A method for improving the coefficient of thermal expansion of a material

Abstract

The application relates to a method for improving the thermal expansion coefficient of a material, which comprises modifying the material by using a quenching process, and the quenching process specifically comprises the following steps: S1, heating raw material to a target temperature and keeping the temperature, so as to obtain heated material; S2, cooling treatment of the heated material in a quenching salt solution, so as to obtain target material. According to the method for improving the thermal expansion coefficient of the material, the raw material is heated and then cooled in the quenching solution, the thermal expansion coefficient of the material is improved by using a simple quenching process, the method is economic and feasible, and meanwhile, the operability is high; by adjusting the quenching temperature, the type or concentration of the quenching solution is adjusted, and controllable preparation of the thermal expansion coefficient of the material is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to material modification, more particularly to a method for improving the thermal expansion coefficient of a material. BACKGROUND

[0002] Energy development is related to people's livelihood and well-being. In the long-term plan for the development of hydrogen energy industry (2021-2035), it is emphasized to promote the research and development of solid oxide electrolysis cell hydrogen production technology, to deeply promote the energy production and consumption revolution, to build a clean, low-carbon, safe and efficient energy system, to promote the high-quality development of hydrogen energy industry, and to help achieve the goals of carbon neutrality and carbon peak.

[0003] Solid oxide electrolysis cell (SOEC) has high energy conversion efficiency and is an advanced electrochemical energy storage and conversion device. Under the condition of power supply, it can convert H2O(g) and CO2 into hydrogen and synthesis gas, etc. The development of this technology not only reduces additional carbon dioxide emissions, but also promotes resource recycling. SOEC cell is mainly composed of anode functional layer, electrolyte and cathode functional layer. Solid oxide electrolysis cell operates at a temperature of 600-1000℃. Under the action of electric energy, gaseous H2O and CO2 can be reduced to H2 and CO, respectively, on the fuel side, accompanied by the generation of O 2- , as shown in the following formulas (1) and (2).

[0004] Fuel electrode side reaction:

[0005] H2O + 2e - → H2 + O 2- (1)

[0006] CO2 + 2e - → CO + O 2- (2)

[0007] O 2- generated by the electrolyte diffuses to the air side and is finally oxidized to O2 by releasing electrons on the air side, as shown in the following formula (3).

[0008] Air electrode side reaction:

[0009] O 2- → 1 / 2O2 + 2e – (3)

[0010] The overall reaction is shown in the following formulas (4) and (5).

[0011] Overall reaction:

[0012] H2O → H2 + 1 / 2O2 (4)

[0013] CO2 → CO + ½ O2 (5)

[0014] LSCF perovskite oxides have high electronic and oxygen ionic conductivity, and are a promising commercial oxygen electrode material. LSCF has a high thermal expansion coefficient (TEC), and it is reported that the TEC of LSCF is 17.5 x 10 -6 K -1 , which is 40% higher than the TEC of the barrier layer GDC (12.5 x 10 -6 K -1 ) and 70% higher than the TEC of the electrolyte YSZ (10.5 x 10 -6 K -1 ). The mismatch in the thermal expansion coefficients of the materials can cause intolerable stress in the cell during high-temperature sintering, resulting in micro-gaps at the interfaces of the cell. Large-current operation of a solid oxide electrolysis cell (SOEC) can increase the hydrogen production rate of the stack and reduce the operating cost of the stack, but large-current testing can accelerate the oxygen production rate on the oxygen electrode side, which can cause the oxygen electrode LSCF and the barrier layer GDC to delaminate due to the mismatch in the thermal expansion coefficients of the materials.

[0015] Solving the problem of interface contact caused by the mismatch in the thermal expansion coefficients of the cell has attracted widespread attention in the industry. In 2022, it was reported in the journal Nature that the surface roughness of the electrode can be increased by acid treatment to improve the interface contact of the material. Acid treatment of the material surface can increase the interface contact area of the material to some extent and improve the performance of the stack, but the reaction rate of the acid is uncontrollable, and the acid treatment of the electrolyte surface also puts new requirements on the preparation process of the cell. Most importantly, this method does not fundamentally solve the problem of the mismatch in the thermal expansion coefficients of the materials.

