Preparation method of CVD (Chemical Vapor Deposition) silicon carbide coating

Abstract

The invention discloses a preparation method of a CVD (Chemical Vapor Deposition) silicon carbide coating, and relates to a preparation method of a silicon carbide coating. The invention aims to solve the problems of poor uniformity and non-ideal anti-oxidation effect of the existing silicon carbide coating. The method comprises the following steps: 1, low-temperature plasma treatment; 2, preparing a nano particle dispersion liquid; 3, a CVD (Chemical Vapor Deposition) process; and 4, post-processing. The method is used for preparing the CVD silicon carbide coating.

Description

Technical Field

[0001] The present invention relates to a method for preparing a silicon carbide coating. Background Art

[0002] Carbon fiber sealing strips are widely used in the fields of aerospace, automotive manufacturing, high-end electronic devices, etc. due to their excellent mechanical properties, lightweight characteristics, etc. However, in a high-temperature aerobic environment, carbon fiber sealing strips are prone to oxidation reactions, resulting in serious mass loss and thus structural damage, greatly limiting their scope of use and service life in high-temperature environments. At present, in order to improve the antioxidant performance of carbon fiber sealing strips, common methods include surface coating treatment, chemical modification, etc. Among them, chemical vapor deposition (CVD) technology is an effective method for preparing high-quality coatings, which can form a uniform SiC coating on the surface of materials, effectively blocking the contact between oxygen and carbon fiber sealing strips, thereby improving their antioxidant performance. However, when the existing CVD technology for preparing silicon carbide coatings is applied to carbon fiber sealing strips, there is a problem of poor coating uniformity, and the antioxidant advantages of the silicon carbide coating cannot be fully exerted. In addition, traditional methods are difficult to achieve uniform distribution of silicon carbide nanoparticles on the surface of carbon fiber sealing strips at the microscopic level, affecting the improvement effect of antioxidant performance. Therefore, it is of great practical significance to develop a preparation method capable of uniformly depositing a silicon carbide coating on the surface of carbon fiber sealing strips. Summary of the Invention

[0003] The present invention aims to solve the problems of poor uniformity of the existing silicon carbide coating and unsatisfactory antioxidant effect, and further provides a method for preparing a CVD silicon carbide coating.

[0004] A method for preparing a CVD silicon carbide coating is carried out according to the following steps:

[0005] I. Low-temperature plasma treatment:

[0006] Using argon as the working gas, under the conditions of an argon flow rate of 20 sccm to 500 sccm and a radio frequency power of 20 W to 120 W, the carbon fiber sealing strip is subjected to low-temperature plasma treatment for 5 min to 100 min to obtain a plasma-treated carbon fiber sealing strip;

[0007] II. Preparation of nanoparticle dispersion:

[0008] Adding silicon carbide nanoparticles to absolute ethanol and ultrasonically dispersing them evenly to obtain a nanoparticle dispersion;

[0009] III. CVD deposition process:

[0010] Place the plasma-treated carbon fiber sealing strip in the reaction chamber of the CVD reaction equipment and evacuate it. Then introduce the mixed reaction gas, and at the same time turn on the heating system. Heat the reaction chamber at a heating rate of 10 °C / min to 15 °C / min. During the heating process, evenly spray the nanoparticle dispersion on the surface of the plasma-treated carbon fiber sealing strip through a spraying device. When the temperature rises to 1050 °C to 1550 °C, carry out the deposition reaction for 1 h to 10 h under the conditions of a sample rotation speed of 8 r / min to 100 r / min, a reaction chamber pressure of 1 Pa to 40 Pa, and a temperature of 1050 °C to 1550 °C. After the deposition is completed, stop introducing the mixed reaction gas, maintain the vacuum state, let the reaction chamber cool naturally to room temperature, and finally take it out to obtain the carbon fiber sealing strip after CVD deposition;

[0011] The mixed reaction gas is composed of a silicon source gas, a carbon source gas, and a dilution gas;

[0012] IV. Post-treatment:

[0013] Ultrasonically clean and dry the carbon fiber sealing strip after CVD deposition, and the preparation method of the CVD silicon carbide coating is completed.

