Zinc oxide fine grain ceramic sintering method based on room temperature flash sintering

Abstract

The invention relates to a zinc oxide fine grain ceramic sintering method based on room temperature flash sintering, which comprises the following steps: (1) placing a zinc oxide ceramic green body in room temperature air, and spraying a layer of black insulating material on the surface layer of the green body; respectively arranging positive and negative electrodes at two ends of the ceramic green body, and connecting the positive and negative electrodes to a power supply through wires; the ceramic green body is wrapped by using a black thermal insulation material as a sheath; (2) turning on a power supply, increasing the voltage until the ceramic green body generates a milliampere-level micro current, then keeping the voltage unchanged, and continuously increasing the temperature of the ceramic green body under the action of Joule heat and heat preservation of the micro current; and (3) after the temperature of the ceramic green body rises to a target temperature, further increasing the voltage to enable the current of the ceramic green body to rise to a target current density value, keeping for a target duration, and then turning off the power supply to obtain the zinc oxide fine-grain ceramic. Compared with traditional low-voltage flash burning of zinc oxide, a heating furnace body is not needed to provide excitation temperature, and complexity of an experimental device and an operation process is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic sintering, and in particular relates to a method for sintering zinc oxide fine-grained ceramics based on room temperature flash sintering. Background Art

[0002] At present, ceramic materials, with their excellent mechanical strength, insulation performance, high temperature resistance and other characteristics, show broad application and development prospects, and are essential key materials in modern society and construction development. The manufacture of ceramic materials is still mainly based on traditional sintering. The traditional sintering process has high sintering temperature and long sintering time, which causes grain growth and generates huge energy consumption. Therefore, it is very important to seek a method for rapid densification of ceramic green bodies. In order to reduce the energy consumption in the ceramic sintering process, various new sintering processes, such as flash sintering, microwave sintering, and spark plasma sintering, have been proposed and put into practical application.

[0003] Among them, flash firing is a new type of ceramic sintering method, that is, by applying appropriate AC or DC voltage at both ends of the ceramic green body, the ceramic green body can be highly densified in just a few seconds to a few minutes; such a short sintering time and relatively low furnace temperature mean that the energy consumption required for flash firing technology is greatly reduced compared with the traditional sintering process. The survey found that before the flash occurred, the heat absorbed by the sample in the furnace body heating the sample was limited, and most of it was dissipated by the furnace body space, resulting in a certain amount of energy waste. However, the existing flash firing technology cannot get rid of the limitations of the heating furnace. Only a few high-conductivity green body systems directly apply heat to the sample, achieving room temperature flash firing and reducing energy loss.

[0004] In order to realize room temperature flash sintering to prepare fine-grained ceramics, the existing technology performs room temperature flash sintering of zinc oxide by applying ultra-high pressure to generate a high-temperature electric arc, and also improves the conductivity of the powder so that titanium dioxide powder can be quickly Joule heated under room temperature and high pressure conditions to obtain a dense embryo. In addition, there is also the use of water-assisted high voltage conduction at room temperature to perform Joule heating on the zinc oxide embryo.

[0005] However, the use of high voltage flash firing at room temperature to prepare fine-grained ceramics has high requirements for high-voltage equipment. At the same time, the high-temperature arc generated by high voltage has great safety hazards and can easily cause personal injury. Using liquid-assisted (water or ethanol) room temperature flash firing, it is difficult to obtain high-density and high-strength fine-grained ceramics due to the voids left by the evaporation of the liquid. The ceramics prepared by flash firing at room temperature with intrinsically high conductivity powders change their intrinsic high insulation properties. Summary of the invention

[0006] Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the objects of the present invention is to at least solve one or more of the above-mentioned problems in the prior art. In other words, one of the objects of the present invention is to provide a room temperature flash sintering method for zinc oxide fine-grained ceramics that meets one or more of the above-mentioned needs.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

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

[0009] (1) placing a zinc oxide ceramic green body in room temperature air, and spraying a layer of black insulating material on the surface of the green body; arranging positive and negative electrodes at both ends of the ceramic green body, respectively, and connecting the positive and negative electrodes to a power source through wires; and wrapping the ceramic green body with a black insulation material as a sheath;

[0010] (2) Turning on the power supply, increasing the voltage until the ceramic green body generates a micro-current of milliampere level, and then keeping the voltage constant, the temperature of the ceramic green body continues to rise under the effect of Joule heat of the micro-current and heat preservation;

[0011] (3) When the temperature of the ceramic green body rises to the target temperature, the voltage is further increased to make the current of the ceramic green body rise to the target current density value, and the power supply is turned off after maintaining the target time to obtain zinc oxide fine-crystalline ceramics.

