Method for forming an ultra-pure silica coating on a quartz substrate surface

Abstract

The application provides a method for forming an ultra-pure silica coating on the surface of a quartz substrate, which comprises the following steps: using ultra-pure silica powder doped with ultra-pure silicon carbide powder as plasma spraying powder, using oxygen as powder feeding gas, and performing plasma spraying on the surface of the to-be-sprayed region of the quartz substrate to obtain an ultra-pure silica coating; the quartz substrate is a non-preheated quartz substrate. The coating obtained by the method has lower coating porosity, higher coating bonding strength and lower surface roughness, and does not affect the size precision, sealing property and optical performance of the quartz product. The method can also avoid the problem of cracking of the quartz product caused by uneven preheating and induced stress.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ultra-pure quartz coating, in particular to a method for forming an ultra-pure silica coating on the surface of a quartz substrate. BACKGROUND

[0002] The total impurity content of high-purity quartz products is defined according to the total content of metal elements such as Al, B, Li, Na, K, Ca, Mg, Ti, Fe, Mn, Cu, Cr and Ni. According to the types of elements, the elements can be divided into alkali metals, transition metals, aluminum, boron and phosphorus. Alkali metal elements can reduce the use temperature and mechanical strength of quartz glass, transition metal elements can cause discoloration of quartz materials, affecting their optical properties, and aluminum, boron and phosphorus elements can reduce the service life of quartz materials. The total impurity content of ultra-pure quartz materials is less than 10 ppm, and the purity is more than 99.999%. Compared with ordinary quartz (purity of 99.9%), it has better optical performance, thermal stability, chemical stability and electrochemical performance, and is a key material for precision manufacturing and cutting-edge technology. However, due to the complex production process of ultra-pure quartz materials and high production cost, its application field is limited.

[0003] At present, the main technologies for ultra-pure silica coating are chemical vapor deposition (CVD) and plasma spraying. The coating prepared by CVD has high purity and is mainly used in high-end product fields. However, it has obvious disadvantages, such as complex production process, high production cost, and is not suitable for large-scale application in ordinary quartz product coating. Plasma spraying of silica has low cost and simple operation, and is suitable for large-scale application in ordinary quartz material products. However, the existing plasma spraying method requires high temperature preheating of the quartz product to soften the surface of the quartz product and increase its surface viscosity, and then uses plasma flame to adhere the silica powder to the surface of the quartz product. The existing plasma spraying method has at least the following disadvantages, such as the surface roughness of the ultra-pure silica coating is large, which reduces the size accuracy, sealing performance and optical performance of the quartz product; and the quartz substrate is broken due to thermal stress induced by high preheating temperature and uneven preheating.

[0004] The information disclosed in this BACKGROUND section is only for the purpose of increasing the understanding of the background of the present application and should not be taken as an acknowledgment or any form of suggestion that this information forms prior art that is publicly known. SUMMARY

[0005] The technical problem solved by the present application is to provide a method for forming an ultra-pure silica coating on the surface of a quartz substrate to solve the problem that the silica coating formed on the surface of a quartz substrate by the current plasma spraying technology has a large roughness, which affects the dimensional accuracy, sealing performance and optical performance of the quartz product, and to reduce the porosity of the coating and enhance the bonding strength of the coating.

[0006] To solve the above technical problem, the present application discloses a method for forming an ultra-pure silica coating on the surface of a quartz substrate, comprising the following steps:

[0007] The surface of the to-be-sprayed region of the quartz substrate is plasma sprayed by using ultra-pure silica powder doped with ultra-pure silicon carbide powder as the plasma spraying powder and oxygen as the powder feeding gas to obtain an ultra-pure silica coating.

[0008] Specifically, the quartz substrate is a non-preheated quartz substrate.

[0009] In the present application, the non-preheated quartz substrate is relative to the preheated quartz substrate, and the preheating temperature is usually above 500 DEG C, preferably above 900 DEG C.

[0010] Specifically, the particle size of the ultra-pure silica powder and the ultra-pure silicon carbide powder is 30-50 μm, and the doping amount of the ultra-pure silicon carbide powder is 3-8 wt% of the weight of the ultra-pure silica powder, preferably 5 wt%.

[0011] Specifically, the process parameters of the plasma spraying are as follows: the spraying current is 300-500 A; the main gas is helium, and the gas flow rate is 30-50 L / min; the secondary gas is hydrogen, and the gas flow rate is 5-9 L / min; the flow rate of the powder feeding gas oxygen is 1-3 L / min, and the powder feeding speed is 2-25 g / min; the gas pressures of the main gas, the secondary gas and the powder feeding gas are 0.6-1.0 MPa, respectively, preferably 0.8 MPa; the spraying distance is 100-120 mm; and the spraying speed is 0.8-1.2 mm / s, preferably 1 mm / s.

[0012] Further, the quartz substrate is subjected to sanding treatment, cleaning and drying in sequence before plasma spraying; and the surface roughness Ra of the to-be-coated region of the quartz substrate after sanding treatment is greater than or equal to 1.6 μm.

[0013] Specifically, the to-be-sprayed region of the quartz substrate is uniformly sanded by using emery.

