Li2tio3 tritium breeder ceramic with mesoporous grain boundary structure and method of making

Abstract

The application belongs to the technical field of nuclear materials, and discloses a Li2TiO3 tritium breeder ceramic with mesoporous grain boundary structure and a preparation method thereof. Li2TiO3 powder is prepared first, then Li2TiO3 green bodies are prepared, and then Li2TiO3 tritium breeder ceramics are prepared. The Li2TiO3 green bodies are sintered through a flash sintering device to obtain high tritium release Li2TiO3 tritium breeder ceramics with mesoporous grain boundary structure. Based on the flash sintering technology, the application realizes accurate regulation of the mesoporous pore size and pore density in the Li2TiO3 tritium breeder ceramic material by regulating the flash sintering technical parameters, so that efficient tritium release of the Li2TiO3 tritium breeder is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear materials, and relates to a Li2TiO3 tritium breeder ceramic with a mesoporous grain boundary structure and a preparation method thereof. BACKGROUND

[0002] Nuclear fusion energy has the advantages of being clean, safe and sustainable. However, tritium, as one of the reaction fuels, is a radioactive isotope of hydrogen that almost does not exist in nature, and is generally obtained through the reaction of neutrons and lithium ceramics. Lithium ceramics, as a main tritium breeder candidate material, have the following advantages: good chemical stability, good compatibility with structural materials, and no magneto-hydrodynamic effect. Among a large number of lithium ceramic tritium breeders, lithium titanate (Li2TiO3) has a moderate lithium density, a low tritium release temperature and excellent mechanical properties, and is selected as an optimal tritium breeder by the International Thermonuclear Experimental Reactor Program (ITER) and the China Fusion Engineering Test Reactor Program (CFETR).

[0003] The tritium breeding process mainly includes the generation and diffusion of tritium in the grain, the adsorption and desorption of tritium in the grain boundary, and the diffusion of tritium in the interface or pores. Among them, the diffusion of tritium in the interface or pores as the last link of tritium release plays a decisive role in whether tritium can be successfully extracted. However, research shows that the tritium breeding efficiency of lithium ceramics is low, which cannot meet the engineering design requirements of tritium self-sustaining. It is imperative to improve the tritium production and release efficiency of tritium breeders. SUMMARY

[0004] The purpose of the present application is to provide a Li2TiO3 tritium breeder ceramic with a mesoporous grain boundary structure and a preparation method thereof, to solve the problem of low tritium release efficiency of the existing Li2TiO3 tritium breeder. The present application is based on flash technology, and by adjusting the flash technology parameters, the pore size and density of the grain boundary mesopores in the Li2TiO3 tritium breeder ceramic material are precisely controlled, thereby realizing the efficient release of the Li2TiO3 tritium breeder.

[0005] The present application can be realized by the following technical scheme: a preparation method of a Li2TiO3 tritium breeder ceramic with a mesoporous grain boundary structure is provided, comprising:

[0006] (1) preparing Li2TiO3 powder;

[0007] (2) preparing Li2TiO3 green body: placing the Li2TiO3 powder in a mold, then placing the mold in a tablet press to form a mold, and demolding to obtain a Li2TiO3 green body;

[0008] (3) Li2TiO3 tritium breeder ceramic preparation: punch holes in the middle of the two ends of the Li2TiO3 green body, measure the distance between the two holes and the width and height of the middle of the Li2TiO3 green body, and calculate the cross-sectional area of the Li2TiO3 green body;

[0009] Then smear silver paste on the inner wall of the holes at the two ends of the Li2TiO3 green body and the periphery;

[0010] Then pass two platinum wire electrodes in the box furnace through the holes at the two ends of the Li2TiO3 green body and fix them, and close the furnace door;

[0011] According to the distance between the two holes and the cross-sectional area of the Li2TiO3 green body, set the furnace temperature and flash parameters, and after the furnace temperature is stable, flash the Li2TiO3 green body, turn off the power after the flash is completed, and cool down with the furnace to obtain the Li2TiO3 tritium breeder ceramic; the flash parameters include electric field intensity, current density and flash time.

[0012] The beneficial effects of the above technical solution are: the Li2TiO3 ultrafine powder is synthesized and screened by a low-temperature solid-phase method, then the mold filled with the Li2TiO3 ultrafine powder is placed in a tablet press to press the Li2TiO3 green body, and finally the green body is sintered by a flash sintering device to obtain a high-tritium-release Li2TiO3 tritium breeder ceramic with a mesoporous grain boundary structure.

[0013] The Li2TiO3 grain boundary is modified by the superplastic deformation, i.e. dislocation pile-up effect, in the flash sintering process, a new type of Li2TiO3 tritium breeder with rich mesoporous grain boundaries is obtained, the tritium desorption and diffusion rate of the tritium breeder is improved by increasing the proportion of interfaces or pores, and the application provides a theoretical and experimental basis for the structural design of the new type of ceramic tritium breeder.

[0014] Flash sintering is a new type of sintering process in which a direct current or alternating current field is applied to a sample through a wire, the field intensity is increased during the sintering heating process, and when the critical values of the field intensity and temperature are reached, the material is instantaneously densified, and the sintering temperature is low and the sintering speed is fast. Compared with traditional sintering processes such as normal pressure sintering, hot-pressing sintering and discharge plasma sintering, flash sintering only needs to be completed in a short time at a relatively low temperature, has high sintering efficiency and is energy-saving and environmentally friendly; most importantly, flash sintering can make the sample produce superplastic deformation due to the fast sintering speed, form high-density stacking defects, and further produce rich nanometer mesoporous grain boundaries, which is helpful to accelerate the diffusion of tritium.

