Recycling method of quartz crucible after application of Czochralski single crystal

Abstract

The invention discloses a recovery method of a quartz crucible after application of a Czochralski single crystal, and relates to the technical field of waste recovery. The method comprises the steps of sorting, grading and screening, preliminary cleaning, high-temperature treatment (500-1000 DEG C, heat preservation for 4-8 hours), water quenching and cooling, secondary screening, high-purity fused quartz treatment and cristobalite treatment. The core is that the fused quartz and the cristobalite are efficiently separated by utilizing the thermophysical property difference between the fused quartz (the thermal expansion coefficient is 0.5 * 10 <-6 > / DEG C) and the cristobalite (the thermal expansion coefficient is 11 * 10 <-6 > / DEG C) and the stress generated by crystal form transformation (beta-alpha, and the volume expansion is 2.8%) of the cristobalite. The fused quartz silica powder (used for ceramic crucible coatings, PCBs and the like) and the high-purity cristobalite silica powder (used for high-end ceramics, coatings and the like) with the purity larger than or equal to 99.995% can be obtained, the fused quartz recovery rate reaches 74% or above, the whole process is environmentally friendly and free of pollution, the problems that an existing recovery method is low in additional value and poor in product quality are solved, and the method is suitable for industrial production. And high value-added utilization of the scrapped quartz crucible is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste recycling, in particular to a recovery method of quartz crucible applied in Czochralski single crystal, which is suitable for high-value-added recovery of discarded quartz crucible in Czochralski single crystal production, can obtain high-purity fused quartz and high-purity cristobalite products, and is used in high-end material field. BACKGROUND

[0002] In the production process of Czochralski single crystal, the quartz glass crucible is a core consumable, which mainly serves to hold high-temperature molten silicon material and provides a stable container environment for single crystal silicon growth. Due to long-term exposure to high temperature (above 1400℃) and strong chemical corrosion, the quartz crucible will gradually be eroded by the silicon material and crystallize on the surface, eventually being discarded and removed from the single crystal furnace.

[0003] At present, the treatment of discarded quartz crucibles has obvious limitations:

[0004] Low added value utilization: Most of the discarded crucibles are directly crushed and used to prepare building materials, ordinary ceramics and other low added value products, which fails to take advantage of the core component-high purity quartz, resulting in serious waste of high-quality quartz resources;

[0005] Unstable recovery quality: A small number of attempts to recycle discarded crucibles to prepare glass products, but due to the presence of silicon residue and impurities on the surface of the crucible, and the formation of a 3-5mm thick cristobalite layer on the surface after high temperature use (cristobalite and fused quartz have large differences in crystal form and performance), existing technologies cannot efficiently separate cristobalite and fused quartz, resulting in low purity and large performance fluctuations of recycled glass products, which are difficult to meet the requirements of high-end fields such as PCB circuit boards and chip packaging.

[0006] Therefore, it is of great significance to develop a method that can efficiently separate cristobalite and fused quartz and realize high-value-added recovery of discarded quartz crucibles for resource conservation and economic benefit improvement. SUMMARY

[0007] In view of the problems of low added value, difficulty in separating cristobalite and fused quartz, and unstable product quality in the recovery of discarded quartz crucibles in the prior art, the present application provides a recovery method of quartz crucible applied in Czochralski single crystal, which realizes efficient separation of fused quartz and cristobalite by utilizing the difference in thermal physical properties of the two, obtains high-purity fused quartz and cristobalite products, and improves resource utilization and recovery added value.

