CN107365168B - A method for improving the tensile strength of silica ceramic matrix composites - Google Patents

Abstract

The invention proposes a kind of methods for improving SiO 2-ceramic based composites tensile strength, gas phase graft processing is carried out to SiO 2-ceramic based composites using trimethylmethoxysilane, by it is dry pre-process, preheat, vacuumize, gas phase graft, the techniques such as drying and heat treatment, SiO 2-ceramic based composites are enhanced, tensile strength of material can be improved 15% or more.Present invention process is controllable, can improve the technical bottleneck that tensile strength of material is relatively low in existing moulding process, the enhancing particularly suitable for the wave transparents component such as SiO 2-ceramic antenna house, antenna windows.

Description

A method for improving the tensile strength of silica ceramic matrix composites

technical field

The invention relates to a method for improving the tensile strength of a silicon dioxide ceramic matrix composite material, belonging to the technical field of ceramic wave-transparent composite materials.

Background technique

The radome/antenna window is a component that integrates multiple functions such as wave penetration, heat insulation, load bearing and erosion resistance, and is an important part of the warhead structure of the weapon platform. Radome wave-transparent materials are mainly divided into resin-based wave-transparent materials and ceramic-based wave-transparent materials, but resin-based wave-transparent materials have poor heat resistance, and only ceramic wave-transparent materials can meet the supersonic and high-speed flight requirements of high-tech weapon radomes. Therefore, it has become a hot spot and focus of current weapon development. However, homogeneous ceramics such as fused silica and glass-ceramics are extremely brittle, and the preparation technology of nitride materials is still immature. Therefore, the quartz fiber fabric reinforced silica ceramic composite material with mature technology and high reliability has gradually become the material of choice for high temperature resistant ceramic radome/antenna window.

In the field of radome/antenna window, there are mature fabric-reinforced silica composite material systems, and its fabric structure includes 2.5D fabric, three-way orthogonal fabric, laminated stitching fabric, needle-punched fabric, etc. With the rapid development of high-tech weapons, the impact resistance requirements for radome/antenna window products are more stringent, so the silica ceramic-based wave-transparent composite materials used need to have higher mechanical properties. Since the silica ceramic material is a brittle material, the short board in its mechanical properties is undoubtedly the tensile property. The existing silica ceramic-based wave-transparent composite materials still cannot fully meet the design requirements in some aspects. When used in products, it may lead to a decrease in the impact resistance of radome/antenna window products, which in turn will lead to a decrease in the reliability of the entire weapon system. Therefore, there is a need for an effective reinforcement method for improving the tensile strength of the silica ceramic-based wave-transparent composite material, so as to ensure that the performance of the radome/antenna window product meets the design requirements.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a convenient and effective reinforcement method for silica ceramic matrix composites on the premise of ensuring that other related properties meet the requirements.

The technical solution of the present invention: a method for improving the tensile strength of a silica ceramic matrix composite material is achieved through the following steps:

The first step, pretreatment of silica ceramic matrix composites,

The pretreatment of the silica ceramic matrix composite material is to remove the water in the composite material, and it can be dried in an oven. The drying is a well-known technology in the field, and those skilled in the art can set it by themselves, generally at about 100°C That's it.

The second step, preheating,

The dried silica ceramic matrix composite material is put into a closed container, and the composite material and the closed container are preheated together.

The purpose of increasing preheating is to avoid the phenomenon of "heat impermeability" inside the closed container after subsequent vacuuming, resulting in incomplete vaporization of the reagents, mainly to preheat the closed container. However, since the silica ceramic matrix composite material is easy to absorb water when placed in the air, the silica ceramic matrix composite material is preheated together with the airtight container. Therefore, the preheating temperature is generally between 100°C and 200°C. Yes, oven and other equipment can be used for preheating.

The third step, vacuuming,

Vacuumize the airtight container filled with silica ceramic matrix composite material at a certain temperature until the vacuum degree is less than or equal to -0.095MPa, close the vacuum valve, turn off the vacuum pump, keep the pressure for more than 5min, and check whether the airtight container is leaking. If the vacuum degree is still less than or equal to -0.095MPa, it can be proved that the airtight container is not leaking, and the next step can be carried out. The main purpose of the present invention is to realize the vacuum vaporization of trimethylmethoxysilane. The lower the pressure, the lower the boiling point of trimethylmethoxysilane. At a lower pressure, trimethylmethoxysilane can be fully realized Vaporization facilitates subsequent dispersion and grafting.

