Homogenization modification method and device for eliminating quartz glass stripes

Abstract

The invention relates to a homogeneous modification method and device for eliminating quartz glass stripes, and belongs to the technical field of quartz glass stripe elimination. According to the invention, the glass liquid is homogenized through planetary rotation, the temperature difference of each part can be reduced, stripes in the middle of the quartz glass ingot after thermal modification can be effectively eliminated, the stripes are concentrated on the edge of the quartz glass ingot, and the stripes can be completely eliminated by cutting off the quartz glass in the stripe area, so that the uniformity and the optical performance of the quartz glass ingot are greatly improved. As the uniformity is improved in a planetary rotation mode, compared with the mode of eliminating stripes by improving the purity, the internal quality of the quartz ingot with the stripes can be improved and improved, the production cost can be effectively reduced, and the utilization rate of the quartz ingot material can be improved. The problems that fringes are not easy to eliminate and the cost is high due to a boundary effect existing in an existing method are solved.

Description

TECHNICAL FIELD

[0001] The application relates to a homogenization modification method and device for eliminating quartz glass stripes and belongs to the technical field of quartz glass stripe elimination. BACKGROUND

[0002] Quartz glass is widely used in various high-tech fields such as semiconductor manufacturing, optical instruments and laser equipment due to its excellent optical performance and chemical stability. However, in the production process, the internal material distribution of quartz glass ingot is prone to unevenness due to temperature difference, which is manifested as a linear or banded structure (commonly known as optical stripe) formed by a small refractive index difference. This structure can be seen under polarized light or special detection equipment. The formation reason of the linear or banded structure is that, in the melting process of quartz glass, due to the difference in raw material purity, temperature distribution or cooling rate, the local slight difference in internal refractive index is caused. For example, in the process of melting quartz glass by CVD method, SiO2 is deposited on the rotating target surface, the torch is fixed near the top center, and the target surface forms an annular temperature field with an internal and external temperature difference (the inner ring temperature is about 100-200℃ higher than the outer ring), which causes the refractive index gradient of the inner and outer ring materials in the cooling process due to the difference in thermal shrinkage. These refractive index differences (Δn≥1×10⁻ 5 ) can be identified by the stripe detection method in item 6.6 of JC / T185-2013 standard, which is manifested as concentric distribution of light and dark stripes (see Figure 1 ). This stripe phenomenon can cause beam transmission distortion, uneven light spot or system error in high-precision optical elements, which has a negative impact on the quality and precision of high-performance applications such as laser, optical lens and optical window. It can cause the optical system to reduce the function and affect the precision of optical design and optical instruments.

[0003] To solve this problem, the patent document with the publication number CN105502897A discloses a preparation method of ultra-pure quartz glass, but the stripes are eliminated by improving the purity and uniformity of quartz glass. This method is only for the quartz glass being melted, and does not involve the quartz glass which has completed melting and has detected internal partial area with stripes. Only the quartz glass required for processing optical elements can be obtained from the center stripe-free area, and the material utilization rate is low.

[0004] At present, the industry mostly adopts the static heat reforming method of quartz glass ingot to achieve the purpose of expanding the non-striated area, but in the traditional static heat reforming process of the quartz glass ingot, the side and upper part of the quartz glass ingot is heated and melted, and then the glass liquid expands outward to the edge of the mold under the action of gravity. Because the thermal conductivity of quartz glass is relatively low (about 1.3-1.5 W / (m•K)), the temperature rising rate of the internal area is slower than that of the external area, which causes the outer ring glass liquid to melt and fill the gap between the quartz ingot and the crucible first. In this process, the outer area expands excessively (magnification > 5%), while the center area lags behind in heating, and further, due to the installation deviation of the heating body, there is a local temperature fluctuation of 5-30℃ in the internal temperature field of the heating chamber, which aggravates the unevenness in the reforming process, and finally forms the striated distribution of "sparse in the center, dense in the middle, and sparse in the periphery" (see Figure 1 ). Therefore, it is necessary to further improve. SUMMARY

[0005] The purpose of the present application is to provide a homogeneous reforming method and device for quartz glass striation which can effectively eliminate quartz glass striation and improve the uniformity of quartz glass material.

