Lecture 8

chichi's version from 2018-02-27 07:09


Question Answer
Solution based synthesisSol-Gel, Sonochemical, Microwave, Self Assembly
Sol-gel processinga wet chemical synthesis approach that can be used to generate nanoparticles by: gelation, precipitation an hydrothermal treatment
Conventional sol-gel synthesis involves, the fomation of a ____________ suspension (sol), usually obtained by controlled acid-or base-catalyzed hydrolysis an partial condensation of metal alkoxide precursors in alcoholic or other non hydrolytic organic solvents.colloidal
Further condensation leads to a viscous gel or dispersion of colloidal particles, depending on...depending on composition, pH and reaction conditions

Section 2

Question Answer
Sol gel process (step 1)formation of stable solutions of the alkoxide or solvated metal precursor (the sol).
Sol gel process (step 2)gelation resulting from the formation of an oxide-or alochol-bridged network (the gel) polycondensation or polyesterification reaction that results in a dramatic increase in the viscosity of the solution. If so desired, the gel may be cast into a mold during this step
Sol gel process (step 3)Aging of the gel (syneresis), the gel transforms into a solid mass, accompanied by contraction of the gel network and expulsion of solvent from the gel pores. The aging process of gels can exceed 7 days and is critical to the prevention of crack in gels that have been cast
Sol gel process (step 4)Drying of the gel, water and other volatile liquids are removed from the gel network
Sol gel process (step 5)Dehydration, during which surface-bound M-OH groups are removed
Sol gel process (step 6)Densification and decomposition of the gels at high temperatures (T > 800C). Th pores of the gel network are collapsed, and remaining organic species are volatilized

Section 3

Question Answer
GelationAt gelation, the viscosity increases sharply
Agingaging of a gel, also called syneresis, involves maintaining the cast object for a period of time, hours to days, completely immersed in liquid
DryingDuring drying the liquid is removed from the interconnected pore network
DensificationHeating the porous gel at high temperatures causes densification to occur

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