[0014] The beneficial effects of the present invention are:

[0015] The preparation method of the CVD silicon carbide coating provided by the present invention is an improvement on the existing preparation method of the CVD silicon carbide coating. Using this method, an antioxidant silicon carbide coating can be evenly deposited on the surface of the carbon fiber sealing strip, significantly optimizing the antioxidant performance of the carbon fiber sealing strip. In the antioxidant test, the mass loss rate after oxidation at 700 °C is only 5.7% to 8.4%. It solves the problems of poor coating uniformity and unsatisfactory antioxidant effect in the prior art. This sealing strip can be used in the field of high-temperature sealing. Description of the Drawings

[0016] Figure 1 It is a SEM schematic diagram of the original carbon fiber sealing strip in Step 1 of Example 1;

[0017] Figure 2 It is a SEM schematic diagram with a scale of 20 μm of the carbon fiber sealing strip coated with a silicon carbide coating prepared in Example 1;

[0018] Figure 3 It is a SEM schematic diagram with a scale of 500 nm of the carbon fiber sealing strip coated with a silicon carbide coating prepared in Example 1;

[0019] Figure 4 It is a SEM schematic diagram with a scale of 300 μm of the carbon fiber sealing strip coated with a silicon carbide coating prepared in Example 1;

[0020] Figure 5TG schematic diagram of the carbon fiber sealing strip coated with silicon carbide coating prepared in Example 1;

[0021] Figure 6 Antioxidant performance diagram of the carbon fiber sealing strip coated with silicon carbide coating prepared in Examples 1 to 2 and the carbon fiber sealing strip after CVD treatment prepared in Comparative Example 1. Detailed implementation manners

[0022] Detailed implementation manner 1: A preparation method of a CVD silicon carbide coating is carried out according to the following steps:

[0023] I. Low-temperature plasma treatment:

[0024] Using argon as the working gas, under the conditions of an argon flow rate of 20 sccm to 500 sccm and a radio frequency power of 20 W to 120 W, the carbon fiber sealing strip is subjected to low-temperature plasma treatment for 5 min to 100 min to obtain the carbon fiber sealing strip after plasma treatment;

[0025] II. Preparation of the nanoparticle dispersion:

[0026] The silicon carbide nanoparticles are added to anhydrous ethanol and ultrasonically dispersed evenly to obtain the nanoparticle dispersion;

[0027] III. CVD deposition process:

[0028] The carbon fiber sealing strip after plasma treatment is placed in the reaction chamber of the CVD reaction equipment and evacuated, and then the mixed reaction gas is introduced. At the same time, the heating system is turned on, and the reaction chamber is heated at a heating rate of 10 °C / min to 15 °C / min. During the heating process, the nanoparticle dispersion is evenly sprayed on the surface of the carbon fiber sealing strip after plasma treatment through the spraying device. When the temperature rises to 1050 °C to 1550 °C, under the conditions of a sample rotation speed of 8 r / min to 100 r / min, a reaction chamber pressure of 1 Pa to 40 Pa, and a temperature of 1050 °C to 1550 °C, the deposition reaction is carried out for 1 h to 10 h. After the deposition is completed, the introduction of the mixed reaction gas is stopped, and the vacuum state is maintained to allow the reaction chamber to cool naturally to room temperature. Finally, it is taken out to obtain the carbon fiber sealing strip after CVD deposition;

[0029] The mixed reaction gas is composed of a silicon source gas, a carbon source gas, and a dilution gas;

[0030] IV. Post-treatment:

[0031] The carbon fiber sealing strip after CVD deposition is ultrasonically cleaned and dried, and thus the preparation method of the CVD silicon carbide coating is completed.

[0032] In Step 1 of this specific embodiment, the surface of the sealing strip is activated by low-temperature plasma treatment, increasing the surface roughness and active groups, and improving the bonding strength with the subsequent coating.

