A method for sintering fine-grained zinc oxide ceramics based on room temperature flash firing.

Abstract

This invention relates to a method for sintering fine-grained zinc oxide ceramics based on room temperature flash firing, comprising the following steps: (1) placing a zinc oxide ceramic green body in room temperature air and spraying a layer of black insulating material onto the surface of the green body; setting positive and negative electrodes at both ends of the ceramic green body, and connecting the positive and negative electrodes to a power source via wires; the ceramic green body is also wrapped with a black insulating material; (2) turning on the power source and increasing the voltage until the ceramic green body generates a microcurrent at the milliampere level, then keeping the voltage constant, and under the Joule heating and heat preservation effect of the microcurrent, the temperature of the ceramic green body continuously rises; (3) when the temperature of the ceramic green body rises to the target temperature, further increasing the voltage to make the current of the ceramic green body climb to the target current density value, maintaining the target time and then turning off the power source to obtain fine-grained zinc oxide ceramics. Compared with traditional low-voltage flash firing of zinc oxide, this invention does not require heating the furnace body to provide the excitation temperature, avoiding the cumbersome experimental equipment and operation process.

Description

Technical Field

[0001] This invention belongs to the field of ceramic sintering technology, specifically relating to a method for sintering fine-grained zinc oxide ceramics based on room temperature flash sintering. Background Technology

[0002] Currently, ceramic materials, with their excellent mechanical strength, insulation properties, and high-temperature resistance, demonstrate broad application and development prospects, making them indispensable key materials in modern society and construction. The manufacturing of ceramic materials is still mainly based on traditional sintering. Traditional sintering processes involve high sintering temperatures and long sintering times, leading to grain growth and significant energy consumption. Therefore, finding methods for rapid densification of ceramic blanks is crucial. To reduce energy consumption during ceramic sintering, various novel sintering processes, such as flash sintering, microwave sintering, and electric discharge plasma sintering, have been proposed and put into practical application.

[0003] Flash sintering is a novel ceramic sintering method that involves applying appropriate AC or DC voltages to both ends of a ceramic green body, enabling it to achieve high densification within seconds to minutes. This short sintering time and relatively low furnace temperature mean that flash sintering significantly reduces energy consumption compared to traditional sintering processes. Research has found that during the initial furnace heating of the sample before flash sintering, the sample absorbs only a limited amount of heat, with most of it dissipated within the furnace space, resulting in energy waste. However, current flash sintering technologies are still limited by the heating furnace; only a few high-conductivity green body systems can directly apply heat to the sample, achieving room-temperature flash sintering and reducing energy loss.

[0004] To achieve room temperature flash calcination for the preparation of fine-grained ceramics, existing technologies employ methods such as generating a high-temperature electric arc under ultra-high pressure to perform room temperature flash calcination of zinc oxide, or increasing the electrical conductivity of the powder to enable rapid Joule heating of the sample by titanium dioxide powder under room temperature and high pressure conditions to obtain a dense preform. Additionally, water-assisted high-voltage room temperature conduction is used to perform Joule heating of zinc oxide preforms.

[0005] However, the preparation of fine-grained ceramics using high-voltage flash calcination at room temperature places high demands on the high-voltage equipment, and the high-temperature electric arc generated by the high voltage poses a significant safety hazard, easily causing personal injury. Using liquid-assisted (water or ethanol) room-temperature flash calcination, due to the voids left by the liquid's evaporation, makes it difficult to obtain highly dense and strong fine-grained ceramics. Using intrinsically highly conductive powders for room-temperature flash calcination alters the ceramic's intrinsic high insulating properties. Summary of the Invention

[0006] 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 room temperature flash sintering method for zinc oxide fine-grained ceramics that satisfies one or more of the aforementioned requirements.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A method for sintering fine-grained zinc oxide ceramics based on room temperature flash calcination includes the following steps:

[0009] (1) The zinc oxide ceramic green body is placed in room temperature air and a layer of black insulating material is sprayed on the surface of the green body; positive and negative electrodes are set at both ends of the ceramic green body, and the positive and negative electrodes are connected to the power supply through wires; the ceramic green body is also wrapped with black heat-insulating material as a sleeve.

[0010] (2) Turn on the power supply and increase the voltage until the ceramic green body generates a microcurrent in the milliampere range. Then keep the voltage constant. Under the Joule heating and heat preservation effect of the microcurrent, the temperature of the ceramic green body continues to rise.

[0011] (3) After the temperature of the ceramic green body rises to the target temperature, the voltage is further increased so that the current of the ceramic green body climbs to the target current density value. After maintaining the target time, the power is turned off to obtain zinc oxide fine-grained ceramic.

