Lead-free diode glass bulb and preparation method thereof

Abstract

The invention discloses a lead-free diode glass bulb and a preparation method thereof, belongs to the technical field of diode glass bulbs, and creatively introduces a modified bismuth phosphate complex to solve the key problems that a traditional lead-free glass bulb is prone to causing thermal damage, devitrification defects, insufficient dielectric strength, weak acid corrosion resistance and the like in the low-temperature sealing process. The components form an amorphous wetting layer at a high temperature, so that the sealing activation energy is remarkably reduced, and thermal damage is avoided while low-temperature sealing is realized; meanwhile, the dielectric density is enhanced by filling micropores with bismuth ions, and the dielectric strength and the insulation reliability are improved; the phosphorus component is combined with aluminum ions to form a passive film, so that the acid corrosion resistance is greatly enhanced; according to the present invention, the bottleneck in the prior art is broken through, the glass bulb is suitable for the severe environments such as miniaturized equipment, automotive electronics and industrial high-temperature systems, and the packaging safety, the durability and the reliability of the glass bulb are significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of diode glass bulbs, in particular to a lead-free diode glass bulb and a preparation method thereof. BACKGROUND

[0002] In the field of electronic packaging, diode glass bulbs, as key protective components of semiconductor devices, bear the core functions of ensuring electrical insulation, mechanical support and environmental sealing, which are crucial to ensuring the long-term reliability and safety of diodes in harsh working conditions such as high temperature, high humidity and corrosion. With the increasing strictness of global environmental regulations and the popularity of green manufacturing requirements, lead-free glass systems have become the mainstream choice for diode glass bulbs, aiming to eliminate the environmental and health risks of traditional lead-containing materials.

[0003] However, the existing lead-free glass bulb technology faces significant technical bottlenecks in achieving high-performance packaging: traditional lead-free materials require high processing temperatures during sealing, which can easily cause thermal damage to miniaturized chips, leading to functional failure; the introduction of alkali metal fluxes to reduce the melting point often induces glass crystallization, forming microscopic defects and uneven structures, which compromise the optical transparency and mechanical strength of the glass bulb; in high temperature and humidity operating environments, insufficient dielectric strength leads to degradation of insulation performance and a significant increase in leakage current density, increasing the risk of device short circuits and failure; when exposed to strong acid corrosive environments, the chemical stability is poor, the corrosion rate is high, and the protection ability and service life are weakened; at the same time, the mismatch of thermal expansion coefficients generates a large thermal stress under conditions of dramatic temperature changes, resulting in low thermal shock resistance and high breakage rate, which seriously threatens the structural integrity and reliability.

[0004] These bottlenecks limit the reliability and wide applicability of lead-free diode glass bulbs in miniaturized devices, automotive electronics, industrial high-temperature systems and other high-demand applications, and breakthrough innovations are urgently needed to improve their performance and durability in harsh environments. SUMMARY

[0005] In view of the above, in order to overcome the defects of the prior art, the application provides a lead-free diode glass bulb and a preparation method thereof, which effectively solves the problems of low-temperature sealing performance, weak dielectric strength and weak acid corrosion resistance of lead-free diode glass bulbs on the market.

[0006] The technical scheme adopted by the application is as follows: the application provides a lead-free diode glass bulb and a preparation method thereof, which comprises the following raw materials by weight: modified BiPO4 complex 0.5-2 parts; silicon dioxide 40-60 parts; boron oxide 8-22 parts; phosphorus pentoxide 1-3 parts; lithium oxide 6-18 parts; magnesium oxide 1-10 parts; calcium oxide 1-10 parts; aluminum oxide 1-5 parts; titanium dioxide 2-14 parts; zinc oxide 0.8-5 parts; clarifying agent 1-4 parts; The preparation method of the modified BiPO4 composite comprises the following steps: Dissolve bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) in dilute nitric acid and stir until transparent; mix phosphoric acid (H3PO4) and deionized water, and adjust the pH to 1.5-2.0; drop the phosphorus source solution into the bismuth source solution to generate white flocculent precipitate, maintain stirring at 65±5℃ and ensure complete reaction; transfer to a high-pressure reaction kettle, wait for the product to cool after the reaction is completed, centrifugal separation, wash with 50% ethanol solution for 3 times, and add polyethylene glycol (PEG-4000) and ultrasonic dispersion for 30 minutes; ceramic membrane step-by-step filtration, collect the powder with a particle size of 0.3-0.8 μm; calcine for 2 hours to obtain the modified composite.