[0015] In one specific embodiment of the application, the following steps are further included: the preparation process of the Li2TiO3 powder, comprising:

[0016] (11) placing LiOH H2O and TiO(OH)2 in a ball mill tank equipped with a plurality of agate balls, adding ball mill medium, and sealing the ball mill tank;

[0017] (12) placing the sealed ball mill tank in a planetary ball mill to perform ball milling, to obtain a slurry;

[0018] (13) performing rotary evaporation drying on the ball-milled slurry, to obtain a mixed powder;

[0019] (14) placing the mixed powder in a crucible, and placing the crucible in a box furnace to perform pre-sintering in an air atmosphere; after grinding and sieving, Li2TiO3 powder is obtained.

[0020] In one specific embodiment of the present application, in step (11), the molar ratio of LiOH H2O to TiO(OH)2 is 2:1; the diameter of the agate balls is 2-5 mm.

[0021] In one specific embodiment of the present application, in step (11), the ball mill medium is anhydrous ethanol.

[0022] In one specific embodiment of the present application, in step (12), the ball milling speed is 200-300 r / min, and the ball milling time is 6-8 h.

[0023] In one specific embodiment of the present application, in step (13), the rotary evaporation temperature is 40-60℃, and the rotary evaporation time is 2-4 h.

[0024] In one specific embodiment of the present application, in step (14), the pre-sintering temperature of the mixed powder is 500-600℃, and the pre-sintering time is 2-4 h; the temperature rising rate is 5℃ / min.

[0025] In one specific embodiment of the present application, in step (14), the mesh size of the sieve used for sieving is 80-120 mesh.

[0026] In one specific embodiment of the present application, in step (2), the mold is a dog bone-shaped mold, and the obtained Li2TiO3 green body is a dog bone-shaped green body.

[0027] In one specific embodiment of the present application, in step (2), during the compression molding process, the mold pressing pressure is 2.5-3.5 MPa, and the pressure holding time is 1-1.5 min.

[0028] In one specific embodiment of the present application, in step (3), the pore size of the hole punched at the middle position of the two ends of the Li2TiO3 green body is 0.8-1.2 mm.

[0029] In one specific embodiment of the present application, in step (3), the furnace temperature is 600-800 DEG C, and the temperature is generally kept for 1-2 hours until the temperature is stable; the electric field intensity is 70-100 V / cm, the current density is 40-80 mA / mm 2 , and the flash sintering time is 10-30 s; in the flash sintering process, the furnace temperature is first raised to 600-800 DEG C, and then kept for 1-2 hours until the temperature is stable, and then the flash sintering is started.

[0030] The present application also provides the Li2TiO3 tritium breeder ceramic with mesoporous grain boundary structure prepared by the above method.

[0031] Compared with the prior art, the Li2TiO3 tritium breeder ceramic with mesoporous grain boundary structure and the preparation method thereof have the following beneficial effects:

[0032] (1) The precursor powder is pressed into a dog-bone-shaped green body, and then the flash sintering process is used; compared with the traditional sintering method, the lithium volatilization caused by continuous high-temperature heating is reduced, and the high lithium density of the breeder is ensured;

[0033] (2) The flash sintering process is used to obtain the "annual ring" grain boundary structure, the specific surface area of the grain boundary is increased, the diffusion channels of tritium are enriched, and the tritium release efficiency is improved;

[0034] (3) The "annual ring" grain boundary structure of the lithium titanate tritium breeder ceramic prepared by the present application is beneficial to reducing the number of irradiation cavities, hindering the accumulation of interstitial atoms and the formation of helium bubble clusters, improving the vacancy-interstitial atom recombination efficiency, and effectively improving the radiation resistance. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a schematic diagram of the dog-bone-shaped Li2TiO3 green body prepared by the present application;

[0036] Figure 2 It is an XRD pattern of the Li2TiO3 ceramic prepared by the flash sintering of Example 1 of the present application;

[0037] Figure 3 It is the SEM test results of the Li2TiO3 ceramic prepared by the present application and Example 1; (a) is the SEM image of the Li2TiO3 ceramic obtained by the conventional box furnace sintering; (b) is the SEM image of the Li2TiO3 ceramic prepared by the flash sintering of Example 1;

[0038] Figure 4 It is a high-magnification SEM image of the Li2TiO3 ceramic prepared by the flash sintering of Example 1 of the present application; wherein, (b) is an enlarged schematic view of the dashed box part in (a);

[0039] Figure 5SEM (5x10 4 times) images of Li2TiO3 ceramic prepared in Example 1-5 of the present application (corresponding to (a)-(e), respectively) to determine the effect of current density on grain boundary structure; wherein (a) 630℃-40mA / mm 2 ; (b) 630℃-60mA / mm 2 ; (c) 630℃-80mA / mm 2 ; (d) 680℃-60mA / mm 2 ; (e) 730℃-60mA / mm 2 .

[0040] Figure 6 SEM (5x10 3 times) images of Li2TiO3 ceramic prepared in Example 1-5 of the present application (corresponding to (a)-(e), respectively) under different flash conditions; (a) 630℃-40mA / mm 2 ; (b) 630℃-60mA / mm 2 ; (c) 630℃-80mA / mm 2 ; (d) 680℃-60mA / mm 2 ; (e) 730℃-60mA / mm 2 .