[0014] Specifically, the cleaning comprises: soaking the ground quartz substrate into a washing pool of hydrofluoric acid aqueous solution, rinsing with pure water until the pH of the quartz substrate surface is neutral, and then placing the quartz substrate into an ultrasonic pure water cleaning pool for ultrasonic cleaning.

[0015] In the hydrofluoric acid aqueous solution, the concentration of hydrofluoric acid is 8-12 wt%, preferably 10 wt%; the soaking time is 12-18 min, preferably 15 min; the frequency of the ultrasonic is 30-50 kHz, preferably 40 kHz; and the time of the ultrasonic is 8-12 min, preferably 10 min.

[0016] The drying comprises: placing the cleaned quartz substrate into a drying room for drying at 34-36℃.

[0017] Optionally, the quartz substrate is a quartz tube, a quartz sheet, a quartz rod, a quartz boat or a quartz plate.

[0018] Specifically, the plasma spraying powder is sprayed onto the surface of the to-be-sprayed region of the quartz substrate by a plasma spraying device.

[0019] Specifically, the purity of the ultrapure silicon dioxide powder and the purity of the ultrapure silicon carbide powder are respectively more than 99.99%, preferably more than 99.999%, and more preferably more than 99.9999%.

[0020] Advantages:

[0021] 1. By mixing the ultrapure silicon carbide powder into the ultrapure silicon dioxide powder, the silicon dioxide powder is directly adhered to the surface of the quartz product in a molten state by using the high-speed plasma flame formed by the silicon carbide in a molten state under low power conditions, the silicon dioxide generated by the high-temperature oxidation of the ultrapure silicon carbide fills the pores of the ultrapure silicon dioxide coating, making the coating more dense, reducing the porosity of the coating, improving the bonding strength of the coating, improving the performance of the coating, and at the same time, the preheating operation before spraying is omitted, avoiding the problem of product cracking caused by uneven preheating and other factors inducing stress, and at the same time, the powder feeding gas is changed to oxygen, ensuring that the silicon dioxide generated by the high-temperature oxidation of the ultrapure silicon carbide and the free carbon do not introduce additional impurities, do not affect the purity, and at the same time, the roughness of the silicon dioxide particles in a molten state is very small, the surface is smooth, the surface roughness of the formed coating is low, and the dimensional accuracy, sealing performance and optical performance of the quartz substrate are not affected.

[0022] 2. The ultrapure silicon dioxide coating prepared by the present application has excellent coating effect, low porosity, high bonding strength, and the coating thickness is controllable, the porosity of the prepared coating can reach 7%±1%, the bonding strength of the coating is 20MPa±1MPa, and the performance of the coating prepared by the present application is obviously better than that of the coating prepared by using the ultrapure silicon dioxide after preheating and plasma spraying, and at the same time, the coating thickness is controlled within the range of 5-150μm. Attached Figure Description

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0024] Figure 1 This is a scanning electron microscope image of the ultrapure silica coating obtained in Example 1 of the present invention.

[0025] Figure 2 This is a scanning electron microscope image of the surface morphology of ultrapure silica obtained in Example 1 of the present invention.

[0026] Figure 3 This is a scanning electron microscope image of the ultrapure silica coating obtained in Example 2 of the present invention.

[0027] Figure 4 This is a scanning electron microscope image of the ultrapure silica coating obtained in Example 3 of the present invention.

[0028] Figure 5 This is a scanning electron microscope image of the ultrapure silica coating obtained in Example 4 of the present invention.

[0029] Figure 6 This is a scanning electron microscope image of the ultrapure silica coating obtained in Example 5 of the present invention.

[0030] Figure 7 This is a scanning electron microscope image of the ultrapure silica coating obtained in Example 6 of the present invention.

[0031] Figure 8 This is a scanning electron microscope image of the ultrapure silica coating prepared in Comparative Example 2 of the present invention.

[0032] Figure 9 This is a scanning electron microscope image of the surface morphology of ultrapure silica in Comparative Example 2 of the present invention. Detailed Implementation

[0033] When conventional plasma spraying technology coats ordinary-purity quartz materials with ultrapure silica to form an ultrapure silica coating, excessively high plasma power causes the silica to volatilize and generate silicon and oxygen, while insufficient power prevents the silica from reaching a molten state. Therefore, it is necessary to preheat the quartz substrate at high temperature to increase the viscosity of the quartz surface before using a plasma flame to adhere the silica to the quartz surface.

[0034] The applicant found that using only ultra-pure silicon dioxide as the plasma spraying powder, the ultra-pure silicon dioxide cannot reach the molten state by using the plasma technology, but only adheres to the surface of the quartz. Since the particle size of the silicon dioxide itself is usually tens of microns, the roughness of the sprayed silicon dioxide is large, the formed ultra-pure silicon dioxide coating has high roughness and weak bonding strength, and the thickness of the coating that can be formed is limited. At the same time, since the quartz substrate needs to be preheated at a high temperature before spraying, there is also a problem that the quartz substrate may be broken due to thermal stress induced by factors such as excessively high preheating temperature and uneven preheating.

[0035] To solve the above problems, the present application provides a method for forming an ultra-pure silicon dioxide coating on the surface of a quartz substrate, which forms a more dense ultra-pure silicon dioxide coating, has lower coating porosity, higher coating bonding strength, and allows the formation of a thicker coating thickness.

