A method of oxidizing a Kovar alloy

Abstract

This invention belongs to the field of glass-metal sealing technology, specifically relating to an oxidation method for Kovar alloy. The method includes sequentially cleaning, purifying, and weighing the Kovar alloy, followed by oxidation at 700–900°C in a mixed atmosphere of dry and wet nitrogen for 20–50 minutes, and then weighing again to obtain a weight gain of 0.02–0.05 mg / cm². 2 Within the scope of this invention, the main component of the oxide film is Kovar alloy with iron oxide. By rationally controlling the oxidation process parameters, a scientific and reasonable weight gain is achieved. This not only realizes the generation of an oxide film with stable composition, uniform thickness, reasonable weight gain per unit area, and uniform color, but also improves the process repeatability, the interfacial bonding strength and airtightness between Kovar alloy and glass.

Description

Technical Field

[0001] This invention belongs to the field of glass-metal sealing technology, specifically relating to an oxidation method for Kovar alloy. Background Technology

[0002] Glass-metal sealing technology is a key process in the manufacturing of hermetically sealed connectors. Kovar alloy is an important metallic material for glass sealing, mainly used in processing the housing and leads to achieve a mating seal with the glass. The manufacturing process of glass-sealed connectors involves: first, oxidizing the Kovar alloy housing and leads; then assembling the glass insulator, metal housing, and leads onto a graphite mold; and finally, using a high-temperature fusion sealing process, sintering the metal housing, leads, and glass together to form a hermetically sealed connector.

[0003] Oxidation is a crucial step in the glass sealing process, and the sealing strength and airtightness of glass-sealed components are closely related to the oxidation process. Kovar alloy (4J29) is the most widely used metal material in glass sealing. Kovar is a type of metal expansion alloy, mainly composed of iron, nickel, and cobalt, and is well-matched with glasses such as DM-305 and DM-308; therefore, its sealing method is also called matching sealing. For a long time, airtightness has been the most important indicator in sintered glass products. Besides optimizing the component structure, the oxidation process of Kovar alloy is also a key research focus in improving product airtightness. In the glass-metal sealing process, pre-oxidation of the metal before sealing is an essential step. Because metal itself has poor wettability with glass, it is difficult to achieve a good seal. Only by oxidizing the metal at high temperature to form an oxide film on its surface, and through good wetting of the oxide film with the glass, can the metal and glass bond firmly during the sealing process. Therefore, the pre-oxidation of metal parts is the most important step in glass sealing, and the quality of the oxide film on the metal surface directly affects the sealing strength and airtightness.

[0004] In glass-to-metal sealing technology, the oxidation process of Kovar alloys has always been a research hotspot for experts and scholars both domestically and internationally. Although some progress has been made, many challenges remain. On the one hand, pre-oxidation itself plays a crucial role in improving product sealing performance. Only by thoroughly understanding pre-oxidation can the airtightness of the product be improved. In recent decades, the pre-oxidation process of Kovar alloys has continuously developed, with various oxidation methods emerging, from the initial oxidation in air to oxidation in nitrogen-hydrogen-water mixtures and saturated wet nitrogen. On the other hand, the mechanism of Kovar alloy pre-oxidation is complex, its composition is difficult to analyze accurately, and the oxide film is very thin, making accurate quantitative detection of its thickness difficult. Furthermore, effective methods for oxide film analysis and detection are lacking. Therefore, in the pre-oxidation process, effectively detecting the oxide film and achieving quantitative analysis of it is a crucial prerequisite for judging the quality of the pre-oxidation process and an important guarantee for the stability of pre-oxidation quality. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by proposing an oxidation method for Kovar alloys.

[0006] Specifically, this is achieved through the following technical solutions:

[0007] An oxidation method for Kovar alloy includes sequentially cleaning, purifying, and weighing the Kovar alloy, followed by oxidation at a temperature of 700–900°C under a moist nitrogen atmosphere for 20–50 minutes.

[0008] An oxidation method for Kovar alloy includes the following steps:

[0009] Step 1 Cleaning: Degrease and pickle the Kovar alloy parts to remove impurities adhering to the surface of the parts and obtain clean Kovar alloy.

[0010] The second step is purification: Kovar alloy is placed in a hydrogen furnace or vacuum furnace for purification treatment to remove residual impurities from the metal surface.

[0011] The third step is weighing: Weigh the purified Kovar alloy and record the weight clearly;

[0012] The fourth step is oxidation: Kovar metal is placed on the chain in the inlet area of ​​the oxidation furnace and conveyed to the high-temperature oxidation zone of the furnace for oxidation. After forming an oxide film, it is cooled and removed from the furnace.