[0033] The beneficial effects of this embodiment are as follows:

[0034] The method for preparing the CVD silicon carbide coating provided in this embodiment is an improvement based on the existing method for preparing the CVD silicon carbide coating. Using this method, an antioxidant silicon carbide coating can be uniformly deposited on the surface of the carbon fiber sealing strip, significantly optimizing the antioxidant performance of the carbon fiber sealing strip. In the antioxidant test, the mass loss rate after oxidation at 700 °C is only 5.7% - 8.4%. This solves the problems of poor coating uniformity and unsatisfactory antioxidant effect in the prior art. This sealing strip can be used in the field of high-temperature resistant sealing.

[0035] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: the carbon fiber sealing strip described in Step 1 is a pretreated carbon fiber sealing strip, and the pretreatment is specifically carried out according to the following steps: successively placed in acetone and absolute ethanol under the condition of ultrasonic power of 10W - 500W for ultrasonic cleaning for 15min - 120min respectively, and then dried for 1h - 10h under the condition of temperature of 60 °C - 180 °C. Others are the same as Specific Embodiment 1.

[0036] This specific embodiment removes oil stains, impurities, release agents, etc. on the surface through cleaning.

[0037] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that: the carbon fiber sealing strip described in Step 1 is woven from T300 carbon fiber bundles. Others are the same as one of Specific Embodiments 1 or 2.

[0038] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is that: the particle size of the silicon carbide nanoparticles described in Step 2 is 20nm - 100nm; the concentration of the nanoparticle dispersion liquid described in Step 2 is 1g / L - 10g / L. Others are the same as Specific Embodiment 3.

[0039] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is that: the silicon source gas described in Step 3 is SiH4; the carbon source gas described in Step 3 is C2H2; the dilution gas described in Step 3 is hydrogen. Others are the same as Specific Embodiments 1 to 4.

[0040] Specific Embodiment 6: The difference between this embodiment and one of Specific Embodiments 1 to 5 is that: the purity of the silicon source gas, carbon source gas, and dilution gas described in Step 3 is ≥4N. Others are the same as Specific Embodiments 1 to 5.

[0041] Embodiment 7: The difference between this embodiment and any one of Embodiments 1 to 6 is that: in Step 3, the volume ratio of the silicon source gas to the carbon source gas is 1:(1 - 5); in Step 3, the volume ratio of the silicon source gas to the dilution gas is 1:(1 - 20). Others are the same as those in Embodiments 1 to 6.

[0042] Embodiment 8: The difference between this embodiment and any one of Embodiments 1 to 7 is that: in Step 3, evacuate to 10 -4 Pa to 10 -2 Pa. Others are the same as those in Embodiments 1 to 7.

[0043] Embodiment 9: The difference between this embodiment and any one of Embodiments 1 to 8 is that: in Step 3, under the conditions of a spray pressure of 0.1 MPa to 0.5 MPa and a sample rotation speed of 10 r / min to 20 r / min, uniformly spray the nanoparticle dispersion on the surface of the plasma-treated carbon fiber sealing strip for 5 min to 100 min. Others are the same as those in Embodiments 1 to 8.

[0044] Embodiment 10: The difference between this embodiment and any one of Embodiments 1 to 9 is that: in Step 4, the ultrasonic cleaning and drying are specifically carried out under the condition of an ultrasonic power of 150 W to 180 W, placed in deionized water for ultrasonic cleaning for 1 min to 150 min, and then dried for 1 h to 24 h under the condition of a temperature of 60 °C to 180 °C.. Others are the same as those in Embodiments 1 to 9.

[0045] This specific embodiment removes residual impurities and unreacted substances on the surface through cleaning.

[0046] The following examples are used to verify the beneficial effects of the present invention:

[0047] Example 1:

[0048] A method for preparing a CVD silicon carbide coating, which is carried out according to the following steps:

[0049] I. Low-temperature plasma treatment:

[0050] Using argon as the working gas, under the conditions of an argon flow rate of 50 sccm and a radio frequency power of 100 W, perform low-temperature plasma treatment on the carbon fiber sealing strip for 8 min to obtain a plasma-treated carbon fiber sealing strip;

[0051] II. Preparation of nanoparticle dispersion:

[0052] Under the condition of an ultrasonic power of 150 W, add silicon carbide nanoparticles to absolute ethanol and ultrasonically disperse them evenly for 60 min to obtain a nanoparticle dispersion;

