RU2568495C1 - Method of producing carbon-carbon composite material based on carbon fibre filler and carbon matrix - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing carbon composite material based on carbon fibre filler and a carbon matrix includes successive processes for dry layout of a frame based on reinforced filler in the form of fabric made of high-modulus carbon fibre on an holder, mounting the holder with the fabric in a tool for soaking the dry frame by placing in a soaking container and soaking the frame with coal tar and carbonising, followed by soaking the frame with coal tar and carbonising in a sealed container in a high-pressure apparatus, where the pressure transmitting medium used is quartz sand, followed by retrieving workpieces and vacuum graphitisation. The soaking and carbonisation procedures are carried out under pressure and vacuum graphitisation is repeated until a material with density of 1.88-1.91 g/cm³ is obtained.

EFFECT: invention enables to obtain carbon-carbon composite material based on reinforcing filler in the form of fabric made of high-modulus carbon fibre, having improved physical and mechanical properties at minimal costs.

4 cl, 4 dwg, 1 tbl

Description

The invention relates to the field of creation and production of carbon materials with high physical and mechanical characteristics, in particular carbon-carbon composite materials based on woven reinforcing fillers of carbon high-modulus fiber and a carbon matrix formed from pitch during carbonization and subsequent high-temperature treatments.

A known method of producing carbon-carbon composite materials using the required number of cycles of impregnation and carbonization under pressure [1]. This method is as follows. The first stage previously increases the rigidity of the frame by conducting several cycles of transfer impregnation in an autoclave. The second step is carbonation at normal pressure. And the third stage is graphitization, as a result of which there is no interaction at the “rod – carbon matrix” interface. The obtained billet is characterized by rigidity sufficient for the further process of the main compaction using impregnation - carbonization under pressure. The process of impregnation - carbonization under pressure is carried out in gas baths. The medium transmitting pressure and thermal energy in the gas bath is an inert gas. After high-temperature processing - graphitization, the normal strength significantly decreases, the surface electrical resistance increases and the dynamic modulus of elasticity decreases.

A significant disadvantage of this method is that the steps of preliminary increasing the rigidity of the frame and carbonization require special equipment, such as an autoclave, and specialized carbonization furnaces at atmospheric pressure. Also, impregnation and carbonization in a gas bath require significant costs for the manufacture of the gas bath itself, its maintenance, and the construction of an explosion-proof room in which the gas bath will be installed. In addition, a significant disadvantage is the high cost of inert gas.

A known method of producing carbon material with a high bulk density, in particular carbon-carbon composites based on multidirectional fiber frames (n = 2, 3, 4 ...) and a carbon matrix obtained from pitch or resin during carbonization and subsequent high-temperature treatments [2] .

The method includes sequential processes of impregnation of the preform with molten hydrocarbons, carbonization in a sealed container in a high-pressure apparatus, where quartz sand is used as a pressure transmitting medium, extraction of the preform and its graphitization in vacuum. The processes are repeated until a material with a density of 1.95-2.01 g / cm ^{3 is} obtained.

According to this method, a hydrocarbon layer is placed on the bottom of the container, a preform is placed on the layer, the space between the side surfaces of the container and the preform is filled with a powder material whose thermal conductivity exceeds the thermal conductivity of the molten hydrocarbons, while the powder material is taken with grain sizes that prevent their penetration into the pores of the preform. For the first process of impregnation and carbonization, a preform is taken, made in the form of a multidirectional reinforcing frame made of carbon material, for example carbon fiber. As a hydrocarbon, pitch is used. As a powder material - graphite powder.

A significant disadvantage of this method is that the material produced has limited mechanical characteristics (tensile strength 85-95 MPa). Structurally, this method is poorly applicable to blanks that do not have rigidity, for example, for dry frames made of layers of carbon fabric. Without the use of special equipment, such frames are irreversibly deformed.

The objective of the proposed method is to obtain a carbon - carbon composite material (CCCM) based on reinforcing fillers in the form of fabrics of carbon high-modulus fibers with high physical and mechanical characteristics, at the lowest cost.

The task is implemented in a method for producing CCCM on the basis of a carbon fiber filler and a carbon matrix, including sequential operations of dry laying of the frame based on the reinforcing filler in the form of carbon fiber fabric on a mandrel, securing the mandrel with the fabric in a device for impregnating a dry frame, placing it in impregnation container and pitch loading, impregnation of molten pitch laid on a fixed mandrel of a dry skeleton and subsequent carbonization, further impregnating and carbonizing the preform using graphite tooling in a sealed container in the apparatus of high pressure, where the pressure transmitting medium is a quartz sand, and extracting the preform mechanical removal of the mandrel, the preform graphitization in vacuo. Moreover, the operation of impregnation and carbonization under pressure and vacuum graphitization is repeated to obtain a material with a density of 1.88-1.91 g / cm ³ . At this density level, the material has physico-mechanical characteristics that significantly exceed the prototype [2], which at a density of 1.95-2.01 g / cm ³ has a greater degree of disorientation of the fibers and, therefore, a lower level of strength in an arbitrary direction of measurement.

