阅读说明：本技术 一种碳基表面形成的碳化钽涂层及其形成方法和用途 (Tantalum carbide coating formed on carbon-based surface and forming method and application thereof ) 是由 薛卫明 马远 潘尧波 于 2021-01-20 设计创作，主要内容包括：本发明公开了一种碳基表面形成碳化钽涂层方法,所述方法包括：提供一碳基体；于所述碳基体表面形成至少一预涂层,所述预涂层的原料由碳化钽粉末和/或五氧化二钽、石墨粉,以及酚醛树脂的混合物组成；于所述预涂层表面涂覆五氧化二钽以形成表层；经加热和退火步骤,所述五氧化二钽和碳反应还原生成碳化钽,所述预涂层形成所述碳和所述碳化钽混合涂层,所述表层形成所述碳化钽涂层,其中,所述碳由所述碳基体、所述石墨粉和所述酚醛树脂提供。根据本发明提供的碳基表面形成碳化钽涂层方法可有效改善因碳化钽涂层和碳基体膨胀系数差异过大引起的热失配问题,防止制备或使用过程中涂层裂纹的产生。(The invention discloses a method for forming a tantalum carbide coating on a carbon-based surface, which comprises the following steps: providing a carbon substrate; forming at least one precoating layer on the surface of the carbon substrate, wherein the raw material of the precoating layer consists of tantalum carbide powder and/or tantalum pentoxide, graphite powder and a mixture of phenolic resin; coating tantalum pentoxide on the surface of the precoating layer to form a surface layer; and through the heating and annealing steps, the tantalum pentoxide and carbon react and are reduced to generate tantalum carbide, the pre-coating layer forms the carbon and tantalum carbide mixed coating, and the surface layer forms the tantalum carbide coating, wherein the carbon is provided by the carbon matrix, the graphite powder and the phenolic resin. According to the method for forming the tantalum carbide coating on the carbon-based surface, provided by the invention, the problem of thermal mismatch caused by overlarge difference of the expansion coefficients of the tantalum carbide coating and the carbon matrix can be effectively solved, and the generation of coating cracks in the preparation or use process is prevented.)

1. A method of forming a tantalum carbide coating on a carbon-based surface, comprising:

providing a carbon substrate;

forming at least one precoating layer on the surface of the carbon substrate, wherein the raw material of the precoating layer consists of tantalum carbide powder and/or tantalum pentoxide, graphite powder and a mixture of phenolic resin;

coating tantalum pentoxide on the surface of the precoating layer to form a surface layer;

and through the heating and annealing steps, the tantalum pentoxide and carbon react and are reduced to generate tantalum carbide, the pre-coating layer forms the carbon and tantalum carbide mixed coating, and the surface layer forms the tantalum carbide coating, wherein the carbon is provided by the carbon matrix, the graphite powder and the phenolic resin.

2. The method of forming a tantalum carbide coating on a carbon-based surface according to claim 1, wherein the method of forming the precoat comprises:

mixing and grinding the mixture, and modulating the mixture by using ethanol to obtain a viscous slurry;

coating the sticky slurry on the surface of the carbon substrate, and drying the coated carbon substrate at 70-90 ℃ for 8-12 h;

and sintering the dried carbon substrate in an inert atmosphere at the sintering temperature of 1400 ℃ and 1600 ℃ for 1-3h, and cooling after sintering to form the precoat layer.

3. The method of claim 1, wherein the intermixed layer has a porosity of 7% or less and the tantalum carbide coating has a porosity of 1% or less.

4. The method of claim 1, wherein the mixed layers comprise 1-6 layers, and the mixed layers between each layer have a gradually decreasing carbon content and an increasing tantalum carbide content.

5. The method for forming a tantalum carbide coating on a carbon-based surface according to any one of claims 1 to 4, wherein the mixture comprises 0 to 80 weight percent of tantalum carbide powder, 0 to 80 weight percent of tantalum pentoxide, 5 to 30 weight percent of graphite powder and 5 to 30 weight percent of phenolic resin.

6. The method of forming a tantalum carbide coating on a carbon-based surface according to claim 1, wherein the carbon substrate is a graphite substrate.

