Hot-press sintering method of optical zinc sulfide dome

Abstract

A hot-pressing sintering method for an optical zinc sulfide rectifier includes the following steps: zinc sulfide powder pretreatment; loading: mixing the pretreated zinc sulfide powder with a sintering additive with a melting point lower than zinc sulfide and loading it into a mold with a thermal expansion coefficient smaller than that of polycrystalline zinc sulfide, placing it in a hot press furnace, closing the furnace, the weight of the mixed powder loaded into the mold exceeding the raw material weight required for the ideal product of the mold, the mold being pre-coated with a release agent; starting up, when the absolute pressure drops below 500 Pa, starting the heating, while continuing to evacuate to no more than 5 Pa; the first stage heating at 5-10℃ / min to the second stage heating at 300-400℃ / min. 00℃ and hold for 1-4 hours; S4, the vacuum pressure at the second stage target temperature of 300-400℃ should not exceed 5Pa; 10 minutes before the end of the second stage, pre-pressurize in a cold state to 40-60% of the process pressure; in the third stage, continue to raise the temperature to 900-1000℃ at 5-10℃ / min, hold for 30-60 minutes after reaching the temperature, raise the process pressure to 20-40MPa in 30 minutes, and finally hold for 60-120 minutes; after the holding and pressure holding are completed, release the pressure, turn off the heating, let it cool naturally, cool with the furnace to room temperature, and then remove from the furnace.

Description

Technical Field

[0001] This disclosure relates to the field of optical materials, and more specifically to a hot-pressing sintering method for an optical zinc sulfide hood. Background Technology

[0002] Currently, ZnS can be prepared using methods such as hot pressing (HP), chemical vapor deposition (CVD), and physical vapor deposition (PVD). CVD-prepared zinc sulfide exhibits good uniformity, excellent transmittance, thermal shock resistance, and rain erosion resistance, but its hardness and fracture strength are relatively low, and it requires significant equipment investment and has a low yield. Compared to CVD-prepared ZnS, HP-prepared ZnS has smaller grain size and stronger mechanical properties. Furthermore, the hot pressing method is more widely used due to its simpler equipment and lower cost compared to CVD. Hot-pressed polycrystalline zinc sulfide exhibits high transmittance and good mechanical properties in the mid-to-long wavelength range, making it an ideal material for missile fairings.

[0003] Currently, the common process for preparing hot-pressed zinc sulfide is to use a high-temperature, high-pressure, and high-vacuum method. The main process parameters used are a pressure of 150-400 MPa and a temperature of 750℃-950℃. The higher the process pressure, the higher the requirements for equipment and molds. Moreover, the fairing mold needs to be made of high-temperature alloy, which increases the manufacturing cost of the mold. The coefficient of thermal expansion of the high-temperature alloy mold is almost twice that of hot-pressed polycrystalline zinc sulfide. During the cooling process, the hot-pressed zinc sulfide fairing is easily squeezed by the mold, leading to cracking and low yield. Summary of the Invention

[0004] In view of the problems existing in the background art, one object of this disclosure is to provide a hot pressing sintering method for optical zinc sulfide hoods, which can use relatively low pressure hot pressing sintering to form optical zinc sulfide hoods.

[0005] Another objective of this disclosure is to provide a hot-pressing sintering method for optical zinc sulfide hoods, which can produce products with better mechanical properties and spectral transmission properties.

[0006] Therefore, a hot-pressing sintering method for an optical zinc sulfide hood includes the following steps:

[0007] S1, Zinc sulfide powder pretreatment: Zinc sulfide powder is loaded into a crucible container and then placed in a reduction furnace. After evacuating to remove oxygen, ammonia is introduced. The reduction furnace is heated and kept at a certain temperature. After the holding period, the ammonia is stopped, the furnace is evacuated and cooled. After natural cooling, nitrogen is introduced to atmospheric pressure, the powder is removed, and it is bagged and vacuum-sealed for later use.

[0008] S2, Loading: The pretreated zinc sulfide powder is mixed with a sintering additive with a melting point lower than that of zinc sulfide to form a mixed powder. The mixed powder is loaded into a mold with a coefficient of thermal expansion smaller than that of polycrystalline zinc sulfide. The mold filled with the mixed powder is placed in a hot press furnace. After adjusting the position, the furnace is closed. The weight of the mixed powder loaded into the mold exceeds the weight of the raw material required for the ideal product of the mold. The mold is pre-coated with a release agent on the part that contacts the mixed powder.