[0041] Figure 7 H2 desorption peak area of Li2TiO3 ceramic prepared in Example 1-5 of the present application under different flash conditions; wherein (a) shows H2 desorption peak area of Li2TiO3 ceramic under different flash current densities; (b) shows H2 desorption peak area of Li2TiO3 ceramic under different flash furnace temperatures. DETAILED DESCRIPTION

[0042] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0043] The preparation method of Li2TiO3 tritium breeder ceramic with mesoporous grain boundary structure provided by the present application mainly comprises:

[0044] Synthesis of Li2TiO3 ultrafine powder by low-temperature solid-phase method: weigh a certain amount of LiOH·H2O and TiO(OH)2 respectively and put them into a ball mill tank with a certain amount of agate ball mill ball, then add an appropriate amount of ball milling medium (anhydrous ethanol, solid-liquid mass ratio of 1:6-1:8) into the ball mill tank, then dry the suspension after ball milling in a rotary evaporator, and finally obtain the precursor powder by sieving, and then calcine the precursor powder in a box furnace to obtain Li2TiO3 ultrafine powder;

[0045] Dog bone-shaped Li2TiO3 green body forming: weigh a certain amount of Li2TiO3 ultrafine powder and put it into a dog bone-shaped mold, compact it, then put the mold into a tablet press to form a mold, apply a certain pressure to the sample, keep the pressure for a period of time, then demold to obtain a dog bone-shaped Li2TiO3 green body (as shown in Figure 1

[0046] Flash preparation of Li2TiO3 ceramic with mesoporous grain boundary structure: use a punch to punch holes in the middle of both ends of the green body, measure the distance between the two holes with a vernier caliper and record it, then measure the width and height of the middle of the green body, set the voltage and current according to the calculation results of the distance between the two holes and the cross-sectional area; then smear silver paste around the holes and on the inner wall to increase its conductivity; finally, use two platinum wire electrodes in the box furnace to pass through the holes at both ends of the green body and fix them, close the door, set the program (heating rate, holding time and other related parameters) on the panel interface, then start the flash program, turn off the power after flashing for a period of time, and take out the Li2TiO3 ceramic after cooling with the furnace.

[0047] The preparation method of Li2TiO3 tritium breeder ceramic with mesoporous grain boundary structure provided by the present application will be explained and verified in detail in combination with the following comparative examples and examples.

[0048] The names, models and manufacturers of the experimental equipment used in the following comparative examples and examples are shown in Table 1.

[0049] Table 1 Main instruments and equipment

[0050]

[0051]

[0052] The purity of the raw material LiOH·H2O used in the following comparative examples and examples is 99%, and the purity of the raw material TiO(OH)2 is 98%.

[0053] Comparative example

[0054] The preparation method of Li2TiO3 tritium breeder ceramic provided by the present example is as follows:

[0055] (1) Preparation of Li2TiO3 powder; this step includes the following sub-steps:​

[0056] (11) Raw material weighing: LiOH-H2O and TiO(OH)2 are used as raw materials, LiOH-H2O and TiO(OH)2 are weighed according to a molar ratio of 2:1, anhydrous ethanol is added in an amount of 6 times the mass of LiOH-H2O and TiO(OH)2 to fully mix them, and then the mixture is placed in a ball mill tank cleaned and dried with alcohol, a certain amount of 5mm agate balls and a certain amount of 2mm agate balls cleaned with alcohol are added to the ball mill tank, and the ball mill tank is sealed with plastic wrap;

[0057] (12) Planetary ball milling: the sealed ball mill tank is placed in a planetary ball mill, then the ball mill tank is fixed in the planetary ball mill, the ball milling speed is set to 300r / min, the ball milling time is 8h, and then the slurry is taken out after the ball milling is completed;

[0058] (13) Rotary evaporation: the slurry after ball milling is poured into a rotary evaporation flask through a funnel, the rotary evaporation flask is fixed on a rotary evaporator, the rotary evaporation temperature is set to 50℃, the rotary evaporation time is 2h, and then the mixed powder is taken out after the rotary evaporation is completed;

[0059] (14) Pre-sintering: the mixed powder after rotary evaporation is placed in a crucible and placed in a box furnace for pre-sintering in an air atmosphere; the pre-sintering conditions are: from room temperature to 500℃ at a heating rate of 5℃ / min, holding time of 4h, and then cooling in the furnace to obtain Li2TiO3 powder; the obtained Li2TiO3 powder is ground in a mortar and sieved through a 100 mesh sieve, and then dried and stored;

[0060] (2) Preparation of Li2TiO3 green body

[0061] 1.5g of Li2TiO3 powder is weighed and placed in a cylindrical mold, and then molded into a Li2TiO3 green body disc with a diameter of 20mm by a tablet press at a molding pressure of 3MPa and a holding time of 1min;

[0062] (3) Preparation of Li2TiO3 tritium breeder ceramic

[0063] The green body disc is placed in a crucible of a box furnace for sintering; the sintering conditions are: from room temperature to 500℃ at a heating rate of 10℃ / min, from 500℃ to 800℃ at a heating rate of 5℃ / min, then holding at 800℃ for 4h, then cooling from 800℃ to 500℃ at a cooling rate of 5℃ / min, and then cooling in the furnace after 500℃ to obtain Li2TiO3 tritium breeder ceramic.

