ZSM-5/MCM-41 zeolite composites with varying mesopore sizes were prepared through alkalidesilication and surfactant-directed recrystallization with different chain length of alkyltrimethylammonium bromide. XRD and TEM revealed that the composites possessed the characteristics of both ZSM-5 and mesoporous MCM-41 with hexagonal symmetry. N 2-adsorptiondesorption, 27 Al MAS NMR, NH 3-TPD and in situ FT-IR results suggested that the sizes of the mesopores and the accessibility of acid sites could be affected greatly by the chain length of alkyltrimethylammonium bromide used. Catalytic cracking of n-dodecane over ZSM-5/MCM-41 composites was studied in the form of coatings on the inside of a tubular reactor at 550°C and 4 MPa. The conversion of n-dodecane increased gradually with increasing the mesopore sizes of ZSM-5/MCM-41 composites, implying a positive effect of the mesopores on the diffusion inside pore channels and the accessibility of acid sites by the reactants.
Fixed appliance orthodontic treatment may affect local saliva secretion; however, there is limited information available about this respect in the literature. Understanding how fixed appliance orthodontic treatment affects local saliva secretion could provide insight on possible contributions of salivary changes towards decalcification. In this study, we found that during the first month of fixed orthodontic treatment, the whole saliva flow rate, upper labial saliva flow rate and concentrations of whole saliva sodium and chlorine increased significantly, while the concentrations of calcium, phosphorous and potassium in whole saliva decreased. However, all these were in normal levels after 3 months. This study demonstrated that saliva flow rate was increased and saliva electrolytes were changed at early stage when placing fixed orthodontic appliances, which was considered due to increased mechanosensation.
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