An apparatus and method for preparing fluorine-zirconium-based glass with ultra-low hydroxyl content

Abstract

This invention discloses a method and apparatus for preparing fluorozirconium-based glass with ultra-low hydroxyl content. In this apparatus, pressurization of the upper furnace chamber causes molten glass to seep out from a small hole in a platinum crucible, forming a "mist-like melt" that falls under gravity. Activating gas is introduced into the lower furnace chamber from bottom to top. By controlling the gas flow rate, the "mist-like melt" is briefly suspended in the air. As the melt collides with each other, larger and heavier droplets are formed, eventually dripping into the collection crucible to obtain the target molten glass. This preparation method utilizes the large specific surface area of ​​the "mist-like melt" to increase the contact area between the melt and the activation gas. Simultaneously, the suspension increases the effective fluorination time, ultimately achieving efficient dehydration of the fluorozirconium-based glass and realizing the preparation of ultra-low hydroxyl glass.

Description

Technical Field

[0001] This invention relates to an apparatus and method for preparing ultra-low hydroxyl content fluorine-zirconium-based glass, and is particularly suitable for the preparation of fluorine-zirconium-based glass with hydroxyl content of ppb. Technical Background

[0002] Mid-infrared (3~5μm) laser sources have important applications in civilian and military fields such as atmospheric remote sensing, laser surgery, precision machining, and optoelectronic countermeasures. Fluorozirconium-based glass has low phonon energy (~550cm⁻¹) in the mid-infrared band. -1 Extremely low theoretical loss (~10) -3 (dB / km) and a high damage threshold (4.3 MW / cm) 2 Fluoride optical fibers (@3μm) are one of the ideal transmission media for mid-infrared laser sources. Currently achievable fluoride optical fibers have losses far exceeding theoretical losses. One key factor is the presence of a large amount of -OH groups in the glass, which are difficult to remove using conventional processes. On one hand, under high-temperature melting conditions, H2O reacts with fluoride raw materials to generate refractory oxide impurities, significantly increasing the fiber's scattering loss. On the other hand, -OH groups themselves exhibit strong absorption near 2.9μm, resulting in increased loss around this wavelength. The sources of -OH groups in fluorinated zirconium-based glass are mainly as follows: 1. H2O in the glass raw materials; 2. Small amounts of H2O in the high-purity N2 introduced during the glove box and glass melting process. Common dehydration processes include: 1. Adding NH3HF to the raw materials for fluorination and dehydration, as described in the patent "A Method for Preparing Fluoride Optical Fiber Precursor Glass"; 2. Introducing activating gases such as CCl4 into the glass melt for reaction dehydration; 3. Increasing the glass melting temperature and maintaining melting at high temperatures for an extended period. In the above processes, process 3 can remove a small amount of -OH in the glass melt, but its efficiency is low. Processes 1 and 2 achieve water removal through chemical reactions, and their water removal intensity is high, which can greatly reduce the -OH content in the glass melt (generally at the ppm level). However, due to the small effective activation area and short reaction time, it is difficult to further reduce the -OH content to the ppb level. In order to further reduce the -OH content in fluorozirconium-based glass and achieve lower optical fiber transmission loss, there is an urgent need for a new type of glass dehydration equipment and preparation process to prepare fluorozirconium-based glass with ultra-low hydroxyl content. Therefore, we designed a high-efficiency dehydration equipment and process technology for fluorozirconium-based glass, which can obtain fluorozirconium-based glass with -OH content at the ppb level. This glass is expected to further reduce the transmission loss of fluoride optical fibers and increase the optical and mechanical properties of optical fibers, and can be applied to the preparation of high-power mid-infrared fiber lasers.

[0003] The hydroxyl content can be calculated using the following formula:

[0004]

[0005] Where α is the absorption coefficient, in cm⁻¹ -1 T1 represents the transmission of 5mm thick glass at 2.9μm, T2 represents the transmission of 10mm thick glass at 2.9μm, and ΔL represents the thickness difference between the two pieces of glass.

