A method for preparing rare earth doped quartz glass by composite acid catalyzed sol-gel

Abstract

The application discloses a method for preparing rare earth doped quartz glass by composite acid catalyzed sol-gel, comprising the following steps: mixing tetraethyl orthosilicate, ethanol and deionized water, and adding HCl and HF to make the tetraethyl orthosilicate hydrolyze and polycondensate to form an initial silicon-oxygen network; adding an aluminum salt precursor and a rare earth salt precursor into the obtained system to obtain a doped silica sol, making the doped silica sol gelate and performing aging treatment; performing stage drying on the obtained whole wet gel to obtain a whole dry gel; performing stage heat treatment on the whole dry gel to obtain a porous precursor which maintains a whole form; and directly placing the porous precursor under low-pressure high-temperature conditions for densification treatment without performing powderization, grinding, powder pressing or re-molding to obtain transparent rare earth doped quartz glass. The application does not need powderization and secondary melting, and is suitable for preparation of rare earth doped quartz glass and optical fiber preform materials.

Description

Technical Field

[0001] This invention relates to the field of quartz glass and rare earth-doped optical material preparation technology, specifically to a method for preparing low-hydroxyl rare earth-doped quartz glass by using a composite acid system of HF and HCl to regulate the hydrolysis and condensation behavior of sol and the pore structure of gel, and by overall aging, staged drying, staged heat treatment and low-pressure high-temperature direct densification. Background Technology

[0002] Rare-earth-doped quartz glass possesses high thermal stability, chemical stability, and excellent optical properties, making it a crucial foundational material for rare-earth-doped optical fibers, fiber lasers, fiber amplifiers, and other photonic devices. The preparation of quartz-based rare-earth-doped materials typically involves techniques such as vapor deposition, high-temperature melting, and sol-gel processes.

[0003] The sol-gel method can achieve the mixing of silicon sources and multiple dopant components in the liquid phase and form a uniform silicon-oxygen precursor network at relatively low temperatures through hydrolysis and condensation reactions, thus offering certain advantages for multi-component rare-earth-doped quartz materials. However, the preparation of bulk gels still faces challenges such as long gelation cycles, susceptibility to cracking during drying, and high final glass hydroxyl content.

[0004] The wet gel contains a large amount of pore fluid. During the drying process, the pore fluid gradually evaporates and forms menisci within the nanopores. The resulting capillary pressure causes the gel skeleton to shrink. When the fluid migration rate and shrinkage degree differ in different regions of the gel, large internal stresses can easily be generated, eventually leading to cracks. As the overall gel size increases, these problems become more pronounced.

[0005] On the other hand, when using only conventional acid catalysis, the polycondensation and gel formation processes of the silanolate system may take a long time, which is not conducive to shortening the overall preparation cycle. Experiments in this invention show that, under the same basic formulation, the gelation time can reach approximately 200 hours when using only HCl catalysis.

[0006] Some sol-gel quartz glass technologies require further processing after obtaining the dry gel or porous material, including crushing, grinding, sieving, pressing, or high-temperature remelting. This increases the number of processing steps and the possibility of introducing impurities during powder handling, and also makes it difficult to fully utilize the molding advantages of the overall sol-gel route.

[0007] Furthermore, hydroxyl groups in quartz glass can produce significant absorption in the infrared and near-infrared bands, which can adversely affect the spectral properties of rare earth ions. Therefore, achieving rapid gel formation, overall crack resistance, low hydroxyl content, and direct densification of transparent glass without relying on complex powder processing and secondary melting processes is of great significance for the preparation of rare earth-doped quartz glass. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a method for preparing rare-earth-doped quartz glass using a composite acid-catalyzed sol-gel process. This method controls the hydrolysis, condensation, and gel pore structure of the silanolate system by adjusting the ratio of HF and HCl, significantly shortening the gelation time while obtaining a suitable nanoporous structure, reducing capillary stress during the drying stage and the risk of overall gel cracking. Furthermore, staged heat treatment and low-pressure, high-temperature direct densification transform the porous precursor into transparent rare-earth-doped quartz glass without powdering or secondary melting, and reduces the hydroxyl content in the final glass.

[0009] This invention discloses a method for preparing rare earth-doped quartz glass using a composite acid-catalyzed sol-gel, comprising: Step 1: Mix tetraethyl orthosilicate, ethanol and deionized water, and add HCl and HF to cause the tetraethyl orthosilicate to hydrolyze and condense to form an initial silicon-oxygen network. Step 2: Add aluminum salt precursor and rare earth salt precursor to the system obtained in Step 1 to obtain doped silica sol, and then perform aging treatment on the doped silica sol. Step 3: Dry the overall wet gel obtained in Step 2 in stages to obtain the overall dry gel; Step 4: Perform staged heat treatment on the monolithic dry gel to obtain a porous precursor that maintains its overall morphology; Step 5: Without crushing, grinding, powder pressing or reshaping, the porous precursor is directly placed under low pressure and high temperature conditions for densification treatment to obtain transparent rare earth doped quartz glass.

