Abstract: A process for the preparation of pure melamine, in which liquid, ammonia-containing melamine is rapidly depressurized from an ammonia partial pressure p1 between 400 and 50 bar to an ammonia partial pressure p2 between 200 bar and atmospheric pressure, where p1 is always greater than p2, at a temperature which is 0 to 60° C. higher than the melamine solidification point dependent on the particular prevailing ammonia partial pressure, higher pressures permitting a greater temperature interval from the melamine solidification point than lower pressures, by which means pure melamine separates out in solid form, whereupon, in any sequence, the product is further depressurized if appropriate to atmospheric pressure, cooled to room temperature and the pure melamine is isolated.

Abstract: Process for cooling liquid melamine by mixing with solid melamine or with solid inert substances or with a mixture of solid melamine and solid inert substances.

Abstract: Process for the production of highly pure melamine in which an aftertreatment of the melamine is carried out, comprising the stepsa) separating off the NH.sub.3 /CO.sub.2 gas mixture from the liquid melamine, if appropriateb) reducing the CO.sub.2 dissolved in the liquid melamine by introducing gaseous ammoniac) allowing the liquid melamine to remain for a mean residence time of 0 to 8 hours at a temperature between 430.degree. C. and the melting point of melamine and an ammonia partial pressure of 50 to 400 bar andd) slow, controlled cooling by lowering the temperature from the temperature present in a), b) respectively c) to 330.degree. to 270.degree. C. at a cooling rate of up to 150.degree. C.

Abstract: A melamine preparation consisting of 80 to 99.9% by weight of melamine having an average particle size of 0.01 to 0.1 mm and 0.1 to 20% by weight of urea, thiourea, biuret or urea or thiourea substituted by lower alkyl groups and a stable dispersion in polyether polyols prepared therefrom, which is used for the preparation of flame-resistant polyurethane foams.