[0064] Example 1

[0065] The preparation method of the Li2TiO3 tritium breeder ceramic provided in this embodiment comprises the following steps:

[0066] (1) Preparation of Li2TiO3 powder; this step includes the following sub-steps:

[0067] (11) Raw material weighing: LiOH H2O and TiO(OH)2 are used as raw materials, LiOH H2O and TiO(OH)2 are weighed according to a molar ratio of 2:1, and anhydrous ethanol is added to the LiOH H2O and TiO(OH)2 raw materials in an amount of 6 times the mass of the raw materials to fully mix them, and then placed in a ball mill tank that has been cleaned with alcohol and dried, a number of 5mm agate balls and a number of 2mm agate balls are added to the ball mill tank, and the ball mill tank is sealed with plastic wrap;

[0068] (12) Planetary ball milling: place the sealed ball mill tank in the planetary ball mill, then fix the ball mill tank in the planetary ball mill, set the ball milling speed to 300r / min, the ball milling time is 8h, after ball milling, take out the slurry;

[0069] (13) Rotary evaporation: pour the ball-milled slurry into a rotary evaporation flask through a funnel, fix the rotary evaporation flask on the rotary evaporator, set the rotary evaporation temperature to 50℃, the rotary evaporation time is 2h, after rotary evaporation, take out the mixed powder;

[0070] (14) Pre-burning: place the mixed powder after rotary evaporation in a crucible and place it in a box furnace for pre-burning in an air atmosphere; the pre-burning conditions are: from room temperature to 500℃ at a heating rate of 5℃ / min, holding time is 4h, after the program is completed, the furnace is cooled to obtain Li2TiO3 powder; the obtained Li2TiO3 powder is ground in a mortar and sieved through a 100 mesh sieve, then dried and stored;

[0071] (2) Preparation of Li2TiO3 green body

[0072] Weigh 0.5g of Li2TiO3 powder into a dog bone-shaped mold, place it in a tablet press to form a mold, the mold pressing pressure is 2.88MPa, the holding time is 1min, then demold to obtain a dog bone-shaped Li2TiO3 green body;

[0073] (3) Preparation of Li2TiO3 tritium breeder ceramic, this step includes the following sub-steps:

[0074] (31) Hole punching measurement: use a hole puncher to punch a hole with a diameter of 1mm in the middle of both ends of the dog bone green body, measure the distance between the two holes with a vernier caliper and record it, then continue to measure the width and height of the middle of the dog bone green body, the size of the green body is A1(20.15mm x 3.34mm x 1.80mm), then calculate the cross-sectional area of the green body;

[0075] (32) Apply silver paste: apply silver paste to the inner wall of the holes at both ends of the green body to increase its conductivity;

[0076] (33) Flashing: two platinum wire electrodes were respectively inserted into the holes at both ends of the dog-bone shaped Li2TiO3 ceramic and fixed, and the door of the furnace was closed; then the program was set on the power interface, the furnace temperature was set to 630℃, the electric field strength was set to 80V / cm, the current density was set to 40mA / mm2, the flashing time was set to 30s, the heating rate was set to 6℃ / min, and the holding time was set to 2h; after the furnace temperature was stable, the flashing program was started, the power was turned off after the flashing was completed, and the furnace was cooled to room temperature, thereby obtaining the dog-bone shaped Li2TiO3 ceramic. 2 , the flashing time was 30s, the heating rate was 6℃ / min, and the holding time was 2h; after the furnace temperature was stable, the flashing program was started, the power was turned off after the flashing was completed, and the furnace was cooled to room temperature, thereby obtaining the dog-bone shaped Li2TiO3 ceramic.

[0077] Example 2

[0078] The preparation method of the Li2TiO3 tritium breeder ceramic provided in this embodiment comprises the following steps:

[0079] (1) Preparation of Li2TiO3 powder; this step comprises the following sub-steps:

[0080] (11) Raw material weighing: LiOH·H2O and TiO(OH)2 were used as raw materials, LiOH·H2O and TiO(OH)2 were weighed according to a molar ratio of 2:1, 7 times the mass of LiOH·H2O and TiO(OH)2 was added to anhydrous ethanol to fully mix them, then they were placed in a ball mill tank cleaned with alcohol and dried, a certain amount of 5mm agate balls and a certain amount of 2mm agate balls cleaned with alcohol were added to the ball mill tank, and the ball mill tank was sealed with plastic wrap;

[0081] (12) Planetary ball milling: the sealed ball mill tank was placed in a planetary ball mill, then the ball mill tank was fixed in the planetary ball mill, the ball milling speed was set to 300r / min, the ball milling time was set to 8h, and the slurry was taken out after the ball milling was completed;

[0082] (13) Rotary evaporation: the slurry after ball milling was poured into a rotary evaporation flask through a funnel, the rotary evaporation flask was fixed on a rotary evaporator, the rotary evaporation temperature was set to 50℃, the rotary evaporation time was set to 2h, and the mixed powder was taken out after the rotary evaporation was completed;

[0083] (14) Pre-sintering: the mixed powder after rotary evaporation was placed in a crucible and pre-sintered in an air atmosphere in a box furnace; the pre-sintering conditions were as follows: the temperature was increased from room temperature to 500℃ at a rate of 5℃ / min, the holding time was 4h, and the furnace was cooled to obtain Li2TiO3 powder; the obtained Li2TiO3 powder was ground in a mortar and sieved through a 100 mesh sieve, and then dried and stored;

[0084] (2) Preparation of Li2TiO3 green body

[0085] Weigh 0.5 g of Li2TiO3 powder into a dog bone-shaped mold, and place it in a tablet press to form a mold, with a mold pressing pressure of 2.88 MPa and a pressure holding time of 1 min, and then demold to obtain a dog bone-shaped Li2TiO3 green body;

[0086] (3) Preparation of Li2TiO3 tritium breeder ceramic, which comprises the following steps:

[0087] (31) Punch measurement: a 1 mm diameter hole is punched in the middle of both ends of the dog bone green body using a puncher, and the distance between the two holes is measured and recorded using a vernier caliper, and then the width and height of the middle of the dog bone green body are measured to obtain the size of the green body A2 (18.98 mm x 3.37 mm x 1.81 mm), and then the cross-sectional area of the green body is calculated;

[0088] (32) Apply silver paste: apply silver paste to the inner wall of the holes at both ends of the green body to increase its conductivity;

[0089] (33) Flashing: two platinum wire electrodes in the box furnace are inserted through the holes at both ends of the dog bone green body and fixed, and the furnace door is closed; then set the program on the power supply interface, set the furnace temperature to 630℃, the electric field strength to 80V / cm, the current density to 60mA / mm 2 , the flashing time to 30s, and the heating rate to 6℃ / min, and the holding time to 2h; after the furnace temperature stabilizes, start the flashing program, turn off the power supply after flashing is completed, and cool the furnace to room temperature, obtaining a dog bone-shaped Li2TiO3 ceramic.

