Preparation method of stable oxide coated lanthanum oxide powder

Abstract

The invention discloses a preparation method of stable oxide coated lanthanum oxide powder, and relates to a method for coating lanthanum oxide powder. The problems that existing lanthanum oxide powder is poor in stability in the atmospheric environment, and a coating layer is too thick due to a conventional coating method are solved. The method comprises the following steps: 1, adding an organic solvent into lanthanum oxide powder under the relative humidity of the environment, dropwise adding a main element source reagent of a surface nano-modified oxide, stirring and mixing, and finally standing, performing suction filtration and performing vacuum drying; and 2, circulating for multiple times. The method is used for preparing the stable oxide coated lanthanum oxide powder.

Description

Technical Field

[0001] The invention relates to a method for coating lanthanum oxide powder. Background Art

[0002] Lanthanum oxides (lanthanum oxide, lanthanum hydroxide oxide, etc.) are an important class of rare earth compounds, which are widely used in petroleum cracking catalysts, automobile exhaust purification catalysts, production of optical glass and optical fiber, manufacturing of optical components such as cameras, and manufacturing of high-temperature ceramic materials. However, when lanthanum oxide is placed in the air, it is easy to contact with water vapor in the air to generate lanthanum hydroxide, which will change its chemical properties and physical state, thereby affecting its performance in industrial applications, such as catalytic activity and optical properties. On the one hand, lanthanum hydroxide produced by lanthanum oxide after absorbing water / moisture is corrosive, causing corrosion to equipment and containers, reducing the service life of equipment, and increasing maintenance costs; at the same time, lanthanum hydroxide has completely different physical and chemical properties from lanthanum oxide or lanthanum hydroxide oxide. For example, its light absorption and optical reflection properties change due to the presence of a large number of hydroxyl groups, making its photothermal properties unable to meet the requirements of thermal control coatings and other optical devices. Therefore, by modifying the method, delaying or shielding the reaction of lanthanum oxide with water vapor in the atmosphere or environment, the performance and stability of the material can be improved while preparing related materials.

[0003] However, the current methods for reducing the reaction rate of lanthanum oxide with water vapor are limited to controlling storage humidity conditions, etc., and cannot guarantee the stability of the processing and service process. The use of nano-silicon coated on the surface of the material can serve as a drainage point for defects, which can improve the environmental stability of the material. Conventional sol-gel coating of silicon oxide usually uses TEOS and other variable concentrations to control the thickness of the film layer. The common thickness range is usually hundreds of nanometers to several microns. For thermal control powders, the film layer is thicker, and an appropriate amount of catalyst needs to be added during the preparation process to promote the hydrolysis reaction. Summary of the invention

[0004] The present invention aims to solve the problem that the existing lanthanum oxide powder has poor stability in the atmospheric environment and the conventional coating method will lead to an overly thick coating layer, and further provides a method for preparing a stable oxide-coated lanthanum oxide powder.

[0005] A method for preparing a stable oxide-coated lanthanum oxide powder is carried out according to the following steps:

[0006] 1. Coating:

[0007] Under the condition of an ambient relative humidity of 20RH% to 30RH%, an organic solvent is added to lanthanum oxide powder, and then a main element source reagent of the surface nano-modified oxide is added dropwise, followed by stirring and mixing, and finally standing, filtering and vacuum drying to obtain a powder after primary coating;

[0008] The main element source reagent of the surface nano-modified oxide is an anhydrous metal salt or silicon halide;

[0009] 2. Multiple cycles:

[0010] The powder coated once is repeatedly coated according to step 1 to obtain powder coated multiple times, thus completing the preparation method of stable oxide-coated lanthanum oxide powder.