[0008] According to an aspect of the present application, a recovery method of quartz crucible applied in Czochralski single crystal, comprising the following steps:

[0009] Step S1, sorting: using manual sorting or equipment sorting to sort the discarded quartz crucible material after the application of the straight pull single crystal, and removing the mixed silicon material and other visible impurities;

[0010] Step S2, grading and screening: grading and screening the quartz glass material after sorting in step S1 by using a vibrating screen, the mesh size of the vibrating screen is 30-50 mm, and the quartz glass blocks on the screen are taken to the subsequent process after screening;

[0011] Step S3, preliminary cleaning: the quartz glass blocks obtained in step S2 are subjected to preliminary cleaning to remove dust, oil stains and other visible impurities adhered to the surface;

[0012] Step S4, high temperature treatment: the quartz glass blocks after cleaning in step S3 are put into a high temperature sintering kiln, the temperature in the kiln is controlled to be 500-1000℃, and the temperature is kept for 4-8 hours; after the temperature keeping is finished, the waste heat is recycled by air circulation, and the quartz glass blocks are taken out of the kiln when the surface temperature of the quartz glass blocks cools to 300-350℃;

[0013] Step S5, water quenching: the quartz glass blocks taken out of the kiln in step S4 are immediately placed in water for rapid cooling, so that the cristobalite layer on the surface of the quartz glass blocks cracks and falls off;

[0014] Step S6, secondary screening: the quartz glass blocks after water quenching in step S5 and the cristobalite layer that cracks and falls off are put into a vibrating screen for screening, the mesh size of the vibrating screen is 15-30 mm, the product on the screen is high-purity fused quartz glass block with cristobalite content ≤1.5%, and the product under the screen is high-purity cristobalite particles;

[0015] Step S7, high-purity fused quartz treatment: purity detection is performed on the high-purity fused quartz glass block on the screen in step S6, and the glass block with purity ≥99.995% is selected for crushing to obtain high-purity fused quartz silicon micro powder;

[0016] Step S8, cristobalite treatment: the cristobalite particles under the screen in step S6 are crushed and ball milled to obtain high-purity cristobalite silicon micro powder.

[0017] Preferably, in step S3, the preliminary cleaning is performed by using a high-pressure water gun or by soaking in a pure water solution and then ultrasonic cleaning; if ultrasonic cleaning is used, the soaking time is 30-60 minutes, and the ultrasonic power is 200-400 W.

[0018] Preferably, in step S4, the high temperature sintering kiln is an electric furnace or a tunnel kiln, the temperature in the kiln is controlled to be 600℃, and the temperature keeping time is 6 hours.

[0019] Preferably, in step S5, the water is room temperature cold water, and the water temperature is 20-25℃.

[0020] Preferably, in step S2, the screen aperture of the vibrating screen is 50 mm; in step S6, the screen aperture of the vibrating screen is 25 mm.

[0021] Preferably, in step S7, the purity detection adopts ICP-OES (inductively coupled plasma optical emission spectrometry), and the high-purity fused quartz silicon powder after crushing is used for coating of a quartz ceramic crucible, a PCB circuit board, or a chip package.

[0022] Preferably, in step S8, the high-purity cristobalite silicon powder is used for high-end ceramics, coatings, building materials, or as a functional filler for compounding with organic high-molecular polymers.

[0023] Compared with the prior art, the application has the following advantages:

[0024] 1. The fused quartz and cristobalite are separated by stress generated by volume change due to different quartz crystal form conversion and different thermal expansion coefficients after temperature change, and the recovery rate of the fused quartz is more than 74%, and the purity is more than 99.995%.

[0025] 2. Through the combined process of "high-temperature treatment + water quenching", the cristobalite layer on the surface of the crucible cracks and falls off due to the dramatic change in volume, realizing separation from the fused quartz, greatly increasing the separation efficiency and the qualified rate of the product, and without the use of acid and alkali reagents, green and environmentally friendly.

