A melting process and a melting device for low-expansion quartz glass

Abstract

The application relates to a melting process and a melting device of low-expansion quartz glass, and belongs to the technical field of quartz glass production. The process path of the application comprises high-temperature water (heat) dissociation of raw materials, generation of fused quartz glass microdroplets, and deposition and fusion processes of the quartz glass, and does not involve a burner and a combustion process. The application effectively improves the uniformity of the CTE of the low-expansion quartz glass product and avoids the generation of color spots, starting from the terminal demand of the low-expansion quartz glass. The melting device of the application can melt the low-expansion quartz glass product with a size of about 500 mm in diameter under single-body conditions, can expand the melting size to about 700 mm in diameter under double-body configuration shared crucible conditions, and can reach 800 mm in diameter under three-body configuration melting size conditions. The effective use range of the low-expansion quartz glass product under single-body conditions is about 85% of the inner diameter range, the Ti element content distribution range value can be controlled to be less than 0.07 wt%, and the CTE fluctuation range can be controlled to be less than 15 ppb.

Description

TECHNICAL FIELD

[0001] The present application relates to a melting process and a melting device of low-expansion quartz glass, and belongs to the technical field of quartz glass production. BACKGROUND

[0002] Ultra-low expansion quartz glass, also known as ULE Glass, is a special glass with extremely low thermal expansion coefficient. The main feature of this glass is its almost zero thermal expansion property, which makes it the preferred material in a variety of unique applications. Its unique properties mainly include the following aspects:

[0003] 1) Extreme thermal stability: Low-expansion quartz glass can remain stable under extreme temperature changes without thermal hysteresis and has delayed elasticity.

[0004] 2) Near-zero thermal expansion coefficient: Its thermal expansion coefficient is very close to zero, which means that the size change is minimal when the temperature changes.

[0005] 3) Large size manufacturing capability: Low-expansion quartz glass can form a fused block of more than 1 meter, from which products of almost any size or shape can be manufactured.

[0006] 4) High uniformity: The high uniformity of the thermal expansion coefficient throughout the fused block makes the material utilization efficiency extremely high.

[0007] Currently, the production process of low-expansion quartz glass is to deposit titanium-doped quartz glass ingots in a crucible by CVD method (see Figure 2 ). In this process, the combustion of fuel gas and oxygen produces high heat and H2O (gas), and the raw materials containing silicon and titanium elements participate in pyrolysis or hydrolysis reaction in gaseous form, forming tiny molten glass droplets, which are deposited in the crucible with the burner jet, and finally form a glass ingot of a certain size (one-step synthesis); or deposit a loose body at a slightly lower temperature, and then form a glass ingot through a controlled heating process (two-step synthesis).

[0008] In the one-step or two-step quartz glass synthesis process, due to the opposite direction of the burner jet and gravity, there is a deficiency that during the melting process, the scattered materials will adhere to the opening position of the burner at the top of the furnace and will drop on the surface of the glass ingot after a certain period of time, thereby forming color spots.

[0009] On the other hand, the one-step or two-step quartz glass synthesis process relies on a combustion process to produce glassified SiO2 melt droplets deposited on the quartz ingot surface to form the product. However, the severe mass and heat transfer process existing in the combustion process has a negative impact on the uniformity of the generated particles, and the generated particles have a wide particle size distribution. In the process of generating TiO2-SiO2 particles, the reaction rate of TiCl4 is faster than that of SiCl4, which leads to the nucleation process of TiO2 being earlier than that of SiO2, and then the Ti content of TiO2-SiO2 particles of different sizes is different. Further, the inhomogeneity of the Ti element composition of the particles leads to the spatial inhomogeneity of the Ti element distribution of the melted quartz ingot (ingot). SUMMARY

[0010] The purpose of the present application is to provide a low-expansion quartz glass melting process and device that can effectively improve the uniformity of quartz glass products and avoid the generation of color spots.

[0011] The technical solution of the present application is:

[0012] A low-expansion quartz glass melting process, characterized in that it comprises the following steps:

[0013] 1) First, place the liquid raw materials in the raw material box, and at the same time, turn on the heater of the melting device to preheat the atomization mixing cylinder, high-temperature flow guide cylinder and crucible;

[0014] 2) When the preheating temperatures of the atomization mixing cylinder, high-temperature flow guide cylinder and crucible reach 800℃, 1700℃ and 1750℃ respectively, open the liquid flow pump, and pump the liquid raw materials in the raw material box into the atomizer in the atomization mixing cylinder under the condition of a flow rate of 300-2000 ml / h; At the same time, the liquid raw materials are pumped in; open the gate valve on the connecting pipe, and the high-temperature water-containing gas (inlet amount 30-60 SLPM, water (gas) content 6-86 vol%) enters the atomization mixing cylinder through the connecting pipe;

