Preparation method of bubble-free low-expansion quartz glass

Abstract

The present invention relates to a preparation method of bubble-free low-expansion quartz glass, belonging to the technical field of quartz glass preparation and production. Through the secondary forming processes of die pressing and cold isostatic pressing, the present invention obtains a high-density quartz green body, ensuring the tight contact between quartz glass powder particles. After three-stage heating vacuum sintering, the prepared quartz glass has no bubble formation, solving the problem that the low-expansion quartz glass prepared by traditional methods is prone to bubble defects, resulting in poor mechanical and optical properties. At the same time, the present invention uses the waste materials, tailings, and discarded materials generated in the production of low-expansion quartz glass by the existing CVD method as raw materials to prepare high-quality quartz glass products, realizing "waste utilization", which has a positive significance for the development of enterprises.

Description

Technical Field

[0001] The invention relates to a method for preparing bubble-free low-expansion quartz glass, belonging to the technical field of quartz glass production. Background Art

[0002] Low-expansion quartz glass can achieve a near-zero thermal expansion coefficient in the room temperature range and exhibits excellent thermal stability, and is therefore widely used in technical fields such as aerospace, high-precision optics, and semiconductor manufacturing. It is a key preparation material for high-end optical instrument components such as EUV lithography machines, laser gyroscope resonant cavities, and astronomical telescope mirrors.

[0003] Bubbles are one of the common defects in low expansion quartz glass and are a key factor affecting its physical properties. The presence of bubbles will reduce the strength and hardness of low expansion glass, and the gaps formed by bubbles in series will also increase the brittleness of the glass. In addition, since the refractive index of bubbles and low expansion quartz glass to light is different, the presence of a large number of bubbles will also affect its use in the optical field.

[0004] The most common method for preparing low-expansion quartz glass is the vapor deposition method (CVD method), which is to mix the raw materials containing silicon and titanium and then react with hydrogen and oxygen flame to form nanoparticles, which are then deposited on the target. During the melting process, some nanoparticles will be directly deposited on the target, which is usually called direct deposition; the other part will fly after impacting the target surface, and a small part of them will be blocked by the crucible wall to form reflux and be melted by the flow field in the melting environment (see the simulation diagram of the flow field of the CVD melting process). Figure 1 ) is guided to the material surface, also known as secondary deposition, and most of them are extracted by the exhaust system as waste. Since nanoparticles tend to agglomerate with other particles to form larger particles when moving in the melting environment, they cannot melt into glass as quickly as possible when they fall to the material surface. Bubbles are formed when they melt later. Most of these bubbles are distributed at the edge of the raw ingot (see Figure 2 ,Depend on Figure 2 It can be seen that the low expansion quartz glass prepared by CVD method contains a large number of bubbles of varying sizes). This leads to the generation of waste (unqualified products) and poor mechanical and optical properties. On the other hand, low expansion quartz glass will inevitably produce a large amount of waste (scraps) and tailings during the subsequent machining process. Usually, these wastes, tailings and scraps are treated as garbage, which not only pollutes the environment, but also causes unnecessary waste. Therefore, it is necessary to improve them. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing bubble-free low-expansion quartz glass, which can effectively solve the problems that low-expansion quartz glass prepared by the existing CVD method contains bubbles, resulting in poor mechanical and optical properties, and that waste, tailings and discarded materials generated by the production of low-expansion quartz glass are all treated as garbage, which not only causes environmental pollution but also leads to unnecessary waste.

[0006] The technical solution of the present invention is:

[0007] A method for preparing bubble-free low-expansion quartz glass comprises the following steps:

[0008] 1) Collect waste materials generated by low-expansion quartz glass production or waste materials generated by machining, or a mixture of waste materials and waste materials; pickle and wash in a conventional manner to remove surface impurities, and then crush and ball-mill to prepare low-expansion quartz glass powder with an average particle size of 7-8 μm;

[0009] 2) placing the obtained low expansion quartz glass powder in a molding mold, and then performing molding with the aid of a molding device, wherein the molding pressure is 3t and the holding time is 10 min; obtaining a quartz glass powder preform;

[0010] 3) Use a sealing bag to vacuum seal the quartz glass powder preform, and then place it in a cold isostatic pressing device for secondary pressing. Under the conditions of a cold isostatic pressing pressure of 200 MPa and a holding time of 5 min, a high-density, low-expansion quartz glass powder green body is obtained;

[0011] 4) Place the green body of high-density low-expansion quartz glass powder in a muffle furnace and perform debinding at 700 °C in air atmosphere for 2 h;