[0036] The method for forming an ultra-pure silicon dioxide coating on the surface of a quartz substrate provided by the present application comprises the following steps:

[0037] The ultra-pure silicon dioxide powder doped with ultra-pure silicon carbide powder is used as the plasma spraying powder, and oxygen is used as the powder feeding gas to perform plasma spraying on the surface of the to-be-sprayed region of the quartz substrate, thereby obtaining an ultra-pure silicon dioxide coating. The quartz substrate is a cold quartz substrate that has not been preheated.

[0038] In the present application, the purity of the ultra-pure silicon dioxide powder and the purity of the ultra-pure silicon carbide powder are each greater than 99.99%, preferably greater than 99.999%, and more preferably greater than 99.9999%.

[0039] The method of the present application directly adheres the silicon dioxide powder in a molten state to the surface of the quartz substrate by doping ultra-pure silicon carbide powder into the ultra-pure silicon dioxide powder and using the high-speed plasma flame formed by the silicon carbide reaching a molten state under low power conditions. The silicon dioxide generated by the high-temperature oxidation of the ultra-pure silicon carbide can fill the pores of the ultra-pure silicon dioxide coating, making the coating more dense, reducing the porosity of the coating, improving the bonding strength of the coating, and improving the performance of the coating. At the same time, the preheating operation can be omitted, and the loss of product breakage due to thermal stress caused by preheating can be reduced. Oxygen is used as the powder feeding gas to ensure that the silicon dioxide generated by the high-temperature oxidation of the ultra-pure silicon carbide and the free carbon do not introduce additional impurities and do not affect the purity of the formed coating.

[0040] Compared with the conventional plasma spraying method, the method of the present application does not require preheating, and the silicon dioxide powder can reach a molten state and directly adhere to the surface of the quartz substrate. The roughness of the silicon dioxide particles in the molten state is very small, and the surface is smooth, which makes the coating surface roughness low and does not affect the dimensional accuracy, sealing performance, and optical performance of the quartz substrate.

[0041] Specifically, the particle size of the ultra-pure silicon dioxide powder and the ultra-pure silicon carbide powder is 30-50 μm, respectively, and the doping amount of the ultra-pure silicon carbide powder is 3-8 wt% of the weight of the ultra-pure silicon dioxide powder, preferably 5 wt%.

[0042] Preferably, the quartz substrate is subjected to sanding, cleaning and drying in sequence before plasma spraying; the surface roughness Ra of the region to be coated of the quartz substrate after sanding is ≥1.6 μm.

[0043] More specifically, the sanding includes uniformly sanding the region to be sprayed of the quartz substrate with 120-mesh diamond sand.

[0044] More specifically, the cleaning includes immersing the quartz substrate after sanding in a hydrofluoric acid aqueous solution tank, rinsing with pure water until the pH of the surface of the quartz substrate is neutral, and then placing in an ultrasonic pure water cleaning tank for ultrasonic cleaning.

[0045] In the hydrofluoric acid aqueous solution, the concentration of hydrofluoric acid is 8-12 wt%, preferably 10 wt%; the immersion time is 12-18 min, preferably 15 min; the frequency of the ultrasonic is 30-50 kHz, preferably 40 kHz, and the time of the ultrasonic is 8-12 min, preferably 10 min.

[0046] More specifically, the drying includes placing the quartz substrate after cleaning in a drying room for drying at 34-36 °C. The quartz substrate can also be blown with high-purity nitrogen gas during drying to shorten the drying time.

[0047] Preferably, the process parameters of the plasma spraying are as follows: the spraying current is 300-500 A; the main gas for spraying is helium, and the gas flow rate is 30-50 L / min; the secondary gas is hydrogen, and the gas flow rate is 5-9 L / min; the flow rate of the powder feeding gas oxygen is 1-3 L / min, and the powder feeding speed is 2-25 g / min; the gas pressures of the main gas, the secondary gas and the powder feeding gas are 0.6-1.0 MPa, respectively, preferably 0.8 MPa; the spraying distance is 100-120 mm; and the spraying speed is 0.8-1.2 mm / s, preferably 1 mm / s.

[0048] More specifically, the hydrogen, oxygen, helium and nitrogen used in the plasma spraying process are all high-purity gases, and the purities are all above 99.99%, preferably above 99.999%, and more preferably above 99.9999%.

[0049] Preferably, the quartz substrate after plasma spraying is subjected to pure water cleaning and drying by blowing with high-purity nitrogen gas in sequence.

[0050] Optionally, the quartz substrate is a quartz tube, a quartz sheet, a quartz rod, a quartz boat or a quartz plate.

[0051] Specifically, the quartz substrate after being dried is placed on a graphite platform for the plasma spraying.

[0052] Specifically, the plasma spraying powder is sprayed on the surface of the to-be-sprayed region of the quartz substrate by a plasma spraying device.

[0053] It should be understood that the plasma spraying processes are all operated in a thousand-level clean room to ensure the purity of the quartz substrate and the prepared coating during the production process and prevent the introduction of impurities.

[0054] In the following, the preparation method of the composite coating will be further explained and described in combination with specific examples. The quartz tubes, sheets, rods, boats and plates used in each example are all prepared from the same batch of ordinary high-purity quartz sand raw materials.