[0026] 3. The different particle sizes of different products after separation can quickly separate the products to obtain the required products. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a flowchart of a recycling method of a quartz crucible used for a direct pulling single crystal according to an embodiment of the application;

[0028] Figure 2 is a photograph of a quartz crucible before treatment; it can be seen from the photograph that the surface of the crucible is covered with a layer of gray-white cristobalite, and a small amount of silicon impurities are attached;

[0029] Figure 3 is a photograph of a quartz crucible after treatment; in the photograph, the cristobalite layer has completely fallen off, exposing a transparent high-purity fused quartz glass block, and the surface has no obvious impurities;

[0030] Figure 4 is an XRD detection spectrum of high-purity fused quartz glass after treatment (detection equipment: D8 Advance, Cu target); in the spectrum, only the amorphous diffuse peak of fused quartz (2θ≈21.5°) appears, and no characteristic peak of cristobalite (2θ≈26.6°, 36.1°) appears, indicating that there is no cristobalite residue in the product. DETAILED DESCRIPTION

[0031] In order to make the content of the present application more easily understood, the following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Figures 1-4 In order to make the content of the present application more easily understood, the following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application.

[0032] The core principle of the present application is based on the difference in thermal expansion coefficients of fused quartz and cristobalite and the volume change of cristobalite during phase transformation. On the one hand, the difference in thermal expansion coefficients is that the thermal expansion coefficient of fused quartz is 0.5*10 -6 / ℃, and the thermal expansion coefficient of cristobalite is 11*10 -6 / ℃, and the difference between them is significant, which will cause different degrees of volume change when the temperature changes. On the other hand, the volume change during phase transformation is that cristobalite exists in the reversible transformation of alpha phase (low temperature phase) and beta phase (high temperature phase) - when the temperature drops to about 250℃, beta-cristobalite will quickly transform into alpha-cristobalite, with a volume expansion of 2.8%; when the temperature rises, alpha-cristobalite will also transform into beta-cristobalite, with a volume contraction of 2.8%.

[0033] Based on the above characteristics, through the combined process of "high temperature treatment + water quenching", the cristobalite layer on the surface of the crucible can be cracked and separated from the fused quartz due to the dramatic change in volume; and then through grading screening, products with different purities and different purposes can be obtained.

[0034] In combination with Figure 1 As shown in the drawings, a recycling method of a quartz crucible used for Czochralski single crystal application, characterized in that it comprises the following steps:

[0035] Step S1, sorting: using manual sorting or equipment sorting (such as photoelectric sorting machine) to sort the scrapped quartz crucible used for Czochralski single crystal application, remove the mixed bulk silicon material, metal impurities and other non-quartz foreign matters, and ensure that the subsequent processing raw material is single quartz component;

[0036] Step S2, grading screening: grading the quartz glass material after sorting in step S1 by a vibrating screen, the mesh size of the vibrating screen is 30-50mm, and the quartz glass blocks on the screen after screening are transferred to the subsequent process, and the small quartz fragments under the screen can be temporarily stored for subsequent mixing of cristobalite powder;

[0037] Step S3, preliminary cleaning: preliminarily cleaning the quartz glass blocks obtained in step S2 to remove dust, oil stains and residual silicon powder attached to the surface:

[0038] Option 1: using a high-pressure water gun (pressure 0.8-1.2MPa) for direct washing, and the washing time is 5-10 minutes;

[0039] Option 2: soak in pure water solution (deionized water or distilled water) for 30-60 minutes, then send to ultrasonic cleaning machine (power 200-400W) for 15-20 minutes to ensure removal of surface micro impurities;

[0040] The preliminary cleaning method is high-pressure water gun washing or ultrasonic cleaning after soaking in pure water solution. If ultrasonic cleaning is used, the soaking time is 30-60 minutes and the ultrasonic power is 200-400W;

[0041] Step S4, high temperature treatment: place the quartz glass block cleaned in step S3 into a high temperature sintering kiln (electric furnace or tunnel kiln), control the temperature in the kiln to be 500-1000℃ (preferably 600℃), and keep the temperature for 4-8 hours (preferably 6 hours); after the heat preservation is completed, the residual heat in the kiln is introduced into the preheating zone through an air circulation pipeline to realize residual heat reuse; when the surface temperature of the quartz glass block decreases to 300-350℃ (higher than the α-β phase transition temperature of cristobalite 250℃ to avoid premature crystal type conversion), the kiln is taken out;