[0015] 3) Under the action of the atomizer, the liquid raw materials entering the atomizer are atomized into fine droplets and flow downward along the atomization mixing cylinder, and the downward droplets are mixed with the 800℃ high-temperature water-containing gas entering the atomization mixing cylinder at the same time through the connecting pipe;

[0016] 4) In the process of mixing the liquid droplets atomized from the liquid raw materials with the high-temperature water-containing gas, the liquid droplets hydrolyze under the action of the high-temperature water-containing gas: the composite solid particles generated by the hydrolysis reaction continue to flow downward under the entrainment of the high-temperature water-containing gas, and enter the high-temperature flow guide cylinder through the lower end of the atomization mixing cylinder;

[0017] 5)The complex solid particles generated by the hydrolysis reaction enter the high-temperature guide cylinder and descend; in this process, the high-temperature anhydrous gas (30-100 SLPM) enters the annulus between the gas pipe and the electric heater in the high-temperature guide cylinder and is heated to 1700℃;

[0018] 6)The high-temperature anhydrous gas heated to 1700℃ enters the high-temperature guide cylinder from the gap between the atomizing mixing cylinder, the top port of the high-temperature guide cylinder and the atomizing mixing cylinder, and the through hole on the circumference of the high-temperature guide cylinder, thereby forming a protective sheath gas on the inner wall of the high-temperature guide cylinder to reduce the adhesion of the complex solid particles on the inner wall of the high-temperature guide cylinder;

[0019] 7)In the high-temperature environment of 1700-1800℃, the complex solid particles entering the high-temperature guide cylinder and descending are melted into glassy droplets (glassy droplets);

[0020] 8)The glassy droplets continue to descend in the high-temperature guide cylinder with the high-temperature anhydrous gas, are sprayed from the nozzle at the lower end of the high-temperature guide cylinder towards the crucible, and are deposited in the crucible to form a quartz glass melt, which, after cooling, forms a quartz product; in this process, the protective gas (100-300 SLPM) enters the protective gas input pipe and the mounting sleeve, respectively; the protective gas entering the protective gas input pipe enters the crucible intermittently between the protective gas input pipe and the high-temperature guide cylinder to sweep the top of the crucible and reduce the adhesion of the droplets on the top of the crucible; the protective gas entering the mounting sleeve is used to protect the inner cavity heater of the crucible to avoid the influence of the oxidizing atmosphere on the inner cavity heater of the crucible.

[0021] The liquid raw material is a mixed liquid composed of any proportion of silicon-containing raw material and titanium-containing raw material.

[0022] The silicon-containing raw material is one of octamethylcyclotetrasiloxane and silicon tetrachloride.

[0023] The titanium-containing raw material is one of titanium tetrachloride and tetraisopropyl titanate.

[0024] The melting device in step (1) is composed of a heat preservation shell, an atomizing mixing cylinder, a high-temperature guide cylinder and a crucible; the atomizing mixing cylinder is arranged in the heat preservation shell; the high-temperature guide cylinder is arranged below the atomizing mixing cylinder in the heat preservation shell; the guide cylinder heater is arranged in the heat preservation shell on both sides of the atomizing mixing cylinder and the high-temperature guide cylinder; and the crucible is mounted below the high-temperature guide cylinder through lifting equipment.

[0025] The atomizing mixing cylinder is symmetrically provided with a communication pipe on both sides; the atomizing cylinder is provided with an atomizer, and the atomizer is in communication with the raw material box; and the lower end of the atomizing mixing cylinder extends into the high-temperature guide cylinder.

[0026] The high-temperature guide cylinder is provided with a gap between the top port and the atomizing mixing cylinder.

[0027] The high-temperature flow guide cylinder is uniformly distributed with through holes on the upper end circumference, and the lower end of the high-temperature flow guide cylinder extends into the crucible.

[0028] The heat preservation shell corresponding to the flow guide cylinder heater is provided with a gas conveying pipe.

[0029] The heat preservation shell below the gas conveying pipe is provided with a protective gas input pipe, and a gap is arranged between the protective gas input pipe and the high-temperature flow guide cylinder.

[0030] The bottom of the heat preservation shell below the protective gas input pipe is provided with a crucible inner cavity heater through a mounting sleeve, and the bottom of the mounting sleeve is uniformly distributed with air holes.

[0031] The protective gas is nitrogen or argon.