[0055] Specifically:

[0056] Example 1

[0057] The present example provides a method for forming an ultrapure silicon dioxide coating on the surface of a quartz substrate, comprising the following steps:

[0058] Step one: the quartz substrate is sequentially subjected to sanding treatment, cleaning and drying before plasma spraying; the surface roughness Ra of the to-be-coated region of the quartz substrate after sanding treatment is ≥1.6 μm;

[0059] Step two: using ultrapure silicon dioxide powder doped with ultrapure silicon carbide powder as the plasma spraying powder, and using oxygen as the powder feeding gas, the surface of the to-be-sprayed region of the quartz substrate is subjected to plasma spraying to obtain an ultrapure silicon dioxide coating; the quartz substrate is a cold quartz substrate without preheating;

[0060] In this example, the quartz substrate is a quartz tube, and the to-be-coated region of the quartz substrate is the outer surface of the quartz substrate.

[0061] In step one of this example, the sanding treatment comprises uniformly sanding the to-be-sprayed region of the quartz substrate with 120-mesh diamond sand.

[0062] In step one of this example, the cleaning comprises immersing the quartz substrate after sanding treatment in a hydrofluoric acid aqueous solution washing pool, rinsing with pure water until the pH of the surface of the quartz substrate is neutral, and then placing in an ultrasonic pure water cleaning pool for ultrasonic cleaning; in the hydrofluoric acid aqueous solution, the concentration of hydrofluoric acid is 10 wt%; the immersion time is 15 min; the frequency of the ultrasonic is 40 kHz, and the time of the ultrasonic is 10 min.

[0063] In step one of this embodiment, the drying includes: placing the cleaned quartz substrate in a drying room for drying at 34-36℃. At the same time, the quartz substrate is purged with high-purity nitrogen.

[0064] In step two of this embodiment, the particle size of the ultra-pure silicon dioxide powder and the ultra-pure silicon carbide powder is 30-50μm, and the doping amount of the ultra-pure silicon carbide powder is 5wt%.

[0065] In step two of this embodiment, the dried quartz substrate is placed on a rotating graphite platform for plasma spraying. The rotating graphite platform drives the quartz substrate to rotate automatically. According to the position of the quartz substrate, the teach pendant is used to position the mechanical arm, and the mechanical arm operation program is set to ensure that the spraying process can cover the surface of the quartz tube. The plasma spraying powder of this embodiment is placed in the feeder of the plasma spraying equipment, and the process parameters of the plasma spraying are adjusted. The process parameters of the plasma spraying are as follows: the spraying current is 300A; the main gas for spraying is helium, and the gas flow rate is 30L / min; the secondary gas is hydrogen, and the gas flow rate is 5L / min; the flow rate of the powder feeding gas oxygen is 1L / min, and the powder feeding speed is 2g / min; the gas pressure of the main gas, the secondary gas and the powder feeding gas is all 0.8MPa; the spraying distance is 100mm; and the spraying speed is 1mm / s.

[0066] The spraying is performed by the mechanical arm, thereby ensuring uniform spraying.

[0067] After the plasma spraying is completed, the ultra-pure silicon dioxide coated quartz tube product of this embodiment is obtained by natural cooling.

[0068] In this embodiment, the purity of hydrogen, oxygen, helium and nitrogen used in the plasma spraying process is above 99.9999%.

[0069] The ultra-pure silicon dioxide coating prepared in this embodiment is tested. The coating thickness is detected by SEM scanning electron microscope, the coating surface morphology is observed by SEM scanning electron microscope, and the coating thickness is measured; the coating surface roughness is measured by a roughness meter; the coating porosity is tested by using a color permeation liquid to permeate into the coating pores, and the porosity is calculated by the color area; and the coating bonding strength is tested by a shear test, a shear force parallel to the coating is applied, and the bonding strength of the coating is calculated by the stress during separation.

[0070] The scanning electron microscope photos of the surface morphology of the ultra-pure quartz coating obtained based on this embodiment can be referred to Figure 1 and Figure 2 . As Figure 1As shown, the thickness of the ultra-pure silica coating prepared in this embodiment at two spaced positions was 5.186 μm and 5.186 μm, respectively. As shown in the figure, the surface topography of the ultra-pure quartz coating obtained in this embodiment showed that the coating surface was relatively smooth and had a low roughness. The surface roughness of the ultra-pure silica coating prepared in this embodiment was 1.80 μm, the porosity of the coating was 7.5%, and the bonding strength of the coating was 21 MPa. Figure 2 As shown, the surface topography of the ultra-pure quartz coating obtained in this embodiment showed that the coating surface was relatively smooth and had a low roughness. The surface roughness of the ultra-pure silica coating prepared in this embodiment was 1.80 μm, the porosity of the coating was 7.5%, and the bonding strength of the coating was 21 MPa.

[0071] Further, the method of this embodiment further comprises step three: the quartz substrate after plasma spraying is sequentially cleaned with pure water and dried by blowing with high-purity nitrogen.

