Polishing solution for diamond as well as preparation method and application of polishing solution

Abstract

The invention provides a polishing solution for diamond as well as a preparation method and application thereof, and belongs to the technical field of polishing processes. The polishing solution for the diamond comprises diamond micro-powder, a dispersing agent, an oxidizing agent, an oxidizing auxiliary agent, metal peroxide and water according to the mass ratio of (2-10): (0.5-5): (3-10): (1-5): (1-5): 100. The pH value of the polishing solution for the diamond is 4-7; the oxidation auxiliary agent comprises percarbonate and / or perborate; the metal peroxide comprises any one or a combination of at least two of barium peroxide, calcium peroxide and magnesium peroxide. According to the polishing solution for the diamond, chemical-mechanical synergistic polishing of the diamond is achieved, the polishing efficiency of the diamond is greatly improved, and the polished diamond is low in roughness and good in quality.

Description

Technical Field

[0001] The invention relates to the technical field of polishing technology, and in particular to a diamond polishing liquid and a preparation method and application thereof. Background Art

[0002] Diamond, as a material with extremely high hardness and brittle properties, is widely used in various fields, such as electronics, optics or tool processing. Currently, diamond crystals need to be cut, ground, polished and other processes before they can be used industrially.

[0003] Chemical mechanical polishing is an effective polishing method to obtain ultra-smooth surfaces, and can be used for processing low-damage surfaces of diamond substrates. Chemical mechanical polishing uses the chemical reaction between chemical substances to form a softer oxide layer between the polishing liquid and the substrate. The oxide layer is removed under the mechanical action of the abrasive particles, and finally an ultra-smooth surface is obtained. The composition of the chemical polishing liquid directly affects the reaction speed, polishing quality and efficiency during the polishing process. For ultra-hard materials with extremely high chemical inertness, the oxidation effect of the polishing liquid plays a decisive role in the final surface quality. The chemical mechanical polishing method is currently a mature polishing method for obtaining ultra-smooth and ultra-low damage surfaces, but the current efficiency of polishing diamonds is extremely low. Relying solely on the mechanical action of abrasive particles cannot meet the needs of diamond processing. The hard and brittle characteristics of single crystal diamonds make them difficult to process, and their extremely low chemical inertness makes them difficult to oxidize.

[0004] CN115305013A discloses a diamond polishing liquid and a preparation method thereof. The preparation method of the diamond polishing liquid comprises the following steps: using diamond powder, lipids, alcohols, fatty acids and mineral oil as raw materials to prepare a polishing paste; dispersing the polishing paste in a sodium dodecyl sulfonate solution to obtain a polishing intermediate liquid; and mixing the polishing intermediate liquid with water to obtain a diamond polishing liquid.

[0005] CN112251146A discloses a method for preparing a diamond polishing liquid, comprising the following steps: (1) placing diamond micropowder treated with hydrogen peroxide twice into a nitric acid solution, reflux reaction, washing the residual acid on the surface of the diamond micropowder with pure water, and drying; (2) weighing 6-8% of modified diamond micropowder, 0.1-0.3% of tannic acid, 0.5-2% of hyaluronic acid, 2-3% of polyethylene glycol, and the balance being water; (3) dissolving tannic acid in water to obtain a tannic acid solution, adding hyaluronic acid to the tannic acid solution to obtain a mixed solution, adding the modified diamond micropowder to the mixed solution, and ultrasonically treating for 1-2 hours to obtain a dispersed system; (4) adding polyethylene glycol to the system obtained in step (3), cooling the system to 10-15°C, stirring for 0.5 hours, then adjusting the pH to 7-8 with a saturated calcium hydroxide solution, heating and continuing to stir the reaction for 2-3 hours, and cooling to room temperature.