[0007] Further, the weight percentage of the dilute nitric acid solution is 4-6wt%.

[0008] Further, the dropping speed of the phosphorus source solution into the bismuth source solution is 4-6mL / min.

[0009] Further, the filling degree of the transfer to the high-pressure reaction kettle is controlled at 60-80%.

[0010] Further, the temperature of the transfer to the high-pressure reaction kettle is set to 160-200℃, and the reaction time is 12h.

[0011] Further, the weight percentage of the polyethylene glycol (PEG-4000) is 0.3-0.7wt%.

[0012] Further, the ceramic membrane step-by-step filtration is performed, and the pore size of the ceramic membrane is 5 μm, 1 μm, and 0.45 μm from large to small.

[0013] Further, the calcination temperature is 460-500℃, the heating rate is 3℃ / min, the organic residues are eliminated, and the crystallinity is enhanced.

[0014] Further, the preparation method of the lead-free diode glass shell is as follows: Grind the modified BiPO4 powder and each raw material in anhydrous ethanol medium by weight parts for 2 hours, stir and mix, and send into an electric melting furnace to melt at a temperature of 1000-1500℃ to form a glass liquid; the obtained glass liquid is clarified and homogenized at a temperature of 1000-1300℃ for 20-30min, and pipe forming is performed at a temperature of 600-1000℃ to obtain a glass shell blank; sand blasting is performed by using a sand blasting machine, and cutting is performed to obtain a lead-free diode glass shell.

[0015] Further, the ultrafine grinding is performed in a zirconia ball mill jar, and the ball-to-material ratio is 10:1.

[0016] The beneficial effects achieved by the application with the above structure are as follows: By adding the modified BiPO4 complex in the raw material, a thermal decomposition reaction occurs at high temperature, the sealing activation energy is reduced, the sealing temperature of the glass shell is reduced, and the thermal expansion coefficient is maintained relatively stable, thereby avoiding the crystallization defect problem prone to occur in the traditional system, and realizing the breakthrough of low-temperature sealing performance.

[0017] The bismuth ions in the modified BiPO4 complex fill the micropores in the glass structure, and together with the silicon ions, the medium density is improved, and the dielectric strength of the modified glass shell is improved. Under high temperature and high humidity conditions, the leakage current density is reduced, the dielectric strength and insulation reliability are improved, and it is suitable for the packaging safety demand of high-voltage diodes.

[0018] The decomposition product of the phosphorus component in the modified BiPO4 complex can form AlPO4 with aluminum ions in the raw material, and under the synergistic action of BiPO4 in a strong acid environment, the corrosion rate and corrosion degree are reduced, the acid corrosion resistance is enhanced, and long-term corrosion resistance can be realized in strong corrosion scenes such as automobile electroplating modules; at the same time, BiPO4 is combined with SiO2 to absorb the cooling stress during sealing, so that the thermal shock threshold of the glass shell is improved, the thermal stress matching performance is optimized, and the structural integrity of the glass shell under temperature changes is improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A sealing temperature comparison chart of a lead-free diode glass shell and a preparation method thereof is provided for the present application.

[0020] Figure 2 A breakdown strength comparison chart of a lead-free diode glass shell and a preparation method thereof is provided for the present application.

[0021] Figure 3 An acid corrosion resistance comparison chart of a lead-free diode glass shell and a preparation method thereof is provided for the present application.

[0022] Figure 4 A thermal shock experiment result comparison chart of a lead-free diode glass shell and a preparation method thereof is provided for the present application.

[0023] Figure 5 A failure damage degree image of a lead-free diode glass shell and a preparation method thereof is provided for the present application, the left chart is Example 1, and the right chart is Comparative Example 2.