[0032] The beneficial effects of the present application are:

[0033] The composite solid particles formed during the hydrolysis reaction of the liquid raw materials of this invention have relatively uniform particle size. 90% of the generated particles are within the range of 3.2–0.56 μm by mass. Within this particle size range, the chemical composition (titanium content) of the product particles is also highly similar. Therefore, the TiO2 / SiO2 ratio of the quartz ingot product differs from the content of the input raw material by no more than 5%. This is because the atomization-evaporation-reaction process of the raw materials in this invention is based on the physicochemical process of molecular diffusion. During this process, the Reynolds number of the flow field in the reaction region is in the laminar flow range, and the airflow has minimal disturbance to the reaction, making the nucleation process of the composite solid particles closer to homogeneous nucleation. The growth processes between particles are almost identical. Given sufficient reaction time, the generated particles will have a relatively concentrated particle size distribution and chemical composition. Due to the homogenization of the chemical composition of the generated particles, the molten quartz ingot product also has a highly uniform chemical composition. Its Ti element distribution is no longer affected by other factors and exhibits positional fluctuations, thus solving the problems of uneven Ti element distribution and subsequent CTE (coefficient of linear expansion) fluctuations caused by traditional combustion deposition processes. The melting device of this invention can melt low-expansion quartz glass products with a diameter of approximately 500 mm under single-unit conditions. With a dual-unit configuration sharing a crucible, the melting size can be expanded to approximately 700 mm in diameter, and with a three-unit configuration, the melting size can reach 800 mm. Under single-unit conditions, the effective usable range of the low-expansion quartz glass product is approximately 85% of its inner diameter, and the Ti element content distribution range can be controlled within 0.07 wt%; the CTE fluctuation range can be controlled within 15 ppb. This invention addresses the end-user demand for low-expansion quartz glass. Compared to existing technologies, the process path of this invention includes high-temperature hydrolysis (thermal) of raw materials, generation of molten quartz glass microdroplets, and deposition and fusion of quartz glass. It does not involve burners or combustion processes. This invention effectively improves the uniformity of CTE in low-expansion quartz glass products and avoids the generation of color spots, based on the end-user demand for low-expansion quartz glass. Attached Figure Description

[0034] Figure 1 This is a cross-sectional view of the melting apparatus of the present invention;

[0035] Figure 2 This is a schematic diagram of the existing crucible method for synthesizing quartz glass;

[0036] Figure 3 This is a K-line diagram showing the particle size distribution and TiO2 mass fraction of the composite solid particles of the present invention.

[0037] Figure 4 This is a graph showing the fluctuation of titanium content in the low-expansion quartz glass produced by this invention.

[0038] Figure 5Low expansion quartz glass CTE uniformity test chart produced by the present application.

[0039] In the figure: 1, heat preservation shell, 2, atomization mixing cylinder, 3, high temperature flow guide cylinder, 4, crucible, 5, communication pipe, 6, atomizer, 7, raw material box, 8, flow guide cylinder heater, 9, lifting device, 10, gas conveying pipe, 11, protective gas input pipe, 12, mounting sleeve, 13, crucible inner cavity heater, 14, crucible heater, 15, quartz glass melt, 16, exhaust port, 17, melting furnace, 18, hearth, 19, lifting device, 20, burner. DETAILED DESCRIPTION

[0040] The melting device of the present application is composed of heat preservation shell 1, atomization mixing cylinder 2, high temperature flow guide cylinder 3 and crucible 4, and the atomization mixing cylinder 2 is arranged in the heat preservation shell 1. The atomization mixing cylinder 2 is a cavity body with an open bottom, and the top end thereof extends above the heat preservation shell 1. The atomization mixing cylinder 2 is symmetrically provided with communication pipes 5 on both sides; the communication pipes 5 are communicated with the inner cavity of the atomization mixing cylinder 2, and the other ends thereof are communicated with the high temperature water-containing gas source (Air+H2O; wherein the air is filtered to remove impurities). The atomization mixing cylinder 2 is provided with an atomizer 6 therein, and the atomizer 6 is communicated with a raw material box 7. The heat preservation shell 1 below the atomization mixing cylinder 2 is provided with a high temperature flow guide cylinder 3, and the high temperature flow guide cylinder 3 is a conical cylindrical body with an upper and lower opening. The upper end of the high temperature flow guide cylinder 3 is uniformly provided with through holes.

[0041] The lower end of the atomization mixing cylinder 2 extends into the high temperature flow guide cylinder 3. A gap is arranged between the top port of the high temperature flow guide cylinder 3 and the atomization mixing cylinder 2. The heat preservation shell 1 on both sides of the atomization mixing cylinder 2 and the high temperature flow guide cylinder 3 is provided with a flow guide cylinder heater 8. The lower part of the high temperature flow guide cylinder 3 is provided with a crucible 4 through a lifting device 9 (existing machine). The outer periphery of the crucible 4 is provided with a crucible heater 14; the lower end of the high temperature flow guide cylinder extends into the crucible 4. Among them, the lower port of the high temperature flow guide cylinder 3 and the bottom of the crucible 4 are provided (left) with a gap of 15-18mm in diameter.

