Method for calcining high purity silicon dioxide

Abstract

The application discloses a calcination method of high-purity silicon oxide, and belongs to the technical field of high-purity silicon oxide synthesis and preparation. The method is characterized in that a disturbance environment is created by introducing a calcination gas at a certain flow rate, so that the silicon oxide is fully contacted with the calcination gas, thereby enabling the residual organic matter to be fully combusted and the residual carbon to be effectively removed. The residual oxygen in the pores of the silicon dioxide is fully removed by adopting a two-step replacement mode, and the oxygen in the pores is replaced by helium with a lower density. Further, high-temperature calcination is performed in a vacuum environment, and after the residual gas in the pores of the silicon dioxide is discharged, the pores in the silicon dioxide particles are closed. In order to avoid the introduction of water or other gases and impurities again in the cooling process, the inert gas helium is introduced for cooling to room temperature after the vacuum environment is cooled to a certain temperature, and high-purity and high-quality synthetic silicon oxide is obtained.

Description

Technical Field

[0001] This invention relates to the technical field of silicon oxide preparation methods, and in particular to a calcination method for high-purity silicon oxide (synthetic silicon oxide). Background Technology

[0002] High-purity silica products, such as quartz crucibles, quartz tubes, and quartz devices, are crucial materials supporting the development of strategic emerging industries like semiconductors, photovoltaics, and optical communications. The purity of silica determines the quality of these products, thus affecting their performance in the semiconductor field. With economic development and technological advancements, new requirements are being placed on the purity of silica. Quartz products made from silica with a purity of 5N or higher have become the highest value-added downstream quartz products.

[0003] With the increasing demand for high-purity silicon oxide, its preparation technology has become a research hotspot in the field. Mitsubishi Corporation of Japan has used a tetramethoxysilane hydrolysis process to produce silica with a purity of 5N or higher, and has successfully applied its quartz crucibles in the semiconductor industry. After researching the alkoxysilane hydrolysis process, the applicant discovered that even when using alkoxysilanes with a purity of 5N or higher and hydrolyzing them with high-purity water to obtain silica sol, black spots and bubbles still exist in the product after drying and calcination. This results in bubbles in the prepared quartz crucibles, affecting their transparency and lifespan.

[0004] The applicant has conducted extensive experimental research on the calcination process of high-purity silicon dioxide. The main reason for the black spots and bubbles is that the silicon dioxide before calcination has pores, and organic matter remains in the pores. The organic matter does not react fully during the calcination process to form residual carbon. In addition, the oxygen or air used in the calcination process is not effectively discharged and remains in the pores of the silicon dioxide to form bubbles. In response to the above problems, the applicant has developed a calcination method that can effectively solve the above problems. Summary of the Invention

[0005] To address the issues that arise during the calcination process of preparing high-purity silicon dioxide from siloxane hydrolysis, such as incomplete combustion of residual organic matter leading to carbon buildup and incomplete removal of gases from the internal pores of silicon dioxide, thus affecting the quality of the final prepared crucible, this invention provides a calcination method for high-purity silicon dioxide.

[0006] The technical solution of this invention: a calcination method for high-purity silicon dioxide, comprising the following steps:

[0007] S1) The dried and pulverized silicon dioxide is calcined at 900~1000 ℃ in an oxygen atmosphere for 2~20 h, with an oxygen flow rate of 1~3 L / min;

[0008] S2) Calcination at 600~900 ℃ in a mixed atmosphere of oxygen and helium with a weight ratio of 2:1 for 1~10 h, with a flow rate of 1~3 L / min for the mixed oxygen and helium gas.

[0009] S3) Calcination at 500~800 ℃ in a helium atmosphere for 1~10 h, with a helium flow rate of 3~6 L / min;

[0010] S4) Remove helium under reduced pressure, and calcine at 1100-1300 ℃ for 2-10 h at 10-100 Pa; after calcine, cool to room temperature in a helium atmosphere.

[0011] In some specific roasting methods, the roasting time for step S1 is 2~10 h, the roasting time for step S2 is 1~5 h, the roasting time for step S3 is 1~5 h, and the roasting time for step S4 is 2~5 h.

[0012] In some specific roasting methods, the heating rate in step S1 is 50~100 ℃ / h;

[0013] The heating rate in step S4 is 200~300 ℃ / h.

[0014] In some specific roasting methods, oxygen and helium are used during the roasting process with a purity of not less than 99.999%.

[0015] The calcination method provided by this invention is applicable to the calcination of most high-purity silicon dioxide prepared by hydrolysis.

[0016] Specifically, the high-purity silicon dioxide in the calcination method is prepared by hydrolysis of tetraalkoxysilane.

[0017] Specifically, the high-purity silicon dioxide in the calcination method is prepared by hydrolysis of tetramethoxysilane, tetraethoxysilane, or tetraisopropoxysilane.

[0018] Specifically, the high-purity silicon dioxide in the calcination method is prepared by hydrolysis of tetramethoxysilane or tetraethoxysilane.