7. The method of forming a tantalum carbide coating on a carbon-based surface according to claim 1, wherein the heating step comprises heating by laser cladding, and/or,

the annealing step adopts the temperature of 800-1000 ℃, the heating rate of 5-20 ℃/min and the heat preservation time of 2-4 h.

8. The method of forming a tantalum carbide coating on a carbon-based surface according to claim 1, wherein the thickness of the hybrid coating after the heating step is 0.01mm to 0.3mm, and/or the thickness of the tantalum carbide coating is 0.01mm to 0.3 mm.

9. A tantalum carbide coating formed according to the method of any one of claims 1 to 8.

10. Use of a tantalum carbide coating according to claim 10 in a graphite crucible.

Technical Field

The invention relates to the field of material preparation, in particular to a tantalum carbide coating formed on a carbon-based surface, a forming method and application thereof.

Background

Carbon, which is the most commonly used material in daily life, has high temperature resistance, good thermal conductivity and chemical stability, so that it plays a crucial role in daily life and in the development of science and technology. One of the important applications is in the field of silicon carbide crystal growth, a crucible made of graphite plays an important role in the process of preparing the silicon carbide crystal by a physical vapor transport method, but the graphite crucible cannot be directly used for crystal growth due to the corrosion effect of raw materials on the crucible wall at high temperature. The covering of the graphite surface tantalum carbide coating can well solve the problem. Tantalum carbide is used as a ceramic material, can be obtained by direct reaction of a tantalum-containing compound and carbon at high temperature, has the characteristics of high melting point and high chemical stability, can effectively resist corrosion of various chemical substances at high temperature, can effectively play a role in protection when being used as a coating to cover the surface of a graphite crucible, improves the crystal quality, increases the reuse rate of the crucible and reduces the generation cost.

At present, the common methods for preparing the tantalum carbide coating on the graphite surface mainly comprise a sol-gel method, a plasma spraying method, a molten salt method, a chemical vapor deposition method and a slurry sintering method. However, due to the brittleness of the tantalum carbide ceramic and the large difference between the thermal expansion coefficients of the coating and the carbon substrate, the bonding force between the coating and the carbon substrate is poor, and the coating can generate obvious cracks during the preparation or use process and even fall off from the substrate, thereby finally affecting the quality of the product. Therefore, the method for preparing the high-bonding-force tantalum carbide coating is significant.

Disclosure of Invention

In view of the above-mentioned disadvantages of the prior art, the present invention provides a tantalum carbide coating formed on a carbon-based surface, and a method for forming the same and a use thereof, which can effectively improve the thermal mismatch problem caused by an excessively large difference between the expansion coefficients of tantalum carbide and carbon matrix, and prevent the generation of cracks in the coating during the preparation or use thereof. In the growth process of the silicon carbide crystal, the tantalum carbide coating prepared on the surface of the graphite crucible by adopting the method can greatly improve the quality of the crystal, increase the use times of the graphite crucible and reduce the production cost.

To achieve the above and related objects, the present invention provides a method of forming a tantalum carbide coating on a carbon-based surface, the method comprising: providing a carbon substrate; forming at least one precoating layer on the surface of the carbon substrate, wherein the raw material of the precoating layer consists of tantalum carbide powder and/or tantalum pentoxide, graphite powder and a mixture of phenolic resin; coating tantalum pentoxide on the surface of the precoating layer to form a surface layer; and through the heating and annealing steps, the tantalum pentoxide and carbon react and are reduced to generate tantalum carbide, the pre-coating layer forms the carbon and tantalum carbide mixed coating, and the surface layer forms the tantalum carbide coating, wherein the carbon is provided by the carbon matrix, the graphite powder and the phenolic resin.

In one embodiment of the present disclosure, a method of forming the precoat layer comprises: mixing and grinding the mixture, and modulating the mixture by using ethanol to obtain a viscous slurry; coating the sticky slurry on the surface of the carbon substrate, and drying the coated carbon substrate at 70-90 ℃ for 8-12 h; and sintering the dried carbon substrate in an inert atmosphere at the sintering temperature of 1400 ℃ and 1600 ℃ for 1-3h, and cooling after sintering to form the precoat layer.

In one embodiment of the present disclosure, the porosity of the mixed layer is 7% or less, and the porosity of the tantalum carbide coating layer is 1% or less.