[0024] The accompanying drawings are included to provide a further understanding of the application, and constitute a part of the specification, and are used to explain the application together with embodiments of the application, and do not constitute a limitation on the application. DETAILED DESCRIPTION

[0025] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be clearly and completely described below, obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments; based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the protection scope of the present application. Embodiment 1

[0026] A lead-free diode glass bulb and a preparation method thereof First, a modified BiPO4 composite is prepared, 0.1 mol of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) is dissolved in 200 mL of dilute nitric acid (5 wt%), and stirred at 60℃ for 30 min until transparent, 0.1 mol of phosphoric acid (H3PO3) is mixed with 100 mL of deionized water, and ammonia water is added to adjust the pH to 1.5; the phosphorus source solution is added dropwise into the bismuth source solution, the dropwise speed is 5 mL / min, and white flocculent precipitate is immediately generated, and stirring is maintained at 65 for 1 hour to ensure complete reaction; the reaction product is transferred to a high-pressure reaction kettle, the filling degree is controlled at 70%, and reaction is carried out at 180℃ for 12 hours; after the product is cooled, centrifugal separation is carried out, and the product is washed with 50% ethanol solution for 3 times; 0.5 wt% polyethylene glycol (PEG-4000) is added and ultrasonic dispersion is carried out for 30 min to form an anti-agglomeration coating layer; the product is filtered through 5 μm, 1 μm and 0.45 μm ceramic membranes in sequence, and the powder with a particle size of 0.3-0.8 μm is collected; after the organic residues are eliminated, the modified composite is obtained by calcining at 480℃ in an air atmosphere for 2 hours, and the temperature rising rate is 3℃ / min.

[0027] The modified BiPO4 composite 0.5 parts, silica 40 parts, boron oxide 8 parts, phosphorus pentoxide 1 part, lithium oxide 6 parts, magnesium oxide 1 part, calcium oxide 1 part, aluminum oxide 1 part, titanium dioxide 2 parts, zinc oxide 0.8 parts, clarifying agent 1 part are weighed, the modified BiPO4 powder and each raw material are superfine ground in anhydrous ethanol medium for 2 hours, stirred and mixed, and sent into an electric melting furnace to melt to form a glass liquid under the condition that the temperature is 1000℃; the obtained glass liquid is clarified and homogenized at 1000℃ for 20 min, pipe forming is carried out at a temperature of 600℃, and a glass bulb blank is obtained; sand blasting treatment is carried out by using a sand blasting machine, and lead-free diode glass bulbs are obtained by cutting. Embodiment 2

[0028] A lead-free diode glass bulb and a preparation method thereof First, the modified BiPO4 composite is prepared. 0.1 mol of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) is dissolved in 200 mL of dilute nitric acid (5 wt%), and stirred at 60°C for 30 min until transparent. 0.1 mol of phosphoric acid (H3PO3) is mixed with 100 mL of deionized water, and ammonia water is added to adjust the pH to 1.5. The phosphorus source solution is added dropwise into the bismuth source solution at a rate of 5 mL / min, and white flocculent precipitate is immediately generated. The stirring is maintained at 65°C for 1 hour to ensure complete reaction. The reaction product is transferred to a high-pressure reaction kettle, and the filling degree is controlled at 70%. The reaction is carried out at 180°C for 12 hours. After cooling, the product is centrifuged and washed with 50% ethanol solution for 3 times. 0.5 wt% polyethylene glycol (PEG-4000) is added and ultrasonically dispersed for 30 min to form an anti-agglomeration coating layer. The powder with a particle size of 0.3-0.8 μm is collected by sequentially filtering through 5 μm, 1 μm and 0.45 μm ceramic membranes. The modified composite is obtained after calcining at 480°C for 2 hours in an air atmosphere at a heating rate of 3°C / min to eliminate organic residues.

[0029] The modified BiPO4 composite 1.2 parts, silica 50 parts, boron oxide 15 parts, phosphorus pentoxide 2 parts, lithium oxide 12 parts, magnesium oxide 5 parts, calcium oxide 5 parts, aluminum oxide 3 parts, titanium dioxide 8 parts, zinc oxide 2.5 parts, clarifying agent 2.5 parts are weighed, and the modified BiPO4 powder and each raw material are superfine ground in anhydrous ethanol medium for 2 hours, stirred and mixed, and sent into an electric melting furnace to melt at a temperature of 1300°C to form a glass liquid. The obtained glass liquid is clarified and homogenized at a temperature of 1200°C for 25 min, and pipe forming is carried out at a temperature of 800°C to obtain a glass shell blank. Sand blasting is carried out by using a sand blasting machine, and cutting is carried out to obtain a lead-free diode glass shell. Example 3