[0006] CN111647356A discloses a diamond polishing liquid for metallographic polishing and capable of meeting different polishing precision requirements, and a preparation method thereof. The diamond polishing liquid is composed of the following raw materials in parts by weight: 70-95 parts of water; 0.1-15 parts of diamond micropowder; 2-5 parts of suspending agent; 0.01-0.1 parts of antioxidant; 10-20 parts of lubricant; 1-5 parts of dispersant; The preparation method of the diamond polishing liquid comprises the following steps: adding dispersant, lubricant and diamond micropowder to stirred water in sequence; adding antioxidant to water; adding suspending agent to water under the condition that the stirring speed is not less than 800rpm and dispersing for 20-30min.

[0007] However, the above diamond polishing liquid still has the problems of low polishing efficiency and high roughness of the diamond surface after polishing. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a diamond polishing liquid and a preparation method and application thereof. By adopting a specific diamond polishing liquid to realize a continuous oxidation process under a pH condition of 4 to 7, chemical-mechanical synergistic polishing is performed, thereby improving the polishing efficiency and ensuring that the diamond surface roughness is low.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a diamond polishing liquid, comprising diamond powder, a dispersant, an oxidant, an oxidizing agent, a metal peroxide and water in a mass ratio of (2-10):(0.5-5):(3-10):(1-5):(1-5):100; the pH value of the diamond polishing liquid is 4-7;

[0011] The oxidation aid includes percarbonate and / or perborate;

[0012] The metal peroxide includes any one of barium peroxide, calcium peroxide or magnesium peroxide, or a combination of at least two of them.

[0013] The diamond polishing liquid of the present invention comprises diamond micropowder, dispersant, oxidant, oxidizing agent, metal peroxide and water in a specific mass ratio, wherein the oxidizing agent and the metal peroxide slowly release hydrogen peroxide under the condition of pH 4-7 to make up for the loss of oxidizability during the polishing process, and no additional oxidant needs to be added during the polishing process; the metal ions after the metal peroxide releases hydrogen peroxide can react with carbonate ions or borate ions in the oxidizing agent to form barium carbonate, calcium carbonate, magnesium carbonate, calcium borate, barium borate and magnesium borate, and these substances can play an auxiliary role in the process of physical grinding of diamond by diamond micropowder, so as to ensure that the diamond surface has a lower roughness.

[0014] The pH of the diamond polishing liquid of the present invention is 4-7. When the pH is low or high, the hydrogen peroxide release rate will be too fast, and the hydrogen peroxide oxidation agent cannot be replenished for a long time, which leads to a higher roughness of the diamond after polishing.

[0015] The diamond polishing liquid of the present invention comprises diamond powder, dispersant, oxidant, oxidizing agent, metal peroxide and water in a mass ratio of (2-10):(0.5-5):(3-10):(1-5):(1-5):100, for example, it can be 2:0.5:3:1:1:100, 3:0.8:3.3:1:3:100, 5:3:3:5:2.5:100, 6:3.5:3:6:3:100, 7:4:3:9:3.5:100 or 10:5:3:10:5:100, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] The pH value of the diamond polishing liquid is 4-7, for example, 4, 4.5, 5, 6, 6.5 or 7, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0017] Preferably, the particle size of the diamond powder is 0.1-1.5 μm, for example, 0.1 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm or 1.5 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] Preferably, the dispersant comprises any one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate or a fatty acid salt, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate, a combination of a fatty acid salt and sodium dodecyl sulfate, or a combination of sodium dodecylbenzene sulfonate and a fatty acid salt.

[0019] The function of the dispersant of the present invention is to disperse the diamond powder so that it is evenly dispersed in the polishing liquid.

[0020] Preferably, the fatty acid salt comprises any one of sodium stearate, potassium stearate, calcium stearate, sodium oleate, potassium oleate or calcium oleate, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of sodium stearate and potassium stearate, a combination of calcium stearate and sodium oleate, a combination of potassium oleate and calcium oleate, or a combination of sodium stearate and sodium oleate.

[0021] Preferably, the oxidant comprises hydrogen peroxide.