[0009] S3, start the hot press furnace, turn on the vacuum pump to evacuate the hot press furnace. When the absolute pressure of the hot press furnace drops below 500Pa, start the heating program of the hot press furnace, while continuing to evacuate the vacuum to no more than 5Pa. The first stage of the temperature program heats up to 300-400℃ in the second stage of the temperature program at a rate of 5-10℃ / min and holds for 1-4 hours.

[0010] S4, the vacuum pressure of the second segment of the temperature program at a target temperature of 300-400℃ should not exceed 5Pa; 10 minutes before the end of the second segment of the temperature program, start to pre-press the mold in a cold state, and the pre-press pressure should be 40-60% of the process pressure.

[0011] S5, in the third stage of the temperature program, continue to heat up to the process temperature of 900-1000℃ at a rate of 5-10℃ / min. After reaching the process temperature, hold for 30-60 minutes. Then, increase the pressure applied to the mold to the process pressure of 20-40MPa in 30 minutes. Finally, maintain at the process temperature and process pressure for 60-120 minutes.

[0012] S6. After the heat preservation and pressure holding are completed, the pressure applied to the mold is released, and the heating of the hot press furnace is turned off. The mold is allowed to cool down naturally to room temperature and then removed from the furnace.

[0013] The beneficial effects of this disclosure are as follows.

[0014] In the hot pressing sintering method of the optical zinc sulfide hood disclosed herein, the use of step S1 (zinc sulfide powder pretreatment) can improve the transmittance of the obtained polycrystalline zinc sulfide hood product.

[0015] In the hot-pressing sintering method of the optical zinc sulfide hood disclosed herein, the use of a sintering additive with a melting point lower than that of zinc sulfide in step S2 results in improved transmittance, smaller average grain size, higher Knoop hardness, and higher density of the obtained product. This is because the sintering additive greatly promotes the rearrangement, pore filling, and mass transfer processes of ZnS particles during the hot-pressing ZnS process. Under relatively low pressure, high densification of hot-pressed ZnS can be achieved, maintaining the excellent mechanical properties and spectral transmission performance of hot-pressed ZnS.

[0016] In the hot pressing sintering method of the optical zinc sulfide hood disclosed herein, the use of a mold with a smaller coefficient of thermal expansion than zinc sulfide polycrystalline in step S2 avoids the risk of low yield caused by molds with a higher coefficient of thermal expansion than zinc sulfide polycrystalline in the prior art (the product is squeezed and cracked by the mold during the cooling process).

[0017] In the hot pressing sintering method of the optical zinc sulfide hood disclosed herein, step S4 presses the powder into blocks, which can improve heat transfer, prevent the agglomeration of raw materials caused by the third stage of the temperature program in step S5, and suppress the formation of large grains.

[0018] In the hot-pressing sintering method of the optical zinc sulfide hood disclosed herein, the low process pressure of 20-40 MPa in step S5 and the 40-60% pre-pressing pressure used in step S4 allow the use of a low-tonnage vacuum hot press to prepare the hot-pressed polycrystalline zinc sulfide hood. The vacuum hot press is correspondingly cheaper, reducing costs and making it suitable for large-scale industrial production.

[0019] In the hot-pressing sintering method for optical zinc sulfide hoods disclosed herein, steps S1 to S6 together achieve a polycrystalline zinc sulfide hood product with better mechanical properties and spectral transmission performance. Attached Figure Description

[0020] Figure 1 This is a schematic assembly diagram of the mold used in the hot pressing sintering method of the optical zinc sulfide hood according to the present disclosure.

[0021] Figure 2 yes Figure 1 The exploded diagram. Detailed Implementation

[0022] The accompanying drawings illustrate embodiments of this disclosure, and it will be understood that the disclosed embodiments are merely examples of this disclosure, which can be implemented in various forms. Therefore, the specific details disclosed herein should not be construed as limiting, but are intended only as the basis for the claims and as an illustrative basis to teach those skilled in the art how to implement this disclosure in various ways.