[0019] The beneficial effects of this invention are as follows: This invention provides a calcination method for high-purity silicon dioxide. The method creates a disturbed environment by introducing calcining gas at a certain flow rate, allowing for sufficient contact between the silicon dioxide and the calcining gas, thereby enabling the complete combustion of residual organic matter and effectively removing residual carbon. A two-step displacement method is used to thoroughly remove residual oxygen from the pores of silicon dioxide, replacing the oxygen in the pores with helium gas, which has a lower density. Furthermore, high-temperature calcination is performed in a vacuum environment, closing the pores of the silicon dioxide particles after the remaining gas in the pores is expelled. To avoid the reintroduction of water or other gases and impurities during the cooling process, this invention first cools the silicon dioxide to a certain temperature in a vacuum environment before introducing inert helium gas to cool it to room temperature, obtaining high-purity, high-quality synthetic silicon dioxide. Detailed Implementation Example 1

[0020] First, add 2000 g of ultrapure water and 3 g of concentrated nitric acid to a round-bottom flask. Under vigorous stirring, slowly add 99.9999% pure tetramethoxysilane dropwise into the reaction flask. React at room temperature for 3 h. After removing methanol by vacuum distillation, gel for 12 h. Then dry at 135℃ for 15 h and crush into 40-80 mesh particles.

[0021] 1000 g of dried and pulverized high-purity silica was placed in a calcining furnace. After evacuation, high-purity oxygen was introduced at a flow rate of 1.0 L / min, and the furnace was heated to 900 °C at 80 °C / h. After holding at this temperature for 12 h, the furnace temperature was lowered to 750 °C, and a mixture of oxygen and helium in a weight ratio of 2:1 was introduced at a flow rate of 1 L / min. The furnace temperature was then held at 750 °C for 3 h. The furnace temperature was then lowered to 600 °C, and the furnace gas was replaced with high-purity helium. Helium was continuously introduced at a flow rate of 3 L / min, and the furnace temperature was held at 600 °C for 2 h.

[0022] Then, the helium was removed by depressurization, and the temperature was increased to 1200 ℃ at 300 ℃ / h for 3 h, during which the pressure inside the furnace was maintained at about 100 Pa. After the calcination was completed, the pressure inside the furnace was maintained at 100 Pa and the temperature was reduced to 900 ℃. Helium was then introduced and the furnace was cooled to room temperature in a helium environment. Example 2

[0023] 1000g of the high-purity silica prepared in Example 1 was placed in a calcining furnace. After evacuation, high-purity oxygen was introduced at a flow rate of 1.5 L / min, and the furnace was heated to 950 °C at 60 °C / h. After holding at this temperature for 10 h, the furnace temperature was lowered to 800 °C, and a mixture of oxygen and helium in a weight ratio of 2:1 was introduced at a flow rate of 2 L / min. The furnace was then held at 800 °C for 3 h. The furnace temperature was then lowered to 600 °C, and the furnace gas was replaced with high-purity helium. Helium was continuously introduced at a flow rate of 4 L / min, and the furnace was held at 600 °C for 2 h.

[0024] Then, the helium was removed by depressurization, and the temperature was increased to 1200 ℃ at 300 ℃ / h for 3 h, during which the pressure inside the furnace was maintained at about 100 Pa. After the calcination was completed, the pressure inside the furnace was maintained at 100 Pa and the temperature was reduced to 900 ℃. Helium was then introduced and the furnace was cooled to room temperature in a helium environment. Example 3

[0025] 1000g of the high-purity silica prepared in Example 1 was placed in a calcining furnace. After evacuation, high-purity oxygen was introduced at a flow rate of 2 L / min, and the furnace was heated to 1000 °C at a rate of 100 °C / h. After holding at this temperature for 6 h, the furnace temperature was lowered to 800 °C, and a mixture of oxygen and helium in a weight ratio of 2:1 was introduced at a flow rate of 2 L / min. The furnace temperature was then held at 800 °C for 3 h. The furnace temperature was then lowered to 500 °C, and the furnace gas was replaced with high-purity helium. Helium was continuously introduced at a flow rate of 4 L / min, and the furnace temperature was held at 500 °C for 2 h.

[0026] Then, the helium was removed by depressurization, and the temperature was increased to 1200 ℃ at 300 ℃ / h for 3 h, during which the pressure inside the furnace was maintained at about 100 Pa. After the calcination was completed, the pressure inside the furnace was maintained at 100 Pa and the temperature was reduced to 900 ℃. Helium was then introduced and the furnace was cooled to room temperature in a helium environment. Example 4

[0027] 1000 g of the high-purity silica prepared in Example 1 was placed in a calcining furnace. After evacuation, high-purity oxygen was introduced at a flow rate of 3 L / min, and the furnace was heated to 900 °C at 50 °C / h. After holding at this temperature for 10 h, the furnace temperature was lowered to 600 °C, and a mixture of oxygen and helium in a weight ratio of 2:1 was introduced at a flow rate of 3 L / min. The furnace temperature was then held at 600 °C for 3 h. The furnace temperature was then lowered to 500 °C, and the furnace gas was replaced with high-purity helium. Helium was continuously introduced at a flow rate of 5 L / min, and the furnace temperature was held at 500 °C for 2 h.

