Direct preparation and conversion of copper hydroxide-based monolithic xerogels with hierarchical pores

Copper hydroxide-based xerogels with hierarchical pores were prepared directly and converted to porous materials with a different valency of copper by heat treatment.

Dialkylenecarbonate-Bridged Polysilsesquioxanes: Hybrid Organic-Inorganic Sol-Gels with a Thermally Labile Bridging Group

ABSTRACTIn this paper, we introduce a new approach for altering the properties of bridged polysilsesquioxane xerogels using post-processing modification of the polymeric network. The bridging organic group contains latent functionalities that can be liberated thermally, photochemically, or by chemical means after the gel has been processed to a xerogel. These modifications can produce changes in density, solubility, porosity, and or chemical properties of the material. Since every monomer possesses two latent functional groups, the technique allows for the introduction of high levels of functionality in hybrid organic-inorganic materials. Dialkylenecarbonate-bridged polysilsesquioxane gels were prepared by the sol-gel polymerization of bis(triethoxysilylpropyl)carbonate (1) and bis(triethoxysilylisobutyl)-carbonate (2). Thermal treatment of the resulting non-porous xerogels and aerogels at 300–350°C resulted in quantitative decarboxylation of the dialkylenecarbonate bridging groups to give new hydroxyalkyl and olefinic substituted polysilsesquioxane monolithic xerogels and aerogels that can not be directly prepared through direct sol-gel polymerization of organotrialkoxysilanes.

Sintering of the ultrahigh pressure densified hydroxyapatite monolithic xerogels

Dense and translucent ceramics were prepared by sintering of cylindrical preforms of hydroxyapatite extruded from xerogels. Extruded specimens were dried as monoliths and then consolidated by applying cold isostatic pressure, ranging from 500 to 1500 MPa. Upon heating the samples began to densify at 610 °C, and the densification/sintering was completed at 870 °C as was evidenced by the dilatometry plot indicating no further shrinkage. The sintered specimens thus formed were translucent in appearance. Further heating of the samples up to 1200 °C resulted in their “bloating” or creation of pores in the originally dense matrix. Pore creation within the structure is reproducible, it proceeds from the surface to the interior of the sample, and its spreading can be thermally controlled. Pore evolution within the single phase dense polycrystalline material is not related to the frequently occurring phenomenon of microcracking in ceramics during cooling.