[0012] As a preferred solution, the step (3) specifically comprises:

[0013] When the current reaches the target current density value, the power supply switches from voltage control mode to current control mode and is turned off after maintaining the target time.

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

[0015] As a preferred solution, the target current density value is controlled to be 100-1000 mA / mm 2 .

[0016] As a preferred solution, the target duration is 30 to 180 seconds.

[0017] As a preferred solution, in step (2), the electric field strength of the voltage applied to the ceramic green body is adjusted in 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, and black polyurethane.

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

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

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

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

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] Based on the semiconductor characteristics of zinc oxide, when the voltage is within a certain range during the external electric field treatment, a certain amount of microcurrent (mA level) will accumulate. According to Joule's law, the process of continuous microcurrent is the process of continuous Joule heat generation by the current. In the process of traditional low-voltage flash burning of zinc oxide materials, a certain excitation temperature is usually provided by a heating furnace. 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 device and process cumbersome.

[0025] Compared with the traditional low-voltage flash sintering of zinc oxide, the present invention does not need to heat the furnace to provide the excitation temperature, thus reducing energy consumption and avoiding the cumbersomeness of the experimental device and operation process; compared with the existing high-voltage flash sintering technology, the present invention adopts conventional low-voltage sintering, effectively ensuring the personal safety during the experimental operation; in addition, during the sintering process, it is not necessary to add liquid (water or ethanol) as an auxiliary material, thus avoiding the sintering non-density caused by the residual voids due to the volatilization of the liquid;

[0026] The present invention utilizes a method for reducing black body radiation, coats the surface of the ceramic green body with black insulating material, and covers it with black heat preservation material to prevent heat dissipation; utilizes the zinc oxide green body sample under the continuous action of low voltage and the Joule heat generated by low current to accumulate heat rapidly under the action of the heat preservation sleeve, thereby slowly reaching an excitation temperature similar to that of the furnace body, thereby promoting the occurrence of flash burning; the present invention has the advantages of low energy consumption and energy saving, simple equipment, simple and efficient operation, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a structural diagram of the packaged insulation room temperature flash-burned zinc oxide according to the first embodiment 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 Example 1 of the present invention;

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

[0030] In order to more clearly illustrate the embodiments of the present invention, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other accompanying drawings and other implementation methods can be obtained based on these accompanying drawings without creative work.

[0031] Embodiment 1:

[0032] The sintering method of zinc oxide fine-grained ceramic based on room temperature flash sintering of this embodiment comprises the following steps:

[0033] (1) Pressing the green embryo;

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

[0035] (2) Debonding treatment;

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

[0037] (3) coating electrodes;

[0038] Positive and negative platinum electrodes are set 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 coated on both ends of the ceramic green body and baked at 650°C for 10 minutes to solidify the silver paste.

[0039] (4) Applying black coating;

[0040] In order to better keep warm and reduce the heat loss of micro-current accumulation, the surface of the ceramic green body is sprayed with insulating carbon black and 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 shown.

[0041] (5) Wrapping with thermal insulation bag;

[0042] The ceramic green body (i.e., sample) coated with black coating was wrapped in 5 cm thick black glass wool (referred to as insulation wool), and the positive and negative platinum electrodes were connected to an AC power supply with a copper wire (i.e., conductor) with a radius of 0.5 mm to prepare for the flash burning experiment. Figure 1 shown.