[0011] The beneficial effects of the present invention are:

[0012] The present invention uses a novel surface sol-gel method to deposit a nano oxide film (such as silicon dioxide, titanium oxide, etc.) on the surface of lanthanum oxide, to block the reaction between water vapor in the environment and lanthanum oxide, to solve the disadvantage of poor stability of lanthanum oxide powder in the atmospheric environment, to eliminate or slow down the moisture absorption of the powder, and thus to improve the environmental stability of lanthanum oxide powder. At the same time, the film thickness can be controlled within a range of several nanometers to tens of nanometers and the film thickness can be controlled by the number of coatings. There is no need to control the pH value of the solution during the operation, and the method requires a low reaction temperature, low energy consumption, simple operation, and easy control.

[0013] In the method of the present invention, anhydrous metal salts or silicon halides are used as the main element source reagents of the surface nano-modified oxides, an organic solvent is used to dissolve the anhydrous salts or silicon halides to form a surface sol-gel solution, and the ambient temperature and humidity are controlled to allow the organic solution to absorb trace water molecules, and a surface sol-gel reaction occurs on the surface of the lanthanum oxide added to the organic solution, gradually depositing a nano-oxide coating layer (such as a silicon dioxide surface film or a titanium dioxide surface film).

[0014] The stable oxide-coated lanthanum oxide powder of the present invention can be used to prepare thermal control coating pigments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The results of phase analysis of the lanthanum oxide powder before and after coating in Example 3 after being placed in a constant temperature and humidity chamber (25°C, 50RH%) for 24 hours;

[0016] Figure 2 The moisture absorption kinetics curve of the lanthanum oxide powder coated once to four times in Examples 3, 5, 6 and 7 in a constant temperature and humidity chamber (25° C., 50 RH%) for 24 h to 96 h;

[0017] Figure 3 The phase analysis results of the lanthanum oxyhydroxide powder before and after coating in Example 9 after being placed in a constant temperature and humidity chamber (25°C, 50RH%) for 48 hours;

[0018] Figure 4TEM images of the coating thickness of lanthanum oxide powder after one to four coatings in Examples 3, 5, 6 and 7, (a) one coating, (b) two coatings, (c) three coatings, and (d) four coatings. DETAILED DESCRIPTION

[0019] Specific implementation method 1: This implementation method is a method for preparing a stable oxide-coated lanthanum oxide powder, which is carried out according to the following steps:

[0020] 1. Coating:

[0021] Under the condition of an ambient relative humidity of 20RH% to 30RH%, an organic solvent is added to lanthanum oxide powder, and then a main element source reagent of the surface nano-modified oxide is added dropwise, followed by stirring and mixing, and finally standing, filtering and vacuum drying to obtain a powder after primary coating;

[0022] The main element source reagent of the surface nano-modified oxide is an anhydrous metal salt or a silicon halide.

[0023] 2. Multiple cycles:

[0024] The powder coated once is repeatedly coated according to step 1 to obtain powder coated multiple times, thus completing the preparation method of stable oxide-coated lanthanum oxide powder.

[0025] The coated dry powder of this specific embodiment can be used directly, or stored under vacuum or dry conditions for later use.

[0026] The beneficial effects of this embodiment are:

[0027] This embodiment uses a new type of surface sol-gel method to deposit a nano-oxide film (such as silicon dioxide, titanium oxide, etc.) on the surface of lanthanum oxide, blocking the reaction between water vapor in the environment and lanthanum oxide, solving the disadvantage of poor stability of lanthanum oxide powder in the atmospheric environment, eliminating or slowing down the moisture absorption of the powder, thereby improving the environmental stability of lanthanum oxide powder. At the same time, the film thickness can be controlled within the range of a few nanometers to tens of nanometers and the film thickness can be controlled by the number of coatings. There is no need to control the pH value of the solution during the operation, and the method requires a low reaction temperature, low energy consumption, simple operation, and easy control.

[0028] In the method of this embodiment, anhydrous metal salts or silicon halides are used as the main element source reagents of the surface nano-modified oxides, an organic solvent is used to dissolve the anhydrous salts or silicon halides to form a surface sol-gel solution, and the ambient temperature and humidity are controlled to allow trace water molecules to be absorbed in the organic solution. The surface of the lanthanum oxide added to the organic solution undergoes a surface sol-gel reaction, and a nano-oxide coating layer (such as a silicon dioxide surface film or a titanium dioxide surface film) is gradually deposited.

