Method for rapid sintering of high-density lithium titanate fine-grain ceramics based on electric pulses

Abstract

The application discloses a high-density lithium titanate fine-grain ceramic rapid sintering method based on electric pulse, which comprises the following steps: lithium titanate powder is prepared by a solid phase method; lithium titanate ceramic green bodies are obtained by tabletting the lithium titanate powder; the lithium titanate ceramic green bodies are placed in the middle of two pieces of graphite felt; and the rapid sintering is carried out under the action of a high-frequency direct-current pulse power, so that the high-density lithium titanate fine-grain ceramic is obtained. The high-frequency pulse direct-current is applied to both ends of the graphite felt, so that the Joule heat is generated in the graphite felt, the lithium titanate ceramic green bodies sandwiched in the middle of the graphite felt are rapidly sintered and densified, the lithium ceramic grain growth and lithium evaporation under long-time sintering are overcome, the density and grain size of the lithium titanate ceramic can be controlled by adjusting the pulse voltage and time; due to the high heating rate and short sintering time, the prepared fine-grain high-density lithium titanate ceramic has high compressive strength and bending strength, and the comprehensive mechanical properties of the lithium titanate ceramic during service are ensured to a certain extent.

Description

Technical Field

[0001] This invention belongs to the field of solid-state tritium breeding materials technology, and relates to a rapid sintering method for high-density lithium titanate fine-grained ceramics based on electrical pulses. Background Technology

[0002] Lithium ceramics play a crucial role in tritium production and heat transfer. Among them, lithium titanate (Li₂TiO₃) ceramics have become one of the preferred materials for solid tritium breeding agents due to their excellent chemical stability, high melting point, and good low-temperature tritium release performance. Studies have shown that refining the grain size of lithium titanate ceramics is beneficial to improving its mechanical strength and tritium release performance. Furthermore, with grain refinement, the number of grain boundaries available for pinning irradiation defects increases, thus improving the radiation resistance of the ceramic. However, the preparation of highly dense, fine-grained lithium titanate ceramics still faces many challenges.

[0003] Although some literature, such as the Journal of Nuclear Materials and Ceramics International (Wang, Hailiang, et al. Low-temperature preparation of nanostructured Li2TiO3 tritium breeder ceramic pebbles using CTAB-modified ultrafine powders by a mixed solvent-thermal method, Journal of Nuclear Materials, 2019, 519:315-321; and Wang, Hailiang, et al. An innovative process for synthesis of superfinenanostructured Li2TiO3 tritium breeder ceramic pebbles via TBOT hydrolysis-solvothermal method, Ceramics International, 2019, 45(5):5189-5194), has successfully prepared fine-grained lithium titanate ceramics by lowering the sintering temperature, the prepared lithium titanate ceramics have low density, which seriously affects the mechanical and physical properties of lithium titanate ceramics.

[0004] Chinese patent application number 201810873029.9, published on November 3, 2020, entitled "A high-sphericity tritium breeding agent nanostructured lithium titanate ceramic spheres and its preparation method," and literature Ceramics International (Wang, Hailiang, et al. Fabrication of nanostructured Li2TiO3 ceramic pebbles astritium breeders using powder particles synthesized via a CTAB-assisted method, Ceramics International, 2017, 43(7):5680-5686) use the surfactant CTAB (hexadecyltrimethylammonium bromide) assisted hydrothermal method to synthesize lithium titanate nanopowder, and then sinter it at 800℃ for 4 h to obtain lithium titanate ceramic with an average grain size of 90 nm and a ceramic density of 89.71%. However, the above methods require the use of a large amount of surfactant, which is not conducive to large-scale production, and insufficient volatilization of surfactant will lead to the residue of carbon impurities, which seriously affects the release and extraction of tritium.

