A method for preparing an alkali metal corrosion resistant coating on the inner surface of a glass of a rubidium atomic clock rubidium bulb

Abstract

The application provides a preparation method of an alkali metal corrosion resistant coating on the inner surface of a rubidium bulb of a rubidium atomic clock, and mainly comprises the following steps: preparing boehmite sol with a molar concentration of 0.25-1 mol / L by using inorganic aluminum salt; immersing the prepared boehmite sol into the high borosilicate glass bulb of the atomic clock rubidium bulb; setting the rotating speed at 1000-2000 r / min after uniform coating, and spinning the glue for 30 seconds; pre-burning in a vacuum drying box at 120 DEG C for 10 minutes to remove the main adsorbed water on the surface of the coating; and annealing according to the annealing temperature point of the high borosilicate glass to form an aluminum oxide coating. The inorganic method is used to prepare the aluminum oxide sol gel, the aluminum oxide coating is prepared on the inner surface of the rubidium bulb by using the immersion coating process, the annealing treatment is used to form the aluminum oxide coating, the preparation problem of the alkali metal corrosion resistant coating on the inner surface of the rubidium atomic clock is solved, and the beneficial technical effects that the aluminum oxide coating is uniformly coated on the inner surface of the rubidium bulb glass to make the rubidium bulb of the rubidium atomic clock more resistant to alkali metal corrosion are achieved.

Description

Technical Field

[0001] This application relates to the field of rubidium atomic clock technology, and in particular to a method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of a rubidium atomic clock bulb glass. Background Technology

[0002] Since its first application in military communication satellites in 1985, passive rubidium atomic clocks have been widely used in satellite navigation systems and space stations due to their characteristics of low drift, high stability, radiation resistance, small size, light weight, and low power consumption.

[0003] The rubidium bulb is the core component of a rubidium atomic clock, filled with rubidium (Rb) vapor. Rubidium is a reactive alkali metal that readily reacts chemically with glass or cavity materials, leading to contamination or performance degradation. Alkali-resistant metal coatings (such as special ceramic coatings or inert inorganic non-metallic films) prevent rubidium vapor from reacting with the container walls, maintaining the purity and stability of rubidium atoms and ensuring the stability of atomic resonance transition signals.

[0004] Rubidium bulbs for rubidium atomic clocks require materials with properties such as resistance to alkali metal (especially rubidium vapor) corrosion, high airtightness, long-term stability, and radiation resistance. Domestically produced rubidium bulb materials mainly include: high borosilicate glass, high-purity alumina ceramics, sapphire, and special metal-ceramic composite materials. Among these, high borosilicate glass is low-cost, has a mature manufacturing process, and boasts a low coefficient of thermal expansion; however, it has poor resistance to metal corrosion. At high temperatures, rubidium may slowly diffuse and penetrate into the glass, causing surface discoloration and affecting the bulb's lifespan.

[0005] Investigations into the causes of the end-of-life of early navigation satellites revealed that rubidium clock failure was the primary reason. The main mechanism was the depletion of rubidium due to the physicochemical interaction between rubidium and the glass bulb wall. The chemical interaction between rubidium and glass primarily involves the combination of rubidium atoms with non-bridging oxygen in the glass network framework, forming Rb-silicates, Rb-borates, and other chemical structures. The physical interaction between rubidium and glass refers to the penetration and diffusion of rubidium into the glass. Analysis of the penetration depth of rubidium in various glasses using SIMS (Secondary Ion Mass Spectrometry) revealed that the penetration depth can reach tens of micrometers.

[0006] High borosilicate glass falls short of the requirements for rubidium atomic clock space applications in terms of its resistance to alkali metal corrosion. It is necessary to improve its resistance to alkali metal corrosion and to achieve a controllable alkali metal corrosion resistant coating preparation process to facilitate the low-cost application and development of rubidium clock glass.

[0007] Therefore, those skilled in the art are dedicated to developing a method for preparing an alkali metal corrosion resistant coating on the inner surface of a rubidium atomic clock bulb, thereby improving the long-term chemical stability of the high borosilicate glass used in rubidium bulb preparation, reducing rubidium penetration and diffusion, and enhancing the alkali metal corrosion resistance of the rubidium bulb to promote the application and technological extension of rubidium clocks. Summary of the Invention

[0008] This application provides a method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of a rubidium atomic clock bulb. For a high borosilicate glass bulb, boehmite sol is prepared using inorganic aluminum salts. The boehmite sol is then uniformly coated onto the inner surface of the rubidium bulb using dip-coating and spin-coating processes. An annealing process is formulated based on the annealing temperature of the high borosilicate glass and the thermal analysis results of the gel-to-coating transition. After annealing, an alumina coating is formed on the inner surface of the high borosilicate glass bulb, thus solving the problem of preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of the rubidium atomic clock bulb.