[0029] The stable oxide-coated lanthanum oxide powder of this embodiment can be used to prepare thermal control coating pigments.

[0030] Specific embodiment 2: This embodiment is different from specific embodiment 1 in that: the lanthanum oxide powder in step 1 is lanthanum oxide powder or lanthanum oxyhydroxide powder; the anhydrous metal salt in step 1 is titanium tetrachloride; the silicon halide in step 1 is silicon tetrachloride; the organic solvent in step 1 is carbon tetrachloride or acetone. The rest is the same as specific embodiment 1.

[0031] Specific embodiment 3: This embodiment is different from specific embodiment 1 or 2 in that: the lanthanum oxide powder is a lanthanum oxide powder after surface hydroxylation treatment, and the surface hydroxylation treatment is specifically to stand for 5min to 10min under the condition of an ambient relative humidity of 20RH% to 30RH%. Others are the same as specific embodiment 1 or 2.

[0032] Specific embodiment 4: This embodiment is different from the specific embodiments 1 to 3 in that: the lanthanum oxyhydroxide powder is prepared according to the following steps:

[0033] ① At a speed of 300 r / min to 400 r / min, lanthanum oxide powder and deionized water are stirred and mixed for 1.5 h to 2 h, and then filtered to obtain a powder cake, and the powder cake is vacuum dried at a temperature of 60° C. to 80° C. for 3 h to 4 h to obtain lanthanum hydroxide powder;

[0034] ② Place the lanthanum hydroxide powder in a muffle furnace, heat it to 350°C to 400°C at a heating rate of 8°C / min to 10°C / min, and then keep it at 350°C to 400°C for 30min to 120min to obtain lanthanum hydroxide powder. The rest is the same as the first to third embodiments.

[0035] Specific embodiment 5: This embodiment differs from Specific embodiments 1 to 4 in that the volume ratio of the mass of the lanthanum oxide powder described in step ① to deionized water is 1 g: (10-20) mL. The rest is the same as Specific embodiments 1 to 4.

[0036] Specific embodiment 6: This embodiment is different from specific embodiments 1 to 5 in that the average particle size of the lanthanum oxide powder in step 1 is 10 nm to 10 μm. Other aspects are the same as specific embodiments 1 to 5.

[0037] Specific embodiment 7: This embodiment differs from Specific embodiments 1 to 6 in that the mass ratio of the lanthanum oxide powder to the volume ratio of the organic solvent in step 1 is 1 g: (10-20) mL. The rest is the same as Specific embodiments 1 to 6.

[0038] Specific embodiment 8: This embodiment differs from Specific embodiments 1 to 7 in that the volume ratio of the main element source reagent of the surface nano-modified oxide to the organic solvent in step 1 is 1:(333-2000). Others are the same as Specific embodiments 1 to 7.

[0039] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the stirring and mixing described in step 1 is carried out for 5 to 40 minutes under the conditions of an ambient relative humidity of 20 RH% to 30 RH% and a rotation speed of 300 r / min to 400 r / min. The rest is the same as specific embodiments 1 to 8.

[0040] Specific embodiment 10: This embodiment differs from Specific embodiments 1 to 9 in that the vacuum drying in step 1 is carried out at a temperature of 60° C. to 80° C. for 3 to 4 hours. The rest is the same as Specific embodiments 1 to 9.

[0041] The following examples are used to verify the beneficial effects of the present invention:

[0042] Embodiment 1:

[0043] A method for preparing a stable oxide-coated lanthanum oxide powder is carried out according to the following steps:

[0044] Under the condition of an ambient relative humidity of 20RH%, 100mL of carbon tetrachloride liquid was added to 5g of lanthanum oxide powder, and then 0.05mL of silicon tetrachloride liquid was added dropwise, and then the mixture was stirred and mixed for 30min under the conditions of an ambient relative humidity of 20RH% and a rotation speed of 400r / min, and finally allowed to stand for 2min, filtered and vacuum dried at a temperature of 80°C for 4h to obtain a powder after primary coating, i.e., a stable oxide (silicon dioxide) coated lanthanum oxide powder;

[0045] The lanthanum oxide powder is lanthanum oxide powder; the lanthanum oxide powder is lanthanum oxide powder after surface hydroxylation treatment, and the surface hydroxylation treatment is specifically performed under the condition of relative humidity of 20RH% and standing for 5 minutes;

[0046] The average particle size of the lanthanum oxide powder is 1 μm.