In a specific embodiment disclosed by the invention, the mixed layer comprises 1-6 layers, the carbon content in the mixed layer between each two layers is gradually reduced, and the tantalum carbide content is gradually increased.

In a specific embodiment disclosed by the invention, the weight ratio of each component in the mixture is 0-80% of tantalum carbide powder, 0-80% of tantalum pentoxide, 5-30% of graphite powder and 5-30% of phenolic resin.

In one embodiment of the present disclosure, the carbon substrate is a graphite substrate.

In a specific embodiment disclosed by the invention, the heating step adopts laser cladding for heating treatment, and/or the annealing step adopts the temperature of 800-1000 ℃, the heating rate of 5-20 ℃/min and the heat preservation time of 2-4 h.

In a specific embodiment of the present disclosure, after the heating step, the thickness of the hybrid coating is 0.01mm to 0.3mm, and/or the thickness of the tantalum carbide coating is 0.01mm to 0.3 mm.

The invention also provides a tantalum carbide coating formed according to the method described above.

The invention also provides the use of a tantalum carbide coating according to the above in a graphite crucible.

As described above, the present invention provides a tantalum carbide coating formed on a carbon-based surface, a method for forming the same, and uses thereof. According to the method, at least one precoat layer is formed between a carbon substrate and a surface layer by utilizing a mixture of tantalum carbide, tantalum pentoxide, graphite powder and phenolic resin, so that a tantalum carbide coating with a gradient coating structure is finally obtained, the substrate is the carbon substrate, a mixed coating containing both a carbon structure and tantalum carbide is formed in the middle layer, a compact tantalum carbide coating is formed on the surface layer, the compact tantalum carbide coating can effectively protect the carbon substrate, the precoat layer positioned between the carbon substrate and the surface layer plays a role in buffering, the thermal expansion coefficient of the middle layer is between the thermal expansion coefficient of the carbon substrate and the thermal expansion coefficient of the tantalum carbide coating on the surface layer due to the characteristic that excessive carbon components are reserved while the tantalum carbide is generated in the precoat layer, the problem that the coating is prone to cracking and even falling in the conventional preparation method can be effectively solved. In addition, the invention adopts laser cladding to further improve the binding force among the intermediate layer, the surface layer and the matrix, and the particles of the reinforcing phase in the coating prepared by the method are relatively small, so that the coating is more uniform and compact.

Drawings

FIG. 1 is a schematic flow chart of a method for forming a tantalum carbide coating on a carbon-based surface according to the present invention.

FIG. 2 shows a schematic flow diagram of a method of forming a precoat layer provided for the present invention.

FIG. 3 is a schematic structural diagram of one embodiment of a tantalum carbide coating formed by the method of the present invention.

FIG. 4 is a schematic structural diagram of another embodiment of a tantalum carbide coating formed by the method of the present invention.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be readily apparent to those skilled in the art from the disclosure herein. The invention is capable of other and different embodiments and its several details are capable of modifications and various changes in detail without departing from the spirit of the invention.

It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.

In the present invention, it should be noted that, as the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, their indicated orientations or positional relationships are based on the orientations or positional relationships shown in the drawings, and are only for convenience of describing the present application and simplifying the description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present application. Furthermore, the terms "first" and "second," if any, are used for descriptive and distinguishing purposes only and are not to be construed as indicating or implying relative importance.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice of the present invention, the preferred methods, devices, and materials are described below.

As shown in fig. 1 to 4, the present invention provides a method for forming a tantalum carbide coating on a carbon-based surface, which forms at least one precoat 200 between a carbon substrate 100 and a surface layer 300 by using a mixture of tantalum carbide and/or tantalum pentoxide, graphite powder, and a phenolic resin, thereby obtaining a tantalum carbide coating having a gradient coating structure that effectively alleviates the problem of an excessive difference in thermal expansion coefficient between tantalum carbide coatings formed on the carbon substrate 100 and the surface layer 300, and makes up the problem of easy cracking and even peeling of the coating in the conventional preparation method. In addition, in the growth process of the silicon carbide crystal, the tantalum carbide coating prepared on the surface of the graphite crucible by the method can greatly improve the quality of the crystal, increase the use times of the graphite crucible and reduce the generation cost. The method includes, but is not limited to, the following steps S1-S4:

