Formation and stabilization of tetragonal phase in sol–gel derived ZrO2 treated with base-hot-water

Zirconia (ZrO2) nanoparticles have been prepared by sol–gel route. Low temperature crystallization using base-hot-water treatment (BHWT) was conducted for the sol–gel derived ZrO2 gel powders at 90 °C and at pH 14 for various periods of time. Single phase nanocrystalline tetragonal ZrO2 (t-ZrO2) was successfully obtained by immersing the dry gel powders into hot, basic condition water and kept at rest for given time. BHWT at pH 14 with sodium hydroxide (NaOH) medium by digestion for 12 h and then continuing with stirring for 12 h resulted in the formation of t-ZrO2 with surface area of 292 m2/g and crystal size of 7 nm. Study on base solution medium, using NaOH, shows that the sodium ions play an important role for the formation of t-ZrO2 by incorporating into the crystal structure during the treatment. BHWT also effectively removed organic groups of the sol–gel derived ZrO2 nanoparticles

Formation and stabilization of tetragonal phase in sol–gel derived ZrO2 treated with base-hot-water

Zirconia (ZrO2) nanoparticles have been prepared by sol–gel route. Low temperature crystallization using base-hot-water treatment (BHWT) was conducted for the sol–gel derived ZrO2 gel powders at 90 °C and at pH 14 for various periods of time. Single phase nanocrystalline tetragonal ZrO2 (t-ZrO2) was successfully obtained by immersing the dry gel powders into hot, basic condition water and kept at rest for given time. BHWT at pH 14 with sodium hydroxide (NaOH) medium by digestion for 12 h and then continuing with stirring for 12 h resulted in the formation of t-ZrO2 with surface area of 292 m2/g and crystal size of 7 nm. Study on base solution medium, using NaOH, shows that the sodium ions play an important role for the formation of t-ZrO2 by incorporating into the crystal structure during the treatment. BHWT also effectively removed organic groups of the sol–gel derived ZrO2 nanoparticles

外部場温水処理によるゲルーゾルSiO2-TiO2系コーティング膜の表面ナノ構造制御 : 総説

This review paper is focused on the area of titania nanocoatings prepared from sol-gel derived films by hot-water treatment under external reaction fields to design their functionality through the control of their surface morphology and crystallinity at low processing temperatures. First, the formation of titania nanocrystalline coatings at low temperatures by wet chemical procedures is briefly reviewed. Second, a concept of material design based on an external-field hot-water treatment for sol-gel derived films and the effects of the external fields on the formation of titania nanocrystals from the sol-gel derived films are discussed. Finally, promising characteristics of the resultant titania nanocrystal-dispersed coatings with unique morphology are described. External fileds of vibrations and electric voltages affect the nanostructure of titania crystallites formed on SiO2-TiO2 gel coatings during hot-water treatment. Without the external fields granular anatase nanocrystals of 30-50 nm in size are formed on the coatings during the hot-water treatment, whereas the shape of the precipitates becomes sheetlike by applying a vibration to the substrate during hot-water treatment. Similar changes in shape of the precipitates on the coatings are also observed, and ramiform (branchlike) crystallites are formed at the negative electrode by applying an electric field between the substrates. The sheetlike and ramiform crystallites are mainly composed of a hydrated titania, m(TiO2)•nH2O, with the lepidocrocite-like layered structure with a d-spacing of 0.6-0.8 nm. Titania nanosheets are characterized by a large surface-to-volume ratio, which gives rise to the excellent wettability for water and antifogging properties. Processing temperatures for the preparation of the coatings are lower than 100°C under atmospheric pressure, so that the coatings have a great potential for applications to various substrates including organic polymers with poor heat resistance

Mechanical properties comparison of phenylsilsesquioxane–methylsilsesquioxane hybrid films by indentation

Sol­gel derived phenylsilsesquioxane (PhSiO3/2)­methylsilsesquioxane (MeSiO3/2) films were prepared on soda-lime-silicate (SLS) glass substrates by dropping and spreading method. The mechanical properties of the pure MeSiO3/2 and 20PhSiO3/2· 80MeSiO3/2 (inmol%) films were measured as a function of heat treatment times and temperatures using a nanoindentation test with a Berkovich indenter. The relative residual depth (²r)offilms decreased and the film hardness (HM)significantly increased with increasing heat treatment times and temperatures. The mechanical properties of the films well reflect the changes in the chemical structures and the evolution of siloxane networks with the heat treatment