DE1076550B - Method of manufacturing refractory bodies - Google Patents

Description

GERMAN

The invention relates to a method for producing refractory bodies with a bond cubic silicon carbide.

Silicon carbide-bonded refractory bodies have heretofore been mostly made using silicon carbide produced as a mass in a resistance furnace, crushed into the desired grain size and then, with or without the addition of a binder, pressed into a certain shape and then fired became.

It has also been proposed to start from a body made of carbon and to use this to siliconize at very high temperatures in order to convert the carbon into silicon carbide.

Both known methods require the use of extremely high temperatures. For example the temperature to be used in the conventional silicon carbide furnace is above 2000 ° C, and similarly high temperatures are required for the siliconization of carbon bodies. The application Such high temperatures make production considerably more expensive.

In another known method, lower temperatures can be used, by the silicon carbide bodies pressed before firing from a stoichiometric mixture of Silicon metal and carbon, with or without filler material, are produced and thereafter during several Hours at temperatures between 1200 and 1500 ° C in a reducing or non-oxidizing Atmosphere to be burned. This atmosphere can be achieved by having the molded Body embedded in a mass of carbon or coke to split off the oxygen, and that then the carbon and silicon contained in the body react to form silicon carbide. In this process, exceptionally high temperatures are avoided, but it is disadvantageous that the free solid carbon is in the still unfired body and that in the bedding Combine carbon with existing ferrous materials, for example with deposits from steel.

According to the invention, from a slightly moistened mixture of powdered silicon, optionally with a neutral refractory filler, shaped by pressing at high pressure, which are then dried and placed in a carbonaceous atmosphere to convert the silicon into cubic Silicon carbide can be burned.

For example, good results have been obtained when burning in an atmosphere of carbon monoxide at a temperature of 1350 ° C. Surprisingly, it has been found that in the Bren process for production
fireproof body

Applicant:

The Carborundum Company,
Niagara Falls, NY (V. St. A.)

ίο Representative: Dipl.-Ing. W. Cohausz

and Dipl.-Ing. W. Florack, patent attorneys,
Düsseldorf, Schumannstr. 97

Kenneth Charles Nicholson, Niagara Falls, N.Y.

(V. St. A.),
has been named as the inventor

NEN bodies composed in this way the maximum temperature only for a short time of about a few minutes to about an hour needs to be applied to the silicon to full To let the transformation react to silicon carbide. The time of application of the maximum temperature varies, of course, depending on the body being made and depends on the thickness of the refractory body and the percentage of silicon in the body. For example, in a refractory body made almost entirely of silicon metal, time is for the transformation of the silicon into silicon carbide longer than with those made from granular silicon carbide Bodies or in the case of bodies made of other refractory filling material with a lower one Percentage of silicon.

Due to the short-term use of relatively low temperatures that are necessary for the conversion of the Silicon in silicon carbide are necessary according to the invention, it is possible also with metal parts to produce coherent refractory bodies and to burn them together with the metal parts, without causing an undesirable destructive effect on the metal parts.

Burning in a carbonaceous atmosphere, e.g. B. carbon monoxide, is from further Advantage for the application of the process for the production of certain material compositions. So For the first time, silicon carbide-bonded refractory bodies can be used as linings according to the process of metal parts and burn together with these metal parts.

909 757/429

The silicon carbide produced by the process according to the invention is different from that produced by the previously customary process, according to which a mixture of sand and carbon is wrapped around a graphite core and heated up to 2000 to 2600 ° C. The silicon carbide produced by the previously known method has either large flat crystals or elongated needle-like crystals, both types of crystals in a hexagonal shape. The silicon carbide from the method according to the invention has very small crystals which, when viewed with the naked eye, appear amorphous. However, an X-ray examination reveals that the product has cubic crystals.
In the drawings, in

Fig. 1 is an end view of a rocket propulsion chamber shown with a steel tube 10 fitted with a refractory lining 11 made of silicon carbide bonded refractory material is provided;

FIG. 2 shows a cross section along line 2-2 of FIG. 1.

The process of the invention can be carried out by making the desired body essentially entirely from silicon metal, with the exception of a small addition of an intermediate binder, and then allowing it to react by reacting the silicon with a surrounding carbonaceous atmosphere. Preferably, however, an essential component of refractory filler material which is neutral at the firing temperature is added to the silicon, and this filler material is added to the silicon metal in the desired proportion from the start. As such a filler material, for example, normal hexagonal silicon carbide with a grain size of 1 to 2 mm or another refractory grain come into consideration. Clay can also be used. If clay is used in sufficient amount as an additional bond, for example 20 to 30 weight percent ^1, the product has a mechanical strength and toughness to withstand the tough conditions of particularly mechanical, or heat shock.

