The membrane microstructures and their forming mechanism of two coated ureas formed through solid-liquid reaction were observed
by scanning electron microscope and infrared spectra, the relation of the structuralcharacteristics and the
nitrogen release feature were also discussed combining with nitrogen dissolution in water.Theresults showed that the membranes were made of solid particles, tightly connected each other and were piled up layer bylayer through liquid glue. Porosity and aperture of membrane were determined by compactness of pilled layers and theparticles in a single layer and also related to the characteristics of coating materials. Research of the infrared spectra ofmembrane, made of a solid powder and a liquid glue, has proved that O-H on the solid surface was bonded with the doublebond of the liquid glue, thus forming membrane and keeping it stable. It is found that the two coated ureas showed obviousdifference in nitrogen release due to their membrane structures, the porosity and aperture of membrane were critical factorsfor nitrogen release.