NL2030967B1

NL2030967B1 - Method for graphene-assisted flash sintering of ceramic materials at room temperature

Info

Publication number: NL2030967B1
Application number: NL2030967A
Authority: NL
Inventors: Jiang Juan; Xiao Weiwei; Hao Wei; Ni Na; Yu Yali; Fan Xiaohui
Original assignee: Univ Shanghai Jiaotong
Priority date: 2022-02-16
Filing date: 2022-02-16
Publication date: 2023-08-22

Abstract

The disclosure relates to a method for graphene-assisted flash sintering of ceramic materials at room temperature. The method comprises the following steps that, graphene is dispersed into solvent and mixed to obtain a graphene solution; ceramic powder is added into the graphene solution and uniformly mixed, and the solvent is removed to obtain composite powder; and the composite powder is molded into a green body, electric fields are applied to the two ends of the green body at room temperature, and the flash sintering is completed within a time of less than 60 s. The method has the advantages that flash sintering can be generated under the room temperature condition, joule heat generated by electrifying is utilized, the temperature of the ceramic green body is increased to the starting temperature of flash sintering, and the green body shrinks after flash sintering, and sintering is completed in a short time.

Description

METHOD FOR GRAPHENE-ASSISTED FLASH SINTERING OF CERAMIC

MATERIALS AT ROOM TEMPERATURE

TECHNICAL FIELD

[01] The disclosure relates to a method for manufacturing ceramic materials, in particular to a method for graphene-assisted flash sintering of ceramic materials at room temperature.

BACKGROUND ART

[02] Flash sintering is to apply an electric field (7.5 -1000 V/cm) and a temperature field (the temperature of a furnace rises at a certain rate) to a ceramic green body, and when the temperature of the furnace reaches a certain specific value (below the sintering temperature, the temperature is the initiation temperature of the flash sintering, shortened from “flash sintering temperature”), flash sintering is generated, and the accompanying energy density rises rapidly to the extreme value (up to 10-1000 mW/mm?*). With the nonlinear increase of sample conductivity during the process, the time from beginning of flash sintering to completion of flash sintering is only less than

I minute. [Raj et al in a patent No US 9, 334, 194 (2011)] Compared with traditional sintering, this method can complete sintering at a lower temperature and in a very short time. A sintered sample tends to have the characteristics of fine grain. Flash sintering is initially only applicable to the ionic conductor ceramic material with NTC effect (the resistance decreases as the temperature increases), and later expanded to an insulator (Al203), a semiconductor (SiC) and a metal conductor (aluminum alloy). Although the flash sintering temperature is very low compared to conventional sintering, a great deal of researches focuses on how to generate flash sintering by reducing the flash sintering initiation temperature, and even at room temperature (room temperature sintering can reduce costs and save energy, and sintering equipment is simplified, directly removing the furnace necessary for traditional sintering). For example, hydrogen containing steam is introduced into a tube furnace for flash sintering of zinc oxide at room temperature [Jiuyuan Nie, et al. Water-assisted flash sintering: Flashing ZnO at room temperature to achieve 98% density in seconds [J]. Scripta Materialia, 142 (2018) 79-82], aluminum alloy 1s subject to flash sintering at room temperature [Brandon McWilliams, et al.

Sintering aluminum alloy powder using direct current electric fields at room temperature in seconds[J]. J Mater, Sci., (2018) 53:9297-9304]. In the first method, the requirements for equipment are not reduced, and the sintering temperature of zinc oxide is not high; and in the second method, a sintered material 1s metal material, and the metal material have high conductivity, and the method is not suitable for most of inorganic non-metallic materials with relatively low conductivity. Therefore, the above method is not universal, and a method that is simple and has an effect on most ceramic materials shall be sought.

SUMMARY

[03] An object of the present disclosure is to provide a method for graphene-assisted flash sintering of ceramic materials at room temperature in order to overcome the defects existing in the prior art.