Depending on its origin and method of manufacture, the refractory filling material can be a conventional granular or pulverized form or be sintered, ground or calcined material. Aside from that usual granular material can also be fillings in the form of refractory balls, cubes or hollow bodies, fibers can also be used.

Two or more filling materials can also be used.

The filling materials are evenly distributed within the refractory body, as are those in between cubic silicon carbide crystals. By changing the proportions of the filler material or materials one can adjust the resistance of the refractory body, in terms of mechanical Stress, coefficient of expansion, thermal conductivity and resistance to thermal shocks as well as resistance to corrosion and erosion. This works when using silicon alone formed silicon carbide with its small intervening crystals itself as a binder, so that the final product has a very high mechanical strength. The cubic silicon carbide that is by the reaction between the carbon of the carbon monoxide or the carbonaceous Atmosphere and the silicon contained in the body forms, binds itself and the filler material into a tightly cohesive mass, because the cubic silicon carbide crystals under and with the granular filling lie close to one another and because between the adjacent cubic silicon carbide crystals there is an at least partial interdiffusion entry.

When the refractory body is in a neutral or non-oxidizing atmosphere at higher temperatures is treated as that used in its pressing, it solidifies itself because one ίο such temperature a further interdiffusion between the silicon carbide crystals. This changes at a correspondingly high temperature cubic silicon carbide partially or entirely in hexagonal silicon carbide with distributed and united Crystals around.

The reaction between, the carbon monoxide or another carbon-containing atmosphere with the silicon of the body to be burned goes like this quickly realize that the body to be burned will not be exposed to the maximum temperature for a long time needs. Usually the reaction occurs within a few minutes.

The steps of the process according to the invention are as follows: The components of the mixture from which the refractory body is composed, e.g. B. finely divided silicon and (if usual granular silicon carbide is added as filler material) the silicon carbide filler material in the desired grain size, are mixed for so long that there is an even distribution of the ingredients in the mixture results. In order for the mixture to be "pressed", a small portion is usually added before it is fired an intermediate binder added. Any of the commonly known intermediate binders in dryers or liquid form can be used, such as. B. resins, dextrin, lignose, bentonite, waxes, Stearates or the like, optionally combinations of such substances. The mixture is then made in any Manner, for example by pressing, and the shaped bodies are slowly placed in an oven dried at a moderate temperature. After drying, the bodies are then placed in a carbonaceous Atmosphere, e.g. B. carbon monoxide, burned.

The heating process during burning can be different, of course it must be such that the bodies gradually brought to the maximum temperature to prevent cracking. The body are then kept at the maximum temperature between 1200 and 1350 ° C until a complete reaction between the silicon metal of the body and the carbon of the carbonaceous atmosphere has taken place. No generally valid length can be specified for this time, as this is up to to a certain extent on the firing temperature, the size of the shape of the body and the proportion of the Silicon in the body. Usually, however, the maximum temperature only needs to be applied for minutes to become. For a tile about 20 mm thick, heating to 200 ° C per Hour from room temperature to about 1250 ° C and an application of this maximum temperature during 15 minutes. The body is then slowly cooled to room temperature.

If you manufacture such a silicon carbide-bonded refractory body against a metal part want, z. B. as the inner lining of a cylindrical steel part, the mixture is the desired Components manufactured as usual and brought into position or pressed, and the so assembled Item is delivered in the usual way

Claims (1)

