Non-stoichiometric cerium oxide, preparation method and CeOx powder for water-oxygen barrier film

Abstract

The invention belongs to the technical field of non-stoichiometric cerium oxide, and discloses non-stoichiometric cerium oxide, a preparation method and CeOx powder for a water-oxygen barrier film, the preparation method of the non-stoichiometric cerium oxide comprises the following steps: step 1, heating cerium dioxide to 295-305 DEG C under the protection of inert gas; 2, hydrogen is continuously introduced, the cerium dioxide is heated to 850-1300 DEG C, and heat preservation is conducted for 1.5-3 h; 3, after heat preservation is completed, hydrogen is continuously introduced, the temperature is reduced to 500 DEG C, then the temperature is reduced to the room temperature under inert gas protection, and non-stoichiometric cerium oxide is obtained. The invention discloses a preparation method of non-stoichiometric cerium oxide, cerium oxide with different non-stoichiometric ratios can be obtained by controlling the reduction temperature and the heat preservation time on the basis of the method, and the method does not need to adjust the humidity of hydrogen, reduces the requirements on raw materials, and is suitable for large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of non-stoichiometric cerium oxide, and particularly relates to a non-stoichiometric cerium oxide, a preparation method thereof, and CeOx powder used for a water and oxygen barrier film. Background Art

[0002] Cerium ions have two different valence states, trivalent and tetravalent. Therefore, the most common stoichiometric cerium oxides are: hexagonal cerium sesquioxide (Ce 2 O 3 ) containing only trivalent cerium ions and cerium dioxide (CeO 2 ).

[0003] Cerium oxide belongs to the cubic crystal system and has a fluorite structure; the coordination number of Ce is 8, and the coordination number of O is 4. Even in the case of oxygen deficiency, there are still a large number of oxygen vacancies, maintaining the fluorite crystal structure; based on this characteristic, cerium oxide has extremely excellent redox ability during valence transformation; while cerium dioxide at normal temperature and pressure is relatively stable, but at high temperature or in a reducing atmosphere, the tetravalent cerium ions in cerium dioxide can be reduced to trivalent and partially transformed into non-stoichiometric cerium oxide.

[0004] Based on the variable valence characteristics of cerium ions, cerium oxide has been widely used in the fields of catalysis, energy conversion, and biomedicine; thus, a new substance has emerged: non-stoichiometric cerium oxide. For example, in the prior art 1: the book "Rare Earth Oxides" introduces that cerium dioxide forms an oxygen-deficient phase at low temperature and low pressure, such as Ce n O 2n-2 (n = 4, 6, 7, 9, 10, 11), which is usually blue. Ce 6 O 10 is a blue solid; Ce 7 O 12 lacks one-seventh of the oxygen on the basis of the CeO 2 unit cell structure and is a blue-black solid; Ce 9 O 16 is a dark blue solid; Ce 10 O 18 lacks one-tenth of the oxygen on the basis of the CeO 2 unit cell structure and is a dark blue solid; Ce 11 O 20 is a dark blue solid.

[0005] However, the prior art 1 did not deeply study the preparation of cerium oxide with a specific stoichiometric ratio. Based on the prior art 1, it is difficult to control the stable cerium oxide with a specific stoichiometric ratio, especially the non-stoichiometric cerium oxide used in the water-oxygen barrier film. The main application fields of the water-oxygen barrier film are flexible electronic devices and their integration, and it can also be used in industries such as OLED display, solar photovoltaics, OLED lighting, and quantum dot films. It plays an important role in the manufacturing fields of flexible electronic displays, quantum dot light-emitting semiconductors (QLEDs), organic light-emitting semiconductors (OLEDs), thin-film solar panels, printed RFID, etc.

[0006] When the non-stoichiometric cerium oxide CeO x , when x is around 1.7, its application effect on the water-oxygen barrier film is the best.

[0007] Prior art 2: The paper "The Structures of C+Ce 2 O 3 +φ,Ce 7 O 12 ,and Ce 11 O 20 》, using H 2 as a reducing agent to prepare CeO x . In order to reduce the sample to a definite CeO composition, using the relationship between the post-composition y and the oxygen pressure of Bevan and Kordis, CeO x (1.71 < x < 1.78) can be obtained by heating in hydrogen (purity 5) atmosphere with different humidities at 971 °C or in dry hydrogen at different temperatures for about 20 h. After reduction, some specimens were tempered in argon with the original purity of 4.8, cleaned with Oxisorb and porous zirconium at 800 °C, which would obviously cause a certain degree of re-oxidation, and then the crystals were sealed in thin-walled aluminum containers to prevent re-oxidation under argon atmosphere. All specimens were black after reduction.

