RU2008298C1 - Method of impregnating hollow articles of porous material containing silicon carbide and/or carbon with silicon and device for effecting the same - Google Patents

Abstract

FIELD: production of refractory articles. SUBSTANCE: method involves the steps of: applying silicon melt supplied through a member with capillary structure at temperature of an article to be impregnated of 1260-1400 degrees C and a temperature of the melt of 1430-1700 degrees C and keeping the article, cooling at axial temperature gradient in the article of 25-60 degrees C/m. Device for impregnating hollow articles with silicon has a hermetically sealed chamber, cylindrical resistive heater, crucible, feeder mounted in the chamber. The feeder is made of material with capillary structure. The device furthermore is provided with a support and shield, the shield thickness being variable in height and determined from the expression given in the invention description. EFFECT: enhanced efficiency. 2 cl, 1 dwg, 1 tbl

Description

 The invention relates to the production of refractory products based on silicon carbide and / or carbon, for example, high-purity products from siliconized graphite or silicon carbide-silicon products for semiconductor technology, in particular, the manufacture of equipment for diffusion and oxidation processes in IP manufacturing technology.

 A known method is the impregnation of products based on silicon carbide or the manufacture of special technological equipment (muffles, reactors, carriers, etc.) for high-temperature processes for the production of IP. The impregnation of products by this method is carried out in two stages. At the first stage, the product is subjected to heat treatment in the flow of organosilicon compounds and hydrogen, forming a silicon layer on its surface. Then, in a non-oxidizing atmosphere, the product is heated above the melting temperature of silicon, which fills the intergranular space of the product [1].

 The disadvantages of this method are the low productivity and complexity of the process, not allowing with sufficient accuracy to control the amount deposited on the surface of the silicon product. This leads either to incomplete filling of pores with silicon, or to the formation of droplets on the surface of the product.

 There is also a method of impregnating products from a porous carbon material by immersing them in a silicon melt in a non-oxidizing atmosphere in order to completely impregnate them throughout the volume [2]. The method allows to obtain products of good quality with a complete filling of the pores of the carbon base with silicon.

 However, this method is not acceptable for the impregnation of thin-walled products. Such products usually collapse or deform when immersed or removed from the melt. In addition, the method is difficult to implement, since in the installation example it is necessary to have a tank with a molten silicon larger than the product volume and mechanical devices for immersing and removing products. The difficulty of the hardware design of the method increases with increasing dimensions of the impregnated products.

The closest in technical essence is the method of silicon impregnation of hollow porous products in a non-oxidizing medium by contacting the heated material with an overheated molten silicon. The supply of silicon to the product is carried out using a feeder, which is a ribbon of carbon-graphite felt. When this silicon temperature 1430-1700 ^{° C,} products 1260-1400 ^C. After the impregnation is carried out and the cooling of the product melt, which takes place during crystallization of silicon in item [3].

 To implement this method, a device is used to impregnate silicon hollow articles made of porous material, containing a sealed chamber, a cylindrical resistive heater installed in it, a crucible for silicon melt, a feeder for supplying silicon melt from the crucible made of a material with a capillary structure, and a cylindrical screen, having a constant wall thickness [3].

 The disadvantage of this method and device is the low surface quality of silicon-impregnated products, due to the following reasons. Since the thermal unit has a characteristic temperature profile with a maximum temperature in the middle part and a minimum along the edges of the heater, the crystallization of silicon passes from the edges of the product to the middle, as silicon, increasing in volume, is pushed to the middle part of the product and is released as drops in the last stage both on the external and internal surfaces of the product.

 To remove the drops using mechanical processing with an abrasive tool. Processing the inner surface in the middle part, especially long products, is extremely difficult, time-consuming and often leads to their destruction. In addition, obtaining products of complex shape is almost impossible due to the great technical difficulties associated with machining the inner surface.

 The aim of the invention is to improve the surface quality of products.

 The drawing shows the proposed device.

 A device for impregnating silicon hollow articles made of porous material contains a sealed chamber 1, inside which a cylindrical resistive heater 2, a screen 3 of variable thickness, a crucible 4, a feeder 5, one end of which is inside the crucible 4 and the other between the bottom of the crucible and the end of the impregnated product are placed 6 mounted on the stand 7. When the crucible 4 is located above the product 6, the crucible can be installed, for example, on the disk 8, under which the end of the feeder 5, which is in contact with the product 6, is tucked.

 The method is not critical to the relative position of the crucible and the impregnated product. The impregnation can be carried out both from the crucible located above the product (the example under consideration), and from the crucible located under the product.

 Tapes (at least two) made of carbon-graphite felt or graphite fabric can be used as a feeder.

[(H-h)/H-0,1] , обеспечивает создание необходимого (25-60^оС м^-1) осевого градиента температуры в изделии.The use of a cylindrical screen 3 having a height of not less than the height of the product and the wall thickness b = 30

[(Hh) / H-0,1], provides the creation of the necessary (25-60 ^about With m ^-1 ) axial temperature gradient in the product.