[0006] The technical solution of the present application is: A homogeneous reforming method for eliminating quartz glass striation, characterized in that it comprises the following steps: 1) First, clean the surface of the quartz glass ingot with 10-20% hydrofluoric acid in the conventional way to remove surface impurities, and then dry it after cleaning; place the quartz glass ingot in the crucible of the homogeneous reforming device, and fix it on the self-rotating disc of the homogeneous reforming device with a pressure cover; 2) Raise the revolution disc and the self-rotating disc of the homogeneous reforming device into the hearth of the electric heating furnace through the lifting bracket; thus, the bottom port of the hearth is relatively blocked by the revolution disc of the homogeneous reforming device to prevent the subsequent heat from being dissipated too quickly from the bottom port of the hearth during the homogeneous reforming process; after the revolution disc of the homogeneous reforming device is raised into position, lock the lifting bracket to ensure the stability of the rotation of the homogeneous reforming device during the reforming process; 3) After the above preparation is completed, close the exhaust valve of the heating furnace, start the vacuum pump, and pump the pressure in the furnace to below 1 pa; after the pressure is stabilized, maintain the exhaust valve in the closed state, raise the heating furnace to 300℃, and remove the moisture and part of the impurities in the furnace to achieve a certain cleanliness of the air inside the hearth; then close the vacuum pump, open the inert gas valve to allow inert gas (argon or helium) to enter the hearth of the heating furnace, and when the pressure exceeds 101Kpa, open the exhaust valve, and then close the inert gas valve to maintain a slight positive pressure inside the hearth of the heating furnace and continue to heat the inside of the hearth; 4), when the hearth temperature rises to 1600-1800 ℃, keep the temperature, then start the revolution motor and the rotation motor of the homogenization modification device, drive the revolution disc and the rotation disc to rotate, and then drive the crucible and the quartz glass ingot in the crucible to rotate while revolving, wherein the revolution radius of the revolution disc is 100-400 mm, the revolution speed is 1-10 rpm, the rotation radius of the rotation disc is 300-500 mm, and the rotation speed is 1-20 rpm; while the revolution disc and the rotation disc rotate, the quartz glass ingot in the crucible gradually melts; 5), after 1-2 hours, after the quartz glass ingot in the crucible completely melts; keep the rotation of the revolution disc and the rotation disc according to the above conditions to maintain the uniform heat treatment effect; then close the electric heating furnace, and the hearth temperature naturally cools down; when the hearth temperature naturally cools down to 700-750 ℃, stop the rotation of the revolution disc and the rotation disc, and the homogenization modification operation of the quartz glass strip is completed.

[0007] Step 1) the homogenization modification device comprises a lifting support and a heating furnace, the hearth of the heating furnace is correspondingly embedded with a revolution motor below through the lifting support, a revolution disc is fixed on the rotating shaft of the revolution motor, a rotation motor is mounted on the lower surface of the edge position of the revolution disc through a fixed frame, the rotating shaft of the rotation motor extends to the upper side of the revolution disc, and the top of the rotating shaft extending to the upper side of the revolution disc is provided with a crucible through a rotation disc. The revolution disc, the rotation disc and the crucible are telescoped in the hearth of the heating furnace through the lifting support.

[0008] The side wall of the heating furnace is provided with an exhaust valve and a vacuum pump in an upper and lower spaced manner, and the side wall of the heating furnace is provided with an inert gas valve communicated with an inert gas source, and the inert gas valve, the exhaust valve and the vacuum pump are communicated with the hearth of the heating furnace respectively.

[0009] The beneficial effects of the present application are as follows: The present application is simple and efficient, and through the rotation of the revolution disc and the rotation disc, the planet rotation is formed in the process of homogenization modification, the glass liquid inside the quartz glass ingot in the crucible is homogenized, and under the pushing of the centrifugal force generated by the rotation of the revolution disc and the rotation disc, the strip (uneven material part) moves to the outside, the regulation of the inner quality of the glass liquid is realized, thereby effectively eliminating the strip in the quartz glass ingot, and the uniformity and optical performance of the quartz glass ingot are greatly improved. The present application solves the problem that the volume of the optical material is too small due to the strip in the produced blank ingot through the planet rotation mode, compared with the mode of eliminating the strip by improving the purity, the present application does not have the boundary effect, can effectively reduce the production cost, and improve the material utilization.