[0009] The specific implementation methods of this application are described below.

[0010] This application provides a method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of a rubidium atomic clock bulb glass, the steps of which include:

[0011] Boehmite sol with a molar concentration of 0.25–1 mol / L was prepared using inorganic aluminum salts;

[0012] The particles that agglomerate in the boehmite sol are filtered using a hydrophilic microporous filter membrane;

[0013] Boehmite sol was repeatedly injected into the exhaust pipe of the high borosilicate glass blister using a syringe, and after multiple dips, the sol was evenly coated on the inner surface of the blister.

[0014] Fix the high borosilicate glass blister to the spin coater, with the vent pipe of the blister facing outwards, and spin coater at a speed of 1000-2000 r / min for 20-40 seconds;

[0015] The borosilicate glass bubble shell is pre-fired in a vacuum drying oven to remove adsorbed water from the surface of the borosilicate glass coating.

[0016] The annealing process was formulated based on the annealing temperature of the borosilicate glass and the thermal analysis results of the gel-to-coating transition. A stepped heating rate was adopted: 5℃ / min for room temperature to 200℃; 2℃ / min for 200℃ to 560℃; holding at 560℃ for 1 hour; and -5℃ / min for cooling from 560℃ to room temperature. After annealing, an alumina coating resistant to alkali metal corrosion was formed on the inner surface of the borosilicate glass bulb.

[0017] In one possible implementation, the hydrophilic microporous filter membrane has a pore size of 0.15 μm.

[0018] In one possible implementation, the syringe is a disposable clean syringe.

[0019] In one possible implementation, the spinning time is 30 seconds.

[0020] In one possible implementation, the borosilicate glass is pre-fired in a vacuum drying oven at a temperature of 120°C for 10 minutes.

[0021] In one possible implementation, the preparation steps of boehmite sol are as follows: prepare a 0.5 mol / L aluminum nitrate solution, and generate Al(OH)3 precipitate by adding ammonia water to the 0.5 mol / L aluminum nitrate solution to remove nitrate ions by washing the Al(OH)3 precipitate, adding deionized water, dispersing and stirring evenly, adding nitric acid as a solvent for resolution, and obtaining a transparent light blue boehmite sol after constant temperature stirring and stabilization in a constant temperature drying oven.

[0022] In one possible implementation, before impregnating with boehmite sol, the borosilicate glass bulb shell of the atomic clock is cleaned with acetone and anhydrous ethanol. First, the borosilicate glass bulb shell is ultrasonically cleaned with acetone to remove organic matter from its surface, and then ultrasonically cleaned with anhydrous ethanol to further remove organic residues from its surface. After rinsing with deionized water, it is placed in analytical grade alcohol for later use. When ready for use, it is taken out, rinsed with deionized water, and dried with dry nitrogen gas.

[0023] In one possible implementation, 46.875 grams of analytical grade aluminum nitrate are weighed and dissolved in 250 ml of deionized water to prepare a 0.5 mol / L aluminum nitrate solution.

[0024] In one possible implementation, to obtain Al(OH)3 precipitate, analytical grade ammonia water is diluted to a 1 mol / L ammonia solution and added dropwise to a 0.5 mol / L aluminum nitrate solution under magnetic stirring until the pH reaches 8.3. Neutral filter paper is used as the filtration layer, and the precipitate suspension is filtered in a vacuum filtration apparatus to obtain a fine white Al(OH)3 precipitate. The precipitate is then washed with deionized water at least three times to remove NO from the precipitate. 3- ion.

[0025] In one possible implementation, after the Al(OH)3 precipitate is generated, the washed Al(OH)3 precipitate is weighed and placed in an Erlenmeyer flask. 250 mL of deionized water is added, and the precipitate is dispersed and stirred at 85°C and a speed of 3000–4000 r / min to prepare a sol with a solid content of 3%. After the precipitate is evenly dispersed, 20 wt% nitric acid is added as a solvent for resolution. When the pH of the colloid reaches 3.5, it is stirred at a constant temperature for 1 hour to form a transparent boehmite hydrosol. Finally, the colloidal solution is sealed and placed in a 65°C constant temperature drying oven for stabilization treatment for 24 hours to obtain a transparent light blue boehmite sol.

[0026] In one possible implementation, the borosilicate glass bulb is cylindrical.

[0027] In one possible implementation, in order to obtain boehmite sols with different molar concentrations, different volumes of deionized water are added to prepare the sols after precipitation, filtration, and washing.