The fourth step, gas phase grafting,

Slowly draw an appropriate amount of trimethylmethoxysilane reagent from the lower end of the airtight container into the airtight container, so that the trimethylmethoxysilane vapor is fully dispersed in the airtight container, and the silica ceramic matrix composite is fully exposed to the trimethylmethoxysilane Vapor-phase grafting was carried out under vacuum in the vapor of methoxysilane.

The addition amount and steam concentration of trimethylmethoxysilane should be strictly controlled, which directly affects the increase in tensile strength and process safety of the final silica ceramic matrix composite.

The optimal addition amount of trimethylmethoxysilane is 6% to 9% of the mass of the silica ceramic matrix composite material. Under the premise of the same concentration, the greater the addition amount, the more obvious the strengthening effect. The fracture mode will change with the addition of trimethylmethoxysilane, thereby changing the tensile strength of the material. If the addition of trimethylmethoxysilane is too small, the fracture mode tends to be ductile fracture, and the bonding force between quartz fibers is not enough to effectively strengthen; if the addition of trimethylmethoxysilane is too much, the interface bonding between quartz fiber bundles If the force is too strong, the fibers cannot be pulled out at all during stretching, and can only be brittle. At the same time, due to the large amount of grafting, too much and too tight grafting agent on a bundle of fibers will obviously damage the fibers themselves, resulting in fiber damage. The possibility of brittle fracture is greatly increased, resulting in a decrease in tensile strength. However, within the scope required by the present invention, an appropriate amount of grafting improves the fiber, matrix or the bonding force between the fiber and the matrix in the ceramic matrix composite material, improves the tensile mechanical properties of the material to a certain extent, and helps to improve The resistance of the radome/antenna window to thermal stress; the effective connection between the fiber bundles can be achieved, the interface bonding force is strong, and it becomes difficult to pull out a single fiber, and the tensile strength is significantly improved at this time. The grafting agent is like a rope tied to a bundle of fibers. A proper amount of binding will not cause much damage to the surface fibers, but more will enhance the bonding force between the fiber bundles, making ductile fracture more difficult.

The optimal range of trimethylmethoxysilane vapor concentration is 1g/L～3g/L. Under the premise of the same addition amount, the greater the concentration, the more obvious the enhancement effect; A low concentration may lead to insufficient vapor pressure of trimethylmethoxysilane, incomplete grafting, and insignificant enhancement effect; and excessive concentration of vaporization may cause the inside of the closed container to become positive pressure, and may even burst. Therefore, During the gas-phase grafting process, a vacuum must be maintained.

The temperature of gas-phase grafting should be higher than the vacuum vaporization temperature of trimethylmethoxysilane and lower than 150°C. If the temperature is too high, the gas-phase grafting process is prone to danger. The time of gas-phase grafting is not less than 48 hours. If the holding time is too short, the grafting reagent cannot be firmly grafted on the material, and a large amount will escape after subsequent drying, and the enhancement effect is poor.

The fifth step, drying,

The grafted silicon dioxide ceramic matrix composite material is taken out from the airtight container, and dried to remove excess grafting reagent. The drying temperature should not be lower than 80°C and not higher than 200°C. Since the boiling point of trimethylmethoxysilane is 57-58°C, drying at around 80°C can basically discharge the ungrafted silica ceramic matrix composites. The reagent, and then drying at about 100 ° C can further discharge the ungrafted reagent, and remove the trace water that may adhere to the surface and internal pores of the silica ceramic matrix composite.

The sixth step, heat treatment,

After drying, the silica ceramic matrix composite material is subjected to high-temperature treatment. The purpose of high-temperature treatment is to convert the organic functional groups formed by grafting into silica, and connect them with the matrix silica as a whole, so as to realize the high-temperature treatment in different material properties. The enhancement of mechanical properties can be achieved under the condition of changing; after heat treatment, the effect of enhancing the tensile strength of silica ceramic matrix composites has no obvious change.