[0090] Example 3

[0091] The preparation method of the Li2TiO3 tritium breeder ceramic provided in this embodiment comprises the following steps:

[0092] (1) Preparation of Li2TiO3 powder; which comprises the following steps:

[0093] (11) Weigh the raw materials: take LiOH·H2O and TiO(OH)2 as raw materials, weigh LiOH·H2O and TiO(OH)2 according to a 2:1 molar ratio, and add anhydrous ethanol 8 times the mass of LiOH·H2O and TiO(OH)2 to mix them thoroughly, then place them in an alcohol-washed and dried ball mill jar, add a number of 5mm and 2mm agate balls washed with alcohol to the ball mill jar, and seal the ball mill jar with plastic wrap;

[0094] (12) Planetary ball milling: place the sealed ball mill jar in the planetary ball mill, then fix the ball mill jar in the planetary ball mill, set the ball milling speed to 300r / min, and the ball milling time to 8h, then take out the slurry after ball milling is completed;

[0095] (13) Rotary evaporation: the slurry after ball milling is poured into a rotary evaporation flask through a funnel, the rotary evaporation flask is fixed on a rotary evaporator, the rotary evaporation temperature is set to 50℃, the rotary evaporation time is 2h, and after the rotary evaporation is completed, the mixed powder is taken out;

[0096] (14) Pre-sintering: the mixed powder after rotary evaporation is placed in a crucible and placed in a box furnace for pre-sintering in an air atmosphere; the pre-sintering conditions are: from room temperature to 500℃ at a heating rate of 5℃ / min, holding time of 4h, and after the program is completed, the furnace is cooled to obtain Li2TiO3 powder; the obtained Li2TiO3 powder is ground in a mortar and sieved through a 100 mesh sieve, and then dried and stored;

[0097] (2) Preparation of Li2TiO3 green body

[0098] 0.5g of Li2TiO3 powder is weighed into a dog bone-shaped mold and placed in a tablet press for molding, the molding pressure is 2.88MPa, the holding time is 1min, and then the dog bone-shaped Li2TiO3 green body is obtained after demolding;

[0099] (3) Preparation of Li2TiO3 tritium breeder ceramic, which comprises the following steps:

[0100] (31) Hole punching measurement: a hole with a diameter of 1mm is punched in the middle of both ends of the dog bone green body using a hole puncher, the distance between the two holes is measured and recorded using a vernier caliper, and then the width and height of the middle of the dog bone green body are measured to obtain the size of the green body A3 (18.97mm x 3.37mm x 1.78mm), and then the cross-sectional area of the green body is calculated;

[0101] (32) Apply silver paste: apply silver paste to the inner wall of the holes at both ends of the green body to increase its conductivity;

[0102] (33) Flash sintering: two platinum wire electrodes in the box furnace are inserted through the holes at both ends of the dog bone green body and fixed, and the furnace door is closed; then a program is set on the power supply interface, the furnace temperature is set to 630℃, the electric field strength is 80V / cm, the current density is 80mA / mm 2 , the flash sintering time is 30s, the heating rate is 6℃ / min, and the holding time is 2h; after the furnace temperature is stabilized, the flash sintering program is started, the power is turned off after the flash sintering is completed, and the furnace is cooled to room temperature to obtain a dog bone-shaped Li2TiO3 ceramic.

[0103] Example 4

[0104] The preparation method of the Li2TiO3 tritium breeder ceramic provided in this embodiment comprises the following steps:

[0105] (1) Preparation of Li2TiO3 powder; this step comprises the following sub-steps:

[0106] (11) Raw material weighing: LiOH H2O and TiO(OH)2 are used as raw materials, LiOH H2O and TiO(OH)2 are weighed according to a molar ratio of 2:1, anhydrous ethanol is added in an amount of 7 times the mass of LiOH H2O and TiO(OH)2 to fully mix them, and then the mixture is placed in a ball mill tank cleaned and dried with alcohol, a certain amount of 5mm agate balls and a certain amount of 2mm agate balls cleaned with alcohol are added to the ball mill tank, and the ball mill tank is sealed with plastic wrap;

[0107] (12) Planetary ball milling: the sealed ball mill tank is placed in a planetary ball mill, then the ball mill tank is fixed in the planetary ball mill, the ball milling speed is set to 300r / min, the ball milling time is 8h, and the slurry is taken out after ball milling;

[0108] (13) Rotary evaporation: the solution after ball milling is poured into a rotary evaporation flask through a funnel, the rotary evaporation flask is fixed on a rotary evaporator, the rotary evaporation temperature is set to 50℃, the rotary evaporation time is 2h, and the mixed powder is taken out after rotary evaporation;

[0109] (14) Calcination: the mixed powder after rotary evaporation is placed in a crucible and placed in a box furnace for calcination in an air atmosphere; the calcination conditions are: the temperature is increased from room temperature to 500℃ at a rate of 5℃ / min, the holding time is 4h, and the Li2TiO3 powder is obtained after the program is completed and the furnace is cooled; the obtained Li2TiO3 powder is ground in a mortar and sieved through a 100 mesh sieve, and then dried and stored;

