Method for forming a protective layer on the inner wall of a high-pressure vessel for hydrothermal quartz crystal growth

Abstract

The present application relates to the technical field of hydrothermal quartz crystal growth, and discloses a method for generating an inner wall protective layer of a high-pressure kettle for hydrothermal quartz crystal growth, wherein a seed crystal holder and a raw material basket are arranged in the inner cavity of the high-pressure kettle, and the method comprises the following steps: calculating the area of the generated protective layer and the required SiO2; calculating the solution for generating the protective layer; preparing the protective layer reagent solution; arranging a temperature measuring point outside the high-pressure kettle; setting the temperature rising temperature (including the temperature rising curve); placing the calculated SiO2 and the protective layer reagent solution into the high-pressure kettle, and then sealing the high-pressure kettle; starting the high-pressure kettle to rise in temperature according to the set constant temperature, and then operating the high-pressure kettle in a constant temperature mode; after the operation is completed, cleaning the inner kettle wall of the high-pressure kettle with deionized water to obtain the inner kettle wall of the high-pressure kettle with the protective layer. The present application can effectively remove the attached inclusion impurities, and can also generate a sodium iron silicate protective layer.

Description

Technical Field

[0001] This invention relates to the field of hydrothermal quartz crystal growth technology, specifically to the process technology for generating an anti-corrosion protective layer inside a high-pressure autoclave. Background Technology

[0002] Hydrothermal temperature difference method is a widely used crystal growth technology. The main principle of this technology is to mimic the physical and chemical conditions of mineral formation in nature within a sealed autoclave. It utilizes the principle that mineralizers formed by water and corresponding concentrations of chemical reagents under high pressure and specific temperature can dissolve certain natural minerals. By artificially controlling the temperature difference between the upper and lower parts of the autoclave, the mineralizer aqueous solution, which has dissolved the minerals in the high-temperature zone at the bottom, rises through a baffle with a certain opening ratio in the autoclave to the relatively lower temperature crystal growth zone, forming a supersaturated solute. Crystallization and growth then occur on the seed crystal. The solution then returns to the raw material dissolution zone to continue dissolving the raw material (SiO2). Through a continuous cycle of dissolution-rising-crystallization-falling-redissolution, the raw material at the bottom eventually grows into the crystal at the top.

[0003] The raw material for growing artificial quartz crystals is SiO2, which dissolves in a hot solution of NaOH alkaline mineralizing agent under pressure. This dissolves into sodium iron silicate or pyrite (NaFeSi2O6·2H2O or Na2FeSi2O6·2H2O) on the inner wall of the autoclave, forming a protective layer. This effectively prevents deep corrosion of the autoclave steel, ensuring the safe growth of the quartz crystal. After crystal growth, impurities in the raw material (Al, Fe, Ca, K, etc.) and residual sodium iron silicate or pyrite adhere to the inner wall of the autoclave, forming inclusions. These inclusions must be removed before the next crystal growth. Reducing the capture of these impurities during the next crystal growth and improving the quality of inclusions is generally referred to as the "autoclave sealing and boiling process."

[0004] The current common "pressure autoclave sealed boiling process" simply involves adding NaOH alkaline mineralizer to the pressure autoclave, placing the raw material basket and seed crystal holder that have already grown crystals inside, sealing and heating it. The NaOH concentration and heating temperature are both lower than in normal crystal growth processes. Because SiO2 is not added, the hot NaOH alkaline mineralizer solution, under pressure, only dissolves sodium iron silicate or calcite and other attached impurities on the inner walls of the pressure autoclave and the raw material basket, thus reducing the capture of inclusions in the next crystal growth process. This current process has the drawback of continuing to dissolve the inner wall of the pressure autoclave after dissolving impurities.

[0005] Several high-pressure reactors used for hydrothermal quartz crystal growth have experienced leaks and explosions due to steel corrosion. The U.S. Chemical Hazard Investigations and Safety Board (CSB) investigated the metallographic structure of the reactor's inner wall and found that unevenness or absence of the sodium ferrosilicate or pyrite protective layer deepened metal corrosion cracks, ultimately leading to the reactor explosion. Therefore, for safe production, it is necessary to implement a process to generate an inner protective layer in high-pressure reactors used for hydrothermal quartz crystal growth.

[0006] Currently, the general process for sealing and boiling autoclaves is as follows:

[0007] No fused quartz is added; the mineralizing agent is sodium hydroxide; the concentration is 0.16N; the constant temperature and pressure is 105-110 MPa; the filling degree is 82% of the effective volume; the set temperature of each point in the autoclave is:

[0008] The temperature control for lower part III is 345℃; the temperature control for lower part II is 345℃; the temperature control for lower part I is 345℃; the temperature control for upper part II is 335℃; and the temperature control for upper part I is 335℃. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a process for the production of an inner wall protective layer of a high-pressure reactor for hydrothermal quartz crystal growth.

