Preparation method of high-purity graphite powder auxiliary cathode briquette for glow discharge mass spectrometry test

Abstract

The invention relates to a preparation method of a high-purity graphite powder auxiliary cathode pressing block for glow discharge mass spectrometry test. According to the method, high-purity graphite powder is adopted as a matrix, a sample is efficiently, simply and rapidly prepared at low cost through two simple steps of sample loading and pressure applying, and compared with a traditional indium-assisted cathode determination method, the method is simple in sample preparation, low in cost, high in sample determination accuracy and safe in invented process and can be completed in the environment at normal temperature and normal pressure.

Description

Technical Field

[0001] The invention belongs to the field of measuring equipment, and in particular relates to a method for preparing a high-purity graphite powder auxiliary cathode compact for glow discharge mass spectrometry testing. Background Art

[0002] SiC particles are the main raw material for preparing silicon carbide crystals. They are mainly made by mixing carbon raw materials such as tar, anthracite, charcoal and silicon materials such as quartz sand and silica, and then sintering them at high temperature to obtain silicon carbide. SiC powder is obtained through processing, crushing, pickling, drying and other methods. It is widely used in refractory materials, abrasives and semiconductor fields.

[0003] With the increasing requirements for test accuracy of SiC powder in some demanding application scenarios, the existing chemical analysis can no longer meet the test needs. Glow discharge mass spectrometry (GDMS) shows great advantages in the determination of silicon carbide powder. Its detection concentration can reach ng / g, which meets the test needs. It also has the advantages of high sensitivity, high detection accuracy, short detection time, and high efficiency. The principle is to use the sample to be tested as the cathode material, use glow discharge to ionize the low-pressure inert gas, and bombard the cathode with positive ions under the action of the electric field, so that the sample to be tested is sputtered into the plasma and further ionized. According to the mass-to-charge ratio of different elements and the difference in response signals, the sample to be tested can be qualitatively and quantitatively analyzed. Since glow discharge mass spectrometry is a method for direct analysis of solid samples, it tests the surface composition of the sample, and the shape and size of the sample will affect the strength of the response signal. Therefore, the sample is required to have a regular shape, a flat surface, and the area of ​​the sample to be tested is larger than the sputtering hole.

[0004] As an impurity element that often appears in SiC powder, W has a great influence on the parameters of subsequent SiC crystal growth or processing technology. Accurately determining the W content in SiC can provide guidance for the entire process of SiC. However, for SiC, the GDMS method cannot directly analyze non-conductor samples. Appropriate pre-treatment techniques are required to make the samples conductive before they can be measured, such as the second cathode method, mixing method, penetration method, high-purity indium pressing method, and high-purity indium covering method. The commonly used measurement method is the indium-assisted cathode test method, but high-purity indium is expensive, there is waste liquid pollution in the pickling of indium sheets, and the sample preparation is complicated, resulting in high testing costs.

[0005] Therefore, in order to promote the development and application of GDMS testing of SiC powder, it is of great significance to develop a new type of auxiliary cathode with high efficiency and low cost for the testing method. Summary of the invention

[0006] In view of the shortcomings of the prior art, especially the problems that the high-purity indium pressing method in the existing glow discharge mass spectrometry is expensive, the sample preparation is complicated, and the detection cost is high, the present invention provides a method for preparing a high-purity graphite powder auxiliary cathode pressing block for glow discharge mass spectrometry testing.

[0007] The high-purity graphite powder-assisted cathode compact prepared by the present invention can conveniently, efficiently, low-cost and more accurately test the W element in silicon carbide powder.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing a high-purity graphite powder-assisted cathode compact for glow discharge mass spectrometry testing comprises the following steps:

[0010] 1) After the briquetting mold is cleaned and dried, a filter membrane is added to the mold, and high-purity graphite powder is placed in the briquetting mold to serve as a conductive matrix;

[0011] 2) Slowly adding SiC particles to the central area of ​​the graphite powder surface layer, and then covering the top layer with a filter membrane; manually pressurizing the compacting mold to obtain a high-purity graphite powder-assisted cathode compact.