[0022] Preferably, the mass concentration of the hydrogen peroxide is 20% to 30%, for example, it can be 20%, 22%, 25%, 27%, 28%, 29% or 30%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] The mass concentration of the hydrogen peroxide in the present invention is preferably 20% to 30%, which can effectively oxidize the diamond surface and soften the diamond surface to a certain extent, making it easier for the subsequent polishing machine to perform mechanical grinding.

[0024] In a second aspect, the present invention further provides a method for preparing the diamond polishing liquid as described in the first aspect, the preparation method comprising the following steps:

[0025] (1) mixing and dispersing diamond powder, a dispersant and a portion of water to form a first mixture;

[0026] (2) mixing and dispersing the oxidant, the oxidizing aid, the metal peroxide and the remaining water to form a second mixture;

[0027] (3) The first mixture and the second mixture are mixed and stirred, and the pH value is adjusted to obtain the diamond polishing liquid.

[0028] The preparation method of the diamond polishing liquid of the present invention is simple to operate. Firstly, diamond micropowder, a dispersant and a part of water are mixed and dispersed to form a first mixture, which is conducive to full contact between the dispersant and the diamond micropowder. The diamond micropowder in the polishing liquid finally formed is more evenly dispersed and has better dispersion performance. Then, an oxidant, an oxidizing aid, a metal peroxide and the remaining water are mixed and dispersed to form a second mixture. The first mixture and the second mixture are mixed and stirred, and the pH is adjusted to obtain a polishing liquid with high diamond polishing efficiency.

[0029] Preferably, the mass of the water in step (1) accounts for 30% to 40% of the total water volume, for example, it can be 30%, 32%, 35%, 37%, 38%, 39% or 40%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In the preparation method of the present invention, the mixing mass ratio of diamond powder, dispersant, oxidant, oxidizing aid and metal peroxide is (2-10):(0.5-5):(3-10):(1-5):(1-5), except that in step (1), 30% to 40% of the total water is first used for mixing, and the remaining water is used for mixing in step (2).

[0031] Preferably, the mixing and dispersing methods in step (1) and step (2) each independently include any one of ultrasonic dispersion, magnetic stirring dispersion or electric stirring dispersion.

[0032] The present invention does not specifically limit the time and dispersion speed of the mixing and dispersing in step (1) and step (2). Those skilled in the art can stir the mixture evenly based on existing experimental experience.

[0033] Preferably, in step (2), an acid is used to adjust the pH.

[0034] Preferably, the acid comprises any one of acetic acid, carbonic acid, citric acid, formic acid or boric acid or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of acetic acid and carbonic acid, a combination of citric acid and formic acid or a combination of boric acid and acetic acid.

[0035] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0036] (1) mixing and dispersing diamond powder, a dispersant, and water accounting for 30% to 40% of the total water volume to form a first mixture;

[0037] (2) mixing and dispersing the oxidant, the oxidizing aid, the metal peroxide and the remaining water to form a second mixture;

[0038] The mixing and dispersing methods in step (1) and step (2) each independently include any one of ultrasonic dispersion, magnetic stirring dispersion or electric stirring dispersion;

[0039] (3) The first mixture and the second mixture are mixed and stirred, and the pH is adjusted with an acid to obtain the diamond polishing liquid; the acid comprises any one of acetic acid, carbonic acid, citric acid, formic acid or boric acid, or a combination of at least two of them.

[0040] In a third aspect, the present invention further provides a use of the diamond polishing liquid as described in the first aspect, wherein the diamond polishing liquid is used to polish a diamond substrate to be polished;

[0041] The polishing method comprises: fixing and placing a diamond substrate to be polished on a polishing cloth, passing the diamond polishing liquid between the diamond substrate to be polished and the polishing cloth, and polishing the diamond substrate to be polished using a polishing machine.

[0042] The present invention applies diamond polishing liquid to the process of mechanically polishing a diamond substrate to be polished by a polishing machine, and at the same time uses hydrogen peroxide slowly released by the polishing liquid to chemically corrode the diamond, thereby realizing chemical-mechanical synergistic polishing treatment and greatly improving the polishing efficiency of the diamond; and the specific diamond polishing liquid in the application slowly releases hydrogen peroxide, thereby ensuring that the polished diamond has low roughness and good quality.