[0010] To solve the above-mentioned technical problems, the present invention provides a method for generating an inner wall protective layer in a high-pressure autoclave for hydrothermal quartz crystal growth. The autoclave cavity is equipped with a seed crystal holder and a raw material basket. The seed crystal holder includes a seed crystal holder ring for binding seed crystal wafers, a seed crystal holder support column, and an inner baffle. The method includes the following steps:

[0011] 1) Calculation of the area of ​​the protective layer and the required SiO2;

[0012] 2) Calculation of the solution that forms the protective layer;

[0013] 3) Preparation of protective layer reagent solution;

[0014] 4) Set up temperature measuring points on the outside of the autoclave;

[0015] 5) Set the heating temperature (including the heating curve):

[0016] 6) Loading into the pot:

[0017] Place the SiO2 calculated in step 1) and the protective layer reagent solution calculated in step 3) into the autoclave; then seal it.

[0018] 7) Start the autoclave at the constant temperature set in step 5) and then maintain the temperature.

[0019] After the pressure inside the autoclave is kept constant at 110-120 MPa, and after (48±2) hours, the heating power supply used to maintain the constant temperature of the autoclave is turned off so that it can cool down naturally.

[0020] 8) After step 7), clean the inner wall of the autoclave with deionized water to obtain an inner wall of the autoclave with a protective layer.

[0021] As an improvement to the method for generating the inner wall protective layer of the high-pressure reactor for hydrothermal quartz crystal growth according to the present invention, it specifically includes the following steps:

[0022] 1) Calculation of the area of ​​the protective layer and the required SiO2:

[0023] The surface area of ​​the autoclave is set as S1, the surface area of ​​the seed crystal support column is set as S2, the surface area of ​​the seed crystal ring is set as S3, the surface area of ​​the inner baffle is set as S4, and the surface area of ​​the raw material basket is set as S5.

[0024] The area of ​​the protective layer is S6 = S1 + S2 + S3 + S4 + S5;

[0025] The required weight of SiO2 = S6 × δ × ρ + w1;

[0026] δ represents the required thickness of the protective film, ρ represents the specific gravity of SiO2, and w1 represents the supersaturated dissolved weight of SiO2 in the mineralizer.

[0027] 2) Calculation of the solution that forms the protective layer:

[0028] Deionized water is used as the solution; the volume of deionized water is 80-83% of the effective volume inside the autoclave.

[0029] That is, set the deionized water to a filling degree of 80~83%;

[0030] The effective volume inside the autoclave is V = π × (D1 / 2). 2 ×H1-(W1+W2) / 7.8-W / 2.65

[0031] Where: D1 is the inner diameter of the autoclave; H1 is the effective height inside the autoclave; W is the weight of SiO2 (Kg); W1 is the weight of the seed crystal frame; W2 is the weight of the raw material basket; 7.8 and 2.65 are the specific gravities of steel and silicon dioxide (quartz), respectively.

[0032] That is, W1 is the sum of the weights of the seed crystal support column, the seed crystal ring, and the inner baffle.

[0033] 3) Preparation of protective layer reagent solution:

[0034] The dosage ratio of NaOH, Na2CO3, and NaNO2 should be (0.5±0.01) mol to 1 L of deionized water.

[0035] In step 2), NaOH, Na2CO3, and NaNO2 were added to the calculated amount of deionized water to prepare protective layer reagent solutions.

[0036] 4) Five temperature measuring points are set on the outside of the autoclave from top to bottom: upper temperature measuring point I, upper temperature measuring point II, lower temperature measuring point I, lower temperature measuring point II, and lower temperature measuring point III.

[0037] All inner baffles are located at the height between the upper II temperature measuring point and the lower I temperature measuring point, and the raw material basket is located at the height between the lower I temperature measuring point and the lower III temperature measuring point;

[0038] 5) Set the heating temperature (including the heating curve):

[0039] The constant temperature of the upper part I temperature measuring point is set to (336±6)℃; the constant temperature of the upper part II temperature measuring point is set to (336±6)℃; the constant temperature of the lower part I temperature measuring point is set to (366±6)℃; the constant temperature of the lower part II temperature measuring point is set to (366±6)℃; the constant temperature of the lower part III temperature measuring point is set to (366±6)℃.

[0040] 6) Loading into the pot:

[0041] The SiO2 calculated in step 1) is loaded into the raw material basket. Then, the raw material basket containing the raw material and the entire seed crystal frame (including the inner baffle) are loaded into the autoclave in the conventional manner, and the protective layer reagent solution calculated in step 3) is poured into the autoclave. At this time, the raw material basket containing the raw material is completely immersed in the protective layer reagent solution, and the seed crystal frame is partially immersed in the protective layer reagent solution. Then, the inner cavity of the autoclave is sealed.

[0042] 7) Start the autoclave to heat up according to the constant temperature set in step 5). The upper part I temperature measuring point, the upper part II temperature measuring point, the lower part I temperature measuring point, the lower part II temperature measuring point, and the lower part III temperature measuring point will rise to their respective set constant temperature in the same time.