[0042] Step S5, water quenching: immediately place the quartz glass block taken out of the kiln in step S4 into room temperature cold water (20-25℃) to realize rapid cooling (cooling rate > 50℃ / min); during this process, the cristobalite layer experiences a crystal type conversion (volume expansion 2.8%) of “β-cristobalite→α-cristobalite” due to a large thermal expansion coefficient, resulting in a large volume difference between the cristobalite layer and the fused quartz, which causes the cristobalite layer to crack and fall off from the surface of the fused quartz;

[0043] Step S6, secondary screening: send the quartz glass block after water quenching in step S5 together with the fallen cristobalite layer into a vibrating screen, and select a screen with a pore size of 15-30mm for screening:

[0044] Screened product: high-purity fused quartz glass block with a particle size ≥15-30mm, and the cristobalite content is ≤1.5%;

[0045] Screened product: high-purity fused quartz glass block with a particle size ≥15-30mm, and the cristobalite content is ≤1.5%;

[0046] Step S7, high-purity fused quartz treatment: purity detection (using ICP-OES method) is performed on the high-purity fused quartz glass block screened in step S6, and glass blocks with a purity ≥99.995% are selected and sent into a crusher (such as a jaw crusher + impact crusher) to be crushed to a particle size of 1-50μm to obtain high-purity fused quartz silicon micro powder; the micro powder can be used for quartz ceramic crucible coating (to improve the denseness of the coating), PCB circuit board substrate (to reduce the dielectric constant), or chip packaging material (to improve the insulation);

[0047] Step S8, cristobalite treatment: the undersize cristobalite particles of step S6 are sent to a crusher to crush to a particle size of 50-100 pm, and then sent to a ball mill (agate ball mill jar, ball-to-material ratio of 3:1) for ball milling for 2-4 hours to prepare high-purity cristobalite silicon micropowder (particle size of 5-20 pm); the micropowder can be used for high-end ceramics (to improve high-temperature resistance), high-temperature resistant coatings (to improve hardness), or as a functional filler to be compounded with organic high polymer polymers such as polypropylene and epoxy resin to improve the mechanical properties and thermal stability of the composite material.

[0048] Example 1: Recycling process based on electric furnace

[0049] According to the above scheme, for the straight-lift single-crystal crucible material, after sorting, the material is sieved through a 50 mm sieve, the sieve is cleaned by a high-pressure water gun, and then the straight-lift single-crystal material is sintered using a 600°C electric furnace, and then the sintered product is quenched in cold water at room temperature after natural air cooling to 330°C. After filtering the water, the product is sieved through a 25 mm sieve to obtain high-purity quartz glass as shown above. Figure 3 The product is subjected to XRD detection of quartz glass to determine that there is no cristobalite in the glass, and ICP-OES is used to detect the purity of the product to determine that the purity is >99.995%. The product is ball milled to obtain high-purity slurry, and the crucible is brushed and coated with the slurry. The customer uses the coated crucible normally, and the yield recovery of high-purity fused quartz blocks prepared by the electric furnace is 75.36%.

[0050] Example 2: Recycling process based on tunnel kiln

[0051] According to the above scheme, for the straight-lift single-crystal crucible material, after sorting, the material is sieved through a 50 mm sieve, the sieve is cleaned by a high-pressure water gun, and then the straight-lift single-crystal material is sintered using a 600°C electric furnace, and then the sintered product is quenched in cold water at room temperature after natural air cooling to 330°C. After filtering the water, the product is sieved through a 25 mm sieve to obtain high-purity quartz glass as shown above. Figure 3 The product is subjected to XRD detection of quartz glass to determine that there is no cristobalite in the glass, and ICP-OES is used to detect the purity of the product to determine that the purity is >99.995%. The product is ball milled to obtain high-purity slurry, and the crucible is brushed and coated with the slurry. The customer uses the coated crucible normally, and the yield recovery of high-purity fused quartz blocks prepared by the electric furnace is 75.36%.