[0028] This application employs low-temperature hydrolysis of inorganic aluminum salts to prepare boehmite sol, which features mild conditions and a simple process. An alumina coating is prepared on the inner surface of a rubidium bulb using dip-coating and spin-coating methods. The coating is uniform and dense, with good surface smoothness and continuity. The average transmittance in the visible and near-infrared light range is >90%. Because no surfactants or dispersants are used in the sol preparation process, the sol obtained after multiple filtration, washing, and dialysis has minimal organic residue and impurities. No reaction with metallic rubidium occurs during the vacuum preparation and operation of the rubidium bulb. Furthermore, this method avoids defects such as coating cracking and high porosity caused by the use of organic solvents, thus providing a simple and easy method for preparing a transparent alumina protective coating. The alkali-resistant metal corrosion-resistant protective coating prepared by this invention, when applied to a rubidium bulb, improves the bulb's resistance to alkali-metal corrosion and reduces the aging drift rate caused by light intensity attenuation.

[0029] The beneficial effects of this application are also reflected in:

[0030] 1) Inorganic aluminum nitrate was selected as the reaction precursor, ammonia was used as the precipitant, and nitric acid was used as the colloidal solvent. Boehmite (γ-AlOOH) sol with an average particle size of approximately 35 nm was prepared using the sol-gel method. Low-temperature hydrolysis of inorganic aluminum salts was used to prepare the boehmite sol instead of organic alkoxides as the reaction precursor. No dispersants or surfactants were added during the colloidal dispersion and homogenization process. High-speed rotating mechanical stirring and shear dispersion methods were used to form the nano-sol, ensuring that the alumina coating after annealing was free of organic residues. Impurities are the main cause of the depletion of alkali metal reaction within the rubidium bubble.

[0031] 2) The selection of the annealing process is determined based on the thermal analysis results of the gel-to-coating transition. Below 200℃, the main process is the precipitation of physically adsorbed water in the gel; a relatively fast heating rate can be adopted at this stage to facilitate rapid evaporation of the water. Above 200℃, the main processes are the desorption of chemically adsorbed water in the gel and the thermal decomposition and volatilization of chemical reaction products. Above 300℃, the alumina transformation and crystallization begin. In both stages, the heating rate needs to be controlled to reduce film cracking caused by localized thermal stress. Simultaneously, a lower heating rate allows the crystal phase transformation of the coating to be more complete, reducing the generation of lattice defects. The maximum annealing temperature is determined by the annealing temperature point of the glass used.

[0032] 3) Because the prepared alumina coating has a dense structure, stable chemical properties, and contains no organic impurities or volatiles, it forms a barrier layer on the inner surface of the glass that is resistant to alkali metal corrosion. When the rubidium bulb operates at a high temperature (greater than 150℃), it can effectively resist the thermal diffusion corrosion of alkali metals, ensuring the stability of its optical performance.

[0033] 4) This alumina coating can be widely applied to other similar surface modification fields that require glass to resist alkali metal corrosion. It can improve the chemical and optical stability of ordinary glass and has good application prospects.

[0034] 5) A transparent alumina coating with a thickness of about 3 μm was prepared on the inner surface of the rubidium bulb using the dip-coating method. The average transmittance in the visible and near-infrared range is greater than 90%. The rubidium consumption tracking test over 6 months showed that the transparent alumina coating significantly improved the ability of the reaction and diffusion of rubidium and glass surface compared with ordinary extra-hard glass. The rubidium consumption of the coated rubidium bulb was reduced by more than 50% compared with that of the uncoated rubidium lamp.

[0035] In summary, this application employs an inorganic method to prepare alumina sol-gel, avoiding defects such as coating cracking and high porosity caused by the use of organic solvents. An alumina coating is applied to the inner surface of the rubidium bulb using a dip-coating process, achieving uniform coating of the inner surface of the atomic clock rubidium bulb glass to resist alkali metal corrosion. Annealing is used to form the alumina coating; the annealing process is selected based on the thermal analysis results of the gel-to-coating transition, reducing film cracking caused by localized thermal stress, ensuring a more complete crystal phase transformation of the coating, and reducing the generation of lattice defects. This application can improve the alkali metal corrosion resistance of the rubidium bulb and reduce the aging drift rate caused by the attenuation of surface coloring light intensity. Attached Figure Description

[0036] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0037] Figure 1 - Schematic diagram of a rubidium clock;

[0038] Figure 2 - Schematic diagram of the three-dimensional structure of a cylindrical rubidium bubble;

[0039] Figure 3 - TG-DSC curve of boehmite gel;

[0040] Figure 4 - Particle size distribution curve of boehmite sol;

[0041] Figure 5 - XRD patterns of the coatings before and after annealing at 560℃;

[0042] Figure 6- UV / VIS / IR transmission spectra of alumina coatings with different thicknesses: (a) Coating thickness approximately 2 μm; (b) Coating thickness approximately 1 μm; (c) Coating thickness approximately 0.5 μm;

[0043] Figure 7 - Rubidium consumption curves with and without coating;

[0044] Figure 8 -Top view of a cylindrical rubidium bulb;

[0045] Figure 9 - Side view of a cylindrical rubidium bubble.