[0072] Example 2

[0073] Unlike Example 1, in the method provided in this embodiment, the quartz substrate is a quartz sheet; the region to be coated of the quartz substrate is the outer surface of the quartz sheet. The process parameters of the plasma spraying are as follows: the spraying current is 350 A; the main gas for spraying is helium with a gas flow rate of 35 L / min; the secondary gas is hydrogen with a gas flow rate of 6 L / min; the flow rate of the powder feeding gas oxygen is 1.5 L / min, and the powder feeding speed is 5 g / min; the gas pressure of the main gas, the secondary gas, and the powder feeding gas is all 0.8 MPa; the spraying distance is 110 mm; and the spraying speed is 1 mm / s. The other steps and process parameters are the same as in Example 1.

[0074] After the plasma spraying is completed, the ultra-pure silica coating quartz sheet product of this embodiment is obtained by natural cooling.

[0075] The ultra-pure silica coating prepared in this embodiment was tested (the testing method was the same as in Example 1). As shown in the figure, Figure 3 It can be seen that the thickness of the ultra-pure silica coating prepared in this embodiment at two spaced positions was 9.714 μm and 9.770 μm, respectively. The surface roughness of the ultra-pure silica coating prepared in this embodiment was 1.75 μm, the porosity of the coating was 7.3%, and the bonding strength of the coating was 20.8 MPa.

[0076] Example 3

[0077] Different from embodiment 1, in the method provided in the embodiment, the quartz substrate is a quartz rod; the region to be coated of the quartz substrate is the outer surface of the quartz rod. The process parameters of the plasma spraying are as follows: the spraying current is 400 A; the main gas for spraying is helium, and the gas flow rate is 40 L / min; the secondary gas is hydrogen, and the gas flow rate is 7 L / min; the flow rate of the powder feeding gas oxygen is 2.0 L / min, and the powder feeding speed is 6.0 g / min; the gas pressures of the main gas, the secondary gas and the powder feeding gas are all 0.8 MPa; the spraying distance is 115 mm; and the spraying speed is 1 mm / s. The other steps and process parameters are the same as those in embodiment 1.

[0078] After the plasma spraying, the quartz rod product with the ultrapure silica coating is obtained by natural cooling.

[0079] The ultrapure silica coating prepared in the embodiment is tested (the testing method is the same as that in embodiment 1). It can be known that the thicknesses of the ultrapure silica coating prepared in the embodiment at two interval positions are 15.33 μm and 15.26 μm respectively. Figure 4 The coating surface roughness of the ultrapure silica coating prepared in the embodiment is 1.78 μm, the porosity is 6.9%, and the coating bonding strength is 20.5 MPa.

[0080] Embodiment 4

[0081] Different from embodiment 1, in the method provided in the embodiment, the quartz substrate is a quartz boat; the region to be coated of the quartz substrate is the outer surface of the quartz boat. The process parameters of the plasma spraying are as follows: the spraying current is 450 A; the main gas for spraying is helium, and the gas flow rate is 45 L / min; the secondary gas is hydrogen, and the gas flow rate is 8 L / min; the flow rate of the powder feeding gas oxygen is 2.5 L / min, and the powder feeding speed is 8.0 g / min; the gas pressures of the main gas, the secondary gas and the powder feeding gas are all 0.8 MPa; the spraying distance is 115 mm; and the spraying speed is 1 mm / s. The other steps and process parameters are the same as those in embodiment 1.

[0082] After the plasma spraying, the quartz boat product with the ultrapure silica coating is obtained by natural cooling.

[0083] The ultrapure silica coating prepared in the embodiment is tested (the testing method is the same as that in embodiment 1). It can be known that the thicknesses of the ultrapure silica coating prepared in the embodiment at two interval positions are 30.71 μm and 30.61 μm respectively. Figure 5 The coating surface roughness of the ultrapure silica coating prepared in the embodiment is 1.88 μm, the porosity is 6.5%, and the coating bonding strength is 21.1 MPa.

[0084] Embodiment 5

[0085] Different from example 1, in the method provided by the present example, the quartz substrate is a quartz plate; the region to be coated of the quartz substrate is the outer surface of the quartz plate. The process parameters of the plasma spraying are as follows: the spraying current is 500 A; the main gas for spraying is helium, and the gas flow rate is 50 L / min; the secondary gas is hydrogen, and the gas flow rate is 9 L / min; the flow rate of the powder feeding gas oxygen is 3.0 L / min, and the powder feeding speed is 15.0 g / min; the gas pressures of the main gas, the secondary gas and the powder feeding gas are all 0.8 MPa; the spraying distance is 120 mm; and the spraying speed is 1 mm / s. The other steps and process parameters are the same as those of example 1.

[0086] After the plasma spraying, the quartz plate product with the ultrapure silica coating of the present example is obtained by natural cooling.

[0087] The ultrapure silica coating prepared in the present example is tested (the testing method is the same as that of example 1). It can be known that the thicknesses of the ultrapure silica coating prepared in the present example at the two interval positions are both 50.69 μm. The detection shows that the coating surface roughness of the ultrapure silica coating prepared in the present example is 1.79 μm, the porosity is 7.1%, and the coating bonding strength is 20.2 MPa. Figure 6

[0088] Example 6

[0089] Different from example 1, in the method provided by the present example, the quartz substrate is a quartz plate; the region to be coated of the quartz substrate is the outer surface of the quartz plate. The process parameters of the plasma spraying are as follows: the spraying current is 500 A; the main gas for spraying is helium, and the gas flow rate is 50 L / min; the secondary gas is hydrogen, and the gas flow rate is 9 L / min; the flow rate of the powder feeding gas oxygen is 3.0 L / min, and the powder feeding speed is 25.0 g / min; the gas pressures of the main gas, the secondary gas and the powder feeding gas are all 0.8 MPa; the spraying distance is 120 mm; and the spraying speed is 1 mm / s. The other steps and process parameters are the same as those of example 1.

