CN114644809A - Composition of buoyancy material, buoyancy material and manufacturing method thereof - Google Patents

Abstract

The invention discloses a buoyancy material composition, a buoyancy material and a manufacturing method thereof. The composition of the buoyancy material includes a thermosetting resin, a plurality of micron-sized hollow spheres, a plurality of nano-sized metal oxide particles and a curing agent. Through the roughened surfaces of these hollow spheres and these metal oxide particles, the buoyant material produced by this production method has a low water absorption rate.

Description

Composition of buoyancy material, buoyancy material and method of making the same

technical field

The present invention relates to a buoyant material composition, a buoyancy material and a manufacturing method thereof, and particularly relates to a low water absorption buoyancy material, its composition and its manufacturing method.

Background technique

Buoyant materials are widely used in civil, commercial and military fields. For example, the counterweight of underwater equipment, floating cables floating on the water surface or suspended in the water, buoys, submarine cable buried machinery, zero buoyancy support, life-saving devices, submarine detection devices and unmanned remote control submersibles, etc. In addition, with the development of marine technology, high-strength buoyancy materials play an important role in Unmanned Underwater Vehicles (UUVs). Operated Underwater Vehicles, ROV) and autonomous underwater vehicles (Autonomous Underwater Vehicles, AUV) that do not require user operation.

When the buoyant material is used in the aforementioned fields, the buoyant material must have a low density (eg, 0.3g/cm ³ to 0.8g/cm ³ ) to float stably in the water, thereby providing buoyancy and ensuring the balance of the equipment it is loaded with state. Secondly, the buoyant material must also have high pressure resistance (for example, the uniaxial compressive strength is greater than 5.5MPa) to resist high temperature sunlight and seawater erosion. Furthermore, the buoyant material must also have a low water absorption rate (eg, not more than 1%) to avoid the problems of buoyancy change and material creep after the material absorbs water.

At present, the composition of buoyancy materials is to mix hollow glass spheres with smaller size into epoxy resin to serve as light fillers, and to make buoyancy materials, such as buoyancy modules. The prepared buoyancy material has higher compressive strength and therefore has a longer service life. However, when the hollow glass spheres are mixed with epoxy resin, the hollow glass spheres tend to increase the viscosity of the epoxy resin, and the usage amount thereof must be limited. Although this problem can be solved by adding reactive diluents, reactive diluents can cause embrittlement of the cured resin and reduce its mechanical properties. In addition, the curing agent used will shorten the handling time of the composition of the buoyant material and reduce its workability.

On the other hand, when the composition of the buoyancy material undergoes a curing reaction, it must be in an environment with an extremely low water absorption rate. However, during preparation, free water easily enters the embedded voids between the heterogeneous composite components (eg, hollow glass spheres and epoxy resin), and increases the water absorption rate of the buoyant material, thus shortening its service life.

In view of this, there is an urgent need to develop a new buoyancy material composition, buoyancy material and its manufacturing method, so as to improve the above-mentioned shortcomings of the known buoyant material and its manufacturing method.

SUMMARY OF THE INVENTION

In view of the above problems, an object of the present invention is to provide a buoyant material composition. The prepared buoyant material has low water absorption through surface-roughened micron-scale hollow spheres and nano-scale metal oxide particles.

Another object of the present invention is to provide a manufacturing method of a buoyancy material. This manufacturing method utilizes the aforementioned composition to manufacture a buoyant material, wherein surface roughening of the hollow sphere can reduce the water absorption rate of the buoyant material.

Another object of the present invention is to provide a buoyant material, which is prepared by the aforementioned manufacturing method.

According to an object of the present invention, a composition of buoyancy material is proposed. The composition comprises a thermosetting resin, a plurality of hollow spheres, a plurality of metal oxide particles, and a curing agent, wherein the average particle diameter (D ₅₀ ) of the hollow spheres is 10 μm to 100 μm, and the average particle diameter of the metal oxide particles is 5nm to 35nm. Based on 100 parts by weight of the thermosetting resin, these hollow spheres are used in an amount of 20 to 65 parts by weight, these metal oxide particles are used in an amount of 0.5 to 4.0 parts by weight, and the curing agent is used in an amount of 40 to 60 parts by weight.

According to an embodiment of the present invention, the thermosetting resin includes epoxy resin, phenolic resin, unsaturated polyester resin and any combination thereof.