[0010] As a further improvement of the present invention, in step 1, the molar ratio of tetraethyl orthosilicate, ethanol and deionized water is 1:(3~6):(3~6), the molar ratio of HCl to tetraethyl orthosilicate is 0.05~0.15, and the molar ratio of HF to tetraethyl orthosilicate is 0.025~0.15; preferably, the molar ratio of tetraethyl orthosilicate, ethanol and deionized water is 1:4:5, the molar ratio of HCl to tetraethyl orthosilicate is 0.10, and the molar ratio of HF to tetraethyl orthosilicate is 0.05~0.125; more preferably, the molar ratio of HF to tetraethyl orthosilicate is 0.10.

[0011] As a further improvement of the present invention, in step 1, a 40% hydrofluoric acid aqueous solution is used as the HF source, and a 36% hydrochloric acid aqueous solution is used as the HCl source.

[0012] As a further improvement of the present invention, in step 2, the aluminum salt precursor is a water-soluble aluminum salt, and the rare earth salt precursor is a water-soluble rare earth salt.

[0013] As a further improvement of the present invention, in step 2, the aluminum salt precursor is aluminum nitrate, and the rare earth salt precursor includes one or more of neodymium salt, ytterbium salt and erbium salt; preferably, the aluminum salt precursor is aluminum nitrate nonahydrate, and the rare earth salt precursor is neodymium nitrate hexahydrate.

[0014] As a further improvement of the present invention, in step 2, the aging treatment temperature is 50~90℃ and the aging time is 2~24 h; preferably, the aging treatment is aging at 70℃ for 6 h.

[0015] As a further improvement of the present invention, in step 3, the staged drying includes drying at 90°C for 10 h and then drying at 120°C for 6 h.

[0016] As a further improvement of the present invention, in step 4, the staged heat treatment includes heating to 250°C at a heating rate of 2°C / min and holding for 1 hour, continuing to heat to 550°C and holding for 1 hour, and then heating to 750°C and holding for 1 hour.

[0017] As a further improvement of the present invention, in step 5, the low-pressure high-temperature densification includes pretreatment in the range of 900~1100℃, followed by densification at 1300~1500℃; preferably, the pressure of the low-pressure condition is 0.015 Torr, first held at 1000℃ for 5 min, and then held at 1400℃ for 5~6 min.

[0018] As a further improvement of the present invention, based on the molar percentage of oxides, the rare earth-doped quartz glass obtained in step 5 has an Al2O3 content of 0.05~1.5 mol%, a rare earth oxide content of 0.01~0.5 mol%, a hydroxyl content of 4~10 ppm, and the balance is mainly SiO2; furthermore, the rare earth-doped quartz glass is neodymium-doped quartz glass, and its composition is 0.4 mol% Nd2O3, 1 mol% Al2O3 and 98.6 mol% SiO2.

[0019] As a further improvement of the present invention, by adjusting the amount of HF added, the BJH desorption pore size of the obtained dry gel is in the range of 2~20 nm; preferably, when the molar ratio of HF to tetraethyl orthosilicate is 0.10, the BJH desorption pore size of the obtained dry gel is 9.585 nm.

[0020] As a further improvement of the present invention, the resulting gel maintains a continuous integral block morphology during gelation, aging, drying and heat treatment, and the resulting porous precursor is directly densified to form quartz glass without undergoing powdering and secondary melting steps.

[0021] Compared with conventional sol-gel rare earth-doped quartz glass preparation methods, the advantages of this invention are as follows: 1. Significantly shortened gelation cycle: Under the condition of HCl / TEOS molar ratio of 0.10, the gelation time is about 200.07 h when using HCl as the catalyst alone, while the gelation time is about 0.63 h when the HF / TEOS molar ratio is 0.10, which significantly shortens the gelation preparation cycle.

[0022] 2. The gel nanopore structure can be continuously regulated: As the HF / TEOS molar ratio increases from 0 to 0.15, the BJH desorption pore size gradually increases from about 3.059 nm to 17.537 nm, indicating that HF ​​can effectively regulate the gel framework and pore structure.

[0023] 3. Significantly improves the overall gel crack resistance: When HCl is used as the catalyst alone, 6 out of 10 parallel samples showed macroscopic cracking, with a cracking rate of 60%; while when the molar ratio of HF / TEOS and HCl / TEOS was 0.10, all 10 samples remained intact, with a cracking rate of 0% and an integrity rate of 100%.