[0008] Prior art 2 reduces cerium dioxide with hydrogen with different humidities to obtain non-stoichiometric cerium oxide CeO x close to x = 1.7. However, it has high humidity requirements for the hydrogen raw material, resulting in an increase in production costs and is not suitable for large-scale production. And this scheme cannot accurately control the stoichiometric ratio of cerium oxide, and the quality of the products produced is unstable, making it difficult to meet the application requirements of the subsequent water-oxygen barrier film. Summary of the Invention

[0009] One of the purposes of the present invention is to provide a preparation method of non-stoichiometric cerium oxide. Through this method, non-stoichiometric cerium oxide can be obtained, and this method does not require humidity requirements for the hydrogen raw material, can effectively reduce the production difficulty, and is suitable for large-scale production.

[0010] Another object of the present invention is to provide a non-stoichiometric cerium oxide, which can fully exhibit its characteristic of valence transformation and has excellent redox ability.

[0011] Meanwhile, the present invention also provides a CeO x powder for a water and oxygen barrier film. x For the powder, 1.69 < x < 1.71, which can fully exhibit its characteristics and meet the application requirements of the water and oxygen barrier film.

[0012] To achieve the above object, the present invention provides a preparation method of non-stoichiometric cerium oxide, comprising the following steps:

[0013] Step 1: Under the protection of an inert gas, heat cerium dioxide to 295 - 305 °C.

[0014] Step 2: Continuously introduce hydrogen, heat cerium dioxide to 850 - 1300 °C and keep it warm for 1.5 - 3 h.

[0015] Step 3: After the heat preservation is completed, continuously introduce hydrogen to cool down to 500 °C, and then cool it to room temperature under the protection of an inert gas to obtain non-stoichiometric cerium oxide.

[0016] Preferably, the specific operation of Step 1 is: Put cerium dioxide into a reduction furnace, evacuate to 1.0×10 -1 -1.0×10 -4 Pa, introduce an inert gas, and heat it to 295 - 305 °C at a heating rate of 10 ± 1 °C / min.

[0017] Preferably, the flow rate of the introduced inert gas is 1 - 5 L / min; the inert gas is one of nitrogen and argon.

[0018] Preferably, the hydrogen flow rate in Step 2 and Step 3 is 1 - 5 L / min.

[0019] Preferably, the heating rate in Step 2 is 5 - 15 °C / min.

[0020] The present invention also provides a non-stoichiometric cerium oxide, which is prepared by the above preparation method of non-stoichiometric cerium oxide. The chemical formula of the non-stoichiometric cerium oxide is CeO x , 1.5 < x < 2.

[0021] Furthermore, the present invention also provides a CeO x powder for a water and oxygen barrier film, which is prepared by the above preparation method of non-stoichiometric cerium oxide to obtain a CeO x powder, 1.69 < x < 1.71;

[0022] Among them, the specific operation of step 2 is as follows: continuously introduce hydrogen at a flow rate of 1 - 5 L / min, and heat cerium dioxide to 1250 °C and keep it for 2 - 3 h.

[0023] Beneficial effects

[0024] Compared with the prior art, the present invention has at least the following advantages:

[0025] (1) The present invention discloses a preparation method of non-stoichiometric cerium oxide. Based on this method, cerium oxides with different non-stoichiometric ratios can be obtained by controlling the reduction temperature and holding time. Moreover, this method does not require adjusting the humidity of hydrogen, reducing the requirements for raw materials and being suitable for large-scale production;

[0026] (2) The present invention prepares a CeO x powder for a water and oxygen barrier film. The x of this CeO x powder can satisfy 1.69 < x < 1.71, and its use in the water and oxygen barrier film can give full play to its characteristics and meet the application requirements. Description of the drawings

[0027] The present invention will be further described below in conjunction with the drawings and embodiments;

[0028] Figure 1 is the XRD pattern of Example 1 of the present invention;

[0029] Figure 2 is the XRD pattern of Example 2 of the present invention;

[0030] Figure 3 is the XRD pattern of Example 3 of the present invention;

[0031] Figure 4 is the XRD pattern of Example 4 of the present invention;

[0032] Figure 5 is the XRD pattern of Comparative Example 1 of the present invention. Specific embodiments

[0033] The present invention will be further described below in conjunction with the embodiments, but it does not constitute any limitation to the present invention. Any limited modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0034] In order to illustrate the technical content of the present invention in detail, the following further explanations are made in conjunction with the embodiments.

