RU2520171C1 - Adjustment of penetration of butts between retort parts in siliconising tool set - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: fusible gate is formed between retort parts of siliconising plant at butts on the side of its outer surface. Said fusible gate is formed in end recess while fusible gate material is composed by Si₃N₄-Si or Ti₃SiC₅-Ti Si₂-Si, or TiSi₂-Si.Said materials are produced by impregnating them or Si₃N₄-or mix of TiC and Ti, or Ti-based porous blanks formed at circular recess bottom to overlap the butt with the melt of silicon melt or its alloys with Cu and Al.

EFFECT: higher degree and homogeneity of siliconising, longer life.

6 cl, 6 dwg

Description

The invention relates to the field of production of structural materials operating under conditions of high thermal loading and an oxidizing environment.

There is a method of reducing the permeability of joints between parts of a retort in a tool for siliconizing products by applying the thermal cycling mode. It reduces the permeability of the joints due to the condensation of silicon vapors in them at the stages of intermediate cooling [Promising materials; No. 9a, 2010, p. 122-126]. The method does not provide a reliable reduction in the permeability of joints. So, when the gap in the joint is exceeded 2 mm (and this may occur in some sections of the joint), the silicon vapor condensate is not retained in the joint and this joint section remains permeable. There is also a limitation on the temperature to which the silicon vapor condensate is held in the joint.

The closest in technical essence and the achieved effect is a method of reducing the permeability of joints between parts of a retort in a tool for siliconizing products, including the formation of a fusible shutter at the locations of the joints, on the side of its outer surface. In this case, glass is used as the fusible closure material. Siliconization of products in the retort, reduction of the permeability of joints between the parts of which is carried out by this method, is carried out at a relatively low temperature (1300-1400С °), a deeper vacuum, but in the absence of the latter, starting from the melting of the glass (during this period the vacuum pump is turned off) [G.V.Samsonov et al. Refractory coatings. M. Met-I, 1973, pp. 84-85].

This method cannot be applied when silicification is carried out at higher temperatures and with a constantly operating vacuum pump. The need for continuous operation of the vacuum pump is caused by the need to remove from the reactor gases that are constantly released from the carbon-graphite lining.

The objective of the invention is to increase the likelihood of obtaining reproducibly stable high results in the degree and uniformity of silicification while maintaining a high service life of the retorts and the device for siliconizing in general.

The problem is solved due to the fact that in the known method of reducing the permeability of the joints between the parts of the retort in a tool for siliconizing products, including forming in the locations of the joints, on the side of the outer surface of the retort, a fuse, in accordance with the claimed method, a fuse is formed in an annular deepening, and as the material of the fusible closure using materials such as composition material Si ₃ N ₄ -Si or Ti ₃ SiC ₅ -Ti Si ₂ -Si, or TiSi ₂ -Si, obtained by impregnation with a melt of silicon or its alloy mi with Cu and Al - installed on the bottom of the annular recess with the overlap of the junction of porous preforms based on Si ₃ N ₄ or a mixture of TiC and Ti, or Ti, respectively. To simplify the method, porous preforms based on Si ₃ N ₄ or TiC-Ti, or Ti are obtained by filling the annular recess with a slip composition based on powders of these substances and a siloxane binder.

For the same purpose, impregnation with a molten silicon or its alloys with Cu and Al is carried out directly in the process of siliconizing products.

To ensure high-quality impregnation with a silicon melt or its alloys with Cu and Al by reducing its carbidization under the influence of carbon-containing reactor gases, silicon or its Cu and Al alloys are castings of the corresponding form.

For the same purpose, impregnation with a silicon melt or its alloys with Cu and Al is carried out before the siliconization process; in this case, the evacuation of the retort during silicification is carried out through a central hole made in its lid.

In order to simplify the method and reduce the likelihood of silicon carbidization, silicon and its alloys with Cu and Al are powders; however, based on them, a slip composition is prepared in which a siloxane binder is used.