[0042] The heat preservation shell 1 corresponding to the flow guide cylinder heater 8 is provided with a gas conveying pipe 10. The gas conveying pipe 10 is communicated with the high temperature water-free gas source (Air / N2). The heat preservation shell 1 below the gas conveying pipe 10 is provided with a protective gas input pipe 11,

[0043] The bottom of the heat preservation shell 1 below the protective gas input pipe 11 is provided with a crucible inner cavity heater 13 through a mounting sleeve 12, and the bottom of the mounting sleeve 12 is uniformly provided with air holes. The mounting sleeve 12 and the protective gas input pipe 11 are respectively communicated with the protective gas source (nitrogen or argon). A gap is arranged between the protective gas input pipe 11 and the high temperature flow guide cylinder 3; Example 1

[0044] The melting process of low expansion quartz glass comprises the following steps:

[0045] First, 7 mol% titanium tetrachloride (TiCl4) and 93 mol% silicon tetrachloride (SiCl4) are mixed to form a liquid raw material and placed in the raw material tank 7, and the heater is turned on to preheat the atomizing mixing cylinder 2, the high-temperature flow guide cylinder 3, and the crucible 4; when the preheating temperatures of the atomizing mixing cylinder 2, the high-temperature flow guide cylinder 3, and the crucible 4 reach 800°C, 1700°C, and 1750°C, respectively, the liquid flow pump is turned on, and the liquid raw material in the raw material tank 7 is pumped into the atomizer 6 in the atomizing mixing cylinder 2 at a flow rate of 2000 ml / h. At the same time as the liquid raw material is pumped in, the gate valve on the connecting pipe is opened, and the high-temperature water-containing gas (Air + H2O) enters the atomizing mixing cylinder 2 through the connecting pipe (60 SLPM of entry; 6-86 vol% of water (gas) content); the liquid raw material entering the atomizing mixing cylinder 2 is atomized into fine droplets by the atomizer 6 and flows downward along the atomizing mixing cylinder 2, and the downward flowing droplets mix with the 800°C high-temperature water-containing gas entering the atomizing mixing cylinder 2 at the same time through the connecting pipe.

[0046] In the process of mixing the liquid droplets atomized from the liquid raw material with the high-temperature water-containing gas, the droplets undergo a hydrolysis reaction under the action of the high-temperature water-containing gas; the reaction formula is:

[0047] TiCl4(g) + 2H2O (g) → TiO2(s)+ 4HCl (g)

[0048] SiCl4(g) + 2H2O (g) → SiO2(s)+ 4HCl (g)

[0049] The composite solid particles generated by the hydrolysis reaction are entrained by the high-temperature water-containing gas and flow downward, entering the high-temperature flow guide cylinder 3 through the lower port of the atomizing mixing cylinder 2.

[0050] The composite solid particles generated by the hydrolysis reaction enter the high-temperature guide cylinder and continue to descend; in this process, the high-temperature anhydrous gas enters the annulus between the gas delivery pipe and the electric heater under the condition of 100 SLPM; and the high-temperature anhydrous gas heated to 1700℃ enters the high-temperature guide cylinder 3 through the gap between the top port of the high-temperature guide cylinder 3 and the atomizing mixing cylinder 2, and the through holes on the circumference of the high-temperature guide cylinder 3, and forms a protective sheath gas on the inner wall of the high-temperature guide cylinder 3 to reduce the adhesion of the composite solid particles on the inner wall of the high-temperature guide cylinder 3, thereby prolonging the service life of the high-temperature guide cylinder 3. In the high-temperature environment of 1700℃, the TiO2 and SiO2 contained in the composite solid particles entering the high-temperature guide cylinder 3 and descending are melted into glassy micro-droplets (glassy droplets); the glassy droplets continue to descend in the high-temperature guide cylinder 3 with the high-temperature anhydrous gas, and are sprayed into the crucible 4 through the nozzle at the lower end of the high-temperature guide cylinder 3, and are deposited in the crucible 4 to form a quartz glass melt 15, and after cooling, a quartz product is formed.