[0024] 4. Low-hydroxyl quartz glass can be obtained: By adjusting the HF content, performing staged heat treatment and low-pressure high-temperature densification, the hydroxyl content of the glass can be controlled at 4~10 ppm, and the hydroxyl content of the 2 mm thick neodymium-doped quartz glass sample was measured to be about 8 ppm.

[0025] 5. Achieve direct densification of the entire precursor: The entire process, from wet gel, dry gel, porous precursor to final dense glass, is maintained. There is no need to crush, ball mill, sieve, press and remelt the dry gel, which can reduce the preparation steps and possible impurities and contamination during powder processing. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process flow for preparing rare earth-doped quartz glass using a composite acid-catalyzed sol-gel method disclosed in this invention.

[0027] Figure 2 The curves show the changes in sol-gel time under different HF / TEOS molar ratios.

[0028] Figure 3 N2 adsorption-desorption isotherms for dry gels obtained with different HF / TEOS molar ratios.

[0029] Figure 4 BJH desorption pore size distribution curves for dry gels obtained with different HF / TEOS molar ratios.

[0030] Figure 5 The cumulative pore volume curves of BJH desorption for dry gels obtained with different HF / TEOS molar ratios.

[0031] Figure 6 The images show a comparison of the physical states of the dry gel, the deesterified porous quartz glass precursor, and the dense quartz glass obtained in this invention.

[0032] Figure 7 The Fourier transform infrared spectrum of the final dense quartz glass obtained in this invention.

[0033] Figure 8 This is the absorption spectrum of the neodymium-doped quartz glass obtained in this invention.

[0034] Figure 9 This is the fluorescence emission spectrum of the neodymium-doped quartz glass obtained in this invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The present invention will now be described in further detail with reference to the accompanying drawings: like Figure 1 As shown, this invention provides a method for preparing rare-earth-doped quartz glass using a composite acid-catalyzed sol-gel, comprising: Step 1: Mix tetraethyl orthosilicate, ethanol, and deionized water, and add HCl and HF to cause the tetraethyl orthosilicate to hydrolyze and condense to form an initial silicon-oxygen network; wherein, The molar ratio of tetraethyl orthosilicate, ethanol, and deionized water is 1:(3~6):(3~6), the molar ratio of HCl to tetraethyl orthosilicate is 0.05~0.15, and the molar ratio of HF to tetraethyl orthosilicate is 0.025~0.15; preferably, the molar ratio of tetraethyl orthosilicate, ethanol, and deionized water is 1:4:5, the molar ratio of HCl to tetraethyl orthosilicate is 0.10, and the molar ratio of HF to tetraethyl orthosilicate is 0.05~0.125; more preferably, the molar ratio of HF to tetraethyl orthosilicate is 0.10.

[0037] A 40% hydrofluoric acid aqueous solution was used as the HF source, and a 36% hydrochloric acid aqueous solution was used as the HCl source.

[0038] Step 2: Add aluminum salt precursor and rare earth salt precursor to the system obtained in Step 1 to obtain doped silica sol, and then perform an aging treatment on the doped silica sol; wherein, The aluminum salt precursor is a water-soluble aluminum salt, and the rare earth salt precursor is a water-soluble rare earth salt; preferably, the aluminum salt precursor is aluminum nitrate, and the rare earth salt precursor includes one or more of neodymium salt, ytterbium salt, and erbium salt; more preferably, the aluminum salt precursor is aluminum nitrate nonahydrate, and the rare earth salt precursor is neodymium nitrate hexahydrate.

[0039] The aging treatment temperature for the doped silica sol to complete the gel formation is 50~90℃, and the aging time is 2~24 h; preferably, the aging treatment is aging at 70℃ for 6 h; this allows the internal condensation reaction of the gel to proceed further and strengthens the overall gel skeleton.

[0040] Step 3: The overall wet gel obtained in Step 2 is dried in stages to obtain the overall dry gel; wherein, The staged drying process involves first drying at 90℃ for 10 hours, and then drying at 120℃ for 6 hours, which gradually drains the pore liquid in the gel and reduces the difference in shrinkage between the inside and outside during the drying process.

[0041] Step 4: Perform staged heat treatment on the monolithic dry gel to obtain a porous precursor that maintains its overall morphology; wherein, The staged heat treatment involves heating to 250°C at a rate of 2°C / min and holding for 1 hour, then heating to 550°C and holding for 1 hour, and then heating to 750°C and holding for 1 hour to gradually remove residual solvents, organic components, and moisture, thereby obtaining a porous quartz glass precursor that maintains its overall morphology.