[0006]

[0007] Where N OH Hydroxyl content per unit volume (cm³) -3 ), NA is Avogadro's constant (6.02 × 10⁻⁶). 23 ε is the molar absorption rate of the free hydroxyl group (valued at 49.1 × 10⁻⁶). 3 cm 2 / mol)

[0008]

[0009] In the formula, C0 represents the hydroxyl content, and N... OH The content of hydroxyl groups per unit volume, N GLASS W represents the glass unit content per unit volume. OH W is the molecular weight of the hydroxyl group. GLASS This is the molecular weight of glass. Summary of the Invention

[0010] The purpose of this invention is to provide an apparatus and process for preparing ultra-low hydroxyl content fluorine-zirconium-based glass. In this apparatus, by pressurizing the upper furnace chamber, molten glass seeps out from a small hole in a platinum crucible, forming a "mist-like melt" that falls under gravity. An activation gas is introduced from bottom to top into the lower furnace chamber. By controlling the gas flow rate, the "mist-like melt" is briefly suspended in the air. As the melt collides with each other, larger and heavier droplets are formed, eventually dripping into the collection crucible to obtain the target molten glass. Compared with traditional equipment and processes, this apparatus can achieve efficient preparation of fluorine-zirconium-based glass with -OH content down to the ppb level, providing conditions for further reducing fiber loss and realizing the fabrication of high-power mid-infrared fiber lasers.

[0011] The technical solution of the present invention is as follows:

[0012] An apparatus for preparing ultra-low hydroxyl content fluorine-zirconium-based glass includes a heating furnace, a melting crucible, a collecting crucible, a heating rod, a thermal sensor, a metal cap, an inlet valve, a pressure gauge, a circulating cooling water pipe, a rigid support structure, an activation gas inlet valve, an activation gas outlet valve, and a stage.

[0013] The heating furnace is sealed by a rotating metal cap, which maintains internal pressure during normal operation. A circulating cooling water pipe is installed on the metal cap to reduce its temperature. An inlet valve and a first pressure gauge are also installed on the cap for pressurizing and controlling the upper furnace chamber. The furnace is divided into upper and lower chambers, with heating rods evenly distributed around each chamber, allowing for independent heating of both chambers. The chamber temperatures are monitored in real-time by two independent first and second thermal sensors. A rigid support structure is located at the bottom of the upper chamber to support the molten crucible and isolate the upper and lower chambers. The lower chamber has an inlet and outlet valve for the activation gas. A second pressure gauge at the outlet valve monitors the lower chamber pressure, ensuring it remains lower than the upper chamber pressure by adjusting the outlet valve. A platform is located at the bottom of the lower chamber to support and precisely position the crucible for collection.

[0014] The molten crucible is a cylindrical structure made of platinum, with small round holes distributed at the bottom and precision grooves cut into the bottom for engagement with a rigid support structure. The collecting crucible is also made of platinum, with its top naturally fitting against the bottom of the molten crucible to collect the molten glass flowing out of the molten crucible.

[0015] A method for preparing ultra-low hydroxyl content fluorozirconium-based glass using the aforementioned apparatus for dehydrating fluorozirconium-based glass is characterized by comprising the following steps:

[0016] Step 1. Open the metal cap. First, place the collecting crucible according to the position of the stage. Then, put in the molten crucible and make it engage with the rigid support structure to form a support. After putting the fluorine-zirconium-based glass raw material into the molten crucible, put the metal cap back on. Connect the gas inlet valve on the metal cap to high-purity nitrogen.

[0017] Step 2. Set the heating temperature of the upper furnace chamber to 750℃~900℃ and the heating temperature of the lower furnace chamber to 850~900℃. Connect the inlet valve to the activation gas CCl4 and the outlet valve to the tail gas treatment device. After the glass melts for 40~60 minutes, open the inlet valve to blow in high-purity nitrogen. Control the pressure of the upper furnace chamber at 0~5kPa using the first pressure gauge, so that the glass melt seeps down through the small hole of the melting crucible. Open the inlet valve to blow in the activation gas CCl4, and control the gas flow rate at 30~60L / h. Control the size of the outlet valve using the second pressure gauge to keep the pressure of the lower furnace chamber at 2~4kPa. When the pressure of the lower furnace chamber increases, close the inlet valve and the outlet valve. Wait 5~10 minutes and then close the inlet valve to keep the pressure of the upper and lower furnace chambers consistent. After the glass melt is kept at 850~900℃ for 30~60 minutes, open the outlet valve of the lower furnace chamber to depressurize to atmospheric pressure.