[0043] Preferably, the rotation speed of the polishing machine is 40-70 rpm, for example, it can be 40 rpm, 45 rpm, 50 rpm, 55 rpm, 60 rpm or 70 rpm, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the pressure of the polishing machine on the diamond substrate to be polished is 10-30 kPa, for example, 10 kPa, 15 kPa, 20 kPa, 25 kPa, 27 kPa or 30 kPa, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] Preferably, the flow rate of the polishing liquid during the polishing process is 1 to 5 L / min, for example, it can be 1 L / min, 1.5 L / min, 2 L / min, 2.5 L / min, 3 L / min, 4 L / min or 5 L / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] Preferably, the polishing time is 10 to 30 hours, for example, 10 hours, 13 hours, 15 hours, 20 hours, 22 hours, 25 hours or 30 hours, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] As a preferred technical solution of the present invention, the polishing method comprises: fixing and placing the diamond substrate to be polished on the polishing cloth, passing the diamond polishing liquid between the diamond substrate to be polished and the polishing cloth at a flow rate of 1 to 5 L / min, and polishing the diamond substrate to be polished for 10 to 30 hours using a polishing machine with a rotation speed of 40 to 70 rpm; the pressure of the polishing machine on the diamond substrate to be polished is 10 to 30 kPa.

[0048] Compared with the prior art, the present invention has at least the following beneficial effects:

[0049] (1) The oxidizing agent and metal peroxide in the diamond polishing liquid provided by the present invention slowly release hydrogen peroxide under the condition of pH 4 to 7, thereby compensating for the loss of oxidizing property during the polishing process, and no additional oxidizing agent is required during the polishing process; and the metal ions after the metal peroxide releases hydrogen peroxide can combine with the carbonate ions or borate ions in the oxidizing agent to form a precipitate, thereby assisting the physical grinding of diamond;

[0050] (2) The diamond polishing liquid provided by the present invention utilizes chemical-mechanical synergy to significantly improve the polishing efficiency of diamond and reduce the roughness, and is suitable for large-scale promotion and application. DETAILED DESCRIPTION

[0051] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0052] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0053] The following are typical but non-limiting embodiments of the present invention:

[0054] Example 1

[0055] This embodiment provides a diamond polishing liquid, which includes diamond powder, dispersant, oxidant, oxidizing agent, metal peroxide and water in a mass ratio of 3:0.8:3.3:1:3:100; the pH value of the diamond polishing liquid is 6.5;

[0056] The oxidation aid is percarbonate; and the metal peroxide is barium peroxide.

[0057] The particle size of the diamond powder is 1 μm.

[0058] The dispersant is sodium lauryl sulfate.

[0059] The oxidant includes hydrogen peroxide; the mass concentration of the hydrogen peroxide is 27%.

[0060] This embodiment also provides a method for preparing the diamond polishing liquid, the preparation method comprising the following steps:

[0061] (1) ultrasonically dispersing the diamond powder, the dispersant and 37% of water in the total water volume according to the above mass ratio to form a first mixture;

[0062] (2) dispersing the oxidant, the oxidizing aid, the metal peroxide and the remaining water by magnetic stirring according to the above mass ratio to form a second mixture;

[0063] (3) The first mixture and the second mixture are mixed and stirred, and the pH is adjusted with acetic acid to obtain the diamond polishing liquid.

[0064] Example 2

[0065] This embodiment provides a diamond polishing liquid, which includes diamond powder, dispersant, oxidant, oxidizing agent, metal peroxide and water in a mass ratio of 2:0.5:3:1:1:100; the pH value of the diamond polishing liquid is 4;

[0066] The oxidation aid is perborate; and the metal peroxide is calcium peroxide.

[0067] The particle size of the diamond powder is 1.5 μm.

[0068] The dispersant is sodium dodecylbenzene sulfonate.