s1, providing a carbon substrate 100;

s2, forming at least one precoat layer 200 on the surface of the carbon matrix, wherein the raw material of the precoat layer 200 consists of a mixture of tantalum carbide powder and/or tantalum pentoxide, graphite powder and phenolic resin;

s3, coating tantalum pentoxide on the surface of the precoat layer 200 to form a surface layer 300;

s4, reacting and reducing the tantalum pentoxide and the carbon to tantalum carbide through heating and annealing steps, wherein the precoat layer 200 forms the carbon and tantalum carbide mixed coating layer, and the surface layer 300 forms the tantalum carbide coating layer, wherein the carbon is provided by the carbon matrix, the graphite powder and the phenolic resin.

As shown in fig. 1 and 3, in step S1, the carbon substrate 100 is, for example, a graphite substrate, and further, in order to ensure better binding force and reaction force and remove surface impurities, the graphite substrate may be roughened by, for example, sand paper, and then ultrasonically cleaned, and then placed in an oven at 70 to 90 ℃, for example, 80 ℃, for drying for 6h to 8h, for example, 8h, and further, the cleaning solution used in the ultrasonic cleaning process is ethanol or acetone, and the ultrasonic time is controlled to be 30min to 60min, for example, 60 min.

As shown in fig. 1 and 3, in step S2, at least one pre-coating layer 200, further including a plurality of layers, for example, 1 to 6 layers, for example, 1 layer, 2 layers, and 3 layers, is formed on the surface of the carbon substrate 100, and the pre-coating layer 200 is subjected to the heating and annealing step in step S4 to form a mixed coating layer of carbon and tantalum carbide, so that the carbon content in the mixed coating layer between each layer is gradually decreased, the tantalum carbide content is gradually increased, and the expansion coefficient of the mixed coating layer between each layer is gradually decreased, and therefore, a buffer layer is formed between the carbon substrate 100 and the tantalum carbide coating layer 300 having a large difference in expansion coefficient, and the occurrence of cracks due to a large difference in expansion coefficient when the two layers are directly bonded is alleviated. In addition, the porosity in the mixed coating is less than or equal to 7 percent, and further less than or equal to 5 percent, and the product performance is not influenced

The precoating layer 200 is made of a mixture of tantalum carbide powder and/or tantalum pentoxide, graphite powder and phenolic resin, such as tantalum carbide powder, graphite powder and phenolic resin, wherein the added tantalum carbide powder forms a tantalum carbide layer in a mixed layer with good compactness and no pores, or tantalum pentoxide, graphite powder and phenolic resin, wherein the tantalum pentoxide and carbon react to form a tantalum carbide layer in the mixed layer, so that the tantalum carbide layer has good gripping force and no cracking occurs, or the tantalum carbide powder, the tantalum pentoxide, the graphite powder and the phenolic resin are formed, so that the formed tantalum carbide has tantalum carbide generated by the reaction of the added tantalum carbide powder, and at the moment, the mixed coating fully avoids the problems that pure oxides and organic substances are utilized to generate carbides, pores exist in the coating and corrosion can start from the pores, meanwhile, when the surface layer 300 ensures sufficient tantalum carbide, the pores can be closed, and meanwhile, the surface layer and the inner layer of tantalum carbide form stable combination, namely, the surface layer has good compactness and high gripping force without cracking. The phenolic resin has adhesive force to perform tackifying mixing on the phenolic resin, and further volatilizes hydrogen and oxygen under high-temperature sintering to finally obtain the porous carbon material, the tantalum carbide powder and/or the tantalum pentoxide and the graphite powder are dispersed in pores of the porous carbon material, and the tantalum pentoxide reacts with carbon at high temperature to be reduced to obtain the tantalum carbide. In the mixture of the precoat 200, the mass ratio of each component is 0 to 80% of tantalum carbide powder, 0 to 80% of tantalum pentoxide, 5 to 30% of graphite powder, and 5 to 30% of phenolic resin, and from the viewpoint of forming a mixed coating, the tantalum carbide powder and the tantalum pentoxide cannot be 0 at the same time, and in this range, the ratio of each component is adjusted, thereby obtaining a plurality of different precoat structures, ensuring that the carbon content in the mixed coating between each layer is gradually reduced, and the tantalum carbide content is gradually increased. Furthermore, metal cosolvents, such as Au, Ag, Cu, Al, may also be added to the mixture to reduce the risk of cracking.