[0090] After the plasma spraying, the quartz plate product with the ultrapure silica coating of the present example is obtained by natural cooling.

[0091] The ultrapure silica coating prepared in the present example is tested (the testing method is the same as that of example 1). It can be known that the thicknesses of the ultrapure silica coating prepared in the present example at the two interval positions are both 50.69 μm. The detection shows that the coating surface roughness of the ultrapure silica coating prepared in the present example is 1.79 μm, the porosity is 7.1%, and the coating bonding strength is 20.2 MPa. Figure 7 ​​

[0092] Example 7

[0093] Different from Example 1, in this example, the particle size of the ultra-pure silicon dioxide powder and the ultra-pure silicon carbide powder is 30 μm respectively, the doping amount of the ultra-pure silicon carbide powder is 3wt% of the weight of the ultra-pure silicon dioxide powder; the purity of the ultra-pure silicon dioxide powder and the purity of the ultra-pure silicon carbide powder is 99.99% respectively; the process parameters of the plasma spraying are: the spraying current is 300 A; the spraying main gas is helium, the gas flow rate is 30 L / min; the secondary gas is hydrogen, the gas flow rate is 5 L / min; the flow rate of the powder feeding gas oxygen is 1 L / min, the powder feeding speed is 2 g / min; the gas pressure of the main gas, the secondary gas and the powder feeding gas is 0.6 MPa respectively; the spraying distance is 100 mm; the purity of the hydrogen, oxygen, helium and nitrogen used in the plasma spraying process is more than 99.99% respectively; in the cleaning step, the concentration of hydrofluoric acid in the hydrofluoric acid aqueous solution is 8wt%; the soaking time is 8 min; the frequency of the ultrasonic is 30 kHz, the time of the ultrasonic is 8 min. Other process conditions are the same as those of Example 1.

[0094] After the plasma spraying, the ultra-pure silicon dioxide coated quartz tube product of this example is obtained by natural cooling.

[0095] Example 7

[0096] Different from Example 1, in this example, the particle size of the ultra-pure silicon dioxide powder and the ultra-pure silicon carbide powder is 30 μm respectively, the doping amount of the ultra-pure silicon carbide powder is 3wt% of the weight of the ultra-pure silicon dioxide powder; the purity of the ultra-pure silicon dioxide powder and the purity of the ultra-pure silicon carbide powder is 99.99% respectively; the process parameters of the plasma spraying are: the spraying current is 300 A; the spraying main gas is helium, the gas flow rate is 30 L / min; the secondary gas is hydrogen, the gas flow rate is 5 L / min; the flow rate of the powder feeding gas oxygen is 1 L / min, the powder feeding speed is 2 g / min; the gas pressure of the main gas, the secondary gas and the powder feeding gas is 0.6 MPa respectively; the spraying distance is 100 mm; the purity of the hydrogen, oxygen, helium and nitrogen used in the plasma spraying process is more than 99.99% respectively; in the cleaning step, the concentration of hydrofluoric acid in the hydrofluoric acid aqueous solution is 8wt%; the soaking time is 8 min; the frequency of the ultrasonic is 30 kHz, the time of the ultrasonic is 8 min. Other process conditions are the same as those of Example 1.

[0097] After the plasma spraying, the ultra-pure silicon dioxide coated quartz tube product of this example is obtained by natural cooling.

[0098] Comparative Example 1

[0099] Different from Example 1, in the method of the present comparative example, only ultra-pure silicon dioxide is used as the plasma spraying powder, and the powder feeding gas is hydrogen. The other process conditions are the same as those of Example 1.

[0100] It should be understood that neither Comparative Example 1 nor Example 1 preheats the quartz substrate before plasma spraying.

[0101] Specifically, the implementation process of the method of the present comparative example is as follows:

[0102] After the surface of the quartz tube is ground and treated, cleaned and dried, it is placed on a graphite platform with a motor-driven rotation, and the quartz tube can automatically rotate;

[0103] According to the position of the quartz tube, the mechanical arm is positioned using a teach pendant, and the operation program of the mechanical arm is set to ensure that the spraying process can cover the surface of the quartz tube;

[0104] The process parameters of the plasma spraying are adjusted as follows: the spraying current is 300 A; the main gas for spraying is helium, and the gas flow rate is 30 L / min; the secondary gas is hydrogen, and the gas flow rate is 5 L / min; the flow rate of the powder feeding gas helium is 1.0 L / min, and the powder feeding speed is 2.0 g / min; the gas pressures of the main gas, the secondary gas and the powder feeding gas are all 0.8 MPa; the spraying distance is 100 mm; and the spraying speed is 1 mm / s.

[0105] The spraying is performed by the mechanical arm to ensure uniform spraying;

[0106] After the plasma spraying is completed, the quartz tube product with an ultra-pure silicon dioxide coating is obtained by natural cooling.

[0107] It is found through detection that the surface of the quartz tube treated in the present example has no coating. It can be known that the quartz substrate is not preheated before plasma spraying by using the traditional plasma spraying technology, and a coating cannot be formed on the surface of the quartz tube.