[0110] (2) Preparation of Li2TiO3 green body

[0111] 0.5g of Li2TiO3 powder is weighed and placed in a dog bone-shaped mold, and then molded into a dog bone-shaped Li2TiO3 green body by a tablet press with a molding pressure of 2.88MPa and a holding time of 1min;

[0112] (3) Preparation of Li2TiO3 tritium breeder ceramic, which comprises the following steps:

[0113] (31) Hole punching measurement: a 1mm diameter hole is punched in the middle of both ends of the dog bone green body using a hole puncher, the distance between the two holes is measured and recorded using a vernier caliper, and then the width and height of the middle of the dog bone green body are measured to obtain the size of the green body A4 (17.70mm x 3.38mm x 1.76mm), and then the cross-sectional area of the green body is calculated;

[0114] (32) Silver paste smearing: silver paste is smeared on the inner wall of the holes at both ends of the green body to increase its conductivity;

[0115] (33) Flashing: two platinum wire electrodes in the box furnace were respectively inserted through the holes at both ends of the dog-bone-shaped lithium titanate ceramic and fixed, and the furnace door was closed; then the program was set at the power interface, the furnace temperature was set to 680℃, the electric field strength was set to 80V / cm, the current density was set to 60mA / mm, the flashing time was set to 30s, the heating rate was set to 6℃ / min, and the holding time was set to 2h; after the furnace temperature was stable, the flashing program was started, the power was turned off after the flashing was completed, and the furnace was cooled to room temperature, thereby obtaining the dog-bone-shaped lithium titanate ceramic. 2 , the flashing time was 30s, the heating rate was 6℃ / min, and the holding time was 2h; after the furnace temperature was stable, the flashing program was started, the power was turned off after the flashing was completed, and the furnace was cooled to room temperature, thereby obtaining the dog-bone-shaped lithium titanate ceramic.

[0116] Example 5

[0117] The preparation method of the Li2TiO3 tritium breeder ceramic provided in the embodiment comprises the following steps:

[0118] (1) Preparation of Li2TiO3 powder; the step comprises the following sub-steps:

[0119] (11) Raw material weighing: LiOH·H2O and TiO(OH)2 were used as raw materials, LiOH·H2O and TiO(OH)2 were weighed according to a molar ratio of 2:1, anhydrous ethanol was added in an amount of 6 times the mass of LiOH·H2O and TiO(OH)2 to fully mix them, and then the mixture was placed in a ball mill tank cleaned with alcohol and dried, a certain amount of 5mm agate balls and a certain amount of 2mm agate balls cleaned with alcohol were added to the ball mill tank, and the ball mill tank was sealed with plastic wrap;

[0120] (12) Planetary ball milling: the sealed ball mill tank was placed in a planetary ball mill, and then the ball mill tank was fixed in the planetary ball mill, the ball milling speed was set to 300r / min, the ball milling time was set to 8h, and the slurry was taken out after the ball milling was completed;

[0121] (13) Rotary evaporation: the solution after ball milling was poured into a rotary evaporation flask through a funnel, the rotary evaporation flask was fixed on a rotary evaporator, the rotary evaporation temperature was set to 50℃, the rotary evaporation time was set to 2h, and the mixed powder was taken out after the rotary evaporation was completed;

[0122] (14) Pre-sintering: the mixed powder after rotary evaporation was placed in a crucible and pre-sintered in an air atmosphere in a box furnace; the pre-sintering conditions were as follows: the temperature was increased from room temperature to 500℃ at a rate of 5℃ / min, the holding time was 4h, and the program was completed, and the Li2TiO3 powder was obtained by cooling in the furnace; the obtained Li2TiO3 powder was ground in a mortar and sieved through a 100 mesh sieve, and then dried and stored;

[0123] (2) Preparation of Li2TiO3 green body

[0124] 0.5g of Li2TiO3 powder was placed in a dog-bone-shaped mold, and a tablet press was used to press the mold to form a dog-bone-shaped Li2TiO3 green body, the mold pressing pressure was 2.88MPa, the holding time was 1min, and then the mold was removed to obtain the dog-bone-shaped Li2TiO3 green body.

[0125] (3) preparing Li2TiO3 tritium breeder ceramic, comprising the following steps:

[0126] (31) punching measurement: punching a 1mm diameter hole in the middle of both ends of the dog bone-shaped green body respectively, measuring the distance between the two holes with a vernier caliper and recording, then measuring the width and height of the middle of the dog bone-shaped green body to obtain the size of the green body A5 (18.72mm x 3.34mm x 1.80mm), and then calculating the cross-sectional area of the green body;

[0127] (32) silver paste smearing: smearing silver paste on the inner wall of the holes at both ends of the green body to increase its conductivity;

[0128] (33) flashing: inserting two platinum wire electrodes in the box furnace through the holes at both ends of the dog bone-shaped green body and fixing, closing the furnace door; setting the program at the power interface, setting the furnace temperature to 730℃, the electric field strength to 80V / cm, the current density to 60mA / mm 2 , the flashing time to 30s, the heating rate to 6℃ / min, and the holding time to 2h; starting the flashing program after the furnace temperature is stable, closing the power supply after flashing, and cooling to room temperature with the furnace to obtain the dog bone-shaped Li2TiO3 ceramic.

[0129] The Li2TiO3 tritium breeder ceramic prepared in the above comparative examples and examples is analyzed in terms of morphology and structure:

[0130] According to the Archimedes principle, the density of the Li2TiO3 ceramic is measured by using a Mettler-Toledo electronic analytical balance; the densities of the Li2TiO3 ceramics prepared in examples 1-5 of the application are 2.727g / cm 3 , 2.835g / cm 3 , 2.844g / cm 3 , 2.856g / cm 3 and 2.953g / cm 3 , respectively; and the density of the Li2TiO3 ceramic in the comparative example is 2.751g / cm 3 .