[0005] Currently, the sintering method for lithium ceramic tritium breeding agents mainly adopts conventional sintering, making it difficult to simultaneously achieve densification (requiring high sintering temperatures) and grain refinement (requiring low sintering temperatures) in lithium ceramics. Rapid sintering is a feasible path to solve the grain growth problem during the sintering process of lithium ceramics. The literature "Ceramics International (Yang M, et al. CoMParison of the microwave and conventional sintering of Li2TiO3 ceramic pebbles. Ceramics International, 2018, 44(16):19672-19677)" uses microwave sintering to reduce the sintering temperature (800℃) and shorten the sintering time, obtaining lithium titanate fine-grained ceramics with a density of 89%. However, the heating rate of microwave sintering is still limited (generally 0.83℃ / s), and the equipment is complex and costly. If a new rapid sintering method for lithium ceramics can be developed to improve the heating rate and shorten the sintering time, it will provide a guarantee for the large-scale preparation of high-density lithium titanate fine-grained ceramics. Summary of the Invention

[0006] The purpose of this invention is to provide a rapid sintering method for high-density lithium titanate fine-grained ceramics based on electrical pulses, which can rapidly achieve densification without significant grain growth.

[0007] The technical solution adopted in this invention is a rapid sintering method for high-density lithium titanate fine-grained ceramics based on electrical pulses, comprising the following steps:

[0008] Step 1: Prepare lithium titanate powder using a solid-state method, including mixing TiO2 and Li2CO3 evenly, drying and calcining to obtain lithium titanate powder;

[0009] Step 2: Press the lithium titanate powder into tablets to obtain lithium titanate ceramic green bodies;

[0010] Step 3: Place the lithium titanate ceramic green body between two graphite felts and sinter it rapidly under the action of a high-frequency DC pulse power supply to obtain high-density lithium titanate fine-grained ceramic.

[0011] The specific process of step 1 is as follows:

[0012] Step 1.1: Weigh out TiO2 and Li2CO3 in a molar ratio of 1:1 to 1:1.1, place them in a WC ball mill jar, add WC grinding balls in a ball-to-material ratio of 15:1 to 20:1, and pour in 50 mL to 70 mL of alcohol.

[0013] Step 1.2: Place the ball mill jar from Step 1.1 into a high-energy ball mill for ball milling;

[0014] Step 1.3: Pour the ball-milled product into a petri dish and then place it in a drying oven for drying at 80-100℃;

[0015] Step 1.4: Grind the dried powder and calcine it in a muffle furnace at 400-600℃ to obtain lithium titanate powder.

[0016] In step 1.2, the high-energy ball mill rotates at 180-200 rpm, and the ball milling time is 12-24 hours, with a 10-minute break after every 1-2 hours of ball milling.

[0017] In step 1.3, the drying time is 10h to 12h.

[0018] In step 1.4, the sample is placed in a muffle furnace and calcined at 400-600℃ for 2-4 hours.

[0019] Step 2 involves pouring the lithium titanate powder prepared in Step 1 into a mold, pressing it to 6MPa~14MPa in a tablet press, and holding it for ≥90s to obtain lithium titanate ceramic green body.

[0020] Step 3 is as follows:

[0021] Step 3.1: Align the two graphite felt pieces, secure them between the two copper electrodes with nuts, and place them in the glove box;

[0022] Step 3.2: Place the lithium titanate ceramic green body between two graphite felts and evacuate the glove box to a vacuum level greater than 0.09 MPa.

[0023] Step 3.3: Turn on the high-frequency DC pulse power supply connected to the copper electrode, set the voltage to 40-50V, maintain it for a period of time, then adjust the voltage to zero and remove the vacuum to obtain high-density lithium titanate fine-grained ceramic.

[0024] In step 3.3, the frequency of the high-frequency DC pulse power supply is 500Hz.

[0025] In step 3.3, set the voltage to 40-50V, maintain it for 5-10 minutes, and then adjust the voltage to zero.

[0026] The beneficial effects of this invention are that by applying a high-frequency pulsed DC current to both ends of the graphite felt, Joule heating is generated in the graphite felt, thereby rapidly sintering and densifying the lithium titanate ceramic green body sandwiched in the middle of the graphite felt. This overcomes the grain growth and lithium volatilization of lithium ceramics under long-term sintering. By adjusting the pulse voltage and time, the density and grain size of lithium titanate ceramics can also be controlled. Due to the fast heating rate and short sintering time, the prepared fine-grained high-density lithium titanate ceramic has high compressive strength and flexural strength, which to a certain extent ensures its comprehensive mechanical properties during service. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the electric pulse ceramic sintering device in this invention;

[0028] Figure 2 These are the XRD patterns of the high-density lithium titanate fine-grained ceramics in Examples 1-3 of this invention;

[0029] Figure 3 This is a SEM image of the cross-section of the lithium titanate ceramic sheet in Example 1;

[0030] Figure 4 This is a SEM image of the cross-section of the lithium titanate ceramic sheet in Example 2;

[0031] Figure 5 This is a SEM image of the cross-section of the lithium titanate ceramic sheet in Example 3.