[0012] Preferably according to the present invention, in step 1), the briquetting mold is cleaned by using ultrapure water, and the resistivity of the ultrapure water is greater than or equal to 18 MΩ·cm.

[0013] Preferably according to the present invention, in step 1), the briquetting mold is a manual briquetting mold, weighing 30-50 kg, and the mold is a stainless steel mold.

[0014] Preferably according to the present invention, in step 1), the charging cavity of the briquetting mold is cylindrical.

[0015] Preferably according to the present invention, in step 1), the filter membrane is a microporous filter membrane with a diameter of 20-30 mm and a pore size of 0.45 um, and the number of layers of the filter membrane is 2-4.

[0016] Preferably according to the present invention, in step 1), the amount of graphite powder added is 3-9 g.

[0017] Preferably according to the present invention, in step 2), the particle size of the SiC particles is 0.5-5 mm.

[0018] According to the preferred embodiment of the present invention, in step 2), the contact area between the added SiC particles and the graphite powder is 16-64 mm 2 .

[0019] Preferably according to the present invention, in step 2), SiC particles are added using weighing paper.

[0020] Preferably according to the present invention, in step 2), the filter membrane is a microporous filter membrane with a diameter of 20-30 mm, a pore size of 0.45 um, and 3-5 layers.

[0021] Preferably according to the present invention, in step 2), the pressure applied is 10-25 MPa.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The invention provides a method for preparing a high-purity graphite powder-assisted cathode compact suitable for glow discharge mass spectrometry testing, which uses high-purity graphite powder as a matrix, and prepares samples in two simple steps of sample loading and pressure application, with high efficiency, low cost, and simple and fast preparation. Compared with the traditional indium-assisted cathode test W, the high-purity graphite powder-assisted cathode compact of the invention is simple, efficient, low-cost, and has a safe preparation process, and can be completed in an environment at normal temperature and pressure, thereby making the measurement process simple and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the surface morphology of the high-purity graphite powder-assisted cathode compact;

[0025] Figure 2 This is a schematic diagram of the briquetting mold structure; 1. SiC particles, 2. high-purity graphite powder, 3. loading cavity, 4. mold base, 5. pressurized column. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0027] In order to realize the test of SiC particles of non-conductive material, the present invention provides a method for preparing a high-purity graphite powder-assisted cathode compact suitable for glow discharge mass spectrometry testing, that is, high-purity graphite powder is used as a matrix to assist SiC particles in conducting electricity, and a glow discharge mass spectrometry compact method is used to test the W element, so as to accurately obtain the result of DC-GDMS determination of the impurity element content.

[0028] The present invention provides a method for preparing a high-purity graphite powder auxiliary cathode compact suitable for glow discharge mass spectrometry testing, comprising the following steps:

[0029] 1) After the briquetting mold is cleaned and dried, a filter membrane is added to the mold, and high-purity graphite powder is placed in the briquetting mold to serve as a conductive matrix;

[0030] 2) Slowly adding SiC particles to the central area of ​​the graphite powder surface layer, and then covering the top layer with a filter membrane; manually pressurizing the compacting mold to obtain a high-purity graphite powder-assisted cathode compact.

[0031] In step 1), the briquetting mold is cleaned by using ultrapure water, and the resistivity of the ultrapure water is greater than or equal to 18 MΩ·cm.

[0032] In step 1), the briquetting mold is a manual briquetting mold, weighing 30-50 kg, and the mold is a stainless steel mold.

[0033] In step 1), the filter membrane is a microporous filter membrane with a diameter of 20-30 mm, a pore size of 0.45 um, and 2-4 layers.

[0034] In step 1), the amount of graphite powder used is 3-9g.

[0035] In step 2), the particle size of SiC particles is 0.5-5 mm.