[0018] Step 3. Open the metal cap, take out the molten crucible, and then use the collection crucible to pour the molten glass into the preheated metal template to obtain the target glass.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1) This invention differs from the traditional method of introducing reactive gas into glass melt. Instead, the glass melt is treated and then introduced into an environment filled with reactive gas. By utilizing the large specific surface area of ​​the "mist melt", the contact area between the melt and the activation gas is increased. At the same time, the floating is used to increase the effective fluorination time, and finally the efficient dehydration of fluorinated zirconium-based glass is completed, realizing the preparation of fluorinated zirconium-based glass with hydroxyl content at the ppb level.

[0021] 2) The equipment of this invention has a simple structure, short process cycle, and simple and effective method. It is expected to further reduce the transmission loss of fluoride optical fibers and increase the optical and mechanical properties of optical fibers, and can be applied to the preparation of high-power mid-infrared fiber lasers. Attached Figure Description

[0022] Figure 1 A schematic diagram of the equipment used to prepare ultra-low hydroxyl content fluorine-zirconium-based glass;

[0023] Figure 2 This is a schematic diagram of a three-dimensional model of a melting crucible;

[0024] Figure 3 To collect schematic diagrams of the three-dimensional model of the crucible

[0025] Figure 4 Infrared transmittance spectrum of the glass in Example 1;

[0026] Figure 5 Infrared transmittance spectrum of the glass in Example 2;

[0027] Figure 6 Infrared transmittance spectrum of the glass in Example 3;

[0028] Figure 7 The infrared transmittance spectrum is shown in the comparative glass. Detailed Implementation

[0029] The following specific embodiments are provided to illustrate the present invention and help to further understand the present invention. However, the specific details of the embodiments are only for illustrating the present invention and do not represent all the technical solutions under the concept of the present invention. Therefore, they should not be construed as limiting the overall technical solution of the present invention. Some non-substantial additions and modifications that do not deviate from the concept of the present invention in the view of those skilled in the art, such as simple substitution or replacement of technical features with the same or similar technical effects, are all within the protection scope of the present invention.

[0030] Figure 1 This is a schematic diagram of an apparatus for ultra-low hydroxyl content fluorine-zirconium based glass, including a heating furnace 1, a melting crucible 2 located inside the furnace, and a collecting crucible 3.

[0031] The heating furnace 1 is divided into upper and lower furnace chambers. Heating rods 4 are evenly distributed around the furnace chambers. The upper furnace chamber 101 and the lower furnace chamber 102 are respectively equipped with a first thermal sensor 51 and a second thermal sensor 52. The first thermal sensor (51) and the second thermal sensor (52) are specifically thermocouples. The furnace opening is threaded and closed by rotating a metal cover 6. The metal cover 6 is equipped with a first air inlet valve 7, a first pressure gauge 801 and a circulating cooling water pipe 9. A rigid support structure 10 is designed at the bottom of the upper furnace chamber for placing the melting crucible 2. The lower furnace chamber is equipped with a second air inlet valve 11 and an air outlet valve 12 on both sides. A second pressure gauge 802 is installed on the pipe of the air outlet valve 12. A platform 13 is placed at the bottom of the lower furnace chamber for positioning and collecting the crucible 3.

[0032] Example 1

[0033] Open the metal cap 6, place the 5cm diameter collection crucible 3 on the stage 13, and then place the 8cm diameter melting crucible 2. The bottom hole of the melting crucible 2 has a diameter of 0.5mm. Put the prepared 300g of fluorine-zirconium-based glass raw material into the melting crucible 2, close the metal cap 6, and connect the first air inlet valve 7 on the cap to high-purity nitrogen gas, so that the cooling water in the circulating cooling water pipe 9 is in a flowing working state.