[0030] A lead-free diode glass shell and a preparation method thereof Firstly, the modified BiPO4 composite is prepared. 0.1 mol of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) is dissolved in 200 mL of dilute nitric acid (5 wt%), and stirred at 60°C for 30 min until transparent. 0.1 mol of phosphoric acid (H3PO3) is mixed with 100 mL of deionized water, and ammonia water is added to adjust the pH to 1.5. The phosphorus source solution is added dropwise into the bismuth source solution at a rate of 5 mL / min, and white flocculent precipitate is immediately generated. Stirring is maintained at 65°C for 1 hour to ensure complete reaction. The reaction product is transferred to a high-pressure reaction kettle, and the filling degree is controlled at 70%. The reaction is carried out at 180°C for 12 hours. After cooling, the product is centrifuged and washed with 50% ethanol solution for 3 times. 0.5 wt% polyethylene glycol (PEG-4000) is added and ultrasonically dispersed for 30 min to form an anti-agglomeration coating layer. The product is filtered through 5 μm, 1 μm, and 0.45 μm ceramic membranes in sequence, and the powder with a particle size of 0.3-0.8 μm is collected. The product is calcined at 480°C for 2 hours in an air atmosphere, and the heating rate is 3°C / min. After eliminating organic residues, the modified composite is obtained.

[0031] The modified BiPO4 composite 2 parts, silica 60 parts, boron oxide 22 parts, phosphorus pentoxide 3 parts, lithium oxide 18 parts, magnesium oxide 10 parts, calcium oxide 10 parts, aluminum oxide 5 parts, titanium dioxide 14 parts, zinc oxide 5 parts, and clarifying agent 4 parts are weighed. The modified BiPO4 powder and each raw material are ultrafine ground in anhydrous ethanol medium for 2 hours, stirred and mixed, and sent into an electric melting furnace to melt and form a glass liquid at a temperature of 1500°C. The obtained glass liquid is clarified and homogenized at 1300°C for 30 min, and pipe forming is carried out at a temperature of 1000°C to obtain a glass shell blank. Sand blasting is carried out using a sand blasting machine, and a lead-free diode glass shell is obtained by cutting.

[0032] Comparative Example 1 Silica 40 parts, boron oxide 8 parts, phosphorus pentoxide 1 part, lithium oxide 6 parts, magnesium oxide 1 part, calcium oxide 1 part, aluminum oxide 1 part, titanium dioxide 2 parts, zinc oxide 0.8 parts, and clarifying agent 1 part are weighed. The modified BiPO4 powder and each raw material are ultrafine ground in anhydrous ethanol medium for 2 hours, stirred and mixed, and sent into an electric melting furnace to melt and form a glass liquid at a temperature of 1000°C. The obtained glass liquid is clarified and homogenized at 1000°C for 20 min, and pipe forming is carried out at a temperature of 600°C to obtain a glass shell blank. Sand blasting is carried out using a sand blasting machine, and a lead-free diode glass shell is obtained by cutting.

[0033] Comparative Example 2 Take 50 parts of silicon dioxide, 15 parts of boron oxide, 2 parts of phosphorus pentoxide, 1 part of magnesium oxide, 1 part of calcium oxide, 3 parts of aluminum oxide, 8 parts of titanium dioxide, 2.5 parts of zinc oxide, 2.5 parts of clarifying agent, and then mix lithium oxide, sodium oxide and potassium oxide according to the weight percentage mixing ratio of 1:1.2:1. The modified BiPO4 powder and each raw material are superfine ground in anhydrous ethanol medium for 2 hours, stirred and mixed, and then sent into an electric furnace to melt under the condition of a temperature of 1000°C to form a glass liquid. The obtained glass liquid is clarified and homogenized at 1000°C for 20 minutes, and then pipe forming is carried out at a temperature of 600°C to obtain a glass shell blank. Sand blasting is carried out by using a sand blasting machine, and cutting is carried out to obtain a lead-free diode glass shell.

[0034] Comparative Example 3 Take 5 parts of fluorine, 60 parts of silicon dioxide, 22 parts of boron oxide, 3 parts of phosphorus pentoxide, 24 parts of alkali metal oxide, 10 parts of alkaline earth metal oxide, 5 parts of aluminum oxide, 14 parts of titanium dioxide, 5 parts of zinc oxide, and 4 parts of clarifying agent. The modified BiPO4 powder and each raw material are superfine ground in anhydrous ethanol medium for 2 hours, stirred and mixed, and then sent into an electric furnace to melt under the condition of a temperature of 1500°C to form a glass liquid. The obtained glass liquid is clarified and homogenized at 1300°C for 30 minutes, and then pipe forming is carried out at a temperature of 1000°C to obtain a glass shell blank. Sand blasting is carried out by using a sand blasting machine, and cutting is carried out to obtain a lead-free diode glass shell.