[0036] In step 2), the contact area between the added SiC particles and the graphite powder is 16-64 mm 2 .

[0037] In step 2), SiC particles are added using weighing paper.

[0038] In step 2), the filter membrane is a microporous filter membrane with a diameter of 20-30 mm, a pore size of 0.45 um, and 3-5 layers.

[0039] In step 2), the applied pressure is 10-25 MPa.

[0040] Example 1

[0041] A method for preparing a high-purity graphite powder-assisted cathode compact for glow discharge mass spectrometry testing, comprising the following steps:

[0042] (1) Preliminary preparation

[0043] The briquetting mold was washed three times with ultrapure water and dried, two layers of filter membrane were added to the mold loading cavity, and then 5 g of high-purity graphite powder was added using a medicine spoon folded from weighing paper;

[0044] (2) Sample preparation

[0045] On the surface of high-purity graphite powder 20mm 2 SiC particles with a diameter of 0.5 mm are slowly added to the central area to contact the graphite powder, and then three layers of filter membranes are covered on the surface of the SiC particles. Then, a pressure of 20 MPa is applied to the mold to obtain a high-purity graphite powder-assisted cathode compact.

[0046] The sample was placed in a flat sample holder, cooled, and then the glow discharge was turned on. The appropriate peak shape and resolution were tuned to test the graphite powder-based silicon carbide powder block. The W content value was stable and similar to the result of the traditional indium-assisted cathode test method. The glow parameters are as follows: discharge current 1.5mA, discharge voltage 950-1050V, glow discharge GDMS instrument is Nu Astrum model, and the test resolution is 4000.

[0047] Example 2

[0048] A method for preparing a high-purity graphite powder-assisted cathode compact for glow discharge mass spectrometry testing, comprising the following steps:

[0049] (1) Preliminary preparation

[0050] The briquetting mold was washed three times with ultrapure water and dried, two layers of filter membrane were added to the mold loading cavity, and then 4 g of high-purity graphite powder was added using a medicine spoon folded from weighing paper;

[0051] (2) Sample preparation

[0052] On the surface of graphite powder 30mm 2 SiC particles with a diameter of 1 mm are slowly placed in the central area to contact the graphite powder, three layers of filter membranes are covered on the surface of the SiC powder, and then a pressure of 15-20 MPa is applied to the mold to obtain a high-purity graphite powder auxiliary cathode compact.

[0053] The sample was placed in a flat sample holder, cooled, and then the glow discharge was turned on. The appropriate peak shape and resolution were tuned to test the graphite-based silicon carbide powder block. The glow parameters were as follows: discharge current 1.5 mA, discharge voltage 950-1050 V, and the W content value was stable. The W content value was similar to the result of the traditional indium-assisted cathode test method. The glow discharge GDMS instrument was a Nu Astrum model with a test resolution of 4000.

[0054] Example 3

[0055] A method for preparing a high-purity graphite powder-assisted cathode compact for glow discharge mass spectrometry testing, comprising the following steps:

[0056] (1) Preliminary preparation

[0057] The briquetting mold was washed three times with ultrapure water and dried, two layers of filter membrane were added to the mold loading cavity, and then 5 g of high-purity graphite powder was added using a medicine spoon folded from weighing paper;

[0058] (2) Sample preparation

[0059] On the graphite powder surface 40mm 2SiC particles with a diameter of 2 mm are slowly placed in the central area to contact the graphite powder, 4 layers of filter membranes are covered on the surface of the SiC powder, and then a pressure of 15-20 MPa is applied to the mold to obtain a high-purity graphite powder auxiliary cathode compact.

[0060] The sample was placed in a flat sample holder, cooled, and then the glow discharge was turned on. The appropriate peak shape and resolution were tuned to test the graphite-based silicon carbide powder block. The glow parameters were as follows: discharge current 1.5 mA, discharge voltage 1050 V, and the W content value was similar to the result of the traditional indium-assisted cathode test method. The glow discharge GDMS instrument was a Nu Astrum model with a test resolution of 4000.

