Preparation method of microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry test

Abstract

The invention relates to a preparation method of a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry test, high-purity graphite powder is used as a conductive substrate, microcrystalline cellulose is mixed to improve the cohesiveness of the graphite felt, and the sample can be simply and quickly prepared. Meanwhile, compared with a traditional indium auxiliary cathode test result, the sample matrix is high in strength, good in stability and low in sample preparation cost. The preparation process is safe and can be completed in a normal-temperature and normal-pressure environment.

Description

Technical Field

[0001] The invention belongs to the field of measuring equipment, and in particular relates to a method for preparing a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry testing. Background Art

[0002] Graphite felt is made by treating carbon felt at temperatures exceeding 2000°C under vacuum or inert atmosphere. It is widely used in single crystal growth, clean energy, electronics, and other fields. With the development of wide-bandgap semiconductor materials, graphite felt plays a key role in the physical vapor transport growth of silicon carbide crystals. Its primary functions are to maintain a uniform temperature field, reduce heat loss, minimize external contamination, and provide support. Therefore, extremely high purity is required. Currently, the main techniques for testing graphite felt purity include ash combustion, plasma-coupled plasma mass spectrometry (ICP-MS), and high-resolution fluorescence density mass spectrometry (GDMS). While ash combustion equipment is simple and easy to operate, it suffers from low accuracy and large variance. ICP-MS offers high precision, but sample preparation is difficult due to graphite felt's resistance to acid and alkali corrosion. GDMS testing offers significant advantages for graphite felt testing. GDMS equipment offers a wide linear detection range, high sensitivity, and high accuracy, with a detection limit of up to 0.01 μg / g.

[0003] Although graphite felt is conductive, it's difficult to directly prepare flat or pin-shaped samples for GDMS testing. Currently, GDMS testing of graphite felt primarily uses the indium sheet cathode-assisted method. This complex sample preparation process requires contact with strong acids, and the substrate has low strength, resulting in poor test stability. Furthermore, the high price of high-purity indium cathodes contributes to high testing costs.

[0004] Therefore, in order to promote the practical application of GDMS testing of graphite felt, it is particularly important to develop a low-cost, cathode-free and efficient sample preparation method. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, especially the problems that the existing test method of graphite felt in glow discharge mass spectrometry requires indium sheet cathode assistance, the sample preparation process is complicated, strong acid contact is required, the matrix strength is low, and the test stability is poor, the present invention provides a method for preparing microcrystalline cellulose-high-purity graphite powder-based graphite felt samples suitable for glow discharge mass spectrometry testing.

[0006] In order to achieve the above object, the technical solution adopted in the present invention is:

[0007] A method for preparing a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry testing comprises the following steps:

[0008] 1) After cleaning and drying the mold, the filter membrane is placed. High-purity graphite powder is first added to the mold to serve as a conductive matrix, and then a mixed powder of microcrystalline cellulose and high-purity graphite powder is added;

[0009] 2) Clamp the graphite felt fiber and place it on the mixed powder to fill the inner diameter of the mold, then cover it with a filter membrane, and pressurize the mold with a briquetting machine to obtain a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample.

[0010] According to a preferred embodiment of the present invention, in step 1), the mold is made of stainless steel and has an inner diameter of 20-30 mm.

[0011] According to the preferred embodiment of the present invention, in step 1), the mold is cleaned using ultrapure water, and the resistivity of the ultrapure water is greater than or equal to 18 MΩ*cm.

[0012] According to the preferred embodiment of the present invention, in step 1), the filter membrane is a microporous filter membrane with a diameter of 20-30 mm, a pore size of 0.45 μm, and 2-4 layers.

[0013] According to the preferred embodiment of the present invention, in step 1), the microcrystalline cellulose is purified by column chromatography in accordance with Q / CYDZ 2320-2009, and the high-purity graphite powder is grade 7N with a purity greater than 99.99999%.

[0014] According to the preferred embodiment of the present invention, in step 1), the amount of high-purity graphite powder used in the bottom layer is 1-5 g.

[0015] Preferably, according to the present invention, in step 1), the weight ratio of microcrystalline cellulose to high-purity graphite powder in the mixed powder of microcrystalline cellulose and high-purity graphite powder is 0.8-1.2:1.

[0016] Preferably, according to the present invention, in step 1), the amount of high-purity graphite powder in the mixed powder of microcrystalline cellulose and high-purity graphite powder is 2-4 g.

[0017] According to a preferred embodiment of the present invention, in step 2), the graphite felt fibers are clamped using tweezers made of polytetrafluoroethylene.

[0018] Preferably according to the present invention, in step 2), the length of the graphite felt fibers is 4-10 mm.

