Abstract: According to the patent^[5], the size of zeolite ZSM-5 crystals obtained in the system of (TPA)₂O-Na₃ O-Al₂O₃-SiO₂-H₂O is merely about 1 Mm. The growth of ZSM-5 single crystals is investigated by the author in the system diethanolamine (DEA)-Na₂O-Al₂O₃-SiO₂-H₂O and batch samples (3 g each) of maximum size 50 × 50 × 120μmi (Fig. 1) can be obtained, They are transparent and perfect, suitable for X-ray crystal structure determination and diffusion measurement. Raw materials used are water glass, Al₂,(SO₄)₃, H₂SO₄, and DEA. Proper amount of DEAis added to 30g of water glass, which has been filtered carefully beforehand. Gel (1) is formed. Fixed amounts of Al₂(SO₄)₃, H₂O and DEA are mixed, forming gel (2). Then gel (1) and (2) are mixed again. The mixture is poured into a hard glass tube and crystallized statically at about 160 to 220℃ in a small autoclave for 50 to 300 hours until crystallization is completed.DEAnot only acts as the "template" to initiate the formation of ZSM-5 but also serves as a buffering or complexing agent. However,the spontaneous crystallization in the DEAsystem always contains Mordenite and a-SiO₂. Adding seeds (<1 μm in size) obtained by grinding the single crystals of ZSM-5 can obviously improve the purity of ZSM-5. Pure ZSM-5 of 20×20×50μm in size is produced by adding more seeds. The size is obviously increased by adding fewer seeds. Small Amounts of other phase appeared during the later period of crystallization can be removed by elutriation and shifting. The perfection of the single crystals can be improved by adding glycerine to the reacting mixture.In the system of DEA, the compositions of reaction mixture for growth of single crystals have the following ranges (in terms of mole ratios): H₂O:SiO₂ = 200 to 600; OH:SiO₂ = 5 to 20; SiO₂: Al₂O₃ = 50 to 150; DEA:SiO₂ = 0.4 to 4. Better materials for the autoclave wall are hard glass (GGl7),quartz glass and high purity graphite.Stainless steel produces smaller crystals while Teflon forms large quantities of a-SiO_2.The species of "Templete" molecules exerts great influence. Methylamine forms smaller crystals of less than 20 um in size. Ethylamine, n-propyla-mine, ethylene diamine, 1, 6-hexamethylene diamine and tetraethylene pentamine produce primarily blocks of polycrystals. Afew crystals, having large size and regular shape, are less perfect. It is difficult to obtain single crystals of good quality and large size by means of methanol, ethanol, n-butanol and ammonia. The effect of triethanolamine and ethanolamine is less than DEA.Some Xpenetration twins are observed. Uniform interference colors from tangerine to greenish blue appear on the single crystals of ZSM-5 between crossed polars of microscope with Gypsum plate. However, this uniform interference color has not been observed on blocks of polycrystals. The clear diffraction spots are shown on the X-ray single crystals Laue photograph. The peaks of X-ray powder diffraction pattern are fine and have high resolving power. The lines of CuKa and CuKa can be resolved at about 45° (2μ).The measured specific gravity of single crystals ZSM-5 is 2.05. Its chemical composition is. Al₂O₃ = 3.15%; SiO₂ = 83.41%; Na₂O = 0.26%; N = 1.09% ;SiO₂: Al₂O₃(mol) = 45. So, the composition of unit cell is Na 0.6 (HOC₂H₄)₃NH₂) 5.1(Al₄Si₉₂O₁₉₂)·16H₂O. After calculation for 11 hours at about 540℃, the surface area measured is 497.2M2/g and the adsorption of water is 8.2% wt.The autor is grateful to Professors Xu Ru-Ren and Xu Guo-Xian for their guidence.