[0053] The average particle size of the silicon carbide nanoparticles is 30 nm; the concentration of the nanoparticle dispersion is 8.5 g / L;

[0054] III. CVD Deposition Process:

[0055] Place the plasma-treated carbon fiber sealing strip in the reaction chamber of the CVD reaction equipment, evacuate to 5.5×10 -3 Pa, then introduce the mixed reaction gas, and at the same time turn on the heating system. Heat the reaction chamber at a heating rate of 10 °C / min. During the heating process, through the spraying device, under the conditions of a spraying pressure of 0.25 MPa and a sample rotation speed of 20 r / min, evenly spray the nanoparticle dispersion on the surface of the plasma-treated carbon fiber sealing strip for 8 min. When the temperature rises to 1100 °C, under the conditions of a sample rotation speed of 15 r / min, a reaction chamber pressure of 30 Pa, and a temperature of 1100 °C, carry out the deposition reaction for 5 h. After the deposition is completed, stop introducing the mixed reaction gas, maintain the vacuum state, let the reaction chamber cool naturally to room temperature, and finally take out to obtain the carbon fiber sealing strip after CVD deposition;

[0056] The mixed reaction gas is composed of a silicon source gas, a carbon source gas, and a dilution gas;

[0057] The silicon source gas is SiH4; the carbon source gas is C2H2; the dilution gas is hydrogen;

[0058] The purities of the silicon source gas, the carbon source gas, and the dilution gas are all ≥4N;

[0059] The volume ratio of the silicon source gas to the carbon source gas is 1:2.4; the volume ratio of the silicon source gas to the dilution gas is 1:4.17;

[0060] IV. Post-treatment:

[0061] Ultrasonically clean and dry the carbon fiber sealing strip after CVD deposition to obtain a carbon fiber sealing strip coated with a silicon carbide coating.

[0062] The carbon fiber sealing strip described in Step I is a pre-treated carbon fiber sealing strip, and the pretreatment is specifically carried out according to the following steps: Place it in acetone and absolute ethanol in turn under the condition of an ultrasonic power of 400 W and ultrasonically clean for 18 min each, and then dry for 2.5 h under the condition of a temperature of 70 °C.

[0063] The carbon fiber sealing strip described in Step I is woven from T300 carbon fiber bundles, and the length of the carbon fiber sealing strip is 200 mm.

[0064] The ultrasonic cleaning and drying described in Step 4 are specifically carried out by placing it in deionized water and ultrasonically cleaning for 12 min under the condition of an ultrasonic power of 180 W, and then drying for 1.5 h under the condition of a temperature of 70 °C.

[0065] Example 2:

[0066] A preparation method of a CVD silicon carbide coating is carried out according to the following steps:

[0067] I. Low-temperature plasma treatment:

[0068] Using argon as the working gas, under the conditions of an argon flow rate of 40 sccm and a power of 80 W, the carbon fiber sealing strip is subjected to low-temperature plasma treatment for 10 min to obtain a carbon fiber sealing strip after plasma treatment;

[0069] II. Preparation of nanoparticle dispersion:

[0070] Under the condition of an ultrasonic power of 200 W, silicon carbide nanoparticles are added to absolute ethanol and ultrasonically dispersed for 40 min to obtain a nanoparticle dispersion;

[0071] The average particle size of the silicon carbide nanoparticles is 25 nm; the concentration of the nanoparticle dispersion is 5.5 g / L;

[0072] III. CVD deposition process:

[0073] The carbon fiber sealing strip after plasma treatment is placed in the reaction chamber of the CVD reaction equipment, evacuated to 10 - 2 Pa, and then a mixed reaction gas is introduced. At the same time, the heating system is turned on, and the reaction chamber is heated at a heating rate of 10 °C / min. During the heating process, through the spraying device, under the conditions of a spraying pressure of 0.2 MPa and a sample rotation speed of 20 r / min, the nanoparticle dispersion is evenly sprayed on the surface of the carbon fiber sealing strip after plasma treatment for 10 min. When the temperature rises to 1050 °C, under the conditions of a sample rotation speed of 30 r / min, a reaction chamber pressure of 20 Pa, and a temperature of 1050 °C, the deposition reaction is carried out for 5 h. After the deposition is completed, the introduction of the mixed reaction gas is stopped, and the vacuum state is maintained to allow the reaction chamber to cool naturally to room temperature. Finally, it is taken out to obtain a carbon fiber sealing strip after CVD deposition;