[04] The object of the present disclosure can be implemented by the following technical scheme:

[05] A method for graphene-assisted flash sintering of ceramic materials at room temperature, wherein applying high electric fields to both ends of a graphene-reinforced ceramic composite material, limiting the current at a relatively low current, utilizing the characteristics of high conductivity of graphene, and performing flash sintering at room temperature. The initiation temperature of flash sintering is provided by graphene, so that a green body is made conducting, the temperature of the ceramic green body rapidly increases to the sintering temperature by means of joule heat generated by electrifying, the green body shrinks rapidly, and sintering is completed within a short time (1 min).

The method comprises the following steps that

[06] Graphene is dispersed into solvent and mixed to obtain a graphene solution;

[07] Ceramic powder is added into the graphene solution and uniformly mixed, and the solvent is removed to obtain composite powder;

[08] The composite powder is molded into a green body, and electric fields are applied to the two ends of the green body at room temperature, and flash sintering is completed in less than 60 s.

[09] Further, the electric field strength is 20-1000 V/cm; and furthermore, the electric field strength is 20-1000 V/cm.

[10] Further, the current density is 40-500 mA/mm?; and furthermore, the current density is 40-500 mA/mm?.

[11] Further, after the electric field is applied, the increase speed of the current is first controlled to be less than 1 mA/s, and the slow increase time is referred to as the “inoculation period”. The period is related to the field strength and lasts for 1-30 s.

Metaphase current rapidly increases at a speed of 10-1000 mA/s and lasts for 1-10 s.

Final current reaches the maximum value, enters the stable period, and lasts for 5-20 s. 5S The material is subject to sintering densification.

[12] Further, the graphene is graphene nanoplatelets, graphene oxide or reduced graphene oxide, and solvent is deionized water, ethanol, DMF or NMP.

[13] Further, the graphene solution has a concentration of 0.02-8 mg/mL.

[14] Further, the ceramic powder is YSZ, a semiconductor, or an insulator.

[15] Still further, the semiconductor comprises silicon carbide, and the insulator comprises aluminum oxide.

[16] Further, the ceramic powder is ball-milled and uniformly mixed in the graphene solution, and the solvent is removed in an oven.

[17] Further, the content of the graphene in the composite powder is 1-10 wt%.

[18] Further, a shape of the green body is dog bone shape, a long strip shape, a cylindrical shape or a disc shape, electric fields are applied to the two ends of the pressed green body, and the length of the green body in the direction of the electric field is 1-50 cm.

[19] Compared with the prior art, the disclosure has the following beneficial effects that:

[20] (1) Flash firing at room temperature is fast, saving the energy consumed during the heating time of the furnace and during this period. A conventional ceramic sintering method is to heat the green body by radiant heat transfer of the furnace, which requires several tens of minutes or even several hours, and the efficiency is much lower than that of the direct flash sintering of the green body to generate joule heat, so that the green body can be sintered by only a few minutes.

[21] (2) Sintering at room temperature can reduce costs and save energy, but more importantly, sintering equipment can be greatly simplified, and the furnace essential for both traditional sintering and flash sintering process can be removed. The green body needs to be heated by the furnace to provide a certain amount of heat to reach the initiation temperature of flash sintering, but according to the method, the heat generated by graphene electrification and uniformly dispersed in the green body replaces the heat of the furnace.

[22] (3) According to the method, the addition amount of graphene filler is very small, so that compared with other conductive fillers that need to be added in large quantities, it will not have a great adverse effect on sintering. This is related to the characteristics of graphene, such as super-large specific surface area and high conductivity.

BRIEF DESCRIPTION OF THE DRAWINGS

[23] FIG. 1 is a photograph of a product prepared in Embodiment 1;

[24] FIG. 2 is a diagram of variation of field strength and current density over time in Embodiment 1;

[25] FIG. 3 is a diagram of variation of energy density and sample shrinkage rate over time in Embodiment 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[26] The disclosure will be further described in detail with reference to the drawings.

The following embodiments will be helpful for persons skilled in the art further understand the disclosure, but do not limit the disclosure in any form. It should be noted that persons of ordinary skill in the art may make several modifications and improvements without departing from the concept of the present disclosure. These all fall under the protection scope of the present disclosure.