[0013] Step 6: Weighing the oxide film: Weigh the Kovar alloy again after oxidation and record the weight clearly. Calculate the average weight gain per unit area of ​​the oxide film.

[0014] The pickling solution is prepared by mixing water, hydrochloric acid and sulfuric acid in a volume ratio of 3:1:1 to 3:1.5:1.5.

[0015] The purification process conditions are as follows: temperature 900–1050℃, holding time 20–60 min.

[0016] The oxidation process conditions are: temperature 700–900℃, time 20–50 min.

[0017] The oxidation furnace is divided into an inlet zone, a high-temperature oxidation zone, and an outlet zone. Stainless steel gas curtains are installed in the inlet and outlet zones and nitrogen is introduced for protection, which effectively prevents outside air from entering the furnace. A mixed atmosphere of dry nitrogen and wet nitrogen is introduced into the high-temperature oxidation zone.

[0018] The flow rate ratio (L / min) of dry nitrogen to wet nitrogen in the mixed atmosphere of dry nitrogen and wet nitrogen is 1:0.5 to 1:1.5.

[0019] The wet nitrogen is produced by passing dry nitrogen gas into a water tank.

[0020] The oxygen content in the high-temperature oxidation zone of the furnace is ≤50ppm.

[0021] The dew point temperature of the wet nitrogen is 0–25°C.

[0022] Beneficial effects:

[0023] This invention uses a controlled atmosphere of wet nitrogen for oxidation. The dew point of wet nitrogen is the key to controlling the oxidation reaction rate. If the dew point is too low, the oxidation reaction is slow, the oxide film is thin, and the weight gain per unit area of ​​the oxide is low. If the dew point is too high, over-oxidation will occur, the oxide film will turn red, and it may even peel off from the metal substrate, exhibiting a peeling phenomenon. Therefore, it is detrimental to the strength of the subsequent metal-glass sealing and the airtightness of the product.

[0024] This invention effectively achieves qualitative and quantitative analysis of oxide films. Specifically: 1. This invention employs high-temperature oxidation, i.e., an oxidation temperature greater than 700℃. Based on the oxidation reaction mechanism of iron and water vapor under high-temperature conditions, below 570℃, the main oxidation product of the reaction between iron and water vapor is ferrous oxide, while above 570℃, the main product is iron(III) oxide (Fe3O4). Verification shows that the ferrous oxide oxide film produced by low-temperature oxidation is thinner, with a weight gain per unit area of ​​<0.02 mg / cm². 2 This fails to meet the sealing process requirements and is detrimental to improving the product's airtightness. Weight gain per unit area > 0.05 mg / cm². 2 If the oxide film is too thick, more bubbles will form at the glass-metal sealing interface, which is detrimental to improving the sealing strength. Furthermore, the high-temperature oxidation product, iron(III) oxide film, is relatively stable, with a significant increase in thickness, and a weight gain per unit area of ​​0.02–0.05 mg / cm². 2 Within this range, it is applicable to weighing calculations using high-precision analytical balances with a weighing accuracy of 0.1 mg. A thicker oxide film is beneficial for improving the sealing strength between glass and metal, significantly enhancing the airtightness of the product. 2. The Kovar alloy parts oxidized using this invention have an oxide film whose main component is iron(III) oxide (Fe3O4). The valence of iron can be detected using potassium permanganate and potassium thiocyanate solution titration, which is beneficial for the qualitative analysis of the oxide film.

[0025] This invention, by rationally controlling process parameters such as oxidation temperature and wet nitrogen dew point temperature, forms an oxide film with stable composition, uniform thickness, reasonable weight gain per unit area, and uniform color. It not only has good process repeatability, but also improves the interfacial bonding strength and airtightness of subsequent sealing, thereby increasing the overall product qualification rate. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in further detail below, but the present invention is not limited to these embodiments. Any improvements or substitutions based on the basic spirit of these embodiments shall still fall within the scope of protection claimed by the claims of the present invention.

[0027] Examples 1-5

[0028] An oxidation method for Kovar alloy, specifically for oxidizing small pin-type parts, includes the following steps:

[0029] Step 1 Cleaning: The Kovar alloy parts are degreased using a water-based degreasing agent, and then pickled to remove impurities adhering to the surface of the parts, resulting in a clean Kovar alloy. The pickling solution is prepared by mixing water, hydrochloric acid and sulfuric acid in a volume ratio of 3:1:1.

[0030] The second step of purification: The cleaned Kovar alloy is placed in a vacuum furnace and kept at 950°C for 30 minutes to remove residual impurities from the metal surface.