[0012] 5) Place the high-density low-expansion quartz glass powder green body that has completed the binder removal treatment in a crucible corresponding to its diameter, and place it in a vacuum sintering furnace, and then perform segmented temperature rise sintering under the condition that the vacuum degree of the vacuum furnace is less than 1 Pa to obtain bubble-free low-expansion quartz glass;

[0013] Step 5) The staged heating includes three stages;

[0014] In the first stage, the temperature is raised from room temperature to 1000-1100℃ at a heating rate of 8℃ / min and kept at this temperature for 5-10 minutes;

[0015] In the second stage, the temperature is raised from 1000-1100℃ to 1400-1500℃ at a heating rate of 5℃ / min and kept at this temperature for 5-10 minutes;

[0016] In the third stage, the temperature is increased from 1400-1500 ℃ to 1800-1900 ℃ at a heating rate of 1 ℃ / min and kept at this temperature for 120-180 min.

[0017] In actual work, it is found that the uniformity of the particle size of the raw material affects the quality of the quartz glass bubbles after sintering. If the particle size of the powder is uneven, the pores formed by the particles squeezing each other under pressure during the molding process will be uneven in size (see Figure 3 At the same time, due to the difference in surface activation energy, during the melting process, small particles melt first than large particles, and the first melted quartz melt covers the surface of the unmelted quartz powder particles, making it difficult for large particles to melt completely and form particle defects. The pores around the large particles will also be difficult to discharge, resulting in an increase in the number of bubbles inside the low-expansion quartz glass after sintering. On the contrary, when the particle size of the powder particles is uniform, the pores formed by the mutual compression of the particles under pressure during the molding process will be uniform in size (see Figure 3 Right picture). In addition, during the melting process, since the powder particles are of the same size, their melting rates are the same, so it is not easy to produce particle defects, which is conducive to the discharge of bubbles.

[0018] The molding parameters have a direct impact on the quality of the pressed green body. Different pressing parameters produce different results on the quality of the pressed green body. In order to prove the optimal pressing parameters, the applicant conducted experiments using different pressing parameters, and the results are shown in Table 1.

[0019] Comparison table of green bodies with different pressing parameters

[0020] Table 1

[0021]

[0022] It can be seen from Table 1 that under the pressing parameter condition of 3t-10 min, the molding quality of the green body is the best. The raw material particles are in close contact with each other, and the particles are firmly connected by internal friction to maintain a certain shape, thus forming a complete green body (see Figure 4 ).

[0023] After confirming the optimal molding parameters of 3t-10 min, the applicant tested the density of the molded green body and the result was 1.25 g / cm 3 This density is similar to the density of quartz glass 2.2 g / cm 3 The gap is large, so the applicant conducted a re-pressurization densification test on the green body by cold isostatic pressing based on the molding parameters of 3t-10min; different groups of cold isostatic pressing parameters were used in the pressurization densification test. Each group of parameter test samples was more than 5 pieces, and the specific results are shown in Table 2.

[0024] Table 2 shows the green density results before and after the cold isostatic pressing test (the data in the table are the results after taking the average value)

[0025] Table 2 Green density before and after cold isostatic pressing test

[0026]

[0027] It can be seen from Table 2 that with the increase of pressure, the green body density increases significantly, and the increase gradually weakens, indicating that the green body has gradually reached the ultimate dense state. The green body density of 200 MPa pressure for 5 min reaches 1.68 g / cm 3 , the density increased by 34.4%. However, with the extension of holding time, the green density did not change much.

[0028] The low expansion quartz glass finally obtained by the present invention has a CTE uniformity of 7.23 ppb / ℃ (see Figure 5 ), retains the advantages of the low expansion quartz glass raw material prepared by the CVD method used in the present invention, and at the same time, there are no bubbles inside the product (see Figure 6 ).

[0029] The beneficial effects of the present invention are:

[0030] 1. The present invention uses waste, tailings and discarded materials generated by the production of low-expansion quartz glass as raw materials, and produces bubble-free low-expansion quartz glass through crushing, ball milling, molding, cold isostatic pressing and sintering processes, thus realizing "waste utilization";

[0031] 2. The present invention does not modify the raw materials, thus retaining the advantage of high CTE uniformity of low expansion quartz glass prepared by CVD method;

[0032] 3. The present invention obtains a high-density (high-density) low-expansion quartz green body through a molding and cold isostatic pressing secondary molding process, thereby ensuring the tightness of contact between powder particles. The green body is sintered in a three-stage vacuum sintering process to eliminate the pores between powder particles, so that the obtained low-expansion quartz glass reaches a bubble-free level, thereby solving the problem that the low-expansion quartz glass prepared by the existing CVD method contains bubbles, resulting in poor mechanical and optical properties, and the waste, tailings and discarded materials generated by the production of low-expansion quartz glass are all treated as garbage, which not only causes environmental pollution, but also causes unnecessary waste problems, which is of great significance to the development of enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flow field simulation diagram of the CVD melting process;