The formation of a fusible valve in an annular recess creates the prerequisites for its long-term functioning at high temperatures.

The use of materials such as Si ₃ N ₄ -Si or Ti ₃ SiC ₅ -Ti Si ₂ -Si, or TiSi ₂ -Si, obtained by impregnation of a silicon melt — or its alloys with Cu and Al — installed on a fusible closure material the bottom of the annular recess with the overlap of the junction of porous preforms based on Si ₃ N ₄ or a mixture of TiC and Ti, or Ti, respectively (or formed at the bottom of the annular recess), together with the formation of a fusible closure in the annular recess, provides on the one hand the possibility of its long functioning at. high temperatures, namely: up to 1600-1700 ° С, on the other hand, provides the possibility of its removal due to decomposition at the holding stage at 1800-1850 ° С with possible final removal from the annular recess (before the disassembly of the charge) with metalwork and / or chemical by way.

In addition, not only the long-term functioning of the fusible shutter is ensured, but also its low permeability is ensured. This is achieved in turn due to the fact that the silicon melt is in the pores of materials that are more heat-resistant than it, and therefore the process of sweating it out of the pores proceeds only at temperatures above 1700-1800 ° C in vacuum or when the porous material itself begins decompose and therefore cannot retain the silicon melt (first of all, this refers to silicon nitride, which in vacuum in the absence of saturated silicon vapors begins to decompose at temperatures above 1500 ° C).

The decomposition of fusible seal materials is shifted to higher temperatures if they are surrounded by their decay product. Thus, a material of the composition Si ₃ N ₄ -Si decomposes at a reactor pressure of ≤27 mm Hg. in the temperature range 1650-1700 ° C.

Removing most of the material of the fusible shutter occurs at the stage of exposure in vacuum at 1800-1850 ° C.

Thus, during the decomposition of Si ₃ N ₄ , Si and N _{2 are formed} and, if it were not for the partial carbidization of Si and Si ₃ N ₄ under the influence of carbon-containing reactor gases, then nothing would have remained of the fusible shutter material.

As for Ti ₃ SiC ₅ , the products of its decomposition are TiC and Si. The decomposition products of TiSi ₂ are Ti and Si. Titanium carbide can be removed from the annular recess by chemical means (by dissolving in a mixture of hydrofluoric and nitric acids in the cold), because the annular recess is a sealed chemical container.

In the new set of essential features, the object of the invention has a new property: the ability to minimize the removal of the supersaturated state of silicon vapors in the vicinity of the siliconized product by reducing the permeability of the joints between the parts of the retort, achieved by overlapping them with a fusible shutter, while maintaining the possibility of separation after the siliconizing regime, thanks to on the one hand, sufficiently high heat resistance and low permeability of the fusible seal material, and on the other hand, it is possible NOSTA nevertheless its decomposition in the final stage siliciding process, namely aging in a vacuum at 1800-1850 ° C.

Thanks to the new property, the task is solved, namely: the likelihood of obtaining reproducible, stably high results in the degree and uniformity of silicification is increased while maintaining a high service life of the retorts and, in general, the siliconizing device.

The invention is illustrated by examples and drawings.

Figure 1 shows a General view of the design of the device for silicification by the vapor-liquid-phase method.

Figure 2 - design of the retort, consisting of 2 parts, around the junction between which is made an annular recess under the fuse.

Figure 3 is an example of a circuit for forming a fusible shutter.

In Fig.4, 5, 6 - examples of the design of the retort, consisting of 2 parts, around the junction between which there is an annular recess filled with a fusible shutter; in Fig.4 the joint is made of a castle shape, and in Fig.5, 6 - wedge-shaped.

A device for siliconizing products by the vapor-liquid-phase method contains graphite heaters 1 located around a closed volume retort 2 made of several parts 2a, 2b for placing silicon crucibles and siliconized products (not shown in Fig. 1), a water-cooled flow reactor 3 , thermal insulation 4 of porous carbon-graphite materials and a pneumatic-gas-vacuum system (not shown in Fig. 1).