[0047] The stable oxide-coated lanthanum oxide powder prepared in this example was placed in a constant temperature and humidity chamber (25° C., 50 RH%) for 24 h, taken out and subjected to phase analysis, and the relative mass of lanthanum hydroxide was found to be 31.2 wt %.

[0048] Embodiment 2: This embodiment is different from Embodiment 1 in that the volume of silicon tetrachloride liquid is 0.1 mL. Other aspects are the same as Embodiment 1.

[0049] The stable oxide-coated lanthanum oxide powder prepared in this example was placed in a constant temperature and humidity chamber (25° C., 50 RH%) for 24 h, taken out and subjected to phase analysis, and the relative mass of lanthanum hydroxide was found to be 19.1 wt %.

[0050] Embodiment 3: This embodiment is different from Embodiment 1 in that the volume of silicon tetrachloride liquid is 0.2 mL. Other aspects are the same as Embodiment 1.

[0051] The stable oxide-coated lanthanum oxide powder prepared in this example was placed in a constant temperature and humidity chamber (25° C., 50 RH%) for 24 h, taken out and subjected to phase analysis, and the relative mass of lanthanum hydroxide was found to be 15 wt %.

[0052] Embodiment 4: This embodiment is different from Embodiment 1 in that the volume of silicon tetrachloride liquid is 0.3 mL. Other aspects are the same as Embodiment 1.

[0053] The stable oxide-coated lanthanum oxide powder prepared in this example was placed in a constant temperature and humidity chamber (25° C., 50 RH%) for 24 h, taken out and subjected to phase analysis, and the relative mass of lanthanum hydroxide was found to be 27 wt %.

[0054] Embodiment 5: This embodiment is different from Embodiment 3 in that the powder coated once is coated repeatedly to obtain powder coated twice. The rest is the same as Embodiment 3.

[0055] The stable oxide-coated lanthanum oxide powder prepared in this example was placed in a constant temperature and humidity chamber (25° C., 50 RH%) for 24 h, taken out and subjected to phase analysis, and the relative mass of lanthanum hydroxide was found to be 10 wt %.

[0056] Embodiment 6: This embodiment is different from Embodiment 3 in that the powder coated once is coated repeatedly to obtain powder coated three times. The rest is the same as Embodiment 3.

[0057] The stable oxide-coated lanthanum oxide powder prepared in this example was placed in a constant temperature and humidity chamber (25° C., 50 RH%) for 24 h, taken out and subjected to phase analysis, and the relative mass of lanthanum hydroxide was found to be 5 wt %.

[0058] Embodiment 7: This embodiment is different from Embodiment 3 in that the powder coated once is coated repeatedly to obtain powder coated four times. The rest is the same as Embodiment 3.

[0059] The stable oxide-coated lanthanum oxide powder prepared in this example was placed in a constant temperature and humidity chamber (25° C., 50 RH%) for 24 hours, taken out and subjected to phase analysis, and the relative mass of lanthanum hydroxide was found to be 1.2 wt %.

[0060] Embodiment 8: This embodiment differs from Embodiment 3 in that: the mass of lanthanum oxide powder is 10 g; the mixture is stirred and mixed for 10 min under the condition of relative humidity of 20 RH% and rotation speed of 400 r / min. The other conditions are the same as Embodiment 3.

[0061] The stable oxide-coated lanthanum oxide powder prepared in this example was placed in a constant temperature and humidity chamber (25° C., 50 RH%) for 24 h, taken out and subjected to phase analysis, and the relative mass of lanthanum hydroxide was found to be 29.4 wt %.