[0046] Component descriptions: 1. Rubidium bulb; 2. Exhaust pipe.

[0047] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0048] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0049] The technical solution of this application and how it solves the above-mentioned technical problems will be described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will be described below with reference to the accompanying drawings.

[0050] Example 1

[0051] To clearly understand the technical solution of Embodiment 1 of this application, the solutions of the prior art will first be described in detail. Since its first application in military communication satellites in 1985, passive rubidium atomic clocks have been widely used in satellite navigation systems and space stations due to their characteristics of low drift, high stability, radiation resistance, small size, light weight, and low power consumption. The most typical application is the US GPS navigation satellite system. Investigations into the causes of the end of service life of early navigation satellites showed that rubidium clock failure was the main reason. The main mechanism of failure is the depletion of rubidium due to the physicochemical interaction between rubidium and the glass bulb wall. The following formula gives the functional relationship between the total amount of material M that permeates into the glass and time. Wherein, R is a constant, which is related to the type of glass used in the bulb, the surface area of ​​the bulb, the density of rubidium vapor, the surface temperature of the rubidium bulb, the radio frequency power of the rubidium oscillator, etc.; A is the surface area; C is the concentration of the material permeating into the glass surface; and D is the diffusion coefficient of rubidium in the glass.

[0052]

[0053] The interaction between rubidium and glass is highly complex, involving both chemical and physical processes. The chemical interaction primarily involves the combination of rubidium atoms with non-bridging oxygen atoms in the glass network framework, forming Rb-silicates, Rb-borates, and other compound structures. The physical interaction refers to the penetration and diffusion of rubidium into the glass. Analysis of the penetration depth of rubidium in various glasses using SIMS (Secondary Ion Mass Spectrometry) reveals that the penetration depth can reach tens of micrometers, and the diffusion coefficient is related to the type of glass.

[0054] like Figure 1 As shown, the atomic gas cell of the rubidium atomic clock involves a spectral lamp, a filter bulb, and an absorption bulb. The glass of the rubidium bulb needs to be resistant to alkali metal corrosion. A coating resistant to alkali metal corrosion can be prepared on the inner surface of the rubidium bulb glass to improve the stability of the rubidium atomic clock.

[0055] Alumina coatings possess excellent properties such as high rigidity, low loss factor, high dielectric constant, resistivity, corrosion resistance, and compressive strength, making them widely used in high-tech fields such as electronics, mechanical engineering, chemical engineering, medicine, and optics. Typically, boehmite sol is prepared using organoaluminum salts (aluminum isoacetone, aluminum sec-butoxide) as raw materials, followed by dehydration and annealing to obtain the alumina coating. However, this method suffers from coating cracking and high porosity due to the large amount of organic solvents used, and the raw materials are flammable and expensive. Another approach is to prepare alumina coatings using inorganic methods. These methods produce coatings with good density, and the preparation process is simpler than organic methods, making it easier to obtain thinner, dense alumina coatings. However, current technologies have not successfully applied alumina coatings to the inner surfaces of electrovacuum devices such as lamps. This is because for the semi-enclosed inner surface of a rubidium bulb, uniform coating is impossible, and excess sol cannot be removed.

[0056] In view of this, Embodiment 1 of the present invention provides a method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of a rubidium atomic clock, the steps of which include:

[0057] 1. Preparation of Boehmite sol

[0058] a) Glass cleaning

[0059] The coating was prepared by ultrasonically cleaning the borosilicate glass with acetone to remove larger organic particles from the surface. To further remove organic residues, it was ultrasonically cleaned with anhydrous ethanol, then rinsed thoroughly with deionized water and placed in analytical grade ethanol for later use. Before use, it was rinsed thoroughly with deionized water and dried with dry nitrogen gas.

[0060] b) Prepare a 0.5 mol / L aluminum nitrate solution

[0061] Weigh 46.875g of analytical grade aluminum nitrate (Al(NO3)3·9H2O) on an analytical balance (sensitivity 0.01mg), dissolve it in 250ml of high-purity deionized water, and prepare a 0.5mol / L solution.