[0043] After the pressure inside the autoclave is kept constant at 110-120 MPa, after (48±2) hours of constant temperature operation, the heating power supply used to maintain the constant temperature of the autoclave is turned off so that it can cool down naturally.

[0044] 8) Open the autoclave when it cools to room temperature; and clean the inner wall of the autoclave with deionized water (scrub it clean) to obtain an inner wall of the autoclave with a protective layer; that is, the process of generating the protective layer of the inner wall of the autoclave is completed.

[0045] Meanwhile, the seed crystal holder, inner baffle, and raw material basket with the seed crystal holder ring are cleaned (brushed clean) with deionized water; this is to prepare for the subsequent formal production of crystals.

[0046] As a further improvement to the method for generating the inner wall protective layer of the high-pressure reactor for hydrothermal quartz crystal growth of the present invention, in step 1):

[0047] Wherein: δ is 5~10μm, w1 is 10~30Kg; ρ is 2.65.

[0048] illustrate:

[0049] When a new autoclave is put into use, the value of δ is 8~10μm and w1 is 25~30Kg;

[0050] When the autoclave is used after at least one crystallization process, the value of δ ranges from 5 to less than 8 μm, and w1 ranges from 10 to less than 25 kg.

[0051] As a further improvement to the method for generating the inner wall protective layer of the high-pressure reactor for hydrothermal quartz crystal growth of the present invention, in step 5):

[0052] The temperatures at the upper temperature measuring points I, II, I, II, and III were uniformly raised from room temperature to 100℃ over (7±0.25) hours; then uniformly raised to 250℃, 250℃, 260℃, 260℃, and 260℃ respectively over (14±0.5) hours; and then uniformly raised to their respective set constant temperatures over (10±0.5) hours.

[0053] In step 7), the autoclave is started to heat up according to the constant temperature and heating curve set in step 5, thereby obtaining the set temperature.

[0054] The method for generating the inner protective layer in this invention can replace the traditional high-pressure autoclave sealing process. It can effectively remove attached inclusions and impurities, and also generate a sodium iron silicate protective layer. Specifically, this invention is configured as follows:

[0055] The raw material in the raw material dissolution zone is fused quartz; the mineralizing agents are sodium hydroxide (NaOH), sodium carbonate (Na2CO3), and sodium nitrite (NaNO2), with concentrations of 0.5±0.01N, 0.1±0.01N, and 0.08±0.01N, respectively; the constant temperature and pressure is 110-120 MPa; the filling degree is 80-83% (preferably 82%) of the effective volume; the preferred set temperatures for each point in the autoclave are:

[0056] The temperature control for lower part III is 366℃; the temperature control for lower part II is 366℃; the temperature control for lower part I is 366℃; the temperature control for upper part II is 336℃; and the temperature control for upper part I is 336℃.

[0057] The key technical points of this invention are as follows:

[0058] 1. Set and select the weight of SiO2 to be added. The addition of SiO2 effectively ensures that the original sodium iron silicate protective layer will not be dissolved by the alkaline mineralizer. In addition, the weight of SiO2 is determined based on the thickness of the protective film and the solubility required to form supersaturation. If there is too little SiO2 (less than the weight of solute required for SiO2 to form supersaturation in the mineralizer hydrothermal solution), the protective film will be too thin and will not be able to protect the inner vessel wall from corrosion, and metal rust will also occur. If there is too much SiO2 (more than the weight of solute required for SiO2 to form supersaturation in the mineralizer hydrothermal solution), impurities will be generated on the inner vessel wall. At the same time, it is also necessary to consider whether it is a newly put into use or a high-pressure vessel after multiple crystallization processes to determine the calculated weight of SiO2.

[0059] 2. The concentrations of mineralizing agents NaOH, NaNO2, and Na2CO3 were set. The combination of mineralizing agents and their concentrations ensured that the corrosion and dissolution of the original sodium iron silicate protective layer were reduced before SiO2 was dissolved.

[0060] 3. The temperature setting and heating rate are both lower than those of the crystal growth process. Since the weight of the raw material SiO2 is much lower than that of the crystal growth process, the lower temperature setting is lower than that of the crystal growth process. At the same time, it is also necessary to ensure the full dissolution of the raw material SiO2. The upper temperature setting is also necessary to ensure the crystallization and adhesion of SiO2 to form a sodium iron silicate protective film.

[0061] The temperature difference between the upper and lower parts ensures the density of the sodium iron silicate protective film, while the heating rate ensures its uniformity.

[0062] The pressure generated by the degree of filling and controlled temperature is an important condition for SiO2 to begin dissolving. For newly put into use high pressure reactors, rapid pressure increase is required to dissolve the SiO2 and reduce the corrosion of the reactor wall metal by the mineralizing agent. For high pressure reactors that have already been put into use, the pressure increase needs to be slowed down to fully dissolve the crystallization impurities that adhered to the reactor wall from the previous crystallization process.

