DE1471280C - Method for increasing the heat resistance of silicon carbide - Google Patents

Description

Binder formed by pressing, dried and then fired at around 1900 ° C. It has shown, that such a heating element has a normal and a maximum load capacity, which is essentially is the same as that in Example 1.

Even if only the treatment with dilute phosphoric acid is mentioned in the two examples of course, the same results can be obtained when using undiluted phosphoric acid be achieved.

Claims (2)

1 2 is achieved according to the invention in that the powdery, granular or sintered silicon carbide is heat-treated with porous acid and the adhering phosphoric acid is removed by washing with water 1. Method for increasing the heat resistance 5 and then dried the silicon carbide of silicon carbide for heating elements. ter use of phosphorus compounds, According to the invention, surprisingly- characterized in that, after the phosphoric acid treatment, the phosphorus deformed, granular or sintered silicon carbonic acid are washed away again in such a way that bid heat-treated with phosphoric acid, the an- io no residues of phosphoric acid remain, adhering phosphoric acid by washing with Nevertheless, however, the heat resistance of the Removed water and then significantly increased the silicon-treated silicon carbide, for example carbide is dried. by 150 to 200 ° C. This increase in heat resistance 2. The method according to claim 1, characterized in that the speed is based on the diffusion of phos that the silicon carbide with 15 phate radicals of phosphoric acid in the crystal be-85% Phosphoric acid 2 hours at 130 ° C nen the silicon carbide, then treated the phosphate will. dikal in the manner of a vaccine the heat resistance elevated. In this case, the amount of phosphate radical diffused into the carbide becomes as in 20 the case of a usual diffusion, the greater, the more the higher the concentration of phosphoric acid, the higher the treatment temperature and the longer the treatment time is. The main advantage of the invention The invention relates to a method for increasing the extent that the finished silicon carbide bodies, i.e. the heat resistance of silicon carbide for heating elements, can be post-treated in such a way that elements using phosphorus compounds increase their heat resistance,
gen. The invention is described below with reference to Explained in more detail in the magazine "Brick an Clay Record" from playing.
August 1950, is already mentioned, phosphates to increase the heat resistance of silicon carbide to 30 B ice ρ ie 1 1
use. Aluminum phosphate is used as a heat-resistant composite material or as a filler material. Commercially available silicon carbide heating elements are used so that the aluminum phosphate surrounds the elements in 85% silicon carbide crystals for two hours. This process phosphoric acid solution of 130 ⁰ C heated. The heating method can only be used if the elements are then washed in order to completely remove particles mixed with foreign matter on the surfaces, but not in those cases where and at 110 ° C dried. Then each of the finished bodies made of pure silicon carbide with respect to elements treated in this way will have to be improved in one of their heat resistance in air. Subjected to heat resistance test, and also in U.S. Patent 2,852,401 a 40 described by passing electric current through refractory manufacturing process the element and measuring its surface temperature at which a mass of about 65% of a door by means of an optical pyrometer . The verinactive substance, for example silicon carbide, search results show that the heating elements treated in the above manner and about 35% aluminum hydroxide or active heating elements ^{mixed a normal load capacity of aluminum oxide with a few percent more concentrated 45 of 1700 0} C and a maximum load capacity of phosphoric acid Mix then at 1800 ° C. In comparison, it shows that it is too dry. The reaction product that results and is distributed in the borrowed silicon carbide elements without the substance in accordance with the invention acts, if treated at a normal working temperature, in the manner of cement, that is, as a binder. Here, too, of 1550 ° C and a maximum working temperature, it is a mixed product. A similar 50 by 1680 ° C.
ches method is disclosed in the Austrian patent specification 171 888, which deals with the improvement example 2
tion of the binding properties of quartz crystals by adding phosphoric acid to quartzites Common silicon carbide powder becomes 2 hours long concerned to erphosphat the clay contained in the mass to Orto- 55 in 85% phosphoric acid solution to 130 ° C tie off. Any measures to keep it warm, then washed and dried. If that Improvement of the heat resistance of the quartz itself in this way with dilute phosphoric acid cannot be found in this patent specification, silicon carbide powder traded for one hour in just as little as US Pat. No. 2,805,174, an oxygen stream of 1400 ° C is heated, so which the manufacture of high-density heat-resistant 60 it showed a weight gain of 1.12%. VerMaterials by introducing phosphoric acid - similarly shows the same silicon carbide powder Anhydrite in 5 to 30% of the pores of the molded SiIi- without phosphoric acid treatment, if it is in one Ziumkarbidkörper concerns, so the pores with the oxygen flow in the above-mentioned manner be-reaction product to fill. is a weight gain of 7.78%. The object of the invention is a method for producing a heating element the heat resistance of silicon carbide mixture of in the above manner with phosphoric acid for heating elements, without the requirement of treated silicon carbide powders of about 1 to Production of a substance mixture. This task 10% silica, water glass and pitch or the like. As