[0051] In the process of spraying the glassy droplets into the crucible 4, the protective gas enters the protective gas input pipe 11 and the mounting sleeve 12 under the condition of 300 SLPM. Among them, the protective gas entering the protective gas input pipe 11 enters the crucible 4 through the gap between the protective gas input pipe 11 and the high-temperature guide cylinder 3 to sweep the top of the crucible 4 to avoid the adhesion of droplets on the top of the crucible 4; the protective gas entering the mounting sleeve 12 is used to protect the crucible inner cavity heater 13 to avoid the influence of the oxidizing atmosphere on the crucible inner cavity heater 13. At the same time, the temperature of the crucible 4 is maintained at 1750 o C by the crucible inner cavity heater 13 and the crucible heater 14. The tail gas of the melting process is discharged through the top of the crucible 4; the gas pressure in the crucible 4 is maintained at a micro-negative pressure state of -100 Pa-150 Pa through the dynamic feedback of the gas extraction device (not shown in the figure) to ensure that the glassy droplets sprayed from the nozzle at the lower end of the high-temperature guide cylinder 3 have enough momentum to impact the deposition surface of the glass melt and adhere to the upper surface of the quartz glass melt 15 and finally fuse with it. In the process of spraying the glassy droplets into the crucible 4, the liquid level of the quartz glass melt 15 in the crucible 4 will continue to rise, therefore, the height of the crucible 4 needs to be lowered in real time through the lifting device 9 to ensure that there is always a distance of 15-18mm between the lower end nozzle of the high-temperature guide cylinder 3 and the liquid level of the quartz glass melt 15 to prevent the long distance from causing the speed loss of the quartz micro-droplets in the spray stream to be too much to be captured by the deposition surface, resulting in a decrease in deposition efficiency; a too short distance will cause the rebound turbulence formed by the spray impacting the melt surface to increase the particles adhering to the lower end nozzle of the high-temperature guide cylinder 3 and form accumulated material, which may cause blockage; the descending speed of the crucible 4 is determined according to the material balance principle and calculated in a conventional manner.

[0052] That is; V=G / Ap

[0053] wherein V = falling velocity (cm / min), G = feed rate (g / min)

[0054] A = cross-sectional area of the crucible (cm2), p = density of the quartz glass (g / cm3); Example 2

[0055] First, the liquid silicon-containing raw material octamethylcyclotetrasiloxane and the liquid titanium-containing raw material tetraisopropyl titanate are mixed in any ratio to form a liquid raw material and placed in the raw material tank 7, and the heater is turned on to preheat the atomizing mixing cylinder 2, the high-temperature flow guide cylinder 3, and the crucible 4; when the preheating temperatures of the atomizing mixing cylinder 2, the high-temperature flow guide cylinder 3, and the crucible 4 reach 800°C, 1700°C, and 1750°C, respectively, the liquid flow pump is turned on, and the liquid raw material in the raw material tank 7 is pumped into the atomizer 6 in the atomizing mixing cylinder 2 at a flow rate of 300 ml / h. At the same time as the liquid raw material is pumped in, the gate valve on the connecting pipe is opened, and the high-temperature water-containing gas (Air + H2O) enters the atomizing mixing cylinder 2 through the connecting pipe (30 SLPM of entry, 6-86 vol% of water (gas) content); the liquid raw material entering the atomizing mixing cylinder 2 is atomized into fine droplets by the atomizer 6 and flows downward along the atomizing mixing cylinder 2, and the downward flowing droplets mix with the 800°C high-temperature water-containing gas entering the atomizing mixing cylinder 2 at the same time through the connecting pipe.

[0056] In the process of mixing the liquid droplets atomized from the liquid raw material with the high-temperature water-containing gas, the droplets undergo a hydrolysis reaction under the action of the high-temperature water-containing gas; the reaction formula is:

[0057] [(CH3)2SiO]4(g) + 8O2(g) → 4SiO2(s) + 8CO2(g) + 8H2O (g)

[0058] Ti[OCH(CH3)2]4(g) + 2H2O (g) → TiO2(s) + 4(CH3)2CHOH (g)

[0059] Ti[OCH(CH3)2]4(g) + 18O2(g) → TiO2(s) + 12CO2(g) + 14H2O (g)

[0060] The composite solid particulate matter generated by the hydrolysis reaction is entrained by the high-temperature water-containing gas and flows downward, entering the high-temperature flow guide cylinder 3 through the lower end of the atomizing mixing cylinder 2.

[0061] The composite solid particulate matter generated by the hydrolysis reaction enters the high-temperature flow guide cylinder and continues to flow downward; in this process, the high-temperature water-free gas enters the annular space between the high-temperature flow guide cylinder 3 and the heater at a flow rate of 30 SLPM under the condition of 1700 oC; high temperature anhydrous gas heated to 1700°C enters high temperature guiding cylinder 3 through the gap between the top port of high temperature guiding cylinder 3 and atomizing mixing cylinder 2, and the through holes on the circumference of high temperature guiding cylinder 3, and forms a protective sheath gas on the inner wall of high temperature guiding cylinder 3 to reduce the adhesion of composite solid particles on the inner wall of high temperature guiding cylinder 3, thereby prolonging the service life of high temperature guiding cylinder 3. In the high temperature environment of 1700°C, TiO2 and SiO2 contained in the composite solid particles entering high temperature guiding cylinder 3 and descending in it are melted into glassy tiny droplets (glassy droplets); the glassy droplets continue to descend in high temperature guiding cylinder 3 with high temperature anhydrous gas, are sprayed into crucible 4 through the nozzle at the lower end of high temperature guiding cylinder 3, and are deposited in crucible 4 to form glass melt, which, after cooling, forms quartz product.

