SIMChapter4题库.doc

Chapter 4 In precipitation reactions the initial formation of particles from solution proceeds as indicated in LaMer model. Explain the relation between the concentration and the reaction time in the figure. c0: the minimum concentration for nucleation; cN: the maximum concentration for nucleation; cS: supersaturation Describe the six processes involved in a precipitation reaction. Explain the electric double layer as show below. The original surface is positively charged. For precipitating from solution, the concentration of the precipitating solute species must be increased until nuclei are formed. Describe the way of precipitate from solution. Describe the formation mechanism of amorphous and crystalline. Define “sol” and “gel” Sol-gel reactions can be described using two major chemical reactions. What are these two reactions? Single crystalline materials can be synthesized via hydrothermal reaction. The schematic representation of an autoclave is shown in the margin. Explain the functions of it. Sol-gel reactions under acidic or basic conditions reveal different effects upon the final products – chain-like and spherical powders. These reactions undergo SN1 and SN2 mechanism, respectively. Discuss these phenomena in detail. Explain the function and compound of mineralizer. Explain the factors that result in coagulation of sol particle. Explain the advantages of sol - gel processes. Describe the four processes involved in a sol-gel processing proceed. Describe the parameters which influence hydrolysis and condensation . Illustrate the ways to avoid particle aggregation in a liquid system. The evaporation of the liquid from a wet gel by conventional methods are vary complex way, describe to the three processes involved in a drying process. Draw the structures of TMOS and TEOS. Explain the dependence of the relative rates of hydrolysis and condensation reactions of Si(OR)4 on pH. (fig4-50) Condensation can happen either via an alcohol -producing-m