The advantage of the proposed method also lies in the absence of the need for preliminary impregnation or coating of the frame with polymer binders and curing them to give the frame stiffness, which greatly simplifies the process. For laying out the frame, linen, satin, satin or twill weave from carbon high-modulus fiber is used. The figure 1 presents the mandrel for the calculation of the woven frame: 1 - woven frame; 2 - mandrel. The layout of the woven frame with a diameter of D ₁ and a length of L _{1 is} carried out on a mandrel with a diameter of D ₂ and a length of L ₂ by winding the fabric on the surface of the mandrel fixed in the machine centers, for which holes are made in the ends of the mandrel with a diameter of D ₃ and a length of L ₃ . The mandrel material is artificial graphite, which has a thermal linear expansion coefficient (KTLR) in the temperature range of 300-1300 K equal to (4.5-5.5) × 10 ^-6 K ^-1 , necessary to compensate for the KTLR of a dry carbon frame lying in area of negative values and some compressive deformation that occurs during impregnation. The mandrel with the fabric laid out is installed in the device for impregnation of the dry frame. A similarly collected cage is placed in a container for impregnation with molten pitch and subsequent carbonization. The device for impregnation of a dry frame consists of two welded frames with seats for fixing mandrels with frames and zones of the screed of the frames with metal wire (Fig. 2). Frame height H ₁ . The length of the lower crossbar A ₁ , the upper - A ₂ . Screed areas (for example, in the form of loops) are located on the upper and lower rungs and are separated from the corners of the frame by distances A ₃ and A _4, respectively. To ensure the stability of the frame to its lower crossbeam, legs A _{5 are} welded. Seats for fixing mandrels with frames are located at a distance of H ₂ from the upper and lower crossbeams and are bolts A ₆ in diameter welded to the frame corresponding to the end hole in the mandrel. The distance between the seats N ₃ . The device allows to avoid deformation of the frames at the stage of their impregnation and subsequent carbonization and facilitates the process of loading and unloading blanks from the impregnating container. The free space of the container is full

the pitch. An example of the loading container loading scheme is shown in Figure 3. A cage with six blanks with a diameter of D ₁ arranged in three rows along the height of the C ₂ cage is installed in a container of size B ₁ × B ₂ × C ₁ . The distance between the rows of blanks With ₃ , between the blanks in a row - In ₃ , from the walls of the container - In ₄ . The impregnation operation is carried out in a vacuum cabinet, and the carbonization operation is carried out in an electric furnace for heat treatment or in a shaft furnace for carbonization in a coke bed environment according to known conditions.

Graphite equipment for the impregnation and carbonization of workpieces in a sealed container in a high-pressure apparatus is shown in Figure 4. A number of holes (in the number of workpieces placed) with a diameter of Q ₃ slightly larger than the diameter of the workpiece are made around the circumference of the larger base Q ₁ . The small tool base has a diameter of Q ₂ . The empty space of the container after installing the blanks is covered with pitch. The graphite tooling into which the workpieces are placed significantly reduces the time of their loading and unloading from the container at the stages of impregnation and carbonization in a high-pressure apparatus. Since the container in which the process of impregnation and carbonization under pressure is carried out has a cylindrical shape, for the convenience of placing blanks in it, graphite tooling is also made in the form of a cylinder with a flange. The total height of the equipment is E ₁ , the thickness of the flange is E ₂ . The material of the equipment is artificial graphite of the MPG type, which has high compressive strength. The advantage of using equipment is the possibility of vertical placement of workpieces in a container for more efficient impregnation. In the process of impregnation and carbonization due to the high mechanical properties of graphite, its destruction does not occur under the pressure created in the apparatus. This allows, with increasing pressure on the container in the vertical direction, to increase the pressure in the horizontal direction between the workpiece and the tooling surface in the area of the hole, which contributes to the maximum penetration of the molten pitch into the workpiece.

The container is sealed by welding the lid and the container body. Next, the container is placed in a high-pressure apparatus. Quartz sand is used as the pressure transmitting medium. The container is heated and pressurized. The process of impregnation and carbonization under pressure is carried out according to known modes. The container is removed from the apparatus, and the workpiece is removed from the container, and graphitized in a vacuum oven. The operations of impregnation and carbonization under pressure and subsequent vacuum graphitization of the workpiece from CCCM in a normal (direct) electric single-phase furnace with direct heating resistance are repeated until a material with a density of 1.88-1.91 g / cm ³ has high physical and mechanical characteristics.