[0063] The beneficial effects of this invention are mainly reflected in:

[0064] The process for generating an inner protective layer in a hydrothermal quartz crystal growth autoclave of the present invention uses a lower concentration of alkaline mineralizer and lower operating temperature and pressure than the quartz crystal growth process. The SiO2 raw material added under the set temperature and pressure is effectively dissolved and forms a sodium iron silicate protective layer with the inner wall of the autoclave and the surface of the autoclave accessories, preventing the metal from being deeply corroded by the alkaline mineralizer. After more than ten years of production practice, it has effectively protected the operational safety of the autoclave and has a significant effect on reducing inclusions. Attached Figure Description

[0065] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0066] Figure 1 This is a schematic diagram showing the positional relationship between the seed crystal holder 1, the inner baffle 2, and the raw material basket 3 located inside the autoclave.

[0067] Figure 2 This is a schematic diagram of seed crystal frame ring 11;

[0068] Figure 3 This is a schematic diagram of the shape of the autoclave and the temperature control points. Detailed Implementation

[0069] Example 1: A process for generating a protective layer on the inner wall of an autoclave for hydrothermal quartz crystal growth, wherein a seed crystal holder 1 and a raw material basket 3 are provided inside the autoclave. The seed crystal holder 1 includes a seed crystal holder ring 11 for binding seed crystal wafers, a seed crystal holder support column 12, and an inner baffle 2;

[0070] The method involves performing the following steps sequentially:

[0071] 1) Calculation of the area of ​​the protective layer and the required SiO2:

[0072] This includes: calculating the inner surface area based on the height and inner diameter of the autoclave; calculating the surface area of ​​the seed crystal support column 12; calculating the surface area of ​​the seed crystal ring 11; calculating the surface area of ​​the inner baffle 2; calculating the surface area of ​​the raw material basket 3; and calculating the required weight of SiO2 based on the thickness of the inner wall protective layer.

[0073] The calculation of surface area is a standard technique, and the formula is as follows:

[0074] The internal surface area of ​​the autoclave is S1 = π × D1 × H1 + π × r 2 ×2;

[0075] Where: D1 = inner diameter of the autoclave; H1 = effective height inside the autoclave; r = radius of the autoclave.

[0076] The surface area of ​​seed crystal support column 12 is S2 = π × D2 × H2 × N1;

[0077] Where: D2 = diameter of the seed crystal support pillar; H2 = effective height of the seed crystal support pillar; N1 = number of seed crystal support pillars.

[0078] Surface area S3 of seed crystal ring 11 = (π×D3×π×d3+π×d3×L1×K1+π×d3×L2×K2+π×d3×L3×K3+)×M1;

[0079] Where: D3 = diameter of the seed crystal holder ring; d3 = diameter of the holder wire; L1, L2, L3 = different lengths of the holder beams; K1, K2, K3 = different numbers of holder beams; M1 = number of holder rings on the seed crystal holder.

[0080] The surface area of ​​the inner baffle 2 is S4 = [π × R] 2 – (π×r2 2 ×n1+π×r3 2 [×n2)]×N2×2;

[0081] Where: R = radius of the inner baffle; r2 = radius of the center hole on the inner baffle; n1 = number of center holes on each inner baffle; r3 = radius of the outer holes of the inner baffle; n2 = number of outer holes of the inner baffle; N2 = number of inner baffles; 2 represents the two exposed surfaces of the inner baffle.

[0082] The surface area of ​​raw material basket 3, S5, is calculated as follows: S5 = π × D5 × H3 × 2 + π × R1 2 ×2

[0083] Where D5 = diameter of the raw material basket; H3 = height of the raw material basket; 2 represents the two exposed surfaces of the raw material basket. R1 is the radius of the bottom plate of the raw material basket.

[0084] Total surface area S6 = S1 + S2 + S3 + S4 + S5;

[0085] The required weight of SiO2 = S6 × δ × ρ + w1;

[0086] in:

[0087] The data unit for S6 is cm. 2 ;

[0088] δ = protective film thickness, typically set to 5-10 μm.

[0089] The specific gravity of SiO2 is generally taken as 2.65.

[0090] w1 = the supersaturated dissolved weight of SiO2 in the mineralizer, generally taken as 10-30Kg.

[0091] 2) Calculation of the solution that forms the protective layer:

[0092] Deionized water is used as the solution; the volume of deionized water is 80-83% of the effective volume inside the autoclave; that is, deionized water with a filling degree of 80-83% is set.

[0093] Based on the effective volume of the autoclave, the volume of seed crystal rack 1, and the volume of raw material basket 3, the effective volume inside the autoclave and the weight of deionized water with a filling degree of 80-83% are calculated.

[0094] In the industry, the effective volume of the autoclave is generally calculated by weighing the seed crystal rack and raw material basket and then dividing by the specific gravity of steel.

[0095] The effective volume inside the autoclave is V = π × (D1 / 2). 2 ×H1-(W1+W2) / 7.8-W / 2.65

[0096] Where: D1 is the inner diameter of the autoclave; H1 is the effective height inside the autoclave; W is the weight of SiO2 (Kg); W1 is the total weight of seed crystal holder 1; W2 is the weight of raw material basket 3; 7.8 and 2.65 are the specific gravities of steel and silicon dioxide (quartz), respectively.