[0035] For the following examples and comparative examples, cerium dioxide is used as the raw material with a purity of ≥2N5 cerium dioxide powder, and the mass of cerium dioxide is the same.

[0036] The hydrogen gas used in the following examples and comparative examples is dry hydrogen with a purity of 99.999%.

[0037] Example 1

[0038] A non-stoichiometric cerium oxide was prepared by the following steps:

[0039] Step 1: Put cerium dioxide into an alumina boat, place the alumina boat in a hydrogen reduction furnace, evacuate to 1.0×10 -4 Pa, continuously introduce nitrogen at a flow rate of 2 L / min, and heat up to 300 °C at a heating rate of 10 °C / min;

[0040] Step 2: Close the nitrogen, continuously introduce hydrogen at a flow rate of 2 L / min, heat up to 850 °C at a heating rate of 10 °C / min and then keep it warm for 3 h, and continuously introduce hydrogen at a flow rate of 5 L / min during the heat preservation period;

[0041] Step 3: After the heat preservation is completed, cool down to 500 °C by continuously introducing hydrogen at a flow rate of 2 L / min, then close the hydrogen, and introduce nitrogen at a flow rate of 2 L / min to cool to room temperature to obtain non-stoichiometric cerium oxide powder.

[0042] Example 2

[0043] It is generally the same as Example 1, except that in Step 2: close the nitrogen, continuously introduce hydrogen at a flow rate of 2 L / min, heat up to 900 °C at a heating rate of 10 °C / min and then keep it warm for 2 h, and continuously introduce hydrogen at a flow rate of 5 L / min during the heat preservation period.

[0044] Example 3

[0045] It is generally the same as Example 1, except that in Step 2: close the nitrogen, continuously introduce hydrogen at a flow rate of 2 L / min, heat up to 1100 °C at a heating rate of 10 °C / min and then keep it warm for 2 h, and continuously introduce hydrogen at a flow rate of 5 L / min during the heat preservation period.

[0046] Example 4

[0047] It is generally the same as Example 1, except that in Step 2: close the nitrogen, continuously introduce hydrogen at a flow rate of 2 L / min, heat up to 1250 °C at a heating rate of 10 °C / min and then keep it warm for 2 h, and continuously introduce hydrogen at a flow rate of 5 L / min during the heat preservation period.

[0048] Comparative Example 1

[0049] It is generally the same as Example 1, except that in step 2, nitrogen is turned off, hydrogen is continuously introduced at a flow rate of 2 L / min, the temperature is raised to 700 °C at a heating rate of 10 °C / min and then held for 2 h, and hydrogen is continuously introduced at a flow rate of 5 L / min during the holding period.

[0050] The non-stoichiometric cerium oxide powders obtained in Examples 1-4 and Comparative Example 1 were characterized by XRD analysis, and the test data are as Figures 1 - 5 , and the data were summarized to obtain Table 1.

[0051] Among them Figure 1 is the XRD pattern of Example 1, Figure 2 is the XRD pattern of Example 2, Figure 3 is the XRD pattern of Example 3, Figure 4 is the XRD pattern of Example 4, Figure 5 is the XRD pattern of Comparative Example 1.

[0052] Figure 1 is the XRD pattern of the non-stoichiometric cerium oxide prepared in Example 1. As can be seen from Figure 1 , the diffraction peaks of the prepared powder are consistent with the characteristic peaks of the standard cards PDF#89-8435 and PDF#43-1002; it shows that the Ce 11 O 20 cerium oxide powder was prepared in Example 1, and at the same time, there was also a part of the powder in which CeO 2 was not completely reduced.

[0053] Figure 2 is the XRD pattern of the non-stoichiometric cerium oxide prepared in Example 2. As can be seen from Figure 2 , the diffraction peaks of the prepared powder are consistent with the characteristic peaks of the standard card PDF#89-8435, and there are also some miscellaneous peaks at the same time. The diffraction peak positions of the miscellaneous peaks match PDF#43-1002; it shows that the Ce 11 O 20 cerium oxide powder was prepared in Example 2, and at the same time, there was also a small amount of powder in which CeO 2 was not completely reduced.