[0131] The Li2TiO3 ceramic prepared in example 1 of the application is subjected to XRD test after flashing, and the test results are shown in Figure 2 From the figure, it can be seen that the diffraction peaks in the figure correspond to the product monoclinal Li2TiO3, and no impurity peaks appear.

[0132] The Li2TiO3 ceramic prepared in the comparative example and example 1 of the application is subjected to SEM test after flashing, and the test results are shown in Figure 3The sintered sample has large pores and low density, while the flash sintered sample has obvious sintering necks and the pore size is significantly reduced, indicating that flash sintering helps to densify Li2TiO3 ceramics, which is also confirmed by density testing; at the same time, the cross section of Li2TiO3 ceramic has a "ring" shaped grain boundary structure (as shown in Figure 4 ) ; these "ring" shaped grain boundary structures provide a large number of nanoscale channels, which not only increase the specific surface area of the grain boundary, but also enrich the diffusion channels of tritium, thereby improving the tritium release efficiency of the tritium breeder.

[0133] In order to study the effect of current density on the grain boundary structure of the prepared Li2TiO3 ceramic, high-magnification SEM testing was performed on Li2TiO3 ceramics prepared at different current densities, and the test results are shown in Figure 5 and 6 .

[0134] From Figure 5 , the effects of current density and furnace temperature on the grain boundary structure can be observed: as shown in Figure 5 (a)-(c), when the current density is 40mA / mm 2 , 60mA / mm 2 and 80mA / mm 2 respectively, the diameters of the grain boundary nanochannels are close, and the continuity of the nanochannel structure is observed at the grain boundary of the two grains, indicating that the plastic deformation strain can efficiently propagate along the grain boundary during flash sintering; when the current density increases to 80mA / mm 2 , the nanochannel diameter decreases significantly and the channel density increases significantly, which may be caused by the increase of flash sintering power consumption, resulting in a serious accumulation of dislocations; as shown in Figure 5 (b), (d), (e), as the furnace temperature increases from 630℃ to 730℃, the diameter of the grain boundary nanochannel increases significantly; however, the power consumption gradually decreases as the furnace temperature increases, especially for the samples with a furnace temperature of 680℃ and 730℃, the power consumption decreases from 170mW / mm 3 to 150mW / mm 3 ; the decrease of power consumption leads to a decrease of plastic deformation rate, which may be the main reason for the increase of nanochannel diameter.

[0135] The effect of current density on the grain size of Li2TiO3 is shown in Figure 6 (a)-(c); when the current density is 40mA / mm 2 , the Li2TiO3 grains are small and uniform; when the current density increases to 60mA / mm 2 , small grains appear around the large grains, but the overall grain size is still small, and the average grain size of both is about 3μm; as the current density increases to 80mA / mm 2At this time, the grain growth is obvious, and the average grain size is about 6 μm. In addition, the effect of furnace temperature on the Li2TiO3 grain size is shown in Figure 6 (b), (d), (e); with the furnace temperature increasing from 630 ℃ to 730 ℃, the sample grain size slightly increases, and the maximum grain size is about 7 μm; it is shown that the increase of the furnace temperature promotes the grain growth. The comparison of the effects of the current density and the furnace temperature on the Li2TiO3 grain size shows that the effect of the current density is much greater than that of the furnace temperature.

[0136] The tritium release capacity of the Li2TiO3 tritium breeder ceramic prepared in the above examples 1-5 is analyzed:

[0137] In order to further prove that the "annual ring" grain boundary structure is beneficial to the tritium release efficiency of the tritium breeder, H2 is used as a replacement gas to study the H2 desorption behavior of the Li2TiO3 ceramic after flashing. The experimental test process is as follows:

[0138] (1) Pretreatment: heated from room temperature to 800 ℃ under the atmosphere of 10% H2-90% Ar (flow rate is 30 mL / min), and the heating rate is 10 ℃ / min;

[0139] (2) Cooling treatment: cooled to room temperature under the atmosphere of Ar (flow rate is 30 mL / min), and the cooling rate is 10 ℃ / min; adsorption: adsorption is started at room temperature by using 10% H2-90% Ar mixed gas (mixed gas flow rate is 30 mL / min), and the adsorption is saturated until the baseline is stable;

[0140] (3) Purging: after the adsorption is saturated at room temperature, purging is started by using Ar (flow rate is 30 mL / min) until the baseline is stable; programmed temperature desorption: the programmed temperature is started under the atmosphere of Ar (flow rate is 30 mL / min), and the data is recorded, and the temperature is increased to 800 ℃ at the heating rate of 10 ℃ / min;

[0141] (4) Test end: then cooled to room temperature under the atmosphere of Ar (flow rate is 30 mL / min), and the test is ended.