[0097] That is, W1 is the sum of the weights of the seed crystal support column 12, the seed crystal ring 11, and the inner baffle 2;

[0098] A filling rate of 80-83% deionized water means that the effective volume of the autoclave is filled with deionized water to 80-83% of its volume.

[0099] 3) Calculation of the chemical reagents used to form the protective layer (calculation of the weight of the chemical reagents in the protective layer reagent solution):

[0100] Based on the amount of deionized water calculated in step 2), calculate the weight of NaOH, the chemical reagent for the protective layer process, at a concentration of 0.5 equivalents; calculate the weight of Na2CO3, the chemical reagent for the protective layer process, at a concentration of 0.1 equivalents; and calculate the weight of NaNO2, the chemical reagent for the protective layer process, at a concentration of 0.08 equivalents.

[0101] That is, prepare the protective layer reagent solution according to the ratio of 0.5 mol NaOH, 0.1 mol Na2CO3, and 0.08 mol NaNO2 in 1 L of deionized water.

[0102] 4) Five temperature measuring points are set on the outside of the autoclave from top to bottom: upper part I temperature measuring point 4, upper part II temperature measuring point 5, lower part I temperature measuring point 6, lower part II temperature measuring point 7, and lower part III temperature measuring point 8.

[0103] The inner baffle 2 is located at the height between the upper II temperature measuring point 5 and the lower I temperature measuring point 6, and the raw material basket 3 is located at the height between the lower I temperature measuring point 6 and the lower III temperature measuring point 8;

[0104] therefore:

[0105] Temperature measurement point 4 in the upper part corresponds to the temperature of the protective film formation zone 1 inside the autoclave;

[0106] Temperature measurement point 5 in the upper part II corresponds to the temperature of the second protective film formation zone inside the autoclave;

[0107] Temperature measuring point 6 in the lower part corresponds to the temperature of the SiO2 dissolution zone 1 inside the autoclave;

[0108] Temperature measuring point 7 in the lower part II corresponds to the temperature of the second SiO2 dissolution zone inside the autoclave;

[0109] The temperature measuring point 8 in the lower part III corresponds to the temperature of the SiO2 dissolution zone III inside the autoclave.

[0110] 5) Set the temperature of the heating curve:

[0111] Set the constant temperature of temperature measuring point 4 in the upper part I to 336℃; the constant temperature of temperature measuring point 5 in the upper part II to 336℃; the constant temperature of temperature measuring point 6 in the lower part I to 366℃; the constant temperature of temperature measuring point 7 in the lower part II to 366℃; and the constant temperature of temperature measuring point 8 in the lower part III to 366℃.

[0112] The temperatures at measuring points 4 (Upper Part I), 5 (Upper Part II), 6 (Lower Part I), 7 (Lower Part II), and 8 (Lower Part III) were uniformly raised from room temperature to 100℃ over 7 hours; then, over 14 hours, the temperatures at measuring points 4 (Upper Part I), 5 (Upper Part II), 6 (Lower Part I), 7 (Lower Part II), and 8 (Lower Part III) were uniformly raised to 250℃, 250℃, 260℃, 260℃, and 260℃ respectively; then, over 10 hours, the temperatures at measuring points 4 (Upper Part I), 5 (Upper Part II), 6 (Lower Part I), 7 (Lower Part II), and 8 (Lower Part III) were uniformly raised to the set temperatures of 336℃, 336℃, 366℃, 366℃, and 366℃ respectively; finally, the temperature was maintained for 48 hours before power was cut off and the temperature was lowered (as described in the following steps).

[0113] 6) Perform the autoclave loading operation according to the protective layer process. Load the SiO2 (as raw material) calculated in step 1) into the raw material basket 3. Then, load the raw material basket 3 and the entire seed crystal frame 1 (including the inner baffle 2, etc.) into the autoclave in a conventional manner. Pour a solution containing dissolved chemical reagents (i.e., the protective layer reagent solution calculated in step 3) into the autoclave. At this point, the raw material basket 3 is completely immersed in the reagent solution, and the seed crystal frame 1 is partially immersed. Then, seal the inner cavity of the autoclave.

[0114] Note: The amount of raw material (SiO2) is calculated according to step 1); the amount of deionized water and dissolving mineralizer in the reagent solution is calculated according to steps 2) and 3).

[0115] 7) Start the autoclave to heat up according to the constant temperature and heating curve set in step 5) to reach the set temperature;

[0116] After the pressure inside the autoclave is kept constant at 110-120 MPa, the autoclave heating power is turned off and the pressure is allowed to cool down naturally after 48 hours of constant temperature operation.

[0117] 8) Open the autoclave when it cools to room temperature; and clean the inner wall of the autoclave with deionized water (scrub it clean) to obtain an inner wall of the autoclave with a protective layer; that is, the process of generating the protective layer of the inner wall of the autoclave is completed.