[0023] [Hot-pressing sintering method for optical zinc sulfide radomes]

[0024] The hot-pressing sintering method for the optical zinc sulfide hood according to this disclosure includes the following steps:

[0025] S1, Zinc sulfide powder pretreatment: Zinc sulfide powder is loaded into a crucible container and then placed in a reduction furnace. After evacuating to remove oxygen, ammonia is introduced. The reduction furnace is heated and kept at a certain temperature. After the holding period, the ammonia is stopped, the furnace is evacuated and cooled. After natural cooling, nitrogen is introduced to atmospheric pressure, the powder is removed, and it is bagged and vacuum-sealed for later use.

[0026] S2, Loading: The pretreated zinc sulfide powder is mixed with a sintering additive with a melting point lower than that of zinc sulfide to form a mixed powder. The mixed powder is loaded into a mold with a coefficient of thermal expansion smaller than that of polycrystalline zinc sulfide. The mold filled with the mixed powder is placed in a hot press furnace. After adjusting the position, the furnace is closed. The weight of the mixed powder loaded into the mold exceeds the weight of the raw material required for the ideal product of the mold. The mold is pre-coated with a release agent on the part that contacts the mixed powder.

[0027] S3, start the hot press furnace, turn on the vacuum pump to evacuate the hot press furnace. When the absolute pressure of the hot press furnace drops below 500Pa, start the heating program of the hot press furnace, while continuing to evacuate the vacuum to no more than 5Pa. The first stage of the temperature program heats up to 300-400℃ in the second stage of the temperature program at a rate of 5-10℃ / min and holds for 1-4 hours.

[0028] S4, the vacuum pressure of the second segment of the temperature program at a target temperature of 300-400℃ should not exceed 5Pa; 10 minutes before the end of the second segment of the temperature program, start to pre-press the mold in a cold state, and the pre-press pressure should be 40-60% of the process pressure.

[0029] S5, in the third stage of the temperature program, continue to heat up to the process temperature of 900-1000℃ at a rate of 5-10℃ / min. After reaching the process temperature, hold for 30-60 minutes. Then, increase the pressure applied to the mold to the process pressure of 20-40MPa in 30 minutes. Finally, maintain at the process temperature and process pressure for 60-120 minutes.

[0030] S6. After the heat preservation and pressure holding are completed, the pressure applied to the mold is released, and the heating of the hot press furnace is turned off. The mold is allowed to cool down naturally to room temperature and then removed from the furnace.

[0031] In the hot pressing sintering method of the optical zinc sulfide hood disclosed herein, the use of step S1 (zinc sulfide powder pretreatment) can improve the transmittance of the obtained polycrystalline zinc sulfide hood product.

[0032] In the hot-pressing sintering method of the optical zinc sulfide hood disclosed herein, the use of a sintering additive with a melting point lower than that of zinc sulfide in step S2 results in improved transmittance, smaller average grain size, higher Knoop hardness, and higher density of the obtained product. This is because the sintering additive greatly promotes the rearrangement, pore filling, and mass transfer processes of ZnS particles during the hot-pressing ZnS process. Under relatively low pressure, high densification of hot-pressed ZnS can be achieved, maintaining the excellent mechanical properties and spectral transmission performance of hot-pressed ZnS.

[0033] In the hot pressing sintering method of the optical zinc sulfide hood disclosed herein, the use of a mold with a smaller coefficient of thermal expansion than zinc sulfide polycrystalline in step S2 avoids the risk of low yield caused by molds with a higher coefficient of thermal expansion than zinc sulfide polycrystalline in the prior art (the product is squeezed and cracked by the mold during the cooling process).

[0034] In the hot pressing sintering method of the optical zinc sulfide hood disclosed herein, step S4 presses the powder into blocks, which can improve heat transfer, prevent the agglomeration of raw materials caused by the third stage of the temperature program in step S5, and suppress the formation of large grains.

[0035] In the hot-pressing sintering method of the optical zinc sulfide hood disclosed herein, the low process pressure of 20-40 MPa in step S5 and the 40-60% pre-pressing pressure used in step S4 allow the use of a low-tonnage vacuum hot press to prepare the hot-pressed polycrystalline zinc sulfide hood. The vacuum hot press is correspondingly cheaper, reducing costs and making it suitable for large-scale industrial production.

[0036] In the hot-pressing sintering method for optical zinc sulfide hoods disclosed herein, steps S1 to S6 together achieve a polycrystalline zinc sulfide hood product with better mechanical properties and spectral transmission performance.