[0010] Invention mechanism: The present application promotes the strip (inhomogeneous material part) in the quartz glass ingot molten glass liquid to move outward (edge) by the centrifugal force generated by the revolution disc and rotation disc rotation, realizes the regulation of the quality of the glass liquid, and the strip promoted to the outside (edge) of the quartz glass ingot is cut off as the machining allowance in the subsequent production, so as to achieve the purpose of eliminating the strip. In order to verify the influence of the centrifugal force generated by the revolution disc and rotation disc rotation on the homogeneity of the quartz glass ingot, the inventor has carried out experiments and theoretical verification, specifically: I. Optimization of glass liquid under mechanical action: 1. Only rotation mode: When the quartz glass rotates at an angular velocity , the glass liquid element is subjected to a centrifugal force:

[0011] In the formula, F 离心 is the centrifugal force of the glass liquid rotation, m is the mass of the glass liquid, is the rotation radius.

[0012] When the centrifugal force F 离心 of the glass liquid exceeds the gravity of the glass liquid, the edge glass liquid flows upward along the crucible wall (see Figure 4 ). The glass liquid flow in the edge region drives the synchronous expansion of the center region, so that the glass liquid is gradually homogenized from the center to the edge, and then the strip is restructured from the concentric circle distribution to the "center without strip -peripheral low density" distribution (see Figure 3 ). After the rotation is finished, the speed is reduced to zero at ≤1 rpm / min, the surface tension makes the liquid surface flat, and the raised edge liquid layer backflows to form a surface layer (thickness of 1-5mm) which can be polished and removed.

[0013] 2. Rotation mode: After introducing revolution (angular velocity ω1, radius r1), the force acting on the glass liquid element is expanded as:

[0014] ;

[0015] In the formula, F 合 is the force acting on the glass liquid in the state of planetary rotation (rotation and revolution), is the Coriolis force acting on the glass liquid in the state of revolution, θ is the rotation angle.

[0016] The rotation centrifugal force dominates the radial laminar flow, so that the strip-free area diffuses outward; The Coriolis force induces tangential weak vortex, destroys the laminar flow boundary, promotes the exchange of inner and outer layer materials, homogenizes the quartz glass, and eliminates the stripes; when the Coriolis force is too large, irregular turbulent flow is formed, and the exchange of inner and outer layer materials is too violent to be conducive to the uniform distribution of the glass liquid.

[0017] II. Heat transfer optimization: The low thermal conductivity of quartz glass causes a significant temperature difference between the inner and outer layers at the initial stage of thermal modification (ΔT≈80-150℃). During planetary rotation, although the quartz glass is in a high-temperature softened state , its macroscopic fluidity is extremely low due to its high viscosity, and it cannot achieve heat transfer through traditional liquid convection. In this process, the shear stress driven by rotation and periodic thermal relaxation play a key role: 1. Shear stress promotes heat diffusion: Rotational motion generates periodic shear stress (τ≈10-100 Pa) in the glass, which breaks the local binding of molecular chains, accelerates the heat transfer rate of molecules, and increases the thermal conductivity efficiency by 2-3 times.

[0018] 2. Dynamic thermal relaxation homogenizes temperature: Rotation causes different regions of the quartz glass to alternately expose to the high-temperature radiation zone and the relatively low-temperature zone of the heating chamber, through a dynamic heat absorption-release cycle (the frequency is positively correlated with the rotation speed), the temperature difference between the inner and outer layers is reduced to ΔT≤15℃.

[0019] This mechanism effectively suppresses the regeneration of stripes caused by uneven heat conduction. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a photo of the distribution of stripes under polarized light of quartz glass in a traditional process; Figure 2 is a structural schematic diagram of the homogenization modification device of the application; Figure 3 is a photo of the distribution of stripes under polarized light of quartz glass in the application; Figure 4 is a schematic diagram of the flow state of the glass liquid in the application.