[0034] Figure 2 This is a micrograph of the interior of low expansion quartz glass produced by CVD method;

[0035] Figure 3 It is a schematic diagram of the extrusion state of powder particles during the molding process of the present invention;

[0036] Figure 4 A real picture of the green body prepared by the present invention;

[0037] Figure 5 This is a test chart of the CTE uniformity of the low expansion quartz glass prepared by the present invention;

[0038] Figure 6 Micrograph of the interior of low expansion quartz glass prepared for the present invention. DETAILED DESCRIPTION Example 1

[0039] The waste produced by the CVD method of producing low-expansion quartz glass is pickled in a conventional manner using hydrochloric acid with a concentration of 30-40%, or other single acids with a concentration of 30-40%, such as nitric acid and hydrofluoric acid pickling solutions, to remove impurities on the surface of the waste. After the pickling is completed, the residual pickling solution on the surface is removed by water washing and dried, and then crushed and ball-milled into quartz glass powder particles with a particle size of 7-8 μm by a crusher and a ball mill, wherein the particle size difference of the quartz glass powder particles is required not to be greater than 1 μm. The obtained quartz glass powder particles are placed in a forming mold, and then molded by a molding machine under the conditions of a pressure of 3t and a holding time of 10 min. After the molding is completed and demolded, a quartz glass powder preform is obtained. The quartz glass powder preform was vacuum sealed in a sealing bag and then placed in a cold isostatic pressing device. Cold isostatic pressing secondary molding was performed under the conditions of a cold isostatic pressing pressure of 200 MPa and holding pressure for 5 min to obtain a quartz glass powder green body with volume shrinkage. In this process, the quartz glass powder preform was subjected to high pressure and secondary molding to obtain a green body with a higher density, and the gaps between the powder particles were compressed, which could ensure the uniformity of heating of the powder particles in the subsequent melting process, thereby obtaining bubble-free low-expansion quartz glass.

[0040] In the process of preparing quartz glass powder preforms, in order to facilitate demolding, a release agent is usually used to wipe the inner wall of the sleeve, the base and the pressure head of the molding die; as a result, there will be some release agent on the surface of the obtained preform. The secondary molded quartz glass powder green body is placed in a muffle furnace and debinded for 2 hours in an air atmosphere at 700 ℃ to remove the release agent on its surface. The debinded quartz glass powder green body is placed in a molybdenum sheet crucible corresponding to its diameter, and the whole is placed in a vacuum sintering furnace, and then sintered in stages under the condition of vacuum degree <1 Pa, where:

[0041] In the first stage, the temperature was raised from room temperature to 1050°C at a heating rate of 8°C / min and kept at this temperature for 10 min. During this process, the contact between the quartz glass powder particles gradually changed from point to surface, bonding occurred at the contact points, and the large pores disappeared, but the total specific surface area did not change much.

[0042] In the second stage, the temperature was raised from 1050°C to 1500°C at a heating rate of 5°C / min and kept at this temperature for 8 min. During this process, the quartz glass powder particles began to grow, the pores further shrank and deformed, and were discharged along the grain boundaries, and the density was significantly improved.

[0043] In the third stage, the temperature was raised from 1500 ℃ to 1800 ℃ at a heating rate of 1 ℃ / min, and the temperature was kept for 120 min to obtain bubble-free low-expansion quartz glass. In this process, the sintering temperature gradually reached the softening point temperature of the green body particles. When the temperature exceeds the softening point temperature (1730 ℃), the atoms or ions on the surface of the powder particles constituting the high-density green body begin to diffuse along the surface, interior or boundary of the particles. At the same time, since quartz glass exhibits viscous fluidity at high temperature, the glassy material between the particles flows, fills the pores and makes the material completely dense, thereby obtaining highly uniform low-expansion quartz glass; the obtained highly uniform low-expansion quartz glass was tested to have no bubble defects inside; the CTE uniformity was 7.23 ppb / ℃, which retained the advantage of high CTE uniformity of low-expansion quartz glass prepared by CVD method. Example 2

[0044] The waste material generated by low expansion quartz glass machining is pickled in a conventional manner using hydrochloric acid and hydrofluoric acid with a concentration of 30-40% and a mixed acid solution in a mass ratio of 10:1, or a mixed acid solution formed by two other acid solutions with a concentration of 30-40% and an arbitrary mass ratio to remove impurities on the surface of the waste material. After the pickling is completed, the residual acid solution on the surface is removed by water washing and dried, and then crushed and ball-milled into quartz glass powder particles with a particle size of 7-8 μm by a crusher and a ball mill, wherein the particle size difference of the quartz glass powder particles is required to be no greater than 1 μm. The obtained quartz glass powder particles are placed in a forming mold, and then molded by a molding machine under a pressure of 3t and a holding time of 10 min. After the molding is completed and demolded, a quartz glass powder preform is obtained.

