In this work, two ZSM-12 zeolites with stellar morphology and dendritic morphology were synthesized from the synthesis system containing nanorod-aggregated hexagonal prism seed and microrod seed, respectively, in the presence of CTAB. The stellar ZSM-12 zeolite was composed of core and branches, while the dendritic ZSM-12 zeolite consisted of stem and branches. For the two zeolites, the branches grew on {310} planes of seed and were in twin relation with the seed. The c -axes of branch and seed were parallel to each other, while the b -axes of them exhibited the angular relation of 65°. The crystallization process of the two zeolites were investigated by using XRD , SEM, and TEM characterizations. It was demonstrated that the branched growth on seeds was controlled by two factors: diffusion of reactive species and adsorption of CTAB. The Mullins-Sekerka instability occurred under the diffusion-limited condition, resulting in the formation of branches on seed. The adsorption of CTAB on side facets of branches inhibited the occurrence of secondary branching.
Jing Yang,Yingdan Cui,Mingyang Chen,Yan Wang,Shijie Xu,Songgu Wu,Jingkang Wang,Junbo Gong
Spherulitic growth, categorized as central multidirectional growth and unidirectional growth via small-angle branching, has increasingly been explored as a method to improve the flowability and bulk density of needle-like crystals. However, the formation of two categories of spherulites in solutions is still unclear. In this work, the formation mechanism of two categories of spherulite was studied in a supercooled nitroguanidine (NQ) aqueous solution with a small amount of gelatin. It is proposed that spherulitic growth depends on the initial morphology of the crystallite, wherein the gelatin concentration, temperature, and initial supersaturation play a vital role. Gelatin can significantly inhibit NQ nucleation, promote branching, and modify the morphology of NQ subunits. At high initial supersaturation and low temperatures, the aspect ratio of the crystal precursor increases and branching is accelerated, so that the lateral faces provide more branching sites than the end faces to promote the unidirectional growth. In comparison, high temperatures promoting the multipoint branching should be mainly responsible for the formation of cauliflower-like spherulites. Furthermore, the bulk densities of the cauliflower-like and compact spherulites of NQ are about triple those of needle-like crystals and their evolutions were observed. Compared with the reported methods, the macromolecule-induced spherulitic growth of NQ without an organic solvent is a green method and will have a bright future for the design and fabrication of other organic spherulites.
危险品化学品经营许可证（带存储）