[0062] c) Formation of Al(OH)3 precipitate

[0063] Analytical grade ammonia solution (NH4·H2O) was diluted to prepare a 1 mol / L ammonia solution, which was then added dropwise to a 0.5 mol / L aluminum nitrate solution while stirring at high speed. The ammonia solution was slowly added dropwise while stirring at room temperature until the pH reached 7.8, at which point large, snowflake-like precipitates formed. The addition of ammonia solution was stopped when the pH reached 8.3, at which point the precipitate gradually transformed into fine, granular precipitates. If excess ammonia solution was added, the pH of the solution would continue to increase, resulting in partial dissolution of the precipitate and the formation of large granular particles.

[0064] Neutral, rapid filter paper was selected as the filter layer. An appropriate amount of the precipitate suspension was filtered in a vacuum filtration device to obtain a fine, white Al(OH)3 precipitate. The precipitate was then repeatedly washed with a large amount of deionized water for at least three cycles to remove NO from the precipitate. 3- ion.

[0065] d) Preparation of boehmite (γ-AlOOH) sol by reflux

[0066] Weigh the washed Al(OH)3 precipitate (filter cake) and place it in an Erlenmeyer flask. Add 250 mL of deionized water and re-disperse and stir at high speed at 85°C (using an IKA heated magnetic stirrer manufactured in Germany, with a speed of 3000–4000 r / min) to prepare a boehmite sol with a solid content of approximately 3%. After the precipitate is evenly dispersed, add nitric acid (diluted to a concentration of approximately 20 wt%) as a solvent for resolution. When the pH of the colloid reaches 3.5, continue stirring at a constant temperature for 1 hour to form a transparent boehmite hydrosol. During the stirring process, add water promptly to compensate for water evaporation loss. Finally, seal the colloidal solution and age it in a constant temperature drying oven at 65°C for 24 hours to obtain a transparent light blue boehmite (γ-AlOOH) sol.

[0067] In the above sol preparation experiments, in order to obtain boehmite sols with different molar concentrations, after precipitation, filtration and washing, different volumes of deionized water were added for high-speed dispersion and then the colloid was re-dissolved. This allowed the preparation of boehmite sols with molar concentrations of approximately 0.25M (adding 500mL of deionized water) and 1M (adding 125mL of deionized water).

[0068] 2. Coating preparation

[0069] Before coating preparation, the colloid was filtered using a hydrophilic microporous membrane with a pore size of 0.15 μm to remove larger particles that would agglomerate. For cylindrical rubidium bulbs, a suitable amount of sol was drawn with a disposable syringe, injected through the vent pipe 2 on the cylindrical surface of the bulb shell 1, and then withdrawn. After multiple dip-coatings, the sol was uniformly coated on the inner surface of the bulb shell 1. Subsequently, the cylindrical bulb shell 1 was fixed on a disc-shaped fixture fixed to the spin coater shaft, with the vent pipe 2 opening outwards. To control the film thickness and coating uniformity, the spin coater speed was set to 1000–2000 r / min, and the spin coater was operated for 30 seconds to remove excess sol from the bulb shell 1. The bulb shell 1 and vent pipe 2 of the rubidium bulb are shown below. Figure 2 As shown. Then, it is pre-fired in a vacuum drying oven at 120°C for 10 minutes to remove the main adsorbed water from the coating surface.

[0070] 3. Annealing heat treatment of the coating

[0071] An alumina coating was formed by annealing the glass in a box annealing furnace for 1 hour according to the annealing temperature point. The annealing regime is shown in Table 1. The selection of the annealing process for the alumina protective coating needs to be determined based on the thermal analysis results of the gel-to-coating transition. The phase transition points occurring during the transformation from boehmite (γ-AlOOH) sol to γ-Al2O3 correspond to the endothermic and exothermic peaks at different temperatures in the thermal analysis diagram (see details). Figure 3 The Beijing Extra Hard (BJTY) glass used in the manufacture of rubidium bulbs is a high borosilicate glass. After the coating preparation is completed, an annealing temperature of 560℃ is selected for the rubidium bulb blank made of this glass.

[0072] Table 1 Annealing process for top coating of borosilicate glass

[0073] heating rate 5℃ / min 2℃ / min Keep warm for 1 hour -5℃ / min

[0074] To facilitate understanding of the technical effects achieved in Example 1 and the improved performance of the rubidium atomic clock through the preparation method of the alkali-resistant metal corrosion-resistant coating on the inner surface of the rubidium atomic clock provided in this proposal, the alumina coating was tested and analyzed.