[0062] In the process of spraying glassy droplets into crucible 4, protective gas enters protective gas input pipe 11 and mounting sleeve 12 under the condition of 100 SLPM. The protective gas entering protective gas input pipe 11 enters crucible 4 through the gap between protective gas input pipe 11 and high temperature guiding cylinder 3 to blow the top of crucible 4 to avoid the adhesion of droplets on the top of crucible 4; the protective gas entering mounting sleeve 12 is used to protect crucible inner cavity heater 13 to avoid the influence of oxidizing atmosphere on crucible inner cavity heater 13. At the same time, the temperature of crucible 4 is maintained at 1700-1800°C by crucible inner cavity heater 13 and crucible heater 14. The tail gas of the melting process is discharged through the top of crucible 4; the air pressure in crucible 4 is maintained at a micro negative pressure state of -100 Pa-150 Pa through the dynamic feedback of the air extraction device (not shown in the figure) to ensure that the glassy droplets sprayed from the nozzle at the lower end of high temperature guiding cylinder 3 have enough momentum to impact the deposition surface of quartz glass melt 15, adhere to the upper surface of quartz glass melt 15, and finally fuse with it. In the process of spraying glassy droplets into crucible 4, the liquid level of quartz glass melt 15 in crucible 4 will continue to rise, therefore, the height of crucible 4 needs to be lowered in real time by lifting device 9 to ensure that there is always a distance of 15-18 mm between the lower end nozzle of high temperature guiding cylinder 3 and the liquid level of quartz glass melt 15 to prevent the excessive distance from causing the speed loss of quartz micro-droplets in the jet stream to be too much to be captured by the deposition surface, resulting in a decrease in deposition efficiency; the short distance will cause the rebound turbulence formed by the jet stream impacting the melt surface to increase the particles adhering to the lower end nozzle of high temperature guiding cylinder 3 and form accumulated material, which may cause blockage. The descending speed of crucible 4 is determined according to the material balance principle and calculated in a conventional manner.

[0063] Example 3

[0064] The melting process of low-expansion quartz glass, which comprises the following steps;

[0065] Firstly, 7 mol% titanium tetrachloride (TiCl4) and 93 mol% silicon tetrachloride (SiCl4) are mixed to form a liquid raw material and placed in the raw material tank 7, and the heater is turned on to preheat the atomizing mixing cylinder 2, the high-temperature guide cylinder 3 and the crucible 4; when the preheating temperatures of the atomizing mixing cylinder 2, the high-temperature guide cylinder 3 and the crucible 4 reach 800℃, 1700℃ and 1750℃ respectively, the liquid flow pump is started, and the liquid raw material in the raw material tank 7 is pumped into the atomizer 6 in the atomizing mixing cylinder 2 at a flow rate of 1200ml / h. At the same time, the liquid raw material is pumped in; the gate valve on the connecting pipe is opened, and the high-temperature water-containing gas (Air+H2O) enters the atomizing mixing cylinder 2 through the connecting pipe 5 (the entering amount is 40 SLPM; the water (gas) content is 6-86 vol%); the liquid raw material entering the atomizing mixing cylinder 2 is atomized into fine droplets under the action of the atomizer 6 and flows downward along the atomizing mixing cylinder 2, and the downward droplets are mixed with the 800℃ high-temperature water-containing gas entering the atomizing mixing cylinder 2 at the same time through the connecting pipe 5.

[0066] In the process of mixing the liquid droplets atomized from the liquid raw material with the high-temperature water-containing gas, the liquid droplets undergo hydrolysis reaction under the action of the high-temperature water-containing gas; the reaction formula is:

[0067] TiCl4(g) + 2H2O (g) → TiO2(s)+ 4HCl (g)

[0068] SiCl4(g) + 2H2O (g) → SiO2(s)+ 4HCl (g)

[0069] The composite solid particles generated by the hydrolysis reaction are carried downward by the high-temperature water-containing gas and enter the high-temperature guide cylinder 3 through the lower port of the atomizing mixing cylinder 2.