[0062] Embodiment nine:

[0063] A method for preparing a stable oxide-coated lanthanum oxide powder is carried out according to the following steps:

[0064] Under the condition of an ambient relative humidity of 20RH%, 100mL of carbon tetrachloride liquid was added to 5g of lanthanum oxide powder, and then 0.2mL of silicon tetrachloride liquid was added dropwise, and then stirred and mixed for 30min under the conditions of an ambient relative humidity of 20RH% and a rotation speed of 400r / min, and finally allowed to stand for 2min, filtered and vacuum dried at a temperature of 80°C for 4h to obtain a powder after primary coating, i.e., a stable oxide-coated lanthanum oxide powder;

[0065] The lanthanum oxide powder is lanthanum oxyhydroxide powder; the lanthanum oxyhydroxide powder is specifically prepared according to the following steps:

[0066] ① At a speed of 400 r / min, 10 g of lanthanum oxide powder and 200 mL of deionized water were stirred and mixed for 1.5 h, and then filtered to obtain a powder cake, which was vacuum dried at a temperature of 80 ° C for 4 h to obtain lanthanum hydroxide powder;

[0067] ② Place the lanthanum hydroxide powder in a muffle furnace, heat it to 400°C at a heating rate of 10°C / min, and then keep it at 400°C for 120 minutes to obtain lanthanum hydroxide powder.

[0068] The stable oxide-coated lanthanum oxide powder prepared in this example was placed in a constant temperature and humidity chamber (25° C., 50 RH%) for 48 hours. After being taken out, phase analysis showed that no lanthanum hydroxide was generated.

[0069] Figure 1The results of phase analysis of the lanthanum oxide powder before and after coating in Example 3 were placed in a constant temperature and humidity chamber (25°C, 50RH%) for 24 hours. As can be seen from the figure, under the constant humidity condition of 50RH%, after adding 0.2mL SiCl4 to achieve a single coating, the relative mass of lanthanum hydroxide in the powder was 15wt% after 24 hours of constant humidity treatment, while the uncoated La2O3 sample was tested to have been completely reacted into La(OH)3 within 24 hours. The comparison shows that the SiO2@La2O3 powder coated once has a certain environmental storage stability.

[0070] Figure 2 The moisture absorption dynamics change curve of the lanthanum oxide powder after one to four coatings in the constant temperature and humidity chamber (25°C, 50RH%) for 24 hours to 96 hours in the embodiment three, five, six and seven. As can be seen from the figure, after the SiO2@La2O3 powder coated twice is treated with constant humidity for 24 hours, the relative mass of lanthanum hydroxide in the powder is 10wt%, after the SiO2@La2O3 powder coated three times is treated with constant humidity for 24 hours, the relative mass of lanthanum hydroxide in the powder is 5wt%, and after the SiO2@La2O3 powder coated four times is treated with constant humidity for 24 hours, the relative mass of lanthanum hydroxide in the powder is 1.2wt%, which can prove that multiple coatings can significantly improve the coating effect, so the density of the coating can be improved by multiple coatings.

[0071] Figure 3 The results of phase analysis of the lanthanum hydroxide powder before and after coating in Example 9 were placed in a constant temperature and humidity chamber (25°C, 50RH%) for 48 hours. Under the constant humidity condition of 50RH%, the uncoated LaOOH sample was tested to have been completely reacted into La(OH)3 within 24 hours. Compared with the powder after the first coating, there was no obvious characteristic peak of lanthanum hydroxide after 48 hours of constant humidity treatment, which proved that the coated powder had better stability.

[0072] Figure 4 The TEM images of the coating thickness of lanthanum oxide powder after one to four coatings in Examples 3, 5, 6 and 7 are (a) one coating, (b) two coatings, (c) three coatings, and (d) four coatings. As can be seen from the figure, as the number of coatings increases, the thickness of the film layer on the surface of lanthanum oxide gradually increases from the initial 1.2nm to 7.2nm, indicating that the growth rate of the film layer thickness is relatively uniform and the thickness is controlled within 10nm, and the thickness of the surface film layer can be controlled by changing the number of coatings.