[0019] According to the preferred embodiment of 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 μm, and 2-4 covering layers.

[0020] According to the present invention, preferably, in step 2), the briquetting machine is a manual briquetting machine, and the applied pressure is 5-15 MPa.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention relates to a method for preparing microcrystalline cellulose-high-purity graphite powder-based graphite felt samples suitable for glow discharge mass spectrometry testing. High-purity graphite powder is used as the conductive matrix, and the addition of microcrystalline cellulose enhances the bonding properties of the graphite felt, allowing for simple and rapid sample preparation. Furthermore, compared to conventional indium-assisted cathode test results, the present invention demonstrates high matrix strength and stability, while reducing sample preparation costs. The preparation process is safe and can be completed at ambient temperature and pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry testing, prepared in Example 1;

[0024] Figure 2 This is a surface morphology of a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry testing, prepared in Example 1. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below with reference to the accompanying drawings.

[0026] In order to realize graphite felt testing, the present invention provides a method for preparing a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample, that is, using high-purity graphite powder and microcrystalline cellulose as a matrix to assist in testing the graphite felt, and adopting glow discharge mass spectrometry to obtain the result of DC-GDMS determination of impurity element content.

[0027] A method for preparing a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry testing comprises the following steps:

[0028] 1) After cleaning and drying the mold, place the filter membrane in it. First, add high-purity graphite powder into the mold to serve as a conductive matrix, then add microcrystalline cellulose and high-purity graphite powder and mix them evenly;

[0029] 2) Clamp the graphite felt fiber and place it on the mixed powder to fill the inner diameter of the mold, then cover it with a filter membrane, and press the mold with a briquetting machine to obtain a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample.

[0030] In step 1), the mold is made of stainless steel and has an inner diameter of 20-30 mm.

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

[0032] In step 1), the filter membrane is a microporous filter membrane with a diameter of 20-30 mm, a pore size of 0.45 μm, and 2-4 layers.

[0033] In step 1), the microcrystalline cellulose is purified by column chromatography in accordance with Q / CYDZ 2320-2009, and the high-purity graphite powder is grade 7N with a purity greater than 99.99999%.

[0034] In step 1), the amount of high-purity graphite powder used in the bottom layer is 1-5g.

[0035] In step 1), microcrystalline cellulose and high-purity graphite powder are uniformly mixed, and the weight ratio of microcrystalline cellulose to high-purity graphite powder in the powder is 0.8-1.2:1.

[0036] In step 1), microcrystalline cellulose and high-purity graphite powder are uniformly mixed, and the amount of high-purity graphite powder in the powder is 2-4 g.

[0037] In step 2), the graphite felt fibers are clamped using tweezers made of polytetrafluoroethylene.

[0038] In step 2), the length of the graphite felt fiber is 4-10 mm.

[0039] In step 2), the filter membrane is a microporous filter membrane with a diameter of 20-30 mm, a pore size of 0.45 μm, and 2-4 covering layers.

[0040] In step 2), the briquetting machine is a manual briquetting machine, and the applied pressure is 5-15 MPa.

[0041] Example 1

[0042] A method for preparing a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry testing comprises the following steps:

[0043] (1) Preliminary preparation

[0044] The mold was cleaned with ultrapure water and dried, two layers of filter membrane were added to the bottom of the mold, weighing paper was prepared into a spoon-shaped transfer sample, and the weighing paper was folded in half to form a spoon-shaped transfer sample. 3 g of high-purity graphite powder was first added to the mold using weighing paper to act as a conductive matrix, and then microcrystalline cellulose and high-purity graphite powder were added to evenly mix the powders; 2 g of graphite powder was contained in the mixed matrix layer, and the weight ratio of microcrystalline cellulose to graphite powder was 0.8.

[0045] (2) Sample placement

[0046] Use tweezers to pick up 4 mm graphite felt fibers and place them on the mixed powder, covering the inner diameter of the mold. Finally, cover it with two layers of filter membranes and apply a pressure of 5 MPa to the mold to form a microcrystalline cellulose-graphite powder-based graphite felt block sample 1.

[0047] The sample purity was determined using high-resolution GDMS (GDMS) discharge parameters for the Nu-Astrum GDMS: 2 mA discharge current, 900 V discharge voltage. The test results are shown in Table 4 and are close to those obtained from Eurofins. The Eurofins test results are shown in Table 1 below.