[0012] As a preferred embodiment, step (3) specifically includes:

[0013] Once the current reaches the target current density value, the power supply switches from voltage control mode to current control mode, maintains the target duration, and then shuts down.

[0014] As a preferred embodiment, the target temperature is 150–200°C.

[0015] As a preferred embodiment, the target current density value is controlled to be 100–1000 mA / mm². 2 .

[0016] As a preferred embodiment, the target duration is 30–180 seconds.

[0017] As a preferred embodiment, in step (2), the electric field strength of the voltage applied to the ceramic green body is adjusted within the range of 50 to 300 V / cm.

[0018] As a preferred embodiment, in step (1), the black insulating material is one of insulating carbon black, insulating rubber, or black polyurethane.

[0019] As a preferred option, in step (1), the black insulation material is one of black glass wool, rock wool, mineral wool, or extruded polystyrene.

[0020] As a preferred embodiment, in step (1), the electrode is one of a platinum electrode, a silver electrode, or a copper electrode.

[0021] As a preferred embodiment, the ceramic green body is in the shape of a round sheet, a strip, or a dog bone.

[0022] As a preferred embodiment, the ceramic green body is prepared by granulation, pressing, debinding, and pre-firing, and the binder used in granulation is polyvinyl alcohol.

[0023] Compared with the prior art, the beneficial effects of this invention are:

[0024] Based on the semiconductor properties of zinc oxide, when the voltage is within a certain range during external electric field treatment, a certain amount of microcurrent (mA level) will accumulate. According to Joule's law, the process of continuous microcurrent action is the process of continuous Joule heat generation. In the traditional low-voltage flash burning process of zinc oxide materials, a heating furnace is usually used to provide a certain excitation temperature. In this process, the heat absorbed by the sample is limited, and most of it is dissipated by the furnace space, resulting in a certain amount of energy waste. At the same time, furnace heating makes the experimental setup and process cumbersome.

[0025] Compared with traditional low-voltage flash zinc oxide, this invention does not require heating the furnace to provide the excitation temperature, reducing energy consumption and avoiding the cumbersome experimental setup and operation process. Compared with existing high-voltage flash technology, this invention uses conventional low-voltage sintering, which effectively ensures personal safety during experimental operations. In addition, no liquid (water or ethanol) is needed as an auxiliary material during the sintering process, avoiding the liquid evaporation and residual voids that would result in non-dense sintering.

[0026] This invention utilizes a method to reduce blackbody radiation by coating the surface of the ceramic green body with a black insulating material and then covering it with a black heat-insulating material to prevent heat dissipation. Under the continuous action of low voltage and low current, the Joule heat generated by the zinc oxide green body sample is rapidly accumulated by the heat-insulating cover, thus slowly reaching an excitation temperature similar to that of the furnace body, thereby promoting flash firing. It has the advantages of low energy consumption, energy saving, simple equipment, and simple and efficient operation. Attached Figure Description

[0027] Figure 1 This is a structural diagram of the encapsulated and insulated room temperature flash-burning zinc oxide according to Embodiment 1 of the present invention;

[0028] Figure 2 This is a SEM image of the zinc oxide fine-grained ceramic obtained by room temperature sintering in Embodiment 1 of the present invention;

[0029] Figure 3 This is the XRD pattern of the zinc oxide fine-grained ceramic obtained by room temperature sintering in Example 1 of the present invention. Detailed Implementation

[0030] 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.

[0031] Example 1:

[0032] The sintering method for fine-grained zinc oxide ceramics based on room temperature flash firing in this embodiment includes the following steps:

[0033] (1) Pressing the embryo;

[0034] Polyvinyl alcohol (PVA, molecular weight 40000) was added to deionized water to make a 10wt% binder. High-purity nano zinc oxide powder was mechanically mixed with the binder and dried. 0.5g of the dried mixed powder was added to a mold and pressed into a dog bone shape under a pressure of 300MPa. The size of the blank was 20×3×2mm.

[0035] (2) Degumming treatment;

[0036] The pressed green body is placed in a muffle furnace and heated to 400°C at a heating rate of 2°C / min. After holding at this temperature for 2 hours, it is cooled with the furnace to obtain a zinc oxide ceramic green body.

[0037] (3) Coating electrodes;

[0038] Positive and negative platinum electrodes are placed at both ends of the ceramic green body; in order to reduce the contact resistance between the ceramic green body and the platinum electrodes, high-temperature silver paste is applied to both ends of the ceramic green body and baked at 650°C for 10 minutes to cure the silver paste.