[0070] The composite solid particles generated by the hydrolysis reaction enter the high-temperature guide cylinder 3 and continue to flow downward; in this process, the high-temperature water-free gas enters the annulus between the high-temperature guide cylinder 3 and the electric heater at a flow rate of 60 SLPM under the condition of 60 SLPM; and the high-temperature water-free gas is heated to 1700℃, and the high-temperature water-free gas enters the high-temperature guide cylinder 3 through the gap between the top port of the high-temperature guide cylinder 3 and the atomizing mixing cylinder 2, and the through holes on the circumference of the high-temperature guide cylinder 3, and forms a protective sheath gas on the inner wall of the high-temperature guide cylinder 3, so as to reduce the adhesion of the composite solid particles on the inner wall of the high-temperature guide cylinder 3, thereby prolonging the service life of the high-temperature guide cylinder 3. In the high-temperature environment of 1700℃, the TiO2 and SiO2 contained in the composite solid particles entering the high-temperature guide cylinder 3 are melted into glassy tiny droplets (glassy droplets); the glassy droplets continue to flow downward in the high-temperature guide cylinder 3 with the high-temperature water-containing gas, and are sprayed into the crucible 4 through the nozzle at the lower end of the high-temperature guide cylinder 3, and are deposited in the crucible 4 to form a quartz glass melt 15, and after cooling, a quartz product is formed.

[0071] During the process of spraying the vitrified droplets into the crucible 4, the protective gas 200 SLPM enters the protective gas input pipe 11 and the mounting sleeve 12 respectively under the condition of the protective gas 200 SLPM. Among them, the protective gas entering the protective gas input pipe 11 enters the crucible 4 intermittently between the protective gas input pipe 11 and the high-temperature guide cylinder 3, so as to blow the top of the crucible 4 and avoid the adhesion of droplets on the top of the crucible 4; the protective gas entering the mounting sleeve 12 is used to protect the crucible inner cavity heater 13, so as to avoid the influence of the oxidizing atmosphere on the crucible inner cavity heater 13. At the same time, the temperature of the crucible 4 is maintained at 1750 oC by the crucible inner cavity heater 13 and the crucible heater 14. The tail gas of the melting process is discharged through the top of the crucible 4; the gas pressure in the crucible 4 is maintained at a micro-negative pressure state of-100 Pa-150 Pa through the dynamic feedback of the air extraction device (not shown in the figure), so as to ensure that the glassified droplets sprayed from the nozzle at the lower end of the high-temperature guide cylinder 3 have enough momentum to hit the deposition surface of the quartz glass melt 15 and adhere to the upper surface of the quartz glass melt 15 and finally fuse with it. During the process of spraying the vitrified droplets into the crucible 4, the liquid level of the quartz glass melt 15 in the crucible 4 will continue to rise, therefore, the height of the crucible 4 needs to be lowered in real time through the lifting device 9, so as to ensure that there is always a distance of 15-18 mm between the lower end nozzle of the high-temperature guide cylinder 3 and the liquid level of the quartz glass melt 15, so as to prevent that the long distance will cause the speed loss of the quartz micro-droplets in the jet flow during the impact process to be too much to be captured by the deposition surface, resulting in a decrease in deposition efficiency; the short distance will cause the rebound turbulence formed by the jet flow hitting the melt surface to increase the particles attached to the lower end nozzle of the high-temperature guide cylinder 3 and form accumulated materials, which will cause the risk of blockage; the descending speed of the crucible 4 is determined according to the material balance principle and calculated in a conventional manner.

[0072] (41) That is; V=G / Ap

[0073] In the formula, V is the descending speed (cm / min), G is the feeding speed (g / min)

[0074] A is the cross-sectional area of the crucible (square centimeter), and p is the density of quartz glass (g / cm3)