[0045] The quartz glass powder preform was vacuum sealed with a sealing bag, and then placed in a cold isostatic pressing device, and cold isostatic pressing was performed for secondary molding under the conditions of a cold isostatic pressing pressure of 200 MPa and a holding pressure of 5 min to obtain a quartz glass powder green body with volume shrinkage; in this process, the quartz glass powder preform was subjected to high pressure and secondary molding, and the green body density obtained was high, and the gaps between the powder particles were compressed, which could ensure the uniformity of heating of the powder particles in the subsequent melting process, thereby obtaining bubble-free low-expansion quartz glass. In the process of preparing quartz glass powder preforms, in order to facilitate demolding, a release agent is usually used to wipe the inner wall, base and pressure head of the sleeve of the molding mold; as a result, some release agent will exist on the surface of the obtained preform, and the secondary molded quartz glass powder green body is placed in a muffle furnace and debinded for 2 hours in an air atmosphere at 700 ℃ to remove the release agent on its surface. The debinding quartz glass powder green body is placed in a molybdenum crucible corresponding to its diameter, and the whole is placed in a vacuum sintering furnace, and sintered in stages under the condition of vacuum degree <1 Pa, wherein:

[0046] In the first stage, the temperature was raised from room temperature to 1100°C at a heating rate of 8°C / min and kept at this temperature for 10 min. During this process, the contact between the quartz glass powder particles gradually changed from point to surface, bonding occurred at the contact points, and the large pores disappeared, but the total specific surface area did not change much.

[0047] In the second stage, the temperature was increased from 1100 ℃ to 1400 ℃ at a heating rate of 5 ℃ / min and kept at this temperature for 5 min. During this process, the quartz glass powder particles began to grow, the pores further shrank and deformed, and were discharged along the grain boundaries, and the density was significantly improved.

[0048] In the third stage, the temperature was raised from 1400 ℃ to 1900 ℃ at a heating rate of 1 ℃ / min and kept at this temperature for 180 min to obtain bubble-free low-expansion quartz glass. In this process, the sintering temperature gradually reached the softening point temperature of the green body particles. When the temperature exceeds the softening point temperature (1730 ℃), the atoms or ions on the surface of the powder particles constituting the high-density green body begin to diffuse along the surface, interior or boundary of the particles. At the same time, since quartz glass exhibits viscous fluidity at high temperature, the glassy material between the particles flows, fills the pores and makes the material completely dense, thereby obtaining highly uniform low-expansion quartz glass. The obtained highly uniform low-expansion quartz glass was tested to have no bubble defects inside; the CTE uniformity was 7.26 ppb / ℃, which retained the advantage of high CTE uniformity of low-expansion quartz glass prepared by CVD method. Example 3

[0049] After the waste and discarded materials are mixed, they are pickled in a conventional manner using a mixed acid solution formed by hydrochloric acid, nitric acid and hydrofluoric acid with a concentration of 30-40% and a mass ratio of 10:1:1 to remove impurities on the surface of the waste. After the pickling is completed, the residual pickling liquid on the surface is removed by water washing and dried, and then crushed and ball-milled into quartz glass powder particles with a particle size of 7-8 μm by a crusher and a ball mill, wherein the particle size difference of the quartz glass powder particles is required to be no greater than 1 μm. The obtained quartz glass powder particles are placed in a forming mold, and then molded by a molding machine under a pressure of 3t and a holding time of 10min. After the molding is completed and demolded, a quartz glass powder preform is obtained.

