

[0032] A method for displaying the metallographic structure of platinum comprises the following steps:

[0033] 1) Inlay

[0034] Take a cubic platinum sample, select the metallographic observation surface of the platinum sample, and mount and fix the platinum sample so that the metallographic observation surface of the platinum sample is closely attached to the bottom of the metallographic soft glue mounting mold;

[0035] 2) Grinding and polishing

[0036] Take out the mounted platinum sample from the metallographic soft glue mounting mold, and use a metallographic grinder to grind the metallographic observation surface of the platinum sample. During the grinding process, the speed of the metallographic grinder is 250 r / min~600 r / min, and 400#, 800#, and 1000# metallographic sandpapers are used for grinding in turn. During the grinding process, the grinding direction forms 90° with the direction of the old scratches. It is particularly important to note that once the wear marks produced by the metallographic sandpaper used for this grinding are completely eliminated, immediately replace it with a larger type of metallographic sandpaper used for the next grinding.

[0037] For example, when the wear marks produced by the 400# metallographic sandpaper are completely eliminated, it is necessary to immediately replace it with the 800# metallographic sandpaper to continue grinding, and so on until the grinding process is completed.

[0038] After the grinding process is completed, the metallographic observation surface is polished with a polishing machine with a rotation speed of 250 r / min to 1000 r / min until there are no obvious scratches and contamination points on the metallographic observation surface;

[0039] It is particularly important to note that when polishing the metallographic observation surface, the polishing agent is water, the polishing paste is diamond grinding paste, the polishing direction forms a 90° angle with the scratch direction, and there are no obvious scratches or contamination points on the observation surface. The polished surface is cleaned with anhydrous ethanol.

[0040] 3) Corrosion of platinum samples

[0041] The polished platinum sample is used as the positive electrode and the graphite rod is used as the negative electrode. They are placed in a corrosion solution composed of water, concentrated hydrochloric acid and hydrogen peroxide and are corroded by direct current for 2 minutes to 10 minutes to obtain a sample showing the metallographic structure of platinum.

[0042] The mass concentration of concentrated hydrochloric acid in the etching solution is 36% to 38%, and the mass concentration of hydrogen peroxide is 30%.

[0043] The volume ratio of water: concentrated hydrochloric acid: hydrogen peroxide is 2-9:10-14:1-4.

[0044] According to the above method, a sample showing the metallographic structure of platinum was prepared:

[0045] Step 1. Inlay of metal platinum samples: Use a shearing machine to cut a metal platinum sample with a size of 5mm×5mm×1mm from a metal platinum sheet, select a 5mm×5mm flat surface as the metallographic observation surface, and inlay the sample using a metallographic soft glue inlay mold. The specific process is: place the cut metal platinum sample in the inlay mold, and the metallographic observation plane of the platinum sample is close to the inlay mold, and then pour a mixed solution of epoxy resin or acrylic mounting resin and curing agent into the inlay mold, and cool it naturally for 10 minutes until the cold mounting material solidifies to obtain a mounted platinum sample.

[0046] Step 2, polishing of the platinum sample: Use metallographic sandpaper to polish the metallographic observation plane of the mounted platinum sample described in step 1. The model of the grinder is: MP-2B grinding and polishing machine, with a diameter of 220mm and a rotation speed of 250r / min~600r / min. During the polishing process, 400#, 800#, and 1000# metallographic sandpapers are used for polishing in sequence. During the polishing process, attention should be paid to the polishing direction and force control. When the previous wear mark is completely eliminated, immediately replace it with a finer sandpaper for the next polishing, and the grinding direction forms 90° with the old scratch direction. After polishing, the metallographic observation surface of the platinum sample is rinsed with water.

[0047] Step 3, polishing of the platinum sample: use an MP-2B grinding and polishing machine to mechanically polish the metallographic observation surface of the platinum sample after grinding in step 2. The speed of the polishing machine is 250 r / min~1000r / min, the polishing agent is tap water, and the polishing paste is diamond grinding paste. The polishing process uses W5 and W2.5 polishing pastes for polishing in turn. The polishing cloth is velvet. During the polishing process, the polishing direction forms a 90° angle with the direction of the old scratches until no obvious scratches and contamination points are seen on the observation surface under a 100x metallographic microscope. Then, the polished surface of the platinum sample is rinsed with anhydrous ethanol and blown dry.

[0048] Step 4: Corrosion of platinum sample:

[0049] Add water, concentrated hydrochloric acid with a mass concentration of 36% to 38%, and hydrogen peroxide with a mass concentration of 30% into a beaker in sequence, stir and let stand to obtain a corrosion solution with a volume ratio of water: concentrated hydrochloric acid: hydrogen peroxide of 2 to 9: 10 to 14: 1 to 4.