[0118] Meanwhile, the seed crystal holder 1 with the seed crystal holder ring 11, the inner baffle 2, and the raw material basket 3 are cleaned with deionized water (brushed clean); this is to prepare for the subsequent formal production of crystals.

[0119] Experiment 1: Following the method described in Example 1, the specific parameters are as follows:

[0120] The Φ30cm high-pressure autoclave has a total internal height (effective height) of 541cm, including 3 raw material baskets with a height of 244cm and 1 seed crystal rack with a height of 276cm.

[0121] therefore:

[0122] The internal surface area of ​​the autoclave, S1, is calculated as: S1 = 3.1416 × 30 × 541 + 3.1416 × 15 2 ×2=52401.88cm 2 ;

[0123] The surface area of ​​the seed crystal support, S², is calculated as: S² = 3.1416 × 0.5 × 276 × 4 = 1734.16 cm². 2 ;

[0124] The surface area of ​​the seed crystal ring, S3, is calculated as follows: S3 = (3.1416 × 29.5 × 3.1416 × 0.5 + 3.1416 × 0.5 × 17.1 × 2 + 3.1416 × 0.5 × 26.1 × 2 + 3.1416 × 0.5 × 28.5 × 1) × 11 = 3586.77 cm² 2 ;

[0125] The surface area of ​​the inner baffle is S4 = [3.1416 × 14.75]. 2 -(3.1416×1.6 2 ×1+3.1416×1.1 2 ×4) ]×2×2=2640.92 cm 2 ;

[0126] The surface area of ​​the raw material basket, S5, is calculated as: S5 = 3.1416 × 29.5 × 244 × 2 + 3.1416 × 14.75 2 ×2=46593.46cm 2 ;

[0127] Total surface area S6 = 52401.88 + 1734.16 + 3586.77 + 2640.92 + 46593.46 (unit: cm²) 2

[0128] The total surface area inside the autoclave (i.e., the area S6 of the protective layer) is calculated as shown above. The thickness δ of the sodium iron silicate protective layer is set to 10 μm, and the specific gravity ρ of SiO2 is 2.65. Considering that SiO2 needs to reach a supersaturated state in the mineralizer, the required weight of SiO2 is W = S6 × δ × ρ + w1; δ = protective film thickness, selected as 10 μm. ρ = specific gravity of SiO2, generally taken as 2.65.

[0129] w1 = the supersaturated dissolved weight of SiO2 in the mineralizer, which is generally taken as 28Kg.

[0130] W= S6×0.001×2.65+28000≈28283g≈28.28Kg.

[0131] 2) Calculation of the solution that forms the protective layer:

[0132] The effective volume inside the autoclave is V = 3.1416 × (30 / 2). 2 ×541-(9700+22000) / 7.8-28280 / 2.65=367675.57ml

[0133] If the fill level is set to 82%, then the weight W3 of the deionized water in the mineralizing agent solution is:

[0134] W3=367675.57×82%=301490g=301.49Kg.

[0135] 3) Calculation of the chemical reagents used to form the protective layer:

[0136] The weight of NaOH (W3) used in the protective layer process was calculated based on a concentration of 0.5 equivalents; the weight of Na2CO3 (W4) used in the protective layer process was calculated based on a concentration of 0.1 equivalents; and the weight of NaNO2 (W5) used in the protective layer process was calculated based on a concentration of 0.08 equivalents.

[0137] W3=301490×0.5×40 / 1000=6029.9g;

[0138] W4=301490×0.1×106 / 1000=3195.8g;

[0139] W5=301490×0.08×69 / 1000=1664.2g.

[0140] 4) The distance between temperature measuring point 4 at the top I and temperature measuring point II at the top of the autoclave is 138.2 cm;

[0141] The distance between temperature measuring point 5 at the upper part II and temperature measuring point I at the lower part of the autoclave is 181.6 cm;

[0142] The distance between temperature measuring point 6 at the bottom I and temperature measuring point II at the bottom of the autoclave is 151.3 cm;

[0143] The distance between temperature measuring point 7 in the lower part II and temperature measuring point III in the lower part of the autoclave is 64.6 cm;

[0144] The distance between temperature measuring point 8 in the lower part (Ⅲ) and the bottom plane of the autoclave is 9cm;

[0145] The autoclave treated with this protective layer generation method showed that the inner wall surface was intact after ultrasonic testing, which prevented the metal from being deeply corroded by alkaline mineralizers.

[0146] This invention adopts the classification of GB / T 7895-2008 Artificial Optical Quartz Crystals 4.5 and is tested according to GB / T 7896-2008 Artificial Optical Quartz Crystals Test Methods 6.2.