[0052] The difference in recovery rate at the same temperature between the two processes is small.

[0053] The above examples are only used to illustrate the technical solutions of the embodiments of the present application, and not to limit them. Although the embodiments of the present application have been described in detail with reference to the foregoing examples, those skilled in the art should understand that, without departing from the spirit and scope defined by the claims of the present application, they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement to some of the technical features.

Claims

1. A method for recycling a quartz crucible after Czochralski single crystal application, characterized in that, Includes the following steps: Step S1, Sorting: The waste quartz crucible material after the application of Czochralski single crystal is sorted by manual sorting or equipment sorting to remove mixed silicon material and other visible impurities. Step S2, Grading and Screening: The quartz glass material sorted in step S1 is graded by a vibrating screen with a screen aperture of 30-50mm. After sieving, the quartz glass blocks on the screen are transferred to the subsequent process. Step S3, Preliminary cleaning: Perform preliminary cleaning on the quartz glass block obtained in step S2 to remove dust, oil and other visible impurities adhering to the surface; Step S4, High-temperature treatment: Place the quartz glass block cleaned in step S3 into a high-temperature sintering kiln, control the kiln temperature to 500-1000℃, and keep it at that temperature for 4-8 hours; after the holding time is over, reuse the residual heat through air circulation, and remove the kiln when the surface temperature of the quartz glass block cools down to 300-350℃. Step S5, water quenching and cooling: Immediately place the quartz glass block that came out of the kiln in step S4 into water for rapid cooling, so that the cristobalite layer on the surface of the quartz glass block cracks and falls off. Step S6, Secondary screening: The quartz glass blocks quenched in step S5 and the cracked and detached cristobalite layers are placed into a vibrating screen for screening. The screen mesh size of the vibrating screen is 15-30mm. The product on the screen is a high-purity fused quartz glass block with a cristobalite content of ≤1.5%, and the product under the screen is a high-purity cristobalite particle. Step S7, High-purity fused silica treatment: The purity of the high-purity fused silica glass blocks on the sieve from step S6 is tested, and glass blocks with a purity ≥ 99.995% are selected and crushed to obtain high-purity fused silica silica powder. Step S8, Quartz Processing: The quartz particles below the sieve in Step S6 are crushed and ball-milled to prepare high-purity quartz silica micro powder.

2. The method for recycling a quartz crucible after Czochralski single crystal application according to claim 1, characterized in that, In step S3, the preliminary cleaning method is high-pressure water gun rinsing or ultrasonic cleaning after soaking in pure water solution; if ultrasonic cleaning is used, the soaking time is 30-60 minutes and the ultrasonic power is 200-400W.

3. The method for recycling a quartz crucible after Czochralski single crystal application according to claim 1, characterized in that, In step S4, the high-temperature sintering kiln is an electric furnace or a tunnel kiln, the kiln temperature is controlled at 600℃, and the holding time is 6 hours.

4. The method for recycling a quartz crucible after Czochralski single crystal application according to claim 1, characterized in that, In step S5, the water is room temperature cold water with a temperature of 20-25℃.

5. The method for recycling a quartz crucible after Czochralski single crystal application according to claim 1, characterized in that, In step S2, the mesh size of the vibrating screen is 50mm; in step S6, the mesh size of the vibrating screen is 25mm.

6. The method for recycling a quartz crucible after Czochralski single crystal application according to claim 1, characterized in that, In step S7, the purity detection is performed using ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy). The high-purity fused silica micropowder after crushing is used for coating quartz ceramic crucibles, PCB circuit boards, or chip packaging.

7. The method for recycling a quartz crucible after Czochralski single crystal application according to claim 1, characterized in that, In step S8, the high-purity cristobalite silica micropowder is used in high-end ceramics, coatings, building materials, or as a functional filler in combination with organic polymers.

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