TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: The purification is simultaneously carried out by grinding and/or dispersing by means of dissolver. The grinding process takes place by means of a microniser, roller mill, ball mill or an attritor. The purification of the silicon nitride powder takes place by acid-leaching at 20-1300degreesC. The silicon nitride powder is separated by decantation, centrifugation or filtration. The washing process takes place with highly pure water with a resistance of greater than or equal to 18 MOmega cm. The purification, separation and washing process takes place for 2-5 times. The cleaning process takes place at 200-1300degreesC and the acid is added with a halogen containing treatment gas. The purified powder is dried by means of microwave. Preferred Components: The silicon nitride powder exhibits a sum of metallic impurities of less than 1 ppm, preferably less than 100 ppb. In the method, a silicon nitride powder having metallic impurities of 20-1000 ppm is used. The average grain size of the powder is 0.2-0.5 microns. The halogen containing treatment gas is fluorine, chlorine, bromine and/or iodine gas and their gaseous chemical compounds. EXAMPLE - Silicon nitride powder with an average grain size of 2.5 microns and a contamination of 103.5 ppm related to the element iron, nickel, chromium, calcium, sodium, potassium and titanium was grinded with a microniser to obtain an average grain size of 0.5 microns. The milled silicon powder (100 g) was leached with concentrated hydrochloric acid (200 ml) at 100degreesC for 10 hours. A cooler was provided for recondensing the evaporated acid. The acid was decanted and fresh concentrated hydrochloric acid (200 ml) was added and the powder was again leached for 10 hours at 100degreesC. The acid was again decanted. The leached silicon nitride was mixed with highly pure water (400 ml). After 30 minutes, the water was decanted and the silicon nitride powder was dried by means of microwave. The resulting silicon powder contained only 4 ppm of impurities.