[0021] In the figure: 1, lifting support, 2, electric heating furnace, 3, heating furnace hearth, 4, revolution motor, 5, revolution disc, 6, rotation motor, 7, rotation disc, 8, crucible, 9, emptying valve, 10, vacuum pump, 11, inert gas valve. DETAILED DESCRIPTION

[0022] The quartz glass stripe homogenization modification device comprises a lifting support 1 and an electric heating furnace 2. A heating furnace hearth 3 of the electric heating furnace 2 is correspondingly embedded below with a revolution motor 4 through the lifting support 1. A rotation shaft of the revolution motor 4 is fixed with a revolution disc 5. An edge position lower surface of the revolution disc 5 is embedded with a rotation motor 6 through a fixed frame. A rotation shaft of the rotation motor 6 extends to above the revolution disc 5. A top of the rotation shaft extending to above the revolution disc 5 is embedded with a crucible 8 through a rotation disc 7. The revolution disc 5, the rotation disc 7 and the crucible 8 are lifted in the heating furnace hearth 3 through the lifting support 1. An emptying valve 9 and a vacuum pump 10 are arranged on the furnace wall of one side of the electric heating furnace 2 in an up-down interval. An inert gas valve 11 communicating with an inert gas source is arranged on the furnace wall of the other side of the electric heating furnace 2. The inert gas valve 11, the emptying valve 9 and the vacuum pump 10 respectively communicate with the heating furnace hearth 3.

[0023] The revolution disc 5 and the rotation disc 7 of the homogenization modification device form planetary rotation in the process of homogenization modification. The function is to drive the crucible 8 and the glass liquid in the crucible 8 to make planetary motion, that is, to drive the glass liquid to rotate simultaneously while revolving, so as to ensure the middle homogenization of the quartz glass liquid through centrifugal force, that is, to push the stripe (inhomogeneous material part) in the molten glass liquid of the quartz glass ingot to the outside (edge), realize the regulation of the internal quality of the glass liquid, and push the stripe to the outside (edge) of the quartz glass ingot to be cut off as a processing allowance in subsequent production, so as to achieve the purpose of eliminating the stripe.

[0024] The quartz glass stripe homogenization modification method comprises the following steps: First, the surface of the quartz glass ingot is cleaned in a conventional manner using 10-20% hydrofluoric acid, and then placed in the crucible 8 of the homogenization modification device and fixed on the self-rotation disc 7 of the homogenization modification device with the aid of a pressing cover; the public rotation disc 5 and the self-rotation disc 7 of the homogenization modification device are raised into the heating furnace hearth 3 of the electric heating furnace 2 through the lifting support 1; in this process, the public rotation disc 5 forms a relative block to the bottom port of the heating furnace hearth 3 to avoid subsequent heat from being too quickly dissipated from the bottom port of the heating furnace hearth 3 during the homogenization modification process; after the public rotation disc 5 of the homogenization modification device is raised into position, the lifting support 1 is locked to ensure the stability of the rotation of the homogenization modification device during the modification process. After the above preparation is completed, the exhaust valve 9 is closed, the vacuum pump 10 is opened, the pressure in the furnace is pumped to below 1 pa, and after the pressure is stabilized, the vacuum pump 10 is kept open. The heating furnace hearth 3 is heated to 300℃, and the moisture and part of the impurities in the furnace are removed to make the air inside the furnace hearth reach a certain cleanliness. Then the vacuum pump 10 is closed, the inert gas valve 11 is opened to make the inert gas (argon or helium) enter the heating furnace hearth 3, and when the pressure exceeds 101 Kpa, the exhaust valve 9 is opened, and then the inert gas valve 11 is closed to maintain a slight positive pressure inside the heating furnace hearth 3, and the electric heating furnace 2 continues to heat the heating furnace hearth 3. When the temperature of the furnace hearth rises to 1600-1800℃, the temperature is maintained, and then the public rotation motor 4 and the self-rotation motor 6 are started to drive the public rotation disc 5 and the self-rotation disc 7 to rotate, thereby driving the crucible 8 and the quartz glass ingot in the crucible 8 to rotate while rotating; wherein the public rotation radius of the public rotation disc 5 is 100-400mm, the public rotation speed is 1-10rpm, the self-rotation radius of the self-rotation disc 7 is 300-500mm, and the self-rotation speed is 1-20rpm; while the public rotation disc 5 and the self-rotation disc 7 rotate, the quartz glass ingot in the crucible 8 gradually melts; after 1-2 hours, the quartz glass ingot in the crucible 8 is completely melted; the rotation of the public rotation disc 5 and the self-rotation disc 7 is continued under the above conditions to maintain uniform heat treatment effect; then the electric heating furnace 2 is turned off, and the furnace hearth temperature is naturally cooled; when the furnace hearth temperature naturally cools to 700-750℃, the rotation of the public rotation disc 5 and the self-rotation disc 7 is stopped, and the homogenization modification operation of the quartz glass strip is completed.