[0035] Experimental Example 1 Take the samples of Examples 1-3 and Comparative Examples 1-3, grind the glass shells into fine powder, sieve, dry, load into an aluminum crucible, and compact. Open the DSC, stabilize and carry out temperature and heat flow calibration, and then pass nitrogen to purge for 10 minutes to remove oxygen. Put the crucible loaded with the sample into the DSC sample chamber, and place an empty crucible on the reference side. After setting the temperature rising program, start the experiment, and collect data in real time by using the software. Three tests are carried out, and the average value is taken.

[0036] As Figure 1 shown in the table, in Examples 1-3 containing modified BiPO4, the samples show a lower glass transition starting temperature (Tg), and the temperature difference between Tg and Tc is larger, indicating higher thermal stability. The samples of Comparative Examples 1-3 lacking the component generally show lower thermal stability. The expansion coefficient of the samples of Examples 1-3 is higher than that of Comparative Examples 1-3, meaning that the material is more easily softened and flowed at a lower temperature, which indicates that the samples of Examples 1-3 play a decisive role in realizing low-temperature sealing.

[0037] Experimental Example 2 The glass shell blank was prepared, each blank was cut into a standard disc sample, the surface was ensured to be smooth and scratch-free, the sample was cleaned and dried in anhydrous ethanol to remove residues, the sample was placed in a constant temperature and humidity chamber to balance the temperature and humidity, and then placed in a dielectric strength tester, the sample was placed between the electrodes, the center of the sample was ensured to be aligned with the center of the electrodes, the tester was started, the test was performed by gradually increasing the voltage until the sample was broken down, the tester was automatically stopped and the breakdown voltage was recorded, and the test was repeated three times for each sample, and the average value was taken.

[0038] Table 1 Breakdown strength test results

[0039] As shown in Table 1 and Figure 2 , the experimental results show that the lead-free diode glass shell samples prepared by different formulations and processes have significant differences in breakdown resistance performance, the examples 1-3 containing the modified BiPO4 complex all show more excellent breakdown resistance, and the insulation performance shows an increasing trend with the increase of the amount of the complex; the comparative examples 1-3 without the modified BiPO4 all show weaker performance; in addition, the increase of the melting temperature has a synergistic enhancement effect on the samples of examples 1-3, and the above phenomena confirm that the introduction of the modified BiPO4 complex can significantly improve the breakdown resistance of the glass shell.

[0040] Experimental example 3 The glass samples in each group were cut into thin pieces, cleaned by ultrasonic cleaning in anhydrous ethanol and dried, and then placed in an etching degree tester to weigh the initial mass; the sample was completely immersed in a constant temperature sulfuric acid solution and sealed for a specified time; after taking out, it was first washed to neutral with deionized water, and then treated by ultrasonic cleaning in anhydrous ethanol and drying; after cooling, it was placed in the etching degree tester to weigh the mass after corrosion, and the corrosion weight loss rate was recorded, and the test was repeated three times for each sample, and the average value was taken.

[0041] As Figure 3 shown, in the acid corrosion experiment, the corrosion resistance of the glass samples in each group showed significant differences, the examples 1-3 added with the modified complex showed excellent acid resistance, among which example 3 showed the best corrosion resistance; the corrosion degree of comparative examples 1-3 was more obvious, among which comparative example 2 had the weakest acid resistance, and comparative example 3 was slightly better than comparative example 1, but its performance was still much lower than that of the samples of examples 1-3, which comprehensively indicated that the introduction of the modified BiPO4 complex played a key role in improving the acid resistance of the glass.

[0042] Experimental example 4 First, the sample is gradually raised to the set temperature in a high-temperature furnace and fully heat-insulated, then quickly transferred and completely immersed in a constant low-temperature water bath, the sample is taken out immediately after quenching, the surface and edge are carefully checked, and whether visible cracks or breakage and other failure phenomena occur are recorded, by repeating the test of different samples and gradually increasing the quenching starting temperature, the critical thermal shock temperature of each sample is determined, finally by comparing the critical temperatures of all samples, the difference in thermal stability is evaluated, and each test sample is repeated three times, and the average value is taken.