[0037] In one example, in step S1, the crucible container is made of a chemically stable material such as quartz, alumina, or zirconium oxide.

[0038] In one example, in step S1, the zinc sulfide powder is an infrared-grade nanoparticle with a particle size range of 500-800 nm and a purity of not less than 4N, for example, a purity of 4N.

[0039] In one example, in step S1, the purity of ammonia is not less than 4N, and the flow rate of ammonia is 10-50 L / min, for example, 20 L / min.

[0040] In one example, in step S1, the reduction furnace is heated to 200-400°C and held for 60-200 min, preferably to 300°C and held for 100 min.

[0041] In one example, in step S2, the sintering additive is selected from sulfide additives. Further, in step S2, the sulfide additive is selected from one or more of B2S3, Al2S3, and Ga2S3, preferably B2S3.

[0042] In one example, in step S2, the sintering additive accounts for 0.2-1.0 wt% of the mixed powder, preferably 0.6 wt%.

[0043] In one example, in step S2, the purity of the sintering additive is not less than 4N, preferably 4N.

[0044] In one example, in step S2, the particle size of the sintering additive is less than 5 μm.

[0045] In one example, in step S2, there should be no floating dust or lint in the working space of the loading environment to avoid contamination of the product by the dust or lint.

[0046] In one example, in step S2, the weight of the mixed powder loaded into the mold exceeds the weight of the raw material required for the ideal product of the mold by 5%-10%, preferably 8%, to compensate for the loss of powder during hot pressing.

[0047] In one example, in step S2, the mold is made of graphite, preferably with a flexural strength of not less than 60 MPa and a compressive strength of not less than 130 MPa. The cost of manufacturing graphite molds is low, eliminating the need for expensive high-temperature alloys.

[0048] like Figure 1 and Figure 2 As shown, the mold includes an upper mold, an outer mold, and a lower mold. After the upper mold, outer mold, and lower mold are assembled, a product sintering zone is formed between the convex surface of the upper mold and the concave surface of the lower mold. In step S2, the curvature of the convex surface of the upper mold, the curvature of the concave surface of the lower mold, the height, and other dimensions can be determined according to the specific dimensions of the product.

[0049] In one example, in step S2, the release agent is a liquid graphite release agent.

[0050] In one example, the mold is pre-dried and polished after the release agent is applied to the parts that come into contact with the mixed powder.

[0051] In one example, in step S3, the temperature program first segment heats up to 350-400℃ in the temperature program second segment at a rate of 10℃ / min and holds for 3-4 hours.

[0052] In one example, in step S4, a vacuum is drawn to ≤3 Pa.

[0053] In one example, in step S4, the pre-compression pressure is 15-20 MPa.

[0054] In one example, in step S5, in the third segment of the temperature program, the temperature continues to rise at a rate of 10℃ / min to the process temperature of 970-1000℃. After reaching the process temperature, the temperature is held at that process temperature for 30 minutes. Then, the pressure applied to the mold is increased to the process pressure of 30-40MPa over 30 minutes. Finally, the temperature and pressure are maintained at that process temperature and pressure for 100-120 minutes.

[0055] In one example, after the product was unloaded from the furnace, samples were taken for testing. The transmittance of the samples was 69.0-69.8% in the 3-5μm band and 73.2-74% in the 7.5-10.5μm band. The average grain size was 1.6-2μm, and the density was 4.09 g / cm³. 3 Knuckle hardness is 230-240 kg / mm². 2 .

[0056] [test]

[0057] Example 1

[0058] The hot-pressing sintering method for the optical zinc sulfide rectifier in Example 1 adopts the following steps:

[0059] S1, Zinc sulfide powder pretreatment: Zinc sulfide powder with a purity of 4N and a particle size range of 500-800nm ​​is loaded into a clean zirconium oxide crucible container, and then placed in a reduction furnace. After evacuating to remove oxygen, ammonia gas with a purity of 4N is introduced at a flow rate of 20L / min. The reduction furnace is heated to 300℃ at a rate of 10℃ / min and held for 100min. After the holding period, the ammonia gas is stopped, the furnace is evacuated and cooled. After natural cooling, nitrogen is introduced to atmospheric pressure, the powder is removed, and it is bagged and vacuum-sealed for later use.