[0025] Comparative Example 1: A quartz ingot with a specification of Φ400*100mm is selected, and through testing, the non-stripe area is a center Φ200mm caliber. After the quartz glass ingot is cleaned, it is placed in the heating furnace hearth 3 through the lifting support 1 and the crucible 8 without rotating. After being treated at a maximum temperature of 1750℃ for 6 hours, it is modified to 420*90mm, and after processing, testing shows that the center Φ210mm caliber area of the quartz ingot has no stripes.

[0026] Comparative Example 2: A quartz ingot with a specification of Φ500*80mm is selected, and through testing, the non-streak region is a center Φ240mm aperture. After the quartz glass ingot is cleaned, it is placed in the center of the heating chamber through the lifting support 1, the rotating device, and the crucible 8, the rotating device is started to rotate, and the rotation speed is 3rpm. After treatment at a maximum temperature of 1750℃ and a constant temperature time of 6 hours, it is modified to Φ520*74mm, and after processing, testing shows that the quartz ingot center Φ300mm aperture region is non-streaked. Example 3

[0027] A quartz ingot with a specification of Φ450*120mm is selected, and through testing, the non-streak region is a center Φ220mm aperture. In this embodiment, the scheme of the application is adopted; wherein, the rotation speed is 3rpm, the revolution radius is 150mm, and the revolution speed is 6rpm. After treatment at a maximum temperature of 1750℃ and a constant temperature time of 6 hours, it is modified to Φ480*107mm, and after processing, testing shows that the quartz ingot center Φ330mm aperture region is non-streaked.

[0028] Example 4 A quartz ingot with a specification of Φ480*100mm is selected, and through testing, the non-streak region is a center Φ230mm aperture. In this embodiment, the scheme of the application is adopted; wherein, the rotation speed is 6rpm, the revolution radius is 150mm, and the revolution speed is 3rpm. After treatment at a maximum temperature of 1750℃ and a constant temperature time of 6 hours, it is modified to Φ500*92mm, and after processing, testing shows that the quartz ingot center Φ420mm aperture region is non-streaked.

[0029] Example 5 A quartz ingot with a specification of Φ480*130mm is selected, and through testing, the non-streak region is a center Φ200mm aperture. In this embodiment, the scheme of the application is adopted; wherein, the rotation speed is 10rpm, the revolution radius is 150mm, and the revolution speed is 3rpm. After treatment at a maximum temperature of 1750℃ and a constant temperature time of 6 hours, it is modified to Φ500*120mm, and after processing, testing shows that the quartz ingot center Φ440mm aperture region is non-streaked.

[0030] The data statistics of Examples 1-5 are as follows:

[0031] Table 1 is a data statistics table of Examples 1-5

[0032] Table 2 is an effect statistics table under different speed ratios Note: The vortex intensity is based on the laminar shear stress According to multiple group data experiments, the planet rotation heat modification device can enlarge the non-stripe area to about 75% of the final modification aperture area (88% in diameter). The rotation speed is 1-20 rpm, preferably 6-10 rpm, the revolution radius is 100-400 mm, preferably 150-300 mm, and the revolution speed is 1-10 rpm, preferably 3-5 rpm.

[0033] The method for eliminating quartz glass stripes by planet rotation heat modification is simple and efficient. The planet rotation can homogenize the glass liquid and reduce the temperature difference everywhere, thereby effectively eliminating the stripes in the middle of the quartz glass ingot after heat modification, concentrating the stripes on the edge of the quartz glass ingot, and completely eliminating the stripes by cutting off the quartz glass in the stripe area, greatly improving the uniformity and optical performance of the quartz glass ingot. Since it improves uniformity by planet rotation, compared with eliminating stripes by improving purity, it does not have boundary effect, can effectively reduce production cost, and improve the effect of stripe elimination. The optimized quartz glass is suitable for high-end application scenarios such as precision optical instruments, aerospace optical instruments, lasers and optical communication, semiconductors and solar industry due to its excellent optical properties. At the same time, it also solves the problem of existing methods that have boundary effect, leading to difficulty in eliminating stripes and high cost.