[0034] The temperature of the upper furnace chamber 101 and the lower furnace chamber 102 are both set to 850℃. After the glass is melted at 850℃ for 40 minutes, the first inlet valve 7 on the metal cover 6 is opened to control the pressure in the upper furnace chamber 101 to 3 kPa. Simultaneously, the second inlet valve 11 and outlet valve 12 of the activation gas in the lower furnace chamber 102 are opened. The activation gas CCl4 connected to the second inlet valve 11 is set to a flow rate of 40 kPa. L / h, the pressure of the lower furnace chamber 102 is controlled to 1 kPa by adjusting the size of the activation gas outlet valve 12. When the outlet valve pressure suddenly increases to 2 kPa, the first inlet valve 7 of the upper furnace chamber 101 and the outlet valve 12 of the lower furnace chamber 102 are closed. After 5 minutes, when the first and second pressure gauges (801, 802) are both stable at 2 kPa, the second inlet valve 11 of the activation gas is closed. After the glass melt is kept at 850°C for 30 minutes, the activation gas outlet valve 12 is opened to depressurize to normal pressure. Then, the metal cap 6 is opened, the molten crucible 2 is taken out, and the collection crucible 3 is taken out. The dehydrated glass melt is poured onto the preheated metal template to obtain the glass of the target embodiment 1 and then annealed.

[0035] Example 2

[0036] Open the metal cap 6, place the 5cm diameter collection crucible 3 on the stage 13, and then place the 8cm diameter melting crucible 2. The bottom hole of the melting crucible 2 has a diameter of 0.5mm. Put the prepared 500g of fluorine-zirconium-based glass raw material into the melting crucible 2, close the metal cap 6, and connect the first air inlet valve 7 on the cap to high-purity nitrogen gas, so that the cooling water in the circulating cooling water pipe 9 is in a flowing working state.

[0037] The temperature of the upper furnace chamber 101 is set to 900℃, and the temperature of the lower furnace chamber 102 is set to 850℃. After the glass is melted at 900℃ for 55 minutes, the first gas inlet valve 7 on the metal cover 6 is opened to control the pressure of the upper furnace chamber 101 to 4 kPa. At the same time, the second gas inlet valve 11 and the gas outlet valve 12 of the lower furnace chamber 102 are opened. The second gas inlet valve 11 is connected to the activation gas CCl4, and the gas flow rate is set to 50. The pressure in the lower furnace chamber is controlled to 2 kPa by adjusting the size of the outlet valve 12. When the pressure of the outlet valve 12 suddenly increases to 3 kPa, the first inlet valve 7 of the upper furnace chamber 101 and the outlet valve 12 of the lower furnace chamber are closed. After 8 minutes, when the second and second pressure gauges (801, 802) are both stable at 3 kPa, the second inlet valve 11 for activation gas is closed. After the glass melt is held at 850°C for 45 minutes, the activation gas outlet valve 12 is opened to depressurize to atmospheric pressure. Then, the metal cap 6 is opened, the molten crucible 2 is removed, and the collecting crucible 3 is removed. The dehydrated glass melt is poured onto the preheated metal template to obtain the glass of the target embodiment 2 and then annealed.

[0038] Example 3

[0039] Open the metal cap 6, place the 5cm diameter collection crucible 3 on the stage 13, and then place the 8cm diameter melting crucible 2. The bottom hole of the melting crucible 2 has a diameter of 0.5mm. Put the prepared 600g of fluorine-zirconium-based glass raw material into the melting crucible 2, close the metal cap 6, and connect the first air inlet valve 7 on the cap to high-purity nitrogen gas, so that the cooling water in the circulating cooling water pipe 9 is in a flowing working state.

[0040] The temperature of the upper furnace chamber 101 is set to 950℃, and the temperature of the lower furnace chamber 102 is set to 900℃. After the glass is melted at 950℃ for 60 minutes, the first inlet valve 7 on the metal cover 6 is opened to control the pressure of the upper furnace chamber 101 to 5 kPa. At the same time, the second inlet valve 11 and the outlet valve 12 of the activation gas in the lower furnace chamber 102 are opened. The second inlet valve 11 is connected to the activation gas CCl4, and the gas flow rate is set to 60. The pressure in the lower furnace chamber 102 is controlled to 3 kPa by adjusting the size of the outlet valve 12. When the pressure of the outlet valve 12 suddenly increases to 4 kPa, the first inlet valve 7 of the upper furnace chamber 101 and the outlet valve 12 of the lower furnace chamber 102 are closed. After 8 minutes, when the first and second pressure gauges (801, 802) are both stable at 4 kPa, the second inlet valve 11 of the activation gas is closed. After the glass melt is held at 900°C for 60 minutes, the activation gas outlet valve 12 is opened to depressurize to atmospheric pressure. Then, the metal cap 6 is opened, the molten crucible 2 is removed, and the collecting crucible 3 is removed. The dehydrated glass melt is poured onto the preheated metal template to obtain the glass of the target embodiment 3 and then annealed.