[0042] Step 5: Without crushing, grinding, powder pressing, or reshaping, the porous precursor is directly placed under low-pressure, high-temperature conditions for densification treatment to obtain transparent rare-earth-doped quartz glass; wherein, Low-pressure high-temperature densification includes pretreatment in the range of 900~1100℃, followed by densification in the range of 1300~1500℃; preferably, the pressure of the low-pressure condition is 0.015 Torr, first holding at 1000℃ for 5 min, and then holding at 1400℃ for 5~6 min.

[0043] Based on the molar percentage of oxides, the rare earth-doped quartz glass obtained in step 5 contains 0.05~1.5 mol% Al2O3, 0.01~0.5 mol% rare earth oxides, and 4~10 ppm hydroxyl groups, with the remainder being mainly SiO2. Furthermore, the rare earth-doped quartz glass is neodymium-doped quartz glass, with a composition of 0.4 mol% Nd2O3, 1 mol% Al2O3, and 98.6 mol% SiO2.

[0044] Research on the regulation of gel formation time and pore structure by HF While keeping the HCl / TEOS molar ratio constant at 0.10, the HF / TEOS molar ratio was set to 0, 0.025, 0.050, 0.075, 0.100, 0.125 and 0.150, respectively, to study the effect of HF addition on the gel time and pore structure of the system.

[0045] The gel time is defined as the time from the completion of sol preparation until it loses its macroscopic fluidity. The test results are shown in Table 1.

[0046] Table 1 The results showed that, under the condition of constant HCl addition, HF could significantly accelerate the gel formation process of the system. When no HF was added, the gel time was approximately 200.07 h; when the HF / TEOS molar ratio was increased to 0.025, the gel time rapidly decreased to approximately 11.17 h; when the HF / TEOS molar ratio was 0.10, the gel time further decreased to approximately 0.63 h.

[0047] Compared with HCl catalysis alone, the gel formation time was shortened by more than two orders of magnitude when the HF / TEOS molar ratio was 0.10, indicating that the addition of HF can significantly change the sol-condensation kinetics and effectively shorten the overall gel preparation cycle.

[0048] Nitrogen adsorption-desorption test results showed that as the amount of HF added increased, the BJH desorption pore size of the gel gradually increased from about 3.059 nm to 17.537 nm, and the cumulative pore volume generally showed an increasing trend, indicating that HF ​​can effectively regulate the nanoporous structure of silica gel.

[0049] The specific surface area of ​​BET exhibits a trend of first increasing and then decreasing, reaching 1219.034 m² when the HF / TEOS molar ratio is 0.05. 2 The specific surface area (BET) initially decreased by 1 / g, then decreased further with increasing HF content. This phenomenon indicates that the specific surface area does not simply change monotonically with HF content, but is influenced by factors such as pore size, pore volume, and the degree of openness of the pore structure. As the pore size continues to increase under higher HF content conditions, the internal surface area corresponding to a unit pore volume decreases, thus the BET specific surface area decreases accordingly.

[0050] This invention is not aimed at obtaining the highest BET specific surface area, but rather takes into account gelation time, pore size, pore volume, overall drying stability and subsequent densification performance, and preferably has an HF / TEOS molar ratio of 0.10.

[0051] Mechanism of overall gel crack resistance and experimental results During the drying process of wet gel, the pore liquid forms a meniscus inside the gel channels and generates capillary pressure, the magnitude of which can be expressed as: In the formula For capillary pressure, The surface tension of the pore fluid, The contact angle between the liquid and the gel pore wall. Let be the pore radius. Under conditions where the liquid phase composition and wetting state are essentially the same, increasing the pore radius can reduce the capillary pressure generated during the drying process.

[0052] When the pore fluid composition and wetting conditions are basically similar, appropriately increasing the pore radius can reduce the capillary pressure generated during the drying process. This invention utilizes HF content to adjust the gel nanopore structure, gradually transforming the small pore size under HCl catalysis into a suitable mesoporous structure. Combined with 70℃ aging treatment to strengthen the gel framework, and then through two-stage drying at 90℃ and 120℃, the pore fluid is gradually discharged, thereby reducing the risk of large stress differences within the overall gel.

[0053] It should be noted that this invention does not achieve crack resistance by infinitely increasing the pore size. Excessively large pore sizes may alter the gel skeleton structure and mechanical stability; therefore, a comprehensive adjustment is needed between gelation speed, pore size, pore volume, and skeleton stability.

[0054] To verify the overall anti-cracking effect, 10 parallel monolithic gel samples were prepared under the same basic composition, aging and drying conditions, using only an HCl catalytic system and an optimized HF and HCl composite acid system.

[0055] Among them, when only HCl catalysis was used and the HCl / TEOS molar ratio was kept at 0.10, 6 out of 10 samples showed obvious macroscopic cracks after drying, with a cracking rate of 60% and an overall integrity rate of 40%.