[0075] a) Particle size analysis of sol

[0076] The prepared sol was stored in a sealed container in a constant-temperature drying oven at 65℃. Before use, particles with a size of approximately several hundred nanometers were dispersed or filtered using high-speed magnetic stirring and a nanofiltration membrane, followed by ultrasonic dispersion to improve the surface energy and dispersibility of the sol particles. The particle size of the 0.5M boehmite sol was analyzed using a Zetasizer Nano ZS dynamic laser scattering analyzer, and the results are as follows: Figure 4 As shown, the prepared boehmite sol has a particle size mainly distributed between 20-80 nm, with an average particle size of 68 nm. The sol is light blue overall and exhibits obvious Tyndall effect. No colloidal aggregation occurred after several days of sealed storage at room temperature.

[0077] The particle size analysis shows that the boehmite sol prepared in this proposal for preparing the alkali-resistant metal corrosion coating on the inner surface of the rubidium atomic clock has a uniform small particle size distribution and fewer impurities, which can effectively avoid defects such as coating cracking and high porosity.

[0078] b) TG-DSC analysis of the gel

[0079] TG-DSC analyzes "Thermogravimetric Analysis-Differential Scanning Calorimetry". This is a simultaneous thermal analysis technique that combines thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). It can simultaneously obtain information on the mass change and heat change of a sample in a single measurement, thereby comprehensively revealing the thermal properties and thermochemical reactions of the material.

[0080] The boehmite sol used in Example 1 was appropriately concentrated at 80°C and allowed to stand for a period of time to form a gel. The boehmite gel was tested using a NETZSCH STA 449C TG-DSC, and the test results are as follows. Figure 3 As shown.

[0081] The test temperature range for the samples is 20-1000℃, and the heating rate is 10℃ / min. Mass loss data are as follows: Figure 3As shown in the TG curves, the weight loss above 520℃ is not significant. The weight loss below 520℃ is mainly due to boehmite dehydration, impurity volatilization, and transition to products. The endothermic peak at 125℃ is caused by the volatilization of physically adsorbed water on the boehmite surface, corresponding to a mass loss of 9%-10% on the TG curve. The endothermic peak near 235℃ is caused by the removal of water adsorbed in the micropores, thermal decomposition of ammonium nitrate, and volatilization of chemically adsorbed water on the boehmite surface, corresponding to a mass loss of 12%-16% on the TG curve. The endothermic peak near 300℃ is caused by the dehydration and transition to transition alumina in boehmite (γ-AlOOH) due to the breaking and condensation of -OH groups. The exothermic peak near 500℃ is caused by the dehydration of transition alumina.

[0082] The TG-DSC analysis shows that the boehmite sol prepared in this proposal for preparing the alkali-resistant metal corrosion coating on the inner surface of the rubidium atomic clock, after undergoing dehydration, impurity volatilization, physical and chemical adsorption water volatilization, transformation to transition alumina, and transition alumina dehydration below 520℃, tends to be stable above 520℃, which can to a certain extent characterize its chemical stability against alkali-resistant metal corrosion on glass surfaces.

[0083] c) XRD analysis before and after coating annealing

[0084] X-ray diffraction (XRD) is a non-destructive analytical technique based on the diffraction characteristics of crystals to X-rays, used to study the composition, microstructure, and macroscopic properties of materials.

[0085] XRD analysis of the coatings before and after annealing at 560℃ is as follows: Figure 5 As shown in the left figure, the coating was hardened in a vacuum drying oven at 120℃ before annealing. Although the coating has not yet crystallized and the so-called "bun peak" appeared due to the influence of the substrate, a small number of characteristic peaks of γ-Al2O3 still appeared, indicating that the adsorbed water in the boehmite gel began to transform into γ-Al2O3 after heating and evaporation. In the right figure, (311), (400), and (440) are the main characteristic diffraction peaks of γ-Al2O3, and the positions of the diffraction peaks are consistent with the standard spectrum (JCPDS Card No. 04-0858). Since the γ state is an unstable state and its peak shape is not sharp, it indicates that its crystallinity is low and it is polycrystalline γ-Al2O3. Since the annealing temperature required for complete crystallization of γ-Al2O3 is above 650℃, the coating has not been completely crystallized due to the limitation of the annealing temperature of the high borosilicate glass itself, resulting in the broadening of the XRD spectrum peaks. The main grain size was calculated to be about 100nm by the Scherer formula. The XRD pattern showed no other impurity peaks, indicating that the product is a pure single-phase γ-Al2O3.

