Method for preparing fine-grained ceramic by preformed metal conductor switch-regulated flash-off outside the furnace

Abstract

The application relates to a method for preparing fine-grain ceramic by pre-preparing metal conductor switch control out-of-furnace flash, comprising the following steps: pre-preparing a metal conductor with a preset width on the surface of a blank by using a metal slurry by screen printing and solidifying to obtain a ceramic green body with a pre-prepared metal conductor; placing the ceramic green body in air, setting electrodes at both ends of the ceramic green body, and connecting to a power supply through the conductor; turning on the power supply, adjusting the current size to control the size of the Joule, controlling the temperature rising speed and the peak temperature; when the metal conductor is fused, automatically switching to the target voltage value of the set power supply, keeping the constant current value for a target time length after the current of the ceramic green body climbs to the target current density value, and turning off the power supply to obtain dense fine-grain ceramic. The application prepares a metal conductor on the surface of a ceramic blank by screen printing, and since the metal conductor has a melting point, it will be fused, at which time the ceramic sample under high-temperature excitation can realize flash at a lower voltage to prepare fine-grain ceramic.

Description

Technical Field

[0001] This invention belongs to the field of ceramic sintering technology, specifically relating to a method for preparing fine-grained ceramics by controlling flash sintering outside the furnace with a pre-fabricated metal wire switch. Background Technology

[0002] The structure of a material determines its properties. Compared with traditional polycrystalline ceramics, fine-grained ceramics with significantly refined grains exhibit significantly improved properties, displaying higher strength, hardness, and toughness, enhanced diffusivity, higher coefficient of thermal expansion, lower thermal conductivity, higher resistivity, and superior soft magnetic properties. Controlling grain growth and achieving sufficient densification during sintering is key to obtaining high-density and fine-grained ceramic materials. Densification and grain growth, these two fundamental sintering behaviors, share the same thermodynamic driving force and compete with each other. They can only be distinguished by controlling the sintering process and utilizing their kinetic differences. Increasing the sintering rate is the most common and effective method.

[0003] Commonly used rapid sintering techniques include microwave sintering, spark plasma sintering, and flash sintering. Spark plasma sintering utilizes high-temperature plasma generated by a large current to sinter materials while simultaneously applying additional pressure. It has advantages such as rapid heating rate and short sintering time, but also suffers from problems such as uneven densification of the sintered body. Microwave sintering utilizes the heat released from the interaction between microwaves and the material to rapidly heat the material and complete the sintering process. It features a rapid heating rate, but this method is selective in its application, requiring materials that absorb microwaves for optimal results, thus having certain limitations.

[0004] The novel rapid heating flash sintering technology utilizes electric field-assisted sintering technology to apply appropriate AC or DC voltages to both ends of the ceramic green body, thereby creating a conductive path within the green body. Under the action of Joule heating, the sample is highly densified within a few seconds to a few minutes. It has advantages such as rapid heating, activation of particle surface, and flexible process adjustment. Numerous studies have shown that it can promote densification and inhibit grain growth, making it very suitable for the sintering of structural ceramic materials.

[0005] However, existing flash calcination techniques are still limited by the furnace; the activation temperature of flash calcination depends on traditional furnace heating, which places certain demands on the experimental site and equipment. Furthermore, the slow heating rate of the sample before flash calcination inevitably leads to problems such as grain growth and the volatilization of low-melting-point elements. To achieve flash calcination without furnace heating, many researchers have developed room-temperature flash calcination techniques through various pathways. For example, room-temperature flash calcination of zinc oxide is achieved by generating a high-temperature electric arc under ultra-high pressure. Another method involves adding ethanol to the preform, utilizing ethanol volatilization to promote the generation of a high-temperature electric arc under high pressure, which rapidly Joule-heats the sample to obtain a dense preform. Additionally, water-assisted high-voltage room-temperature conduction is used to Joule-heat zinc oxide preforms. Still another method involves adding graphene to the preform to assist in constructing internal thermal conductivity pathways, achieving room-temperature flash calcination for the preparation of graphene composite ceramic materials.