[0031] The third step is weighing: Weigh the purified Kovar alloy and record the weight accurately;

[0032] Step 4: Plating: Spread the weighed Kovar alloy evenly in a breathable stainless steel box, placing two layers;

[0033] Fifth step of oxidation: The metal box containing Kovar alloy is placed on the chain in the inlet area of ​​the oxidation furnace and conveyed to the high-temperature oxidation zone of the furnace through the chain. After oxidation for 30 minutes under the condition of oxygen content of 30 ppm, it is conveyed into the outlet area by the chain for cooling and then removed from the furnace.

[0034] In this embodiment, the oxidation furnace is divided into an inlet zone, a high-temperature oxidation zone, and an outlet zone. Stainless steel gas curtains are installed in both the inlet and outlet zones, and nitrogen is introduced for protection, effectively preventing outside air from entering the furnace. A mixed atmosphere of dry and wet nitrogen is introduced into the high-temperature oxidation zone, with a flow rate (L / min) ratio of dry to wet nitrogen of 1:0.7. The wet nitrogen is obtained by introducing dry nitrogen into a water tank. The dew point temperature of the wet nitrogen is 10°C.

[0035] Step 6: Weighing the oxide film: Weigh the Kovar alloy again after oxidation and record the weight clearly. Calculate the average weight gain per unit area of ​​the oxide film.

[0036] The difference between Examples 1-5 lies in the oxidation temperature. The oxidation temperature and the weight gain per unit area of ​​the oxide film are shown in Table 1. Furthermore, Examples 1-5 were sealed using traditional sealing methods after oxidation, and the leakage rate of the products was detected at room temperature using a helium mass spectrometer, as shown in Table 1.

[0037] Table 1. Effect of different oxide film weight gain on product leakage rate

[0038]

[0039]

[0040] Note 1: The lower the product leakage rate, the better the product's airtightness.

[0041] Note 2: The traditional sealing method involves assembling the contact and the oxidized part on a sintering mold, then placing the DM-305 glass blank into the gap between the contact and the oxidized part, and then placing it in a sintering furnace. The furnace is then sintered at 950°C for 25 minutes under a high-purity nitrogen atmosphere (purity ≥99.99%). After sintering, the glass is slowly cooled to room temperature to obtain the glass-sealed product.

[0042] Examples 6-10

[0043] An oxidation method for Kovar alloy, specifically for oxidizing a large outer shell, includes the following steps:

[0044] Step 1 Cleaning: The Kovar alloy parts are degreased using a water-based degreasing agent, followed by pickling to remove impurities adhering to the surface of the parts, resulting in a clean Kovar alloy surface; the pickling solution is prepared by mixing water, hydrochloric acid and sulfuric acid in a volume ratio of 3:1.5:1.5.

[0045] The second step of purification: The cleaned Kovar alloy is placed in a vacuum furnace and kept at 1000℃ for 50 minutes to remove residual impurities from the metal surface.

[0046] The third step is weighing: Weigh the purified Kovar alloy and record the weight accurately;

[0047] Step 4: Plating: Spread the weighed Kovar alloy evenly in a breathable stainless steel box, placing two layers;

[0048] Fifth step of oxidation: The metal box containing Kovar alloy is placed on the chain in the inlet area of ​​the oxidation furnace and conveyed to the high-temperature oxidation zone of the furnace through the chain. After oxidation for 40 minutes at a temperature of 900℃ and an oxygen content of 40ppm, it is conveyed into the outlet area by the chain for cooling and then removed from the furnace.

[0049] In this embodiment, the oxidation furnace is divided into an inlet zone, a high-temperature oxidation zone, and an outlet zone. Stainless steel air curtains are installed in both the inlet and outlet zones and nitrogen is introduced for protection, effectively preventing outside air from entering the furnace. A mixed atmosphere of dry nitrogen and wet nitrogen is introduced into the high-temperature oxidation zone, wherein the flow rate (L / min) ratio of dry nitrogen to wet nitrogen is 1:1, and the wet nitrogen is obtained by introducing dry nitrogen into a water tank.

[0050] Step 6: Weighing the oxide film: Weigh the Kovar alloy again after oxidation and record the weight clearly. Calculate the average weight gain per unit area of ​​the oxide film.

[0051] The difference between Examples 6-10 lies in the wet nitrogen dew point temperature. The wet nitrogen dew point temperature and the weight gain per unit area of ​​the oxide film are shown in Table 1. Meanwhile, Examples 1-5 were sealed using traditional sealing methods after oxidation, and the product leakage rate was detected at room temperature using a helium mass spectrometer leak detector, as shown in Table 1.