[0050] Use enameled copper wire to connect the platinum sample after mechanical polishing in step 3 to the positive pole of the DC power supply model APS3005D, and connect the negative pole of the DC power supply to the graphite rod. Then insert the platinum sample and the graphite rod into the beaker filled with etching solution respectively. Note that short circuit must not be caused by contact, and the etching solution needs to immerse the corrosion surface of the sample, and the graphite rod only needs to be inserted about 10mm below the etching solution surface.

[0051] Turn on the power supply and adjust the voltage to 6V~30V. A large number of bubbles will be generated on the corrosion surface. The corrosion time is 2min~10min. After the corrosion is completed, take out the platinum sample with plastic tweezers, rinse it with water, rinse the metallographic observation surface with anhydrous ethanol and blow it dry. Place it under a metallographic microscope and observe the metallographic structure of the platinum sample, such as Figure 1 shown.

[0052] The specific method of using conventional chemical corrosion metal platinum is as follows:

[0053] According to the above steps 1 and 2, prepare the platinum sample to be corroded, and immerse the platinum sample completely in a beaker filled with aqua regia (the volume ratio of concentrated hydrochloric acid to concentrated nitric acid is 1:3), let it stand for 100 minutes, and obtain the metallographic structure of platinum after conventional chemical etching, as shown in Figure 1. Figure 2 shown.

[0054] Will Figure 2 and Figure 1 By comparison, it can be seen that the metallographic structure of the metal platinum after conventional chemical etching is relatively rough, and the corrosion degree between the grains varies greatly. The metallographic structure of the metal platinum prepared by the electrochemical etching method of the present invention is relatively uniform, and the grain boundaries are obvious.

[0055] Moreover, when comparing the corrosion time, the electrochemical corrosion of the present invention only takes 4 minutes, while the conventional chemical corrosion takes 100 minutes. Obviously, the electrochemical corrosion speed of the present invention is faster and the corrosion process is easier to control.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for displaying the metallographic structure of platinum, characterized in that: The following steps are involved: 1) Inlay: Take a cubic platinum sample, select the metallographic observation surface of the platinum sample, and mount and fix the platinum sample so that the metallographic observation surface of the platinum sample is closely attached to the bottom of the metallographic soft glue mounting mold; 2) Grinding and polishing: The metallographic observation surface of the platinum sample in step 1) is polished with metallographic sandpaper, and the model of the polishing machine is MP-2B grinding and polishing machine, with a diameter of 220 mm and a rotation speed of 250 r / min to 600 r / min; 400#, 800#, and 1000# metallographic sandpapers are used in turn during the polishing process. When the previous scratch is completely eliminated, a finer sandpaper is immediately replaced for the next polishing, and the grinding direction forms 90° with the direction of the old scratch. After the polishing is completed, the metallographic observation surface of the platinum sample is rinsed with water; Then, the metallographic observation surface of the polished platinum sample was mechanically polished by using an MP-2B grinding and polishing machine, the speed of the polishing machine was 250 r / min to 1000 r / min, the polishing agent was tap water, the polishing paste was diamond grinding paste, the polishing process was polished by using W5 and W2.5 polishing pastes in turn, the polishing cloth was brocade, and the polishing direction formed 90° with the old scratch direction during the polishing process, until no obvious scratches and contamination points were seen on the observation surface under a 100x metallographic microscope, and then the polished surface of the platinum sample was rinsed with anhydrous ethanol and blown dry; 3) Corrosion of platinum specimens: The polished platinum sample is used as the positive electrode, and the graphite rod is used as the negative electrode. They are placed in a corrosion solution composed of water, concentrated hydrochloric acid, and hydrogen peroxide, so that the corrosion solution immerses the corrosion surface of the sample, and the graphite rod is inserted about 10 mm below the corrosion liquid surface, and the voltage is adjusted to 6V to 30V. A DC power supply is used to energize and corrode for 2min to 10min. After the corrosion is completed, the platinum sample is taken out with plastic tweezers, rinsed with water, and the metallographic observation surface is rinsed with anhydrous ethanol and blown dry to obtain a sample showing the metallographic structure of platinum; The mass concentration of concentrated hydrochloric acid in the etching solution is 36% to 38%, the mass concentration of hydrogen peroxide is 30%, and the volume ratio of water: concentrated hydrochloric acid: hydrogen peroxide in the etching solution is 2 to 9: 10 to 14: 1 to 4.

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