The Serpek Process for the Manufacture of Aluminium Nitride
Journal of Industrial & Engineering Chemistry
double chloride of aluminum and potassium the chances of securing pure alumina are very favorable. Upon heating to a dull red heat, aluminum sulfate breaks down into alumina with liberations of sulfuric acid (SO,) and the potassium sulfate can then be leached aTTay. In the case of a double chloride of aluminum and potassium a t a very low heat in the presence of the vapor of n-ater, hydrochloric acid is given off with the formation of alumina; the chloride of potassium remains and can be
... s and can be leached aivay from the alumina. To secure pure alumina from the above solution of chloride or sulfate salts with phosphoric acid is promising. The potash alum, however, cannot be separated by crystallization. By precipitation with sodic or potassic aluminate, if too much of either of these salts be not used, pure phosphate of aluminum may be secured. POTASH PHOSPHATE FERTILIZER In the foregoing. I have described the sintering a t a comparatively low temperature of rock phosphate and potash silicates. T wish to call attention to the fact that this mixture is in some cases of greater fertilizer value than rock phosphate when used alone: for this use sinter and treat with the proper amount of sulfuric acid or of hydrochloric acid, if hygroscopic properties are not detrimental. By this new process the silica has taken the place of much acid that would be required, and the product is not loaded down with calcium sulfate, but instead, is loaded with potassium sulfate m-hile the lime and silica is in such form as to be sufficiently soluble to furnish silica to plant food; further, the soluble lime is in a condition to act on the potash minerals in the soil displacing pc tash and thus rendering more potash available for plant food. The production of aluminium nitride (AlN) on a commercial scale is proposed in the process of Ottokar Serpek, followed by the decomposition of the same by water or caustic soda solution, thereby liberating the nitrogen as ammonia and producing alkaline aluminate solution from which pure alumina can be obtained. This rather daring chemical proposition has directed attention to aluminium nitride, the conditions of its formation and its properties. Thc existence of aluminium nitride was suspected for some time before i t was isolated. A rather indefinite number of years ago, about 1890, the writer's attention was directed by his father to the fact that when metallic aluminium in a melted condition was skimmed and the skimmings or dross laid to one side, that on sprinkling water upon them these skimmings gave off an odor of ammonia. The only explanation which came then to be figured out for this phenomenon was that the hot aluminium in the skimmings oxidized to alumina, and that the rather high temperature thus produced locally caused the aluminium also to unite with the nitrogen of the air and form the nitride. In other words, that the aluminium united first with the oxygen and immediately thereafter also with the nitrogen of the air. On sprinkling these with water, the nitride would react according to the following reaction: In the light of subsequent investigation and formation of aluminium nitride in other ways i t appears that the explanation given in these early days was correct and that aluminium nitride is formed directly under such conditions from metallic aluminium and the nitrogen of the air. Le Verrier, later, proved the presence of traces of nitrogen in commercial aluminium by dissolving i t in caustic potash and 2 AlN + 3 H,O = &ll2O3 + 2 NH,.