According to another embodiment of the present invention, the compressive strength of the hollow spheres is greater than 3000 psi.

According to yet another embodiment of the present invention, the wall thickness of the hollow spheres is 0.5 μm to 2.5 μm.

According to another object of the present invention, a method for manufacturing a buoyancy material is provided. In this manufacturing method, a surface roughening step is performed on a plurality of hollow spheres, and then a surface modification step is performed on the roughened hollow spheres, wherein the average particle diameter (D ₅₀ ) of the hollow spheres is 10 μm to 100 μm. Next, the modified hollow spheres, the thermosetting resin and the plurality of metal oxide particles are mixed to obtain a homogenized mixture, wherein the average particle diameter of the metal oxide particles is 5 nm to 35 nm. Then, a curing agent is added to the homogenized mixture to perform a curing reaction step to obtain a buoyant material.

According to an embodiment of the present invention, the surface roughening step includes cleaning the hollow spheres with an alkaline solution.

According to another embodiment of the present invention, the surface modification step comprises modifying the hollow spheres with a silane coupling agent.

According to another object of the present invention, a buoyant material is proposed. The buoyant material includes a thermosetting resin, a plurality of hollow spheres, and a plurality of metal oxide particles. The hollow spheres have an average particle diameter (D ₅₀ ) of 10 μm to 100 μm, at least part of the metal oxide particles are filled between the hollow spheres, wherein the average particle diameter of the metal oxide particles is 5 nm to 35 nm, and the buoyant material has an average particle diameter of 5 nm to 35 nm. The water absorption rate is not more than 1%.

According to yet another embodiment of the present invention, the buoyant material selectively includes the bonds formed by the reaction between the silane coupling agent and the hollow spheres, and/or the bonds formed by the silane coupling agent and the metal oxide particles.

According to yet another embodiment of the present invention, the compressive strength of the hollow spheres is greater than 3000 psi.

The composition of the buoyancy material and the manufacturing method thereof of the present invention are applied, wherein the surface-roughened micron-scale hollow spheres can increase the wettability of the bonding interface with the thermosetting resin, and the nano-scale metal oxide particles can be filled in the thermosetting resin and the thermosetting resin. The voids between the hollow spheres reduce the water absorption rate of the buoyant material, so the obtained buoyancy material has low water absorption rate, and maintains low density and high compressive strength.

Description of drawings

For a more complete understanding of the embodiments of the present invention and their advantages, please refer to the following description in conjunction with the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are for illustrative purposes only. The contents of the relevant drawings are described as follows:

FIG. 1 is a flow chart illustrating a method for manufacturing a buoyancy material according to an embodiment of the present invention.

2 is a scanning electron microscope photograph of a buoyant material according to an example of the present invention.

Description of main reference signs:

100 - Method; 110, 120, 130, 140 - Operation.

Detailed ways

The making and using of embodiments of the present invention are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are provided for illustration only, and are not intended to limit the scope of the invention.

Please refer to FIG. 1 , which is a flowchart illustrating a method for manufacturing a buoyancy material according to an embodiment of the present invention. In the manufacturing method 100 , a surface roughening step is first performed on a plurality of hollow spheres, as shown in operation 110 . In the surface roughening step, the surface of the hollow sphere can be roughened by using an alkali solution, thereby increasing the surface energy of the surface of the hollow sphere, so as to facilitate subsequent surface modification.

In some embodiments, the surface roughening step comprises caustic washing the surface of the hollow spheres with lye. In other embodiments, the surface roughening step selectively includes the use of acoustic waves (eg, ultrasonic waves) or electromagnetic waves to assist in alkaline cleaning, so as to promote the roughening of the surface of the hollow sphere, thereby greatly increasing its surface energy. In other words, in some embodiments, the lye solution can remove impurities and/or oil stains on the surface of the hollow spheres. In some embodiments, the lye contains alkali metal hydroxides, specific examples of which may include but are not limited to lithium hydroxide, sodium hydroxide and potassium hydroxide, and preferably sodium hydroxide.

In addition, in some embodiments, the usage amount of the lye solution is 500 to 800 parts by weight based on 100 parts by weight of the glass microspheres, and the concentration of the lye solution may be 1 to 3 wt %.