5 6 dries. The workpiece is then burned as described above, ie the aluminum oxide particles in the body were burned. Due to the fact that it is only necessary to stay for a short time due to the interstitial maximum cubic silicon temperature, carbide crystals are bound,
nevertheless the body to be burned is in one. _
Carbon monoxide or another carbon 5 ± 5 e ι s ρ ι e 1 ill
Containing atmosphere is located, the metal shell or rocket drive parts with an outer steel shell of different types of metal parts from adverse influences and protected with an inner lining of refractory solution during the burning process. Silicon carbide with a composition according to The following are examples of typical mixtures. Example I could be produced satisfactorily according to the invention without about io. For example, a cylindrical steel, the invention is limited to these examples. pipe with 6.35 mm wall thickness and 114 mm diameter. . knife with a 9.5 mm thick silicon carbide lining by inserting the silicon carbide small nozzles and other products consisting essentially entirely of silicon mixture according to example I into the steel tube. Silicon carbide was introduced from 15, dried and then together with the The following mixture is produced: Steel pipe in a closed furnace at 1350 ° C Parts by weight was burned and carbon monoxide _c ., .., uj-ic ^ -nc ", / ic was passed through the combustion chamber. The body Silicon carbide, _1.5-0.5mm 45, onu. ,. ^ö,. _ΛΟ! * γ \ ο r- x. 1/ Silicon carbide, 0.4 to 0.2 mm 13.5 £ ^{urde only} f ^{Mmuten lan} | ^au A ¹ J ⁵ ? ζ ^ ^old Silicon carbide, 0.18 mm and finer 31.5 ³ ° ^The S ^ ze firing process of the workpiece, the m e-r- tiii took place in an electrically heated furnace chamber, Silicon metal powder 10,. ,,, ·, _ο · ι · · ι -lj -l ^ 1j ^{Dry lignosis} 4 ^ obe \ electrical, consisting of silicon carbide Bentonite gel (1 part bentonite heating elements were used lasted approximately to 4 parts of water) 5 ⁵ TT ^ · t. «. · 1. * u ■ u 25 The child's report had a hard, mechanical, After thorough mixing, the nozzles were dried with a resistant silicon carbide lining, which was ^{pressed at a pressure of 3500 kg per cm 2} and pressed tightly against the steel pipe, and peeled off at about 90 ° C. After that, the silicon carbide from the steel pipe was not noticed on body in a carbon monoxide atmosphere. The steel pipe showed only a surface temperature of 1350 ° C. The 30 borrowed dark film on the outside, but was fired in an oven in which the temperature would not otherwise be attacked. gradually increased by 200 ° C per hour until the examples above show just some of the 1350 ° C was brought to the fore for 15 minutes for possible applications. was retained. Then you let the. Furnace itself again The filler material can be any particle size cooling down. During the whole period of 35 years in the furnace, and also the proportion of the filler-burning process a flow of carbon monoxide against the silicon metal can be highly variable. The end products were hard and mechanically opposed to the physical properties and the type of filling material stable and are made up of hexagons - desired end product depend as well as nal silicon carbide mixed with cubic silicon 4.0 depending on the density of the finished product and the type carbide was bound. A try with one of its uses. Acetylene-oxygen gas burner showed that the cor- The carbon monoxide can be passed through extremely high resistance to erosion of oxygen or carbon dioxide over and against tearing in the event of local heat surges. heated charcoal or other reducing agents . 45 can be produced. It can also be a carbon üebeispiel 11 containing atmosphere are used in which the Refractory body made of refractory oxide, which carbon is used to convert silicon carbide cubic silicon carbide was bound, it is obtained from other sources, e.g. B. by made according to the invention from the following mixture: conducting reactive gases such as methane or others Parts by weight of So hydrocarbon gases. Molten aluminum oxide, patent claims 0.18mm 85 Silicon metal powder 15! Process for the production of refractory bodies Powdered phenolic resin 5 P ^{er with} a bond of cubic silicon Calcium stearate 1 55 carbide, characterized in that from one Butyl stearate 5 slightly moistened mixture of powdered Silicon, if necessary with a new The above ingredients were mixed with each other refractory filler, by pressing mixed, and from this, under a pressure of high pressure, bodies were formed, which then 1400 kg per cm ² small body formed and dried at a 60 and in a carbonaceous atmosphere Dried at a temperature of about 90 ° C. The getrock sphere for converting the silicon into cubic Neten workpieces were then burned in a carbon-s silicon carbide, monoxide atmosphere fired at 1350 ° C and 2. The method according to claim 1, characterized Maintained at maximum temperature for 15 minutes. by adding a significant amount of one The small sticks fired in this way showed selectively 65 intermediate binders to the mixture after rend of the burning process a weight gain, the saying 1. End products were hard and mechanically resistant. 3. Method according to claim 1 or 2, characterized capable of a tensile strength of about 245 kg per marked that SiIi- cm ² . An X-ray analysis of the workpieces showed that zium carbide had a hexagonal crystal form Alpha alumina and cubic silicon carbide, 70 will. 4. The method according to claim 1 or 2, characterized in that as a refractory filler refractory oxide or a silicate is used. 5. The method according to any one of claims 1 to 4, characterized in that the shaped body in the carbonaceous. Fired atmosphere at temperatures between 1200 and 1400 ° C will. 6. The method according to any one of claims 1 to 5, characterized in that the refractory body adjacent to a metal part, e.g. B. as the lining of a metal cylinder, together with the Metal part is subjected to the burning process. Considered publications:
German Patent Nos. 1020 556, 920504, 222, 736 810; British Patent No. 632,247;
S ear le, Refractory Materials, 1950, p. 484. 1 sheet of drawings