胶体的制备与纯化.ppt
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1、胶体的制备和纯化,溶胶是指有胶体颗粒悬浮其中的液体,而凝胶是指内部呈网络结构,网络间隙中含有液体的固体。 按原料的不同,可分为胶体工艺和聚合工艺。,溶胶凝胶(Sol-Gel)法简介:,一、 胶体的制备和净化,胶体工艺的前驱体(precursor)是无机盐,盐溶液的水解产生胶体沉淀,利用胶溶作用使沉淀转化为溶胶,通过控制溶液的温度、pH值可以控制胶粒的大小。通过使溶胶脱水或改变溶胶的浓度,溶胶凝结转变成三维网络状凝胶。 聚合工艺的前驱体是金属醇盐,将醇盐溶解在有机溶剂中,加入适量的水,醇盐水解,通过脱水、脱醇反应缩聚合,形成三维网络。,(1)金属醇盐(metal alkoxide): 也称金属酸
2、酯或金属烷氧基化合物,化学式为M(OR)n 。M是价态为n的中心金属原子,R为烷基或芳香基。 填补了有机化学和无机化学之间空白,是广义金属有机化合物的一部分。 以金属醇盐为原料的溶胶凝胶法的优点: 金属醇盐易溶于普通有机溶剂,制备温度低,可获得高纯和分子级分散均匀度; 容易实现化学组成配比并可调,控制金属醇盐水解缩聚过程从而实现“预定”的分子结构设计; 可避免不期望的盐副产物的生成 。,Sol-Gel法中的几个常见术语:,(2)水解(Hydrolysis): The reaction of a metal alkoxide (M-OR) with water, forming a metal
3、hydroxide (MOH). M-OR H2O M-OH R-OH,Sol-Gel法中的几个常见术语:,(3)缩聚(Condensation): A condensation reaction occurs when two metal hydroxides (M-OH + HO-M) combine to give a metal oxide species (M-O-M). The reaction forms one water molecule.,Sol-Gel法中的几个常见术语:,M-OH + HO-M M-O-M + H2O,(4) 溶胶(Sol): 溶胶是指有胶体颗粒悬浮其中
4、的液体。 A solution of various reactants that are undergoing hydrolysis and condensation reactions. The molecular weight of the oxide species produced continuously increases. As these species grow, they may begin to link together in a three-dimensional network.,Sol-Gel法中的几个常见术语:,(5)凝胶点(Gel Point): The p
5、oint in time at which the network of linked oxide particles spans the container holding the Sol. 相互联结的氧化物微粒的网络横跨盛装溶胶的容器时所需要的时间。 At the gel point the Sol becomes an Alcogel. 在凝胶点溶胶变成醇凝胶。,Sol-Gel法中的几个常见术语:,(6)醇凝胶(Alcogel): At the gel point, the mixture forms a rigid substance called an alcogel, or Wet
6、 gel . The alcogel can be removed from its original container and can stand on its own. An alcogel consists of two parts, a solid part and a liquid part. The solid part is formed by the three-dimensional network of linked oxide particles. The liquid part (the original solvent of the Sol) fills the f
7、ree space surrounding the solid part. The liquid and solid parts of an alcogel occupy the same apparent volume.,Sol-Gel法中的几个常见术语:,(7)超临界流体(Supercritical fluid): A substance that is above its critical pressure and critical temperature. A supercritical fluid possesses some properties in common with a
8、liquids (density, thermal conductivity) and some in common with gases. (fills its container, does not have surface tension).,Sol-Gel法中的几个常见术语:,(8)气凝胶(Aerogel): What remains when the liquid part of an alcogel is removed without damaging the solid part (most often achieved by supercritical extraction)
9、. If made correctly, the aerogel retains the original shape of the alcogel and at least 50% (typically 85%) of the alcogels volume. 当醇凝胶中的液体被驱除后,其形状不被破坏的固体物质,称为气凝胶。 气凝胶保持原醇凝胶的形状,其体积至少应不小于醇凝胶的50%,一般大于85%。,Sol-Gel法中的几个常见术语:,(9)干凝胶(Xerogel): What remains when the liquid part of an alcogel is removed by
10、 evaporation, or similar methods. Xerogels may retain their original shape, but often crack. The shrinkage during drying is often extreme (90%) for xerogels.,Sol-Gel法中的几个常见术语:,溶胶凝胶法的应用,溶胶凝胶法的应用,溶胶凝胶法制备SiO2气凝胶,气凝胶? 主要是指一种以纳米量级超细微粒所聚集成的多孔固态材料。 孔隙率5099%,孔洞1100nm,密度3600kgm-3。 气凝胶的典型代表是SiO2气凝胶。 世界上密度最小的S
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- 胶体 制备 纯化
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