[0041] The tests on the fluorozirconium-based glasses of Examples 1, 2, and 3 are as follows:

[0042] Two samples were cut from the annealed glass and polished into glass sheets of 10mm × 10mm × 5mm and 10mm × 10mm × 10mm respectively. The transmittance T1 and T2 of the two glasses at 2.9µm were measured. Figure 3 , Figure 4 , Figure 5 As shown in Table 1, the hydroxyl content is as shown in the table.

[0043] Table 1. Hydroxyl content of ZBLAN glass in Examples 1-3

[0044]

[0045] Comparative Example 1

[0046] To melt glass in a dry environment, 500g of fluorozirconium-based glass raw material was placed in a platinum crucible with a diameter of 8cm. The crucible containing the raw material was then transferred to a resistance furnace at 850℃ and melted for 60min. A mixture of CCl4 and N2 gas was then introduced into the glass melt at flow rates of 30ml / min and 0.3L / min, respectively, for 1h. After the gas introduction was completed, the glass melt was poured into a preheated metal mold to obtain the target glass, which was then annealed.

[0047] The following tests were conducted on the fluorozirconium-based glass of Comparative Example 1:

[0048] Two samples were cut from the annealed glass and polished into glass sheets of 10mm × 10mm × 5mm and 10mm × 10mm × 10mm respectively. The transmittance T1 and T2 of the two glasses at 2.9µm were measured. Figure 6 As shown in Table 2, the hydroxyl content is as shown in the table.

[0049] Table 2. Hydroxyl content of ZBLAN glass in Comparative Example 1

[0050]

[0051] As shown in Tables 1 and 2, after efficient dehydration, the hydroxyl content in the glasses prepared in Examples 1, 2, and 3 was 0.7864 ppm (786.4 ppb), 0.6552 ppm (655.2 ppb), and 0.7698 ppm (769.8 ppb), respectively, achieving a ppb-level dehydration effect. In contrast, the glass in the comparative example, after traditional dehydration treatment, had a hydroxyl content of 5.3 ppm, which is an order of magnitude higher than that of the glasses prepared in Examples 1, 2, and 3. Therefore, the dehydration solution provided by this patent is more effective, which is beneficial for further improving glass quality and reducing optical fiber transmission loss in the mid-infrared band.

Claims

1. An apparatus for preparing ultra-low hydroxyl content fluorine-zirconium-based glass, characterized in that, It includes a heating furnace (1), a melting crucible (2), and a collecting crucible (3); The heating furnace (1) is divided into an upper furnace chamber (101) and a lower furnace chamber (102); the melting crucible (2) is located in the upper furnace chamber (101), and the collecting crucible (3) is located in the lower furnace chamber (102); the bottom of the melting crucible (2) has small round holes with a diameter of 0.5 mm to 1 mm evenly distributed, and the glass melt can flow into the collecting crucible (3) through the holes. Heating rods (4) are distributed around the upper furnace chamber (101) and the lower furnace chamber (102). The upper furnace chamber (101) and the lower furnace chamber (102) are respectively equipped with a first thermal sensor (51) and a second thermal sensor (52). The upper furnace chamber (101) is provided with a metal cover (6) for sealing the upper opening of the heating furnace (1). The metal cover (6) is provided with a first air inlet valve (7), a circulating cooling water pipe (9) and a first pressure gauge (801). A rigid support structure (10) is provided at the bottom of the upper furnace chamber (101) for placing a molten crucible (2). The outer wall of the lower furnace chamber (102) is provided with a second air inlet valve (11) and an air outlet valve (12). The air outlet valve (12) is provided with a second pressure gauge (802). A platform (13) is placed at the bottom of the lower furnace chamber (102) for positioning and placing a collection crucible (3). The second inlet valve (11) is connected to the activation gas, which comes into contact with the glass melt after the glass melt flows out from the bottom hole of the melting crucible (2).