At the end of part 2b of the retort 2, located under the junction 5, an annular recess 7 is made for forming a fusible shutter 6 in it 5-10 mm wide, the bottom and top of which are respectively lower and higher than the junction 5, and the retort material is impermeable to melts and solutions.

In this case, the annular recess 7 is turned to the side opposite to the inner volume of the retort 2, and the junction 5 is made either of a castle shape, in which the portion 5a located most high from the bottom of the annular recess 7 is facing the inner volume of the retort 2 (Fig. 4), or the junction 5 is made wedge-shaped (figure 5), the gap in the joint 5 is 1-2 mm, and the height of the joint 5-10 ÷ 30 mm

The decrease in the permeability of the joints 5 between parts 2A and 2B of the retort 2 in accordance with the claimed method in the above-described device for silicification by the vapor-liquid-phase method is as follows.

In the annular recess 7 form a fuse 6. In this case, materials such as Si ₃ N ₄ -Si or Ti ₃ SiC ₅ -Ti Si ₂ -Si, or TiSi ₂ -Si, or other materials with properties similar to the specified materials. For this purpose, porous preforms 6a based on Si ₃ N ₄ or a mixture of TiC and Ti or Ti, respectively, of the materials used for the fusible shutter 6, are mounted on the bottom of the annular recess 7 or are formed on its bottom.

In particular, the formation of porous preforms can be carried out by filling the annular recess 7 with a slip composition based on these substances and a siloxane binder. In this case, the porous preforms 6a installed or formed at the bottom of the annular recess 7 should overlap the joint 5.

Then, silicon or its alloy with Cu and Al, which is either castings 6b of the corresponding form, or a slip composition 6b based on powders of silicon or its alloy with Cu and Al and a siloxane binder, is placed on top of the porous preforms 6a.

Then, the porous preform 6a is impregnated with a silicon melt or its alloy with Cu and Al, representing either castings 6b or the above-described slip composition 6b.

Impregnation with a molten silicon - or its alloy with Cu and Al - can be carried out directly in the process of siliconizing the product or before carrying out the specified process.

As a result, a fusible shutter 6 is obtained in the annular recess 7 (see Figs. 4, 5, 6). Moreover, if the impregnation of the porous preform 6a was carried out before the process of siliconizing the product, then strictly speaking, a fuse 6 is formed upon reaching the melting temperature of silicon or its alloy with Cu and Al, and before that it is in the solid state, and therefore, the retort is evacuated during siliconization through a central hole made in the retort lid.

The above description of the proposed method is quite sufficient in order not to dwell on examples of its specific implementation, because in fact, they are already here.

More informative is the description of the operation of the device for silicification, in which the regulation of the permeability of the joints between the parts of the retort is carried out by the proposed method.

A device for siliconizing products by the vapor-liquid-phase method, containing a retort, on one part of which an annular recess is made with a fuse closure formed in it in accordance with the claimed method, overlapping the joint, as follows.

By switching on the vacuum pumps of the pneumatic-gas-vacuum system, the water-cooled reactor 3 and retort 2 are evacuated.

By supplying power to the heaters 1, the retort 2 and the crucibles with silicon and siliconized product placed in it are heated.

Upon reaching 1300-1400 ° C, the evaporation of silicon begins. Moreover, with increasing temperature, the vapor pressure of silicon increases.

The presence of thermal insulation and porous carbon-graphite materials in the device allows heating up to a temperature of more than 1800-1850 ° С; moreover, in separate temperature ranges - with a fairly high speed. In turn, this allows you to create a temperature difference between the silicon vapor and the siliconized product. As a result, a state of supersaturated silicon vapors arises in the vicinity of the latter. In the temperature range of 1420-1650 ° C, the presence of a fusible shutter 6 can significantly reduce the permeability of the joints 5 between parts 2a and 2b of the retort 2. Therefore, the supersaturated state of silicon vapor in the vicinity of the siliconized product is maintained. The consequence of this is the condensation of silicon vapor on the surface and / or directly in the pores of the material of the siliconized product.