[0028] Then, the helium was removed by depressurization, and the temperature was increased to 1200 ℃ at 300 ℃ / h for 3 h, during which the pressure inside the furnace was maintained at about 100 Pa. After the calcination was completed, the pressure inside the furnace was maintained at 100 Pa and the temperature was reduced to 900 ℃. Helium was then introduced and the furnace was cooled to room temperature in a helium environment. Example 5

[0029] The preparation and calcination methods for high-purity silicon oxide are the same as in Example 1, except that in step S4 the furnace pressure is maintained at about 50 Pa. After calcination, when the furnace pressure is maintained at 50 Pa and the temperature is lowered to 800 °C, helium is introduced and the mixture is cooled to room temperature in a helium environment.

[0030] Comparative Example 1

[0031] The preparation and calcination methods for high-purity silicon oxide are the same as in Example 1, except that the calcination process in step S2 is omitted.

[0032] Comparative Example 2

[0033] The preparation and calcination methods for high-purity silicon oxide are the same as in Example 1, except that the calcination process in step S3 is omitted.

[0034] Comparative Example 3

[0035] The preparation method and calcination method of high-purity silicon oxide are the same as in Example 1. In the calcination process of step S4, the temperature is increased to 1200 ℃ for 3 h in an argon atmosphere at a rate of 300 ℃ / h. After the calcination is completed, the temperature is cooled to room temperature in a helium atmosphere.

[0036] Comparative Example 4

[0037] The preparation method and calcination method of high-purity silicon oxide are as described in Example 1. During the calcination process in step S4, helium is removed under reduced pressure, and the temperature is raised to 1200 ℃ at 300 ℃ / h for 3 h. During this period, the pressure inside the furnace is maintained at about 500 Pa. After the calcination is completed, helium is introduced and cooled to room temperature in a helium environment.

[0038] Test case

[0039] The samples from Examples 1-5 were subjected to a temperature of 2200 °C and a curvature of 2.0 × 10⁻⁶. 4 The sample was melted under a vacuum atmosphere for 48 hours. After cooling to room temperature, a 20 mm (longitudinal) × 20 mm (lateral) × 40 mm (depth) area was selected, and the number of bubbles generated was measured; a 40 mm (length) × 40 mm (width) × 40 mm (depth) area was selected, and the number of black spots generated was measured. The specific input is shown in Table 1.

[0040] Table 1 Test Data

[0041] sample Silica purity Number of black dots Number of bubbles after melting Example 1 99.999% 0 1 Example 2 99.999% 0 3 Example 3 99.999% 0 2 Example 4 99.999% 0 1 Example 5 99.999% 0 3 Test Example 1 99.998% 15 30 Test Example 2 99.998% 9 20 Test Example 3 99.998% 13 28 Test Example 4 99.998% 11 25

[0042] The data in the table shows that the number of bubbles and black spots in the quartz blocks calcined by the method of the present invention is significantly reduced.

Claims

1. A method for calcining high-purity silicon dioxide, characterized in that, Includes the following steps: S1) The dried and pulverized high-purity silica is calcined at 900~1000 ℃ in an oxygen atmosphere for 2~20 h, with an oxygen flow rate of 1~3 L / min; S2) Calcination at 600~900 ℃ in a mixed atmosphere of oxygen and helium with a weight ratio of 2:1 for 1~10 h, with a flow rate of 1~3 L / min for the mixed oxygen and helium gas. S3) Calcination at 500~800 ℃ in a helium atmosphere for 1~10 h, with a helium flow rate of 3~6 L / min; S4) Remove helium under reduced pressure, and calcine at 1100-1300 ℃ for 2-10 h at 10-100 Pa; after calcine, cool to room temperature in a helium atmosphere. The heating rate in step S1 is 50~100℃ / h; the heating rate in step S4 is 200~300℃ / h. The high-purity silicon oxide is prepared by hydrolysis of tetraalkoxysilane.

2. The calcination method for high-purity silicon oxide according to claim 1, characterized in that, The roasting time for step S1 is 2-10 h, the roasting time for step S2 is 1-5 h, the roasting time for step S3 is 1-5 h, and the roasting time for step S4 is 2-5 h.

3. The calcination method for high-purity silicon dioxide according to claim 1, characterized in that, During the roasting process, oxygen and helium are used with a purity of not less than 99.999%.

4. The calcination method for silicon oxide according to claim 1, characterized in that, The high-purity silicon oxide is prepared by hydrolysis of tetramethoxysilane, tetraethoxysilane, or tetraisopropoxysilane.