The temperature of high-temperature heat treatment is 500°C to 700°C, and the time is not less than 1 hour, and it can be carried out in high-temperature furnaces such as pit furnaces or muffle furnaces. Those skilled in the art can select the high temperature heat treatment process according to the actual situation, as long as the purpose of high temperature treatment can be achieved.

Analysis of the principle of the present invention: since the silica ceramic matrix composite material is a fiber-reinforced composite material, its tensile strength mainly comes from the strength of the fiber bundle and the interface bonding force between the fiber bundle and the matrix. There are certain pores between the fiber bundles and between the fibers and the matrix, and the chemical structure of silica determines that there are certain hydroxyl groups on the surface and in the internal pores. Using trimethylmethoxysilane as a reagent, use the gas phase method to graft the silica material, introduce an appropriate amount of reagent, the reagent reacts with the hydroxyl group in the material, and the organic functional group is grafted to the original hydroxyl position and interacts with each other. Cross-linking forms a chain or network structure, which increases the interfacial bonding strength, thereby increasing the tensile strength of the material. After heat treatment, the organic functional groups formed by the original grafting are converted into silica and connected with the matrix silica as a whole, which can enhance the mechanical properties without changing the properties of the material. At the same time, since the conversion into silicon dioxide has the same composition as the matrix, it can ensure that the properties of the matrix material do not change, and the weight of the matrix will increase. Not only can it achieve excellent reinforcement effect, but it can also be used as a method to increase the density of the material.

The beneficial effect of the present invention compared with prior art:

(1) The present invention uses trimethylmethoxysilane as a reagent, and after the silica ceramic matrix composite material is grafted, the bonding between the fiber, the matrix or the fiber and the matrix in the fiber reinforced ceramic matrix composite material is improved force, improving the tensile mechanical properties of the composite material, which helps to improve the resistance of the radome/antenna window to thermal stress;

(2) The present invention has determined the optimum dosage and the concentration range of grafting reagent, can realize effective connection between fiber bundles, the interfacial binding force is stronger, the pull-out of single fiber becomes difficult, and tensile strength improves most effectively, average Tensile strength increased by more than 15%;

(3) The process technology of the present invention is controllable, easy to operate, and has a good reinforcing effect, which can effectively improve the technical bottleneck of low material tensile strength in the existing molding process, and can process multiple radome/antenna window products at one time;

(4) The preparation process of the present invention does not need to change the preparation process of the original composite material, and can be implemented in a wide range, which is of great help to the rapid and batch processing of products, and is especially suitable for the reinforcement of wave-transparent components such as ceramic radome and antenna window. ;

(5) The present invention uses trimethylmethoxysilane to graft the silica ceramic matrix composite material, which not only can achieve excellent reinforcement effect, but also produces silica after heat treatment, which can ensure the properties of the matrix material There is no change, and all the properties after treatment meet the requirements, and it can also be used as a method to increase the density of the material.

Description of drawings

Fig. 1 is the flow chart of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific examples.

As shown in Figure 1, the present invention adopts trimethylmethoxysilane as a reagent, and uses silica ceramic-based wave-transparent composite material as a sample, and carries out enhancement treatment through a gas-phase method grafting scheme, and selects the sample after treatment and The original samples were tested and compared. (in the following examples, M is the sample weight, and the mechanical properties are compared between the same batch of samples. In each embodiment, 5 samples are used as a group, and the average value is obtained)

Example 1

Using trimethylmethoxysilane with a weight of M*7.5% (concentration: 1.25g/L) as a reagent, preheat the dried parent direction tensile specimen together with an airtight container, and then vacuumize and connect with the gas phase. Branches were dried in an oven and heat-treated at 600°C. Compared with the ungrafted samples, the average weight gain of the treated samples was 0.95%, and the average tensile strength changed from 48.578MPa to 57.653MPa, an average increase of 18.68%.