[0006] In existing technologies, the preparation of fine-grained ceramics using high-voltage flash calcination at room temperature places high demands on high-voltage equipment. Furthermore, the high-temperature electric arc generated by the high voltage poses significant safety hazards and can easily cause personal injury. Using liquid (water or ethanol)-assisted room-temperature flash calcination results in voids due to liquid evaporation, making it difficult to obtain highly dense and strong fine-grained ceramics. Adding graphene to the green body to assist in constructing internal thermally conductive pathways is helpful for graphene-toughened composite materials, but it is not suitable for the preparation of highly insulating ceramic materials. Summary of the Invention

[0007] Based on the aforementioned shortcomings and deficiencies in the prior art, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide a method for preparing fine-grained ceramics by prefabricated metal wire switch control in a furnace flash firing process that meets one or more of the aforementioned requirements.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A method for preparing fine-grained ceramics by controlling flash sintering outside a furnace with a pre-fabricated metal wire switch includes the following steps:

[0010] (1) A pre-fabricated metal wire with a preset width is pre-fabricated on the surface of the green body using screen printing and then cured to obtain a ceramic green body with pre-fabricated metal wire; the ceramic green body with pre-fabricated metal wire is placed in the air, and electrodes are set at both ends of the ceramic green body and connected to the power source through wires.

[0011] (2) Turn on the power supply, adjust the current to control the Joule size, and control the temperature rise rate and peak temperature;

[0012] (3) When the metal wire melts, it automatically switches to the target voltage value set by the power supply. After the current of the ceramic green body rises to the target current density value, the constant current value is maintained for the target duration, and the power supply is turned off to obtain dense fine-grained ceramic.

[0013] As a preferred embodiment, the metal paste is a platinum paste, a silver paste, or a tin paste.

[0014] As a preferred embodiment, in step (1), the curing temperature is 60-600℃.

[0015] As a preferred option, in step (1), the preset width is 0.2-1.2mm.

[0016] As a preferred embodiment, in step (2), the adjustable range of the current is 0.1-50A.

[0017] As a preferred embodiment, in step (2), the temperature rise rate is 10-200℃ / s, and the peak temperature is determined according to the melting point of the metal wire.

[0018] As a preferred embodiment, in step (3), the target current density value is 100–1000 mA / mm². 2 The target voltage is 50–300 V / cm.

[0019] As a preferred option, in step (3), the target duration is 30 to 180 seconds.

[0020] As a preferred embodiment, the embryo is in the shape of a strip, a round piece, or a dog bone.

[0021] As a preferred embodiment, the powder used for the preform is titanium dioxide, zinc oxide, vanadium oxide, cerium oxide, aluminum oxide, barium titanate, potassium sodium niobate, or sodium bismuth titanate.

[0022] Compared with the prior art, the beneficial effects of this invention are:

[0023] This invention utilizes screen printing to prepare metal wires on the surface of ceramic blanks. The temperature of the ceramic blank is rapidly increased by heating the pre-made metal wires with an external power source. Since the pre-made metal wires have a certain melting point, they will melt and break when the temperature reaches a certain value. At this time, the ceramic sample under high temperature excitation can achieve flash firing at a lower voltage to prepare fine-grained ceramics.

[0024] By adjusting the type of metal in the metal wire (such as low-melting-point tin and high-melting-point silver) and the width of the wire (according to Joule's law, the thinner the wire, the greater its resistance, and the greater its Joule heat under the same current), the peak temperature and temperature rise rate of the sample can be adjusted; rapid heating of the metal wire can also ensure that the ceramic grains do not grow before flash burning occurs and avoid the volatilization of low-melting-point elements. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the prefabricated metal wire switch-controlled furnace flash firing method for preparing fine-grained ceramics according to Embodiment 1 of the present invention;

[0026] Figure 2 This is a SEM image of the fine-grained zinc oxide ceramic prepared in Example 1 of the present invention. Detailed Implementation

[0027] To more clearly illustrate the embodiments of the present invention, specific implementation methods will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0028] Example 1:

[0029] This embodiment utilizes low-melting-point tin wires to flash-fire zinc oxide ceramic. The specific process is as follows:

[0030] (1) Pressing the green body;

[0031] Polyvinyl alcohol (PVA) was added to deionized water to prepare a 10 wt% binder. Nano zinc oxide powder was mechanically mixed with the binder and dried. 0.5 g of the dried mixture was added to a mold and pressed into a dog bone shape under a pressure of 300 MPa. The dimensions of the blank were 20 × 3 × 2 mm. 3 .