Claims

1. A method for homogenizing quartz glass to eliminate striations, characterized in that: It includes the following steps: 1) First, the surface of the quartz glass ingot is cleaned with 10-20% hydrofluoric acid in the conventional manner to remove surface impurities. After cleaning and drying, the quartz glass ingot is placed in the crucible (8) of the homogenization modification device and fixed on the rotating disk (7) of the homogenization modification device after being covered with a pressure cap. 2) The orbital disk (5) and the self-rotating disk (7) of the homogenization modification device are raised into the furnace chamber (3) of the electric heating furnace (2) by the lifting bracket (1); thereby, the orbital disk (5) of the homogenization modification device forms a relative blockage at the bottom port of the furnace chamber (3) to prevent the heat from dissipating too quickly from the bottom port of the furnace chamber (3) during the homogenization modification process; after the orbital disk (5) of the homogenization modification device is raised to the position, the lifting bracket (1) is locked to ensure the stability of the rotation of the homogenization modification device during the modification process; 3) After the above preparations are completed, close the vent valve (9) of the electric heating furnace (2), turn on the vacuum pump (10), and pump the furnace pressure to below 1 Pa. After the pressure stabilizes, keep the vacuum pump (10) on and heat the furnace chamber (3) to 300°C to remove moisture and some impurities from the furnace so that the air inside the furnace chamber reaches a certain level of cleanliness. Then turn off the vacuum pump (10), open the inert gas valve (11) to allow inert gas (argon or helium) to enter the furnace chamber (3), and when the pressure exceeds 101 kPa, open the vent valve (9), and then close the inert gas valve (11) to maintain a slight positive pressure inside the furnace chamber (3). Turn on the electric heating furnace (2) to heat the inside of the furnace chamber (3). 4) When the temperature of the furnace chamber (3) of the heating furnace rises to 1600-1800℃, stop heating and maintain the temperature. Then start the revolution motor (4) and rotation motor (6) of the homogenization modification device to drive the revolution disk (5) and rotation disk (7) to rotate, thereby driving the crucible (8) and the quartz glass ingot in the crucible (8) to rotate while revolutionizing. The revolution radius of the revolution disk (5) is 100-400mm and the revolution speed is 1-10rpm. The rotation radius of the rotation disk (7) is 300-500mm and the rotation speed is 1-20rpm. While the revolution disk (5) and rotation disk (7) are rotating, the quartz glass ingot in the crucible (8) gradually melts. 5) After 1-2 hours, when the quartz glass ingot in the crucible (8) has completely melted, continue to rotate the revolution disk (5) and the rotation disk (7) under the above conditions to maintain a uniform heat treatment effect; then turn off the electric heating furnace (2) and let the furnace temperature cool down naturally; when the furnace temperature cools down naturally to 700-750℃, stop the rotation of the revolution disk (5) and the rotation disk (7), and the homogenization modification operation of the quartz glass stripes is completed.

2. The homogeneous modification method for eliminating striations in quartz glass according to claim 1, characterized in that: The homogenization modification device described in step 1) includes a lifting bracket (1) and an electric heating furnace (2). A revolution motor (4) is embedded in the lower part of the furnace chamber (3) of the heating furnace through the lifting bracket (1). A revolution disk (5) is fixed on the shaft of the revolution motor (4). A self-rotating motor (6) is mounted on the lower surface of the edge position of the revolution disk (5) through a fixed frame. The shaft of the self-rotating motor (6) extends to the top of the revolution disk (5). A crucible (8) is mounted on the top of the shaft extending to the top of the revolution disk (5) through the self-rotating disk (7). The revolution disk (5), the self-rotating disk (7), and the crucible (8) are extended and retracted in the furnace chamber (3) of the heating furnace through the lifting bracket (1).

3. The homogeneous modification method for eliminating striations in quartz glass according to claim 2, characterized in that: On one side of the electric heating furnace (2), an exhaust valve (9) and a vacuum pump (10) are arranged in an alternating pattern. On the other side of the electric heating furnace (2), an inert gas valve (11) connected to an inert gas source is provided. The inert gas valve, (11), (9) and vacuum pump (10) are respectively connected to the furnace chamber (3) of the heating furnace.

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