[0069] The oxidant includes hydrogen peroxide; the mass concentration of the hydrogen peroxide is 20%.

[0070] This embodiment also provides a method for preparing the diamond polishing liquid, the preparation method comprising the following steps:

[0071] (1) dispersing the diamond powder, the dispersant and 40% of the water by electric stirring in the above-mentioned mass ratio to form a first mixture;

[0072] (2) dispersing the oxidant, the oxidizing aid, the metal peroxide and the remaining water by magnetic stirring according to the above mass ratio to form a second mixture;

[0073] (3) The first mixture and the second mixture are mixed and stirred, and the pH is adjusted with carbonic acid to obtain the diamond polishing liquid.

[0074] Example 3

[0075] This embodiment provides a diamond polishing liquid, which includes diamond powder, dispersant, oxidant, oxidizing agent, metal peroxide and water in a mass ratio of 10:5:3:10:5:100; the pH value of the diamond polishing liquid is 5;

[0076] The oxidation aid is percarbonate; and the metal peroxide is magnesium peroxide.

[0077] The particle size of the diamond powder is 0.1 μm.

[0078] The dispersant is potassium stearate.

[0079] The oxidant includes hydrogen peroxide; the mass concentration of the hydrogen peroxide is 30%.

[0080] This embodiment also provides a method for preparing the diamond polishing liquid, the preparation method comprising the following steps:

[0081] (1) dispersing the diamond powder, the dispersant and 30% of the water in the above mass ratio by magnetic stirring to form a first mixture;

[0082] (2) dispersing the oxidant, the oxidizing aid, the metal peroxide and the remaining water by magnetic stirring according to the above mass ratio to form a second mixture;

[0083] (3) The first mixture and the second mixture are mixed and stirred, and the pH value is adjusted with citric acid to obtain the diamond polishing liquid.

[0084] Example 4

[0085] This embodiment provides a diamond polishing liquid, and the diamond polishing liquid is the same as that in Embodiment 1.

[0086] This embodiment also provides a method for preparing the diamond polishing liquid, the preparation method comprising:

[0087] Diamond micropowder, dispersant, oxidant, oxidizing aid, metal peroxide and water are mixed and stirred at a mass ratio of 3:0.8:3.3:1:3:100 at one time, and the diamond polishing liquid is obtained after adjusting the pH to 5 with acetic acid.

[0088] Comparative Example 1

[0089] This comparative example provides a diamond polishing liquid, which is the same as Example 1 except that the oxidation aid percarbonate is not added.

[0090] Comparative Example 2

[0091] This comparative example provides a diamond polishing liquid, which is the same as Example 1 except that the metal peroxide barium peroxide is not added.

[0092] Comparative Example 3

[0093] This comparative example provides a diamond polishing liquid, which is the same as Example 1 except that the pH value of the diamond polishing liquid is 3.

[0094] Comparative Example 4

[0095] This comparative example provides a diamond polishing liquid, which is the same as Example 1 except that the pH value of the diamond polishing liquid is 8.

[0096] The diamond substrate to be polished is polished using the diamond polishing liquid in the above embodiment and comparative example; the polishing method comprises: fixing the diamond substrate to be polished and placing it on the polishing cloth, passing the diamond polishing liquid between the diamond substrate to be polished and the polishing cloth at a flow rate of 3L / min, and polishing the diamond substrate to be polished for 10 hours using a polishing machine with a rotation speed of 60rpm; the pressure of the polishing machine on the diamond substrate to be polished is 15kP a .

[0097] The roughness of the diamond-polished surfaces of the embodiment and the comparative example was measured by atomic force microscopy, and the removal rate was tested by thickness measurement. The results are shown in Table 1.