Claims

1. A melting process for low-expansion quartz glass, characterized in that: It includes the following steps; 1) First, place the liquid raw material in the raw material box (7), and at the same time turn on the heater of the melting device to preheat the atomizing mixing cylinder (2), the high temperature guide cylinder (3) and the crucible (4); 2) When the preheating temperatures of the atomizing mixing cylinder (2), the high-temperature guide cylinder (3), and the crucible (4) reach 800℃, 1700℃, and 1750℃ respectively, the liquid flow pump is turned on. Under the condition of a flow rate of 300-2000ml / h, the liquid raw material in the raw material box (7) is pumped into the atomizer (6) in the atomizing mixing cylinder (2). At the same time as the liquid raw material is pumped in, the gate valve on the connecting pipe (5) is opened, and the high-temperature water-containing gas enters the atomizing mixing cylinder (2) through the connecting pipe (5) under the condition of 30-60 SLPM. 3) Under the action of the atomizer (6), the liquid raw material entering the atomizer (6) is atomized into fine droplets and flows down along the atomizing mixing cylinder (2). The downward droplets mix with the 800°C high-temperature water-containing gas that enters the atomizing mixing cylinder (2) simultaneously through the connecting pipe (5). 4) During the process of mixing the liquid droplets formed by atomization of liquid raw materials with high temperature water-containing gas, the droplets undergo hydrolysis reaction under the action of high temperature water-containing gas: the composite solid particles generated by the hydrolysis reaction continue to descend under the entrainment of high temperature water-containing gas and enter the high temperature guide tube (3) through the lower port of the atomizing mixing tube (2). 5) The composite solid particles generated by the hydrolysis reaction enter the high-temperature guide tube (3) and descend; during this process, the high-temperature anhydrous gas enters the annulus between the high-temperature guide tube (3) and the electric heater through the gas delivery pipe (10) under the condition of 30-100 SLPM; and is heated to 1700℃; 6) The high-temperature anhydrous gas heated to 1700℃ enters the high-temperature guide tube (3) through the gap between the top port of the high-temperature guide tube (3) and the atomizing mixing tube (2), as well as through the through hole on the circumference of the high-temperature guide tube (3), thereby forming a protective sheath gas on the inner wall of the high-temperature guide tube (3) to reduce the adhesion of composite solid particles on the inner wall of the high-temperature guide tube (3); 7) In a high-temperature environment of 1700-1800℃, the composite solid particles that enter the high-temperature guide tube (3) and descend are melted into vitrified micro-droplets; 8) The glass droplets continue to descend in the high-temperature guide tube (3) with the high-temperature gas, and are sprayed into the crucible (4) through the nozzle at the lower end of the high-temperature guide tube (3), and are deposited in the crucible (4) to form glass melt. After cooling, they form quartz ingot products. During this process, the protective gas enters the protective gas input pipe (11) and the mounting sleeve (12) respectively under the condition of 100-300 SLPM. The protective gas entering the protective gas input pipe (11) enters the crucible (4) through the intermittent between the protective gas input pipe (11) and the high-temperature guide tube (3) to purge the top of the crucible (4) to reduce the adhesion of droplets on the top of the crucible (4). The protective gas entering the mounting sleeve (12) is used to protect the crucible inner cavity heater (13) to avoid the crucible inner cavity heater (13) being affected by the oxidizing atmosphere. The liquid raw material is a mixture of silicon-containing raw materials and titanium-containing raw materials in any proportion; The silicon-containing raw material is one of octamethylcyclotetrasiloxane and silicon tetrachloride; The titanium-containing raw material is one of titanium tetrachloride and tetraisopropyl titanate.

2. The melting process for low-expansion quartz glass according to claim 1, characterized in that: The protective gas mentioned in step 8) is nitrogen or argon.

3. The melting process for low-expansion quartz glass according to claim 1, characterized in that: The melting device described in step 1) consists of an insulating shell (1), an atomizing mixing cylinder (2), a high-temperature guide cylinder (3), and a crucible (4). The atomizing mixing cylinder (2) is installed inside the insulating shell (1). The high-temperature guide cylinder (3) is installed inside the insulating shell (1) below the atomizing mixing cylinder (2). Guide cylinder heaters (8) are installed inside the insulating shell (1) on both sides of the atomizing mixing cylinder (2) and the high-temperature guide cylinder (3). The crucible (4) is installed below the high-temperature guide cylinder (3) via a lifting device (9).

4. The melting process for low-expansion quartz glass according to claim 3, characterized in that: The atomizing mixing cylinder (2) is symmetrically provided with connecting pipes (5) on both sides; the atomizing mixing cylinder (2) is equipped with an atomizer (6), which is connected to the raw material box (7); the lower end of the atomizing mixing cylinder (2) extends into the high temperature guide cylinder (3).

5. The melting process for low-expansion quartz glass according to claim 3, characterized in that: A gap is provided between the top port of the high-temperature guide tube (3) and the atomizing mixing tube (2).

6. The melting process for low-expansion quartz glass according to claim 3, characterized in that: The high-temperature guide tube (3) has through holes evenly distributed on the upper circumference, and the lower end of the high-temperature guide tube (3) extends into the crucible (4); the heat insulation shell (1) corresponding to the guide tube heater (8) is provided with a gas supply pipe (10).

7. The melting process for low-expansion quartz glass according to claim 6, characterized in that: A protective gas input pipe (11) is provided on the heat insulation shell (1) below the gas supply pipe (10), and a gap is provided between the protective gas input pipe (11) and the high temperature guide tube (3); the bottom of the heat insulation shell (1) below the protective gas input pipe (11) is equipped with a crucible inner cavity heater (13) through an installation sleeve (12), and the bottom of the installation sleeve (12) is evenly distributed with ventilation holes.

Images