[0032] (2) Degumming treatment;

[0033] The pressed green body is placed in a muffle furnace, heated to 400°C at a heating rate of 2°C / min, held at that temperature for 2 hours, and then cooled with the furnace to obtain a ceramic green body.

[0034] (3) Coating electrodes;

[0035] To reduce the contact resistance between the ceramic green body and the circuit, high-temperature silver paste was applied to both ends of the ceramic green body and then baked at 500°C for 10 minutes to cure the silver paste.

[0036] (4) Pre-formed tin wire;

[0037] A thin line, 1 mm wide, is coated between two electrodes using screen printing of solder paste and then dried in a 60°C oven to obtain the desired result. Figure 1 The screen-printed conductor shown.

[0038] (5) such as Figure 1 As shown, the ceramic green body is connected to an AC power source with a copper wire (i.e., a conductor) with a radius of 0.5 mm in preparation for flash firing.

[0039] (6) Under room temperature conditions, after turning on the power switch, the preset voltage value is 400V (electric field strength is 200V / cm) and the current value is 0.6A (current density is 100mA / mm). 2 After the start button is pressed, the current stabilizes at 0.6A. At this point, the tin wire continues to heat up under the influence of the current, while the billet temperature rises at a rate of 50℃ / s to a peak temperature of 250℃. After one minute of continuous application of the 0.6A current, some sections of the tin wire melt into spherical shapes due to heat, causing the wire to break, the current to disappear, and the voltage across the billet returns to 400V. At this point, under the conditions of 250℃ and 400V, the current rapidly increases at a rate of 10mA / s, eventually reaching the preset value of 0.6A and entering a stable period, thus entering the current control mode. This state is maintained for 30 seconds to achieve material densification, thus realizing the sintering of the zinc oxide ceramic material.

[0040] like Figure 2 As shown, the zinc oxide sintered at room temperature in this embodiment has high density and a grain size in the range of 1-3 μm.

[0041] Example 2:

[0042] This embodiment utilizes low-to-medium melting point silver wires for flash sintering of titanium dioxide ceramics. The specific process is as follows:

[0043] (1) Pressing the green body;

[0044] Polyvinyl alcohol (PVA) was added to deionized water to prepare a 10 wt% binder. Nano-anatase titanium dioxide powder was mechanically mixed with this binder and dried. 0.4 g of the dried mixture was added to a mold and pressed into a dog-bone shape under 300 MPa pressure. The dimensions of the blank were 20 × 3 × 2 mm. 3 .

[0045] (2) Degumming treatment;

[0046] The pressed green body is placed in a muffle furnace and heated to 400°C at a heating rate of 2°C / min. It is then held at that temperature for 2 hours and cooled with the furnace.

[0047] (3) Coating electrodes;

[0048] To reduce the contact resistance between the ceramic green body and the circuit, high-temperature silver paste is applied to both ends of the ceramic green body;

[0049] (4) Prefabricated silver conductors;

[0050] A thin line, 0.5 mm wide, was coated between the two electrodes using screen printing silver paste, and then baked at 500°C for 10 minutes to cure the silver paste.

[0051] (5) Connect the titanium dioxide green blank to the AC power supply with a copper wire with a radius of 0.5 mm in preparation for flash firing.

[0052] (6) Under room temperature conditions, after turning on the power switch, the preset voltage value is 500V (electric field strength is 250 V / cm) and the current value is 1.2A (current density is 200mA / mm). 2 After the start button is pressed, the current stabilizes at 1.2A. At this time, the silver wires continuously heat up under the influence of the current, while the temperature of the billet rises at a rate of 100℃ / s to a peak temperature of approximately 800℃. After the 1.2A current is applied for one minute, some sections of the silver wires oxidize, shrink, and melt under the influence of heat, the current disappears, and the voltage across the billet returns to 500V. At this point, under the conditions of approximately 800℃ and 500V, the current rapidly increases at a rate of 10mA / s, eventually reaching the preset value of 1.2A and entering a stable period, thus entering the current control mode. This state is maintained for 60 seconds to achieve material densification, realizing the sintering of the titanium dioxide ceramic material.