In some embodiments, the materials of the hollow spheres include inorganic materials and organic materials. Specific examples of the hollow spheres can be, but are not limited to, hollow glass spheres, hollow ceramic spheres and hollow plastic spheres, and preferably can be hollow glass spheres.

In some embodiments, the average particle size (D ₅₀ ) of the hollow spheres is 10 μm to 100 μm, and preferably 15 μm to 30 μm. When the average particle size (D ₅₀ ) of the hollow spheres is not within the aforementioned range, although a smaller hollow sphere can improve the compressive strength of the buoyant material, too small or too large a hollow volume will increase the density of the buoyant material. It is difficult to meet the requirements of low density (for example: 0.3g/cm ³ to 0.8g/cm ³ ). In addition, the hollow spheres with large particle size have relatively poor compressive strength, which is easy to cause the buoyant material to have poor water depth pressure resistance characteristics.

In some embodiments, the compressive strength of these hollow spheres is greater than 3000 psi, and preferably greater than 3000 psi and no greater than 16000 psi. When the compressive strength of the hollow ball is greater than 3000psi, the prepared buoyant material can meet the requirements of high pressure resistance (for example, the compressive strength is greater than 5.5MPa), so as to increase the service life of the buoyant material in water.

In some embodiments, the wall thickness of these hollow spheres is 0.5 μm to 2.5 μm, and preferably 1 μm to 1.5 μm. When the wall thickness of the hollow sphere is 0.5 μm to 2.5 μm, the prepared buoyant material can meet the aforementioned requirements of high pressure resistance and low density.

These hollow spheres are used in an amount of 20 to 65 parts by weight, and preferably 40 to 60 parts by weight, based on 100 parts by weight of the thermosetting resin described later. When the usage amount of the hollow balls is less than 20 parts by weight, the buoyant material will have an excessively large density and cannot meet the specification requirements. When the usage amount of the hollow ball is more than 65 parts by weight, the density of the buoyant material becomes smaller, and the specification requirement cannot be met.

After the aforementioned operation 110 , the roughened hollow spheres are subjected to a surface modification step, as shown in operation 120 . The surface modification step is to modify the roughened surface of the hollow sphere to increase the wettability of the subsequently added thermosetting resin to the surface of the hollow sphere.

In some embodiments, the surface modification step comprises modifying the roughened surfaces of the hollow spheres with a silane coupling agent. This silane coupling agent includes a silane coupling agent having a hydroxyl group, an alkoxy group, an amino group, an epoxy group, an alkenyl group, and a combination thereof. In some specific examples, the alkoxy group of the silane coupling agent can react with the silanol group of the hollow sphere to form a silicon-oxygen bond, thereby reducing the water absorption rate of the buoyant material. Specific examples of the silane coupling agent may include, but are not limited to, aminopropyltriethoxysilane, tetraethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, N-β-aminoethyl- γ-aminopropyl-trimethoxysilane, γ-aminopropyltriethoxysilane and (3-glycidoxypropyl)trimethoxysilane, preferably aminopropyltriethoxysilane base silane.

In some embodiments, the used amount of the silane coupling agent is 1 to 10 parts by weight based on 100 parts by weight of the hollow spheres.

After the aforementioned operation 120 , the modified hollow spheres, the thermosetting resin, and the metal oxide particles are mixed to obtain a homogenized mixture, as shown in operation 130 . During the mixing process, since the metal oxide particles are of nano-scale, they can be filled in the voids between the thermosetting resin and the micron-sized hollow spheres and/or in the voids between the micron-sized hollow spheres to prevent moisture from entering into these voids. Therefore, the water absorption rate of the buoyant material can be reduced. In some embodiments, the alkoxy groups of the silane coupling agent can react with the metal atoms of the metal oxide particles to form silicon-oxygen-metal bonds, thereby reducing the water absorption of the buoyant material. In some specific examples, the amine group, epoxy group and/or alkenyl group of the silane coupling agent can react with the thermosetting resin.

In some embodiments, the thermosetting resin and the metal oxide particles are mixed first, and then the modified hollow spheres are added. In other embodiments, the modified hollow spheres and the metal oxide particles are added to the thermosetting resin simultaneously. In some embodiments, the type of resin is a thermoset resin. In still other embodiments, the order of adding the three is not particularly limited, but the purpose is that the three can be uniformly mixed and the uniformity of the material of the buoyancy material is achieved.