[0060] S2, Loading: Pretreated zinc sulfide powder is mixed with B2S3 sintering additive with a purity of 4N and a particle size of less than 5µm, which has a melting point lower than zinc sulfide, to form a mixed powder. The sintering additive accounts for 0.6wt% of the mixed powder. The mixed powder is loaded into a mold made of graphite with a lower coefficient of thermal expansion than polycrystalline zinc sulfide. The graphite has a flexural strength of 65MPa and a compressive strength of 136MPa. The mold includes an upper mold, an outer mold, and a lower mold. After assembly, the upper mold, outer mold, and lower mold form a product sintering zone between the convex surface of the upper mold and the concave surface of the lower mold. First, a release agent is applied to the parts that come into contact with the mixed powder. The release agent is a liquid graphite release agent. The mold is pre-dried and polished after the release agent is applied to the parts that come into contact with the mixed powder. There should be no floating dust or cotton-like floating matter in the working space of the loading environment. The weight of the mixed powder loaded into the mold exceeds the raw material weight required for the ideal product of the mold. The weight of the mixed powder loaded into the mold is 755g, and the raw material weight required for the ideal product of the mold is 700g. The mold filled with the mixed powder is placed in the hot press furnace, and the furnace is closed after the position is adjusted.

[0061] S3, start the hot press furnace, turn on the vacuum pump to evacuate the hot press furnace. When the absolute pressure of the hot press furnace drops below 500Pa, start the heating program of the hot press furnace, while continuing to evacuate the vacuum to no more than 5Pa. The first stage of the temperature program heats up to 400℃ in the second stage of the temperature program at a rate of 10℃ / min and holds for 3 hours.

[0062] S4, the second stage of the temperature program targets a vacuum pressure of 3 Pa at a temperature of 400°C; 10 minutes before the end of the second stage of the temperature program, the mold is pre-pressed in a cold state, and the pre-pressing pressure is 50% of the process pressure, i.e., 20 MPa.

[0063] S5, in the third stage of the temperature program, continue to heat up to the process temperature of 970℃ at a rate of 10℃ / min. After reaching the process temperature, hold for 30 minutes. Then, increase the pressure applied to the mold to the process pressure of 40MPa in 30 minutes. Finally, maintain the process temperature of 970℃ and the process pressure of 40MPa for 100 minutes.

[0064] S6. After the heat preservation and pressure holding are completed, the pressure applied to the mold is released, and the heating of the hot press furnace is turned off. The mold is allowed to cool down naturally to room temperature and then removed from the furnace.

[0065] Example 2

[0066] The hot-pressing sintering method for the optical zinc sulfide rectifier in Example 2 adopts the following steps:

[0067] S1, Zinc sulfide powder pretreatment: Zinc sulfide powder with a purity of 4N and a particle size range of 500-800nm ​​is loaded into a clean zirconium oxide crucible container, and then placed in a reduction furnace. After evacuating to remove oxygen, ammonia gas with a purity of 4N is introduced at a flow rate of 20L / min. The reduction furnace is heated to 300℃ at a rate of 10℃ / min and held for 100min. After the holding period, the ammonia gas is stopped, the furnace is evacuated and cooled. After natural cooling, nitrogen is introduced to atmospheric pressure, the powder is removed, and it is bagged and vacuum-sealed for later use.

[0068] S2, Loading: Pretreated zinc sulfide powder is mixed with B2S3 sintering additive with a purity of 4N and a particle size of less than 5μm, which has a melting point lower than zinc sulfide, to form a mixed powder. The sintering additive accounts for 0.6wt% of the mixed powder. The mixed powder is loaded into a mold made of graphite with a lower coefficient of thermal expansion than polycrystalline zinc sulfide. The graphite has a flexural strength of 65MPa and a compressive strength of 136MPa. The mold includes an upper mold, an outer mold, and a lower mold. After the upper mold, outer mold, and lower mold are assembled, a product sintering zone is formed between the convex surface of the upper mold and the concave surface of the lower mold. First, a release agent is applied to the parts that come into contact with the mixed powder. The release agent is a liquid graphite release agent. The mold is pre-dried and polished after the release agent is applied to the parts that come into contact with the mixed powder. There should be no floating dust or cotton-like floating matter in the working space of the loading environment. The weight of the mixed powder loaded into the mold exceeds the raw material weight required for the ideal product of the mold. The weight of the mixed powder loaded into the mold is 755g, and the raw material weight required for the ideal product of the mold is 700g. The mold filled with the mixed powder is placed in the hot press furnace, and the furnace is closed after the position is adjusted.