[0032] In the figure, 1. glove box, 2. graphite felt, 3. lithium titanate ceramic green body, 4. wire, 5. high-frequency DC pulse power supply. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0034] This invention relates to a rapid sintering method for high-density lithium titanate fine-grained ceramics based on electrical pulses, comprising the following steps:

[0035] Step 1: Prepare lithium titanate powder using a solid-state method. The specific process is as follows:

[0036] Step 1.1: Weigh out TiO2 and Li2CO3 in a molar ratio of 1:1 to 1:1.1, place them in a WC ball mill jar, add WC grinding balls in a ball-to-material ratio of 15:1 to 20:1, and pour in 50 mL to 70 mL of alcohol.

[0037] Step 1.2: Place the ball milling jar from Step 1.1 into a high-energy ball mill for ball milling. During the ball milling process, the high-energy ball mill speed is 180-200 rpm, the ball milling time is 12-24 hours, and there is a 10-minute break every 1-2 hours of ball milling.

[0038] Step 1.3: Pour the ball-milled product into a petri dish and then place it in a drying oven at 80-100℃ for 10-12 hours.

[0039] Step 1.4: Grind the dried powder and calcine it in a muffle furnace at 400-600℃ for 2-4 hours to obtain lithium titanate powder.

[0040] Step 2: Pour the lithium titanate powder prepared in Step 1 into a mold, press it in a tablet press to 6MPa~14MPa, and hold it for ≥90s to obtain lithium titanate ceramic green body.

[0041] Step 3: High-density lithium titanate fine-grained ceramics are prepared using an electric pulse ceramic sintering apparatus, referring to... Figure 1 The specific process is as follows:

[0042] Step 3.1: Align the two graphite felts 2, fix them between the two copper electrodes with nuts, and place them in the glove box 1. The two copper electrodes are connected to the high-frequency DC pulse power supply 5 through the wires 4.

[0043] Step 3.2: Place the lithium titanate ceramic green body 3 between two graphite felts 2, and evacuate the glove box 1 to make the vacuum degree greater than 0.09 MPa.

[0044] Step 3.3: Turn on the 500Hz high-frequency DC pulse power supply 5, set the voltage to 40-50V, maintain it for 5-10 minutes, then adjust the voltage to zero and remove the vacuum to obtain high-density lithium titanate fine-grained ceramic.

[0045] Example 1

[0046] A rapid sintering method for high-density lithium titanate fine-grained ceramics based on electrical pulses includes the following steps:

[0047] Step 1: Prepare lithium titanate powder using a solid-state method. The specific process is as follows:

[0048] Step 1.1: Weigh out TiO2 and Li2CO3 in a molar ratio of 1:1, place them in a WC ball mill jar, add WC grinding balls in a ball-to-material ratio of 15:1, and pour in 50 mL of alcohol.

[0049] Step 1.2: Place the ball milling jar from Step 1.1 into the high-energy ball mill for ball milling. During the ball milling process, the high-energy ball mill rotates at 180 rpm and the ball milling time is 12 hours, with a 10-minute break after every 1 hour of ball milling.

[0050] Step 1.3: Pour the ball-milled product into a petri dish and then place it in a drying oven at 80°C for 10 hours.

[0051] Step 1.4: Grind the dried powder and calcine it in a muffle furnace at 400°C for 2 hours to obtain lithium titanate powder.

[0052] Step 2: Weigh 0.6g of lithium titanate powder and pour it into the mold. Press it to 6MPa in the tablet press and hold the pressure for 90s to obtain lithium titanate ceramic green body.