[0039] (4) Apply a black coating;

[0040] To improve heat preservation and reduce heat loss due to microcurrent accumulation, insulating carbon black is sprayed onto the surface of the ceramic green body, and then baked in an 80℃ oven for 30 minutes to form a non-conductive carbon black coating on the surface of the ceramic green body. Figure 1 As shown.

[0041] (5) Thermal insulation wrapping treatment;

[0042] A ceramic green body coated with a black coating (i.e., the sample) was wrapped in 5cm thick black glass wool (referred to as insulation wool). Positive and negative platinum electrodes were connected to an AC power supply using copper wires (i.e., conductors) with a radius of 0.5mm. This was in preparation for a flash firing experiment. Figure 1 As shown.

[0043] (6) Under room temperature conditions, after connecting the power supply, gradually and slowly increase the voltage across the ceramic green body to 400V (the electric field strength is the ratio of voltage to the length of the ceramic green body, 200V / cm). When a current density of 6mA (the current density is the ratio of current to the cross-sectional area of ​​the ceramic green body, 1mA / mm²) appears in the circuit, 2 After applying the current, maintain this electric field strength and current for 5 minutes, during which time the sample temperature continuously rises to approximately 150℃. Next, rapidly increase the voltage to 600V (electric field strength 300V / cm), at which point the current increases rapidly at a rate of 15mA / s, eventually reaching the preset current density of 600mA / mm². 2 Once the stabilization period begins, the power supply switches from voltage control mode to current control mode, maintaining material sintering density for 30 seconds to achieve the sintering of zinc oxide ceramic material.

[0044] 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 0.5-2 μm;

[0045] like Figure 3 As shown, in this embodiment, the zinc oxide ceramic after encapsulation, heat preservation, and flash firing does not produce any impurity phases.

[0046] Example 2:

[0047] The difference between the room temperature flash sintering method for zinc oxide fine-grained ceramics in this embodiment and that in Embodiment 1 is as follows:

[0048] Based on the dimensions of the zinc oxide ceramic green body, the corresponding target temperature is 150–200℃, and the target current density is controlled at 100–1000 mA / mm². 2 The target duration is 30–180 s, and the electric field strength applied to the ceramic green body is adjustable from 50 to 300 V / cm, which can be determined according to the actual application requirements.

[0049] Other steps can be found in Example 1.

[0050] Example 3:

[0051] The difference between the room temperature flash sintering method for zinc oxide fine-grained ceramics in this embodiment and that in Embodiment 1 is as follows:

[0052] Insulating carbon black can also be replaced by insulating rubber or black polyurethane.

[0053] Black glass wool can also be replaced by one of rock wool, mineral wool, or extruded polystyrene.

[0054] The platinum electrode can also be replaced by either a silver electrode or a copper electrode;

[0055] Ceramic green bodies can also be in the form of round pieces or strips;

[0056] To meet the needs of different applications;

[0057] Other steps can be found in Example 1.

[0058] 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.

[0059] 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 sintering fine-grained zinc oxide ceramics based on room temperature flash calcination, characterized in that, Includes the following steps: (1) Place the zinc oxide ceramic green body in room temperature air and spray a layer of black insulating material on the surface of the green body; set positive and negative electrodes at both ends of the ceramic green body, and connect the positive and negative electrodes to the power supply through wires; the ceramic green body is also wrapped with black heat-insulating material as a sleeve. (2) Turn on the power supply and increase the voltage until the ceramic green body generates a microcurrent in the milliampere range. Then keep the voltage constant. Under the Joule heating and heat preservation effect of the microcurrent, the temperature of the ceramic green body will continue to rise. The electric field strength of the voltage acting on the ceramic green body can be adjusted in the range of 50 to 300 V / cm. (3) After the temperature of the ceramic green body rises to the target temperature, the voltage is further increased so that the current of the ceramic green body climbs to the target current density value. Then, the power supply is switched from voltage control mode to current control mode, and the power supply is turned off after maintaining the target time to obtain zinc oxide fine-grained ceramic. The target temperature is 150-200℃, and the target current density value is controlled to be 100-1000 mA / mm. 2 .

2. The sintering method according to claim 1, characterized in that, The target duration is 30–180 seconds.

3. The sintering method according to claim 1, characterized in that, In step (1), the black insulating material is one of insulating carbon black, insulating rubber, or black polyurethane.

4. The sintering method according to claim 1, characterized in that, In step (1), the black insulation material is one of black glass wool, rock wool, mineral wool, or extruded polystyrene.

5. The sintering method according to claim 1, characterized in that, In step (1), the electrode is one of a platinum electrode, a silver electrode, or a copper electrode.

6. The sintering method according to claim 1, characterized in that, The ceramic green body is in the shape of a round sheet, a long strip, or a dog bone.

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