[0147] Actual production case 1

[0148] Using the high-pressure autoclave with the inner protective layer obtained in Experiment 1, production was carried out according to the conventional hydrothermal quartz crystal growth method. The set production process parameters were:

[0149] A reagent solution was prepared by adding 1.1 equivalents of NaOH, 0.1 equivalents of Na2CO3, and 0.08 equivalents of NaNO2 to 1L of deionized water. The solution was filled to 83%, with a raw material weight of 220 kg of SiO2. The constant temperatures at measuring points 4 (upper part I), 5 (upper part II), 6 (lower part I), 7 (lower part II), and 8 (lower part III) were 345℃, 345℃, 375℃, 375℃, and 380℃, respectively. The pressure after constant temperature was 135-145 MPa. Other process parameters were as described in Experiment 1.

[0150] A total of 142 optical crystals were produced, with 98% of the inclusions meeting the Class I standard.

[0151] Comparative Experiment 1-1 (Excessive SiO2 usage)

[0152] The weight of SiO2 in step 1) of Experiment 1 was increased from 28.28 kg to 50 kg. The rest remained the same as in Experiment 1.

[0153] The autoclave treated by this protective layer generation method showed the following results: a large amount of white silica precipitate adhered to the autoclave wall, and the sodium iron silicate protective layer on the autoclave wall was visually uneven.

[0154] Comparing the actual production case 1-1 with the high-pressure autoclave that produced the inner wall protective layer obtained in comparative experiment 1-1, the remaining processes were the same as in actual production case 1. The results showed that the final crystal inclusion level I index reached 93%, and some crystals exhibited large-particle inclusions.

[0155] Comparative Experiment 1-2 (Insufficient SiO2 dosage)

[0156] The weight of SiO2 in step 1) of Experiment 1 was reduced from 28.28 kg to only 10 kg, while the rest remained the same as in Experiment 1.

[0157] The results obtained by the high-pressure vessel after being treated by this protective layer generation method are as follows: the inner wall protective layer is grayish-red, there are gray spots on the vessel wall, some red deposits have fallen off, and the protective film on the vessel wall is uneven, with some areas showing no protective layer.

[0158] Comparing actual production case 1-2, and using the high-pressure reactor with the inner wall protective layer already formed in comparative experiment 1-2, crystal growth was performed, with the remaining processes being the same as in actual production case 1. The results showed that the inclusions in the final crystal were layered, and the final crystal inclusion level I index reached 88%.

[0159] Comparative Experiment 2 (referring to the mineralizer concentration in the conventional "pressure autoclave sealed cooking process")

[0160] A reagent solution was prepared using 0.16 equivalents of NaOH; no silica was added to the autoclave; other process parameters were as per Experiment 1. The results showed that the autoclave wall turned red, and after washing, a large amount of rust-like powder detached from the wall. Visually, the protective film on the autoclave wall was uneven, with some areas showing no protective layer.

[0161] Compared with actual production case 2, the autoclave with the inner wall protective layer obtained from comparative experiment 2 was used, and the rest of the process was the same as in actual production case 1. The results are as follows: the inclusions in the final crystal are distributed in a hazy manner, and the final crystal inclusion level I index reaches 84%.

[0162] Comparative Experiment 3 (referring to the temperature setting, heating rate, operating temperature, and pressure of the conventional "high-pressure autoclave sealing cooking process")

[0163] Set the constant temperature of temperature measuring point 4 in the upper part I to 330℃; the constant temperature of temperature measuring point 5 in the upper part II to 330℃; the constant temperature of temperature measuring point 6 in the lower part I to 350℃; the constant temperature of temperature measuring point 7 in the lower part II to 350℃; and the constant temperature of temperature measuring point 8 in the lower part III to 350℃.

[0164] The temperatures at measuring points 4 (Upper Part I), 5 (Upper Part II), 6 (Lower Part I), 7 (Lower Part II), and 8 (Lower Part III) were raised from room temperature to 100℃ over 7 hours; then, over 14 hours, the temperatures at measuring points 4 (Upper Part I), 5 (Upper Part II), 6 (Lower Part I), 7 (Lower Part II), and 8 (Lower Part III) were raised to 250℃, 250℃, 260℃, 260℃, and 260℃ respectively; then, over 10 hours, the temperatures at measuring points 4 (Upper Part I), 5 (Upper Part II), 6 (Lower Part I), 7 (Lower Part II), and 8 (Lower Part III) were raised to 330℃, 330℃, 350℃, 350℃, and 350℃ respectively; finally, the temperatures were maintained for 48 hours.

[0165] The pressure is set to 110 MPa.

[0166] The remaining process parameters are the same as in Experiment 1.

[0167] Experimental results showed that white crystalline particles appeared on the upper inner wall of the autoclave, while the lower part was red. Analysis indicated that the low temperature caused excessive precipitation of SiO2 from the solution, which then crystallized and adhered to the upper autoclave wall.

[0168] Compared with actual production case 3, the autoclave with the inner wall protective layer obtained from comparative experiment 3 was used, and the rest of the process was the same as in actual production case 1. The results are as follows: the inclusions in the final crystal are distributed in a hazy manner, and the final crystal inclusion level I index only reaches 80%. Due to the presence of inclusions, the internal stress of the crystal increases, and some crystals crack during processing.