[0108] Comparative Example 2

[0109] Different from Comparative Example 1, the method of the present comparative example preheats the quartz tube before plasma spraying, and the other process conditions are the same as those of Comparative Example 1.

[0110] It should be understood that Comparative Example 2 and Comparative Example 1 both use only ultra-pure silicon dioxide as the plasma spraying powder.

[0111] Specifically, the implementation process of the method of the present comparative example is as follows:

[0112] After the surface of the quartz tube is ground and treated, cleaned and dried, it is placed on a graphite platform with a motor-driven rotation, and the quartz tube can automatically rotate;

[0113] The quartz spray gun is fixed on a bracket next to the graphite platform. The distance between the oxyhydrogen flame and the quartz tube is adjusted to 50mm. The quartz tube rotates at a constant speed. At the same time, the temperature of the oxyhydrogen flame is 900-1000℃ during the preheating process, and the preheating time is 5min. This ensures that the quartz tube is heated evenly during the plasma spraying process.

[0114] Based on the position of the quartz tube, the robotic arm is positioned using a teach pendant, and the robotic arm's operating program is set to ensure that the plasma spraying process can cover the surface of the quartz tube.

[0115] The plasma spraying powder of this comparative example was placed into the feeder of the plasma spraying equipment. The plasma spraying process parameters were adjusted as follows: spraying current was 300A; the main spraying gas was helium with a gas flow rate of 30L / min; the secondary gas was hydrogen with a gas flow rate of 5L / min; the helium powder feeding gas had a flow rate of 1.0L / min and a powder feeding speed of 2.0g / min; the gas pressures of the main gas, the secondary gas, and the powder feeding gas were all 0.8MPa; the spraying distance was 100mm; and the spraying speed was 1mm / s.

[0116] The spraying is performed by a robotic arm to ensure uniform coating.

[0117] After the quartz tube cooled naturally, it was cleaned and dried to obtain an ultrapure quartz-coated quartz tube product. Testing revealed cracks in the quartz tube. The electron microscope (EM) image of the ultrapure quartz coating surface obtained in this embodiment can be referenced. Figure 8 and Figure 9 .like Figure 9 As shown, the surface roughness of the ultrapure quartz coating obtained based on this embodiment is relatively large, much larger than that of other coatings. Figure 2 The surface roughness of the ultrapure quartz coating obtained based on the example is shown. The ultrapure silica coating prepared in this example was tested (using the same test method as in Example 1). Figure 8 It can be seen that the thickness of the ultrapure silica coating prepared in this embodiment is 232.1 μm and 172.5 μm at the two interval positions, respectively. Meanwhile, from... Figure 9 The surface morphology of the ultrapure silica coating prepared in this embodiment shows that the coating surface is composed of granular silica with a relatively large surface roughness. This verifies that the mechanism of ultrapure silica spraying using plasma technology after preheating the quartz substrate surface is simply that the viscosity of the quartz substrate surface increases at high temperature, causing the ultrapure silica powder particles to adhere to the quartz substrate surface. Since the particle size of ultrapure silica powder is 30-50 μm, this results in a high surface roughness and a large coating thickness. Testing showed that the ultrapure silica coating prepared in this embodiment has a surface roughness of 22 μm, a porosity of 20%, and a coating bonding strength of 10 MPa.

[0118] Table 1 is the process conditions and performance test results of each example and each comparative example. Table 2 is the metal impurity content of the ultra-pure silica coating and the uncoated quartz substrate of each example of the present application. The uncoated quartz substrate and the quartz substrate to be treated of each example are of the same batch.

[0119] In combination with Table 1, by comparing Comparative Example 2 with Comparative Example 1, it can be seen that the traditional plasma spraying technology must preheat the quartz substrate at high temperature before spraying, in order to prepare an ultra-pure quartz coating.

[0120] In combination with Table 1, by comparing Example 1 to Example 6 with Comparative Example 2, it is found that the performance of the ultra-pure silica coating prepared by the method proposed in the present application is more superior, that is, it has lower coating porosity and higher coating bonding strength. Higher coating bonding strength allows the formation of a thicker coating. Referring to Table 1, the coating thickness can be controlled at 5-150 μm according to different application fields. At the same time, from Table 2, it can be seen that the metal impurity content of the ultra-pure silica coating prepared in each example of the present application is less than 10 ppm, which meets the purity standard of ultra-pure silica.

[0121] Table 1 is the process conditions and performance test results of each example and each comparative example.

[0122]

[0123] Table 2 is the metal impurity content of the ultra-pure silica coating and the uncoated quartz substrate of each example of the present application.

[0124]

[0125]

[0126] Therefore, the method for forming an ultra-pure silica coating on the surface of a quartz substrate provided in the present application can form an ultra-pure silica coating on the surface of a quartz substrate of ordinary purity by using plasma spraying technology. When conventional plasma technology is used to spray ultra-pure silica, too high plasma power will cause the volatilization of silica to generate silicon and oxygen, and too low power will not reach the melting state, so the quartz product needs to be preheated at high temperature to increase the surface viscosity of the quartz, and then the silica is adhered to the surface of the quartz by using the plasma flame. The ultra-pure silica coating prepared by this method has high surface roughness, which affects the dimensional tolerance of the product.