[0054] Figure 3 is the XRD pattern of the non-stoichiometric cerium oxide prepared in Example 3. As can be seen from Figure 3 , the diffraction peaks of the prepared powder are consistent with the characteristic peaks of the standard card PDF#89-8430, and there are no other miscellaneous peaks; it shows that the pure-phase CeO 1.675 cerium oxide powder was prepared in Example 3, and the CeO2 powder has been completely reduced to CeO 1.675 cerium oxide powder.

[0055] Figure 4 XRD pattern of the non-stoichiometric cerium oxide prepared in Example 4. It can be seen from Figure 4 that the diffraction peaks of the prepared powder are consistent with the characteristic peaks of standard cards PDF#89-8429 and PDF#89-8431, and there are no other impurity peaks; this indicates that the cerium oxide powder prepared in Example 4 is 1.695 Ce 7 O 12 cerium oxide powder, and the CeO 2 powder has been completely reduced to CeO x (where x is about 1.7) cerium oxide powder.

[0056] Figure 5 XRD pattern of the non-stoichiometric cerium oxide prepared in Comparative Example 1. It can be seen from Figure 5 that the diffraction peaks of the prepared powder are consistent with the characteristic peak of standard card PDF#65-5923, and there are no other impurity peaks; this indicates that the powder in Example 5 is still CeO 2 powder and has not been completely reduced to non-stoichiometric cerium oxide.

[0057] Table 1 XRD characterization analysis results of Examples 1-4 and Comparative Example 1

[0058]

[0059] According to Figures 1 - 5 and the data in Table 1, it can be known that:

[0060] According to the data of Examples 1-4, it can be known that in this application, by first heating to 300 °C under nitrogen protection and then introducing hydrogen for heating and holding reactions, and strictly controlling the final holding temperature, non-stoichiometric cerium oxide can be produced, and this preparation method does not require controlling the humidity of hydrogen, can reduce the requirements for raw materials, and can be effectively applied to large-scale production.

[0061] At the same time, according to the data comparison of Examples 2, 3, 4 and 1, it can be known that the optimal holding temperature in this application should be above 900 °C to ensure that all cerium dioxide is reduced to non-stoichiometric cerium oxide.

[0062] According to the results of Comparative Example 1, if the reduction holding temperature is too low, non-stoichiometric cerium oxide cannot be prepared.

[0063] The embodiments presented herein are only implementation manners selected according to combinations of all possible embodiments. The appended claims should not be limited by the implementation manners illustrating the invention. Some numerical ranges used in the claims include sub-ranges within them, and variations within these ranges should also be covered by the appended claims.

Claims

1. A method for preparing non-stoichiometric cerium oxide, characterized in that: The steps include: Step 1: heating cerium dioxide to 295-305°C under inert gas protection; Step 2: Continue to introduce hydrogen and heat the cerium dioxide to 850-1300°C for 1.5-3h; Step 3: After the insulation is completed, hydrogen is continuously introduced to cool the temperature to 500° C., and then cooled to room temperature under the protection of an inert gas to obtain non-stoichiometric cerium oxide.

2. The method for preparing non-stoichiometric cerium oxide according to claim 1, characterized in that: The specific operation of step 1 is: put cerium dioxide into a reduction furnace and evacuate to 1.0×10 -1 -1.0×10 -4 Pa, introduce inert gas and heat to 295-305°C at a heating rate of 10±1°C / min.

3. The method for preparing non-stoichiometric cerium oxide according to claim 2, characterized in that: The inert gas has an inlet flow rate of 1-5 L / min; the inert gas is one of nitrogen and argon.

4. The method for preparing non-stoichiometric cerium oxide according to claim 1, characterized in that: The hydrogen flow rate in step 2 and step 3 is 1-5 L / min.

5. The method for preparing non-stoichiometric cerium oxide according to claim 1, characterized in that: The heating rate of step 2 is 5-15°C / min.

6. A non-stoichiometric cerium oxide, characterized in that: The non-stoichiometric cerium oxide is prepared by the method for preparing the non-stoichiometric cerium oxide according to any one of claims 1 to 5, wherein the chemical formula of the non-stoichiometric cerium oxide is CeO x , 1.5<x<2.

7. CeO for water and oxygen barrier film x The powder is characterized by: CeO is prepared by the non-stoichiometric cerium oxide preparation method according to any one of claims 1 to 5. x Powder, 1.69<x<1.71; The specific operation of step 2 is: continuously introducing hydrogen at a flow rate of 1-5 L / min, and heating the cerium dioxide to 1250° C. and keeping the temperature for 2-3 hours.

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