[0056] When the molar ratios of HCl / TEOS and HF / TEOS were both 0.10, all 10 parallel samples remained intact under the same aging and drying conditions, with no obvious macroscopic cracks observed, a cracking rate of 0%, and an overall integrity rate of 100%.

[0057] The above results indicate that adjusting the gel pore structure using a composite acid system of HF and HCl, combined with appropriate aging and staged drying regimes, can significantly improve the overall crack resistance of the gel.

[0058] Direct densification of integral porous precursor After obtaining the overall dry gel, the present invention gradually removes the solvent, organic residues and other volatile components in the gel by staged heat treatment at 250℃, 550℃ and 750℃, and obtains a porous quartz glass precursor that maintains a continuous bulk morphology.

[0059] The porous precursor does not require crushing, grinding, sieving, powder pressing or other reshaping steps, but is directly densified at high temperature in a low-pressure environment.

[0060] Under conditions of approximately 0.015 Torr, the porous precursor was first held at 1000℃ for 5 min, then raised to 1400℃ and held for 5-6 min. The porous precursor underwent significant shrinkage, and the nanopores gradually closed, eventually forming a transparent and dense quartz glass.

[0061] Therefore, the present invention forms a continuous integral molding route from integral wet gel, integral dry gel, integral porous precursor to transparent dense quartz glass, avoiding traditional powdering treatment and subsequent remelting or reshaping steps.

[0062] Reduce hydroxyl content In addition to regulating sol hydrolysis, condensation and pore structure, the introduction of HF can also affect the fluorine-containing structure and hydroxyl-related structure in the final silicon-oxygen network.

[0063] The fluorine (F) introduced by HF can form Si-F related structures in the silicon-oxygen network, thereby reducing some Si-OH sites and facilitating the reduction of hydroxyl group retention in the subsequent glass network. Simultaneously, the open nanoporous structure of the porous precursor provides mass transfer channels for the removal of adsorbed water and hydroxyl-containing volatile components. Combined with staged heat treatment at 250℃, 550℃, and 750℃, and subsequent low-pressure high-temperature densification, the removal of residual moisture, organic residues, and hydroxyl-related components can be further promoted.

[0064] By adjusting the amount of HF added, the hydroxyl content of the quartz glass obtained by this invention can be controlled within the range of 4 to 10 ppm. Specifically, neodymium-doped quartz glass was prepared under the condition of an HF / TEOS molar ratio of 0.10, and the final dense glass was processed to a thickness of 2 mm and subjected to infrared spectroscopy, which showed that the hydroxyl content was approximately 8 ppm.

[0065] Example 1: A method for preparing rare-earth-doped quartz glass using a composite acid-catalyzed sol-gel process includes: S1, Preparation of silica sol Tetraethyl orthosilicate was used as the silicon source, anhydrous ethanol as the solvent, and deionized water as the hydrolysant. Tetraethyl orthosilicate, anhydrous ethanol, and deionized water were mixed in a molar ratio of 1:4:5.

[0066] A 40% hydrofluoric acid aqueous solution was used as the HF source, and a 36% hydrochloric acid aqueous solution was used as the HCl source, with a molar ratio of HCl to TEOS of 0.10 and a molar ratio of HF to TEOS of 0.10. HF and HCl jointly participated in the hydrolysis and polycondensation process of tetraethyl orthosilicate, gradually forming an initial silicon-oxygen network in the system.

[0067] S2, Introduction of doping components After the initial silicon-oxygen network is formed, aluminum nitrate nonahydrate and neodymium nitrate hexahydrate are added to ensure that the Al and Nd components are uniformly dispersed in the sol system.

[0068] The representative glass composition is as follows: 0.4 mol% Nd2O3–1 mol% Al2O3–98.6 mol% SiO2.

[0069] S3, gelation and aging The resulting doped sol was allowed to stand to complete gelation. In this example, with an HF / TEOS molar ratio of 0.10, the gelation time was approximately 0.63 h. After gelation, the entire wet gel was aged at 70°C for 6 h to further condense the silicon-oxygen network and strengthen the gel framework.

[0070] S4. Staged drying The aged wet gel was first dried at 90°C for 10 h to allow the pore liquid to gradually drain out; then it was dried at 120°C for another 6 h to further remove the residual liquid phase inside the gel, thus obtaining a dry gel that maintains its complete block shape.

[0071] S5, Staged Heat Treatment The resulting whole dry gel was heated to 250°C at 2°C / min and held for 1 h, then heated to 550°C at 2°C / min and held for 1 h, and then heated to 750°C at 2°C / min and held for 1 h.