[0127] The application can form a thickness-controllable ultra-pure quartz coating on a common purity quartz material by adjusting the ultra-pure silicon dioxide powder feeding amount parameter and using a plasma flame under the condition that the quartz substrate does not need high-temperature preheating, and the powder feeding gas is changed to oxygen to ensure that the ultra-pure silicon carbide is oxidized to generate silicon dioxide and free carbon, without introducing additional impurities, which does not affect the performance of the ultra-pure silicon dioxide, and the introduction of the ultra-pure silicon carbide can improve the performance of the coating, so that the coating has lower porosity and better bonding strength.

[0128] Meanwhile, the method of the application solves the problem that the quartz product is prone to cracking due to high preheating temperature and uneven preheating, and solves the problem that the coating surface roughness is high due to the fact that the plasma sprayed silicon dioxide cannot reach a molten state, thereby affecting the product size precision, product sealing performance and causing the optical performance of the quartz to decline.

[0129] The method of the application can improve the purity, optical performance, corrosion resistance and other key performances of common quartz tubes at a lower cost, and expand the applicability of common purity quartz products in high-end fields.

[0130] The application provides a method for forming an ultra-pure silicon dioxide coating on the surface of a quartz substrate. There are many methods and approaches to realize this technical solution, and the above description is only the preferred embodiment of the application. It should be noted that for ordinary technical personnel in this technical field, without departing from the principle of the application, several improvements and refinements can be made, which should be considered as the protection scope of the application. The components not explicitly described in the embodiment can be realized by using existing technology.

Claims

1. A method for forming an ultrapure silica coating on a quartz substrate, characterized in that, Includes the following steps: Using ultrapure silicon dioxide powder doped with ultrapure silicon carbide powder as plasma spraying powder and oxygen as powder feeding gas, plasma spraying is performed on the surface of the area to be sprayed on the quartz substrate to obtain an ultrapure silicon dioxide coating. The quartz substrate is an unheated quartz substrate.

2. The method according to claim 1, characterized in that, The ultrapure silica powder has a particle size of 30μm-50μm, the ultrapure silicon carbide powder has a particle size of 30μm-50μm, and the doping amount of the ultrapure silicon carbide powder is 3-8 wt% of the weight of the ultrapure silica powder.

3. The method according to claim 2, characterized in that, The doping amount of the ultrapure silicon carbide powder is 5 wt% of the weight of the ultrapure silicon dioxide powder.

4. The method according to claim 2 or 3, characterized in that, The plasma spraying process parameters are as follows: spraying current is 300-500A; the main spraying gas is helium with a flow rate of 30L / min-50L / min; the secondary gas is hydrogen with a flow rate of 5L / min-9L / min; the oxygen flow rate for powder feeding is 1L / min-3L / min, and the powder feeding speed is 2g / min-25g / min; the gas pressures of the main gas, the secondary gas, and the powder feeding gas are all 0.6-1.0MPa; the spraying distance is 100mm-120mm; and the spraying speed is 0.8-1.2mm / s.

5. The method according to claim 4, characterized in that, The pressure of the main gas, the secondary gas, and the powder delivery gas is all 0.8 MPa; the spraying speed is 1 mm / s.

6. The method according to claim 1 or 2, characterized in that, Before plasma spraying, the quartz substrate is subjected to sanding, cleaning and drying in sequence; the surface roughness Ra of the area to be sprayed on the quartz substrate after sanding is ≥1.6μm.

7. The method according to claim 6, characterized in that, The area of ​​the quartz substrate to be coated is uniformly sanded using diamond abrasive.

8. The method according to claim 6, characterized in that, The cleaning process includes: immersing the sand-treated quartz substrate in a hydrofluoric acid aqueous solution washing tank, rinsing it with pure water until the pH of the quartz substrate surface is neutral, and then placing it in an ultrasonic pure water cleaning tank for ultrasonic cleaning. The hydrofluoric acid aqueous solution has a concentration of 8-12 wt% and a soaking time of 12-18 min; the ultrasonic frequency is 30-50 kHz and the ultrasonic time is 8-12 min. The drying process includes: placing the cleaned quartz substrate in a drying room and drying it at 34℃-36℃.

9. The method according to claim 8, characterized in that, The hydrofluoric acid aqueous solution has a concentration of 10 wt% and a soaking time of 15 min; the ultrasonic frequency is 40 kHz and the ultrasonic time is 10 min.

10. The method according to claim 1, characterized in that, The quartz substrate is a quartz tube, quartz sheet, quartz rod, quartz boat, or quartz plate.

11. The method according to claim 1, characterized in that, The plasma powder is sprayed onto the surface of the area to be coated on the quartz substrate using a plasma spraying device.

12. The method according to claim 1, characterized in that, The purity of the ultrapure silica powder is above 99.99%, and the purity of the ultrapure silicon carbide powder is above 99.99%.

13. The method according to claim 12, characterized in that, The purity of the ultrapure silica powder is above 99.999%, and the purity of the ultrapure silicon carbide powder is above 99.999%.

14. The method according to claim 13, characterized in that, The purity of the ultrapure silica powder is above 99.9999%, and the purity of the ultrapure silicon carbide powder is above 99.9999%.

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