[0169] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for generating an inner wall protective layer in a high-pressure autoclave for hydrothermal quartz crystal growth, wherein a seed crystal holder (1) and a raw material basket (3) are provided in the inner cavity of the autoclave, the seed crystal holder (1) including a seed crystal holder ring (11) for binding seed crystal wafers, a seed crystal holder support column (12) and an inner baffle (2), characterized in that Includes the following steps: 1) Calculation of the area of ​​the protective layer and the required SiO2: Set the surface area of ​​the high pressure vessel to S1, the surface area of ​​the seed crystal support column (12) to S2, the surface area of ​​the seed crystal ring (11) to S3, the surface area of ​​the inner baffle (2) to S4, and the surface area of ​​the raw material basket (3) to S5. The area of ​​the protective layer is S6 = S1 + S2 + S3 + S4 + S5; The required weight of SiO2 = S6 × δ × ρ + w1; δ represents the required thickness of the protective film, ρ represents the specific gravity of SiO2, and w1 represents the supersaturated dissolved weight of SiO2 in the mineralizer. 2) Calculation of the solution that forms the protective layer: Deionized water is used as the solution; the volume of deionized water is 80-83% of the effective volume inside the autoclave. The effective volume inside the autoclave is V = π × (D1 / 2). 2 ×H1-(W1+W2) / 7.8-W / 2.65; Where: D1 is the inner diameter of the autoclave; H1 is the effective height inside the autoclave; W is the weight of SiO2 (Kg); W1 is the weight of the seed crystal frame (1); W2 is the weight of the raw material basket (3); 7.8 and 2.65 are the specific gravities of steel and silicon dioxide, respectively. 3) Preparation of protective layer reagent solution: The dosage ratio of NaOH, Na2CO3, and NaNO2 should be (0.5±0.01) mol to 1 L of deionized water. In step 2), NaOH, Na2CO3, and NaNO2 were added to the calculated amount of deionized water to prepare protective layer reagent solutions. 4) Five temperature measuring points are set on the outside of the autoclave from top to bottom, namely upper part I temperature measuring point (4), upper part II temperature measuring point (5), lower part I temperature measuring point (6), lower part II temperature measuring point (7), and lower part III temperature measuring point (8). All the inner baffles (2) are located at the height between the upper II temperature measuring point (5) and the lower I temperature measuring point (6), and the raw material basket (3) is located at the height between the lower I temperature measuring point (6) and the lower III temperature measuring point (8); 5) Set the heating temperature: The constant temperature of the upper part I temperature measuring point (4) is set to (336±6)℃; the constant temperature of the upper part II temperature measuring point (5) is set to (336±6)℃; the constant temperature of the lower part I temperature measuring point (6) is set to (366±6)℃; the constant temperature of the lower part II temperature measuring point (7) is set to (366±6)℃; and the constant temperature of the lower part III temperature measuring point (8) is set to (366±6)℃. 6) Loading into the pot: The SiO2 calculated in step 1) is loaded into the raw material basket (3), and then the raw material basket (3) and the entire seed crystal frame (1) are loaded into the high pressure vessel, and the protective layer reagent solution calculated in step 3) is poured into the high pressure vessel; at this time, the raw material basket (3) is completely immersed in the protective layer reagent solution, and the seed crystal frame (1) is partially immersed in the protective layer reagent solution; then the inner cavity of the high pressure vessel is sealed. 7) Start the autoclave to heat up according to the constant temperature set in step 5). The upper part I temperature measuring point (4), the upper part II temperature measuring point (5), the lower part I temperature measuring point (6), the lower part II temperature measuring point (7), and the lower part III temperature measuring point (8) will rise to their respective set constant temperatures in the same time. After the pressure inside the autoclave is kept constant at 110-120 MPa, after (48±2) hours of constant temperature operation, the heating power supply used to maintain the constant temperature of the autoclave is turned off, so that it can cool down naturally. 8) Open the autoclave when it cools to room temperature; and clean the inner wall of the autoclave with deionized water to obtain an inner wall of the autoclave with a protective layer.

2. The method for generating the inner wall protective layer of an autoclave for hydrothermal quartz crystal growth according to claim 1, characterized in that... In step 1): Wherein: δ is 5~10μm, w1 is 10~30Kg; ρ is 2.

65.

3. The method for generating the inner wall protective layer of an autoclave for hydrothermal quartz crystal growth according to claim 2, characterized in that: In step 5): The temperatures at the upper part I temperature measuring point (4), upper part II temperature measuring point (5), lower part I temperature measuring point (6), lower part II temperature measuring point (7), and lower part III temperature measuring point (8) were uniformly raised from room temperature to 100℃ over (7±0.25) hours; then uniformly raised to 250℃, 250℃, 260℃, 260℃, and 260℃ respectively over (14±0.5) hours; and then uniformly raised to their respective set constant temperatures over (10±0.5) hours. In step 7), the autoclave is started to heat up according to the constant temperature and heating curve set in step 5, thereby obtaining the set temperature.

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