[0016] In 2021, it was reported in Nature that a negative thermal expansion coefficient compensation strategy was introduced to prepare a composite electrode with a matching thermal expansion coefficient by "adding and subtracting". The thermal expansion compensation strategy is to react and sinter a cobalt-containing perovskite material with a "negative thermal expansion" material. The negative thermal expansion material has the property of "thermal contraction and cold expansion", which can offset the negative effects of the positive thermal expansion coefficient of the perovskite material, thereby forming a new composite material that matches the thermal expansion coefficient of the electrolyte. The composite material can exhibit excellent electrochemical performance when prepared into an electrode. However, the introduction of a negative thermal expansion coefficient material can reduce the catalytic activity of the raw material, and it can also introduce unknown interface reactions. More unfortunately, this method is limited to specific materials and is not universal, and cannot be applied to commercial material batch process.

[0017] At present, many new materials with matching thermal expansion coefficients have been reported, but few of them are in practical commercial application. The development of new materials needs a lot of experiments to verify, and the experimental period is long. The preparation of many new materials involves complex synthesis process, high technical difficulty, or requires expensive equipment or laborious modification treatment, which restricts the practical application of new materials.

[0018] CN 115537598 A discloses a wide temperature range adjustable linear low thermal expansion titanium niobium alloy and its preparation method. The invention patent uses vacuum consumable electrode arc melting technology. CN202011361309.5 discloses a titanium niobium shape memory alloy with adjustable negative thermal expansion and its preparation method. By controlling the alloy composition Ti, Nb and TiO2 as raw materials, the prepared raw materials are placed in a magnetic stirring vacuum non-consumable arc furnace for repeated melting. Finally, the ingot is hot forged into a rod at 900℃-1000℃, and cooled to obtain a β+α" phase material. These methods all need special equipment and the operation is complex. SUMMARY

[0019] In order to solve the problems of mismatching thermal expansion coefficient in the prior art, the present application provides a method for improving the thermal expansion coefficient of a material.

[0020] The method for improving the thermal expansion coefficient of a material according to the present application comprises modifying the material by using a quenching process, which specifically comprises: S1, heating the raw material to a target temperature and keeping it at the target temperature to obtain a heated material; S2, cooling the heated material in a quenching salt solution to obtain a target material.

[0021] Preferably, the thermal expansion coefficient of the target material is smaller than that of the raw material.

[0022] Preferably, the raw material is an oxygen electrode material of a solid oxide electrolysis cell.

[0023] Preferably, the raw material is LSCF.

[0024] Preferably, the raw material is slowly heated to the target temperature.

[0025] Preferably, the raw material is heated to the target temperature at a rate of 1-5℃ / min.

[0026] Preferably, the target temperature is 600-1000℃.

[0027] Preferably, the keeping time is 5min.

[0028] Preferably, the quenching salt solution is yttrium nitrate hexahydrate.

[0029] Preferably, the concentration of the quenching salt solution is between 0.1 mol / L and 1 mol / L.

[0030] According to the method for improving the thermal expansion coefficient of a material, the raw material is heated and then cooled in a quenching salt solution, the thermal expansion coefficient is improved by using a simple quenching process, which is economical and feasible and has strong operability, and the controllable preparation of the thermal expansion coefficient of the material is realized by adjusting the quenching temperature, the type or concentration of the quenching salt solution. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is the thermal expansion coefficient curve of the commercial material LSCF without any treatment.

[0032] Figure 2 is the experimental data graph of LSCF after heating treatment at 800℃ and quenching with 0.1 mol / L yttrium nitrate hexahydrate.

[0033] Figure 3 is the experimental data graph of LSCF after heating treatment at 800℃ and quenching with 1 mol / L yttrium nitrate hexahydrate.

[0034] Figure 4 is Figure 1 , Figure 2 and Figure 3 is a data summary graph of

[0035] Figure 5 is the XRD spectrum of the commercial material.

[0036] Figure 6 is the XRD spectrum of the material after quenching process treatment. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0038] The present application first performs modification treatment on commercial LSCF material.