[27] A method for graphene-assisted flash sintering of ceramic materials at room temperature, comprising the following steps that,

[28] (1) A certain amount of graphene (graphene nanoplatelets, graphene oxide or reduced graphene oxide) is weighed, dispersed in appropriate solvent (deionized water, ethanol, DMF or NMP) and stirred for 20-180 min to obtain a uniform graphene solution, and the concentration of the graphene solution is controlled to be 0.02-8 mg/mL;

[29] (2) A certain amount of ceramic powder (ion conductor, such as YSZ, semiconductor, such as silicon carbide, insulator, such as aluminum oxide) is added into the prepared graphene solution and uniformly mixed with a ball milling method, wherein the ball milling speed is 100-1000 r/min, the ball milling time is 2-24 h, and the solvent is removed in an oven to obtain composite powder (the final graphene content is 1-10 wt% by mass fraction);

[30] (3) A proper amount of the prepared composite powder is added into a mold and pressed into a dog bone shape, a long strip shape, a cylindrical shape or a disc shape, and electric fields are applied to the two ends of the pressed green body, wherein the length of the green body in the direction of the electric field is 1-50 cm; and

[31] (4) Under the condition of room temperature, the required electric field strength of the sintered green body is greater than 20 V/cm, the current density is greater than 40 mA/mm’, the current will increase slowly and then rapidly after electrifying, and the final current reaches the maximum value, so that the sintering of the ceramic material is achieved, and the whole process takes less than 60 s.

[32] The following is more detailed embodiments, and the technical scheme of the present disclosure and the technical effects that can be obtained are further described by the following embodiments.

[33] A ball mill used in various embodiments is a planetary ball mill produced by

Nanjing Nanda Instrument Plant. An electrothermal air drying oven is a DHG 9040 HA type electrothermal air drying oven produced by Hangzhou Lantian Chemical

Examination Instrument Factory. The tablet press is produced by a Hefei Crystal

Company. The power supply is produced by Dinghua. The range is 0-1000 V of voltage and 0-1 A of current.

Embodiment 1

[34] A method for graphene-assisted flash sintering of ceramic materials at room temperature, comprising the following steps that,

[35] (1) A certain amount of graphene oxide produced by Tan Yuan Graphene (Shanghai) Co., Ltd. is weighed, dispersed in deionized water and stirred for 60 min to obtain a uniform graphene oxide solution, and the concentration of the solution is 2 mg/mL;

[36] (2) A certain amount of YSZ (yttrium stabilized zirconia) is added into the prepared graphene oxide solution and uniformly mixed with a planetary ball milling method, wherein the ball milling speed is 300 r/min, the ball milling time is 12 h, and the solvent is removed in an oven to obtain composite powder of the YSZ and the graphene oxide, and the final graphene oxide content is 2 wt% by mass fraction);

[37] (3) The prepared composite powder 0.8 gis added into a mold and pressed into a dog bone shape, as shown in FIG. 1. The size of the green body is 20 = 3 x 2 mm’, and the platinum wire is used to apply the field strength through holes at the two ends.

Electric fields are applied to the two ends of the pressed green body, and the length of the green body in the direction of the electric field is 20 mm; and

[38] (4) Under the condition of room temperature, the required electric field strength of the sintered green body is 60 V/cm, and the current density is 160 mA/mm?. After electric fields are applied, the current first increases at a speed of less than 1 mA/s and then increase slowly for 30 s, the metaphase current increases rapidly at a speed of 10 mA/s and lasts for 10 s, the final current reaches the maximum value and enters the stable period and lasts for 20 s,the material is subject sintering densification, the sintering of the ceramic material is achieved, and the whole process takes 60 s.