In some embodiments, the aforementioned mixing can be carried out using a mechanical homogenizing stirring method to uniformly mix the hollow spheres resembling a non-viscous liquid with a higher viscosity thermosetting resin, such as using a vacuum stirring method.

In some embodiments, the thermosetting resin comprises epoxy resins, phenolic resins, unsaturated polyester resins, and any combination thereof. Preferably, the thermosetting resin may be epoxy resin. Further, specific examples of the thermosetting resin may include, but are not limited to, bisphenol A epoxy resin. Furthermore, in some embodiments, the viscosity of the thermosetting resin at 25° C. may be 1000 cpscps to 2100 cps.

The average particle diameter of the aforementioned metal oxide particles is 5 nm to 35 nm, and preferably 15 nm to 25 nm. When the average particle size of the metal oxide particles is less than 5 nm, the disadvantage is that the specific surface area is too large, which makes it difficult to operate in the process of mixing. When the average particle size of the metal oxide particles is greater than 35 nm, the excessively large metal oxide particles cannot fill the voids between the thermosetting resin and the hollow spheres, thus increasing the water absorption rate of the buoyant material.

In some embodiments, the metal oxide particles may comprise particles of oxides of alkali metals, alkaline earth metals, transition metals, and any combination thereof. Further, specific examples of the metal oxide particles may include but are not limited to particles of aluminum oxide, zinc oxide, calcium oxide, sodium oxide, magnesium oxide, barium oxide, iron oxide, copper oxide and tungsten oxide, and preferably aluminum oxide particles .

The metal oxide particles are used in an amount of 0.5 to 4.0 parts by weight, and preferably 2.0 to 4.0 parts by weight, based on 100 parts by weight of the thermosetting resin. When the amount of metal oxide particles used is less than 0.5 parts by weight, it is difficult for too little metal oxide particles to fill the gap between the thermosetting resin and the hollow sphere, and it is easy to guide water into the buoyant material, thereby increasing its water absorption rate, and excessive A large volume of voids will reduce the density of the buoyant material. On the contrary, when the amount of metal oxide particles used is greater than 4.0 parts by weight, excessive metal oxide particles tend to aggregate, thereby reducing the mixing uniformity of thermosetting resin, hollow spheres and curing agent.

After the aforementioned operation 130 , a curing agent is added to the homogenized mixture to perform the curing reaction step to obtain a buoyant material, as shown in operation 140 . Curing agents include, but are not limited to, amine curing agents, acid anhydride curing agents, and phenolic curing agents. The curing agent of the present invention is not particularly limited, and may be a curing agent known to those skilled in the art to which the present invention pertains, but the curing agent needs to be capable of curing the aforementioned thermosetting resin.

The usage amount of the curing agent is 40 to 60 parts by weight, and preferably 45 to 55 parts by weight, based on 100 parts by weight of the thermosetting resin. When the amount of curing agent used is less than 40 parts by weight, too little curing agent will lead to incomplete curing of the thermosetting resin, thereby reducing its crosslinking density and thus reducing the compressive strength of the buoyant material. On the contrary, when the amount of curing agent used is more than 60 parts by weight, too much curing agent shortens the operation time of the thermosetting resin after adding the curing agent, which is not conducive to injection molding, and reduces the material uniformity of the buoyancy material.

In some embodiments, after mixing the thermosetting resin, hollow spheres, metal oxide particles and curing agent, injection molding is performed to prepare the buoyant material in the desired shape. In other embodiments, after injection molding, pre-curing, high-temperature curing (ie, curing reaction), cooling and demolding may be selectively performed in sequence. In still other embodiments, post-processing (eg, cutting and burr trimming) may optionally be performed after demolding.

The aforementioned production method is to produce a buoyancy material using the composition of the buoyancy material of the present invention. In other words, the composition of the buoyancy material includes a thermosetting resin, a plurality of hollow spheres, a plurality of metal oxide particles and a curing agent, wherein the description of each component has been described in detail in the manufacturing method, so it will not be repeated here.

The water absorption rate of the buoyant material prepared by the above method is not more than 1% under the 24-hour test, and preferably not more than 0.08%, so the buoyancy material has a long-term low water absorption rate and can increase its service life.