[0072] By gradually removing residual solvents, organic groups and other volatile components through the above-mentioned staged heat treatment, a porous quartz glass precursor that maintains its overall morphology is obtained.

[0073] S6, Low-pressure, high-temperature direct densification The resulting porous precursors are not subjected to crushing, ball milling, grinding, sieving, powder pressing, or other reshaping processes.

[0074] The precursor was placed directly in a low-pressure environment of about 0.015 Torr and held at 1000℃ for 5 min. Then it was raised to 1400℃ and held for 5~6 min to cause the porous precursor to shrink at high temperature and close the pores, and finally obtained a transparent and dense neodymium-doped quartz glass.

[0075] S7, pore structure and crack resistance The BET specific surface area of ​​the dry gel obtained in this embodiment is 469.063 m². 2 / g, the BJH desorption pore size is 9.585 nm, and the cumulative pore volume of BJH desorption is 1.384 cm³. 3 / g.

[0076] Ten monolithic gel samples were prepared using the same process. After aging at 70℃ for 6 h, drying at 90℃ for 10 h, and drying at 120℃ for 6 h, all ten samples remained intact, with no obvious macroscopic cracks observed. The cracking rate was 0%, and the overall integrity rate was 100%.

[0077] S8, hydroxyl content The obtained neodymium-doped dense quartz glass was processed to a thickness of 2 mm and tested by Fourier transform infrared spectroscopy, which showed that the hydroxyl content of the sample was approximately 8 ppm.

[0078] Example 2: Effects of different HF contents on gel time and pore structure To investigate the effect of HF addition on the sol-gel formation process and the pore structure of the dry gel, the amount of HF was varied while keeping the amounts of tetraethyl orthosilicate, anhydrous ethanol, deionized water, and HCl constant. The molar ratios of HF to tetraethyl orthosilicate were 0, 0.025, 0.050, 0.075, 0.100, 0.125, and 0.150, respectively. The molar ratio of HCl to tetraethyl orthosilicate was fixed at 0.10, and the other preparation, aging, and drying conditions remained the same.

[0079] The gel time is defined as the time from the completion of sol preparation until it loses its macroscopic fluidity. The gel times corresponding to different amounts of HF added are 200.07 h, 11.17 h, 3.63 h, 1.35 h, 0.63 h, 0.32 h, and 0.17 h, respectively. The results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the gelation time of the system is significantly shortened with the increase of HF addition. Specifically, the gelation time is about 200.07 h when HCl is used as the catalyst alone; when the HF / TEOS molar ratio is 0.10, the gelation time is shortened to about 0.63 h, indicating that the addition of HF can significantly promote the polycondensation and gelation process of the system, thereby shortening the overall preparation cycle.

[0080] Nitrogen adsorption-desorption tests were performed on the dry gels obtained with different amounts of HF. The isothermal adsorption-desorption curves are shown below. Figure 3 As shown, the adsorption capacity and adsorption-desorption hysteresis behavior of each sample changed significantly with the amount of HF added, indicating that the HF content can affect the gel skeleton formation process and pore structure.

[0081] The BJH desorption pore size distribution curves of samples with different HF addition amounts are shown below. Figure 4 As shown, when the HF / TEOS molar ratios are 0, 0.025, 0.050, 0.075, 0.100, 0.125, and 0.150, the corresponding characteristic pore sizes of BJH desorption are approximately 3.059 nm, 3.415 nm, 4.321 nm, 6.562 nm, 9.585 nm, 12.423 nm, and 17.537 nm, respectively. (From...) Figure 4 It is evident that as the amount of HF added increases, the overall pore size distribution shifts towards larger pore sizes, indicating that HF ​​can effectively modulate the nanoporous structure of the dry gel.

[0082] The cumulative pore volume curves of BJH desorption for samples with different HF addition amounts are shown below. Figure 5 As shown, the cumulative pore volumes of BJH desorption for the above seven groups of samples are approximately 0.061 cm³. 3 / g, 0.308 cm 3 / g, 1.162 cm 3 / g, 1.252 cm 3 / g, 1.384 cm 3 / g, 1.625 cm 3 / g and 1.685 cm 3 / g. From Figure 5 It can be seen that as the amount of HF added increases, the cumulative pore volume of the sample generally shows an increasing trend, further indicating that the introduction of HF can change the internal pore structure and pore volume of the gel.

[0083] The BET specific surface area of ​​each sample was 734.066 m². 2 / g, 998.657 m 2 / g、1219.034 m 2 / g、696.166 m 2 / g、469.063 m 2 / g、395.486 m 2 / g and 288.020 m 2 The BET specific surface area exhibits a trend of first increasing and then decreasing, reaching its maximum value at an HF / TEOS molar ratio of 0.050. This result indicates that the BET specific surface area is influenced by factors such as pore size, pore volume, and the degree of pore structure openness, and does not change simply and monotonically with the amount of HF added. When the HF content is high, the pore size continues to increase, and the internal surface area corresponding to a unit pore volume decreases, thus the BET specific surface area gradually decreases.