2. The apparatus for preparing ultra-low hydroxyl content fluorine-zirconium-based glass according to claim 1, characterized in that, The heating rod (4) can independently heat the upper furnace chamber (101) and the lower furnace chamber (102) respectively. The temperatures of the upper furnace chamber (101) and the lower furnace chamber (102) are independently monitored by the first thermal sensor (51) and the second thermal sensor (52) respectively.

3. The apparatus for preparing ultra-low hydroxyl content fluorine-zirconium-based glass according to claim 1, characterized in that, The metal cover (6) is made of 310s stainless steel, the first air intake valve (7) is a 304 stainless steel pagoda ball valve, and the metal cover is equipped with a circulating cooling water pipe (9) to keep the temperature of the metal cover always below 40℃.

4. The apparatus for preparing ultra-low hydroxyl content fluorine-zirconium-based glass according to claim 1, characterized in that, The rigid support structure (10) and the upper furnace cavity (101) are integrally formed by casting with high-temperature refractory material, and the rigid support structure (10) matches the bottom size of the molten crucible (2).

5. The apparatus for preparing ultra-low hydroxyl content fluorine-zirconium-based glass according to claim 1, characterized in that, The second inlet valve (11) and outlet valve (12) are both 321 stainless steel ball valves.

6. The apparatus for preparing ultra-low hydroxyl content fluorine-zirconium-based glass according to claim 1, characterized in that, The stage (13) has a groove that matches the bottom size of the collecting crucible (3) and is used to support and precisely position the collecting crucible (3).

7. The apparatus for preparing ultra-low hydroxyl content fluorine-zirconium-based glass according to claim 1, characterized in that, The melting crucible (2) is made of cylindrical platinum material. A groove is precisely cut at the bottom of the crucible to engage with the rigid support structure (10), which supports the melting crucible (2) while isolating the upper furnace chamber (101) from the lower furnace chamber (102).

8. The apparatus for preparing ultra-low hydroxyl content fluorine-zirconium-based glass according to claim 1, characterized in that, The collection crucible (3) is made of platinum.

9. The apparatus for preparing ultra-low hydroxyl content fluorine-zirconium-based glass according to claim 1, characterized in that, The activating gas is CCl4 gas, and the first inlet valve (7) is connected to N2 gas.

10. A method for preparing fluorozirconium-based glass using the apparatus for preparing ultra-low hydroxyl content fluorozirconium-based glass according to any one of claims 1-9, characterized in that, The method includes the following steps: Step 1. Open the metal cap (6), first place the collecting crucible (3) according to the position of the stage (13), then put in the melting crucible (2) and make it engage with the rigid support structure (10) to form a support. After putting the fluorine-zirconium-based glass raw material into the melting crucible (2), put the metal cap (6) on it. Connect the first gas inlet valve (7) on the metal cap (6) to high-purity nitrogen. Step 2. Set the heating temperature of the upper furnace chamber of the heating furnace (1) to 750℃~900℃ and the heating temperature of the lower furnace chamber to 850~900℃. Connect the second inlet valve (11) to the activation gas CCl4 and the outlet valve (12) to the tail gas treatment device. After the glass melts for 40~60 minutes, open the first inlet valve (7) to blow in high-purity nitrogen. Control the pressure of the upper furnace chamber at 3~5 kPa through the first pressure gauge (801) so that the glass melt seeps down through the small hole of the melting crucible. Open the second inlet valve (11) to blow in the activation gas CCl4. Control the gas flow rate at 30~60 L / h. Control the size of the outlet valve (12) through the second pressure gauge (802) so that the pressure of the lower furnace chamber is 2~ 4 kPa. When the pressure in the lower furnace chamber increases, close the first inlet valve (7) and the outlet valve (12). After waiting for 5 to 10 minutes, close the second inlet valve (11) to keep the pressure in the upper furnace chamber (101) and the lower furnace chamber (102) consistent. After the glass melt is kept at 850 to 900°C for 30 to 60 minutes, open the outlet valve (12) of the lower furnace chamber (102) to depressurize to atmospheric pressure. Step 3. Open the metal cap, take out the molten crucible (2), then take out the collection crucible (3) and pour the molten glass into the preheated metal template to obtain the target glass.

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