[0074] The mixed reaction gas is composed of a silicon source gas, a carbon source gas, and a dilution gas;

[0075] The silicon source gas is SiH4; the carbon source gas is C2H2; the dilution gas is hydrogen;

[0076] The purity of the silicon source gas, carbon source gas, and dilution gas is ≥ 4N;

[0077] The volume ratio of the silicon source gas to the carbon source gas is 1:2; the volume ratio of the silicon source gas to the dilution gas is 1:15;

[0078] IV. Post-treatment:

[0079] The carbon fiber sealing strip after CVD deposition is ultrasonically cleaned and dried to obtain a carbon fiber sealing strip coated with a silicon carbide coating.

[0080] The carbon fiber sealing strip described in Step 1 is a pretreated carbon fiber sealing strip, and the pretreatment is specifically carried out according to the following steps: under the condition of an ultrasonic power of 400 W, it is successively placed in acetone and absolute ethanol for ultrasonic cleaning for 50 min respectively, and then dried for 3 h under the condition of a temperature of 60 °C.

[0081] The carbon fiber sealing strip described in Step 1 is woven from T300 carbon fiber bundles, and the length of the carbon fiber sealing strip is 300 mm.

[0082] The ultrasonic cleaning and drying described in Step 4 are specifically carried out under the condition of an ultrasonic power of 180 W, placed in deionized water for ultrasonic cleaning for 15 min, and then dried for 2 h under the condition of a temperature of 60 °C.

[0083] Comparative Example 1: The difference between this comparative example and Example 1 is: Step 1 and Step 2 are cancelled; in Step 3, the carbon fiber sealing strip is placed in the reaction chamber of the CVD reaction equipment, evacuated to 10 -3 Pa, then the mixed reaction gas is introduced, and at the same time, the heating system is turned on, and the reaction chamber is heated at a heating rate of 10 °C / min. After heating to 950 °C, under the conditions of a sample rotation speed of 30 r / min, a reaction chamber pressure of 80 Pa, and a temperature of 950 °C, the deposition reaction is carried out for 6 h. After the deposition is completed, the introduction of the mixed reaction gas is stopped, and the vacuum state is maintained to allow the reaction chamber to cool naturally to room temperature. Finally, it is taken out to obtain a carbon fiber sealing strip after CVD deposition; the mixed reaction gas is composed of a silicon source gas and a carbon source gas; the silicon source gas is SiH4; the carbon source gas is methane; the volume ratio of the silicon source gas to the carbon source gas is 1:2; in Step 4, the ultrasonic cleaning is replaced by simple water washing to obtain a carbon fiber sealing strip after CVD treatment. Others are the same as in Example 1.

[0084] Figure 1 It is a SEM schematic diagram of the original carbon fiber sealing strip in Step 1 of Example 1; as can be seen from the figure, the surface of the carbon fiber sealing strip is smooth and there are no SiC particles on the surface.

[0085] Figure 2SEM schematic diagram of the carbon fiber sealing strip coated with silicon carbide coating prepared in Example 1 with a scale of 20 μm; Figure 3 SEM schematic diagram of the carbon fiber sealing strip coated with silicon carbide coating prepared in Example 1 with a scale of 500 nm; Figure 4 SEM schematic diagram of the carbon fiber sealing strip coated with silicon carbide coating prepared in Example 1 with a scale of 300 μm; It can be seen from the figure that a large number of nanoparticles appear on the surface of the microstructure of the carbon fiber sealing strip in Example 1, and the particle sizes are uniform.

[0086] Figure 5 TG diagram of the carbon fiber sealing strip coated with silicon carbide coating prepared in Example 1; It can be seen from the figure that after oxidation in air at 700 °C for 8 h in Example 1, the mass loss is only 5.7%.