This is a very effective process of mass transfer of silicon into the pores of the material and therefore it provides reproducible, stably high results in terms of the degree and uniformity of silicification.

During heating, carbon-containing gases are released from the thermal insulation 4 made of porous carbon-graphite materials. They could chemically bind part of the silicon vapor in retort 2 and thereby reduce the amount of their supersaturation in the vicinity of the siliconized product. However, due to the low permeability of joints 5 in the range of 1420-1650 ⁺⁵⁰ ° C, this does not happen.

Upon reaching a temperature of 1650 ⁺⁵⁰ ° C, either the process of decomposition of the material of the fusible shutter 6 begins (this occurs with materials of the compositions Si ₃ N ₄ -Si and TiSi ₂ -Si), or the process of sweating of silicon from the pores of the material of the fusible shutter (this occurs with the material of the composition Ti ₃ SiC ₅ -Ti Si ₂ -Si). Upon reaching a temperature of 1800-1850 ° C, there is a complete decomposition and removal from the annular recess 7 of such materials as Si ₃ N ₄ -Si and Ti Si ₂ -Si.

Upon decomposition of the fusible gate material of the composition Ti ₃ SiC ₅ -Ti Si ₂ -Si, TiC remains in the annular recess 7. This leads to the opening of the joints 5 and the release for the most part of the annular groove 7 from the fuse 6.

As a result of the chemical interaction of the starting materials of the fuse with carbon-containing reactor gases, SiC is also formed in a small amount.

Upon final cooling, silicon vapors leak from retort 2 through joints 5 that have become permeable. Moreover, part of them condenses on the inner surface of retort 2. Since the gap in joints 5 is 1-2 mm, silicon vapors do not condense in them. They also do not condense in a sufficiently wide annular recess 7. However, some of them may condense in the TiC pores.

The SiC present in the annular recess is removed by metalwork, and TiC (including knitted with silicon vapor condensate) by chemical means, because this is possible due to the tightness of the chemical container, which is the annular recess 7.

Claims (6)

1. A method for controlling the permeability of joints between parts of a retort in a tool for siliconizing products, comprising forming a fuse at the joints on the outer surface of the retort, characterized in that the fuse is formed in an annular recess, and such materials are used as the fuse material, as a material of the composition Si ₃ N ₄ -Si or Ti ₃ SiC ₅ -TiSi ₂ -Si, or TiSi ₂ -Si, obtained by impregnating porous preforms based on Si ₃ N ₄ , or a mixture of TiC and Ti, or Ti, respectively, established or formed GOVERNMENTAL at the bottom of the annular recess with an overlap splice, the melt of silicon or its alloys with the Cu and Al. 2. The method according to claim 1, characterized in that the porous preforms based on Si ₃ N ₄ , or TiC-Ti, or Ti are obtained by filling the annular recess with a slip composition based on powders of these substances and a siloxane binder. 3. The method according to claim 2, characterized in that the impregnation with a molten silicon or its alloys with Cu and Al is carried out directly in the process of siliconizing products. 4. The method according to claim 3, characterized in that the melt of silicon or its alloys with Cu and Al for impregnation is obtained from castings of silicon or its alloys with Cu and Al placed in an annular recess in a shape corresponding to the shape of the annular recess. 5. The method according to claim 3, characterized in that silicon or its alloys with Cu and Al are powders, and on the basis of them a slip composition is prepared in which a siloxane binder is used. 6. The method according to claim 2, characterized in that the impregnation of the silicon melt or its alloys with Cu and Al is carried out before the siliconization process, while the evacuation of the retort during siliconization is carried out through a Central hole made in the lid of the retort.

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