Embodiment 2

[39] A method for graphene-assisted flash sintering of ceramic materials at room temperature, comprising the following steps that,

[40] (1) A certain amount of graphene nanoplatelets is weighed, dispersed in ethanol and stirred for 120 min to obtain a uniform graphene solution, and the concentration of the solution is 4 mg/mL;

[41] (2) A certain amount of alumina powder is added into the prepared graphene solution and uniformly mixed with a planetary ball milling method, wherein the ball milling speed is 300 r/min, the ball milling time is 12 h, and the solvent is removed in an oven to obtain composite powder of the alumina powder and the graphene, and the final graphene content is 5 wt% by mass fraction);

[42] (3)0.8 g of the prepared composite powder is added into a mold and pressed into a dog bone shape. The size of the green body is 20 x 3 x 2 mm), electric fields are applied to the two ends of the pressed green body, and the length of the green body in the direction of the electric field is 30 mm; and

[43] (4) Under the condition of room temperature, the required electric field strength of the sintered green body is 70 V/cm, and the current density is 100 mA/mm?. After electric fields are applied, the initial current increases slowly at a speed of less than

ImA/s and lasts for 10 s, the metaphase current increases rapidly at a speed of 1000 mA/s and lasts for 10 s, the final current reaches the maximum value and enters the stable period and lasts for 10 s, the material is subject sintering densification, the sintering of the ceramic material 1s achieved, and the whole process takes 30 s.

Embodiment 3

[44] A method for graphene-assisted flash sintering of ceramic materials at room temperature, comprising the following steps that,

[45] (1) A certain amount of reduced graphene oxide reduced by ascorbic acid is weighed, dispersed in ethanol and stirred for 60 min to obtain a uniform reduced graphene oxide solution, and the concentration of the solution is 4 mg/mL;

[46] (2) A certain amount of silicon carbide powder is added into the prepared reduced graphene oxide solution and uniformly mixed with a planetary ball milling method, wherein the ball milling speed is 300 r/min, the ball milling time is 12 h, and the solvent is removed in an oven to obtain composite powder of the silicon carbide and the reduced graphene oxide, and the final reduced graphene oxide content is 2 wt% by mass fraction);

[47] (3) 0.8 g of the prepared composite powder is added into a mold and pressed into a dog bone shape. The size of the green body is 20 x 3 x 2 mm’, electric fields are applied to the two ends of the pressed green body, and the length of the green body in the direction of the electric field is 20mm; and

[48] (4) Under the condition of room temperature, the required electric field strength of the sintered green body is 100 V/cm, and the current density is 160 mA/mm?. After electric fields are applied, the initial current increases slowly at a speed of less than

ImA/s and lasts for 5s, the metaphase current increases rapidly at a speed of 800 mA/s and lasts for 10 s, the final current reaches the maximum value and enters the stable period and lasts for 5 s, the material is subject sintering densification, the sintering of the ceramic material is achieved, and the whole process takes 20 s.

[49] FIG. 2 and FIG. 3 are curve graphs of field strength, current density, energy density and sample shrinkage rate over time according to the present disclosure. As can be seen from the figures, a high field strength (60 V/cm) is applied, the current begins to slowly increase and then increase rapidly to reach a preset value (160 mA/mm?), a sample begins to shrink at this time and shrinks by 25% after 20 s, thus completing sintering.

Embodiment 4

[50] A method for graphene-assisted flash sintering of ceramic materials at room temperature, comprising the following steps that,

[51] (1) A certain amount of graphene nanoplatelets is weighed, dispersed in deionized water and stirred for 20 min to obtain a uniform graphene solution, and the concentration of the solution is 0.02 mg/mL;

[52] (2) A certain amount of YSZ powder is added into the prepared graphene solution and uniformly mixed with a planetary ball milling method, wherein the ball milling speed is 100 r/min, the ball milling time 1s 2 h, and the solvent is removed in an oven to obtain composite powder of the YSZ and the graphene, and the final graphene content is 1 wt% by mass fraction;

[53] (3) 0.8 g of the prepared composite powder is added into a mold and pressed into a long strip shape. The size of the green body is 20 x 3 x 2 mm’, electric fields are applied to the two ends of the pressed green body, and the length of the green body in the direction of the electric field is 20 mm; and

[54] (4) Under the condition of room temperature, the required electric field strength of the sintered green body is 80 V/cm, and the current density is 100 mA/mm?. After electric fields are applied, the initial current increases slowly at a speed of less than

ImA/s and lasts for 1s, the metaphase current increases rapidly at a speed of 500 mA/s and lasts for 5s, the final current reaches the maximum value and enters the stable period and lasts for 14s, the material is subject sintering densification, the sintering of the ceramic material is achieved, and the whole process takes 30 s.

