DE1188056B - Process for the production of a starting material suitable for the production of silicon carbide - Google Patents

Description

Method of making one for the production of silicon carbide Suitable starting material for the production of technical silicon carbide is a mixture of quartz sand and coke is generally used as the starting material. Around To get a high quality product you need a very pure one Quartz sand from selected deposits and a low-ash coke, such as it occurs particularly in refineries and in the tar processing industry. Quartz sand and coke are in the form of grains with a grain size of several millimeters in approximate stoichiometric ratio mechanically mixed with each other and then stand - possibly still with additives such as sawdust, table salt and the like - for the production of silicon carbide z. B. in the resistance furnace according to A c h e s o n available.

There are several disadvantages associated with this approach. Of the The high-purity coke required is relatively expensive. It continues to segregate Sand-coke mixture very light due to the difference in specific weight when handling and when pouring into the oven. In addition, occurs when heated The quartz grains melt together and thus the tendency to form larger lumps of quartz melt on, whereby the reaction with coke to silicon carbide is inhibited and continuous Working is extremely difficult.

There has now been a method of making one for the production of silicon carbide certain existing starting material found, which thereby is characterized in that one to above 600 ° C, especially to 800 to 1000 ° C, Such amounts of liquid or gaseous hydrocarbons act on held sand allows carbon to be deposited on the sand particles in such an amount that the Carbon content of the carbon sand particles 20 to 50 percent by weight, especially 25 to 40 percent by weight, with the action either in with stirrers provided shaft furnaces or with internals for entrainment and whirling of the Sand provided, indirectly heated rotary kilns is completed.

Tars and tar-containing substances in particular are used as coke-forming substances Materials and petroleum products, in particular residual oils, are considered. But can also higher-boiling products and / or gaseous hydrocarbons, e.g. B. natural gas, be used.

Under these conditions the individual quartz grains are firmly adhering, shiny black, dense carbon layer. The carbon content of the coated resin sand should be at least 20 percent by weight, based on the Total weight of the starting materials. The material obtained can be used immediately can be used for silicon carbide production, if necessary by appropriate Additions beforehand the Si02: C ratio to approximately stoichiometric Ratios are corrected.

When this material is heated, the quartz grains do not melt together into larger lumps of melt. Furthermore, the raw material thus produced is not segregated, and it is more reactive than the traditional mechanical one Mixture because the entire surface of the quartz is in contact with carbon. As an additional, unforeseeable advantage, it was also found that the Heating the starting material produced according to the invention to that for silicon carbide production necessary temperatures above about 1600 ° C, the evaporation losses of Si02 are significantly lower than when using a mechanically produced mixture the starting materials.

In addition to that which is deposited on the quartz sand, this occurs during coking Coke still produces significant amounts of gaseous products. A small part of it can be used as a Fuel can be used for the coking furnace, the greater part is available for others Purposes available as heating gas. The high calorific value of these gases contributes to economic efficiency of the new procedure. The further processing of the produced according to the invention The starting material for silicon carbide can be used in hearth furnaces, rotary kilns or even carried out in every furnace otherwise used for the production of silicon carbide will.

In order to carry out the procedure, an order is required at precise dosing of the raw materials and keeping the degree of coking constant and the sand dwell time in the furnace is guaranteed. It turned out to be special an indirectly heated shaft furnace is very suitable for smaller quantities. In The sand is poured in from above and the hydrocarbons are injected from below. In contact with the hot sand, the hydrocarbons evaporate and coke in the process Penetration of the sand layer. The gaseous products leave the shaft furnace at the upper end, while the carbon-coated sand is continuously withdrawn at the bottom can be. Appropriately, the quartz sand in a drum furnace and the Hydrocarbons are preheated as high as possible beforehand in a tube furnace.

An indirectly heated rotary kiln with built-in components is available for larger quantities to increase the degree of filling, so that the initially formed hydrocarbon vapors Stay in constant contact with the hot sand, especially suitable. Here too is the direct preheating of the quartz sand or the preheating of the hydrocarbons useful in a tube furnace.

Example 1 1000g of quartz sand (grain size 0.4 to 0.6 mm) were in a Shaft furnace with stirrer heated to 800 ° C. and 700 g for 1 / f hour Coal tar introduced from below. Coke deposited on the sand while the gaseous products formed were withdrawn at the top of the furnace. Of the The carbon content, based on the total mixture, was 361%. Example 2 500 g Quartz sand (grain size 0.4 to 0.6 mm) were placed in a shaft furnace with a stirrer heated to 1050 ° C and for 1 hour 3001 propane gas with a residence time of initiated from below for about 5 seconds. The one consisting primarily of hydrogen Exhaust gas was withdrawn from the top of the furnace. On the quartz sand, 28.5% Carbon deposited.

Example 3 250 g of quartz sand (grain size 0.4 to 0.6 mm) were heated to 1250 ° C. in a rotary kiln with internals for mixing the sand and 3501 of methane gas were passed over it in countercurrent for 1 hour. The exhaust gas escaped at the other end of the furnace. 27% carbon was deposited on the sand. The residence time was about 1.5 seconds. Example 4 30 g of sand (grain size 0.4 to 0.6 mm) and 18 g of coke (grain size 0.1 to 0.4 mm) were mechanically mixed and then heated in an electric furnace at 1700 ° C. for 2 hours. After cooling, 19.2 g of reaction product with a silicon carbide content of 84.4% were obtained. The loss of 5i0 = was 8.5% of the quartz sand used. 48 g of a carbon-coated quartz sand obtained according to Examples 1 to 3 were heated under the same conditions as mentioned above. This gave 20.5 g of reaction product with a silicon carbide content of 86.41%. The loss of SiO was 5.1%, based on the quartz sand used.

Claims (1)

Claim: Process for the production of one for the production raw material consisting of sand and carbon made up of silicon carbide, characterized in that one to above 600 ° C, especially to 800 to 1000 ° C, held sand act in such amounts of liquid or gaseous hydrocarbons allows carbon to be found on the sand particles in amounts from 20 to 50, especially 25 to 40 percent by weight, based on the total weight of the particles, settles, the action either in shaft furnaces equipped with stirrers or in with Internals for entrainment and swirling of the sand provided, indirectly heated Rotary kilns is completed.