[0084] comprehensive Figures 2-6Based on the drying integrity of the overall gel under different conditions, it can be seen that the amount of HF added affects both the gel formation kinetics and the pore size and pore volume of the dried gel. Considering gelation time, pore structure, drying crack resistance, and subsequent high-temperature densification effect, this invention preferably uses an HF / TEOS molar ratio of 0.10. Under this condition, the gelation time is approximately 0.63 h, and the BET specific surface area is approximately 469.063 m². 2 / g, the characteristic pore size of BJH desorption is approximately 9.585 nm, and the cumulative pore volume of BJH desorption is approximately 1.384 cm³. 3 / g, and is able to obtain a dry gel that maintains overall integrity.

[0085] Comparative Example 1: Catalysis using only HCl Except for the absence of HF, the composition of the sol, the proportion of HCl added, the aging conditions and the drying regime were kept the same as in Example 1, wherein the HCl / TEOS molar ratio was 0.10.

[0086] Under these conditions, the gelation time was approximately 200.07 h, and the resulting dry gel had a BET specific surface area of ​​734.066 m². 2 / g, the BJH desorption pore size is 3.059 nm, and the cumulative pore volume of BJH desorption is 0.061 cm³. 3 / g.

[0087] Ten monolithic gel samples were prepared in parallel under these conditions and subjected to the same treatment regime of aging at 70℃ for 6 h, drying at 90℃ for 10 h, and drying at 120℃ for 6 h.

[0088] After drying, 6 out of 10 samples showed obvious macroscopic cracks, while only 4 remained intact, corresponding to a cracking rate of 60% and an integrity rate of 40%.

[0089] In contrast, in Example 1, when the molar ratios of HF / TEOS and HCl / TEOS were both 0.10, all 10 samples remained intact with a cracking rate of 0%.

[0090] The results indicate that the change in pore structure resulting from the addition of HF, combined with a staged drying regime, can significantly improve the overall drying stability of the gel.

[0091] Example 3: Fourier transform infrared characterization of the final dense glass Fourier transform infrared spectroscopy was performed on the final dense quartz glass obtained by this invention, and the results are as follows: Figure 7 As shown.

[0092] The resulting glass exhibits high infrared transmittance across the entire test area, while hydroxyl-related absorption remains low. For Nd:Y quartz glass prepared at an HF / TEOS molar ratio of 0.10, the sample was processed to a thickness of 2 mm for testing, and the calculated hydroxyl content in the glass was approximately 8 ppm.

[0093] Based on the experimental results of glasses obtained under different HF addition conditions, the hydroxyl content in quartz glass can be controlled within the range of approximately 4 to 10 ppm.

[0094] The results indicate that the introduction of HF, combined with the porous precursor structure, staged heat treatment, and low-pressure high-temperature direct densification, is beneficial for obtaining low-hydroxyl transparent quartz glass.

[0095] Example 4: Absorption and luminescence properties of neodymium-doped quartz glass The absorption spectrum of the neodymium-doped quartz glass prepared using the process of this invention was tested, and the results are as follows: Figure 8 As shown.

[0096] Multiple Nd groups can be observed in the visible to near-infrared region. 3+ Characteristic absorption bands indicate that Nd 3+ The final compact quartz glass retains typical 4f level absorption characteristics, with significant Nd2 absorption near approximately 800 nm and 880 nm. 3+ Absorption band.

[0097] Further fluorescence emission testing was conducted, and the results were as follows: Figure 9 As shown, the obtained Nd:14 silica glass exhibits distinct near-infrared emission peaks at approximately 903 nm, 1058 nm, and 1330 nm. The emission at approximately 903 nm corresponds to Nd:14. 3+ of 4 F 3 / 2 → 4 I 9 / 2 Transition; approximately 1058nm emission corresponds 4 F 3 / 2 → 4 I 11 / 2 Transition; emission at approximately 1330 nm corresponds to 4 F 3 / 2 → 4 I 13 / 2 The emission is strongest near 1058 nm, while significant Nd transitions are also observed near 903 nm and 1330 nm. 3+ Characteristic luminescence.

[0098] The above results indicate that, after staged heat treatment and high-temperature direct densification, the resulting Nd-doped quartz glass still exhibits typical Nd characteristics. 3+The characteristic absorption and near-infrared emission indicate that this preparation process can produce transparent neodymium-doped quartz glass with good rare-earth luminescence properties.

[0099] Comprehensive experimental results Based on the above experimental results, this invention achieves effective regulation of gel formation kinetics and pore structure through a composite acid system of HF and HCl.