Embodiment 5

[55] A method for graphene-assisted flash sintering of ceramic materials at room temperature, comprising the following steps that,

[56] (1) A certain amount of graphene oxide is weighed, dispersed in ethanol and stirred for 180 min to obtain a uniform graphene oxide solution, and the concentration of the solution is 8 mg/mL;

[57] (2) A certain amount of alumina powder is added into the prepared graphene oxide solution and uniformly mixed with a planetary ball milling method, wherein the ball milling speed is 1000 r/min, the ball milling time is 24 h, and the solvent is removed in an oven to obtain composite powder of alumina and the graphene oxide, and the final graphene oxide content 1s 10 wt% by mass fraction);

[58] (3) 0.8 g of the prepared composite powder is added into a mold and pressed into a cylindrical shape, electric fields are applied to the two ends of the pressed green body, and the length of the green body in the direction of the electric field is 20 mm; and

[59] (4) Under the condition of room temperature, the required electric field strength of the sintered green body is 200 V/cm, and the current density is 100 mA/mm?. After electric fields are applied, the initial current increases slowly at a speed of less than

ImA/s and lasts for 30 s, the metaphase current increases rapidly at a speed of 1000 mA/s and lasts for 5s, the final current reaches the maximum value and enters the stable period and lasts for 15 s, the material is subject sintering densification, the sintering of the ceramic material is achieved, and the whole process takes 50 s.

[60] Reference throughout this specification to “one embodiment”, “an example”, “a specific example” and the like refers to that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[61] The above description of the embodiments is intended to facilitate understanding and use of the present disclosure by persons of ordinary skill in the art.

The persons skilled in the art can readily make various modifications to these embodiments, and apply the general principles described herein to other embodiments without involving an inventive effort. Therefore, the present disclosure is not limited to the embodiments described above, and improvements and modifications made by the persons skilled in the art without departing from the scope of the present disclosure shall fall within the protection scope of the present disclosure.

Claims

Conclusies l. Werkwijze voor het grafeenondersteunde flitssinteren van keramische materialen bij kamertemperatuur met het kenmerk dat deze de volgende stappen omvat: grafeen wordt verdeeld in oplosmiddel en wordt gemengd om zo een grafeenoplossing te verkrijgen; keramiekpoeder wordt toegevoegd aan de grafeenoplossing en wordt uniform gemengd, en het oplosmiddel wordt verwijderd om composietpoeder te verkrijgen, waarbij de grafeeninhoud in het composietpoeder 1 — 10 gew.% bedraagt; het composietpoeder wordt gevormd tot een groen lichaam, en elektrische velden worden aangelegd op de twee uiteinden van het groene lichaam bij kamertemperatuur; en nadat de elektrische velden zijn aangelegd, wordt een beginstroom langzaam verhoogd met een snelheid van minder dan 1 mA/s die 1 — 30 s aanhoudt, wordt een metafasestroom snel verhoogd met een snelheid van 10 — 1000 mA/s die 1 — 10 s aanhoudt, bereikt een eindstroom de maximumwaarde, treedt de stabiliteitsperiode in en die 5 — 20 s aanhoudt, waarbij een materiaal is onderhevig aan sinterverdichting, waarbij het flitssinteren voltooid is, waarbij de flitssintersnelheid hoog is, en waarbij de energie die verbruikt wordt gedurende de verwarmingstijd en deze periode wordt bespaard.Conclusions l. Method for the graphene-assisted flash sintering of ceramic materials at room temperature, characterized in that it comprises the following steps: graphene is dispersed in solvent and mixed to obtain a graphene solution; ceramic powder is added to the graphene solution and mixed uniformly, and the solvent is removed to obtain composite powder, where the graphene content in the composite powder is 1 — 10% by weight; the composite powder is formed into a green body, and electric fields are applied to the two ends of the green body at room temperature; and after the electric fields are applied, an initial current is increased slowly at a rate of less than 1 mA/s lasting 1 — 30 s, a metaphase current is increased rapidly at a rate of 10 — 1000 mA/s lasting 1 — 10 s persists, a final current reaches the maximum value, enters the stability period and lasts for 5 — 20 s, where a material is subject to sintering densification, where flash sintering is completed, where the flash sintering rate is high, and where the energy consumed during the heating time and this period is saved.

