Diamond polishing liquid and its preparation method and application

Abstract

The present invention provides a diamond polishing liquid and its preparation method and application, belonging to the field of polishing process technology. The diamond polishing liquid comprises diamond micropowder, 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 oxidizing agent comprises percarbonate and / or perborate; the metal peroxide comprises any one of barium peroxide, calcium peroxide or magnesium peroxide or a combination of at least two thereof. The diamond polishing liquid of the present invention realizes chemical-mechanical coordinated polishing of diamond, greatly improves the polishing efficiency of diamond, and the polished diamond has low roughness and good quality.

Description

Technical Field

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

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

[0003] Chemical mechanical polishing is an effective polishing method for obtaining ultra-smooth surfaces and can be used for processing low-damage surfaces of diamond substrates. Chemical mechanical polishing utilizes 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, ultimately obtaining an ultra-smooth surface. 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 oxidizing 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, and relying solely on the mechanical action of abrasive particles cannot meet the needs of diamond processing. The hard and brittle properties 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: preparing a polishing paste using diamond powder, lipids, alcohols, fatty acids and mineral oil as raw materials; dispersing the polishing paste in a sodium dodecylsulfonate 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, subjecting the solution to reflux reaction, washing the residual acid on the surface of the diamond micropowder with pure water, and drying the solution; (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 remainder 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 the solution 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 the solution for 0.5 hours, adjusting the pH to 7-8 with a saturated calcium hydroxide solution, heating the solution, and continuing the stirring reaction for 2-3 hours, and cooling the solution to room temperature.

[0006] CN111647356A discloses a diamond polishing liquid for metallographic polishing that can meet 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 part of antioxidant; 10-20 parts of lubricant; and 1-5 parts of dispersant. The preparation method of the diamond polishing liquid comprises the following steps: adding the dispersant, lubricant, and diamond micropowder to stirred water in sequence; adding the antioxidant to the water; and adding the suspending agent to the water at a stirring speed of not less than 800 rpm and dispersing for 20-30 minutes.

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

[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 fine 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, a dispersant, an oxidant, an oxidizing aid, a metal peroxide and water in a specific mass ratio. The oxidizing aid and the metal peroxide slowly release hydrogen peroxide at a pH of 4 to 7 to compensate for the loss of oxidizability during the polishing process, and no additional oxidant needs to be added during the polishing process. The metal ions released from the metal peroxide after the hydrogen peroxide is released can react with carbonate ions or borate ions in the oxidizing aid to form barium carbonate, calcium carbonate, magnesium carbonate, calcium borate, barium borate and magnesium borate. These substances can play an auxiliary role in the physical grinding of diamond by the diamond micropowder, ensuring that the diamond surface has a low roughness.

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

[0015] The diamond polishing liquid of the present invention 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, for example, the mass ratio may 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 of the diamond polishing liquid is 4 to 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 numerical range are also applicable.

[0017] Preferably, the particle size of the diamond powder is 0.1 to 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 values ​​not listed within the numerical range are also applicable.

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

[0019] The function of the dispersant of the present invention is to disperse the diamond powder so that the diamond powder 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 values ​​not listed within the numerical range are also applicable.

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

[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. First, diamond micropowder, a dispersant and a portion 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 final polishing liquid 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 values ​​not listed within this numerical range are also applicable.

[0030] In the preparation method of the present invention, the mixing mass ratio of diamond micropowder, dispersant, oxidant, oxidation aid and metal peroxide is (2-10):(0.5-5):(3-10):(1-5):(1-5), except that in step (1), 30%-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 uniformly based on their existing experimental experience.

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

[0034] Preferably, the acid comprises any one or a combination of at least two of acetic acid, carbonic acid, citric acid, formic acid or boric acid, 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 30% to 40% of water 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 includes 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 according to 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 a diamond polishing liquid to a process of mechanically polishing a diamond substrate to be polished using a polishing machine, and simultaneously utilizes hydrogen peroxide slowly released from the polishing liquid to chemically corrode the diamond, thereby achieving a chemical-mechanical synergistic polishing process and significantly improving the polishing efficiency of the diamond. Furthermore, the specific diamond polishing liquid in the present 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, etc., but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

[0047] As a preferred technical solution of the present invention, the polishing method includes: 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 at a pH of 4 to 7, thereby compensating for the loss of oxidizing properties during the polishing process, and no additional oxidizing agent is required during the polishing process. Moreover, the metal ions released from the metal peroxide after the hydrogen peroxide is released can combine with the carbonate ions or borate ions in the oxidizing agent to form a precipitate, thereby assisting in the physical polishing of diamonds.

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

[0051] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to 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 merely 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 examples of the present invention:

[0054] Example 1

[0055] This embodiment 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 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, which comprises the following steps:

[0061] (1) ultrasonically dispersing the diamond powder, the dispersant, and 37% of water in the above-mentioned 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-mentioned 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, comprising diamond powder, a dispersant, an oxidant, an oxidizing agent, a 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 dodecylbenzenesulfonate.

[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, which comprises the following steps:

[0071] (1) dispersing the diamond powder, the dispersant, and 40% of the water by weight 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-mentioned 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, comprising diamond powder, a dispersant, an oxidant, an oxidizing agent, a 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, which comprises the following steps:

[0081] (1) magnetically stirring and dispersing the diamond powder, the dispersant, and 30% of the water in the above-mentioned mass ratio 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-mentioned mass ratio to form a second mixture;

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

[0084] Example 4

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

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

[0087] Diamond fine powder, dispersant, oxidant, oxidation 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 pH value is adjusted to 5 with acetic acid to obtain the diamond polishing liquid.

[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. The diamond polishing liquid 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. The diamond polishing liquid 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 a polishing cloth, passing the diamond polishing liquid between the diamond substrate to be polished and the polishing cloth at a flow rate of 3 L / min, and polishing the diamond substrate to be polished for 10 hours using a polishing machine with a rotation speed of 60 rpm; the pressure of the polishing machine on the diamond substrate to be polished is 15 kP a .

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

[0098] Table 1

[0099] Sample number 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) Comparison of Example 4 with Examples 1 to 3 shows 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 Examples 1 and 2 did not add oxidizing agents or metal peroxides, 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 embodiment of the present invention, but the scope of protection 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 fall within the scope of protection and disclosure 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; the dispersant includes any one of sodium lauryl sulfate, sodium dodecylbenzenesulfonate or fatty acid salts, or a combination of at least two of them; the oxidant includes hydrogen peroxide; and the mass concentration of the hydrogen peroxide is 20% to 30%.

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

3. The diamond polishing liquid according to claim 1, wherein 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.

4. A method for preparing a diamond polishing liquid according to any one of claims 1 to 3, 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.

5. The preparation method according to claim 4, characterized in that The mass of the water in step (1) accounts for 30% to 40% of the total water volume.

6. The preparation method according to claim 4, 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 (3) adjusting the pH with acid; 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.

7. A use of the diamond polishing liquid according to any one of claims 1 to 3, 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.

8. The use according to claim 7, characterized in that The rotating speed of the polishing machine is 40-70 rpm; The polishing machine applies a pressure of 10 to 30 kPa to the diamond substrate to be polished; The flow rate of the polishing liquid during the polishing process is 1-5 L / min; The polishing time is 10 to 30 hours.