[0039] The quenching process is used to realize batch modification treatment of the commercial material LSCF. The commercial LSCF material is placed in a muffle furnace for heating, the muffle furnace is raised from room temperature to a target temperature such as 600-1000℃ at a rate of 5℃ / min, and then the material is taken out with a clamp and quickly poured into a quenching salt solution for cooling treatment, and then placed in an oven for standby.

[0040] Example 1

[0041] The quenching salt solution is selected as yttrium nitrate hexahydrate. The concentration of the quenching salt solution is selected as 0.1 mol / L yttrium nitrate hexahydrate or 1 mol / L yttrium nitrate hexahydrate, etc.

[0042] The thermal expansion coefficient of the material after quenching is measured next.

[0043] The LSCF powder after quenching is compacted by a mold, and then high-temperature sintering is performed to solidify, and a thermal expansion instrument is used to test the thermal expansion coefficient of the material LSCF at different temperatures.

[0044] Figure 1 The thermal expansion coefficient curve of the commercial material LSCF without any treatment is shown, and it can be seen from the data that the thermal expansion coefficient value of the material also increases accordingly as the test temperature increases.

[0045] Figure 2 The experimental data graph of LSCF after heating treatment at 800 DEG C and quenching 0.1 mol / L yttrium nitrate hexahydrate is shown.

[0046] Figure 3 The experimental data graph of LSCF after heating treatment at 800 DEG C and quenching 1 mol / L yttrium nitrate hexahydrate is shown.

[0047] The experimental data after quenching are compared, and the results are shown in Figure 4 The LSCF after quenching shows a lower thermal expansion coefficient than the blank LSCF. Therefore, the quenching process can effectively control the thermal expansion coefficient of the commercial material LSCF, and significantly reduce the thermal expansion coefficient of the commercial material LSCF.

[0048] The crystal structure of the material after quenching is measured next.

[0049] The X-ray diffraction pattern (XRD) of the commercial material LSCF and the LSCF after quenching is characterized.

[0050] Figure 5 The XRD pattern of the commercial material is shown, Figure 6 The XRD pattern of the material after quenching process is shown, and the experimental results of Figure 5 and Figure 6 It can be understood that the quenching process does not affect the crystal structure of the material.

[0051] In summary, the method for improving the thermal expansion coefficient of the material according to the present application uses a simple quenching process to improve the thermal expansion coefficient, which is economically feasible and has strong operability. By adjusting the quenching temperature, the type or concentration of the quenching salt solution, controllable preparation of the thermal expansion coefficient of the commercial LSCF material can be achieved, so that the treated oxygen electrode LSCF can exhibit a thermal expansion coefficient matched with the barrier layer. More importantly, the quenching process only slightly processes the raw material, and does not have any impact on the powder slurry and the sintering process of the battery piece, and the application of the process can definitely promote the process of the industrialization development of the solid oxide fuel cell, and has social practical value.

[0052] The above is only a preferred embodiment of the present application, not to limit the scope of the present application, and various changes can be made to the above embodiment of the present application. That is, any simple, equivalent changes and modifications made according to the content of the claims and description of the present application fall within the scope of the claims of the present patent. The present application is not described in detail, which is a conventional technical content.

Claims

1. A method of improving the coefficient of thermal expansion of a material, characterized by, The method comprises modifying the material by using a quenching process, which specifically comprises: S1, heating the raw material to a target temperature and holding, to obtain a heated material, wherein the raw material is an oxygen electrode material of a solid oxide electrolysis cell; S2, cooling treatment of the heated material in a quenching salt solution to obtain a target material, the crystal structure of the target material is consistent with that of the raw material, the thermal expansion coefficient of the target material is less than that of the raw material, the raw material is LSCF, the target temperature is 600-1000 DEG C, the quenching salt solution is yttrium nitrate hexahydrate, and the concentration of the quenching salt solution is between 0.1 mol / L and 1 mol / L.

2. The method of claim 1, wherein, The raw material is slowly heated to the target temperature.

3. The method of claim 2, wherein, The raw material is heated to the target temperature at 1-5 DEG C / min.

4. The method of claim 1, wherein, Hold for 5 min.

Images