Example 2

Use trimethylmethoxysilane with a weight of M*7.5% (concentration: 2.3g/L) as a reagent, preheat the dried hoop stretched sample together with a closed container, and then vacuumize and connect with the gas phase. Branches were dried in an oven and heat-treated at 600°C. Compared with the ungrafted samples, the average weight gain of the treated samples was 1.04%, and the average tensile strength changed from 27.647MPa to 34.380MPa, an average increase of 24.35%.

Example 3

Using trimethylmethoxysilane with a weight of M*7.5% (concentration: 3.0g/L) as a reagent, preheat the dried hoop stretched sample together with an airtight container, then vacuumize and connect with the gas phase Branches were dried in an oven and heat-treated at 600°C. Compared with the ungrafted samples, the average weight gain of the treated samples was 0.97%, and the average tensile strength changed from 28.860MPa to 37.813MPa, an average increase of 31.02%.

Example 4

Be that the trimethylmethoxysilane of M*6% (concentration is 3.0g/L) by weight is as reagent, all the other are the same as embodiment 3, the average weight gain of sample after treatment is 0.91% compared with non-grafting treatment sample , the average tensile strength changed from 28.860MPa to 36.968MPa, an average increase of 28.09%.

Example 5

Be that the trimethylmethoxysilane of M*9% (concentration is 3.0g/L) by weight is as reagent, all the other are the same as embodiment 3, the average weight gain of sample after treatment is 1.07% compared with non-grafting treatment sample , the average tensile strength changed from 28.860MPa to 38.056MPa, an average increase of 31.86%.

Comparative example 1

Using trimethylmethoxysilane with a weight of M*2.5% (concentration: 0.9g/L) as a reagent, preheat the dried parent direction tensile specimen together with an airtight container, and then vacuumize and connect with the gas phase. After grafting, oven drying and heat treatment at 600°C, the average weight gain of the treated samples was about 0.54% compared with the ungrafted samples, and the average tensile strength increased from 51.168MPa to 53.925MPa, an average increase of 5.39%.

Comparative example 2

Use trimethylmethoxysilane with a weight of M*15% (concentration: 3.0g/L) as a reagent, preheat the dried parent direction tensile specimen together with an airtight container, and then vacuumize and connect with the gas phase. Branches, oven-dried and heat-treated at 600°C, the average weight of the treated samples increased by 1.50% compared with the ungrafted samples, and the average tensile strength changed from 51.168MPa to 45.345MPa, an average decrease of 11.38%.

Parts not described in detail in the present invention are well-known technologies for those skilled in the art.

Claims (5)

1. a kind of method for improving SiO 2-ceramic based composites tensile strength, which comprises the following steps:

SiO 2-ceramic based composites are dried；

SiO 2-ceramic based composites, which are put into closed container, to be vacuumized；

Gas phase graft,

Under vacuum conditions, SiO 2-ceramic based composites carry out gas phase graft in trimethylmethoxysilane steam, The additive amount of trimethylmethoxysilane is the 6%~9% of SiO 2-ceramic based composites quality, and three in closed container Methylmethoxysilane vapour concentration is 1g/L~3g/L；With

SiO 2-ceramic based composites after gas phase graft are dry；

SiO 2-ceramic based composites after gas phase graft and drying carry out high-temperature heat treatment, and the temperature of high-temperature heat treatment is 500 DEG C~700 DEG C, the time is not less than 1 hour.

2. a kind of method for improving SiO 2-ceramic based composites tensile strength according to claim 1, feature Be: the temperature of the gas phase graft is higher than trimethylmethoxysilane vacuum vaporization temperature, lower than 150 DEG C, gas phase graft Time is no less than 48 hours.

3. a kind of method for improving SiO 2-ceramic based composites tensile strength according to claim 1, feature It is: after the SiO 2-ceramic based composites drying process, before vacuumizing, is carried out at preheating together with closed container Reason.

4. a kind of method for improving SiO 2-ceramic based composites tensile strength according to claim 3, feature Be: the temperature range of the pre-heat treatment is 100 DEG C~200 DEG C.

5. a kind of method for improving SiO 2-ceramic based composites tensile strength according to claim 1, feature Be: the SiO 2-ceramic based composites drying temperature range after the gas phase graft is 80 DEG C~200 DEG C.