In some embodiments, the compressive strength of the buoyant material is greater than 5.5 MPa. When the compressive strength of the buoyant material is greater than 5.5 MPa, the buoyant material has high compressive strength. Compared with the buoyant material prepared by the general chemical foaming process, the buoyancy material does not have the problem of creep, so it has a longer service life.

The following examples are used to illustrate the application of the present invention, but it is not intended to limit the present invention. Anyone skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention.

Manufacture of buoyant materials

Example

The production of the buoyancy material of the embodiment is that 100 g of hollow glass spheres (average particle size (D ₅₀ ) of 30 μm and a wall thickness of 1 μm) are first kept under pressure and added with water for 24 hours, and then the settled hollow glass spheres (that is, broken hollow glass spheres) are discarded. Glass ball). Then, 500 ml of a 2% sodium hydroxide aqueous solution was added, and the hollow glass spheres were alkali-washed with ultrasonic waves, and then washed with water and dried. Next, the alkali-washed hollow glass spheres were modified with 60 ml of 20 mM aminopropyltriethoxysilane, and then washed and dried to obtain modified hollow glass spheres.

Then, in a vacuum stirring device (the vacuum degree of this device is maintained at 0.01MPa to 0.1MPa), 50g of modified hollow glass spheres were added to 100g in batches and mixed with alumina particles (the usage amount was 2.2g) , and the particle size is 20 nm) uniformly mixed bisphenol A epoxy resin. After mixing and stirring for 20 to 40 minutes, add 50g of curing agent (low viscosity epoxy resin, or please provide the full name of the curing agent), and after mixing and stirring for 5 to 15 minutes, carry out vacuum defoaming (vacuum 0.01 MPa to 0.1 MPa) to obtain the compositions of the buoyant materials of the examples.

After casting the aforementioned composition into a mold release agent-coated mold, wait for the resin to exotherm (ie, perform pre-curing) at room temperature. Then, high temperature aging (ie, curing reaction) was performed at 80°C. After 120 minutes of reaction, the buoyancy material of the embodiment can be prepared by cooling and demoulding in sequence, and the test is carried out in the following evaluation method.

Comparative example

The comparative example was produced by the same method as the example. The difference is that the comparative example does not use alumina particles, and its specific conditions and test results are shown in Table 1 below.

Evaluation method

1. Compressive strength test

The compressive strength test is to measure the uniaxial compressive strength by the ASTM (1621) standard method, and evaluate the compressive strength of the buoyant material by the uniaxial compressive strength. When the uniaxial compressive strength is greater than 5.5MPa, the buoyancy is determined. The material has good compressive strength.

2. Water absorption test

The water absorption test begins by measuring the unsubmerged weight (W ₀ ) of the buoyant material. Next, after immersing the buoyant material in water for 30 seconds, the water was wiped off and weighed again to obtain the weight (W ₁ ) after being immersed in water for 30 seconds. Then, after immersing the buoyant material in water for 24 hours, the water was wiped dry and weighed again to obtain the weight (W ₂ ) after immersion in water for 24 hours. Finally, according to the following formula (I), calculate the water absorption (%) after immersion in water for 30 seconds and 24 hours:

where _Wi can be W ₁ or W ₂ to calculate the water absorption after immersion in water for 30 seconds or 24 hours.

In addition, the difference between the water absorption rates of 30 seconds and 24 hours is used to determine the stability of the buoyant material in water, wherein when the difference between the two is smaller, the higher the stability of the buoyant material in water is determined.

3. Dielectric constant

The dielectric constant is measured by the ASTM (D2520) standard method of the dielectric constant of any 5 places in the buoyant material, and the difference between the maximum value and the minimum value is calculated to evaluate the material uniformity of the buoyant material, where the difference is not greater than When the value is 0.5, it is judged that the material of the buoyancy material has good uniformity.

4. Observation of Microstructure

The observation of the microstructure is to observe the buoyant material using a scanning electron microscope to evaluate the filling state of the metal oxide particles in the voids between the thermosetting resin and the hollow glass spheres and the voids between the hollow glass spheres. The photos are shown in Figure 2. Show.

5. Measurement of density

Density is measured by a method commonly used by those skilled in the art to which the present invention pertains.

Table 1

N/A indicates that this component was not used or the test was not performed.