[0086] The XRD analysis shows that the annealing mechanism used in this proposal to prepare the alkali-resistant metal etching coating on the inner surface of the rubidium atomic clock has a maximum temperature of 560℃, which takes into account the annealing temperature limit of the borosilicate glass itself. Furthermore, it produces a pure alkali-resistant metal etching coating before and after annealing, making it a feasible and effective preparation method.

[0087] d) Surface morphology analysis of the coating

[0088] The surface morphology of the coatings after three coats with sols of different concentrations was observed using a JSM-5600LV scanning electron microscope (SEM). The alumina coating prepared with 1M boehmite sol showed numerous cracks and a rough surface after heat treatment at 560℃. X-ray energy dispersive spectroscopy (EDS) attached to the SEM analyzed the coating thickness, revealing it to be approximately 2 μm. The alumina coatings prepared with 0.5M and 0.25M boehmite sols did not show any obvious visible cracks after heat treatment at 560℃, and the coating surface was relatively smooth. However, the 0.5M coating showed some shallow cracks and a tendency towards crazing, while the 0.25M coating was more uniform and dense, with better surface smoothness and continuity; some of the small number of pores were formed after annealing.

[0089] The surface morphology analysis shows that the boehmite sol prepared in this proposal for preparing the alkali-resistant metal corrosion coating on the inner surface of the rubidium atomic clock exhibits progressively better performance in terms of crack and crazing index after heat treatment at 560℃, with concentrations of 1M, 0.5M, and 0.25M. The coating with a concentration of 0.25M is more uniform and dense, and has better surface smoothness and continuity.

[0090] e) Optical transmittance test of the coating

[0091] Figure 6 This is the transmission spectrum of an alumina coating prepared on borosilicate glass. For example... Figure 6 As shown: when the coating thickness is 2 μm, the average transmittance of the coating transmission spectrum at 780 nm and 794 nm of the rubidium atomic characteristic spectrum is 70.5%; when the coating thickness is 1 μm, the transmittance is 80.8%; and when the coating thickness is 0.5 μm, the transmittance is 92.7%.

[0092] The optical transmittance test shows that, in preparing the alkali metal corrosion resistant coating on the inner surface of the rubidium atomic clock, the proposed method can adapt the appropriate molar concentration of boehmite sol according to the specific transmittance requirements, or adjust the spin coating time to obtain the ideal coating thickness, thereby meeting the transmittance requirements.

[0093] f) Rubidium consumption test curves for coated and uncoated rubidium bubbles after 6 months of operation are shown in the attached figure. Figure 7As shown, the test results indicate that the uncoated rubidium spectrometer consumes approximately 486 μg of rubidium, while the coated rubidium spectrometer consumes approximately 225 μg. For the uncoated rubidium bulb, the consumption is mainly due to the reaction of rubidium with impurities within the glass bulb and high-temperature physical diffusion. For the coated rubidium spectrometer, the consumption process remains relatively stable, indicating that the inert alumina coating acts as an effective barrier, reducing the concentration gradient of rubidium on the glass surface, inhibiting the reaction consumption of rubidium with impurities on the glass surface, and blocking the diffusion channels of rubidium into the glass interior. This significantly weakens the interaction between rubidium and the glass surface, and the ability to impede the diffusion of alkali metals is significantly improved compared to ordinary extra-hard glass.

[0094] In one specific embodiment of Example 1, the top view of the rubidium bubble is as follows: Figure 8 As shown, the side view is as follows Figure 9 As shown, the dimensions of the rubidium bulb are: D1 = 17.90 ± 0.10 mm, D2 = 19.90 ± 0.10 mm, L = 40.00 ± 0.10 mm, d1 = 2.50 ± 0.10 mm, d2 = 4.30 ± 0.10 mm, H = 16.50 ± 0.10 mm, h = 10.00 ± 0.10 mm, r1 = 1.00 ± 0.10 mm, r2 = 0.90 ± 0.10 mm.

[0095] As can be seen from Example 1 above, by preparing alumina sol-gel using an inorganic method, and then applying an alumina coating to the inner surface of the rubidium bulb using dip-coating and spin-coating processes, and finally annealing to form the alumina coating, the selection of the annealing process is determined based on the thermal analysis results of the gel-to-coating transition. This can effectively solve the existing problems of uneven coating and high porosity in the preparation of alkali metal corrosion resistant coatings on the inner surface of the rubidium bulb glass of the rubidium atomic clock, thereby achieving the beneficial technical effect of making the inner surface of the rubidium bulb glass of the rubidium atomic clock more resistant to alkali metal corrosion.