[0043] Table 2 Thermal shock test results

[0044] As shown in Table 2, Figure 4 and Figure 5 The critical failure temperature of the glass shell samples of Examples 1-3 gradually increased, and the thermal stability was significantly improved. The comparative examples 1-3 generally showed early failure, among which comparative example 2 failed more seriously, and comparative example 3 partially alleviated the failure but appeared local breakage. The failure of the example samples was less damaged, only producing micro-cracks, while the comparative sample generally appeared multiple cracks or structure breakage. The results showed that the examples showed significantly better thermal shock resistance than the control group, and the modified BiPO4 complex played a key role in improving the thermal stability of the lead-free glass shell.

[0045] Although embodiments of the present application have been shown and described, it is to be understood that for the purpose of the present application, the embodiments can be substantially changed without departing from the spirit and the scope of the present application, which are defined by the appended claims and their equivalents.

[0046] The above describes the present application and its embodiments, which are not restrictive, and the drawings only show one of the embodiments of the present application, and the actual structure is not limited thereto. In summary, if a person skilled in the art is inspired by it, without departing from the purpose of the present application, without creative design, similar structure and embodiments of the technical solution can be designed, which should belong to the protection scope of the present application.

Claims

1. A lead-free diode glass shell, characterized in that: The raw materials include the following parts by weight: 0.5-2 parts modified BiPO4 composite; 40-60 parts silicon dioxide; 8-22 parts boron oxide; 1-3 parts phosphorus pentoxide; 6-18 parts lithium oxide; 1-10 parts magnesium oxide; 1-10 parts calcium oxide; 1-5 parts aluminum oxide; 2-14 parts titanium dioxide; 0.8-5 parts zinc oxide; and 1-4 parts clarifying agent. The preparation method of the modified BiPO4 complex includes the following steps: Bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) was dissolved in dilute nitric acid and stirred until transparent. Phosphoric acid (H3PO4) was mixed with deionized water, and the pH was adjusted to 1.5-2.

0. The phosphorus source solution was added dropwise to the bismuth source solution, and a white flocculent precipitate was formed. The mixture was stirred at 65±5℃ and the reaction was ensured to be complete. The mixture was transferred to a high-pressure reactor. After the reaction was completed, the product was allowed to cool and then centrifuged. The product was washed three times with 50% ethanol solution and ultrasonically dispersed in polyethylene glycol (PEG-4000) for 30 minutes. The mixture was filtered through a ceramic membrane stepwise to collect the powder with a particle size of 0.3-0.8 μm. The mixture was calcined for 2 hours to obtain the modified composite.

2. The lead-free diode glass shell according to claim 1, characterized in that: The weight percentage of the dilute nitric acid solution is 4-6 wt%.

3. The lead-free diode glass shell according to claim 2, characterized in that: The phosphorus source solution is added dropwise to the bismuth source solution at a rate of 4-6 mL / min.

4. The lead-free diode glass shell according to claim 3, characterized in that: The mixture is then transferred to a high-pressure reactor, with the filling degree controlled at 60-80%.

5. The lead-free diode glass shell according to claim 4, characterized in that: The mixture is then transferred to a high-pressure reactor, with the temperature set at 160-200℃ and the reaction time at 12 hours.

6. The lead-free diode glass shell according to claim 5, characterized in that: The weight percentage of the polyethylene glycol (PEG-4000) is 0.3-0.7 wt%.

7. The lead-free diode glass shell according to claim 6, characterized in that: The ceramic membrane is used for step-by-step filtration, with the pore sizes of the ceramic membrane decreasing from 5μm, 1μm, and 0.45μm.

8. The lead-free diode glass shell according to claim 7, characterized in that: The calcination temperature is 460-500℃, and the heating rate is 3℃ / min.

9. The method for preparing a lead-free diode glass shell according to any one of claims 1-8, characterized in that: The method for preparing the glass shell of the lead-free diode is as follows: The modified BiPO4 powder and other raw materials were weighed according to weight and ultra-finely ground in anhydrous ethanol for 2 hours. The mixture was stirred and fed into an electric melting furnace and melted at a temperature of 1000-1500℃ to form a glass melt. The resulting glass melt was clarified and homogenized at a temperature of 1000-1300℃ for 20-30 minutes, and then drawn into a tube at a temperature of 600-1000℃ to obtain a glass shell blank. The blank was then sandblasted and cut to obtain a lead-free diode glass shell.

10. The method for preparing a lead-free diode glass shell according to claim 9, characterized in that: The ultrafine grinding is performed in a zirconia ball mill jar with a ball-to-material ratio of 10:1.

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