Please refer to FIG. 2 , which is a scanning electron microscope photograph of the buoyant material of the embodiment. The electron microscope photos of the examples show that the alumina particles fill the gaps between the epoxy resin and the hollow glass spheres and the gaps between the hollow glass spheres, so the microstructure of the buoyancy materials of the examples is dense.

Further, referring to Table 1 above, according to the results of water absorption, compared with the comparative example, the buoyant material of the embodiment has smaller water absorption at 30 seconds and 24 hours, and the difference in water absorption is also smaller. It can be seen that the alumina particles fill the gaps between the epoxy resin and the hollow glass spheres and the gaps between the hollow glass spheres, thereby reducing the water absorption rate of the buoyant material and improving its stability in water.

Second, according to the results of the uniaxial compressive strength (greater than 5.5 MPa), the buoyant materials of the examples have high compressive strength. Furthermore, according to the result of the difference in dielectric constant (not more than 0.5), the material of the buoyancy material of the embodiment has good uniformity.

To sum up, the composition of the buoyancy material of the present invention and the manufacturing method thereof are obtained by using the surface-roughened micron-scale hollow spheres and nano-scale metal oxide particles to obtain a low water absorption rate, and maintain a low density and high resistance. Compressive strength buoyant material. The roughened surface of the hollow sphere can improve the wettability of the bonding interface with the thermosetting resin, and the metal oxide particles can be filled in the gap between the thermosetting resin and the hollow sphere and the gap between the hollow glass spheres to reduce the water absorption of the buoyant material Therefore, the obtained buoyant material has low water absorption rate, and maintains low density and high compressive strength.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Any person skilled in the art to which the present invention pertains can make various modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be determined by the claims.

Claims (10)

1. A composition of buoyant materials, comprising:

a thermosetting resin;

a plurality of hollow spheres, wherein the average particle diameter (D) of the plurality of hollow spheres₅₀) Is 10 μm to 100 μm;

a plurality of metal oxide particles, wherein the plurality of metal oxide particles have an average particle size of 5nm to 35 nm; and

a curing agent for curing the epoxy resin composition,

wherein the plurality of hollow spheres is used in an amount of 20 to 65 parts by weight, the plurality of metal oxide particles is used in an amount of 0.5 to 4.0 parts by weight, and the curing agent is used in an amount of 40 to 60 parts by weight, based on 100 parts by weight of the thermosetting resin.

2. The buoyant material composition of claim 1 wherein the thermosetting resin comprises an epoxy resin, a phenolic resin, an unsaturated polyester resin, and any combination thereof.

3. The buoyant material composition of claim 1 wherein said plurality of hollow spheres have a compressive strength greater than 3000 psi.

4. The composition of buoyant material of claim 1 wherein the plurality of hollow spheres have a wall thickness of 0.5 μ ι η to 2.5 μ ι η.

5. A method of making a buoyant material, the method comprising:

a step of roughening the surfaces of the plurality of hollow spheres;

carrying out surface modification on the plurality of roughened hollow spheres;

mixing the modified plurality of hollow spheres, thermosetting resin, and plurality of metal oxide particles to obtain a homogenized mixture; and

adding a curing agent to the homogenized mixture to perform a curing reaction step to obtain the buoyant material;

wherein the average particle diameter (D) of the plurality of hollow spheres₅₀) Is 10 to 100 μm, and the plurality of metal oxide particles have an average particle diameter of 5 to 35 nm.

6. The method of claim 5, wherein the surface roughening step comprises washing the plurality of hollow spheres with a caustic solution.

7. The method of claim 5, wherein the surface modifying step comprises modifying the plurality of hollow spheres with a silane coupling agent.

8. A buoyant material, comprising:

a thermosetting resin;

a plurality of hollow spheres, wherein the average particle diameter (D) of the plurality of hollow spheres₅₀) Is 10 μm to 100 μm; and

a plurality of metal oxide particles at least a portion of which are filled between the plurality of hollow spheres, wherein the plurality of metal oxide particles have an average particle diameter of 5nm to 35 nm;

wherein the water absorption of the buoyant material is no greater than 1%.

9. The buoyant material of claim 8 wherein the buoyant material further comprises bonds formed by reaction of a silane coupling agent with the plurality of hollow spheres and/or bonds formed by reaction of the silane coupling agent with the plurality of metal oxide particles.

10. The buoyant material of claim 8 wherein said plurality of hollow spheres have a compressive strength of greater than 3000 psi.

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