[0053] Example 3:

[0054] This embodiment utilizes high-melting-point platinum wires to flash-fire alumina ceramics. The specific process is as follows:

[0055] (1) Pressing the embryo;

[0056] Polyvinyl alcohol (PVA) was added to deionized water to prepare a 10 wt% binder. Nano-alumina powder was mechanically mixed with this binder and dried. 0.4 g of the dried mixture was added to a mold and pressed into a dog bone shape under 300 MPa pressure. The dimensions of the blank were 20 × 3 × 2 mm. 3 .

[0057] (2) Degumming treatment;

[0058] The pressed green body is placed in a muffle furnace and heated to 400°C at a heating rate of 2°C / min. It is then held at that temperature for 2 hours and cooled with the furnace.

[0059] (3) Coating electrodes;

[0060] To reduce the contact resistance between the ceramic green body and the circuit, high-temperature silver paste is applied to both ends of the ceramic green body;

[0061] (4) Prefabricated platinum conductors;

[0062] A thin line, 0.3 mm wide, was coated between the two electrodes using screen printing platinum paste, and then cured by baking at 600°C for 10 minutes.

[0063] (5) Connect the aluminum oxide green billet to the AC power supply with a copper wire with a radius of 0.5 mm in preparation for flash firing.

[0064] (6) Under room temperature conditions, after turning on the power switch, the preset voltage value is 600V (electric field strength is 300V / cm) and the current value is 2.4A (current density is 400mA / mm). 2 After the start button is pressed, the current stabilizes at 2.4A. At this point, the platinum wires continuously heat up under the current, while the billet temperature rises at a rate of 200℃ / s to a peak temperature of approximately 1100℃. After about one minute of continuous application of the 2.4A current, some of the platinum wires oxidize, shrink, and melt under heat, the current disappears, and the voltage across the billet returns to 600V. At this point, under the conditions of approximately 1100℃ and 600V, the current rapidly increases at a rate of 10mA / s, eventually reaching the preset value of 2.4A and entering a stable period, thus entering the current control mode. This state is maintained for 120 seconds to achieve material densification, thus realizing the sintering of the alumina ceramic material.

[0065] Given that there are numerous embodiments of the present invention, and the raw materials and quantities involved can be selected within a limited range according to actual needs, and that the experimental data for each embodiment are extensive and numerous, it is not suitable to list and describe them one by one here. However, the content to be verified and the final conclusions obtained in each embodiment are similar. Therefore, the verification content of each embodiment will not be described one by one here.

[0066] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing fine-grained ceramics by a preformed metal conductor switch-regulated flame flash outside a furnace, characterized by The method comprises the following steps: (1) using silk screen printing to preform metal wires with a preset width of 0.2-1.2 mm on the surface of a green body by using a metal paste and curing to obtain a ceramic green body preformed with metal wires; placing the ceramic green body preformed with metal wires in air, setting electrodes at both ends of the ceramic green body, and connecting to a power supply through the metal wires; wherein the green body is in a strip shape or a dog bone shape, the powder used in the green body is titanium dioxide, zinc oxide or aluminum oxide, and the metal paste is platinum paste, silver paste or tin paste; (2) turning on the power supply, adjusting the current size to control the size of Joule heat, controlling the temperature rising speed and the peak temperature; wherein the temperature rising speed is 10-200 ℃ / s, and the peak temperature is determined according to the melting point of the metal wires; (3) When the metal wire is fused, the target voltage value of the set power supply is automatically switched, and the current value of the ceramic green body is clamped to the target current density value, and the constant current value is maintained for a target time, and the power supply is turned off to obtain a dense fine-grained ceramic; wherein the target current density value is 100-1000 mA / mm 2 , and the target voltage is 50-300 V / cm.

2. The method of claim 1, wherein, in the step (1), the curing temperature is 60-600 ℃.

3. The method of claim 1, wherein, in the step (2), the adjustable range of the current is 0.1-50 A.

4. The method of claim 1, wherein, in the step (3), the target time length is 30-180 s.

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