[0069] S3, start the hot press furnace, turn on the vacuum pump to evacuate the hot press furnace. When the absolute pressure of the hot press furnace drops below 500Pa, start the heating program of the hot press furnace, while continuing to evacuate the vacuum to no more than 5Pa. The first stage of the temperature program heats up to 350℃ in the second stage of the temperature program at a rate of 10℃ / min and holds for 4 hours.

[0070] S4, the second stage of the temperature program targets a vacuum pressure of 350℃ to 3Pa; 10 minutes before the end of the second stage of the temperature program, the mold is pre-pressed in a cold state, and the pre-press pressure is 50% of the process pressure, i.e., 15MPa.

[0071] S5, in the third stage of the temperature program, continue to heat up to the process temperature of 1000℃ at a rate of 10℃ / min. After reaching the process temperature, hold for 30 minutes. Then, increase the pressure applied to the mold to the process pressure of 30MPa in 30 minutes. Finally, maintain the process temperature of 1000℃ and the process pressure of 30MPa for 120 minutes.

[0072] S6. After the heat preservation and pressure holding are completed, the pressure applied to the mold is released, and the heating of the hot press furnace is turned off. The mold is allowed to cool down naturally to room temperature and then removed from the furnace.

[0073] Example 3

[0074] Except that the proportion of sintering additive in the mixed powder is 0.8 wt% in step S2, the rest is the same as in Example 1.

[0075] Comparative Example 1

[0076] Except for not performing step S1, the rest is the same as in Example 1.

[0077] Comparative Example 2

[0078] Except that the proportion of sintering additive in the mixed powder is 0 wt% in step S2 (i.e. no sintering additive is added), the rest is the same as in Example 1.

[0079] Comparative Example 3

[0080] Except for the holding time of 50 minutes in step S5, the rest is the same as in Example 2.

[0081] Table 1 provides a list of parameters and product performance for Examples 1-3 and Comparative Examples 1-3. The transmittance, average grain size, Knoop hardness, and density were tested on samples after processing and taking 4 mm samples. The transmittance was tested using a Fourier transform infrared spectrometer, the average grain size was tested using a metallographic microscope after the samples were etched, the density was tested using the Archimedes method, and the Knoop hardness was tested using a hardness tester.

[0082] Table 1 lists the parameters and product performance of Examples 1-3 and Comparative Examples 1-3.

[0083]

[0084] Based on Table 1, a comparison between Comparative Example 1 and Example 1 shows that Comparative Example 1, which did not employ step S1 (zinc sulfide powder pretreatment), resulted in a product with poorer transmittance in both wavelength bands. A comparison between Comparative Example 2 and Example 1 shows that Comparative Example 2, which did not add sintering additives, resulted in a product with poorer transmittance in both wavelength bands, larger average grain size, and lower Knoop hardness and density. Furthermore, the product had more internal pores. A comparison between Comparative Example 3 and Example 2 shows that the product of Comparative Example 3 was not sintered, exhibited a porcelain white color, and was opaque.

[0085] Several exemplary embodiments have been described in detail above, but this document is not intended to limit itself to the explicitly disclosed combinations. Therefore, unless otherwise stated, the various features disclosed herein can be combined to form several other combinations, which are not shown for simplicity.