[0050] The quartz glass powder preform is vacuum sealed with a sealing bag, and then placed in a cold isostatic pressing device, and cold isostatic pressing is performed for secondary molding under the condition of cold isostatic pressing pressure of 200 MPa and holding pressure for 5 minutes to obtain a quartz glass powder green body with volume shrinkage; in this process, the quartz glass powder preform is subjected to high pressure and secondary molding, and the green body density obtained is high, and the gaps between the powder particles are compressed, which can ensure the uniformity of heating of the powder particles in the subsequent melting process, thereby obtaining bubble-free low-expansion quartz glass. In the process of preparing quartz glass powder preforms, in order to facilitate demolding, a release agent is usually used to wipe the inner wall, base and pressure head of the sleeve of the molding mold; as a result, there will be some release agent on the surface of the obtained preform, and the secondary molded quartz glass powder green body is placed in a muffle furnace and debinded for 2 hours in an air atmosphere at 700 ℃ to remove the release agent on its surface. The debinding quartz glass powder green body is placed in a molybdenum crucible corresponding to its diameter, and the whole is placed in a vacuum sintering furnace, and sintered in stages under the condition of vacuum degree <1 Pa, wherein:

[0051] In the first stage, the temperature was raised from room temperature to 1000 °C at a heating rate of 8 °C / min and kept at this temperature for 8 min. During this process, the contact between the quartz glass powder particles gradually changed from point to surface, bonding occurred at the contact points, and the large pores disappeared, but the total specific surface area did not change much.

[0052] In the second stage, the temperature was raised from 1000 ℃ to 1450 ℃ at a heating rate of 5 ℃ / min and kept at this temperature for 5 min. During this process, the quartz glass powder particles began to grow, the pores further shrank and deformed, and were discharged along the grain boundaries, and the density was significantly improved.

[0053] In the third stage, the temperature was raised from 1450℃ to 1850℃ at a heating rate of 1℃ / min and kept at this temperature for 160 minutes to obtain bubble-free low-expansion quartz glass. In this process, the sintering temperature gradually reached the softening point temperature of the green body particles. When the temperature exceeds the softening point temperature (1730℃), the atoms or ions on the surface of the powder particles constituting the high-density green body begin to diffuse along the surface, interior or boundary of the particles. At the same time, since quartz glass exhibits viscous fluidity at high temperatures, the glassy material between the particles flows, fills the pores and makes the material completely dense, thereby obtaining highly uniform low-expansion quartz glass. The obtained highly uniform low-expansion quartz glass was tested to have no bubble defects inside; the CTE uniformity was 7.31 ppb / ℃, which retained the advantage of high CTE uniformity of low-expansion quartz glass prepared by CVD method.

[0054] In the above embodiment, during the compression molding process of the quartz glass powder, the compression pressure is 3 t and the holding time is 10 min. This process parameter is only applicable to the quartz glass powder preform with a diameter of 200 mm. In actual work, the compression molding pressure and holding time process parameters are not fixed. If the diameter of the prepared quartz glass powder preform is greater than or less than 200 mm, the compression pressure and holding time process parameters can be adjusted according to the following conditions: Make corresponding adjustments ( P It is the pressure that the powder bears per unit area; F The total pressure required to press the powder into a preform; S is the stress-bearing area of ​​the preform).

Claims

1. A method for preparing bubble-free low-expansion quartz glass, comprising the following steps: 1) Collect waste materials generated by low-expansion quartz glass production or waste materials generated by machining, or a mixture of waste materials and waste materials; pickle and wash in a conventional manner to remove surface impurities, and then crush and ball-mill to prepare low-expansion quartz glass powder with an average particle size of 7-8 μm; 2) placing the obtained low expansion quartz glass powder in a molding mold, and then performing molding with the aid of a molding device, wherein the molding pressure is 3t and the holding time is 10 min; obtaining a quartz glass powder preform; 3) Use a sealing bag to vacuum seal the quartz glass powder preform, and then place it in a cold isostatic pressing device for secondary pressing. Under the conditions of a cold isostatic pressing pressure of 200 MPa and a holding time of 5 minutes, a high-density, low-expansion quartz glass powder green body is obtained; 4) Place the green body of high-density low-expansion quartz glass powder in a muffle furnace and perform debinding at 700 °C in air atmosphere for 1-2 h; 5) Place the high-density low-expansion quartz glass powder green body that has completed the binder removal treatment in a crucible corresponding to its diameter, and place it in a vacuum sintering furnace, and then perform segmented temperature rise sintering under the condition that the vacuum degree of the vacuum furnace is less than 1 Pa to obtain bubble-free low-expansion quartz glass; Step 5) The staged heating includes three stages; In the first stage, the temperature is raised from room temperature to 1000-1100°C at a heating rate of 8°C / min and kept at this temperature for 5-10 min; In the second stage, the temperature is raised from 1000-1100 ℃ to 1400-1500 ℃ at a heating rate of 5 ℃ / min and kept at this temperature for 5-10 min; In the third stage, the temperature is increased from 1400-1500 ℃ to 1800-1900 ℃ at a heating rate of 1 ℃ / min and kept at this temperature for 120-180 minutes.

Images