[0043] (6) At room temperature, after the power is turned on, the voltage across the ceramic green body is gradually and slowly increased to 400 V (the electric field strength is the ratio of the voltage to the length of the ceramic green body, 200 V / cm). When 6 mA (the current density is the ratio of the current to the cross-sectional area of ​​the ceramic green body, 1 mA / mm) appears in the circuit, 2 ) and maintain this electric field strength and current for 5 minutes. At this time, the sample temperature continues to rise to about 150°C. Next, the voltage is quickly increased to 600V (electric field strength 300V / cm), and the current increases rapidly at a rate of 15mA / s. Finally, the current reaches the preset current density value of 600mA / mm 2 When entering the stable period, the power supply switches from the voltage control mode to the current control mode, and the material is sintered and dense for 30 seconds to achieve the sintering of zinc oxide ceramic materials.

[0044] like Figure 2 As shown, the zinc oxide sintered at room temperature in this embodiment has a high density, and the grain size is in the range of 0.5-2 μm;

[0045] like Figure 3 As shown, no impurity phase is produced in the zinc oxide ceramic after the jacket is flash-fired.

[0046] Embodiment 2:

[0047] The zinc oxide fine-grained ceramic sintering method based on room temperature flash sintering in this embodiment is different from that in the first embodiment in that:

[0048] According to the size of the zinc oxide ceramic green body, the corresponding target temperature is 150-200°C, and the target current density value is controlled to be 100-1000mA / mm 2 , the target duration of maintenance is 30 to 180 seconds and the adjustment range of the electric field strength of the voltage acting on the ceramic green body is 50 to 300 V / cm, which can be determined according to actual application requirements;

[0049] For other steps, please refer to Example 1.

[0050] Embodiment three:

[0051] The zinc oxide fine-grained ceramic sintering method based on room temperature flash sintering in this embodiment is different from that in the first embodiment in that:

[0052] Insulating carbon black can also be replaced by one of insulating rubber and black polyurethane;

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

[0054] The platinum electrode can also be replaced by one of the silver electrode and the copper electrode;

[0055] The ceramic green body can also be in the form of a disc or a strip;

[0056] Meet the needs of different applications;

[0057] For other steps, please refer to Example 1.

[0058] In view of the numerous embodiments of the scheme of the present invention, the raw materials and dosage involved can be selected according to actual needs within the limited range, and the experimental data of each embodiment is huge and numerous, which is not suitable for listing and explaining one by one here, but the content required to be verified and the final conclusion obtained in each embodiment are similar. Therefore, the verification content of each embodiment will not be explained one by one here.

[0059] The above description is only a detailed description of the preferred embodiments and principles of the present invention. For ordinary technicians in this field, according to the ideas provided by the present invention, there will be changes in the specific implementation methods, and these changes should also be regarded as the protection scope of the present invention.

Claims

1. A method for sintering zinc oxide fine-grained ceramics based on room temperature flash sintering, characterized in that: The following steps are involved: (1) placing a zinc oxide ceramic green body in room temperature air, and spraying a layer of black insulating material on the surface of the green body; arranging positive and negative electrodes at both ends of the ceramic green body, respectively, and connecting the positive and negative electrodes to a power source through wires; and wrapping the ceramic green body with a black heat-insulating material as a sheath; (2) Turning on the power supply, increasing the voltage until the ceramic green body generates a micro-current of milliampere level, and then keeping the voltage constant, the temperature of the ceramic green body continues to rise under the effect of Joule heat of the micro-current and heat preservation; (3) When the temperature of the ceramic green body rises to the target temperature, the voltage is further increased to make the current of the ceramic green body rise to the target current density value, and the power supply is turned off after maintaining the target time to obtain zinc oxide fine-crystalline ceramics.

2. The sintering method according to claim 1, characterized in that: The step (3) specifically comprises: When the current reaches the target current density value, the power supply switches from voltage control mode to current control mode and is turned off after maintaining the target time.

3. The sintering method according to claim 1, characterized in that: The target temperature is 150-200°C.

4. The sintering method according to claim 1, characterized in that: The target current density value is controlled to be 100-1000 mA / mm 2 .

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

6. The sintering method according to claim 1, characterized in that: In the step (2), the electric field strength of the voltage applied to the ceramic green body is adjusted in the range of 50 to 300 V / cm.

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

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

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

10. The sintering method according to claim 1, characterized in that: The ceramic green body is in the shape of a disc, a strip or a dog bone.

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