[0087] Figure 6 Antioxidant performance diagram of the carbon fiber sealing strip coated with silicon carbide coating prepared in Examples 1 to 2 and the carbon fiber sealing strip after CVD treatment prepared in Comparative Example 1; It can be seen from the figure that after oxidation in air at 700 °C for 8 h, the mass loss of Comparative Example 1 is as high as 28.1%, while the mass losses of Examples 1 and 2 are 5.7% and 8.4% respectively, controlled within 10%, fully verifying the significant advantages of the preparation methods in Examples 1 to 2 in improving the surface antioxidant performance of the carbon fiber sealing strip.

Claims

1. A method for preparing a CVD silicon carbide coating, characterized in that It is carried out in the following steps:

1. Low temperature plasma treatment: Using argon as the working gas, under the conditions of an argon flow rate of 20 sccm to 500 sccm and a radio frequency power of 20 W to 120 W, the carbon fiber sealing strip is subjected to low-temperature plasma treatment for 5 min to 100 min to obtain a carbon fiber sealing strip treated with plasma; 2. Preparation of Nanoparticle Dispersion: Adding silicon carbide nanoparticles into anhydrous ethanol and uniformly dispersing them by ultrasonication to obtain a nanoparticle dispersion; 3. CVD deposition process: Placing the carbon fiber sealing strip treated with plasma in a reaction chamber of a CVD reaction device and evacuating the chamber, then introducing a mixed reaction gas, and simultaneously starting a heating system to raise the temperature of the reaction chamber at a heating rate of 10°C / min to 15°C / min. During the heating process, spraying a nanoparticle dispersion evenly on the surface of the carbon fiber sealing strip treated with plasma through a spray device. When the temperature rises to 1050°C to 1550°C, the deposition reaction is carried out for 1h to 10h under the conditions of a sample rotation speed of 8r / min to 100r / min, a reaction chamber pressure of 1Pa to 40Pa, and a temperature of 1050°C to 1550°C. After the deposition is completed, the introduction of the mixed reaction gas is stopped, the vacuum state is maintained, the reaction chamber is naturally cooled to room temperature, and finally the strip is taken out to obtain a carbon fiber sealing strip after CVD deposition. The mixed reaction gas is formed by mixing silicon source gas, carbon source gas and dilution gas; 4. Post-processing: The carbon fiber sealing strip after CVD deposition is ultrasonically cleaned and dried, thereby completing the preparation method of the CVD silicon carbide coating.

2. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that The carbon fiber sealing strip described in step one is a pretreated carbon fiber sealing strip, and the pretreatment is specifically carried out according to the following steps: under the condition of ultrasonic power of 10W to 500W, ultrasonic cleaning is carried out in acetone and anhydrous ethanol for 15min to 120min respectively, and then drying is carried out at a temperature of 60℃ to 180℃ for 1h to 10h.

3. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that The carbon fiber sealing strip described in step 1 is woven from T300 carbon fiber bundles.

4. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that The particle size of the silicon carbide nanoparticles described in step 2 is 20nm to 100nm; the concentration of the nanoparticle dispersion described in step 2 is 1g / L to 10g / L.

5. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that The silicon source gas in step three is SiH4; the carbon source gas in step three is C2H2; and the dilution gas in step three is hydrogen.

6. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that The purity of the silicon source gas, carbon source gas and dilution gas described in step 3 is ≥4N.

7. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that The volume ratio of the silicon source gas to the carbon source gas in step 3 is 1:(1-5); the volume ratio of the silicon source gas to the dilution gas in step 3 is 1:(1-20).

8. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that In step 3, vacuum to 10 -4 Pa~10 -2 Pa.

9. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that In step three, under the conditions of a spray pressure of 0.1 MPa to 0.5 MPa and a sample rotation speed of 10 r / min to 20 r / min, the nanoparticle dispersion is evenly sprayed on the surface of the plasma-treated carbon fiber sealing strip for 5 min to 100 min.

10. The method for preparing a CVD silicon carbide coating according to claim 1, characterized in that The ultrasonic cleaning and drying described in step 4 specifically comprises ultrasonic cleaning in deionized water for 1 min to 150 min at an ultrasonic power of 150 W to 180 W, and then drying at a temperature of 60° C. to 180° C. for 1 h to 24 h.

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