[0096] In the above embodiments, the descriptions of each embodiment have their own emphasis. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments. The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0097] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0098] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of a rubidium atomic clock bulb glass, characterized in that, Including the following steps: Before impregnating with boehmite sol, the cylindrical borosilicate glass bulb is cleaned: first, the cylindrical borosilicate glass bulb is ultrasonically cleaned with acetone to remove organic matter on its surface, then ultrasonically cleaned with anhydrous ethanol to further remove organic residues on its surface, then rinsed with deionized water and placed in analytical grade alcohol for later use. When it is ready for use, it is taken out, rinsed with deionized water, and dried with dry nitrogen. Boehmite sol with a molar concentration of 0.25 mol / L was prepared using inorganic aluminum salts; The particles that agglomerate in the boehmite sol are filtered using a hydrophilic microporous filter membrane; Boehmite sol was repeatedly injected into the exhaust pipe of a cylindrical high borosilicate glass bubble using a syringe, and after multiple dips, the sol was evenly coated on the inner surface of the bubble. The cylindrical high borosilicate glass blister is fixed to the spin coater with the exhaust pipe of the blister facing outward, and the blister is spin-coated at a speed of 1000-2000 r / min for 20-40 seconds. The cylindrical borosilicate glass bubble shell is pre-fired in a vacuum drying oven to remove adsorbed water from the surface of the bubble shell coating. The annealing process was formulated based on the annealing temperature of the borosilicate glass and the thermal analysis results of the gel-to-coating transition. A stepped heating rate was adopted: 5℃ / min for room temperature to 200℃; 2℃ / min for 200℃ to 560℃; holding at 560℃ for 1 hour; and -5℃ / min for cooling from 560℃ to room temperature. After annealing, an alumina coating resistant to alkali metal corrosion was formed on the inner surface of the cylindrical borosilicate glass bubble.

2. The method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of the rubidium bulb glass of a rubidium atomic clock according to claim 1, characterized in that, The syringe used is a disposable clean syringe.

3. The method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of the rubidium bulb glass of a rubidium atomic clock according to claim 1, characterized in that, The time for applying the adhesive is 30 seconds.

4. The method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of the rubidium bulb glass of a rubidium atomic clock according to claim 1, characterized in that, The cylindrical borosilicate glass bulb is pre-fired in a vacuum drying oven at a temperature of 120°C for 10 minutes.

5. The method for preparing an alkali-metal corrosion-resistant coating on the inner surface of the rubidium bulb glass of a rubidium atomic clock according to any one of claims 1-4, characterized in that, The preparation steps of the boehmite sol are as follows: prepare a 0.5 mol / L aluminum nitrate solution, and generate Al(OH)3 precipitate by titrating ammonia water into the 0.5 mol / L aluminum nitrate solution. Wash the Al(OH)3 precipitate to remove nitrate ions, add deionized water, disperse and stir evenly, and then add nitric acid as a colloid solvent for resolution. After constant temperature stirring and stabilization in a constant temperature drying oven, a transparent light blue boehmite sol is obtained.

6. The method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of the rubidium bulb glass of a rubidium atomic clock according to claim 5, characterized in that, The method for preparing the 0.5 mol / L aluminum nitrate solution is to weigh 46.875 g of analytical grade aluminum nitrate and dissolve it in 250 ml of deionized water.

7. The method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of the rubidium bulb glass of a rubidium atomic clock according to claim 5, characterized in that, The production method of the Al(OH)3 precipitate is as follows: Analytical grade ammonia water is diluted to a 1 mol / L ammonia solution, and then added dropwise to a 0.5 mol / L aluminum nitrate solution under magnetic stirring until the pH reaches 8.

3. Neutral filter paper is used as the filtration layer, and the precipitate suspension is filtered in a vacuum filtration device to obtain a fine white Al(OH)3 precipitate. The precipitate is then washed with deionized water at least three times to remove NO from the precipitate. 3- ion.

8. The method for preparing an alkali-resistant metal corrosion-resistant coating on the inner surface of the rubidium bulb glass of a rubidium atomic clock according to claim 5, characterized in that, After the Al(OH)3 precipitate was generated, the washed Al(OH)3 precipitate was weighed and placed in an Erlenmeyer flask. 500 mL of deionized water was added, and the precipitate was dispersed and stirred at 85 °C and a speed of 3000–4000 r / min to prepare a sol with a solid content of 3%. After the precipitate was evenly dispersed, 20 wt% nitric acid was added as a solvent for resolution. When the pH of the colloid reached 3.5, it was stirred at a constant temperature for 1 hour to form a transparent boehmite hydrosol. At this time, the Tyndall effect was clearly visible in the sol. Finally, the colloidal solution was sealed and placed in a constant temperature drying oven at 65 °C for 24 hours for stabilization treatment to obtain a transparent light blue boehmite sol.

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