[0052] Table 2. Effects of different dew points on oxide film and product leakage rate.

[0053]

[0054] Note 1: The lower the product leakage rate, the better the product's airtightness.

[0055] Note 2: The traditional sealing method involves assembling the contact and the oxidized part on a sintering mold, then placing the DM-305 glass blank into the gap between the contact and the oxidized part, and then placing it in a sintering furnace. The furnace is then sintered at 1000℃ under a high-purity nitrogen atmosphere (purity ≥99.99%) for 20 minutes. After sintering, the glass is slowly cooled to room temperature to obtain the glass-sealed product.

[0056] Example 11

[0057] An oxidation method for Kovar alloy, specifically for oxidizing large substrate-type parts, includes the following steps:

[0058] Step 1 Cleaning: The Kovar alloy parts are degreased using a water-based degreasing agent, and then pickled to remove impurities adhering to the surface of the parts, resulting in a clean Kovar alloy. The pickling solution is prepared by mixing water, hydrochloric acid and sulfuric acid in a volume ratio of 3:1:1.

[0059] The second step of purification: The cleaned Kovar alloy is placed in a vacuum furnace and kept at 1050℃ for 60 minutes to remove residual impurities from the metal surface.

[0060] The third step is weighing: Weigh the purified Kovar alloy and record the weight accurately;

[0061] Step 4: Plating: Spread the weighed Kovar alloy evenly in a breathable stainless steel box, one layer at a time;

[0062] Fifth step of oxidation: The metal box containing Kovar alloy is placed on the chain in the inlet area of ​​the oxidation furnace and conveyed to the high-temperature oxidation zone of the furnace through the chain. After oxidation for 50 minutes at a temperature of 850℃ and an oxygen content of 10ppm, it is conveyed into the outlet area by the chain for cooling and then removed from the furnace.

[0063] In this embodiment, the oxidation furnace is divided into an inlet zone, a high-temperature oxidation zone, and an outlet zone. Stainless steel gas curtains are installed in both the inlet and outlet zones, and nitrogen is introduced for protection, effectively preventing outside air from entering the furnace. The high-temperature oxidation zone is circulated with a mixed atmosphere of dry nitrogen and saturated wet nitrogen that has been passed through water. The flow rate (L / min) ratio of dry nitrogen to wet nitrogen is 1:1.5, and the wet nitrogen is obtained by introducing dry nitrogen into a water tank. The dew point temperature of the wet nitrogen is 20°C.

[0064] Step 6: Weighing the oxide film: Weigh the Kovar alloy again after oxidation and record the weight clearly. Calculate the average weight gain per unit area of ​​the oxide film.

Claims

1. A method of oxidizing a Kovar alloy, characterized by, Includes the following steps: Step 1 Cleaning: Degrease and pickle the Kovar alloy parts to remove impurities adhering to the surface of the parts and obtain clean Kovar alloy. The second step is purification: Kovar alloy is placed in a hydrogen furnace or vacuum furnace for purification treatment to remove residual impurities from the metal surface. The third step is weighing: Weigh the purified Kovar alloy and record the weight clearly; Step 4: Oxidation: Kovar alloy is placed on a chain in the inlet area of ​​the oxidation furnace and conveyed to the high-temperature oxidation zone of the furnace for oxidation. After forming an oxide film, it is cooled and removed from the furnace. The oxidation process conditions are: temperature 700-900℃, time 20-50min. Step 5: Weighing the oxide film: Weigh the Kovar alloy again after oxidation and record the weight clearly. Calculate the average weight gain per unit area of ​​the oxide film. The average weight gain per unit area of ​​the oxide film is controlled at 0.02-0.05 mg / cm². 2 ; The oxidation furnace is divided into an inlet zone, a high-temperature oxidation zone, and an outlet zone. Stainless steel gas curtains are installed in both the inlet and outlet zones, and dry nitrogen is introduced for protection. A mixed atmosphere of dry nitrogen and wet nitrogen is introduced into the high-temperature oxidation zone. The flow ratio of dry nitrogen to wet nitrogen in the mixed atmosphere is 1:0.5 to 1:1.

5. The oxygen content in the high-temperature oxidation zone of the furnace is ≤50ppm; The dew point temperature of the wet nitrogen gas is 0–25°C.

2. The method of oxidizing a Kovar alloy according to claim 1, wherein The pickling solution is prepared by mixing water, hydrochloric acid and sulfuric acid in a volume ratio of 3:1:1 to 3:1.5:1.

5.

3. The method of oxidizing a Kovar alloy of claim 1, wherein, The purification process conditions are as follows: temperature 900–1050℃, holding time 20–60 min.

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