[0061] Example 4

[0062] A method for preparing a high-purity graphite powder-assisted cathode compact for glow discharge mass spectrometry testing, comprising the following steps:

[0063] (1) Preliminary preparation

[0064] The briquetting mold was washed 3 times with ultrapure water and dried, 5 layers of filter membrane were added to the mold loading cavity, and then 7g of high-purity graphite powder was added using a medicine spoon folded from weighing paper;

[0065] (2) Sample preparation

[0066] 50mm on the surface of graphite powder 2 SiC particles with a diameter of 4 mm are slowly placed in the central area to contact the graphite powder, 5 layers of filter membrane are covered on the surface of the SiC powder, and then a pressure of 10-15 MPa is applied to the mold to obtain a high-purity graphite powder auxiliary cathode compact.

[0067] The sample was placed in a flat sample holder, cooled, and then the glow discharge was turned on. The appropriate peak shape and resolution were tuned to test the graphite-based silicon carbide powder block. The glow parameters were as follows: discharge current 2.5 mA, discharge voltage 1100 V, and the W content value was stable. The W content value was similar to the result of the traditional indium-assisted cathode test method. The glow discharge GDMS instrument was a Nu Astrum model with a test resolution of 4000.

[0068] Experimental example:

[0069] The high-purity graphite powder-assisted cathode compact of Example 1 was used to perform a glow discharge mass spectrometry GDMS test, and compared with a conventional indium-assisted cathode test. The test was performed six times in parallel, the average of the six tests was taken, and the RSD was calculated. The results are shown in Table 1.

[0070] Table 1 Comparison of the test results of high-purity graphite powder auxiliary cathode compact and indium auxiliary cathode

[0071]

[0072] It can be seen from Table 1 that the W content value determined by the glow discharge mass spectrometry GDMS test using the high-purity graphite powder-assisted cathode compact of Example 1 is similar to the result of the traditional indium-assisted cathode test method.

Claims

1. A method for preparing a high-purity graphite powder-assisted cathode compact for glow discharge mass spectrometry testing, comprising the following steps: 1) After the briquetting mold is cleaned and dried, a filter membrane is added to the mold, and high-purity graphite powder is placed in the briquetting mold to serve as a conductive matrix; 2) Slowly adding SiC particles to the central area of ​​the graphite powder surface layer, and then covering the top layer with a filter membrane; manually pressurizing the compacting mold to obtain a high-purity graphite powder-assisted cathode compact.

2. The preparation method according to claim 1, characterized in that: In step 1), the briquetting mold is cleaned by using ultrapure water, and the resistivity of the ultrapure water is greater than or equal to 18 MΩ·cm.

3. The preparation method according to claim 1, characterized in that: In step 1), the briquetting mold is a manual briquetting mold, weighing 30-50 kg, and the mold is a stainless steel mold.

4. The preparation method according to claim 1, characterized in that: In step 1), the charging cavity of the briquetting mold is cylindrical.

5. The preparation method according to claim 1, characterized in that: In step 1), the filter membrane is a microporous filter membrane with a diameter of 20-30 mm and a pore size of 0.45 um, and the number of layers of the filter membrane is 2-4.

6. The preparation method according to claim 1, characterized in that: In step 1), the amount of graphite powder added is 3-9g.

7. The preparation method according to claim 1, characterized in that: In step 2), the particle size of SiC particles is 0.5-5 mm.

8. The preparation method according to claim 1, characterized in that: In step 2), the contact area between the added SiC particles and the graphite powder is 16-64 mm 2 .

9. The preparation method according to claim 1, characterized in that: In step 2), the filter membrane is a microporous filter membrane with a diameter of 20-30 mm, a pore size of 0.45 um, and 3-5 layers.

10. The preparation method according to claim 1, characterized in that: In step 2), the applied pressure is 10-25 MPa.

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