Examples of specific performance are carried out on standard equipment [3], material testing is carried out on test equipment and according to the methods of the certification center of NIIgrafit JSC.

Concrete example

Conduct sequentially operations:

- dry laying of the frame based on carbon fabric plain weave of high modulus fiber (any brand) on the mandrel;

- fixing the mandrel with the fabric in the device for impregnation of a dry frame;

- placing the collected cages in an impregnation container and loading pitch into it;

- loading the impregnation container into a vacuum cabinet;

- impregnation of the dry skeleton with molten pitch in a vacuum oven at a temperature of no higher than 300 ° C and subsequent carbonization in an electric furnace for heat treatment or a shaft furnace for carbonization in a coke bed at a temperature of at least 650 ° C;

- impregnation and carbonization of the workpiece with molten pitch using graphite tooling in a sealed container in a high-pressure apparatus, where quartz sand is used as a pressure transmitting medium according to known modes;

- extraction of the workpiece and the mechanical removal of the mandrel;

- graphitization of the workpiece in a vacuum according to known modes.

Moreover, the operation of impregnation and carbonization under pressure and vacuum graphitization is repeated to obtain a material with a density of 1.88-1.91 g / cm ³ .

The remaining examples are made according to the same technological parameters and techniques as the example of a specific embodiment, with the difference that fabrics of various weaving are used as carbon fiber filler.

Physico-mechanical properties of the obtained material are summarized in table 1.

Table 1 Properties of UUKM based on reinforcing fillers made of high modulus carbon fiber Characteristic Canvas Satin Twill* Weave class the basis weft the basis weft the basis weft Example No. one 2 3 Density, g / cm ³ 1.88 1.88 1.88-1.91 Tensile strength, MPa - in tension 216.61 162.79 171.5 209.9 171.4-230.5 111.3-174.8 - during compression 108.57 153.49 205.85 245.71 123.09-154.97 186.84-237.65 - when bending 227.86 175.52 214.22 298.31 204.09-302.95 205.5-242.28 Modulus of elasticity, GPa - in tension 102.79 71.5 93.84 127.96 122.87-100.76 72.12-95.31 - during compression 78.45 59.54 58.89 68.29 43.06-31.63 58.68-65.99 - when bending 69.97 49.47 49.3 68.66 56.9-73.15 43.91-57.25 Strain,% - in tension 0.21 0.23 0.19 0.17 0.15-0.19 0.15-0.21 - during compression 0.41 0.38 0.39-0.47 0.37-0.45 The work of destruction in tension (at F _max ), J 0.44 0.33 0.15 0.18 0.12-0.21 0.08-0.15 * The table shows the range of average values combining different types of twill weave

findings

The proposed method does not require special equipment and significant maintenance costs, applicable for workpieces that do not have rigidity, for example, for dry frames from layers of carbon fabric, allows to obtain material, including in the form of thin-walled shells, characterized by high physical and mechanical properties.

Information sources

1. Composite materials. Handbook Ed. V.V. Vasiliev, Yu.M. Tarnopolsky. - M .: Mechanical Engineering, 1990, p. 512.

2. RF patent №2119469, priority from 09/27/98, C04B 35/52.

3. Svenchansky A. D. Electric industrial furnaces, 2nd ed., Part 1., M., 1975.

Claims (4)

1. A method of producing a carbon-carbon composite material based on a carbon fiber filler and a carbon matrix, comprising sequential processes of impregnation of a workpiece made in the form of a reinforcing frame of carbon fiber material, molten pitch and carbonization in a sealed container in a high-pressure apparatus, where as a transfer medium pressure use quartz sand, extraction of the workpiece and its graphitization in vacuum with the repetition of the operations of impregnation and carbonization under yes phenomenon and vacuum graphitization to obtain a material with a density of 1.88-1.91 g / cm ³ , characterized in that the frame based on carbon fiber material is assembled by dry laying on the mandrel, fix mandrels with frames in a device for impregnating a dry frame, placing it is in an impregnation container, and the frame is impregnated with pitch and subsequent carbonization, and further impregnation and carbonization in a sealed container in a high-pressure apparatus are carried out in graphite tooling. 2. The method according to p. 1, characterized in that for laying out the frame, carbon fiber material is used in the form of plain fabric, or satin, or satin, or twill weave, or a ribbon of high-modulus carbon fiber. 3. The method according to p. 1, characterized in that the device for impregnation of the dry reinforcing frame on the mandrel consists of two welded frames with seats for fixing mandrels with frames and zones of the screed of the frames with metal wire. 4. The method according to p. 1, characterized in that the graphite tooling is made of high-density graphite and has the shape of a cylinder with a flange in which a number of holes are made in the number of placed blanks with a diameter slightly larger than the diameter of the blank.

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