[0100] When the HF / TEOS molar ratio was increased from 0 to 0.10, the gelation time decreased from approximately 200.07 h to approximately 0.63 h, while the BJH desorption pore size increased from 3.059 nm to 9.585 nm.

[0101] Under the same aging and drying conditions, the overall gel cracking rate of the HCl catalytic system alone was 60%, while when the molar ratios of HF / TEOS and HCl / TEOS were both 0.10, the overall gel cracking rate decreased to 0%, and all 10 parallel samples remained intact.

[0102] After staged heat treatment, the organic components in the gel are effectively removed, forming a porous quartz glass precursor that maintains its overall shape. This porous precursor does not require crushing and reshaping; it can be directly densified under low pressure and high temperature conditions to form transparent quartz glass.

[0103] The final glass has a low hydroxyl content, with the 2 mm thick neodymium-doped quartz glass sample with an HF / TEOS molar ratio of 0.10 having a hydroxyl content of approximately 8 ppm.

[0104] The resulting Nd2+ quartz glass exhibits significant Nd2+ properties. 3+ Characteristic absorption and near-infrared emission at 903 nm, 1058 nm and 1330 nm.

[0105] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing rare earth-doped quartz glass using a composite acid-catalyzed sol-gel, characterized in that, include: Step 1: Mix tetraethyl orthosilicate, ethanol and deionized water, and add HCl and HF to cause the tetraethyl orthosilicate to hydrolyze and condense to form an initial silicon-oxygen network. Step 2: Add aluminum salt precursor and rare earth salt precursor to the system obtained in Step 1 to obtain doped silica sol, and then gel the doped silica sol and perform an aging treatment. Step 3: Dry the overall wet gel obtained in Step 2 in stages to obtain the overall dry gel; Step 4: Perform staged heat treatment on the monolithic dry gel to obtain a porous precursor that maintains its overall morphology; Step 5: Without crushing, grinding, powder pressing or reshaping, the porous precursor is directly placed under low pressure and high temperature conditions for densification treatment to obtain transparent rare earth doped quartz glass.

2. The preparation method according to claim 1, characterized in that, In step 1, the molar ratio of tetraethyl orthosilicate, ethanol, and deionized water is 1:(3~6):(3~6), the molar ratio of HCl to tetraethyl orthosilicate is 0.05~0.15, and the molar ratio of HF to tetraethyl orthosilicate is 0.025~0.15; preferably, the molar ratio of tetraethyl orthosilicate, ethanol, and deionized water is 1:4:5, the molar ratio of HCl to tetraethyl orthosilicate is 0.10, and the molar ratio of HF to tetraethyl orthosilicate is 0.05~0.

125.

3. The preparation method according to claim 1, characterized in that, In step 2, the aluminum salt precursor is a water-soluble aluminum salt, and the rare earth salt precursor is a water-soluble rare earth salt.

4. The preparation method according to claim 3, characterized in that, In step 2, the aluminum salt precursor is aluminum nitrate, and the rare earth salt precursor includes one or more of neodymium salt, ytterbium salt, and erbium salt.

5. The preparation method according to claim 1, characterized in that, In step 2, the aging treatment temperature is 50~90℃ and the aging time is 2~24 h.

6. The preparation method according to claim 1, characterized in that, In step 3, the staged drying includes drying at 90°C for 10 hours and then drying at 120°C for 6 hours.

7. The preparation method according to claim 1, characterized in that, In step 4, the staged heat treatment includes heating to 250°C at a heating rate of 2°C / min and holding for 1 hour, then heating to 550°C and holding for 1 hour, and then heating to 750°C and holding for 1 hour.

8. The preparation method according to claim 1, characterized in that, In step 5, low-pressure high-temperature densification includes pretreatment in the range of 900~1100℃, followed by densification in the range of 1300~1500℃.

9. The preparation method according to claim 1, characterized in that, Based on the molar percentage of oxides, the rare earth-doped quartz glass obtained in step 5 contains 0.05~1.5 mol% Al2O3, 0.01~0.5 mol% rare earth oxides, and 4~10 ppm hydroxyl groups, with the remainder being mainly SiO2.

10. The preparation method according to claim 1, characterized in that, By adjusting the amount of HF added, the BJH desorption pore size of the resulting dry gel is made to be in the range of 2~20 nm; preferably, when the molar ratio of HF to tetraethyl orthosilicate is 0.10, the BJH desorption pore size of the resulting dry gel is 9.585 nm. The resulting gel maintains a continuous bulk morphology during gelation, aging, drying and heat treatment. The resulting porous precursor is directly densified to form quartz glass without undergoing powdering and secondary melting steps.

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