2. Werkwijze voor het grafeenondersteund flitssinteren van keramische materialen bij kamertemperatuur volgens conclusie 1, waarbij de elektrische veldsterkte die benodigd is voor een gesinterd groen lichaam groter is dan 20 V/cm.A method for graphene-assisted flash sintering of ceramic materials at room temperature according to claim 1, wherein the electric field strength required for a sintered green body is greater than 20 V/cm.

3. Werkwijze voor het grafeenondersteund flitssinteren van keramische materialen bij kamertemperatuur volgens conclusie 1, waarbij de stroomdichtheid die benodigd is voor het sinteren van een groen lichaam groter is dan 40 mA/mm? .A method for graphene-assisted flash sintering of ceramic materials at room temperature according to claim 1, wherein the current density required for sintering a green body is greater than 40 mA/mm? .

4. Werkwijze voor het grafeenondersteund flitssinteren van keramische materialen bij kamertemperatuur volgens één van conclusies 1 — 3, waarbij het grafeen grafeennanoplaatjes, grafeenoxide of gereduceerde grafeenoxide omvat, en waarbij het oplosmiddel gedeïoniseerd water, ethanol, DMF of NMP is.A method for the graphene-assisted flash sintering of ceramic materials at room temperature according to any one of claims 1 to 3, wherein the graphene comprises graphene nanoplatelets, graphene oxide or reduced graphene oxide, and wherein the solvent is deionized water, ethanol, DMF or NMP.

S11 -S11 -

5. Werkwijze voor het grafeenondersteund flitssinteren van keramische materialen bij kamertemperatuur volgens één van conclusies 1 — 3, waarbij een grafeenoplossing een concentratie van 0,02 — 8 mg/mL heeft.A method for the graphene-assisted flash sintering of ceramic materials at room temperature according to any one of claims 1 - 3, wherein a graphene solution has a concentration of 0.02 - 8 mg/mL.

6. Werkwijze voor het grafeenondersteund flitssinteren van keramische materialen bij kamertemperatuur volgens één van conclusies | — 3, waarbij keramisch poeder YSZ, een halfgeleider of een isolator is, waarbij de halfgeleider siliciumcarbide omvat, de isolator aluminiumoxide omvat, en het keramiekpoeder bewerkt is met een kogelmolen en uniform vermengd is in de grafeenoplossing, en oplosmiddel verwijderd wordt in een oven.6. Method for the graphene-assisted flash sintering of ceramic materials at room temperature according to any one of claims | — 3, where ceramic powder is YSZ, a semiconductor or an insulator, wherein the semiconductor comprises silicon carbide, the insulator comprises alumina, and the ceramic powder is ball milled and uniformly mixed in the graphene solution, and solvent is removed in a furnace.

7. Werkwijze voor het grafeenondersteund flitssinteren van keramische materialen bij kamertemperatuur volgens één van conclusies 1 — 3, waarbij een vorm van een groen lichaam een hondenbotvorm, een langestrookvorm, een cilindrische vorm of een schijfvorm is, waarbij elektrische velden worden aangelegd op de twee uiteinden van het samengedrukte groene lichaam, en de lengte van het groene lichaam in de richting van het elektrische veld 1 — 50 cm bedraagt.A method for graphene-assisted flash sintering of ceramic materials at room temperature according to any one of claims 1 to 3, wherein a green body shape is a dog bone shape, a long strip shape, a cylindrical shape or a disk shape, with electric fields applied to the two ends of the compressed green body, and the length of the green body in the direction of the electric field is 1 — 50 cm.