[(H-h)/H+0,1] не обеспечивается нижний предел осевого градиента в изделии, т. е. 25^оС м^-1;
- при толщине более

_{[(H-h)/H+0,1]} градиент температуры превышает максимально допустимый, т. е. 60^оС м^-1.The limits for changing the screen thickness are due to the following reasons:
- with a thickness of less than 30

[(Hh) / H + 0.1] the lower limit of the axial gradient in the product is not provided, that is, 25 ^° C m ^-1 ;
- with a thickness of more

_{[(Hh) / H + 0,1} ] temperature gradient exceeds the maximum, ie. E. ^C. 60 m ^-1.

PRI me R 1. Impregnate a cylindrical tube 400 mm long, 165 mm in diameter, with a wall thickness of 5 mm, made of a compressed mixture of powders of silicon carbide grade M-28 and KZ-6 in a ratio of 1: 2.5, respectively, the addition of 5-6% pulverbakelite OST 6-05-441-78 brand SFP-OPA and subjected to heat treatment at 200 and 900 ^about C.

 The impregnation is carried out in vacuum in a sealed chamber 1 with a resistive cylindrical heater 2. The product 6 and the screen 3 with a variable wall thickness defined by the formula b = 35.4 [(400-h) / 400 + 0.1] are mounted on a stand 7. Five feeders 5 are laid on the upper end of the article 6 in the form of ribbons of carbon-graphite felt having a capillary structure. Some ends of the tapes are pressed with a disk 8 of siliconized graphite, onto which the crucible 4 is mounted and the opposite ends of the tapes are tucked into it. Pieces of silicon are poured into crucible 4. The furnace is heated at constant power on the heater 2 at a speed of 30 deg / min.

The temperature of the product 6 before impregnation ¹³⁵⁰ C. The melt temperature ^of 1600 C. The impregnation was continued for 18 min at constant power to the heater 2. When the closure impregnation furnace heating is turned off. In the process of natural cooling in the product 6 creates an axial temperature gradient ▽ T = 45 ^about C · m ^-1 . The surface quality of the product 6 is good. Drops and tears both inside the pipe and outside are absent. At the bottom there were a few drops that were easily removed with an abrasive tool.

 In this example, 10 pipes were obtained. The yield after machining was 95%, which is 25% higher than the prototype after machining (in the prototype, products having silicon droplets and flows on the surface were counted, losses on machining of the products when determining the percent yield were not taken into account).

 PRI me R 2. The impregnation of a cylindrical pipe with a length of 400 mm, made according to example 1, is carried out analogously to example 1. Use a screen 3 with a variable wall thickness, determined by the formula b = 30.6 [(400-h) / 400 + 0,1].

The temperature of the product 6 before impregnation of 1400 ^about C. The melt temperature of 1430 ^about C. In the cooling process in the product 6 create an axial gradient ▽ T = 25 ^about S · m ^-1 . After the end of the process, the pipe has drops at a distance of 7 mm from the lower end. After trimming 7 mm, the usable part with good surface quality was 393 mm.

 In this example, 5 pipes with a diameter of 165 mm were obtained. The yield was 92%.

 Other examples of execution are presented in the table.

 From the above examples it is seen that the use of the invention (see examples N 1-3) allows to obtain products with good surface quality, which ensures high yield.

 When exceeding the limit values of the axial temperature gradient (see examples N 4, 5), the purpose of the invention is not achieved. (56) Japanese Application N 62-22950, cl. C 04 B 35/56, 05.20.87.

 The technological process N 4807-72-81 of the Chelyabinsk electrode plant, approved 11.12.78.

 USSR copyright certificate N 1243311, cl. C 04 B 35/56, 1984.

Claims (2)

1. The method of silicon impregnation of hollow articles of a porous material containing silicon carbide and / or carbon in a non-oxidizing medium by bringing the product into contact with a silicon melt using an element with a capillary structure, heating silicon to 1430 - 1700 ^o C and products to 1260 - 1400 ^o C, holding at the indicated temperatures and cooling, characterized in that, in order to improve the surface quality of the products, cooling is carried out at an axial temperature gradient in the product of 25-60 ^o C · m ^-1 . 2. A device for silicon impregnation of hollow articles of a porous material containing silicon carbide and / or carbon, including a sealed chamber, a cylindrical resistive heater, a crucible, a feeder made of a material with a capillary structure, a stand and a screen located between the heater and product having a height not less than the height of the product, characterized in that, in order to improve the quality of the surface of the products, the screen is made of variable thickness b in height, determined by the formula
b = 30

[(Hh) / H-0.1]
where T ₁ is the temperature of the product, ^o C;
T ₂ - melt temperature, ^o C;
H - screen height, mm;
h is the distance from the base of the screen, mm;
30 - experimental coefficient, mm.

Images