[0098] Table 1

[0099] Sample No. Ra(nm) Removal rate (nm / h) Example 1 0.395 88 Example 2 0.348 96 Example 3 0.369 92 Example 4 0.778 82 Comparative Example 1 1.556 59 Comparative Example 2 1.527 56 Comparative Example 3 1.485 50 Comparative Example 4 1.463 45

[0100] From Table 1 we can see that:

[0101] (1) The diamond polishing liquid provided in Examples 1 to 3 is used for polishing, and the roughness of the diamond is low and the removal rate is high;

[0102] (2) By comparing Example 4 with Examples 1 to 3, it can be seen that the diamond powder was not dispersed with the dispersant mixture in advance, resulting in a decrease in the dispersion performance of the diamond powder in the polishing liquid, resulting in a decrease in the diamond polishing effect, a higher roughness of 0.778 nm, and a lower removal rate;

[0103] (3) Compared with Example 1, Comparative Example 1 and Comparative Example 2 did not add an oxidizing agent or metal peroxide, resulting in insufficient oxidant replenishment during the polishing process, reduced oxidation effect and durability, and ultimately reduced diamond polishing effect and removal rate;

[0104] (4) Compared with Example 1, in Comparative Examples 3 to 4, the pH is too low or too high, causing the oxidation aid and metal peroxide to release hydrogen peroxide too quickly, resulting in insufficient oxidation effect in the later stage of polishing, resulting in higher roughness of the diamond after polishing and lower removal rate.

[0105] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A diamond polishing liquid, characterized in that: The diamond polishing liquid comprises diamond powder, a dispersant, an oxidant, an oxidizing agent, a metal peroxide and water in a mass ratio of (2-10):(0.5-5):(3-10):(1-5):(1-5):100; the pH value of the diamond polishing liquid is 4-7; The oxidation aid includes percarbonate and / or perborate; The metal peroxide includes any one of barium peroxide, calcium peroxide or magnesium peroxide, or a combination of at least two of them.

2. The diamond polishing liquid according to claim 1, characterized in that: The particle size of the diamond powder is 0.1-1.5 μm.

3. The diamond polishing liquid according to claim 1, characterized in that: The dispersant includes any one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate or fatty acid salt, or a combination of at least two of them.

4. The diamond polishing liquid according to claim 3, characterized in that: The fatty acid salt includes any one of sodium stearate, potassium stearate, calcium stearate, sodium oleate, potassium oleate or calcium oleate, or a combination of at least two of them.

5. The diamond polishing liquid according to claim 1, characterized in that: The oxidant includes hydrogen peroxide; The mass concentration of the hydrogen peroxide is 20% to 30%.

6. A method for preparing a diamond polishing liquid as claimed in any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: (1) mixing and dispersing diamond powder, a dispersant and a portion of water to form a first mixture; (2) mixing and dispersing the oxidant, the oxidizing aid, the metal peroxide and the remaining water to form a second mixture; (3) The first mixture and the second mixture are mixed and stirred, and the pH value is adjusted to obtain the diamond polishing liquid.

7. The preparation method according to claim 6, characterized in that: The mass of the water in step (1) accounts for 30% to 40% of the total water.

8. The preparation method according to claim 6, characterized in that: The mixing and dispersing methods in step (1) and step (2) each independently include any one of ultrasonic dispersion, magnetic stirring dispersion or electric stirring dispersion; Step (2) using acid to adjust pH; The acid includes any one of acetic acid, carbonic acid, citric acid, formic acid or boric acid, or a combination of at least two thereof.

9. Use of the diamond polishing liquid according to any one of claims 1 to 5, characterized in that: Polishing the diamond substrate to be polished using the diamond polishing liquid; The polishing method comprises: fixing and placing a diamond substrate to be polished on a polishing cloth, passing the diamond polishing liquid between the diamond substrate to be polished and the polishing cloth, and polishing the diamond substrate to be polished using a polishing machine.

10. The use according to claim 9, characterized in that: The rotating speed of the polishing machine is 40 to 70 rpm; The polishing machine applies a pressure of 10 to 30 kPa to the diamond substrate to be polished; During the polishing process, the flow rate of the polishing liquid is 1 to 5 L / min; The polishing time is 10 to 30 hours.