In one embodiment, as shown in FIG. 3, the precoat 200 comprises one layer and forms a mixed carbon and tantalum carbide coating after heating and annealing. Specifically, the precoat layer 200 includes, for example, 45% tantalum carbide powder, 30% tantalum pentoxide, 20% graphite powder, and 5% phenol resin. In another embodiment, the precoat 200 comprises 50% tantalum pentoxide, 25% graphite powder, 25% phenolic resin, and 5% porosity after sintering. In another embodiment, the material also can be tantalum carbide powder 60%, tantalum pentoxide 20%, graphite powder 5% and phenolic resin 15%.

In another specific embodiment, as shown in FIG. 4, the precoat 200 includes a first precoat 210, a second precoat 220, and a third precoat 230, with the carbon content between the first 210, second 220, and third 230 precoats gradually decreasing, and the tantalum carbide content gradually increasing. Specifically, in the first precoat layer 210, tantalum carbide powder 25%, tantalum pentoxide 30%, graphite powder 40%, and phenol resin 5%, in the second precoat layer 220, tantalum carbide powder 40%, tantalum pentoxide 30%, graphite powder 25%, and phenol resin 5%, in the third precoat layer 230, tantalum carbide powder 45%, tantalum pentoxide 30%, graphite powder 20%, and phenol resin 5%.

As shown in fig. 2, the method of forming the precoat 200 in step S2 includes steps S201 to S203, the step S201 is performed, the mixture is mixed and ground, and the mixture is prepared into a paste using ethanol, specifically, the tantalum carbide powder, the tantalum pentoxide, the graphite powder, and the phenolic resin powder are mixed in a specific ratio, and the mixture is pulverized and uniformly stirred, for example, in a mortar, and then a proper amount of ethanol is added to prepare the mixed powder into a paste.

As shown in fig. 2, step S202 is performed to coat the sticky slurry on the surface of the carbon substrate 100, and the coated carbon substrate is dried at 70 to 90 ℃ for 8 to 12 hours, for example, at 80 ℃ for 12 hours, so that the sticky slurry is stably molded on the surface of the carbon substrate 100 after the ethanol is volatilized.

As shown in fig. 2, step S203 is performed, the dried carbon substrate 100 is sintered under an inert atmosphere at 1400 ℃ to 1600 ℃ for 1h to 3h, and is cooled after sintering, for example, the dried carbon substrate 100 is placed in a high temperature furnace to be subjected to high temperature heat treatment under an argon atmosphere, the temperature in the furnace is controlled at 1400 ℃ and the treatment time is 3h, and is cooled with the furnace after the treatment is completed, so as to obtain the precoat 200, thereby forming the precoat 200, and hydrogen and oxygen in the precoat 200 are volatilized to obtain a carbon source, and further, reaction sites and reactants are provided for the subsequent heating reaction to form tantalum carbide.

Further, when more precoats 200 are formed, the proportions of the components in the mixture may be adjusted as needed, and the above steps S201 to S203 are repeated, thereby obtaining corresponding precoats 200 of a multilayer structure. For example, in forming the 3-layer precoat structure shown in FIG. 4, the carbon source to tantalum source ratio of the precoat 200 is adjusted, and steps S201 to 203 are repeated until the precoat material mass ratio is within the desired range. It should be noted that the pre-coating 200 has a thickness after sintering of 0.5mm to 1.5mm, such as 0.5mm, 1mm, 1.4mm, in order to ensure that the coating is able to continuously protect the carbon substrate in a corrosive atmosphere.

As shown in fig. 1 and 3, in step S3, a surface layer 300 formed of the tantalum pentoxide powder is coated on the surface of the pre-coating layer 200, so that the tantalum pentoxide and the carbon in the carbon substrate 100 and pre-coating layer 200 are reduced at a high temperature to form the tantalum carbide coating layer, which has high denseness and a porosity of 1% or less, for example, 0.5% or less and 0.3% or less.