Claims

1. A hot-pressing sintering method for an optical zinc sulfide rectifier, characterized in that, Including the following steps: S1, Zinc sulfide powder pretreatment: Zinc sulfide powder is loaded into a crucible container and then placed in a reduction furnace. After evacuating to remove oxygen, ammonia is introduced. The reduction furnace is heated and kept at a certain temperature. After the holding time is completed, the ammonia supply is stopped, the furnace is evacuated and cooled. After natural cooling, nitrogen is introduced to atmospheric pressure, the powder is removed, and it is bagged and vacuum-sealed for later use. The purity of ammonia is not less than 4N, and the flow rate of ammonia is 10-50 L / min. The reduction furnace is heated to 200-400℃ and held for 60-200 min. S2, Loading: Pretreated zinc sulfide powder is mixed with a sintering additive with a melting point lower than zinc sulfide to form a mixed powder. The mixed powder is loaded into a mold with a thermal expansion coefficient smaller than that of polycrystalline zinc sulfide. The mold filled with the mixed powder is placed in a hot press furnace. After adjusting the position, the furnace is closed. The weight of the mixed powder loaded into the mold exceeds the weight of the raw material required for the ideal product of the mold. The mold is pre-coated with a release agent on the part that contacts the mixed powder. The sintering additive is selected from B2S3 and the proportion of the sintering additive in the mixed powder is 0.2-1.0 wt%. The mold is made of graphite with a bending strength of not less than 60 MPa and a compressive strength of not less than 130 MPa. The mold includes an upper mold, an outer mold and a lower mold. After the upper mold, outer mold and lower mold are assembled, a product sintering zone is formed between the convex surface of the upper mold and the concave surface of the lower mold. S3, start the hot press furnace, turn on the vacuum pump to evacuate the hot press furnace. When the absolute pressure of the hot press furnace drops below 500Pa, start the heating program of the hot press furnace, while continuing to evacuate the vacuum to no more than 5Pa. The first stage of the temperature program heats up to 300-400℃ in the second stage of the temperature program at a rate of 5-10℃ / min and holds for 1-4 hours. S4, the vacuum pressure of the second segment of the temperature program, with a target temperature of 300-400℃, should not exceed 5Pa; 10 minutes before the end of the second segment of the temperature program, start cold pre-pressing the mold, with the pre-pressing pressure being 40-60% of the process pressure; S5, in the third stage of the temperature program, continue to heat up to the process temperature of 900-1000℃ at a rate of 5-10℃ / min. After reaching the process temperature, hold for 30-60 minutes. Then, increase the pressure applied to the mold to the process pressure of 20-40MPa in 30 minutes. Finally, maintain at the process temperature and process pressure for 60-120 minutes. S6. After the heat preservation and pressure holding are completed, the pressure applied to the mold is released, and the heating of the hot press is turned off. The mold is allowed to cool down naturally to room temperature and then removed from the furnace. After the samples were removed from the furnace, they were sampled and tested. Fourier transform infrared spectroscopy was used to measure the transmittance of a 4mm thick sample: 69.0-69.8% in the 3-5μm band and 73.2-74% in the 7.5-10.5μm band. After etching, the average grain size was measured to be 1.6-2μm using a metallographic microscope, and the density was measured to be 4.09 g / cm³ using the Archimedes method. 3 The Knoop hardness, measured using a hardness tester, is 230-240 kg / mm². 2 .

2. The hot-pressing sintering method for the optical zinc sulfide rectifier according to claim 1, characterized in that, In step S1, the zinc sulfide powder is an infrared-grade nanoparticle with a particle size range of 500-800 nm and a purity of not less than 4N.

3. The hot-pressing sintering method for the optical zinc sulfide rectifier according to claim 2, characterized in that, In step S1, the purity of the zinc sulfide powder is 4N.

4. The hot-pressing sintering method for the optical zinc sulfide rectifier according to claim 1, characterized in that, In step S1, the flow rate of ammonia gas is 20 L / min; In step S1, the reduction furnace is heated to 300°C and held for 100 minutes.

5. The hot-pressing sintering method for the optical zinc sulfide rectifier according to claim 1, characterized in that, In step S2, the sintering additive accounts for 0.6 wt% of the mixed powder.

6. The hot-pressing sintering method for the optical zinc sulfide rectifier according to claim 1, characterized in that, In step S2, the release agent is a liquid graphite release agent.

7. The hot-pressing sintering method for the optical zinc sulfide rectifier according to claim 1, characterized in that, In step S3, the temperature program first segment heats up to 350-400℃ in the second segment of the temperature program at a rate of 10℃ / min and holds for 3-4 hours.

8. The hot-pressing sintering method for the optical zinc sulfide rectifier according to claim 1, characterized in that, In step S4, the vacuum is evacuated to ≤3Pa; In step S4, the applied pressure is 15-20 MPa.

9. The hot-pressing sintering method for the optical zinc sulfide rectifier according to claim 1, characterized in that, In step S5, in the third segment of the temperature program, the temperature continues to rise at a rate of 10℃ / min to the process temperature of 970-1000℃. After reaching the process temperature, the temperature is held constant for 30 minutes. Then, the pressure applied to the mold is increased to the process pressure of 30-40MPa over 30 minutes. Finally, the temperature and pressure are maintained at the process temperature and pressure for 100-120 minutes.

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