[0142] Figure 7 The H2 desorption peak areas of the Li2TiO3 ceramic under different flashing current densities are shown in (a), and the H2 desorption peak areas of the Li2TiO3 ceramic under different flashing furnace temperatures are shown in (b); for the samples prepared under different flashing current densities, the greater the current density, the greater the total amount of H2 desorption of the sample, which is mainly due to the decisive role of the increase of the density of the grain boundary nanochannel; and for the samples prepared under different flashing furnace temperatures, the higher the furnace temperature, the greater the total amount of H2 desorption of the sample, which is mainly due to the decisive role of the increase of the diameter of the nanochannel. Figure 7 (a)) and the H2 desorption peak areas of the Li2TiO3 ceramic under different flashing furnace temperatures are shown in (b); for the samples prepared under different flashing current densities, the greater the current density, the greater the total amount of H2 desorption of the sample, which is mainly due to the decisive role of the increase of the density of the grain boundary nanochannel; and for the samples prepared under different flashing furnace temperatures, the higher the furnace temperature, the greater the total amount of H2 desorption of the sample, which is mainly due to the decisive role of the increase of the diameter of the nanochannel. Figure 7 (a)) and the H2 desorption peak areas of the Li2TiO3 ceramic under different flashing furnace temperatures are shown in (b); for the samples prepared under different flashing current densities, the greater the current density, the greater the total amount of H2 desorption of the sample, which is mainly due to the decisive role of the increase of the density of the grain boundary nanochannel; and for the samples prepared under different flashing furnace temperatures, the higher the furnace temperature, the greater the total amount of H2 desorption of the sample, which is mainly due to the decisive role of the increase of the diameter of the nanochannel.

[0143] In summary, the application synthesizes and screens Li2TiO3 superfine powder by low-temperature solid-phase method, then places the dog bone-shaped mold filled with Li2TiO3 superfine powder in a tablet press to press the dog bone-shaped Li2TiO3 blank, and finally sinter the dog bone-shaped blank through a flash firing device to obtain high-tritium-release Li2TiO3 tritium breeder ceramic with mesoporous grain boundary structure. Compared with the traditional sintering method, the lithium volatilization caused by continuous high-temperature heating is reduced, and the lithium density of the breeder is ensured to be high; the application adopts the flash firing process to obtain the "annual ring" shaped grain boundary structure, increases the specific surface area of the grain boundary, enriches the diffusion channels of tritium, improves the tritium release efficiency, and has great application prospect.

[0144] Those skilled in the art will appreciate that the embodiments herein are presented to aid the reader in understanding the principles of the application and should be construed as not limiting the scope of the protection of the application to such specifically recited embodiments and examples. Those skilled in the art can make various other specific modifications and combinations according to the technical inspiration disclosed in the application without departing from the spirit of the application, and these modifications and combinations are still within the scope of protection of the application.

Claims

1. A method for preparing Li2TiO3 tritium breeder ceramic with mesoporous grain boundary structure, comprising: (1) preparing Li2TiO3 powder; (2) preparing Li2TiO3 green body: placing the Li2TiO3 powder in a mold, then placing the mold in a tablet press to form a Li2TiO3 green body, and removing the mold to obtain a Li2TiO3 green body; (3) preparing Li2TiO3 tritium breeder ceramic: punching holes in the middle of the Li2TiO3 green body, measuring the distance between the two holes and the width and height of the middle of the Li2TiO3 green body, and calculating the cross-sectional area of the Li2TiO3 green body; then applying silver paste to the inner wall of the holes at both ends of the Li2TiO3 green body and the periphery; then inserting two platinum wire electrodes in the box furnace through the holes at both ends of the green body and fixing them, and closing the furnace door; the preparation process of the Li2TiO3 powder comprises: (11) placing LiOH·H2O and TiO(OH)2 in a ball mill tank containing a plurality of agate balls, and adding ball milling medium, and sealing the ball mill tank; (12) placing the sealed ball mill tank in a planetary ball mill for ball milling to obtain a slurry; (13) performing rotary evaporation drying on the ball-milled slurry to obtain a mixed powder; (14) placing the mixed powder in a crucible and placing it in a box furnace for pre-sintering in an air atmosphere; then grinding and sieving to obtain Li2TiO3 powder. In the step (11), the molar ratio of LiOH·H2O to TiO(OH)2 is 2:1, and the diameter of the agate balls is 2-5 mm. In the step (13), the rotary evaporation temperature is 40-60℃, and the rotary evaporation time is 2-4 h. In the step (14), the pre-sintering temperature of the mixed powder is 500-600℃, and the pre-sintering time is 2-4 h. In the step (2), the mold is a dog bone-shaped mold, and the obtained Li2TiO3 green body is a dog bone-shaped green body. In the step (2), during the mold forming process, the mold pressure is 2.5-3.5 MPa, and the pressure holding time is 1-1.5 min. In the step (3), the hole diameter punched in the middle of the Li2TiO3 green body is 0.8-1.2 mm.

9. Li2TiO3 tritium breeder ceramic with mesoporous grain boundary structure prepared by the method of any one of claims 1-8. ​ ​ ​ ​ According to the two-hole spacing and Li2TiO3 blank cross-sectional area, the furnace temperature is set to 600-800℃ and the flash parameters, after the furnace temperature is stable, the Li2TiO3 blank is flash-fired, the power is turned off after the flash firing is completed, and the furnace is cooled to obtain the Li2TiO3 tritium breeder ceramic; the flash parameters include an electric field intensity of 70-100 V / cm, a current density of 40-60 mA / mm 2 and a flash time of 10-30s.

2. The method for preparing the Li2TiO3 tritium breeder ceramic having a mesoporous grain boundary structure according to claim 1, wherein: ​ ​ ​ ​ ​ 3. The method of claim 2, wherein the method is characterized by: ​ 4. The method of claim 2, wherein the Li2TiO3 tritium breeder ceramic with mesoporous grain boundary structure is prepared by the steps of: ​ 5. The method for preparing the Li2TiO3 tritium breeder ceramic having a mesoporous grain boundary structure according to claim 2, wherein: ​ 6. The method of claim 1, wherein the method is characterized by: ​ 7. The method of claim 1 or 6, wherein the method is characterized by, ​ 8. The method of claim 1, wherein the method is characterized by: ​ ​

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