[0048] Table 1

[0049]

[0050] Example 2

[0051] A method for preparing a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry testing comprises the following steps:

[0052] (1) Preliminary preparation

[0053] The mold was cleaned with ultrapure water and dried, and two layers of filter membrane were added to the bottom of the mold. A weighing paper was folded in half to form a spoon-shaped transfer sample. 3g of high-purity graphite powder was first added to the mold using the weighing paper to serve as a conductive matrix. Microcrystalline cellulose and high-purity graphite powder were then added and uniformly mixed. The mixed matrix layer contained 3g of graphite powder, with a weight ratio of microcrystalline cellulose to graphite powder of 1.0.

[0054] (2) Sample placement

[0055] Use tweezers to pick up 8mm graphite felt fibers and place them on the mixed powder, covering the inner diameter of the mold. Finally, cover it with 3 layers of filter membrane and apply a pressure of 15 MPa to the mold to form a microcrystalline cellulose-graphite powder-based graphite felt block sample.

[0056] The sample purity was determined using high-resolution GDMS (Glow Discharge Mass Spectrometry). Nu-Astrum GDMS discharge parameters were as follows: discharge current 3 mA, discharge voltage 1100 V. The test results are shown in Table 4. These results are close to those obtained from Eurofins. The Eurofins test results are shown in Table 2 below.

[0057] Table 2

[0058]

[0059] Example 3

[0060] A method for preparing a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry testing comprises the following steps:

[0061] (1) Preliminary preparation

[0062] The mold was cleaned with ultrapure water and dried, and two layers of filter membrane were added to the bottom of the mold. A weighing paper was folded in half to form a spoon-shaped transfer sample. 3g of high-purity graphite powder was first added to the mold using the weighing paper to serve as a conductive matrix. Microcrystalline cellulose and high-purity graphite powder were then added and uniformly mixed; the mixed powder contained 2.5g of graphite powder, with a weight ratio of microcrystalline cellulose to graphite powder of 1.2.

[0063] (2) Sample placement

[0064] Use tweezers to pick up 6mm graphite felt fibers and place them on the mixed powder, covering the inner diameter of the mold. Finally, cover it with 4 layers of filter membrane and apply a pressure of 10 MPa to the mold to form a microcrystalline cellulose-graphite powder-based graphite felt block sample.

[0065] The sample's purity was determined using high-resolution GDMS (Glow Discharge Mass Spectrometry). Nu-Astrum GDMS discharge parameters were as follows: discharge current 2.5 mA, discharge voltage 1000 V. The test results are shown in Table 4 and are close to those obtained by Eurofins.

[0066] The Eurofins test results are shown in Table 3 below.

[0067] Table 3

[0068]

[0069] Table 4 Comparison of Al element results of microcrystalline cellulose-high purity graphite powder-based graphite felt sample test and third-party testing agency test (unit: ug / g)

[0070]

[0071] It can be seen from Table 1 that the test results of the three samples prepared by the present invention are similar to the external test results, and have good stability.

Claims

1. A method for preparing a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample suitable for glow discharge mass spectrometry testing, comprising the following steps: 1) After cleaning and drying the mold, the filter membrane is placed. High-purity graphite powder is first added to the mold to serve as a conductive matrix, and then a mixed powder of microcrystalline cellulose and high-purity graphite powder is added; 2) Clamp the graphite felt fiber and place it on the mixed powder to fill the inner diameter of the mold, then cover it with a filter membrane, and pressurize the mold with a briquetting machine to obtain a microcrystalline cellulose-high-purity graphite powder-based graphite felt sample.

2. The preparation method according to claim 1, characterized in that In step 1), the mold is made of stainless steel and has an inner diameter of 20-30 mm.

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

4. 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 μm, and the number of layers is 2-4.

5. The preparation method according to claim 1, characterized in that In step 1), the microcrystalline cellulose is purified by column chromatography, and the high-purity graphite powder is 7N grade with a purity greater than 99.99999%.

6. The preparation method according to claim 1, characterized in that In step 1), the amount of high-purity graphite powder used in the bottom layer is 1-5g.

7. The preparation method according to claim 1, characterized in that In step 1), microcrystalline cellulose and high-purity graphite powder are uniformly mixed, and the weight ratio of microcrystalline cellulose to high-purity graphite powder in the powder is 0.8-1.2:

1.

8. The preparation method according to claim 1, characterized in that In step 1), microcrystalline cellulose and high-purity graphite powder are uniformly mixed, and the amount of high-purity graphite powder in the powder is 2-4 g.

9. The preparation method according to claim 1, characterized in that In step 2), the graphite felt fibers are clamped using tweezers made of polytetrafluoroethylene, and the length of the graphite felt fibers is 4-10 mm.

10. 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 μm, 2-4 covering layers, and a manual briquetting machine, and the applied pressure is 5-15 MPa.

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