[0053] Step 3: High-density lithium titanate fine-grained ceramics are prepared using an electric pulse ceramic sintering apparatus. The specific process is as follows:

[0054] Step 3.1: Align the two graphite felt pieces (80mm×40mm×5mm), fix them between the two copper electrodes with nuts, and place them in the glove box 1. The two copper electrodes are connected to the high-frequency DC pulse power supply 5 through the wire 4.

[0055] Step 3.2: Place the lithium titanate ceramic green body 3 between two graphite felts 2, and evacuate the glove box 1 to make the vacuum degree greater than 0.09 MPa.

[0056] Step 3.3: Turn on the 500Hz high-frequency DC pulse power supply 5, set the voltage to 40V, maintain it for 10 minutes, then adjust the voltage to zero and remove the vacuum to obtain high-density lithium titanate fine-grained ceramic.

[0057] Example 2

[0058] A rapid sintering method for high-density lithium titanate fine-grained ceramics based on electrical pulses includes the following steps:

[0059] Step 1: Prepare lithium titanate powder using a solid-state method. The specific process is as follows:

[0060] Step 1.1: Weigh out TiO2 and Li2CO3 in a molar ratio of 1:1.1, place them in a WC ball mill jar, add WC grinding balls in a ball-to-material ratio of 20:1, and pour in 70 mL of alcohol.

[0061] Step 1.2: Place the ball milling jar from Step 1.1 into a high-energy ball mill for ball milling. During the ball milling process, the high-energy ball mill rotates at 200 rpm and the ball milling time is 24 hours, with a 10-minute break every 2 hours of ball milling.

[0062] Step 1.3: Pour the ball-milled product into a petri dish and then place it in a drying oven at 90°C for 12 hours.

[0063] Step 1.4: Grind the dried powder and calcine it in a muffle furnace at 600°C for 3 hours to obtain lithium titanate powder.

[0064] Step 2: Weigh 0.6g of lithium titanate powder and pour it into the mold. Press it to 14MPa in the tablet press and hold the pressure for 90s to obtain lithium titanate ceramic green body.

[0065] Step 3: High-density lithium titanate fine-grained ceramics are prepared using an electric pulse ceramic sintering apparatus. The specific process is as follows:

[0066] Step 3.1: Align the two graphite felt pieces (100mm×20mm×3mm), fix them between the two copper electrodes with nuts, and place them in the glove box 1. The two copper electrodes are connected to the high-frequency DC pulse power supply 5 through the wire 4.

[0067] Step 3.2: Place the lithium titanate ceramic green body 3 between two graphite felts 2, and evacuate the glove box 1 to make the vacuum degree greater than 0.09 MPa.

[0068] Step 3.3: Turn on the 500Hz high-frequency DC pulse power supply 5, set the voltage to 45V, maintain it for 10 minutes, then adjust the voltage to zero and remove the vacuum to obtain high-density lithium titanate fine-grained ceramic.

[0069] Example 3

[0070] A rapid sintering method for high-density lithium titanate fine-grained ceramics based on electrical pulses includes the following steps:

[0071] Step 1: Prepare lithium titanate powder using a solid-state method. The specific process is as follows:

[0072] Step 1.1: Weigh out TiO2 and Li2CO3 in a molar ratio of 1:1.1, place them in a WC ball mill jar, add WC grinding balls in a ball-to-material ratio of 20:1, and pour in 70 mL of alcohol.

[0073] Step 1.2: Place the ball milling jar from Step 1.1 into a high-energy ball mill for ball milling. During the ball milling process, the high-energy ball mill rotates at 190 rpm and the ball milling time is 20 hours, with a 10-minute break every 1.5 hours of ball milling.

[0074] Step 1.3: Pour the ball-milled product into a petri dish and then place it in a drying oven at 100°C for 11 hours.

[0075] Step 1.4: Grind the dried powder and calcine it in a muffle furnace at 500°C for 4 hours to obtain lithium titanate powder.

[0076] Step 2: Weigh 0.6g of lithium titanate powder and pour it into the mold. Press it to 14MPa in the tablet press and hold the pressure for 90s to obtain lithium titanate ceramic green body.

