Microwave effect in the fast synthesis of microporous materials: which stage between nucleation and crystal growth is accelerated by microwave irradiation?
Microporous materials, such as silicalite-1 and VSB-5 molecular sieves, have been synthesized by both microwave irradiation (MW) and conventional electric heating (CE). The accelerated syntheses by microwave irradiation can be quantitatively investigated by various heating modes conducted in two steps such as MW-MW, MW-CE, CE-MW, and CE-CE (in the order of nucleation-crystal growth). In the case of synthesis by MW-CE or CE-MW, the heating modes were changed for the second step just after the appearance of X-ray diffraction peaks in the first step. We have quantitatively demonstrated that the microwave irradiation accelerates not only the nucleation but also crystal growth. However, the contribution to decrease the synthesis time by microwave irradiation is larger in the nucleation stage than in the step of crystal growth. The crystal size increases in the order of MW-MW<MW-CE approximately CE-MW<CE-CE synthesis. The fast crystal growth and small crystal size observed in the synthesis from microwave-nucleated precursor can be explained in terms of the fact that the microwave-nucleated samples have higher population of nuclei with smaller size than the samples nucleated by conventional heating.
Jhung
Sung Hwa
SH
Research Center for Nanocatalysts, Korea Research Institute of Chemical Technology (KRICT), P.O. Box, 107, Yusung, Daejeon 305-600, Korea. sung@krict.re.kr
Jin
Taihuan
T
Hwang
Young Kyu
YK
Chang
Jong-San
JS
D003460:Crystallization; D008872:Microwaves; D009532:Nickel / Q000737:chemistry / Q000528:radiation effects*; D010316:Particle Size; D016062:Porosity; D012822:Silicon Dioxide / Q000138:chemical synthesis* / Q000528:radiation effects*; D017550:Spectroscopy, Fourier Transform Infrared; D013997:Time Factors; D014961:X-Ray Diffraction; D017641:Zeolites / Q000138:chemical synthesis* / Q000737:chemistry / Q000528:radiation effects*
D017641:Zeolites; D012822:Silicon Dioxide; D009532:Nickel