[0073] The above determination of the phase structure and content in the powder is mainly to determine the coated pure lanthanum oxide powder and the lanthanum hydroxide generated after moisture absorption and their relative content, which can determine the isolation effect of the coating layer or the moisture absorption degree of the coated powder.

Claims

1. A method for preparing a stable oxide-coated lanthanum oxide powder, characterized in that It is carried out in the following steps:

1. Coating: Under the condition of an ambient relative humidity of 20RH% to 30RH%, an organic solvent is added to lanthanum oxide powder, and then a main element source reagent of the surface nano-modified oxide is added dropwise, followed by stirring and mixing, and finally standing, filtering and vacuum drying to obtain a powder after primary coating; The main element source reagent of the surface nano-modified oxide is an anhydrous metal salt or silicon halide; 2. Multiple cycles: The powder coated once is repeatedly coated according to step 1 to obtain powder coated multiple times, thus completing the preparation method of stable oxide-coated lanthanum oxide powder.

2. The method for preparing a stable oxide-coated lanthanum oxide powder according to claim 1, characterized in that The lanthanum oxide powder described in step one is lanthanum oxide powder or lanthanum hydroxide oxide powder; the anhydrous metal salt described in step one is titanium tetrachloride; the silicon halide described in step one is silicon tetrachloride; the organic solvent described in step one is carbon tetrachloride or acetone.

3. The method for preparing a stable oxide-coated lanthanum oxide powder according to claim 2, characterized in that The lanthanum oxide powder is a lanthanum oxide powder after surface hydroxylation treatment, and the surface hydroxylation treatment is specifically performed by standing for 5 minutes to 10 minutes under the condition of an ambient relative humidity of 20RH% to 30RH%.

4. The method for preparing a stable oxide-coated lanthanum oxide powder according to claim 2, characterized in that The lanthanum oxyhydroxide powder is specifically prepared according to the following steps: ① At a speed of 300 r / min to 400 r / min, lanthanum oxide powder and deionized water are stirred and mixed for 1.5 h to 2 h, and then filtered to obtain a powder cake, and the powder cake is vacuum dried at a temperature of 60° C. to 80° C. for 3 h to 4 h to obtain lanthanum hydroxide powder; ② Place the lanthanum hydroxide powder in a muffle furnace, heat it to 350°C to 400°C at a heating rate of 8°C / min to 10°C / min, and then keep it at 350°C to 400°C for 30min to 120min to obtain lanthanum hydroxide powder.

5. The method for preparing a stable oxide-coated lanthanum oxide powder according to claim 4, characterized in that The volume ratio of the mass of the lanthanum oxide powder described in step ① to deionized water is 1g:(10-20)mL.

6. The method for preparing a stable oxide-coated lanthanum oxide powder according to claim 1, characterized in that The average particle size of the lanthanum oxide powder described in step 1 is 10 nm to 10 μm.

7. The method for preparing a stable oxide-coated lanthanum oxide powder according to claim 1, characterized in that The mass ratio of the lanthanum oxide powder described in step 1 to the volume ratio of the organic solvent is 1 g: (10-20) mL.

8. The method for preparing a stable oxide-coated lanthanum oxide powder according to claim 1, characterized in that The volume ratio of the main element source reagent of the surface nano-modified oxide described in step 1 to the organic solvent is 1:(333-2000).

9. The method for preparing a stable oxide-coated lanthanum oxide powder according to claim 1, characterized in that The stirring and mixing in step 1 is specifically carried out under the conditions of an ambient relative humidity of 20 RH% to 30 RH% and a rotation speed of 300 r / min to 400 r / min for 5 min to 40 min.

10. The method for preparing a stable oxide-coated lanthanum oxide powder according to claim 1, characterized in that The vacuum drying described in step 1 is specifically performed at a temperature of 60° C. to 80° C. for 3 h to 4 h.

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