[0077] Step 3: High-density lithium titanate fine-grained ceramics are prepared using an electric pulse ceramic sintering apparatus. The specific process is as follows:

[0078] Step 3.1: Align the two graphite felt pieces (100mm×30mm×3mm), fix them between the two copper electrodes with nuts, and place them in the glove box 1. The two copper electrodes are connected to the high-frequency DC pulse power supply 5 through the wire 4.

[0079] Step 3.2: Place the lithium titanate ceramic green body 3 between two graphite felts 2, and evacuate the glove box 1 to make the vacuum degree greater than 0.09 MPa.

[0080] Step 3.3: Turn on the 500Hz high-frequency DC pulse power supply 5, set the voltage to 50V, maintain it for 5 minutes, then adjust the voltage to zero and remove the vacuum to obtain high-density lithium titanate fine-grained ceramic.

[0081] The XRD patterns of the high-density lithium titanate fine-grained ceramics prepared in Examples 1-3 are as follows: Figure 2 ,from Figure 2 As can be seen from the data, the main component of this high-density lithium titanate fine-grained ceramic is lithium titanate;

[0082] The high-density lithium titanate fine-grained ceramic prepared in Example 1 was subjected to performance testing, and its density was 85.15%. Its microstructure was observed, and a SEM image of its cross-section is shown below. Figure 3 As can be seen from the figure, the grain size in this ceramic is approximately 540 nm.

[0083] The high-density lithium titanate fine-grained ceramic prepared in Example 2 was subjected to performance testing, and its density was 93.89%. Its microstructure was observed, and a SEM image of its cross-section is shown below. Figure 4 As can be seen from the figure, the grain size in this ceramic is approximately 900 nm.

[0084] The high-density lithium titanate fine-grained ceramic prepared in Example 3 was subjected to performance testing, and its density was 87.06%. Its microstructure was observed, and a SEM image of its cross-section is shown below. Figure 5As can be seen from the figure, the grain size in this ceramic is approximately 9.95 μm.

[0085] contrast Figure 3-5 It is known that the present invention can adjust the pulse voltage and time to control the density (87% to 94%) and grain size (0.5 to 10 μm).

Claims

1. A method for rapid sintering of high-density lithium titanate fine-grained ceramics based on electric pulses, characterized in that, The method comprises the following steps: Step 1, a solid phase method is used to prepare lithium titanate powder, and the specific process is as follows: Step 1.1, TiO2 and Li2CO3 with a molar ratio of 1:1.1 are weighed respectively and placed in a WC ball mill jar, then WC grinding balls with a ball-to-material ratio of 20:1 are put into the jar, and 70 mL of alcohol is poured into the jar; Step 1.2, the ball mill jar in step 1.1 is put into a high-energy ball mill, and during the ball milling process, the high-energy ball mill rotates at a speed of 200 rpm, the ball milling time is 24 h, and the ball milling is stopped every 2 h for 10 min; Step 1.3, the ball milling product is poured into a culture dish, and then placed in a drying oven for 90°C drying treatment, and the drying treatment time is 12 h; Step 1.4, the dried powder is ground and placed in a muffle furnace for calcination at 600°C, and the calcination time is 3 h, to obtain lithium titanate powder; Step 2, 0.6 g of lithium titanate powder is weighed and poured into a mold, and is pressed to 14 MPa in a tablet press, and the pressure is maintained for 90 s, to obtain lithium titanate ceramic green body; Step 3, a high-density lithium titanate fine-grained ceramic is prepared by using an electric pulse ceramic sintering device, and the specific process is as follows: Step 3.1, two pieces of 100mm×20mm×3mm graphite felt are aligned and fixed between two copper electrodes by nuts, and are placed in glove box 1, and the two copper electrodes are connected to high-frequency direct current pulse power supply 5 through wires 4; Step 3.2, lithium titanate ceramic green body 3 is placed between the two pieces of graphite felt 2, and glove box 1 is vacuumized to a vacuum degree greater than 0.09 MPa; Step 3.3, the 500Hz high-frequency direct current pulse power supply 5 is turned on, the voltage is set to 45V, and after 10 min, the voltage is adjusted to zero, and the vacuum is removed, to obtain a high-density lithium titanate fine-grained ceramic.

Images