As shown in fig. 1, in step S4, after the surface layer 300 is coated on the surface of the precoat 200, the tantalum carbide coating is obtained through heating and annealing steps. Specifically, after the heating step, the tantalum pentoxide and the carbon in the carbon substrate 100 and the pre-coating layer 200 are reduced to form the tantalum carbide, the pre-coating layer 200 forms the carbon and tantalum carbide mixed coating layer, the surface layer 300 forms the tantalum carbide coating layer, the thickness of the mixed coating layer obtained after heating is 0.01mm to 0.3mm, such as 0.01mm, 0.15mm and 0.17mm, the thickness of the tantalum carbide coating layer formed after heating is 0.01mm to 0.3mm, such as 0.01mm, 0.13mm and 0.21mm, and further, the total coating thickness formed between the mixed coating layer and the tantalum carbide coating layer after heating is 0.02mm to 0.6mm, such as 0.38mm and 0.28mm, so as to ensure good densification effect and thermal stability of the tantalum carbide coating layer with the gradient structure.

As shown in fig. 1, in step S4, the heating process may be performed by irradiating a laser to the surface of tantalum pentoxide to perform a laser cladding process, where the laser is used at a power of 1600W-2000W, such as 1600W, 1800W, a spot diameter of 4mm-10mm, such as 4mm, a scanning speed of 5mm/S-10mm/S, such as 5mm/S, and the cladding process is performed under the protection of argon gas, and the laser cladding may precisely control a cladding area, so that the carbon matrix 100, the pre-coating layer 200, and the tantalum pentoxide are melted together with the cladding material, and after interaction and rapid solidification, a tantalum carbide coating is formed, and the formed bonding force is higher, and due to the rapid thermal quenching, the particles of the reinforcing phase in the coating are smaller, and the coating is more uniform and dense. Of course, the method is not limited to this, and may be realized by directly heating, for example, a mixed coating and a tantalum carbide coating may be sequentially formed on the carbon substrate 100 by a gradient temperature rise.

As shown in fig. 1, in step S3, the annealing process may be, for example, placing the heated coating into an annealing furnace, annealing in an argon atmosphere, where the temperature of the annealing furnace is set to 800 ℃ to 1000 ℃, for example 800 ℃, the heating rate is 5 ℃/min to 20 ℃/min, for example 5 ℃/min, the holding time is 2h to 4h, for example 3h, and finally cooling with the furnace to obtain the tantalum carbide coating with the gradient structure.

As described above, the present invention provides a tantalum carbide coating formed on a carbon-based surface, a method for forming the same, and uses thereof. The method comprises the steps of taking a graphite material which is sanded and coarsened by abrasive paper as a substrate, coating a pre-coating layer, drying, sintering, covering tantalum pentoxide powder, and finally treating the surface of the material by a laser cladding technology. The gradient coating obtained by the method has a compact tantalum carbide layer as a surface layer, and a pre-coating layer which is a mixed coating containing a carbon structure and tantalum carbide. The upper-layer compact tantalum carbide layer can effectively protect the carbon material substrate, the stability and the corrosion resistance of the whole material at high temperature are improved, the middle layer positioned between the carbon substrate and the surface coating plays a role in buffering, the thermal expansion coefficient of the middle layer is between the thermal expansion coefficient of the carbon substrate and the thermal expansion coefficient of the tantalum carbide coating due to the characteristic that the middle layer contains excessive carbon components while containing tantalum carbide, the problem that the thermal expansion coefficient difference between the carbon substrate and the thermal expansion coefficient of the tantalum carbide coating is too large can be effectively solved, and the problem that the coating is easy to crack and even fall off in the conventional preparation method is solved. The tantalum carbide coating obtained by the method has strong bonding force with the substrate, and is more uniform and compact.

While the invention has been described with respect to a preferred embodiment, it will be understood by those skilled in the art that the foregoing and other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention. Those skilled in the art can make various changes, modifications and equivalent arrangements, which are equivalent to the embodiments of the present invention, without departing from the spirit and scope of the present invention, and which may be made by utilizing the techniques disclosed above; meanwhile, any changes, modifications and variations of the above-described embodiments, which are equivalent to those of the technical spirit of the present invention, are within the scope of the technical solution of the present invention.